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What is Plastic Welding?

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  • Written By: M. Rosario
  • Edited By: C. Wilborn
  • Last Modified Date: 22 September 2016
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    Conjecture Corporation
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Plastic welding is a method of fabrication used to fuse plastic parts together. The process works by heating parts of each piece until they soften or liquefy. When the plastics cool, a chemical bond is formed between them that fuses the pieces together. A thermoplastic welding rod is commonly used to act as glue between the two pieces.

Several methods of plastic welding are employed for different purposes. They vary according to the type of welding equipment and welding supplies used. The base material the plastic component is made of also affects the method used for plastic welding. Thermoplastics are generally preferred because of their ability to be repeatedly melted and re-solidified.

Hot gas welding uses a jet of heated air to weld the plastic. The hot air softens and melts the plastic to allow the pieces to fuse. A heat gun designed for this technique guides the airflow for better precision. Welding rods, usually made of the same material as the two base plastics, fill the gap between the pieces.

An airless welder heats the welding rod through a heating machine or process. This method helps prevent excessive materials from the rod from accumulating and the base materials from warping. Airless welding is particularly useful for welding thermosets. These are plastics that do not easily melt when exposed to high heat.

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Light and vibration are two plastic welding techniques for airless welding. Different materials that cannot be welded by hot gas can often be fused using these processes. They are also used to weld parts that typically need to maintain their relative thinness. These methods include ultrasonic, vibration, laser, and thermoplastic welding.

Ultrasonic welding applies low amplitude and high frequency vibration to weld the pieces. The vibration produces heat, just like when hands are rubbed together, that joins the two pieces. The heat and pressure from the ultrasonic welder create a quick and seamless weld between the two pieces. This is suitable for producing small components like flash drives and semiconductors.

Vibration welding has higher amplitude and lower frequency compared to ultrasonic welding. Pressure added to the materials as they are vibrated causes additional heat. The concentration of energy on the materials' surfaces reduces unintended melting and gives a stronger weld without additional weight.

Laser welding uses light to melt the materials. To laser weld, one material should be transmissive to light while the other should be absorptive. The two materials are joined under pressure. A laser beam is then passed from the transmissive material through the absorptive one. This generates heat and creates a permanent weld.

Thermoplastic welding is the opposite of laser welding. In this technique, the laser passes from a transparent material through a colored material that traps the light. The transmissive material then melts into the absorptive material which fuses them.

There are a wide array of applications for plastic welding. Plastic parts that might be expensive to replace can often be repaired when new parts are welded in. Waterproof and airtight containers like water tanks and ventilation ducts are sometimes assembled by plastic welding. It is also commonly used to manufacture products such as car parts and large panels.

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