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What is High Frequency Welding / HF welding?

What is HF welding or High Frequency welding?



High frequency welding (often abbreviated HF welding or RF welding) is a manufacturing process where two plastic parts are welded together using an electromagnetic field.

Common products manufactured with high frequency welding are tarpaulins, tents, ceilings, advertising banners, waterbeds, inflatable boats, medical and especially blod and urine-bags, tensile structures, conveyor belts, rain clothing etc.

Example of using a stand-alone HF electrode for HF welding PVC Cleat



Principle and advantage of high frequency welding

The main principle of high frequency welding (HF welding) is based on di-electric heating of the material to be welded.

The objects that needs to be welded are clamped together between two metal electrodes and a high frequency voltage is supplied. As a result the molecyles in the material starts to vibrate and heat up. Eventually the material will melt, and the force supplied by the electrode will melt (fuse) the two surfaces together. After cooling a permanent seam has been created. The resulting weld seam can be as strong - or even stronger - than the surrounding material.

The great advantage of HF welding is the speed of welding: The material is heated from the inside and fuses quickly, within few seconds.

Compared to high frequency welding, a lot of other methods (hot air, infrared radiation, laser) the energy /heat is supplied from the outside. This means that the heat must first penetrate the material in order to heat the contact-surfaces, thus risking to burn the top layer of the welded material.

You could compare this to heating your food in the microwave oven vs in a traditional oven.


What materials can be HF welded?

The material most common in High frequency welding is PVC (sometimes called simply vinyl) and PU (Polyurethane). The material can be thick or thin, reinforced or coated. It can also be plain, coloured or structures / patterened.

Observe that bonding requires the two materials to flow and mix easily. Thus PVC materials can be welded with PVC components and PUR sheets needs special PUR components. Carmo has developed a unique PVC/PUR material that maintain a lot of the properties of the PVC and still allow for good bonding on PUR based foils and sheets.


What are the main parts involved in HF welding?

The three main parts involved in High frequency welding are:



Carmo supplies electrodes for each of our weldable componenents and a series of machines for automatic welding of eyelets.

For suppliers of HF generators and barwelders, we suggest the following companies and ressources as a starting point:

What are the important factors for high frequency welding?

The four most importent factors / process parameters influence High frequency welding are

  • Electrical power
  • Pressure applied
  • Welding time
  • Cooling time

Finding the optimal process parameters will depend on your specific equipment, the materials involved and the specific geometries including thichkness and area to be welded.


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Carmo has a 60 year track record of delivering highly specialized technical and medical components.

We design, produce and sell quality injection moulded plastic components globally. We service industries as diverse as Medico, Maritime, Mining, Agriculture and Automotive.

Quality, Service and Flexibility are the key words of our production and in all aspects of our interaction with our customers. We are focused on minimizing hassle and maximizing service, while helping our customers turning ideas into products.

We are based in Denmark and run a highly automated production. By leveraging robotics and vision technology, we are able to deliver components with very high quality, well-defined properties and functionality at competitive prices.

We put all our knowhow and experience in ensuring our customers an easy integration and stability in their products and production.

From our sales offices and inventories in Denmark, France and the UK we are able to supply our core markets and customers within days.

Our core competency is components for High Frequency welding, with a special focus on valves, eyelets and components for medical bags. We maintain PVC as a special focus, however deliver 50% of our turnover in other plastic materials.

Our four main business areas are:

Technical Components Medical Components Modular storage boxes Product Development Services

Weldable eyelets and fittings

Valves for inflating, over pressure and vacuum

Threaded nozzles and caps

HF/RF welding machines

Market leader in drainage valves, connectors and fittings for medical bags

Customization and OEM production

Modular, high quality transparent boxes

Approved for storage of food and fragile objects

Sold under the brand UltraPlast

Product design and realisation

Pilot production, test and documentation

Ramp-up and production

In addition to above, our main manufacturing strength is quality injection moulding in all technical
plastics - including PVC. Carmo PVC products are made in a number of different PVC grades - all special and protected Carmo recipes.

We can manufacture in cleanroom down to class 10.000.
2K moulding

We have chosen quality to be the keyword for our production and
distribution. Since 1993 Carmo has been holding an ISO certification and we are today ISO certified according to ISO 9001:2008.