Application of Six Sigma DMAIC Methodology in Welding Assembly Quality Improvement

Abstract

During the welding assembly process of automotive exhaust system, several welding defects will occur if the process parameters are incorrect, which affects the quality of products seriously. Six Sigma quality management is an advanced methodology for reducing the manufacturing costs, shortening the production cycle, and improving the product quality significantly. In this paper, the Six Sigma DMAIC method is applied to control the welding assembly process of automobile exhaust system. It is observed that the biting edge and stomata are the two main weld defects accounting about 85% of the total number of defects. In order to reduce the number of biting edge, causal diagram is used for analyzing the factors influencing the welding process. After the experiment, it is convinced that the process parameters of welding torch angle, welding speed and argon flow are the key factors affecting the biting edge significantly. Then, the optimum process parameters are determined by means of the DOE method, and the control chart is adopted to monitor the effect of process improvement. The results show that defects per million opportunities (DPMO) of biting edge could be controlled less than 1500 which is better than the target number of 5000. It is also proved that the Six Sigma DMAIC methodology is efficiently. Therefore, the stomata defects are reduced in the same way, the level of product quality is raised from 3.55σ to 4.52σ, and the competitiveness of the enterprise would be enhanced greatly.