High-speed x-ray imaging system for the investigation of laser welding processes

A high-speed x-ray imaging system was built to investigate the fundamentals of laser material processing, such as laser welding. The system allows visualizing and analyzing the laser-induced process dynamics occurring also inside optically nontransparent workpieces. The details of the setup are presented together with the resulting performance with regard to edge sharpness, contrast, contrast transfer, and spatial as well as temporal noise. For voids with a depth (in respect to the x-ray radiation) of 100–500 μm, which is a typical range for focal diameters used in laser beam welding, a maximum contrast of 3%–19%, respectively, can be achieved. Due to the edge blurring, caused by the imaging system, the contrast is further decreased by 20% for voids with a lateral size of 100 μm and less than 10% for voids with a lateral size of 500 μm, when a magnification of 5.4 is used. The image intensifier, needed to increase the number of photons to saturate the camera, induces a noise floor of ±15% in respect to the mean gray value and results in a maximum achievable signal to noise ratio for a 100 μm step of 1.2.