Adjustment of isotropic part properties in laser sintering based on adapted double laser exposure strategies

Abstract

Laser sintering of polymers gets more and more importance for small series production. However, laser sintered parts have often an explicit anisotropy of mechanical properties. Due to the layer-wise production, parts show no homogenous morphological structure as known from injection molded parts. Voids appear within the part and are concentrated in the area between two consecutive layers, resulting in reduced bonding. Therefore, mechanical properties and in particular the elongation at break show significantly lower values in the direction of build compared to the properties within the build plane. Sometimes, these effects are an obstacle in the usage of laser sintering for series production of parts.The aim of the experiments was to investigate to what extent an improvement of the layer-to-layer bonding and thus of the characteristic values in the building direction can be achieved by alternative exposure strategies. For this purpose, the influence of adaptive double laser exposure strategies on layer-to-layer bonding and anisotropy was investigated. The influence of different parameter settings for the first and second exposure was investigated. In a further step it was examined to what extent the influence of disturbances on the process, such as the inhomogeneous temperature distribution or cycle time variations can be reduced by applying the developed double laser exposure strategies. For this purpose, a comparison was made between an optimized double laser exposure parameter set and the standard parameter set.