| Plasma arc welding is a welding process with high temperature and high energy density.It is suitable for the manufacturing of large parts in the fields of aviation,aerospace and military industry.However,due to the obvious heat accumulation effect of plasma arc in additive manufacturing process,the forming quality of plasma arc additive is poor.Therefore,the method of external magnetic field assisted plasma arc welding is proposed to solve this problem.By adding an external magnetic field,an upward electromagnetic force is generated in the molten pool to inhibit the effect of surface tension and gravity,so as to improve the forming quality and increase the material addition efficiency of plasma arc welding,which provides a certain theoretical basis for the magnetic field assisted molten pool forming technology in material addition manufacturing.Considering the internal force of molten pool,solid-liquid phase transformation and latent heat of phase transformation,the mathematical model of three-dimensional plasma arc welding molten pool is established and solved by COMSOL software.The results show that the molten pool temperature reaches a steady state at 2.5s,and the maximum temperature is 2410 k.The flow field on the upper surface of the molten pool is distributed in a "divergent" shape,flows around from the center,and the maximum velocity is near the fusion line;The flow field in the longitudinal section of the molten pool is double vortex,and the maximum velocity is the intersection of the upper surface and the longitudinal section.With the increase of welding speed,the temperature of molten pool decreases,and the flow velocity on the upper surface and longitudinal section of molten pool increases;With the increase of welding current,the temperature and velocity of molten pool increase continuously,and the distribution of maximum velocity changes greatly.The three-dimensional electromagnetic coil model is established to solve the magnetic flux density in the preset molten pool area,and then the mathematical model of plasma arc welding molten pool under the action of magnetic field is established,which is solved by COMSOL software.The results show that the bath temperature and flow velocity decrease under the action of magnetic field.The angle between the distribution direction of the maximum velocity on the upper surface of the molten pool and the width direction of the molten pool changes from 77.5 ° to 59 °;The central velocity of the longitudinal section of the molten pool is obviously enhanced.In addition,the additional electromagnetic force promotes the forward fluid flow of the molten pool and inhibits the backward fluid flow of the molten pool.Under the action of magnetic field,the influence form of process parameters on the temperature field and flow field of plasma arc welding pool is the same as that without magnetic field,but the overall amplitude decreases.A plasma arc welding test platform under magnetic field is built to verify the calculation results of three-dimensional electromagnetic coil and the heat source of three-dimensional molten pool model,and the verification results are good.Plasma arc welding experiments under different process parameters and different magnetic field intensity were carried out.The experimental results show that the width of cladding layer increases and the height decreases with the increase of current intensity;With the increase of welding speed,the width of cladding layer decreases and the height increases.When the magnetic field strength is 0-10 mt,the melting width and melting depth decrease with the increase of magnetic field strength,while when the magnetic field strength is 15 mt,the melting pool width decreases and the melting depth increases.From the microscopic point of view,the magnetic field has a certain refining effect on the microstructure and grains,and the greater the magnetic field intensity,the more obvious the refining degree. |
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