welding for semi-finished plastic materials is described in ISO 472 as a process of uniting softened surfaces of materials, generally with the aid of heat (except solvent welding). Welding of thermoplastics is accomplished in three sequential stages, namely surface preparation, application of heat and pressure, and cooling. Numerous welding methods have been developed for the joining of semifinished plastic materials. Based on the mechanism of heat generation at the welding interface, welding methods for thermoplastics can be classified as external and internal heating methods,as shown Fig. 1. Classification of welding methods for semi-finished polymeric materials.
On the other hand, production of a good quality weld can not only depend on the welding methods, but also weldability of base materials. Therefore, the evaluation of weldability is of critical importance before welding operation (see Rheological Weldability) for plastics.