DE102019206976B3 - Optical system for generating two laser focus lines as well as a method for the simultaneous processing of two opposite, parallel workpiece sides of a workpiece - Google Patents

Abstract

The optical system (1) according to the invention for generating two, in particular parallel, laser focus lines (2a, 2b) comprises at least one optical unit (10) which has: a first optical element (11) for splitting an incident laser beam (2) into several beam strips (4) in a first direction (x) at right angles to the beam axis (z) of the laser beam (2) and for superimposing the individual beam stripes (4) in a focal plane (F) of the first optical element (11) to form a single beam stripe, whose stripe width corresponds to at least the stripe width (B) of the widest beam stripe (4) in the focal plane (F) and corresponds to the length (L) of the two laser focus lines (2a, 2b) in the focal plane (F), - a second optical element ( 13) for focusing the incident laser beam (2) in a second direction (y) perpendicular to the first direction (x) and the beam axis (z) in the focal plane (F), and one in the beam path of the laser beam (2) first and the second optical element (11, 13) downstream, geometric beam splitter (14) for dividing the laser beam (2) in half in the second direction (y) into two partial beams (5a, 5b), which in the focal plane (F) die form two laser focus lines (2a, 2b).

Description

The invention relates to an optical system for generating two, in particular parallel, laser focus lines, in particular for the simultaneous laser processing of two mutually opposite, parallel workpiece sides of a workpiece, as well as a method for the simultaneous processing of two mutually opposite, parallel workpiece sides of a workpiece by means of a laser beam.

A laser application that is becoming increasingly important in the field of electromobility consists in stripping / stripping wires with a rectangular cross-section (so-called hairpins) in preparation for a subsequent joining or welding process. Scanner optics are currently used for this purpose, but these are very complex for this application.

From the DE 11 2005 003 207 B4 optical systems for generating a single laser focus line are already known.

From the DE 10 2015 112 537 A1 an optical device for reshaping a laser radiation propagating along a propagation axis is also known. This known optical device comprises a beam-shaping optical module for generating a focus geometry in a processing plane with a main laser spot and a secondary laser spot. The optics module has two cylindrical lens arrays arranged one behind the other in the propagation axis, each with a multiplicity of elongated cylindrical lenses, the two cylindrical lens arrays being arranged crossed to one another and being designed to generate the main laser spot. Between the two cylindrical lens arrays there is a wedge plate arrangement which is designed to generate the secondary laser spot.

Finally, WO 2003/079 067 A1 discloses a coating method in which a laser beam expands through the beam expander and is then divided into two beams, each with a light quantity of approximately 50%. Each of the two beams is focused into a linear laser beam by a cylindrical lens. These two linear laser beams strike an optical fiber from opposite directions, which is coated from both sides with the aid of the two laser beams.

In contrast, the present invention is based on the object of specifying a simple and cost-effective optical system for generating two parallel laser focus lines and a method for simultaneous processing of two mutually opposite, parallel workpiece sides of a workpiece.

• - mindestens ein erstes optisches Element zum Zerlegen eines einfallenden, insbesondere kollimierten Laserstrahls in mehrere Strahlstreifen in einer zu der Strahlachse des Laserstrahls rechtwinkligen, ersten Richtung und zum Überlagern der einzelnen Strahlstreifen in einer Fokalebene des mindestens einen ersten optischen Elements zu einem einzigen Strahlstreifen, dessen Streifenbreite mindestens der Streifenbreite des in der Fokalebene breitesten Strahlstreifens entspricht und jeweils der Länge der beiden Laserfokuslinien in der Fokalebene entspricht,
• - mindestens ein zweites optisches Element zum Fokussieren des einfallenden Laserstrahls in einer zur ersten Richtung und zur Strahlachse rechtwinkligen, zweiten Richtung in die Fokalebene des mindestens einen ersten optischen Elements, und
• - einen im Strahlengang des Laserstrahls dem mindestens einen ersten und dem mindestens einen zweiten optischen Element nachgeordneten, geometrischen Strahlteiler zum hälftigen Aufteilen des Laserstrahls in der ersten oder zweiten Richtung in zwei Teilstrahlen, die in der Fokalebene die beiden Laserfokuslinien ausbilden. Die Strahlstreifen können in der Fokalebene die gleiche Streifenbreite oder aber unterschiedliche Streifenbreiten aufweisen.

According to the invention, this object is achieved by an optical system for generating two, in particular parallel, laser focus lines, in particular for the simultaneous laser processing of two mutually opposite, parallel workpiece sides of a workpiece, with at least one optical unit which has:

• - At least one first optical element for splitting an incident, in particular collimated, laser beam into several beam stripes in a first direction perpendicular to the beam axis of the laser beam and for superimposing the individual beam stripes in a focal plane of the at least one first optical element to form a single beam stripe, the stripe width of which corresponds at least to the stripe width of the widest beam stripe in the focal plane and corresponds in each case to the length of the two laser focus lines in the focal plane,
• - At least one second optical element for focusing the incident laser beam in a second direction at right angles to the first direction and to the beam axis in the focal plane of the at least one first optical element, and
• - A geometric beam splitter arranged downstream of the at least one first and the at least one second optical element in the beam path of the laser beam for splitting the laser beam in half in the first or second direction into two partial beams which form the two laser focus lines in the focal plane. The beam stripes can have the same stripe width or different stripe widths in the focal plane.

Laser processing is, for example, a thermal treatment of workpieces, in particular a stripping or paint stripping of coated workpieces, e.g. of wires with an essentially square or rectangular cross-section (hairpins).

In contrast to the previously pursued strategy of serving such applications with scanner optics, the advantage of the invention is that a corresponding optics concept is simpler, cheaper and more robust than scanner optics; the operation of such optics is also simpler. If the homogeneity of the intensity distribution along the laser focus lines is not of great importance, astigmatic focusing of the beam can also be carried out (possibly in connection with a (bifocal) double wedge plate to rearrange the intensity distribution).

The at least one second optical element can be arranged upstream or downstream of the at least one first optical element in the beam path of the laser beam, a downstream arrangement having the advantage of a more compact design.

The at least one optical unit particularly preferably has at least one mirror for deflecting the two partial beams towards one another or towards the two parallel workpiece sides of a workpiece arranged between the two mirrors. The mirrors are arranged in such a way that the linear beam cross-sections of the two deflected partial beams - without a workpiece arranged between the mirrors - are congruent when the laser beam is split in half in the first direction in the yz plane and in the second when the laser beam is split in half Superimpose congruent direction in the xz plane. The mirrors are arranged in such a way that the deflected partial beams are aligned at right angles or at an angle to the yz plane or to the xz plane, in the latter case there is no reflection on the workpiece sides back into the optical unit if the laser beam is switched on no workpiece should be in the intended machining position. The mirrors are preferably arranged in such a way that the focus lines of the deflected partial beams are aligned parallel to the optical axis (beam axis) when the laser beam is split in half in the first direction and parallel to the first direction when the laser beam is split in half in the second direction.

Various optical arrangements are conceivable for producing the two parallel laser focus lines. A simple and relatively inexpensive arrangement consists of a facet plate with several facet strips of the same facet width parallel in the first direction, which splits a collimated raw beam in the first direction into a number of beam strips and superimposes these in the focal plane to form the single beam strip, as well as a cylindrical lens that focuses the beam in the second direction at right angles to it. A very homogeneous linear intensity distribution along the laser focus lines can thus be generated. Alternatively, a corresponding linear focus geometry can also be generated, for example, by means of micro-optics.

The geometric beam splitter is particularly preferably designed, for example, as a transmissive double wedge plate or as a reflective roof edge mirror.

In a particularly preferred embodiment of the invention, the optical unit is mounted so as to be rotatable about the beam axis of the incident laser beam or about the optical axis, in particular by 90 °. In the case of a workpiece with a square or rectangular cross-section, the other two parallel workpiece sides can also be machined by rotating the optical unit.

In another preferred embodiment of the invention, the optical structure has two optical units that can be moved into the beam path of the incident laser beam (retractable or pivotable) and rotated in the beam path of the incident laser beam about the beam axis of the incident laser beam or about the optical axis to each other , in particular at 90 °, are arranged and produce different focus line lengths adapted to the cross section of the workpiece. This embodiment is particularly useful when the cross section of the workpiece to be machined deviates significantly from a square shape. The two optical units are used one after the other to machine the two pairs of surfaces of the rectangular cross-section.

The invention also relates to a method for the simultaneous processing of two opposite, parallel workpiece sides of a workpiece by means of a laser beam, whereby two partial beams with the same laser focus line are generated from the laser beam by means of the optical system constructed as above, which are directed onto the two with respect to the optical axis of the optical system are directed opposite, parallel workpiece sides for a laser processing of the workpiece sides.

The optical system and the workpiece are preferably moved relative to one another in the direction of the optical axis of the optical system in order to generate a feed movement of the two laser focus lines on the two parallel workpiece sides in the direction of the optical axis. In this way, it is possible to machine two opposite, parallel workpiece surfaces simultaneously with a single feed movement.

For laser processing of a workpiece with several pairs of mutually opposite, parallel workpiece sides, either the workpiece or the two partial beams are rotated around the optical axis of the optical system after the processing of two mutually opposite, parallel workpiece sides by means of the two partial beams, and then two others are opposite one another , machined parallel workpiece sides by means of the two partial beams. If the length-to-width ratio of the workpiece cross-section deviates significantly from 1, this would mean that when machining the narrower Workpiece side, part of the output radiates past the workpiece and is lost for the process. If this is not desired, a second optical unit, rotated by 90 ° to the first optical unit, which is constructed identically or functionally identical to the first optical unit, but provides a shorter linear focus geometry adapted to the workpiece geometry, can be used instead of the first optical unit are moved into the beam path of the laser beam.

• 1a, 1b ein erstes Ausführungsbeispiel des erfindungsgemäßen optischen Systems mit einer optischen Einheit zum Erzeugen zweier Teilstrahlen mit jeweils einem Linienfokus in einer perspektivischen Ansicht (1a) und schematisch den zugehörigen Strahlengang samt den jeweiligen Strahlquerschnitten (1b), wobei die beiden Teilstrahlen jeweils rechtwinklig auf zwei einander gegenüberliegende, parallele Werkstückseiten auftreffen;
• 2 das optische System von 1a, wobei die beiden Teilstrahlen jeweils schräg auf die beiden parallelen Werkstückseiten auftreffen;
• 3 das optische System von 1a, wobei die optische Einheit um 90° drehbar um die optische Achse des optischen Systems gelagert ist;
• 4 das optische System von 1a mit zwei wahlweise in den Strahlengang des einfallenden Laserstrahls hineinbewegbaren, optischen Einheiten, die im Strahlengang des einfallenden Laserstrahls um die Strahlachse des einfallenden Laserstrahls zueinander um 90° verdreht angeordnet sind; und
• 5a, 5b ein zweites Ausführungsbeispiel des erfindungsgemäßen optischen Systems in einer Ansicht analog zu den 1a, 1b.

Further advantages and advantageous configurations of the subject matter of the invention emerge from the description, the claims and the drawings. The features mentioned above and those listed below can also be used individually or collectively in any combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary character for describing the invention. Show it:

• 1a , 1b a first embodiment of the optical system according to the invention with an optical unit for generating two partial beams, each with a line focus in a perspective view ( 1a) and schematically the associated beam path including the respective beam cross-sections ( 1b) , wherein the two partial beams impinge at right angles on two mutually opposite, parallel workpiece sides;
• 2 the optical system of 1a , the two partial beams impinging on the two parallel workpiece sides at an angle;
• 3 the optical system of 1a , wherein the optical unit is mounted rotatably through 90 ° about the optical axis of the optical system;
• 4th the optical system of 1a with two optical units which can optionally be moved into the beam path of the incident laser beam and which are arranged in the beam path of the incident laser beam rotated by 90 ° to one another about the beam axis of the incident laser beam; and
• 5a , 5b a second embodiment of the optical system according to the invention in a view analogous to the 1a , 1b .

This in 1a , 1b optical system shown 1 is used to generate two parallel laser focus lines 2a , 2 B for the simultaneous laser processing of two opposite, parallel workpiece sides 3a , 3b of a workpiece 3 by means of a laser beam 2 .

• - eine Facettenplatte 11 mit mehreren parallelen, hier beispielhaft gleichbreiten Facettenstreifen 12 zum Zerlegen des einfallenden, kollimierten Laserstrahls (Rohstrahl) 2 in mehrere Strahlstreifen 4 in einer zu der Strahlachse z des Laserstrahls 2 rechtwinkligen x-Richtung und zum Überlagern der einzelnen Strahlstreifen 4 in der Fokalebene F der Facettenplatte 11 zu einem einzigen Strahlstreifen, dessen Streifenbreite der Streifenbreite des in der Fokalebene F breitesten Strahlstreifens 4 entspricht und jeweils der Länge L der beiden Laserfokuslinien 2a, 2b in der Fokalebene F entspricht. Im gezeigten Ausführungsbeispiel weisen lediglich beispielhaft alle Facettenstreifen 12 die gleiche Breite B in der ersten x-Richtung auf, so dass die Strahlstreifen 4 in der Fokalebene F unterschiedlich breit sind. Alternativ können die Facettenbreiten der Facettenstreifen 12 auch unterschiedlich und insbesondere so gewählt sein, dass alle Strahlstreifen 4 in der Fokalebene F gleich breit sind.
• - eine Zylinderlinse 13 zum Fokussieren der einzelnen Strahlstreifen 4 in einer zur x-Richtung und zur Strahlachse z rechtwinkligen y-Richtung in die Fokalebene F der Facettenplatte 11;
• - eine bifokale Doppelkeilplatte 14 zum hälftigen Aufteilen des von der Zylinderlinse 13 fokussierten Laserstrahls 2 in der y-Richtung in zwei Teilstrahlen 5a, 5b, die in der Fokalebene F die beiden Laserfokuslinien 2a, 2b ausbilden; und
• - jeweils einen Spiegel 15a, 15b zum Umlenken der beiden Teilstrahlen 5a, 5b in Richtung auf die bezüglich der optischen Achse 16 des optischen Systems 1 einander gegenüberliegenden, parallelen Werkstückseiten 3a, 3b.

The optical system 1 includes an optical unit 10 , which has:

• - a facet plate 11 with several parallel, here for example equally wide facet strips 12 for breaking down the incident, collimated laser beam (raw beam) 2 into several beam strips 4th in one to the beam axis z of the laser beam 2 right-angled x-direction and for superimposing the individual beam stripes 4th in the focal plane F of the facet plate 11 to a single beam stripe, the stripe width of which is the width of the beam stripe widest in the focal plane F. 4th corresponds to the length L of the two laser focus lines 2a , 2 B corresponds in the focal plane F. In the exemplary embodiment shown, all of the facet strips are merely exemplary 12 the same width B in the first x-direction so that the beam stripes 4th are of different widths in the focal plane F. Alternatively, the facet widths of the facet strips 12 also be chosen differently and in particular so that all beam stripes 4th are equally wide in the focal plane F.
• - a cylindrical lens 13 for focusing the individual beam strips 4th in a y-direction at right angles to the x-direction and to the beam axis z into the focal plane F of the facet plate 11 ;
• - a bifocal double wedge plate 14th for dividing the half of the cylinder lens 13 focused laser beam 2 in the y-direction in two partial beams 5a , 5b , the two laser focus lines in the focal plane F. 2a , 2 B form; and
• - one mirror each 15a , 15b to deflect the two partial beams 5a , 5b in the direction of the with respect to the optical axis 16 of the optical system 1 opposite, parallel workpiece sides 3a , 3b .

A feed movement (double arrow 17th ) of the laser focus lines 2a , 2 B relative to the workpiece 3 can be done by moving both the optical unit 10 as well as the workpiece 3 in the direction of the optical axis 16 be generated. In this way it is possible with a single feed movement 17th two parallel workpiece sides 3a , 3b to be machined simultaneously in the axial direction.

The two mirrors 15a , 15b are arranged such that the partial beams 5a , 5b are aligned at right angles to the xz plane and intersect the xz plane at the same z height and that their beam cross sections in the xz plane - without a workpiece arranged between the mirrors - overlap congruently. The two focus lines 2a , 2 B of the deflected partial beams 5a , 5b are aligned parallel to the x-direction.

Because the length of the laser focus lines 2a , 2 B by the width of the individual facets of the facet plate 11 is determined to change the length of the laser focus lines 2a , 2 B the replacement of the facet plate 11 required.

With the workpiece shown 3 it is, for example, a wire with its longitudinal axis along the optical axis 16 is aligned. The feed movement 17th takes place in the direction of the optical axis 16 to process the upper end of the wire, e.g. to strip the insulation.

From 1a differs in 2 optical system shown 1 only by the fact that here the mirror 15a , 15b the partial beams 5a , 5b Align obliquely to the yz plane. This means that the partial beams do not reflect back 5a , 5b on the workpiece sides 3a , 3b back to the optical unit 10 when no workpiece is positioned between the two mirrors.

To with a workpiece 3 with a square cross-section also the other two parallel workpiece sides 3c , 3d edit will, as in 3 shown the optical unit 10 around the beam axis z of the incident laser beam 2 rotated by 90 ° (double arrow 18th ). This is the optical unit 10 around the optical axis 16 Can be rotated by 90 °. Alternatively, the workpiece 3 by 90 ° around the optical axis 16 can be rotated as indicated by the double arrow 19th is indicated.

With the workpiece 3 For example, it can be an insulation-coated wire with a square cross-section, the coating of which on a length section by means of the two partial beams 5a , 5b removed (stripped).

Such wires with their ends stripped are used, for example, in e-mobility as so-called hairpins in the manufacture of stators.

In 4th instructs the optical system 1 two each in the beam path of the incident laser beam 2 movable optical units 10 , 20th in the beam path of the incident laser beam 2 around the beam axis z of the incident laser beam 2 rotated to each other, in particular by 90 °, are arranged. For laser processing of one parallel workpiece side 3a , 3b becomes the one optical unit 10 moved into the beam path, eg pushed in (arrow direction A) or swiveled in, and for laser processing of the other parallel workpiece sides 3c , 3d becomes the other optical unit 20th moved into the beam path, eg pushed in (arrow direction B) or swiveled in. The two optical units 10 , 20th can be used to generate laser focus lines of the same length 2a , 2 B identical or for generating laser focus lines of different lengths 2a , 2 B be designed differently.

The optical system according to the invention 1 creates two linear intensity distributions with which two opposite surfaces of a wire can be treated / stripped simultaneously. By subsequently rotating either the wire or the optical system or parts thereof by 90 ° or by moving a second optical unit into it, the other two surfaces of the rectangular or square wire can then be treated.

From 1a , 1b differs in 5a , 5b optical system shown 1 only in that the facet plate 11 and the cylinder lens 13 including the associated x and y axes opposite the double wedge plate 14th and the mirrors 15a , 15b are arranged rotated by 90 ° about the z-axis. As in 1a is therefore the facet plate 11 continue in the x-direction and the cylinder lens 13 continue to be effective in the y-direction. As in 5b shown, the two focus lines are in the focal plane F. 2a , 2 B arranged collinear in the x-axis on both sides of the y-axis. The mirror 15a , 15b are arranged so that the focus lines 2a , 2 B of the deflected partial beams 5a , 5b parallel to the beam axis z or to the optical axis 16 are aligned and their beam cross-sections in the yz-plane - without a workpiece arranged between the mirrors - superimpose congruent. Alternatively, the deflected partial beams can be 5a , 5b also only partially overlap or also be aligned offset to one another. The longitudinal axis of the workpiece 3 is aligned along or parallel to the y-axis and thus runs at right angles to the optical axis 16 . With this embodiment it is possible to treat a wire that has not yet been bent in its raw state, ie the wire can in a continuous process along the y-axis through the space between the two deflection mirrors 15a , 15b moved (feed direction 17th ). In this way, two opposite sides can be placed at the desired locations 3a , 3b of the wire 3 be treated.

In order to treat the other two sides of a wire with a right-angled cross-section, which are perpendicular thereto, a further optic rotated by 90 ° can preferably be used. These optics can either be fed by a second beam source, or alternatively a single beam source could alternately supply the two optics with laser light by means of an integrated, switchable switch via separate fiber optic cables.

Claims (17)

Optical system (1) for generating two laser focus lines (2a, 2b), with at least one optical unit (10; 20) which has: At least one first optical element (11) for splitting an incident laser beam (2) into several beam strips (4) in a first direction (x) at right angles to the beam axis (z) of the laser beam (2) and for superimposing the individual beam strips (4) ) in a focal plane (F) of the at least one first optical element (11) to form a single beam stripe, the stripe width of which corresponds to at least the stripe width (B) of the beam stripe (4) widest in the focal plane (F) and the length (L) of the corresponds to both laser focus lines (2a, 2b) in the focal plane (F), at least one second optical element (13) for focusing the incident laser beam (2) in a second direction at right angles to the first direction (x) and to the beam axis (z) ( y) into the focal plane (F) of the at least one first optical element (11), and one after the at least one first and at least one second optical element (11, 13) in the beam path of the laser beam (2) Ordered, geometric beam splitter (14) for dividing the laser beam (2) in half in the first or second direction into two partial beams (5a, 5b) which form the two laser focus lines (2a, 2b) in the focal plane (F). Optical system (1) according to Claim 1 , characterized in that the at least one second optical element (13) is arranged downstream of the at least one first optical element (11) in the beam path of the laser beam (2). Optical system (1) according to Claim 1 or 2 , characterized in that the at least one optical unit (10; 20) each has at least one mirror (15a, 15b) for deflecting the two partial beams (5a, 5b) towards one another. Optical system (1) according to Claim 3 , characterized in that the mirrors (15a, 15b) are arranged in such a way that the beam cross-sections of the two deflected partial beams (5a, 5b) are split in half of the laser beam (2) in the first direction (x) in the yz plane and cut congruently in the xz plane when the laser beam (2) is split in half in the second direction (y). Optical system (1) according to Claim 3 or 4th , characterized in that the mirrors (15a, 15b) are arranged in such a way that the deflected partial beams (5a, 5b) when the laser beam (2) is split in half in the first direction (x) at right angles or at an angle to the yz plane and when the Distribution of the laser beam (2) in the second direction (y) at right angles or at an angle to the xz plane. Optical system (1) according to one of the Claims 3 to 5 , characterized in that the mirrors (15a, 15b) are arranged in such a way that the focus lines (2a, 2b) of the deflected partial beams (5a, 5b) when the laser beam (2) is split in half in the first direction (x) parallel to the beam axis (z) and when the laser beam (2) is split in half in the second direction (y) are aligned parallel to the first direction (x). Optical system (1) according to one of the preceding claims, characterized in that the first optical element (11) is designed as a facet plate with several facet strips (12) parallel in the first direction (x). Optical system (1) according to one of the preceding claims, characterized in that all beam stripes (4) have the same stripe width at least in the focal plane (F). Optical system (1) according to one of the preceding claims, characterized in that the second optical element (13) is designed as a cylindrical lens effective in the second direction (y). Optical system (1) according to one of the preceding claims, characterized in that the geometric beam splitter (14) is designed as a double wedge plate or as a roof edge mirror. Optical system (1) according to one of the preceding claims, characterized in that the optical unit (10) is mounted rotatably about the beam axis (z) of the incident laser beam (2). Optical system (1) according to one of the Claims 1 to 10 , characterized by two optical units (10, 20) which can be moved into the beam path of the incident laser beam (2) and are rotated in the beam path of the incident laser beam (2) about the beam axis (z) of the incident laser beam (2). Optical system (1) according to Claim 12 , characterized in that the two optical units (10, 20) are designed to generate laser focus lines (2a, 2b) of the same length or of different lengths. A method for the simultaneous processing of two mutually opposite, parallel workpiece sides (3a, 3b) of a workpiece (3) by means of a laser beam (2), whereby two partial beams (5a) from the laser beam (2) by means of the optical system (1) according to one of the preceding claims , 5b) are generated with the same laser focus line (2a, 2b) in each case, which are directed to the two parallel workpiece sides opposite one another with respect to the optical axis (16) of the optical system (1) (3a, 3b) for laser processing of the two workpiece sides (3a, 3b) are steered. Procedure according to Claim 14 , characterized in that the optical system (1) and the workpiece (3) are moved relative to one another in the direction of the optical axis (16) of the optical system (1) or obliquely to the optical axis (16) of the optical system (1) in order to generate a feed movement (17) of the two laser focus lines (2a, 2b) on the two parallel workpiece sides (3a, 3b) in the direction of the optical axis (16). Procedure according to Claim 15 , characterized in that the workpiece (3) is aligned with its longitudinal axis along the feed direction (17). Procedure according to Claim 15 or 16 , characterized in that in the case of a workpiece (3) with several pairs of mutually opposite, parallel workpiece sides after machining of two mutually opposite, parallel workpiece sides (3a, 3b) by means of the two partial beams (5a, 5b) either the workpiece (3) or the two partial beams (5a, 5b) are rotated around the optical axis (16) of the optical system (1) and then two other opposite, parallel workpiece sides (3c, 3d) are processed by means of the two partial beams (5a, 5b).

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