nokia制程能力控制(英文)-經(jīng)營(yíng)管理-文庫(kù)吧資料
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【正文】 cess variability ? The Cpk Index accounts for process variability and centering of the process mean to the design nominal ? Therefore, Cp ? Cpk ? NOTE: Same applies also for Pp and Ppk Cp = Cpk (both low) LSL USL Mean = Nominal Reject parts Reject parts Cp high, Cpk low Process should be optimized! Nominal LSL Mean USL Reject parts 32 169。 NOKIA 2020 Defining Cp and Pp Sample mean Process variation 6*s stp sL S LU S LC*6? USLLSL LSL USL Nominal dim ltp sL SLU SLP*6?The tolerance area divided by the total process variation, irrespective of process centring. 30 169。 NOKIA 2020 Exercise 1: Sample Distributions 1. In Excel file Data exercise you find 100 measurements being the result of a capability study. The specification for the dimension is 15,16?,01 2. How well does the sample population fit the specification, . should we expect any parts outside spec? 3. Mention possible consequences of having a part outside spec . 4. Mention possible causes of variation for parts. 5. Calculate the sample mean and sample standard deviation for the 100 measurements. Use the average and stdev functions Excel. 28 169。 NOKIA 2020 The difference between the standard deviations sLT and sST gives an indication of how much better one can do when using appropriate production control, like Statistical Process Control (SPC). s x x x x x xNLTN? ? ? ? ? ? ??( ) ( ) . . . ( )1 2 2 2 21s R N d R dST jjN????? ???? ???12 2* *Shortterm standard deviation : Longterm standard deviation : The difference between sST and sLT 26 169。 NOKIA 2020 ? ? ? ? ? ? ? x3 ? x2 ? x1 ? x10 x _ t 1)(...)()( 222212?????????Nxxxxxxss NLTLT15)()()()()( 22222?????????????LTsExample: What Measurements Can Be Used to Describe Process variation? 24 169。 NOKIA 2020 d2* values for SST Where: N = no. of subgroups, n = no. of samples in each subgroup d2* d2 Typical: N=20 amp。 NOKIA 2020 ),...,m i n (),...,m a x ( 2121 NN xxxxxxR ??Example: x1 = 5 x2 = 7 x3 = 4 x4 = 2 x5 = 6 527)6,2,4,7,5m i n ()6,2,4,7,5m a x ( ?????R? The most simple measure of variability is the range. The range of a sample is defined by as the difference between the largest and the smallest observation from samples in a subgroup, . 5 consecutive parts from the manufacturing process. What Measurements Can Be Used to Describe Process variation? 21 169。 (m252。 NOKIA 2020 The Normal Distribution 19 169。s) to the process are randomly influenced. 17 169。 NOKIA 2020 Section 2. Population, Sample and Normal Distribution 16 169。 NOKIA 2020 Why Make Process Capability Studies LSL (lower specification limit) 10,7 USL (upper specification limit) 10,9 Nominal 10,8?0,1 This part is within spec. The tool would be approved if only this part was measured These parts are out of spec and could be approved if only one good part was measured A process capability study would reveal that the tool should not be accepted When a dimension needs to be kept properly within spec, we must study the process capability …. but still this is no guarantee for the actual performance of the process as it is only an initial capability study 14 169。 NOKIA 2020 Example of Capability Analysis Data ? For some critical dimensions we need to measure more than 1 part ? For capability data we usually measure 5 pcs 2 times/hour=100 pcs (but sampling plan needs to be made on the basis of production quantity, run duration and cycle time) 1 s t Su b g r o u p 2 n d Su b g r o u p 3 r d Su b g r o u p 4 th Su b g r o u p1 1 8 . 5 3 1 1 8 . 5 2 1 1 8 . 5 4 1 1 8 . 5 61 1 8 . 5 4 1 1 8 . 5 4 1 1 8 . 5 2 1 1 8 . 5 51 1 8 . 5 1 1 1 8 . 5 1 1 1 8 . 5 0 1 1 8 . 5 51 1 8 . 5 3 1 1 8 . 5 1 1 1 8 . 5 2 1 1 8 . 5 51 1 8 . 5 1 1 1 8 . 5 4 1 1 8 . 5 4 1 1 8 . 5 55 th Su b g r o u p 6 th Su b g r o u p 7 th Su b g r o u p 8 th
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