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
- - process done in vacuum, so it is best suited to small parts, but vacuum also reduces contamination
- - 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,
- - mechanics of material removal - melting, vaporization
- - medium - vacuum
- - tool - beam of electrons moving at very high velocity
- - maximum mrr = 10 mm3/min
- - specific power consumption = 450W/mm3/min
- - critical parameters - accelerating voltage, beam current, beam diameter, work speed, melting temperature
- - materials application - all materials
- - shape application - drilling fine holes, cutting contours in sheets, cutting narrow slots
- - 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)
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