Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/36—Removing material
  • B23K26/362—Laser etching
  • B23K26/364—Laser etching for making a groove or trench, e.g. for scribing a break initiation groove

Definitions

• the present invention relates to making an elongate cut using high energy radiation focussed to a focal spot in the cut, the radiation usually being a laser beam.
• a blind groove or hole may be formed in the workpiece, or the workpiece may be cut or pierced right through.
• the invention has general applicability and in general terms, unnecessary material removal must be avoided as this slows down the cutting process; however, the invention is particularly applicable to gemstones, where it is specially important to avoid unnecessary material removal, and it is also necessary to avoid applying excessive thermal stress; in addition, a particular problem with gemstones such as diamond is that usually only a small percentage of the radiation may be absorbed, so it is important that coupling of the energy to the workpiece be as effective as possible.
• the laser cutting can be referred to as forming a kerf (a groove, either for cleaving or for later sawing), or sawing (cutting right through).
• a blind hole or a through-hole may be formed in order to employ the stone as a bearing.
• a fundamental problem is that the energy density in the focal spot should be as great as possible, but a smaller focal spot (and thus higher energy density) can only be obtained by increasing the cone angle of the focussed beam (i.e. higher numerical aperture).
• the machined V-section has then to be wider, otherwise the laser energy focussed into the cut is apertured (vignetted) at the entrance to the cut as the depth increases.
• a system which converges the radiation at a substantially greater angle of convergence in the plane in which the cut lies than in the plane transverse to the cut.
• the energy density of the focal spot can be increased without widening the machined V-section, as the uninterrupted access provided longitudinally of the cut is utilised. Consequently the angle of the V-section may be reduced and rate of propagation of the cut increased.
• the amount of laser energy entering the cut can be increased by cylindrically compressing a spherically expanded beam in the transverse direction. This allows the use of higher spherical beam expansion ratios than is possible without use of the invention because the effect of vignetting by the cut opening is reduced.
• the numerical aperture of the optical system is higher in the longitudinal direction than in the transverse direction.
• the focii must be at the same depth in each plane (transverse and longitudinal).
• the focal spot (as seen on the flat bottom of the cut) will be an ellipse with its major axis transverse of the longitudinal direction of the cut.
• the size of the focal spot in the major axis (transverse) direction will be larger than that without using the invention.
• the full advantage of the invention cannot be observed unless the spherical beam expansion coefficient is increased, so that the focal spot area is reduced without a proportional reduction in the energy entering the cut.
• the beam can be expanded and then focused in both planes in order to achieve a sufficiently high focal spot energy density.
• any increase in energy density resulting from a reduction in focal spot area will be at least partially offset by a reduction in energy entering the cut, due to vignetting at the opening, as cutting progresses.
• the ratio of convergence angles (included angle) of the transverse to longitudinal directions can be any value less than unity but the preferred values are from 0.5 to 0.25.
• cylindrical optics may be used, preferably with a beam compressor or beam expander having cylindrical lenses.
• Figure 1 is a schematic view, showing the optical system ar, ⁇ a stone being cut, in section transversely to the cut; and Figure 2 is a schematic view of the optical system, as seen in section normal to that of Figure 1.
• a cut 1 is being formed in a diamond 2.
• the optical system includes a laser 3. a spherical beam expander 4, a beam contractor formed by two lenses 5,6, and a focussing lens 7.
• the lenses 5,6 are cylindrical lenses, forming a beam compressor for contracting the beam in the plane of Figure 1 but not in the plane of
• the focussing lens 7 can be a conventional spherical lens.
• the laser 3 can be a high-power
• magnification values of 10 to 20x have been used for the beam expander 4 and 0.25 to 0.5x for the beam contractor 5,6. If the width of the beam between the laser 3 and the beam expander 4 is w, it is typically 3w - 5w between the lenses 6,7 in Figure 1 and lOw - 20w between the lenses 6,7 in Figure 2.
• the present invention has been described above purely by way of example, and modifications can be made within the spirit of the invention.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Mechanical Engineering (AREA)
• Laser Beam Processing (AREA)

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Publications (1)

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ID=10642146

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Citations (1)

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• 1988
  • 1988-08-15 GB GB888819351A patent/GB8819351D0/en active Pending
• 1989
  • 1989-08-14 CA CA000608274A patent/CA1325042C/en not_active Expired - Fee Related
  • 1989-08-15 EP EP89909587A patent/EP0428609B1/en not_active Expired - Lifetime
  • 1989-08-15 WO PCT/GB1989/000942 patent/WO1990001392A1/en not_active Ceased
  • 1989-08-15 JP JP89509001A patent/JPH05506185A/ja active Pending
  • 1989-08-15 US US07/655,401 patent/US5248877A/en not_active Expired - Fee Related
  • 1989-08-15 ZA ZA896206A patent/ZA896206B/xx unknown
  • 1989-08-15 AU AU40774/89A patent/AU628073B2/en not_active Ceased
  • 1989-08-15 IL IL91320A patent/IL91320A/xx not_active IP Right Cessation
  • 1989-08-16 IN IN612MA1989 patent/IN174289B/en unknown

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