Innovative process control and microstructure analysis in laser welding of nickel-plated copper, steel and aluminium joints for e-mobility components.

This thesis investigates novel laser welding techniques to guarantee reliable, high-quality joints in nickel-plated copper, steel, and aluminium components for e-mobility battery packs. The study addresses three interrelated research requirements: measuring the impact of input material variability, optimising process techniques for heterogeneous joints, and enabling advanced in-situ monitoring framework of weld quality. The impact of nickel-plating thickness on Cu-steel tab joints for cylindrical cells is assessed using a two-stage study that integrates statistical analysis of industrially electroplated busbars with regulated continuous-wave laser welding experiments. Variability in coating thickness exhibit a statistical correlation with weld morphology for two laser technologies: a high-brightness single-mode source and a beam-shaping source, underscoring disparities in process robustness and sensitivity to surface conditions. An optimised laser processing technique is formulated for thick Cu–Al junctions which representative of high-current busbar connections. An Archimedean spiral scanning pattern is utilised to separate energy input from interface geometry, facilitating concurrent regulation of penetration depth, interface width, and the generation of intermetallic compounds and porosity. Advanced metallographic and image analysis techniques, encompassing automated phase segmentation and semi-quantitative defect quantification, are employed to determine an energy-density range that reduces brittle intermetallic compounds while preserving sufficient joint geometry. A novel in-situ monitoring system is described, integrating a spectrally focused optical sensor with Continuous Wavelet Transform analysis of coaxial photodiode signals. Following the spectroscopic characterisation of material-specific emissions, filtered photodiode data are obtained during overlap welds and analysed in the time-frequency domain to extract characteristics that differentiate non-penetration, full-penetration, and over-penetration regimes. Quantitative criteria for the automatic classification of regimes are established, illustrating the viability of real-time quality evaluation for battery welding in industrially pertinent settings. The results collectively offer a systematic approach that connects input variability, process design, and monitoring to facilitate zero-defect laser welding in e-mobility manufacturing.