316L不锈钢粉末激光选区熔化成形仿真及单层多熔道形貌重构

Simulation of SLM Formation of 316L Stainless Steel Powder and Reconstruction of Single-Layer Multi-Channel Morphology

为定量预测不同工艺参数下316L不锈钢粉末激光选区熔化(SLM)成形熔道形貌并完成其单层多熔道形貌重构,首先对SLM成形熔道的过程进行了模拟,接着完成了SLM成形单熔道实验,得到了工艺参数与熔道宽度及其标准差系数之间的关系,并建立了单熔道截面轮廓数学模型,在此基础上完成了接近真实轮廓的单层多道轮廓三维模型重构。研究结果表明:当激光功率恒为200 W时,随着扫描速度从1.0 m·s^(-1)增大到2.0 m·s^(-1)时,熔道宽度从69.82μm减小到46.65μm,熔道宽度标准差系数从9.84%增大到22.65%;当扫描速度恒为1.3 m·s^(-1)时,随着激光功率从100 W增大到300 W,熔道宽度增加到69.64μm后开始减小,熔道宽度标准差系数减小到13.11%后开始增大;同一线能量密度下得到的熔道宽度值的变化正常,但熔道宽度标准差系数在12.26%到22.65%之间波动;当激光功率约为200 W、扫描速度约为1.0 m·s^(-1)时,成形的单道熔道宽度均匀,标准差系数低于15%,熔道质量较好。

Objective Selective laser melting(SLM)is an additive manufacturing technology that utilizes a multi-channel overlapping process to form a single layer,followed by powder deposition and formation of multiple layers to accumulate the final part.The morphology of the single-layer multi-channel directly affects the powder deposition process and the quality of interlayer bonding and porosity in the subsequent SLM process.Additionally,owing to the heat transfer boundary conditions and thermal accumulation effects in the layerby-layer process,there is a certain fluctuation in the width of the molten channel along the scanning direction,as well as differences in the morphology between the first and last formed melt tracks and between the surface and bottom layers.Currently,research on the quality of SLM parts mainly focuses on the final surface roughness and porosity.However,the quality and precision of SLM parts depend largely on the quality of single-channel and single-layer multi-channel formation during the manufacturing process.In this study,we investigate the SLM process and analyze the quality of single-channel and single-layer multi-channel formation.This study aims to provide insights into controlling the surface and internal quality of SLM parts.Methods This study employed a 316L stainless steel material.First,a powder bed model was established using the discrete element method,considering various factors such as surface tension,evaporation,recoil pressure,Marangoni effect,and gravity.A fluid dynamic model of the powder melting process was then constructed in FLUENT to simulate the process of single-channel formation in SLM.The dynamic behavior of the molten pool during the process was analyzed.Single-channel SLM experiments were designed,and the formed parts were observed and measured microscopically.The simulation and experimental results were combined to identify the optimal process parameters for achieving high-quality single-channel formation.Finally,a geometric reconstruction of the single layer multi-channel model was performed by MATLAB based on the experimental and simulation findings.Results and Discussions The molten channel width and its coefficient of standard deviation of the SLM process were investigated by varying the laser power and scanning speed for 316L stainless steel powder.When the laser power is maintained at a constant200 W,increasing the scanning speed to 2 m·s~(-1)results in a decrease in the molten channel width to 46.65μm,accompanied by an increase in the coefficient of standard deviation of the molten channel width to 22.65%(Fig.7).High-quality single-channel formation is difficult to achieve at excessive scanning speeds,as indicated by interruptions in the molten channel at scanning speeds greater than2 m·s~(-1).When the laser scanning speed is maintained at 1.3 m·s~(-1),within the laser power range 100?300 W,the molten channel width initially increases to 69.64μm before decreasing.Similarly,the coefficient of standard deviation initially decreases to 13.11%and then increases(Fig.11).Notably,different molten channel widths and coefficients of standard deviation are obtained under the same line energy density,and the coefficient of standard deviation varies significantly,fluctuating between 12.26%and 22.65%(Table 4).Based on these findings,a laser power of approximately 200 W and a scanning speed of around 1.0 m·s~(-1)are found to be optimal for achieving high-quality single-channel formation(Fig.15).To further analyze the molten channel morphology,a mathematical representation of the molten channel cross-section was developed,dividing the contour curve into upper and lower parts.The computed contour curve exhibits good agreement with the actual contour curve,indicating that the mathematical model accurately represents the molten channel cross-section shape(Fig.17).Furthermore,based on this representation,a three-dimensional reconstruction of the multi-channel morphology was performed,providing a basic characterization of the single-layer multi-channel morphology(Fig.19).Conclusions In this study,the SLM process of 316L stainless steel powder was investigated through a multi-field coupled simulation,experimental tests,and microscopic observations of the molten channel morphology.The results reveal that the molten channel width is inversely proportional to the scanning speed,whereas the coefficient of standard deviation is directly proportional to the scanning speed,at a constant laser power.When the scanning speed is constant,an increase in laser power initially leads to an increase in the molten channel width,followed by a decrease,whereas the coefficient of standard deviation initially decreases and then increases.The line energy density has no significant effect on the signal molten channel and its coefficient of standard deviation,it is concluded that a laser power of approximately 200 W and a scanning speed of around 1.0 m·s~(-1)are optimal for achieving a coefficient of standard deviation below 15%,that is,high-quality single-channel formation.Furthermore,a mathematical model based on the well-formed single molten channel cross-section and overall contour was developed,which accurately represents the molten channel shape.This model provides a new method for further research on controlling the surface roughness and porosity of SLM-formed parts.