Residual stress and distortion modeling of electron beam direct manufacturing Ti-6Al-4V

Abstract

In this work, a finite element model is developed for predicting the thermo-mechanical response of Ti-6Al-4V during electron beam deposition. A three-dimensional thermo-elasto-plastic analysis is performed to model distortion and residual stress in the workpiece and experimental in situ temperature, and distortion measurements are performed during the deposition of a single-bead-wide, 16-layer-high wall built for model validation. Post-process blind hole–drilling residual stress measurements are also performed. Both the in situ distortion and post-process residual stress measurements suggest that stress relaxation occurs during the deposition of Ti-6Al-4V. A method of accounting for such stress relaxation in thermo-elasto-plastic simulations is proposed where both stress and plastic strain are reset to 0, when the temperature exceeds a prescribed stress relaxation temperature. Inverse simulation is used to determine the values of the absorption efficiency and the emissivity of electron beam–deposited, wire-fed Ti-6Al-4V, as well as the appropriate stress relaxation temperature.

Metal additive-manufacturing process and residual stress modeling

“…They are computed separately, presenting a one-way coupling of the thermo-mechanical computation. The transient temperature field is stored at every time step and is then applied as a thermal load in the quasi-static thermo-mechanical analysis [56][57][58]. As shown in Fig.…”

“…In spite of advanced numerical tools (adaptive remeshing, Hamilton-Jacobi resolution algorithm among others), the finest of inherent numerical parameters make the approach too complex for the modeling of large and complex AM. In comparison, the Lagrangian framework enables easy handling of an activation/deactivation element technique, named differently by the authors according to the FE codes used: activation element method with Sysweld® [58] or MSC Marc® [64], element birth technique with Abaqus® [55], and quiet or inactive element method with Cubic® [56]. All these methods can be classified into two categories, the "quiet" and the "inactive" element methods [59].…”

“…Similarly, electron beams are characterized by a Gaussian distributed source [51]. Hence, a very common approach is the definition of a Gaussian or Goldak [66] heat source scaled by an appropriate absorption efficiency factor η representing process optical losses [26,29,56,[67][68][69]. In spite of the much simpler energy equation considered (compare Eqs.…”

“…(17), ϵ the emissivity, σ the Stefan-Boltzmann constant, and T S and T ∞ are the surface temperature and the far field temperature. The emissivity value will depend both on the process and the material and can be characterized both experimentally and numerically [56].…”

Macroscopic simulation and experimental measurement of melt pool characteristics in selective electron beam melting of Ti-6Al-4V

“…For this purpose, the finite element method (FEM) seems to be more appropriate since it considers the powder material as a continuum. This method is applied in [11,18,30] to simulate the mechanical stresses and warpage of the re-solidified Ti-6Al-4V material in the SEBM process. The simulation of the temperature distribution with FEM in the SEBM process is conducted in [32,33] to analyze the preheating of the metallic powder material and to study the impact of scan speed and beam power on the temperature distribution and the part quality.…”