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現在,我們將從第一張表格中得到的具有兩面規格的CP的最小需求量設置為1.33,假設測試的問題就將變為:H0: Cp= 1.33 H1: Cp≥ 1.33
Now we want to be sure, at the 95% confidence level, that the process capability is bigger or lower than 1.33 before we accept or reject it. And we set the high value as 2, which is actually 6-sigma quality level. Namely, Cp(high)=2, Cp(low)=1.33 , α =β=1-0.95=0.05.
目前,在信度為95%的水平下,我們通過加工能力值的高1.33或低1.33來確定是接受還是否定。同時,我們把高的值設定為2,其實際的質量水平為6-Σ,即為Cp(high)=2, Cp(low)=1.33 , α =β=1-0.95=0.05. Cp(high)/Cp(low)=2/1.33=1.504
Then check the table, the corresponding sample size is about n=32. And 接下來核對該表,對應的樣品大小為n=32 C/Cp(low)= 1.2 So, C= 1.2*Cp(low)=1.2*1.33=1.6 Thus, to demonstrate the capability, the supplier must take a sample of n=32,and the sample process capability ratio must exceed C=1.6. This is obtained using minimum process capability requirement in the industry. The higher the requirements, the smaller the Cp(high)/Cp(low) value will be. From the second table we know that the required sample sizes are increasing. It‘s fairly common practice to accept the process as capable at the level Cp≥ 1.33 based on a sample of size 30≤n≤50 parts. Clearly, this procedure does not account for sampling variation in the estimate of sigma,and larger values of sample size may be necessary in practice.
因此, 就示范能力而言,供應者定會提供一個 n=32 的樣品,而且樣品加工能力比一定超過 C=1.6.這被視為獲得到使用工業的最小程序能力需求。需求愈高,Cp(高度)/Cp(低點)的比值愈小。從第二張表格中我們知道必需的樣品尺寸正在逐漸增加。公平而常見的做法是接受程序能力在以一個大小 30 ≤ n ≤ 50個部份的樣品為基礎的 Cp ≥ 1.33 的水平上。清楚地,這個程序不涉及到在Σ的估算中考慮樣本的不同,同時,樣本尺寸的值不斷變大在實踐中是很必要的。
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