The transition to vehicle electrification presents considerable challenges for automotive manufacturers, particularly in the development and production of electric traction drives. Emerging stator winding technologies, such as hairpin, I-pin, and X-pin configurations, are increasingly adopting rectangular copper wires in place of traditional round wires. These configurations necessitate a high number of interconnections between individual winding segments, typically achieved through laser welding. The integrity of these weld joints is critical to both functional performance and overall product quality. Consequently, the implementation of in-process sensor-based monitoring systems is gaining prominence to ensure consistent welding quality. This work, therefore, focuses on whether the quality of the welds can be monitored using an optical microphone. The acoustic emissions arising from the laser welding process are analyzed, and correlations between the airborne acoustics and features of welding quality, such as pore formation or bonding area, are investigated. For this purpose, the study is based on a design of experiments, which provides welds of varying quality. While welding, the optical microphone records the signal curve as well as the energy curve of the sound emissions as relevant process parameters. The quality of the welds is subsequently determined by 3D X-ray computer tomography analysis. Some of the features derived from the signals were found to correlate with the weld quality. The findings demonstrate that optical microphones can serve as effective sensors for monitoring weld quality; however, establishing clear correlations between acoustic emissions and specific welding errors remains challenging and needs to be improved for enhanced industrial applicability.
Laser wakefield accelerators (LWFAs) provide a transformative approach to compact, high-energy particle acceleration by harnessing the intense electric fields generated in plasma wakefields driven by high-intensity laser pulses. In the laser-based electron accelerators utilizing a preformed plasma channel, an electrical discharge within a capillary generates a stable and uniform plasma prior to the arrival of the laser pulse, facilitating efficient laser propagation and wakefield formation. Operating at high repetition rates, such as 100 Hz, is crucial for practical applications. Achieving stable plasma formation at such high repetition rates presents significant thermal challenges due to the intense heat loading on the capillary. The repeated energy deposition from electrical discharges and/or laser–plasma interactions causes potentially rapid temperature rises, material stress, and potential degradation of the capillary structure. Understanding and mitigating heat loading effects are vital for optimal capillary design, ensuring long-term operational stability and advancing the scalability of LWFAs. This article examines the mechanisms of heat loading in discharge capillaries, the related thermal management challenges. There are two types of heat balance. The first one corresponds to the mean heat balance averaged over the many repetition periods. The second type corresponds to the damages caused by single-shot pulsed energy deposition in the capillary. For both cases, we consider energy (or heat) income caused by the driving laser pulse. The extra heat caused by the electrical discharge, if it occurs, gives relatively lower energy output.
High-power laser welding is widely used due to its ability to achieve deep penetration with a small heat-affected zone. However, this process often leads to spatter, caused by the interaction between unstable keyhole capillary behavior and metal vapor ejection, which can result in welding defects such as pits and material loss. Stabilizing the keyhole capillary is, thus, essential for spatter suppression. This study investigates the effect of keyhole capillary stabilization using a 3spot laser profile, in which a high-power central laser is combined with low-power preheating and postheating lasers positioned at the forward and back. Welding experiments were conducted using this configuration, and the results were compared with those obtained from conventional single-spot laser beams. The mechanism by which beam profile control using a 3spot laser contributes to spatter reduction is elucidated in this study.
Composite layers of Ti80 reinforced with SiCp and Ni-coated SiCp were prepared using laser melt injection (LMI). The effect of pre-Ni coating on SiCp was investigated in terms of the microstructural characteristics and mechanical properties of the resulting LMI layers. The results showed that the initially irregular SiCp, characterized by sharp edges, transformed into more rounded morphologies and exhibited numerous fine protrusions on their surfaces, with an average Ni-P coating thickness of approximately 2.875 μm after the electroless nickel plating process. Interface defects and a mixed TiC/Ti5Si3 reaction layer were observed in the LMI SiC/Ti80 layer. The pre-Ni coating on SiCp improved the wettability between the SiCp and the molten Ti80 alloy, resulting in defect-free interfaces and continuous TiC cellular reaction layers in the LMI Ni-coated SiC/Ti80 layer. This layer inhibited the continuous dissolution of SiCp into the Ti80 melt, allowing the injected SiCp to be retained to the greatest extent possible. Additionally, this SiCp pretreatment increased the surface hardness of the LMI SiC/Ti80 layer by 6.8% and reduced the wear rate per unit load and distance by 5.1%. The high interfacial bonding strength and the larger residual SiCp in the LMI Ni-coated SiC/Ti80 layer delayed the peeling of residual SiCp, leading to improved wear resistance compared to the LMI SiC/Ti80 layer. The wear behavior of the Ti80 substrate is predominantly governed by adhesive wear mechanisms, supplemented by oxidation and abrasive wear processes. Conversely, the LMI layers primarily experience abrasive wear, accompanied by simultaneous oxidation and adhesive wear phenomena.
Although femtosecond-laser micromachining of bulk metals has been extensively studied, the coupled effects of energy input, pulse accumulation, and focal position on the material-removal behavior and cross-sectional evolution of ultrathin molybdenum remain insufficiently understood. In this study, the effects of laser energy density, equivalent pulse number, and defocus on cutting-front stability, sidewall morphology, redeposition, and taper formation were systematically investigated. The laser energy density was found to define the stable ablation window and govern the development of periodic sidewall features. The equivalent pulse number controlled the progressive advance of the cutting front and was, therefore, critical to maintaining cross-sectional uniformity. Small variations in defocus near the focal plane produced only limited improvements in taper, whereas large positive defocus substantially reduced the difference in material removal between the entrance and exit surfaces, thereby enabling low-taper cutting. These results establish a direct relationship between processing conditions, sidewall evolution, and cross-sectional geometry in ultrathin Mo sheets. Under the optimized conditions, pure-Mo grids were fabricated with a maximum relative dimensional error of 3.8%, an average relative error below 2%, and a half-taper angle of 14.3°. The findings provide a mechanistic and practical basis for the precision fabrication of Mo-based electron-gun grids and other thin-metal functional microstructures.
