The meaning of geometry-dependent exposure temperatures for laser sintering of polymers
Laser sintering of polymers allows for the fabrication of parts with almost unlimited geometrical freedom through layer-by-layer production. Originally, the process was used for prototype generation, but in the last decade, the process emerged towards the field of rapid manufacturing and individualized industrial component production of individualized parts or small series. However, the defined setting of reproducible material and component properties, such as dimensional accuracy, porosity or mechanics remains a challenge. This is due to the manifold and interacting material and process influences that affect the temperature history of the component during part generation. According to the state of the art, the exposure process plays a decisive role in controlling the temperature fields and thus the component properties. For this reason, the temperature fields during exposure are analyzed within the framework of this dissertation. Therefore, exposure parameters and cross-sectional areas are varied. The layer-dependent and geometry-specific temperature values are measured via thermal imaging and validated with respect to the resulting component properties during processing of polyamide 12. It is found that the geometry-dependent maximum temperatures are layer-independent and, due to the short effective time of material-beam interaction, are not decisive for the resulting component properties. The decay time and the heating of the powder bed above the melt can be identified as decisive thermal variables. These values can be interpreted as measure for the thermal interactions between the subsequently manufactured layers. Regarding constant cross-sectional areas, a layer dependency can be detected, that is valid for different exposure parameters. Constant values can be measured after ten to 15 layers, which is correlating to the amount of material that has to be melted with respect to the melting depth. Based on these findings, the need for layer- and geometry-dependent exposure parameters or geometry invariant processing parameters can be derived to further increase the reproducibility of component properties.