L9_ECE4001_Fall_2008

L9_ECE4001_Fall_2008 - Define a Process Capability Index...

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Slide #1 ECE 4001 L9 © 2008 Lecture 9 Statistical Models of Manufacturing Variation Process Capability Slide #2 ECE 4001 L9 © 2008 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 LSL -3 σ USL 3 σ P P Define a process capability index: design margin C natural variation of process USL LSL C 6 σ = - = ( ) 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. Slide #3 ECE 4001 L9 © 2008 Process Is Not Capable Of Producing Parts Which Meet The Specifications μ LSL -3 σ USL 3 σ P When C 1 , the process is said to be "incapable", i.e., incapable of meeting the desired specifications. < Slide #4 ECE 4001 L9 © 2008 Process Is Capable Of Producing Parts Which Meet The Specifications LSL -3 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 = =

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Slide #9 ECE 4001 L9 © 2008 Introduce Process Capability Terms P( ) y y LSL USL m μ A B C D ( ) 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 = - = = - = = - = Slide #10 ECE 4001 L9 © 2008 Introduce Process Capability Terms P( ) y y LSL USL m μ A B C D ( ) 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

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