Chapter 6-1: Failure Modes Effect Analysis (FMCEA)

Transcription

1 Chapter 6-1: Failure Modes Effect Analysis (FMCEA) Learning Outcomes: After careful studying this lecture You should be able: To Define FMEA To understand the use of Failure Modes Effect Analysis (FMEA) To be informed about the history of FMEA To learn the steps to developing FMEA To discuss benefits and pitfalls of FMEA To summarize the different types of FMEA 1

2 Key Definitions Customer: persons and organizations that are affected by the process. Failure: any malfunction, defect or error that causes the process not to perform its intended function(s) or meet requirements satisfactorily. Failure Mode: the appearance, manner or form in which the process failure manifests itself. (Short circuit or handling damage) Cause(s) of the Failure: Possible mechanism(s) and/or way(s) in which the failure mode can be produced. Effect(s) of the Failure: the experience the customer encounters as a result of the failure mode What is FMEA? A bottoms-up, iterative approach for analyzing a design of a product or process in order to determine what could go wrong how badly it might go wrong and what needs to be done to prevent it Another definition: Any formal, structured activity which is applied in developing something new to assure that as many potential problems as are reasonably possible to predict have considered, analyzed, and their causes improved before the item under development reaches the hands of the end user. 2

3 What is it? Actions Prevention / reduction of failures Tool for risk reduction What it is not? The FMEA is not a stand-alone tool to be used to solve problems The FMEA presents the opportunities but does not solve the problems What is FMEA? (cont.) FMEA--a tool to identify risks in your process Can be used in multiple places in process improvement Determine where problems are Help identify cause/effect relationships Highlight risks in solutions and actions to take Starts with input from processes Identifies three risk categories Severity of impact Probability of occurrence Ability to detect the occurrence 3

4 When to Conduct an FMEA? Early in the process improvement investigation When new systems, products, and processes are being designed When existing designs or processes are being changed When carry-over designs are used in new applications After system, product, or process functions are defined, but before specific hardware is selected or released to manufacturing When to Use? Early stages (Define) to understand process and identify problem areas Analyze data (Analyze) to help identify root causes Determine best solutions (Improve) with lowest risk Close out stage (Control) to document improvement and identify actions needed to continue reducing the risk 4

5 Failure Mode, Effects, and Criticality Analysis (FMECA) What s a FMECA? A more expanded version of FMEA includes a determination of the criticality or severity of a particular failure mode. Failure Mode Effects and Criticality Analysis (FMECA) Another similar technique, extension of FMEA The FMECA is the result of two steps: Failure Mode and Effect Analysis (FMEA) Criticality Analysis (CA) to evaluate the frequency of occurrence of the problems identified. 5

6 Why is FMEA / FMECA Important? FMEA provides a basis for identifying root failure causes and developing effective corrective actions The FMEA identifies reliability/safety of critical components It facilitates investigation of design alternatives at all design stages Provides a foundation for other maintainability, safety, testability, and logistics analyses A Pro-active engineering quality method What s In It for Me? Allows us to identify areas of our process that has most impact on our customers Helps us identify how our process is most likely to fail Points to process failures that are most difficult to detect 6

7 What can FMEA be used for? Competing Prevention of Litigation Identify Weak areas of a process/product A bottom-up approach To evaluate the effectiveness of the current control plan Prioritize tasks Benefits Improved product or process functionality and safety Reduced warranty and replacement costs Improve product/process reliability and quality Increase customer satisfaction Early identification and elimination of potential product/process failure modes Prioritize product/process deficiencies Capture engineering/organization knowledge Emphasizes problem prevention Documents risk and actions taken to reduce risk Identify critical to quality (CTQs) 7

8 Application Examples Manufacturing: A manager is responsible for moving a manufacturing operation to a new facility. He/she wants to be sure the move goes as smoothly as possible and that there are no surprises. Design: A design engineer wants to think of all the possible ways a product being designed could fail so that robustness can be built into the product. Software: A software engineer wants to think of possible problems a software product could fail when scaled up to large databases. What Is A Failure Mode? What Can Go Wrong? A Failure Mode is: The way in which the component, subassembly, product, input, or process could fail to perform its intended function Failure modes may be the result of upstream operations or may cause downstream operations to fail Things that could go wrong 8

9 FMEA Why Methodology that facilitates process improvement Identifies and eliminates concerns early in the development of a process or design Improve internal and external customer satisfaction Focuses on prevention FMEA may be a customer requirement FMEA may be required by an applicable Quality System Standard FMEA A structured approach to: Identifying the ways in which a product or process can fail Estimating risk associated with specific causes Prioritizing the actions that should be taken to reduce risk Evaluating design validation plan (design FMEA) or current control plan (process FMEA) 9

10 Evolution 1960 s: NASA moon program engineers devised a method of forecasting problems s: Method becomes known as FMEA and is adopted by various quality organizations. In the late 1970 s, the automotive industry was driven by liability costs to use FMEA Later, the automotive industry saw the advantages of using this tool to reduce risks related to poor quality Evolution (cont.) 1980 s: With increased emphasis on quality, method spreads to large corporations s: Large corporations are, in turn, pressing suppliers to adopt the method s: Method is being applied elsewhere such as HealthCare. 10

11 The FMEA Form A Closer Look Identify failure modes and their effects Identify causes of the failure modes and controls Prioritize Determine and assess actions Types of FMEAs Specialized Uses Design Analyzes product design before release to production, with a focus on product function Analyzes systems and subsystems in early concept and design stages Process Used to analyze manufacturing and assembly processes after they are implemented FMCEA 11

12 Product versus Process Product or Design FMEA. What could go wrong with a product while in service as a result of a weakness in design. Product design deficiencies Process FMEA. What could go wrong with a product during manufacture or while in service as a result of non-compliance to specification or design. Manufacturing or assembly deficiencies Focus on process failures and how they cause bad quality products to be produced FMEA: A Team Tool Team Input Required A team approach is necessary. Team should be led by the Process Owner who is the responsible manufacturing engineer or technical person, or other similar individual familiar with FMEA. The following should be considered for team members: Design Engineers Operators Process Engineers Reliability Materials Suppliers Suppliers Customers 12

13 FMEA Procedure Process Steps 1. For each process input (start with high value inputs), determine the ways in which the input can go wrong (failure mode) 2. For each failure mode, determine effects Select a severity level for each effect 3. Identify potential causes of each failure mode Select an occurrence level for each cause 4. List current controls for each cause Select a detection level for each cause FMEA Procedure (Cont.) Process Steps 5. Calculate the Risk Priority Number (RPN) 6. Develop recommended actions, assign responsible persons, and take actions Give priority to high RPNs MUST look at severities 7. Assign the predicted severity, occurrence, and detection levels and compare RPNs 13

14 FMEA Inputs and Outputs Information Flow Inputs Outputs Brainstorming Cause & Effect Matrix (C&E) Process Map Process History Procedures Knowledge Experience FMEA List of actions to prevent causes or detect failure modes History of actions taken Severity, Occurrence, and Detection Analyzing Failure & Effects Severity Importance of the effect on customer requirements Occurrence Frequency with which a given cause occurs and creates failure modes Detection The ability of the current control scheme to detect or prevent a given cause 14

15 Rating Scales Assigning Rating Weights There are a wide variety of scoring anchors presenters, both quantitative or qualitative Two types of scales are 1-5 or 1-10 The 1-5 scale makes it easier for the teams to decide on scores The 1-10 scale may allow for better precision in estimates and a wide variation in scores (most common) Rating Scales Assigning Rating Weights Severity 1 = Not Severe, 10 = Very Severe Occurrence 1 = Not Likely, 10 = Very Likely Detection 1 = Easy to Detect, 10 = Not easy to Detect 15

16 Risk Assessment Factors Severity (S): A number from 1 to 5 (10), depending on the severity of the potential failure mode s effect 1 = no effect 5 (10) = maximum severity Probability of occurrence (O): A number from 1 to 5 (10), depending on the likelihood of the failure mode s occurrence 1 = very unlikely to occur 5 (10) = almost certain to occur Risk Assessment Factors Probability of detection (D): A number from 1 to 5 (10), depending on how unlikely it is that the fault will be detected by the system responsible (design control process, quality testing, etc.) 1 = nearly certain detention 5 (10) = impossible to detect Risk Priority Number (RPN): The failure mode s risk is found by the formula RPN = S x O x D. RPN = Severity x Probability of Occurrence x Probability of Detection. RPN will be a number between 1 (virtually no risk) and 125 (1000) (extreme risk). 16

17 Risk Priority Number (RPN) Calculating a Composite Score RPN is the product of the severity, occurrence, and detection scores. Severity X Occurrence X Detection = RPN Difficulties in Implementation Time and resource constraints Lack of understanding of the purpose of FMEA Lack of management commitment Employee training requirements Initial impact on product and manufacturing schedules Financial impact required to upgrade design, manufacturing, and process equipment and tools 17

18 FMEA Cycle Extend to FMECA 18

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20 IN-CLASS PROBLEM 1 For Change Oil in Car generate a partial FMEA. IN-CLASS PROBLEM 2 For the cordless screwdriver generate a partial FMEA. a) List the three most significant functions of the case. b) For most potentially difficult function, name Potential Failure Modes c) For each Potential Failure Mode, name Potential Effects d) For each Potential Failure Mode, name Potential Causes e) For each Potential Failure Mode, assign Severity, Occurrence, and Detection values 20

21 Summary Key Points An FMEA: Identifies the ways in which a product or process can fail Estimates the risk associated with specific causes Prioritizes the actions that should be taken to reduce risk FMEA is a team tool There are two different types of FMEAs: Design Process Inputs to the FMEA include several other Process tools such as C&E Matrix Key Points END of the Chapter A collection of information including links to examples, guides, standards, etc. 21

22 Risk Priority Number (RPN) RPN is a quantitative measure to evaluate and assess the failure mode The RPN is comprised of the following three criteria: S = Severity or seriousness of the failure mode O = Probability of the occurrence of the failure mode D = Probability that a potential failure will be detected before it can have any consequences The ranking system for each criterion is typically based on a linear scale: 1-10 ranking scale, 1-5 ranking scale depending on team preference Low number corresponds to low risk High number corresponds to high risk Severity Rating Scale (1-10 Scale) Rating Description Definition 10 Extremely Dangerous Failure could injure the patient 9 8 Very Dangerous Failure could cause major or permanent injury 7 Dangerous Failure causes minor to moderate injury with a high degree of patient dissatisfaction 6 5 Moderate Danger Failure cause minor injury with some customer dissatisfaction 4 3 Low to Moderate Danger Failure causes very minor or no injury but annoys customers 2 Slight Danger Failure causes no injury and customer is unaware 1 No Danger Failure causes no injury and has no impact on system Adapted from: The Basics of FMEA, Productivity, Inc. Copyright 1996 Resource Engineering, Inc. 22

23 Occurrence Rating Scale (1-10 Scale) Rating Description Potential Failure Rate 10 Certain probability Failure occurs at least once a day; or, failure occurs almost every time 9 Failure is almost inevitable Failure occurs predictably; or, failure occurs every 3 or 4 days Very high probability Moderately high probability Moderate probability Failure occurs frequently; or. Failure occurs about once per week Failure occurs about once per month Failure occurs occasionally; or, failure occurs once every 3 months 2 Low probability Failure occurs rarely; or, failure occurs about once per year 1 Remote probability Failure almost never occurs; no one remembers last failure Adapted from: The Basics of FMEA, Productivity, Inc. Copyright 1996 Resource Engineering, Inc. Detection Rating Scale (1-10 Scale) Rating Description Definition 10 No chance of detection 9 8 Very Remote/Unreliabl e There is no known mechanism for detecting the failure The failure can be detected only with thorough inspection and this is not feasible or cannot be readily done 7 6 Remote The failure can be detected with manual inspection but no process is in place so that detection is left to chance 5 Moderate chance of detetion 4 3 High There is a process for double-checks or inspection but it is not automated an/or is applied only to a sample and/or relies on vigilance There is 100% inspection or review of the process but it is not automated 2 Very High There is 100% inspection of the process and it is automoated 1 Almost certain There are automatic shut-offs or constraints that prevent failure 23

24 Risk Priority Number (1-5 Scale) Rating Severity (S) Occurrence (O) Detection (D) 1 Failure did not reach pt. 1 failure per year 100% of the time 2 Failure reached pt. 1 failure per quarter Almost always 3 Failure requires monitoring 4 Failure requires intervention 1 failure per month 75% of the time 1 failure per week 50% of the time 5 Failure results in death 1 failure per day Not detectable Severity: Assessment of the seriousness of the effect Occurrence: Estimation of likelihood that a failure will occur. Detection: How likely will the failure be detected Risk Priority Number (RPN) RPN = Severity Rank x Occurrence Rank x Detection Rank The highest RPN s and Occurrence Ranking should be given the first consideration for corrective actions. As a general rule, special attention should be given when the severity ranking is high, regardless of the resultant RPN. 24