8 Plastic Welding Techniques & Methods

Plastic has become one of the most common materials on the planet!  Many electronic appliances, toys, mechanical parts and food containers are manufactured from hard plastics.  These days’ plastics are commonly found in numerous everyday items ranging from automobiles and motorbikes through to clothing.

Plastic is a low cost, versatile material that can be formed into virtually any shape and this is the reason that manufacturers love using it!  Unfortunately, hard plastics can be easy to damage and some forms of plastic degrade when exposed to harsh weather conditions.  When plastic breaks or cracks, most people either throw the object away or pull out the superglue.  However many people do not realise that it is also possible to weld plastic!

With this in mind, we have collated a few interesting and innovative solutions for repairing cracked or broken plastic objects. This will help you rejuvenate your plastic objects instead of discarding them in the bin!

Friction Welding

Just as the name indicates this form of welding uses friction to generate heat and fuse two pieces together. The two pieces are in relative motion to one another and a lateral force displaces the materials, joining them together.  This form of welding is commonly used by the aviation and automotive industries when joining both metals and plastics.

This technique has a couple of significant advantages.  The act of friction is very efficient at cleaning the surfaces that are to be joined. Friction welding can also weld objects together very efficiently in a matter of seconds.

Extruded Bead Sealing

A bead of very hot plastic is applied between two other sections of plastic.  This is typically done with a welding rod and a hand held plastic extruder.  In industrial settings, a plastic extrusion machine may be used.  After the super hot plastic is applied, the sections are pressed together.  Sometimes the two sections are heated to help form a bond.

High-frequency Welding

Materials that contain chemical dipoles (containing electrons) may be welded together using high-frequency electromagnetic waves.  Polyurethane and PVC are welded this way.  The two pieces are placed on a table press and the high-frequency waves are applied to the section that is to be joined.  Pressure is applied to the pieces after a set amount of time to facilitate the bonding process.

Hot Gas Welding

This technique uses a specially designed heat gun to soften the two pieces that are to be joined, along with a filler rod.  The technique is similar to extruded bead sealing in that it uses directly applied heat to help the plastic pieces bond.  This technique is often used to create small plumbing fittings, water tanks and other pieces of industrial equipment.

Hot Plate Welding 

Hot plate welding uses a heated metal plate to apply heat to two plastic surfaces before they are joined. The heated metal surface is coated with PTFE (polytetrafluoroethylene) to prevent the plastic from sticking to the surface.  Once the two pieces of plastic have melted and merged, they are held together until cooled.

Solvent Welding

This method uses a solvent, which softens the two pieces of plastic so the polymer chainscan be merged.  The solvent eventually evaporates, leaving the two pieces to harden again, forming a weld. This method is often used to join PVC or ABS pipes used in household plumbing.  Dichloromethane or tetrahydrofuran are the solvents commonly used in this process.

Laser Welding

This is one of the more “high tech” ways of joining or repairing plastics.  The two pieces of plastic are held together while a laser beam heats the join line.  The heat welds the two pieces together.  This method requires the plastic to be absorbent to the laser beam or for another absorbent material to be placed on the join line. 

There are many advantages to laser welding including speed, and very precise control. This is also a fantastic way to repair cracks in plastics.

Induction Welding

A piece of conductive metal is positioned between the two pieces of plastic that are to be joined.  A high-frequency generator heats the metal until it heats the surrounding plastic material.  Once softened, the two pieces are merged as one.