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.
Few 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.
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.
Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.