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Unformatted text preview: Lecture 8 Statistical Models of Manufacturing Variation Process Capability Define a Process Capability Index USL = Upper specification limit LSL = Lower specification limit Standard deviation of process Design Margin USL LSL Process Variation 6 σ σ = = = μ LSL3 σ USL 3 σ P P Define a process capability index: design margin C natural variation of process USL LSL C 6 σ = = ( 29 P For USL LSL 6 C 1 σ = = P When C 1 , the process is said to be "capable", i.e., capable of meeting the desired specifications. ≥ Process Is Not Capable Of Producing Parts Which Meet The Specifications μ LSL3 σ USL 3 σ P When C 1 , the process is said to be "incapable", i.e., incapable of meeting the desired specifications. < Process Is Capable Of Producing Parts Which Meet The Specifications LSL3 σ USL 3 σ P When C 1 , the process is said to be "capable", i.e., capable of meeting the desired specifications. ≥ A B P Distance A Design Margin C Distance B Process Variation = = NonSymmetrical Tolerance Limits P( ) y y LSL USL m μ A B C D Introduce Process Capability Terms P( ) y y LSL USL m μ A B C D ( 29 USL upper specification limit LSL lower specification limit average specification limit 0.5 USL LSL mean of population distribution Allowable process spread USL LSL Distance A Upper side spread from m μ = = = = + = = = mean USL Distance B Lower side spread from mean LSL Distance C Skew of distribution from mean Distance D m μ μ μ = = = = = = Introduce Process Capability Terms P( ) y y LSL USL m μ A B C D ( 29 USL upper specification limit LSL lower specification limit average specification limit 0.5 USL LSL mean of population distribution Allowable process spread USL LSL Distance A Upper side spread from m μ = = = = + = = = mean USL Distance B Lower side spread from mean LSL Distance C Skew of distribution from mean Distance D m μ μ μ = = = = = = Introduce Process Capability Terms P( ) y y LSL USL m μ A B C D ( 29 USL upper specification limit LSL lower specification limit average specification limit 0.5 USL LSL mean of population distribution Allowable process spread USL LSL Distance A Upper side spread from m μ = = = = + = = = mean USL Distance B Lower side spread from mean LSL Distance C Skew of distribution from mean Distance D m μ μ μ = = = = = = Introduce Process Capability Terms P( ) y y LSL USL m μ A B C D ( 29 USL upper specification limit LSL lower specification limit average specification limit 0.5 USL LSL mean of population distribution Allowable process spread USL LSL Distance A Upper side spread from m μ = = = = + = = = mean USL Distance B Lower side spread from mean LSL Distance C Skew of distribution from mean Distance D m μ μ μ = = = = = = Introduce Process Capability Terms P( ) y y LSL USL m μ A B C D ( 29 USL upper specification limit LSL lower specification limit average specification limit 0.5 USL LSL mean of population distribution Allowable process spread USL LSL Distance A Upper side spread from...
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 Spring '09
 FRAZIER
 Standard Deviation, Probability theory, Process capability, USL, Process capability index

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