Electron Beam is highly energy efficient and precise with respect to power density, focus, and deflection
Electron Beam Generation - Principle
Most commonly, a triode set-up is used to generate the electron.
The heating current IH causes the Tungsten filament to emitt electrons. These are accelerated by the acceleration voltage UA, between the cathode and the anode.
The Wehnelt cylinder applies the control voltage UW and allows very fast adjustments of the flux of electrons through the anode as an electron beam (EB).
The generation of a precise EB requires high vacuum conditions better than 10-4 mbar in the EB Generator chamber are mandatory.
Then the EB passes the electrical field of the focusing lense. The following deflection yokes enable a quasi inertia-free extremely dynamic and flexible handling and controlling of the beam properties with respect to geometry, focus levels, multi-process, multi-bed, oscillation figures, up-slope, down-slope, seam finding, seam tracking.
The vacuum (pressure, humidity) directly impacts the beam properties. This applies for the vacuum in the EB Generator as well as for the vacuum in the actual work chamber (see pictures below).
The vacuum is generated by specific pumps which evacuate the vacuum chamber and the housing of the EB Generator separately.
The vacuum chamber and its design shields the X-rays generated by the EB reliably in order to meet the safety requirements.
Evobeam's electron beam machining systems generally features pumps that minimize the evacuation time to optimize productivity.
Picture: Schematic structure of a triode / Source: Evobeam
Picture: Schematic structure of an electron beam generator / Source: Tech Briefs Mai 2011
The following pictures display the impact of vacuum on the electron beam. The visible beams are actually atoms that have been energized by the electron beam and emitt photons. The electron beam itself is invisible.
High Vacuum: 5 x 10-4 mbar
Medium Vacuum: 5 x 10-2 mbar
Non-Vacuum: 1000 mbar
Fields of application
Most common electron beam applications are: welding, drilling, cladding, surface treatment (e.g. hardening, surface structuring, engraving, polishing)
Electron Beam Welding
The electron beam creates very deep and slender weld with minimized heat input and warpage of the workpiece.