Selective Laser Melting of Polymer Powder - Part mechanics as function of exposure speed

The selective laser melting of polymer powders is a well-established technology for additive manufacturing applications, although there is still a deficit in basic process knowledge. Considering the demands of series production, the technique of selective laser melting of polymers is faced with various challenges concerning suitable material systems, process strategies and part properties. Consequently, basic research is necessary to understand and optimize processes in order to enable a shift from prototyping applications to serial production of small-lot sized series. A better understanding of the interaction between the sub-processes of selective laser melting and the resulting part properties is necessary for the derivation of new process strategies for increased part quality. Selective laser melting of polymers is mainly divided in the three phases of powder feeding, tempering and geometry exposure. By the interaction of these sub-processes, the resulting temperature fields determine the part properties through microstructural changes in the pore number and distribution. In addition to absolute temperature values, the time dependency of the thermal fields has an influence on the porosity of the molten parts. Current process strategies aim for a decrease in building time by increasing scan speed and laser power, although the absolute energy input into the material does not change when scan speed and laser power are increased at a constant ratio. In prior investigations, the authors showed a correlation between the heating rate and the shape of the resulting melt pool. Based on this correlation, the interaction between heating rates (on a fixed level of exposure energy) and mechanical part properties (tensile test) is analyzed within the paper. The study also implies additional results for other levels of energy input during geometry exposure, which allow for a cross-check of the results. Furthermore, part positioning in the build chamber as well as part density are taken into account. Based on these basic investigations, new process strategies considering the time dependent material behavior can be derived. (c) 2015 The Authors. Published by Elsevier B.V.