Quality control notes week 1
Quality control notes week 1 MECH6074003
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This 64 page Class Notes was uploaded by Nikhil Notetaker on Tuesday February 23, 2016. The Class Notes belongs to MECH6074003 at University of Cincinnati taught by Thomas R. Huston in Spring 2016. Since its upload, it has received 29 views. For similar materials see Quality control in Mechanical Engineering at University of Cincinnati.
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Date Created: 02/23/16
Quality Control Thomas R. Huston, PhD, PE 513-556-2645 (UC Office) email@example.com (email) 2Thomas R. Huston, Ph.D., P.E. 1 Engineering • Creative application of scientific principles for practical purposes • Engineers design and develop • Products • Structures • Machines and devices • Systems • Processes Thomas R. Huston, Ph.D., P.E. 2 Engineering • Engineers must address: – Alternatives – Constraints • Customer needs • Productivity • Costs – Quality 2Thomas R. Huston, Ph.D., P.E. 3 Management • Coordinating human efforts and allocating resources to reach specific goals such as quality level • Management activities: – Planning – Leading – Controlling – Resourcing – Organizing Thomas R. Huston, Ph.D., P.E. 4 Quality Definitions • Dictionary: degree of excellence of an object, person, or process – Merchandise of high quality – Inadequate quality of service – Acceptable air quality – Workmanship of superior quality Thomas R. Huston, Ph.D., P.E. 5 Quality Definitions cont’d American Society for Quality (ASQ): • Subjective term for which each person has his or her own definition. • Quality has two meanings in technical usage – Characteristics of a product or service satisfy stated or implied needs – Product or service is free of deficiencies Thomas R. Huston, Ph.D., P.E. 6 Quality Definitions cont’d Armand Feigenbaum, Total Quality Control: Quality—a customer determination which is based on the consumer’s actual experience with the product or service measured against his/her requirements—stated or unstated, conscious or merely sensed, technically operational or entirely subjective—and always representing a moving target in a competitive market. Thomas R. Huston, Ph.D., P.E. 7 Quality Definitions cont’d Philip Crosby: • Quality—conformance to requirements • Nonquality—nonconformance to requirements Peter Drucker: • Quality in a product or service is not what the supplier puts in; rather it is what the customer gets out and is willing to pay for it 2Thomas R. Huston, Ph.D., P.E. 8 Quality Definitions cont’d Six Sigma: • Number of defects per million opportunities ISO 9000: • Degree to which a set of inherent characteristics fulfills requirements. Thomas R. Huston, Ph.D., P.E. 9 Quality Definitions cont’d W . Edwards Deming, PhD: • Quality—nonfaulty systems • Nonfaulty systems—error free systems with capability to provide consumer with product or service specified Thomas R. Huston, Ph.D., P.E. 10 Quality Definitions cont’d Genichi Taguchi: • Uniformity around a target value – [lower standard deviation in outcomes] • The loss a product imposes on society after it is shipped Thomas R. Huston, Ph.D., P.E. 11 Quality Definitions cont’d Dr . Joseph M. Juran: • Quality—fitness for use Thomas R. Huston, Ph.D., P.E. 12 Evolution of Quality Control • Quality of goods has been monitored since ancient times • Commitment to quality seen in ancient cultures: – Egyptian pyramids – Greek architecture – Roman bridges and roads Thomas R. Huston, Ph.D., P.E. 13 Evolution of Quality Control cont’d th • Middle ages – 19 century – Goods and services produced mainly by individual or small group – Operator Quality Control Period • Quality of product controlled by single person— operator • Quality linked to pride in workmanship • Volume of production limited 2Thomas R. Huston, Ph.D., P.E. 14 Evolution of Quality Control cont’d • Foreman Quality Control Period: 1900-20 – Mass production and specialization of labor – Person not responsible for entire product only portion – Decrease in workers’ sense of accomplishment – Workers performing similar work grouped – Foreman controlled quality of product 2Thomas R. Huston, Ph.D., P.E. 15 Evolution of Quality Control cont’d • Inspection Quality Control Period, 1920-40 – Products and processes increase in complexity – Production volume increases – Foreman no longer able to adequately watch individual operations – Inspectors used to check quality against standards at certain stages of production – Deficient product either scrapped or reworked 2Thomas R. Huston, Ph.D., P.E. 16 Evolution of Quality Control cont’d • Initial development of statistical quality control – Walter Shewhart of Bell Telephone Laboratories • Introduces control charts, 1924 – H.F. Dodge and H.G. Romig, Bell Telephone Laboratories • Introduce acceptance sampling plans Thomas R. Huston, Ph.D., P.E. 17 Evolution of Quality Control cont’d • Statistical Quality Control Period, 1940-60 – Sampling plans gain acceptance due to production requirements and infeasibility of 100% inspection – American Society of Quality Control (ASQC) formed in 1946 – ASQC developed sampling inspection plans for military • MIL-STD-105A and later revisions – Department of Defense develops Quality Control and Reliability Handbook, H-107, 1957 Thomas R. Huston, Ph.D., P.E. 18 Evolution of Quality Control cont’d • Japan post World War II – W. Edwards Demming visits Japan 1950 and lectures on statistical quality control – J.M. Juran visits Japan and stresses importance of management in achieving quality program – Japan endorses and commits to statistical quality control – Japanese reap benefits of stronger industries 2Thomas R. Huston, Ph.D., P.E. 19 Evolution of Quality Control cont’d • Total Quality Control, 1960s – Marked gradual involvement of several departments and management in quality control • No longer was quality control restricted to inspection department – NASA introduced concept of zero defects – Quality circles introduced in Japan • Volunteer group of workers trained to analyze and solve work related problems • Solutions improve performance of organization • Enrich work experience of employees 2Thomas R. Huston, Ph.D., P.E. 20 Evolution of Quality Control cont’d • Total Quality System, 1970-80s – Involves participation of everyone in organization • Operator to CEO – Quality system is agreed upon companywide – Increased emphasis on vendor quality control • Ford Motor Company demands documentation of statistical process control from vendors • Smaller companies adopted statistical quality control 2Thomas R. Huston, Ph.D., P.E. 21 Evolution of Quality Control cont’d – Japan • Cause-and-Effect Diagrams (a.k.a. Fishbone)—identifies reasons for a process to go out of control • G. Taguchi introduces concept of quality improvement through statistically designed experiments – USA • Introduction of Malcolm Baldrige National Quality Award introduced to motivate American companies to improve quality Thomas R. Huston, Ph.D., P.E. 22 Evolution of Quality Control cont’d • Global standards development, 1980-present – ISO develops standards to emphasize customer satisfaction and continuous quality improvement • ISO 9000-9004 – ANSI/ASQC similarly introduced standards • Q90-94, 1987 • ANSI/ASQC 9000-Q9004 • ANSI/ISO/ASQ Q9000-2000 – Transcends type of industry 2Thomas R. Huston, Ph.D., P.E. 23 Quality Characteristics • Customer is driving force in determining level of quality – Not a universal constant – Different levels of expectations for different consumers • Structural characteristics—elements such as volume, length, strength, etc. • Sensory characteristics—taste, smell, beauty • Time-oriented—warranty, reliability, maintainability • Ethical—honesty, courtesty, friendliness 2Thomas R. Huston, Ph.D., P.E. 24 Quality Characteristics cont’d • Variables—characteristics that are measurable – Time – Weight • Attributes—characteristics classified as conforming or nonconforming – Color of bolt of fabric – Aroma of perfume Thomas R. Huston, Ph.D., P.E. 25 Quality Characteristics cont’d • National Bureau of Standards (NBS) defines – Specification—set of conditions and requirements, of specific and limited application that provide detailed description of procedure, process, material, product or service for use in procurement and manufacturing Thomas R. Huston, Ph.D., P.E. 26 Quality Characteristics cont’d – Standard: prescribed set of conditions and requirements, of general or broad application, established by authority or agreement to be satisfied by a material, product, process, procedure, convention, test method and the functional, physical, or conformance thereof. – Defect—quality characteristic that does not meet certain standards. 2Thomas R. Huston, Ph.D., P.E. 27 Quality Forms • Quality of design—product has been designed to successfully fill a consumer need • Quality of conformance—product or service meeting specific requirements set in the design stage • Quality of performance—product or service performs its intended function when put to use as identified by the consumer 20 MECH 6074 Quality Control 28 Quality of Design Source: A. Mitra. Fundamentals of Quality Control and Improvement. 3 Edition, Hoboken, N.J.: Wiley & Sons, Inc., 2008 20 MECH 6074 Quality Control Thomas R. Huston, Ph.D., P.E. 29 Quality Control T opics Thomas R. Huston, Ph.D., P.E. 1 Quality Control • General definition: process that maintains a level of quality in a product or service • Features: – Feedback on characteristics – Comparison with standard – Remedial action if there is deviation from standard • Subareas – Off-line quality control – Statistical process control – Acceptance sampling Thomas R. Huston, Ph.D., P.E. 2 Off-line Quality Control • Relies on measures at the product and process design stages • Product and process parameters are selected to reduce sources of variation so that output meets the standard • Objective – Improve product manufacturability – Improve reliability – Reduce product development costs – Reduce Lifetime costs • Taguchi Methods Thomas R. Huston, Ph.D., P.E. 3 Statistical Process Control • Compares output of process with a standard – Remedial measures are then undertaken if there is a deviation from norm – Also used to determine if process can meet specifications • On-line statistical process – Information collected while process is functional – Inspections used to rectify a system to an acceptable state Thomas R. Huston, Ph.D., P.E. 4 Acceptance Sampling • Technique that uses statistical sampling to accept or reject a lot of material – Used when 100% inspection is not feasible – Sample size much less than lot size – Lot is accepted or rejected based on number of nonconforming items in sample • Various general acceptance sampling plans have been developed • Risks – Producer’s risk--reject good lot – Consumer’s risk—accept inferior lot 2Thomas R. Huston, Ph.D., P.E. 5 Quality Assurance • Formal system in an organization that continually surveys the quality procedures within the organization for compliance • Quality assurance team uses audits – ie, is measuring equipment calibrated? – ie, does design have adequate safety margin • Principles: – Fit for purpose—product should be its intended purpose – Right the first time—eliminate mistakes Thomas R. Huston, Ph.D., P.E. 6 Quality Assurance cont’d • Quality Assurance transcends whole organization—all have responsibility for quality product/service – Engineering – Marketing – Purchasing – Production – Maintenance Thomas R. Huston, Ph.D., P.E. 7 Quality Circles Quality Circle: informal group of workers that get together to analyze and solve work related problems • Members – Operators – Supervisors – Managers • Problems – Improve product design – Improve manufacturing process Thomas R. Huston, Ph.D., P.E. 8 Quality Circles cont’d • Benefits – Enrich work of employees – Effective means to improve performance of organization – Create harmony in workers Thomas R. Huston, Ph.D., P.E. 9 Quality Improvement T eam Quality improvement team—group of employees charged with the task of identifying and resolving quality control problems • Groups are cross functional – Various disciplines • Leader should be selected with multiple skills – Accomplish task concerns – Deal with needs of team – Motivate team members – Team dynamics Thomas R. Huston, Ph.D., P.E. 10 Quality Improvement T eam cont’d • Procedures: – Team objectives clearly defined at outset – Team leader prepares and distributes agenda at each meeting – Assignments made to individuals or subgroups – Team leader encourages differing points of view – All team members encouraged to contribute – Action plans proposed – Regular feedback on results Thomas R. Huston, Ph.D., P.E. 11 Customer Needs • Satisfying customers is critical to growth and market share • Must identify customer needs and wants in design phase • Needs vary in importance – Needs may be taken for granted Thomas R. Huston, Ph.D., P.E. 12 Kano Model • Noriaki Kano, Japanese consultant – Developed model relating customer satisfaction to design characteristics • Prioritized Categories – Basic needs (dissatisfiers) – Performance needs (satisfiers) – Excitement needs (delighters) Thomas R. Huston, Ph.D., P.E. 13 Kano Model cont’d • Basic needs – Taken for granted by customers – Meeting these needs does not increase customer satisfaction – Failing to meet these needs leads to dissatisfaction – ie, Hotel room does not have color TV Thomas R. Huston, Ph.D., P.E. 14 Kano Model cont’ d • Performance needs – Needs that the customer expects – Not absolutely necessary – Better these are satisfied; more satisfied the customer – ie, hotel provides expedited checkout option Thomas R. Huston, Ph.D., P.E. 15 Kano Model cont’ d • Excitement needs – Needs customers did not know they wanted but are delighted when they find them – Ordinarily, not identifiable from surveys – ie, Hotel provides significant discount on tickets to local attraction 2Thomas R. Huston, Ph.D., P.E. 16 Source: A. Mitra. Fundamentals of Quality Control and Improvement. 3 Edition, Hoboken, N.J.: Wiley & Sons, Inc., 2008 20 MECH 6074 Quality Control 17 Thomas R. Huston, Ph.D., P.E. Benefits of Quality Control • Improvement in quality of products and services • Continual reevaluation of system to meet customer needs • Decrease in scrap and rework • Total costs decrease • Improved delivery dates to customer 20 MECH 6074 Quality Control 18 Quality and Reliability • Reliability—ability of a product to perform its function over a period of time – Often expressed as a probability – Can use reliability of components and laws of probability to assess reliability of total systems • Reliability is addressed in quality of design 2Thomas R. Huston, Ph.D., P.E. 19 Quality Improvement • On-going effort – No deviation from a standard is acceptable • Quality improvement—identification and elimination of common not special causes of variation • Common causes—inherent in system – Management must address common cause problems – Always present – decision to replace a machine with a superior machine • Special causes of variation— – Controlled by operator – ie, tool wear 2Thomas R. Huston, Ph.D., P.E. 20 Quality Improvement cont’d • Even though a product meets specifications; strive to reduce variability about target value e.g., – Specification is 12.0 ± 0.05 oz – To improve quality reduce variability about target value 2Thomas R. Huston, Ph.D., P.E. 21 Quality Costs • Quality cost—difference between actual cost and cost if product/service was conforming to requirements • Categories of quality cost – Prevention costs – Appraisal costs – Internal failure costs – External failure costs Thomas R. Huston, Ph.D., P.E. 22 Quality Costs cont’d • Prevention costs—costs associated with planning, implementing and maintaining quality system – Developmental costs of product – Costs of education and training – Cost of quality audit – Costs of making it right the first time Thomas R. Huston, Ph.D., P.E. 23 Quality Costs cont’d • Appraisal costs—associated with measuring product/service for conformance to specific standards – Inspection and testing – Calibrating test equipment – Loss of product to testing Thomas R. Huston, Ph.D., P.E. 24 Quality Costs cont’d • Internal failure costs—nonconformance of product/services to standards prior transfer of ownership to customer – Scrap – Rework – Loss of revenue due to downgrading of product – Costs of determining internal failure Thomas R. Huston, Ph.D., P.E. 25 Quality Costs cont’d • External failure costs—nonconformance of product/services to standards after transfer of ownership to customer – Customer complaints – Cost of investigation – Warranty charges – Product liability 2Thomas R. Huston, Ph.D., P.E. 26 Quality Costs cont’d • Data must be collected to monitor quality costs – Will help identify root causes of failure – Initiate remedial actions 2Thomas R. Huston, Ph.D., P.E. 27 Source: A. Mitra. Fundamentals of Quality Control and Improvement. 3 Edition, Hoboken, N.J.: Wiley & Sons, Inc., 2008 20 MECH 6074 Quality Control 28 Thomas R. Huston, Ph.D., P.E. Measuring Quality Costs • Magnitude not always best measure because conditions change – Inflation – Number of units change • Labor-based index—quality costs per direct- labor hour • Cost-based index—quality costs per dollar of manufacturing costs Thomas R. Huston, Ph.D., P.E. 29 Measuring Quality Costs cont’d • Sales-based—quality costs per sales dollar – Affected by selling price changes • Unit based index—quality cost per unit of production – Valid with standard product and similar production lines Thomas R. Huston, Ph.D., P.E. 30 Quality and Productivity • Quality improves productivity – Lowers total costs – Frees valuable resources • Increase in market share • Increase in profitability – Focus on long term profits not short term Thomas R. Huston, Ph.D., P.E. 31 Example What is the unit cost for a conforming product if the production costs are $20 and the proportion conforming is 0.92? Thomas R. Huston, Ph.D., P.E. 32 Solution Unit Cost = Production Cost/Proportion Conforming Unit Cost = $20/0.92 Unit Cost = $21.73 2Thomas R. Huston, Ph.D., P.E. 33 Example A given product consists of two assemblies. The production cost of the assemblies is c = $20 an1 c2= $30. The proportion conforming for each assembly is p = 0.92 and p = 0.88. What is the 1 2 unit cost of the product? Assembly 1 Assembly 2 2Thomas R. Huston, Ph.D., P.E. 34 Solution Proportion conforming = (p )(p ) = (0.92)(0.88) 1 2 = 0.8096 Overall production cost = c + c1= $22 + $30 = $50 Unit cost = $50/0.8096 = $61.75 Thomas R. Huston, Ph.D., P.E. 35
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