Q&A: Cpk and SPC Standards (Part 3)
SPC
? Knowledge Sharing
?
We have covered the general concepts of for? Cpk. let’s explore what we expect about Cpk and how to improve Cpk? performance. If you’d like to review the previous sharing sessions, please click? the following links.
我們已經(jīng)了解了Cpk的基礎(chǔ)概念。本次我們來探討一下對(duì)Cpk的期望以及如何提高Cpk的性能。單擊下方鏈接回顧之前的分享丈甸。
?
Q: How do we measure how well a process? is running within the spec limits?
A:?If Cpk is 1.33 or higher, it is commonly? considered that the process is capable.??It is useful to show the real performance? by graphing a trend chart (SPC chart) of process variation against? specification limits.
問：如何衡量制程在規(guī)格限制中的表現(xiàn)？
答：如果Cpk為1.33或更高饶唤，則通常認(rèn)為該制程是有能力的。繪制表現(xiàn)制程變化的趨勢(shì)圖（SPC圖）可以直觀展示制程的實(shí)際性能贯钩。
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Q: Why 1.33 of Cpk?
A: 1.33 of Cpk satisfies the SPC? standards of “Key” charts. Based on the formula, we know when Cpk is 1.33, the? distance between spec limits and process mean is at least 4 sigma. At this? time, the specification width is wider enough than the process spread.? Besides, DPPM is only 63.3.
問：為什么Cpk需要達(dá)到1.33募狂？
根據(jù)公式，Cpk為1.33時(shí)魏保，規(guī)格限制和制程均值之間的距離至少是4倍標(biāo)準(zhǔn)差熬尺。此時(shí)摸屠，相比制程分布谓罗，規(guī)格限制足夠?qū)挘褼PPM僅為63.3季二。
Cpk# of SigmaDPPM (Defects parts per Million)
0.331317,311
0.67245,500
1.0032,700
1.33463.3
1.504.53.4
1.6750.57
2.0060.002
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Q: Wait, what are “Key” charts? Are they? important?
A: Of course, they are important.? However, “Key” in “Key charts” does not mean “important”. Instead, it is one? of the 4 chart classifications of importance level at DMTM.
Any SPC
? chart at DMTM is classified as one of the? following classifications, ranking from the most to the least important? level.
[if !supportLists]1.???????
? [endif]Program? Control
[if !supportLists]2.????
? [endif]Key
[if !supportLists]3.????
? [endif]Control
[if !supportLists]4.????
? [endif]Engineering
問：等等檩咱，什么是 “Key? 圖表”？它們很重要嗎胯舷？
答：當(dāng)然刻蚯，它們很重要。然而桑嘶，“Key圖表”中的 “Key” 并不代表 “重要”炊汹。實(shí)際上，它是DMTM圖表的4個(gè)重要性級(jí)別之一逃顶。
DMTM的任何SPC圖表都被歸類為下列其中一個(gè)級(jí)別讨便，重要性從高到低排序。
[if !supportLists]1.???????
? [endif]Program? Control
[if !supportLists]2.????
? [endif]Key
[if !supportLists]3.????
? [endif]Control
[if !supportLists]4.????
? [endif]Engineering
Q: What are SPC standards to evaluate? Cpk? Can you specify them?
A: Yes.?For Cpk, we only monitor the two most? important classifications, Program Control and Key charts. They have a direct? relation to one or more output parameters (i.e. yield, quality, reliability,? or performance). Here are the specific SPC rules.
We monitor Cpk based on the latest 28-day? data:
[if !supportLists]·????????
? [endif]For Program? Control charts, the process is manufacturable if Cpk >= 1.67 (5 sigma)
[if !supportLists]·????????
? [endif]For Key? charts, the process is manufacturable if Cpk >= 1.33 (4 sigma)
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? [endif]For Control? and Engineering charts, we do not monitor Cpk
問：評(píng)估Cpk的SPC標(biāo)準(zhǔn)是什么以政？能具體說明嗎霸褒？
答：對(duì)于Cpk，我們只監(jiān)測(cè)兩類最重要的圖表盈蛮，Program
? Control 和? Key废菱。它們與一個(gè)或多個(gè)輸出參數(shù)（即產(chǎn)量、質(zhì)量、可靠性或性能）有直接關(guān)系殊轴。以下是具體的SPC規(guī)則衰倦。
我們根據(jù)最新28天的數(shù)據(jù)來監(jiān)測(cè)Cpk。
[if !supportLists]·????????
? [endif]對(duì)于 Program
? Control 圖表梳凛，如果Cpk >=1.67（5倍標(biāo)準(zhǔn)差)耿币，則該制程是可制造的。
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? [endif]對(duì)于 Key 圖表韧拒，如果Cpk >= 1.33（4倍標(biāo)準(zhǔn)差）淹接，則該制程是可制造的。
[if !supportLists]·????????
? [endif]對(duì)于 Control 和Engineering圖表叛溢，我們不對(duì)Cpk進(jìn)行監(jiān)控塑悼。
Q: How can we improve the Cpk performance?
A: Technically, Cpk can be improved by
[if !supportLists]1.???????
? [endif]Optimize? process
[if !supportLists]a.?????
? [endif]Centering the? process on target
[if !supportLists]b.????
? [endif]Reducing the? variation in the site-level process
[if !supportLists]2.????
? [endif]Optimize spec? limits
問：我們?nèi)绾翁岣逤pk的性能？
答：從技術(shù)上講楷掉，Cpk可以通過以下方式改進(jìn)
[if !supportLists]1.???????
? [endif]優(yōu)化工藝
[if !supportLists]a.?????
? [endif]將制程以目標(biāo)為中心進(jìn)行
[if !supportLists]b.????
? [endif]減少量測(cè)點(diǎn)級(jí)別制程的變化
[if !supportLists]2.????
? [endif]優(yōu)化規(guī)格限制
References
[if !supportLists]·????????
? [endif]WBT:? INTRODUCTION TO SPC
[if !supportLists]o??
? [endif]Saba ID:
? 00015598
[if !supportLists]·????????
? [endif]ILT: SPC? Concept_Statistics Process Control
[if !supportLists]o?? [endif]Saba ID: 20016444
Question: Data being used in the initial set-up? of a process are assumed to have a normal distribution. If the nominal? (target) is set at the center of the distribution, and the specification? limits are set at ±3s from the center, then the Cpk is equal to:
(A) –0.25
(B) 1.00
(C) 1.33
(D) 1.67
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