RF welding (High Frequency (HF) welding or Dielectric welding) is the process of joining thin sheets of polar thermoplastic materials together. It uses high frequency electromagnetic energy to bond the materials together.
The plastic material is placed between two electrodes where electromagnetic field is created when RF energy is applied to the electrodes. As the electromagnetic energy passes through the polar molecules of the thermoplastics, The molecules begin to reorient themselves in accordance with the direction of the electromagnetic waves. When enough energy is applied, heat is produced from inter molecular friction to melt the plastics. As the two electrodes compress the melted thermoplastic layers the electrode shape is imprinted onto the molten product. Once the RF energy is turned off the material is cooled and solidifies under the pressure, bonding the materials together. For a list of thermoplastic materials that can be welded read click here.
RF Welding is typically achieved by the use of a RF Welding Machine. The machine traditionally looks like a large air or hydraulic cylinder controlled press. To form material in the operators desired shape, a heat sealing die is designed and fabricated to match the shape using materials, such as aluminum, brass 360, or bronze.
For a more exhaustive explanation please read Radio Frequency Welding Process Overview.