Study On Characteristics Of Arc And Evolution Of Weld Pool And Keyhole In Gas Focusing Plasma Arc Welding Process

As a high energy density arc welding process,plasma arc welding can directly weld 6-8mm steel plates without groove to achieve single-sided welding and double-sided forming,and has application prospects in the field of medium-thick and thick plate welding.However,there are still some problems in the practical application of plasma arc welding: such as insufficient stability of the keyholing process,a narrow welding process window when welding thick plates.These problems restrict the application of plasma arc welding in manufacturing field.In order to solve the problems of conventional plasma arc welding,researchers modified plasma arc welding.Among them,the gas focusing plasma arc welding is to restrain the arc by the focusing gas to improve the arc penetrability.Compared with conventional plasma arc welding,gas focusing plasma arc welding has higher arc voltage and stronger arc penetrability.At present,these phenomena have been confirmed experimentally,but the key scientific problems,such as the essential cause of the enhanced penetrability of gas focusing plasma arc welding and the action mechanism of focusing gas on the arc,have not been solved.It is of great significance to study the characteristics of gas focusing plasma arc and the weld pool-keyhole behavior for enriching the theory of plasma arc welding and guiding gas focusing plasma arc welding.In this paper,the method of combining numerical simulation and experimental research is used to study the arc characteristics and the weld pool-keyhole behavior in gas focusing plasma arc welding.Based on fluid dynamics and electromagnetic theory,ANSYS Fluent software is used to modeling and simulation with secondary development by C program language.In this work a twodimensional steady-state gas focusing plasma arc model is established.The arc temperature field distribution,arc pressure distribution and current density distribution of plasma arc are calculated quantitatively,and the influence laws of welding current,plasma gas flow rate,focusing gas flow rate and shielding gas flow rate on arc characteristics are studied.The characteristics of the gas focusing plasma arc and the conventional plasma arc are compared to explore the mechanism of focusing gas on the arc.The research results show that the cooling effect of the focusing gas on the arc is the key to restraining the arc.The focusing gas has basically no effect on the arc temperature inside the nozzle,while has a great influence on the arc temperature distribution outside the nozzle.The focusing gas has basically no effect on the arc pressure.And the measured arc pressure data are basically consistent with the simulation results.In order to analyze the keyholing process of gas focusing plasma arc welding,gas focusing plasma arc welding model is established on considering the coupling relationship of "keyholefluid flow-heat transfer".The temperature distribution,fluid flow in weld pool and keyhole evolution in gas focusing plasma arc welding are simulated and calculated.The shape of the weld pool and the fluid flow after open keyhole establishing are studied.The keyhole shape after open keyhole establishing is simulated.The weld shape is calculated and compared with fusion lines measured in the welding experiment,and the simulation results agree with the experimental results basically.