EP2844417A1

EP2844417A1 - Laser-assisted plasma cutting or plasma welding method, and device for this purpose

Info

Publication number: EP2844417A1
Application number: EP13718787.8A
Authority: EP
Inventors: Andreas Popp; Tim Hesse; Tobias Kaiser
Original assignee: Trumpf Werkzeugmaschinen SE and Co KG
Current assignee: Trumpf Werkzeugmaschinen SE and Co KG
Priority date: 2012-04-30
Filing date: 2013-04-24
Publication date: 2015-03-11
Also published as: US9849545B2; CN104395032A; WO2013164076A1; DE102012207201B3; US20150053656A1; CN104395032B

Abstract

The invention relates to a method for the laser-assisted plasma cutting or plasma welding of a workpiece (3), having the following steps: generating a plasma jet (1) which extends between an electrode (2) and a machining point on the workpiece (3), said plasma jet (1) having a central region (4) which is internal relative to a plasma jet central axis (M) that runs in the propagation direction (Z) and having an external edge region (6); and conducting laser radiation (7) into the edge region (6) of the plasma jet (1), the laser radiation (7) which is conducted into the edge region (6) running parallel to the central axis (M). The invention also relates to a corresponding device (10) which is designed for laser-assisted plasma cutting and/or plasma welding.

Description

The present invention relates to a method and a device for the laser assisted plasma cutting or plasma welding and apparatus therefor

Laser-assisted plasma cutting or plasma welding.

In plasma cutting or welding, an arc burns between a cathode and an anode. By impact ionization, this produces a hot plasma or a plasma jet of a plasma gas with a temperature of more than 20,000 K. In plasma cutting or welding of metallic workpieces, the cathode is typically arranged in a machining head, while the electrically conductive workpiece to be machined is the anode forms.

CONFIRMATION COPY Due to the commonly used pointed shape of the cathode and the resulting density distribution of the electric field lines is shortest

Connecting line between cathode and anode, which the center axis of the

Plasma jet corresponds as well as in the center axis adjacent

Central area of the plasma torch or the plasma jet, the burst rate of the charged particles in the plasma particularly high. The high burst rate leads to a high

Temperature and high electrical conductivity of the plasma. This central region of the plasma torch is strongly constricted due to the increased conductivity and stable in shape. With increasing radial distance from the central region, the burst rate of the charged particles becomes significantly lower and the temperature, density and electrical conductivity of the plasma torch decrease. This leads to fluctuations and to a widening of the plasma jet. This instability and widening of the edge area of the plasma jet produces an irregular and thus poor cutting result in plasma cutting. In plasma welding, the

Welded seam, so that a smaller depth can be achieved and a greater heat distortion occurs.

To guide, constrict and stabilize a plasma jet are

various approaches known:

From DE102009006132B4 it is known, by a targeted cooling of the plasma jet with the aid of a water-cooled nozzle the plasma on

Kathodenfußpunkt energy to escape. By supplying and / or removing cooling liquid at right angles to the longitudinal axis of the plasma burner head, a significantly longer contact of the cooling liquid with the nozzle is produced there. As a result, the plasma jet constricts at the cathode base.

From DE102010005617A1 it is known, a current flowing through the plasma torch at least during a temporal portion of the

Plasma cutting process targeted or controlled to bring pulsation. Among other things, it is also proposed there to put the plasma gas and / or a secondary gas through specially shaped nozzles of the machining head in a rotating flow. From WO2000064618A2 it is known in plasma welding a

Plasma jet and a laser beam to superimpose to ignite the plasma jet and to guide along the laser beam direction. The laser beam is used in the

Plasmagas to stimulate molecules to vibrate and thus to specify a beam path for the plasma jet.

From WO2011029462A1 an apparatus and a method for processing workpieces with an arc device and a laser device have become known in which a laser beam is guided within the plasma jet, the laser beam in the plasma jet forms a channel to increase the conductivity of the plasma jet. The electrode of the

Arc device may be formed as a ring electrode and the laser beam may extend within the central opening of the ring electrode. Alternatively, one or more laser beams can be guided from the outside to the plasma jet immediately adjacent to the processing point and this cutting to the processing point.

From DE19944469A1 a device for hybrid welding is known, in which at least one focused (alternatively optionally defocused) laser beam is slid onto the workpiece to be machined and an electric arc between an electrode and the workpiece is generated, wherein the axis of the arc concentric to Laser radiation is aligned. The laser beam and the arc substantially strike the same location on the workpiece

(Processing point) and influence or support each other.

Object of the invention

The object of the present invention is to provide a method and a method

Apparatus for laser-assisted plasma cutting or welding

to provide improved stabilization and guidance of the

Enable plasma jet. Subject of the invention

This object is achieved by a method for laser-assisted

Plasma cutting or plasma welding of a typical plate-shaped workpiece, comprising the steps of: generating a plasma jet extending between an electrode and a processing point on the workpiece, wherein the plasma jet has a center region (radially) inside with respect to its center axis extending in the direction of propagation and a (radially ) has outer substantially annular edge region; and supplying laser radiation, in particular collimated laser radiation or of

Laser radiation with a long Rayleigh length, in the edge area of the

Plasma beam, wherein the supplied laser radiation is parallel to the center axis of the plasma jet. An essential aspect of the invention is not to coaxially illuminate the entire plasma torch or the entire plasma jet by the laser radiation, but to concentrate the intensity of the supplied laser radiation on the edge region of the plasma jet, so that only a negligible proportion of the intensity of the laser radiation Central area is supplied. In this case, typically, collimated laser radiation or laser radiation with a long Rayleigh length is used in order to ensure that the laser radiation (in the

Essentially) is aligned parallel to the center axis of the plasma jet and has a uniform beam shape along the plasma jet. Typically, the laser radiation is applied to the plasma jet at its end remote from the workpiece (i.e., in the region of the electrode) so as to achieve a uniform beam guidance over the entire length of the plasma jet. This is particularly favorable in plasma cutting, since above all thick sheets (10 mm - 180 mm) are processed there and a cutting edge with the smallest possible edge slope is to be achieved, so that the supplied laser radiation should pass as parallel to the center axis when passing through the workpiece. In order to achieve this, collimated laser radiation may be used, but it is also possible to use slightly focused or defocused laser radiation having a Rayleigh length that is so large that the

Laser radiation when passing through the workpiece (approximately) parallel to the Center axis runs. To ensure this, the Rayleigh length of the laser radiation used should be at least as large as the thickness of the machined workpiece. The inventors have recognized that the laser radiation supplied to the central region of the plasma jet has no or very little influence on its energetic state due to the already high impact rate. In the radially outer

Edge region of the plasma jet, which has a lower plasma density, the laser radiation, however, can be targeted and used effectively. The laser radiation thus acts exactly on the area of the plasma jet, which diminished for the

Cutting quality and welding depth is responsible. The action of the

Laser radiation typically leads in the edge region of the plasma jet by the opto-galvanic effect to increased ionization of the plasma gas, whereby the temperature, density and electrical conductivity in the irradiated

Plasma area increased. This stabilizes and constricts the plasma jet specifically in the edge region and makes it possible to guide the plasma jet over its entire length.

In one variant of the method, a wavelength of the laser radiation is chosen such that a plasma gas used for generating the plasma jet is excited by the laser radiation (electronically). The wavelength of the laser used or the laser radiation should be selected so that an electronic excitation takes place in the plasma gas, which leads to the optogalvansichen effect. Since argon is a commonly used plasma gas, for example, with the help of a

Diode laser with a wavelength of 800 nm - 900 nm argon ions are excited. Alternatively, it is also possible to ionize argon atoms directly or

to stimulate. For this short wavelengths of 200 nm - 500 nm are needed, for example, by frequency doubled or frequency tripled

Solid state lasers can be generated. It is understood that when using plasma gases other than argon, the wavelength of the laser radiation should be suitably adjusted.

In one variant, the laser radiation supplied to the plasma jet has a power of less than 1000 watts, preferably of less than 500 watts. Of the Laser beam or the laser radiation typically does not have enough energy or power to contribute itself to the workpiece machining, but serves exclusively to stimulate the opto-galvanic effect in the edge region of the plasma. The laser power required to stabilize the plasma jet is dependent on the length of the plasma torch or the plasma jet and thus on the

cutting or welding workpiece or sheet thickness dependent. Furthermore, the performance depends on the Bouguer-Lambert-Beer ^'s

Absorptionsgesetzes of the ion density and the cross section of each electrically excited ion or molecule of the plasma gas in the

Laser wavelength off. A few hundred watts of laser power are typically sufficient for stabilization. For example, the laser power supplied to the plasma jet may be between about 100 W and about 500 W.

In an advantageous variant of the method according to the invention, the plasma jet is generated by means of a rod-shaped electrode, typically a pointed electrode. By using such an electrode, the

Excitation of the opto-galvanic effect in the edge region of the plasma jet without a complex processing head with coaxial guidance of the laser beam within the ring cathode done. Due to their geometry, a pointed electrode can generate a high field strength at a lower electrical voltage than one

Coaxial cathode, which is energetically of great advantage.

For supplying the laser radiation to the plasma jet, in particular when using a rod-shaped electrode, the laser radiation can be deflected in at least one laterally offset to the center axis in a direction parallel to the center axis of the plasma jet. The amount of lateral displacement of the deflection to the central axis of the rod-shaped electrode, which corresponds to the center axis of the plasma jet, more specifically the distance between the center axis and the point at which the laser radiation impinges on the deflection at a 90 ° deflection corresponds to typical manner the (average) radius of the substantially annular edge region of the

Plasma jet.

The deflection can, for example, as a deflection mirror or possibly as be formed mirrored portion of an electrode holder and may have a flat or possibly a curved, eg frusto-conical mirror surface. It goes without saying that a 90 ° deflection of the laser radiation does not necessarily have to take place at the deflection device, but that, if appropriate, a larger or a smaller deflection angle can also be used in order to align the laser radiation parallel to the center axis.

In a further variant, the laser radiation is supplied to the plasma jet through a gas supply space of a gas nozzle for applying a plasma gas to the workpiece. In this variant, the laser radiation in the typically annular gas supply space runs parallel to the center axis of the gas nozzle, which generally corresponds to the center axis of the electrode, so that it is possible to dispense with a deflection device in the region of the gas nozzle of the plasma processing head, possibly an interference contour for the flow of the plasma gas to the workpiece forms.

In a further variant, the laser radiation supplied to the plasma jet has an annular, rotationally symmetric or non-rotationally symmetrical

Intensity distribution on. In the simplest case, the action of the laser radiation can take place annularly in the entire edge region of the plasma jet. Alternatively, a non-rotationally symmetrical intensity distribution of the laser radiation is possible. The intensity distribution of the laser radiation can be formed, for example, during cutting so that the laser radiation acts only on the cut front and on the side of the good part, since the cut quality on the side of the residual grid, which is typically disposed of as waste, is irrelevant.

A further aspect of the invention relates to a device for laser-assisted plasma cutting and / or plasma welding of a workpiece, comprising: a plasma generating device configured to generate a plasma jet extending between an electrode of the plasma generating device and a processing point on the workpiece, wherein the plasma jet with respect to its (radially) inner central region extending in the propagation direction and having a (radially) outer, substantially annular edge region, and a beam supply device for supplying (collimated) laser radiation (or radiation of high Rayleigh length) into the Edge region of the plasma jet, wherein the laser radiation supplied to the edge region is parallel to the center axis. In the inventive

Device is according to the method of the invention the

Randbereich supplied laser radiation used to the plasma jet

stabilize and improve the cutting or welding result. The apparatus may optionally be used for plasma cutting or plasma welding, depending on how the parameters for generating the plasma or the pressure of the gases used are selected. In one embodiment, the device comprises at least one laser source for generating laser radiation. The laser source may be, for example, a diode laser or a solid-state laser. When selecting a suitable laser source, the spectral properties (central wavelength and line width) as well as the quality of the generated wavefront are of particular importance, since optimal colimimation corresponds to a planar wavefront and thus enables particularly good stabilization and constriction of the plasma jet.

In a development, the laser source is designed to generate laser radiation at a wavelength which is suitable for exciting the plasma gas used to generate the plasma jet. The spectral transitions of plasma gases can be taken from databases, for example under

The plasma gas used is often argon or argon-hydrogen mixtures, but other gases, such as nitrogen, oxygen or hydrogen and their mixtures as plasma gases can also be used be used, even air is possible in rare cases.

The power of the laser for generating the laser radiation should not exceed 1 kW, typically not more than 500 W. The laser power required to stabilize or constrict the plasma jet is comparatively small and less than the laser power that would be required to effect a cutting or welding operation on the workpiece. The maximum power of the laser source stated above assumes that there is only a single laser source whose laser power is substantially equal lossless is supplied to the edge region of the plasma jet. Is more than one laser source for supplying laser radiation in the edge region of the

Plasma beam used, the maximum laser power of each

Laser source can be reduced accordingly.

In a further embodiment, the electrode is rod-shaped, typically with a tapered end at which the field strength upon application of a voltage between the electrode and the to be machined

Workpiece is particularly high. As has been shown above, the use of a rod-shaped electrode allows the use of a

Plasma processing head with respect to an annular electrode greatly simplified design. It is understood, however, that the inventive

Device may optionally also have an annular electrode. In one embodiment, the device has at least one laterally to

Center axis staggered deflection to the laser radiation in a

Direction parallel to the center axis of the plasma jet to redirect. The

Deflection device (s) can, for example, as by the electrode

be formed spaced deflecting mirror.

In an advantageous development, the deflection device is formed on a cooled holder of the electrode. The holder may have one or more cooling channels for cooling with the aid of a cooling fluid, for example water. The

In particular, the deflection device can be formed on an eg frustoconical portion of the holder, which merges into the electrode or on which the electrode is attached. To increase the reflectivity of the typically metallic holder may optionally be provided in the beam deflection with a reflective coating. The deflection to perform on the holder is cheaper than the deflection at the electrode itself, since it is not usually cooled directly and has a very high temperature, which can lead to an expansion of the metallic material of the electrode as well as to local deformations that for a Targeted deflection of laser radiation in the edge region of the plasma jet is unfavorable. In a further embodiment, the beam supply device is designed to supply the laser radiation to the plasma jet through a gas supply space of a gas nozzle for applying a plasma gas to the workpiece, so that a deflection of the laser radiation in the region of the electrode can be dispensed with.

In a further embodiment, the beam feeding device is for

Generation of laser radiation, in particular of collimated laser radiation or of laser radiation with a large Rayleigh length, formed with an annular, rotationally symmetric or non-rotationally symmetrical intensity distribution. The beam delivery device in this case typically has one or more optical elements on which or on which a typically divergent, possibly also convergent, laser beam is collimated (approximately). The annular intensity distribution is rotationally symmetric in the simplest case, but it is also possible to generate a high radiation intensity only in one or more limited angular ranges. It is understood that the (average) radius of the annular intensity distribution substantially corresponds to the (average) radius of the annular edge region of the plasma jet. The annular

Intensity distribution can be generated by a centrally arranged circular aperture, but it is more favorable if the annular intensity distribution can be generated substantially without loss of intensity.

In a further development, the beam delivery device has an axicon which has at least one conical lens surface in order to generate a ring-shaped, typically collimated, beam from a typically divergent laser beam

Intensity distribution to produce, without this being a worth mentioning

Intensity loss of the laser radiation occurs.

In a further development, the beam delivery device has a diffractive optical element. With the aid of a diffractive optical element, diffraction orders of the laser radiation can be used in order to form a distribution of a typically divergent intensity distribution impinging on the diffractive optical element into an almost arbitrarily shaped exit side

Intensity distribution. A diffractive optical element can thus be used to form an annular, rotationally symmetric or not To generate rotationally symmetric intensity distribution. The latter can be used, for example, to produce a stabilization of the plasma jet in plasma cutting only on one side of the cutting front, on which a good part is formed, in which a high cut quality of the cutting edge is required.

In a further embodiment, the beam feed device has a plurality of optical fibers arranged annularly around the center axis, which are typically aligned parallel to the center axis and to which a respective microlens for collimation of emerging laser radiation is associated. The latter is necessary since the laser end emerging on a workpiece facing the fiber end of a respective (glass) fiber usually exits divergent and therefore (approximately) must be collimated. The microlenses can be arranged at a predetermined distance from the respective fiber end or a respective fiber end can be provided with a microlens by melting it so that the fiber end itself acts as a microlens (also referred to as "lensed silica fiber").

Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and the features listed further can be used individually or in combination in any combination. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.

Show it:

Fig. 1a, b are schematic representations of a plasma jet for

Workpiece processing without stabilization (FIG. 1 a) and with stabilization and constriction by collimated laser radiation (FIG. 1 b) running in an edge region of the plasma jet,

Fig. 2 is a schematic representation of an embodiment of an apparatus for laser-assisted plasma cutting or welding with a Beam delivery device with an axicon for generating a laser beam with an annular intensity distribution, a beam shaping device with a collimating lens and a circular aperture for generating an annular

Intensity distribution,

4 shows a further beam shaping device with a diffractive optical

Element for generating an annular intensity distribution,

Fig. 5a, b is a plurality of annular around the center axis of an electrode

arranged optical fibers in a side view and a plan view,

Fig. 6a, b one of the optical fibers of Fig. 5a, b with one of a fiber end

spaced microlens (Figure 6a) and a microlens formed at a fiber end (Figure 6b),

7 shows a further embodiment of a device for laser-assisted

Plasma cutting or welding with two deflecting mirrors for deflecting laterally supplied laser radiation in the

Propagation direction of the plasma jet,

Fig. 8 shows a single deflection mirror for deflecting laser radiation in the

Propagation direction of the plasma jet, as well

Fig. 9 shows an electrode with a liquid-cooled holder, as

Deflection device for laser radiation is used, which is supplied to the holder side. Fig. 1a shows a plasma jet 1, which serves between a serving as a cathode

Pointing electrode 2 and serving as an anode metallic workpiece 3 (plate) and which serves to edit the workpiece 3, depending on the application, cutting or welding. The plasma jet 1 has a central, radially inner region 4, in the center of which a central axis M, which represents the shortest connecting line between the tip electrode 2 and the workpiece 3, and which corresponds to the center axis of the rod-shaped electrode 2. In the central region 4 of the plasma jet 1, the collision rate of charged (ionized) particles 5 of a plasma gas, argon in the present example, is particularly high. The high burst rate results in a high temperature and high electrical conductivity of the plasma in the central region 4, which is severely constricted and stable in shape, ie, the plasma is typically substantially in thermodynamic equilibrium. As the radial distance from the center axis M increases, the collision rate decreases, as a result of which a radially outer (substantially annular) edge region 6 of the plasma jet 1 surrounding the substantially circular central region 4 has a lower collision rate and correspondingly lower temperature, density, and electrical conductivity having. As a result, the plasma jet 1 is widened in the edge region 6 and instabilities occur there, which can lead to an irregular and thus poor cutting result during plasma cutting and during plasma welding to a broadening of the weld seam.

Fig. 1b shows the plasma jet 1 of Fig. 1a, in which in addition to the radially outer edge region 6 parallel to the center axis M of the plasma jet 1 (i.e.

perpendicular to the workpiece 3) extending, collimated laser radiation 7 is supplied. The laser radiation 7 supplied to the edge region 6 leads to a stabilization and in particular to a constriction of the plasma jet 1 in the edge region 6, as can be clearly recognized by a comparison of FIGS. 1 a and 1 b. As shown in FIG. 1 b, the laser radiation 7 is supplied only to the edge region 6, but not to the central region 4, since laser radiation 7 fed into the central region 4 would have only a negligible influence on the stability of the plasma due to the high impact rate. The laser radiation 7 thus acts precisely on the edge region 6 of the plasma jet 1, which is responsible for the reduced cutting quality and the low welding depth.

Fig. 2 shows an example of a device 10 which is designed to be a

perform laser assisted plasma cutting and / or plasma welding. The device 10 comprises a plasma generating device 11, which has a Power supply 12 to generate between the tip electrode 2, which serves as a cathode, and the metallic plate-shaped workpiece 3, which serves as an anode, a voltage or an electric field. The electrical connection of the workpiece 3 with the power supply 12 is effected for example by a laterally attached to the workpiece 3 contact terminal 3. When using a pointed electrode 2 as the cathode required for the generation of the plasma jet 1 voltages are comparatively low, the field strength in the Electrode tip is particularly high. Another part of the plasma generating device 11 is a gas supply for supplying a plasma gas 14 to a gas nozzle 15. More specifically, the plasma gas 14 is provided in the gas nozzle 15 annular

Gas supply chamber 16 supplied. The gas nozzle 15 forms part of a plasma processing head (not shown) to which the plasma gas 14 is supplied via feed channels not described in detail. The gas supply furthermore has a gas reservoir 17, in which the plasma gas 14, for example a mixture of argon and hydrogen, and process gases are stored. The gas reservoir 17 communicates with a device 18 for pressure adjustment for the plasma gas 14, in which, if appropriate, a mixture with other gases can also take place.

The plasma gas 14 supplied to the gas nozzle 15 exits the gas nozzle 15 at a nozzle opening facing the workpiece 3. By creating a

High voltage, the plasma torch is ignited (ignition phase). The plamagas is ionized, whereby between the electrode 2 and the workpiece 3, the plasma jet 1 is formed, which consists of positive and negative ions, electrons and excited and neutral atoms and molecules. In order to allow the plasma and process gas 14 to pass freely through the workpiece 3 during plasma cutting (cutting phase) at a kerf (not shown), a plurality of support webs 19 are provided as spacers on a workpiece support 20 (workpiece table). The gas mixture during the ignition and the

Cutting phase can differ in its composition and in the volume flow. In the machining of the resting on the workpiece support 20 workpiece 3 is typically a relative movement between the

Workpiece 3 and the gas nozzle 5 and the (not shown) Plasma processing head to which the gas nozzle 15 is attached. The

Relative movement typically occurs at the workpiece level, i. in the X and / or Y direction of an XYZ coordinate system. To generate the relative movement, the gas nozzle 15 can be moved with the plasma processing head, the workpiece 3 relative to the workpiece support 20 and / or the workpiece support 20 itself by means of conventional displacement units not described in detail here.

In the device 10 shown in Fig. 2, a diode laser is used with a

Wavelength λ in the range between about 800 to 1000 nm as the laser source 21. The wavelength λ of the laser radiation 7 is in this case matched to the plasma gas 14 that the ions 5 (see Fig. 1a) of the plasma gas 14, in the present case the

Argon ions, electronically excited (opto-galvanic effect). Alternatively or additionally, it is also possible to directly ionize gas atoms in the plasma gas 14, for which short wavelengths in the range between approximately 200 nm and 500 nm are typically required for argon as the plasma gas 14, which generates, for example, frequency-doubled or frequency-tripled solid-state lasers can be. It is understood that in addition to or as an alternative to argon, other plasma gases can also be used, for example nitrogen, oxygen or hydrogen, wherein the wavelength λ of the laser source 21 to the respective

Plasma gase can be adjusted and preferably between about 200 nm and 1000 nm. If desired, mixtures of a plurality of gases may also be used as the plasma gas 14, wherein the electronic excitation or ionization of a single constituent of the plasma gas 14 may possibly be sufficient to effect the desired constriction and stabilization of the plasma jet 1.

For generating the opto-galvanic effect in the edge region 6 of the

Plasma beam 1 typically has low laser powers, so that a maximum power of the laser source 21 of approximately 1000 W, typically between approximately 100 W and approximately 500 W, is sufficient if it is assumed that the available laser power of the laser source 21 (FIG. almost) is completely supplied to the edge region 6 of the plasma jet 1.

For the supply of the laser radiation 7 of the laser source 21 to the plasma jet 1, the device 10, a beam feed device 22, which is part of the Machining head can be. In the example shown in FIG. 2, this has an axicon 23 with a conical lens surface 23a in order to be divergent

Intensity distribution of the emerging from the laser source 21 laser radiation 7 to generate an annular intensity distribution and to collimate the laser radiation 7.

The axicon 23 is in this case at a position in the divergent beam path of

Laser radiation 7 is arranged, in which the (average) diameter of the generated by the axicon 23 annular intensity distribution substantially to

(average) diameter of the substantially annular edge region 6 of

Plasma beam 1 corresponds so that the laser radiation 7 collimated on the axicon 23 can be supplied directly (i.e., without additional optical elements) to the edge region 6 of the plasma jet 1 through the gas supply chamber 16 of the gas nozzle 15. Since the thickness d of workpieces 3 in plasma cutting is generally between about 10 mm and 180 mm, a low edge slope and a good contour accuracy of the cut edges formed during plasma cutting is particularly important. This can be obtained with the aid of the collimated laser radiation 7, which has a uniform beam shape along the plasma jet 1.

Another possibility for generating collimated laser radiation 7 with an annular, rotationally symmetrical intensity distribution is shown in FIG. 3, in which the axicon 23 of the feed device 22 of FIG

Collimating lens 24 and a downstream in the beam path circular aperture 25 has been replaced, which is the radially inner region of

Intensity distribution of the laser radiation 7 hides, so that a total of an annular intensity distribution is formed. A corresponding diaphragm effect may in particular also have the gas nozzle 15 or optionally the upper end of the pointed electrode 2, so that the provision of an additional diaphragm, as shown in FIG. 3, may possibly be completely dispensed with.

While in the beam feeders 22 shown in Fig. 2 and in Fig. 3, collimated laser radiation having an annular intensity distribution and

Rotational symmetry is generated is shown in the in Fig. 4 Beam delivery device 22, a diffractive optical element 26 is provided, which - depending on the design - allows the divergent intensity distribution of the laser source 21 either in an annular intensity distribution with a

Rotational symmetry about the center axis M or - if desired - to transform into a non-rotationally symmetric intensity distribution.

Such a non-rotationally symmetric intensity distribution may e.g. be beneficial when the apparatus 10 is used for plasma cutting along a cutting front on the workpiece 3, at one cutting edge is a good part, while the other cutting edge belongs to a skeleton, which is disposed of after the cutting process or after several other cutting operations. In this case, a high cut quality is only on the side of the cutting front

required at which the cut edge of the good part runs, since the cut quality on the side of the residual grid is irrelevant. Therefore, the diffractive optical

Element 26 (unlike that shown in FIG. 4) produces a non-rotationally symmetric annular intensity distribution at which a high intensity

For example, limited to that half of a circular ring, along which runs the cut edge of the good part. In order to realize intensity distributions with different geometries, the diffractive optical element 26 can optionally be exchanged for other diffractive optical elements by means of a changing device (not shown). As can also be seen in FIG. 4, the gas nozzle 15 for applying the plasma gas 14 to the workpiece 3 can be annularly surrounded by a further gas nozzle 27 which has a further annular feed space 28 for a (not shown) hull gas (oxygen , Nitrogen or gas mixtures of nitrogen and oxygen.

A feeding device 22, which also allows a supply of parallel to the center axis M of the rod-shaped electrode 2 aligned laser radiation 7 through the annular feed space 16 of the gas nozzle 15 is shown in Fig. 5a, b. The feed device 22 in this case has a plurality of optical fibers 29 (fiber bundles) which are distributed in an annular arrangement about the center axis M of the electrode 2, in particular in the plan view of FIG Fig. 5b can be seen. A distance A between the center axis M of the electrode 2 and a respective optical fiber substantially corresponds to the (average) radius of the annular edge region 6 of the plasma jet 1. For collimation of the laser radiation 7 divergently emerging from the optical fibers 29 microlenses 30 can be used, either from respective fiber end

6a) or formed on a remelted fiber end of a respective optical fiber 29 (so-called "lensed silica fiber"), see Fig. 6b.

Additionally or alternatively to the procedure described above, in which the laser radiation 7 takes place through the gas supply space 16 of the gas nozzle 15 of a plasma processing head (not shown), typically also a respective beam-forming or collimating element 23, 24, 26, 29 integrated is, can also be a lateral supply of laser radiation 7 in the field of

Nozzle opening of the gas nozzle 15 take place, as will be described in more detail below with reference to a further embodiment of the device 10, which is shown in Fig. 7. In the device 10 of FIG. 7, laser radiation 7 is guided substantially parallel to the workpiece 3 laterally into the exit-side region of the gas nozzle 15, specifically into the region of the pointed end of the rod-shaped electrode 2. There, in the present example, two plane deflection mirrors 31 a, Mounted 31b, which deflect the laser radiation 7 by 90 ° and these in the direction of the center axis M the edge region 6 of the plasma jet 1 out. The laser radiation 7 is generated in the example shown in FIG. 7 by two different laser sources 21a, 2b, but it is understood that the laser radiation 7 can be generated only by one or more laser sources and split, for example by means of a beam splitter, so that the respective partial beams are fed to one of the deflection mirrors 31a, 3b.

The point at which the laser radiation impinges on the respective deflection mirror 31 a, 31 b, is positioned so that the laser radiation 7 in the annular

Edge region 6 of the plasma jet 1 (but not in the central region 4) deflected becomes. It is understood that more than two deflecting mirrors can also be provided in the region of the electrode 2 in order to supply laser radiation 7 to the edge region 4 of the plasma jet 1, which can be arranged at regular angular intervals relative to one another, for example in the circumferential direction.

If appropriate, one or more surrounding conical mirror surfaces in the region of the electrode 2 can be provided instead of a plurality of planar deflection mirrors, in order to radiate in the radial direction

Redirecting laser radiation 7 in the edge region 4 of the plasma jet 1. Since the plasma jet 1 burns only from the top of the electrode 2, the

Deflection mirror 31a, 31b differently than shown in Fig. 7 also in the above in the

Gas nozzle 15 are attached. In this case, for the lateral supply of the laser radiation 7, the wall of the gas nozzle 15 may be provided with a transparent material (for example glass or the like). In order to avoid that the deflection mirrors 31 a, 31 b form a disturbing contour for the flow of the plasma gas, at the gas nozzle 15 instead of an annular feed space, if necessary, several, e.g. four, distributed in the circumferential direction around the electrode 2 supply spaces are provided, between which the deflecting mirrors are arranged. The laser radiation 7 of the laser sources 21a, 21b can collide with the deflection mirrors 31a, 31b (by means of optical elements not shown in FIG. 7). Alternatively or additionally, the deflecting mirrors 31a, 31b or their mirror surfaces may have a curvature in order to typically collimate divergently upon the incident laser radiation 7 during the deflection. As shown in FIG. 8, possibly only a single laterally offset to the electrode 2 deflecting mirror 31a may be provided in the apparatus 10 to supply the laser radiation 7 in a circumferentially relatively small portion of the edge region 6 of the plasma jet 1. Typically, in this case, in the portion of the edge region 6 of the plasma jet 1 in which the laser radiation 7 is supplied, the cutting edge of the cutting front which faces the good part and in which a high quality of cut is to be obtained.

A further possibility for the lateral supply of laser radiation 7 to the edge region 6 of the plasma jet 1 is shown in FIG. 9, in which a mirrored, tapered portion of a holder 32 for the rod-shaped electrode 2 serves as a deflection device 34. As a mirror image, for example, a

dielectric or metallic coating, e.g. made of aluminum, serve. In the electrode holder 32, a cooling passage 33 is inserted to move the holder 32 or the rod-shaped electrode 2 by means of a cooling liquid (not shown), e.g. with water, to cool. The provision of the deflection device 34 for the laser radiation 7 in a cooled region is favorable, since the electrode 2 itself is typically heated to very high temperatures, so that expansion and possibly deformation of the material of the electrode 2 can occur targeted

Deflection of collimated laser radiation 7 or a collimation of the

Laser radiation 7 in the deflection in the edge region 4 difficult.

With the aid of the devices 10 described above, with the aid of the in the

Edge region 6 of the plasma beam 1 irradiated collimated laser radiation 7, which typically extends along the entire plasma beam 1 from the electrode 2 to the workpiece 3 and has a constant beam shape, a constant beam guidance of the plasma jet 1 and thus a stabilization or constriction of the plasma jet first be achieved. In this way, in plasma cutting, an improvement in the quality of cut in terms of

Edge slope and contour accuracy and an increase in the possible

Feed speeds can be achieved by a narrower kerf. When plasma welding using the devices 10 can be deeper, thinner

Achieve welds and a lower heat affected zone. A

Processing quality improvement can also be achieved if incompletely collimated laser radiation having a large Rayleigh length is used instead of collimated laser radiation (as described above).

Laser radiation that runs as parallel as possible or approximately parallel to the center axis.

Claims

claims

A method of laser assisted plasma cutting or plasma welding of a workpiece (3) comprising the steps of:

Generating a plasma jet (1) extending between an electrode (2) and a processing point (3a) on the workpiece (3), wherein the

Plasma jet (1) with respect to its in the propagation direction (Z) extending center axis (M) inner central region (4) and an outer edge region (6), and

Supplying laser radiation (7) in the edge region (6) of the plasma jet (1), wherein the supplied laser radiation (7) parallel to the center axis (M).

2. The method of claim 1, wherein a wavelength (λ) of the supplied

Laser radiation (7) is selected such that a plasma gas used for generating the plasma jet (1) plasma gas (14) is excited by the laser radiation (7).

3. The method of claim 1 or 2, wherein the plasma jet (1) supplied laser radiation (7) has a power of less than 1000 watts, preferably of less than 500 watts.

4. The method according to any one of the preceding claims, wherein the generation of the plasma jet (1) by means of a rod-shaped electrode (2).

5. The method according to any one of the preceding claims, wherein the

Laser radiation (7) at at least one laterally to the center axis (M) offset deflection (31 a, 31 b, 34) in a direction (Z) parallel to the center axis (M) of the plasma jet (1) is deflected.

6. The method according to any one of the preceding claims, wherein the

Laser radiation (7) the plasma jet (1) through a gas supply space (16) of a gas nozzle (15) for applying a plasma gas (14) is supplied to the workpiece (3).

7. The method according to any one of the preceding claims, wherein the the

Plasma jet (1) supplied laser radiation (7) an annular,

having rotationally symmetric or non-rotationally symmetric intensity distribution.

8. Device (10) for laser-assisted plasma cutting and / or

Plasma welding a workpiece (3), comprising:

a plasma generating device (11), which is formed, a

To produce a plasma jet (1) which lies between an electrode (2) of the

Plasma generating device (11) and a processing point (3a) on the workpiece (3), wherein the plasma jet (1) with respect to its in the propagation direction (Z) extending center axis (M) lying inside

Central area (4) and an outer edge region (6), and a beam feed device (22) for supplying laser radiation (7) in the edge region (6) of the plasma jet (1), wherein the supplied laser radiation (7) parallel to the center axis ( M) of the plasma jet (1).

9. Apparatus according to claim 8, further comprising: at least one laser source (21, 21 a, 21 b) for generating the laser radiation (7).

10. Apparatus according to claim 9, wherein the laser source (21, 21 a, 21 b)

is formed, laser radiation (7) at a wavelength (λ) to generate, which is suitable for exciting in a gas storage (17) of the device (10) befindlichem, for generating the plasma jet (1) used plasma gas (14). 1. Device according to one of claims 8 to 10, wherein the electrode (2) is rod-shaped.

12. Device according to one of claims 8 to 11, which at least one laterally to the center axis (M) offset deflection means (31a, 31b, 34), to the laser radiation (7) in a direction (Z) parallel to the center axis (M) of the

To redirect plasma jet (1).

13. The apparatus of claim 12, wherein the deflecting device (34) on a cooled holder (32) of the electrode (2) is formed.

14. Device according to one of claims 8 to 13, wherein the

Beam feed device (22) is adapted to the laser radiation (7) the plasma jet (2) through a gas supply space (16) of a gas nozzle (15) for applying a plasma gas (14) to the workpiece (3) supply.

15. Device according to one of claims 8 to 14, wherein the

Beam feed device (22) for generating laser radiation (7) with an annular, rotationally symmetric or non-rotationally symmetrical

Intensity distribution is formed.

16. Device according to one of claims 8 to 15, wherein the

Beam feed device (22) has an axicon (23).

17. Device according to one of claims 8 to 16, wherein the

Beam feed device (22) has a diffractive optical element (26).

18. Device according to one of claims 8 to 17, wherein the

Beam feeding device (22) a plurality of annular around the

Center axis (M) arranged optical fibers (29), each associated with a microlens (30) for collimating emerging laser radiation (7).