SPC基本認識培訓教材英文(ppt 12頁)

Ppk 與 Cpk 之差異
Ppk
The 6 range of a process’s total variation, where is usually estimated by the sample
standard deviation
--This is the variation due to both common and special cause.
Cpk
The 6 range of a process’s inherent variation, for statistically stable processes only, where is usually
estimated by
--That portion of process variation due to common causes only.
Ca 意義說明
評估產品製程平均與規格中心之偏移量
製程偏移越大, Ca值越大
Ca 值
> 0 時, 代表製程平均偏上限
= 0 時, 代表製程平均與規格中心一致
< 0 時, 代表製程平均偏下限
改善方向
(1)調整模具, 製程參數, 材料等以達到規格中心值
(2)與客戶討論變更規格中心值, 但需考慮組裝性問題
(3)與客戶討論變更規格公差, 但需考慮組裝性問題
-允差設計, 決定最適之規格公差

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