Electron Beam Machining

· The basic physics is an electron beam is directed towards a work piece, the electron heat and vaporize the metal.

· Typical applications are,

•   annealing
•   welding
•   metal removal

· electrons accelerated with voltages of approx. 150,000V to create velocities over 200,000 km/sec. 

· beam can be focused to 10 to 200 micro m and a density of 6500 GW/mm2

· good for narrow holes and slots.

            e.g. a hole in a sheet 1.25 mm thick up to 125 micro m diameter can be cut almost instantly with a taper of 2 to 4 degrees

· the electron beam is aimed using magnets to deflect the stream of electrons

· a vacuum is used to minimize electron collision with air molecules.

· beam is focussed using an electromagnetic lens.

 

· The process looks like,

· Some examples of cutting performance are given below,

 

 

· typical energy requirements for cutting are,

· e.g. to cut a 150 micro m wide slot in a 1mm thick tungsten sheet, using a 5KW power source, determine the cutting speed.

 

· Basic mechanics,

· e.g.

· the heat rise can be estimated using a one dimensional heat flow equation

 

· We can estimate the melting temperature with,

· e.g.

· Other effects of EBM

1. - process done in vacuum, so it is best suited to small parts, but vacuum also reduces contamination
2. - very high heat concentration reduces peripheral heating of surface less that 50 micro m from the cut the part is at room temperature.

· Summary of EBM characteristics,

1. - mechanics of material removal - melting, vaporization
2. - medium - vacuum
3. - tool - beam of electrons moving at very high velocity
4. - maximum mrr = 10 mm3/min
5. - specific power consumption = 450W/mm3/min
6. - critical parameters - accelerating voltage, beam current, beam diameter, work speed, melting temperature
7. - materials application - all materials
8. - shape application - drilling fine holes, cutting contours in sheets, cutting narrow slots
9. - limitations - very high specific energy consumption, necessity of vacuum, expensive machine.

( Kaynak: Engineer On a Disk - Ghosh, A., Manufacturing Science, Ellis Horwood Ltd., Chichester, UK, 1986)