1. 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.

 

 

1.1 REFERENCES

1.2 PRACTICE PROBLEMS

[an error occurred while processing this directive]