Investigation On Forming Quality Of Laminar Plasma Metal Additive Manufacturing

The laminar plasma metal additive manufacturing has the advantages of high forming speed,low production cost,high material utilization rate,and is suitable for forming large parts with low precision requirements.However,till now there have been no sufficient investigations about the laminar plasma metal additive manufacturing,especially systematic research on the influence of the process on the forming quality such as defect formation.In this paper,the effects of process parameters such as current,wire feeding speed,wire-to-melt distance,argon flow rate and lap ratio on the forming quality including defect formation,surface quality,and density were systematically studied.Based on this,the ER83-G high-strength steel thin-walled sample was manufactured by an optimized process.The forming quality,microstructure and mechanical properties of the high-strength steel sample were analyzed and the temperature field of the forming process was simulated and calculated by ANSYS software.The results showed that the main defects in the sample formed by laminar plasma metal additive manufacturing were incomplete fusion and pores.The formation of incomplete fusion was mainly affected by the heat input.When the wire feed speed was high,the heat input was low,thus the molten wire could not fully fill the valleys between the lap junction leading to incomplete fusion in the sample.The formation of pores was affected by both heat input and argon flow.The smaller the current,the smaller the heat input,and the more pores were found in the sample.The decease of the argon flow reduced the protection effect and caused more pores.The process parameters had a great influence on the forming quality and density.As the current decreased,the molten wire could not spread completely,the surface quality degraded,and the density also decreased.When the wire feeding speed was large,the surface formed a"peak-to-valley"morphology,and the density was also small.When the distance from the welding wire to the molten pool was small,the welding wire transitted to the forming substrate based on"melting pool model",the surface was continuous and smooth.When the distance was large,the welding wire transitted to the forming substrate based on"droplet model",ball defects appeared on surface.The density decreased as the wire-to-pool distance increased.As the flow rate of argon gas increased,both the surface quality and density increased firstly and then decreasesd.The lap ratio had little effect on the surface quality and nearly no effect on the density.When the current was70A,the wire feeding speed was 20mm/s,the wire pool distance was 1mm,and the argon gas flow rate was 5L/min,the forming quality was the best,and the density was higher,and the density reached ovre 98%.On the basis of understanding the influence of process parameters on defect formation,surface quality and density,a ER83-G high-strength steel thin-walled sample was formed by an optimized laminar plasma metal additive manufacturing process(I=70A,v_wire=20mm/s,d_wire-to-melt=1mm,T_Ar=10L/min).The sample had good formability and the density of the sample was over 96%.The microstructure at different areas of the sample was same and was bainite.The hardness at the top and bottom area of the sample was high?330³60HV?due to high cooling rate,while the hardness in the middle region was stable at about 300 HV.The tensile strengths in the horizontal and vertical directions were 1041MPa and 803MPa,respectively.The temperature field of the forming process of the ER83-G high-strength steel thin-walled sample was simulated and calculated by ANSYS software.According to the cooling rate obtained by the simulation and the continuous cooling c curve,the microstructure should be bainite,which was consistent with the microstructure observations.