This paper addresses in-process monitoring of weld penetration depth (WPD) during remote laser welding of battery tab connectors using optical coherence tomography (OCT). The research aims at studying the impact of welding process parameters on the accuracy of WPD measurements. In general, the highest measurement accuracy is achievable by positioning the OCT measuring beam toward the bottom of the keyhole. However, finding and maintaining the alignment between the OCT measuring beam and the bottom of the keyhole is a challenging task because of the dynamic changes in the size and shape of the keyhole itself. The paper addresses the above challenge by (1) developing welding process parameters for the Al-Cu thin foil lap joint (Al 1050 foil 450 μm and Ni-plated Cu foil 300 μm) using a novel adjustable ring mode (ARM) laser and (2) integrating OCT technology with two beams: one targeting the bottom of the keyhole and another as a reference to the part surface (TwinTec technology). The methodology is underpinned by the “Keyhole Mapping” approach, which helps one to identify the optimal placement of the OCT measuring beam with considerations to both measurement accuracy and stability of the keyhole. Findings indicated that welding with the ARM laser results in a more stable process, reduces fluctuations of the keyhole opening, and, therefore, helps one to improve the measurement accuracy by a factor of 50% (from the average error of 0.22 mm to 0.11 mm). Results further identified that the feasible operating window of the OCT measuring beam, corresponding to the highest measurement accuracy, is below 20 μm in length.

In the present work, the mechanical and magnetic properties of pure iron manufactured by laser-powder bed fusion (L-PBF) were investigated both in the as-built (AB) and stress relieved (HT) conditions, with the aim of elucidating their relationship with the microstructure and evaluating whether and to what extent it can be suitable for industrial applications. The L-PBF process was optimized to obtain high density, crack-free components. Specimens for microstructural analyses, tensile and magnetic tests were manufactured under the optimized conditions and tested both in the as-built and annealed (850 °C for 1 h, to relieve the residual stresses) conditions. Tensile tests showed high tensile strength in both AB and HT conditions (larger than those of conventionally produced pure iron), with higher ductility and lower strength after stress relieving. The magnetic study indicated a not optimal magnetic softness although the heat treatment enhanced the permeability and reduced the coercivity with respect to the as-built condition. The high mechanical strength and low magnetic softness came from the very fine grain size (about 5 μm) of L-PBF pure iron. Instead, the improvement of magnetic softness and ductility after heat treatment was attributed to the possible reduction of dislocation density and consequent stress relief. The results indicated the possibility to achieve a considerably high mechanical strength, in pure iron manufactured by L-PBF, although the fine grain size limits its magnetic softness.

A model for laser milling simulation is presented in this paper. A numerical model able to predict the physical phenomena involved in laser ablation of metals was developed where the heat distribution in the work piece, the prediction of the velocity of the vapor/liquid front, and the physical state of the plasma plume were taken into account. The model is fully 3D and the simulations makes it possible to predict the ablated workpiece volume and the shape of the resulting craters for a single laser pulse or multiple pulses, or for any path of the laser spot. The numerical model was implemented in C++ and an overview of the code capacities is presented.

Studies have shown the influence of WAAM process parameters on mechanical properties, bead formation, dimensional accuracy, and microstructure. However, metal transfer modes and their interactions with input variables have not been investigated thoroughly. Therefore, short/spray, pulse and double pulse modes were investigated in this study at different current levels. Bead-on-plate trials were conducted by depositing ER70S-6 wire to investigate bead morphology, dilution, microstructure, and hardness. The study was supported by a detailed statistical approach, including analysis of variance (ANOVA) and regression analysis. Similarly, the combined effects of hatch distance and current were studied on bead formation in multi-layer deposits. Moreover, a thin wall and a cubic structure were deposited to realize the WAAM capability for larger depositions. The microstructures of thin wall and cubic structure were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). The study concludes that metal transfer modes at various currents significantly influence bead geometry, microstructure and hardness. The microstructure of bead-on-plate trials show fine lamellar structure at low current in all modes. Higher current results in coarse grains with a polygonal and columnar morphology. The hardness shows a decreasing trend as the current increases. The combined effects of current and hatch distance alter bead morphology; however, an optimized combination yields smoother surfaces. The microstructure of thin wall showed a slight anisotropy along the building direction. The presence of small pores was witnessed from OM and SEM images. Similarly, the cubic structure showed a more homogeneous microstructure with much lower porosity. The hardness profile of the thin wall exhibited small fluctuations along the building direction, while that of the cubic structure was more uniform.

Laser processing of metallic thin sheets has gained undoubted industrial interest in the last decade especially due to its implications in the e-mobility field. In particular, dissimilar welding of thin sheets made of different materials, such as aluminum, copper, and steel is nowadays recognized as an effective solution for many joining applications in battery and related component production. According to these considerations, the present paper is aimed at evaluating the possibility to perform a sound joining of thin copper sheets on thin steel ones in a lap-welding configuration. This application is of particular interest especially when cylindrical cells have to be electrically connected to any of the elements constituting the battery, such as printed circuit boards, busbars, etc. By means of a continuous wave fiber laser and a galvo scanner, an experimental campaign was carried out in order to define a process window for characterizing the above-mentioned welding application. The results were characterized by means of metallographic analyses, microhardness measurements, electrical conductivity tests, and scanning electron microscopy-energy dispersive system analyses. Particular attention was placed on the role of process parameters in controlling the penetration depth on the lower steel layer, since it constitutes the external housing of the single cell and a drop through can seriously damage the cell itself.