This project will address the distortion issues currently seen in all EB wire-fed additive layer manufactured test components. These are generally focussed around aerospace components where reduction in material usage and scrap is a hot topic. Current demonstrator parts being built using this process on behalf of TWI Member companies include large high value added builds (for instance >700kg of Ti-6Al-4V wire deposited onto either side of a >2.2m diameter core plate) where distortion control is effected through occasional inter-pass post weld heat treatment, the need for which is based on visual inspection and judgment only. Clearly this style of distortion mitigation carry’s some risk, time and cost implication which cannot be deemed if the process is to find viable industrial scale application. The work proposed here will take a measured analytical approach to solving distortion control issues and work towards industrially viable solutions.
Electron beam (EB) welding and processing generally takes place in a vacuum environment and is normally autogenous in nature, as no additional material is used to locally fill, reinforce or modify the composition of the joint or processed region. Conversely, over the recent years EB additive layer manufacturing has become a research and early stages industrial process. Drivers for development and use of this technology come from sectors such as aerospace where buy-to-fly material usage ratio is paramount due to the increased use of titanium, and the medical sector where the advantages of tailored macro structures in orthopaedic applications are exciting. EB additive layer manufacturing mainly falls into two categories, wire-fed and powder-bed.
In powder-bed processing, commercially known as EB Melting (EBM) and almost exclusively executed using Arcam AB machines, a thin (~50µm) layer of powder is fused using a deflected electron beam, and through repeating the process many times over a period which can be in excess of 100 hours one or more parts are built. Excess powder is then removed from around the parts, for re-use, leaving near to finished components. EBM is generally considered to be competitive with similar laser based processes but is relatively slow and limited in scale in comparison to the wire-fed process where material delivery and build in considerably more rapid.
Distortion predication through modelling and practical validation of mitigation techniques in wire-fed EB additive layer manufacture is the proposed focus of this project. To date control of resultant stresses and distortion in EB wire-fed processing has been very rudimentary from work reported globally and TWIs experiences and know-how in beam-material interaction, melt pool and structural modelling may be applied here to overcome the technical challenges.
The proposed project objectives are as follows:
- Develop effective and representative melt pool and structural FEA models to analyse the EB additive layer manufacturing process
- Explore, theoretically and practically, residual stress mitigation methodologies such as, changes in beam parameters, deposition rates, deposition patterns/sequences, tooling optimisation, use of diffuse EB to effect in-process and/or inter-pass in-chamber stress relieving heat treatments and consider use of non-standard feedstocks
- Address the above objectives with an underlying aim to minimise the development of undesirable microstructural grain growth while working to maintain commercially viable build rates
Relevant Industry Sectors