Mathematical modeling of thermal behavior in layer-by-layer part fabrication by direct metal laser sintering process for different scanning patterns

In direct metal laser sintering process (DMLS), the nonuniform heat transfer and resulting temperature gradient across the part result in thermal residual stress within the part which introduces local deformation. This overall effect ultimately leads to part distortion and affects the mechanical properties of the part. As far as temperature gradient and thermal residual stress are concerned, the crucial process parameter that can be tailored to alleviate the thermal anisotropic effect from the laser heat source is the scanning pattern. In this study, an in-house transient three-dimensional computational model has been developed to analyze thermal behavior in the DMLS process for different scanning patterns. The governing equations for heat transfer are discretized using a finite volume method. An implicit scheme is used for time integration. The thermo-physical properties, thermal conductivity of the metal powder, convection heat transfer coefficient, and specific heat of the metal powder are updated for every time step. The model considers convective and radiative Neumann boundary conditions for the lateral and top surfaces and a constant temperature boundary condition for the bottom surface of rectangular geometries. The laser power is implemented as a moving radiative Neumann boundary condition that follows any given scanning pattern. In this study, two contour parallel (spiral) scanning patterns, center to edge and edge to center, and their corresponding thermal effects have been analyzed. The results show that rectangular spiral pattern with a center to edge scanning direction has the lowest thermal gradient which results in the lowest residual stresses.