Life Cycle Assessment of Welding Methods for EV Battery Enclosures | Environmental Impact Comparison

Life Cycle Assessment of Welding Methods for EV Battery Enclosures | Environmental Impact Comparison

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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:

  1. 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.
  2. 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
  3. 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.
  4. Evaluation: Reviewing findings and providing recommendations regarding the environmental impact of the compared processes
Considered system boundaries of the LCA comprising supply of materials and energy, the joining process and disposal of consumables.

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.

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.

 

Thanks go to Dr.-Ing Max Biegler, Group Lead, Joining & Coating Technology
Fraunhofer Institute for Production Systems and Design Technology IPK

Source

  1. 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
Press Hardening Steel Grades: Unlocking Strength Through Innovation

Press Hardening Steel Grades: Unlocking Strength Through Innovation

“Bainitizing, 20MnB8, 22MnB5, 22MnSiB9-5, AlSi, Bainitizing, Blog, BQP, direct press hardening, furnace, grades, high ductility PHS, homepage-featured-top, indirect press hardening, main-blog, Manganese-Boron, multi-step press hardening, PHS, PQS, pre-cooled stamping, Press Hardened Steels, Press Hardening Steel, Press Quenched Steel, Quenching and Partitioning”, SIBORA, Unisteel

You’ll find most of this content as part of our page on Press Hardening Steel Grades, but this month, we want to highlight it in our AHSS Insights blog. Thanks to Eren Billur, Ph.D., President, Billur Metal Form, for providing this information.     What...
Four Steps to Mitigate Liquid Metal Embrittlement When Welding Steel

Four Steps to Mitigate Liquid Metal Embrittlement When Welding Steel

Arc Welding, Automotive Welding Process Comparison, Blog, homepage-featured-top, Joining, main-blog, Resistance Spot Welding, Resistance Welding Processes, resistance welding projection

Liquid Metal Embrittlement (LME) during Resistance Spot Welding (RSW) can cause cracks when welding advanced high strength steels. Recent advances in steel metallurgy, resistance spot welding processing and accompanying simulation tools have substantially improved the way that LME can be handled in industrial practice. This article gives a brief overview of easy measures to implement when LME might potentially occur during production.

 

 

Introduction 

During resistance spot welding of zinc-coated advanced high strength steels (AHSS) liquid metal embrittlement -related cracking may be observed. Since LME is often associated with a reduction of steel’s mechanical properties, it is desired to control its occurrence during production. An exemplary LME crack, forced with increased weld heat and deliberate electrode misalignment, is shown below. 

 

 

Image of LME Cracks in Automotive Parts

Figure 1: A typical LME crack created under laboratory conditions by deliberately increasing the welding time and introducing 5° electrode tilt 

 

Over the past several years, LME has been a a focus in welding research. It is now well-understood to the degree that it can be predicted and avoided with easy measures. Below is an  overview of four key steps to address the potential of LME during automotive production.

 

Obtain the latest steel grades from your steel supplier

Over the past decade, steel producers have released AHSS with improved chemical compositions, helping to significantly reduce  the occurrence of LME iIt is beneficial to talk with steel suppliers and ask about their latest AHSS grades, as these are likely far less sensitive to LME than previously tested grades. A recent study commissioned by WorldAutoSteel demonstrated that all five chosen material stack-ups from current production data did not show any LME even under exacerbated conditions. Only by choosing an especially difficult material stack-up could LME be forced to appear at all to conduct the study.

 

Read up on the current state of research for LME

WorldAutoSteel has published two studies on liquid metal embrittlement: One focused on lab conditions and the second on real-life stamped components. These studies provide an overview of all aspects of LME and how to manage and avoid LME issues.

 

Establish in-house testing protocols to gauge the sensitivity of your material stack-ups  

To investigate LME in-house, it’s critical to establish a testing protocol that forces the cracks to appear and allows for comparison of different steels, stack-ups and welding parameters.  as there  There is currently no industry-wide agreed-upon testing standard.  

Still, there is a good selection of well-documented procedures to choose from. The easiest procedure is to increase the welding time until cracks start to appear – keep in mind that you need to remove the zinc coating before you can observe any cracks on the surface.  

Other methods are based on so-called “Gleeble testing” or on deliberately introducing imperfections like tilted electrodes or large gaps into the welds. As you establish a testing procedure in your lab, you can use it to evaluate LME occurrence in the stack-ups that you want to implement into body-in-whites.

 

Think about implementing LME mitigation strategies in your most difficult welds

Suitable measures should always be adapted to the specific use case. Generally, the most effective measures for LME prevention or mitigation are: 

  • Avoidance of excessive heat input (e.g. excess welding time, current) 
  • Avoidance of sharp edges on spot welding electrodes; instead use electrodes with larger working plane diameter, while not increasing nugget-size 
  • Employing extended hold times to allow for sufficient heat dissipation and lower surface temperatures 
  • Avoidance of improper welding equipment (e.g. misalignments of the welding gun, highly worn electrodes, insufficient electrode cooling) 

These measures can be implemented in the planning stage and in an ongoing production environment to increase the LME-free process windows. 

 

In Conclusion 

While Liquid Metal Embrittlement may present a challenge when welding AHSS, it’s no longer an unpredictable threat. Thanks to advancements in steel development, welding techniques, and testing methods, manufacturers have the tools they need to reliably mitigate LME during production.  

Staying informed, working closely with steel suppliers, implementing smart testing protocols, and applying targeted welding strategies can help automakers maintain both strength and quality in AHSS joints. With this proactive approach, LME doesn’t have to stand in the way of innovation in automotive manufacturing. 

Download the Phase 2 LME Report

Download the Phase 1 LME Report

Fraunhofer IPK simulation site 

  

Thanks go to Dr.-Ing Max Biegler, Group Lead, Joining & Coating Technology at Fraunhofer Institute for Production Systems and Design Technology IPK