SPC基本认识培训教材英文(ppt 12页)
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点击下载Ppk 与 Cpk 之差异
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 意义说明
评估产品制程平均与规格中心之偏移量
制程偏移越大, Ca值越大
Ca 值
> 0 时, 代表制程平均偏上限
= 0 时, 代表制程平均与规格中心一致
< 0 时, 代表制程平均偏下限
改善方向
(1)调整模具, 制程参数, 材料等以达到规格中心值
(2)与客户讨论变更规格中心值, 但需考虑组装性问题
(3)与客户讨论变更规格公差, 但需考虑组装性问题
-允差设计, 决定最适之规格公差
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