CN114473255A

CN114473255A - Method for producing countersunk holes

Info

Publication number: CN114473255A
Application number: CN202210193455.4A
Authority: CN
Inventors: F·塞普; P·马赫; C·魏斯
Original assignee: Ws Optical Technology Co ltd; Trumpf Werkzeugmaschinen SE and Co KG
Current assignee: Ws Optical Technology Co ltd; Trumpf Werkzeugmaschinen SE and Co KG
Priority date: 2021-10-25
Filing date: 2022-03-01
Publication date: 2022-05-13
Also published as: DE102021005297A1; CN217344054U9; CN217167005U; CN217344054U

Abstract

The invention relates to a method for laser beam machining a workpiece (9) by means of a focused laser beam (14), wherein the laser beam (14) can be used in a mode for cutting or for non-cutting the workpiece (9) by varying the unit length of the laser beam (14), comprising the following steps in the following order: in a cutting mode, directing a laser beam (14) along a closed cutting line (21), thereby creating a hole (16) in the workpiece (9); in the non-cutting mode, the laser beam (14) is guided one or more times along at least one closed countersunk line (29), wherein the countersunk line (29) is arranged relative to the cutting line (21) such that a countersunk head (18) is produced which surrounds the hole (16) and opens into the hole (16).

Description

Method for producing countersunk holes

Technical Field

The invention is based on the technical field of laser beam machining of metal workpieces by means of a focused laser beam and relates to a method for laser beam machining of plate-shaped or tubular workpieces, in which method a countersunk hole is produced in the workpiece.

Background

Commercially available laser cutting equipment enables automated manufacturing of parts of workpieces in large quantities and with high precision. In this case, the workpiece part is cut off from the metal workpiece by means of a laser beam along a cutting line, which corresponds to the contour of the workpiece part. In addition, holes, i.e. portions with a small diameter, can be introduced into the workpiece parts to be cut off at high speed by the movement of the laser beam along the circular cutting line.

Depending on the application of the cut-off workpiece part, the workpiece part may require elaborate mechanical reworking. The hole in which the countersunk head bolt is to be arranged in the subsequent application of the workpiece part is usually machined by cutting with a drill in order to form a countersunk head for receiving the head of the countersunk head bolt. In principle, the machining operation, which is carried out after the cutting-out of the workpiece part, is very costly in terms of time and also in terms of manpower in most cases, in particular the machining operation is often carried out manually. Furthermore, such reworking is costly, so that the production of the workpiece part is extended in an undesirable manner and becomes expensive. This is particularly relevant for the cutting and machining of the hole for producing the countersunk head, which is very time-consuming.

It is known in the patent literature to produce holes with countersunk heads by means of a laser beam. For example, document WO 2020225448 a1 shows a method in which a circular recess is first produced in a workpiece and subsequently a hole is introduced into the recess.

Disclosure of Invention

In contrast, the object of the present invention is to improve the conventional method in such a way that a countersunk hole in the workpiece can be produced by a focused laser beam without costly mechanical reworking, in particular for forming a countersink by means of a drill and removing burrs on the workpiece surface. In general, the creation of a countersunk hole and the fabrication of a workpiece portion having a countersunk hole should be able to be performed more quickly, inexpensively, and efficiently in an automated fashion.

This and further objects are achieved by a method for laser beam machining a workpiece according to the invention. The following also shows an advantageous embodiment according to the invention.

In the sense of the present invention, the term "workpiece" denotes a plate-like or tubular, typically metallic, component from which at least one workpiece part (a qualified piece) can be produced. Plate-like workpieces are typically planar or flat.

The laser beam is guided by a laser processing head and emerges at a distal nozzle. The laser beam is configured as usual in a focused, rotationally symmetrical beam cone with a central beam axis (axis of symmetry). The beam diameter represents the lateral extension of the beam or a physical parameter of the beam perpendicular to the propagation direction. In the case of focusing, the laser beam is focused by a focusing lens or a focusing mirror. The focal point of the laser beam is defined by the location at which the laser beam has its smallest cross-section or smallest beam diameter. The focal length describes the distance of the principal plane of the lens (or mirror principal plane) from the focal point of the ideally focused parallel beam. The smaller the focal distance, the more strongly the laser beam is focused and the smaller the focal spot diameter and vice versa.

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

The workpiece, in particular a plate-shaped workpiece, rests with its underside on a workpiece support. On the upper side of the workpiece, the workpiece has a (upper) workpiece surface. In the case of a plate-shaped workpiece, the workpiece surface is planar. If no other application is present, here and in addition the upper workpiece surface is understood to be the "workpiece surface", which is opposite to or faces the nozzle. The opposite workpiece surface is the workpiece underside, on which the workpiece is usually placed on a base (Unterlage).

The laser processing head for directing the laser and process gas jets 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 description of the invention, the reference system is always stationary relative to the workpiece, so that the laser processing head is considered to be moving and the workpiece is considered to be stationary. However, local considerations are not important whether the laser processing head or the workpiece or both are moving. In this case, it is likewise possible to move the workpiece instead of or in addition to the moving laser processing head.

The energy of the laser beam is related to the specific design of the laser source and is typically given in joules (J). The power of the laser beam (i.e., the energy per unit time), typically measured in joules per second (J/s) or watts (W), describes the optical output power of a continuous wave laser (CW) or the average power of a pulsed laser. A pulsed laser is also characterized by its pulse energy, which is directly proportional to the average power of the laser and inversely proportional to the repetition rate of the laser. "energy density" means the energy of the laser beam with respect to the irradiated surface of the workpiece. Energy density, for example, measured as J/mm²。

In addition to energy density, the speed of movement of the laser processing head or the laser beam, i.e. the time: how long a certain surface of the workpiece is irradiated by the laser beam. Generally, the term "energy per unit length (Streckenenergie)" is used for this purpose. This is the laser beam power absorbed by the workpiece per unit speed of the laser processing head or laser beam, measured for example in watts/(mm/sec). If the power of the laser beam is stated in watts (W) as joules per second (J/s), the unit length can therefore be measured as J/mm.

Therefore, important in laser machining is the energy per unit length of the laser beam, wherein the energy absorbed by the workpiece is related to the energy density. The energy absorbed by the workpiece at a certain power of the laser beam is dependent on the size of the beam spot on the workpiece and accordingly on the beam diameter at the location where the laser beam reaches the workpiece. The beam diameter of the laser beam on the workpiece is determined by the focal point position, i.e. the position of the focal point of the laser beam relative to the workpiece (perpendicular shortest distance), in particular relative to the workpiece surface (to which the laser beam is directed) or relative to the workpiece holder. If the workpiece is located in the divergent region of the beam cone (the focal point is above the surface of the workpiece that the laser beam reaches), the beam diameter on the workpiece can be increased by increasing the spacing between the focal point and the workpiece, and vice versa. The energy density of the laser beam and thus the energy absorbed by the workpiece, which energy is introduced into the energy per unit length, can thus be varied in a targeted manner by changing the beam diameter at the workpiece, by changing the focal point position. The larger the beam diameter, the less energy is absorbed by the workpiece, and vice versa. In the case of a laser, the beam intensity outside the focal point varies with respect to the cross-section. Ideally, the power intensity is a gaussian curve (Gau β profile). In any case, the energy density is smaller towards the edges, especially outside the focal point.

The unit length can also be related to the speed of the laser beam, i.e. the speed of movement of the laser processing head is also referred to as the "feed speed". The greater the feed speed, the shorter the determined face of the workpiece is illuminated, and vice versa. Thus, the unit length of the laser beam can be reduced with increasing feed speed, and vice versa.

Of course, the energy density and thus the energy per unit length can also be varied by varying the power of the laser beam itself.

Further possibilities are known to the person skilled in the art: the energy introduced into the workpiece is varied, in particular by varying the type and/or composition of the process gas used in the laser machining.

According to the invention, the workpiece is machined in such a way that a countersunk or sunk hole, i.e. a hole with a countersunk portion, is produced in the workpiece by means of the laser beam. The holes of the countersunk head generally belong to the part of the workpiece to be cut off, which part of the workpiece is to be cut off from the workpiece (for example a sheet metal) together with a plurality of further parts of the workpiece, i.e. the part of the workpiece is also connected to the remaining grid when the holes of the countersunk head are produced. However, it is also conceivable for the workpiece itself to be a part of the workpiece which has been cut off previously by means of a laser beam (for example a laser beam).

In the method according to the invention for machining a workpiece by means of a focused laser beam, the laser beam is used in a "cut workpiece mode" or a "non-cut workpiece mode". In the cutting mode, the unit length of the laser beam on the workpiece can be so large that the laser beam cuts (separates) the machined workpiece so as to penetrate the workpiece, for example in order to produce a cutting gap. In the non-cutting mode, the unit length of the laser beam on the workpiece can be so small that the laser beam does not cut (does not separate) the machined workpiece and thus does not penetrate the workpiece, whereby a countersunk head can be produced.

The energy per unit length of the laser beam or the energy per unit length of the laser beam on the workpiece can be varied by a change in the energy or power of the laser beam, a change in the feed speed through the laser processing head, a focusing/defocusing of the laser beam and in particular by a change in the beam diameter at the workpiece surface, in particular by a change in the focal position relative to the workpiece. In order to vary the energy introduced into the workpiece, the type and/or composition of the process gas used in the laser machining can additionally be varied.

The change in the energy per unit length of the laser beam on the workpiece is preferably effected by a change in the focal position relative to the workpiece, which is preferably caused by a change in the height of the laser processing head above the workpiece or above the workpiece surface facing the laser processing head, i.e. the laser processing head is typically moved in the vertical direction with a component of motion perpendicular to the workpiece surface. In the method according to the invention, the following method steps are carried out gradually, but not necessarily, directly in succession in time:

in a first step, in a cutting mode, a laser beam is guided along a closed, preferably circular, closed cutting line, thereby producing a closed, preferably circular, cutting gap. A part (central piece (Butzen)) is cut out of the workpiece. By removing the central slug from the workpiece, a hole (through-penetration) is created in the workpiece, which is preferably circular in cross-section. In any case, the center slug has fallen downward due to its own weight, thereby creating a hole in the workpiece. The cross section of the bore relates to the plane of the workpiece or the workpiece surface facing the beam nozzle. Preferably, the hole is produced in the contour of the part of the workpiece to be cut out of the workpiece. The cutting line is a process line or a track along which the laser beam is guided, wherein it is understood that no cutting line is formed on the workpiece. Preferably, the cutting line is a circular line (circular trajectory).

If the bore is configured as a circle, its symmetry or central axis defines a radial direction, wherein, starting from the central axis, "radially inwards" points towards the central axis and "radially outwards" points away from the central axis.

Subsequently, in a second step, in a non-cutting mode, the laser beam is guided one or more times along at least one closed, preferably circular or spiral line (trajectory) (further referred to as "countersunk line"). For this purpose, the focal point position of the laser beam is preferably changed before the first guidance along the countersunk-head generating line in such a way that the laser beam has a larger beam diameter on the workpiece than when the hole is produced. The at least one countersunk-head generating line is arranged such that a countersunk head is generated around the hole, which countersunk head always opens into the hole. The countersunk head therefore deepens toward the bore and transitions directly into the bore. As with the cutting line, the countersunk line is also a process line or path along which the laser beam is guided, wherein no countersunk line is formed on the workpiece.

At least one countersunk generation line surrounds the cutting line and is always spaced apart from the cutting line. Preferably, the cutting line and the at least one sinker head generating line are each a circular line (circular trajectory), wherein the at least one sinker head generating line is arranged concentrically to the cutting line and at a radial distance. The at least one countersunk generating line is then arranged radially outwardly with respect to the cutting line, i.e. the diameter of the countersunk generating line is greater than the diameter of the cutting line.

The at least one countersunk-head generating line preferably extends along a cutting edge of the bore, which cutting edge surrounds the bore on the workpiece surface opposite the beam nozzle. The at least one countersink generating line may be within the closed cutting edge of the hole and/or outside the cutting edge. The at least one countersunk-head generating line may in particular have the same profile as the cutting edge of the hole. In the case of a circular path, the at least one countersunk head generating line can be arranged radially outward or radially inward of the likewise circular cutting edge of the hole. Preferably, the at least one countersunk generating line is arranged radially outward with respect to the circular cutting edge of the hole.

In the method according to the invention for laser beam machining of plate-shaped or tubular workpieces, a countersunk hole is produced in the workpiece. It has been found according to the present invention that: the countersunk bore can be produced in the metal workpiece with high edge quality in a particularly simple, reliable and efficient manner.

The method according to the invention for producing countersunk holes is a preferred part of a method in which a workpiece part is cut out of a workpiece, wherein the countersunk holes are produced in the part of the workpiece to be cut out which is also connected to the remaining grid. After the production of the countersunk hole, the workpiece part is removed from the workpiece, wherein this workpiece part can already be partially cut off during the production of the countersunk hole, but is always still fixedly connected to the remaining workpiece (remaining grid), for example by means of one or more webs (micro-or nano-joints) having a small dimension.

The above-described method is used for producing countersunk holes in workpieces, wherein in the case of producing a single countersunk hole. In a first step, a hole is produced in the workpiece, and after the hole is produced, a countersunk portion surrounding the hole is produced in a second step.

In a preferred embodiment of the method according to the invention, the hole has a diameter which is equal to or smaller than the workpiece thickness of the workpiece. As the inventors have shown, particularly small countersunk holes can be produced by the method according to the invention. As with the angled cut used to create the countersink, there is no risk of damage to adjacent holes when the countersink is formed.

According to a preferred embodiment of the method according to the invention, the countersunk holes are produced in three steps, wherein the two steps for producing countersunk holes are included. In this case, a hole is produced in the workpiece (by observing the hole of the individual countersunk head) in a first method step, a countersunk head surrounding the hole is produced in a second step, and the hole which has been produced is widened or widened in an additional third step.

The method with three steps for producing a countersunk hole is further explained, wherein, for easier reference, the hole produced in the workpiece in the first step is referred to as a "preformed hole" and the hole widened or widened in the third step is referred to as a "final hole". Accordingly, the term "pre-hole cutting line" is used for cutting lines used for producing pre-holes, whereas the term "final hole cutting line" is used for cutting lines used for producing final holes.

In a first step, in a cutting mode, a laser beam is guided along a closed, preferably circular, closed cutting line (also referred to as "pre-hole cutting line" as described above), thereby producing a closed, preferably circular, cutting slit. Where a part (central panel) is cut from the workpiece. By removing the central slug from the workpiece, a hole (through-penetration) is created in the workpiece, preferably circular in cross-section, also referred to as a "pre-hole" as described above. In any event, the center slug has fallen downward due to its own weight, thereby creating a preformed hole in the workpiece. The cross section of the preformed hole relates to the plane of the workpiece or the workpiece surface facing the beam nozzle. Preferably, the preformed hole is produced in the contour of the part of the workpiece to be cut from the workpiece. The pre-hole cutting line is a process-technical line or track along which a laser beam is guided, wherein it is understood that no pre-hole cutting line is formed on the workpiece.

If the preformed hole is configured as a circle, its symmetry or central axis defines a radial direction, wherein, starting from the central axis, "radially inwards" is directed towards the central axis and "radially outwards" is directed away from the central axis.

Subsequently, in a second step, in a non-cutting mode, the laser beam is guided one or more times along at least one closed, preferably circular or spiral line (trajectory) (otherwise referred to as "countersunk line" as described above). For this purpose, the focal point of the laser beam is preferably changed before the first guidance along the countersunk line in such a way that the laser beam has a larger beam diameter on the workpiece than when producing the preformed hole. The at least one countersunk head generating line is arranged such that a countersunk head is created around the preformed hole, which countersunk head always opens into the preformed hole. The countersunk portion therefore deepens towards the preformed hole and transitions directly into the preformed hole. As with the pre-hole cutting line, the countersunk line is also a process-technical line or track along which the laser beam is guided, wherein no countersunk line is formed on the workpiece.

At least one countersink generating line surrounds and is always spaced from the pre-hole cut line. Preferably, the pre-hole cutting line and the at least one countersink generating line are each circular lines (circular tracks), wherein the at least one countersink generating line is arranged concentrically and at radial intervals to the pre-hole cutting line. At least one countersunk generating line is then arranged radially outwardly with respect to the pre-hole cutting line, i.e. the diameter of the countersunk generating line is larger than the diameter of the pre-hole cutting line.

The at least one countersunk-head generating line preferably runs along a cutting edge of the preformed hole, which surrounds the preformed hole on the workpiece surface opposite the beam nozzle. The at least one countersink generating line may be within the closed cutting edge of the preformed hole and/or outside the cutting edge. The at least one countersunk head generating line may in particular have the same profile as the cutting edge of the preformed hole. In the case of a circular path, the at least one countersunk-head generating line can be arranged radially outward or radially inward with respect to the likewise circular cutting edge of the preformed hole. Preferably, the at least one countersunk generating line is arranged radially outwardly with respect to the circular cutting edge of the preformed hole.

Subsequently, in a third step, in a cutting mode, the laser beam is guided along a closed, preferably circular, cutting line (also referred to as "final hole cutting line" as described above), thereby producing a closed, preferably circular, cutting slit. Whereby a section, preferably hollow-cylindrical in cross-section, is cut from the workpiece. Before starting the guidance of the laser beam along the final hole cutting line, the focal point 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 countersunk head is produced. The final hole cutting line is a process line or a track along which the laser beam is guided, wherein no final hole cutting line is formed on the workpiece. In any case, the cut-off portion falls downward due to its own weight. The preformed hole is widened within the countersink by removing the portion from the workpiece. The widened hole is here produced from a prefabricated hole, also referred to as "final hole" as described above.

The final hole cutting line is arranged relative to the preformed hole cutting line such that the preformed hole is widened. The preformed hole is thus widened in the countersunk head, viewed perpendicularly to the plane of the workpiece, so that the final hole is also located in the countersunk head or in the edge of the countersunk head which delimits it on the workpiece surface facing the beam nozzle (first workpiece surface). A line of sight perpendicular to the first workpiece surface corresponds to the projection of the preformed and final holes and the countersunk head into the plane of the first workpiece surface. In the case of widening the preformed hole, the shortest dimension of the preformed hole, measured in the plane of the workpiece, is increased.

The third method step therefore involves directing the laser beam in the cutting mode along a closed final hole cutting line, which is arranged relative to the pre-hole cutting line in such a way that, viewed perpendicularly to the (planar) workpiece or to the plane of the workpiece surface facing the beam nozzle (first workpiece surface), the pre-hole is widened in the countersunk portion or in the edge of the countersunk portion that delimits the countersunk portion on the workpiece surface facing the beam nozzle (first workpiece surface), in order to produce the final hole. The final opening, which is produced by widening the preformed opening, is therefore also located in the countersink or in the edge of the countersink which delimits it on the workpiece surface facing the beam nozzle (first workpiece surface), viewed perpendicularly to the workpiece.

The final hole cutting line surrounds the pre-hole cutting line, wherein the final hole cutting line always has a non-zero distance to the pre-hole cutting line. Furthermore, the final hole cutting line is arranged in the edge of the closed workpiece surface facing the beam nozzle, which encloses the countersunk head.

Preferably, the pre-hole cutting lines and the final hole cutting lines are each circular lines (circular tracks), wherein the final hole cutting lines are arranged concentrically and with a radial distance from the pre-hole cutting lines in such a way that the diameter of the pre-holes is increased and, in this case, a final hole with a circular cross section is produced in the countersunk portion. The final hole cutting line is thus arranged radially outwardly with respect to the preformed hole cutting line, i.e. the diameter of the final hole cutting line is larger than the diameter of the preformed hole cutting line, such that the diameter of the final hole is larger than the diameter of the preformed hole. Furthermore, the final bore cutting line is arranged radially inward with respect to a preferably circular edge surrounding the countersink on the workpiece surface facing the beam nozzle.

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

The final hole cutting line is configured such that a part of the countersunk head is removed when the final hole is produced, wherein the countersunk head is not completely removed here, but a part of the countersunk head remains when the final hole is produced. Thus, viewed perpendicularly to the plane of the planar workpiece or first workpiece surface, the final hole is arranged in the countersunk portion. In the case of a circular countersink and a circular final hole, the countersink always has a larger diameter than the final hole.

In a preferred embodiment of the method according to the invention, the final bore has a diameter which is equal to or smaller than the workpiece thickness of the workpiece. As already explained, particularly small countersunk bores can be produced by the method according to the invention.

The designations "pre-hole" and "final hole" used in the above-described configuration of the method according to the invention for producing a countersunk hole by means of three steps are used to distinguish different stages of the method for producing a countersunk hole, wherein the final hole is produced by widening the pre-hole. The countersunk hole is made by creating a final hole in the countersink.

The inventors have found that: if a pre-drilled hole is first produced, a countersunk hole can be produced in the metallic workpiece with high edge quality in a particularly simple, reliable and efficient manner, so that the melt (slag) formed during the production of the countersunk head can be removed from the workpiece by means of a working gas jet through the pre-drilled hole. This advantageously makes it possible to avoid: burrs are formed on the surface of the workpiece facing the beam nozzle. This burr not only impairs the subsequent use of the countersunk head and may require elaborate reworking of the countersunk head, but may also lead to collisions with the jet nozzle in the worst case. Furthermore, the slag adhering to the wall of the preformed hole and to the cutting edge thereof on the workpiece surface facing away from the jet nozzle can advantageously be removed together during widening of the preformed hole, so that a final hole with a countersunk head (i.e. a countersunk hole) can be produced without burrs.

The method according to the invention for producing countersunk holes is a preferred part of a method in which a workpiece part is cut out of a workpiece, wherein the countersunk holes are produced in the part of the workpiece to be cut out which is also connected to the remaining grid. After the production of the countersunk holes, the workpiece parts are removed from the workpiece, wherein the workpiece parts can already be partially cut off during the production of the countersunk holes, but are always still fixedly connected to the remaining workpiece (remaining grid), for example by means of one or more webs (micro-or nano-joints) having a small dimension.

As used herein and in addition, the term "countersink" refers to a recess of a workpiece on a surface of a first workpiece. The countersunk head does not penetrate the workpiece. In contrast, the terms "gap", "hole", "pre-hole" and "final hole" respectively denote an opening or a through-penetration of the workpiece.

In the production of holes, in particular pre-drilled or final holes and countersunk heads, the beam axis of the laser beam is moved along a circular path with two mutually perpendicular motion components parallel to the plane of the workpiece or the first workpiece surface.

The laser beam for producing the countersunk head and the laser beam for producing the hole, in particular the preformed or final hole, preferably have different focal positions from one another. In particular, the focal point position of the laser beam is changed in such a way that the beam diameter at the workpiece is smaller when producing a hole, in particular a pre-drilled or final hole, than when producing a countersunk head. By means of this variation of the beam diameter on the workpiece, which is based on the change in the focal point position, it is possible to achieve that the energy per unit length of the laser beam on the workpiece and thus the energy introduced into the workpiece is smaller when producing countersunk heads than when producing holes, in particular prefabricated holes or final holes. The focal point position is preferably adjusted in a desired manner by a movement of the beam head perpendicular to the workpiece base or perpendicular to the first workpiece surface and is changed in such a way that a suitable energy per unit length is present on the workpiece for producing countersunk heads or holes, in particular prefabricated holes or final holes. Typically, the beam head is moved in a vertical direction. If the workpiece is located in the region of the divergence of the laser beam (the focal point is above the workpiece), the beam diameter on the workpiece can be reduced by movement of the beam head towards the workpiece (the spacing between the beam head and the workpiece is reduced). Conversely, the beam diameter on the workpiece can be increased by movement of the beam head away from the workpiece (increased spacing between the beam head and the workpiece). In creating holes, particularly pre-made or final holes, the focal point is typically near or within the workpiece. Additionally or alternatively to the movement of the beam head, the focal position of the laser beam can be optically changed.

Preferably, the unit length of the laser beam on the workpiece for producing the countersink can be less than 50%, less than 40%, less than 30%, less than 20%, less than 10% or even less than 1% of the unit length of the laser beam on the workpiece for producing the hole, in particular the pre-or final hole. This difference in energy per unit length preferably reflects beam diameter variations across the workpiece. Preferably, the beam diameter on the workpiece for producing the aperture, in particular the pre-fabricated or final aperture, 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 producing the countersink. In laser cutting devices which are currently in use, the beam diameter at the workpiece is typically 1/10 to 5/10mm during the separating process. For producing the countersunk head by means of a laser beam, the beam diameter on the workpiece is preferably at least 1.5mm and lies, for example, in the range from 3 to 25 mm.

The countersunk head is bounded on the workpiece surface facing the beam nozzle by a countersunk head edge. The countersink edge is the region of the workpiece in which the countersink begins to deepen. The holes in the countersunk head, in particular the preformed holes or the subsequent final holes, always have a distance from the edge of the countersunk head which is not zero, as viewed in the workpiece perpendicular to the plane. The countersink deepens towards the hole, in particular not only towards the preformed hole but also towards the final hole that is subsequently produced. The hole, in particular both the prefabricated hole and the final hole produced subsequently, therefore has the deepest position in the countersunk head and appears to be arranged on the bottom of the countersunk head, wherein the hole can preferably also occupy a central position in the countersunk head.

Preferably, the shortest distance between the aperture, in particular the final aperture, and the countersunk edge delimiting the countersunk head on the workpiece surface facing the beam nozzle, as viewed perpendicularly to the workpiece (i.e. in projection onto the first workpiece surface), is always at least 0.5mm, in particular at least 1mm, and lies, for example, in the range from 0.5mm to 10 mm.

In the method according to the invention, the countersunk head and/or the hole, in particular the preformed hole, is preferably produced by a laser beam in the form of a continuous wave. I.e. not switching off the laser beam during the production of the countersunk head and/or the hole, in particular the pre-drilled hole. In contrast, the widening of the preformed hole, in particular the increase in the diameter of the circular preformed hole, is preferably carried out with a pulsed laser beam. This has the following advantages: the material of the workpiece is not heated so strongly when widening the preformed hole, so that the melt produced at the sharp or clearly defined edge of the preformed hole can flow down well.

According to one advantageous embodiment of the method according to the invention, the energy per unit length of the laser beam on the workpiece is varied during the production of the countersunk head. By this measure, the depth and/or the shape of the countersunk head can be set in a targeted manner.

Typically, the beam axis of the laser beam is always directed perpendicular to the planar workpiece support or perpendicular to the plane of the first workpiece surface to be irradiated during the production of the countersunk head or hole, in particular the pre-drilled or final hole, i.e. the angle between the beam axis and the workpiece support is 90 °. This brings control-technical advantages. Furthermore, the costs for technical realization of the corresponding pivotability of the laser beam with respect to the plane of the workpiece holder can be saved. However, it is also conceivable to change the beam axis during the irradiation of the workpiece, wherein the beam axis, at least temporarily, adopts an angle of other than 90 ° relative to the plane of the workpiece support or of the first workpiece surface to be irradiated. The orientation of the laser beam can be achieved by the pivotability of the beam head (mechanically) and/or by the pivotability of the laser beam (optically). It may be advantageous, for example, to sweep a larger area of the workpiece by pivoting the laser beam during the production of the countersunk head.

According to a further advantageous embodiment of the method according to the invention, the beam nozzle is moved in time after the production of the countersunk head and before the widening of the preformed hole for the production of the final hole with at least one movement component directed toward the workpiece in such a way that during the widening of the preformed hole the nozzle tip of the beam nozzle from which the laser beam emerges lies within the countersunk head and therefore also lies below the plane defined by the workpiece surface facing the beam nozzle. The positioning of the beam nozzle close to the preformed hole or close to the part of the preformed hole remaining after the production of the countersunk head has particular advantages: a final hole having a very precise geometry can be produced and the melt occurring when the final hole is produced can be expelled from the workpiece particularly effectively through the preformed hole.

According to a further advantageous embodiment of the method according to the invention, the preformed hole (and also the countersink) is actively cooled in time by contact with a fluid cooling medium before widening the preformed hole. Preferably, for this purpose, a working gas beam consisting of compressed working gas, which interacts with the laser beam in the cutting and non-cutting mode, is directed at the workpiece without switching on the laser beam. This measure also makes it possible to: the metallic material of the pre-perforated edge on the workpiece surface facing away from the beam nozzle is stronger, so that the pre-perforated edge is sharply defined, which improves the flow-down of the melt when the final hole is produced. In this respect, it is particularly advantageous to combine active cooling of the preformed hole with the generation of the final hole by means of a pulsed laser beam, since both measures bring about the same advantageous effect. This applies increasingly if the beam nozzle sinks into the countersunk portion during the production of the final bore, which brings about a further improvement.

In the method according to the invention, at least one countersunk-head generating line is moved past the beam nozzle one or more times, wherein the laser beam is guided along the countersunk-head generating line. A single countersunk generating line may be provided here. Advantageously, the laser beam is guided along a single countersunk-head portion generating line a plurality of times for generating the countersunk head portion. According to one advantageous embodiment, a plurality of preferably concentric countersunk generating lines is provided for generating the countersunk head, which have a distance between two directly adjacent countersunk generating lines that is different from zero. Advantageously, the laser beam is directed along each of the plurality of countersunk head generating lines a plurality of times for generating the countersunk head. This can be advantageous in particular when producing countersunk heads having a large diameter.

According to a further advantageous embodiment of the method according to the invention, the central panel to be cut off for producing the hole, in particular the preformed hole, is cut in a cutting mode by the laser beam before the laser beam is guided along the cutting line, in particular the preformed hole cutting line. This measure ensures that: the cut central piece or parts thereof always fall downwards due to its own weight and the preformed hole is reliably empty so that the melt which subsequently occurs when the countersunk head is produced can be driven off the workpiece.

In the method according to the invention it may be advantageous to produce a preformed hole of circular shape having a diameter of 0.5 to 2mm, preferably about 1mm, smaller than the diameter of the final hole. This measure ensures that: the burrs in the region of the preliminary hole, which are produced when the countersink is produced, are reliably and safely removed when the final hole is produced.

It can furthermore be advantageous if the round-shaped countersunk generating line has a radial offset (radially outward) from the cutting edge of the round-shaped preformed hole in the plane of the workpiece surface facing the beam nozzle, which is at least 0.5mm, preferably at least 1mm and in particular approximately 2 mm. Advantageously, the countersunk head generating line is moved by the beam nozzle or the laser beam a plurality of times (preferably 2 to 25 times) for producing the countersunk head.

It may furthermore be advantageous to provide a plurality of circular, concentric countersunk generating lines, the diameter of which increases radially outwards by 0.5 to 2mm, respectively. Advantageously, the radially innermost countersunk generating line has a radial offset (radially outward) from the cutting edge of the preformed hole in the plane of the workpiece surface facing the beam nozzle, which radial offset is 0.25 to 1mm, wherein the radial offset of the directly adjacent countersunk generating line is likewise 0.25 to 1 mm. Advantageously, the countersunk head generating line is moved over (preferably over 2 to 25) a plurality of times in each case for generating a countersunk head.

It may also be advantageous to provide a helical counter sink generating line which has a diameter increase of 0.25 to 1mm when a complete revolution is completed. Advantageously, the trajectory is moved a plurality of times (preferably 2 to 25 times) after the target diameter is reached. In order to produce larger countersunk holes in particular, it can be advantageous, for example, for countersunk bolts from the size M8 (see, for example, standard DIN-EN-ISO 10642) to guide the laser beam along a helical countersunk-head generating line in the second method step in a non-cutting mode. In this case, the spiral countersink generating line can be moved first through by the laser beam from the inside to the outside (abgefahren) and then, preferably at half laser power, through again from the outside to the inside. By finally moving through the spiral countersink generating line from the outside to the inside at half laser power, the surface quality of the countersink, in particular the roughness on the surface of the countersink, can be improved.

If the countersunk head is intended to receive the head of a countersunk head bolt, it can furthermore be advantageous if the countersunk head generating line of the radially outermost circular configuration has a maximum diameter which is approximately smaller than the head of the countersunk head bolt which can be arranged in the bore. Generally, the number of countersunk lines is related to the diameter of the hole or preformed hole or to the thread diameter of the countersunk bolt to be installed and the desired depth of the countersunk portion. For a countersunk bolt with metric threads M3 to M6 (i.e. with a diameter of the preformed hole of 3 to 6 mm) typically at least two passes are required, wherein the typical number of passes lies between 2 and 25. For a countersunk bolt with metric threads M8 to M12 (i.e. with a diameter of the hole or pre-drilled hole of 8 to 12 mm) typically at least 5 passes, preferably at least 10 passes are required, wherein the typical number of passes lies between 10 and 25.

In the method according to the invention, the laser beam is brought into cutting and non-cutting modes, preferably by a change in the position of the focal spot. In the cutting mode, the nozzle tip which emits the laser beam preferably has a spacing of less than 2mm from the first workpiece surface facing the beam nozzle or from a plane defined by the first workpiece surface. Preferably, the countersunk head is produced in the non-cutting mode with a greater spacing of the beam nozzle from the first workpiece surface, which spacing is at least 30mm, in particular at least 40mm and particularly preferably about 50 mm. On the one hand, the laser beam is therefore sufficiently defocused and can reach the workpiece surface with a large beam diameter, wherein a lower working gas pressure (for example oxygen pressure) with a high degree of coverage of the machining region results. On the other hand, it can be ensured that: contamination of the nozzle tip and the protective gas by the upwardly sprayed slag does not occur.

In the production of the sink head, it can also be advantageous if the working gas (e.g. oxygen) has a gas pressure of less than 5bar, in particular 2bar to 3.5 bar. Furthermore, it can be advantageous if the feed speed of the beam nozzle is at least 4m/min when producing the countersunk head and the power of the laser beam (e.g. laser) used for the machining is at least 1500W.

In widening the preformed hole, in particular in increasing the diameter of a preformed hole of circular configuration, it can be advantageous if the laser beam (for example laser beam) used in pulsed operation has an average power of at least 200W, a pulse peak power of at least 2000W and a pulse frequency between 10Hz and 200 Hz.

In the above-described configuration of the method according to the invention, a plurality of countersunk holes is in any case produced. In this case, it is possible to produce the countersink directly after the production of the corresponding hole, in particular the prefabricated hole, and if necessary directly after the final hole. However, it is also possible to carry out corresponding method steps for other bores, in particular final bores with associated countersinks (i.e. countersunk bores), between the method steps for producing identical bores, in particular final bores with associated countersinks (i.e. countersunk bores). For example, it may be advantageous to first continue the method steps for producing a hole for a further countersink (for example producing a preformed hole for a further countersink) after producing a countersink on a preformed hole, so that the preformed hole and the countersink have time for cooling. In particular, a plurality of preformed holes can be produced directly one after the other, followed by the countersunk head being produced directly one after the other in the preformed hole, and in addition, the final hole being produced directly one after the other. Of course, the respective method steps for producing a plurality of countersunk holes can be carried out in any manner when producing these countersunk holes, provided that it is ensured that: in the case of the same countersunk hole, the production of the prefabricated hole, the countersunk portion, and the final hole are sequentially performed in this order.

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

The invention also extends to a laser beam machining device having a laser beam guided by a beam head for laser beam machining of a plate-shaped or tubular workpiece, having an electronic control device for controlling/regulating the laser beam machining of the workpiece, which is provided for (programmatically) carrying out the method according to the invention.

The invention also extends to a program code means of an electronic control device for data processing for a laser beam machining apparatus, which program code means contain control commands which cause the control device to carry out the method according to the invention.

Furthermore, the invention also extends to a computer program product (storage medium) with stored program code means for an electronic control device suitable for data processing for such a laser beam machining apparatus, which program code means contain control commands which cause the control device to execute the method according to the invention.

Of course, the above-described configurations of the present invention may be used alone or in any combination without departing from the scope of the present invention.

Drawings

The invention will now be further elucidated on the basis of embodiments, in which reference is made to the appended drawings. The figures show:

fig. 1 is a schematic view of an exemplary laser beam machining apparatus for carrying out the method for laser beam machining a plate-like or tubular workpiece according to the present invention;

FIGS. 2A-2C are configurations for a method of laser beam machining a workpiece in which a countersunk hole is created in accordance with the present invention;

3A-3D are additional configurations of a method for laser beam machining a workpiece according to the present invention in which a countersunk hole is created;

fig. 4 is a flow chart of a method for laser beam machining a workpiece according to the invention, in which method a countersunk bore is produced.

Detailed Description

If reference is first made to fig. 1, a laser beam machining apparatus for beam cutting a plate-shaped workpiece is shown diagrammatically. A laser beam machining apparatus, generally designated by reference numeral 1, comprises a beam cutting device 2 with a beam head 3 and a table 4 with a workpiece support 5 for a workpiece 9 (not shown in fig. 1, see fig. 2A-2C, 3A-3D), for example a planar sheet material. The workpiece support 5 is spanned by a cross beam 6, which is guided movably in the first axial direction (x direction).

A guide slide 7 for the beam head 3 is mounted on the beam 6, which guide slide is guided on the beam 6 so as to be movable in a second axial direction (y direction) perpendicular to the first axial direction. The beam head 3 can thus be moved parallel in a plane spanned by the two axial directions and relative to the horizontal workpiece support 5, for example. The beam head 3 is also configured to be movable in its height in a third axial direction (z direction) perpendicular to the plane, whereby the spacing perpendicular to the workpiece support 5 or the workpiece 9 can be changed. In the case of a horizontal workpiece support 5, the z direction corresponds to the direction of gravity. The beam head 3 has a beam nozzle 13 on its side facing the workpiece support 5, which tapers conically towards the workpiece support 5. The beam head 3 serves to guide a laser beam 14 and a process or working gas beam, which emerge from a distal nozzle tip 33 (see fig. 2A, for example). The laser beam 14 is generated by a laser beam source 8 and is guided to the beam head 3, for example, by means of a beam guide and a plurality of deflection mirrors or optical cables. The laser beam may be directed in a beam set (i.e., focused) at the workpiece by a focusing lens or adaptive optics. Due to the movability of the beam head 3 in the first axis direction (x direction) and the second axis direction (y direction), it is possible to move to every arbitrary point on the workpiece 9 with the laser beam 14.

The workpiece 9 has two workpiece surfaces 10, 11 lying opposite one another (see, for example, fig. 2A), wherein the first or upper workpiece surface 10 faces the beam nozzle 13 and the second or lower workpiece surface 11 faces away from the beam nozzle 13. By means of the high degree of movability of the beam head 3 in the z direction, the working distance of the beam nozzle 13 from the workpiece 9 can be adjusted by varying the distance from the upper workpiece surface 10. The spacing of the beam head 3 from the upper workpiece surface 10 can be adjusted before, during and after laser beam machining. The focal position of the laser beam 14 can be adjusted by varying the distance between the beam nozzle 13 and the upper workpiece surface 10 and by optical elements, for example adaptive optics, in the beam head 3.

The working gas jet 15 is generated by a gas jet generating device, not shown. As inert process or working gas, for example, helium (He), argon (Ar) or nitrogen (N) is used₂). Oxygen (O) is generally used as the reactive working gas₂). It is also known to use gas mixtures. 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 onto the machining point and there reaches the workpiece 9 at a (initial) gas pressure (which typically lies in the range of 2 to 20 bar) predetermined by the gas jet generating device. The working gas jet 15 is used to expel the melt produced in the laser machining by means of gas pressure through a through-opening (e.g. a preformed hole 16, see for example fig. 2B) in the workpiece 9 produced by the laser beam 14.

As shown in fig. 1, the planar workpiece support 5 is composed, for example, of a plurality of support elements, which have, for example, triangular-shaped bearing point tips (trackpunktspitzen) which together define a bearing plane for the workpiece 9 to be machined. The support elements are designed here, for example, as elongated support webs which each extend in the y direction and are arranged next to one another in the x direction, for example, at a constant distance apart in a parallel arrangement. Not shown in detail is a suction device by means of which cutting fumes, debris particles and small waste pieces generated during the beam cutting can be sucked away.

The program-controlled control device 12 serves to control/regulate the method according to the invention for laser beam machining a workpiece 9 in a laser beam machining apparatus 1.

Reference is now made to fig. 2A to 2C and 3A to 3D, in which exemplary configurations of the method according to the invention for laser beam machining a workpiece 9 by means of the beam apparatus 1 of fig. 1 are shown visually. For reasons of simplicity of illustration and for reasons of a sufficient understanding of the invention, the beam nozzle 13 and the laser beam 14 and the working gas beam 15 are each shown only in connection with the workpiece 9. The workpiece 9 is located in a horizontal position on the workpiece support 5 as usual.

Reference is first made to fig. 2A to 2C, in which a plate-shaped workpiece 9 with two planar workpiece surfaces 10, 11 and a vertical cross-sectional view of a beam nozzle 13 are each schematically illustrated in a left-hand side view. The right-hand side views of fig. 2A to 2C show the method steps in a schematic manner in a visual manner from the respective top views.

The upper workpiece surface 10 faces the beam nozzle 13 and the lower workpiece surface 11 faces away from the beam nozzle 13. The laser beam 14 and the working gas beam 15 emitted from the nozzle tip 33 of the beam nozzle 13 reach the workpiece 9. The laser beam 14 has a focused beam cone shape with a central beam axis 19. The central beam axis 19 and therefore the laser beam 14 are directed perpendicularly to the upper workpiece surface 10 or perpendicularly to the plane of the plate-shaped workpiece 9.

In fig. 2A, the beam nozzle 13 is moved from the starting position at least with a vertical movement component toward the workpiece 9, so that the beam nozzle 13 has a small working distance a from the workpiece 9. Preferably, the working distance a of the beam nozzle 13 from the upper workpiece surface is less than 2 mm. The focal position of the laser beam 14 causes a narrow beam spot with a small beam diameter on the workpiece 9. The focal point position and thus the beam diameter are selected such that the unit length of the laser beam 14 on the workpiece 9 can be so large that the laser beam 14 is suitable for cutting or separating the workpiece 9. Thus, the laser beam 14 is in the cutting mode.

As shown in fig. 2A, the cutting laser beam 14 is guided along a circular pre-hole cutting line 21 for producing the (pre) hole 16, thereby producing a circular closed cutting slit. The workpiece part (central piece) which is circular or disc-shaped in cross section is thereby completely cut off from the workpiece 9. The central slug that is cut falls downward due to its own weight. By removing the central slug from the workpiece 9, a preformed hole 16 of circular cross-section of a determined diameter is created in the workpiece 9. The diameter of the (pre) hole 16 is measured in the plane of the workpiece 9. A widened hole, i.e. a final hole 17 (see fig. 2C), can optionally be produced in a further method by widening the diameter from the (pre-) hole 16.

The circular (pre) hole 16 is a through hole according to its manner of manufacture and penetrates the workpiece 9, wherein the (pre) hole 16 is surrounded by a pre-hole wall 23 formed by the workpiece 9, the pre-hole wall 23 extending continuously from the upper workpiece surface 10 to the lower workpiece surface 11. On the upper workpiece surface 10, the (pre-) holes 16 are surrounded by a circular upper (pre-) hole cutting edge 20, and on the lower workpiece surface 11, the (pre-) holes 16 are surrounded by a circular lower (pre-) hole cutting edge 21. The two (pre)

hole cutting edges

21, 22 are each part of a (pre) hole wall 23. In fig. 2A, the (pre-drilled) cutting edge 21 and the upper (pre-drilled) cutting edge 20 are shown relatively far apart from one another on the basis of a clearer illustration, wherein this is not necessarily the case in practice, of course. The circular (prefabricated) bore 16 is configured radially symmetrically with respect to its central axis 31 (see fig. 2B). In the plane of the workpiece 9, a radial direction is defined with respect to the (pre) hole 16 and its central axis 31.

The method may optionally be supplemented by a step which is carried out before the cutting (prefabrication) of the holes 16. This step is preferably used if (pre) holes 16 with a diameter of at least 7mm are to be made and/or if there is a workpiece 9 thickness of at least 4 mm. In this case, the central panel to be cut off later on in its contour is divided into smaller parts by one or more cutting slits, whereby it is always possible to: the central slug reliably and safely falls down from the workpiece 9 and the cut-off (pre-fabricated) hole 16 is always empty. For example, in the region of the central panel to be cut, intersecting cutting slits are introduced, if necessary by overlapping spiral cutting slits. A possible method for dividing the central mass is described, for example, in document US 8716625B 2.

After the circular (pre) hole 16 is created, a circular countersink 18 concentric with the (pre) hole 16 is created. This is also shown visually in accordance with fig. 2B.

For the production of the countersunk head 18, the beam nozzle 13 has a relatively large working distance a from the first workpiece surface 10 or the workpiece 9, wherein the workpiece 9 is located in the expansion region of the laser beam 14, which results in a wide beam spot with a large beam diameter on the workpiece 9. The beam head 3 or the beam nozzle 13 is moved away from the workpiece 9 for this purpose at least with a vertical movement component, so that a larger working distance a exists between the beam nozzle 13 and the first workpiece surface 10 than is the case with the (pre-) holes 16. The working distance a for producing the countersunk head 18 is, for example, at least 6 times, in particular at least 10 times, greater than the working distance a for producing the (pre) opening 16 and is preferably at least 30mm, particularly preferably at least 40mm and in particular approximately 50mm, with a range of 30mm to 50mm being preferred. Accordingly, the beam spot and the beam diameter on the workpiece 9 are 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 focal point of the laser beam 14 is located well above the workpiece 9. The focal point position and the beam diameter of the laser beam 14 are selected such that the unit length of the laser beam 14 on the workpiece 9 can be small and the laser beam 14 only produces the countersinking region 18 and does not penetrate the workpiece 9 (non-separating machining). The laser beam 14 is in a non-cutting mode.

In the production of the countersunk head 18, the non-cutting laser beam 14 is moved in a (horizontal) plane parallel to the plane of the workpiece holder 5, wherein the laser beam 14 is moved along at least one countersunk head generating line 29. At least one countersunk head generating line 29 runs concentrically to the (pre-drilled) cutting line 21 and along the upper (pre-drilled) hole cutting edge 20, wherein the countersunk head generating line 29 corresponds, for example, to the upper (pre-drilled) hole cutting edge 20 or is preferably displaced further outward for this purpose. This means that: the countersunk generating line 29 has a diameter which is equal to or preferably greater than the diameter of the upper (pre-made) hole cutting edge 20.

For generating countersunk head 18, a single countersunk head generating line 29 may be provided, wherein laser beam 14 is moved along countersunk head generating line 29 one or more times for generating countersunk head 18. Preferably, laser beam 14 is moved along countersunk generation line 29 a plurality of times for generating countersunk head 18 (typically beam nozzle 13 is moved 2 to 20 times). The offset (i.e. the radial distance) of the countersunk-head generating line 29 from the upper (pre) hole cutting edge 20 is preferably at least 0.5mm, particularly preferably at least 1mm and in particular 2 mm. The countersunk head generating line 29 must be arranged such that the resulting countersunk head 18 directly adjoins the (prepared) hole 16, i.e. opens into the (prepared) hole 16.

Multiple countersunk head generation lines 29 may also be provided for the generation of countersunk heads 18, wherein the laser beam 14 is moved one or more times along each of the countersunk head generation lines 29 for generating the countersunk head 18. Preferably, laser beam 14 is moved along each of the countersunk head generation lines 29 a plurality of times for generating countersunk head 18 (typically beam nozzle 13 is moved 2 to 20 times). The plurality of countersunk generating lines 29 are arranged concentrically with respect to each other. The offset (i.e. the radial spacing) between the countersunk-head generating line 29 and the upper (pre-fabricated) hole cutting edge 20 or two directly adjacent countersunk-head generating lines 29 is preferably 0.25mm to 1 mm. The diameter increase of two directly adjacent countersunk generating lines 29 is therefore preferably 0.5mm to 1 mm. The countersunk head generating line 29 must be arranged such that the resulting countersunk head 18 directly adjoins the (prepared) hole 16, i.e. opens into the (prepared) hole 16.

The circular movement of the laser beam 14 around the central axis 31 of the (pre) hole 16 along the at least one countersunk generation line 29 is illustrated in fig. 2B schematically by means of arrows.

It is also conceivable to move the laser beam 14 along a helically configured countersunk head generating line 29 for generating the countersunk head 18. Preferably, an increase of the radius of the helical trajectory from 0.25mm to 1mm is achieved in a correspondingly complete revolution. After reaching the target diameter, it is advantageous to move over the target diameter several times. In this case, too, the countersunk-head generating line 29 must be arranged in such a way that the countersunk head 18 produced is directly adjacent to the (pre) hole 16, i.e. opens into the (pre) hole 16.

The countersunk head 18 is a recess of the workpiece 9 on the first workpiece surface 10. The counter-sunk portion 18 surrounds the (pre) opening 16 concentrically, wherein the counter-sunk portion 18 extends from a (radially) outer counter-sunk edge 27 from the upper workpiece surface 10 into the workpiece 9 to a (radially) inner counter-sunk edge 28, but not to the lower workpiece surface 11, i.e. the counter-sunk portion 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 the region of the workpiece 9 where the countersink 18 begins to deepen toward the interior of the workpiece 9. The inner countersunk edge 28 is defined as the region of the workpiece 9 at which the countersunk head 18 merges into the remainder of the (pre) hole 16, wherein the inner countersunk edge 28 is formed by the (pre) hole wall 23. The sides 30 of the countersink 18 extend from the outer countersink edge 27 to the inner countersink edge 28.

In the radial direction, the countersunk head 18 can be provided with a defined cross-sectional shape in a freely selectable manner. In particular, the focal point position and thus the beam diameter can be varied during the production of the countersunk head 18 in order to specifically adjust the depth and/or the cross-sectional shape of the countersunk head 18. As the beam diameter on the workpiece 9 decreases, the countersink 18 becomes deeper, i.e. the sides 30 of the countersink 18 become steeper, compared to if the beam diameter on the workpiece 9 increases, the countersink 18 becomes flatter, i.e. the sides 30 of the countersink 18 become less steep. Fig. 2B shows an exemplary countersunk portion 18 with inclined flanks 30 having a slope of approximately 45 °, wherein a greater or lesser slope of the flanks is also possible.

The countersunk head 18 can in principle be used in any manner, wherein it is preferably provided in this embodiment as a head for receiving a countersunk screw. Preferably, the radially outermost countersink generating line 29 has the following diameter for generating the countersink 18: which is slightly smaller than the maximum diameter of the head of the countersunk bolt to be arranged in the countersunk portion 18. The number of countersunk lines 29 is dependent on the diameter of the (prepared) hole 16 or on the thread diameter of the bolt to be installed and the desired depth of the countersunk portion 18. In any case, for a (pre) bore 16 for receiving a countersunk bolt having a metric thread size M3 to M6 (i.e. in the case of a diameter of the (pre) bore 16 of 3 to 6 mm), it is necessary for the beam nozzle 13 to be moved at least twice over the (pre) bore 16The same countersink creates line 29, wherein the typical number of passes is between 2 and 25. For a countersunk bolt having metric thread sizes M8 to M12, the amount moved is in any case at least 5, preferably at least 10 and typically between 10 and 25. As process or working gas, oxygen (O) is used, for example, in the production of countersink 18₂) It has a gas pressure of, for example, less than 5bar, in particular between 2 and 3.5 bar. The feed speed of the beam nozzle 13 in the production of the countersunk head 18 is preferably at least 4m/min and the laser power of the laser beam 14 is preferably at least 1500W.

The (pre) bores 16 advantageously allow the melt (slag) formed during the production of the countersunk head 18 to flow off very well downwards and thus prevent: the melt reaches the upper workpiece surface 10 of the workpiece 9 and solidifies there and forms burrs. This burr not only impairs the subsequent use of the countersunk head 18, but may also require elaborate reworking of the countersunk head 18 and, in the worst case, may also lead to collisions with the jet nozzle 13. By means of the optional division of the central piece to be cut off when producing the (pre) opening 16, it can always be ensured that: the (pre) opening 16 is empty and the melt accumulated during the production of the countersunk head 18 is reliably and safely removed by means of the working gas through the (pre) opening 16. This is a great advantage of the present invention.

Likewise, the melt may deposit on the (pre) hole wall 23, in particular also in the region of the lower (pre) hole cutting edge 21, and form a burr 32 after cooling, as is shown visually in fig. 2B. However, this burr 32 is advantageously removed together when optionally widening (pre-fabricated) hole 16 in order to produce final hole 17, so that a final hole 17 with burr-free final hole wall 24 can be produced. If this further step is performed, the hole 16 produced so far constitutes a "preformed hole" which is widened in its diameter to a final hole 17.

Furthermore, the optional widening of the diameter of the hole or pre-fabricated hole 16 in order to produce the final hole 17 is described:

in this case, it is also apparent from fig. 2C that the preformed hole 16 is widened after the countersunk head 18 has been produced, or that the remaining part of the preformed hole after the countersunk head 18 has been produced is widened.

To increase the diameter of the preformed hole 16, the laser beam 14 is used in a cutting mode similar to that used to create the preformed hole 16. The beam nozzle 13 has a relatively small working distance a from the first workpiece surface 10, which results in a narrow beam spot with a small beam diameter on the workpiece 9. For this purpose, the beam head 3 or the beam nozzle 13 is moved at least with a vertical component of motion toward the workpiece 9, so that a smaller working distance a exists between the beam nozzle 13 and the first workpiece surface 10 than when the countersunk head 18 is produced. The focal point position and thus the beam diameter of the laser beam 14 are selected such that the unit length of the laser beam 14 on the workpiece 9 can be relatively large and penetrates the workpiece 9 (separation machining).

In widening the preformed hole 16, the cutting laser beam 14 is guided along the circular final hole cutting line 22, thereby producing a circular closed cutting slit. The final hole cutting line 22 is arranged concentrically to the preformed hole cutting line 21 and is spaced radially outward therefrom, i.e. has a larger diameter than the preformed hole cutting line 21. The final hole cutting line 22 is located between the preformed hole cutting line 21 and the outer countersunk edge 27 in the radial direction, with the following criteria: the radial area of side 30 is removed, but not the entire side 30, i.e. countersink 18, remains partially. The final hole 17 is thus produced in the counter-sunk portion 18. When widening the preformed hole 16, a disc with a hollow cylindrical cross section is completely cut from the workpiece 9. The disk falls downward by its own weight, so that the disk is removed from the workpiece 9.

By widening the preformed hole 16, a final hole 17 of circular cross-section is produced in the workpiece 9, which final hole has a larger diameter than the preformed hole 16. The final hole 17 is surrounded by a final hole wall 24 formed through the workpiece 9 and extends from an upper final hole cutting edge 25 (which is located between the upper workpiece surface 10 and the lower workpiece surface 11) to a lower final hole cutting edge 26, which is formed by the lower workpiece surface 11. The diameter D of the final hole 17 is preferably between 0.5 and 2mm and is in particular about 1mm larger than the diameter of the previously produced preformed hole 16. This can be achieved: the burrs 32 adhering to the prefabricated hole wall 32 and to the lower workpiece surface 11 in the region of the lower prefabricated hole cutting edge 21 are reliably and safely removed.

Preferably, the pulsed laser beam 14 (pulsed laser beam) is used when widening the preformed hole 16 in order to produce the final hole 17. This advantageously makes it possible for the workpiece 9 to heat up less strongly when the final hole 17 is produced, so that the metal material of the workpiece 9 is stronger at the machining point and a well-defined or sharp lower final hole cutting edge 26 is produced, which facilitates the flow-down of the melt when widening the preformed hole 16. This measure helps to prevent: the melt is deposited mainly on the lower workpiece surface 11 and forms burrs there.

Preferably, a pulsed laser beam 14 (laser beam) is used, which has an average power of at least 200W and a pulse peak power of at least 2000W and a pulse frequency between 10Hz and 200 Hz. Depending on the workpiece material and the desired edge quality, nitrogen (N), compressed air or oxygen (O) is used₂) As the working gas.

As fig. 2C shows, the beam nozzle 13 is advantageously moved downward so far that the final opening 17 is produced, that the beam nozzle 13 is sunk into the countersunk portion 18, i.e. the nozzle tip 33 is located below the upper workpiece surface 10 or below the plane defined by the upper workpiece surface 10. This has particular advantages: not only the laser beam 14 but also the working gas jet 15 are fanned out less strongly at the impact point on the workpiece 9: (

) So that the final hole 17 can be cut more accurately and can be manufactured with a particularly high precision. Thereby also preventing: the melt formed in the production of the final hole 17 is deposited on the upper workpiece surface 10 and forms a burr there. Furthermore, the melt can be expelled particularly efficiently through the preformed hole 16 by the particularly strongly focused working gas jet 15, so that the deposition of the melt on the upper workpiece surface 10 is also counteracted. This is a great advantage that can be achieved by this measure.

Reference is now made to fig. 3A to 3D, in which a further exemplary embodiment of the method according to the invention for laser beam machining a workpiece 9 by means of the beam apparatus 1 of fig. 1 is shown visually in a schematic manner. The method steps of fig. 3A, 3B and 3D correspond to the method steps of fig. 2A, 2B and 2C, wherein reference is made to the above description of fig. 2A, 2B and 2C in order to avoid unnecessary repetitions. The configuration according to the invention shown in perspective in fig. 3A to 3D differs from the configuration shown in perspective in fig. 2A to 2C only in the method steps of fig. 3C.

Thus, active cooling of the countersink 18 and the pre-hole 16 (or the remainder of the pre-hole 16) is achieved by a gaseous or liquid cooling medium in time after the countersink 18 is created (fig. 3B) and before the pre-hole 16 is widened to create the final hole 17 (fig. 3D). As is shown visually in fig. 3C, for this purpose, a working gas is advantageously used from a working gas jet 15, wherein the laser beam 14 is switched off. The impact point on the workpiece 9 is typically loaded with a working gas having an (initial) gas pressure in the range of 2 to 20 bar. The expanding working gas thus leads to a very effective cooling of the metal workpiece 9, wherein the hotter the workpiece 9 to be cooled, the better the cooling effect. By active cooling, the metal material of the workpiece 9 is made stronger, so that the lower pre-hole cutting edge 26 is precisely defined, which facilitates the flow-down of the melt through the pre-hole 16. This measure also contributes to the possibility of very accurate adjustment of the geometry of the final bore 17. Furthermore, the adhesion of burrs on the lower workpiece surface 11 can be resisted.

A flow chart of the method according to the invention is shown in fig. 4. The method comprises at least three stepwise steps.

In step I, a laser beam is first guided in a cutting mode along a closed (pre-drilled) cutting line, thereby producing a (pre-drilled) hole in the workpiece. Subsequently, in step II, the laser beam is guided in a non-cutting mode one or more times along at least one closed countersunk line, wherein the countersunk line is arranged such that a countersunk portion is produced around the (pre) hole, which countersunk portion leads into the (pre) hole.

Then, in an optional step III, the laser beam is guided in a cutting mode along a closed final hole cutting line, wherein the final hole cutting line is arranged such that the hole (which is now a prefabricated hole) is widened in the countersunk portion and thereby a final hole is produced.

Optionally, the central panel to be cut off for producing the (pre) hole is divided in a cutting mode by the laser beam before the laser beam is guided along the (pre) hole cutting line in time.

Optionally, the preformed hole is actively cooled by contact with a fluid cooling medium prior to widening the preformed hole, preferably by working gas of a working gas jet directed at the workpiece.

Example 1:

countersunk heads for countersunk bolts having metric thread sizes M3-M6 are produced by means of a laser beam.

First, a preformed hole having a diameter which is about 1mm smaller than the average core hole diameter of the countersunk head bolt is cut out so that the melt accumulated in the next step when the countersunk head portion is produced can be expelled through the preformed hole.

Subsequently, the trajectory is generated by means of a large distance (approximately 50mm) of the beam nozzle from the upper workpiece surface and the ignited laser beam moving over a circular countersunk head with a diameter of 5mm to 15mm, oxygen (O) being used as the working gas₂). The number of passes is dependent on the depth of the countersunk portion to be introduced, wherein in each case 2 to 25 passes are carried out. Thereby creating a countersunk head for the head of the countersunk head bolt. Instead moving over a spiral trajectory.

The preformed hole is then cut to standard size by a laser beam used in a pulsed operation, wherein the final hole diameter is about 1mm larger than the diameter of the preformed hole. This ensures that the slag adhering to the preformed hole and in particular to the lower workpiece surface in the region of the cutting edges of the lower preformed hole is reliably removed. Advantageous cutting parameters are: pulsed average laser power (pulse frequency 10 Hz): 400W, pulse peak power: 3000W or 6000W, feed: 0.1m/min, the spacing between the beam nozzle and the upper workpiece surface: 1.2mm, pressure of working gas: 3.3 bar.

Example 2:

countersunk heads for countersunk bolts having a metric thread size M8-M12 are produced by means of a laser beam.

The division of the central panel is carried out before the cutting of the preformed holes, by: a cutting slit in the shape of a cross with an overlapping spiral is introduced into the central piece to be cut. Thereby ensuring that: the central mass of the preformed hole falls reliably and the preformed hole is therefore always empty, so that the melt accumulated when the countersink is produced can be expelled through the preformed hole. Then, a preformed hole having a diameter less than about 1mm of the average core hole diameter of the countersunk bolt is cut.

Subsequently, the trajectory is generated by means of a large distance (approximately 50mm) of the beam nozzle from the upper workpiece surface and the ignited laser beam moving over a circular countersunk head with a diameter of 10mm to 15mm, oxygen (O) being used as the working gas₂). The number of passes is dependent on the depth of the countersunk portion to be introduced, wherein in each case 10 to 25 passes are carried out. Thereby creating a countersunk head for the head of the countersunk head bolt. Instead, moves through a spiral trajectory.

The preformed hole is then cut to standard size by a laser beam used in a pulsed operation, wherein the final hole diameter is about 1mm larger than the diameter of the preformed hole. Advantageous cutting parameters: pulsed average laser power (pulse frequency 10 Hz): 400W, pulse peak power: 3000W or 6000W, feed: 0.1m/min, the spacing between the beam nozzle and the upper workpiece surface: 1.2mm, pressure of working gas: 3.3 bar.

Example 3:

the countersunk head for a countersunk bolt having a metric thread size M8 was produced by means of a laser beam in 8mm structural steel.

The division of the central panel is carried out before the cutting of the preformed holes, by: a cutting slit in the shape of a cross having an overlapping spiral is introduced into the center panel to be cut. Oxygen (O) is used as the working gas₂) Nitrogen (N) or compressed air. A preformed hole having a diameter of 8mm, which is less than about 1mm the average core hole diameter of the countersunk bolt, is then cut.

Subsequently, the laser beam is moved over by means of a large distance (approximately 50mm) of the beam nozzle from the upper workpiece surface and the ignitionCircular countersunk head generating track with a diameter of 12.6mm, in which oxygen (O) is used as the working gas₂). 17 passes were made in which a countersunk head of 14mm diameter and 4.4mm to 4.5mm depth was produced in the plate. Instead, moves through a spiral trajectory. Advantageous laser parameters: laser power: 4000W, feeding: 10m/min, the spacing (A) between the beam nozzle and the upper workpiece surface: 50mm, pressure of working gas: 3.3bar, focal diameter: 210 μm/150 μm.

Then, a 9mm diameter preformed hole was cut to a standard size by a laser beam used in a pulsed operation, in which oxygen (O) was used as a working gas₂). Advantageous cutting parameters: pulsed average laser power (pulse frequency 10 Hz): 400W, pulse peak power: 4000W, feed: 0.7m/min, the spacing (A) between the beam nozzle and the upper workpiece surface: 0.7mm, pressure of working gas: 17bar, focal diameter: 210 μm.

As has been brought about by the above description, the invention provides a novel method for laser beam machining workpieces, in which method the countersunk holes can be produced in the workpiece in a simple and cost-effective manner with high precision and quality. The countersunk hole can be produced in two steps, wherein in a first step a hole is produced in the workpiece, followed by a second step in which a countersunk head (surrounding countersunk head) is constructed around the hole. Optionally, a third step may be added, wherein the production of the countersunk hole then comprises three steps: in a first step, a hole is produced in the workpiece, which hole forms a preformed hole, followed by a second step, a counter-sunk part (surrounding counter-sunk part) is constructed around the preformed hole, followed by a third step, in which the preformed hole is widened in its diameter, so that a final hole is produced.

The melt formed in the production of the countersunk head can be driven off the workpiece very well downwards through the (pre) hole. The residues possibly adhering to the wall of the (pre) hole and to the lower workpiece surface in the region of the (pre) hole are automatically removed together when the hole is optionally widened, which then constitutes the pre-hole, so that a burr-free final hole is formed, which has burr-free cutting edges. The complex mechanical reworking for the cutting-in of the countersunk head and for the removal of the burr at the cutting edge can be dispensed with. The implementation of the method according to the invention in already existing laser beam machining installations can be carried out in a simple manner, for which no elaborate technical measures have to be provided. The desired laser beam machining of the workpiece by the method according to the invention can be realized by a simple intervention in the machine control.

List of reference numerals

1 laser beam machining apparatus

2-beam cutting device

3 beam head

4 working table

5 workpiece support

6 crossbeam

7 guide slide block

8 laser beam source

9 workpiece

10 upper workpiece surface

11 lower workpiece surface

12 control device

13-beam nozzle

14 laser beam

15 working gas jet

16 (prefabricated) holes

17 final hole

18 countersunk head

19 beam axis

20 upper (prefabricated) hole cutting edge

21 lower (prefabricated) hole cutting edge

21 (PRE-PRODUCT) HOLE CUTTING LINE

22 final hole cutting line

23 (prefabricated) hole wall

24 final hole wall

25 final hole cutting edge

26 lower final hole cutting edge

27 outer countersunk edge

28 inner countersunk edge

29 countersunk generating line

30 side surface

31 central axis

32 burrs

33 nozzle tip

Claims

1. A method for laser beam machining a workpiece (9), which is carried out by means of a focused laser beam (14), in which method the laser beam (14) can be used in a mode of cutting the workpiece (9) or in a mode of non-cutting the workpiece (9) by changing the unit length of the laser beam (14), the method having the following steps in the following order:

-in a cutting mode, directing the laser beam (14) along a closed cutting line (21), thereby producing a hole (16) in the workpiece (9),

-in a non-cutting mode, directing the laser beam (14) one or more times along at least one closed countersunk head generating line (29), wherein the countersunk head generating line (29) is arranged with respect to the cutting line (21) such that a countersunk head (18) surrounding the hole (16) is created, which countersunk head opens into the hole (16).

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

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

4. Method for laser beam machining a workpiece (9) according to claims 2 and 3, in which method the at least one circular countersunk generation line (29) is arranged concentrically and at a radial spacing with respect to the circular cutting line (21).

5. Method for laser beam machining a workpiece (9) according to claim 1 or 2, in which method the holes (16) and the countersunk heads (18) are each produced in the form of a continuous wave by means of the laser beam (14).

6. The method for laser beam machining a workpiece (9) according to one of claims 1 to 5, in which method a central panel to be cut off for producing the hole (16) is divided by the laser beam (14) in the cutting pattern before the laser beam (14) is guided along the cutting line (21).

7. The method according to claim 1 or 2 for laser beam machining a workpiece (9), in which method the shortest distance between the hole (16) and an outer countersunk edge (27) bounding the surrounding countersunk head (18) is always at least 0.5mm when the workpiece (9) is viewed perpendicularly.

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

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

-in the cutting mode, directing the laser beam (14) along a closed pre-hole cutting line (21), thereby creating a pre-hole (16) in the workpiece (9),

-in the non-cutting mode, directing the laser beam (14) one or more times along at least one closed countersunk generation line (29), wherein the countersunk generation line (29) is arranged with respect to the preformed hole cutting line (21) such that a countersunk portion (18) is created around the preformed hole (16), which countersunk portion opens into the preformed hole (16),

-in the cutting mode, the laser beam (14) is guided along a closed final hole cutting line (22), wherein the final hole cutting line (22) is arranged relative to the pre-hole cutting line (21) such that the pre-hole (16) is widened for producing a final hole (17), wherein the final hole (17) is located within the countersink (18) when the workpiece (9) is viewed perpendicularly.

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

11. Method for laser beam machining a workpiece (9) according to claim 9, in which method the laser beam (14) is directed along a circular final hole cutting line (22).

12. Method for laser beam machining a workpiece (9) according to claims 10 and 11, in which method the circular final hole cutting lines (22) are arranged concentrically and at a radial spacing with respect to the circular pre-hole cutting lines (21).

13. Method for laser beam machining a workpiece (9) according to claim 9, in which method the laser beam (14) is directed along at least one circular countersunk generation line (29) one or more times.

14. Method for laser beam machining a workpiece (9) according to claims 10 and 13, in which method the at least one circular countersunk generation line (29) is arranged concentrically and at a radial spacing with respect to the circular pre-hole cutting line (21).

15. The method for laser beam machining of a workpiece (9) according to claim 9, in which method a nozzle tip (33) of a beam nozzle (13) that emits the laser beam (14) is located within the countersink (18) and below a plane defined by a workpiece surface (10) facing the beam nozzle (13) during enlarging the pre-made hole (16).

16. Method for laser beam machining a workpiece (9) according to claim 9, in which method the enlargement of the preformed hole (16) is effected by means of a laser beam (14) running in a pulsed manner.

17. Method for laser beam machining a workpiece (9) according to claim 16, in which method the laser beam used in pulsed operation has an average power of at least 200W, a pulse peak power of at least 2000W and a pulse frequency between 10Hz and 200 Hz.

18. Method for laser beam machining a workpiece (9) according to one of claims 9 to 17, in which method the preformed hole (16) and the countersunk head (18) are each produced in the form of a continuous wave by means of a laser beam (14).

19. Method for laser beam machining a workpiece (9) according to claim 9, in which method the preformed hole (16) is actively cooled by contact with a fluid cooling medium before the preformed hole (16) is enlarged in time.

20. Method for laser beam machining a workpiece (9) according to claim 19, in which method a working gas beam (15) of compressed working gas co-acting with the laser beam (14) in the cutting mode and in the non-cutting mode is directed onto the workpiece (9) for the active cooling of the preformed hole (16).

21. Method for laser beam machining a workpiece (9) according to claim 9, in which method the central panel to be cut off for producing the preformed hole (16) is divided in the cutting pattern by the laser beam (14) before the laser beam (14) is directed along the preformed hole cutting line (21).

22. The method according to claim 9 for laser beam machining a workpiece (9), in which method the shortest distance between the final hole (17) and an outer countersunk edge (27) bounding the surrounding countersunk head (18) is always at least 0.5mm when the workpiece (9) is viewed perpendicularly.

23. Method for laser beam machining a workpiece (9) according to claim 22, in which method the shortest distance between the final hole (17) and an outer countersink edge (27) bounding a surrounding countersink (18) is always in the range of 0.5mm to 10 mm.

24. Method for laser beam machining a workpiece (9) according to claim 9, in which method a circular preformed hole (16) is produced, the diameter of which is 0.5 to 2mm smaller than the diameter of the final hole (17).

25. Method for laser beam machining a workpiece (9) according to claim 1 or 2, in which method the laser beam (14) is directed along a single countersunk-head generation line (29) only once in order to produce the countersunk head (18).

26. Method for laser beam machining a workpiece (9) according to claim 1 or 2, in which method the laser beam (14) is guided a plurality of times along a single countersunk-head generation line (29) in order to produce the countersunk head (18).

27. Method for laser beam machining a workpiece (9) according to claim 1 or 2, in which method a plurality of countersunk-head generating lines (29) are provided for producing the countersunk head (18), wherein two directly adjacent countersunk-head generating lines (29) always have a spacing which is not zero, and wherein, for producing the countersunk head (18), the laser beam (14) is guided one or more times along each of the plurality of countersunk-head generating lines (29).

28. Method for laser beam machining a workpiece (9) according to claim 27, in which method a plurality of circular concentric countersunk head generating lines (29) are provided, which increase in diameter radially outwards by 0.5 to 2mm, respectively.

29. The method for laser beam machining a workpiece (9) according to claims 1 and 28, in which method the radially innermost counter-sunk generating line has a radial offset of 0.25 to 1mm from the cutting edge of the hole (16).

30. The method for laser beam machining a workpiece (9) according to claims 9 and 28, in which method the radially innermost counter-sunk generating line has a radial offset of 0.25 to 1mm from the cutting edge of the pre-drilled hole (16).

31. Method for laser beam machining a workpiece (9) according to claim 1 or 2, in which method the laser beam (14) is guided one or more times along at least one helical countersink generating line (29).

32. Method for laser beam machining a workpiece (9) according to claim 31, in which method a helical counter-sunk generating line is provided, which increases in diameter by 0.25 to 1mm on completion of a complete revolution.

33. The method for laser beam machining a workpiece (9) according to claim 1 or 2, in which method the unit length of the laser beam (14) on the workpiece (9) in the non-cutting mode can be smaller than the unit length of the laser beam (14) on the workpiece (9) in the cutting mode by a percentage value selected from the group consisting of 50%, 40%, 30%, 20%, 10% and 1%.

34. Method for laser beam machining of a workpiece (9) according to claim 33, in which method the unit length of the laser beam (14) can be varied by varying the beam diameter of the laser beam (14) on the workpiece surface (10) of the workpiece (9).

35. Method for laser beam machining a workpiece (9) according to claim 1 or 2, in which method the beam diameter of the laser beam (14) on the workpiece (9) in the cutting mode is smaller than the beam diameter in the non-cutting mode by a percentage value selected from the group consisting of 50%, 40%, 30%, 20%, 10% and 1%.

36. Method for laser beam machining of a workpiece (9) according to claim 34, in which method the beam diameter of the laser beam (16) on the workpiece surface (10) of the workpiece (9) is changed by changing the focal position relative to the workpiece (9).

37. Method for laser beam machining of a workpiece (9) according to claim 36, in which method the focal position of the laser beam (16) relative to the workpiece (9) is changed by moving a beam nozzle (13) for emitting the laser beam (14) with a component of motion perpendicular to the workpiece surface (10).

38. Method for laser beam machining of a workpiece (9) according to claim 1 or 2, in which method the distance of a beam nozzle (13) for emitting the laser beam (14) from the workpiece surface (10) is less than 2mm in the cutting mode and at least 30mm in the non-cutting mode.

39. Method for laser beam machining a workpiece (9) according to claim 1 or 2, in which method the beam axis of the laser beam (14) is oriented perpendicularly to the workpiece (9) at all times in the cutting mode and in the non-cutting mode.

40. Method for laser beam machining of a workpiece (9) according to claim 1 or 2, in which method one or more countersunk holes are produced in the part of the workpiece that is connected to the remaining workpiece (9).

41. The method for laser beam machining of a workpiece (9) according to claim 40, in which method the workpiece part is cut off from the workpiece (9) after the hole of the countersink is produced.

42. The method for laser beam machining a workpiece (9) according to claim 1, in which method the hole (16) has a diameter equal to or smaller than a workpiece thickness of the workpiece (9).

43. The method for laser beam machining of a workpiece (9) according to claim 9, in which method the final hole (17) has a diameter equal to or smaller than the workpiece thickness of the workpiece (9).

44. A laser beam machining apparatus (1) having a laser beam (14) guided by a beam head (3), having an electronic control device (12) for controlling the laser beam machining of a workpiece (9), which control device is provided for the programmed execution of a method according to one of claims 1 to 43.

45. Program code means for an electronic control device adapted for data processing for a laser beam machining apparatus (1) according to claim 44, said program code means comprising control commands for causing said control device (12) to perform the method according to any one of claims 1 to 43.

46. Storage medium having stored program code means for an electronic control device adapted for data processing for a laser beam machining apparatus (1) according to claim 44, said program code means containing control commands for causing the control device (12) to perform the method according to any one of claims 1 to 43.