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Induction welding: (Electromagnetic welding): Induction welding can be done by
pressing two pieces of plastic material together around a metal insert. When passed
through a magnetic field, the encased metal is heated, and the compression
produces a fusion weld. The metal remains sealed inside the part. Bonding agents
heated inductively reach temperatures of 300°F in 0.1 sec to fuse with the heat-
resistant substances. Thermoplastic bonding agents filled with either
electromagnetic or ferrite materials may also be used in induction welding. A metal
grid or insert placed between mating thermoplastic substrates before induction
heating. When the joint is positioned between induction coils, the hot insert causes
the plastic to melt and fuse together. Slight pressure is maintained as the induction
field is turned off and the joint hardens. If metallic particles are used, the alternating
magnetic field induces current flow within the particles, generating heat. When
ferrite is used, no current is produced. Instead, heat is produced by molecular
friction as the particles try to retain their magnetic charge when the fields are
reversed. Induction welding is a high-cost technique and is suitable for difficult-to-
weld plastics such as polypropylene, and for shapes that cannot be fitted into an
ultrasonic welding machine. The process is best suited for bonding most
polypropylene, polyethylene, styrene, ABS, polyester and nylon in high-volume,
highly automated joining operations.
Dielectric welding: This process works on the principle that causing a molecule to
oscillate & generates heat. An alternating electric field is imposed on the joint, which
causes rapid reorientation of polar molecules. As a result, heat is generated within
the polymer by molecular friction. The heat causes the polymer to melt and pressure
is applied to the joint. The field is then removed, and the joint is held until the weld
cools. Blood, intravenous-infusion and ostomy bags, vinyl (PVC) sheeting such as
automobile upholstery, swimming pool liners, and rainwear are examples of
products joined in this way.
Welding by Frictional Heat: In friction welding, the joint interface alone is heated due
to mechanical friction caused by one substrate surface contacting and sliding over
another substrate surface. The frictional heat generated is sufficient to create a melt
zone at the interface. Once a melt zone is created, the relative movement is
stopped, and the parts are held together under slight pressure until the melt cools
and sets. Common friction welding processes include:
Spin welding: Spin welding uses frictional forces to provide the heat of fusion at the
interface. Spin welding joins thermoplastic parts with a circular joint area by bringing
the part interfaces together, under pressure, with a circular, spinning motion. One
part is held stationary in a fixture, while the other is rotated against it under pressure.
At least one section must be circular. The frictional heat that is generated causes
the part interfaces to melt and fuse together, creating a strong, hermetic seal. Once
the rotation is stopped, position and pressure are maintained until the weld sets.
Vibrational welding: Spin welding depends on rotation and joins circular parts,
whereas in vibrational welding, surfaces rectangular or irregular in plan to be joined
are pushed together in linear and orbital motion to generate frictional heat. The
parts are frictionally heated by pressing them together and vibrating one of the parts
at 120 to 240 Hz, in the plane of the joint. After 2 to 3 sec, vibration is stopped at the
exact required relative position of the two pieces. Pressure is maintained briefly

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