Study On Thermal Process And Deformation Of Additive Manufacturing By Double Electrode Micro-plasma Arc Welding

Wire Arc Additive Manufacture(WAAM)technology is a new type of manufacturing method that utilizes wire arc to melt welding wires.The basic principle is “layered manufacturing,stacked layer by layer”.The forming parts have high density,high production efficiency and low cost.But under the continuous thermal cycle,complex transformation of material structure will be caused and large residual stress and deformation in parts will occur,which affect the accuracy of part forming and increase the difficulty of part property control.In this paper,wire arc additive manufacture process of 304 stainless steel was studied using double electrode micro-plasma arc welding.The effects of the process parameters,the stacking layer number and the stacking sequence on the thermal process,the grain structure and the distortion of the substrate were analyzed during the forming process of single-pass multi-layer thin wall parts.It will provide experimental basis and theoretical foundation for better control of heat input,optimization of part structure,prediction and decrease of substrate deformation during the additive process.First of all,aiming at the thermal physical process of double electrode micro-plasma arc welding in additive manufacturing process,K type thermocouple was used to measure the thermal cycle curves at different welding speeds,different bypass currents and different stacking sequences in stacking forming.And the influence of each parameter on the thermal process was studied.The results show that the heat input of the base metal decreases with the increase of welding speed.In the appropriate bypass current range,the heat input of the base metal is reduced with bypass current increasing.At the same time,the heat dissipation of unidirectional stacking is better than that of reciprocating stacking.Then,by means of metallographic microscope and vickers micro-hardness tester,combined with the thermal cycle curve measured in the process of additive manufacturing,the grain structure and microhardness of the 304 stainless steel stacking parts were studied.The effects of stacking height,bypass current and stacking sequence on the microstructure and hardness were analyzed.The results show that when the bypass current is increased,the dendrite arm spacing of the stacking part decreases first and then increases.Meanwhile,the effect of stacking sequence on microstructure is that the direction of dendrite growth is changed by different direction of heat dissipation.The microhardness decreases slowly along the direction of stack height.And with the increase of the bypass current,the hardness increases first and then decreases.The stacking order has no obvious effect on th e hardness.Finally,the CCD camera was used to record the warping deformation of the substrate under the single-end constraint during the additive manufacturing process.The effects of various parameters on the deformation of the substrate along the Z-axis were analyzed,such as the deposition layer number,welding current,bypass current,and stacking sequence.The results show that the Z-axis deformation of the substrate always increases first and then decreases,and finally tends to be stable with the increase of the stacking layer number.When the welding current is increased,the deformation of the substrate is also increased.And under different bypass current,the deformation of the substrate is different.At the same time,the deformation of the substrate in unidirectional stacking is larger than that of reciprocating stacking.To sum up,accurately controlling the bypass current and reasonably planning the stacking path can better control the thermal process,optimize the structure of the stacking part and decrease the deformation of the substrate during additive manufacturing,thereby improving the performance and accuracy of the stack ing part.