Study On The Additive Method Of Double-pulse TIG Arc With Stepping Wire Filling And The Behavior Of The Molten Pool

As an important branch in the field of additive manufacturing,metal additive manufacturing is one of the most important technical supports for the future transformation,upgrading and transformation of traditional processing and manufacturing to industry 4.0-oriented digital intelligent manufacturing.The arc additive manufacturing technology(WAAM)using electric arc as the energy-carrying beam has the advantages of high material utilization,fast forming speed,and low manufacturing cost.Compared with high-energy beam metal additive manufacturing,it is more suitable for the rapid development of large-scale and complex structural parts.However,WAAM developed based on methods such as argon tungsten arc welding and gas metal arc welding has the characteristics of strong arc-melt-melt pool coupling,nonlinear time-varying interaction,and complex heat exchange with the external environment.The changes in the material forming structure and heat dissipation boundary conditions make it difficult to control the stability of the forming process.The surface quality of the formed parts is rough,the dimensional accuracy is low,the residual stress is large,and the structure and performance are different,which severely restricts its large and complex structure in the modern industrial field Application in high-efficiency and low-cost manufacturing of parts.The WAAM developed for the traditional heat source method has a strong coupling of arc-droplet-melt pool,which leads to the problem that the stability of the forming process is difficult to control.This paper proposes a stepping wire-filled double pulse argon tungsten arc welding(DP-TIG)additive manufacturing method.The stepping wire feeding system matches the double pulse waveform timing wire feeding of the welding machine,and the heat-mass transfer solution of the arc-melt drop system is solved.Coupling independently controls the dynamic behavior of the molten pool to improve the forming accuracy of the deposited layer.To this end,a test system was built based on the principle of DP-TIG additive manufacturing.And carried out the following theoretical process research and obtained important results.Aiming at the stability of the droplet transfer during the step-filling DP-TIG arc additive process,the effect of the welding parameters in the high pulse group stage on the droplet transfer mode and the droplet transfer frequency was studied through a high-speed camera system.The analysis showed that the short arc Welding is more suitable for step-filled wire DP-TIG additive manufacturing.The high pulse group pulse frequency and the peak base current difference have a greater impact on the droplet transition frequency.When the high pulse group pulse frequency is 90 Hz,the peak base current difference At a value of 30 A,there is an optimal droplet transition frequency.The height of the welding wire and the substrate has a great influence on the droplet transfer method.As the height of the welding wire and the substrate increases,the droplet transfer method gradually changes from small drop bridge transition to large drop bridge transition and free transition.Comparing the transition process and the formed parts,it is found that the droplet bridging transition is more suitable for step-filled DP-TIG additive manufacturing.Secondly,for the stepped wire-filled DP-TIG side-axis wire feeding,the welding wire and the arc are not coaxial,the welding wire melting and the stability of the droplets entering the molten pool are poor,which is not conducive to the all-round deposition of complex structures.The welding wire melting model during the DP-TIG welding with step-fill wire was established,and the key factors affecting the melting position of the welding wire were studied.The analysis shows that the welding wire angle has little effect on the welding wire melting position.The wire feeding speed,the diameter of the welding wire,and the height of the welding wire and the substrate have a greater influence on the welding wire melting position.After the model is optimized,there is a wire feeding speed range,and the welding wire melting position is as good as possible The ground is close to the tungsten electrode,and the melting position of the welding wire is not very sensitive to the change of the wire feeding speed at this time.Finally,adopt the optimal droplet transfer method and the welding wire melting position to carry out the deposition experiment on the straight wall.The behavior of the molten pool during the continuous deposition process was studied,and the results showed that the main cause of the instability of the molten pool was the increase in the volume of the molten pool caused by heat accumulation.The heat-mass distribution model is used to explain the compensation mechanism of the step-filled DP-TIG arc additive heat accumulation,which maintains the thermal stability of the molten pool and improves the accuracy of the formed parts.