Study Of Arc Behavior And Droplet Transfer In Two-Wire AC Cross-Coupled Arc Additive Manufacturing Process

Arc additive manufacturing technology has a broad development prospect because of its high flexibility,high technology integration,high deposition efficiency,high material utilization,and low equipment cost.However,arc additive manufacturing still faces numerous problems,such as coarse grain size due to high heat input and single composition of welding wire makes the component unable to meet the needs of complex applications.In order to realize the arc additive manufacturing of gradient functional materials with good tissue properties,"double wire + AC" is introduced on the basis of the existing TIG arc additive manufacturing,which increases the manufacturing efficiency and agitates the molten pool through the arc-winding behavior generated by cross-coupled arcs,thus realizing the tissue uniformity in the manufacturing process of gradient functional materials.In this paper,we focus on the cross-coupling of two filaments and AC.In this paper,we analyze and study the physical behavior of the dual filament AC cross-coupled arc additive manufacturing process,and demonstrate the stability and feasibility of the dual filament cross-coupled arc additive manufacturing process through a combination of experiments and simulations to provide a theoretical basis for further automation control of the process.Firstly,a Ti-Ni dual filament AC cross-coupled arc additive manufacturing platform is established and applied to achieve high quality and rapid manufacturing of Ti-Ni gradient materials through the regulation of the Ti-Ni dual filament feeding ratio,and during the deposition process,the main arc oscillates periodically under the influence of AC to achieve the stirring effect on the molten pool,which makes the nickel elements uniformly distributed in the pool and ensures the uniformity of the tissue.The Ti-Ni alloy with gradient function is successfully prepared,which proves the feasibility and advancement of the process in the preparation of gradient function materials.In order to better optimize the process parameters and provide theoretical guidance for further optimization of the manufacturing process,it is particularly important to study the physical behavior of melt drop transfer and arc oscillation during the process.Firstly,the melt drop transfer pattern and arc oscillation in dual filament cross-coupled arc additive manufacturing are analyzed by in-situ observation with high-speed photography to reveal the influencing factors of deposition molding quality and the key mechanisms of process stability.The experiments show that three different droplet transfer patterns,namely "free transfer + free transfer,bridge transfer + free transfer,bridge transfer + bridge transfer",can be observed for the dual filament at different feed rates under the main arc current of 100 A and dual filament AC arc current of 10 A provided by TIG.The corresponding deposition and arc swing qualities are also very different.Through comparative analysis,it was found that the frequent arc extinguishing and re-arcing of the indirect arc between the dual filaments was the main factor leading to the instability of the additive manufacturing process.The "bridging transfer + free transfer" mode can achieve a large arc swing angle and stable deposition,in which the crossed arc has a significant stirring effect on the molten pool and the resulting components are well formed.A model of wire melting behavior of dual-filament AC cross-coupling additive manufacturing process was established,and the mathematical model was simulated by MATLAB/SIMULINK programming software to study the effects of dual-filament AC current,TIG current and wire feeding speed and angle on the stability of the model.The simulation results show that the step of the dual filament AC current will cause a sudden increase of the melting speed,which will lead to the frequent critical state of arc initiation and arc extinguishment,which will seriously affect the stability of the additive manufacturing process,while the influence of the TIG current change on the system stability is smaller than that of the AC current change on the stability.Under the condition of sufficient wire feeding speed,the increase of both AC current and TIG current of the double wire will cause the increase of double wire melting rate.The change in wire feed speed has little effect on the stability of the system,and changing the wire feed speed will result in a new equilibrium position of the dual wire tip position.For both wires,an increase in wire feed angle will result in an increase in dry elongation,while a change in wire feed angle for the left and right wires will have a diametrically opposite effect on the other wire.In order to further clarify the arc oscillation mechanism,a numerical model of the dual-wire AC cross-coupled arc was established by COMSOL Multiphysics numerical simulation software.The arc oscillation behavior and the distribution of arc parameters such as temperature and current density were simulated by coupled multiphysics solution for a single parameter using the established two-wire AC cross-coupled arc numerical model for different AC currents and different tungsten currents.The current density and temperature are increased.The change of AC current will have a greater impact on the current swing behavior,with the increase of AC current,the arc swing angle increases,and a better arc swing behavior is obtained at 30 A.The increase of TIG current does not affect the arc swing behavior,but mainly affects the current density distribution and temperature field of the arc.