WO2023072641A1

WO2023072641A1 - Method for machining countersunk holes by means of a laser beam

Info

Publication number: WO2023072641A1
Application number: PCT/EP2022/078751
Authority: WO
Inventors: Florian Sepp; Patrick Mach; Christoph Weiss
Original assignee: TRUMPF SE + Co. KG; Wsoptics Technologies Gmbh
Priority date: 2021-10-25
Filing date: 2022-10-15
Publication date: 2023-05-04

Abstract

The invention relates to a method for machining a workpiece (9) by means of a focused laser beam (14). The laser beam (14) can be used in a workpiece (9) cutting mode or in a non-cutting mode by changing the energy per unit length of the laser beam (16). The method has the following steps in said order: - guiding the laser beam (14) along a closed cutting line (21) in the cutting mode, whereby a hole (16) is produced in the workpiece (9), and - guiding the laser beam (14) once or multiple times along at least one closed countersink-producing line (29) in the non-cutting mode, wherein the countersink- producing line (29) is arranged relative to the cutting line (21) such that a countersink (18) which surrounds the hole (16) is produced, said countersink leading into the hole (16).

Description

METHOD OF CREATING COUNTERSINKING HOLES USING LASER BEAM MACHINING

The invention lies in the technical field of laser beam machining of metallic workpieces with a focused laser beam and relates to a method for laser beam machining of a plate-shaped or tubular workpiece in which countersunk holes are produced in the workpiece.

Commercially available laser cutting devices enable automated production of workpiece parts in large numbers and with high precision. Here, workpiece parts are cut out of a metal workpiece with a laser beam along cutting lines that correspond to the contours of the workpiece parts. In addition, by moving the laser beam along circular cutting lines, holes, i.e. cutouts with a small diameter, can be made in the workpiece parts to be cut out at high speed.

Depending on the use of the cut-out workpiece parts, the workpiece parts may require complex mechanical post-processing. Holes in which countersunk screws are to be placed during later use of a workpiece part are usually finished by machining with a drill to form the countersinks to receive the heads of the countersunk screws. In principle, mechanical processing following the cutting out of a workpiece part is very time-consuming and usually also very labor-intensive, especially since it is often carried out manually. In addition, such post-processing is cost-intensive, so that the production of workpiece parts is undesirably longer and more expensive. This applies in particular to the post-machining of holes to create countersinks, which is very time-consuming.

The generation of holes with countersinks by means of a laser beam is known in the patent literature. For example, WO 2020225448 A1 shows a method in which a circular trough is first produced in a workpiece and then a hole is made within the trough.

In contrast, the object of the present invention is to improve conventional methods in such a way that countersunk holes can be produced in a workpiece using a focused laser beam, without the need for complex mechanical ones Post-processing, in particular for forming countersinks using a drill and removing burrs on the workpiece part surfaces, are required. Overall, the production of countersunk holes and the production of workpiece parts with countersunk holes should be able to take place in an automated manner faster, more cost-effectively and more efficiently.

According to the proposal of the invention, these and other objects are achieved by a method for laser beam machining of a workpiece with the features of the independent patent claim. Advantageous configurations of the invention are specified by the features of the dependent claims.

For the purposes of the present invention, the term "workpiece" designates a plate-shaped or tubular, typically metallic, component from which at least one workpiece part (good part) is to be produced. The panel-shaped workpiece is typically flat.

The laser beam is guided by a laser processing head and emerges from a nozzle at the end. As usual, the laser beam is designed in the form of a focused, rotationally symmetrical beam cone with a central beam axis (axis of symmetry). Beam diameter characterizes the transverse extent of the beam, or the physical size of the beam perpendicular to the direction of propagation. When focusing, the laser beam is bundled by a focusing lens or a focusing mirror. The focus of the laser beam is defined by that point at which the laser beam has its smallest cross-section or the smallest beam diameter. The focal length indicates the distance from the main plane of the lens (or main plane of the mirror) to the focal point of an ideal, focused parallel beam. The smaller the focal length, the more the laser beam is focused and the smaller the focus diameter, and vice versa.

The laser processing head is also used to guide a process gas jet, which is typically, but not necessarily, emitted from the same nozzle as the laser beam and is preferably guided coaxially with the laser beam. The process gas jet emerging from the nozzle is typically, but not necessarily, designed in the form of a gas cone impinging on the workpiece.

The workpiece, in particular a plate-shaped workpiece, rests with a workpiece underside on a workpiece support. This shows on the top of the workpiece Workpiece on a (top) workpiece surface. In the case of a plate-shaped workpiece, the workpiece surface is flat. Unless otherwise used, the “workpiece surface” here and in the following is understood to mean the upper-side workpiece surface which is opposite or facing the nozzle. The opposite workpiece surface, on which the workpiece usually rests on a base, is the workpiece underside.

The laser processing head for guiding the laser and process gas beam can be moved relative to the workpiece in a typically horizontal plane parallel to the plane of the workpiece surface and in a typically vertical direction perpendicular thereto.

In the present description of the invention, the reference system is always stationary with respect to the workpiece, so that the laser processing head is considered to be moving and the workpiece is considered to be stationary. Viewed locally, however, it is irrelevant whether the laser processing head or the workpiece or both are moved. In this respect, it would be equally possible for the workpiece to be moved as an alternative to the moving laser processing head, or for both the laser processing head and the workpiece to be moved.

The energy of the laser beam depends on the specific design of a laser source and is typically specified in joules (J). The power of the laser beam (ie energy per time), typically measured in joules per second (J/s) or in watts (W), describes the optical output power of a continuous wave laser (CW) or the average power of a pulsed laser. Pulsed lasers are also characterized by their pulse energy, which is directly proportional to the average power and inversely proportional to the laser's repetition rate. "Energy density" refers to the energy of the laser beam related to the irradiated area of the workpiece. The energy density is measured in J/mm ² , for example.

In addition to the energy density, the traversing speed of the laser processing head or laser beam is important for the laser processing of the workpiece, ie the time for how long a certain area of the workpiece is irradiated by the laser beam. It is customary to use the term "path energy" for this. This is the power of the laser beam absorbed by the workpiece per speed of the laser processing head or laser beam, measured, for example, in watts/(mm/s). Will the performance of the Laser beam watts (W) are specified as joules per second (J/s), so the distance energy is measured in J/mm.

In laser processing, the distance energy of the laser beam is essential, with the energy absorbed by the workpiece depending on the energy density. The energy absorbed by the workpiece at a given power of the laser beam depends on the size of the beam spot on the workpiece, corresponding to the beam diameter at the point where the laser beam hits the workpiece. The beam diameter of the laser beam on the workpiece results from the focus position, i.e. the position of the focus of the laser beam relative to the workpiece (vertical shortest distance), in particular relative to the workpiece surface on which the laser beam is directed, or also relative to the workpiece support. If the workpiece is in the divergent area of the beam cone (focus above the workpiece surface where the processing beam hits), increasing the distance between the focus and the workpiece can increase the beam diameter on the workpiece, and vice versa. Thus, by changing the beam diameter on the workpiece by changing the focus position, the energy density of the laser beam and thus the energy absorbed by the workpiece, which is included in the path energy, can be changed in a targeted manner. The larger the beam diameter, the smaller the energy absorbed by the workpiece, and vice versa. With a laser, the beam intensity is not constant outside the focus, based on the cross-section. Ideally, the power intensity is a Gaussian profile. In any case, the energy density is relatively low towards the edge, especially out of focus.

The energy per line also depends on the speed of the laser beam, i.e. the traversing speed of the laser processing head, also known as "feed speed". The greater the feed rate, the shorter a given area of the workpiece is irradiated, and vice versa. Thus, as the feed rate increases, the line energy of the laser beam decreases, and vice versa.

It goes without saying that the energy density and thus also the distance energy can be changed by changing the power of the laser beam itself.

The person skilled in the art is aware of further options for changing the energy introduced into the workpiece, in particular by changing the type and/or Composition of the process gas used in laser processing.

According to the invention, the workpiece is processed in such a way that the laser beam is used to produce countersunk or countersunk holes, i.e. holes with countersinks, in the workpiece. The countersunk holes usually belong to a workpiece part to be cut out, which is to be cut out of a workpiece (e.g. sheet metal) together with many other workpiece parts, i.e. the workpiece part is still connected to the residual skeleton when the countersunk holes are produced. However, it is also conceivable that the workpiece itself is a workpiece part that has already been cut out by a laser beam (e.g. laser beam).

In the method according to the invention for laser beam machining of a workpiece with a focused laser beam, the laser beam is used in a "cutting mode" or in a "non-cutting mode" the workpiece. In the cutting mode, the distance energy of the laser beam on the workpiece is so great that the laser beam cuts (separates) the workpiece so that the workpiece is penetrated, e.g. to create a kerf. In the non-cutting mode, the line energy of the laser beam on the workpiece is so small that the laser beam non-cutting (non-cutting) the workpiece, so that the workpiece is not penetrated, which can generate a countersink.

The distance energy of the laser beam on the workpiece or the distance energy of the laser beam can be changed by changing the energy or power of the laser beam, changing the feed speed of the laser processing head, focusing/defocusing the laser beam, and in particular by changing the beam diameter on the workpiece surface , in particular by changing the focus position relative to the workpiece. In order to change the energy introduced into the workpiece, the type and/or composition of the process gas used in laser processing can also be changed.

Preferably, the distance energy of the laser beam on the workpiece is changed by changing the focus position relative to the workpiece, which is preferably caused by changing the height of the laser processing head above the workpiece or the workpiece surface facing the laser processing head, i.e. the laser processing head is moved with a movement component perpendicular to the workpiece surface typically move in the vertical direction. In the method according to the invention, the following method steps are carried out successively, but not necessarily in immediate succession:

In a first step, the laser beam is guided in the cutting mode along a closed, preferably circular-closed cutting line, as a result of which a closed, preferably circular-closed cutting gap is produced. A part (slug) is cut out of the workpiece. By removing the slug from the workpiece, a hole (perforation) with a preferably circular cross-section is produced in the workpiece. As a rule, the slug falls down due to its own weight, creating a hole in the workpiece. The cross section of the hole refers to the plane of the flat work piece or the work piece surface facing the jet nozzle. The hole is preferably created within the contour of a workpiece part to be cut out of the workpiece. The cutting line is a process engineering line or path along which the laser beam is guided, it being understood that the cutting line is not formed on the workpiece. The cutting line is preferably a circular line (orbit).

If the hole is circular, its axis of symmetry or central axis defines a radial direction, starting from the central axis, "radially inwards" being directed towards the central axis and "radially outwards" away from the central axis.

Subsequently, in a second step, the laser beam is guided once or several times in the non-cutting mode along at least one closed, preferably circular or spiral line (path), referred to below as the “sink generation line”. For this purpose, the focus position of the laser beam is preferably changed before it is guided for the first time along the countersinking production line in such a way that the laser beam has a larger beam diameter on the workpiece than when the hole was produced. The at least one countersink generation line is arranged such that a countersink is generated around the hole, which countersink always flows into the hole. Consequently, the depression deepens towards the hole and merges directly into the hole. Like the cutting line, the countersink generation line is a process line or path along which the laser beam is guided, the countersink generation line not being formed on the workpiece.

The at least one counterbore generation line surrounds and is always spaced from the line of intersection. Preferably, the line of intersection and the at least one Lowering generation line each circular lines (orbits), wherein the at least one lowering generation line is arranged concentrically and at a radial distance from the cutting line. The at least one countersink generation line is then arranged radially outwards of the line of intersection, ie the diameter of the countersink generation line is larger than the diameter of the line of intersection.

The at least one countersink generation line preferably extends along the cut edge of the hole, which delimits the hole on the workpiece surface opposite the jet nozzle. The at least one countersink generation line may run inside and/or outside the closed cut edge of the hole. The at least one countersink generation line can, in particular, run identically to the cutting edge of the hole. In the case of circular paths, the at least one countersink generation line can be arranged radially outwards or radially inwards of the cutting edge of the hole, which is then likewise circular. Preferably, the at least one countersink generating line is located radially outward of the circular cutting edge of the hole.

In the method according to the invention for laser beam machining of a plate-shaped or tubular workpiece, countersunk holes are produced in the workpiece. According to the invention, it was recognized that countersunk holes can be produced in a metal workpiece in a particularly simple, reliable and efficient manner with high edge quality.

The method according to the invention for producing countersunk holes is preferably part of a method in which workpiece parts are cut out of the workpiece, the countersunk holes being produced in the workpiece parts to be cut out which are still connected to the residual skeleton. After the countersunk holes have been created, the workpiece parts are removed from the workpiece. The workpiece parts can already be partially cut out when the countersunk holes are created, but are always firmly connected to the rest of the workpiece (residual grid), for example by one or more webs with small dimensions ( micro or nanojoints).

The method described above is for creating countersunk holes in a workpiece, wherein when creating a single countersunk hole, the hole is created in the workpiece in a first step, and after the hole has been created, in a second step, the countersink is created around the hole . In an advantageous embodiment of the method according to the invention, the hole has a diameter which is equal to or smaller than a workpiece thickness of the workpiece. As the inventors were able to show, particularly small countersunk holes can be produced by the method according to the invention. As with an oblique cut to create a countersink, there is no risk of neighboring holes being damaged when the countersink is formed.

According to a preferred embodiment of the method according to the invention, the production of countersunk holes takes place in three steps, the two steps described above for producing countersunk holes being included. Considering a single countersunk hole, the hole is produced in the workpiece in a first step, the countersink around the hole is produced in a second step and the hole already produced is widened or widened in an additional third step.

The three-step method of creating countersunk holes is further described below, for ease of reference the hole created in the workpiece in the first step is referred to as the "pre-hole" and the hole widened in the third step is referred to as the "final hole". Correspondingly, the term “pre-hole cutting line” is used for the cutting line for producing the pilot hole, and the term “end hole cutting line” is used for the cutting line for producing the final hole.

In a first step, the laser beam is guided in the cutting mode along a closed, preferably circular-closed cutting line, as already stated hereinafter referred to as "pre-hole cutting line", whereby a closed, preferably circular-closed cutting gap is produced. A part (slug) is cut out of the workpiece. By removing the slug from the workpiece, a hole (perforation) with a preferably circular cross-section, referred to below as the “pre-hole”, as already explained, is produced in the workpiece. As a rule, the slug falls down due to its own weight, which creates the pilot hole in the workpiece. The cross-section of the pilot hole refers to the plane of the flat workpiece or the workpiece surface facing the jet nozzle. The pilot hole is preferably produced within the contour of a workpiece part to be cut out of the workpiece. The pre-hole cutting line is a process engineering line or path along which the laser beam is guided, it being understood that the pre-hole cutting line is not formed on the workpiece. If the pilot hole is circular, its axis of symmetry or central axis defines a radial direction, starting from the central axis, "radially inwards" being directed towards the central axis and "radially outwards" away from the central axis.

Then, in a second step, the laser beam is guided once or several times in the non-cutting mode along at least one closed, preferably circular or spiral line (path), as already stated, referred to below as the "sinking generation line". For this purpose, the focal position of the laser beam is preferably changed before it is first guided along the countersinking production line in such a way that the laser beam has a larger beam diameter on the workpiece than when the pilot hole was produced. The at least one countersink generation line is arranged in such a way that a countersink is generated around the pre-hole, which always ends in the pre-hole. Consequently, the countersinking deepens towards the forehole and goes directly into the forehole. Like the pre-punch cut line, the countersink generation line is a process line or path along which the laser beam is guided, and the countersink generation line is not formed on the workpiece.

The at least one counterbore generation line surrounds and is always spaced from the prehole cutting line. Preferably, the pre-hole cutting line and the at least one countersink generation line are each circular lines (orbits), the at least one countersink generation line being arranged concentrically and at a radial distance from the pre-hole cutting line. The at least one countersink generation line is then arranged radially outwards of the pre-hole intersection line, i.e. the diameter of the countersink generation line is larger than the diameter of the pre-hole intersection line.

The at least one countersink generation line preferably extends along the cutting edge of the pilot hole, which delimits the pilot hole on the workpiece surface opposite the jet nozzle. The at least one countersink generation line can run inside and/or outside of the closed cutting edge of the pilot hole. The at least one countersink generation line can, in particular, run identically to the cutting edge of the pilot hole. In the case of circular paths, the at least one countersink generation line can be arranged radially outwards or radially inwards of the cutting edge of the pilot hole, which is then also circular. The at least one countersink generating line is preferably arranged radially outward of the circular cutting edge of the pilot hole. Then, in a third step, the laser beam is guided in the cutting mode along a closed, preferably circular, cutting line, referred to below as the "end hole cutting line", as already explained, whereby a closed, preferably circular-closed cutting gap is produced. As a result, a part that is preferably hollow-cylindrical in cross section is cut out of the workpiece. Before the laser beam begins to be guided along the end hole cutting line, the focus position of the laser beam is preferably changed in such a way that the laser beam has a smaller beam diameter on the workpiece than when the countersink was produced. The end hole cutting line is a process engineering line or path along which the laser beam is guided, the end hole cutting line not being formed on the workpiece. As a rule, the cut-out part falls away under its own weight. Removing this part from the workpiece widens the pilot hole inside the countersink. In this case, a widened hole, referred to below as the "final hole", as already explained, is produced from the preliminary hole.

The final hole cutting line is arranged in relation to the pre-hole cutting line in such a way that the pre-hole is widened. Thus, based on a vertical view through the flat workpiece, the pilot hole within the countersink is widened, so that the final hole is also within the countersink or within an edge of the countersink delimiting the countersink on the workpiece surface facing the jet nozzle (first workpiece surface). . The vertical view through the first workpiece surface corresponds to a projection of the pilot hole and end hole and countersinking in the plane of the first workpiece surface. When the pilot hole is widened, a shortest dimension of the pilot hole measured in the plane of the workpiece is increased.

The third method step thus relates to guiding the laser beam in cutting mode along a closed end hole cutting line, with the end hole cutting line being arranged in relation to the pre-hole cutting line in such a way that, when viewed perpendicularly through the (flat) workpiece or through the plane of the the workpiece surface facing the jet nozzle (first workpiece surface), the pilot hole within the countersink, or within an edge of the countersink delimiting the countersink on the workpiece surface facing the jet nozzle (first workpiece surface), is widened to produce an end hole. In a vertical view through the workpiece, the end hole created by widening the pilot hole is therefore also located within the countersink or within a countersink on the workpiece surface facing the blasting nozzle (first workpiece surface) delimiting edge of the countersink.

The end-hole cutting line surrounds the pre-hole cutting line, with the end-hole cutting line always having a non-zero distance from the pre-hole cutting line. In addition, the end hole cutting line is arranged within a closed edge that delimits the countersink on the workpiece surface facing the jet nozzle.

Preferably, the pre-hole intersection line and the final hole intersection line are each circular lines (orbits), the end hole intersection line being arranged concentrically and at a radial distance from the pre-hole intersection line in such a way that a diameter of the pre-hole is increased and the end hole, which is circular in cross section, is inside of the subsidence is generated. The final hole cut line is thus located radially outward of the pre-hole cut line, i.e. the diameter of the final hole cut line is larger than the diameter of the pre-hole cut line, so that the diameter of the final hole is larger than the diameter of the pre-hole. In addition, the end hole cutting line is arranged radially inwards of a preferably circular edge delimiting the countersink on the workpiece surface facing the jet nozzle.

In the third method step, the countersunk hole is brought to a predetermined (desired) final dimension, in particular diameter.

The end hole cut line is designed such that when the end hole is created, some of the countersink is removed, but the countersink is not completely removed at the same time. Rather, part of the countersink remains when the end hole is created. Accordingly, the end hole is located within the countersink when viewed perpendicularly through the planar workpiece or the plane of the first workpiece surface. With a circular countersink and a circular end hole, the diameter of the countersink is always larger than the diameter of the end hole.

In an advantageous embodiment of the method according to the invention, the end hole has a diameter which is equal to or smaller than a workpiece thickness of the workpiece. As already explained, particularly small countersunk holes can be produced by the method according to the invention.

The terminology used in the three-step embodiment of the inventive method for producing countersunk holes described above "Pre-hole" and "final hole" are used only to distinguish different phases of the process of making a countersunk hole, where the final hole results from an enlargement of the pre-hole. With the creation of the final hole within the countersink, the countersunk hole is made.

The inventors have recognized that countersunk holes can be produced in a metallic workpiece in a particularly simple, reliable and efficient manner with high edge quality if a pilot hole is first produced so that the melt (slag) formed when the countersink is produced can be removed by means of the working gas jet can be expelled downwards from the workpiece through the pilot hole. In this way, it is advantageously possible to prevent burrs from forming on the workpiece surface facing the jet nozzle. This not only impairs the later use of the countersink and can require complex post-processing of the countersink, but in the worst case can also lead to a collision with the blasting nozzle. In addition, slag adhering to the walls of the pilot hole and to its cutting edge on the workpiece surface facing away from the blasting nozzle can advantageously be removed when the pilot hole is widened, so that the final hole with a countersink (i.e. countersunk hole) can be produced without burrs.

As used herein and hereinafter, the term "countersink" refers to a depression in the workpiece at the first workpiece surface. The countersink does not break through the workpiece. In contrast to this, the terms "gap", "hole", "pre-hole" and "end hole" each refer to openings or openings in the workpiece.

When creating a hole, in particular a pilot hole or end hole, and a countersink, the beam axis of the laser beam is moved with two mutually perpendicular movement axes parallel to the plane of the workpiece or the first workpiece surface. Components moved along circular paths.

The laser beam for producing a countersink and the laser beam for producing a hole, in particular a preliminary or final hole, preferably have different focus positions. In concrete terms, the focus position of the laser beam is changed here in such a way that the beam diameter on the workpiece when creating a hole, in particular a preliminary or final hole, is smaller than when creating a countersink. Such a change in the beam diameter on the workpiece due to a change in the focus position can ensure that the energy per line of the laser beam on the workpiece and thus the energy introduced into the workpiece when creating a countersink is smaller than when creating a hole, in particular a pre- or end hole. The focus position is preferably set in the desired manner by moving the beam head perpendicular to the workpiece support or perpendicular to the first workpiece surface and changed in such a way that there is a suitable energy per unit area on the workpiece to produce a countersink or a hole, in particular a preliminary or final hole. The beam head is typically moved in the vertical direction. If the workpiece is in the divergent area of the laser beam (focus is above the workpiece), the beam diameter on the workpiece can be reduced by moving the blasting head towards the workpiece (the distance between the blasting head and the workpiece is reduced). Conversely, by moving the blasting head away from the workpiece (the distance between the blasting head and the workpiece is increased), the blasting diameter on the workpiece can be increased. When creating a hole, in particular a preliminary or final hole, the focus is typically close to or within the workpiece. In addition or as an alternative to moving the beam head, the focus position of the laser beam can be changed optically.

Preferably, the energy per radius of the laser beam on the workpiece to produce a countersink is less than 50%, less than 40%, less than 30%, less than 20%, less than 10% or even less than 1% of the energy per radius of the laser beam on the workpiece for creating a hole, in particular a preliminary or final hole. This difference in energy per unit area is preferably reflected in a change in beam diameter on the workpiece. Preferably, the beam diameter on the workpiece for creating a hole, in particular a preliminary or final hole, is less than 50%, less than 40%, less than 30%, less than 20%, less than 10% or even less than 1% of the beam diameter for creating a countersink. In currently common laser cutting devices, the beam diameter is up to typically 1/10 to 5/10 mm on the workpiece during cutting. In order to produce a countersink using a laser beam, the beam diameter on the workpiece is preferably at least 1.5 mm and is, for example, in the range from 3 to 25 mm.

A countersink is delimited by a countersink edge on the workpiece surface facing the jet nozzle. The countersink edge is the area of the workpiece where the countersink begins to deepen. The hole located in the vertical view through the flat workpiece within the countersink, in particular the pre-hole or later the end hole, always has a non-zero distance from the edge of the countersink. The sinking deepens towards the hole, in particular both towards the pre-hole and towards the end hole produced later. The hole, in particular both the preliminary hole and the final hole produced later, thus has a deepest position within the countersink and is arranged at the bottom of the countersink, so to speak, whereby it can preferably also assume a centered position within the countersink.

In a vertical view through the workpiece (i.e. in projection onto the first workpiece surface), the shortest distance between the hole, in particular the end hole, and the edge of the countersink delimiting the countersink on the surface of the workpiece facing the jet nozzle is preferably always at least 0.5 mm, in particular at least 1 mm , and is, for example, in the range from 0.5 mm to 10 mm.

In the method according to the invention, a countersink and/or a hole, in particular a pre-hole, is preferably produced by a continuous-wave laser beam. This means that the laser beam is not switched off while the countersink and/or hole, in particular the pre-hole, is being produced. In contrast to this, the widening of the pilot hole, in particular an increase in the diameter of a round pilot hole, is preferably carried out with a pulsed laser beam. This has the advantage that the material of the workpiece is not heated so much when the pilot hole is widened, so that the melt produced in this way can flow off easily at a sharp or well-defined edge of the pilot hole.

According to an advantageous embodiment of the method according to the invention, a path energy of the laser beam on the workpiece is changed during the production of the countersink. This measure allows the depth and/or shape of the depression to be adjusted in a targeted manner. Typically, the beam axis of the laser beam is always directed perpendicular to the flat workpiece support or perpendicular to the plane of the irradiated first workpiece surface during the production of a countersink or hole, in particular a preliminary or final hole, ie the angle between the beam axis and the workpiece support is 90°. This entails technical control advantages. In addition, costs for the technical implementation of a corresponding pivotability of the laser beam relative to the plane of the workpiece support can be saved. However, it is also conceivable for the beam axis to be changed when the workpiece is irradiated, with the beam axis at least temporarily assuming an angle other than 90° to the workpiece support or to the plane of the irradiated first workpiece surface. The laser beam can be aligned by pivoting the beam head (mechanically) and/or by pivoting the laser beam (optically). For example, a larger area of the workpiece can be covered by pivoting the laser beam while the countersinking is being produced, which can be advantageous.

According to a further advantageous embodiment of the method according to the invention, after the creation of the countersink and before the widening of the pilot hole to produce the end hole, the blasting nozzle is moved with at least one movement component directed towards the workpiece in such a way that during the widening of the pilot hole a nozzle tip of the blasting nozzle, from which the laser beam exits, is located within the depression and thus also below the plane defined by the workpiece surface facing the jet nozzle. This close placement of the jet nozzle to the pilot hole or to the part of it that remains after the countersink has been created has the particular advantage that the end hole can be produced with a very precise geometry and the melt that occurs when the end hole is created is driven particularly effectively through the pilot hole out of the workpiece can be.

According to a further advantageous embodiment of the method according to the invention, the pilot hole (and also the countersink) are actively cooled by contact with a fluid cooling medium before the widening of the pilot hole. For this purpose, the working gas jet made of compressed working gas, which interacts with the laser beam in the cutting and non-cutting mode, is preferably directed onto the workpiece without the laser beam being switched on. This measure can also be used to ensure that the metallic material of the pre-hole edge is firmer on the workpiece surface facing away from the jet nozzle, so that the pre-hole edge is sharply defined is, which improves the drainage of the melt when creating the end hole. In this regard, it is particularly advantageous if the active cooling of the preliminary hole is combined with the production of the final hole by means of a pulsed laser beam, since both measures have the same advantageous effect. This applies all the more if the blasting nozzle dips into the countersink during the production of the end hole, which entails an even further improvement.

In the method according to the invention, the blasting nozzle runs over at least one line of depression generation one or more times, with the laser beam being guided along the line of depression generation. Here, a single countersink generation line can be provided. Advantageously, the laser beam is guided several times along the single line for producing the countersink to produce the countersink. According to an advantageous embodiment, a plurality of preferably concentric countersink generation lines with a non-zero distance between two directly adjacent countersink generation lines are provided for generating the countersink. Advantageously, the laser beam is guided several times along each of the several lines for producing the countersink in order to produce the countersink. This can be particularly beneficial when making large diameter countersinks.

According to a further advantageous embodiment of the method according to the invention, before the laser beam is guided along the cutting line, in particular the pre-hole cutting line, a slug to be cut out to produce the hole, in particular the pre-hole, is divided by the laser beam in the cutting mode. This measure ensures that the cut-out slug or its parts always fall down under their own weight and the pilot hole is reliably free, so that the melt that occurs later when the depression is created can be driven out of the workpiece.

In the method according to the invention it can be advantageous if a round pilot hole is produced which has a diameter which is 0.5 to 2 mm, preferably approx.

1 mm smaller than a diameter of the end hole. This measure can ensure that any burr produced in the area of the pre-hole during the production of the countersink is reliably and safely removed when the end hole is produced.

Furthermore, it can be advantageous if a circular designed countersink generation line in the plane of the workpiece surface facing the jet nozzle radial offset (radially outwards) from the cutting edge of the round pre-hole, which is at least 0.5 mm, preferably at least 1 mm, and in particular approx. 2 mm. Advantageously, the jet nozzle or the laser beam passes over the lowering generation line several times (preferably 2 to 25 passes) to generate the lowering.

Furthermore, it can be advantageous if a plurality of circular, concentric reduction generation lines are provided, the diameter of which increases by 0.5 to 2 mm in each case radially outward. Advantageously, the radially innermost countersink generation line in the plane of the workpiece surface facing the blasting nozzle has a radial offset (radially outward) from the cutting edge of the pilot hole, which is from 0.25 to 1 mm, with a radial offset of immediately adjacent countersink generation lines likewise of 0.25 is up to 1 mm. Advantageously, the lowering generation lines are each passed several times to generate the lowering (preferably 2 to 25 passes).

Furthermore, it can be advantageous if a spiral-shaped countersinking line is provided, which has an increase in diameter of 0.25 to 1 mm when it has completed a complete revolution. Advantageously, after reaching the target diameter, this path is traversed several times (preferably 2 to 25 passages). In particular for the production of comparatively large countersunk holes, e.g. for countersunk screws from size M8 (cf. e.g. DIN-EN-ISO 10642), it can be advantageous to guide the laser beam in non-cutting mode along a spiral countersink generation line in the second process step. In this case, the laser beam can first traverse the spiral-shaped lowering generation line from the inside to the outside, and then again, preferably with half the laser power, from the outside to the inside. The surface quality of the countersink can be improved, in particular the roughness on the surface of the countersink can be reduced, by finally traversing the spiral countersink generation line from the outside inwards with half the laser power.

If the countersink serves to receive the head of a countersunk screw, it can also be advantageous if the radially outermost, circular countersink generation line has a diameter that is slightly smaller than the maximum diameter of the head of the countersunk screw to be arranged in the bore. In general, the number of countersink generation lines depends on the diameter of the hole or pilot hole or the thread diameter of the countersunk screw to be inserted and the desired depth of the countersink. For countersunk screws with a metric thread M3 to M6 (ie with a pilot hole diameter of 3 to 6 mm) at least two passes are typically required, with a typical number of passes being between two and 25 passes. For countersunk screws with a metric thread M8 to M12 (ie with a hole or pilot hole diameter of 8 to 12 mm) at least five passes are typically required, preferably at least 10, with a typical number of passes being between 10 and 25 passes.

In the method according to the invention, the laser beam is preferably brought into the cutting or non-cutting mode by changing the focus position. In the cutting mode, the nozzle tip at which the laser beam emerges is preferably at a distance of less than 2 mm from the first workpiece surface facing the jet nozzle or from the plane defined by it. The countersinking is preferably produced in the non-cutting mode with a much greater distance between the jet nozzle and the first workpiece surface, which is at least 30 mm, in particular at least 40 mm and particularly preferably around 50 mm. On the one hand, the laser beam is thus sufficiently defocused and can hit the workpiece surface with a large beam diameter, with a relatively low working gas pressure (e.g. oxygen pressure) with a high coverage of the processing zone. On the other hand, it can be ensured that the nozzle tip and the protective glass are not soiled by slag splashing upwards.

When creating depressions, it can also be advantageous if the working gas (e.g. oxygen) has a gas pressure of less than 5 bar, which is in particular from 2 bar to 3.5 bar. It can also be advantageous if the feed rate of the jet nozzle when creating the countersink is at least 4 m/min and the power of a laser beam (e.g. laser) used for processing is at least 1500 W.

When widening the pre-hole, in particular increasing the diameter of a round pre-hole, it can be advantageous if a laser beam used in pulse mode (e.g. laser beam) has an average power of at least 200 W, a pulse peak power of at least 2000 W and a pulse frequency between 10 Hz and has 200 Hz. In the above-described configurations of the method according to the invention, as a rule, many countersunk holes are produced. Here it is possible that after the production of a respective hole, in particular a pilot hole, the countersinking is produced immediately thereafter and, if necessary, the final hole is produced immediately thereafter. However, it is also possible that between the respective method steps for producing the same hole, in particular end hole, with associated depression (ie countersunk hole), respective method steps for other holes, in particular end holes, with associated depressions (ie countersunk holes) are carried out. For example, after countersinking one pilot hole, it may be advantageous to first proceed with a process step for another countersinking hole (eg, producing the pilot hole for the other countersinking hole) so that the countersunk pilot hole has time to cool. In particular, many pre-holes can be produced in immediate succession, followed by the countersinks in the pre-holes being produced in immediate succession, further followed by the end holes being produced in immediate succession. It goes without saying that when producing a plurality of countersunk holes, the respective method steps for producing the countersunk holes can be carried out in any manner, as long as it is ensured that in the case of the same countersunk hole, the production of the pilot hole, countersink and final hole are produced in this order done one after the other.

The invention also extends to a method in which a plurality of workpiece parts are cut out of a workpiece by a laser beam in the cutting mode, one or more countersunk holes being produced by the method according to the invention in at least one workpiece part before it is cut out of the workpiece. As a rule, one or more countersunk holes are produced in each case by the method according to the invention in a plurality of workpiece parts before they are cut out of the workpiece.

The invention also extends to a laser beam processing device with a laser beam guided by a beam head for laser beam processing of a plate-shaped or tubular workpiece, for example, which has an electronic control device for controlling/regulating the laser beam processing of the workpiece, which is set up (in terms of programming) to carry out the method according to the invention . Furthermore, the invention extends to a program code for an electronic control device suitable for data processing for such a laser beam processing device, which contains control commands that cause the control device to carry out the method according to the invention.

The invention also extends to a computer program product (storage medium) with a stored program code for an electronic control device suitable for data processing for such a laser beam machining device, which contains control commands that cause the control device to carry out the method according to the invention.

It goes without saying that the above-mentioned configurations of the invention can be used alone or in any combination without departing from the scope of the present invention.

Brief description of the drawings

The invention will now be explained in more detail using exemplary embodiments, reference being made to the accompanying figures. Show it:

1 shows a schematic representation of an exemplary laser beam processing device for carrying out the method according to the invention for laser beam processing of a plate-shaped or tubular workpiece;

2A-2C embodiments of the method according to the invention for laser beam machining of a workpiece in which countersunk holes are produced;

3A-3D further embodiments of the method according to the invention for laser beam machining of a workpiece in which countersunk holes are produced;

4 shows a flow chart of the method according to the invention for laser beam machining of a workpiece, in which countersunk holes are produced. Detailed description of the drawings

First, consider FIG. 1, in which a laser beam machining device known per se for beam cutting of plate-like workpieces is illustrated. The laser beam processing device, designated overall by the reference number 1, comprises a beam cutting device 2 with a beam head 3, and a work table 4 with a flat workpiece support 5 for a workpiece 9 (not shown in Figure 1, see Figures 2A-2C, 3A-3D), for example a flat sheet metal. The workpiece support 5 is spanned by a crossbeam 6, which is guided to be movable along a first axial direction (x-direction).

A guide carriage 7 for the blasting head 3 is mounted on the crossbeam 6 and is movably guided on the crossbeam 6 along a second axis direction (y-direction) perpendicular to the first axis direction. The blasting head 3 can thus be moved in a plane spanned by the two axial directions parallel and relative to the workpiece support 5, which is horizontal, for example. The height of the blasting head 3 is also designed to be movable in a third axial direction (z-direction) perpendicular to this plane, as a result of which the distance perpendicular to the workpiece support 5 or workpiece 9 can be changed. With a horizontal workpiece support 5, the z-direction corresponds to the direction of gravity. On its side facing the workpiece support 5 , the blasting head 3 has a blasting nozzle 13 that tapers conically towards the workpiece support 5 . The jet head 3 serves to guide a laser beam 14 and a process or working gas jet 15, which emerge from a terminal nozzle tip 33 (see, for example, FIG. 2A). The laser beam 14 is generated by a laser beam source 8 and guided to the beam head 3, for example, through a beam guiding tube and a plurality of deflection mirrors or a fiber optic cable. The laser beam can be directed onto the workpiece 9 in a bundled form (i.e. focused) via a focusing lens or adaptive optics. Due to the movability of the beam head 3 along the first axial direction (x-direction) and second axial direction (y-direction), any point on the workpiece 9 can be approached with the laser beam 14 .

The workpiece 9 has two opposite workpiece surfaces 10, 11 (see, for example, FIG. 2A), a first or upper workpiece surface 10 facing the jet nozzle 13 and a second or lower workpiece surface 11 facing away from the jet nozzle 13. Due to the vertical mobility of the blasting head 3 in the z-direction, a change in the distance from the upper workpiece surface 10 of the Working distance of the jet nozzle 13 to the workpiece 9 can be adjusted. The distance of the beam head 3 from the upper workpiece surface 10 can be adjusted before, during and after the laser beam processing. The focal position of the laser beam 14 can be adjusted by changing the distance between the jet nozzle 13 and the first workpiece surface 10 and by means of optical elements in the jet head 3, for example adaptive optics.

The working gas jet 15 is generated by a gas jet generating device, not shown. Helium (He), argon (Ar) or nitrogen (N2), for example, is used as the inert process or working gas. Oxygen (O2) is usually used as the reactive working gas. The use of gas mixtures is also known. The working gas jet 15 emerges from the nozzle tip 33 of the jet nozzle 13 and is guided coaxially to the laser beam 14 to the processing point, where it hits the workpiece with an (initial) gas pressure specified by the gas jet generating device, which is typically in the range of 2 to 20 bar 9 on. The working gas jet 15 serves to drive the melt produced during the laser processing through an opening (e.g. pilot hole 16, see e.g. Figure 2B) in the workpiece 9 produced by the laser beam 14 by means of gas pressure.

As shown in FIG. 1, the flat workpiece support 5 consists, for example, of a large number of support elements with, for example, triangular support point tips, which together define a support plane for the workpiece 9 to be machined. The support elements are designed here, for example, as elongate support webs, each of which extends along the y-direction and are arranged next to one another in a parallel arrangement along the x-direction, for example with a constant spacing between them. Not shown is a suction device, through which cutting smoke, slag particles and small pieces of waste produced during jet cutting can be sucked off.

A program-controlled control device 12 is used to control/regulate the method according to the invention for laser beam machining of the workpiece 9 in the laser beam machining device 1.

Reference is now made to FIGS. 2A to 2C and 3A to 3D, in which exemplary configurations of the method according to the invention for laser beam machining of a workpiece 9 by the beam device 1 from FIG. 1 are illustrated. For the purpose of a simplified representation and because it is sufficient for understanding the invention, only the jet nozzle 13 and the laser beam 14 and working gas jet 15 are shown in combination with the workpiece 9. The workpiece 9 is, as usual, in a horizontal position on the workpiece support 5.

First consider FIGS. 2A to 2C, in which the plate-shaped workpiece 9 with the two flat workpiece surfaces 10, 11 and the jet nozzle 13 are shown schematically in a vertical sectional view in the illustrations on the left. The right-hand images in FIGS. 2A to 2C illustrate the process steps in a schematic manner using respective top views.

The upper workpiece surface 10 faces the jet nozzle 13 and the lower workpiece surface 11 faces away from the jet nozzle 13 . The laser beam 14 emerging from the nozzle tip 33 of the jet nozzle 13 and the working gas jet 15 strike the workpiece 9. The laser beam 14 has the shape of a focused beam cone with a central beam axis 19. The central beam axis 19 and thus the laser beam 14 is perpendicular to the upper workpiece surface 10 or directed to the plate-shaped workpiece 9 level.

In FIG. 2A, the jet nozzle 13 has been moved from a starting position towards the workpiece 9 with at least one vertical movement component, so that the jet nozzle 13 has a relatively small working distance A from the workpiece 9 . The working distance A of the jet nozzle 13 from the upper workpiece surface is preferably less than 2 mm. The focal position of the laser beam 14 results in a narrow beam spot with a small beam diameter on the workpiece 9. The focal position and thus the beam diameter are selected in such a way that the energy per unit length of the laser beam 14 on the workpiece 9 is large enough for the laser beam 14 to be used for cutting or separating machining of the workpiece 9 is suitable. Thus, the laser beam 14 is in a cutting mode.

As shown in FIG. 2A, the cutting laser beam 14 is guided along a circular pre-hole cutting line 21 to produce a (pre-)hole 16, as a result of which a circular closed cutting gap is produced. As a result, a workpiece part (slug) with a round or disc-shaped cross section is completely cut out of the workpiece 9 . The cut-out slug falls away under its own weight. By removing the slug from the workpiece 9 is a round in cross-section Pilot hole 16 with a specific diameter in the workpiece 9 is generated. The diameter of the (pre)hole 16 is measured in the plane of the workpiece 9. A widened hole, namely a final hole 17, can optionally be produced from the (pre)hole 16 in the further process by widening the diameter (see Figure 2C). .

The round (pre-)hole 16 is a through-hole according to its production method and breaks through the workpiece 9, the (pre-)hole 16 being surrounded by a pre-hole wall 23 formed by the workpiece 9, which extends continuously from the upper workpiece surface 10 to the lower one Workpiece surface 11 extends. On the upper workpiece surface 10, the (pre)hole 16 is delimited by a circular upper (pre)hole cutting edge 20, on the lower workpiece surface 11 by a circular lower (pre)hole cutting edge 21. The two (pre) Hole cutting edges 21, 22 are each part of the (pre)hole wall 23. In Figure 2A, the (pre)hole cutting line 21 and the upper (pre)hole cutting edge 20 are shown relatively far apart from each other due to the better graphic representation, it being understood that this need not be the case in practice. The round (pre-)hole 16 is radially symmetrical with respect to its central axis 31 (see FIG. 2B). A radial direction is defined in the plane of the workpiece 9 in relation to the (pilot) hole 16 and its central axis 31 .

Optionally, the method can be supplemented by a step that is carried out before the (pre-)hole 16 is cut. This step is preferably used when (pre-)holes 16 are to be produced with a diameter of at least 7 mm and/or the workpiece 9 is at least 4 mm thick. Here, the slug to be cut later on its contour is cut into smaller parts by one or more cutting gaps, which can always ensure that the slug falls reliably and safely down out of the workpiece 9 and the cut (pre-)hole 16 is always free . For example, in the area of the slug to be cut out, intersecting kerfs are introduced, possibly superimposed by a kerf in spiral form. A possible method for dividing the slug is described, for example, in US Pat. No. 8,716,625 B2.

After the round (pre)hole 16 has been produced, a round countersink 18 concentric with the (pre)hole 16 is produced. This is illustrated below with reference to FIG. 2B. To create the countersink 18, the jet nozzle 13 has a relatively large working distance A from the first workpiece surface 10 or from the workpiece 9, with the workpiece 9 being in the divergent area of the laser beam 14, which results in a wide beam spot with a large beam diameter on the Workpiece 9 leads. For this purpose, the blasting head 3 or the blasting nozzle 13 was moved away from the workpiece 9 with at least one vertical movement component, so that there is a larger working distance A between the blasting nozzle 13 and the first workpiece surface 10 compared to the production of the (pre-)hole 16 . The working distance A for producing the countersink 18 is, for example, at least 6 times larger, in particular at least 10 times larger, than the working distance A for producing the (pre-)hole 16 and is preferably at least 30 mm, particularly preferably at least 40 mm and in particular about 50 mm, with a range of 30 mm to 50 mm being preferred. Correspondingly, the beam spot and the beam diameter on the workpiece 9 are significantly larger. For example, the cross-sectional area of the beam spot on the workpiece 9 is at least 6 times larger, in particular at least 10 times larger. The focus of the laser beam 14 is far above the workpiece 9. The focal position and the beam diameter of the laser beam 14 are selected in such a way that the energy per unit area on the workpiece 9 of the laser beam 14 is relatively low and the laser beam 14 only creates the depression 18 and the workpiece 9 is not penetrated here (non-separating processing). The laser beam 14 is in a non-cutting mode.

When producing the countersink 18 , the non-cutting laser beam 14 is moved in a (horizontal) plane parallel to the plane of the workpiece support 5 , the laser beam 14 being moved along at least one countersink production line 29 . The at least one countersink generation line 29 is concentric to the (pre)hole cutting line 21 and extends along the upper (pre)hole cutting edge 20, with the countersink generation line 29 corresponding, for example, to the upper (pre)hole cutting edge 20 or preferably further radially thereto is offset to the outside. This means that the countersink generating line 29 has a diameter equal to or preferably larger than the diameter of the upper (pre-)hole cut edge 20.

A single line 29 for producing the countersink can be provided for producing the countersink 18 , with the laser beam 14 being moved one or more times along the line 29 for producing the countersink 18 . Preferably, the laser beam 14 for generating the reduction 18 several times along the Process reduction generation line 29 (typically 2 to 20 passes of the jet nozzle 13). An offset (ie radial distance) of the lowering generation line 29 from the upper (pre)hole cut edge 20 is preferably at least 0.5 mm, particularly preferably at least 1 mm and in particular 2 mm. The lowering generation line 29 must be arranged in such a way that the lowering 18 generated is directly adjacent to the (pre)hole 16 , ie opens into the (pre)hole 16 .

A plurality of lowering generation lines 29 can also be provided for the generation of the lowering 18, with the laser beam 14 being moved one or more times along each of the lowering generation lines 29 in order to generate the lowering 18. In order to produce the depression 18, the laser beam 14 is preferably moved several times along each of the depression production lines 29 (typically 2 to 20 passes of the jet nozzle 13). The multiple countersink generation lines 29 are arranged concentrically with each other. An offset (i.e. radial distance) of the countersink generation line 29 from the upper (pre)hole cut edge 20 or between two immediately adjacent countersink generation lines 29 is preferably from 0.25 mm to 1 mm. The increase in the diameter of two immediately adjacent countersink generation lines 29 is thus preferably 0.5 mm to 1 mm. The countersink generation lines 29 must be arranged in such a way that the countersink 18 produced is directly adjacent to the (pre)hole 16, i.e. opens into the (pre)hole 16.

In FIG. 2B, the circular movement of the laser beam 14 along the at least one countersink generation line 29 around the center axis 31 of the (pre-)hole 16 is illustrated schematically by an arrow.

It would also be conceivable for the laser beam 14 to be moved along a countersinking production line 29 of spiral design in order to produce the countersink 18 . An increase in the diameter of the spiral track of 0.25 mm to 1 mm is preferably achieved with each complete revolution. After reaching the target diameter, it is advantageous if this is crossed several times. In this case, too, the line 29 for producing the countersink must be arranged in such a way that the countersink 18 produced is directly adjacent to the (pre)hole 16 , i.e. opens into the (pre)hole 16 .

The countersink 18 is a depression of the workpiece 9 on the first workpiece surface 10. The countersink 18 surrounds the (pre)hole 16 concentrically, the countersink 18, starting from a (radial) outer countersink edge 27, from the top Workpiece surface 10 extends into the workpiece 9 up to a (radially) inner countersink edge 28, but not as far as the lower workpiece surface 11, ie the countersink 18 does not extend over the entire thickness of the workpiece part. The inner countersink edge 28 is thus located between the upper workpiece surface 10 and the lower workpiece surface 11.

The outer countersink edge 27 is defined as that area of the workpiece 9 at which the countersink 18 begins to deepen towards the interior of the workpiece 9 . The inner countersink edge 28 is defined as that area of the workpiece 9 where the countersink 18 merges into the remaining part of the (pre)hole 16 , the inner countersink edge 28 being formed by the (pre)hole wall 23 . A flank 30 of the countersink 18 extends from the outer countersink edge 27 to the inner countersink edge 28.

In the radial direction, the depression 18 can optionally be provided with a defined cross-sectional shape. In particular, the focus position and thus the beam diameter can be varied during the production of the countersink 18 in order to set the depth and/or cross-sectional shape of the countersink 18 in a targeted manner. When the beam diameter on the workpiece 9 decreases, the countersink 18 becomes deeper, i.e. the flank 30 of the countersink 18 becomes steeper, whereas the countersink 18 becomes flatter, i.e. the flank 30 of the countersink 18 becomes less steep when the beam diameter on the workpiece 9 is enlarged. FIG. 2B shows an example of a countersinking 18 with a sloping flank 30 with an inclination of approximately 45°, with larger or smaller flank inclinations also being possible.

In principle, the countersink 18 can be used in any desired manner, and in this exemplary embodiment it is preferably intended to accommodate the head of a countersunk screw. Preferably, the radially outermost countersink generation line 29 for producing the countersink 18 has a diameter that is slightly smaller than the maximum diameter of the head of the countersunk screw to be arranged in the countersink 18 . The number of lowering generating lines 29 depends on the diameter of the (pilot) hole 16 or the thread diameter of the screw to be inserted and the desired depth of the lowering 18 . As a rule, at least two passages of the jet nozzle 13 over a same Subsidence generation line 29 required with a typical number of passes being between two and 25. For For countersunk screws with a metric thread size M8 - M12, the number of passes is generally at least 5, preferably at least 10 and is typically between 10 and 25. Oxygen (O2), for example, is used as the process or working gas when creating the countersink 18, with a gas pressure of, for example, less than 5 bar, which is in particular from 2 to 3.5 bar. The feed speed of the jet nozzle 13 when creating the countersink 18 is preferably at least 4 m/min and the laser power of the laser beam 14 is preferably at least 1500 W.

Through the (pre-)hole 16, the melt (slag) produced when creating the depression 18 can advantageously flow downwards very well and it can thus be prevented that the melt reaches the upper workpiece surface 10 of the workpiece 9 and accumulates there hardens and forms a ridge. This not only impairs the later use of the countersink 18 and can require complex post-processing of the countersink 18, but can also lead to a collision with the jet nozzle 13 in the worst case. By optionally splitting up the slug to be cut out when creating the (pre)hole 16, it can always be ensured that the (pre)hole 16 is free and that the melt, which occurs when the countersink 18 is created, can be reliably and safely removed by means of of the working gas is expelled through the (pre)hole 16. This is a great advantage of the invention.

Nevertheless, melt can settle on the (pre-)hole wall 23, especially in the area of the lower (pre-)hole cut edge 21, and form a burr 32 after cooling, as illustrated in FIG. 2B. However, this burr 32 is advantageously also removed during the optional widening of the (pre-)hole 16 to produce the end hole 17 (see FIG. 2C), so that an end hole 17 with a burr-free end hole wall 24 can be produced. If such a further step is carried out, the hole 16 produced so far represents a "pre-hole" which is widened in diameter towards the end hole 17 .

The optional widening of the diameter of the hole or pre-hole 16 to create the end hole 17 is described below:

After the countersink 18 has been produced, the preliminary hole 16 or the part thereof remaining after the countersink 18 has been produced is widened, which is illustrated below with reference to FIG. 2C. Analogous to the production of the preliminary hole 16, the laser beam 16 is used in the cutting mode to increase the diameter of the preliminary hole 16 . In this case, the jet nozzle 13 has a relatively small working distance A from the first workpiece surface 10, which leads to a narrow jet spot with a small jet diameter on the workpiece 9. For this purpose, the blasting head 3 or the blasting nozzle 13 was moved towards the workpiece 9 with at least one vertical movement component, so that there is a smaller working distance A between the blasting nozzle 13 and the first workpiece surface 10 compared to the production of the depression 18 . The focus position and thus the beam diameter of the laser beam 14 are selected in such a way that the distance energy on the workpiece 9 of the laser beam 14 is relatively large and the workpiece 9 is penetrated in the process (separating processing).

When widening the pilot hole 16, the cutting laser beam 14 is guided along a circular end-hole cutting line 22, as a result of which a circular-closed cutting gap is produced. The end hole cutting line 22 is concentric with the pre-hole cutting line 21 and spaced radially outwards therefrom, i.e. has a larger diameter than the pre-hole cutting line 21. The end hole cutting line 22 is located in the radial direction between the pre-hole cutting line 21 and the outer countersink edge 27, with the proviso that a radial portion of the flank 30 is removed, but not the complete flank 30, i.e. the countersink 18 is partially preserved. The end hole 17 is thus created within the countersink 18 . When the pilot hole 16 is widened, a disk with a hollow-cylindrical cross-section is completely cut out of the workpiece 9 . This falls away under its own weight, so that it is removed from the workpiece 9 .

By widening the pilot hole 16, an end hole 17 with a round cross section is produced in the workpiece 9, which has a larger diameter than the pilot hole 16. The end hole 17 is bounded by an end hole wall 24 formed by the workpiece 9 and extends from an upper end hole cut edge 25 , which lies between the upper workpiece surface 10 and the lower workpiece surface 11, up to a lower end hole cutting edge 26, which is formed by the lower workpiece surface 11. The diameter D of the end hole 17 is preferably between 0.5 and 2 mm and in particular about 1 mm larger than the diameter of the pre-hole 16 previously produced. This allows the pre-hole wall 32 and the lower Workpiece surface 11 in the area of the lower pre-cut edge 21 adhering burr 32 is reliably and safely removed.

A pulsed laser beam 14 (pulsed laser beam) is preferably used when widening the preliminary hole 16 to produce the final hole 17 . This advantageously allows the workpiece 9 to heat up less when the end hole 17 is created, so that the metallic material of the workpiece 9 is stronger at the machining point and a well-defined or sharp lower end hole cut edge 26 results, which Drainage of the melt easier when widening the pilot hole 16. This measure helps to prevent the melt from being deposited primarily on the lower workpiece surface 11 and forming a burr there.

A pulsed laser beam 14 (laser beam) with an average power of at least 200 W and a pulse peak power of at least 2000 W and a pulse frequency between 10 Hz and 200 Hz is preferably used. Depending on the workpiece material and the desired edge quality, nitrogen (N), compressed air or oxygen (O2) can be used as the working gas.

As shown in Figure 2C, it is advantageous if the jet nozzle 13 is moved so far down to create the end hole 17 that it dips into the countersink 18, i.e. the nozzle tip 33 is below the upper workpiece surface 10 or below the Plane defined by the upper workpiece surface 10. This has the particular advantage that both the laser beam 14 and the working gas jet 15 fan out less at the point of impact on the workpiece 9, so that cutting can be carried out more precisely and the final hole 17 can be produced with particularly high precision. In addition, this counteracts the situation where the melt produced when the end hole 17 is produced is deposited on the upper workpiece surface 10 and forms a burr there. In addition, the melt can be expelled particularly efficiently through the pilot hole 16 by the particularly strongly focused working gas jet 15, so that a deposit of melt on the upper workpiece surface 10 is also counteracted. These are great advantages that can be achieved by this measure.

Reference is now made to FIGS. 3A to 3D, in which a further exemplary embodiment of the method according to the invention for laser beam machining of a workpiece 9 by the beam device 1 from FIG. 1 is shown in a schematic manner is illustrated. The method steps in FIGS. 3A, 3B and 3D correspond to the method steps in FIGS. 2A, 2B and 2C, reference being made to the above statements on FIGS. 2A, 2B and 2C in order to avoid unnecessary repetition. The embodiment of the method according to the invention illustrated with reference to FIGS. 3A to 3D differs from the embodiment illustrated with reference to FIGS. 2A to 2C only in the method step of FIG. 3C.

Accordingly, the countersink 18 and the pilot hole 16 (or the remaining part of the pilot hole 16) are actively cooled after the creation of the countersink 18 (Figure 3B) and before the widening of the pilot hole 16 to produce the end hole 17 (Figure 3D). a gaseous or liquid cooling medium. As illustrated in FIG. 3C, the working gas from the working gas jet 15 is advantageously used for this purpose, with the laser beam 14 being switched off. The point of impact on the workpiece 9 is typically subjected to a working gas with an (initial) gas pressure in the range from 2 to 20 bar. The expanding working gas therefore leads to a very efficient cooling of the metallic workpiece 9, the efficiency of the cooling being all the better the hotter the workpiece 9 to be cooled is. The metallic material of the workpiece 9 becomes firmer as a result of the active cooling, so that the lower pre-hole cutting edge 26 is precisely defined, which facilitates the flow of the melt through the pre-hole 16 . This measure also contributes to the fact that the geometry of the end hole 17 can be adjusted very precisely. In addition, sticking of burr to the lower workpiece surface 11 can be counteracted.

FIG. 4 shows a flow chart of the method according to the invention. The procedure comprises at least three successive steps.

In step I, the laser beam is first guided in the cutting mode along a closed (pre-)cutting line, whereby a (pre-)hole is produced in the workpiece. Then, in step II, the laser beam is guided once or several times in non-cutting mode along at least one closed countersink generation line, the countersink generation line being arranged in such a way that a countersink is generated around the (pre)hole, which in the (pre) hole.

Then, in an optional step III, the laser beam is guided in the cutting mode along a closed end-hole intersection line, the end-hole intersection line being arranged such that the hole, which now represents a pilot hole, is inside the countersink widened and thereby an end hole is created.

Optionally, before the laser beam is guided along the (pre-)cutting line, a slug to be cut out to produce the (pre-)hole is divided by the laser beam in the cutting mode.

Optionally, the pilot hole is actively cooled before the widening of the pilot hole by contact with a fluid cooling medium, preferably by the working gas of the working gas jet, which is directed onto the workpiece.

example 1

Production of countersinks for countersunk screws with metric thread sizes

M3 - M6 using a laser beam

First, a pilot hole is cut out with a diameter that is approx. 1 mm smaller than the average core hole diameter of the countersunk screw, so that the melt that occurs in the next step when creating the countersink can be expelled through the pilot hole.

Then, with the blasting nozzle at a large distance from the upper workpiece surface (approx. 50 mm) and the laser beam ignited, a circular countersinking path with a diameter of 5 mm to 15 mm is traversed, with oxygen (O2) being used as the working gas. The number of passes depends on the depth of the sinking to be made, with two to 25 passes usually being carried out. This creates the countersink for the head of the countersunk screw. Alternatively, a spiral path is traversed.

Then the pre-hole is cut to standard size by a laser beam used in pulse mode, with the diameter of the final hole being approx. 1 mm larger than the diameter of the pre-hole. As a result, the slag adhering in the pilot hole and in particular on the lower tool surface in the area of the lower pilot hole cutting edge can be reliably removed. Advantageous cutting parameters are: pulsed average laser power (pulse frequency 10 Hz): 400 W, pulse peak power: 3000 W or 6000 W, feed: 0.1 m/min, distance between jet nozzle and upper workpiece surface: 1.2 mm, gas pressure of the working gas: 3 .3 bars. example 2

Production of countersinks for countersunk screws with metric thread sizes M8 - M12 using a laser beam

Before the pilot hole is cut, the slug is divided by cutting gaps in the shape of a cross with a superimposed spiral shape in the slug to be cut out. This ensures that the slug of the pilot hole falls reliably and the pilot hole is therefore always free, so that the melt that occurs when the countersink is created can be expelled through the pilot hole. Then the pilot hole is cut with a diameter that is approx. 1 mm smaller than the middle core hole diameter of the countersunk screw.

Then, with the blasting nozzle at a large distance from the upper surface of the workpiece (approx. 50 mm) and the laser beam ignited, a circular countersinking path with a diameter of 10 mm to 15 mm is traversed, with oxygen (O2) being used as the working gas. The number of passes depends on the depth of the sinking to be made, with generally 10 to 25 passes being made. This creates the countersink for the head of the countersunk screw. Alternatively, a spiral path is traversed.

Then the pre-hole is cut to standard size by a laser beam used in pulse mode, with the diameter of the final hole being approx. 1 mm larger than the diameter of the pre-hole. Advantageous cutting parameters are: pulsed average laser power (pulse frequency 10 Hz): 400 W, pulse peak power: 3000 W or 6000 W, feed: 0.1 m/min, distance between jet nozzle and upper workpiece surface: 1.2 mm, gas pressure of the working gas: 3 .3 bars.

Example 3

Production of a countersink for a countersunk screw with a metric thread size M8 in 8 mm mild steel using a laser beam

Before the pilot hole is cut, the slug is divided by cutting gaps in the shape of a cross with a superimposed spiral shape in the slug to be cut out. Oxygen (O2), nitrogen (N) or compressed air is used as the working gas. Then the pilot hole is cut with a diameter of 8 mm, which is approx. 1 mm smaller than the middle core hole diameter of the countersunk screw. Then, with the jet nozzle at a large distance from the upper surface of the workpiece (approx. 50 mm) and the laser beam ignited, a circular depression generation path with a diameter of 12.6 mm is traversed, with oxygen (O2) being used as the working gas. 17 passes are made, creating a countersink with a diameter of 14 mm and a depth of 4.4 mm to 4.5 mm in the sheet. Alternatively, a spiral path is traversed. Advantageous laser parameters are: laser power: 4000 W, feed rate: 10 m/min, distance between jet nozzle and upper workpiece surface (A): 50 mm, gas pressure of the working gas: 3.3 bar, focus diameter: 210 pm/150 pm.

The pilot hole is then cut to a standard size with a diameter of 9 mm using a pulsed laser beam, with oxygen (O2) being used as the working gas. Advantageous cutting parameters are: pulsed average laser power (pulse frequency 10 Hz): 400 W, pulse peak power: 4000 W, feed: 0.7 m/min, distance between jet nozzle and upper workpiece surface (A): 0.7 mm, gas pressure of the working gas: 17 bar, focus diameter: 210 pm.

As can be seen from the above description, the invention relates to:

A method of laser beam machining a workpiece with a focused laser beam, in which the laser beam can be used in a workpiece-cutting or non-cutting mode by changing the line energy of the laser beam, comprising the following steps in order:

Guiding the laser beam in cutting mode along a closed cutting line, creating a hole in the workpiece, guiding the laser beam in non-cutting mode one or more times along at least one closed countersink generation line, the countersink generation line being arranged in relation to the cutting line in such a way that the hole surrounding countersink is created, which opens into the hole.

According to a preferred embodiment of the method according to the invention, the laser beam is guided along a circular cutting line. According to a preferred embodiment of the method according to the invention, the laser beam is guided one or more times along at least one circular depression generation line. According to a preferred embodiment of the method according to the invention at least one circular counterbore generating line disposed concentrically and radially spaced from the circular cutting line. According to a preferred embodiment of the method according to the invention, the hole and the countersink are each produced with a continuous-wave laser beam. According to a preferred embodiment of the method according to the invention, before the laser beam is guided along the cutting line, a slug to be cut out to produce the hole is divided by the laser beam in the cutting mode. According to a preferred embodiment of the method according to the invention, the shortest distance between the hole and an outer edge of the countersink delimiting the surrounding countersink when viewed vertically through the workpiece is always at least 0.5 mm. According to a preferred embodiment of the method according to the invention, the shortest distance between the hole and the outer edge of the countersink delimiting the countersink is always in the range of 0.5 mm to 10 mm. According to a preferred embodiment of the method according to the invention, the laser beam for generating the countersink is guided once along a single countersink generation line. According to a preferred embodiment of the method according to the invention, the laser beam is guided several times along a single countersink generation line to produce the countersink. According to a preferred embodiment of the method according to the invention, a plurality of countersink generation lines are provided for producing the countersink, with two directly adjacent countersink generation lines always being at a distance other than zero, and with the laser beam being guided one or more times along each of the multiple countersink generation lines to produce the countersink. According to a preferred embodiment of the method according to the invention, a plurality of circular, concentric countersink generation lines is provided, the diameter of which increases radially outward by 0.5 to 2 mm in each case. According to a preferred embodiment of the method according to the invention, a radially innermost countersink generation line has a radial offset from the cut edge of the hole which is from 0.25 to 1 mm. According to a preferred embodiment of the method according to the invention, the laser beam is guided one or more times along at least one spiral depression generation line. According to a preferred embodiment of the method according to the invention, a helical countersink generation line is provided which, when it has completed a complete revolution, has an increase in diameter of 0.25 to 1 mm. According to a preferred embodiment of the method according to the invention, a distance energy of the laser beam on the workpiece in the non-cutting mode is less than a percentage selected from 50%, 40%, 30%, 20%, 10% and 1%, a distance energy of the laser beam on the workpiece in cutting mode. According to a preferred embodiment of the method according to the invention, the line energy of the laser beam is changed by changing a beam diameter of the laser beam on a workpiece surface of the workpiece. According to a preferred embodiment of the method according to the invention, the beam diameter of the laser beam on the workpiece in the cutting mode is less than a percentage selected from 50%, 40%, 30%, 20%, 10% and 1% of the beam diameter in the non-cutting mode . According to a preferred embodiment of the method according to the invention, the beam diameter of the laser beam on the workpiece surface of the workpiece is changed by changing a focus position relative to the workpiece. According to a preferred embodiment of the method according to the invention, the focus position of the laser beam is changed relative to the workpiece by moving a jet nozzle for emitting the laser beam with a movement component perpendicular to the workpiece surface. According to a preferred embodiment of the method according to the invention, a distance of a jet nozzle for emitting the laser beam from a workpiece surface is less than 2 mm in the cutting mode and at least 30 mm in the non-cutting mode. According to a preferred embodiment of the method according to the invention, a beam axis of the laser beam is always directed perpendicular to the workpiece in the cutting and non-cutting mode. According to a preferred embodiment of the method according to the invention, one or more countersunk holes are produced in a workpiece part which is connected to the rest of the workpiece. According to a preferred embodiment of the method according to the invention, the workpiece part is cut free from the workpiece after the countersunk holes have been produced. According to a preferred embodiment of the method according to the invention, the hole has a diameter which is equal to or smaller than a workpiece thickness of the workpiece.

According to a preferred embodiment of the method according to the invention, it comprises the following steps in this order:

Guiding the laser beam in cutting mode along a closed pre-hole cutting line, creating a pre-hole in the workpiece, guiding the laser beam in non-cutting mode one or more times along at least one closed countersink generation line, the countersink generation line being arranged in relation to the cutting line such that a the countersink surrounding the pilot hole is produced, which flows into the pilot hole,

Guide the laser beam in cutting mode along a closed End hole cut line, the end hole cut line being positioned relative to the pre-hole cut line such that the pre-hole is widened to create an end hole, the end hole being within the countersink when viewed perpendicularly through the workpiece.

According to a preferred embodiment of the method according to the invention, the laser beam is guided along a circular pre-hole cutting line. According to a preferred embodiment of the method according to the invention, the laser beam is guided along a circular end hole cutting line. According to a preferred embodiment of the method according to the invention, the circular final hole cutting line is arranged concentrically and at a radial distance from a circular pre-hole cutting line. Preferably, the laser beam is guided one or more times along at least one circular countersink generation line. According to a preferred embodiment of the method according to the invention, at least one circular countersink generation line is arranged concentrically and at a radial distance from the circular pilot hole cutting line. According to a preferred embodiment of the method according to the invention, during the enlargement of the preliminary hole, a nozzle tip of a jet nozzle from which the laser beam emerges is located within the countersink and below a plane defined by the workpiece surface facing the jet nozzle. According to a preferred embodiment of the method according to the invention, the preliminary hole is enlarged with a pulsed laser beam. The laser beam used in pulsed mode preferably has an average power of at least 200 W, a pulse peak power of at least 2000 W and a pulse frequency of between 10 Hz and 200 Hz. According to a preferred embodiment of the method according to the invention, the pilot hole and the countersink are each produced with a continuous-wave laser beam. According to a preferred embodiment of the method according to the invention, the pilot hole is actively cooled by contact with a fluid cooling medium before the pilot hole is enlarged. According to a preferred embodiment of the method according to the invention, a working gas jet of compressed working gas, which interacts with the laser beam in the cutting and non-cutting mode, is directed onto the workpiece for active cooling of the pilot hole. According to a preferred embodiment of the method according to the invention, before the laser beam is guided along the pre-hole cutting line, a slug to be cut out to produce the pre-hole is divided by the laser beam in the cutting mode. According to a preferred embodiment of the method according to the invention, when viewed perpendicularly through the workpiece, a shortest distance between the end hole and a surrounding countersink is limiting outer edge of countersinking is always at least 0.5 mm. According to a preferred embodiment of the method according to the invention, the shortest distance between the end hole and the outer edge of the countersink delimiting the surrounding countersink is always in the range of 0.5 mm to 10 mm. According to a preferred embodiment of the method according to the invention, a round preliminary hole is produced which has a diameter which is 0.5 to 2 mm smaller than a diameter of the final hole. According to a preferred embodiment of the method according to the invention, a radially innermost countersink generation line has a radial offset from the cutting edge of the pilot hole, which is from 0.25 to 1 mm. According to a preferred embodiment of the method according to the invention, the end hole has a diameter which is equal to or smaller than a workpiece thickness of the workpiece.

As is apparent from the foregoing, the present invention provides a novel method for laser beam machining of a workpiece, in which counterbored holes can be efficiently formed in a workpiece with high precision and quality in a simple and inexpensive manner. A countersunk hole can be made in two steps, with a first step creating a hole in the workpiece, followed by a second step forming a countersink around the hole (circumferential countersink). Optionally, a third step can be added, whereby the production of a countersunk hole then comprises three steps: in a first step, a hole is created in the workpiece, which represents a pilot hole, followed by a second step in which a countersink is formed around the pilot hole (Circumferential countersinking), followed by a third step in which the diameter of the pre-hole is widened so that a final hole is produced.

The melt formed when creating the countersink can be expelled very easily through the (pilot) hole downwards out of the workpiece. Any slag adhering to the walls of the (pre-)hole and to the lower workpiece surface in the area of the (pre-)hole is automatically removed with the optional widening of the hole, which then represents a pre-hole, so that a burr-free end hole with burr-free cutting edge is formed. There is no need for time-consuming mechanical post-processing to machine countersinks and remove burrs on the cut edges. An implementation of the method according to the invention in already existing laser beam processing devices is possible in a simple manner without having to provide complex technical measures for this purpose. Rather, through Mere intervention in the machine control a desired laser beam processing of a workpiece can be realized by the method according to the invention.

Reference character list

1 laser beam processing device

2 jet cutting device

3 jet head

4 work table

5 workpiece support

6 crossbars

7 guide carriages

8 laser beam source

9 workpiece

10 upper workpiece surface

11 lower workpiece surface

12 controller

13 jet nozzle

14 laser beam

15 working gas jet

16 (first) hole

17 end hole

18 lowering

19 beam axis

20 upper (pre-)hole cutting edge

21 lower (pre-)hole cut edge

21 (pre-punch) cutting line

22 end hole cutting line

23 (pre-) hole wall

24 end hole wall

25 top end hole cut edge

26 bottom end hole cut edge

27 outer countersink edge

28 inner countersink edge

29 subsidence generation line

30 flank

31 center axis

32 ridges

33 nozzle tip

Claims

patent claims

1 . Method for laser beam processing of a workpiece (9) with a focused laser beam (14), in which the laser beam (14) can be used in a mode that cuts or does not cut the workpiece (9) by changing the line energy of the laser beam (14), with the following steps in this order:

Guiding the laser beam (14) in cutting mode along a closed cutting line (21), creating a hole (16) in the workpiece (9), one or more guiding of the laser beam (14) in non-cutting mode along at least one closed line Countersink generating line (29), wherein the countersink generating line (29) is arranged to the cutting line (21) in such a way that a countersink (18) surrounding the hole (16) and opening into the hole (16) is generated.

2. Method for laser beam machining of a workpiece (9) according to claim 1, in which the laser beam (14) is guided along a circular cutting line (21).

3. Method for laser beam machining of a workpiece (9) according to one of claims 1 or 2, in which the laser beam (14) is guided one or more times along at least one circular countersink generation line (29).

4. Method for laser beam machining of a workpiece (9) according to claims 2 and 3, in which the at least one circular countersink generating line (29) is arranged concentrically and at a radial distance from the circular cutting line (21).

5. A method for laser beam machining of a workpiece (9) according to any one of claims 1 to 4, wherein the hole (16) and the countersink (18) are each produced with a laser beam (14) in the continuous wave.

6. Method for laser beam machining of a workpiece (9) according to one of Claims 1 to 5, in which, before the laser beam (14) is guided along the cutting line (21), a slug to be cut out to produce the hole (16) is cut out by the laser beam (14) is cut in cutting mode.

7. A method for laser beam machining of a workpiece (9) according to any one of claims 1 to 6, wherein in a vertical view through the workpiece (9) a shortest The distance between the hole (16) and an outer edge (27) of the countersink that surrounds the countersink (18) is always at least 0.5 mm.

8. Method for laser beam machining of a workpiece (9) according to claim 7, in which the shortest distance between the hole and the countersink (18) delimiting outer edge (27) is always in the range of 0.5 mm to 10 mm.

9. Method for laser beam machining of a workpiece (9) according to claim 1, with the following steps in this order:

Guiding the laser beam (14) in the cutting mode along a closed pre-hole cutting line (21), whereby a pre-hole (16) is produced in the workpiece (9), guiding the laser beam (14) in the non-cutting mode along at least one or more times a closed countersink generation line (29), the countersink generation line (29) being arranged relative to the cutting line (21) in such a way that a countersink (18) surrounding the pilot hole (16) is produced, which opens into the pilot hole (16),

Guiding the laser beam (14) in the cutting mode along a closed end hole cutting line (22), the end hole cutting line (22) being arranged in relation to the pre-hole cutting line (21) in such a way that the pre-hole (16) is used to create an end hole (17) is widened, the end hole (17) being in a vertical view through the workpiece (9) inside the countersink (18).

10. Method for laser beam machining of a workpiece (9) according to claim 9, in which the laser beam (14) is guided along a circular pre-hole cutting line (21).

11. A method for laser beam machining of a workpiece (9) according to claim 9 or 10, wherein the laser beam (14) along a circular end hole cutting line (22) is guided.

12. Method for laser beam machining of a workpiece (9) according to claims 10 and 11, in which the circular end hole cutting line (22) is arranged concentrically and at a radial distance from a circular pre-hole cutting line (21).

13. A method for laser beam machining of a workpiece (9) according to any one of claims 9 to 12, in which the laser beam (14) is guided one or more times along at least one circular countersink generation line (29).

14. Method for laser beam machining of a workpiece (9) according to claims 10 and 13, in which the at least one circular countersink generating line (29) is arranged concentrically and at a radial distance from the circular pre-hole cutting line (21).

15. Laser beam processing device (1) with a laser beam (14) guided by a beam head (3), which has an electronic control device (12) for controlling the laser beam processing of a workpiece (9), which is used for carrying out the method according to one of claims 1 to 14 is set up programmatically.