IL86559A - Apparatus for laser cutting - Google Patents

Description

APPARATUS FOR LASER CUTTING ΊΤ·>·Ϊ> imy.. iit n!? Tton SHULAMIT MARGALIOT C:06312 06312foc.las 1-494 29.5-1988 FIELD OF THE INVENTION The present Invention relates to laser cutting of materials and more particularly to focussing of laser beams used in laser cutting.

BACKGROUND OF THE INVENTION o Various techniques are known for focussing of laser beams for cutting applications. Enhancement of the energy concentration produced by a laser of given power and wavelength at a given location is customarily achieved by reducing the ratio of F/D, where F is the focal length of the focussing lens which is employed and D is the effective beam diameter.

It has been generally accepted that the use of a short focal length lens is impractical, since the lens must be placed very close to the material sought to be cut and might be damaged. Furthermore, the use of a short focal length lens limits the depth that may be practically cut in a material. Accordingly, in the prior art it has been conventional to widen the beam diameter, a technique known as "beam expansion".

A difficulty encountered in deep laser cutting using beam expansion is that the beam invariably has conical convergence. It may be appreciated that in such a case, a relatively small part of the beam energy is effectively focussed on the cut region, the major part of the beam being reflected by portions of the material adjacent to an earlier, less deep cut. σ SUMMARY OF THE INVENTION O The present Invention seeks to provide improved apparatus and techniques for laser cutting which enables more efficient laser cutting including deep cutting.

There is thus provided in accordance with a preferred embodiment of the present invention apparatus for laser cutting comprising a laser producing an output beam, beam focussing apparatus including cylindrical lenses for expanding the output beam in a non-circularly uniform manner and focussing a non-circular beam onto a workpiece to be cut. 0 Further in accordance with a preferred embodiment of the present invention the beam focussing apparatus includes a first cylindrical lens for providing beam contraction along an axis perpendicular to the axis of the output beam and a second cylindrical lens for providing beam expansion along the same axis perpendicular to the axis of the output beam.

Additionally in accordance with a preferred embodiment of the present invention, the beam focussing apparatus comprises a focussing lens for focussing the output beam from the first and second cylindrical lens onto a focal spot on the workpiece.

Additionally in accordance with an embodiment of the present invention there is provided a technique for laser cutting of a workpiece comprising the steps of: producing an laser output beam of a cwavelength and intensity suitable for cutting the workpiece; passing the laser output beam through beam focussing apparatus including cylindrical lenses for expanding the output beam in a non-circularly uniform manner; and focussing a non-circular beam onto a workpiece to be cut.

Further in accordance with a preferred embodiment of the present invention the step of passing the laser output beam through beam focussing apparatus includes the steps of: passing the output beam through a first cylindrical lens for providing beam contraction along an axis perpendicular to the axis of the output beam; and passing the output beam through a second cylindrical lens for providing beam expansion along the same axis perpendicular to the axis of the output beam.

Additionally in accordance with a preferred embodiment of the invention, the step of passing the output beam through beam focussing apparatus also includes the step of: passing the expanded output beam through a focussing lens for focussing the output beam from the first and second cylindrical lens onto a focal spot on the workpiece.

Additionally in accordance with an alternative embodiment of the present invention, the output beam from the laser may also undergo conventional beam expansion prior to or following passage through the first and second cylindrical lenses .

Further in accordance with a preferred embodiment of the present invention suitable for cutting hydrocarbons, such as plastic materials and diamonds, apparatus may be provided for directing a flow of oxygen at the cutting location for providing a clean cut.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: Fig. 1A is a pictorial view illustration of laser cutting apparatus constructed and operative in accordance with one preferred embodiment of the invention; Fig. IB is a pictorial view illustration of laser cutting apparatus constructed and operative in accordance with one preferred embodiment of the invention; Fig. 2 is a pictorial view illustration of laser cutting apparatus constructed and operative in accordance with another preferred embodiment of the invention; Fig. 3 is a pictorial view illustration of laser cutting apparatus constructed and operative in accordance with yet another preferred embodiment of the invention; Fig. 4 is a pictorial illustration of beam expansion apparatus useful in the apparatus of Figs. 1 - 3» Fig. 5 is a sectional illustration taken along lines V - V of Fig. 3; Fig. 6 is a sectional illustration taken along lines VI - VI of Fig. 3; Fig. 7 is a sectional illustration taken along lines VII - VII of Fig. 3; and Fig. 8 is a sectional illustration taken along lines VIII - VIII of Fig. 3- DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Figs. 1A and IB, which illustrate apparatus for laser cutting constructed and operative in accordance with a preferred embodiment of the present invention and comprising a beam expander 10, receiving a laser beam 12 of generally circular cross section. Beam expander 10 typically comprises a pair of oppositely directed convex cylindrical lenses 14 and 16, which are operative first to contract the beam and subsequently to expand it, thus producing an output beam 18 of generally oval configuration. A focussing lens 20 is operative to focus the output beam 18 to a narrow focus at a cutting location 22.

Fig. IB illustrates an alternative embodiment of the apparatus of Fig. 1A. Here, the beam expander 10 comprises a plano-concave cylindrical lens 30 instead of a convex lens 14 as illustrated in the embodiment of Fig. 1A. The plano-concave lens is generally less convenient and more expensive to manufacture than conventional convex cylindrical lenses of the type illustrated at reference number 14 in Fig. 1A.

Fig. 2 illustrates apparatus of the type shown in Fig. 1A, but with the addition of a preliminary beam expansion stage comprising a beam expander 40. The structure of the beam expander 40 is illustrated in Fig. 4, which illustrates a convex/convex lens 50 and a convex cylindrical lens 52.

Reference is now made to Fig. 3 and to Figs. 5 " 8. which respectively show apparatus for cutting hydrocarbon materials, such as diamonds and sections of the cutting beam as it passes through various stages in the apparatus.

As in the embodiment of Fig 1A, or alternatively as in the embodiment of Fig. 2, an input laser beam 60 of generally circular cross section, as shovm in Fig 5t is expanded by a beam expander 62, comprising first and second convex cylindrical lenses 64 and 66. Lens 64 is operative to contract the beam to a cross section seen in Fig. 6 and lens 66 is operative to expand the contracted beam to have a cross sectional configuration as shown in Fig. 7· A focussing lens 68 is operative to focus the contracted beam to have a very narrow aspect, as seen in Fig. 8, at a cutting location 70· This narrow aspect provides a highly efficient, high precision cut, even at significant depths.

According to a preferred embodiment of the present invention, a jet of oxygen or any other suitable gas is caused to impinge on the cutting location by means of a pressurized gas supply 72 and a nozzle 74. The supply of oxygen results irrelative complete burning of carbon compounds and thus produces a relatively clean cut.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow: 86559/4

Claims (6)

1. Apparatus for laser cutting of a workpiece comprising: — a laser producing an output beam of circular cross-section; — a beam- expansion unit, consisting of a pair ofcylindncal lenses, with cylinder axes parallel to each other and perpendicular to the laser beam propagation direction, the first lens having a focal length fi, and the second - a focal length — a spherical focusing lens with a diameter sufficiently large to accept the full laser beam after expansion, to form the laser focal spot on the workpiece being cut.

2. Apparatus according to the preceding claim, and also comprising means for directing a stream of oxidizing gas onto the focal spot on the workpiece.

3. A method for laser cutting of a workpiece , comprising the steps of: — producing a parallel laser beam of circular cross section; — passing said laser beam via a beam expander in which the first cylindrical lens increases the beam divergence in a direction parallel to the cutting direction, and the second cylindrical lens reduces again the beam divergence, thus forming a parallel laser beam of elliptical cross-section; — passing the expanded laser beam, via a spherical focusing lens to form the focal spot of the laser beam on the workpiece.

4. An apparatus substantially as shown and described hereinabove.

5. An apparatus substantially as illustrated in any of the drawings.

6. A technique substantially as shown and described hereinabove.