Additive Manufacturing Method For MIG Welding Based On Heat Input Control

Additive manufacturing technology is a new type of material forming method.It integrates many research results such as digital modeling technology,electromechanical control technology,information technology,materials science and chemistry,and is also called rapid prototyping technology and 3D printing technology.In recent years,with the gradual commercialization of additive manufacturing products,the increasing attention has been paid to forming methods with the goal of pursuing low cost and high efficiency.Therefore,the arc additive manufacturing method has developed rapidly.However,due to the severe heat input and heat accumulation of the arc,the accuracy of the formed parts has always been a major bottleneck to curb the development of arc additive manufacturing technology.This paper focuses on the problems of large heat input and serious heat accumulation in the process of arc additive manufacturing,and has explored and researched the low heat input arc additive manufacturing process of MIG welding.The subject has mainly supported by a three-axis sliding table motion system,and combined with the method of controlling the output current of the constant current welding power based on the LabVIEW arc welding parameter measurement and control system,a constant current MIG welding arc additive manufacturing experiment system has been built and based on a series of process experiments were carried out.At the first,using LabVIEW arc welding parameter measurement and control system to generate rectangle wave,sine wave,triangle wave and sawtooth wave,and use these four waveforms to conduct arc additive manufacturing process experiments,calculated and compared the welding line energy size and forming accuracy under the conditions of each waveform current.It is found that the rectangle wave current welding has the largest line energy and the highest forming accuracy,and the sawtooth wave current welding line has the lowest energy and the worst forming accuracy,while the sine and triangle waves are centered.By observing and comparing the U-I phase diagram and the current-voltage correlation curve of the welding process under various waveform currents,it is known that the rectangle wave current is the most ideal for the droplet transfer control,the sine wave and the triangle wave are the second,and the sawtooth wave is the worst.With the worst performance,the sawtooth wave current is not suitable for arc additive manufacturing process.Secondly,on the basis of welding with rectangle wave control output current,related welding parameters affecting welding heat input were determined,and orthogonal tests were designed to select the optimal welding parameters that can effectively reduce welding heat input and droplet transition control.Using this welding parameter,the single-layer single-pass welding process experiment and additive manufacturing experiment were carried out.The results show that the optimized welding parameters reduce the line energy significantly;the droplet transfer law is strong,the droplet size is small;the weld seam is beautiful;and the accuracy of the additive-manufacturing formed parts has been greatly improved.Based on this,the dual-pulse MIG welding process performance was investigated,and it was found that under the conditions of similar parameter specifications,the line energy of dual-pulse waveform current welding was significantly lower than that of single-pulse;the forming part is almost similar to the original model.Finally,based on the serious problem of heat accumulation in arc additive manufacturing,a heat dissipation method with a water-cooling copper plate on the back of the substrate was introduced.And Abaqus finite element simulation software was used to simulate and compare the temperature distribution of arc additive manufacturing with and without water cooling.The simulation process used the model change technology and Dflux welding heat source subroutine,and use d the equivalent heat dissipation method to simulate the heat dissipation process under the water-cooling condition.The simulation results were verified experimentally,and the results show that the simulation results are basically in accordance with the experimental results;under the same heat input conditions,the temperature of the additive manufacturing substrate reaches the maximum at the seventh layer under both the conditions of heat dissipation with or without water cooling;the temperature of the molten pool and the temperature of the substrate under the condition of no water cooling are higher than those of the water cooling condition,but the cooling speed and average temperature gradient of the formed part are significantly lower than those under the water-cooling condition.