Investigations into effect of weld-deposition pattern on residual stress evolution for metallic additive manufacturing

Twin-wire welding based additive manufacturing (TWAM) is a novel additive manufacturing (AM) process for creating metallic objects using gas metal arc welding (GMAW). The twin-wire welding, apart from offering higher deposition rates, also makes it possible to create gradient objects by the use of dissimilar filler wires. However, there is necessity to manage the thermal stresses while depositing multiple layers on the substrate plate; this is one of the major challenges to be addressed. With the help of finite element analysis (FEA) and experimental methods, this paper studies the effect of area-filling paths on the residual stresses developed during weld-deposition. Three area-filling patterns viz. raster, spiral-in, and spiral-out were chosen. FEA for these three patterns was done using ANSYS Mechanical APDL. The twin-wire arc weld-deposition was modeled as a set of two moving heat sources separated at a fixed distance. The deposited material was activated by element birth method once the arc passes over a location, simulating the weld material deposition. The temperature gradient induced residual stresses produced during and post material deposition was predicted using passively coupled thermo-mechanical simulations. For validation, the weld-deposition experiments were done using twin-wire GMAW welding set up, and residual stresses were measured using an X-ray diffraction (XRD) system. Temperature distribution plays a critical role in the evolution of the residual stresses during weld-deposition. Hence, two metrics viz., thermal mismatch profile, and secant-temperature rate were introduced to quantify preheat and conduction. It was observed that raster patterns had the lowest thermal mismatch and secant rates resulting in the lowest residual stresses of the three area-fill patterns. Residual stresses from experiments has reasonable correlation with those obtained from elastic-FE simulations in order as well as trend and provide valuable insights into the evolution of the stresses for various area-fill patterns in TWAM.