Principle of electron beam processing
The electron beam technology consists in the use of accelerated electrons for the processing of materials. For this purpose in an evacuated electron beam generator (eb gun) a cathode will be heated by direct or indirect heating. Through the heating free electrons are emitted and it come to a cloud of electrons.
Between the cathode and the anode a high voltage of several kilovolts is plugged and the electrons will be accelerated in the direction of the anode. The accelerated electrons will be magnetically centred (centring), bundled (focussing) and optionally deflected (deflection). They move as electron beam with a speed of nearly two thirds of the light velocity through the generator valve to the work piece surface. Normally the work piece is located in a vacuum chamber. As well there exist electron beam material processing on atmosphere (non-vac electron beam) but it’s not in focus here.
At the work piece surface the largest part of kinetic energy of the impacted electrons is transformed into thermal energy. Through heat conduction the thermal energy is transported into deeper zones of the work piece. The further mode of action depends on the desired processing. If the material will be heat treated, melted or vaporised depends on the electron beam power density and the relative processing speed between the electron beam and the work piece.
For electron beam welding the power density is high and the material will be melted and partly vaporized. Above a specific power density it comes to a vaporised capillary (key hole) called deep weld effect. The weld seam is the result of the relative movement between the weld capillary and the work piece.
For electron beam hardening in solid phase the power density is lower. The temperatures at the work piece surface are between the transformation and melting temperature of the material. It exist an electron beam hardening process in liquid phase too there the surface temperatures are above the melting temperature of the material.
For electron beam remelting only the surface of the work piece is melted again.
For electron beam drilling the material is locally and temporary vaporized by short single or repeated electron beam pulses at high frequencies with a very high power density.
There are known numerous other electron beam material processes.