Fundamental investigation of part properties at accelerated beam speeds in the selective laser sintering process

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Abstract
Purpose: Despite the recent progress in basic process understanding considering the selective laser sintering (SLS) of thermoplastics, several aspects of the mechanisms of the beam and powder interaction are not fully understood yet. Recent studies covered the correlation of mechanical properties and part density with the heating rate. The surface roughness of the test specimens was also considered but showed no distinct relation to the part mechanics. The purpose of this paper is to provide a new fundamental model for describing the decreasing mechanical properties with increasing beam speed. Design/methodology/approach: While the dependence of mechanical properties with total energy input during exposure is well published, the correlation of the exposure speed with the degree of particle melt (DPM) is the subject of the present study. The DPM is accessible through differential scanning calorimetry measurements. Supporting the previously introduced method of the core-peak height, the interpretation via the core-peak area is proposed as a means to ascertain the melting behaviour for different processing conditions. Further support of the observations is given by x-ray computed tomography and microscopy which allows for a correlation with the respective porosity and inner structure of the parts. Findings: The authors show a novel way of describing the decreasing mechanical properties with increasing speed of energy input by showing the dependence of the DPM on the heating rate during exposure. Practical implications: The results offer an addition to the understanding considering the reliability and reproducibility of the SLS process. Originality/value: The paper extends the existing models of the time-dependent material behaviour, which allows for the derivation of new efficient and stable process strategies.

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