Effects of Thermal Gradient Control on Residual Stress and Distortion in DED-LB/M Fabricated Parts

Additive manufacturing has emerged as a revolutionary process in industry to produce geometrically complex parts by precisely layering deposited material. Although offering great promise, the nature of the process involves repetitive thermal cycling and steep thermal gradients, presenting challenges as they are the root cause of residual stress formation. This study aims to reduce the formation of residual stresses by reducing the thermal gradients through laser reheating and preheating strategies. A rapid screening approach based on an in-situ implemented digital image correlation (DIC) setup is used to quantify distortion in thin walls produced by laser-based directed energy deposition. First, thin pre-walls were processed in AISI 316L stainless steel and subsequently heat-treated to minimize the existing residual stresses, serving as the reference state for the DIC analysis. Fifty additional layers were then added on top of the pre-wall using different processing conditions. The tests revealed that distortion is strongly influenced by thermal cycles and strain direction. Build-plate preheating effectively reduces strain in both directions, while additional laser passes between layers have a direction-dependent impact. The feasibility of the in-situ DIC setup as a rapid screening tool was also confirmed.