Wire Arc Additive Manufacturing (WAAM) has redefined manufacturing norms through its innovative capabilities. However, the environmental impact of this technology is increasingly under scrutiny. This article delves into the environmental consequences of various recycling scenarios within Wire Arc Additive Manufacturing, utilizing Life Cycle Assessment (LCA) as a framework to evaluate their sustainability.
Environmental Context of Wire Arc Additive Manufacturing
Wire Arc Additive Manufacturing is lauded for its potential to reduce material waste and energy consumption compared to traditional manufacturing methods. Its applications across industries provide unprecedented opportunities for environmentally friendly production.
LCA as a Decision-Making Tool
Life Cycle Assessment offers a comprehensive approach to assessing environmental impacts. It considers the entire lifecycle of a product, from raw material extraction to end-of-life treatment. By employing LCA, we can gain insights into the overall environmental impacts of different recycling strategies in Wire Arc Additive Manufacturing.
Focus on Recycling Strategies
a. Closed-Loop Recycling
The closed-loop approach involves recycling post-production waste and failed print models within the same manufacturing cycle. LCA assists in evaluating the environmental benefits achieved through reduced raw material extraction and waste generation, considering the energy inputs and emissions associated with recycling processes.
b. Open-Loop Recycling
In an open-loop context discarded printed objects or materials are recycled for secondary production of resources with lower quality than the original one, or a totally different product line. Thus, this often leads to material down-cycling. LCA helps weigh the advantages of extended material life against energy-intensive reprocessing and potential emissions.
Environmental Impact Assessment through LCA
a. Energy Intensity
LCA allows us to compare energy consumption between different recycling scenarios. Generally, recycling is much less energy intensive than virginal material production. For instance, the energy required to manufacture new aluminum is twenty times greater than the energy needed to recycle aluminum waste [1].
b. Emissions Analysis
LCA provides insights into the emissions profiles of different recycling strategies. Due to reduced material production, closed- and open-loop recycling might lead to lower emissions in comparison to products manufactured only with primary resources.
c. Resource Efficiency
LCA quantifies the benefits derived from resource conservation achieved through recycling. Both recycling strategies aligns with circular economy principles. However, closed-loop recycling promotes prolonged resource utilization and keep the same material quality, contrarily to open-loop, which often has lower recovery efficiency.
Case Study using EDF holding ring
Three scenarios using the WAAM holding ring in the Grade2XL project were calculated with ReCiPe2016 (H) midpoint life cycle impact assessment (LCIA) methodology. Table 1 shows the recycling rates of three scenarios of the WAAM holding ring retrieved from the literature [2]–[5]. In this context, 'Secondary raw materials' are recycled materials that can be used in manufacturing processes instead of or alongside virgin raw materials. Those originate from the same product in closed-loop recycling conditions or other sources if an open-loop approach is taken. ‘Recycled new scrap’ is the scrap generated from processing and manufacturing processes (e.g., machining chips from holding ring fabrication). Particularly, in scenario S.3 it is possible to notice that the recycled new scrap from production of first holding ring can partially substitute virgin material input in a new holding ring following a closed-loop approach. Additionally, the End-of-Life of the holding ring is assumed to follow an open-loop recycling strategy in which CuAl8, steel 410 and 355 are down-cycled into low-alloyed steel.
Scenarios | S.1 | S.2 | S.3 |
Description | 1 piece of WAAM holding ring | 1 piece of WAAM holding ring with secondary material input | 1 piece of WAAM holding ring with secondary material input and recycled new scrap |
End-of-Life Recycling Rate | Low-alloyed steel 53% [3] | Low-alloyed steel 53% [3] | Low-alloyed steel 53% [3] |
Secondary Material Input | 0% | Steel (410) 52% [5]Steel (S460) 42% [5] CuAl8 33% [4] | Steel (410) 52% [5]Steel (S460) 42% [5] CuAl8 33% [4] |
Recycled new scrap | 0% | 0% | Steel (410) 46% [2]Steel (S460) 46% [2]CuAl8 45% [2] |
Table 1: Recycling rate of three scenarios of WAAM holding ring.
Table 2 reports that S.1 has the highest impact score of all scenarios. This is in accordance with the results of Figure 1, which illustrate that with the introduction of a second material input and the recycling of new scrap, a large amount of the environmental impact can be reduced. For instance, in S.3 the impact score in “Global warming” is reduced of approximately one third the value of the first scenario.
Impact category | S.1 | S.2 | S.3 |
Global warming | 5.21E+03 | 3.33E+03 | 3.33E+03 |
Stratospheric ozone depletion | 1.77E-03 | 1.31E-03 | 1.31E-03 |
Ionizing radiation | 9.40E+02 | 8.56E+02 | 8.56E+02 |
Ozone formation, Human health | 1.31E+01 | 8.07E+00 | 8.05E+00 |
Fine particulate matter formation | 1.12E+01 | 5.22E+00 | 5.22E+00 |
Ozone formation, Terrestrial ecosystems | 1.38E+01 | 8.48E+00 | 8.46E+00 |
Terrestrial acidification | 2.04E+01 | 1.20E+01 | 1.20E+01 |
Freshwater eutrophication | 3.97E+00 | 2.93E+00 | 2.93E+00 |
Marine eutrophication | 3.77E-01 | 3.12E-01 | 3.12E-01 |
Terrestrial ecotoxicity | 1.56E+05 | 1.00E+05 | 1.00E+05 |
Freshwater ecotoxicity | 1.53E+03 | 1.49E+03 | 9.73E+02 |
Marine ecotoxicity | 1.98E+03 | 1.88E+03 | 1.26E+03 |
Human carcinogenic toxicity | 3.43E+03 | 5.94E+02 | 5.89E+02 |
Human non-carcinogenic toxicity | 1.50E+04 | 9.82E+03 | 9.71E+03 |
Land use | 5.34E+02 | 4.77E+02 | 4.77E+02 |
Mineral resource scarcity | 2.13E+02 | 6.60E+01 | 6.60E+01 |
Fossil resource scarcity | 1.31E+03 | 8.80E+02 | 8.79E+02 |
Water consumption | 5.55E+01 | 4.20E+01 | 4.20E+01 |
Table 2: Impact results of three recycling scenarios of WAAM holding ring calculated with ReCiPe2016 (H) midpoint life cycle impact assessment (LCIA) methodology.
Figure 1: Characterized results of WAAM holding ring in three scenarios calculated with ReCiPe2016 (H) midpoint life cycle impact assessment (LCIA) methodology.
Challenges, Gaps, and Future Directions
a. Data Availability and Quality
LCA's accuracy depends on reliable data. Future efforts should focus on gathering detailed data for Wire Arc Additive Manufacturing processes and recycling scenarios.
b. Complexity of Material Streams
The diversity of materials employed in multi-material Wire Arc Additive Manufacturing poses challenges for recycling. LCA can help understand how different materials affect the environmental performance of each recycling strategy and avoid burden-shifting.
Conclusive Insight
By employing a Life Cycle Assessment, we can understand the environmental impacts of various recycling strategies in Wire Arc Additive Manufacturing. These insights can guide decision-making and steer the industry toward more sustainable practices.
In conclusion, utilizing Life Cycle Assessment to evaluate the environmental impact of diverse recycling strategies enhances our comprehension of their sustainability in Wire Arc Additive Manufacturing. As Wire Arc Additive Manufacturing continues to evolve, recycling approaches guided by LCA have the potential to shape a greener and more efficient future for manufacturing.
Authors
DTU
References
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[2] U. N. M. I. Center, “Mineral Commodity Summaries 2020,” 2020.
[3] J. Oda, K. Akimoto, and T. Tomoda, “Long-term global availability of steel scrap,” Resources, Conservation and Recycling, vol. 81, pp. 81–91, 2013, doi: 10.1016/j.resconrec.2013.10.002.
[4] T. Henckens, “Scarce mineral resources: Extraction, consumption and limits of sustainability,” Resources, Conservation and Recycling, vol. 169, Jun. 2021, doi: 10.1016/j.resconrec.2021.105511.
[5] P. Wang et al., “Efficiency stagnation in global steel production urges joint supply- and demand-side mitigation efforts,” Nature Communications, vol. 12, no. 1, Dec. 2021, doi: 10.1038/s41467-021-22245-6.