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Dynamic beam control takes on fuel cell welding challenges

The challenge of climate change and the problem of environmental pollution was brought to the forefront of everyone’s minds at the beginning of November with COP26 in Glasgow: we all need to lead more environmentally sustainable lives.

One of the more obvious polluters in many people’s daily lives is their car, with the majority of those being sold continuing to rely on conventional petrol and diesel internal combustion engines.

However, advances in the production of hydrogen fuel cells could help bring about a greener future, with lasers set to play a crucial role in helping make hydrogen-powered vehicles commercially viable.

Fuel cell vehicles (FCVs) provide an alternative to the plug-in electric vehicles (PEVs) that have been the focus of many countries’ push towards greener transportation. While PEVs have been making inroads in the market in recent years – with falling prices and an increase in the range they can travel before needing to be recharged – they continue to have some significant downsides, most notably in terms of the infrastructure required and the time needed to recharge their batteries.

Fuel cells, however, offer a potential alternative to these problems. They could enable electric vehicles to be filled with hydrogen at the fuel station as quickly and easily as vehicles are today with petrol and diesel.

‘Which technology will be the gamebreaker in the end has not yet been decided,’ said Eric Punzel, a laser technology process engineer at BBW Lasertechnik, a German production specialist in laser materials processing. ‘Maybe it will never be. I’m sure we will need both technologies, because with PEVs you don’t have the possibility to recharge the batteries everywhere. Sometimes you just need some kind of conventional refuelling, and with hydrogen it’s much easier to have a remote infrastructure for refuelling cars and trucks.’

As his colleague Florian Hugger pointed out, who heads up R&D at BBW Lasertechnik, even within cities, it can take decades for the infrastructure to be built, and if you don’t want to charge your vehicle overnight, fast charge can be quite damaging to the lifetime of the battery.

Overcoming the hump

While FCVs provide a useful alternative to PEVs, especially for long haul and heavy goods vehicles where the weight of the battery could become an issue, significant improvements need to be made in reducing the costs and improving the production speed of fuel cells, and this is where lasers have an important role to play.

Fuel cells for FCVs typically contain a stack of 200-400 bipolar plates welded together, and while lasers have the potential to contribute to many stages of the manufacturing process, including the cutting and cleaning of the plates, it is the welding that could potentially have the greatest impact on driving down the cost of producing the cells.

Roi Yaacov, business development manager from Israeli laser manufacturer Civan Lasers, explained: ‘What limits the industry breakthrough, is that the bipolar plates are a very significant part of the production cost of the fuel cells. There are other challenges of course, such as the scaling up of hydrogen production and the scaling up of distribution and retail, but improving the manufacture of bipolar plates could have the biggest impact on cost reduction, as it currently accounts for 28 per cent of the cost of fuel cells.’

Fuel cell vehicles could provide an alternative form of electromobility to plug-in electric vehicles. (Image: iStock)

While BBW Lasertechnik doesn’t directly produce bipolar plates, it does help in their manufacture, with customers going to the firm to have parts laser processed. As Punzel explained, lasers are ideal for welding bipolar plates: ‘Bipolar plates, depending on the use, are very thin sheets, typically 100 micrometres or less. To weld these thin metal sheets you need a very precise tool, and we can focus a laser to a very small area, with a small heat-affected zone compared to conventional welding methods, and this makes the laser so unique and perfect for welding applications with bipolar plates.

‘We currently use a single-mode laser that has a very small focused diameter of 20 to 50 micrometres, and to achieve high welding speed we use a continuous-wave laser because a pulsed laser is too slow. We use a remote system and a scanner optic that the laser beam goes through. The scanner has two mirrors, and you can tilt each mirror in one axis to create a two-dimensional process field. However, there is a physical limit when welding at high speeds, and that is called “humping”.’

Humping is a big problem at the moment. Each plate has a weld seam of 1-2m, for example, those in Toyota’s commercially available Mirai have a weld seam of 1.4m, and as Yaacov explained, welding together hundreds of them slows down the production process considerably: ‘Using regular lasers, when you go with a speed that’s higher than 0.5m per second, the humping effect occurs as the melt reflow of the melt velocity makes a hump, and because this metal should be completely sealed without any gaps, you cannot exceed this 0.5m per second. Today, the technology the industry uses is glueing and electron- beam welding, but they are very expensive and very slow. Each vehicle needs to have around 200 bipolar plates welded, and with a weld-seam of between 1-2m, and a top feed-rate of 0.125m per second, it takes more than 35 minutes per car. It’s a huge obstacle in the industry.’

This point was echoed by Hugger of BBW Lasertechnik: ‘There’s a demand for 10 bipolar plates per second from producers, and the laser is still too slow for this high demand.’ One of the solutions BBW Lasertechnik is therefore considering for the future is beam shaping. As a result, it has been exploring the potential of Civan’s dynamic beam shaping laser, based on coherent beam combining technology.

‘Civan is the first company in the world that has managed to make a commercial product out of coherent beam combining technology,’ remarked Yaacov. ‘It’s a laser that combines tens of different lasers, while being able to control the phases of each of the tens of beams. What this technology permits us to have, besides different levels of power, is a dynamic beam that enables us to produce any arbitrary shape that we’d like to have within the beam. If we’d like to have, for example, a spiral beam, a circle, a doughnut, or whatever beam that you think of, we can, and all without any moving parts. We can change the different parameters, so we can control the melt pool better, and eliminate the phenomena of humping. That’s why we think this laser can be a breakthrough in the welding of bipolar plates.’

Civan Laser’s dynamic beam laser can produce shapes such as spirals, circles, or doughnuts. (Image: Civan Lasers)

In addition to BBW Lasertechnik, Civan Lasers is providing its technology to partners such as Fraunhofer ILT and scan head manufacturer, Smartmove, to optimise welding in fuel cell production. In the recently announced ‘Eureka’ project, for example, Fraunhofer ILT will be looking to use advanced sensors and complex beam shapes in high frequencies – enabled by Civan’s technology – to produce faster, more accurate welds of the bipolar plates. Indeed, as testing continues, it is becoming clearer to the project partners that the dynamic beam control of Civan’s lasers could provide the required solution for fuel cell manufacturers today.

Reaching the masses

Overcoming the current limitations of welding bipolar plates will ultimately be a crucial step towards extending the use of electric vehicles.

‘The bottom line is that hydrogen fuel cells are a technology that needs to reach mass production to complete the evolution of clean energy, and do the things that plug-in electric vehicles can’t do,’ said Yaacov. ‘The current limitation in mass production is the welding challenge, and that is what everyone is trying to solve, so hopefully in a few years we’ll come up with a solution for this.

‘Development is the first step, but then you have to monitor the full process in real time, and analyse and discover in real time whether you have defects. Because of our laser’s capabilities to change shape, change frequency, change power, and change any other parameter that is needed, we can make adjustments in real time to ensure a good product at the end. It will not be necessary to do the post-processing that is necessary for the glueing, stamping and other methods that are used today. It will be faster, more cost effective, and the quality will be much better than today’s solutions.’

Punzel of BBW Lasertechnik also pointed to the increasing research and development in the field: ‘There are not yet many hydrogen cars on the streets, but there is still a high demand for research and optimisation. We have a research project in-house, TopLamp, a collaboration between Korean and German partners, developing a platform for the flexible production of bipolar plates, solving problems such as how to weld big bipolar plates, because here there are also limits with remote applications.’

Fuel cells don’t only have applications in cars, according to Punzel. They also have a big application in heating, with studies showing it may be possible to use the infrastructure of natural gas pipelines for hydrogen. For this application, one of the disadvantages of fuel cells – that they are less efficient because they produce a lot of heat – would no longer be a problem.

Whether changing the vehicles on our roads, or the way we heat our homes, fuel cells have the potential to play an important role in creating a greener future, and laser welding is an essential part of this. While the challenge of speeding up the welding process has not yet been met, techniques such as beam shaping make it likely this will one day be a thing of the past.

Dana and Bosch to produce metallic bipolar plates for fuel cell stacks

Dana, a manufacturer of power-conveyance and energy-management solutions for the automotive industry, has signed a long-term cooperation agreement with Robert Bosch to mass-produce metallic bipolar plates for fuel-cell stacks. Dana’s licensed intellectual property will serve as the foundation for the companies to co-develop and co-produce the next generation of metallic bipolar plates. 

Dana’s metallic bipolar plates are an integral component in the fuel cell stack and deliver improved cost, performance and seamless assembly, aiding OEMs in realising commercialisation of fuel-cell-powered mobility. 

The Bosch overall fuel cell stack system know-how will enable both companies to further improve the bipolar plates' design for future generations with regards to cost competitiveness and performance. Furthermore, Bosch contributes strong process competence in mass production, especially on laser welding, testing and automation concepts. This will support a successful launch of the serial production of bipolar plates. 

To address increasing market demand, the total production volume will exceed 100 million metallic bipolar plates for Europe, Asia Pacific and North America. The plates are expected to support fuel-cell powertrains for commercial-vehicle applications beginning in 2022. 

‘Dana has innovated a game-changing metallic bipolar plate technology that is helping customers deliver zero-emission, fuel-cell powered vehicles at a cost that enables market adoption today,’ said Antonio Valencia, president of Dana Power Technologies and Global Electrification. ‘This agreement demonstrates our ability to deliver a market-ready metallic bipolar plate that eliminates the traditional cost, complexity and performance barriers, which is a crucial step for the growth of the fuel-cell market.’ 

The highly durable bipolar plate is designed to meet the extreme demands for sealing, coating and absolute precision of the extra-fine embossing structures.

In addition, Dana’s fully integrated, high-speed forming process further enables high-volume production efficiency at a lower cost, as well as driving increased power density.

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