Laser beam brazing is now increasingly being used to joinhigh-end series-produced components in the automotiveindustry. The early detection of process faults and jointimperfections is therefore crucial in terms of costs. The EQOS»Development and Qualification of a Simple Online QualityMonitoring System for Industrial Laser Beam Brazing« researchproject funded by the German Federal Ministry of Economicsand Technology (BMWi) aims to replace the plethora ofmonitoring systems currently in use with a single system whichcombines multiple familiar functions and new functions.

Method

The quality of the laser-brazing joint is being recorded forthe first time not only in the visible, but also in the nearinfrared spectrum (NIR) using space- and time-resolved imageprocessing. The combined analysis of both signals enablesprocess parameters and the occurrence of various jointimperfections to be identified during the process itself. Thecoaxial implementation of two camera systems in the beampath of the processing laser (Nd:YAG) and the coaxial couplingof a secondary light source for the visible spectrum presents aparticular challenge.

Result

In the visible spectrum, the brazing wire in the forwarddirection and the solidified joint in the backward direction arevisualized. Feed rate and wire orientation can be measuredusing image processing. Pores with a diameter of under150 μm can be detected in the NIR spectrum. The symmetry ofthe heat distribution provides an insight into other categoriesof error such as ‘one-sided wetting’ or imprecise laser-beamorientation.

Applications

Currently the most important application is brazing two-pieceautomobile tailgates. A cleanly brazed joint is particularlyimportant here since the joints are visible. Other applicationsinclude process monitoring when joining tailored hybrid blanksmade of non-weldable steel-Al hybrid compounds, or the laserbrazing of transmission components.