Fundamental Study On The Arc Additive High Quality Forming Technique Of 316L Stainless Steel

Owing to its superior corrosion resistance,weldability,and ductility,316 L stainless steel was frequently utilized in the automotive and nuclear sectors.Some 316 L stainless steel structural parts have been produced using arc additive manufacturing due to its high efficiency and low production costs.However,the low solidification rate of the melt pool results in low forming accuracy,coarse organization,and poor mechanical properties of arc additive structural parts,which affected the widespread application of arc additive manufacturing technology in the engineering field.This was because heat accumulation and dissipation were difficult at the high cladding layer.Therefore,this paper attempted to achieve high quality forming of 316 L stainless steel by measuring the substrate preheating temperature and adjusting the arc line energy density in real time to ensure proper energy input to alleviate the heat accumulation phenomenon.The main research contents and conclusions of the paper were as follows:Jmat Pro was used to simulate the thermal physical characteristics of 316 L stainless steel,take into account the dynamic effects of molten droplets,gravity,the Lorentz force,buoyancy,arc pressure,and surface tension on the model,establish a three-dimensional transient melt pool numerical model of 316 L stainless steel arc additive manufacturing,and analyze the dynamic changes of the melt pool temperature field and flow field throughout the process.The findings demonstrate that as additive manufacturing advances,the length and depth of the melt pool gradually expand until they finally reach steady state in the longitudinal section.To expand the volume of the melt pool,the upper portion flows in a counterclockwise direction and the lower portion in a clockwise direction.In the x = 0 mm cross section,the high temperature zone contracts as the arc advances away from the melt pool,and liquid metal flows from the top center to the sides and eventually to the bottom to aid in heat transfer.The effect of process parameters on the morphology of 316 L stainless steel arc additive forming was investigated based on the single-factor test,and the process parameters at the arc starting and quenching end were adjusted to resolve the issue of height difference of multi-layer single-pass cladding layer in isotropic arc additive manufacturing.The results show that the arc energy density and preheating temperature were proportional to the melt width and inversely proportional to the residual height,while increasing the wire feeding speed decreases the melt width and increases the residual height.Decreasing the arc energy density and wire feeding speed at the arc starting end,while gradually decreasing the arc energy density at the arc quenching end can improve the dimensional defects at the arc starting and quenching ends.In the process study,the geometric characteristics of the high melt layer and the multivariate regression model of the process parameters were established by stepwise regression fitting,and the regression model’s residual analysis and misfit test were conducted,respectively.The effects of two process strategies,heat matching and controlled interlayer dwell time of 10 s,on the quality of thin-walled parts made of 316 L stainless steel by arc additive manufacturing were investigated using the evaluation methods of macroscopic morphology,effective additive efficiency,tissue evolution,microhardness,tensile properties and fracture morphology.The results showed that the heat matching strategy alleviated the heat accumulation phenomenon,improved the surface morphology,and increased the effective rate from 70.88% to 82.91%.The microhardness and tensile strength of the formed parts increased due to the grain refinement,which proved that the heat matching strategy was effective in improving the quality of the formed parts made by arc additive manufacturing.The effect of different heat ratios on the quality of thin-walled parts at equal melt width values was further investigated based on the melt width mathematical model.The results showed that the boundary of each melt layer of the thin-walled part was clearly visible with three heat ratios,and the sidewalls were straight without obvious flow and collapse phenomena.With the increase of preheating temperature,the effective efficiency of the thin-walled parts was 69.65%,83.58%and 74.62%,respectively,and the microstructure of the middle part changed from cellular dendrites to columnar dendrites and the spacing between primary dendrites also increased gradually,and the microhardness and horizontal tensile strength showed a trend of increasing and then decreasing.The vertical specimens at 152 ℃ and the horizontal specimens at 267 ℃showed more destructive surfaces on the fractures,which may be due to internal defects and a significant decrease in the number of tough nests compared with other cases,resulting in a decrease in plasticity.