Fri, 06 November, 2020
A new TWI members’ Core Research Project (CRP) has been launched, bringing together expertise from three different technology groups in TWI to investigate various integrated additive manufacturing strategies, from feedstock customisation to online monitoring techniques, to ensure build consistency and part quality.
Industrial Need
With its high deposition rates and large build envelope, Directed Energy Deposition with Arc, known as Wire and Arc Additive Manufacturing (WAAM), has gained significant interest in various industries. The use of relatively simple arc welding equipment and industrial manipulators enables easy uptake of WAAM for production of metallic parts with medium to low complexity. Material wastage is reduced with near-net shape manufacturing, which may be more cost effective for expensive alloys. Deposition via WAAM has been demonstrated to be viable for various alloys of steels, aluminium, titanium and nickel, and may potentially be used with customised feedstock compositions.
Due to the complex thermal characteristics of WAAM builds, the use of conventional welding wire and fixed process inputs can sometimes result in unfavourable deposition conditions, leading to inconsistencies in the deposited bead geometry and microstructure. These inconsistencies can result in excessive scatter in mechanical properties, which hinders part qualification and limits the use of WAAM parts in safety critical applications. Therefore, there is a need to improve the robustness of the WAAM process by means of developing a fundamental understanding of process factors which influence deposition conditions, and use this knowledge to create feedback control systems to ensure consistent deposited bead geometry. In addition, inconsistencies in the microstructure may also be influenced by composition, and conventional welding consumables may not be optimal for the type of thermal history experienced by a WAAM deposit. Therefore, there is a need to explore the use of feedstock with tailored compositions to reduce microstructural inhomogeneity in WAAM deposits.
Concept
This multidisciplinary CRP project will combine TWI’s expertise in microstructural analysis, non-destructive testing (NDT) and arc welding engineering, to develop a constant output approach to WAAM deposition. This will involve identification of critical deposition parameters that control weld bead geometry and microstructure for a variety of build geometries. In parallel, conventional NDT techniques will be adapted to monitor WAAM deposition, from which key information can be extracted for feedback control. In addition, this project will also draw on a catalogue of over 1500 samples of multi-pass butt welds with varying levels of 16 different alloying elements, to identify the relationships between alloying elements and reheated microstructures. This will be used to develop improved consumable composition for WAAM applications. Finally, the improved consumable will be deposited using the developed constant output approach to demonstrate the potential for high quality WAAM builds.
Key Objectives
- To identify critical deposition parameters and control methods for WAAM to ensure consistent bead cross sections for various geometries.
- To apply existing NDT techniques to monitor the WAAM process and identify key information that can be extracted for feedback control.
- To identify relationships between weld metal alloying additions and reheated microstructure in order to develop improved weld consumable compositions for WAAM applications.
Key Deliverables
- Comprehensive data sets of WAAM process parameters, thermal history, deposited bead geometry and microstructures for various build geometries, which will feed into future process and microstructure modelling efforts.
- Validated methods of applying existing monitoring techniques and analysis tools for WAAM deposition.
- Clear understanding of the effect of alloy element additions on reheated microstructures and identification of consumable compositions optimised for WAAM deposition.