A three dimensional transient model for heat transfer and fluid flow of weld pool during electron beam freeform fabrication of Ti-6-Al-4-V alloy

A three-dimensional transient model is proposed to understand the heat transfer and fluid flow behaviors of weld pool during single track electron beam freeform fabrication (EBF3) of Ti-6-Al-4-V alloy. Fluid flows driven by recoil pressure, surface tension and thermal capillary effect are coupling considered in the model. Free surface evolutions of weld pool are incorporated with Level Set method. An improved heat source model is also proposed to simulate the energy interactions between high energy electrons and deposits. Results indicate that there are vigorous fluid flows in the front part of weld pool and thermal-capillary force is the main driven force of fluid flow. Effect of droplet impacting could periodically influence the heat transfer and fluid flow of weld pool. High frequency elliptical scanning of electron beam could decrease the temperature gradient and the magnitude of fluid flow of weld pool. However, beam scanning does not essentially change the flow patterns. A good agreement is obtained between the simulations and experiments.