3D in-situ based methodology for optimizing the mechanical performance of selective laser melted aluminium alloys

Additive Manufacturing (AM), also known as 3D printing, is a common term used to describe the technology in which three-dimensional (3D) objects are fabricated by successive layers of material. The UK has been at the forefront of global innovation in AM and has also set up applications for commercialisation of this technology. While AM has been commonly employed for producing prototypes and tooling for decades, UK manufacturing industry has more recently been making revolution by using this technology for end-use products in various key sectors due to its economic and technical benefits in comparison with traditional manufacturing techniques. Once the current barrier to adoption of AM (i.e., quality, uncertainty of the final component and expertise) has been addressed, it is expected that this new emerging time-efficient AM technology has obvious capability to considerably boost UK economic production.

Selective laser melting (SLM) is one of the most promising metal AM methods where 3D components are fabricated by using a high-energy laser beam to fuse the pre-deposited metal powder. The use of SLM has been progressively increasing in a number of UK industrial sectors (i.e., aerospace, automotive, medical, oil & gas, marine and defence etc.) owing to its capability to produce near-net shape complex components from a CAD model and hence offering robust design flexibility without the constraints of conventional manufacturing methods that require a series of manufacturing processes, more material consumption, higher cost and energy. For manufacturing industry that targets to fabricate their products rapidly and access to wider purchaser markets, SLM appears to be an ideal route for their businesses if the inter-related relationships between process parameters and their ultimate effect on the structural integrity and performance has been established.

SLM is prevalently used to build in a range of metallic materials including stainless steel, titanium, nickel and aluminium alloys. Unlike the other alloys, manufacturing aluminium alloys by SLM involves more complexities due to being their high reflectivity and thermal conductivity which contribute to stimulate porosity in manufactured parts. Hence, there is presently a lack of understanding about the effect of SLM process parameters on microstructure and material performance in aluminium alloys. Determining such unknown relationships are an essentially important engineering mission that presently represents a major barrier to widespread usage of SLM processed aluminium alloys.

The overall aim of this First Grant proposal is to develop a robust methodology to optimize the manufacture of aluminium alloy components using selective laser melting. In achieving this, the combined use of X-ray microcomputed tomography with an in-situ microtensile testing stage (allowing observations of the 3D in-situ deformation) will be employed to investigate the impact of process parameters on porosity, material properties and failure behaviour. In addition, an experimentally based porous plasticity finite element model will be developed to understand the effect of void size and shape on deformation behaviour.

This project will provide a method to optimize the manufacture of aluminium alloy components produced using selective laser melting (SLM), a metal additive manufacturing (3D printing) method. The possible benefits of this research proposal to society beyond the academic world is projected to be high as the methodology developed in this study can be widened to include a range of additive manufactured metallic materials such as steel, titanium and nickel alloys.

There having been continuous investment and innovation in producing SLMed parts by companies and the UK funding agencies, the use of SLM of aluminium alloys (similar to the other SLMed materials) has been progressively increasing in a number of UK industrial sectors. The outcomes of the research will assist UK and worldwide organizations in adopting SLMed aluminium alloys for next generation designs.

Particular benefits will be to: better understand the impact of process parameters on mechanical performance and quality assurance; determine limits for acceptable void sizes and shapes for designs; obtain key material properties to be standardized; provide a better understating of the effect of residual stresses on the material properties; lower development cost and time, gain confidence in design and reduce material wastage. The more widespread uses of SLM will allow decreases in carbon dioxide footprint associated with manufacturing.

The proposal has been developed based on series of discussions with the collaborators (e.g., Lloyd's Register (LR), The Welding Institute (TWI)) and project partners (the Advanced Materials & Processing Laboratory (AMPLab) at the University of Birmingham, the Manufacturing Technology Centre (MTC) and the Los Alamos National Lab (LANL)), certifying that directions of the proposed work will address their issues. The MTC and AMPLab will benefit from the outcomes of the project by correlating the process parameters with the volumetric defect formation and their effect on failure. The experimental results obtained will provide a detailed database for the LANL researchers working in additive manufacturing.

Potential wider beneficiaries in the UK and worldwide working with SLM will be sought through the existing collaborators and partners. Arranged meetings and discussions with industrialists and policy-makers by means of the MTC will enable the outcomes of the project to be exploited broadly. Any datasets produced in this project will be made available to other researchers via PURE which is the university's repository used to comply with EPSRC requirements. A budget for data storage is allocated and the presence of such data will be publicized through the project website, conference disseminations and Dr Kartal's social media accounts (i.e. LinkedIn and ResearchGate). This will help wider beneficiaries to accesses data obtained from projects.

This project will train a PDRA to develop transferable skills in materials modelling, characterization and testing which can be applied to a broad range of materials.