Ti6Al4V的激光选区熔化单道成形数值模拟与实验验证

对于Ti6Al4V材料的激光选区熔化（SLM）成形工艺，基于离散元方法（DEM）建立粉末颗粒随机分布的三维介观模型.采用流体体积法（VOF）对SLM成形过程的三维自由表面进行动态追踪；考虑TC4颗粒随机分布的粉床、随温度呈非线性变化的热物性参数、熔池自由液面演化、由温度梯度引起的表面张力以及蒸发作用；通过数值模拟研究激光与粉末颗粒相互作用过程中的传热、熔化、流动、凝固等过程. 结果表明，由温度梯度及表面张力梯度产生的马兰戈尼对流是影响熔池内部传热传质和熔池三维形貌的主要因素；线能量密度（LED）与马兰戈尼对流的强度呈正相关，当LED=92.9~183.0 J/m时，单道表面质量较优. 通过单道成形实验对熔池与熔道的三维尺寸与形貌进行观察分析，有效验证了数值模拟的正确性.

Numerical simulation and experimental verification for selective laser single track melting forming of Ti6Al4V

For selective laser melting (SLM) forming of Ti6Al4V, a three-dimensional (3D) mesoscopic model of random distribution of powder particles was established based on the discrete element method (DEM). The volume of fluid method (VOF) was used to track the 3D dynamic free surface in SLM forming process. Various factors were considered in the numerical model, such as the TC4 powder bed with randomly distributed particles, the thermophysical parameters changing nonlinearly with temperature, the free surface evolution of the molten pool, the surface tension caused by temperature gradients, and the evaporation effect. The heat transfer, melting, flow and solidification in the interaction between laser and powder particles were studied according to the numerical simulation. Results show that the Marangoni convection induced by temperature gradient and surface tension gradient is the main factor affecting the heat and mass transfer within the melt pool and the 3D morphology of the melt pool. The line energy density (LED) is positively correlated with the Marangoni effect. The quality of single track surface was good when the optimized LED ranged from 92.9 J/m to 183.0 J/m. The three-dimensional size and the morphology of the molten pool and the molten track were observed and analyzed by the single track forming experiment, by which the numerical results were validated.