With the rise of electric vehicles, evaluating the environmental impact of each manufacturing process is essential. This article presents an EV battery enclosure welding LCA to compare the sustainability of different joining methods. As automotive manufacturers strive to reduce their carbon footprints, understanding the impact of production processes becomes crucial—especially the joining techniques used in car body assembly. Using Life Cycle Assessment, these impacts can be analyzed in terms of their reduction potential. This article focuses on the example of an all-steel EV battery case joined using several different welding methods.
Life Cycle Assessment (LCA) and Why It Matters in Automotive Welding
Life Cycle Assessment is a systematic method for evaluating the environmental impacts of a product or process throughout its life cycle—from raw material extraction to production, use, and disposal. According to DIN EN ISO 14040 standards, LCA is structured into four main components:
- Goal and Scope Definition: Setting the purpose of the assessment, defining the functional unit, and establishing system boundaries.. In this article, the joining processes were in focus with associated inputs of electricity and filler materials as well as outputs of worn consumables.
- Inventory Analysis: Gathering data on material and energy flows using measurements of electricity and consumables consumption as well as database values for associated material extraction and production impacts
- Impact Assessment: Evaluating potential environmental impacts in different impact categories. This article shows global warming potential and acidification to compare climate change emissions and show the effect of different filler materials on acidification. Other impact categories relevant for joining processes are eutrophication, emission of photooxidants and ozone layer depletion.
- Evaluation: Reviewing findings and providing recommendations regarding the environmental impact of the compared processes
Figure 1: Considered system boundaries of the LCA comprising supply of materials and energy, the joining process and disposal of consumables.
Welding Methods Compared: Processes, Assumptions, and System Boundaries
The assessed joining processes include:
- Laser Remote Welding
- Laser Welding with Wire
- Laser Brazing
- Resistance Spot Weld Bonding (RSW-Bonding) with single- and two-component adhesive
In the context of joining processes for EV battery cases, this LCA aims to compare the environmental impacts of different welding methods on a meter of weld length. The assessment uses both primary and secondary data from literature and established LCA databases. As not all data is available in-detail for welding processes, several simplifications and assumptions are required:
For example, filler wires aresimplified to pure steel or copper wire rather than taking their complex chemical composition into account. Therefore, it is likely that the actual impact of the filler material production is higher than assumed here. For electricity emissions, the German grid mix is used and to compare resistance spot welding and laser beam welding per weld length, 20 resistance spot welds per meter are assumed.
The emissions from the structural materials are not considered, as the same design is used for all welding processes. Second-order effects due to the switching a joining technology, i.e. the material savings due to reduced flange-widths for laser welding, are also not considered. The second-order material saving effects are known to be larger in comparison to the environmental impact of the joining processes and should be optimized together with the choice of joining process. Further information on these effects can be found in this study.
Figure 2 All-steel EV battery case with zones marked for laser beam and resistance spot welding
LCA Results: Emissions Impact by Welding Type in EV Battery Enclosures
The results of the LCA are shown in Figure 3 for the two impact categories Global Warming Potential (i.e. CO2 equivalent emissions) and Acidification Potential (i.e. emission of SO2 equivalent). Main driving factors of emissions are electrical energy, compressed air as well as filler material in the form of steel or copper wire (for laser wire and laser brazing respectively) and adhesive for RSW bonding.
Using the German electrical grid mix, RSW bonding shows the lowest GWP impact. As it does not use any filler material, laser remote welding has the largest potential for CO2 emission reduction, if the electricity generation incorporates more renewable energy .
When analyzing the laser processes, a high idle energy consumption of the laser systems is determined. This is due to the electricity demand of the laser source, cooling and control systems. The consumption only rises slightly, when the lasers are operating. This leads to the conclusion that the overall energy efficiency of laser welding systems can be significantly improved by optimizing “beam-on times” in relation to “idle times”.
In terms of the acidification potential, laser brazing stands out with a far larger impact compared to the other processes, because of the emissions associated with mining and extraction of its copper-based filler material. The wear of copper electrode caps also contributes to this impact category.
Figure 3: Environmental impact of the different welding processes in Global Warming Potential (left) and Acidification (right) per meter of weld length.
What This LCA Reveals About Sustainable Welding for EV Manufacturing
Life Cycle Assessment provides invaluable insights into the environmental impacts of joining processes in the automotive industry. By understanding the implications of material choices and energy consumption, manufacturers can make informed decisions that promote sustainability. Both the effect of electricity consumption and filler materials on the environmental impact of automotive joining processes is discussed in this article. Joining processes are one of the major drivers of an OEM’s emissions with ample potential for optimization through LCA analysis.
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Thanks go to Dr.-Ing Max Biegler, Group Lead, Joining & Coating Technology Fraunhofer Institute for Production Systems and Design Technology IPK |
Source
- Brunner-Schwer, J. Lemke, M. Biegler, T. Schmolke, S. Spohr, G. Meschut, L. Eckstein, M. Rethmeier; A life cycle assessment of joining processes in the automotive industry, illustrated by the example of an EV battery case; Laser in Manufacturing Conference, Munich, 2023