Finding the Secondary Effect Factors for the WEDM Surface Roughness by Experiment Design

Quality is the minimum requirement for today’s products. In order to improve the quality of a product, Taguchi method and the experiment design were often applied to different industry processes. The main effect factors and their effects of a specific process can thus be found and estimated. The mathematic model describing the process can then be established. Based on the model, people can well control the manufacturing process and improve their product quality. However, both Taguchi method and the experiment design can find the most important factors that affect a process, and have difficulties to obtain the secondary effect factors of the process to further improve the quality.

This study intends to find the secondary effect factors of a process, and investigate how much improvement can be reached by adding the secondary effect factors into the model. The wire electrical discharge machining is used to perform the experiment, and the work piece surface roughness is the quality index. It is known that the pulse-on time is the main factor affecting the work piece surface roughness. Finding main factor effects and establishing the main factor mathematic model are performed, firstly, to ensure the experiment setup. Then, the block design by choosing the main factor level and fixing it to exclude its effect from the experiment results. After performing five block designs, it is found that the arc pulse-on time and feed speed are the secondary effect factors, and the mathematic model including the secondary factors are established. This study concludes that the work piece surface roughness can be improved about 5％ to 8％ by adding the secondary effect factors in the model.