Compensation of Non-Linear Shrinkage of Polymer Materials in Selective Laser Sintering
Inaccuracies in the selective laser sintering (SLS) process using polymer materials are typically caused by inhomogeneous shrinkage due to inhomogeneous temperature distribution in the powder bed of the SLS machine. These shrinking effects lead to stress in the sintered parts, causing the part to distort. The inhomogeneous shrinkage of benchmark parts has been compensated empirically in a former work. The results cannot been transferred to all geometries, because each geometry requires a specific temperature for laser sintering and, thus, has its own related shrinkage distribution. In a new theoretical approach, shrinkage behavior is to be integrated in a thermal simulation of the SLS process and the thermal shrinkage calculated prior to the building process. In the following, experimental data of the temperature- and pressuredependent shrinkage of laser-sintered powder samples is presented. Possible theories for a physical model of thermal shrinkage are discussed. In particular, these models have to consider granular characteristics such as internal friction, particle sliding, and powder compaction.