Minimal scrap rates with fast cycle times: New developments in ultrasonic welding enable an optimization of production and can permanently reduce manufacturing costs for batteries. A big help comes from the experience gained in the welding of plastics.

As the heart of electric vehicles, the battery cell plays a central role in the production. However, although the industry stands for progress, innovation and sustainability, many companies in the industry accept high reject rates – in some cases of up to 20 percent. Especially in times of long delivery times as well as material shortages, this is increasingly becoming a major cost factor. Thanks to a careful joining process, but also constant research in the ultrasonic laboratory, ultrasonic welding can make a decisive contribution to making production safer, more reliable and thus also more cost-efficient.

“Welding is usually used at the end of the battery production process. This means that if the joining process is failing, the entire battery cell has to be disposed of. For cost reasons, but also for sustainability reasons, this is not acceptable. That’s why we looked for ways to help provide a safe and repeatable process – and found them,” explains Michael Leipold, Business Unit Director Plastics and Metals at Herrmann Ultraschall.

Scrap rates close to 0 percent possible

For the reduction of reject rates, one tool in particular has proven its worth, which has already led to reject rates close to 0 percent in the ultrasonic welding of plastic parts: process visualization and monitoring. Each individual weld is monitored by intelligent control software that graphically displays the most important parameters such as welding force, amplitude, energy and joining distance in real time. In this way, potential for improvement can be identified, parameter settings optimized and the entire process can be continuously improved.

In total, up to 150 parameters per welding process can be recorded, stored and evaluated during ultrasonic welding of non-ferrous metals. And each welding has its own digital fingerprint, which ensures traceability. At the same time, this data forms a valuable basis for permanently low scrap rates and a reliable process.

Precise control even at lowest forces

The joining of battery cells with few foil layers or from thin materials is especially challenging. In order to be able to create strong connections in these applications without damaging the sensitive foils, extremely precise force control is required in a range of up to five newton at a frequency of 35 kHz.

In addition to an elaborate control system, it became clear that a corresponding addition to the hardware, i.e. the ultrasonic welding system, was necessary. Tests in the ultrasonic laboratory revealed that the development of a rocker is necessary to enable a stable process even with the lowest forces.

In general, experience on numerous customer projects has shown that early involvement of the ultrasonics partner is instrumental in reducing the reject rate, thus saving valuable time, resources and costs.