Heat generation is crucial for bonding two or more pieces of thermoplastic materials, forming a welding joint or joint area. Typically, heat is applied to the edges of the materials to melt them, allowing the edges to merge seamlessly.
The process of plastic welding involves three key phases: surface preparation, application of heat and pressure, and cooling.
A variety of plastics can be welded, including acrylic (PMMA), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PETE or PET), polyvinyl chloride (PVC), and acrylonitrile-butadiene-styrene (ABS).
Considerations for Plastics Welding
Successful plastic welding requires appropriate equipment, such as hot air welding tools, plastic welding rods, and extruders. Critical factors include heating and cooling times, and the applied pressure. Devices that hold the plastic components together during heating ensure a complete bond.
Plastic welding is utilised both for joining pieces and repairing cracks.
Applications of Plastics Welding
Plastics are versatile and used across various sectors, including packaging, electronics, construction, medical, aerospace, and automotive industries. Properly applied plastic welding can result in extremely strong joints.
Welding Techniques for Plastics
Selecting the right welding method is essential for achieving high-quality, reliable results. Here are some commonly used techniques in fabrication and production:
Heated Tool Welding
- Also called hot plate, butt fusion, mirror, butt or platen welding
- Hot plate temperature typically 30-1000C above melting point of plastic to be welded
- Can produce high-strength welds, easily automated, can weld some dissimilar materials using heated tools
Hot plate pipe welding video
![Heating Tool Welding]()
INFRARED WELDING
- IR sources include electrically-heated metal plate, metal foils, IR diodes, short-wave IR lamps
- Energy efficient and non-contact process
- Shorter weld times and smaller weld bead than heated tool welding, energy efficient and non-contact process
HOT GAS WELDING
- Manual welding technique where the weld quality is dependent on operator skill
- Uses a consumable filler rod.
- Hot gas temperature ranges between 250-4000C
- Weld speed: 0.2-0.3m/min
- Can weld almost any size and shape of component and low cost and portable equipment
Hot gas extrusion welding video
![Hot Gas Welding]()
EXTRUSION WELDING
- Manual welding technique where the weld quality is dependent on operator skill
- Also uses consumable filler material
- Weld speed: 0.5-1.0m/min
- Joint usually filled in one passed and mainly used for PE and PP, PVC and PVDF as well
- Can weld large components, low cost, with portable equipment
- Faster than hot gas welding
![Extrusion Welding]()
RESISTIVE IMPLANT WELDING
- Uses electrically conducting implant such carbon fibre, graphite fibre, stainless steel foil/wire, copper/nickel braid/mesh
- Not restricted to flat joint lines and welded parts can be disassembled
- Typically applied in pipelines, plastic pallets, thermoplastic composites and dinghy hulls/decks
INDUCTION WELDING
- Also called electromagnetic or EMA welding
- Requires implant at the joint line normally a composite of polymer and metal fibres or ferromagnetic particles
- High frequency (2-10MHz) electromagnetic field from induction (work) coil
- Eddy currents induced in implant which heats up and melts to produce weld
- Can weld three-dimensional joints and complex geometries, welded parts can be disassembled and can weld parts with wide tolerances
FLASH-FREE WELDING
- Also called BCF for pipes (up to 63mm diameter) and Flow fusion for sheets (up to 3mm thick)
- Pipes butted together and clamped
- Heating collar placed around pipe at joint line
- Inflatable bladder placed inside pipe at joint line
- Heat conducted through pipe wall
- No weld flash
- Long weld times.
ULTRASONIC WELDING
- Vertical motion at end of welding horn (sonotrode) (20-40kHz frequency; 30-125µm amplitude)
- Ultrasonic energy transmitted through upper part to joint interface
- Requires specially-designed joint to concentrate the energy (energy director)
- High productivity, easily automated, energy efficient and easy tooling change
Ultrasonic Welding of Plastics video
SPIN WELDING
- Rotational motion; speed: 500-10,000rpm; weld times: 2-5s
- Two modes of operation: Inertia and Direct-drive
- Applicable to almost thermoplastics
- Energy efficient, low equipment costs, easily automated and can weld large parts (1m diameter)
Spin Welding of Plastics video
VIBRATION WELDING
- Linear reciprocating motion (frequency: 100-300Hz, Amplitude 1-4mm, Weld times: 3-15s)
- Applicable to almost thermoplastics- Energy efficient, easily automated, insensitive to surface preparation, and can weld large parts (1.5m)
Vibration Welding video
ORBITAL WELDING
- Orbital motion between parts (Amplitude: 0.5-1.5mm, Weld times: 3-15s
- Better suited for thin walled parts and for parts containing electrical components compared to vibration welding
- Can weld larger parts than ultrasonic welding
LASER WELDING
- Two main variants: transmission laser welding and direct laser welding
- Advantages are automated process, non-contact, complex shapes possible, precise placement of welds (50µm or less), no surface damage
Invisible joining clear plastic to clear plastic video
HEAT SEALING
- Weld times 1-3s
- Low equipment costs and fast welding cycle times
- Used in packaging (bags, lids on pots, blister packs) and electronics
RADIO FREQUENCY WELDING
- Also known as RF, high-frequency or dielectric welding.
- High frequency (27MHz) electric field applied across material
- Generates molecular friction and heating in polar materials
- Use restricted to thin sheet polar thermoplastics (PVC and PU); weld times: 5-10s
- Capable to welding multiple layers simultaneously, easily automated, cut/seal possible
DIFFUSION WELDING
- Advantages are transparent welds and capable of welding multiple layers simultaneously
- Applied in fluidic and microfluidic devices
![Plastics welding inspection training]()
Plastics Welding Training and Certification
TWI MENA offers comprehensive training and certification in plastics welding. Training covers pipe welding, fabrication, lining membrane welding, plastic pipe weld inspection, and construction quality assurance.
Specialist courses include introductions to plastics welding, adhesive bonding, and ultrasonic welding. Training at TWI leads to internationally recognised qualifications, enhancing skills, career progression, and competence verification.
Training courses and examinations are available at TWI’s Plastic Welding Training Centre in the UK, in Malaysia (with upcoming availability in the Middle East), or at customers’ locations globally.
To learn more about the programme visit: https://www.twi-global.com/locations/middle-east/training/plastics/plastics-welder-training-and-qualification or contact Enquiries@twime.com for further assistance.
Useful links and references:
- Plastic Welding Training Course https://www.youtube.com/watch?v=NREHFnUQnKo
- Webinar Recording: Webinar Recording: Introduction to TWI's Plastic Welding Programme - https://www.youtube.com/watch?v=t4THXpB0iX0&t=5s
- S. Andrews and M. Troughton, 2024. Welding of Thermoplastic Components [PowerPoint slides]. TWI Ltd.
![At TWI Malaysia]()
Plastics Training