A 3D Finite Element Model Studying the Transient Analysis of An Electron Beam Welded Aerospace Compressor Disc

Titanium-based alloys are used extensively in modern aero-engines, to produce a number of critical components in the fan and compressor regions, on account of their excellent properties. However, these structural components need high integrity welding methods. Electron beam welding is still one of the most commonly-used welding methods within the aerospace industry to date. The compressor drum component is fabricated by electron beam welding a number of compressor discs together. However, distortion will occur during any welding process, due to the thermal gradients and residual stresses induced by the welding process, requiring further machining processes to rectify. Whilst electron beam welding generally produces smaller weld distortion than other weld methods, it is still significant. It is therefore important to understand the driving mechanisms behind the residual stress and distortion formation.

In this research, numerical modelling was used to investigate the causes of distortion and residual stress, for a multi-pass compressor disc weld. Whilst numerical weld simulation methods have been widely used previously, this was generally performed on simple plate weld geometry, due to computational power limitations. However, this work uses representative compressor disc geometry to perform a 3D transient weld simulation calculation, using the FE code Sysweld. The heating source of the electron beam welding process has been approximated using a double ellipsoid function. An analytic model for this heating function has been considered and results have been compared to the analytic predictions.

The behaviour of the compressor disc during welding was validated by placing laser measurement equipment in to the weld chamber and recording the transient distortion of the disc. Measured transient results were compared to modelled predictions of distortion. The model demonstrated that it was capable of predicting both the transient and final distortion modes accurately, and highlighted a transient deformation mode during welding that was previously unknown.