Thermo-mechanical modelling of wire-fed electron beam additive manufacturing

Electron beam additive manufacturing (EBAM) involves melting and solidification of a metal wire feedstock using an electron beam source to form the part geometry in a layer by layer manner. Although research on laser-based techniques have been more widely reported for AM processing of metal components, EBAM provides valuable advantages such as higher energy efficiency, faster build rate and material versatility (conductive, reflective, refractive). However, EBAM is still not broadly applied and remains limited to cost-intensive parts due to process development complexity associated with parametric optimization and toolpath planning. Thus, the necessary trial-and-error iterative process developments become cost-/time-intensive. So, reliable and efficient models are of utmost importance for furthering development and diversifying process applications.

The primary objective of this research was to develop a 3-dimensional transient fully coupled temperature-displacement finite element model specifically designed for EBAM of Ti-6Al-4V to understand metallurgical and mechanical aspects of the process. Multiple Ti-6Al-4V samples were also fabricated to compare and validate the simulation results. Thermocouple measurements were recorded in order to validate the simulated thermal cycles. The microstructure of the samples was compared with the simulated cooling rates and solidification maps. The model proved to be extremely successful for predicting the cooling rates, grain morphology and the microstructure. Simulated and measured residual stresses and distortion profiles were in good agreement with each other. Tensile residual stresses were observed on the deposit and heat affected zone, while compressive stresses were observed in the core of the substrate. The highest tensile residual stresses observed on the deposit was approximately 1.0 σ_yield. Highest distortion on the substrate was approximately 0.2 mm.