Process Capability Index Cpk.pptVIP

Process Capability Index Cpk Outline SPC and Process Capability Index SPC Concept Index Formula and Meaning Judgment Criteria Relation with Defect Rate Process Capability Confidence Limit Ppk and Cpk Sep 07, 2004 Application of Statistics Sep 07, 2004 Application of Statistics 3 Special Causes Present Out Of Control (RD Pilot Run) In Control But not Capable Of Meeting Specifications Variation from Common Causes is Excessive (Pilot Run / Initial MP) In Control and Capable Of Meeting Specifications Variation From Common Cause Have Been Reduced (Mass Production) Process Variance and SPC Chart Sep 07, 2004 Application of Statistics 4 You can Predict the Outcome only if the Process is Stable Time PREDICTABLE ? UNPREDECTIBLE Concept 1 Time Sep 07, 2004 Application of Statistics 5 Accuracy Precision Low Accuracy Low Precision High Accuracy High Precision Low Accuracy High Precision High Accuracy Low Precision Sep 07, 2004 Application of Statistics 6 Capability of Accuracy : Process Average m : Specification Target USL : Upper Specification Limit LSL : Lower Specification Limit X m USL LSL Sep 07, 2004 Application of Statistics 7 Capability of Accuracy “Ca” Value Assess the Process Bias (Shift) The Larger of Ca Value, The More Serious of Process Shift Ca 0 The Process Shift to Upper Control (Specification) Limit Ca = 0 The Process Meet the Specification Goal Ca 0 The Process Shift to Lower Control (Specification) Limit Sep 07, 2004 Application of Statistics 8 |Ca| = 0 0 |Ca| 1 |Ca| 1 Spec USL LSL Capability of Accuracy Process Sep 07, 2004 Application of Statistics 9 How To Improve Ca Value Improvement Suggestion: Adjust the Process Parameter and Shift Back the Shift Method: DOE, Regression, ANOVA … 2. Engineering Change the Specification Target ( Notice Assembly Issue) Engineering Change the Specification Tolerance ( Notice Assembly Issue) Sep 07, 2004 Application of Statistics 10 Capability of Pre