关键词: 工序流, 工序波动轨迹图, 过程能力指数, 多工序能力, 合格率

Abstract: Process capability index has been widely used to measure the quality level of product in modern manufacturing industry. And most of the process capability indices are only suitable to measure single quality attribute at single stage. However, there are often multiple quality attributes for multiple machining processes. As for this issue, a multiple process capability evaluation method was proposed based on process variation trajectory chart (PVTC). In here, the amplitude of process mean deviating from its target and degree of process stability were used to construct process performance plane (PPP), and the PVTC of different quality attributes at different stages were plotted with time. And then, the mathematical relationships between process capability index and process yield were defined for bilateral and unilateral specifications respectively. Based on this, a multiple process capability index (MPCI) was established based on process yield. In order to measure the performance of the actual machining process, a weighted MPCI was also provided, which was a weighted sum of each process capability of different stages. According to the PVTC and the MPCI, the stages whose process capability were not enough could be identified, and the corresponding improvement opportunity could also be provided. At last, a connecting rod of diesel engine was used to verify the proposed method.

Key words: machining process flow, process variation trajectory chart, process capability index, multi-stage capability index, process yield