In the past, and to some extent still today, resistance spot welding is used in car body construction to join metal sheets. If, for example, a vehicle roof has to be joined to a side panel, the welding robots place many welding points next to each other in this process. Jokingly, this is sometimes referred to as "stapling". Basically, this process is still a suitable joining method, but restrictions with regard to car body design as well as the general technical development partly required alternative solutions.
For resistance spot welding with a spot welding gun, accessibility from both sides is required. Due to the design of the welding gun, a certain distance to the next welding spot is specified. And as soon as different materials – a so-called material mix – with individual properties have to be joined, spot welding reaches its limits.
Added to this is the desire for leaner designs in automotive development. This was the birth of laser welding and laser brazing in automotive production.
Laser welding & laser brazing: new possibilities for joining
Lasers are a non-contact tool. The associated laser optics can be positioned at distances of several hundred millimetres from the component, which makes accessibility much easier. In addition, it is sufficient to weld or braze the component on one side. This gave the designers the chance to realise their creations without the technical limitations previously imposed by spot welding.
Challenge: finding the exact joint
However, as some of the sheets of the car body overlapped, the problem arose with the beginning of the use of laser technology that the joint could not be found exactly. Tactile seam tracking was the solution: This technology uses the wire as a sensor and moves it along the seam to be welded. With the tactile seam tracking, a very precise seam tracking is achieved in this way. In combination with laser optics linked to the seam tracking, these laser seams can be made extremely quickly – up to 5 metres per minute.
In the meantime, tactile laser welding and laser brazing are the processes of choice for almost all mid-range and luxury class vehicles.
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