Stress and Deformation Evaluations of Scanning Strategy Effect in Selective Laser Melting

Selective laser melting (SLM) is one of the Additive manufacturing (AM) processes that can build physical part in an added material method from digital data. In such a process, computer designed part model will be decomposed into hundreds of thousands of layers. The layered information is then transferred to SLM equipment and the part is built in a layer by layer fashion. Each powder layer will be scanned and melted in the required region by a high energy laser beam in a given scanning pattern so as to form a desired geometry. Finally, fully functional parts can be produced by repeatedly powder deposition, melting and solidification process. This process offers numerous advantages such as tooling-free productions and design freedom in geometry. In addition, SLM process is quite suitable for complicated parts such as customer designed medical implants and internal channels which are difficult to manufacture by conventional methods such as casting and machining. However, the localized heating and cooling process can lead to defects such as high residual stress, part distortion or delamination failure in SLM fabricated parts. These potential defects may impede the wide application of this technology. It is known that the laser beam scanning path will affect the thermomechanical behaviors of the build part, and thus, altering the scanning pattern may be a feasible strategy to reduce residual stresses and deformations by influencing the heat intensity input distribution. In this study, a 3D sequentially coupled finite element method (FEM) model, incorporating a volumetric moving Gaussian heat source, powder as well as solid material temperature dependent properties and layer addition features, was developed to study the complex thermomechanical process of SLM. The model was applied to evaluate six different scanning strategies effect on part temperature, stress and deformation. The major results have been summarized as follows. (1) Among all cases tested, the out-in scanning pattern has the maximum stresses along the X and Y directions; while the 45 degree inclined scanning may reduce residual stresses in both directions. (2) Large directional stress difference can be caused by back and forth line scanning strategy while minor directional stress difference is observed for other tested cases. (3) X and Y directional stress concentration is shown around the edge of deposited layers and the interface between deposited layers and substrate for all cases. (4) The 45 degree inclined scanning case has the smallest build direction deformation while the in-out scanning case has the largest deformation among the tested cases.