製程能力弱度指標的管制圖

Abstract

統計圖表是生產監控及改善品質的良好管制工具，它具有簡單易懂且比文字公式更易傳達訊息的優點。Signhal （1990）提出一個新的管制圖表叫MPPAC（Multiprocess Performance Aralysis Chart）。MPPAC是一個以製程能力指標為基礎，同時提供製程能力指標有Cp、Cpk、Cpm、以及Cpmk。這些指標都是良度指標，亦即指標值愈高則製程平均偏移程度、製程變異程度及不良率資訊的整合管制圖。常用的製程能力愈強，反這則愈弱。Greenwich and Jahr-Schaffrath（1995）提出一個製程能力弱度指標Cpp，它是由Cpm轉換得來。Cpp指標可以將造成製程間差異的原因分為平均偏離目標值與製程變異，並分開解釋避免混淆。本篇文章以指標Cpp為基礎，利用MPPAC整合多重製程及易於說明的概念，發展一個Cpp的MPPAC管制圖，並應用這個管制圖在製造電阻零件的多重製程上，實際評估其程的績效。

Statistical process control charts are efficient tools to monitor manufacturing process and quality improvement of the process. These charts are easy to understand as they display essential information conveniently to the engineers. Singhal (1990) introduced a graphicl chart MPPAC (Multiprocess Performance Analysis Chart) based o the process capability indices, which shows the departure of process mean from the target value, process varabilityand the expected fallout outside specification limits on a signal chart. Many capability indices including Cp, Cpk, Cpm, Cpmk, have been used to measure the capability of th process. The greater the indices are, the more capable the processes would be. Greenwich and Jahr-Schaffrath (1995) mnoduced a new index Cpp, a simple transformation of the Cpp index. The index Cpp provides uncontaminated separation between information concerning the process accuracy and process precision. In this paper, we establish an MPPAC which integrates a group of processes base on Cpp. Then, we apply this chart to the case of multiprocess manufacturig resistor components, to evaluate the performance of these processes actually.