# Stability and Heat Input Controllability of Two Different Modulations for Double-Pulse MIG Welding
## 2 Design of Current Waveform Parameters for Double-Pulse MIG Welding with Two Different Modulations  
In double-pulse MIG welding, waveform control refers to the modulation of high-frequency pulses using a low-frequency rectangular waveform. Strong and weak pulse trains are continuously alternated during this process, which forces gases formed by the welding processes out of the weld. Therefore, double-pulse MIG welding reduces the effects of weld pores, reduces the sensitivity of the joint to cracks, and improves the finish and mechanical properties of the weld [18]. Pulsed MIG welding is an important breakthrough in welding technology, as it has eliminated numerous constraints of constant-current welding techniques. Moreover, the advent of this technology has provided a new direction for research and development in the field of arc welding [19]. The energy used by pulsed MIG welding can be controlled by adjusting time and current parameters. This ensures that low current will be used during the welding of aluminum alloy plates, in accordance with the requirements of aluminum alloy processing [20]. The relationship between current and the transfer mode of double-pulsed MIG welding is illustrated in Figure 1.  
The globular transfer mode is essentially open-arc welding, and it has lower levels of current compared to spray transfer. As shown in Figure 2, the welding current of the spray transfer mode increases in proportion with the surface tension of molten metal, and this mode uses higher currents than several other modes of transfer. This mode of transfer is suitable for settings with low base voltages and high peak currents [21]. The streaming transfer mode leads to higher currents, lower droplet volumes, and formation of axial droplet columns. If the current exceeds 300 A, the electrical resistivity of the transfer process increases. The control of current in pulsed transfer is performed by switching between globular transfer and spray transfer [22]. Figure 2 illustrates the current waveform of single-pulse MIG (P-MIG) welding. This process only involves a few factors, and the most important parameters are the peak current of the pulse, \(I_{p}\), and the base current of the pulse, \(I_{b}\). It should be noted that \(I_{p}\) and \(I_{b}\) are the extreme values that manifest during the adjustment period of the pulses. As \(I_{b}\) is typically very small, it is sufficient only for powering idle operation and maintaining the welding arc. \(I_{b}\) also plays a role in the preheating process. Double-pulse MIG welding effectively decreases crack sensitivity and pore generation rates. In addition, the welding patterns formed by this method are aesthetically pleasing. As shown in Figure 3, low-energy and high-energy pulse trains alternate with each other in double-pulse MIG welding. The meanings of the parameters shown in Figure 3 are as follows: \(I_{bw}\) (\(I_{pw}\)) and \(t_{bw}\) (\(t_{pw}\)) represent the base (peak) current and base (peak) time of the pulses in the low-energy pulse train, respectively; \(I_{bs}\) (\(I_{ps}\)) and \(t_{bs}\) (\(t_{ps}\)) represent the base (peak) current and base (peak) time of the high-energy pulse train, respectively; \(T_{w}\) is the period of the low-energy pulse train; and n and m represent the number of high energy pulses and low-energy pulses per unit welding current cycle, respectively. The alternation of high-energy and low-energy pulse trains over the duration of \(T\) (i.e., the time required to complete the processes of double-pulse MIG welding) causes the welder to alternate between hot and cold states [23]. As aluminum alloys have a low melting point and high conductivity, these materials are easily affected by temperature, which could lead to hot cracks and weld damage. The possibility of oxide film breakdown and the weakening of base material strength in the presence of high energy levels make it necessary to strictly control the input of welding energy. Figure 1: Relationship between transfer mode and current. Figure 2: Sketch of the P-MIG scheme.