激光体能量密度对选区激光熔化成形的有限元分析

Finite element analysis of laser volume energy density on selected laser melting forming

建立Ti-6Al-4V合金三维有限元模型,探究低功率密度下不同的激光体能量密度对选区激光熔化多层沉积成形过程热行为及热应力演变的影响。本模拟采用热−结构间接耦合的方式计算应力场,利用Sqarse/PCG自动求解器增加其收敛性。结果表明:随着低功率密度下激光体能量能量密度从37.04 J/mm^(3)增加至74.07 J/mm^(3),温度分布具有相似的变化趋势,熔池深度及宽度先增大后趋于平稳,实验熔宽与模拟结果基本一致。随着激光体能量密度的增加,整体残余应力呈减小趋势,降幅6.30%。表面应力呈“条带状”周期性分布,应力集中处于扫描轨道的搭接区域,基板层边缘处应力较大。通过对比模拟与实验层间残余应力结果,可见随着体能量密度的增加两者具有相同的变化趋势,最大偏差6.28%。在能量密度为37.04~74.07 J/mm^(3)范围内,经线性拟合后,模拟/实验层间残余应力与硬度值呈反比关系。

The three-dimensional finite element model of Ti-6Al-4V alloy was established to study the effect of different laser energy densities on the thermal behavior and thermal stress evolution of the selective laser melting multi-layer deposition process at low power density.In this simulation,the thermal-structural indirect coupling method was used to calculate the stress field,and the Sqarse/PCG automatic solver was used to increase its convergence.The study results show that,as the energy density of the laser body increases from 37.04 J/mm^(3)to 74.07 J/mm^(3)at low power density,the temperature distributions have a similar changing trend.The depth and width of the molten pool first increase and then become stable.The experimental molten pool width and simulation results are basically the same.As the energy density of the laser body increases,the overall residual stress shows a decreasing trend,and the decrement is 6.30%.The surface stress is periodically distributed in a“Stripe”shape,the stress is concentrated in the overlap area of the scanning track,and the stress at the edge of the substrate layer is relatively large.Comparing the results of simulated with the experimental interlayer residual stress,it can be seen that as the volume energy density increases,both of them have the same changing trend,and the maximum deviation is 6.28%.Within the energy density range of 37.04−74.07 J/mm^(3),the simulated/experimental interlayer residual stresses are inversely proportional to the hardness values after fitting.