LECTURE 7

LECTURE 7 - ENGR 4045U Quality Control Lecture 7 1 Schedule...

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ENGR 4045U Quality Control Lecture 7 1
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Schedule Week 3 Part III: Basic Methods of Statistical Process Control and Capability Analysis. Chapter 5: Methods and Philosophy of Statistical Process Control. Chapter 6: Control Charts for Variables. Week 4 Chapter 7: Control Charts for Attributes. Chapter 8: Process and Measurement System Capability Analysis. Week 5 Midterm-1 2
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Process Capability (a) PCR C(p)is greater than unity, this means that the process uses up much less than 100% of the tolerance band, this means that very few non- conforming units will be produced by this process (b) C(p) = 1, which imply about 0.27% (or 2700 ppm) nonconforming units (c) C(p)<1, which means that the process uses up more than 100% of the tolerance band, a large number of nonconforming units will be produced 3
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Continuation of X-bar and R Charts If additional samples of wafers are taken, x- bar and R charts are continued Process instability is shown in figure 6.4 (table 6.2) 4
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Definitions There is no connection or relationship between the control limits on the x-bar and R charts and the specification limits on the process Specification limits are determined externally, by management Control limits are defined by the natural variability of the process, natural tolerance limits UNTL, LNTL, as 3 (around process mean) 5
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Changing Sample Size Engineer might change sample size after process stability Recalculate R and d2, UCL, LCL 6 old old new old old old new old R old d new d D LCL R old d new d R CL R old d new d D UCL R old d new d A x LCL R old d new d A x UCL size sample new for range average R size sample old for range average R ) ( ) ( , 0 max ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( 2 2 3 2 2 2 2 4 2 2 2 2 2 2
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Example For the hard-bake process, if sample size is changed from 5 to 3, define the new control charts (p241) 7 2634 . 1 2422 . 0 5056 . 1 ) 32521 . 0 ( 326 . 2 693 . 1 ) 023 . 1 ( 5056 . 1 ) ( ) ( 7478 . 1 2422 . 0 5056 . 1 ) 32521 . 0 ( 326 . 2 693 . 1 ) 023 . 1 ( 5056 . 1 ) ( ) ( 2 2 2 2 2 2 old old R old d new d A x LCL R old d new d A x UCL
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Example For the R chart changes 8 0 ) ( ) ( , 0 max 2367 . 0 ) 32521 . 0 ( 326 . 2 693 . 1 ) ( ) ( 6093 . 0 ) 32521 . 0 ( 326 . 2 693 . 1 ) 574 . 2 ( ) ( ) ( 2 2 3 2 2 2 2 4 old old new old R old d new d D LCL R old d new d R CL R old d new d D UCL
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Probability Limits Express control limits on the x-bar and R charts as a multiple of standard deviation On x-bar chart, obtain type I error of α by choosing the multiple of sigma for the control limit as k = Z( α /2) Three sigma control limits imply that the type I error probability is α = 0.0027 For α = 0.002, Z( α /2)=Z(0.001)=3.09 9
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If α = 0.002, 10 R D LCL R D UCL d n W D d n W D d R 001 . 0 999
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This note was uploaded on 10/18/2010 for the course ENGR 3360 taught by Professor Ahmadbarari during the Fall '10 term at UOIT.

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LECTURE 7 - ENGR 4045U Quality Control Lecture 7 1 Schedule...

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