GD450 说明书(中英文版） - 第95页

- 95 - Cp: Capability of process. It applies to s tatistical stable process . It is the actual processing ability of process in a con trolled state, regardless of the deviation of the process. It is 6σ range of process n…

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图 6-10（检测界面）Pix 6-10(inspection interface)

6.2 SPC 系统简介及使用说明 SPC system introduction and operation

6.2.1 名词解释 Noun explanation

用 PPPK 衡量过程能力，要求 PPK>=1.67 才能进入量产阶段，所以又把 PPK 称为初期能

力指数。PPK 通过 PPU 或 PPL 的最小值来计算，计算公式 PPU=(USL-X-bar)/3s 和

PPL=(X-bar-LSL)/3s

Measure process capability by PPPK. When the PPK>=1.67, it can enter into mass

production stage. So PPK is called initial capability indices. PPk is calculated by the

minimum value of PPU or PPL. Calculation formula: PPU=(USL-X-bar)/3s and

PPL=(X-bar-LSL)/3s.

很多公司由于对过程能力的一知半解，往往只要求计算 CPK 的指数来衡量过程能力是否

足够，事实上进入正常生产后应该通过 Cp\CPK\PPK 三个指数之间的差别来判断过程是否有

问题，如果有问题是管理上还是技术上有问题，Cp>1.33 表明过程变差比较小，此时还要看

CPK,当 Cp 和 CPK 相差很大时表明过程有较大的偏移,需要做居中处理，再比较 CPK 和 PPK，

如果两者相差不大表明受特殊因素的影响小，如果两者相差很大表明受特殊因素影响大。工

序在稳定状态下的实际加工能力，即在操作者、机器设备、原材料、操作方法、测量方法和

环境等标准条件下，工序呈稳定状态时所具有的加工精度,这时我们一般会通过 CP、CPK、PP

以及 PPK 等参数作为一个评断标准.

Many companies often only require calculating CPK to measure whether the process

capability is enough because that they know a little knowledge of process capability.

Actually, after entering into normal production, whether the process has problems should be

judged by the difference between the three indices Cp\CPK\PPK. If it has problems, where

are the problems, the management or technology? When the Cp>1.33, it indicates

process variation is small. At this time it also should see CPK. When there is big difference

between CP and CPK, it indicates the process had large offset. It needs to do center

processing, and then compare CPK with PPK. If they have little difference, it indicates that it

is less affected by special factors. If they have big difference, it indicates it is affected by

special factors a lot. The process of actual processing capacity at steady state is affected i

special factors. Namely the operator, machinery equipment , raw materials, operating

method, measure method and environment and so on .The process shows the processing

precision when the stable state . At this time we usually do a judge standard by parameters

such as CP, CPK, PP, and PPK etc.

Cp：过程能力，仅适用于统计稳定过程，是过程在受控状态下的实际加工能力，不考虑过程

的偏移，是过程固有变差（仅由于普通原因产生的变差）的 6σ范围，式中σ通常用 R-bar/d2

或者 s-bar/c4 来估计。所以过程能力是用过程在受控状态下短期数据计算的。因此又将过程

能力称为“短期过程能力”，实际中常将短期省略。这个指数只是针对双边公差而计算的，对

于单边公差没有意义。计算公式为:CP=(USL-LSL)/ 6σ.

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Cp: Capability of process. It applies to statistical stable process. It is the actual processing

ability of process in a controlled state, regardless of the deviation of the process. It is 6σ

range of process natural variation (due to the common cause variation). In the formula, the

σ usually is estimated by R-bar/d2 or s-bar/c4 .So process capacity is calculated with

short-term data when the process in controlled condition. Therefore the process capacity

usually is called “short-term process capability”. In fact, short-term often be omitted. The

index is calculated only for bilateral tolerance. For unilateral tolerance, it does not make

sense. Calculation formula: CP=(USL-LSL)/ 6σ .

CPK：过程能力指数，是在过程有偏移情况下的过程能力，前提是要过程稳定且数据是正态分

布，而且数据应该在 25 组以上（建议最少不要低于 20 组，数据组越少风险越大），只考虑

过程受普通原因的影响。因为过程只受到普通原因变差影响是理想状态下的，从长期来说过

程总会受到各种特殊原因的影响，所以又被称为短期过程能力，也叫潜在过程能力。CPK 通

过 CPU 或 CPL 的最小值来计算，计算公式:CPU=(USL-X-bar)/3σ 和 CPL=(X-bar-LSL)/3σ.

CPK: Capability Index of Process, it is the process capability when the process has

deviation. Preconditions are that the process is stable, data is normal distribution and the

data should be above 25 groups (suggestion: at least no less than 20 groups, the less data

groups, the greater the risk), only consider the effect of process by common reason. It is the

ideal situation when the process is just affected by common reasons deviation. In the long

term, process is always affected by all kinds of special reasons. So it is also known as

short-term process capability, also called potential process capability. CPK is calculated by

the minimum of CPU or CPL. Calculation formula: CPU=(USL-X-bar)/3σ and

CPL=(X-bar-LSL)/3σ .

Pp：过程性能，是过程长期运行的实际加工能力，过程总变差（由子组内和子组间二种变差

所引起的变化，如果过程处于不受控状态，过程总变差将包括特殊原因和普通原因）的 6σ

范围，式中 σ通常用则称 x 服从均数为μ，标准差为σ2 的正态分布。样本的标准差 s 来估

计。此时不考虑过程是否受控。因此过程性能也称长期过程能力，也叫性能指数。计算公式

Pp=(USL-LSL)/6s

Pp: Performance of Process, It is actual processing capacity of process in long-term

running. It is 6σ range of process total variation (changed by two variation subgroups

within and between subgroups, if the process is in uncontrolled condition, actual processing

capacity includes special reason and common reason), In the formula, σ is usually called

X obey mean μ, the standard deviation is σ2 normal distribution .The sample standard

deviation uses s to estimate. Whether the process is controlled at this time is regardless. So

process performance is also called the long-term process capability, also is known as

performance index .Calculation formula: PP=(USL-LSL)/6s .

PPK：过程性能指数，因为计算不需要过程稳定（因为在计算公式中已经考虑了普通和特殊两

种原因的影响），所以在 PPAP 手册中要求在产品进行试生产过程不稳定时（此时过程受两种

原因影响），特殊因素的影响往往比较容易找到。如果 Cp 值本身就很小那说明过程受普通因

素的变差影响大，此时若想提升过程能力往往需要更多的投入和更高的决策才能使问题得到

解决。所以即使有时候 CPK 值很高( 比如大于 2) ,如果其与 Cp\PPK 相差较大的话还是需要

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对过程进行改进。

PPK: Performance index of process. The calculation does not need process stability.

Because calculation formula has considered the influence from common reason and

special reason. So PPAP manual had been required during the trial production process is

not stable (this process is affected by two reasons). The special factor is easier to be found.

If the CP value itself is small and then it means that common factor variation has big

influence on the process. At this time it often needs more investment and higher decision to

make the problem solved to improve process capability. So even if sometimes CPU value is

very high (such as above 2) and it has larger difference with CP and PPK ,it still need to

improve the process.

6.2.2 软件操作步骤 Software operation steps

1、将 U 盘中的“CPKDataRT.exe”文件拷贝到“F”盘根目录下。如图 6-2-1

Copy “CPKDataRT.exe” in USB flash card to the root of the disk “F”. See pix 6-2-1.

图 6-2-1