During the laser welding process in automotive production, changes in process parameters can affect the size and properties of a welded joint. Any such changes may compromise the mechanical behavior of the welded component, leading to a failure in performance. Hence, monitoring and controlling the laser welding process have become vitally important to ensure the quality of the weld. Moreover, accelerating manufacturing requires new monitoring capability to upgrade the laser processing components by applying innovative laser monitoring technology.

Several techniques have found industrial implementation in car series production to observe laser processing in-situ. Among them:

  • OCT optical  coherence  tomography
  • WELDEYE camera-monitoring with  external  illumination 


OCT for high quality laser welding

OCT is an proven  technology  for industrial laser process monitoring because  of  its  noncontact  deployment, high dynamic range, micron resolution, and insusceptibility to all optical distortions  (like  processing  laser  light or other radiations). As a three-dimensional imaging module OCT provides “on the fly” height based image analysis. Time saving and material economy are attractive features for automobile manufacturers. In that sense, OCT is a precise tool for real-time, high-speed, adaptive, direct and quantitative process monitoring during laser welding of BIW and powertrain that enables certain quality improvement achievements.

 Both high lateral and axial resolution of OCT allows to resolve the open pores on the weld bead during powertrain welding:


OCT images with respective photographs of the welding faults (marked by arrows) on the fillet welds: (a) a pore of the size of 0.2 mm on the welded seam of zinc coated steel sheets; (b) welding apart the joint, on the bottom sheet of aluminum; (c) welding apart the joint, on the top sheet of zinc coated steel. OCT imaging allows to make an immediate automated “fail” decision.


OCT technology provides tailor-made solutions for real-time, µm- accurate process monitoring and quality assurance for laser welding. Known for its long working distance, OCT became a promising instrument for industrial keyhole depth measurements during laser welding.


Laser power variation (upper graph) and simultaneously measured with OCT keyhole depth (blue crosses on bottom image) overlaid on bright-field microscopy image of longitudinal cross section.


Destructive sample inspection can therefore be reduced.  At welding parameters commonly used in automotive industry, the application of the OCT technique gives satisfactory results for post- and in-process control.


Automated closed loop controlled quality assurance with WELDEYE

Effective laser processing requires a precise online process monitoring, realized, e.g., by WELDEYE. WELDEYE permits automated closed loop controlled visualization of the welding process, and the monitoring of the correct laser welding progress. This technology is based on live camera imaging and real-time gray-scale image processing. The combination of the dynamic WELDEYE camera and an external coaxial planar unstructured illumination with a high power light source is a key technology for the visualization of the welding process area and its surrounding along the entire scanning range. The processing area and the weld bead are revealed in real-time by image analysis with high processing rate in terms of evaluation of the intensity distribution (brightness) of the reflections from the weld. Via the direct and fast communication interface the determined values are transferred to the robot steering software for pass / fail decision. WELDEYE is an established camera imaging technology widely applied to ensure optimum quality welds.

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