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Manufacturing Processes>Non-Traditional Machining >Electron Beam Machining(EBM)

 

Electron Beam Machining(EBM)

 

Process description

An electron gun bombards the workpiece with electrons up to 80 per cent the speed of light generating localized heat and evaporating the workpiece surface. Magnetic lenses focus the electron beam, and electromagnetic coils control its position. The workpiece is contained within a vacuum chamber typically.

Materials

Any material regardless of its type, electrical conductivity and hardness.

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Process variations

  • Electron Beam Welding (EBW) : used to weld a range of material of varying thicknesses giving a small weld area and heat affected zone, with no flux or filler.
  • The electron beam process can also be used for cutting, profiling, slotting and surface hardening, using the same equipment by varying process parameters.

Economic considerations

  • Production rates dependent on size of vacuum chamber and by the ability to process a number of parts in batches at each loading cycle (less than 1 s per hole cycle time on thin workpieces).
  • Parts should closely match size of chamber.
  • Material removal rates low, typically 10mm³/min. Penetration speeds up to 600 mm/min possible.
  • Lead times can be several weeks.
  • Setup times can be short, but the time to create a vacuum in the chamber at each loading cycle is an important consideration.
  • Material utilization good.
  • High degree of automation possible.
  • High energy consumption process.
  • Economical with low to moderate production runs for thin parts requiring small cuts.
  • Tooling costs very high.
  • Equipment costs very high.
  • Direct labor costs high. Skilled labor required.
  • Finishing costs very low.

Typical applications

  • Multiple small diameter holes in very thin and thick materials
  • Injector nozzle holes
  • Small extrusion die holes
  • Irregular shaped holes and slots
  • Engraving
  • Features in silicon wafers for the electronics industry

Design aspects

  • Electron beam path can be programmed to produce the desired pattern.
  • Suitable for small diameter, deep holes with length to diameter ratios up to 100:1.
  • Possible to machine thin and delicate sections due to no mechanical processing forces.
  • Sharp corners difficult to produce.
  • Better to have more small holes requiring less heat than a few large holes requiring considerable heat.
  • Maximum thickness =150 mm.
  • Minimum hole size =Ø0.01 mm.

Quality issues

  • Localized thermal stresses giving very small heat affected zones, small recast layers and low distortion of thin parts possible.
  • Integrity of vacuum important. Beam dispersion occurs due to electron collision with air molecules.
  • The reflectivity of the workpiece surface important. Dull and unpolished surfaces are preferred.
  • Hazardous X-rays produced during processing which require lead shielding.
  • Produces slightly tapered holes, especially if deep holes are required.
  • Critical parameters to control during process: voltage, beam current, beam diameter and work speed.
  • The melting temperature of the material may also have a bearing on quality of surface finish.
  • Surface roughness values ranging 0.4–6.3 µm Ra.
  • Achievable tolerances ranging ±0.013–±;0.125 mm. (Process capability charts have not been included. Capability is not primarily driven by characteristic dimension.)

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