Application of 6-sigma design system to developing an improvement model for multi-process multi-characteristic product quality

Rapid developments in advanced manufacturing techniques and information technology have resulted in significant increases in the functionality, precision, and complexity of products. Most products have multiple quality characteristics, which may include multiple unilateral and bilateral specifications. The process capability for any quality characteristic must be satisfied if customers are to accept a product. The production process of complex products generally consists of several stages and processes. The qualities of these processes can be independent or interdependent. This paper develops an integrated assessment model for the manufacture of multi-process, multi-characteristic products based on the process capability index and process yield rate. The proposed method assess six-sigma improvement using the 'define, measure, analyse, design, verify' model. This study investigates the manufacturing processes of 12.7 mm ordinary-grade machine gun cartridges in order to increase their shooting precision. The proposed assessment model identifies the critical-to-quality processes that affect the precision, and then applies redesign and experimental design to obtain the optimal combination of process parameters. Finally, a mathematical programming method verifies the results, confirming an improvement in shooting precision. The resulting cartridges meet the customer demand for match quality.