The Research On Controlling Of Stability And Metal Transfer Behavior In Consumable DE-GMAW Process

Consumable DE-GMAW (double-electrode gas metal arc welding, DE-GMAW) is the efficient improvement of DE-GMAW. This modification utilizes a GMAW torch to bypass part of the melting current in a conventional GMAW process as illustrated. It can be seen that the main current Im(which melts the main wire) is decoupled into base metal current Ibm(which determines base metal heat input and arc pressure) and bypass current Ibp(which melts the bypass wire), also Ibm=Im-Ibp.As a result, the main current Im can be increased while the base metal current Ibm can be controlled at the desired level. Thus, consumable DE-GMAW would be widely used in efficient welding, low heat input welding or overlay welding.In this paper, due to stability controlling and metal transfer behavior, researches have been carried out in three aspects:1. The research on stability control in consumable DE-GMAW processDue to the instability of consumable DE-GMAW process, a mathematical control model was established at first to descripe the physical welding process. Then, a SISO, MIMO, decoupling control scheme were proposed, simulated and carried out. The results show that:the SISO control scheme can solve the instablity of bypass arc, which adjusts bypass wire feedspeed to stablize the bypass arc; MIMO control scheme can keep the welding process and base metal current stable, which adjusts bypass wire feedspeed to control the bypass arc and bypass current to control the base metal current together; based on the result of MIMO control, a better stability, faster response and higher accuracy can be gotten by decoupling control.2. The research on metal transfer behavior in consumable DE-GMAW processDue to the variety of coupled arc and metal transfer behaviors, this paper applies static force balance theory to analyze the changes in the forces acting on the main and bypass droplets separately. For main torch, the bypass arc changes the forces affecting on the main droplet, and the main metal transfer becomes more desirable. For bypass torch, with direct current electrode negative polarity, the volume of droplet is big and not easily transfers to the weld pool. In order to improve the bypass metal transfer, a method has been proposed which adds CO2to pure argon shielding gas to change the forces affecting on the bypass droplet. Then, with80%Ar+20%CO2shield, the welding experiment is carried out to test the effectiveness of this method. It is found that bypass droplet transfers easily and the diameter of bypass droplet is decreased significantly. At last, based on "mass-spring" theory, the abover results were simulated and proved by mathematical analysis. 3. The research on consumable DE-GMAW process with one power supplyTo decrease the welding costs, an innovation was put forward to realize a stable consumable DE-GMAW process with one power supply. With plenty of welding experimnets, the range of stable welding was fixed. Also the mathematical control model was established to descripe the welding process with one power supply. Then, a control scheme was proposed to control the base metal current stably, which adjusts bypass wire feedspeed to change the bypass current. Also the simulations and welding expriments were carried out to chech the control scheme. At last, to prove that the low heat input could improve tissues and quality in weld seam, expriments of overlay welding between stainless steel and low carbon steel was fullfilled.