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Quality Control

Quality Control. COB 300 C - The Operations Dimension Busing. Causes of Variation. Random Causes difficult or expensive to control e.g., outside humidity, line voltage Assignable Causes easier to correct e.g., employee error, new materials. Comparing Process Variation to Tolerance Limits.

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Quality Control

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  1. Quality Control COB 300 C - The Operations Dimension Busing

  2. Causes of Variation • Random Causes • difficult or expensive to control • e.g., outside humidity, line voltage • Assignable Causes • easier to correct • e.g., employee error, new materials

  3. Comparing Process Variation to Tolerance Limits

  4. High Process Capability After Technological Process Change

  5. Control Charts • Variables - concentrates on mean for some measurable characteristic. • diameter • length • Attribute - data is based on counts or the number of times we observe a particular event. • proportion defective/non-defective • go/no go • proportion pass/fail

  6. Control Limits - Variables Charts X-Bar Chart R Chart

  7. Factors for Control Limits(Slide 1 of 2) Sample of Size n A D D 2 3 4 2 3 4 5 6 7 8 9 10 1.880 1.023 0.729 0.577 0.483 0.419 0.373 0.337 0.308 0 0 0 0 0 0.076 0.136 0.184 0.223 3.268 2.574 2.282 2.114 2.004 1.924 1.864 1.816 1.777

  8. x-bar Chart Example (cont’d)

  9. Range Chart

  10. Warning Conditions • Two successive points near limit • Run of five above or below mean • Trend • Erratic behavior

  11. Process Control for Attributes Proportion defective: Number of defects per unit:

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