# Stability and Heat Input Controllability of Two Different Modulations for Double-Pulse MIG Welding
## 4 Process Control Experiment on Reduction of Heat Input in TP-MIG Welding and DP-MIG Welding  
A comparative experiment was conducted using TP-MIG welding and DP-MIG welding, where the input energy decreased by varying the number of pulses in the pulse train, the frequency of the low-energy pulse train, and the welding speed. The effects of rectangular and trapezoidal modulation on internal weld quality were analyzed by comparing the resulting weld morphologies and metallurgical structures. Table 1 presents the chemical compositions of the base metals and welding wires used in the MIG welding processes. Reducing Heat Input by Varying Base Time by Adjusting the Number of Pulses in the Low-Energy Pulse Train  
The energy of the welding arc is transferred to the base metal, and part of this energy increases the temperature of the welding wire. The total energy of the welding arc is given by \(P=IU\), and the effective welding power is \(P_{\lambda}=\lambda IU\). The effective power of these energy sources is in the range of 0.70-0.80; in this work, \(P_{\lambda}\) is considered to be 0.70. Based on the principles of DP-MIG welding and TP-MIG welding, it can be inferred that if current is to be reduced in these processes, the corresponding number of pulses should also be reduced. If the frequency is unchanged, decreasing the number of pulses will increase the base time. Based on the input energy equation, \(q=P_{\lambda}/v\), decreasing the current will result in a proportionate decrease in the effective power, if the input frequency is fixed. A comparative experiment was conducted using DP-MIG welding and TP-MIG welding at a welding speed of 0.6 m/min and constant current. The other parameters in this experiment are listed in Tables 2 and 3. The appearances of the welds formed by TP-MIG welding and DP-MIG welding at each level of average current are shown in Figures 11 and 12, whereas Figures 13 and 14 are the corresponding waveform plots. Figures 11-14 demonstrate that the average welding current can be reduced by decreasing the number of pulses in the low-energy pulse train if the parameters of the high-energy pulse train are kept unchanged. The input energy can be reduced by approximately 14% using this approach. The welds in Figures 11 and 12 are normal. However, the fish scales of the TP-MIG weld are more uniform. Micrographs of the welds produced by different currents in TP-MIG welding were compared with  
Figure 11: DP-MIG weld under different average currents: (**a**) Average current of 88 A; (**b**) Average current of 80 A.  
Figure 12: TP-MIG weld under different average currents: (**a**) Average current of 88 A; (**b**) Average current of 80 A.  
Figure 13: DP-MIG current waveform diagram of different number of pulses in the low-energy pulse train: (**a**) Average current of 88 A; (**b**) Average current of 80 A. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline \(I_{pu}\), \(I_{pu}\), & \(t_{pu}\), & \(t_{pu}\), & \(t_{pu}\), & & \(t_{pu}\) & & \(t_{pu}\) & & & & **Average** & **Average** & **Input** \\ \(I_{pu}\), \(I_{pu}\) & \(t_{pu}\), & \(t_{pu}\) & **(A)** & **(ms)** & & **(A)** & **(ms)** & & & & **(A)** & **(V)** & **(J)** \\ \hline
210 & 2 & 72 & 6 & 15 & 48 & 25 & 6 & 4 & 4 & 88 & 22 & 135,520 \\
210 & 2 & 72 & 6 & 15 & 48 & 50 & 3 & 4 & 4 & 80 & 21 & 117,600 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: TP-MIG test data at different number of pulses in the low-energy pulse train. those produced by DP-MIG welding, as shown in Figures 15 and 16. Grain growth is more severe in Figures 15a and 16a compared to Figures 15b and 16b, and DP-MIG welds have fewer second-phase particles. These results indicate that a high energy input induces grain growth and reduces the number of second phase particles. Therefore, reducing the number of pulses in the low-energy pulse train effectively reduces the input energy. Furthermore, a comparison of Figures 15 and 16 shows that the TP-MIG weld has finer grain sizes.