As suggested by several past studies (Barkan and Hinckley, 1993; Eking, 1988; Gebala, 1992; Beiter et al., 2000; Shibata et al., 2001), complexity in the assembly process has a strong correlation with the occurrence of defects. The authors propose a new method that uses a product’s complexity to predict defect rate (Shibata et al., 2001 and 2003). This method provides metrics for assembly complexity using two engineering measures: 1) assembly time estimates and 2) ease-of-assembly ratings. Extensive field data for consumer audio equipment assembled at various manufacturing sites around the world provide the means to validate the proposed metrics. A new process-based complexity factor uses a “time standard” defined for a set of assembly tasks. Predicted defect rates, based on this process complexity, exhibit a significant correlation with actual defect data. Another factor, the design-based complexity factor, uses the “Design for Assembly” method for evaluating an assembly and allows the user to predict defect sources not captured by the process-based complexity factor. Combining these complexity factors not only improves prediction accuracy but also provides guidelines for improving the original design concept as well as each process step. The authors conclude with an example of implementing the Assembly Quality Methodology using the new complexity factors for globally distributed manufacturing.

This paper describes the development of the quantitative predictor of defects that works not only on the whole product but also on its modular units. The authors divide the assembly process of a product into small modules, and apply the Assembly Quality Methodology (AQM) to determine the assembly complexity of the modules. The authors also verify the correlation between complexity factor of the modules and their defect rates. The newly proposed floating threshold assembly time improves the correlation between complexity factor and defects per unit (DPU). The authors discuss the comparison of case studies and the interpretation of their results for the future improvement of the method.

The complexities in assembly processes have a strong correlation with the occurrences of defects. This paper develops a design-based complexity factor derived from the “Design for Assembly” method for evaluating assembly to augment factors not captured by the process-based complexity factor proposed by the authors. The authors collected extensive field data including consumer audio equipment assembled at various manufacturing sites around the world, and used defect data for validating the metrics. The quantitative correlation between the design-based complexity factor and defect rates will provide mechanical designers with guidelines for improving the original design.

An autonomous information system design for item management is proposed for an efficient supply chain management. By using rewritable RF-ID tags instead of popular bar codes as a job ID, which represents a manifest of an item, each processing system directly communicates with the tag information of each item, and autonomous item management can he realized. The following four basic functions are designed, to introduce new items, to link each item to processes, to update item information, and to acquire process records. In a prototype system, which handles RF-ID tags as processed items, selecting correct items and processes according to a production plan are confirmed.