Life cycle cost-driven design for additive manufacturing : the frontier to sustainable manufacturing in laser-based powder bed fusion

Abstract

Additive manufacturing (AM) is a manufacturing method that creates components in a layer-wise manner. Laser-based powder bed fusion (L-PBF) is one of the most used AM subcategories to manufacture metal components, referred to in this thesis as metal AM/LPBF. The effective use of AM offers a trifactor of part complexity, simplified manufacturing and improved performance with digital tools to the achievement of resource-efficient, cost-effective, durable components as well as waste and emissions reductions. Currently, this manufacturing method can be used to manufacture optimised, lightweight and multi-material components. AM has inherent limitations that need conscious designing and planning to be able to offer the expected benefits. The design system (designing and manufacturing) can either positively or negatively influence the integrity of the final component. Critical consideration of these is often required to avoid unwanted defects that may influence the performance of the final components. This often increases labour intensiveness, digital tools, time and consequent increase in costs. The practice of sustainable manufacturing focuses on product design that has the least negative environmental impact through economically-sound processes that support waste reduction and long-term cycle usage goals, termed circular economy, (CE). The question then is how can metal AM/L-PBF enhance sustainability and the CE to meet the goals of sustainable manufacturing? How can the benefits offered by metal AM/L-PBF be evaluated from a life cycle (LC) perspective?

The principal motivation of this thesis was to offer a critical fact-based contribution that is free from subjective or commercial considerations to support the sustainability arguments of metal AM/L-PBF. The main aim of the thesis was to identify the hotspots of metal AM/L-PBF that could be optimised to improve sustainable practice. The objective of this thesis was to theoretically and experimentally study how metal L-PBF enhances the achievement of sustainability and the CE through energy-efficient, materialefficient processing and the minimisation of waste and emissions.

Firstly, this thesis includes investigatory studies on the environmental and economic aspects of sustainability of metal AM/L-PBF through life cycle inventory (LCI) and supply chain analyses. A preliminary review of the social aspect of sustainability is generally presented. Secondly, the thesis incorporates a practical investigation of the effect of process parameters in metal L-PBF on melt pool formation and spatial resolution of finely-featured metal components. Thirdly, the thesis uses reviews and case studies to assess the influence of simulation-driven design for additive manufacturing (simulationdriven DfAM) on the life cycle cost (LCC). Fourthly, the thesis investigates the flexibility and suitability of manufacturing intricate and multi-material electrochemical separation units using reviewed data. The review focused on how metal L-PBF manufactured electrodes improved performance and cost-efficiency. The final part of the thesis was carried out as discussions with industrial representatives on the benefits/limitations of metal L-PBF to identify practical strategic approaches to harness the identified benefits/limitations of metal AM/L-PBF. The discussion aimed to modify an initially created LCC-driven model in publication 4 and to highlight its suitability as a useful tool to support decision-making in industries to the adoption of metal AM/L-PBF. Business process modelling, (value chain analysis (VCA); strength, weakness, opportunities and threat (SWOT) models) were used to identify the best adoption plan to maximise value creation from idea generation to end-of-life (EOL).

The results of this thesis showed that metal L-PBF lessens the need and distance of transportation thereby reduces transport-related emissions. Metal L-PBF reduces the need for spare parts and inventory with on-demand manufacturing which reduces cost and waste. Again, this thesis showed that L-PBF allows optimised designs with intricate internal and outer geometries to be manufactured in resource-efficient and cost-efficient manner. The results of the experimental study on the process parameters showed that optimising process parameter values directly enhances part qualify and reduces defects. The potential to control the process efficiency is one way by which raw material and high energy utilisations can be improved in metal L-PBF. The results of the LCC studies identified key drivers to cost and how they could be optimised in metal L-PBF using digital simulations and DfAM rules, referred to in this thesis as LCC-driven DfAM. The simulation-driven DfAM study showed how digital tools allow for the acceleration of sustainable products via product optimisation while maintaining cost-effectiveness and waste reductions. The results of the review on metal L-PBF manufactured separation units for electrochemical application showed that the method made it possible to create intricate structures such as lattices and conformal flow channels. This benefit offered the possibility of improved functional multi-metal separation units.

The main outcome of this thesis is the first-ever integrated LCC-driven DfAM model that can be used as a decision-making tool to the adoption of metal AM/L-PBF towards high performing, resource efficiency, cost-efficient components. The model can be used in industries to identify best practices that can help create optimised metal components without adding to costs. The model highlights the phases in which the greatest cost reductions are achievable from the design, manufacturing, use and EOL phases. The thesis shows that metal AM/L-PBF is constantly developing. These include innovations and new solutions to improve productivity, resource efficiency as well as the reduction of waste and emissions. Metal AM/L-PBF can enhance resource consumption, reduce costs, drive innovations in sustainable business practice and offer means of competitiveness. The main conclusion of this thesis is that metal L-PBF offers means to optimised product design, possibilities of reducing raw material usage, operational costs, waste and emissions.

Plans to experimentally compare the performance of L-PBF and CNC-machining manufactured components and the effect of build platform utilisation on specific energy consumption (SEC) in L-PBF did not materialise due to a lack of funds. The thesis identified that ongoing sustainability studies of metal AM/L-PBF do not include the entire aspects of sustainability and value chain. For example, the social aspects, experimental energy and raw material consumptions during the powder production phases. Further studies could include the limitations of this thesis and provide comprehensive continuity of the subject to overcome some of the identified gaps in literature and process limitations.