Define Principal Process for Electron Beam Machining

• A beam of electrons is emitted from the electron gun which is basically following three points.

1. A cathode which is a hot tungsten filament (2500°c) emitting high negative potential electrons.

2. A grid cup negatively based with respect to the filament.

3. An anode which is heats at ground potential, and through which the high velocity electrons pass.

• The gun is supplied with electronic current from a high voltage D.C source.
• The flow of electrons is controlled by the negative bias applied to the grid cup.
• The electron passing through the anode is accelerated to two-third of the velocity of light by applying 50kv to 100kv at the anode, and this speed is maintained till they strike the work piece.
• Due to the pattern of the electrostatic field produced by the grid cup, the electrons are focused and made to flow in the form of a converging beam through a hole in the anode.
• A magnetic deflection coil is used to make the electron beam circular having a cross-sectional diameter of 0.01 to 0.02 mm and deflect it anywhere.
• A built -in microscope with a magnification of 40 on the work piece enables the operator to accurately locate the beam impact and observe the actual machining operation.
• As the beam impacts on the work piece surface the kinetic energy of high velocity electrons is immediately converted into the thermal energy and it vaporized the material at the spot of its impact.
• The power density being very high (about 1.5 billion w/cm3) it takes a few microseconds to melt and vaporize material on impact.
• The process is carried out in repeated pulses of short duration may range from 1 to 16,000 Hz and from 4 to 64,000 microseconds.