Analysis of the keyhole and weld pool dynamics by imaging evaluation and photodiode monitoring

Process monitoring of laser welding defects by commercial systems based on photodiodes has high potential, but improved understanding is desirable for more systematic industrial use. The signal is generated from spectrally filtered emissions or reflections from the dynamic welding process. Improved knowledge on the cause of the signal was achieved by accompanying high speed imaging. Numerical evaluation of the images and subsequent modelling provided additional information to judge the potential and limits of commercial photodiode sensors. For welding with a 3 kW Nd:YAG-laser, a 15 kW fibre laser or a 14 kW CO2-laser, various joint cases were studied with respect to defects like craters, spatter, blowholes, underfill, root drop-out, lack of penetration, lack of fusion or pores. From the findings a more general theoretical description of the links between the welding process, the defect mechanism and the generated signal was initiated.Godkänd; 2009; 20091211 (alka