TWI Frequently asked questions
There are many techniques (over 20) for joining plastics including:
- Adhesive bonding
- Solvent welding
- Mechanical/snap fits
- Hot plate welding
- Hot bar welding
- Impulse welding
- Hot gas welding
- Extrusion welding
- "Flashfree" or BCF
- Vibration welding
- Spin welding
- Ultrasonic welding
- Friction stir welding
- Resistive implant welding
- Induction welding
- Dielectric welding
- Laser welding
- Infrared welding
- Microwave welding
Further information on many of these processes can be found in the concerning the individual processes or in the Plastics Welding Toolkit.
The most commonly used methods for nylon are spin, vibration, dielectric and ultrasonic welding. Laser welding and non-contact infrared have also successfully been used. The choice of process is affected by the form of the material- moulded component or film
The key issues specific to the welding of nylon are:
- Check which type of nylon it is as there are several types.
- Nylon is hygroscopic, therefore injection mouldings require 'drying' in an oven at 60°C overnight prior to welding.
- Nylon is semicrystalline, with a sharp melting point. To ensure successful ultrasonic welding, mouldings need to be carefully designed with the appropriate joint configuration.
- Glass-filled nylon produces a fine swarf during frictional welding processes such as spin or vibration welding. Flashtraps need to be designed into the mouldings.
- To dielectric weld nylon film, it may be necessary to preheat the welding tool to about 45-50°C. This helps to raise the temperature of the nylon above its T g (glass transition temperature), giving it the capacity to flow and hence to weld.
