Radio frequency welding is a very mature technology that has been around since the 1940s.
The objects that need to be welded are clamped together between two metal electrodes (or sealing dies). These are typically mounted to a pneumatic press that will provide pressure and electromagnetic energy.
When the press is actuated, the electrodes come together and high-frequency waves (usually 27.120 MHz) are passed through a small area between the die and the table where the weld takes place. This high frequency (radio frequency) field causes the molecules in the materials to move and get hot, and eventually, the material will melt, and the force applied by the electrode will melt or fuse the two surfaces together. After cooling, a permanent seam has been created in the shape of the die. No external heat is applied.