Determination of the die profile for the investment casting of aerofoil-shaped turbine blades using the finite-element method

Turbine blades and vanes used in aircraft engines are expected to conform to close dimensional tolerances, but super-alloy blade material cannot be machined easily. Although investment casting is an ideal route for producing such net-shape components, it calls for an accurate determination of the casting-die profile. This investigation outlines a simple finite-element methodology (FEM) for obtaining the die profile, which takes into account the various shrinkages involved in the casting process. The shrinkages are lumped into a single stress-free strain tensor and the FEM-based numerical computation is performed, treating the shrinkage strain as an initial strain. A fictitious sponge-like layer of elements is incorporated at the boundary of the aerofoil cross-section in order to impose the necessary kinematic constraints to restrain rigid-body modes. The applicability of this method is validated using experimental data.