STATISTICAL QUALITY CONTROL Majid Rafiee Department of Industrial Engineering Sharif University of Technology rafiee@sharif.ir
Quality Improvement in Modern Business Environment
Copyright Notice Parts (text & figures) of this lecture adopted from: Introduction to Statistical Quality Control, 5th Edition, by Douglas C. Montgomery, Arizona State University https://www.wikipedia.org 3
Outline Meaning of Quality and Quality Improvement History of Quality Control Statistical Methods for Quality Control Management Aspects of Quality Control 4
Outline Meaning of Quality and Quality Improvement History of Quality Control Statistical Methods for Quality Control Management Aspects of Quality Control 5
Are These High Quality Shoes?? 6
Quality Has Different Dimensions Performance Aesthetics Reliability Features Durability Perceived Quality Serviceability Conformance to Standards 7
Quality Has Different Dimensions Performance Aesthetics Reliability Features Durability Perceived Quality Serviceability Conformance to Standards 8
Performance Refers to a product's primary operating characteristics. Involves measurable attributes. 9
Quality Has Different Dimensions Performance Aesthetics Reliability Features Durability Perceived Quality Serviceability Conformance to Standards 10
Reliability Is the likelihood that a product will not fail within a specific time period. This is a key element for users who need the product to work without fail. 11
Reliability R(Product Name)Time = Probability R(Airbus)10h = 0.999999998 12
Quality Has Different Dimensions Performance Aesthetics Reliability Features Durability Perceived Quality Serviceability Conformance to Standards 13
Durability Measures the length of a product s life. When the product can be repaired, estimating durability is more complicated. The item will be used until it is no longer economical to operate it. 14
Quality Has Different Dimensions Performance Aesthetics Reliability Features Durability Perceived Quality Serviceability Conformance to Standards 15
Serviceability Is the speed with which the product can be put into service when it breaks down. Consumer's ease of obtaining repair service Example: access to service centers Ease of self-service reliability of service example: whether the service is performed right the first time 16
Quality Has Different Dimensions Performance Aesthetics Reliability Features Durability Perceived Quality Serviceability Conformance to Standards 17
Aesthetics or Style The aesthetic properties of a product contribute to the identity of a company or a brand. Aesthetics is the subjective dimension indicating the kind of response a user has to a product. It represents the individual s personal preference. 18
Quality Has Different Dimensions Performance Aesthetics Reliability Features Durability Perceived Quality Serviceability Conformance to Standards 19
Features Features are additional characteristics that enhance the appeal of the product or service to the user. 20
Quality Has Different Dimensions Performance Aesthetics Reliability Features Durability Perceived Quality Serviceability Conformance to Standards 21
Perceived Quality Perceived Quality is the quality attributed to a good or service based on indirect measures. Consumers do not always have complete information about a product's or service's attributes; indirect measures may be their only basis for comparing brands. Made In China Made In Iran Made In Japan 22
Quality Has Different Dimensions Performance Aesthetics Reliability Features Durability Perceived Quality Serviceability Conformance to Standards 23
Conformance to Standards Is the precision with which the product or service meets the specified standards. Target Tolerance the range of permitted deviation from the target 24
What is The Meaning of Quality? 25
What is The Meaning of Quality? Quality means fitness to use 26
What is The Meaning of Quality? Quality means fitness to use This is a traditional definition 27
What is The Meaning of Quality? Quality is inversely proportional to variability This is a modern definition of quality 28
Quality is inversely proportional to variability 29
Quality is inversely proportional to variability The Transmission Example 30
What is The Meaning of Quality Improvement? Elimination of waste useful in service or transactional businesses Reduction of variability in processes & products 31
What Is Quality Engineering? Variability is described in statistical terms Statistical methods play central role in quality improvement Applying statistical methods to quality engineering. 32
What Is Quality Engineering? Quality engineering is the combination of engineering, statistics, and management to reduce variability while maintaining the average. 33
Quality Characteristics Also called Critical-To-Quality ( CTQ ) What the user or consumer thinks of as quality Types of Quality Characteristics Physical Sensory Time Orientation 34
Types of Quality Characteristics Physical Length, weight, voltage, viscosity Sensory Taste, appearance, color Time orientation Reliability, durability, serviceability 35
[from: https://www.latestquality.com/ctq-tree-example/, last seen on January 2019] 36
Classifying Data On Quality Characteristics Data Variables Attributes 37
Classifying Data On Quality Characteristics Variables Often continuous measurements Length, voltage, viscosity Following continuous distribution Attributes Usually discrete data Often taking the form of counts Following discrete distribution 38
Outline Meaning of Quality and Quality Improvement History of Quality Control Statistical Methods for Quality Control Management Aspects of Quality Control 39
History Walter A. Shewhart 1920 s Control chart More on Wiki 40
Outline Meaning of Quality and Quality Improvement History of Quality Control Statistical Methods for Quality Control Management Aspects of Quality Control 41
Statistical Methods for Quality Control 42
Statistical Methods for Quality Control Statistical Methods Acceptance Sampling (AS) Designed experiments (DOX) Statistical process control (SPC) 43
Statistical Methods for Quality Control Statistical Methods Acceptance Sampling (AS) Designed experiments (DOX) Statistical process control (SPC) 44
Acceptance Sampling (AS) Uses statistical sampling to determine whether to accept or reject a production lot of material Off-line technique (after production) Pros Cons Simplest quality control technique Economy of time and money in comparison to 100% inspection Not corrective & preventive likelihood or risk 45
Variations Of Acceptance Sampling outgoing inspection Receiving/ incoming inspection Disposition of lots 46
Variations Of Acceptance Sampling 47
Statistical Methods for Quality Control Statistical Methods Acceptance Sampling (AS) Designed experiments (DOX) Statistical process control (SPC) 48
Designed experiments (DOX) Discovering the key factors that influence process performance for Process optimization Off-line technique (before production) Pros The most desirable quality control technique corrective & preventive Cons Cost & time needed 49
Designed experiments (DOX) A factorial experiment with three factors 50
Statistical Methods for Quality Control Statistical Methods Acceptance Sampling (AS) Designed experiments (DOX) Statistical process control (SPC) 51
Statistical process control (SPC) Using Control charts, plus other problem-solving tools. Useful in monitoring processes, reducing variability through elimination of assignable causes On-line technique (during production) 52
Control chart & Specifications a statistical process control tool used to determine if a manufacturing or business process is in a state of control. Specifications Lower specification limit Upper specification limit Target or nominal values 53
Control chart & Specifications 54
Outline Meaning of Quality and Quality Improvement History of Quality Control Statistical Methods for Quality Control Management Aspects of Quality Control 55
Management Aspects of Quality Control Management Aspects of Quality Control Quality Planning Quality Assurance Quality Control and Improvement 56
Management Aspects of Quality Control Management Aspects of Quality Control Quality Planning Quality Assurance Quality Control and Improvement 57
Quality Planning Strategic activity As important as financial plan, marketing plan, Involves identifying customers & their needs Listening to voice of the customer Developing products or services meet or exceed customer expectations 58
Management Aspects of Quality Control Management Aspects of Quality Control Quality Planning Quality Assurance Quality Control and Improvement 59
Quality Assurance Is the set of activities that ensures the quality level Documentation of quality system Involves for: policy, procedures, work instructions and specifications 60
Management Aspects of Quality Control Management Aspects of Quality Control Quality Planning Quality Assurance Quality Control and Improvement 61
Quality Control and Improvement Involve the set of activities used to ensure that the products & services meet requirements and are improved on a continuous basis Using statistical techniques SPC, DOX, 62
Quality Philosophies and Management Strategies Feigenbaum Total Quality Control quality leadership, quality technology, organizational commitment Juran Trilogy Planning, Control, Improvement Deming PDCA Plan, do, control, act 63
Common Concepts of Quality Philosophies Importance of leadership & management in quality improvement Emphasis on using statistical methods Quality as a competitive advantage 64
International Organization for Standardization (ISO) Wiki is an international standard-setting body composed of representatives from various national standards organizations. ISO 9000, ISO 14000, ISO/TS 16949, 65
Quality Awards EFQM, MBNQA, Deming Prize, 66
Six Sigma Focus of Six Sigma is on Process Improvement with an Emphasis on Achieving Significant Business Impact Involves a five-step process (DMAIC) Define, Measure, Analyze, Improve, Control [from: http:// xlncacademy.com/blog/top- 5-unique-benefits-of-six-sigma, last seen on January 2019] 67
Six Sigma LSL & USL are fixed It is the process which changes 68
Six Sigma 69
Six Sigma A visit to a fast-food store: Hamburger (bun, meat, special sauce, cheese, pickle, onion, lettuce, tomato), fries, and drink. This product has 10 components. Q1) Probability of customer satisfaction for a single meal in Six Sigma & Three Sigma? Q2) Family of four, once a month; Probability of customer satisfaction for all meals in a month & in a year? 70
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The Process Improvement Triad: DFSS, Lean, and DMAIC 72
Design for Six Sigma (DFSS) Only so much improvement can be wrung out of an existing system New process design New product design (engineering) DFSS Matches Customer Needs with Capability & enhances product design methods 73
Lean A set of methods and tools used to eliminate waste in a process identify anything not absolutely required to deliver a quality product on time reduce inventory, lead time, and cost increase productivity, quality, on time delivery, capacity, and sales 74
DMAIC Solves problems by using Six Sigma tools Define problems in processes Measure performance Analyze causes of problems Improve processes/ remove variations and nonvalueadded activities Control processes so problems do not recur [from: http:// xlncacademy.com/blog/top- 5-unique-benefits-of-six-sigma, last seen on January 2019] 75
Six Sigma Pros A limit of 3.4 defects per one million products or services addresses the entire process, rather than just the final outcome It is proactive rather than reactive determines how improvements can be made even before defects are found Useful for product with several components 76
Six Sigma Cons rigidity that can create delays & stifle creativity an inexpensive measure that carries a risk of a higher defect rate is rejected in favor of a more expensive measure that helps to achieve Six Sigma, but adversely affects profitability 77
Quality Costs Quality Costs Prevention Costs Appraisal Costs Internal Failure Costs External Failure Costs 78
Quality Costs Quality Costs Prevention Costs Appraisal Costs Internal Failure Costs External Failure Costs 79
Prevention Costs Quality planning & engineering New products review Product/ process design Process control Burn-in Training Quality data acquisition & analysis 80
Quality Costs Quality Costs Prevention Costs Appraisal Costs Internal Failure Costs External Failure Costs 81
Appraisal Costs Inspection & test of incoming materials Product inspection & test Materials & services consumed Maintaining accuracy of test equipment 82
Quality Costs Quality Costs Prevention Costs Appraisal Costs Internal Failure Costs External Failure Costs 83
Internal Failure Costs Scrap Rework Retest Failure analysis downtime Yield losses Down grading 84
Quality Costs Quality Costs Prevention Costs Appraisal Costs Internal Failure Costs External Failure Costs 85
External Failure Costs Complaint adjustment Returned product/ material Warranty charges Liability costs Indirect costs 86
Backup 87