Simulation-based prediction of the thermal process emission measured by pyrometry of 316L stainless steel

Abstract

Laser Powder Bed Fusion is a common additive manufacturing process in which metal powder is selectively melted by a laser. Meandering stripe hatching is often used in conjunction with constant process parameters such as laser power and scan speed. However, the exposure strategy and the part geometry influence the resulting melt pool. To compensate for these influences, closed-loop process control based on the thermal emission can be used. To enable closed-loop process control via pyrometry, an analysis of the measured thermal emissions is necessary, as the measurement spot of the pyrometry is larger than the melt pool. This paper investigates how accurately the pyrometrically measured thermal emission can be predicted by a thermal simulation and how large the influence of the neighboring vectors is on the pyrometrically measured thermal emission. For this purpose, a thermal simulation model is first developed that takes into account the immediate environment (approx. 1 mm) of a single scan vector. Subsequently, a model is developed that predicts the thermal emission within the measuring spot of the pyrometer based on the simulated temperature. The results show that the thermal emission prediction model provides an accurate prediction with an average deviation of approx. 4.5 %. The evaluation of the influence of neighboring vectors also shows that in areas of small vectors the pyrometrically measured thermal emission is caused by neighboring vectors by approx. 35 %. In further investigations, the influence of the neighboring vectors in the setpoint of the controller is to be considered.