Robot-based friction stir welding – made for the future of mobility

Decisive for the future-oriented topic of e-mobility are not only the range and performance of the vehicles but also economic manufacturing of the vehicles with innovative vehicle concepts.

Friction Stir Welding for Electromobility

With its process know-how in friction stir welding, KUKA has become an important partner for this sector of the automotive industry. Thanks to this technology, heat management for batteries can be optimized and the complex structure, including the storage housing, can be implemented economically.

Electric cars – or at least their batteries - need a "feel-good temperature". Only when they are at the right temperature can they achieve optimum performanceand maximum service life. The batteries must therefore be cooled during operation and heated at a low ambient temperature. This usually happens - especially in hybrid vehicles - with the aid of cooling systems integrated in the base of the battery carriers. The manufacturing of these carriers is extremely difficult but, due to its many years of experience in the friction stir welding process, KUKA can contribute valuable know-how in this field.

The cooling system of the hybrid vehicles is closed by welding a base plate to the cast housing. While doing so, a pressure-tight circuit must be created which can withstand the alternating pressure. This requires a large joining cross-section and a well-mixed and compacted seam. The components should only warp slightly due to heat input. Friction stir welding has proven to be a suitable joining technology for this application.

Welding using Green Technology

The process is particularly suitable for high-quality joining processes using various aluminium alloys and other non-ferrous metals with low melting temperatures. In friction stir welding, a rotating tool is guided along the joining area of the workpieces, thereby creating frictional heat between the firmly clamped workpieces – achieving a more robust and stronger connection than with conventional methods. Depending on the component design, the weld seams are executed as meanders or stitch seam.

Friction Stir Welding_seam — Sample of a meandering seam

An additional advantage: The process is low in emissions and energy consumption is kept at a minimum. A pre-treatment of the components to be joined is not necessary. Friction stir welding is therefore also known as a green technology.

Friction Stir Welding_Robot — Friction stir welding cell for battery housing

Process Know-how in Joining Technology

This technology is increasingly being used not only in the cooling systems of hybrid vehicles, but also in the manufacturing of the storage housings in all-electric cars. Here, the housing occupies a large area of the underbody and is usually located between the axles. Some manufacturers have been installing the storage housings separately. Newer concepts, on the other hand, include structure components in which the vehicle's storage housing are integrated. For this purpose, the structures must be extremely stiff. There are two options available: frame profiles with cross members that are welded to a base plate made of an aluminum sheet or a base plate made of welded double-walled extruded profiles.

Individual aluminum die-casting components are already being used - which presupposes high demands on joining technology for the storage housings. And this is where KUKA comes into play with its process know-how. Friction stir welding is ideal for meeting these requirements. However, in the design of the components or production equipment some special features must be taken into account, such as high process force and bridging gap dimensions.

Friction Stir Welding with a Stationary Shoulder

In order to execute the complex seams in the storage and electronics housings, KUKA relies on a stir friction welding process deploying a stationary shoulder (Stationary Shoulder Friction Stir Welding [SSFSW]. Here only the pin rotates in a stationary shoulder. The stationary shoulder creates a flat, smooth seam surface while it advances along the weld seam. This in turn reduces the amount of post-processing required.

Friction Stir Welding_ESAB Licensed Technology — Robot-based friction stir welding solution

Process Control and Documentation System

The experts are certain that the market potential for friction stir welding equipment and processes will increase over the coming years, as the importance of electromobility continues to grow. KUKA enables the automotive industry to integrate this joining method into the production process in a cost-effectivemanner. At the same time, customers can track all process parameters and have quality data recorded transparently. For integration into Industrie 4.0 KUKA has created a process control and documentation system (PCD).