To demonstrate the future potential of the process Wire-Arc Additive Manufacturing (WAAM), it is important to investigative and quantify its sustainability in comparison to conventional manufacturing techniques by taking a life cycle perspective. Technical University of Denmark is the lead partner responsible for this part in the European project called Grade2XL.
There is agreement among all the countries of the world that we need to become more sustainable. The Paris Agreement on climate change provide the basis for an urgent need of global response to the threat of climate change and the 2030 Agenda for Sustainable Development address sustainability more broadly. A core aim is to increase the ability of countries to reduce and tackle the impacts of climate change, by supporting development and the most vulnerable countries in joining the global effort. To achieve this aim it is important to assess the sustainability impact of anthropogenic activities and technologies in order to understand what contributes most and how to reduce the impacts. Therefore, to do that for WAAM, that is an emerging technology still under development and optimization, two decision-support tools are used to quantify its environmental and economic sustainability impact: Life Cycle Assessment (LCA) and Life Cycle Costing (LCC).
But, why is it important to apply LCA and LCC on WAAM to investigate its sustainability?
Many claim several benefits of additive manufacturing compared to conventional manufacturing. For instance, reduction of waste, energy or fuel consumption during use of product and reduction of cost due to optimization of shapes, lightweight design, and shorter time from ordering a product until you receive it. However, to what extent are these claims valid? Which quantifiable trade-offs are important? LCA and LCC both take a life cycle thinking perspective; this means that all the processes relative to a product or activity from the raw material production to the disposal of it are included in the assessment (see Figure 1).
Figure 1: schematic representation of Life Cycle Assessment (LCA).
A further advantage of the life cycle thinking perspective is the holistic perspective by the comprehensive coverage of environmental issues. Rather than focusing exclusively on climate change, which currently receives generally most attention, LCA covers a broad range of environmental issues. For instance, it usually includes among others: freshwater use, land occupation and transformation, toxic impacts on human health, and depletion of non-renewable resources. In this way the major trade-offs between impacts are addressed and problem shifting can be avoided.
Sustainability comparison of Grade2XL demonstrators manufactured with WAAM
For all the reasons previously mentioned, LCA and LCC frameworks are currently used to compare the sustainability of all Grade2XL demonstrators to the same objects fabricated with the traditional manufacturing processes. Figure 2 below represents a generic overview of all life cycle processes considered for Grade2XL demonstrators produced with WAAM.
Figure 2: System boundaries considered in LCA and LCC models of Grade2XL products
The processes illustrated above are included in the LCA and LCC models, which provide the environmental and economic impact of each Grade2XL demonstrators, respectively. For instance, Figure 3 illustrates the preliminary results of the LCA of the repair of a forging die produced by Kuznia Jawor with WAAM and conventional welding for three selected impact categories, namely Global warming, Human carcinogenic toxicity, and Mineral resource scarcity.
Figure 3: Internally normalized impact score for Kuznia Jawor forging die repair by conventional welding (columns on the left) and WAAM (columns on the right) with process contribution analysis for three-selected impact categories.
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these diagrams enable to see the quite visible better environmental performance of WAAM over conventional processes. It is also clear that, in general, the steel wires and the energy used during repair are the major contributors to both type of manufacturing processes. Therefore, Wire-Arc Additive Manufacturing showed potential in terms of sustainability, which should be further investigate for different products and applications.
About the authors:
Associate Prof. Stig Irving Olsen (siol@dtu.dk) and PhD student Valentina Pusateri (valpu@dtu.dk) are, respectively, Prof. and PhD student in the Quantitative Sustainability Assessment research group at the Technical University of Denmark (DTU), Denmark. Under the supervision of Prof. Peter Fankte (pefan@dtu.dk), the group counts about 33 researchers.
The group's research originates from the life cycle area, e.g. Life Cycle Assessment (LCA), and focuses on developing and improving methodologies to evaluate the sustainability of complex systems. Examples of areas of interest are the evaluation of circular economy, the development of Site Dependent Impact Assessments, Absolute Sustainability Assessments, and toxicity estimation (USEtox).
All of those assessments provide concrete decision-support tools that can be consulted by managers, product developers, and decision-makers in all types of public and private organizations.
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