3.2.2. The Design of Orthogonal Experiments

Orthogonal experimental design is a powerful tool to deal with the system with multiple input parameters. The method can pick some typical parameters combinations from full possible combinations to conduct the experiments. According to corresponding analyses for the experimental results to comprehensively figure out the full experimental situation, and then obtain an optimal parameters combination. This method can reduce the number of the experiments and instruct to seek an optimal parameters combination for a special system.

To further explore the effects of some key operational parameters during the DP-GMAW process on the quality or other performances of the weld bead, according to the principle and characteristics of this welding process combined robot operation, four key operational parameters, which were robot welding speed *VR*, twin pulse frequency TPF, twin pulse relation *DT* and twin pulse current change in percent *I*Δ, were chosen to design orthogonal experiments. The average welding current *Iav* during the process was set to 80 A, and the electrode inclination angle was 86◦ using backward inclination mode in this work. After serious preliminary analyses and process experiments, the value ranges of some main parameters can be confirmed during the ranges which the welding action can be normally conducted. Each chosen operational parameter corresponded to three levels as shown in Table 2, and then a detailed orthogonal experimental design, whose form was L9(34) with a four-element-three-level, can be depicted as shown in Table 3.




**Table 3.** The program of the orthogonal experimental design.

Hence, to sufficiently explore the effects of different operational parameters on the quality or other performances of weld bead, nine experiments with different effective parameters combinations should be conducted.
