Selective laser sintering (SLS) is a promising additive manufacturing technique, where powder particles are fused together under the influence of a laser beam. To obtain good material properties in the final product, the powder particles need to form a homogeneous melt during the fabrication process. On the one hand, you want to give the particles enough time to fuse, such that the original shape is no longer visible, and interdiffusion of polymers can take place. On the other hand, you want the process to be as fast as possible. This is contradictory, thus choosing the right conditions is not trivial. We developed a computational model based on the finite element method to study the material and process parameters concerning the melt flow of the powder particles. In this work, we restrict ourselves to varying the temperature-dependent viscosity, the process parameters, and the convective heat transfer coefficient of the sintering of two polymer (polyamide 12) particles. The simulations allow for a quantitative analysis of the influence of the different material and processing parameters. From the simulations follows that an optimal sintering process has a low ambient temperature, a narrow beam width with enough power to heat the particles only a few degrees above the melting temperature, and a polymer of which the viscosity decreases significantly within these few degrees.