Brief Paper: Discrete Element Based Modeling of Powder Spreading Dynamics for Laser Powder Bed Fusion Process

Abstract

Abstract In the domain of non-conventional manufacturing processes the use of lasers for metal-based additve-manufacturing (AM) processes has got immense push from both industry and academia. And among these processes the use of Laser powder bed fusion (L-PBF) has seen quite interest. But like any other manufacturing process the quality of part produced by l-PBF is a function of raw material characteristics such as size and morphology of the feedstock powder & material-processing conditions throughout the build cycle which includes powder layering and laser melting parameters.Hence, the current study focuses and deals with the study of powder dynamics, especially spreading dynamics in powder-bed based AM systems. This dynamics of powder spreading which can be categorized as bulk phenomenon gets influenced by the particle size distribution, recoater-speed & shape and size of the recoating object employed. The metal powders having approximately spherical shape, with sizes in μm scale, which are used to form a layer of powder and the dynamics associated with them can modeled using Discrete element based approach, which describes the bulk behaviour of powder using a lagrangian approach of tracking the motion of every particle in the bulk medium which is governed by equations of motion & which are differential form of the popular newton’s laws of motion. These equations in terms of force & moment balance laws are then integrated in each time-step to obtain positions & velocities of each particle hence describing their motion in a given domain. The model herein considers the actual size distribution of the Ti6Al4V alloy powder, which was obtained using laser-diffraction analysis. Non-linear force laws were used to model the contact and non-contact interactions among the particles in the bulk. Thus, enabling the model to study how various powder spreading parameters influence the different powder-bed characteristics such as particle segregation and particle packing density.