Nozzle for Laser Processing

The present invention relates to a nozzle for laser processing, such as a cutting, said processing allowing a laser beam to be directed towards an article being processed, and whereby the laser beam is supported by a gas flow directed towards the article through the nozzle.

It is common knowledge to use a laser for cutting metal, as well as it is common knowledge to use a gas beam including for instance oxygen or a gas mixture together with the laser beam towards the processed area.

Under usual conditions a coaxially positioned laser beam is used, i.e. a laser beam situated in the axis (E) through the centre point (C) of the nozzle. In other words the laser beam is situated on the location having the highest gas pressure/gas flow. Furthermore the symmetrical positioning of the laser beam in the nozzle provides a uniform cutting quality irrespective of the cutting direction. A cut groove is obtained by movement of the laser beam/nozzle relative to the material. The purpose of the supporting cutting gas is substantially to remove melt and vapours from the cut groove. The ability of the process to remove the water material depends on the flow conditions in the nozzle and in the cut groove.

According to the invention, the nozzle is able to maintain a displacement of the focusing point of the laser beam relative to a center of gas pressure for the gas flow through the nozzle, whereby the laser beam is displaced forwards in the processing direction relative to the center of gas pressure. As a result the laser beam meets the article first and melts this portion of the article, said portion subsequently being blown away by the gas flow. In this manner the gas flow is efficiently utilized because it does not meet the article until the material to be removed has melted and is thereby removable by blowing.

The nozzle is preferably circular-cylindrical and able to maintain a predetermined eccentric position of the laser beam in the nozzle. According to an alternative embodiment a circular-cylindrical nozzle is also used, but this nozzle is mounted with the laser beam in the center while an eccentrically located outlet nozzle opening is provided for the gas flow. According to a particular embodiment the nozzle may be radially displaceable relative to the laser beam. Within the scope of the invention the nozzle may, however, be of other shapes than the circular-cylindrical shape.

The laser beam is preferably spaced a distance d from the center of gas pressure, whereby 0.01 D is smaller than the distance d in turn being smaller than D/2, D being the diameter of the nozzle. The distance d corresponds preferably to 0.25 times the diameter of the nozzle.

An external control is preferably provided, said control controlling the nozzle and/or the laser beam in response to the desired direction of processing. Such an external control is advantageously connectable to an existing control of a cutting table and/or the laser head. According to a preferred embodiment, the nozzle maintains a predetermined position of the laser beam in the nozzle relative to the direction of processing in such a manner that the center of gas pressure and the laser beam are substantially always situated on the tangent of the direction of processing.

The invention will be described below with reference to the accompanying drawings, in which

FIG. 1 is a sectional view through the outer portion of a nozzle according to the invention,

FIG. 2 illustrates the movement of the nozzle of FIG. 1 during the alteration of a cutting direction,

FIG. 3 illustrates a second embodiment of a nozzle according to the invention,

FIG. 4 illustrates a third embodiment of a nozzle according to the invention,

FIG. 5 illustrates a still further embodiment of a nozzle according to the invention, and

FIGS. 6a-6f illustrate further examples of various nozzle openings.

FIG. 1 illustrates the principles of the nozzle according to the invention. A laser beam A is focused through a nozzle opening by a known laser and optics system 50. The nozzle opening is preferably circularcylindrical but may have other shapes. A gas, such as oxygen or a gas mixture, is sent together with the laser beam A through the nozzle to remove the material being melted by the laer beam by a known source of compressed gas 52. The center of gas pressure--i.e. the location having the highest dynamic gas pressure causing the highest flow velocity--is then situated in the center of the nozzle at point C on the center axis E. The focal point, i.e. focus D, of the laser beam is displaced relative to the center axis F at the distance d from point C.

FIG. 2 shows a cut groove 22 in an article. The arrow 24 indicates the cutting direction, and the arrow 25 indicates a new cutting direction. A nozzle 11 has been shown at four different positions. As it appears from the FIGURE the center of gas pressure 30 is centrally located in the nozzle opening whereas the focal point 26 of the laser beam is displaced forwards in the cutting direction. During the first phase of the movement, the nozzle is displaced in the cutting direction with the focal point of the laser beam in front in a rectilinear movement. When the point of discontinuity 32 has been reached, the rectilinear movement is stopped and the nozzle is rotated about the focal point of the laser beam, cf. the arrow 25 and the angle .theta.. Subsequently the rectilinear movement is continued in the new cutting direction 24'. As illustrated in FIG. 2 the focal point 26 of the laser beam is now situated in front of the center of gas pressure 30 in the new cutting direction.

FIG. 3 illustrates an alternative embodiment. According to this embodiment the laser beam 10 is positioned in such a manner that the axis 20 of the laser beam coincides with the axis of the substantially cylindrical nozzle. In turn the nozzle opening 32 is eccentrically situated. The nozzle of FIG. 3 can be used as illustrated in FIG. 2, said FIGURE illustrating the use of the nozzle of FIG. 1 with the exception that the focal point of the laser beam is centered in the nozzle and the nozzle opening. As a consequence the center of gas pressure is displaced backwards relative to the cutting direction.

FIG. 4 shows a still further embodiment where the nozzle is a radially displaceable plate 34 comprising a nozzle opening 32. The feeding of gas to such a plate can, of course, be established in many ways and has not been shown.

FIG. 5 illustrates an embodiment comprising a fixed nozzle 34 and a centrally located nozzle opening 32 as well as a laser beam 10. The position of the focal point of this laser beam is determined by a movable lens system 36 or another type of movable optical instruments, such as a system of concave mirrors, optical units/plates or the like instruments. The invention may, of course, be varied in many ways, and the various embodiments outlined can be combined. The nozzle and the nozzle opening need not necessarily be circular-cylindrical either but may, as indicated in FIGS. 6a-c, have different shapes. As illustrated by the axial sectional views of FIGS. 6d-f the nozzle, for example may be cylindrical elliptical or otherwise a cylindrical nozzle may be circular-cylindrical of a cross section as outlined in FIG. 6d or ellipticcylindrical of a cross section as outlined in FIG. 6e or of another advantageous shape like the one outlined in FIG. 6f. In order to ensure optimum flow conditions alternative embodiments of the nozzle may, however, also be considered, such as a conical nozzle, cf. FIG. 6b, or a double-frustoconical nozzle, cf. FIG. 6c. A transverse sectional view through these embodiments reveal many possibilities for the embodiment, such as for instance circular, elliptical or other more particular shapes. The essential feature to the invention is that the nozzle is shaped in such a manner that a well-defined center of gas pressure is provided in the cutting plane and a laser beam is allowed to pass through the nozzle with a well-defined focal point also in the cutting plane, and furthermore in such a manner that a well-defined distance exists between the center of gas pressure and the focal point. The nozzle must be mounted in such a manner that the focal point of the laser beam is always in front of the center of gas pressure in the cutting direction. In this manner improved flow conditions are obtained through the nozzle and the cut groove, which implies that the deposition of burrs on the back of the cut is reduced significantly both when oxygen and gas mixtures are employed. The use of particular gas mixtures as supporting cutting gas eliminates the deposition of the so-called "ball burrs" as such burrs are blown out of the cut groove before they harden, and consequently they do not have time to stick to the cutting edge.

The use of particular gas mixtures as supporting cutting gas ensures furthermore slagless cut surfaces when cutting in stainless steel.