Results of The Electron Beam Application
The results of the beam application depend on several factors: Many experiments and innumerable practical applications of electron beam in welding technology prove that the resulting effect of the beam, i.e. the size and shape of the zone influenced by the beam depends on:
(1) power of the beam,
(2) power density (focusing of the beam) but also on:
(3) welding speed,
(4) material properties, and in some cases also on
(5) geometry (shape and dimensions) of the joint.
(ad 1) – The power of the beam is the product of the accelerating voltage and beam current, parameters easily measurable and precisely controllable. The power is controlled by the beam current at constant accelerating voltage, usually the highest accessible.
(ad 2) – The power density in the spot of incidence of the beam with the “workpiece” depends on more factors, like the size of electron source on the cathode, “optical quality” of the accelerating electric lens and the focusing magnetic lens, alignment of the beam, on the value of the accelerating voltage, and on the focal length. All these factors are dependent (except the focal length) on the design of the machine.
(ad 3) – The construction of the welding equipment should enable to adjust the speed of relative motion of the workpiece with respect to the beam in wide enough limits, e.g. between 2 and 50 mm/s.
The final effect of the beam depends on combination of these parameters.
a) Action of the beam at low power density or in a very short time will result in melting only a thin surface layer.
b) A defocused beam will not penetrate and the material at low welding speed will be heated only by conduction of the heat from the surface, producing a hemispherical melted zone.
c) At higher power density and lower speed a deeper and slightly conical melted zone will be produced. In case of very high power density the beam (well focused) penetrates deeper, proportionally to its total power.
For welding thin walled parts, generally, some appropriate welding aids are needed. Their construction must provide the perfect contact of the parts and prevent their deformation during welding. Usually they have to be designed individually for the given workpieces.
Read more about this topic: Electron Beam Welding
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