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Remanufacturing and Advanced Machining
primarily for welding applications, but at present it is also utilized for microdrilling,
cutting, and engraving applications (Bhattacharyya, 2015). Electron beam cutting
can also serve fabrication of multiwalled boron nitride nanotubes when a focused
electron beam with a diameter much smaller than the tube diameter is used. By
controlling the electron beam size, it is possible to cut boron nitride nanotubes and
to form sharp, conical crystalline tips (Celik-Aktas et al., 2007).
In EBM processes, a relatively high power density causes heating of the workpiece material only within the spot where the material is removed from by melting
and evaporation (Okada, 2019). The ratio between these two phenomena depends on
the power density, so that evaporation intensifies as the power density increases. In
the EBM process of a low power density, the temperature on the workpiece surface
reaches the melting point of a respective material, enlarging the melt pool due to
heat conduction, as shown in Figure 1.10a. When the power density is increased,
vaporization of the material is intensified and causes voids and keyholes seen in
Figure 1.10b. Due to the high pressure of evaporation, the melted material is blown
away. Further increases to high power densities of 10 6 –10 7 W/cm 2 lead to heating
above the boiling point at the spot. The pressure in the keyhole becomes higher
than the surface tension of the melting pool so that the material removal effectively
progresses along the depth direction, drilling small and deep holes, as illustrated in
Figure 1.10c (Okada, 2019).
Thus, electron beam drilling involves a deep penetration with high-speed controllability that enables drilling of a large number of micro holes at an extremely
high speed. The drillable workpiece thickness is less than several millimeters at its
maximum even with repeated pulse irradiations. Therefore, electron beam drilling is
applied to drillings of large numbers of holes in difficult-to-drill materials, such as
cooling holes on inlet ducts of gas turbine engines, many types of filters, and spinner
heads for fiber production. It is possible to drill deep holes into ceramic materials,
because the heat conductivity of ceramics is low, so that the high temperature needed
for material removal is easy to obtain. It has also been applied to drilling holes for
drawing dies made of alumina and diamond (Okada, 2019).
FIGURE 1.10 Material removal mechanisms during electron beam machining at different
power densities: a – low, b – medium, c – high power density.
Remanufacturing and Advanced Machining
primarily for welding applications, but at present it is also utilized for microdrilling,
cutting, and engraving applications (Bhattacharyya, 2015). Electron beam cutting
can also serve fabrication of multiwalled boron nitride nanotubes when a focused
electron beam with a diameter much smaller than the tube diameter is used. By
controlling the electron beam size, it is possible to cut boron nitride nanotubes and
to form sharp, conical crystalline tips (Celik-Aktas et al., 2007).
In EBM processes, a relatively high power density causes heating of the workpiece material only within the spot where the material is removed from by melting
and evaporation (Okada, 2019). The ratio between these two phenomena depends on
the power density, so that evaporation intensifies as the power density increases. In
the EBM process of a low power density, the temperature on the workpiece surface
reaches the melting point of a respective material, enlarging the melt pool due to
heat conduction, as shown in Figure 1.10a. When the power density is increased,
vaporization of the material is intensified and causes voids and keyholes seen in
Figure 1.10b. Due to the high pressure of evaporation, the melted material is blown
away. Further increases to high power densities of 10 6 –10 7 W/cm 2 lead to heating
above the boiling point at the spot. The pressure in the keyhole becomes higher
than the surface tension of the melting pool so that the material removal effectively
progresses along the depth direction, drilling small and deep holes, as illustrated in
Figure 1.10c (Okada, 2019).
Thus, electron beam drilling involves a deep penetration with high-speed controllability that enables drilling of a large number of micro holes at an extremely
high speed. The drillable workpiece thickness is less than several millimeters at its
maximum even with repeated pulse irradiations. Therefore, electron beam drilling is
applied to drillings of large numbers of holes in difficult-to-drill materials, such as
cooling holes on inlet ducts of gas turbine engines, many types of filters, and spinner
heads for fiber production. It is possible to drill deep holes into ceramic materials,
because the heat conductivity of ceramics is low, so that the high temperature needed
for material removal is easy to obtain. It has also been applied to drilling holes for
drawing dies made of alumina and diamond (Okada, 2019).
FIGURE 1.10 Material removal mechanisms during electron beam machining at different
power densities: a – low, b – medium, c – high power density.