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Process Capability Studies

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  1. Process Capability Studies Comparison of Process Output to Product Requirements Lynn Taylor – OISM 470W Section 002

  2. Process Capability Studies3 Steps • Gauge Capability • Process Characteristics • Stability • Normality • Control • Process Capability Analysis • Comparison of process output(s) to requirements.

  3. Process Capability StudiesDefinitions • Process – Work performed on a set of inputs to produce a result. • Capability – The predictable result(s) of a process allowed to operate without outside interference. • Process Capability Study – Comparison of process output(s) to product requirements.

  4. Process Capability StudiesUses In Our Plant • Customer 1 < 407, Cpk > 1.25 • Customer 1 > 407, Cpk > 1.50 • Customer 2, Cpk > 1.33 • With new clients, determine if tolerances are reasonable, if our processes are capable and robust, and if improvements are needed.

  5. Process Capability StudiesStep 1 – Gauge Capability Six Measures • Gauge Accuracy • Are the readings correct? • Gauge Linearity • Are the readings correct over the measurement range of the instrument? • Gauge Stability • Does the gauge return similar values over time?

  6. Process Capability StudiesStep 1 – Gauge Capability Six Measures • Gauge Repeatability • Does one operator return a similar result time after time (gauge variability)? • Gauge Reproducibility • Do different operators return similar results? • Gauge Repeatability and Reproducibility • Total variability of a test result (operator & gauge).

  7. Process Capability StudiesStep 2 – Process Characteristics Analyze Process Data • Normality – Evidenced by the descriptive statistics skewness and kurtosis. • Stability – The absence of shifts or trends over time. • Control – Control chart analysis passing tests for special causes.

  8. Process Capability StudiesTests for Normality

  9. Process Capability StudiesTests for Stability and Control

  10. Process Capability StudiesComparing Distributions to Specifications

  11. Process Capability StudiesReal World Example – Part 504

  12. Process Capability StudiesPart 504 Continued

  13. Process Capability StudiesPart 504 Continued

  14. Process Capability StudiesPart 613 - An Exercise

  15. Process Capability StudiesPart 613 – An Exercise

  16. Process Capability StudiesPart 613 – An Exercise

  17. Process Capability StudiesPart 613 – An Exercise And the answer is:

  18. Process Capability StudiesSummation Three Steps: • Gauge Capability • Process Characteristics • Process Capability Analysis

  19. Process Capability StudiesBibliography • Introduction to Statistical Analysis – sixth ed – Dixon and Massey • Introductory Statistics – Weiss and Hassett, 1982 • AT&T Statistical Quality Control Handbook – 11th Printing – 1985 • Experimental Statistics – Mary G. Natrella – 1966 (NBS Handbook 91) • General Motors Statistical Quality Control Handbook – 1982 • LTV Steel Integrated Process Control Handbook – Norman Bresky and Joan Harley – 1986 • North American Refractories Co. SPC Handbook – 1988 • 1994 Annual ASTM Book of Standards- ASTM E 691 - 92