Thermal Numerical Simulations of the Wire-Arc Additive Manufacturing (WAAM) Process

Wire Arc Additive Manufacturing (WAAM) is a Direct Energy Deposition additive manufacturing process that uses well-established welding technology. It consists of a sequential deposition of weld passes and layers to form bases of engineering components later machined to the final shape. The WAAM process is characterised by high heat input, high deposition rate, high surface roughness and the anisotropy of material properties. The high heat input leads to significant development of distortion and residual stresses, which can negatively affect the performance of the final component. At the same time, the high input can lead to the development of a highly textured microstructure. Hence, significant effort is underway to address the development of residual stresses, distortion, or anisotropy in the mechanical properties, which depend on the crystallographic texture. It is, however, impractical, and expensive to test all manufactured components. Therefore, developing validated numerical models is vital to obtain the required information. In this project, the WAAM process has been employed to manufacture multipass, multilayer walls made using 316LSi stainless steel consumable on a 316L substrate at the University of Wollongong. An array of thermocouples on the substrate has been employed to monitor the transient temperature field during the WAAM manufacturing of test specimens. The thermocouple readings are then used to calibrate the thermal model, which will later be used in a phase-field model predicting resulting weld-like microstructure and in a thermo-mechanical model predicting resulting distortion and residual stresses. A microstructural analysis and the assessment of the welding-induced residual stresses support the numerical modelling work by providing means of model validation.