Friction stir welding with robots raises e-vehicle production to a new level

At a major automotive supplier in Portugal, eight KUKA robots – including three friction stir welding application modules for the KR FORTEC in three cell4_FSW cells – take care of the future of driving: electric-car battery housings, created from various aluminum alloys to lighten vehicle weight as much as possible. The robot-based FSW process produces the highest-quality welds cost effectively, and low energy consumption makes it a green technology. According to the customer, one meter of friction stir welding already costs less than the equivalent wire consumption in arc welding.

The heart of an electric car – its battery – fastens to the vehicle's floor through a housing: an arc welded frame made of extruded profiles closed with a sheet metal plate, or double-walled extruded profiles. KUKA has supported its Portuguese customer's production of these housings for several years, and already has supplied three separate systems. “We have grown along with the customer's requirements – from the individual welding task to the fully automated production line,” said Patxi Blanco, Global Key Account Manager at KUKA, who has been involved in the lightweight battery housing process from the outset.

Battery housings for electric cars require special weld seams. Unlike in hybrid vehicles, the battery in a purely electric car is larger, heavier and integrated directly into the floor. In 2019, this customer was dissatisfied with the weld quality of a different type of system from another manufacturer. “This process requires a high degree of rigidity, and because they are integrated into the floor, the housings are crash relevant. They must withstand enormous forces,” explained Stefan Fröhlke, Senior Manager Process Solution at KUKA.

“This single solution provides the same output volume as two systems, without the associated costs for personnel and production space,” said Patxi Blanco. Because fixtures can be loaded and unloaded in a separate safety area during the welding process, KUKA's extremely cost-effective solution uses up to 95% of the capacity of the friction stir welding robot. Another advantage: Thanks to the robot, the process is more dynamic and requires less floor space.

This story did not end with two systems. Three years later, robots handle more than the simple welding process: now, the entire production process has been automated. In three KUKA cell4_FSW cells, eight robots perform four work steps to produce battery housings from various aluminum alloys in accordance with stringent requirements.
The first step welds the base plate while the second step deburrs it. Next, the robots weld the frame to the base plate, and then deburr the entire battery compartment in step four. “We performed Installation and startup at our plant in Augsburg. The customer carried out acceptance of the system there as well, so on-site installation went quickly and smoothly,” said Patxi Blanco, describing this long-term electromobility project.

Developed specifically for the growing electromobility market, the KUKA cell4_FSW friction stir welding cell offers the utmost in versatility and configuration options in addition to outstanding economic efficiency. “Path accuracy within 0.5 mm makes highly accurate and perfect weld seams possible,” explained Stefan Fröhlke. Precise path control takes advantage of the KR FORTEC 500 R2830 MT, which impresses with its high stiffness characteristics and long service life. At the same time, precise laser-assisted path calibration compensates for path deviations and helps ensure that each seam meets high requirements for leak tightness and crash resistance.

This long-term project has created a strong partnership between KUKA and the automotive supplier, with ongoing discussions of new battery platforms. KUKA thus supplies not only the system and the engineering, but also the process expertise for active support of new developments.

After all, one thing is certain: The demand for electric cars, and thus also for battery holders, will continue to increase. Experts anticipate by 2032, for the first time, more electric vehicles will be registered in Germany than vehicles with internal combustion engines – not only because of the reduction in CO2 emissions. This will increase the need for lightweight battery housings with the right strength – and for automated FSW solutions to create them.