單邊規格多品質特性製程能力量測

Abstract

製程能力指標經常被用來衡量製程製造產品符合規格能力，不僅提供品質保證的工具，也是提供品質改善方面的一個方針。Cp, Cpk, Cpm 和 Cpmk這4種指標量測產品具有上下規格界限的製程，然而對於只有單邊規格產品的製程，可用 (產品只有上規格界限)、 (產品只有下規格界限)來衡量其製程能力，但這些指標僅適用於只有單一產品品質特性的時候，針對多品質特性的製程，我們考慮2005年由Pearn和Wu學者提出的指標 並加以導出針對多品質特性製程的近似常態分配 ，包含其自然估計量、抽樣分配、信賴下界。統計假設檢定過程提供製程的表現是否滿足預設的製程基準，最後舉出一個實務例子說明。

Process capability indices (PCIs) have been proposed in the manufacturing industry to provide numerical measures on process capability, which are effective tools for quality assurance and guidance for process improvement. These four indices (Cp, Cpk, Cpm and Cpmk) measure for processes with two-sided specifications. However, the product quality characteristics are with one-sided specification and PCIs , are adopted. But these indices only investigate the process with single characteristic. We consider the index proposal by Wu and Pearn (2005) and an asymptotic normal distribution of is derived from for processes with multiple independent characteristics. The natural estimator, the sample distribution and the lower confidence bound of are obtained. A statistical hypothesis testing procedure is provided for testing whether the performance of a process satisfies the preset capability benchmark. An application example is presented.