The risk of weld defects increases when laser beam welding of round bars is performed in a rotational process. The reason is heat accumulation, which changes process conditions. The analysis of weld pool shape and weld defects in the course of a weld seam is essential for being able to evaluate the overall weld quality and to set up control measures. This study focuses on laser beam welding of round bars with partial welds and various welding speeds. The experiments are carried out with 1.7035 round bars of 30 mm diameter. For partial welds, a laser beam power of 6 kW and welding speed of 1 m/min are used for welding paths of 1/4, 1/2, and 3/4 of the circumference. Welding with various speeds is conducted with 0.5, 1.0, and 1.5 m/min and a constant energy per unit length of 240 kJ/m. The specimens are evaluated by metallographic microsections and scanning acoustic microscopy. The investigations reveal three major weld defects resulting from a gradient in linear welding speed between the specimen surface and the center and from heat accumulation due to specimen geometry. Porosity and hot cracks form under the surface and the weld root bulges, which also result in hot cracks. The weld depth increases to its final weld depth after approximately 1/8 of the circumference.

Laser beam welding is a commonly used technology for joining similar and dissimilar materials. In order to improve the mechanical properties of the weld, the introduction of ultrasonic vibration into the weld zone has been proposed [5]. The ultrasonic system consists of an electronic control, a power supply, a piezoelectric converter and a sonotrode, which introduces the vibration into the weld zone. Its proper design is of great importance for the process performance. Furthermore, the effects of ultrasound in a melt pool need to be understood to evaluate and optimize the process parameters. In addition, it is important to find out the limits of ultrasonic excitation with respect to a maximum vibration amplitude. Therefore, firstly different methods of ultrasonic excitation are investigated and compared with respect to their performance. A system which is based on using longitudinal vibrations turns out to be the best alternative. Secondly, the system design is described in detail to understand the boundary conditions of the excitation and finally, simulations about the influence of ultrasonic vibrations are done by using a simplified model. The system is used to perform experiments, which aim at detecting the maximum vibration amplitude doing bead on plate welds of EN AW-6082 aluminum alloy. The experiments reveal a significant change of the weld shape with increasing ultrasonic amplitude, which matches the simulative findings. If the amplitudes are small, there is a marginal effect on the weld shape. If the amplitudes are high, melt is ejected and the weld shape is disturbed. In the present case, amplitudes over 4 µm were found to disturb the weld shape.

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Laser beam welding is used in many areas of industry and research. There are many strategies and approaches to further improve the weld seam properties in laser beam welding. Metallography is often needed to evaluate welded seams. Typically, the images are examined and evaluated by experts. The evaluation process qualitatively provides the properties of the welds. Particularly in times when artificial intelligence is being used more and more in processes, the quantization of properties that could previously only be determined qualitatively is gaining importance. In this contribution, we propose to use deep learning to perform semantic segmentation of micrographs of complex weld areas to achieve the automatic detection and quantization of weld seam properties. A semantic segmentation dataset is created containing 282 labeled images. The training process is performed with DeepLabv3+. The trained model achieves a value of around 95% for weld contour detection and 76.88% of mean intersection over union (mIoU).

Welding by laser beam is a method for creating deep and narrow welds with low influence on the surrounding material. Nevertheless, the microstructure and mechanical properties change, and highly alloyed materials are prone to segregation. A new promising approach for minimizing segregation and its effects like hot cracks is introducing ultrasonic excitation into the specimen. The following investigations are about the effects of different ultrasonic amplitudes (2/4/6 µm) and different positions of the weld pool in the resonant vibration distribution (antinode, centered, and node position) for bead on plate welds on 2.4856 nickel alloy round bars (30 mm diameter) with a laser beam power of 6 kW. The weld is evaluated by visual inspection and metallographic cross sections. The experiments reveal specific mechanisms of interaction between melt and different positions regarding to the vibration shape, which influence weld shape, microstructure, segregation, cracks and pores. Welding with ultrasonic excitation in antinode position improves the welding results.