61. 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,
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
- tool - beam of electrons moving at very high velocity
- maximum mrr = 10 mm
3/min
- specific power consumption = 450W/mm
3/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.
