Modified Active Control of Metal Transfer and Pulsed Gmaw of Titanium

This paper aims at the development of an advanced control technology for pulsed gas metal arc welding (GMAW) of titanium or other materials which require a highly stable metal transfer process. It is known that conventional pulsed GMAW achieves stable and repeatable spray transfer by using correct pulse parameters. Because the optimal pulse parameters depend on welding parameters such as wire feed speed, arc length, contact tube to work distance, etc., technologies are needed to improve the robustness of the transfer process with respective to the variations in welding parameters. To resolve this problem, active control technology has been proposed to ensure a specific type of desirable repeatable metal transfer modes, i.e., one drop per pulse (ODPP) mode. It uses a peak current lower than the transition current and takes advantage of the downward momentum of the oscillating droplet to enhance the detachment. Such a peak current will not detach the droplet unless it grows to a very large size, which results in a globular transfer and thus eliminates the possibility of accidental detachment. When the droplet grows to a size close to the diameter of the electrode, the current is switched to the background level and the droplet starts to oscillate. When the droplet moves toward the weld pool, the current is switched to the peak level and the combination of the increased electromagnetic detaching force and the downward momentum ensures detachment. Hence, the metal transfer process becomes controllable and robust against variations in welding parameters. However, in order to ensure the combination of increased electromagnetic force and downward momentum, the oscillation process must be monitored. In this study, a modified method is proposed in which the droplet starts to oscillate by first moving toward the weld pool. As a result, the detaching pulse can be applied after a very short period of time and the combination of increased electromagnetic force and downward momentum is guaranteed. Thus, the control system is simplified and the robustness of the metal transfer process is further improved. This modified active control technology has been used to weld titanium.