A Practitioner s Guide to. Deploying AS to Achieve Zero Defects. Process Failure Mode & Effects Analysis and Control Plan

Transcription

1 A Practitioner s Guide to Deploying AS13004 to Achieve Zero Defects Process Failure Mode & Effects Analysis and Control Plan Includes the use of Reference PFMEAs Dr Ian Riggs

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3 CONTENTS CONTENTS 3 LIST OF FIGURES 4 LIST OF TABLES 5 THE AERO ENGINE SUPPLIER QUALITY GROUP (AESQ) 7 FOCUS ON DEFECT PREVENTION 9 INTRODUCTION TO FAILURE MODE & EFFECTS ANALYSIS 13 CHAPTER ONE AS13004 OVERVIEW 19 CHAPTER TWO DESIGN FMEA 25 CHAPTER THREE PROCESS FLOW DIAGRAMS (PFD) 45 CHAPTER FOUR CHARACTERISTICS MATRIX 51 CHAPTER FIVE PROCESS FMEAS 53 CHAPTER SIX CREATING REFERENCE PFMEAS 89 CHAPTER SEVEN USING REFERENCE FMEAS 99 CHAPTER EIGHT CONTROL PLANS 113 APPENDIX A: TYPICAL FAILURE MODE LIBRARY 127 APPENDIX B: SAMPLE REFERENCE PFMEAS (EXTRACTS) 129 APPENDIX C: TERMS & DEFINITIONS 134 APPENDIX D: AS13004 ASSESSMENT CHECKLIST 139 3

4 List of Figures Figure 1: Defect Prevention System (APQP & Process Control) 10 Figure 2: Relative Resource Requirements for early PFMEA Deployment 15 Figure 3: AS13004 Scope and Relationships 19 Figure 4: New Product Introduction Phases 25 Figure 5: Role of the Design FMEA 26 Figure 6 DFMEA Typical Inputs and Outputs 27 Figure 7: DFMEA Example 30 Figure 8: DFMEA Step 1 (extract) 32 Figure 9: DFMEA Potential Effects and Severity Scoring (extract) 34 Figure 10: RPN Calculation 38 Figure 11: DFMEA Potential Causes and Controls (extract) 39 Figure 12: DFMEA Improvement Actions (extract) 40 Figure 13 PFD Typical Inputs 45 Figure 14 Process Flow Diagram based on AS13004 s Figure C3 Example 47 Figure 15: Process Flow Diagram based on AS13004 s Figure C4 Example 48 Figure 16: Simple Characteristics Matrix example (truncated) 51 Figure 17: PFMEA Inputs and Outputs 55 Figure 18: The PFMEA and its Typical Data Source 56 Figure 19: Process FMEA example (truncated) 57 Figure 20: Team Size Effectiveness 60 Figure 21: Process Function and link to Potential Failure Modes in a PFMEA 66 Figure 22: Potential Causes of Failure in a PFMEA 72 Figure 23: RPN Scoring Example 81 Figure 24: RPN Improvement Actions in a PFMEA 83 Figure 25: Detection Scoring Analogy 86 Figure 26: PFMEA Testing the Logic (Read Left to Right) 87 Figure 27: Overview of Reference PFMEA Elements 89 Figure 28: Typical Reference FMEA Database of Required Processes 90 Figure 29: Typical Features for a Drilling Operation 91 Figure 30: Typical Failure Modes for Drilling Features 92 Figure 31: Reference PFMEA for CNC Hole Drilling: Potential Failure Mode Causes 93 Figure 32: Reference PFMEA Prevention Controls 94 Figure 33: Identifying the Typical Detection Controls in the Reference PFMEA 95 Figure 34: Reference PFMEA Database Structure Example 97 Figure 35: Creating a part specific Shell PFMEA 99 4

5 Figure 36: Completing the Process Step and Requirements Column 100 Figure 37: Hole Pattern Example 101 Figure 38: Determining the Required Reference PFMEAs 102 Figure 39: Compiling the Shell Part Number PFMEA using Reference PFMEAs 103 Figure 40: Shell PFMEA example 104 Figure 41: Completing the Effects and Severity Rating 105 Figure 42: Completing the Potential Causes, Prevention Controls and Occurrence Scoring sections. 106 Figure 43: Updating the Detection Controls, Detection Scoring and calculating the RPN 107 Figure 44: Documenting Improvement Actions and Rescoring RPN 108 Figure 45: Prevention & Detection Control Documentation 113 Figure 46: How the Process FMEA Prevention & Detection Controls are managed 114 Figure 47: Typical Inputs to a Production Control Plan 115 Figure 48: Standard Control Plan Template 116 Figure 49: Control Plan Structure 121 Figure 50: Example Production Control Plan for a Drilling Operation 122 Figure 51: Control Plan Data derived from Process FMEA (red text) 124 List of Tables Table 1: Examples of Relevant Expertise for FMEA Development 21 Table 2: AS13004 Additional Application Guidance for products already in production 22 Table 3: Design FMEA Severity Scoring Criteria 33 Table 4: DFMEA Occurrence Scoring Criteria 35 Table 5: Design FMEA Detection Scoring Criteria 37 Table 6: Some Common Issues with Design FMEA Deployment 41 Table 7: Typical Operations and Symbols for creating a Process Flow Diagram 46 Table 8: Deriving Failure Modes from the Requirements Description 62 Table 9: Problems with Poor Requirements Description in a PFMEA 64 Table 10: Using the Correct Requirements Description in the PFMEA 65 Table 11: Failure Mode Examples 68 Table 12: AS13004 Process FMEA Severity Risk Scoring 71 Table 13: Relationship between Cp value and non-conforming parts (Parts per Million PPM) outside specified limits 76 Table 14: Data Sources for Scoring Occurrence 77 Table 15: AS13004 Occurrence Rating Table for Process FMEA 78 Table 16: AS13004 Detection Rating Table 80 Table 17: Example Failure Modes 92 Table 18: Some Common Issues with Process FMEA Deployment 109 Table 19: Some Common Issues with Control Plan Deployment 125 5

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7 The Aero Engine Supplier Quality Group (AESQ) The origins of the AESQ can be traced back to The Aerospace Industry was, and still is, facing many challenges, including; Increasing demand for Aero Engines Customers expecting Zero Defects Increasing supplier / partner engine content Increasing global footprint A step change in Quality, Cost and Delivery performance is required The Aero Engine manufacturers Rolls-Royce, Pratt & Whitney, GE and Snecma (now Safran Aero Engines) began a collaboration project with the aim of improving supply chain performance. Recognising that they shared a significant proportion of their supply chain with one or more other Engine Manufacturers the group set about harmonising their individual requirements into a single set of standards. The objective was to raise the bar for quality performance while simplifying these multitude of customer requirements. This collaboration was formalised under the SAE G-22 Technical Committee in 2013 and the Engine Manufacturers were joined by four major Aero Engine suppliers GKN, Honeywell, PCC and Arconic. AESQ Vision To establish and maintain a common set of Quality Requirements that enable the Global Aero Engine Supply Chain to be truly competitive through lean, capable processes and a culture of Continuous Improvement To date the AESQ have published six standards; AS13000 Problem Solving Requirements for Suppliers (8D) AS13001 Delegated Product Release Verification Training Requirements (DPRV) AS13002 Requirements for Developing and Qualifying Alternate Inspection Frequency Plans 7

8 AS13003 Measurement Systems Analysis Requirements for the Aero Engine Supply Chain AS13004 Process Failure Mode & Effects Analysis and Control Plans AS13006 Process Control The AESQ continue to look for further opportunities to improve quality and create standards that will add value throughout the supply chain. Suppliers to the Aero Engine Manufacturers can get involved through the regional supplier forums held each year or via the AESQ website 8

9 Focus on Defect Prevention It needs no explanation that in the Aerospace industry product quality is critical. In particular for Aero Engines the consequence of failure can be catastrophic. On top of this the impact of poor quality is felt through additional costs and delivery delays. It is estimated that for many Aerospace organisations today the cost of poor quality is 20 25% of sales. This includes not only the cost of scrap, rework and concessions but also those of missed delivery penalties, consequential losses due to product reliability, etc. A recent study has shown that 60% of all delivery problems stem from a quality issue somewhere in the supply chain. Getting quality right first time is the only way to maximise profit and minimise disruption, to the customer and the supply chain. In addition, we continue to see our customers raising the bar on quality and redefining what they are prepared to accept. Traditionally the Aerospace industry has relied heavily on inspection, sorting good from bad, in order to protect the customer from non-conforming products. Unfortunately, we know that inspection can never be 100% effective, which means that there will always be something that gets missed. This reliance on inspection to sort good from bad means that by the time we find a problem it may be too late to prevent delivery delays and hence customer disruption. I have often heard it said that if the Aerospace Industry didn t allow concessions then we would never build another aircraft. It s a sad fact but is probably true, well for today at least. The only way to ensure that we only ship conforming parts is to avoid producing non-conformance in the first place. Defect Prevention must be our aim. The good news is that the quality tools required for Defect Prevention are available and are well proven across many industries. A simple overview of the Defect Prevention tools, and their sequence, is shown in Figure 1. 9

10 Figure 1: Defect Prevention System (APQP & Process Control) There are three key deployment factors that must be adhered to if these defect prevention tools are to be effective, these are; i) The Defect Prevention Tools are a System These defect prevention tools are designed to work as a system, particularly when developed as part of Advanced Product Quality Planning (APQP) for a new product. They all require inputs and outputs from one or more of the other quality tools in order to be truly effective. Being good at only one or two of these tools will undermine the effectiveness of the system. All of these Defect Prevention Tools are required within the Advanced Quality Planning (APQP) and Production Part Approval Process (PPAP) requirements defined within AS9145 for New Product Introduction. ii) This system of tools must be applied at a unique System / Sub-system or Part Number level. The devil is always in the detail. The risk profile of any product will be defined by its application, the specification tolerances, the process capability and process controls. These factors mean that every part number will have a unique DNA requiring a unique solution. In a Zero Defects approach every feature / characteristic must be included in the scope of these defect prevention tools too. 10

11 iii) This system of tools must be deployed using a cross functional team Throughout the application of these tools cross-functional working is critical to ensure that all knowledge and experience is captured and used. Studies have shown that using a team rather than relying on an individual raise the chance of success from 59% to 99%. When things do go wrong we need to understand why. Are there lessons to be learnt from how the quality tools were applied to explain why we had a problem? If we can find out why it happened then we can enhance our defect prevention system for future applications. As you can see in Figure 1 the AESQ has prioritised those standards that align to Defect Prevention. This is because it is widely recognised that as an industry the maturity of deployment of these tools is not where it needs to be. All of the tools have been around for many years and are commonly found in most aerospace company s management systems. However close scrutiny has found large variances in the effectiveness of their deployment. The aim of the AS standards is to address this concern by providing prescriptive requirements developed from industry best practice applications. This is a leadership issue. We must ensure that the organisation has an in depth understanding about what Defect Prevention means and its implications for the way we work. It means that the organisation s leadership creates an environment that is intolerant of non-conformance. Training as well as time to conduct these activities must be made available to the business to enable the effective deployment of these tools. In many cases it will require a mind-set change across the organisation. This should not be underestimated. There will potentially be resistance to the new way of working if the team feel that this change is a criticism of what they have done in the past. It is vital that the introduction of these AS standards is not just seen as a technical challenge but also a cultural one. An effective way to get the businesses attention on this topic is to review the current defect prevention tools every time you have a customer escape or major disruption due to product quality. Ask if the current Process FMEA identified the Failure Mode or if we did a Gauge R&R on that inspection process? By asking these questions each time and reviewing the actual documents it will become very clear if your organisation is deploying them effectively. 11

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13 Introduction to Failure Mode & Effects Analysis Failure Mode and Effects Analysis (FMEA) is the most effective of all the Defect Prevention tools, in my opinion, for achieving zero defects. If done correctly and with the right attention to detail it will enable the organisation to design products and processes that meet the customer s requirements at optimal cost. However, it can also be the most difficult to deploy as it relies not only on technical knowledge and experience but precision of language and the right level of detail. If done poorly it will take a lot of resource for very little benefit and runs the risk of organisations either not to do it at all or only at a cursory level. The purpose of this guide is to help practitioners of FMEA to understand the key success factors and care points in creating effective Process FMEAs (PFMEAs) and their related Production Control Plans. In order to ensure the process is efficient as well as effective this guide will describe the use of Reference PFMEAs as core building blocks to create part number specific PFMEAs. In AS13004 Appendix C it refers to unit FMEAs or Library FMEAs. On face value they sound as if they may be similar to what we describe in this book as a Reference PFMEA. However, the standards definition of a Unit FMEA is a re-usable Failure Mode and as such is only one element of what is included within a Reference PFMEA. I would argue that Failure Modes are finite and can be defined precisely for each type of drawing feature and characteristic. I have included a list of typical Features and their Failure Modes in Appendix A. A Reference PFMEA contains a large amount of knowledge that can be captured and re-used when creating the PFMEA. It ensures that PFMEAs are created with the most up to date learning about the process and becomes a key reference for all things important about the manufacturing and assembly process (see Chapter 6). For Process FMEAs and Control Plans to be effective following rules must be adhered to; They must be part number specific The PFMEA must consider all design features and characteristics on the drawing and related specifications. The PFMEA must be completed at the right time in the NPI process. The role of the PFMEA is to challenge and inform the proposed Process Design and as such must be done as part of the Process design activity. The development of the PFMEA can start very early in the Product Design stages as soon as the initial designs are being created. Conducting a PFMEA after the process has already been established will be less effective as many of the process elements may be difficult to change once the investment has been made. 13

14 This is the same principle for DFMEA as related to the Product Design. The PFMEA and Control Plan must include all process steps from Receipt through to Despatch, where the product is transformed (intentionally or unintentionally). Examples of intentional product transformation are; drilling a hole, welding, cleaning, assembly, etc. Examples of unintentional product transformations are; Damage (including scratches, dents, etc.), Contamination, Foreign Object Debris (FOD), unwanted material conditions (burrs, pitting, porosity, blemishes, etc.) Improvement actions must be identified and implemented for High Severity and High Occurrence risks identified within the PFMEA The PFMEA template must be as defined within the AS13004 standard (see Figure 19). Deviations from this standard template should be discouraged and will require customer approval to use. To ensure that the PFMEA and Control Plans are completed efficiently then the following guidelines should be adhered to; Part Number PFMEAs should be created using standard Reference PFMEAs. This enables the best practice solutions to be shared for all new PFMEAs and is the most efficient way of avoiding a duplication of effort. Reference PFMEAs and Part Number PFMEAs should be created in a dedicated FMEA software tool that can manage the complexity and volume of data created across all part numbers. There are many standard FMEA software solutions available. Some offer a fully integrated solution with the ability to connect the DFMEA, PFMEA, Control Plan, MSA, Initial sample Report, etc. These software solutions offer the opportunity to greatly reduce the time taken to produce key documents, for example some software solutions will also automatically create the Control Plan from the information included within the PFMEA. There should be a program to continually update the PFMEAs and to reduce the overall process risks. There is no value to creating a PFMEA if it does not drive action! The last point is vitally important. We can create the best PFMEA ever but if we take no action as a result to improve the process then it is of no value. This is where engineering judgement comes into play. What risks are you prepared to live with and which ones will you mitigate or eliminate? 14

15 Based on the current issues we have within the Aerospace Industry regarding product quality, process yields, etc. I would expect a well-defined PFMEA to fundamentally challenge the way we do things today. That is not to say we need large investments in new technology but rather than we should look to ensure that the controls we use are appropriate to the risks identified. Many of these actions will be relatively simple to introduce. To be frank, if there was no concession process many companies would need to change the way they manufacture parts the way they do today. This is why this PFMEA process is so key. The Business must establish a cohort of engineers that are trained in FMEA and FMEA software tools to support the process. We need to develop expertise in this and all of the Defect Prevention tools. How long will it take to complete an AS13004 type PFMEA? This is one of the first questions we are often asked. From experience the early PFMEAs created follow a similar pattern (see Figure 2). Figure 2: Relative Resource Requirements for early PFMEA Deployment Relative Man hours % st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th The 1st PFMEA that the team completes will be the hardest. The team will need to learn how it is done, where to get the data from etc. It will depend on the number of unique features that need to be considered. Also remember that the Designer will never have been asked this level of detail before i.e. what happens if this feature is too large? What happens if that feature is too small? In one workshop that I was involved in to create the first PFMEA these questions took a lot of thinking about and discussion, on average I would say 20 minutes per Failure Mode. Once established and documented the next time they were asked it took less than 30 seconds. 15

16 For the 2nd PFMEA, if using the same team on a similar product, with all the learning from the 1st PFMEA now captured then if the 1st took 100 man-hours then the second is likely to take 50 hours. Similarly, for the 3rd PFMEA, using the same team on a product with a similar level of complexity, if the 2nd PFMEA took 50 hours, then the third will take around 30 hours. For the 4th PFMEA and onwards, as the team develops it skills, utilises PFMEA software, etc. the real time of developing a PFMEA can be accurately determined. It will usually be 70 80% less than the first one. It is important to realise that this is a maturity curve that the team must go through before getting to normal operation. There can be no short cut. NOTE: Process FMEAs within AS13004 describe the application of FMEAs to ensure product conformance. It is recognised that FMEA can be used as an improvement tool too and can be applied in a variety of other situations. The AIAG have produced a version that describes the application of an FMEA process for Tooling and Equipment (design and maintenance). Other examples of FMEA application may be to solve a particular process issue such as CMM programming, paperwork errors, storage and transportation of parts. This guide is only concerned with the use of PFMEA to prevent product non-conformance in line with the principles of Advanced Product Quality Planning (APQP) and as described in AS Control Plan This book will also describe the creation of the Control Plan from the part specific prevention and detection control information contained within the Process FMEA (non part specific controls may be contained in other documents such as maintenance plans or asset care requirements). The Control Plan is a part specific key document that defines the methods of managing the process to ensure conforming product. It is to be used alongside the Work Instructions by the operator and should be referred to during manufacture or assembly to ensure that the right controls are being applied. The Control Plan is a live document and will be subject to regular review and updates, linked to the PFMEA. For me the Control Plan is a simple document to create, once you have a fully completed PFMEA. It is usual that the Control Plan is around a single page per Operation and provides a neat summary of the process controls required to be completed by the Operator. The complexity only comes when the business has duplicate documents to achieve the same end. Some companies put these controls within the work instructions and manage to hide the ten critical controls in a 50-page document making the Operator s job even harder. 16

17 So, what s the benefit? There are a number of companies that have now implemented Process FMEAs using the AS13004 standard approach. There are those who have followed the intent of the standard to the letter and by using sound engineering judgment on the introduction of prevention controls and detection controls have demonstrated the achievement of zero defects. Some of the process changes they made were very simple such as re-defining tool life on the CNC machine, installing bar code checking for correct tooling, fixture maintenance improvements and using SPC. Others have tried the approach and not seen much benefit. However, when you analyse this it is typically because they have not applied the standard to the whole scope of the part number (i.e. not all design features) or they have not identified the right improvement actions from what the PFMEA had identified. They made no changes! As Einstein said, Insanity is doing the same things over and over and expecting a different result. The implementation of AS13004 Process Failure Mode & Effects Analysis must make us challenge what we do today and identify the changes for what we are going to do tomorrow. NOTE: In AS13004 there are many caveats that can be applied to reduce the required application of the PFMEA and Control Plan to just a few features, process steps or even to allow the use of alternative methods. This is usually done by including the reference if agreed by the customer. In this book I am going to describe the application of this standard as part of a Zero Defects journey and hence I will interpret the standard in a way that will deliver the most effective results and not the minimum required. The key precept is that these defect prevention tools are applied to all features and characteristics associated with an individual part number. If you apply this approach to anything less then you are accepting that some non-conformance is inevitable. 17

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19 Chapter One AS13004 Overview AS13004 was published in 2017 and immediately adopted by the Aero Engine Manufacturers. Of all the standards developed by the AESQ thus far this was the one that required each member company to change the most. None of the AESQ members were deploying the standard exactly as described in AS It was recognised however that in order to make the step change in Quality performance demanded by the Industry a different approach was necessary. AS13004 is more closely aligned to the deployment approach seen in the automotive industry with the focus very much on preventing product non-conformance. As a result of this change of focus, and in order to gain consensus, the standard has a few areas that need additional interpretation and guidance. That is the purpose of this book. The standard allows many requirements to be caveated by unless approved by the customer or if specified by the customer. I will try to present a case for the most effective and efficient approach to deploy this standard. The standard actually includes three key linked Advanced Product Quality Planning (APQP) tools, Process Flow Diagrams (PFD), Process FMEA and Control Plans. Figure 3 shows the scope and relationships of this standard with other APQP elements. Figure 3: AS13004 Scope and Relationships Product Key Characteristics Measurement System Analysis Design Risk Analysis (aka DFMEA) Process Flow Diagram (PFD) Process failure Mode & Effects Analysis Control Plan Work Instructions AS13004 Scope Product Process Key Characteristics 19

20 Many people have pointed out that it would have been even better had AS13004 included the Design FMEA within the standard. This is true. Unfortunately, Design subjects are out of scope for the AESQ at this time. That said, in this book I will include a chapter on DFMEA to show the differences and key linkages to the PFMEA. Cross Functional Teamwork (Section 4.1.1) The standard puts a clear emphasis on the fact that these tools must be completed by a cross-functional team and provides a list of those functions that are critical to the successful application of the process. Team members should include all those areas impacted by the results of the FMEA. They include (but is not limited to); Manufacturing Engineers, Process Planners, Design Engineers, Quality Engineers, Process Operators, Inspectors, Maintenance Engineers. The team should have facilitation expertise too with knowledge of the FMEA process. At certain phases of the completion of the PFMEA then additional expertise from component suppliers, equipment suppliers, material experts may also be beneficial. Table 1 shows some examples of the types of representation that may be useful at the different stages of FMEA development. Not all will be required to attend the team meetings at the same time and this would not be practical either. Instead some of these representatives may need to provide specific input to questions raised by the team during the FMEA development. They may also be involved in reviewing the output of the FMEA section to check if anything has been left out. 20

21 Table 1: Examples of Relevant Expertise for FMEA Development FMEA Phase Functions, Requirements & Expectations Potential Failure Modes Effects and Consequences of Failure Causes of Potential Failure Modes Frequency of Occurrence of Potential Failure Application of Current Controls-Prevention Application of Current Controls-Detection Recommended Actions Relevant Expertise Customer, Program Management, Service Operations, Product Safety, Manufacturing, Assembly, Packaging, Logistics, Materials Customer, Program Management, Design, Product Safety, Manufacturing, Assembly, Quality, Packaging, Logistics, Materials, Service Operations Customer, Program Management, Design, Product Safety, Manufacturing, Assembly, Quality, Packaging, Logistics, Materials, Service Operations Customer, Manufacturing, Assembly, Quality, Packaging, Logistics, Materials, Maintenance, Equipment Manufacturer Customer, Manufacturing, Assembly, Quality, Packaging, Logistics, Materials, Maintenance, Equipment Manufacturer Manufacturing, Assembly, Quality, Packaging, Logistics, Materials, Maintenance, Equipment Manufacturer Customer, Manufacturing, Assembly, Quality, Packaging, Logistics, Materials, Maintenance Customer, Program Management, Design, Product Safety, Manufacturing, Assembly, Quality, Maintenance, Equipment Manufacturer, Packaging, Logistics, Materials, Service Operations Applicability of AS13004 (Section 4.2) AS13004 defines the applicability of this standard to primarily New Product Introduction. Process Flow Diagrams (PFDs), Process FMEA and Control Plans are a key requirement within AS9145 Advanced Product Quality Planning (APQP) and Production Part Approval Process (PPAP). When directed by the customer, this standard needs to be applied in the following circumstances to part numbers in current production; 21

22 Table 2: AS13004 Additional Application Guidance for products already in production Event Event Changes resulting from root cause investigation Process changes Design Changes Standard parts / commercialoff-the-shelf - Clarification Clari cation Discovery of an unknown failure mode following an inservice issue, product quality escape, major quality issue or manufacturing issue A change in material, method and/or measurement technique that can potentially affect form, t or function Design record modi cation including the addition of new Key Characteristics This standard is not applied to manufacture of standard parts and/or commercial-of-the-shelf items unless requested by the customer Once invoked the FMEA must be maintained for the whole lifecycle of the product (Section 4.2.3). For many products in Aerospace the lifecycle may be years. It will be critical therefore to ensure that the language and descriptions used within the document will be understood by those who will read it in 10, 20 or even 30 years time. We should avoid any form of technical shorthand. The requirements of AS13004 should be flowed down by the organisation to any supplier that manufacturers and/or supplies products and services (Section 4.2.4). In order to comply with this element, the organisation will need to have a documented process for flowing down this requirement to their suppliers, and beyond in some cases. Over time they will be expected to have evidence that this has been done. Training & Competency (Section 4.3) These resources must be suitably trained in the PFMEA and Control Plan approach. In particular the engineering resources, after all this is an engineering discipline. The organisation should also consider having trained FMEA facilitators who can help the team to run the FMEA sessions. Effective FMEA sessions are a difficult thing to achieve. They need to be creative while managing the technical content, team dynamics, energy levels, etc. as well as making sure that the FMEA is process is adhered to. Having a facilitator manage this while the Technical resources focus on their input will be key. 22

23 We must not forget that the organisation s leadership need to understand the Defect Prevention system approach, and FMEA in particular. They will need support the allocation of resources (people and time) to make the activity successful. Providing leadership training and coaching should be considered as a necessary activity to successfully introduce this standard. There are many sources of training and consultancy in FMEA available on the open market mainly as a result of the past 30 years of the automotive industry demanding PFMEAs from its suppliers. However, care should be taken in selecting these providers. Ensure that the provider has tailored their training to meet the intent of this standard and not simply a generic FMEA course. There are some key points of emphasis with AS13004 that are not necessarily evident in a more general approach. A list of recognised training providers is available on the AESQ website. Also, be aware that although the AS13004 writing team aligned their approach to the AIAG FMEA Guidebook Forth Edition the automotive industry is evolving their approach to FMEA and may have a different set of requirements to those of AS13004 in future years. You must ensure that the FMEA course you select meets the requirements of AS The training syllabus must include the use of PFD, PFMEA and Control Plans but should also include the links to DFMEA too. Some available courses also include the use of Reference PFMEAs. The organisation must document the minimum training and competency requirements for conducting PFDs, PFMEAs and Control Plans and ensure that only those team members that meet these criteria are involved in their deployment. Organisational Quality System Requirements (Section 4.4) AS13004 requires organisations to have a defined process within its documented management system that shows how the business will comply with the requirements of this standard. If an alternative approach to that described in AS13004 is to be used it must first be approved by the customer(s) impacted. It is expected that this documented process will be included within the scope of the 3rd Party Certification (ISO9001 or AS9100) audit, as well as the organisation s internal audit program, to provide assurance as to its level of compliance and effectiveness. The standard requires the organisation to fully implement this standard and ensure that it assessed periodically. An Assessment Checklist to assess compliance is included with the standard and the AESQ website (see Appendix D). 23

24 General Requirements (Section 4.5) As with all of the APQP Defect Prevention tools they must be deployed at a specific part number level if they are to be truly effective. This maybe a big change for some companies who use generic or family of parts approaches today. However, in an industry where we live with the consequences of poor product and process design for 20 to 30 years or even longer there is a clear business case to apply these processes with the right level of rigour at the design and development phase. The customer may provide a documented waiver for this requirement in certain circumstances. The PFD, PFMEA and Control Plans need to be kept up to date and should be revised at regular periods with the findings from quality investigations, quality performance data, product and processes changes, lessons learnt from similar products and processes, etc. The tools, and the PFMEA in particular, is our knowledge management hub. It represents everything we know about how to make the product and the controls required to avoid non-conformance. Once developed it is the most important document we have for managing quality and quality risks. When AS13004 talks about Design Risk Analysis, it is referring to Design FMEA or similar (see Chapter 2). As we will see there is a clear link between the DFMEA and PFMEA when evaluating the Potential Effects and Severity of the identified Failure Modes. However, this link is not necessarily as explicit as some may expect. The PFD, PFMEA and Control Plan should be clearly linked to provide an easy read across from one to another. One example of how to do this is to have a common Operation Numbering and Sequencing Reference and Feature Numbering System that will enable clear read across. 24

25 Chapter Two Design FMEA Although Design FMEA is not included within the scope of AS13004 it has a key role in the development of the PFMEA and so it is included here to provide insight into their relationship. AS13004 does refer to Design Risk Analysis in the document and DFMEA is one example of what can constitute this type analysis. NOTE a Failure Mode Effects & Criticality Analysis (FMECA) does not address the same scope as a DFMEA and therefore cannot be considered equivalent (AS9145, Section ). The purpose of the DFMEA is very different to that of a PFMEA. Although the FMEA template is similar and the process steps are the same, it has a completely different currency. The DFMEA process should start as soon as possible in the Product Design phase. Figure 4 illustrates the key product and process development phases for New Product Introduction. As you can see the product Design and Process Design phases begin simultaneously between the Concept Phase and the program Approval Phase. Both the DFMEA and PFMEA will begin their development at this stage. During these phases the DFMEA will be iterative and be refined as new information becomes available or where the DFMEA identifies design risks that result in design changes. Figure 4: New Product Introduction Phases Concept Program Launch Prototype Pilot Launch Planning Product Design & Development Process Design & Development Product & Process Validation Ongoing Production Feedback Assessment, Corrective Action & Improvement Plan & Define Program Product Design & Development Process Design & Development Product & Process Validation Feedback Assessment, Corrective Action & Improvement 25

26 The DFMEA addresses how a design may fail to achieve the customers specified requirements, usually expressed as product functions. Event Clarification Figure 5: Role of the Design FMEA Customer Drawings & Specifications (1) Customer Defines Functional Requirements Design iterations (2) Design Engineering Create a Product Design to meet the Customer s Functional Requirements Feedback to Customer (3) Process FMEA Evaluates how the Design Process may fail to Produce a Product Design that meets the Functional Requirements of the Customer Outputs from the DFMEA are the Design Verification Plan, Key Characteristics List and Design Improvement plans Input Output PFMEA Key Characteristics List Consequence of Product Failure information The Design FMEA evaluates the proposed design to identify and mitigate the ways in which the design may fail to meet the Functional Requirements of the customer (see Figure 5). For example, the customer may specify that an engine must have a fuel efficiency of X. The Design FMEA will evaluate how the design may fail to achieve this requirement. The Failure Mode in this case would be Fuel efficiency specification not met. For a component such as a pipe the customer requirement may be to transfer water at 50 litres per second at a pressure of 50 bar. In this example one of the Design Failure Modes would be unable to transfer 50 litres of water per second. The DFMEA will then proceed to look for ways in which the Design could fail to meet these requirements i.e. the Potential Causes. For the pipe example this may include specified pipe inner diameter too small. When completing a DFMEA the team must assume that the part will be made correctly. Manufacturing failures to meet specification must not be listed as Potential Causes of Failure Modes. 26

27 The DFMEA will then identify the prevention and detection controls within the design process to mitigate the potential for this design failure e.g. computer-modelling, prototype testing, etc. This will form the basis of the Design Verification program. The DFMEA will produce a list of key risks (Risk Priority Numbers or RPNs) that the team will need to address during the design phase i.e. eliminating the risk or mitigating it. Another output from the Design FMEA will be the key design characteristics that have been identified and will have an impact on Safety and/or performance of the product to the customer. Information from the DFMEA can also be used to inform the Process FMEA of the effects and severity of specific product Failure Modes. Figure 6: DFMEA Typical Inputs and Outputs Typical Inputs Typical Outputs Functional Requirements Boundary Diagram, Parameter Diagrams, etc Regulations Interface Diagrams Schematics Bill of Materials (BOM) DFMEA Design Verification Plan Appearance Service Requirements Design for Assembly Quality & Reliability History DFMEA with risk reduction action plans Product and Process KCs The DFMEA will identify the Prevention and Detection Controls required to ensure that the design process is managed effectively. These are captured in the Design Verification Plan in a similar way to the Control Plan for manufacturing. It should be noted however that simply reviewing the DFMEA when compiling the Process FMEA would not be straightforward. 27

28 The currency used in the DFMEA is very different to that of the PFMEA. The DFMEA looks at functions whereas the PFMEA will focus on features / characteristics. It will not be possible to correlate the features on the drawing with a corresponding feature on the DFMEA. The DFMEA is a good input for the Design Engineer to bring to the PFMEA session but the team will need the Engineer s knowledge to interpret the DFMEA for use with the PFMEA. Where no Design FMEA is available then the Designer will need to support the Process FMEA by identifying the Potential Effects of each Failure Mode and quantifying their Severity from their own knowledge of the product. The DESIGN FMEA Approach The purpose of the DFMEA is to reduce the risk of design failures by; Providing an objective evaluation of the design and design alternatives Evaluating the initial design for manufacturing, assembly, in service and recycling requirements Increasing the probability that Potential Failure Modes and Effects have been considered in the design and development process Developing a prioritised list of Potential Failure Modes, based on the Effects on the customer s product Providing a knowledge base for future reference The DFMEA is a living document and should; Be initiated before design concept finalisation Be updated as design changes occur or additional information is available Be fundamentally completed before the production design is released Be a source of lessons learnt for future design iterations. The DFMEA must be developed by a cross-functional team and is typically led by a responsible Design Engineer. The cross-functional team should include the following areas, but not limited to, Assembly, Manufacturing, Design, Analysis / Test, Reliability, Materials, Quality, Service, Suppliers as well as the design area responsible for the next higher or lower assembly or system, sub-system or component. 28

29 Considering Manufacturing, Assembly and Serviceability in the DFMEA Development Process The DFMEA should include consideration of Potential Failure Modes and Causes that can occur during the manufacturing or assembly process, only when they are the result of the design. These Failure Modes may be mitigated by design changes e.g. a design feature that prevents a part being fitted in the wrong orientation i.e. error proofed. If the design does not mitigate such Potential Failure Modes then they must be addressed in the PFMEA. The DFMEA should also include the consideration of the servicing of the product as well as its recyclability. Preparing for the DFMEA The DFMEA process begins with collecting the information required to understand the system, subsystem and component being analysed and the required functional requirements and characteristics. To determine the required scope the team should consider; What does the product need to interface with? What inputs are there from other products or sub system that are required for the product to meet its own functional design? Do the product s functions include the prevention or detection of a possible Failure Mode in a linked component or system? To identify the required functions of a product using a Parameter (P) Diagram or similar e.g. Functional Block Diagrams. 29

30 Figure 7: DFMEA Example 30

31 Completing the DFMEA Template The header fields are quite straightforward. Remember that the DFMEA will be around for many years and so a traceable history should be prepared. The names of those responsible for the latest revisions will need to be kept along with every iteration. Not all of this will be able to be kept on the front sheet so consider developing a separate revision document. a) Item / Function This describes the physical items, interfaces or parts under evaluation typically taken from the P Diagram, or similar. The function should be described based on the customer s requirements and the team s discussion. If the item or interface has more than one function with different modes of failure it is recommended that they be listed separately. b) Requirement This provides the opportunity to further describe the requirements of each function listed in the previous column. If the function has more than one requirement then these should be listed separately. c) Potential Failure Mode(s) The Potential Failure Mode is defined as the way in which a component, subsystem or system could potentially fail to deliver the intended function (as described in the Function column). Each function may have several Failure Modes however a large number of Failure Modes for a function may indicate that the requirement is not well defined. In such cases consider redefining the Function into a more detailed description. If there are Failure Modes that will occur only under certain conditions e.g. Humidity, high vibration, temperature, Foreign Object Debris (FOD), bird strikes, etc. then these will also need to be included in the evaluation. Once identified the list of Potential Failure Modes can be evaluated for completeness by analysing failures from similar products. 31

32 Figure 8: DFMEA Step 1 (extract) Item Function Requirements Potential Failure Mode Too much fuel transferred Fuel Pipe Transfer Fuel 1 litre per 50 bar pressure Too little fuel transferred d) Potential Effect(s) of Failure Potential Effects of Failure are defined as the Effects of the Failure Mode on the function, as perceived by the customer(s). The customer(s) in this case should include internal customer as well as the end user. Failures that affect safety or regulations must be clearly identified. The Effect of Failure may include a description of the effect at different levels of the component, subsystem or system level e.g. for an Aero Engine, a crack in a turbine blade could lead to a blade release which may cause damage to the engine turbine subsystem and lead to whole engine performance degradation. e) Severity Score The Effects identified can be ranked using Severity Scoring criteria (see Table 3). The team should reach consensus on the right score to use for each effect identified. The most severe (highest) score will be the one used when calculating the Risk Priority Number (RPN) later in the DFMEA process. Failure Modes with a severity score of 1 should not be analysed further. 32

33 Table 3: Design FMEA Severity Scoring Criteria Ranking Level Criteria 10 Hazardous 9 Serious Sudden product failure, safety related. Non-compliance with government regulation. Potentially hazardous. Able to close down product without mishap. Compliance to government regulations in jeopardy. 8 Extreme User very dissatis ed. Product inoperable but safe. 7 Major 6 Signi cant 5 Moderate 4 Minor 3 Slight User dissatis ed. Overall product performance severely affected but still operable and safe. Product function impaired. User experience discomfort. Overall product performance is impaired but is operable and safe. User experiences some dissatisfaction. Moderate effect on overall product performance. User experiences minor annoyance. Minor effect on overall product performance. User slightly annoyed. Slight effect on overall product performance. 2 Very slight Very slight effect on overall product performance. 1 No Effect No effect. f) Classification This column may be used to identify high priority Failure Modes and their associated causes e.g. Safety, Performance or Regulatory impacts. Typically, they are the Key Characteristics of the Design. 33

34 Figure 9: DFMEA Potential Effects and Severity Scoring (extract) Item Function Requirements Potential Failure Mode Potential Effects of Failure Sev Class. Poor engine ef ciency 5 Too much SFC target missed 7 fuel transferred Engine over temperature Fuel Pipe Transfer Fuel 1 litre per 50 bar pressure leading to potential in ight shutdown 8 Too little Lower Thrust 7 fuel transferred Potential for in ight 8 shutdown g) Potential Cause(s) of Failure Mode These are the Potential Causes associated with how the design could allow the Failure Mode to occur, described in terms of something that can be controlled. When identifying Potential Causes care should be taken to use detailed concise statements e.g. the specified material plating allows for hydrogen embrittlement. Ambiguous phrases such as poor design must not be used. Typically, there should be several Potential Failure Causes listed per Failure Mode. 34

35 When preparing the DFMEA the team should assume that the design would be manufactured and assembled to the design intent. Exceptions can only be made where the historical data indicates deficiencies in the manufacturing process exist. h) Occurrence Score The Occurrence score is a relative ranking, which tries to evaluate the likelihood of the Failure Mode being caused by the Potential Cause identified in the DFMEA (See Table 4). The Occurrence number in the DFMEA may not reflect the actual likelihood of occurrence. The scoring criteria use the maturity of the design as a way of determining its likelihood of causing the Failure Mode. New designs are therefore scored as a higher risk than proven, well tested ones. Table 4: DFMEA Occurrence Scoring Criteria Ranking Level Criteria 10 Dif cult to predict Innovative new technology combined with unpredictable deployment conditions. 9 Very High New development without any previous experience. 8 High New design employing new technologies with some experience 7 Moderately High New design including technologies with a previously problematic history, now believed to be mastered. 6 Moderate 5 Low Technology is new or partly new to us, but there is experience of successful comparable usage in the industry. Design based on earlier successful development, but with little or no market experience. 4 Very Low Design uses proven elements under novel conditions. 3 Remote Design uses well-proven elements but with alterations to detail. 2 Very Remote Proven design with a long history of use & production without any known failure reports. 1 Almost nil Technology is well tried and tested in use & production without any failures. 35

36 i) Current Design Controls Prevention Prevention Design Controls are used to prevent the Potential Cause of Failure from occurring, or at least to reduce the likelihood. They include such things as; Error proofing Design and material standards (internal and external) Computer Simulation It is always preferred to prevent the failure rather than rely on detection. The initial occurrence rankings will be affected by the identified prevention controls as there will be no in service data to use. j) Current Design Controls Detection Detection Design Controls can be used to detect the existence of the Cause or the Failure Mode either by analytical means or physical means, before the item is released for production. They include such activities as; Design reviews Pre-production / prototype testing Validation testing Mock up using similar parts k) Detection Score Detection is the rank associated with the best detection control for a particular Failure Mode and Cause. Where there is more than one Detection Control it is recommended to include all of them within the FMEA and use the lowest score. By listing out all of the Detection Controls in place it may help to identify duplicate or redundant detection activities that can be removed. When scoring it should be assumed that the Failure Mode has occurred and then assess the detection control for its capability to detect it. The Detection Ranking Criteria is shown in Table 5. 36

37 Table 5: Design FMEA Detection Scoring Criteria Ranking Level Criteria 10 Almost impossible No known method available or no check made. 9 Remote Only unproven or unreliable methods available 8 Very slight 7 Slight Durable tests on existing products with design elements installed. Tests on existing products with design elements installed. 6 Low Tests on similar design elements. 5 Medium Tests on pre-production design elements. 4 Moderately High Tests on early prototype design elements. 3 High Simulation techniques available at early design stage. 2 Very High Proven simulation available at early concept stage. 1 Almost certain Proven detection methods available at early concept stage. l) Risk Priority Number (RPN) The next stage of the Design FMEA is to calculate the Risk Priority Number (RPN) for each Failure Mode and Potential Cause. The calculation is quite simple. Severity x Occurrence x Detection = RPN The Severity Score we use is the highest ranked number for the Failure Mode, i.e. the worst that could happen. The Occurrence Score for each Potential Failure Mode is used i.e. there will be an RPN score for every Potential Cause identified for a particular Failure Mode. The Detection Score is the best (lowest) score identified for the Failure Mode and its associated Potential Cause (see Figure 10). 37

38 Figure 10: RPN Calculation Failure Mode Potential Effects Severity Potential Causes Prevention Controls Occurrence Detection Controls Detection RPN The Highest Severity Score Every Occurrence Score The Lowest Detection Score An RPN Score For every Potential Cause Once the RPNs for each Failure Mode and Potential Cause have been calculated they can be ranked in order of RPN Score (Pareto principle). Being able to see the Risk Profile of the complete process is useful for us to be able to identify those process steps with the highest risk however such as a simple analysis is not enough to prioritise the actions that need to be taken. 38

39 Figure 11: DFMEA Potential Causes and Controls (extract) Requirements Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Prevention Controls Occurrence Detection Controls Detection RPN Poor engine ef ciency 5 Speci ed diameter oversize Design Standard FSX012.B 3 None litre per 50 bar pressure Too much fuel transferred SFC target missed Engine over temperature leading to potential in ight shutdown 7 8 Lower Thrust 7 Fuel pump pressure speci ed is too high Speci ed pipe diameter too small Design Standard FP35.L Design Standard FSX012.B 2 Engine Simulation Test 1 16 None Too little fuel transferred Potential for in ight shutdown 8 Fuel pump pressure speci ed too low Design Standard FP35.L Engine Simulation Test 1 16 m) Improvement Actions For all of the rigour of a Design FMEA, if done well, if we do not then react to the risk profile then it is of no value. The key focus must be on those risks that scored high for severity, regardless of the other scores. What further action do we need to take to reduce the RPN of these items through, ideally, improving the prevention of the Failure Mode, or if not, improving the Detection of the Failure Mode. Remember the only way to reduce the Severity score is usually to redesign the product or to remove the functionality. 39

40 Next, we should focus on reducing the Occurrence Ranking. This can be achieved through the removal or control of one or more of the Causes of the Failure Mode e.g. error proof the design. Revised drawing tolerances, add redundancy, etc. Detection is a last resort but there are things we can do to reduce risk. The preferred method is through mistake proofing although increased design validation and testing may also reduce the Detection score. Some companies use an RPN threshold value to select which RPNs they are going to improve. This can be dangerous as teams soon learn how to get a score that falls below the threshold value (it is not an exact science after all). Remember the continual reduction of the overall risk should be our aim this is an ongoing process that never stops. Improvement actions should be documented in the DFMEA and once implemented and verified the RPN can be recalculated to measure the effect of the improvement action. Figure 12: DFMEA Improvement Actions (extract) Potential Causes of Failure Prevention Controls Occurrence Detection Controls Detection RPN Recommended Action Resp. & Target Date Action taken Severity Occurrence Detection RPN Speci ed diameter oversize Design Standard FSX012.B 3 None Implement simulation testing at early design stage. Validate at prototype engine stage S. Seward Actions in place Fuel pump pressure speci ed is too high Design Standard FP35.L 2 Engine Simulation Test 1 16 Speci ed pipe diameter too small Design Standard FSX012.B None Implement simulation testing at early design stage. Validate at prototype engine stage S. Seward Actions in place Fuel pump pressure speci ed too low Design Standard FP35.L Engine Simulation test

41 Table 6: Some Common Issues with Design FMEA Deployment DFMEAs are only done for key systems, sub-systems and components. If we consider that the application of Defect Prevention tools must be applied as a system to each and every part number then it is only logical that the DFMEA must also be done for all systems, sub-systems and components. This risk analysis helps to ensure that the appropriate risk mitigations are implemented for the design process (Design Veri cation Plan) and will help to inform the risk pro le within the Process FMEA later. Manufacturing Engineering expect DFMEAs to have feature by feature commentary on Effect of Failure and Severity Scores as an input to the PFMEA. The Design FMEA is looking at the risk of the design not meeting the functional requirements needed, as de ned by the customer and other stakeholders. As its currency is Functions not Features it is unlikely that many feature speci c elements will be listed within the DFMEA and therefore the analysis required for the Process FMEA needs to be done by a Design Engineer, armed with the knowledge of the DFMEA, to interpret this document to answer the questions raised by the PFMEA. The DFMEA team does not include the supplier where the part is to be made. We discussed the importance of having the right cross - functional team assembled to develop the DFMEA and this must include the person(s) responsible for the manufacturing or assembly processes. If this is being done by an external supplier it is vital that they are included within the team so that their input can be gathered and used to inform the design team of potential risks. The same will be true for Design for Manufacture and Assembly activities. The DFMEA is completed after the Design has already been nalised. One common issue experienced is that the DFMEA is completed after the design has already been nalised. This means that the DFMEA is only capturing what has already been designed. That is not the purpose of the DFMEA. The DFMEA is a tool to help re ne and enhance the design of the part and therefore must be started, as the design is rst being considered and iterated as the design develops. The same is true for Process FMEAs. The Detection Control refers to obtaining Manufacturing or in-service data. The Detection Controls must rely on testing during the Design Phase. If we wait for data to become available once in production it will be far too late to validate the design and may lead to expensive re-work or investment to address design weaknesses. 41

42 Further Reading: Potential Failure Mode and Effects Analysis (FMEA), 4th Edition, AIAG, 2008 DFMEA Key Questions: 1. Has the DFMEA been conducted by a cross functional team, including Design, Manufacturing Engineering, Service, Quality and Supplier (as applicable)? 2. Has the Cross Functional Team been trained in FMEA? 3. Has the DFMEA been started at the correct time in the program? 4. Are the DFMEA inputs complete and have they been used to scope the DFMEA e.g. Functional Diagrams, Voice of the customer, Production / Assembly capability, Measurement capability, Service history, quality history, etc. 5. Has the DFMEA been completed using the correct template? 6. Do the Design Failure Modes describe how the design could fail to meet the functional requirements? 7. Are multiple Potential Effects identified for each Failure Mode? Have the Severity Scores been assigned in line with the scoring criteria? 8. Are there multiple Potential Causes identified for each Failure Mode? Do they describe how the design process could cause / allow a Failure Mode to occur? 9. Has the Scoring criteria for the Occurrence of the Design Potential Causes been done using the approved scoring criteria based on Product Maturity? Has it been applied consistently? 10. Have Prevention Controls been identified to eliminate / reduce the likelihood of the Potential Cause from occurring? How effective are they? 11. Have Detection Controls been identified to detect the presence of the Failure Mode and/or Potential Cause? How effective are they? 12. Has the Detection Scoring been carried out using the correct criteria? Has it been applied consistently? 13. Have Improvement Actions been identified based on the following priority (i) High Severity scores (ii) High severity and high occurrence combinations, or (iii) High RPNs. 14. Has the Design Verification Plan been developed using the DFMEA Controls identified? 42

43 Design Verification Plan The output of the DFMEA is used to inform the Design Verification Plan (DVP). It is an iterative process that requires the team to ensure that the identified prevention and detection controls listed within the DFMEA are documented. The DVP is similar to the Production Control Plan discussed later. It is a summary of all of the required Verification activities to evaluate that the design meets the design requirements. It will include such things as; Simulation studies Prototype testing Design reviews Validation testing Special Product & Process Characteristics Special Product and Process Characteristics can be identified by the Customer or the business responsible for the design and manufacture based upon the knowledge of the product and process. The purpose of identifying these special characteristics is to ensure that they are highlighted for special attention through the APQP and Process Control phases of design, manufacture and service. Typically, they are identified through the use of DFMEA, PFMEA and historical knowledge of other similar parts and processes. Some customers may require these characteristics to be designated using a specific symbol on the drawings and associated documentation. 43

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45 Chapter Three Process Flow Diagrams (PFD) The Process Flow Diagram (PFD) is a representation of the process steps required to make or assemble a product, in sequential order, from receipt through to shipment. When developing a PFD there are a number of inputs that maybe useful, these are shown in Figure 13. Figure 13: PFD Typical Inputs Typical Inputs DFMEA Design Records Bill of Materials Product & Process KCs Tooling & Equipment Handling Equipment & Packaging Process Flow Diagram (PFD) Process FMEA Subcontracted Process Steps PFD from Similar Products Quality History from Similar Products The PFD needs to be sufficiently detailed to describe the key activities required to make and assemble the product including part movement and storage. The PFD does not need to include the processes for purchased materials, components and assemblies. Instead the supplier of those materials, components and assemblies would be expected to define their own Process Flow Diagrams in line with AS13004, after all this standard must be flowed down through the supply chain. Typical operations to be included in a PFD are shown in Table 7. 45

46 Table 7: Typical Operations and Symbols for creating a Process Flow Diagram Typical Symbols Operation Description Administration Packaging Interaction Lift (mechanical / other) Load / Install Fabrication / Transformation Move Δ Store Inspect Rework Other (Specify) There are many systems in use today that allow organisations to document the Process Flow. AS13004 provides two examples to illustrate what the PFD could look like. One such example is shown in Figure 14 (included in AS13004 Appendix C as Figure C3). 46

47 Figure 14: Process Flow Diagram based on AS13004 s Figure C3 Example Operation Step Administration Packaging Interaction Lift Load / Install Fabrication / Transformation Move Store Inspect rework Other Operation Description Classi cation Product KC Process KC Control Methods 100 CNC Drill - Set Up Δ 1 Select correct NC programme Scan bar code on batch card 100 CNC Drill - Set Up 2 Load tools into CNC Laser tool checker on CNC 100 CNC Drill - Load material 3 Load billet material Bar code check 100 CNC Drill - Drill holes 4 Drill holes KC Fuel port inner diam. CMM at OP CNC Drill - Drill inspection 5 Visually inspect hole condition Visual standard 150 CNC Drill - Deburr 1 Deburr Visual standard The Process Flow Diagram in Figure 14 shows a level of detail for illustration purposes. In practice the business may need to add additional detail such as specifying the hole specifications, addition activities, etc. This needs to be defined by the business and what it finds to be of value. Figure 15 shows the second example of a PFD template included within AS13004 for the same operation and steps as Figure 14. It is a simple text-based format but includes the same types of data as for Figure 14 s example. The notes along-side this template in the standard indicate that the columns for Inputs, Outputs and Controls are not mandated by the standard but are considered good practice. In other words, to satisfy the intent of the standard the PFD only needs to contain the sequence of Operations and a description of the steps within that Operation. This makes sense to some degree as the Characteristics Matrix will include the sequence of inspection operations aligned to where the feature was created and the Control Plan will provide details of the inspection requirements. 47

48 Figure 15: Process Flow Diagram based on AS13004 s Figure C4 Example 48

49 The PFD is a key input when developing a Process FMEA. The FMEA will follow the same sequence as defined in the PFD. The PFMEA shall include all operations listed in the PFD. Details of the steps within each operation shall be used in the PFMEA based on risk (Section 4.7.4). For example, in the process steps for OP 100 listed in Figure 14 not all of these details would be transferred to the PFMEA in the Operation, Step and Requirements columns. The PFMEA focuses on those steps where the product can be transformed, intentionally or unintentionally. Therefore, in this example we would not include the details for; Step 1 Administration load Machine Tool Program Step 2 Load tools Step 3 Load material Step 5 Drilled hole inspection That is not to say that these steps are not considered elsewhere within the PFMEA, they are. Typically, they would feature as Potential Causes of Failure not as Process Requirements or Failure Modes. For example, if we take load CNC program as a step the logical Failure Mode would be load wrong CNC program. What would the effect be? It s hard to say. If it was just a version control issue then maybe it would just have some alternative features whereas if it was the totally wrong program then the machine may crash and damage the machine and the loaded part. Therefore load incorrect program is really a Potential Cause of a Failure Mode of severe damage. Similarly, load incorrect tools can be linked as a Potential Cause for hole oversize or undersize, load incorrect material is a Potential Cause for part made from incorrect material. Inspection processes will be listed in the PFMEA Detection Controls column for Drill Hole and does not need to be considered as a process step in its own right. This is true for all inspection operations. The only reason to include an Inspection operation, as a step in the PFMEA would be to consider the possibility of unintentionally transforming the part e.g. damage, FOD, etc. 49

50 This is a key care point as there have been occasions where Manufacturing Engineers have interpreted section of the standard, which states Details of steps within each operation shall be considered and included [in the PFMEA] based on potential risk as an opportunity to pick and choose what can be left out of the PFMEA. The explanation above shows that all steps that transform the product (intentionally or unintentionally) must be included. There will be some, based on risk, that can be omitted on that basis e.g. Load tooling, documentation checks, etc. The evaluation of the inspection process capability is done through AS13003 Measurement Systems Analysis (MSA). Further Reading: AS13004 Process FMEA and Control Plan for Aerospace, AESQ, 2017 Potential Failure Mode and Effects Analysis (FMEA), 4th Edition, AIAG, 2008 PFD Key Questions: 1. Where available, have all identified inputs to the PFD been included? 2. Does the PFD include detail of all operations in sequential order from receipt of materials through storage and shipment of finished product? 3. Does the PFD provide a clear and complete description of the process required to receive, make, inspect, test, protect, store and ship conforming product? 4. Does the content of PFD align to the requirements of AS13004?, if not, has this been agreed with the customer? 50

51 Chapter Four Characteristics Matrix AS13004 does not provide any details on what a Characteristic Matrix is although it does list it as one of the inputs for a PFMEA. In my opinion this is one of the most important inputs to developing a PFMEA. A Characteristics Matrix is a simple but important document. It shows the relationship between the operations and the features (including specification details) created at that operation. In addition, it also shows where that feature is inspected. Operations that can affect a feature created at an earlier operation are also listed. Examples of these types of processes include Heat Treatment, Coating, Welding (directed heat source), etc. It allows the Planning Engineer to ensure that all features are included in the process and to assess the potential for minimising inspection operations, problems with transformations, etc. In AS13004 the PFMEA should include all operations and all features. The Characteristics Matrix is the only document that includes this detail and the sequence in which the features are created. Some companies may not include all specification requirements in the Characteristics matrix such as material properties, damage, surface finish properties, etc. In such cases the team will also need to refer to the relevant specifications and standards. Figure 16 shows an example of a simple Characteristics Matrix. Figure 16: Simple Characteristics Matrix example (truncated) Feature Details Operations Sequence Feature Number Description Speci cation OP100 Drill OP150 Deburr OP200 Clean OP250 CMM etc. 1 Fuel Port Inner Diameter mm +/- 0.1 mm X A I 2 Fuel Port Location 1450 (x), 761 (y), 600 (z) X 3 Oil Port Inner Diameter mm +/ mm X A I 4 Oil Port Location 1150 (x), 200 (y), 45 (z) X etc. Key: X = Feature Created, A = Feature Affected, I = Inspected 51

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53 Chapter Five Process FMEAs Process FMEA in a Nutshell The Process FMEA will evaluate every feature and specification required defined by the product design and ask the question What are the potential ways I could make this wrong? [Potential Failure Modes] The team will then use the FMEA methodology to understand the potential impact on the customer and the business if the product was made wrong [Potential Effects & Severity Score]. For each Potential Failure Mode, the team will determine the adverse process conditions that would need to occur to create it [Potential Cause(s)]. With this knowledge the team can then identify ways to prevent the adverse process conditions from occurring [Prevention Controls]. The Team will then work out how likely the Failure Mode and the Potential Causes are likely to Occur (Occurrence Score]. In addition, the Team will identify ways to detect the Failure Mode and/or the Potential Cause if they were to occur in Production [Detection Controls]. The Team can then calculate the Risk Profile Number for each Failure Mode and associated Potential Cause [Risk Priority Number (RPN]. The team must use their judgement to determine whether the controls in place are sufficient or whether further improvement actions are required. It s that simple! Cross Functional Team Approach As previously discussed the Process FMEA is a highly detailed assessment and needs to be conducted by a cross functional team including Manufacturing Engineering, Process Planners, Process Operators, Quality Engineers, Design, Inspectors, Supplier(s) (if appropriate), Maintenance, as a minimum. The team must have the right experience and knowledge of the product and process to add value to the PFMEA. Not all Functions will need to be present for all FMEA sessions. The FMEA Facilitator should ensure that the right people are present for each session. There is nothing worse than sitting in an FMEA session with nothing to contribute to the discussion. 53

54 PFMEA Scope For a Process FMEA to be effective it must evaluate ALL the features / characteristics on the design drawing and related specifications and consider every process step (where the product is transformed or has the potential to be transformed including inadvertently such as damage due to storage & handling (Section ). A Process FMEA is required for every individual part number (Section 4.5.1). Section appears to provide a caveat to the requirement for all features to be included in the PFMEA. It states, If specified by the Customer, all product features and potential failure modes shall be documented within the PFMEA to ensure that each are evaluated. The wording suggests that you only need to consider all features if the Customer requires it. However, it provides no details on how to select a sub set of features either. I have seen some approaches suggested to select these important features but none are convincing if we really want to prevent all non-conformance. One proposal to reduce the time taken to complete a PFMEA is to select only those features or process steps where it is believed that are important to the Design, i.e. Design KCs. In all my years of having to evaluate reasons for customer escapes I cannot remember any that were for Design KCs. This method of identifying important features would also limit it to only 1 3% of all the features on the drawing. This significantly reduced scope would not provide me with much confidence that we had completed an effective risk assessment. In addition, remember that what Design sees as important from the DFMEA they are looking at the product through a very different lens to that in Manufacturing & Assembly. Their focus is usually on Safety and Performance issues. We know that Manufacturing & Assembly can take, what Design would judge to be, a very benign feature, and under certain circumstances make it a very disruptive quality issue. There are numerous examples where this pre-selection of what is important has failed to consider something that has gone on to have a significant impact to the customer. The PFMEA is a tool that can evaluate all process steps and product features in order to identify where the risks in the process are. Therefore, if we do not consider all design features and process steps then the risk assessment will always be compromised. 54

55 This may appear to be a daunting task, particularly for those organisations that are new to PFMEA. However, through the use of computer software and a structure of Reference FMEAs the time taken to create a Process FMEA can be greatly reduced and still remain effective. This approach is described in Chapter s Six and Seven. Don t fall into the trap of spending valuable time selection where to start first and select key features or process steps on a priority basis. Once established the PFMEA process will be best deployed by starting and the first operation and working your way through to the last one. I have seen teams spend more time on this prioritisation process than actually doing the PFMEA. Inputs for a PFMEA AS13004 identifies a number of inputs required to create a PFMEA and a number of outputs from the PFMEA. These are shown in Figure 17. Figure 17: PFMEA Inputs and Outputs PFD Identification of all steps within each operations Non conformance data from similar products / processes Characteristics Matrix DFMEA PFMEA Control Plan PFMEA for similar products Products KCs Process KCs Control Plan from similar processes PFMEA with action plans Product and Process KCs I would also add one more input, Reference PFMEAs. We shall discuss this later in Chapter 6. To show how some of these sources are used to create the content of a PFMEA Figure 18 shows a relationship between the data needed in the PFMEA and its source. 55

56 Figure 18: The PFMEA and its Typical Data Source Process Flow Designer armed with A DFMEA Quality Metrics (Cpk, Scrap, Rework, Escapes, etc) Process Step Requirements Failure Modes Effect Severtiy Classification Potential Causes Prevention Controls Occurrence Detection Controls Detection RPN Characteristics Matrix Drawings & Engineering Specifications Reference PFMEA (or team knowledge) Process Flow The following notes are intended as a guide of what to look for to ensure that the Process FMEA has been conducted effectively. Although the example we use here is a CNC machining one the principles can be applied to any process including Processing, Assembly, Casting, Coating, Welding, Surface Preparation, Raw Materials, etc. There are some examples of these applications in Appendix B. Figure 19 shows a part completed Process FMEA for a machining operation that is required to drill four holes to a specified diameter. AS13004 requires organisations to use this template, or one with equivalent content. Any deviation to the use of this template shall be approved by the customer (Section ). Similarly, the Ranking criteria for Severity, Occurrence and Detection documented in the standard should be used although alternative criteria may be acceptable if approved by the customer (Section ). It is vital that the descriptions included within the PFMEA are detailed enough to be understood by engineers who were not directly involved in the creation of the document. These documents will be in use for many years, maybe up to 30 years or more, and it is vital that future teams can read and understand the intent of what has been captured in the PFMEA. The precision of the use of language in a PFMEA is paramount. How to complete a Process FMEA using the AS13004 PFMEA template: 56

57 Figure 19: Process FMEA example (truncated) 57

58 a) Part Number & Description The requirement is to include the full Part Number and a brief description of the part. The description should include the Model / Engine Name, e.g. Engine X and a brief name of the part e.g. Fan, Compressor Blade, etc. The Process FMEA should be specific to an individual part number or assembly. Rarely will it be appropriate for a single Process FMEA to cover more than one part number / assembly. The two main reasons often cited for the use of non-part specific PFMEAs are; Generic Processes It is often thought that processes such as Heat Treatment or Cleaning are exempt from the specific Part Number approach of a PFMEA. On the face of it, this is how it may appear; however, there are always examples where impact of the Failure Mode created by the process is unique. An example may be two similar looking parts, Part A and Part B, with the same function, made out of the same material, with a requirement to be hardened by using a Heat Treatment process. One Failure Mode is that the material is insufficiently Hardened (too soft). The causes of the Failure Mode are the same, as are the Prevention Controls and Detection Controls. So, would the PFMEA be the same? No. The trouble is that this misses out the fact that Part A, if too soft, may only cause minor performance issues for the end product. However, Part B, although similar, is part of a differently designed system and is operated in a different way. If Part B remains soft then it may lead to a high severity event. If we know this then we may decide that we need additional Prevention and Detection Controls when processing Part B because of this analysis. If we only did a Generic PFMEA on the Heat Treatment process we would have missed this difference. Unfortunately, I am aware of many, many instances where this type of approach has missed vital differences such as this. Therefore, it is recommended that these processes are considered in the same way as a machining process and unique to each part number that goes through it. Just as with other processes such as machining, the consequences of a process failure are likely to be specific to the part number specific application. 58

59 Part Families It is often proposed that many parts can be grouped together in a part family and be considered as a single entity for Process FMEA analysis. The risk profile of a PFMEA is based on 3 things; a) The consequence of failure derived from the purpose of the feature [Potential Effects & Severity] b) The likelihood of Occurrence derived from the specification (tolerance) and the relevant process capability [Occurrence Score], and c) The Detection Method derived from the measurement strategy or use of error proofing [Detection Score] If the features on the different parts within the family have the same risk profile then it will need to demonstrate that it has the same features, with the same purpose, identical specifications, and identical detection methods. Very few parts with a different part number will share all of these attributes; if they did why create a separate part number? There are some examples of where this approach can be used though. Some parts will have variants that may require 80% of the features to be identical with some other features modified, removed or added. For example, a Cylinder Head used on a V8 5V engine is also used on a high-powered derivative. In the derivative the cylinder bores are honed to a tighter specification but all other features remain the same. This is an example where the Family of Parts approach can be taken and the additional PFMEA analysis needs only to be completed for the modified cylinder bores. b) Core Team The requirement is to list the core team members and their positions that were responsible for the original document. We should remember that this document will be regularly updated for the life of the part and therefore the team members will change over time. It is important that the team is comprised of the right resources to be able to identify and assess potential product Failure Modes and Potential Process Causes. As a minimum it would be expected to include Manufacturing Engineering, Design Engineering, Operations, Quality and Maintenance. 59

60 It may also be appropriate for a Customer and/or a relevant Supplier representative to be involved at certain stages of compilation or review to capture their insights. Not all members of the team need to be present for all stages of creating the FMEA as their input may be limited to specific aspects e.g. The Design Engineer has input into the effect and severity of the identified Product Failure Modes but may not have knowledge of the process to add any real value. When compiling PFMEAs it is always best to keep the team relatively small and manageable, with those resources applicable to the phase being discussed. Too many team members will only serve to slow the process down and will have little added value. Figure 20: Team Size Effectiveness Effectiveness %s Team Size Once completed, the Part Specific PFMEA can be circulated to a wider group for additional input and sanity checking. c) Original date / Revision date The Process FMEA will be a live document and as such revision control is vital to provide a traceable history of updates etc. Revisions to a Process FMEA will be expected if any of the following occur; Product definition changes Process changes (including inspection processes) Updates from 8D investigations / Continuous Improvement actions Quality Performance data that may influence the RPN scores 60

61 d) Operation / Step The Process FMEA must include all process steps where the product is transformed even where the transformation may be inadvertent, such as during handling and storage. The Process FMEA must include all steps from the first operation through to dispatch. Care must be taken not to fall into the trap of only completing the PFMEA on processes that are seen to be important. The Process Steps should be defined on a Process Flow Diagram that shows the sequence of operations and the purpose (required outcomes) of each operation. A Characteristics Matrix should be developed to show where the features are created, transformed and inspected at each operation. Some common mistakes observed are; Transactional processes are included e.g. complete batch card, load CNC program. These in themselves are not relevant to the Process FMEA although they may appear as a Potential Cause of a failure if a link can be made. Similarly, processes such as Load Tools into CNC similarly do not belong in a PFMEA as a process step. There can be no product Failure Modes created at this process step, as it is not used to transform the product. If the loading of tools has any impact on product quality then this will be recorded as a Potential Cause of a defined Failure Mode, for example oversize hole diameter [Failure Mode] due to tool damage [Potential Cause] in the PFMEA in a later process step. Measurement processes are included as a process step in their own right and identified as the cause of dimensional non-conformance. For example, CMM Measurement of dimensional features [Requirement] can have a Failure Mode of incorrect measurements [Failure Mode] due to Poor calibration [Potential Cause 1] or incorrect CMM programming rules used [Potential Cause 2]. In the context of PFMEA the CMM does not create non-conformance, the manufacturing process does. The Measurement Process will be validated using Measurement Systems Analysis (MSA) separately to prove its capability. If we use the definition of only evaluating process steps that transform the product, intentionally or inadvertently then at the Measurement Operation Step the only aspect we should be evaluating it the potential for Damage, Contamination, FOD, or similar due to part handling and/or storage. The Measurement method is considered at each process step as part of Detection Method. NOTE: The PFMEA Case Study in the Appendix of AS13004 (Fig C5 Case Study PFMEA) is not a great example of how to word the Operation Step or Function Description. 61

62 On the first line of the PFMEA it states Set up drill in both the Operation and Function Description columns. However, the Requirements column describes the hole diameter that the drill is required to produce. The Failure Mode then describes how the diameter can be made wrong (too big, too small). In other words, the PFMEA is not describing the set-up of the drill at all but actually the drilling operation. On the fifth line of the PFMEA when the Process Function does state Drill hole it is clear from the Requirements column that it is only talking about the hole depth feature. Once over these initial steps the logical flow carries on as we would expect to see it. e) Process Function / Requirement For each Operation the function (purpose) and the required outcome (Requirement) should be defined clearly, accurately and concisely. The Potential Failure Mode (next column) should be able to be derived straight from the Function / Requirement description. Some examples are shown in Table 8. Table 8: Deriving Failure Modes from the Requirements Description Requirement Failure Mode Drill hole 10mm +/- 1 mm Hole too big Hole too small Grind Surface with a Max Surface Finish of 3 RA Weld bead with porosity to meet spec xyz Fit seal in correct orientation Fit seal without any damage to surface Surface too rough Porosity exceeds spec xyz Seal tted in wrong orientation Seal not tted Seal surface damaged 62

63 At this step it is important to identify all of the requirements that help to define a feature as conforming or non-conforming. For example, many features will have a general specification associated to it that is not necessarily apparent on first glance. A drilled hole feature will have geometric tolerances but also may be subject to an Engineering Specification that specifies no white layer or similar. All requirements whether on the drawing or written in a related specification must be included. In the AS13004 standard there are some conflicting requirements regarding the scope of what needs to be included in this column. Section states that all product and process characteristics, including KCs shall be documented in the PFMEA while Section states If specified by the customer, all product features and potential failure modes shall be documented in the PFMEA. This implies that unless the customer specifies the requirement for all features the supplier is able to set their own threshold although no guidance is given for how this is to be done. The PFMEA is a tool for assessing the level of risk associated with manufacturing / assembling a product. If features / requirements are excluded from this analysis then the output of the PFMEA will be compromised. Any defect will cause additional costs, delays and performance issues and therefore if we are to apply PFMEA to avoid such defects then it must consider all features to begin with. Simple Mistakes If we are to identify the right Failures Modes (product related) it is critical that the Requirements are defined accurately. However, it is a common mistake to see the team identify the wrong requirements from the input documentation such as the Process Flow Diagram. Consider the case for cleaning operations using a chemical etch process. The process flow diagram provides the details of the steps of the process as described in the Requirements column in Table 9. With this description it is easy for the team to fall into the trap of deriving the Failure Mode from this poor Requirements description. As you can see the Failure Mode describes process non-compliance, and not the product condition. 63

64 Table 9: Problems with Poor Requirements Description in a PFMEA Requirements Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure In bath for too long Removes metal from part and makes non-conforming. Scrap part 7 Timer faulty. Operator distracted Put part in acid bath for 45 seconds In bath for too short a time Contamination & grease remains on part. Needs rework. 5 Timer faulty. Operator distracted Wrong Acid Depends on the acid type. Maybe scrapped or reworked. 7 Operator error. Place Part in water bath for 3 minutes In bath for too long In bath for too short a time Nothing 2 Acid residue remains on part. Rework required. 5 Timer faulty. Operator distracted Timer faulty. Operator distracted Because we now have process non-compliance in the Failure Mode column our analysis goes off track and we exacerbate this error by now describing the effect and severity of the process non-conformance rather than that of the product. This analysis will tend to be inward looking as it does not include the impact on the system or the customer. By the time we get to identify the potential causes of this process error, we will be focussing on a very limited number of options and these are not connected to the Part non-conformance. Using this logic, the PFMEA also loses its ability to be connected to the Design FMEA through the Failure Mode description in the PFMEA. What should we have done? The purpose of this cleaning operation is to remove grease and dirt prior to the E Beam welding operation. Any contamination left on the part may lead to weld porosity, which in turn could lead to a weld failure. If the weld was to fail then it could cause an engine shutdown during operation (high severity issue). With this description the PFMEA will turn out very differently. As you can see in Table 10 the Requirements column did not need all of the individual detail from the Process Flow Diagram. The Failure Mode Column talks about how the product would not conform to requirements, not the process faults. This in turn has led to a better Potential Effects description and one that includes the impact on the customer. The Design Engineer has derived this from the DFMEA. 64

65 Also, the Potential Causes now cover a wider range of issues linked to the process that could cause the part to still be contaminated after the cleaning process. It is this richness of process Potential Causes that we are seeking to identify and then mitigate using the PFMEA process. Table 10: Using the Correct Requirements Description in the PFMEA Requirements Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Clean Part Potential for Porosity at the next Operation (E Beam Welding) This could lead to a weld failure and an in ight shutdown without warning. 9 Acid strength too low Acid bath contaminated (remove grease and surface contamination) Part not clean Y Insuf cient cleaning time Can be reworked a maximum of 3 times if found during production 4 Water bath (rinse tank) contaminated Environmental contamination in cleaning area / storage Do not remove any base material Base material removed Part pro le not to speci cation leading to loss of aerodynamic ow resulting in lower than required ef ciency 7 Acid strength too high Acid Cleaning cycle too long Dealing with Manufacturing Tolerances Some businesses use the practice of stage drawings or manufacturing drawings that include specifications that differ from the Design Drawing. This may be because the manufacturing process needs to work to tighter tolerances because of later tolerance stack up issues or uncontrolled transformations that occur later in the process. The PFMEA must include Manufacturing Tolerances that are used to manufacture of the part. Ideally these Manufacturing Tolerances will be identified in some way within the PFMEA to make it clear that it is a Stage Drawing or Manufacturing tolerance requirement and not a design one (e.g. a designated symbol in the characteristics column or other means). 65

66 Manufacturing tolerances can also refer to processes required for a successful manufacturing step. For example, a cleaning operation may be included prior to welding to ensure there is no contamination that could cause porosity. Although this may not be specified in the drawing or specifications there is an internal requirement to ensure the part is clean prior to welding. Therefore, at the cleaning operation it is allowable to include clean part as a process requirement (the cleaning process may also be referenced as a potential cause of porosity defects when evaluating the welding process). Figure 21: Process Function and link to Potential Failure Modes in a PFMEA Operation Step Function Requirements Potential Failure Mode 10 1 CNC Machining Drill Drill hole 10 0 mm diameter +/- 0.1 mm Too Big Too Small In this example we can see that the Potential Failure Mode is a logical step from the way in which the requirement was described. This is particularly important for assembly operations where the level of detail required may not be so obvious. For example, when fitting two parts together the characteristics of success are not so explicit on the drawing or design notes. Therefore, the Process FMEA (and later the Process Instructions) must provide the detail required. For example; Fit Part A to Part B in the correct orientation without causing any damage to surface D and fix with a single threaded bolt and nut to a torque value of 100N +/- 2 N and an angle of 360 degrees. 66

67 Hence from this description the following Failure Modes could be derived; Incorrect orientation Damage to surface D Torque too high Torque too low No torque Bolt not fitted Angle not achieved We must take care not to infer requirements that are not there. There are examples where the requirement was for a drilled hole at 10mm +/- 0.2 mm and the team went on to list other Failure Modes such as hole not round. Unless there is a specific roundness specification called out on the drawing then this is not relevant and should not be included. There may also be some general drawing specification requirements that need to be considered at certain operations. These include such things as; No Damage / Damage not to exceed specified limits No Sharp edges / burrs No Foreign Object Debris (FOD) / No FOD above specified limits If appropriate to the operation these should be considered as additional requirements of the operation and hence will have associated Potential Failure Modes. f) Potential Failure Modes As described in the previous section the Potential Failure Mode is the way in which the product could fail to meet the design intent (drawing or specification). It is critical that the Potential Failure Mode describes a product feature / characteristic and not a process failure. If this column is not completed correctly all of the subsequent work in the FMEA columns to the right of this one will be irrelevant. A simple question to ask is does the Potential Failure Mode describe something on the product that is not right to the drawing or specification? It should not describe the ways in which the process could fail, that will be considered in the Potential Causes column. There are likely to be several Potential Failure Modes per feature / characteristic. This is another good way to check if sufficient rigour has been applied to the PFMEA, if there are only single Failure Modes identified then something is likely to be wrong. Care should be taken not to simply list degrees of error though. For example, hole too small is often adequate to describe a Failure Mode and its consequences. Avoid using hole just undersize along with hole 10% undersize, and hole twice tolerance undersize, etc. If there is a series of consequences due to hole too small then this should be captured in the Potential Effects column. 67

68 For example, if we consider hole oversize as a Failure Mode then the Potential Effects listed could include; 1. Part would become loose, vibrate and may eventually crack during operation (this would need the hole to be very oversize e.g. 100% above specification) 2. Part may allow some movement and cause difficulty in assembly operation (oversize by up to 50% of tolerance) 3. Part may be non-conforming but acceptable on concession (oversize by a max of 10% of tolerance) Table 11: Failure Mode Examples Valid Failure Mode Description Hole too big / too small Surface nish too rough Torque applied above speci cation Pro le shape incorrect Missing feature Porosity in weld material Hole out of position Part tted in wrong orientation Invalid Process Failure Mode Descriptions Drill broken Machine failure Wrong torque setting used Scrap parts Wrong CNC program used Damaged tooling Incorrect coolant pressure Operator ts part incorrectly Another good sanity check at this stage is to review the identified Failure Modes against known non-conformance on similar parts e.g. customer escapes, scrap causes, rework causes, etc. Have all of these Failure Modes been captured? It is important to capture all potential Failure Modes and not just those that have happened before. This is a Risk Analysis and therefore if it could happen, we must capture it (Section ). g) Potential Effect of Failure This is a key point where the link to the Design FMEA and Design Engineering has an important role to play. Every feature will have a design purpose, otherwise why would it be there? Therefore, if the feature was not present or was nonconforming we must understand the impact that will have on the final product (as seen by the customer or end user) as well as the impact on the manufacturing plant / business. 68

69 This is one of the factors that help to explain why process based (generic) PFMEAs as opposed to product focused PFMEAs are not effective. In a process based PFMEA the risk would be assumed to be equal for all holes drilled during that operation and hence scored identically. The different purposes of each hole mean that the effect and hence the impact for each hole may be different. This would not be identified unless the PFMEA focuses on the specific Product Features. Using the process based PFMEAs also means that the link to the Design FMEA is irrelevant. All relevant effects should be listed for each Potential Failure Mode. We would expect to see multiple effects for most Potential Failure Modes (another good check to make). The most important effects to highlight are those that will be experienced by the customer or end user, particularly if there are safety implications. Internal effects should also be listed e.g. scrap, rework and for certain product Failure Modes where there may be a significant safety impact to the operator, these should be included too (see Severity Scoring guidelines). Providing the Right Level of Detail for the Potential Effects Description When describing the Potential Effects of Failure, it will be important to understand the conditions that need to be present for the Effect to be realised. For example, a dimensional defect may have a range of potential effects depending upon the scale of the non-conformance. This means that the defect may sometimes be cleared on a concession, reworked or scrapped. But to say this is not enough, we need to explain when it is ok to concess it or scrap it. So, for this type of Failure Mode we would expect to see three types of effect description; 1. If the defect is oversize then it may be possible to rework the dimension and bring it inside the specified tolerance 2. If the dimension is marginally out of the bottom of tolerance and therefore cannot be reworked then Design may be able to grant a concession to allow the product to proceed 3. If the part cannot be reworked or concessed then the part will be rejected (scrapped) There may be times where a Failure Mode in one process could cause a different Failure Mode later in the process. For example, contaminated part is a Failure Mode for a cleaning process and one Effect of Failure could be Porosity in weld at a later operation. In this example the team must be as specific as possible in the description of the Effect. NOTE: Operator safety impacts should only be considered if they are resulting from a product failure not a process one, and then only if it meets the criteria specified in the Severity Scoring table i.e. not for minor HSE issues. Safety Risk Assessments are a separate activity. 69

70 h) Severity Rating The severity of each potential effect of failure is made using the scoring table in AS13004, and shown below in Table 12. When calculating the Risk Priority Number (RPN) later on the highest (most severe) score will be used for this Potential Failure Mode. There is sometimes a misconception that the Engineers can look up the effects and severity of a non-conforming feature straight from the Design FMEA. This will rarely be the case. The Design FMEA is focussed on Functional requirements and how the design process could fail to achieve them. It will not necessarily identify specific features. For example, the DFMEA when evaluating the design of a fuel pipe may identify that if 50 litres of fuel will not be transferred at a pressure of 50 bar in 1 minute then the engine may stall. The design will specify a pipe diameter as one of the critical features to enable this functional requirement to be met. In the PFMEA it will identify Potential Failure Modes of diameter too big or too small. This will require the Designer to evaluate the effect and severity of these Failure Modes, informed by the DFMEA, but it is not a simple look up. The presence of the Design Engineering representative is crucial to both identify the potential effects and score the severity. In the same way, even if there is no DFMEA available, having the right Design input can enable an effective Process FMEA to be created. If the Severity Ranking for a Failure Mode is scored as 9 or 10 then this should be reviewed with the Design Authority to see if it can be mitigated in some way. Typically, the only way to reduce a Severity score would be to change the design or remove the need for the Functionality. Failure Modes with a Severity rating of 1 should not be analysed further. 70

71 Table 12: AS13004 Process FMEA Severity Risk Scoring Effect Severity of Effect on Product Rank Effect Severity of Effect on Process (Manufacturing / Assembly Effect) Failure to meet safety and / or regulatory requirements Potential failure mode affects safe operation and / or involves non-compliance with regulations without warning. Potential failure mode affects safe operation and / or involves non-compliance with regulations with warning. 10 Failure to meet safety and / or regulatory 9 requirements May endanger operator, machine or assembly without warning. May endanger operator, machine or assembly with warning. Loss or Loss of primary function (product inoperable, does not affect safe operation). 8 Major disruption 100% of product may have to be scrapped. Line shutdown or stop ship. degradation of A portion of the production run primary function Degradation of primary function (product inoperable but at a reduced level of performance). 7 Signi cant disruption may have to be scrapped. Deviation from primary process, decreased line speed or added manpower. Loss of secondary function (product operable but service life 100% of production may have to greatly reduced, convenience 6 be reworked of ine and Loss or degradation of secondary function items inoperable, customer dissatis ed. Degradation of secondary function (product operable but appearance affected, convenience items operable but at a reduced level, customer 5 Moderate disruption accepted. A portion of production may have to be reworked of ine and accepted. dissatis ed. Appearance, t and nish type items do not conform, defect noticed by most of customers (>79%) 4 Moderate 100% of production may have to be reworked in station before further processing. Annoyance Appearance, t and nish type items do not conform, defect noticed by half of customers (50%) 3 disruption A portion of production may have to be reworked in station before further processing. Appearance, t and nish type items do not conform, defect noticed by discerning customers 2 Minor disruption Slight inconvenience to process, operation or operator. (<2%) No Effect No discernible effect. 1 No effect No discernible effect. 71

72 i) Potential Cause(s) of the Failure Mode In this section we are looking to identify the things in the manufacturing or assembly process that could cause the Potential Failure Mode to exist. This is the reason it is referred to as a Process Failure Mode & Effects Analysis i.e. we are looking for the Process Risks of producing product non-conformance. We would expect to see multiple Potential Causes per Failure Mode. Figure 22: Potential Causes of Failure in a PFMEA Requirements Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Too Big Part may vibrate during operation leading to bracket fatigue & system failure 9 K C Wrong drill used (oversize) Drill oversize from supplier (nonconforming) Drill Hole 10 0 mm Diameter +/- 0.1 mm Part would need to be scrapped if found during manufacture 6 CNC Spindle alignment out of tolerance Tool wear Unable to t bracket 4 Incorrect drill used (too small) Too Small Marginal t causing raised stress and bracket fatigue leading to system failure 9 K C Drill supplied undersize from supplier (non-conforming) The key success factor here is to produce a list of Potential Causes that are controllable in other words where there is a direct cause and effect. Good examples are incorrect drill used oversize or spindle alignment not true. In other words, if these things were to happen then the outcome would almost certainly result in non-conforming product. These examples allow us to take a specific action to control them. 72

73 Common problems here are where the team has identified a long list of Potential Causes that are quite tenuous. For example, operator incorrectly follows procedure, maintenance error. These descriptions are of no value in creating an effective Process FMEA and the required actions will be difficult to define. The team should assume that the incoming parts / materials are correct. The team may make exceptions to this but only where the historical data suggests that this is a known problem. We would expect the PFMEA for the manufacture of the incoming parts to provide the risk assessment for their own processes. Resist too much detail! However, we should also avoid going into unnecessary detail too. In an example where the location of a weld could be misplaced the team identified that one of the Potential Causes could be that the part was incorrectly located in the fixture. This is true. The team went on to list all of the reasons why the part may be incorrectly loaded in the fixture e.g. operator error, fixture worn, fixture damaged, etc. This additional detail adds no further value to the PFMEA than part incorrectly located in fixture. Great care must be taken to avoid unnecessary detail that will prevent us from seeing the wood for the trees. Teams can often over think this section of the PFMEA. The use of Fishbone diagrams to create long lists of Potential Causes by brainstorming machine, method, environment, manpower, maintenance, etc. is rarely required and in my experience actually discouraged. Only bring out this brainstorming tool if the team is struggling to identify any potential causes and then ensure you hone the results into a few meaningful descriptions. The knowledge of the process is usually well understood by the Manufacturing Engineer, Maintenance Engineer and Operator (for example). Using the logic from the PFMEA template it is more usual that a simple list can be created easily from this combined knowledge. The list should be evaluated for opportunities to group similar causes together or to challenge if the potential cause is really linked to the Failure Mode. Typically, we would only expect to see 5 7 Potential causes per Failure Mode. If there are more then we should evaluate them to see if they can be more concisely described. Prevention & Detection Control Requirements in AS13004 AS13004 again adds a potentially contradictory note in Section about the need for the control of characteristics and features. 73

74 It suggests that control is only required where the occurrence and detection ranking is high and/or if the failure is severe. It does not specify what it means by high in this context. While I agree that the extent of control should be determined by the severity ranking and/or by the Occurrence and Detection scores it is the default position of all Aerospace companies, based on the Regulations we comply to, that all features must be inspected (Detection Control) or error proofed (Prevention Control) as a minimum. Inspection may be done through sampling in certain circumstances. Therefore, all features will require some description of how it is controlled, whether through Prevention or Detection, within the PFMEA and the Control Plan. j) Prevention Controls For each Potential Cause identified we now need to identify what controls we have in place (or not) to ensure that the Potential Cause cannot happen. The best form of Prevention Control is Error Proofing e.g. Fixtures that prevent the part being loaded incorrectly. For high severity features (Severity 9 or 10) we must strive for this type of control. There are some controls, whilst not mistake proofing, do offer some protection of preventing the Potential Cause from happening e.g. Calibration, Maintenance routines, etc. For example, one of the Potential Causes for hole oversize is spindle alignment out of specification. In this case the business has recognised this issue and introduced a Maintenance Schedule to check for spindle alignment using two methods; a) a weekly ball bar check completed by the operator and b) a quarterly laser alignment check conducted by the Maintenance Team. Provided that these two activities are done to schedule and any actions identified through the checking process are addressed then we would expect to see very few oversize hole conditions caused by spindle alignment error. Another example would be tool oversize wrong tool used, it may be logical to include checked by operator during set up but this can only be included if it is clearly demonstrated that the set-up checks really would find this error e.g. one of the set-up checks requires a bar code reading of the tool in each tool holder. If it is not a defined activity or check and just down to luck then it should not be included. Unacceptable Prevention Controls Another example to be careful of is the use of Operator Training or Work Instructions as a Prevention Control. Is this really going to prevent a potential cause from happening? 74

75 The danger is that having put this comment in the box the team move on without really questioning what better controls could we have. If the only control was Operator Training then we should be wary of its effectiveness and it may be better not to include it at all. If there are no current Prevention Controls for this specific Potential Cause then be prepared to write none in this column or leave blank. It may be that addressing this gap will become one of the improvement actions. CARE POINT: The controls we identify must be things that can genuinely prevent the cause from happening not just sound like a good thing to do. They will be activities that stop the cause from happening not find it afterwards. AS13004 lists Visual Aid as a Prevention Check, I would not be convinced by this. Another common mistake is to list things in here that detect the Potential Cause rather than prevent it. For instance, a tooling check at the end of the process to ensure that it is not broken is not a Prevention Control but a Detection Control. k) Occurrence Rating The occurrence rating looks to evaluate the potential for the Potential Cause of Failure to occur. Again, as for the Severity Rating, this is done on a scale of 1 to 10 where 10 is will happen nearly always and 1 is will never / unlikely to happen (see Table 15). Each Potential Cause identified needs to be rated separately using the criteria included in Table 15 i.e. How many times per million opportunities would we expect to see the defect (PPM), Likelihood of the Potential Cause occurring or how often have we seen this type of defect (time-based examples). Typical data sources include: customer escapes, process capability performance data (Cp, Cpk), Parts per Million (PPM), maintenance results, warranty metrics, etc. Let s use the example of hole oversize where the potential causes identified were (a) wrong drill used (oversize), (b) drill oversize from supplier, (c) CNC spindle alignment out of specification and (d) part able to move in fixture. How would we calculate the Occurrence scores for this part number? If we consider that the PFMEA will be developed at a time when we may not have produced any of these specific parts the data we will use will need to be based from similar parts and similar processes. First let s determine the expected number of defects we are likely to see related to hole diameter too large. In this case the nominal diameter is 10mm +/- 0.1 mm. To calculate the expected % non-conforming we can use the understanding of our process capability. 75

76 Using drill diameter measurements with a similar (not necessarily identical) diameter we can determine the amount of variation seen by calculating the standard deviation of the measured results (usually a minimum of 30 data points) and multiply by 6. This number can then be compared to the specification tolerance to calculate the Cp value; Process Potential (Cp) = Total Design Tolerance 6 x Standard Deviations of the process If the standard deviation of our current process were 0.02 then the Cp would be; Process Potential (Cp) = 0.2 / 0.12 = 1.67 Once we have determined the Cp value we can estimate the number of conforming parts that the process will produce by using a conversation table (Table 13). Table 13: Relationship between Cp value and non-conforming parts (Parts per Million PPM) outside specified limits. Cp Value PPM Defective if the process was perfectly centred PPP Defective if the process was allowed to move +/- 1.5 Standard Deviation from nominal , , , , , , ,700 66, , , , Therefore, in this example, with a Cp of 1.67 and using the PPM that includes a 1.5 offset to represent true production conditions, the result would be 233 PPM. This equates to an Occurrence score of between 4 and 5 in Table

77 This score is the total non-conforming PPM expected. If this is centred then half would be above top limit and half would be below bottom limit, therefore for the Failure Mode of hole oversize it will still be a score of 4 in Table 15. The next step is to score the individual Potential Causes. Some approaches to do this are shown in Table 14. Table 14: Data Sources for Scoring Occurrence Potential Failure Cause Capability Data Inspection Records Quality History (escapes, scrap, concessions, warranty, etc) Maintenance Records Local Knowledge Wrong drill used (oversize) X X Drill above limit (from supplier) CNC Spindle alignment out of speci cation Part allowed to move in xture X X X X X X X X X X X Important Care Point when scoring Occurrence Ratings The ability to be able to rate the occurrence individual Potential Causes will depend upon the data captured by the company. In many cases this may not be available for the identified individual causes. Therefore, the scoring guidelines for Occurrence provide some options to determine the relative frequency, which can be informed by data and/or team knowledge and experience. As we can see this is not an exact science but we need to ensure that we do not under call individual causes and therefore avoid taking any actions later. A temptation is to score these individual causes very low so that no action will be required. This may be OK for Failure Modes that never happen but if you know that the Failure Mode occurrence has scored a 6 in the table then this needs to challenge the individual scores the team has listed for the linked Potential Causes. 77

78 Table 15: AS13004 Occurrence Rating Table for Process FMEA Rank Description Process PPM Likelihood of Cause (AIAG) Time based example Likelihood Time based of cause example Low volume production 10 Very high persistent failure (failure is almost inevitable) >500,000 PPM > 1 in 10 > 1 per shift 100% of production >1 per shift 9 Very high persistent failure (failure is almost as likely to happen as not) 50,000 PPM > 1 in 20 >1 per day 50% of production >1 per day 8 High frequency of failure (repeated failures) 20,000 PPM > 1 in 50 >1 per 3 days 20% of production >1 per 3 days 7 High frequency of failure (failures occur often) 10,000 PPM > 1 in 100 >1 per we ek 10% of production >1 per w eek 6 High moderate occasional failures 5,000 PPM > 1 in 5 00 >1 per 2 weeks 50% of production >1 per month 5 Moderate occasional failures (minor proportions) 1,000 PPM > 1 in 2,000 >1 per quarter 0.5% of production 2 per year 4 Moderate low: infrequent failures 100 PPM > 1 in 10,000 >1 per 6 months 0.1% of production 1 per year 3 Low; relatively few failures 10 PPM 1 in 100,000 >1 per year 0.05% of production 1 per 5 years 2 Low: failures are few and far between (isolated incidents) 1 PPM <1 in 1,000,000 <1 per year 0.01% of production 1 per 10 years 1 Remote: failure is eliminated through prevention controls. 0 zero Never Less than 0.01% of production <1 per 10 years There is no guidance in AS13004 to determine what is meant by low volume production. When asked, the team who developed the standard refer to pre-production volumes or prototype parts, not production parts. In practice these scores are comparative within the FMEA and therefore provided that the scoring system is used consistently across the whole document there is very little difference to the outcome. l) Detection Controls This is a description of all of the ways in which the Potential Failure Mode (and key Potential Causes) are checked or inspected for conformity throughout the process. 78

79 Typically, it will take the form of in process checks by the operator, automated controls or mistake proofing, or formal inspection routines. The team should document all of the applicable controls in place and score each one using the Detection Scoring Table. As we know that each Potential Cause will have its own RPN value it is important to recognise that each Detection Control must therefore be aligned to each Potential Cause. For example, if we inspect hole diameters using a co-ordinate measuring machine at the end of the line then this detection method would score 7 in our Detection Rating chart (see Table 16). This score would be read across to all Potential Causes for against each Failure Mode identified for Hole Drilling. If there are any other detection methods used for certain Potential Causes then these should be listed against that particular Potential Cause and scored appropriately. See PFMEA RPN Scoring Worked Example for further details. m) Detection Ranking The team will evaluate each of the Detection Controls identified in the previous column using the criteria contained within the Detection Scoring Table. The question they must answer is If the Potential Failure Mode did occur how confident are we that we would detect it before it was despatched to the Customer? The focus of the ranking is on the methods deployed to inspect or prevent the Failure Mode and the stage of the process where the inspection is conducted i.e. at the point the Failure Mode could be created or later on in the process. Particular points to note on this rating table are; There is no reference to the capability of the gauging method. It assumes that whatever gauging method or inspection process is used that is has been proven capable (see AS13003 MSA). The only way to score lower than a 5 on the scale is to employ automated controls to detect the Failure Mode (rank 2 to 4) or an automated control to prevent the Failure Mode Potential Cause (rank score of 1). Automated Controls such as these should be our objective. 79

80 Table 16: AS13004 Detection Rating Table Rank Likelihood of Detection by Process Control - Category Likelihood of Detection by Process Control - Criteria 10 Absolute uncertainty No current process control; Cannot detect or compliance analysis / MSA not performed. 9 Dif cult to detect Defect (Failure Mode) and / or Error (Cause) is not easily detected (e.g. random audits, GR&R above acceptance thresholds). 8 Defect detection post processing Defect (Failure Mode) detection post processing by operator through visual / tactile / audible means with no boundary samples. 7 Defect Detection at Source Defect (Failure Mode) detection in station by operator through visual / tactile / audible means or post processing through use of attribute gauging (go/no go, manual torque checks, clicker wrench, etc.) with no boundary samples. 6 Defect Detection Post Processing Defect (Failure Mode) detection post processing by operator through the use of variable gauging or in station by operator through the use of attribute gauging (go / no go, manual torque checks, clicker wrench, etc.) with boundary samples. 5 Defect Detection at Source Defect (Failure Mode) or error (cause) detection in-station by operator through the use of variable gauging or by use of automated controls that will detect discrepant part and notify operator (light, buzzer, etc.). Gauging performed onsetup and rst piece check (for set up causes only). 4 Defect Detection Post processing Defect (Failure Mode) detection post processing by automated controls that will detect discrepant part and lock part to prevent further processing. 3 Defect Detection at Source Defect (Failure Mode) detection in-station by automated controls that will detect discrepant part and automatically lock part in station to prevent further processing. 2 Error Detection and / or Defect Prevention Error (Cause) detection in-station by automated controls that will detect error and prevent discrepant part from being made. 1 Detection not applicable Error (Cause) prevention as a result of xture design, machine design or part design. n) Risk Priority Score The next stage of the Process FMEA is to calculate the Risk Priority Number (RPN) for each Potential Cause of a particular Failure Mode. The calculation is quite simple. Severity x Occurrence x Detection = RPN 80

81 The Severity Score we use is the highest ranked number for the Failure Mode, i.e. the worst that could happen. The Occurrence Score for each Potential Failure Mode is used i.e. there will be an RPN score for every Potential Cause identified for a particular Failure Mode. The Detection Score is the best (lowest) score identified. This means that, provided that all parts go through each inspection point, the most effective detection activity will catch the Potential Failure Mode before it is shipped to the customer. Figure 23: RPN Scoring Example Failure Mode Potential Effects Severity Potential Causes Prevention Controls Occurrence Detection Controls Detection RPN The Highest Severity Score Every Occurrence Score The Lowest Detection Score An RPN Score For every Potential Cause Figure 23 shows that to calculate the RPN for the Failure Mode we select; 1. The HIGHEST Severity score, multiplied by, 2. EACH Potential Cause Occurrence Score, then multiply by 3. The LOWEST Detection score for each related to each Failure Mode and Potential Cause (if relevant). Therefore, there are three RPNs, one for every Potential Cause. It can often be worth doing a quick sanity check by calculating the overall RPN for a Failure Mode. 81

82 1. It is easy for us to identify the Severity Score for a particular Failure Mode so we should use that 2. The Occurrence Score for an individual Cause can be quite difficult to get but the overall failure rate for the Failure Mode should be relatively easy so we can use that. 3. The Detection Score, especially that associated with Inspection, is also quite easy to get hold of so we can use that. Calculating these three scores will give us an approximation of the Risk profile for that Failure Mode that we can then compare to our individual RPNs for each Potential Cause. We can then adjust the Occurrence Scoring if required for the individual scores if necessary. Process Key Characteristics (Section ) One of the Outputs from the PFMEA is the identification of Process Key Characteristics (KCs). The team should determine these through an evaluation of the risk scores of Severity x Occurrence or from the RPN result. These will be in addition to Product KCs that were identified through the Design process. Product and Process KCs should be identified within the PFMEA and the Control Plan within the Classification columns. o) Improvement Actions For all of the rigour of a Process FMEA, if done well, if we do not then react to the risk profile then it is of no value. The key focus must be on those risks that scored high for severity, regardless of the other scores. What further action do we need to take to reduce the RPN of these items through, ideally, improving the prevention of the Failure Mode, or if not, improving the Detection of the Failure Mode. Remember the only way to reduce the Severity score is usually to redesign the product. High RPNs do need to be addressed. There is no set way of doing this. There is a judgement required. How much risk are you prepared to tolerate? Some RPNs will stand out using the pareto principle as being excessive and will clearly need to be improved. Some companies use an RPN threshold value to select which RPNs they are going to improve. This can be dangerous as teams soon learn how to get a score that falls below the threshold value (it is not an exact science after all). Another strategy is to look at the profile and see where the data suggests a levelling out of RPNs. The risks to the left of this point should be considered for improvement. 82

83 Remember the continual reduction of the overall risk should be our aim this is an on-going process that never stops. Improvement actions should be documented in the PFMEA and once implemented and verified the RPN can be recalculated to measure the effect of the improvement action. Figure 24: RPN Improvement Actions in a PFMEA Action Results Potential Causes of Failure Prevention Controls Occurrence Detection Controls Detection RPN Recommended Action Resp. & Target Date Action taken Severity Occurrence Detection RPN Wrong Drill Used (oversized) Tooling bar code auto check on machine Drill oversize from supplier Tool presetting process CMM Inspection 7 at OP 450 Weekly ball bar check Move inspection to within OP100 process G. Davies CNC Spindle alignment out of speci cation Quarterly laser alignment check Increase frequency of laser alignment check to monthly A. Bonthron Tool Wear Tool presetting process 4 CMM Inspection at OP Tool life speci ed to 10 parts max. before tool change C. Mellish

84 PFMEA RPN Scoring Worked Example Let s assume that the Failure Mode is hole diameter too big. The team have identified four potential effects; 1. Minor deviations may need to be concessed, minor operational disruption, customer would not notice = Severity Score of 2 2. Could cause sub system vibration impacting product performance noticed by the customer = Severity Score of 6 3. Could cause vibration in engine leading to premature wear and potential product failure (not safety related) = Severity Score of 8 4. Could cause vibration noise that would be noticeable to customer = Severity Score of 5 Therefore, in this example the Severity score used will be the highest, which is 8. The team has identified three Potential Failure Causes; 5. Wrong Drill used (oversized). There is no defined Prevention Control for this potential cause. 6. Spindle wear on CNC Machine. The business has two ways of preventing this potential cause (a) weekly ball bar checks conducted weekly by the operator and (b) laser alignment checks conducted by the maintenance function every 6 months. 7. Damaged tool (drill). The machine has a built-in program that uses a vision comparator system for each tool before it is used to check for damage. There will be an Occurrence score for each Potential Cause identified. Occurrence Scoring The team know that this is a problematic feature with a tight tolerance. It causes around 2% of non-conforming parts, most of which are concessed (minor deviation). This would score an Occurrence rating of 8. The team do not have data to show how this non-conformance can be accurately attributed to each of the three causes so they have decided on the following logic. 1. Most likely reason is spindle condition. The data shows a wide spread of results and a Cp of less than 1 which could be due to the machine inaccuracy. They also know that the Maintenance checks sometimes find alignment errors and have reduced the frequency of Ball Bar checks as a result. They have assigned the score of 7 as they believe it is the biggest contribution but does not explain all of the variation. 2. The team knows that incorrect tooling used has happened before, although infrequently (once or twice per year), and as there is no prevention activity for this potential cause they have put a score of 4. 84

85 3. The tooling vision system has prevented broken tools from being used since its implementation over 9 months ago. They decided to score it as a 2 rather than a 1 as it is still relatively new. Detection Methods and Scoring The hole diameter is measured using a variable gauge in process by the operator, that would be a score of 5 for Detection. For the three Potential Causes this Detection Score will be shown against each as a starting point. The Detection Methods for both Wrong Tool Used (oversize) and Spindle Wear rely on the Operator inspection of the Failure Mode, in-station using a bore micrometer. Therefore, these have both been scored a 5 using the Detection Scoring Guidelines. The Potential Cause for Damaged Tool can be detected automatically using the vision system built into the CNC machine. The team have used the same logic as for Occurrence scoring and assigned this a Detection Score of 2. Calculating the RPN Therefore, in our worked example the three RPN Scores (one for each Potential Cause) would be; Potential Cause 1: Wrong Drill Used (oversize) Severity 8 x Occurrence Score of 4 x Detection of 5 = 160 Potential Cause 2: Spindle wear Severity 8 x Occurrence Score of 7 x Detection of 5 = 280 Potential Cause 3: Damaged Tooling Severity 8 x Occurrence Score of 2 x Detection of 2 = 32 Why use the lowest Detection Score? The selection of the lowest Detection Score rather than the highest can often cause some confusion. Think of it as if each Detection Control is like a filter paper of different grade (1 to 10). If you have three detection methods scored at 2, 6 and 8 then if the Failure Mode was to try to pass through them (in series) then the one scored at 2 would be the most effective and hence that is the score we would use. See Figure 25. It will allow us to challenge if we need all three Detection Activities, why not just use the best one and remove the others? 85

86 Figure 25: Detection Scoring Analogy Failure Modes & Potential Causes Detection Filters (scores) Filter Size 8 Detection Control 1 Filter Size 6 Detection Control 2 Filter Size 2 Detection Control 3 Some Failure Modes & Potential Causes will always get through Once the RPNs for each Failure Mode and Potential Cause have been calculated they can be ranked in order of RPN Score (Pareto principle). Being able to see the Risk Profile of the complete process is useful for us to be able to identify those process steps with the highest risk however such as a simple analysis is not enough to determine what actions should be taken. Process FMEA - A Simple Check We have discussed how important the precision of the language we use in the PFMEA is to its effectiveness. An easy check to see if we have applied this correctly is to read the contents from Left to right and see if the logic flows from one column to the other. An example is shown in Figure

87 Figure 26: PFMEA Testing the Logic (Read Left to Right)

88 88

89 Chapter Six Creating Reference PFMEAs Reference Process FMEAs are a useful way to create the re-useable building blocks of what is required to define the part specific Process FMEA required by AS Many of the practices discussed in Chapter Five will be applicable when creating the Reference PFMEA, for example they should be developed using a cross-functional team. We may not necessarily need those people with specific product knowledge as this is really a process for capturing Process Information. Ideally, Reference PFMEAs should be kept at a company level and maintained by the accountable Manufacturing Process Owner. They should be used across the business to create part specific PFMEAs in the most efficient manner. Reference PFMEAs are not simply a cut and paste solution. They are simply using the knowledge from similar features and processes that once created, are relevant for multiple features included in the Part Specific PFMEA. Figure 27 shows what can be included within a Reference PFMEA and why. Figure 27: Overview of Reference PFMEA Elements The purple columns require part specific information and therefore can only be completed when completing the part specific Process FMEA. 89

90 STEP 1: Select the Process for Evaluation A reference Process FMEA will be specific to a process type e.g. CNC machining, Electron Beam Welding, Torque Fastening, Grit blasting, etc. The Team should identify the Reference PFMEAs it needs to complete a full part number specific Process FMEA. Once the list is completed the team can select one specific process type to begin (remember that these Reference PFMEAs, once created can be used for all new PFMEAs). Figure 28: Typical Reference FMEA Database of Required Processes CNC Drilling CNC Milling CNC Turning CNC Grinding E Beam Welding Casting Forging Chemical Etch Cleaning Part Marking Manual Assemble Intelligent Torque Fastening Manual Torque Fastening Some processes will have several sub process types. For example, CNC machining may have sub process types of; Turning Grinding Milling Drilling The team would focus on one of these elements to create a Reference PFMEA. The Reference PFMEA may also be equipment specific. Some CNC machines will be constructed in a unique way and therefore the Potential Causes of Failure may be unique to that equipment type. The Team will need to decide if the best approach is to create a universal Reference PFMEA or to allow derivatives to be developed also. 90

91 Step 2: Define the typical Features and Characteristics of the Process being evaluated Each Process Type will have the potential to create certain features and characteristics. The team should list these out for the process / sub-process under evaluation. A typical characteristics matrix or Assembly Instruction for the process may help to identify these features and characteristics. The team also need to refer to typical drawings and related engineering specifications. For example, in Figure 29 it shows the typical features for a drilling process on a CNC machine. Figure 29: Typical Features for a Drilling Operation Location No Damage Diameter Drilling Through hole Roundness Depth The Reference PFMEA should be structured in such a way that the team can select specific features from the process / sub-process to be used in the creation of a Part Specific PFMEA (see Figure 34) Define all Features and Characteristics needed before moving onto the next step. Step 3: Define Typical Failure Modes for each Characteristic Design Features and Characteristics will have a universal and finite number of Potential Failure Modes associated with them, irrespective of how they are produced. The team can brainstorm these as a start to helping define the Reference FMEA database. 91

92 Figure 30: Typical Failure Modes for Drilling Features Wrong location Location Damage No Damage Diameter Too Big Too Little Drilling Missing feature Through hole Roundness Out of round Depth It can be useful to record these Features and Failure Modes in a document for future reference and to ensure that any new Failure Modes are captured. Some typical examples are shown in Table 17 (see also Appendix B). Table 17: Example Failure Modes Too Deep Too Shallow Requirement Correct orientation Speci ed quantity Diameter Depth Location No Damage Pro le Shape Surface Finish Fit part Potential Failure Mode(s) Wrong orientation Wrong quantity Too big Too small Too deep Too shallow Incorrect location Damaged Incorrect pro le Too rough Too smooth Part missing 92

93 In addition, there may be universal Potential Failure Modes on the Drawing or related Specifications that the team should also consider e.g. Damage, FOD, Surface Finish requirements, cleanliness, etc. These are not necessarily feature specific but are applicable to the process under evaluation e.g. CNC Drilling. STEP 4: Identify Potential Causes of Failure by Process Type The Potential Causes of each Failure Mode will depend upon the process that is being used to create the Feature / Characteristic. For example, drilling a hole with a diameter of 10mm +/- 1 mm the Failure Modes will be the same i.e. Too Big or Too Small. However, the Potential Causes of Hole too Big if created on a CNC will be different to those if created using, for example, laser drilling. Therefore, Reference FMEAs now need to become specific to a process type. In this example we shall consider hole drilling on a CNC machine. The team will need to decide if CNC drilling is a single Reference PFMEA or if there are different types of CNC machines that may require their own Reference PFMEA. This can be decided by looking at the list of Potential Causes for each. If they are similar then we should strive to have only one Reference PFMEA if they are significantly different (due to the mechanical nature of the equipment for example) then separate Reference PFMEAs should be created. The team should consider all of the direct causes that could create the Product Failure Mode. Figure 31: Reference PFMEA for CNC Hole Drilling: Potential Failure Mode Causes Operation Requirement Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Wrong drill used (oversize) Too Big Drill oversize from supplier (nonconforming) Diameter CNC Spindle alignment out of tolerance Tool wear Drill Hole Too Small Incorrect drill used (too small) Drill supplied undersize from supplier (non-conforming) Too Deep Incorrect tool setting Tool offset incorrect Depth Tool setting incorrect Too Shallow CNC program offset incorrectly set Tool wear 93

94 STEP 5: Identifying the Prevention Controls aligned to the Identified Potential Causes in the Reference PFMEA In the next step the team should identify the Prevention Controls that can prevent the Potential Cause(s) identified. Again, great care should be taken to ensure that these Prevention Controls are actually able to prevent the Potential Cause and that they are in place and effective. In practice the Prevention Controls may be unique to a particular plant or site and therefore great care must be taken when reviewing the Part Specific PFMEA to confirm that those listed are actual practice and not just recording another business s best practice. It can be useful however to have a starter list for teams to review and to challenge them on the application of best practice. Figure 32: Reference PFMEA Prevention Controls Requirement Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Prevention Controls Incorrect drill used (oversize) Bar code reader veri es correct tooling Too Big Drill oversize from supplier (nonconforming) Tool preset check Diameter CNC Spindle alignment out of tolerance Tool wear Monthly ball bar check (MC001) & Quarterly laser alignment check (MC015) Tool setting to max. 10 parts before removal. Too Small Incorrect drill used (too small) Bar code reader veri es correct tooling Drill supplied undersize from supplier (nonconforming) Tool preset check Too Deep Incorrect tool setting Tool offset incorrect Tool preset check None Depth Too Shallow Tool setting incorrect CNC program offset incorrectly set Tool preset check None Tool wear Tool setting to max. 10 parts before removal. Do not be afraid to write None in the Prevention Controls column if there really is nothing that is done. It is always preferred to writing in something tenuous. An empty cell in an FMEA will attract attention from the team and challenge them to think of ways to address it. 94

95 STEP 6: Identifying the Typical Detection Controls for the Failure Mode in the Reference PFMEA The next task is to identify the typical Detection Controls for the Failure Mode. These will be used as a guide only and should include the latest thinking from the business experts. As with the Prevention Controls these are often plant / site or business specific and will need to be reviewed closely to confirm that they reflect the actual condition for the application under review (the Part Number specific PFMEA). There may be minimum standards defined for certain Detection Controls and these must be adhered to. For example, there may be a standard method for measuring surface finish inside a bore that requires specific measuring equipment. Mandated Detection Controls should be identified within the column with a comment. If the part specific PFMEA identifies that the mandated Detection Controls are not in place then this should be identified as an improvement action within the PFMEA Figure 33: Identifying the Typical Detection Controls in the Reference PFMEA. Requirement Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Prevention Controls Occurrence Detection Controls Incorrect drill used (oversize) Bar code reader veri es correct tooling Too Big Drill oversize from supplier (nonconforming) Tool preset check Diameter Depth Too Small Too Deep Too Shallow CNC Spindle alignment out of tolerance Tool wear Incorrect drill used (too small) Drill supplied undersize from supplier (nonconforming) Incorrect tool setting Tool offset incorrect Tool setting incorrect CNC program offset incorrectly set Tool wear Monthly ball bar check (MC001) & Quarterly laser alignment check (MC015) Tool setting to max. 10 parts before removal. Bar code reader veri es correct tooling Tool preset check Tool preset check None Tool preset check None Tool setting to max. 10 parts before removal CMM Inspection at OP 450 CMM Inspection at OP

96 Organising the Reference PFMEAs In a mature state the business will have a database of all of the Reference PFMEAs it requires to create part specific PFMEAs. This database will represent the best practice for each process and be a knowledge management hub recording all of the company s insights into managing the process. The Reference PFMEA database should be updated whenever new information comes to light so that it can be shared across the business forming a key part of the continuous improvement activity. As there are no product specific details held within the Reference PFMEA it should be possible for them to be made available to the external supply chain for them to use as well. This will also enable the knowledge management database to be updated by the experienced and knowledge held within the external supply chain as well as within the business making the approach even more powerful. NOTE: Always check with your company experts on the classification of Intellectual Property and Export Control before sharing these files to prevent potential violations. Care must be taken when designing the Reference PFMEA file structure to make it easy to access and find the right element. The typical structure will include three levels. Level 1: The Process Group This is the common name for the process and is usually defined by the equipment or process. Examples include CNC Machining, Joining, Surface Preparation Level 2: Process Type This is where the process can be made more specific and will take the form of the equipment used or more detailed process description. For example, CNC Grinding, CNC Drilling, CNC Turning, Joining by E-Beam Welding, Joining by Inertia Welding, Surface preparation by grit blasting, etc. Level 3: Process Characteristics / Features The Reference PFMEA now needs to identify the typical features / characteristics that the process / equipment is designed to create. E.g. for the CNC grinding operation using the Mazak this could include; Size (length, height, etc.) Radii Angle Surface finish This structure is shown in Figure

97 Figure 34: Reference PFMEA Database Structure Example 1.0 CNC MACHINING REFERENCE FMEA LIBRARY 97

98 98

99 Chapter Seven Using Reference FMEAs In this Chapter we shall describe the steps needed to create a part specific Process FMEA using Reference PFMEAs. STEP 1: Select the Part Number for the PFMEA activity & collate all related documentation required to complete the PFMEA PFMEAs must be completed for a specific part number or assembly. The scope will include all process steps and all features that are created to meet the design intent. In order to create a part specific PFMEA the team will require; 1) Part / Assembly Drawing(s) 2) Related specifications called up on the drawing(s) 3) Process Flow Diagram detailing the method of manufacture 4) Product Characteristic Matrix that specifies the features created at each process step 5) Assembly Instructions (if relevant) The documents should be reviewed to ensure that they are complete and have the required detail to make the PFMEA meaningful. These documents will be used to create the shell PFMEA for the specific part number using the appropriate Reference PFMEAs, as shown in Figure 35. Figure 35: Creating a part specific Shell PFMEA Reference PFMEAs Part Drawing Process Flow Diagram Characteristics Matrix Shell PFMEA Part PFMEA Part Specifications Assembly Instructions 99

100 STEP 2: Complete the Process Step and Requirement columns of the PFMEA using the information collected in STEP 1. For each Operation / Process Step list out the design features and characteristics to be created at that step (taken from the Characteristic Matrix, Part Drawing, Assembly Instructions and related Specification(s)). The description of the design requirements must be in sufficient detail so that the Failure Modes can be easily identified. Include the specifications or acceptance criteria for each feature listed Figure 36: Completing the Process Step and Requirements Column Operation Requirement Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Hole 1 Diameter 10mm +/- 0.1 OP100 Hole 1 Depth 100mm +/- 1.5 Drill Hole Hole 2 Diameter 15mm +/- 0.1 Hole 2 Depth 80mm +/- 1.5 Ideally this step should be completed in dedicated FMEA software so that it can easily link to the Reference PFMEAs. Although PFMEAs should be completed for every feature included within the Design Definition there are some allowable exceptions and care points that should be considered. A) Patterns of Features The Risk Profile (RPN) of a feature within a PFMEA is derived from three attributes; Potential impact of the non-conformance (Severity Score), related to the purpose of the feature, 100

101 Probability of it happening (Occurrence Score), related to the process capability and hence specification(s) limits, and Ability to detect it, if it was nonconforming (Detection Score). Thus, if there are multiple features that have the same purpose, same specification, made in the same way (and at the same step), and inspected in the same way then these features may be considered as a pattern and a single line item within the PFMEA. An example of this may be the bolt holes used to secure one part to another. Let s say there were 26 holes, all with the same specification, created on the same machining process, using the same tooling, inspected in the same way, then these could be considered as one feature in the PFMEA. This approach can have a significant impact on the number of features needed to be evaluated in the PFMEA. Figure 37: Hole Pattern Example B) Profile Features Some parts may have a specified profile with multiple inspection points identified to define how this should be inspected. Do not confuse inspection points with features. The feature in the PFMEA is Profile Shape and not the 100 inspection points that may be identified on the drawing. 101

102 For example, on a Fan Blade there are several profile areas (or zones) defined along the Blade with different Design Consequences if they were non-conforming. The profile areas are specified on the drawing to take account of this. Each profile area that is separately defined should be included on the PFMEA as a separate feature. STEP 3: Add the relevant REFERENCE PFMEA information for each characteristic listed. To determine the Reference PFMEAs required the Characteristics Matrix should be reviewed to identify the process types and features used to create the part. For example, a Crank Shaft uses the following processes to create the defined features: Figure 38: Determining the Required Reference PFMEAs In this example there are four main types of Reference PFMEAs used. 102

103 At feature level there are 10 different Reference PFMEA required to cover the features listed. The Reference PFMEA information will (typically) include; Potential Failure Mode Potential Causes of Failure Prevention Controls Detection Controls Figure 39: Compiling the Shell Part Number PFMEA using Reference PFMEAs Op No. / Step Process Requirement Potential Failure Mode Potential Effects of Failure Severity Classi cation Potential Causes of Failure Prevention Controls Occurrence Detection Controls Detection RPN OP100 CNC Grinding Length 100mm +/- 1mm OP100 CNC Grinding Angle 75 o +/- 2 o OP100 CNC Grinding Surface Finish MAX 1.5 RA OP200 CNC Turning Ø50mm +/- 0.5mm OP300 CNC Grinding Length 250mm +/- 3mm OP300 CNC Grinding Angle 55 o +/- 2 o OP300 CNC Grinding OP400 CNC Drilling Surface Finish MAX 2.5 RA 20 hole Ø 40mm +/- 0.2mm OP400 CNC Drilling Depth 120mm +/ - 0.5mm OP400 CNC Drilling No white layer OP500 EB Weld OP500 EB Weld Weld position 120,X 350,Y Porosity within spec ABC OP500 EB Weld Bead length 25mm +/- 1mm 103

104 The typical data included in the Reference PFMEA is shown in Figure 40. In this example we have used the Reference PFMEA for CNC Machining Hole drilling. We have only shown an excerpt from the full Reference PFMEA. The information included in the Reference PFMEA should be used as a starting point only. Figure 40: Shell PFMEA example Operation Requirement Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Prevention Controls Occurrence Detection Controls Wrong Drill used (oversize) Bar code reader on machine OP100 Drill Hole Hole 1 Diameter 10mm +/- 0.1 Hole Too Big Drill oversize from supplier Spindle out of alignment Tool presetting check Weekly ball bar check. Monthly laser alignment check CMM Inspection at OP 450 Swarf pick up on tool None STEP 4: Complete the Part Specific PFMEA with Cross Functional Team Once the Part Specific PFMEA shell has been populated with the information in STEPS 2 and 3 then the Cross Functional Team should be brought together to review the Shell PFMEA. The Cross Functional team should include Manufacturing Engineering, Design Engineering, Operations, Maintenance and Quality (as appropriate). At certain points other experts may also be required e.g. machine tool supplier, part suppliers, etc. The team will need to ensure that the information taken from the Reference PFMEA is accurate for the Part Number being considered and make any necessary changes. They will need to review the Shell PFMEA and decide if there are any other Potential Failure Modes, Potential Causes, Prevention Controls or Detection Controls that need to be included. 104

105 The next step is to complete the part specific information in the columns not covered by the Reference PFMEA. It can be useful to complete this in three sub steps. 4(a) Complete the Effects and Severity score columns for each identified Failure Mode (Figure 41). This is where it is vital to get the input from the DFMEA and/or the Design Team to reflect the key consequences should the Failure Mode occur. The team should concentrate on the effect to the customer along with the severity score. Internal Effects and Severity Scores associated with consequences such as scrap, rework, etc. should also be considered and recorded, recognising that this should focus on major effects and not all minor or insignificant ones. The scoring of the RPN will focus on the highest severity score. This step cannot be completed without the input of the Design Team. Figure 41: Completing the Effects and Severity Rating Operation Requirement Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Prevention Controls Occurrence Detection Controls Bracket vibration, leading to crack and potential engine failure 8 Wrong Drill used (oversize) Bar code reader on machine OP100 Drill Hole Hole 1 Diameter 10mm +/- 0.1 Hole Too Big Part may be concessed if approved by Design. 4 Drill oversize from supplier Tool presetting check CMM Inspection at OP 450 Part may need to be scrapped if found during process. 5 Spindle out of alignment Weekly ball bar check. Monthly laser alignment check Swarf pick up on tool None 105

106 4(b) Review the Potential Causes and Prevention Controls taken from the Reference PFMEA (Figure 42). The team should review what has been included in the Shell PFMEA and modify to reflect the reality for this particular part number. The team may add or delete elements from the Shell PFMEA if appropriate. In this example we have added an additional Potential Cause and Prevention Control (see blue text). The team then review the relevant performance data to allow them to complete the Occurrence Score element of the PFMEA using the Scoring Guidelines in Chapter Five e.g. customer escapes, DPU (incl. feature RFT), concessions, Maintenance Records, etc. Figure 42: Completing the Potential Causes, Prevention Controls and Occurrence Scoring sections. Operation Requirement Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Prevention Controls Occurrence Detection Controls Bracket vibration, leading to crack and potential engine failure 8 Wrong Drill used (oversize) Bar code reader on machine 2 Part may be concessed if approved by Design. 4 Drill oversize from supplier Tool presetting check 2 OP100 Drill Hole Hole 1 Diameter 10mm +/- 0.1 Hole Too Big Part may need to be scrapped if found during process. 5 Spindle out of alignment Weekly ball bar check. Monthly laser alignment check 4 CMM Inspection at OP 450 Swarf pick up on tool None 3 Part able to move in xture Set up xture check 3 106

107 4(c) Review the Detection Controls and Detection Score. Calculate the RPN for each Potential Cause (Figure 43). The team now review the Detection Controls that have been taken from the Reference PFMEA input and amend as necessary. Detection Controls refer to the part specific checks / inspections carried out to detect the Potential Failure Mode and Potential Causes. Typical Detection Controls are measurement of features, visual inspection, mistake proofing (jigs, fixtures), etc. Once the Detection Controls and Scoring have been confirmed the team can now calculate the Risk Priority Number (RPN) for each Potential Cause listed in the PFMEA. The RPN is calculated by multiplying the Highest Severity Score for the Potential Failure Mode by EACH Potential Cause Occurrence Score and by the best (lowest) Detection Score i.e. there should be an RPN score for each Potential Cause identified in the PFMEA. As you can see the Cross Functional Team is now only required to discuss the items in red text. It will cut down the time required to complete a part number specific PFMEA by around 80%. Figure 43: Updating the Detection Controls, Detection Scoring and calculating the RPN Op No. Requirem ent Potential Failure Mode Potential Effects of Failure Sev Class. Potential Causes of Failure Prevention Controls Occurrence Detection Controls Detection RPN Bracket vibration, leading to crack and potential engine failure Part may be concessed if approved by Design. 8 4 Wrong Drill used (oversize) Drill oversize from supplier Bar code reader on machine Tool presetting check 2 2 CMM Inspection at OP OP 100 Drill Hole Hole 1 Diameter 10mm +/ Hole Too Big Part may need to be scrapped if found during process. 5 Spindle out of alignment Weekly ball bar check. Monthly laser alignment check Swarf pick up on tool None 3 In process check using vernier Part able to move in xture Set up xture check

108 Step 5: Prioritising Improvement Actions The team must now review the output of the PFMEA and identify the key risks and required improvement actions. This is done in a defined sequence; 1. What are the high severity scores (regardless of Occurrence and Detection scores) and are we comfortable with the mitigation in place? We should always strive to mistake proof Potential Failure Modes with Severity scores of 9 or What are the high severity scores (8, 9 and 10) where occurrence is also high (7, 8, 9 and 10)? do we have sufficient Prevention and Detection Controls to mitigate the Potential Failure Mode? 3. What are the high RPN scores and are we comfortable with the current mitigation? 4. Are there any simple controls that can be introduced to reduce the overall RPN? NOTE: Not all RPN scores need an improvement action. It is OK to leave blank if the team feel that there is no action required, based on the rules 1 to 4 above. Actions must be defined in the PFMEA along with the name of the accountable person and the target date for completion. The revised RPN can be calculated based on the improvement action to predict the impact of the improvement but it will only be confirmed once the action has been implemented and proven to work. Figure 44: Documenting Improvement Actions and Rescoring RPN Action Results Potential Causes of Failure Prevention Controls Occurrence Detection Controls Detection RPN Recommended Action Resp. & Target Date Action taken Severity Occurrence Detection RPN Spindle out of alignment Swarf pick up on tool Weekly ball bar check. Monthly laser alignment check 4 In process check using vernier None Part able to move in xture Set up xture check Introduce air detection system on xture to ensure part is loaded correctly M. Davies

109 Table 18: Some Common Issues with Process FMEA Deployment The Process FMEA is done at a generic process level and is not part speci c. PFMEAs must be done for a speci c part number, as should all of the defect prevention tools. The Product Risk (RPN) is dependent on three things (a) the purpose of the feature and the consequences if it is non-conforming (severity) (b) the likelihood of it occurring (Occurrence) and (c) the ability to detect the non-conformance if it happens (Detection). Therefore, if the PFMEA does not consider the part speci c features this Risk Pro le cannot be calculated. The PFMEA cannot be completed as there is no DFMEA available. There is often a belief that the Process FMEA team should have a copy of the DFMEA to allow them to score the severity rating for each identi ed Failure Mode. In practice this is not the case. Where DFMEAs are available they are not necessarily going to discuss individual features in the same granularity, as the PFMEA requires. It will always need the Design representative to interpret the DFMEA to answer these questions. Thus, even if there is no DFMEA for the part available the Design representative will be able to describe the effects and severity of all Failures Modes in the PFMEA. The PFMEA has been conducted by Manufacturing Engineering only. The PFMEA is the collected knowledge from the organisation and hence for it to be accurately captured it requires all functions that can in uence the design and manufacturing process to be included, in particular Design, Operations, Maintenance, Quality and the supplier (if relevant). The PFMEA only covers key features or key process steps. The purpose of the PFMEA is to identify the key risks of manufacturing a speci c product on the proposed manufacturing / assembly process. These risks will determine what is critical to success and hence key. If we prejudge this outcome by only selecting what we think is key from other similar products we may miss something important. Therefore, it is vital for PFMEAs to be effective that they consider all process steps and features. The PFMEA covers more than one part number grouped as a family of parts. There is often a misconception as to what constitutes a family of parts. For this to be the case for the PFMEA then the part must have a high level of commonality to each other i.e. more than 80% of features are the same (purpose, speci cations, manufacturing process, inspection process, etc.). The PFMEA can then be read across for the 80% of identical features and those which are unique will need to be covered by an appendix PFMEA. In reality there will be very few of these, typically only where a part number may have a variant due to design up issue or a performance variant. 109

110 The PFMEA has identi ed too many Potential Causes per Failure Mode. Often the PFMEA team will come up with a large number of Potential Causes, using such tools as Cause and Effects analysis, to brainstorm as many ideas as possible. If these Potential Causes are not simpli ed then the size of the PFMEA will become excessively large with limited value. Often many of the brainstormed ideas are actually varian ts of a single theme e.g. Part not held in xture could be described as incorrect clamping on xture operator loading causes part not be held securely, lack of xture maintenance allows part to move during machining, xture damaged. Care must be taken to rationalise these effectively so that the issue can be clearly seen and controlled through prevention or detection controls. The Prevention Controls are not really prevention controls. Prevention Controls should be controls that can prevent the identi ed Potential Cause from happening. Often the Prevention Controls listed include such things as Work Instructions, Operator Training, Use correct xture or similar. These controls will not PREVENT the cause from happening even though the y are necessary things to have in place. Prevention Controls should be things which can actually prevent the cause from happening e.g. Fixture design is error proof and so prevents part being tted in wrong orientation or CNC vision system checks tool for damage before machining operation begins. Actions are not driven based on Risk Severity. However good the PFMEA is done it is of no value unless it drives action to eliminate or reduce unacceptable risks from the process. In particular for High Severity Risks Management must not allow the process to be developed that does not mitigate the risk through error-proo ng. Too many times we see PFMEAs simply as a way of documenting what we do today and not what we NEED to do. If the PFMEA does not identify changes to the process then it is not doing its job. The PFMEA is completed after the manufacturing / assembly process has been de ned. The purpose of the PFMEA is to help in the identi cation and development of capable manufacturing and assembly methods. The outcome of a good PFMEA should be a number of process changes (including measurement processes). If the PFMEA is only being done after the method has been agreed The PFMEA will be of limited value. 110

111 Further Reading: AS13004 Process FMEA and Control Plan for Aerospace, AESQ, 2017 Potential Failure Mode & Effects Analysis (FMEA), 4th Edition, AIAG, 2008 PFMEA Key Questions: 1. Has the PFMEA been conducted by a cross functional team, including Manufacturing Engineering, Design, Service, Quality and Supplier (as applicable)? Are they trained in FMEA? 2. Is the PFMEA part number specific? 3. Has the PFMEA been started at the correct time in the development program? 4. Is the scope of the PFMEA all process steps and design requirements (features and specification requirements)? 5. Has the PFMEA been completed using the correct template? 6. Do the Process Failure Modes describe how the design intent could fail to be met during manufacture / assembly? i.e. product characteristics. 7. Are multiple Potential Effects identified for each Failure Mode? Have the Severity Scores been assigned in line with the scoring criteria? 8. Are there multiple Potential Causes identified for each Failure Mode? Do they describe how the manufacturing / assembly process could cause / allow a Failure Mode to occur? 9. Has the Scoring criteria for the Occurrence of the Potential Causes been done using the approved scoring criteria? Has it been applied consistently? 10. Have Prevention Controls been identified to eliminate / reduce the likelihood of the Potential Cause from occurring? How effective are they? 11. Have Detection Controls been identified to detect the presence of the Failure Mode and/or Potential Cause? How effective are they? 12. Has the Detection Scoring been carried out using the correct criteria? Has it been applied consistently? 13. Have Improvement Actions been identified based on the following priority (i) High Severity scores (ii) High severity and high occurrence combinations, or (iii) High RPNs. 14. Was the PFMEA completed before the Process Design was formally approved? 15. Is the PFMEA up to date and reflect learning from events? See also the Compliance Assessment Checklist in Appendix D. 111

112 112

113 Chapter Eight Control Plans Creating Production Control Plans from the Process FMEA The Production Control Plan provides a structured approach to the definition of value added process and product controls necessary to ensure conforming product. The Control Plan is designed to work alongside Work or Operator instructions and provides a written summary of the controls required when producing a specific part. The Process FMEA identifies the necessary prevention and detection controls required to manage the associated risks for the part number being manufactured. These controls may appear in various documents. The Control Plan and Work instructions will typically capture the controls that are part specific whilst other controls such as equipment calibration, coolant strength, environmental temperature and lighting, will typically be contained within the maintenance plan or asset care requirements. This is shown in Figure 45. Figure 45 : Prevention & Detection Control Documentation The cross functional team will use the Process FMEA to ensure that all of the prevention and detection controls are adequately defined in the appropriate documentation. An example of this is shown in Figure

114 Figure 46: How the Process FMEA Prevention & Detection Controls are managed The Production Control Plan describes the required controls required at each step of production, from goods receiving through to despatch. It will include product feature checks and inspections e.g. diameters, lengths, surface finishes, evidence of damage, etc. as well as key process checks such as temperatures, pressures, torque values, etc. AS9145 requires the Control Plan to include all Design Requirements as well as those from the DFMEA and PFMEA. The aim of the Control Plan is to control the sources of variation of the product and process. It will promote defect prevention controls, usually through the process characteristics and seek to verify output at the earliest possible operation / step within the process (Section 4.8.3). It is a living document and must be updated as changes to the process, product design or process capability are made. It should retain a link to the Process FMEA. The Control Plan should be created using a cross-functional team using information shown in Figure 47; 114

115 Figure 47: Typical Inputs to a Production Control Plan Process Flow Diagram Key Characteristics List Process FMEA Lessons learnt from similar parts Control Plan MSA MSA Team knowledge The Control Plan methodology is typically used at three stages of the Product Life Cycle, these are; 1. Prototype This is a description of the inspections and tests to be carried out at the prototype stage of design, typically dimensional measurements, material properties and performance tests. 2. Pre-launch This is a description of the product verification processes, typically dimensional, material and performance tests, used as part of APQP and PPAP used to validate the product meets the design intent. 3. Production These Control Plans provide a summary of the required checks of the product and process during normal production to ensure conforming product through the control of the sources of variation (product and process) A standard Control Plan template is shown in Figure 48. Alternatives may be used provided that it contains the same information (as a minimum) and has customer approval. 115

116 Figure 48: Standard Control Plan Template 116

117 A description of what is required in each part of the Control Plan is as follows; 1) Prototype / Prelaunch / Production Tick the box to indicate the Control Plan type i.e. Prototype, Pre-launch or Production. 2) Control Plan Number Every Control Plan should have a unique identification number. 3) Part Number / Latest Change Level Enter the part number of the system, sub-system or component being controlled along with the engineering change level and/or issue date of the drawing. 4) Part Name / description Enter the name and description of the product being controlled e.g. Crank shaft, turbine blade, etc. 5) Organisation / Plant Enter the name of the division / plant where production is taking place. 6) Organisation Code (Supplier Code) Enter the identification number e.g. Customer supplier code, as requested by the customer (if applicable). 7) Key Contact / Phone and other contact information Enter the name, telephone number and other contact information e.g. of the primary contact responsible for the control plan 8) Core Team The names, telephone numbers and other contact information such as addresses, etc. for the team preparing the control plan. It is recommended that this list be appended to the control plan and kept up to date. 9) Organisation / Plant Approval / Date This is evidence that the responsible manufacturing plant has approved the control plan. 10) Date (Original) The date that the original control plan was compiled (published). 11) Date (Revision) This is the date of the latest revision of the control plan. 12) Customer Engineering Approval / Date Obtain the customer engineering approval for the control plan (latest revision), if required by the customer. 117

118 13) Customer Quality Approval / Date Obtain the responsible customer quality representative approval for the latest revision, if required by the customer. 14) Other Approval / Date Obtain any other approvals (if required). 15) Part / Process Number This provides a link to the Process Flow Diagram (PFD) and/or the PFMEA required details of the part being manufactured and the process step / sequence number. 16) Process Name / Operation Description A brief description of the operation being performed should align to the description in the PFD and PFMEA. For example, CNC Drilling, manual assembly, etc. 17) Machine, Device, Jig, Tools for Manufacturing For each operation described identify the processing equipment required e.g. machine, device, jig or other tools for manufacturing as appropriate. This is critical if the process approvals are specific to a particular equipment type or machine number. Characteristics The features, dimensions or properties of a process or its output (product) on which variable or attribute data can be collected. 18) Number This is the feature number referenced from the drawing or specification and linked to the PFD, Characteristics Matrix and PFMEA. 19) Product Product Characteristics are the features or properties of a part, component or assembly that are described on the drawing. This information can be taken from the PFMEA (if compliant to AS13004) or the Characteristics Matrix. The core team should identify the special product characteristics that are a compilation of important product characteristics from all sources (DFMEA, PFMEA, Customer inputs, etc.) All special characteristics must be listed on the control plan. In addition, the Control Plan must include reference to all other product characteristics, and related process characteristics, that are required to be controlled during normal operations. That is not to say that they must all be listed individually. Consider how they are controlled. For example, a machining operation may produce 100 individual features. 118

119 The operator inspects all of these on a CMM after machining. This one activity controls all 100 features and therefore we can group these together as a single line e.g. Features 1 to 100 on the Characteristics Matrix. If, however in addition to this the operator is required to check a feature using a manual gauge independently of the CMM inspection then this should be listed separately. 20) Process Process Characteristics are the process variables that have a cause and effect relationship with the identified product characteristic as identified within the PFMEA. A process characteristic can only be measured at the time it occurs. The core team should identify process characteristics for which variation must be controlled to minimise product variation. There could be more than one process characteristic for each product characteristic listed. In some processes one process characteristic may affect several product characteristics. 21) Special Characteristic Classification Use the appropriate classification as required by the customer to designate the type of special characteristic or this field can be left blank for undesignated characteristics. Methods (includes items 22-25) A systematic plan using procedures and other tools to control a process; 22) Product / Process Specification / Tolerance The specification requirements may be found on the drawing or other documents such as the PFMEA, assembly documents, etc. 23) Evaluation / Measurement Technique This column identifies the measurement system being used. This could include gauges, fixtures, tools and /or test equipment required to measure the part or process. AS9145 requires Measurement Systems Analysis (MSA) to be carried out on all measurement systems and attribute inspection activities (including visual inspection) included in the Control Plan. The MSA acceptance criteria are specified in AS ) Sample Size & (25) Frequency When sampling is allowed, list the corresponding sample size and frequency. 119

120 26) Control Method This is one of the most critical elements to an effective control plan. This column contains a brief description of how the operation will be controlled, including reference to detailed procedures / instructions where applicable. The control method utilised should be based on the risk evaluation conducted when compiling the PFMEA (as a minimum). Typical control methods can include SPC, inspection, attribute data, mistake proofing and sampling plans. The method used for control should be continually reviewed for effectiveness. Changes in product and process capability should lead to an evaluation of the control method. 27) Reaction Plan The reaction plan specifies the corrective actions necessary to avoid producing non-conformance or when operating out of control. The actions should normally be the responsibility of the people closest to the process i.e. the operator, team leader, technical support function, and be clearly identified in the reaction plan. Any actions taken must be documented. Suspect and nonconforming products must be clearly identified and quarantined, and disposition made by the responsible person designated in the reaction plan. This column may also refer to a specific reaction plan number and identify the person responsible for the reaction plan. The Control Plan should be created to align to individual processes. The Control Plan should be displayed (or made available) at the area where the production activity takes place for use by the production team. Therefore, the Control Plan should be structured by Operation Number so that only the appropriate pages are shown in the area (see Figure 49). They should work alongside the work / operator instructions and are a quick reference guide for the operator. 120

121 Figure 49: Control Plan Structure The Control Plan should describe what the operator must do during production. Figure 50 shows how the dimensional features at a CNC drilling operation have been grouped into a single line where the CMM inspection operation inspects all 72 dimensional features created at this operation. It also shows how Dimension No. 1 is required to be measured by the operator as a first off check. This is listed separately. Depending upon the number of features inspected at a single operation the team may decide to list all features within the control plan. It is important that the Control Plan remains an easy to read, simple document. Where the features created at one operation are not inspected until a later process step then they will not be included where they are created but at the operation where they are inspected. Typically, a Production Control Plan for a single operation step should be no longer than a single page. Controls and Reaction Plans specified within the Control Plan shall be documented within a work instruction and/or Inspection Plan. AS13004 describes the Control Plan as a document that can work alongside the Inspection Plan. In my experience the Control Plan is the Inspection Plan. Personally, I see no need for both documents to exist. 121

122 Figure 50: Example Production Control Plan for a Drilling Operation 122

123 The Control Plan includes a lot of information that is also in the related part number Process FMEA. Many FMEA software products have the ability to automatically create the Control Plan straight from the Process FMEA, with minimal additional intervention required. Figure 51 shows the typical information in our Control Plan example that can be derived straight from the Process FMEA (in red text). NOTE : Many companies use Manufacturing Execution Systems to deliver information to the operator on the shopfloor via integrated software. These systems will often include the information required in the Control Plan as described in this chapter. There is no need to duplicate this by using a stand-alone Control Plan. However, when submitting the Control Plan for review or as part of the PPAP Evidence pack then it is recommended that this template is used. 123

124 Figure 51: Control Plan Data derived from Process FMEA (red text) 124

125 Table 19: Some Common Issues with Control Plan Deployment The Control Plan is not available at the work station. The purpose of the Control Plan is to be a quick reference guide for the operator to see exactly what checks are required to be carried out when producing / assembling a specific part number. Therefore, along with the work instructions, these are key production reference documents that should be referenced every time that specific part is manufactured / assembled. The Control Plan is too large. The Control Plan needs to be of a manageable size for the Operator to clearly see what needs to be done. It may refer to other documents e.g. Work Instructions, for more details. It should not list out all features that need to be inspected if they are actually measured on the CMM, for example. This can be covered on a single line within the Control Plan. Typically, the Control Plan will be formatted so that they are aligned to an individual operational sequence e.g. OP10, OP20, etc. You would expect the Control Plan for a single Operation to be no more than one page. The Control Plan is not linked to the PFMEA and updated regularly. The Control Plan is one of the documents that define what needs to be controlled as identified within the PFMEA. There must be a clear link between the PFMEA and the Control Plan to ensure what was identified has been transferred into the production controls. Changes to the Control Plan should come from a change to the PFMEA. For example, if there has been a customer escape and the production area has implemented a containment check then this needs to have been derived from the PFMEA update and flowed down into the Control Plan. Once the investigation has been concluded and the containment check is removed then this will also need to be derived from the review / change to the PFMEA. 125

126 Further Reading: AS13004 Process FMEA and Control Plan for Aerospace, AESQ, 2017 Advanced Product Quality Planning (APQP) and Control Plan, 2nd Edition, AIAG, 2008 Control Plan Key Questions: 1. Have Control Plans been developed from the information contained in the PFMEA? 2. Does the Control Plan cover all product and process checks required during production / assembly to ensure conforming product is produced? 3. Has the correct Control Plan Template been used? 4. Are the relevant elements of the Control Plan available at the workplace for use by the Operator? 5. Are Key Characteristics identified on the Control Plan? 6. Are clear instructions given on what action to take if nonconforming product or out of control conditions are found by the operator? 7. Are the non-product specific controls identified in the PFMEA included in the relevant maintenance schedules, tooling maintenance and asset care schemes? See also the Compliance Assessment Checklist in Appendix D. 126

127 Appendix A: Typical Failure Mode Library Type Characteristic Typical Failure Modes Geometry Length Depth Width Diameter Radii Angle Position / Location Flatness Surface Finish Thickness Parallelism Circularity Squareness Too Long Too Short Too Deep Too Shallow Too Wide Too Narrow Too Big Too Small Too Big Too small Too big Too small Out of position / location error Not at Too rough Too smooth Too thick Too thin Not parallel Not circular Not square 127

128 Type Characteristic Typical Failure Modes Geometry Material Properties Assembly Concentricity True Position Thread Pitch Pro le of a Line Pro le of a Surface Non-porous Splatter free Pitting Scratches Hardness Free from burrs No sharp edges Clean Damage free Fit part Correct orientation Torque to value No FOD Apply Adhesive (any similar material) Out of speci cation Out of True position Pitch too large Pitch too small Pro le not to speci cation Pro le not to speci cation Porosity above allowable limits Splatter above allowable limits Pitting above allowable limits Scratches above allowable limits Too Hard Too Soft Burrs present Sharp edges present Contaminated Damaged Part not tted Wrong part tted Incorrect orientation Over torqued Under torqued Not torqued FOD present Too much Too little Incorrect location 128

129 Appendix B: Sample Reference PFMEAs (extracts) Appendix B.1 CNC Drilling Hole Diameter 129

130 Appendix B.2 Manual Assembly Fit Seal Page 138 of

131 Appendix B.3 CNC Drilling Hole Depth 131

132 Appendix B.4 Manual Torque Fastening Detection Controls (examples) P a g e 140 Visual check at end of opera on by fi er. Part ki ng boxes presents the correct number of bolts to fi er Not all bolts fi ed Missed opera on None Tool Calibra on schedule Tool out of calibra on (with error) None Bar code check for operator sequence and correct tooling Wrong tool used Over Torque None Fi er check prior to opera on tool is damaged None None Opera on not completed None Tool Calibra on schedule Tool out of calibra on (with error) Torque 10 M10 bolts (part number xyz) into bolt holes (1,2, to 10) at 50 Nm and 120 degree angle OP 300 Assembly of Outer Manifold to Hub Under Torque None Bar code check for operator sequence and correct tooling Wrong tool used RPN Detection Reference Failure Mode and Effects Analysis (FMEA) Manual Torque Fastening Occurrence Prevention Controls (examples) Potential Cause(s) of Failure Classification Severity Potential Effect(s) of Failure Potential Failure Mode Process Step Requirements Tool incorrectly set None None Fitter visual inspection within operations No Torques applied Missed operation None Angle too big Angle too small Bolt damaged Thread damaged 132

133 Appendix B.5 Manual Paint Spraying 133