Further Development of a Predictive Tool for Managing Distortion in Electron Beam Direct Manufacturing

Electron Beam Direct Manufacturing (EBDM) is a large-scale, high deposition rate Additive Manufacturing process in which a 3D CAD model of the part is used for deposition path planning to build a near-net shape part in a layer upon layer manner. EBDM introduces metal wire feedstock into a molten pool that is created and sustained using a focused electron beam in a vacuum environment. Residual stress and shape distortion are inherent features of EBDM due to the high thermal gradients associated with the high deposition rates. Uncontrolled distortion can cause deviation from tolerances for dimensions of built parts and lead to high rejection rates. As a result, parts require stress relief heat treatments during and/or after deposition which can add to costs. Accurate predictive models of residual stress and distortion are of high interest as crucial tools in the development of active methods for distortion control and management. In this paper we describe the creation of such a predictive tool based on finite element methods. We apply this tool to predict post-build residual stress and distortion in a T-shaped Ti-6Al-4V part built using different build deposition paths. Predicted results are compared with experimental residual stress and distortion data for model calibration and validation. The results provide an understanding of the evolution of temperature, deformation and stress during and after completion of the build. We describe the application of our developed predictive tool to perform a series of virtual Design of Experiments (DoE) to investigate the effects of various tool paths, process parameters and thermal boundary conditions on the post-manufacturing part distortion and residual stress. Some selected results of virtual DoE will be presented that highlight the importance of thermal boundary conditions in this process.