New approach to clamping in microwelding

For the purpose of manufacturing lithium ion cells, microwelding is a commonly used procedure. It is also applied to new products as vacuum insulation elements which are enclosed in stainless steel foils. Another new application can be found in welding of catalytic converters. Before, they were usually joined by furnace brazing. All these products consist of thin metal foils which can be considered two-dimensional work pieces. They have to be joined in a stable process in order to avoid rejects. One of the biggest challenges in thermal microwelding is the gap forming between the join partners due to thermally induced distortion. In microwelding, the possibility to bridge the gap between the join partners is ensured as long as the gap is smaller than approximately half of the material thickness. Beyond this point, weld seam imperfections occur and the process collapses. In order to minimize gap formation, a new approach to clamping is presented which directly applies the clamping force in the welding zone. Based on this invention, a clamping fixture was constructed and qualified. Thereby, it is possible to close the gap between join partners and adapt the properties of lap joints to bead-on-plate welds. Furthermore, the new concept was compared to a common clamping fixture. Thus, weldable join partner thickness could be reduced, and the feeding rate was extended.