Welding of thermoplastics

Welding of thermoplastics Mechanical movement based plastic welding 

Heat source based welding can be performed by using a preheated tool or heating up the material and or tool at the right location by using laser, gas flame, electrical resistance or induction heating. The type of heating process is dependent on the polymeric material that has been used in the composite and the complexity of the part. 

The focus of this chapter has been to give a general overview of the many manufacturing processes available today for the manufactrrre of fiber reinforced polymer composites. Most of the technologies discussed are subject to continuous improvements as manufacturers from the aerospace, automotive, construction and consumer products industries strive to improve manufacturing costs and overall product quality. 

Schmitt U and Weick T (2004) Autoklaventechnik, in Handbuch Verhundwerkstoffe Werk-stoffe, Verarbeitung, Anwendung (Eds. Neitzel M and Mitschang P), Hanser Publishers, Munich, pp. 229-234. 

Thostenson E T and Chou, T-W (1999) Microwave processing fundamentals and applications, Composites Part A 30 1055-1071. 

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There are at present only a few commercial applications of ultrasound in the plastics industry. The best knovm is probably the welding of thermoplastics, a process which now lends itself readily to automation. In common with the welding of metals, the ultrasonic welding of plastics is primarily a hot stage. In the process ultrasound is applied to two layers of plastic, heat is generated at the interface causing the material... 

In friction or spin-welding of thermoplastics, one of the two pieces to be jointed is fixed in the chuck of a modified lathe and rotated at high speed while the other piece is held against it until frictional heat causes the polymer to flow. The chuck is stopped, and the two pieces are allowed to cool under pressure. The process is limited to objects having a circular configuration. Typical examples are dual-colored knobs, molded hemispheres, and injection-molded bottle halves. 

Infrared Welding of Thermoplastics. Colored Pigments and Carbon Black Levels on Transmission... 

Laser Transmission Welding of Thermoplastics Analysis of the Healing Phase 283 H. Potente, J. Korte, F. Becker Laser Marking... 

Diffusion. This theory proposes that adhesive macromolecules diffuse into the substrate, thereby eliminating the interface, and so can only apply to compatible polymeric substrates. It requires that the chain segments of the polymers possess sufficient mobility and are mutually soluble. The solvent welding of thermoplastics such as PVC (polyvinyl chloride), softened with a chlorinated solvent, is an example of such conditions being met. Diffusion will also take place when two pieces of the same plastic are heat-sealed. The joining of plastic service pipes for carrying gas and water makes use of the diffusion mechanism. 

This theory suggests that adhesion is developed through the interdiffusion of molecules in between the adhesive and the adherend. The diffusion theory is primarily applicable when both the adhesive and the adherend are polymers with relatively long-chain molecules capable of movement. The nature of materials and bonding conditions will influence whether and to what extent diffusion takes place. The diffuse interfacial (interphase) layer typically has a thickness in the range of 10-1,000 A (1-100 nm). Solvent cementing or heat welding of thermoplastics is considered to be due to diffusion of molecules. ... 

This method of curing the adhesive is based on the transmission of mechanical vibrations from an ultrasonic transducer to the adhesive at the interface between the mating parts. It is used most efficiently where a bead or film adhesive can be incorporated. Energy concentrations of 1.085 X 10 W/mVsec are sufficient for melt, flow, and cure of many thermoplastic adhesives. The equipment used is the same as that made for ultrasonic welding of thermoplastics. ... 

The use of plastics and their composites is rapidly increasing in numerous areas. However, the final assembly of products is often limited by the capability of existing joining techniques. The ability of ICPs, especially polyaniUnes, to absorb electromagnetic radiation and convert it into heat introduces another application in the welding of thermoplastics and thermosets [210]. 

Compatibility is an issue of relevance in a number of aspects of adhesion. Perhaps, the most obvious is the selection of solvents in the making of a Solvent-based adhesive, or for Solvent welding of thermoplastics. In both cases, solubility parameters can be employed. 

Seam welding n. Any stitchless procedure for joining fabrics based on the use of thermoplastic resins or the direct welding of thermoplastic materials. Seam welding is an alternative to conventional needle-and-thread seaming operations that is extremely popular in the non-woven field. 

Diffusion Adhesion arises through the interdiffusion of molecules in the adhesive and adherend. Solvent or heat welding of thermoplastic substrates is considered to be due to diffusion of molecules. 

Table 18. Microwave welding of thermoplastics using inherently conducting polymers. Reprinted from (1993) Polymer 34 3105 [148] with permission ...

Gehde, M., Giese, M. and Ehrenstein, G.W. (1997) Welding of thermoplastic reinforced with random glass mat. Polymer Engng Sci., 37, 702-714. 

Hughes, C. (1995) The sealing and welding of thermoplastics materials, in Plastics Surface and Finish, 2nd edn, (ed. Simpson G.W), The Royal Society of Chemistry, Cambridge, pp. 71-89. 

Moser L, Mitschang P and Schlarb A K (2008) Induction welding of thermoplastic polymer composites using robotic techniques, SAMPE J 44 43-49. 

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