SPC基本认识培训教材英文(ppt 12页)

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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