A Deep Learning-based Data-driven Approach for Modeling and Optimization of Laser Transmission Welding of Polypropylene

In this study, a novel multi-stage framework is explored for laser transmission welding of polypropylene by integrating the design of experiments (DoE), artificial neural networks (ANN), non-dominated sorting genetic algorithm-II (NSGA-II), and multi-objective optimization by ratio analysis (MOORA). The framework enables comprehensive experimental investigation, process modeling, and multi-objective optimization. The response surface method (RSM) based DoE is used to develop correlations between welding parameters and responses, which form the foundation for experimental investigations. ANN models, incorporating additional fractional factorial DoE data, are employed for precise non-linear mapping of process parameters and responses, with predictive accuracy surpassing that of RSM models. The 3-6-1 ANN architecture is demonstrated to predict weld strength with high precision, while the 3-7-2-1 model is found to predict weld width accurately. These ANN models are used as objective functions for simultaneous optimization via NSGA-II, generating Pareto-optimal sets. These sets are further prioritized by MOORA, with an optimal parameter set of 220 W laser power, 81.29 mm/s scanning speed, and 63.97 mm defocus distance, yielding a weld strength of 63.86 N/mm and a weld width of 3.24 mm. The proposed synergistic DoE-ANN-NSGA-II-MOORA framework not only confirms its efficacy in this particular case but is also adaptable for other materials and processing applications

Analytical prediction of laser mediated polymer melt and damage width

Far-field (remote) laser net-shape scanning has revolutionary potential across numerous applications which involve localized heating of materials. It offers a very high degree of manufacturing flexibility in concert with process repeatability, traceability and low cycle energy usage when compared to traditional tooling-based solutions if the material response can be accurately predicted. The functional mechanism of such processes is localized heating; in this work, an analytical model of the line width of phase change occurring between a 3mm thick virgin polypropylene, PP, sheet and a visually transparent 25μm thick PP film is presented. Validation of the model is provided empirically by the scanned application of a CO2 laser exhibiting a Gaussian beam profile onto reference materials at varying incident spot diameters, powers and traverse velocities. This work is of value for process parameter prediction, as this analytically based method is computationally light, enabling its real-time implementation in manufacturing environments

Improvements of hybrid laser arc welding for shipbuilding T-joints with 2F position of 8 mm thick steel

One of the main concerns in the early stages of manufacturing flat units of shipbuilding is to ensure the quality of the joints throughout the structure. The flat units are constituted by butt welded flat plates, on which longitudinal T-welded reinforcements are placed to rigidize the structure. Among the different welding technologies, Hybrid Laser Arc Welding (HLAW) is becoming a mature process, profitable and highly productive. In addition, more innovative welding equipment are being developed nowadays, offering greater work flexibility, and raising expectations of achieving better quality, and economic viability. Another key point of HLAW to keep in mind is that structural distortions are reduced, resulting in decreasing the cost and time of straightening work. In the present contribution, the influence of HLAW parameters on the quality of fillet joints of naval steel has been analysed. Experimental HLAW tests were performed with a high power disk laser to join EH36 naval steel plates, with a T configuration. The influence of different processing parameters has been analysed, as the laser power, welding speed, wire feed rate and the configuration of the HLAW processes (including head angle and laser/arc leading process). In addition, FEM simulations were carried out in order to estimate residual stresses and distortion of welded part. The distortion values provided by FEM presented excellent agreement with the measured experimental results. To evaluate the welds, non destructive tests including X-ray tests, metallographic analysis of cross sections, and microhardness mapping tests were performed. Full penetration 8 mm T welds were obtained for the first time at an industrially applicable 2F position with a reasonable HLAW head angle, in one single step without sealing root, and using zero gap square groove edge preparation. The present contribution presents welding rates up to 2.2 m/min for 2F T-joints of this steel thickness, a much higher processing velocity than previously reported for industrial applications