What is HF welding or RF welding?

High Frequency (HF) or Radio Frequency (RF) welding is a technique used to join thermoplastic materials. It employs radio waves and pressure to create strong, high-quality welds. Operating at 27.12 MHz, this process uses electromagnetic energy to generate heat within the materials being joined.

How does HF welding or RF welding work?

HF welding involves a few key steps:

  1. Energy Generation: A generator produces HF energy.
  2. Energy Application: An electrode tool delivers this energy to the material surfaces.
  3. Heat Generation: The energy causes the molecules within the material to move, generating heat internally.
  4. Material Softening: This internal heat softens the material, allowing it to fuse.
  5. Cooling Under Pressure: As the material cools under pressure, a strong, durable weld is formed.

Unlike other welding methods, HF welding does not require an external heat source. The heat is generated within the material itself, leading to weld seams that are often as strong or stronger than the surrounding material.

Why use high frequency or radio frequency?

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.

Repeatable, reliable technology +

HF welding uses high-frequency electromagnetic energy to generate heat, ensuring consistent results with each weld. The precision and control of this technology lead to repeatable outcomes, reducing the likelihood of errors or defects in the welding process.

Strong, durable and even welds +

HF welding creates strong bonds between materials, resulting in durable and long-lasting welds. The process effectively fuses materials together, forming a seamless joint that can withstand considerable stress and strain. Moreover, HF welding produces even welds without inconsistencies, enhancing the structural integrity of the final product.

Air, Gas and Waterproof welds +

The nature of HF welding ensures that the welds are airtight, gas-tight, and waterproof. This characteristic is particularly valuable in applications requiring a barrier against air, gases, or liquids, such as in the production of inflatable products, liquid tanks, or biogas covers.

Multi-Layer Welding Capability +

HF welding can weld multiple layers of material simultaneously, providing versatility in manufacturing processes. This capability allows for the creation of complex products with layered components, enhancing design possibilities and production efficiency.

Environmentally Friendly +

Compared to traditional welding methods that may involve adhesives, solvents, or other chemicals, HF welding is more environmentally friendly. It typically does not require additional consumables or generate harmful byproducts, contributing to sustainable manufacturing practices.

Partners. PVC and PU material.

What Materials Can Be HF or RF welded?

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 or RF 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.

Factors of HF or RF welding


Pressure exerted during HF welding is crucial for ensuring proper contact between the materials being welded. It facilitates intimate contact, enabling the efficient transfer of electromagnetic energy that generates heat to melt the materials and form a bond. Adequate pressure eliminates air gaps and ensures uniformity in the weld, resulting in stronger and more reliable joints.

Welding effect

The welding effect refers to the heating of materials caused by the application of high-frequency electromagnetic energy. This energy generates heat primarily through molecular friction within the materials, leading to localized melting and fusion at the interface. The welding effect must be carefully controlled to achieve the desired level of penetration and bonding without causing excessive heating or damage to the materials.

Welding time

Welding time is the duration for which the high-frequency energy is applied during the welding process. It is critical to control this time to ensure sufficient heating and bonding of the materials while preventing overheating or degradation. Optimal welding time varies depending on factors such as material type, thickness, and desired weld characteristics. Too short a welding time may result in incomplete bonding, while excessively long welding times can lead to material damage or weakening of the weld.

Cooling time

Cooling time is the period after the welding process during which the welded materials cool down and solidify to form a strong bond. Proper cooling stabilizes the weld joint and prevents deformation or stress buildup. The cooling rate must be controlled to avoid rapid cooling, which can induce internal stresses and compromise the integrity of the weld. Additionally, cooling time may influence the final properties of the weld, such as its strength, toughness, and dimensional stability.

When should you use HF wedling or RF welding?

Choosing the right sealing technology relies on factors such as your material, product size and shape, and production volume. Radio Frequency Welding provides consistent, clean seams without the need for adhesives or solvents. If you’re regularly producing the same product with specific weld shapes, Radio Frequency Welding is perfect for your needs. Additionally, a High-Frequency Welding Machine enables multiple weld passes in the same area, unlike some other technologies.

Is HF welding or RF welding right for your application?

Determining whether HF welding or RF welding is right for your application depends on various factors such as material, product requirements, and production volume. HF welding is highly versatile and ideal for many applications. To make an informed decision, it’s best to reach out to us with details about your specific application. Our expert team will assess your needs and provide tailored recommendations, ensuring you choose the ideal welding solution for your project.

Alternatives to High Frequency welding

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.

Advantages +

  • Can be used for non-dielectric materials
  • Advantageously used as a complement to HF for finishing bigger structures and for patches


  • Difficult or impossible to remake the weld if the result is not satisfactory
  • Requires a skilled operator
  • Noisy process which creates hazardous fumes/gas and requires an evacuation system
  • Does not work well on thicker materials (materials heavier than 1000 g/m²)
  • Difficult to create welds that are air-, liquid-, and gas-tight


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.

Advantages +

  • Can be used for non-dielectric materials
  • Most hot wedge systems have very helpful attachments for overlapping, hemming and tubing products


  • Difficult or impossible to remake the weld if the result is not satisfactory
  • Requires a skilled operator
  • Noisy process which can create hazardous fumes/gas
  • Does not work well on thicker materials (materials heavier than 1000 g/m²)
  • Difficult to create welds that are air-, liquid-, and gas-tight



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.

Advantages +


  • The weld is limited to the maximum length of the tool (normally never longer than 6 meter). If used as an accessory on a Forsstrom machine when it can weld the entire length of the welding table
  • 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.

Advantages +

  • Can be used for non-dielectric materials
  • Suitable for detailed welding


  • The technology creates a high pitch sound
  • It is difficult to weld more than two material layers without damaging the surface of the material and causing burns
  • The weld area is very limited and the technology is not suitable for larger applications


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