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are used for plastic parts. Humanly visible light has a wavelength of 400nm to
700nm whereas plastics welding lasers operate in the range 800nm to 1100nm.
Lasers can be used to weld almost all thermoplastics, including dissimilar plastics
provided their respective melt temperature ranges overlap.
Laser welding has a number of advantages that can be used to offset the relatively
high cost of the equipment. Laser welding is a high-speed, non contact process so it
can be used with fragile components such as electronics modules. Heat is
generated directly at the joint so temperature increases can be confined and
minimised. No flash or debris is generated. Computer-guided lasers can deal with
complex three-dimensional joints. Laser welding is therefore particularly suitable
for very large and very small parts, for medical and other 'clean' applications, and for
assemblies incorporating delicate components. Applications exist in automotive,
chemical and packaging industries for the high-speed joining of films
Infrared welding: This process uses an infrared source, which is a tungsten
filament line heater, high -intensity quartz heat lamps or a ceramic plate. The
components to be joined must be brought close enough to the heat source for the
correct amount of time for melting to occur. The heat is then withdrawn and the parts
are pushed together to form a weld. . Infrared radiation can penetrate into a polymer
and create a quick melt zone. Infrared welding is at least 30% faster than heated tool
welding.It is also a non-contact process, meaning that there is nothing to
contaminate the joint and brittle components can be welded without damage
because no shear force is applied to the parts during heating. The advantages of
this process include speed, high reproducibility and bond quality can be obtained,
can be easily automated, and be used for continuous joining.
The depth of the melt zone depends on many factors, including minor changes in
polymer formulation. For example, colorants and pigments will change a polymer's
absorption properties and will affect the quality of the infrared welding process.
Generally, the darker the polymer, the less infrared energy is transferred down
through a melt zone, and the more likely will surface degradation occur through
overheating.
Resistance Wire Welding: The resistance wire welding method of joining
employs an electrical resistance heating element laid between mating substrates to
generate the needed heat of fusion. Once the element is heated, the surrounding
plastic melts and flows together. Heating elements can be anything that conducts
current and can be heated through Joule heating. This includes nichrome wire,
carbon fiber, woven graphite fabric, and stainless steel foil.After the bond has been
made, the resistance element that is exterior to the joint is cut off. Implant materials
should be compatible with the intended application, since they will remain in the
bond line for the life of the product.
Impulse welding: This method uses the same basic principle as a hot bar
mentioned above; heat and pressure are used to produce a weld between two
sheets of thermoplastic. However, impulse welding introduces much greater control
with the same rapid heating experienced with the hot-bar process (1-3 s process
time) and cooling that is managed according to an automatable and precise regime.
This is a rapid and clean method that produces minimal waste.
Indirect Heating Methods or Induced heating:

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