| According to the problem of requiring to precisely control the base metal heat input in the welding of thin plate, high strength steel and dissimilar metal, this paper presented a new type of alternate transition way of bypass pulsed coupled MIG welding(Pulsed DE-GMAW) based on the study of free transition alternates with short circuit transition of GMAW. It can be helpful to precisely control the droplet transfer and the base metal heat input, enhance the bridging capacity of Pulsed DE-GMAW, reduce the requirements of assembly clearance. The theory and practice proved that it was helpful to the low heat input welding process.Firstly, according to the characteristics and the control requirements of the Pulsed DE-GMAW alternating transition process, using the rapid control prototyping technology, the hardware and software test system based on the rapid prototyping of aluminum and steel Pulsed DE-GMAW alternating transition process were established. The system can realize the control and coordination of the main pulse current and the bypass pulse current waveforms, and it can finish the electrical signal and visual signal acquisition, display, processing and storage during the welding process. Through analyzing the collected welding signals, after a certain control algorithm, it can output real-time control signals, optimize the alternate transition process of aluminum and steel Pulsed DE-GMAW, and it can get a stable welding process, complete the control of alternate transition process.Then, the mathmatical model of Pulsed DE-GMAW alternate transition process based on the elastic-qualitative model theory was established, and the control scheme of realizing the alternate transition process by controlling the bypass double pulse current parameters was presented. In open loop state, by using the effect of shunt and force of the bypass arc to the melting welding wire, and by adjusting the bypass double pulse current parameters, the Pulsed DE-GMAW alternate transition process was simulated, and it obtained the ideal simulation results.Secondly, through the test of the process of aluminum and steel Pulsed DE GMAW alternating transition welding, the effects on the match of the synchronous process about the main pulse currents and bypass pulse currents were studied during the welding process. The results showed that among the total alternating transition current filtering waveforms, there would not be a huge difference between high frequency pulse currents and low frequency pulse currents. otherwise there would be fluctuations of the arc. This would lead the process to become unstable. Generally, the differences between high frequency pulse currents and low frequency pulse currents were not more than10A.Though the high speed video camera system, the effects on the transitional manner of the number pulse about high frequency pulse currents and low frequency pulse currents were studied. During the process of welding, the matching number of high frequency pulse currents and low frequency pulse currents would determine the number of freedom transition and short transition in a cycle. With the number of high frequency pulse increasing, the number of free transition would increase. With the number of low frequency pulse increasing, the number of short circuit transition would increase. But the matching method of high frequency pulse currents and low frequency pulse currents had a little influence on the weld forming using Pulsed DE-GMAW alternate transition on the aluminum and steel.Lastly, the bridging process test of the alternate transition process of aluminum and steel Pulsed DE-GMAW was undertaked. The results showed that the designed alternate transition way by controlling the bypass double pulse currents to realize aluminum steel Pulsed DE-GMAW alternate transition way can effectively enhance the bridging capacity of welding lap structure, reduce the requirements of welding assembly clearance, and obtained a good weld forming. |
