Industrial applications such as joining pressure sensors or battery cells often demand short processing times for economic reasons. Thin metal sheets of thickness smaller than 100 μm are suitable for this purpose. The possible maximum feed rate for an efficient welding process is limited by weld defects, which occur at a certain threshold value of feed rate. Materials such as stainless steel, aluminum, and titanium were welded in bead-on-plate welds in order to generate a full penetration weld. Here, our attention is focused on understanding this instability. In this paper, we performed tests to clarify the influence of the thermophysical properties of the applied materials and the process factors laser power and focal diameter on the humping effect. Due to these attributes, the weld seam formation and hydrodynamic behavior of the melt change. By means of microscopical surface line scans and high-speed imaging, the observations were analyzed depending on the feed rate. The results from the line scans provide the possibility to analyze the surface topography of the weld seam. In particular, the distance, height, and axial frequency of the solidified humps can be categorized in order to get a deeper understanding of the solidified hump structure and the phenomenon in general. To avoid the occurrence of humping, a criterion is defined by the ratio of laser power to weld seam cross section for the applied materials.
In optical manufacturing, the depth of subsurface damages (SSD) depicts an important quality aspect of optical elements. Nowadays, the investigation methods of the damage zone are mostly destructive and allow a sampling of the substrates only. This leads to a lack of statistical reliability. In this paper, one aim is to develop an easy and cheap procedure to evaluate the probes. Therefore, a spherical polishing and chemical etching is introduced. By means of imaging processing software the acquired data is analysed, which eliminates the operator influence und increases the reproducibility. Applying binarizing and shape detection algorithms the SSD structures is detected and the number of pixels per structure is calculated. The percentage of SSD over the depth fit with an exponential curve displays a maximum depth as a single value. The development of a method to choose the best threshold value represents an approach to quantify the uncertainty of the resulting SSD-depth.
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