Process Capability Studies

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Process Capability Studies

• Comparison of Process Output to Product
  Requirements

Lynn Taylor OISM 470W Section 002
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Process Capability Studies3 Steps

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

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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.

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Process Capability StudiesUses In Our Plant

• Customer 1 lt 407, Cpk gt 1.25
• Customer 1 gt 407, Cpk gt 1.50
• Customer 2, Cpk gt 1.33
• With new clients, determine if tolerances are
  reasonable, if our processes are capable and
  robust, and if improvements are needed.

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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?

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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).

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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.

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Process Capability StudiesTests for Normality
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Process Capability StudiesTests for Stability
and Control
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Process Capability StudiesComparing
Distributions to Specifications
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Process Capability StudiesReal World Example
Part 504
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Process Capability StudiesPart 504 Continued
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Process Capability StudiesPart 504 Continued
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Process Capability StudiesPart 613 - An Exercise
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Process Capability StudiesPart 613 An Exercise
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Process Capability StudiesPart 613 An Exercise
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Process Capability StudiesPart 613 An Exercise
And the answer is
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Process Capability StudiesSummation

• Three Steps
• Gauge Capability
• Process Characteristics
• Process Capability Analysis

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Process Capability StudiesBibliography

• Introduction to Statistical Analysis sixth ed
  Dixon and Massey
• Introductory Statistics Weiss and Hassett, 1982
• ATT 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