For the detection and evaluation of hot cracks during pulsed micro welding a quality monitoring system is demonstrated consisting of an automatic spot measurement (ASM) and a hot crack monitor (HCM).
The ASM represents a tool for tracking the superposition of two laser foci which have been engaged for diode-laser-enhanced micro welding of delicate aluminum alloys. The ASM is particularly important for ensuring a repeatable setup with a defined overlap of both foci and for verifying the spot diameters.
The ASM is divided into four steps: (i) acquisition of reliable video data, (ii) localization of the weld point within the video data (bitmap), (iii) calculation of the offset between the two foci and (iv) conversion of the result into real metric dimensions. In a final test the influence of the illumination on the measured result is shown.
The second tool represents the HCM for detecting hot cracks. It is developed for a time efficient detection of hot cracks in the welding zone by the use of a microscope objective during or after the welding process.
The HCM development is divided into three steps: (i) localization of the last weld point, (ii) measuring the grayscale profile on the weld point edge and (iii) analyzing the grayscale profile with a previous developed crack criterion. In a functional test the effect of light shifting and for various spot overlapping is demonstrated.
The basis for systematically researches is given by the ASM, which allows to adjust a defined superposition with an accuracy of 4,11 µm per pixel, which leads for the Nd:YAG spot to a deviation of less than 1%. The presented tool is a valuable tool to achieve a defect free welding zone during the diode-laser-enhanced micro welding process because of the high influence of the superposition on the crack behaviour.
The HCM allows for a good quality control of the weld seam under constant illumination conditions and various spot overlapping. The combination of two different crack criterions leads to efficient crack detection independently of the appearance of the seam. With the developed system time efficient crack detection is enabled and allows several researches to improve welding quality of aluminum alloys for diode-laser-enhanced micro welding and quality monitoring in serial production.