Tube Hydroforming of Aerospace Alloys: Experiment and Numerical Simulation

Application of the tube hydroforming (THF) process for the manufacture of aerospace components is relatively new and challenging due to the lower formability limit and high strength of aerospace alloys, such as Inconel 718... [ view full abstract ]

Application of the tube hydroforming (THF) process for the manufacture of aerospace components is relatively new and challenging due to the lower formability limit and high strength of aerospace alloys, such as Inconel 718 (IN718), a nickel-base superalloy that has excellent mechanical properties at high temperatures (~650°C). To understand and address the THF challenges of this material in a cost efficient manner, development of accurate finite element models (FEMs) is required. A reliable material model with the capability of predicting the hydroformability limits is a key element in simulating accurately the process. The material parameters for IN718 tubes with a thickness of 0.9 mm and 1.2 mm were obtained using free expansion testing as the material characterization method. Then, the material models were implemented in the FEM of two generic shapes that are commonly applied in aero-engine components, round to V (similar to an airfoil) and round to square. A 3D dynamic finite element solver, Ls-Dyna, was utilized for the simulations. In addition, to validate the simulations THF experiments of the round to square and round to V shapes were performed on a fully equipped 1000 ton hydroforming press in the Aerospace division of the National Research Council Canada. Specifically, the strain distribution at critical regions and the tube expansion at the sharp corners were measured from experiments and compared to the simulation results. For both tube thicknesses, the simulation results were reasonably close to the experimental data.