基于材料性质转换的金属粉末直接选区激光烧结温度场数值模拟

基于MSC.Marc非线性有限元分析软件，建立金属粉末直接选区激光烧结过程的温度场有限元分析模型。模型中考虑了粉体—实体转化过程中热导率等物理性质随温度的非线性变化规律。对于表面对流和辐射散热条件，采用修正系数的方法，考虑激光冲击加热作用引起的极大温度梯度的影响。同时还采用在不同载荷步之间转换单元材料物理性质，以考虑激光烧结过程中的局部热源输入作用。对采用在不同载荷步之间转换单元材料物理性质的方法和不采用此方法进行模拟对比研究，结果表明：前者在烧结开始时在光斑中心附近具有极大的温度梯度，这与试验结果一致；前者热传播的主要范围集中在已烧结区域，而后者热传播的范围则是整个粉床；前者进入稳态烧结后光斑中心温度变化趋于平缓，而后者的光斑中心温度一直持续上升。这主要是由于已烧结部分的材料热导率比未烧结部分的粉末高约100倍造成的。

FINITE ELEMENT SIMULATION FOR TEMPERATURE EVOLUTION IN DIRECT METAL LASER SINTERING BASED ON MATERIAL PROPERTIES TRANSFORMATION WITH LOAD STEPS

Taking account of temperature-dependent thermal conduction and heat capacity, a three-dimensinnal finite element model of temperature field in DMLS has been established with the employment of the non-linear Finite Element Analysis (FEA)software MSC. Marc. As to the effect of extremely high thermal gradient caused by laser processing, the surface boundary conditions of surface convection and radiation is revised by using a coefficient. A method to transform element material properties between load steps is also taken for consideration of the regional-input high-power laser beam. Comparisons of simulation results between with the method and without it are conducted, and some conclusions are reached: Temperature graclient of the former one in the first steps is very great, which is consistent in the trend with the experimental phenomena; Heat affected zone of the former one is mainly confined in sintered region, while that of the latter one can reach the whole powder bed; The temperature of powder bed under the laser spot with increasing load steps of the former one remains constantly, while that of the latter one increases continuously. These are primarily caused by the hundred times rising of the thermal conductivity after laser sintering.