| Summary: | 博士 === 國立臺灣科技大學 === 工業管理系 === 98 === Supplier selection is a significant decision for enterprises, in which if a supplier and the enterprise cooperate well, it makes possible the creation of greatest profits. Dickson proposed 23 criteria for evaluating suppliers, including quality, delivery, past performance, pricing, productivity and technical abilities, of which quality is most important. Process capability index is a simple and easy-to-know overall measuring tool that is provided for enterprises to evaluate a supplier in terms of product or its quality level and to upgrade its quality performance. This thesis focuses on the index Spk, which is more suitable to use in practice than Cp, Cpk and Cpm, as it has a one-to-one mathematical relation with process yield rate. But, in evaluating process quality, if the estimated value of index point is used to evaluate the process quality, sampling error may occur, which would result in misjudgment of process capability index. The confidence interval has taken the standard error of point estimation into account and it is possible to determine whether a process is good or poor by lower confidence bound. However, because the distribution function of estimating equation for Spk is very complex, the derivation of its confidence interval is thus difficult. The present research converts index Spk into the function of δ＝(μ－T)/d and γ＝σ/d, and sets the simultaneous confidence interval consisting of δ and γ as feasible region and Spk(δ, γ) as target function to solve the confidence interval of index Spk. the confidence interval of index Spk is then used to build an objective selecting mode of suppliers, whereby to compare such interval for various suppliers and obtain the best suppliers and standby suppliers. This selecting mode can be carried out by algorithm on EXCEL, a convenience to the industry. Lastly, applying the above results, the present research proposes a complete quality evaluation and analysis model in respect of the suppliers of upper shaft bearings, a key component of sewing machine, whereby to elevate the quality and yield rate of the bearing they produce and to decrease flaw rates and costs of sewing machine. Given that the four quality characteristics of the upper shaft bearing have nominal-the-best and smaller-the-better characteristics, the process capability index is employed to develop an evaluating method of unilateral and bilateral specifications, which is able to measure whether each of the quality characteristics meets the requirements of quality levels. A multi-process capability analysis chart (MPCAC) is further used to analyze the factors affecting the bearing quality to serve as basis for manufacturers and suppliers to improve. This also can continue to help improve the quality of the upper shaft bearing and further achieve the object of 6-sigma quality level.
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