What is High Frequency Welding?
Radio Frequency welding, sometimes known as RF, Dielectric or High Frequency (HF) welding, is the process of fusing materials together by applying radio frequency energy to the area to be joined. The resulting weld can be as strong as the original materials.
RF welding relies on certain properties of the material being welded to cause the generation of heat in a rapidly alternating electric field. This means that only certain materials can be welded using this technique. The process involves subjecting the parts to be joined to a high frequency (13-100MHz) electromagnetic field, which is normally applied between two metal bars. These bars also act as pressure applicators during heating and cooling. The dynamic electric field causes the molecules in polar thermoplastics to oscillate. Depending on their geometry and dipole moment, these molecules may translate some of this oscillatory motion into thermal energy and cause heating of the material. A measure of this interaction is the loss factor, which is temperature and frequency dependent.
Polyvinylchloride (PVC) and polyurethanes are the most common thermoplastics to be welded by the RF process. It is possible to RF weld other polymers including nylon, PET, EVA and some ABS resins, but special conditions are required, for example nylon and PET are weldable if preheated welding bars are used in addition to the RF power. RF welding is generally not suitable for PTFE, polycarbonate, polystyrene, polyethylene or polypropylene. However, due to the impending restrictions in the use of PVC, a special grade of polyolefin has been developed which does have the capability to be RF welded.
The primary function of RF welding is to form a joint in two or more thicknesses of sheet material. A number of optional features exist. The welding tool can be engraved or profiled to give the entire welded area a decorative appearance or it can incorporate an embossing technique to place lettering, logos or decorative effects on the welded items.
By incorporating a cutting edge adjacent to the welding surface, the process can simultaneously weld and cut a material. The cutting edge compresses the hot plastic sufficiently to allow the excess scrap material to be torn off; hence this process is often referred to as tear-seal welding.
It is also possible to weld additional pieces of material onto the surface of a product for ornamental purposes. This technique is referred to as Appliqué welding.
Sourced from the TWI
A wide range of products can be manufactured using the RF welding technique. A few examples are listed below:
- Stationery - Book covers, stationery wallets, zip bags, binders and office files
- Inflatable Items - Beach balls, toys, air/water beds, rafts and life jackets
- Household Items - Headboards, chair upholstery, quilting and table mats
- Large Items - Tarpaulins, tents, marquees, pool liners and lorry covers
- Medical Items - Blood bags and colostomy bags
- Automotive - Air bags, dashboard fascia and sun-visors