A Predictive Tool for Managing Distortion in Electron Beam Direct Manufacturing

Electron Beam Direct Manufacturing (EBDM) is a rapid metal deposition process that works efficiently with a variety of weldable alloys. A 3D CAD model of the part is used for deposition path planning to build a neat-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.  As a result, parts require stress relief heat treatments during and/or after deposition which can add to costs. Uncontrolled distortion can cause deviation from tolerances for dimensions of built parts and lead to high rejection rates. 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 to manage the deposition process to produce a good part the first time in as close to a distortion- free state as possible. 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. Model results provide an understanding of the evolution of temperature, deformation and stress in the built part during and after additive manufacturing. Comparison with experimental measurements shows good agreement for two different build scenarios.