Basic Of Plastic Welding

Plastic welding and spot welding – both are almost similar to each
other. There is a difference noted. In plastic welding, heat is supplied
through convection of the pincher tips, instead of conduction. The two
plastic pieces are brought together. At the time of welding, a jet of hot
air is liberated. This melts the parts to be joined along with the plastic
filler rod. As the rod starts melting, it is forced into the joint and
causes the fusion of the parts.
Plastic identification is the first point to be noted in order to choose a
suitable plastic welding rod. A plastic welding rod or thermoplastic
welding rod is of a constant cross-section shape. Using this, two plastic
pieces can be joined. It may have a circular or triangular cross-section.
Porosity of the plastic welding rod is an important factor. Air bubbles in
the rod will be created due to its high porosity.
This is responsible for
decreasing the quality of the welding. So, the rods used must
maintain zero porosity.
Otherwise, they should be void less. Products
like chemical tanks, water tanks, heat exchangers and plumbing
fittings are manufactured by using the technique of plastic welding. By
adopting this technique, money can be saved.
Using plastic welding, two plastics can be welded together. This type
of weld is performed on children’s toys, lawn furniture, auto parts and
other plastic equipments which are used daily – both for domestic and
commercial purposes. In order to join the thermoplastics, when they
are heated an under a particular pressure, this type of welding is
employed. In normal practice, using filler material, the pieces are
joined together. There are certain occasions wherein filler material can
be avoided. Generally, plastic is not durable and has a shorter life
span. Natural elements like cold weather, ultraviolet radiation from the
sun or continuous exposure to chemicals causing contamination, will
create damage to plastic products. Plastic can be subjected to damage
if it is hit on a hard surface. But, as the price of new parts is high, it is
preferred to repair the existing products. 
important welding processes used for thermoplastics welding are ultrasonic welding,
vibration welding, spin welding, and induction welding. 

Ultrasonic Welding of Plastics 

Ultrasonic plastic welding is, in principle, the joining of thermoplastics through the use of
heat generated from high frequency mechanical motion. It is accomplished by converting
high frequency electrical energy into high frequency mechanical motion. The mechanical
motion along with the applied force creates the frictional heat at the mating surface of the
plastic components. In effect, the plastic material at the joint surface melts and forms a
molecular bond between the parts. The frequency of the frequency is around 20 to 40 kHz.
Figure 4.6.1 depicts the line diagram of an ultrasonic welding machine. The electrical power
supply provides high-frequency electrical power to a typical piezoelectric based transducer
creating a high frequency mechanical vibration at the end of the transducer. Next, the booster
amplifies the mechanical vibrations produced by the transducer and supplies to the horn.
Further, the horn (also known as sonotrode) transfers the amplified mechanical vibrations to
the workpiece. 
Ultrasonic Welding of Plastics images
Ultrasonic Welding of Plastics

Advantages Of Ultrasonic Plastic welding:

  • Fast, economical and easily automated.
  • Mass production, upto 60 parts per minute is possible.
  • Increased flexibility and versatility
  • Possibility to join large structures.
  • Used in health care industries due to clean welds.
  • Produce the high strength joints consistently. 
Disadvantages Of Ultrasonic Plastic welding:
  • Large joints (>250 x 300 mm) can not be welded in a single operation.
  • Specifically designed joints are required.
  • Ultrasonic vibrations can damage electric components.
  • Tooling costs for fixtures are high
Applications of Ultrasonic Welding of Plastics
(1) Ultrasonic welding is used in the automotive industry to fabricate headlamp parts,
dashboards, buttons and switches, fuel filter, fluid vessels, seat-belt locks, electronic
key fobs, lamp assemblies and air ducts. 
(2) In electronic appliances like switches, sensors and data storage keys are fabricated
using ultrasonic welding. 
(3) Ultrasonic welding is also used to make medical parts like filters, catheters, medical
garment and masks. 
(4) Packing applications like blister packs, pouches, tubes, storage containers and carton
spouts can be fabricated using ultrasonic welding. 
Reference and Download Report :
GATE 2017 Exam Dates, Application Form, Eligibility Criteria
Spread the love