Laser welding of the cell contacts of battery modules

Laser-compatible design and consideration of production technology

A prerequisite for the successful use of laser technology for welding cell contacts is laser-compatible design and therefore consideration of the production technology as early as the development phase. Consequently, coordination between design and production is absolutely essential for the success of the project.

Projects in the field of e-mobility and energy storage are often time-critical - it is important to quickly transition to series production, then scale up and at the same time meet the project-specific quality requirements. For this reason, it has proven to be a good idea to start the laser welding of cell contacts as a separate project at the earliest possible stage. In this phase, it is sufficient if initial CAD models, the specific cell type and the materials used are available.
 

Tests to assess feasibility and costs

The selection of suitable system technology for laser welding depends closely on the specific project requirements and in particular on the cell type used. A suitable beam source with the appropriate optics must be selected. The extent to which integrated process monitoring is possible is also important for the series. This is because it must be ensured for the series that every cell contact is reliably welded. The system technology cannot be changed easily afterwards, so it makes sense to carry out initial tests on individual cells. This process allows the basic feasibility of the task to be confirmed without having to manufacture entire modules. Specific requirements for the connection, such as the connection surface or welding depth, must be taken into account. It must also be ensured that the maximum permissible cell-specific temperature is not exceeded. If the cells are not yet available at this stage, the tests can also be carried out with laser-cut dummy parts. In the next step, the results are evaluated by metallographic examinations. Based on these initial test results, important information for the overall project can be taken into account at an early stage and detailed statements on feasibility and costs can be made.

Production of sample and prototype modules for testing purposes

Within the projects, near-series modules are required for tests at an early stage. It should be noted here that although the suitable system technology for laser welding is known from the tests, complete clamping devices and coordinated production lines for series production are not yet available at this stage. For this reason, existing flexible production systems are used in this phase of the project, which are then equipped with the appropriate system technology. With modular clamping concepts in conjunction with 3D-printed elements, complete modules can be produced in small quantities within a very short time without incurring high costs for new fixtures or systems. At the same time, laser welding can be carried out with the same parameters as in series production.

The degree of automation depends on the volume

Depending on the volume resulting from the project, a different degree of automation is appropriate, as a high degree of automation goes hand in hand with corresponding investments. The quantities to be produced are also often unknown at the start of the project. In this respect, it can be expedient not to invest in new production lines from the outset, but to make use of existing production capacities. For this, existing systems must be equipped with the necessary clamping technology, but one-off costs for investments in machines and automation are eliminated. If the volumes prove to be high enough from the outset or during the course of the project, new investments in optimized production lines often make sense. It is important to consider the entire process chain when assembling the modules: the cells must be tested and categorized in advance, assembled with other individual parts such as housings and cell connectors and then welded together. This process is followed by a final test of the modules.

Comprehensive logistics and quality assurance are in place across all process steps, the scope of which must not be neglected. The quality of each individual step must be assured and documented at every cell level, using suitable software solutions where necessary.
 

Project management connects specialist areas

Although the laser welding of battery contacts can initially be regarded as a single task, the realization of the task involves the participation of a wide range of specialist areas, from the design phase through to series production. Development, design, production, quality and operating technology must be closely coordinated at every stage and take the overall project into account in each individual task. For this reason, it is essential that cooperation between the specialist departments is coordinated through dedicated project management. This is also essential in view of the tight schedules and their realization. The requirement from the projects is that as precise a schedule as possible is drawn up ex ante, even though not all the information is available in full at the start. Against this background, it is important that the experience of the specialist departments involved is integrated into the planning at an early stage.

BBW Lasertechnik as a partner for the laser welding of battery cells

BBW Lasertechnik now has more than ten years of experience in the laser welding of cell contacts and can look back on the successful implementation of numerous projects in this field. From laser-compatible design, trials and prototypes to series production with automated production lines, we are a competent partner for the laser welding of battery cells. The possible applications range from battery modules for mobile applications such as industrial trucks, rail vehicles or air cabs to stationary energy storage systems. Other customized products include coolers for battery modules, module housings, busbars and power connectors.

A contribution by Andreas Bürger