The Thermal Process Model Of Plasma Arc Welding With Considering The Backside Keyhole Deviation

When the plasma torch and the work-piece move relatively in plasma arc welding(PAW), it is found that there is a keyhole deviation distance at the exit between the keyhole center point and the welding torch axis. The keyhole deviation distance can reflect the inclination of the keyhole and the melting state of the weld pool front edge. However, there are a few models of weld pool and keyhole to investigate the physical mechanism of the keyhole deviation in PAW. Therefore, considering the keyhole deviation, studying the interaction of weld pool and keyhole is of great theoretical as well as practical significance to obtain the high-quality welds. In addition, the research can also provide guidelines to optimize the control method, on the basis of taking the backside keyhole deviation distance as the controlled variable.Using the method of "macroscopic heating effect", a combined volumetric heat source model is established, which can be dynamically adjusted with the evolution process of keyhole. That means the action zone of heat source changes in time with the keyhole size. The influence of bending keyhole on heat transfer and force action is considered. Along the thickness of the test plate, a deviation parameter of the volumetric heat source center will be set in the model, which indirectly describes the thermal effect of the keyhole deviation in the PAW. On the rear wall of the keyhole, the backward pushing force of plasma jet will be taken into account in calculating the keyhole shape, which reflects the influence the plasma jet on the weld pool.By using the dynamic heat source model and keyhole model, the simulation of the PAW transient process is conducted on stainless steel plates with thickness of6mm and8mm, respectively. The evolution processes, such as the development of temperature field and the deformation of keyhole are analyzed. The influence of the keyhole deviation on the heat transfer has also been investigated.The experiments are carried out to obtain the geometry of the transverse cross-section, time for opened keyhole, keyhole size and deviation distance. The simulation results basically agree with these measured results, validating the modified mathematical model in different welding conditions.