4.5.3. Orthogonal Experiment Analysis for the Results of FCE

Apart from the appearance and grain size, which were important elements used in FCE, the results of the FCE method can also be analyzed using orthogonal experiment analysis, in order to obtain the influential levels of key operational parameters on the quality of weld bead. The analysis method was the same as in the above two analyses about appearance and grain size, however, all of the *Scores* used the accurate score of FCE in Table 9 and the parameters referred to the Table 3. The corresponding analyses results can be seen in Table 12. It can be seen that the effects of different parameters on the quality of weld bead were so obvious. The most influential factor was the robot welding speed of the welding robot and a corresponding range value achieved 24.283, and then the following factors were twin pulse frequency and twin pulse current change in percent, while the last was the twin pulse relation, whose influential effect was very low. It was because the robot welding speed can influence the heat delivery for weld bead and cooling rate of the weld pool. To obtain a weld bead with satisfactory quality, the system must provide a proper combination of robot welding speed and twin pulse frequency, which should appropriately match the average welding current and thickness of the base plate.


**Table 12.** Orthogonal analyses of FCE scores of the weld bead.

According to the range analysis results, the optimal parameter combination in these nine experiments can be obtained as follows: robot welding speed was 30 cm/min of Level2, the twin pulse frequency was 2 Hz of Level2, the twin pulse relation was 50% of Level3, and the twin pulse current change in percent was 30% of Level1. These parameter combinations can correspond to the L5 in the above experiments. Also, another testifying experiment was conducted to repeat testify this parameter combination. The obtained weld bead is shown in Figure 12.

**Figure 12.** The morphology of the weld bead using optimal parameters combination.

It can be seen that the weld bead was regular with proper bead width. The appearance was bright with compact and smooth fish scale ripples. Also, the welding process was stable without short-circuit and interruption occurring. All of these characteristics meant that the weld bead with satisfactory quality can be obtained using this operational parameter combination.
