Assessing and comparing influencing factors of residual stresses in selective laser melting using a novel analysis method

TLDR

Selective laser melting generates large, rapid temperature fluctuations that induce unwanted thermal stresses. The study develops a simple, fast bridge curvature method to assess thermal stresses. The bridge curvature method, developed for rapid thermal stress assessment, evaluates the influence of scan patterns, laser parameters, and process changes on residual stresses, with statistical analysis confirming its repeatability and uncertainty quantification. Experiments and literature show that reducing temperature gradients via short scan vectors and base‑plate preheating lowers thermal stresses, that orienting scan vectors optimally reduces stresses in specific directions, and that the bridge curvature method is reliable.

Abstract

During selective laser melting, the irradiated material experiences large temperature fluctuations in a short time which causes unwanted thermal stresses. In order to assess thermal stresses in a simple and fast way, a new pragmatic method is developed, namely the bridge curvature method. The bridge curvature method is used to assess and qualitatively compare the influence of different laser scan patterns, laser parameter settings and more fundamental process changes on residual stresses. The results from the experiments, as well as the findings from literature, lead to two general conclusions: changes that reduce the high temperature gradient, like using short scan vectors and preheating of the base plate, reduce the thermal stresses. And, thermal stresses in a particular direction can be reduced by optimal choice of the orientation of scan vectors. The experiments indicate the reliability of the bridge curvature method. Statistical analysis is used to check the repeatability of the method and to quantify the uncertainties during measurement.