Elasto-plastic analysis of thermal stresses in vacuum arc remelting

The vacuum arc remelting (VAR) process has been developed to melt and cast high quality aerospace materials such as titanium alloys. VAR comprises the continuous remelting of a consumable electrode by means of a dc arc under vacuum or a low partial pressure of argon. The molten metal solidifies in a water-cooled copper crucible leading to high cooling rates. This tends to produce large thermal stresses that lead to thermal cracking of ingots. The development of temperature gradients and the resulting thermal stresses during the VAR processes was analyzed using an elasto-plastic material model with temperature dependent thermo-mechanical properties. The analysis includes the development of a finite difference model to determine the thermal history of the ingot, and the use of an analytical solution to solve the elastic model for the thermal stresses. Comprehensive thermal and elasto-plastic solutions were then obtained by using the commercial finite element code ABAQUS.