DE1690637A1 - Method and device for flame cutting of metal with laser beams - Google Patents

Description

Documents for the official publication;

PATENTANWÄLTE I Q V »U P 3 /

ing. H. NEGENDANK - dipl.-ing. H. HAUCK Dipl.-Phys. W. SCHMITZ

HAMBURG-MUNCHEN DELIVERY ADDRESS: HAMB URG 36 · NEUER WALL 41

TELEOR. JiEGEDAPATENT HAMBTTRG MUNICH 15 MOZARTSTR. 23

National Research tel.s38oj86

Development Corporation tkleoh. νε6Ε! ιαραιενι ü

^r5 Hamburg, May 6, 1970

"Process and device for flame cutting of metal with laser beams"

Oxy-fuel cutting and chiselling is widely used for cutting metals when making a wide cut is permissible; the accuracy of the thermal processes is not particularly high, so they are only used as preprocessing can be applied. The reason for this inaccuracy is that the heating is not locally concentrated enough can be used, particularly when a gas stream is used to repel molten metal, which is that it enters into an exothermic reaction with the preheated area of the metal. This exothermic reaction maintains itself if the temperature of the workpiece is low assumes a predetermined value, and hence the width of the cut varies with the width of the oxygen Stromes directed towards the preheated area. In addition, the well-known oxy-fuel cutting methods another disadvantage in that heating a considerable area of the workpiece leads to it

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harm by ζ. Β. its properties or structure is destroyed or attacked.

The laser beam as a heat source allows an extremely high concentration of energy, and a few years ago the laser became known as a piercing instrument suitable for making fine holes. In addition, can the laser to a very small point with "considerable accuracy be concentrated and deliver a level of energy to a workpiece sufficient to hold the metal on the Path of the laser beam to boil, causing cutting is achieved. Consequently, the laser has been considered as a cutting instrument for metals to be very narrow Get cuts that are not possible with conventional oxy-fuel cutting methods.

It has now been found that when a gas jet, the generates an exothermic reaction, is directed so that it flows on the area of the tool on which the laser beam is set, there not only the cutting speed is increased, but also the accuracy and the Essentially the fineness of the cut through the gas flow remains unchanged, despite the fact that the cross-sectional area of this current on the workpiece differs greatly from that of the Lasev Beam may differ. Obviously, the width of the

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The cut was essentially determined by the laser beam and not by the gas jet, which regulated the width of the cut in the older methods of oxy-fuel cutting and chiselling, in which an exothermic reaction was used. Of course, this stems in part from the fact that the part of the workpiece exposed to the laser beam is an extremely narrow strip; however, it is believed that this is also due in part to the fact that the material in this strip is raised very rapidly to a temperature at which it evaporates or melts and there is a very steep temperature gradient in the workpiece. As a result, the ratio of the amount of heat supplied by the laser beam and the exothermic reaction, which is consumed as latent amount of heat during melting and evaporation and thus carried away from the metal body by the gas stream, is significantly greater than in the known oxy-fuel cutting processes. The zone, the temperature of which is high enough to take part in the exothermic reaction, therefore only spreads insignificantly. In this view, the invention has been strengthened by observations of the temperature of the metal in a gas assisted laser cutting operation. In the known methods, e.g. B. when cutting fluids, the exothermic reaction is known to sustain itself when the metal is heated to "ignition" temperature. that is, the oxygen alone intersects the mild steel which is generally estimated to be approximately 875 ⁰ C when it is heated to a temperature. Eb has now been established that the

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laser cutting supported by a gas steel Temperature on the swept strip "considerable is higher than this "ignition temperature", but that anyway at a cutting speed sufficient for the thickness of the metal, the process will not be self-sustaining.

Another factor that convinced the applicants that the temperature of the strip that is cut is considerably higher than that of conventional cutting methods is that stainless steel (i.e., stainless steel and refractory steels with a laser beam assisted by an oxygen beam) high chromium content) is from about 1,375 ⁰ C. With the usual oxy-fuel or flame cutting processes, stainless steel can only be cut if a flux or diluent is introduced in addition to oxygen. The combination of the laser and oxygen beam cuts through stainless steel without the need for a flux or thinner,

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from which we can conclude that a heated by the beam Strip is hot enough that the oxide film melts or evaporates and is then blown away.

Obviously, a very narrow zone of the workpiece must be heated to a temperature for successful work which is much higher than with the known flame cutting devices is achieved, but the heat propagation must be tightly limited, and consequently it must be exothermic reacting gas will noticeably affect the cut face widen.

Accordingly, the present invention relates to a method for cutting or chiselling. It is characterized in that a laser beam is concentrated on a workpiece, Workpiece and beam are moved relative to each other and a beam of a gas that causes an exothermic reaction, is directed to the moving area of the workpiece on which the laser beam is concentrated, one causes exothermic reaction on the heated metal and the Blows away combustion products. Because the exothermic reaction makes better use of the laser's power it is no longer necessary to use a laser, in which the power is concentrated in periodic bursts.

Ss has already been mentioned ₉ that in the process according to the invention no significant heat spread

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takes place. As a self sustaining exotherm If reaction does not take place, the gas-assisted laser beam is clear in the cutting direction, and this represents Another advantage is that the cutting process can be stopped very quickly by switching off the laser beam can. The process itself is particularly suitable good for machine torch cutting devices.

In addition to the above-mentioned gate part, the Process a flame cutting, which occurs without the relatively expensive hot neighboring zone, the two known processes, and without destruction of the workpiece, what often happened in the older procedures »

Although more rustproof by the process of the invention

and
Steel (including simony and other refractory metals) can be cut without a flux, the use of a flux is appropriate for some materials. Ceramic material, brick, tile, cement, stone, rock and the like do not react exothermically with oxygen, and in order to cut these materials with a laser beam, a metal wire is introduced into a compound which allows an exothermic reaction with the gas and a flow effect with the material to be cut at the point where the laser beam passes over this material. The gas jet then blows the molten material or low-eluting mixtures out of it

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heated area away. For example, the flux can in the form of a powder in a gas stream to the heated one GeMet, and this flux can be iron or an alkali metal halide. In one thing: another embodiment the flux can be used as a coating on the surface of the material to be cut, e.g. B. by brushing or spraying.

For most of the above materials, iron can be used as a flux in conjunction with a Oxygen gas flow. So z. B. iron powder in an Iiasersysten introduced in a jet of oxygen gas; the iron powder oxidizes quickly and produces overheated Iron oxide that flows and the ceramic or the other Material cuts. Bas iron can also be introduced as a wire or strip at the point where the gas jet and the laser beam meet. Another option is to use a volatile or volatile Introduce halide (e.g. an iron halide) into a beam of oxygen that hits the part of the workpiece that heated by the laser beam. The combination of iron as a flux with a stream of oxygen can also be used with aluminum, which also forms hard-to-melt oxides when heated.

The oxygen gas jet can be directed onto the workpiece through a nozzle through which the laser beam is directed

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occurs, or it can be directed obliquely to the surface of the workpiece. In the first pail, in which the laser beam and gas exits through the nozzle, this is, although extremely compact, not significantly heated. B. Oxygen. Indeed, it was with the plasma torch, was with what to application of the laser reaches of cutting to the highest heat convergence and concentration _t is not possible to use a gas that causes an exothermic reaction because the hot parts of the burner would have been oxidized to quickly and eaten . In most cases one could only work with inert gas to blow away the molten metal.

An inclined arrangement is required for chiselling, and more than one laser can be used. Two laser beams, each of which is a reactive beam Gas is surrounded, can be arranged at an angle to each other so that the rays at one point converge near the workpiece. These rays can make parallel cuts that converge at a point below the surface of the workpiece, creating a

Part of triangular cross-section along the cutting line is cut out. With a single laser and a separate gas beam is when the laser beam hits the surface perpendicularly, a high gas jet angle suitable for cutting and a low gas jet angle suitable for chiselling; the inclined gas jet "blows then the metal melted by the heat of the laser and the exothermic reaction away · Both the oxygen beam and the laser beam can put the workpiece in meet at an oblique angle, they can hit the workpiece from the opposite sides of a vertical plane occur or in max & hen cases (e.g. in certain Types of chiselling) hit the workpiece from the same side of the plane. In this pail is the gas jet angle preferably less than 45 ° to the workpiece and the laser beam angle greater than 30 ° from the vertical seen from. In this description, the term "chiseling" is used to denote mechanical work processes, like notches on a stick in a lathe, turning and planing.

As stated above, the width of the cut is primarily determined by the width of the laser beam, and it can be increased, provided that the strength

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of the laser is sufficient by increasing the effective diameter of the beam on the, work surface d. &· through this, that the beam over the work surface to a focal point, sometimes in the nozzle itself, is united. The increase in width is sometimes with thicker workpieces desirable where the width is at the base of the cut is not sufficient to let the gas through to the required extent.

Another way to widen the incision is where A laser of such high energy is not necessary, consists in giving the laser a repetitive z ^ dische movement at right angles to the cutting direction, with the gas jet striking the area of the workpiece that is in is coated in the manner described, is directed. In the preferred form the relative motion is between Laser beam and surface a combined linear movement in the cutting direction and a circular movement symmetrical about the center line of the cut. This arrangement has the advantage that when the cutting line changes the circular motion superimposed on the motion in the direction of the cutting line on the laser beam still gives the same movement across the cutting direction.

In order to make the invention even better understood, some exemplary devices for carrying out the inventive method will now be described with reference to the accompanying drawings.

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! Fig. 1 shows a schematic arrangement of a first From the form of such a device.

Pig. 2a, 2h, 2c and 2d

show schematically the cutting and chiselling of metals.

Fig. 5 shows a shape of a nozzle which the laser beam on the surface of the workpiece is circular Gives movement.

Fig. 4 shows a laser tendon head mounted on an in Transversely arranged platform is mounted.

5 shows a further form of a device for moving the cutting head and workpiece relative to one another.

FIG. 6 is a cross-sectional view through a swivel joint used in the device shown in FIG. 5.

Fig. 7 shows a further form of a device with which the cutting head is brought in relation to the workpiece can be, and

Fife. 8 shows the nozzle used in the device shown in FIG is used in cross section.

In Fig. 1, the laser 10 is Trara Eohlendioxyd-nitrogen-

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Heiium-iDyp shown of a length of 10 m and a Has a bore of 30 mm. The tube has five sections, only two of which are shown in the illustration, and each section has its own electrodes and 12. has its own electrical power source. The power source provides 20 kY for start-up and 9 kY at 45 milliamps when the laser is running. The laser body 16 has a fully reflective concave mirror made of gold plated stainless steel on one end and a flat, semi-reflective germanium disc on the other end. The concave mirror has a focal length of a little over 10 m .. The gas in which the discharge is to be generated, flows into the Laserkb'r.per through the inlet 22 and leaves it through the outlet 24.

Of course, the shape and mode of operation of the laser does not and should not form part of the invention suffice to establish that when the laser is in operation, a largely parallel beam of convergent light exits the laser through disk 20. In the present pail, the laser was powered by an AC power source operated at 50 Htz, and consequently the output was 100 rushes per second. In an alternating

beneath gas lasers, the power consumption follows of course.

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borrowed neither the sine wave of the entering current, nor the approximate square-wave voltage of the pipe. The withdrawal of power may be in the form of a distorted rectangular wave with a maxima on the guide side. One knows not how changes in such an extraction would affect the cutting process, but where does the whole The performance standard only differs enough to allow for the gas assisted laser cutting with a certain speed and with a certain thickness, can Changes in the character-to-space ratio or in the Wave form have a damaging effect on the doorway, as they can lead to the reaction no longer being sustained can be.

The exiting beam 26 is through a with aluminum coated mirror 28 and reflected through a security shutter 50 led to a converging lens 32. Of this Lens 32, the beam passes through window 34 into oxygen chamber 36. Oxygen passes through inlet 38 enters this chamber and exits through nozzle 40 in the direction of the workpiece. The axis of the laser beam runs centrally through nozzle 40 and is collected by lens 32 above or near the surface of workpiece 42. The lens 32 can be omitted if the mirror 28 by a parabolic mirror, which is at a suitable point for optical axis is set up, is replaced. A focal length one division of 1.587 mm in front of the nozzle is suitable

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net has been found when an oxygen jet of a diameter 0.254 mm "is used; this arrangement gives a clean and stable cut.

As indicated by the arrow 44, the workpiece is moved in the horizontal direction, so that. the laser, supported by the oxygen atom, _s is possible to make a cut durcL. As the cut continues, the molten or vaporized material is blown away through the cutting zone by the flow of oxygen gas, which also serves to create an exothermic reaction as described above.

In! Mild steel, high carbon tool steel and stainless steel 0.254 mm thick are at speeds Up to 101.6 cm per minute cuts with a width of 0.397 to 0.635 mm have been achieved, provided that that a minimum value of energy density is reached. It appears that the flow of oxygen does not change significantly affects the cutting width, although the additional flow of oxygen makes it possible to cut metals that are many times thicker than the ones that don't can be cut by gas assisted lasers. The cutting width is determined primarily by the diameter and the energy of the laser beam is determined, but also by the speed of movement and dag

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- 15 sion capacity of the workpiece.

The narrow cut gives a precision that Taisher with Acetylene-oxygen cutting torch could not be reached. The increase in laser energy allows one greater cutting speed, but with an AC powered one Laser speed is limited by the frequency of the power source. Using Direct current solves this problem.

The smoothness and stability of the cut depends on exceeding a minimum speed, which in turn depends depends on the strength of the laser beam and the material used should be cut. Below that speed (or below an energy threshold) the laser beam loses the Control, and the melting will begin to spread over the area heated directly by the laser. This leads to the melting of large areas and the interruption of the cutting process. When the speed increases the laser gets control again and gives one clean narrow cut. The threshold or the critical one The value of the laser energy is associated with a minimum speed, because if the energy is insufficient, the critical cutting speed cannot be reached. For cutting mild steel one Thickness of 0.254 mm at a speed of 101 cm

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A laser energy of over 300 was found per minute Watt as appropriate. At thicknesses of 0.794 mm, Watt had a cutting speed of 139 »7 cm per minute reaching a cutting speed of 44.45 cm per minute at 190 watts. Reduced at a thickness of 15 »47 mm the cutting speed at 250 watts is 44.45 cm per minute. In some cases an additional Power may be expedient for starting, and this can be achieved by generating an initial laser burst of energy which is greater than during operation, can be achieved.

In Pig. 1 the laser beam and the gas stream collide vertically on the surface of the workpiece. However, the nozzle, through which the laser stream and the gas stream exit, be arranged at an angle to the workpiece surface, like in Pig. 2a shown. Pig. 2b shows a Meafel process, in which the nozzle is at an angle of about 30 ° to the Workpiece surface is arranged. The oxygen flow blows away the molten metal and workpiece 42 moves in the direction indicated by arrow 44 is. In this way, a notch 46 is made in the workpiece generated.

The width of the notch may be greater than that of a cut obtained with the same nozzle and laser, and it is presumed that this is so because the

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molten material is not blown straight through the workpiece * as in the case of a cut, but something of its heat energy on its way to the sides of the Notch releases.

J ¹ Ig * 2c shows an apparatus in which the nozzle 50 through which the oxygen exits towards the workpiece is separated from the tube 52 through which the laser beam exits. The nozzle is arranged at an angle to the axis of the laser beam. The workpiece is guided in a direction perpendicular to the plane of the paper. As shown in the echematic representation, the direction of the cut 54 in such a workpiece movement is determined more by the direction of the oxygen flow than by the sealing of the laser flow. In this way it was possible to create a beveled edge on a workpiece *

Pig. 2d shows the use of a laser and a gas jet for "shape cutting ¹¹ " forming a notch in a rotating workpiece 56 of round cross-section. The diaphragm 55 prevents excessive light energy from being reflected from the workpiece back into the laser.

As explained above, when cutting thicker workpieces, it may be desirable to increase the cutting width.

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The focal point of the laser beam can be shifted easily, d. H. the laser beam can be brought to a focal point above the work surface, provided that it Has sufficient energy · As an alternative method for deconcentrating the laser beam, a nozzle, as in Pig «3 shown to be used. In this figure, the laser beam hits 23, after exiting the converging lens 32, onto a mirror 58 which is axially fastened on a rotating ring 60. The beam ref-slected by the mirror 58 is transmitted again a mirror 62 mounted on the edge of the ring 60 reflects. The ring 60 is driven by a drive wheel 64- driven so that the mirror 62 rotates around the axis of the nozzle. This arrangement is such that the collected Beam on the surface of the workpiece 42 a result from small circles on the latter describes, and these circles symmetrically around the cutting line resulting from the relative movement of workpiece and nozzle A suitable relationship between circular motion and linear motion can overlap the successive Circles should be such that all elements in the circular path are swept over by the laser beam »However, it has been found has been that when a laser beam sweeps over a circular path in the manner just described, there is a tendency that the reaction expands into a small area of the metal surrounding the circle. «Hence it is possible to go through the entire width of the circle without a complete over-,

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cover to see if the diameter of the laser beam and the oxygen beam are chosen so that the spread of the reaction is just sufficient, the center points
to remove the circles formed by the movement of the laser beam. The gas beam can be coaxial with the laser beam, as shown in Fig. 3, it can also
pass through another separately angled nozzle

In order to avoid the installation of a drive shaft through the wall of the laser tube, the ring 60 can, if desired, be driven by an induction motor. Other possibilities are to use a rotating prism to cause the laser beam to rotate, or to place a transparent plate in the path of the laser beam at an angle
to set up so that the exiting ray is parallel but offset with respect to the incident ray, _β The plate or block is then rotated about the axis of the incident ray so that the exiting ray becomes one
Circumscribes the circle. An elliptical beam movement could be generated by arranging two elements in series in the beam path and at an angle of 90 ° to each other, whereby the angle of each element to its incident beam e.g. by means of an electromechanical, electrostatic or magnetostriction device in vibration
render way can be varied. In Fig. 3 the sour

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Substance through inlet 38 into the nozzle, passes through a distribution ring 66 and passes through a series of holes 68 in the inner wall of the distribution ring into the chamber.

A rack 70 and a gear 72 are provided to to allow alignment of the cutting head.

Fig. 4 shows a cutting head 74 »which is on one in x and y-direction swivel platform is mounted to the Cutting head at any point above the surface to be able to bring the workpiece into position without moving the laser 10. The cutting head 74 · sits on a block 76, which also carries the oxygen supply pipe 78a. Of the Block 76 is attached to a screw guide 78, whose Rotation triggered the guide movement in y-direction Shank 78 is set in rotation by a sliding groove 80, which rests on a splined shaft 82 which is driven by a motor 84-. The movement in the x-direction is made by turning the guide worm 86 caused by a motor 88. The shaft = 78 is from a block 90 which engages in the guide screw 86 is carried. The parallel beam 26 is through the prisms 92 and 94 reflect before it has reached the nozzle 74.

Another device for guiding the laser beam to the workpiece is shown in FIGS. The laser beam runs here along four guide sections 98, 100, 102 and 104, of which at least the last three are at right angles

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are bent. The sections are separated from one another by pivot hinges 106, 108 and 110. One of these Hinges is in Pig. 6 shown in cross section. From this it can be seen that at the corners of the guide sections reflective surfaces 112 and 114 are provided and that each guide section ends in a pool 116 and 118, which is from each other and from the upper and lower Walls of a stuffing box 120 are separated by ball bearings.

In Pig. 5 is the laser nozzle in the tool holder 112 one arranged in a conventional lathe, and the beam is aimed at a round workpiece. The oxygen stream exits a separate pipe 126. In this example, a notch is formed around an annular surface of the workpiece.

Different combinations of rotary hinges result in different possibilities of movement, for example a first Rotary hinge in the vertical plane an angular movement when Raise the cutting head and use a second rotary hinge in the horizontal plane to give an angular movement in azimuth.

In another porm of laser guidance that is in the Pig. and 8, the beam passes telescopic arms. The first of these consists of two parts 130 and 132, the a gear 134 or a rack 136 carry. The part

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132 has a right-angled mood in the corner a reflector 138 is arranged and forms part of it of the further telescopic arm »whose extension can also be adjusted by means of a toothed rack and a toothed wheel is. This arm ends in a further reflector 140, as Fig. 8 shows, which the laser beam in the last telescopic Arm that ends in a nozzle reflects; the nozzle is of the type in the previous examples described «The arrangement allows the movement of the concentrated Laser beam to any point within a three-dimensional space, determined by the length of the telescopic Poor. It also allows a relatively solid construction and contains only two reflectors. These Considerations are important because vibration causes movement of the laser beam and reflection causes the degree the movement on the workpiece. Devices of the type shown perform program control themselves; z. B. Sinus and Cosine signals that control racks 134 and 142 cause the laser beam to cut holes. The nozzle with the guide tube connected in FIG. 8 can also be used in of the device shown in Fig. 4 can be used. The guide tubes of FIGS. 5 to 8 also allow a protective gas to be retained for the optically in a simple manner reflective surfaces. With a carbon dioxide laser z. B., which generates a wavelength of 10 microns, the lenses and windows must be made of a special material

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be. Germanium can be used, but it is expensive and the cheaper callumbromia has the disadvantage that it is hygroscopic and therefore subject to decomposition if no precautions are taken against it. A dry one warm gas, such as nitrogen, in the feed pipe system protects against destruction of the quaiim bromide surfaces.

The highly refractory metals that can be cut by the present invention also include tantalum, a tantalum alloy that contains 10 $> tungsten, and a niobium alloy that contains 10 $ 6 tungsten. An iron-Mckel alloy (Mio K) has also been cut.

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Claims (15)

- 24 claims 1. A method for cutting or chiseling metal, characterized in that a laser beam is applied to a workpiece is concentrated, the beam and the workpiece are "moved relative to each other and a beam of a gas, which creates an exothermic reaction, is directed to the moving area of the workpiece to which the laser beam is concentrated to cause an exothermic reaction on the heated metal, and the combustion products are blown away. 2. The method according to claim 1, characterized in that the laser beam has a continuous circular movement transversely to Direction of cut is granted. 3. The method according to claim 2, characterized in that the laser beam and the surface are combined linear movement in the cutting direction and a circular movement is issued symmetrically around the midpoint of the cutting line. 4. The method according to claim 1, characterized in that the laser beam is concentrated slightly above the surface of the workpiece. - 25 - 6. The method according to claim 1 for chiseling metal, dai characterized in that the gas stream is directed towards the workpiece so that it hits the workpiece or it tangent at an angle less than 45 °. 7. The method according to claim 1 for chiseling metal, characterized characterized in that two laser beams are arranged at an angle to each other so that their beams in a point near the surface of the workpiece converge so that they make parallel cuts at a point below the surface of the workpiece converge. 8. The method according to claim 1 for exercising on a workpiece that does not react exothermically with the gas jet, characterized in that a metal or a compound which enters into an exothermic reaction with the gas and acts as a flux for the workpiece, brought to the point where the laser beam hits the workpiece. 9. The method according to claim 8, characterized in that 2 008U / 0266 - 26 - Λ - 26 - the workpiece with the metal or the compound that acts as a flux, is coated. 10. The method according to claim 8, characterized in that the metal or the compound which acts as a flux is introduced into the gas stream in powder form. 11. The method according to claim 8, characterized in that iron is used as the flux. 12. The method according to claim 11, characterized in that the iron in the form of a wire or strip at the point of convergence of the laser beam and the flow of oxygen is introduced over the workpiece. 13. The method according to claim 11, characterized in that ■ that a piece of aluminum is used as the workpiece. 14. The method according to claim 1, characterized in that a piece of stainless steel is used as the workpiece. ...'-. ₌ - 15. Device for subjecting a workpiece to the effect of a coherent light bar, characterized by a laser (10) for generating a coherent light beam, optical means for sending the laser beam through through the device against the workpiece - 27 209814/0266 (42), a nozzle (50) through which the laser beam emerges from the device in the direction of the workpiece (4-2) and means for directing a gas flow through the nozzle (50) onto the workpiece, 2098U / O? Fifi Blank page