Taguchi-based Six Sigma approach to optimize plasma cutting process: an industrial case study

This case study outlines the use of Taguchi parameter design to optimize the roundness of holes made by an aging plasma-cutting machine. An L-9 array is used in a Taguchi experiment design consisting of four controllable factors, each with three levels. With two non-controllable factors included in the setting, we conduct 36 experiments, compared to the 81 parameter combinations (four factors, three levels or 3(4)) required in a traditional DOE setting. Therefore, using the Taguchi method significantly reduces the time and costs of a quality improvement process. Conducted for two response variables-bevel magnitude and the smallest diameter deviation of the hole-the Taguchi experiments gave the optimal combination A(1)B(2)C(1)D(3) (small for tip size, 93 in/min for feed rate, 100 V for voltage, and 63A for amperage), which is verified with a confirmation run of 30 work pieces. All 30 cuts meet the quality requirement for subsequent assembly. Furthermore, statistical analysis indicates that the mean value and standard deviation of the confirmation run data are smaller than those before Taguchi parameter design is conducted.