Sustainable Additive Manufacturing

It is usually energy intensive and expensive to manufacture high performance and high-value materials, such as titanium alloys. The total energy required is typically more than 600 MJ to get each kg to get the semi-finished Ti products (ingots), with more than 36 kg CO2 carbon footprint. During the subsequent manufacturing stage, mainly subtractive manufacturing (SM) process, a large amount of Ti alloy scrap is generated in the form of swarf and chips (can be up to 95% of the initial Ti ingot) which is far greater than that of the final Ti products. High-grade swarf (with lower O and Fe) is usually recycled downstream to the melting stage for ingots which requires about 225MJ/kg to convert it to wire. Or it can be directly converted into billets using solid state processing methods, such as Confrom, Fastforge, and ECAP, however, they have limitations and challenges for titanium alloy, such as low properties, and sever tool wear. Often, they produce semi-finished products, so further processing into wire or powder is required before they can be used in AM, which usually includes another melting step. Studies have shown that a remarkable reduction in energy consumption and CO2 emission can be achieved by using additive manufacturing (AM). Compared to SM, AM improves the material usability efficiency greatly due to the near or very near shape component production with just minor finishing steps required. Using swarf as feedstock in AM will have a major impact on the economics of AM, which can be more expensive than SM, currently restricting its application and concomitant material and emissions savings. A high Buy-to- Fly (BTF) ratio for SM process needs to be significantly greater than the ratio of the wire cost to the semi-finished product cost for AM to be economically justifiable. Using swarf, the cost of AM will be drastically lowered, which will lead to much more widespread adoption of AM, allowing other important gains to be exploited, including material, energy, and emission savings, and component lead times Therefore, our research vision is Novel metal AM processes that utilise recycled swarf as feedstock, enabling a greatly reduced overall energy and CO2 footprint for high-value near-net-shaped components, and facilitating much wider exploitation of near-net-shape AM technologies throughout industry. To deliver this vision, a new method which facilitate a skin and core concept. The outer skin will be deposited using virgin material, with high resolution providing accurate geometric definition and a smooth outer surface, leading to a near-net shape component. The core will be in-filled with pre-processed high-grade swarf, in a solid/ liquid form, which may be mixed with virgin wire to control oxygen levels. In-situ mechanical work will be applied to control defects and improve the material properties. The research will comprise activities on input swarf material characterisation, process development, material output characterisation, process modelling, SAM concept validation, and environmental and economic assessment. SAM will contribute to the 'net-zero' strategy of the UK. It will also provide wider academic impact as many techniques and tools developed will be of direct relevance and great benefit to other AM and related technologies.