Introducing an algorithm for the automatic detection of interface positions for flange joints based on laser triangulation measurements

Laser brazing is a joining technique widely applied in industrial manufacturing such as automotive production. In order to establish a stable brazing process free of defects, it is necessary to support the process with a track control. Whereas conventional laser brazing processes rely on tactile track control based on the mechanical interaction between the brazing wire and the substrate surface, new approaches like the reflection-assisted laser brazing require vision-based detection of the joining interface for track control as the brazing wire is already molten when contacting the substrate surface. Especially in the case of brazing flange joints the visual detection of the interface position is challenging given the limited visual accessibility of the joint interface. Therefore, in order to reliably detect the interface position, a semi-analytic algorithm is introduced based on the signals from a laser triangulation sensor scanning the joint geometry ahead of the process zone. Hereby information about the joint geometry is used to extrapolate the surface contours of the joining partners into areas that are not visible to the sensor. The algorithm was successfully tested on 90° and 45° flange joints resulting in an uncertainty in the determination of the interface position of less than ±0.5 mm.