Using a high frequency electromagnetic field, the material is heated and pressure added to melt and fuse the two materials together. No outside heat is applied. Instead the heat is generated within the materials. During cooling (under continued pressure), the materials are fused together and a weld has been created. This results in a very strong bond between the two parts.
Key facts:
- Also called: HF welding, RF welding, dielectric welding, radio-frequency welding
- Weldable materials: PVC, polyurethane (PU/TPU), EVA, PET-G
- Not weldable: polypropylene (PP), polyethylene (PE) — non-polar
- Typical cycle: seconds
- Operating frequency: typical 27.12 MHz – depending on HF generator used
- Common uses: medical fluid bags, inflation valves, eyelets, covers
What are the advantages of High Frequency welding or RF welding?
There are many other processes by which PVC components can be bonded to PVC film or other PVC parts. These include ultrasonic welding, friction welding and hot air. Chemical methods are also utilized, PVC bonding adhesive or the chemical cyclohexanone (often used for bonding tubes to flanges).However, High Frequency welding is often the preferred process for the following reasons:
- Rapid welding cycles
- Inexpensive tooling
- Clean process
- No subsequent drying/hardening
How HF welding or RF welding works
Time needed: 2 minutes
High Frequency welding or RF welding of PVC Cleat
- Position the material
Two layers of polar thermoplastic are placed between an electrode and a base.
- Apply the electromagnetic field
A high-frequency field is applied across the material.
- Heat builds inside the material
Polar molecules oscillate in the field and generate heat internally — no external heat source.
- Apply pressure
The electrode presses the layers together as they soften.
- Cool under pressure
The weld sets leaving a sealed, leak-tight join.
Carmo HF-welds a plastic cleat directly onto a PVC banner. The weld bonds the cleat to the fabric over a wide area for a strong, corrosion-free attachment point — using your existing HF equipment.
What Materials can be High Frequency welded or RF welded
Not all materials can be High Frequency welded together. The most common materials are polyvinylchloride (PVC), and urethane. Other materials such as EVA, PET-G and a number of types of formulations in the PET family are also welded with great success using this method. Additionally, a number of adhesives which are activated by the High Frequency field can be used to weld materials that are not normally considered compatible with this process. An example would be sealing either cardboard to cardboard or thermoformed blisters to cardboard as would be the process in a packaging application.
| Weldable (polar) | Not weldable (non-polar) |
|---|---|
| PVC — the most common; strong polarity | Polypropylene (PP) |
| Polyurethane (PU / TPU) | Polyethylene (PE) |
| EVA | PTFE |
| PET-G and parts of the PET family |
Why: HF welding works by agitating polar molecules in an electromagnetic field, so the heat is generated inside the material. Non-polar plastics don’t respond to the field, so they can’t be HF-welded.
Common products manufactured with high frequency welding are
- tarpaulins,
- tents,
- ceilings,
- advertising banners,
- waterbeds,
- inflatable boats,
- medical and especially blood- and urine-bags,
- tensile structures,
- conveyor belts,
- rain clothing etc.
What are the important factors for HF welding or RF welding?
The four most important factors / process parameters influence High frequency welding are
- Pressure applied
- Electrical power
- Welding time
- Cooling time
Finding the optimal process parameters will depend on your specific equipment, the materials involved and the specific geometries including thickness and area to be welded. Achieving optimal results is often an experimental process guided by experience. As a guiding rule, the thicker material and focus on short weld times you need, the stronger electrical power / HF generator you need.
There’s a deeper factor behind all four: the whole RF setup has to be tuned as one resonant system. The generator, the matching network, the HF cable, the press and the electrode form a circuit that must be impedance-matched to the load — the part and substrate between the electrodes. Tuned correctly, the system transfers energy into the material for a clean, repeatable weld; mismatched, power is reflected rather than absorbed, and the weld suffers. This is why both the exact operating frequency and its stability are so decisive: a small drift shifts the match and changes the result. It is also why the setup isn’t plug-and-play — change the HF cable or its length, or move equipment between stations, and the impedance shifts, so the system needs re-tuning to perform at its best.
If you are in doubt please contact our technical team who can guide you.
Alternatives to High Frequency welding or RF welding
While giving unique benefits, other alternatives to HF welding of plastic components do exist: Hot-air, hot-wedge, ultrasonic and gluing. Alternatively metal components can be mechanically applied, but will typically result in much lower strength and durability.
| Process | How heat is made | Typical cycle | Best for | Watch-outs |
|---|---|---|---|---|
| HF / RF welding | Inside the material (dielectric) | Seconds | Sealed, leak-tight seams in polar films & coated fabric | Polar materials only (PVC, PU, EVA, PET-G) |
| Ultrasonic | High-frequency vibration / friction | Under a second | Small rigid parts, spot joins | Less suited to large flexible seams |
| Hot-air / hot-wedge | External hot air or heated wedge | Continuous | Long seams on large fabrications (tarps, roofing) | External heat; slower setup |
| Impulse | Pulsed heated element | Seconds | Thin films, bags, packaging | Thinner materials only |
| Adhesive / solvent | Chemical bond | Minutes–hours cure | Dissimilar or non-weldable materials | Cure time; consistency; VOCs |
Is HF welding or RF welding right for your component?
HF welding is usually the right process when:
- Your part is a polar thermoplastic — PVC, polyurethane (PU), EVA or PET-G.
- The join has to be sealed and leak-tight — fluid bags, valves, inflatables, or covers that hold under load.
- You need fast, repeatable cycles at medium-to-high volume.
- You’re joining flexible film, sheet or coated fabric — not rigid, thick sections.
When it isn’t the answer: if your material is a non-polar plastic such as polypropylene (PP) or polyethylene (PE), HF welding won’t bond it — we’ll tell you that up front and point you to the right process.
Not sure if HF welding is right for your part? Tell us the material and the join you need to make, and our engineers will give you a straight answer — even when the answer is a different process.
High Frequency welding equipment suppliers
Carmo supplies electrodes for each of our weldable components and a series of machines for automatic welding of eyelets. For suppliers of HF generators and barwelders, partners include Forsström and others.
High Frequency welding machines for plastic components
High Frequency Welding (HF welding) machines are specifically designed to create precise and durable welds in plastic materials. By using high-frequency electromagnetic waves, these machines heat the plastic surfaces to the point of fusion, enabling them to bond seamlessly. This process is ideal for welding thin and thick plastic films, ensuring a strong, clean seam without the need for additional adhesives or mechanical fasteners. With a focus on quality and efficiency, our HF welding machines provide consistent performance, ensuring that your plastic products are securely welded with precision every time.
Some customers have also automated the placement of the foil, giving a fully automated production. More information on Carmo’s machines and electrodes are to be found on the website.
Your next step
Now you know how HF welding works — here’s where to go:
