Cooling heated-tool welding

Heated Tool Welding. A bonding method whereby the surfaces to be joined are placed against a heated metal plate, then pressed together until the fused joint has cooled. Applicable primarily wheo joint faces are flat. 

Fusion or heated-tool welding is an excellent method of joining many thermoplastics. In this method, the surfaces to be fused are heated by holding them against a hot surface. When the plastic becomes molten and a flash about half the thickness of the substrate is visible, the parts are removed from the hot surface. They are then immediately joined under slight pressure (5 to 15 Ib/in ) and allowed to cool and harden. The molten polymer acts as a hot-melt adhesive, providing a bond between the substrates. 

Figure 14.13 Pressure vs. time curve showing the four phases of heated tool welding. Parts to be welded are pressed (P,) against the hot tool in phase I, and heat is transferred to the parts by conduction. Melting begins when the melt temperature of the plastic is reached. In phase II, pressure (P ) is reduced in order to increase melt thickness. In phase III, the hot tool is removed, and in phase IV, the parts are brought together under pressure (P ) to cool and solidify.

Heated Tool Welding - A method for joining thermoplastic parts in which a hot plate or hot tool is used to provide heat to melt the joining surfaces. The tool is then removed, and the parts are pressed together. While in the molten state, molecular diffusion across the joint interface occurs, and a homogeneous, permanent bond is formed after the parts are allowed to cool. A hot plate is used for fiat surfaces and a hot tool in the shape of the joint for irregularly shaped surfaces. Also called 5/on... 

Heated tool welding can in practice be more complex than the other forms of heat sealing already described. Its most simple form is an electrically heated plate or knife with polished surfaces. The parts to be bonded are held against the polished surfaces, thus conducting the heat to the interfaces of the plastics components, which become plasticised, after which they are held together under pressure until cool. The temperature requirements vary from about 180°C to 230°C. 

Hot-plate welding (hot-tool welding) n. Two plastic surfaces to be joined are first held lightly against a heated metal surface, which may be coated with polytetrafluor-oethylene to prevent sticking, until the surface layers have melted. The surfaces are then quickly joined and held under fight pressure until the joint has cooled. 

UPVC can be machined without difficulty, but keep the surfaces being cut well cooled. It may be welded by various techniques such as ultrasonic, heated tool, hot gas, friction and solvent. UPVC can be decorated using various methods such as painting, hot foiling, vacuum metallizing, EMI shielding and silkscreening. 

Rorvik (Ref 31) demonstrated that a zirconia-coated steel anvil retained more heat, with the workpiece allowing the tool to travel three times faster to obtain the same heat-affected zone width produced with a steel anvil. A statistical analysis of nine input parameters determined that cooling the anvil had a minimal impact on the friction stir weld in fact, tool rotation rate, travel speed, and tool depth were more important (Ref 24). Weld quality and performance is affected by differences in heat transfers observed when comparing the friction stir welding of flat plate versus extrusions (Ref 97). Extrusions typically have complicated cross sections, with features that quickly draw heat away from the friction stir weld. This dissipation of heat through the extrusion increases the tool heat input necessary to create a quality friction stir weld. 

Schematics of (a) tool position vs. time, (b) thermal cycle with superimposed continuous cooling transformation curve, and (c) pseudobinary phase diagram. Positions "a" and h" on the diagrams correspond to Fig. 7.15(a) and (b) and are used to describe microstructural evolution in the heat-and-deformatlon-affected zone/heat-affected zone for friction stir welding on TI-6AI-4V. 

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