Statistical Test of Two Taguchi Six-Sigma Quality Indices to Select the Supplier with Optimal Processing Quality

Abstract

Abstract Because of rapid changes in consumer needs, diverse and small-batch production has become a crucial strategy for companies progressing toward sustainability in intensely competitive industries. To swiftly meet the diverse needs of consumers using this production strategy, often manufacturers must outsource noncore processes to external contractors or purchase component parts from suppliers. The objective of this article was to develop a supplier selection model based on the processing quality of suppliers. Owing to the fact that the Taguchi Six-Sigma quality index for process with nominal-the-best specification (Qpm) can fully reflect product loss and the achieved quality level for the quality characteristic of the process in question, Qpm is employed as a tool to assess and compare the processing quality level of two-sided specification limits provided by each supplier. In practice, Qpm is based on the sample data collected from a stable process to estimate prior to the processing quality assessment. This can lead to misjudgment because of sampling error. To increase the reliability of supplier selection, we further propose hypothesis testing of the quality index Qpm for two suppliers. The applicability and effectiveness of the proposed model is validated using an example involving the double-sided grinding process of a bicycle disc brake.