In this chapter, a sequential modeling approach has been applied for modeling of laser transmission welding process using finite element method (FEM) and artificial neural network (ANN) technique to predict the weld pool dimensions in a shorter time frame. The scripting language, APDL (ANSYS® Parametric Design Language), is used to develop the three-dimensional FE model. During preprocessing, all the major physical phenomena of laser transmission welding process are incorporated into the model physics. Based on the temperature field predicted by the model, the weld pool dimensions (i.e., weld width and weld penetration depth) are calculated. The weld dimensions predicted by the developed FE model are further used for training a neural network model. It is found from the results of test data sets that the developed ANN model can predict the outputs with significant accuracy and takes less prediction time, which in turn saves time, cost, and the efforts for performing experiments.
TopIntroduction
Plastics are being fastest growing basic materials and the joining techniques of plastics are playing a signifacnt role for manfacturing plastic componensts in a cost effective way. Plastics can be joined using mechnical fasteners, adhesives or by welding. As the use of plastic components become more widespread, joining techniques play an important role in their processing. Since making the complex plastic components in one piece is not always practical and cost effective, various joining techniques have been developed including plastic adhesive joining, mechanical fastening and welding. The general advantages of welding techniques over other joining techniques are the fast and easy processing, tightness of the joint and high strength. The most widely used plastic welding procedures are heated tool welding, ultrasonic welding and vibration welding. In the case of heated tool welding, residues and contamination on the surface of the heated tool can lead to an undefined strength of the weld seam. Also, the fluff development in the ultrasonic welding is still a problem (Herfurth et al., 1999; Bonten & Tüchert, 2002).
In this context, more favorable presupposition is offered by heating of infra-red radiation, because the heat is transmitted without any contact to the plastic parts. Infra-red radiation can be transmitted by infra-red lamps and also by infra-red lasers. Laser can be used in two general ways: (i) irradiating the surfaces to be joined directly or (ii) passing through one transparent material and directly heating only the second material, precisely at the mating surface. This later process, described as laser transmission welding is providing to be very attractive as clean, precise and flexible process for joining plastic surfaces, even of dissimilar plastics (Baylis, 2002). With this technique melt is only created where it is needed, in the joining area of the both partners, reducing the energy input to a minimum (Hansch et al., 1998). This technique is capable of producing an asthetically perfect joint with qualitatively sound joint stregth. This technique is used to weld thermoplastics and thermoplatic elastomers, as the thermostes can not be remelted.
During laser transmission welding, the laser beam is focused at two overlying thermoplastic plaques, among which the top plastic part is transparent to the laser radiation and the bottom part is to be absorbent of that radiation. The laser energy transmitted through the transparent part is absorbed over a certain depth of the bottom opaque part, and the absorbed laser energy is converted into heat. The heat produced in the bottom part is transferred to the top plastic part; subsequently, interfacial layers of both the plastic parts are melted, which results in a firm joint at weld interface after cooling, as weld seam (Acherjeeet al., 2015). Natural thermoplastics have a high transmittance in the wavelength range of 0.8 - 1.1 µm, and thus, the diode lasers, Nd:YAG lasers and fiber lasers are used for the laser transmission welding process, as they are operated at this wavelength range. Figure 1 (a) shows the operational principle of the laser transmission welding process. The isometric view of the sample that is used for the present study is shown in Figure 1. (b).
Figure 1. (a) Laser transmission welding process, and (b) Scheme of the weld sample used in this study
Different laser types have been used for laser transmission welding of plastics. Since most plastics strongly absorb at 10.6µm, CO2 lasers are restricted to thin plastic films joining. By contrast, the Nd: YAG laser and diode laser are well suited for thick part welding due to high transmission of polymers in the near-infrared field. The compact design, modular set-up and high efficiency of diode laser make them convenient for industrial applications.