What is HF welding?

High Frequency (HF) or Radio Frequency (RF) welding is a method of joining thermoplastic materials using radio waves and pressure to create high-quality welds. This process, operating at 27.12 MHz, involves the application of electromagnetic energy to the surfaces to be joined, generating heat within the material itself.

What is HF welding? What is RF Welding? Radio Frequency welding or High Frequency welding?

How does HF welding work?

So, what is HF welding? A generator produces the HF energy, while an electrode tool supplies this energy to the material surfaces. This energy causes the molecules within the material to move, generating heat and softening the material, facilitating fusion. Unlike other welding methods, no external heat source is needed; the heat is generated within the material. After cooling under pressure, a strong, durable weld is formed. The weld seam can be at least as strong as the surrounding material – or even stronger.

What Plastics Can Be 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.

What is the Maximum Frequency of RF?

The maximum frequency for RF welding is typically around 27.12 MHz, which is optimal for creating strong, airtight welds in thermoplastic materials.

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.

Why use high frequency (HF)?

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 / RF welding

Repeatable, reliable technology

HF welding utilizes high-frequency electromagnetic energy to generate heat, ensuring consistent results with each weld. The precision and control offered by 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, creating a seamless joint that can withstand considerable stress and strain. Additionally, 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 formed are airtight, gas-tight, and waterproof. This characteristic is particularly valuable in applications where maintaining a barrier against air, gases, or liquids is essential, such as in the production of inflatable products, liquid tanks, or biogas covers.

Multi-layer welding

HF welding is capable of welding 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 efficiency in production.

An environmentally friendly choice

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

The four important factors of HF / RF welding

Pressure

Pressure exerted during HF welding is essential for ensuring proper contact between the materials being welded. It facilitates the intimate contact necessary for the efficient transfer of electromagnetic energy, which generates heat to melt the materials and form a bond. Adequate pressure helps to eliminate 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 the 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 refers to the duration for which the high-frequency energy is applied during the welding process. It is critical to control the welding 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 is essential for stabilizing the weld joint and preventing 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.

Alternatives to HF / RF 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.

+ 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

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

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!

TDO HF PVC welding machine

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.

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?