What is HF welding?

What is HF welding?

High Frequency (HF) or Radio Frequency (RF) welding is the joining of materials by supplying HF energy in the form of an electromagnetic field (27.12 MHz) and pressure to the material surfaces to be joined.

So, what is HF welding? A generator produces the energy. The tool used to supply the energy is called an electrode. The electrical energy causes the molecules within the material to start moving, which generates heat that causes the material to soften and thereby fuse together. No outside heat is applied. The heat is instead generated within the material. After cooling the welded surface under maintained pressure, the material is fused and a weld has been created. The weld seam can be at least as strong as the surrounding material – or even stronger.

Four important factors

Four important factors that affect the final weld result are pressure, welding effect, welding time and cooling time. These parameters can be adjusted and combined in different ways to achieve the optimal welding result for a specific material.


The material most commonly used with HF-welding is PVC (polyvinyl chloride), also called vinyl and PU (Polyurethane). The material can be thick or thin, reinforced or coated. It can also be plain, coloured or patterned. A few of these material suppliers are Mehler Texnologies, Sioen Industries, Serge Ferrari, Verseidag, Saint Clair Textiles, Dickson Constant and Rivertex.

Who uses HF-welding?

Forsstrom’s customers manufacture a great variety of end products in these materials, such as truck and boat covers, tarps, tents, structures, pool liners, sunshades, billboards, inflatable products, liquid tanks, movie screens, waterbeds, stretch ceilings, valve membranes and oil booms.

So, why use high frequency (HF) rather than other technologies?

HF-welding is by far the best method for joining PVC and PU materials. The weld is much stronger, compared to other technologies, such as hot air, hot wedge or impulse welding. The resulting weld is also airtight and waterproof.

Advantages of HF-welding

  • Repeatable, reliable technology
  • Strong, durable and even welds
  • Air, gas and waterproof welds
  • Multi-layer welding
  • An environmentally friendly choice

Apart from high frequency (HF) there are other technologies for joining material, such as:

Hot air

Hot air is the technology where hot air is blown between layers of material through a nozzle and where rollers press the preheated surfaces together.

+ Can be used for non-dielectric materials

– Difficult or impossible to remake the weld if the result is not satisfactory

Hot wedge

The hot wedge is a process where the material is dragged against a hot surface (wedge) and where rollers press the preheated surfaces together.

+ Can be used for non-dielectric materials

– Difficult or impossible to remake the weld if the result is not satisfactory


Impulse is a technology where a steel band is covered with PTFE tape and where electrical current is running through the steel band.

The level of current generates heat which is transferred mechanically to the fabric.

+ Can be used for non-dielectric materials

– A negative effect with this technology is that the steel band will be significantly hotter towards the ends on the steel band, which can cause burns on sensitive fabrics


Ultrasonic is sound that accelerates down into a ”Sonotrode” (tool) resulting in a mechanical hammering effect. This pounding generates heat in most fabrics. The heat needs to penetrate the first layer in order to join the second layer.

+ Can be used for non-dielectric materials

– It is difficult to weld more than two material layers without damaging the surface of the material and causing burns

What is so fantastic about HF-welding?

High frequency welding is one of the most commonly used technologies for bonding PVC and PU materials. The result of the weld is outstanding and long-lasting.

End products

A Forsstrom machine creates fantastic opportunities to manufacture exciting end products!

This picture show a HF-welding machine, the TDW-Mega. Máquinas de soldar por alta frecuencia. Hochfrequenz-Schweißmaschinen. Maszyny wysokiej częstotliwości

Our machines

Forsstrom has a wide range of HF-welding machine models – each developed to suit different types of manufacturing. We categorize them as stationary, travelling and machines for automation.

This picture shows high frequency welding. What is HF welding? Soldadura HF-svetsning

Why HF?

There are other technologies than high frequency (also called radio frequency) welding which can be used to join sheets of PVC and PU materials. So, why use high frequency (HF) rather than other technologies?

Do you want to learn more?

Contact Forsstrom’s head office at sales@forsstrom.com or your local representative.

Why HF?