Study Of Plasma Arc Welding Model Based On Electro-magneto-thermo-hydrodynamic Coupled Mechanism

Plasma arc welding is a high energy beam welding techniques.The keyhole plasma arc welding can achieve one-side welding with both sides formation of the medium thickness plates without opening the groove,and has great application potential in the industrial field.However,the application of keyhole plasma arc welding is restricted by the influence of process parameters and the poor stability of keyhole.The physical properties of plasma arc welding are complex,and its unique electro-magneto-thermo-hydrodynamic coupled interactions characteristics are the important reasons for the formation of keyhole.Thus,the accurate analysis of the coupled mechanism of electrical,magnetic,temperature and flow field in the welding process has important theoretical guiding significance and engineering practical value for optimization of welding quality.According the combination of electromagnetics,fluid mechanics and heat transfer,an axisymmetric model of plasma arc is established.The conservation equations of electromagnetic,flow and temperature fields in the whole calculation domain are solved by using the secondary development function of the commercial software Fluent.The temperature,velocity and electromagnetic fields of plasma arc are analyzed,and the effects of electromagnetic field calculation methods on the properteis of the plasma arc are compared.The development of an integrated calculational model of plasma arc and workpiece for a keyhole plasma arc welding is described.Based on the experiment and simulation calculation,a simple and applicable arc pressure model is developed.The arc pressure acts on the whole liquid phase region as the source term.The integrated model of plasma arc welding avoids the calculation of the actual shape of keyhole with multiphase flow calculation method,such as VOF,and greatly reduces the computing costs.Based on the model,the physical phenomena of plasma arc and weld pool in the whole welding process,including the transient behaviors of temperature and fluid flow fields in the whole domain,are numerically simulated.The thermal-mechanical effects between plasma arc and weld pool are analyzed.The distribution of electrical and magnetic field in plasma arc and workpiece are obtained.The validity of the integrated model is verified by experiments.The effects of welding current,nozzle diameter and distance between two electrodes on plasma arc welding are discussed by using the model.An unified three-dimensional model of coupling plasma arc-weld pool for moving plasma arc welding is established,which consider the relative movement between the plasma arc and workpiece.The dynamic evolution of plasma arc and weld pool during welding perforation and the morphology of weld pool after perforation are calculated.The results show that the plasma arc shrinks inward at the front and expands outward at the back due to the relative movement between the torch and workpiece.A long and narrow weld pool tail appears behind the weld pool.There is an obvious deviation between the center of weld pool and the torch.The model is validated by experiments.The fusion line of the cross-section obtained by the experiments is basically in agreement with the calculation results,which validate the correctness of the model.