Numerical Simulation And Magnetic Compression Mechanism Of Magnetic-controlled Arc Plasma

Improving the production efficiency of Tungsten Inert Gas Welding(TIG welding)is one of the research hotspots globally,with various types of high-efficiency TIG welding processes were proposed recently.Magnetic field assisted TIG welding can increase the arc energy density by influencing the shape of the arc.Magnetic field,however,has high variability in the types,configurations and parameters.In addition,the shape and performance of the arc treated by magnetic field show complex changes.Therefore,these facts challenging the systematic interpretation of effects of the magnetic field on the arc.This dissertation summaries the widely used methods for arc numerical simulation by referring to extensive literature.Most methods reviewed in literature can merely obtain the macroscopic properties of arc temperature,pressure,flow rate,etc.Hence,this dissertation proposed a way to reveal the interaction mechanism between the magnetic field and the arc through the simulation of the charged particles in the arc from the microscopic view.The cusp magnetic field and the axial magnetic field,which have the greatest influence on the arc shape,are selected as the external magnetic field,based on the effects of various magnetic fields on the arc shape.The magnetic induction intensity and magnetic field frequency are determined as the research parameters in this research.A multifunctional magnetic head and magnetic control welding test system are designed and developed,which can realize TIG welding test treated by a multi-type and multi-parameter magnetic field.Results show that arc shrinkage is observed when treated by the axial magnetic field with a frequency of 1500 Hz and an intensity of 30 m T.The arc cone angle with magnetic field decreases from 87.6° to 24.8°.The compression rate can reach 74.67%.Magnetic field also increase the depth-breadth ratio from 0.31 to 0.47(increased by 51.6%)and thus effectively improved the welding production efficiency.The arc partition method based on MATLAB was proposed.The arc column is divided into three parts: ionization,recombination and energy jump zone,depending on the arc brightness.The influence of the magnetic field on the size and arc energy density of these three zones was quantitatively analyzed.This dissertation proposed the viewpoint that the energy transfer efficiency can be improved by high-frequency magnetic controlled arc,based on the measured current density and arc pressure.The reasons for the increase of arc energy density and the change of arc energy distribution were explained.A magnetic field model and a charged particle motion model were established.In addition,the trajectories of electrons and argon ions were simulated by MATLAB.The underlying mechanisms of arc shape change,and the arc expansion and compression were systematically expounded from the microscopic view.Results showed that the axial magnetic field produced by the magnetic head with a magnetic core structure presents an annular mountain distribution.The magnetic field without magnetic core is a single peak distribution.With the magnetic field,the trajectory of electrons is a convergent spiral around the lines of magnetic force,and the trajectory of argon ions is part of the spiral curve.They can also jump from one position to another and start moving again.Meanwhile,the frequency of the applied magnetic field and the initial velocity of the charged particles can change the radius of gyration of the spiral motion and affect the transition probability of the charged particle.The radius of gyration is large when the frequency is low and the initial velocity is large;Thus,the charged particles are prone to jump from one position to another,their lateral movement distance increases and the arc expands.On the contrary,the charged particles are constrained to move near the lines of magnetic force,and the lateral movement distance decreases,which is manifested as the contraction of the arc.The proposal of this theory and research idea provides a new idea for the subsequent development of high-efficiency magnetic control TIG welding process.COMSOL software was applied to reveal the influence of magnetic head structure on external magnetic field and its distribution.The result can provide a basis for the research and development of integrated small welding gun and lays the foundation for the industrial application of magnetic control TIG welding.