How Does Electron Beam Welding Work?
An electron beam welding machine consists of a device for producing a focused beam of high-speed electrons, velocities of between 0.3 and 0.7 times the speed of light. This is known as an electron gun, which is normally mounted on or in an evacuated chamber which contains tooling/fixtures used for holding and moving a work piece.
An electron beam is usually formed by employing a triode- style electron gun which consists of a cathode (also known as a filament), a heated source (emitter) of electrons that is maintained at a high negative potential, a grid cup (also known as a bias cup), a specially shaped electrode that can be negatively biased with respect to the hot cathode emitter, and an anode, a ground potential electrode through which the electron flow passes in the form of a collimated beam. The hot cathode or filament is made from a high emission material such as tungsten or tantalum. The most commonly tungsten.
A heating current is passed through to a filament that causes it to emit electrons. These are accelerated from the filament to the anode by applying a high negative voltage to the filament. A control electrode, or grid, is situated close to the filament and is held at a negative potential in respect to it. As the voltage potential between the filament and grid is reduced, electrons are allowed to escape. These are then attracted to the anode, which has more positive potential than the electrons, or in the case of electron beam welding the anode has a hole in its centre which allows the electrons to pass through the anode as a stream, and on towards the work piece. As the electrons travel to the work piece they pass through a focus coil, or focusing lens (electromagnetic lens) so that the beam can be focused to a fine point in order to achieve sufficient power density to weld metals.
The electron beam will also pass through a deflection coil (electromagnetic) at the bottom of the column which can manipulate the beam at very high speeds. With the addition of some hardware this enables functions such as backscattered imaging, joint finding, real-time seam tracking, auto beam alignment, engraving, beam splitting and Surfi-Sculpt.