Fuel cells have emerged as a promising solution for clean energy across various sectors, particularly in vehicles, where they can generate power without emitting harmful pollutants. One key component in fuel cells is the bipolar plate, which facilitates the proper functioning of these cells. However, the manufacturing process for these plates has presented significant challenges, specifically during laser welding, a process commonly used to create these components. When welding at high speeds, manufacturers have faced a persistent issue: the formation of humping—surface irregularities along the weld seam.
Recent research led by a team at Penn State University has uncovered critical insights into the causes of humping during rapid laser welding and developed innovative strategies to overcome this limitation. Their work has not only deepened the understanding of the underlying mechanics of humping but also introduced solutions that enable higher welding speeds without sacrificing weld quality. Their findings, which were published in Nature Communications, represent a major step forward in making fuel cell production faster and more efficient.
Fuel Cells and Bipolar Plates
Fuel cells have become a key component of the clean energy landscape, especially in the automotive sector where they are being explored as a zero-emission alternative to traditional internal combustion engines. In fuel cells, bipolar plates play a vital role in energy generation. These plates connect and separate the individual cells within a fuel stack while also conducting the necessary hydrogen and oxygen gases to the system. The channels etched into the plates allow for efficient gas diffusion, enabling the chemical reactions that generate electricity.
Bipolar plates are made by welding two sheets of metal, typically stainless steel, together. The challenge lies in performing this welding at high speeds while maintaining the necessary quality to ensure the plates perform reliably in a fuel cell. Laser welding is preferred for its precision and efficiency, yet until now, it has been limited by the risk of forming surface irregularities such as humping when done too quickly.
The Humping Problem
When laser welding is conducted at speeds that are too high, the process produces molten metal pools that can become unstable, leading to the formation of humping. These irregularities manifest as raised ridges or deformations along the weld seam, which can compromise the integrity of the welded part. The speed of the welding process was thus restricted, as manufacturers could not produce high-quality bipolar plates at speeds faster than a certain threshold without triggering humping.
According to Zen-Hao Lai, the first author of the study and a doctoral student in Penn State’s Department of Materials Science and Engineering, the previous maximum welding speed was about 20 meters of stainless steel per minute, beyond which humping would occur. This restriction posed a barrier to scaling up production, limiting the number of fuel cells that could be produced. With 75 meters per minute as the ideal production rate, these limitations were not just a production inconvenience—they directly impacted the potential for clean, mass-market fuel cell technologies.
Breakthrough in Welding Speed
The research team sought to overcome this limit and find a way to achieve a significant increase in welding speed. Their goal was to enhance the production of bipolar plates by increasing the welding speed without causing the surface defects that came with faster processing. The Penn State team employed both experimental observations and analytical modeling to tackle the problem.
Using a high-speed synchrotron X-ray imaging technique, the researchers observed the welding process in real-time. This technique, previously unavailable for observing such high-speed processes, enabled them to capture unprecedented detail about the behavior of the weld metal during high-speed welding. With this data, the team was able to develop a numerical simulation that accurately reflected the dynamics of the welding process. The simulation became a powerful tool, allowing the team to adjust process parameters and model the behavior of the molten metal pools.
The breakthrough came in the form of a simple yet effective solution: they identified the specific conditions under which humping occurred and used shielding gas as well as adjustments to the laser beam shape to stabilize the molten pools. By modifying these factors, the team developed an equation linking the process parameters directly to the formation of humping.
Key Innovations and Results
The key finding from the study was the ability to stabilize molten metal pools during high-speed welding, preventing them from contributing to humping. Specifically, the shielding gas—a controlled flow of inert gas—helped keep the weld environment stable, while modifying the laser beam’s shape prevented the molten metal from becoming too agitated. These straightforward changes to the welding setup allowed the team to increase the welding speed from 20 meters per minute to an impressive 75 meters per minute, effectively tripling the production rate for bipolar plates.
This breakthrough has profound implications for fuel cell manufacturing. With the ability to produce bipolar plates at a much higher rate, manufacturers could potentially produce up to 80,000 fuel cells per year—each fuel cell consisting of two welded bipolar plates. This increase in production capacity brings fuel cells one step closer to mass adoption in markets such as electric vehicles and stationary power generation.
Further Refinements and Impact
Despite their success, the Penn State team remains committed to refining the process. According to Jingjing Li, the corresponding author and Penn State professor of industrial and manufacturing engineering, the work represents both a significant scientific achievement and an opportunity for further advancement in industrial practices. “We are not stopping here,” Li said. “We are constantly working on improving the process and trying to achieve even higher speeds without introducing defects.”
The team’s findings have implications beyond just fuel cell production. The innovative approach can be adapted to other manufacturing processes where laser welding is used, making this research applicable across a wide range of industries, from electronics manufacturing to aerospace and beyond.
Rethinking Industrial Engineering
For Li and his team, the study also highlights an important lesson about the intersection of fundamental research and industrial manufacturing. Li sees this research as a key example of how traditional engineering can be enhanced by incorporating a deeper understanding of the physical phenomena that underpin the process. “This is a good example of how combining traditional manufacturing techniques with fundamental research can solve real-world problems and lead to practical improvements,” said Li.
The work also challenges typical views of what industrial engineering entails. It’s not only about hands-on problem-solving in a factory setting, but also about using advanced modeling, simulations, and basic research to solve complex challenges. The team’s work exemplifies the evolution of industrial engineering, where cutting-edge scientific knowledge is leveraged to optimize industrial processes and address real-world problems in manufacturing.
Conclusion
The ability to increase laser welding speeds without sacrificing quality represents a significant advancement in the field of fuel cell manufacturing. By understanding the fundamental causes of humping and creating a practical solution using experimental data and simulation models, the Penn State researchers have broken through a longstanding production limitation. Their work not only improves the production rates for fuel cells but also provides a valuable insight into how interdisciplinary research—combining engineering, physics, and materials science—can lead to advancements that tackle some of society’s most pressing technological challenges. As the world transitions to more sustainable energy sources, innovations like this could help make fuel cells a central player in the shift to clean, green energy solutions.
Reference: Zen-Hao Lai et al, Unveiling mechanisms and onset threshold of humping in high-speed laser welding, Nature Communications (2024). DOI: 10.1038/s41467-024-53888-w