Finite Element Simulation Of Warp Distortion In Direct Metal Laser Multi-layers And Multi-tracks Sintering

Direct Metal Laser Sintering process is a significant development branch of Selective Laser Sintering technology. Metal powder is sintered by higher power laser to produce high densification parts directly. The advantages include: post process is unnecessary, research and development cycles are shorten, and manufacture costs are reduced. It is a new Rapid Prototyping technology which has great potential. However, DMLS process is in the laboratory, warp distortion is a universal problem in sintered parts. In this study some key problems are discussed.The process which sintered rectangular plate with 316L stainless steer powder is simulated by ANSYS. When the finite element model is built, thermal conduction, thermal convection, thermal radiation, phase-change latent heat and material nonlinearity are considered comprehensively. APDL language is used to promote the movement of laser and the technique of birth/ death element is introduced in multi-layers sintering simulation. Thermal distribution and thermal stress distribution are investigated, the feature of multi-layers and multi-tracks sintering part, the effects between each layer and each track are analyzed, and the warp distortion rules are deeply researched.Warp deflection and form efficiency are analyzed with four different scan paths and the spiral scan path is selected. The relationship between preheating temperature and warp deflation is researched and the best preheating temperature is 300°C. The method of combination of orthogonal experiment design with numeric simulation is used to optimize the warp deflection with four important process factors such as laser power, scan rate, scan distance and powder depth, and the best group is obtained. The optimal results can be used to guide the practice.The sintering process of complex spiral part is simulated refer to the analysis method and optimize results of rectangular plate, and the distortion trend on the part is analyzed based on thermal distribution. Finally an improvement scheme that add strengthen tendons in spiral part is presented to control the distortion.