Q uality control ch4

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Q uality control ch4

  1. 1. Chapter 11 Quality ControlTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 1
  2. 2. Quality Control (QC) • Control – the activity of ensuring conformance to requirements and taking corrective action when necessary to correct problems • Importance – Daily management of processes – Prerequisite to longer-term improvementsTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 2
  3. 3. Designing the QC System • Quality Policy and Quality Manual – Contract management, design control and purchasing – Process control, inspection and testing – Corrective action and continual improvement – Controlling inspection, measuring and test equipment (metrology, measurement system analysis and calibration) – Records, documentation and auditsTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 3
  4. 4. Inspection/Testing Points • Receiving inspection • In-process inspection • Final inspectionTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 4
  5. 5. Receiving Inspection • Spot check procedures • 100 percent inspection • Acceptance samplingTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 5
  6. 6. Acceptance Sampling Lot received for inspection Sample selected and analyzed Results compared with acceptance criteria Accept the lot Reject the lot Send to production Decide on disposition or to customerTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 6
  7. 7. Pros and Cons of Acceptance Sampling • Arguments for: • Arguments against: – Provides an assessment – Does not make sense of risk for stable processes – Inexpensive and suited – Only detects poor for destructive testing quality; does not help – Requires less time than to prevent it other approaches – Requires less handling – Is non-value-added – Reduces inspector – Does not help suppliers fatigue improveTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 7
  8. 8. In-Process Inspection • What to inspect? – Key quality characteristics that are related to cost or quality (customer requirements) • Where to inspect? – Key processes, especially high-cost and value- added • How much to inspect? – All, nothing, or a sampleTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 8
  9. 9. Economic Model C1 = cost of inspection and removal of nonconforming item C2 = cost of repair p = true fraction nonconforming Breakeven Analysis: p*C2 = C1 If p > C1 / C2 , use 100% inspection If p < C1 / C2 , do nothingTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 9
  10. 10. Human Factors in Inspection • complexity • defect rate • repeated inspections • inspection rate Inspection should never be a means of assuring quality. The purpose of inspection should be to gather information to understand and improve the processes that produce products and services.THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 10
  11. 11. Gauges and Measuring Instruments • Variable gauges • Fixed gauges • Coordinate measuring machine • Vision systemsTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 11
  12. 12. Examples of GaugesTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 12
  13. 13. Metrology - Science of Measurement• Accuracy - closeness of agreement between an observed value and a standard• Precision - closeness of agreement between randomly selected individual measurementsTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 13
  14. 14. Repeatability and Reproducibility • Repeatability (equipment variation) – variation in multiple measurements by an individual using the same instrument. • Reproducibility (operator variation) - variation in the same measuring instrument used by different individualsTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 14
  15. 15. Repeatability and Reproducibility Studies • Quantify and evaluate the capability of a measurement system – Select m operators and n parts – Calibrate the measuring instrument – Randomly measure each part by each operator for r trials – Compute key statistics to quantify repeatability and reproducibilityTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 15
  16. 16. THE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 16
  17. 17. R&R Evaluation • Under 10% error - OK • 10-30% error - may be OK • over 30% error - unacceptableTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 17
  18. 18. Calibration • Calibration - comparing a measurement device or system to one having a known relationship to national standards • Traceability to national standards maintained by NIST, National Institute of Standards and TechnologyTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 18
  19. 19. Example of QC: HACCP System 1. Hazard analysis 2. Critical control points 3. Preventive measures with critical limits for each control point 4. Procedures to monitor the critical control points 5. Corrective actions when critical limits are not met 6. Verification procedures 7. Effective record keeping and documentationTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 19
  20. 20. Quality Control in Services • Identify important quality characteristics – Time, errors, behavior • Measure and collect data using check sheets, check lists, or other means • Take corrective actionTHE MANAGEMENT AND CONTROL OF QUALITY, 5e, © 2002 South-Western/Thomson LearningTM 20

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