Optical measurement of the connection state in laser brazing

The laser brazing of steel sheets is widely applied in car-body manufacturing. The critical value for the strength of the joint is the minimal connection width between the two sheets. However, this value is depending on the feed rate and power of the laser and the feed rate and preheating current of the filler wire used. Furthermore, the wetting behavior of the brazing solder is affected by the surface properties of the joining partners and is thus prone to errors. Currently, mostly destructive testing is used to evaluate the connection state. Therefore, we studied a novel optical measurement technique which is capable of remotely measuring oscillations of the joining partners. In the proposed study, we show how the oscillations are connected to the process behavior and the fusion area and how the setup might be applied as a post- and in-process measurement system.