high velocity beam of electrons is focused
magnetically on a very small area of work piece.
The high velocity beam raises the temperature
locally above the melting point as the kinetic
energy of high velocity electrons is converted
into heat energy. The material melts and
vaporizes at the point of bombardment. It does
not depend on heating of the material to the
point of evaporation.
electrons are obtained by heating the cathode metal in vacuum to the
temperature at which they attain sufficient speed to escape. It leads to
thermo ionic emission of electrons. The electrons are accelerated under
the effect of electric field and focused by controllable magnetic field.
The cathode is generally made of tungsten or tantalum.
cathode is often in the form of a cartridge which is highly negatively
biased. It is done to repel the electrons away from cathode. The
electrons from cathode are attracted by annular anode and get
accelerated. The electrons attain a velocity of about half of the
velocity of light. The electron beam then passes through a series of
magnetic lenses and apertures. Then it passes through final section of
electromagnetic lens and deflection coil to strike the workpiece.
electron beam machining is being carried out in vacuum to avoid
electrons to interact with air molecules. Otherwise the electron will
lose their energy.
Almost all materials can be machined by this process.
metal removal rate is very small so close dimensional tolerances of
0.005 μm can be achieved.
High vacuum is required for free movement of electrons, to prevent the
cathode from chemical contamination and heat losses. It limits the size
of workpiece that can be machined so this process is not for large
workpiece. This process is relatively expensive and requires a skilled
process is best suited for micro-cutting of materials.