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Electron beam machining (EBM):


A 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.

The 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.

The 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.

The 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.

The 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 operator.

The process is best suited for micro-cutting of materials.  
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