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Gaps at part interfaces pose a major challenge for laser transmission welding (LTW) of thermoplastics due to the reliance on contact conduction between the absorptive and transmissive parts. In industrial applications, gaps between parts can occur for a variety of tolerance and process control reasons. Previous experimental and modeling work in LTW has focused on gap-free joints, with little attention to bridging a gap with thermal expansion of the absorbing material. A two-dimensional comprehensive numerical model simulated bridging gaps in LTW. Using the model, operating parameters were selected for welding across a 12.7 μm gap and a 25.4 μm gap by creating sufficient thermal strain to bridge the gap and form a weld. Using these operating parameters, PVC samples were welded in a T-joint geometry with a designed gap. The quality of the welds was assessed visually, by destructive force testing and by measuring the weld size to quantify the weld strength. All the experimental samples, for the two gap sizes, bridged the gap and formed welds. The average weld strength of the 12.7 μm gap samples was 16.1 MPa, while the 25.4 μm gap samples had an average strength of 10.0 MPa Gaps were successfully bridged with LTW by using a two-dimensional model to design the operating parameters. To achieve higher modeling accuracy, a three-dimensional model might better simulate the thermal diffusion in the direction of laser travel. [ABSTRACT FROM AUTHOR]

Two laser transmission welding experiments involving polyvinyl chloride are presented that aim to validate a previously presented welding model while helping to further understand the relationship between welding parameters and weld quality. While numerous previous research papers have presented the results of laser welding experiments, there exists minimal work validating models of the welding process. The first experiment explores the interaction of laser power and welding velocity while the second experiment explores the influence of clamping pressure. Using the weld width as the primary model output, the agreement between the welding experiments and the model have an average error of 5.6%. This finding strongly supports the validity of the model presented in Part I of this two paper set (Van de Ven and Erdman, 2007, ASME J. Manuf. Sci. Eng., 129, pp. 849-858). Additional information was gained regarding the operating window for laser transmission welding and the thermal decomposition of polyvinyl chloride. Clamping pressure was found to provide a small, but not statistically significant, influence on the visual appearance, weld width, and weld strength. [ABSTRACT FROM AUTHOR]

This paper discusses the development of a model of laser transmission welding that can be used as an analytical design tool. Currently the majority of laser transmission welding (LTW) applications rely on trial and error to develop appropriate process parameters. A more rigorous design approach is not commonly used primarily due to the complexity of laser welding, where small material or process parameter changes can greatly affect the weld quality. The model developed in this paper also enables optimizing operating parameters while providing monetary and time saving benefits. The model is created from first principles of heat transfer and utilizes contact conduction that is a function of temperature and pressure, Gaussian laser distribution, and many material properties that vary with temperature including the absorption coefficient. The model is demonstrated through a design example of a joint between two polyvinyl chloride parts. The model is then validated with samples welded with a diode laser system using the operating parameters developed in a design example. Using the weld width as the primary output, the error between the model and the experimental results is 4.3%, demonstrating the accuracy of the model. [ABSTRACT FROM AUTHOR]