Numerical Simulation And Experimental Study On Hybrid Electromagnetic And Micro-Rolling In Additive Manufacturing

Metal additive manufacturing is a cutting-edge technology that surpasses traditional subtractive manufacturing methods.This technology has vast potential and promising prospects for producing complex and high-performance parts in fields such as aerospace,shipbuilding,transportation,and nuclear power.Compared with laser or electron beam additive manufacturing,wire and arc additive manufacturing(WAAM)has several advantages,such as wider application scope,higher material utilization,larger forming size,greater efficiency and lower cost.However,its shortcomings such as coarse microstructure and low dimensional accuracy hinder further development and application.This dissertation presents a study on the effects of longitudinal magnetic field and micro-rolling on wire and arc additive manufacturing.Both numerical simulations and experiments were conducted to investigate the impact of these auxiliary energy fields on heat and mass transfer,stress and strain,and forming morphology.By combining the effects of two auxiliary energy fields,a multi-field composite arc additive manufacturing method was developed.This method provides theoretical and technological support for the application of wire and arc additive manufacturing.The main research work is as follows:(1)A multi-field auxiliary arc additive manufacturing experimental platform was constructed,consisting of additive manufacturing platform,data acquisition platform,auxiliary magnetic field generation device,and micro rolling generation device.The response surface method was used to establish a mathematical model between key process parameters and morphology parameters.The process parameters include wire feeding speed,welding speed and arc length correction coefficient.The morphology parameters include aspect ratio,wetting angle and coefficient of variation.A mathematical model for bead contour was established to calculate the optimal overlapping rate with the goal of flatness.(2)Based on the weak coupling model of the arc melt pool,a numerical model for heat and mass transfer in the process of arc overlap deposition assisted by an external longitudinal magnetic field was established.The impact of the longitudinal magnetic field on the temperature field,flow field,current density,arc pressure,and electromagnetic force distribution of the arc and molten pool were studied.The simulation results indicate that the longitudinal magnetic field interacts with the welding current to generate a circumferential stirring force in the molten pool,which causes the molten metal to flow outward along the circumferential direction.During the overlapping deposition process,the stirring effect brought by the longitudinal magnetic field has a positive impact on the final overlapping quality.(3)A longitudinal magnetic field assisted quality control method is proposed based on the longitudinal magnetic field offset weld bead effect.The results of the longitudinal magnetic field assisted deposition experiment show that the longitudinal magnetic field can stir the molten pool and drive the weld bead offset,change the overlap process,effectively suppress overlapping grooves and edge bead collapse to improve the quality of overlapping.The longitudinal magnetic field assisted quality control method has been used to solve problems such as edge collapse,sharp corner overlap gaps and ring size deviation in arc deposition forming.The experimental results show that the longitudinal magnetic field can suppress edge flow and corner overlap defects,achieving high-quality forming of edge weld beads and corner overlap.In addition,by pushing the ring outward to expand or contract,the longitudinal magnetic field can correct the size deviation of the ring and regulate the forming accuracy of the ring.(4)An overlapping bead model of the hybrid deposited and rolling is established to form the optimal overlapping rate curve as the reduction varied.A finite element model of hybrid magnetic and micro-rolling additive manufacturing was established.Combining experimental research,process parameters such as overlapping rate,reduction and distance between the torch and roller were optimized.Parameter optimization criteria was proposed to achieve an optimal distribution of plastic strain and suppress residual stress.Combining the advantages of longitudinal magnetic fields and micro-rolling methods,the hybrid magnetic and micro-rolling additive manufacturing method was proposed.By using the longitudinal magnetic field coaxial with the torch to assist in regulating the flow of the molten pool and utilizing the plastic deformation of the micro roller that follows the torch to form the weld bead,it is possible to achieve synchronous control of the pool stirring and the plastic formation of the weld bead in terms of "quality" and "shape".The research results indicate that the hybrid magnetic and rolling additive manufacturing method integrates the benefits of both auxiliary energy fields to achieve synchronized regulation of "shape" and "property" in wire arc additive manufacturing.Experimental results demonstrate that the flatness between layers of the composite forming is improved by 15 % compared with free deposition,and the mechanical properties are enhanced by 13.2 %.The findings provide valuable theoretical and technological guidance for further research in wire and arc additive manufacturing.