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. The resulting join can be very strong – often close to the original strength of the materials joined. In some scenarios the weld can be even stronger than the original materials.
Using a high frequency electromagnetic field, the material is heated and pressure added to melt and fuse the two materials together. No outside heart is applied. Instead the heat is generated within the materials. During cooling (under continued preassure), the materials are fused together and a weld has been created. This results in a very strong bond between the two parts.
Example of High Frequency Welding of PVC Cleat
What are the advantages of High Frequency 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
Materials compatible with High Frequency Welding
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.
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.
High Frequency Welding suppliers
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. 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.
Carmo’s approach to High Frequency Welding
Carmo has developed a four level approach to HF welding, mainly dependent on the customer’s production volumes and requirements for automation.
Entry level – standalone electrode
This is a simple way to get started with welding Carmo components. Many customers already have a bar welder. Carmo supply a ready to go electrode which can simply be placed under the bar or screwed onto the bar. Carmo builds extra functionality into these electrodes with a patterned welding area and the capability of clicking the component fast in the electrode where applicable, enabling free placement of the foil. Where components have a hole through, these are punched manually before or after welding with a standalone electrode.
Next level – UG4 housing
The next development for effective production is the UG4 housing system. This consists of a guided electrode enabling punching and welding in one operation. There are three sizes, depending on the area of the component to be welded. The largest can be used for oval parts where the electrode/punch needs to be prevented from rotating. The UG4 is also simply used under the bar of a bar welder and requires no extra electrical connections.
Where the customer does not wish to use a bar welder directly or has only a standalone generator, the EP3 manual press is a good alternative. A coaxial lead and a signal cable are required for communication to the generator. It is a hand operated press with a Carmo standalone electrode. Punching is also possible. When the electrode is down, it triggers a signal from the welder to commence the welding process. Welding time, cooling time and power are set on the generator.
For many of the weldable eyelets Carmo manufactures, an automatic feeder/press is available for large production volume applications. Welding power comes from an external HF generator or an output from a bar welder, via a coaxial cable. The feeder/press transports an eyelet to the welding electrode. The operator places the foil in the correct position under the electrode and starts the cycle, usually by means of a foot pedal. The press punches the hole and welds the eyelet in one operation, then feeds the next eyelet ready for another position on the foil.
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.
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