“Better, cheaper, more sustainable: friction stir welding is the best solution for battery housings”

“Better, cheaper, more sustainable: Friction stir welding is the best solution for battery housings”

Interview with Till Maier (Portfolio Manager Advanced Welding Solutions at KUKA) and Stefan Fröhlke (Head of Process Development AWS at KUKA)

Highest welding quality, high savings potential and a green technology: Friction stir welding (FSW) is the optimal process for non-ferrous metals with low melting temperatures and metallic materials. Especially for e-mobility, as FSW with robots raises the quality of battery housing production to a new level. FSW experts Till Maier and Stefan Fröhlke from KUKA explain the background in an interview.

marketSTEEL: Friction stir welding is becoming increasingly popular with battery manufacturers for e-mobility, especially in the automotive industry. Why is that?

TillMaier: Friction stir welding has many advantages for the production of battery housings. Firstly, the welding quality is extremely high: there are no pores or cracks and the seam strength is very high - with minimal welding distortion. The process also offers a high potential for savings, from material savings through component optimization to the lack of consumables such as shielding gas and filler wire to the elimination of extensive edge preparation. And finally, the process is not only particularly environmentally friendly due to its low energy consumption - up to 80 percent less than metal inert gas or laser welding. It also requires no chemical material pre-treatment or anti-glare measures, as there is no fume or noise pollution. Friction stir welding is a green technology!

marketSTEEL: With more than 270 FSW robots in over 18 countries, KUKA has become one of the global market leaders in robot-based friction stir welding since 2012. Which sectors do the interested parties come from?

Till Maier: On the one hand, we supply Tier 1 companies from various countries that work with OEMs, i.e. the manufacturers of original equipment in the automotive industry. However, the group of our direct customers from the OEM sector is becoming ever larger and more important: we act as a general contractor for them. This means that we not only take care of the robots and the associated technologies, but also the complete logistics as well as upstream and downstream processes - such as the subsequent deburring or brushing of the welding surfaces. As a third group, scientific institutes are researching processes and procedures with R&D robot cells from KUKA.

marketSTEEL: So KUKA offers much more than just the robots and the associated FSW technology?

Stefan Fröhlke (Head of Process Development AWS at KUKA): That's right. A process has to be mastered before it can be industrialized. That's exactly why we have process technology, which defines the process and builds up knowledge first. For example, many customers first buy an R&D cell from us and test various parameters in order to adjust the process. This is very different from the typical product business, where you set up a finished product. That's why we also talk about solutions - and these include not only the products but also the decades of experience of our experts. They can set up the process, carry out tests and find out which solution makes the most sense for the customer. We then put these together. This includes not only the robot with spindle and control system, but also the matching tools and the design for holders or fixtures. We supply a complete package, including preliminary acceptance at our premises and final acceptance at the customer's premises. When you buy a friction stir welding cell from us, you're not just buying a device - you're buying a ready-to-use solution!

marketSTEEL: What exactly does the process of such a project look like?

Stefan Fröhlke: The first steps in the investigation are carried out at a theoretical level: First, we discuss the alloys to be processed and analyze whether they can be welded at all. Accessibility studies are then carried out using 3D models: Can the robot reach all relevant points? Is there a risk of collisions with components, clamps or tools? This is followed by the practical test phase: the weld seams are examined in detail using demonstrators, e.g. sample parts - for example by means of laboratory analyses such as the creation of micrographs, in which the seam can also be viewed from the inside. Bending and tensile tests are also carried out. The process is carried out in stages, similar to a knockout round in sport: at each stage, it is checked whether all technical specifications and quality requirements have been met. Even after all the tests have been successfully completed and the system can be configured accordingly, we do not leave our customers to their own devices: after acceptance, we take care of training the employees, for example. And if process-related questions or problems should arise later, while the system is running, we also continue to provide advice and support.

marketSTEEL: What form does the employee training you mentioned take?

Stefan Fröhlke: First of all, the basic level is our robot training at KUKA College. Here we offer different training courses depending on the role and task, for example for commissioning engineers or system operators. This basic training can be supplemented by FSW process training, which lasts either two to three or five days. This deals with the special features of the process: What do I need to pay attention to in production? What are the framework conditions, criteria and parameters? How do I set up the process? How does reliable process and quality control work? In principle, we can carry out all training courses at our premises in Augsburg or at the customer's site, anywhere in the world - and can respond very specifically to the customer's individual requirements.

marketSTEEL: However, you not only offer customer-specific training courses, but also individualized solutions for the FSW that are tailored to the specific requirements of the respective customer: How should we imagine this?

Till Maier: Basically, we have three solutions in our robot portfolio: Firstly, the new KR FORTEC ultra in the MT version with a payload capacity of 300 kilograms and a reach of up to 2,800 millimetres (KR 300 R2800-2 MT). We offer this robot as a universal, robot-based 3D application module for complex 2D and 3D FSW applications. Then there is the modular friction stir welding cell KUKA cell4_FSW midsize single in combination with the above-mentioned robot for medium-sized applications with maximum process utilization, such as HEV battery housings. And finally, the friction stir welding cell KUKA cell4_FSW large dual, also with the above-mentioned robot, for large applications with maximum process utilization, for example BEV battery boxes. Our FSW robot cells have been specially developed for the growing e-mobility market. They have a modular design and are therefore scalable for different production scopes, making them very versatile with a wide range of configuration options.

Stefan Fröhlke: Our KR FORTEC ultra MT is not a conventional pick-and-place machine, but a special MT, i.e. machine tooling variant. Axes 1 to 3 have been optimized with special gearbox pre-stages and motors, which enables enormous process forces of up to 12 kilonewtons and sometimes even more. Thanks to the new double swing arm and new machine data, it is extremely rigid and has been specially developed for the FSW process. This ability to apply high forces with precise repeatability sets us apart from other robot manufacturers - KUKA was one of the absolute pioneers here. But the individual tools on the robot and the clamping devices are also customized.

marketSTEEL: What tools are these, for example?

Till Maier: The options for different FSW tools are very extensive - from the conventional tool, in which both the shoulder and the pin rotate, to a stationary shoulder, in which only the pin rotates, to bobbin tools and many other special designs. KUKA is heavily involved in the development of FSW tools, designing new tool geometries or researching wear mechanics. We work on coatings to increase the resistance of the tools and extend their service life, and carry out joint development projects with our suppliers to find new materials that offer an optimum price-performance ratio. In our experience, welding tools with a fixed shoulder have proven to be the best solution. They enable high welding quality and ensure a smooth, even welding surface, which significantly reduces the amount of reworking required.

marketSTEEL: Customers often argue that robot-based FSW does not meet their requirements because the robots are not rigid enough, and they invest a lot of money in large portal systems. What do you say to them?

Stefan Fröhlke: Quite clearly that our new KR FORTEC ultra MT and our already widely used KR 500 MT are both sufficiently rigid and highly precise and, thanks to the more powerful motors, have the necessary power to precisely execute the FSW for most e-mobility applications. We have also developed a type of path calibration system for it. We use a laser tracker to measure its position throughout the welding process, enabling us to react online in real time and keep the robot on course. Thanks to a path accuracy of less than 0.5 millimetres, high-precision weld seams are possible. In short, this robot system is very well suited to the high forces involved in FSW.

Till Maier: With the new KR FORTEC ultra MT, we have gone one better, as it can apply up to 20 percent additional process forces. The new models available since spring 2025 are also available with reaches of up to 3,400 mm, which increases the effective working range for KUKA customers in friction stir welding. But the KR FORTEC was already extremely popular before that: no other robot has been sold so often for FSW applications in recent years!

marketSTEEL: Do you have a few examples of applications in practice?

Till Maier: We have just received a follow-up order for 12 FSW cells from a major car manufacturer in the USA, who had previously ordered 23 cells from us. The cells are used in several production steps: the robots weld battery trays together and connect cooling plates to the battery trays in a second production step. However, KUKA not only supplies the technology, but is also responsible for the entire friction stir welding process - including assembly, commissioning, training and final acceptance. What is particularly exciting here is that vehicles with combustion engines, hybrid and electric vehicles can be built on the same production lines in the comprehensively converted production plant.

Stefan Fröhlke: This is remarkable because hybrid electric vehicles and exclusively battery-powered vehicles have very different production requirements. In hybrid vehicles, we have smaller battery housings that are made of cast aluminum. These have cooling channels, and our job is to close these cooling channels. By contrast, the battery housings in battery-only vehicles are much larger and much heavier. This means that many components are made of different aluminum alloys.

Till Maier: Eight of our robots, including three FSW application modules with the KR 500 MT FORTEC in three KUKA cell4_FSW cells, have also been in use at a major automotive supplier in Portugal since 2022. They were dissatisfied with the welding quality of another manufacturer's system. We initially developed a system with two cells and a KR 500 MT FORTEC for them. Due to the flexibility of being able to weld different battery boxes on one system, the customer was so impressed that he immediately ordered another system - a cell with a robot that can operate three fixtures. This allows three different welding tasks to be carried out, which would otherwise require three non-robot-based systems. The friction stir welding robot can be utilized up to 95 percent, as the fixtures can already be loaded and unloaded in a separate safety area during the welding process.

marketSTEEL: You have repeatedly referred to the particular importance of welding quality in e-mobility. How can this be guaranteed?

Till Maier: In the automotive industry, a weld must be 100 percent correct and safe - after all, we are talking about crash-relevant components in the case of battery housings! To avoid costly recalls, process reliability and documentation throughout the entire process and its parameters is a central and mandatory requirement. That is why we at KUKA have developed a special controller for process monitoring: PCD, which stands for “Parameter Control and Documentation”. This enables us to monitor and store all relevant process data at 100 millisecond intervals. The data can also be easily processed in other systems via an interface.

marketSTEEL: What role will AI play in process monitoring in the future?

Stefan Fröhlke: A big one. That's why we are working together with other partners in the AI production network at the University of Augsburg on an AI-based process monitoring system as part of a publicly funded project of the Bavarian Joint Research Program. In this system, various sensors record the forces, temperatures and vibrations that occur during welding. The main focus is on analyzing signals in the ultrasonic range. AI interprets the extensive sensor data and the researchers assign it to processes in the welding process. Certain patterns in the data can then indicate that a weld seam has not been executed properly.

marketSTEEL: You have now provided many good reasons why anyone interested in friction stir welding should contact KUKA. What is the most important one?

Till Maier: What sets us apart from our competitors is our overall expertise. Some companies supply a robot, others a spindle or special tools, but then don't have the necessary process expertise. We can offer all these components, processes and knowledge from a single source. We also design and program our robots so that they are optimally adapted to the customer's individual requirements - from conception to implementation, we have an influence on all relevant process steps.

Stefan Fröhlke: Through our frequent, direct cooperation with end customers, we also gain valuable experience that we continuously incorporate into our solutions. As integrators, we are responsible for the quality of a system and use a wide variety of methods to solve even tricky tasks. If required, we can offer our customers complete, turnkey solutions that are perfectly tailored to their individual requirements.

Till Maier: In other words, KUKA is the right partner for friction stir welding in e-mobility, from the initial product idea to the complete turnkey solution.

Photos: KUKA