DE102021005297A1 - Method of creating countersunk holes - Google Patents

Abstract

The invention relates to a method for laser beam machining of a workpiece (9) that is planar at least in sections, using a focused laser beam (14), in which the laser beam (14) is converted into a beam that cuts or does not cut the workpiece (9) by changing the path energy of the laser beam (16). cutting mode can be used, with the following steps in this order: - guiding the laser beam (14) in the cutting mode along a closed pre-hole cutting line (21), whereby a pre-hole (16) is produced in the workpiece (9), - a - or multiple guiding of the laser beam (14) in the non-cutting mode along at least one closed countersink generation line (29), the countersink generation line (29) being arranged in relation to the pre-hole cutting line (21) in such a way that a countersink surrounding the pre-hole (16) ( 18) is generated, which opens into the pre-hole (16),- guiding the laser beam (14) in the cutting mode along a closed end-hole cutting line (22), the end-hole cutting line (22) being so relative to the pre-hole cutting line (21) is arranged that the pilot hole (16) is widened within the countersink (18) to produce an end hole (17).

Description

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

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

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

The generation of holes with countersinks by means of a laser beam is known in the patent literature. So shows WO 2020225448 A1 a process in which a circular depression is first created in a workpiece and then a hole is made within the depression.

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

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

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

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

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

The workpiece, in particular a plate-shaped workpiece, rests with a workpiece underside on a workpiece support. On the upper side of the workpiece, the workpiece has a (top) workpiece surface. In the case of a plate-shaped workpiece, the workpiece surface is flat. Unless otherwise used, the upper-side workpiece surface that is opposite or facing the nozzle is understood here and below as “workpiece surface”. The opposite workpiece surface, on which the workpiece usually rests on a base, is the workpiece underside.

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

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

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

In addition to the energy density, the traversing speed of the laser processing head or laser beam is important for the laser processing of the workpiece, i.e. the time for how long a certain area of the workpiece is irradiated by the laser beam. It is customary to use the term “line energy” for this. This is the power of the laser beam absorbed by the workpiece per speed of the laser processing head or laser beam, e.g. measured in watts/(mm/s). If the power of the laser beam is given in watts (W) as joules per second (J/s), the energy per unit area is measured in J/mm.

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

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

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

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

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

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

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

Preferably, the path energy of the laser beam on the workpiece is changed by changing the focus position relative to the workpiece, which is preferably effected by changing the height of the laser processing head above the workpiece or the workpiece surface facing the laser processing head, i.e. the laser processing head is moved with a movement component perpendicular to the workpiece surface typically move in the vertical direction.

• Zunächst wird der Laserstrahl im schneidenden Modus entlang einer geschlossenen, vorzugsweise kreisförmig-geschlossenen, Schnittlinie, im Weiteren als „Vorloch-Schnittlinie“ bezeichnet, geführt, wodurch ein geschlossener, vorzugsweise kreisförmig-geschlossener, Schnittspalt erzeugt wird. Hierbei wird ein Teil (Butzen) aus dem Werkstück ausgeschnitten. Durch Entfernen des Butzens vom Werkstück wird ein vorzugsweise im Querschnitt kreisrundes Loch (Durchbrechung), im Weiteren als „Vorloch“ bezeichnet, im Werkstück erzeugt. In aller Regel fällt der Butzen schon durch sein Eigengewicht nach unten weg, wodurch das Vorloch im Werkstück erzeugt wird. Der Querschnitt des Vorlochs bezieht sich auf die Ebene des planen Werkstücks oder der der Strahldüse zugewandten Werkstückoberfläche. Das Vorloch wird vorzugsweise innerhalb der Kontur eines aus dem Werkstück auszuschneidenden Werkstückteils erzeugt. Die Vorloch-Schnittlinie ist eine prozesstechnische Linie bzw. Bahn, entlang welcher der Laserstrahl geführt wird, wobei es sich versteht, dass die Vorloch-Schnittlinie am Werkstück nicht ausgebildet ist.

In the method according to the invention, the following method steps are carried out successively, but not necessarily in immediate succession:

• First, the laser beam is guided in the cutting mode along a closed, preferably circular-closed, cutting line, hereinafter referred to as “pre-hole cutting line”, whereby a closed, preferably circular-closed, cutting gap is produced. A part (slug) is cut out of the workpiece. By removing the slug from the workpiece, a hole (perforation) with a preferably circular cross-section, hereinafter referred to as a “pre-hole”, is produced in the workpiece. As a rule, the slug falls down due to its own weight, which creates the pilot hole in the workpiece. The cross-section of the pilot hole refers to the plane of the flat workpiece or the workpiece surface facing the jet nozzle. The pilot hole is preferably produced within the contour of a workpiece part to be cut out of the workpiece. The pre-hole cutting line is a process engineering line or path along which the laser beam is guided, it being understood that the pre-hole cutting line is not formed on the workpiece.

If the pilot hole is circular, its symmetry or central axis defines a radial direction, starting from the central axis, “radially inward” being directed towards the central axis and “radially outward” being directed away from the central axis.

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

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

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

The laser beam is then guided in the cutting mode along a closed, preferably circular, cutting line, referred to below as the “end hole cutting line”, whereby a closed, preferably circular-closed cutting gap is produced. As a result, a part that is preferably hollow-cylindrical in cross section is cut out of the workpiece. Before the laser beam begins to be guided along the end hole cutting line, the focus position of the laser beam is preferably changed in such a way that the laser beam has a smaller beam diameter on the workpiece than when the countersink was produced. The end hole cutting line is a process engineering line or path along which the laser beam is guided, the end hole cutting line not being formed on the workpiece. As a rule, the cut-out part falls away under its own weight. Removing this part from the workpiece widens the pilot hole inside the countersink. A widened hole, hereinafter referred to as the "end hole", is created from the pre-hole.

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

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

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

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

In this process step, the final hole is brought to a predetermined (desired) final dimension, in particular a diameter.

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

In the method according to the invention for laser beam machining of a plate-shaped or tubular workpiece, countersunk holes are produced in the workpiece. The terms "pilot hole" and "final hole" are used only to distinguish different phases of the process of making a countersink hole, where the final hole results from an enlargement of the pilot hole. With After creating the final hole within the countersink, the countersunk hole is made.

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

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

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

When creating the pre-hole, end hole and countersink, the beam axis of the laser beam is moved along circular paths with two mutually perpendicular movement components parallel to the plane of the workpiece or the first workpiece surface.

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

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

A countersink is made on the workpiece surface facing the jet nozzle by a Sen limited. The countersink edge is the area of the workpiece where the countersink begins to deepen. The pre-hole or later end hole located within the countersink in a vertical view through the flat workpiece always has a non-zero distance to the edge of the countersink. The countersink deepens both towards the pre-hole and towards the end-hole produced later. Both the pilot hole and the final hole produced later have a deepest position within the countersink and are arranged at the bottom of the countersink, so to speak, whereby they preferably also occupy a centered position within the countersink.

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

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

According to an advantageous embodiment of the method according to the invention, a path energy of the laser beam on the workpiece is changed during the production of the countersink. This measure allows the depth and/or shape of the depression to be adjusted in a targeted manner.

Typically, the beam axis of the laser beam is always directed perpendicularly to the flat workpiece support or perpendicular to the plane of the first workpiece surface to be irradiated during the production of countersinking, preliminary or final drilling, i.e. the angle between the beam axis and the workpiece support is 90°. This entails technical control advantages. In addition, costs for the technical implementation of a corresponding pivotability of the laser beam relative to the plane of the workpiece support can be saved. However, it is also conceivable for the beam axis to be changed when the workpiece is irradiated, with the beam axis at least temporarily assuming an angle other than 90° to the workpiece support or to the plane of the irradiated first workpiece surface. The laser beam can be aligned by pivoting the beam head (mechanically) and/or by pivoting the laser beam (optically). For example, a larger area of the workpiece can be covered by pivoting the laser beam while the countersinking is being produced, which can be advantageous.

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

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

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

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

In the method according to the invention it can be advantageous if a round preliminary hole is produced which has a diameter which is 0.5 to 2 mm, preferably approx. 1 mm, smaller than a diameter of the final hole. This measure can ensure that any burr produced in the area of the pre-hole during the production of the countersink is reliably and safely removed when the end hole is produced.

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

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

Furthermore, it can be advantageous if a spiral-shaped countersinking line is provided, which has an increase in diameter of 0.25 to 1 mm when it has completed a complete revolution. Advantageously, after reaching the target diameter, this path is traversed several times (preferably 2 to 25 passages).

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

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

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

When widening the pre-hole, in particular increasing the diameter of a round pre-hole, it can be advantageous if a laser beam used in pulse mode (e.g. laser beam) has an average power of at least 200 W, a pulse peak power of at least 2000 W and a pulse frequency between 10 Hz and has 200 Hz.

In the above-described configurations of the method according to the invention, as a rule, many countersunk holes are produced. It is possible here that after the production of a respective preliminary hole, the countersinking is produced immediately thereafter and then the final hole is produced immediately thereafter. However, it is also possible that between the respective method steps for producing the same end hole with associated depression (i.e. countersunk hole), respective method steps for other end holes with associated depressions (i.e. countersunk holes) are carried out. For example, after creating a countersink on one pilot hole, it may be advantageous to first proceed with a process step for another countersunk hole (e.g. creating the pilot hole for the other countersunk hole) so that the countersunk pilot hole has time to cool. In particular, many pre-holes can be produced in immediate succession, followed by the countersinks in the pre-holes being produced in immediate succession, further followed by the end holes being produced in immediate succession. It goes without saying that when producing a plurality of countersunk holes, the respective method steps for producing the countersunk holes can be carried out in any manner, as long as it is ensured that in the case of the same countersunk hole, the production of the pilot hole, countersink and final hole are produced in this order done one after the other.

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

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

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

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

character list

• 1 eine schematische Darstellung einer beispielhaften Laserstrahlbearbeitungsvorrichtung zur Ausführung des erfindungsgemäßen Verfahrens zur Laserstrahlbearbeitung eines platten- oder rohrförmigen Werkstücks;
• 2A-2C eine Ausgestaltung des erfindungsgemäßen Verfahrens zur Laserstrahlbearbeitung eines Werkstücks, bei dem abgesenkte Löcher erzeugt werden;
• 3A-3D eine weitere Ausgestaltung des erfindungsgemäßen Verfahrens zur Laserstrahlbearbeitung eines Werkstücks, bei dem abgesenkte Löcher erzeugt werden;
• 4 ein Flussdiagramm des erfindungsgemäßen Verfahrens zur Laserstrahlbearbeitung eines Werkstücks, bei dem abgesenkte Löcher erzeugt werden.

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

• 1 a schematic representation of an exemplary laser beam processing device for carrying out the method according to the invention for laser beam processing of a plate-shaped or tubular workpiece;
• 2A-2C an embodiment of the method according to the invention for laser beam machining of a workpiece in which countersunk holes are produced;
• 3A-3D a further embodiment of the method according to the invention for laser beam machining of a workpiece, in which countersunk holes are produced;
• 4 a flow chart of the method according to the invention for laser beam machining of a workpiece in which countersunk holes are produced.

Detailed description of the drawings

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

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

The workpiece 9 has two opposite workpiece surfaces 10, 11 (see e.g 2A) , wherein a first or upper workpiece surface 10 faces the jet nozzle 13 and a second or lower workpiece surface 11 faces away from the jet nozzle 13 . Because the blasting head 3 can be moved vertically in the z-direction, the working distance of the blasting nozzle 13 from the workpiece 9 can be adjusted by changing the distance from the upper workpiece surface 10 . The distance of the beam head 3 from the upper workpiece surface 10 can be adjusted before, during and after the laser beam processing. The focal position of the laser beam 14 can be adjusted by changing the distance between the jet nozzle 13 and the first workpiece surface 10 and by means of optical elements in the jet head 3, for example adaptive optics.

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

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

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

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

First be the 2A until 2C considered, wherein the plate-shaped workpiece 9 with the two flat workpiece surfaces 10, 11 and the jet nozzle 13 are shown in a vertical sectional view in a schematic manner in the left figures. The right figures of the 2A until 2C illustrate the process steps in a schematic way based on respective views.

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

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

As in 2A shown, the cutting laser beam 14 is guided along a circular pre-hole cutting line 21 to produce a pre-hole 16, whereby a circular-closed cutting gap is produced. As a result, a workpiece part (slug) with a round or disc-shaped cross section is completely cut out of the workpiece 9 . The cut-out slug falls away under its own weight.

By removing the slug from the workpiece 9 , a pilot hole 16 with a round cross section and a specific diameter is produced in the workpiece 9 . The diameter of the pre-hole 16 is measured in the plane of the workpiece 9. In the further process, a widened hole, namely the end hole 17, is produced from the pre-hole 16 by widening the diameter (see FIG 2C ).

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

Optionally, the method can be supplemented by a step that is carried out before the pilot hole 16 is cut. This step is preferably used when pilot holes 16 are to be produced with a diameter of at least 7 mm and/or the workpiece 9 is at least 4 mm thick. Here, the slug to be cut later on its contour is cut into smaller parts by one or more cutting gaps, which can always ensure that the slug falls reliably and safely down out of the workpiece 9 and the cut-out preliminary hole 16 is always free. For example, in the area of the slug to be cut out, intersecting kerfs are introduced, possibly superimposed by a kerf in spiral form. A possible method for splitting up the slug is, for example, in US8716625B2 described.

After the round pre-hole 16 has been produced, a round countersink 18 concentric with the pre-hole 16 is produced. This is further illustrated by 2 B illustrated.

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

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

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

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

In 2 B the circular movement of the laser beam 14 along the at least one countersink generation line 29 around the central axis 31 of the pilot hole 16 is illustrated schematically by an arrow.

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

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

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

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

In principle, the countersink 18 can be used in any desired manner, and in this exemplary embodiment it is preferably intended to accommodate the head of a countersunk screw. Preferably, the radially outermost countersink generation line 29 for producing the countersink 18 has a diameter that is slightly smaller than the maximum diameter of the head of the countersunk screw to be arranged in the countersink 18 . The number of lowering generation lines 29 depends on the diameter of the preliminary hole 16 or the thread diameter of the screw to be inserted and the desired depth of the lowering 18 . As a rule, at least two passes of the jet nozzle 13 over the same countersink generation line 29 are required for pilot holes 16 to accommodate countersunk screws with a metric thread size M3 - M6 (ie with a diameter of the pilot hole 16 of 3 mm to 6 mm), with a typical number of crossings is between two and 25. For countersunk screws with a metric thread size M8 - M12, the number of passes is generally at least 5, preferably at least 10 and is typically between 10 and 25. Oxygen (O ₂ ), for example, is used as the process or working gas when creating the countersink 18 . used, with a gas pressure of, for example, less than 5 bar, which is in particular from 2 to 3.5 bar. The feed speed of the jet nozzle 13 when creating the countersink 18 is preferably at least 4 m/min and the laser power of the laser beam 14 is preferably at least 1500 W.

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

Nevertheless, melt can settle on the pre-hole wall 23, especially in the area of the lower pre-hole cut edge 21, and form a burr 32 after cooling, as in 2 B is illustrated. However, this burr 32 is advantageously formed when the preliminary hole 16 is widened to produce the final hole 17 (see FIG 2C ) also removed, so that an end hole 17 with a burr-free end hole wall 24 can be produced.

After the countersink 18 has been produced, the pilot hole 16 or the part thereof remaining after the countersink 18 has been produced is widened, which is explained below with reference to FIG 2C is illustrated.

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

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

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

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

A pulsed laser beam 14 (laser beam) with an average power of at least 200 W and a pulse peak power of at least 2000 W and a pulse frequency between 10 Hz and 200 Hz is preferably used. Depending on the workpiece material and the desired edge quality, nitrogen (N), compressed air or oxygen (O ₂ ) can be used as the working gas.

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

It will now refer to the 3A until 3D taken, wherein a further exemplary embodiment of the method according to the invention for laser beam machining of a workpiece 9 by the beam device 1 of 1 is illustrated in a schematic manner. The process steps of 3A , 3B and 3D correspond to the procedural steps of 2A , 2 B and 2C , whereby to avoid unnecessary repetitions on the above explanations 2A , 2 B and 2C is referred to. The based on 3A until 3D illustrated embodiment of the method according to the invention differs from the basis of 2A until 2C illustrated embodiment only in the process step of 3C .

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

In 4 a flow chart of the method according to the invention is shown. The procedure comprises at least three successive steps.

In step I, the laser beam is first guided in the cutting mode along a closed pre-hole cutting line, as a result of which a pre-hole is produced in the workpiece. Then, in step II, the laser beam is guided once or several times in non-cutting mode along at least one closed countersink generation line, the countersink generation line being arranged such that a countersink is generated around the pilot hole, which opens into the pilot hole. Then, in step III, the laser beam is guided in the cutting mode along a closed end hole cutting line, the end hole cutting line being arranged in such a way that the pilot hole widens within the countersink and an end hole is thereby produced.

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

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

example 1

Production of countersinks for countersunk screws with metric thread sizes M3 - M6 using a laser beam

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

Then, with the blasting nozzle at a large distance from the upper workpiece surface (approx. 50 mm) and the laser beam ignited, a circular path for generating a depression with a diameter of 5 mm to 15 mm is traversed, with oxygen (O ₂ ) being used as the working gas. The number of passes depends on the depth of the sinking to be made, with two to 25 passes usually being carried out. This creates the countersink for the head of the countersunk screw. Alternatively, a spiral path is traversed.

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

example 2

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

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

Then, with the blasting nozzle at a large distance from the upper surface of the workpiece (approx. 50 mm) and the laser beam ignited, a circular countersinking path with a diameter of 10 mm to 15 mm is traversed, with oxygen (O ₂ ) being used as the working gas. The number of passes depends on the depth of the sinking to be made, with generally 10 to 25 passes being made. This creates the countersink for the head of the countersunk screw. Alternatively, a spiral path is traversed.

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

Example 3

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

Before the pilot hole is cut, the slug is divided by cutting gaps in the shape of a cross with a superimposed spiral shape in the slug to be cut out. Oxygen (O ₂ ), nitrogen (N) or compressed air is used as the working gas. Then the pilot hole is cut with a diameter of 8 mm, which is approx. 1 mm smaller than the middle core hole diameter of the countersunk screw.

Then, with the jet nozzle at a large distance from the upper surface of the workpiece (approx. 50 mm) and the laser beam ignited, a circular depression-producing path with a diameter of 12.6 mm is traversed, with oxygen (O ₂ ) being used as the working gas. 17 passes are made, creating a countersink with a diameter of 14 mm and a depth of 4.4 mm to 4.5 mm in the sheet. Alternatively, a spiral path is traversed. Advantageous laser parameters are: laser power: 4000 W, feed: 10 m/min, distance between jet nozzle and upper workpiece surface (A): 50 mm, gas pressure of the working gas: 3.3 bar, focus diameter: 210 µm/150 µm.

Then the pre-hole is cut to a standard size with a diameter of 9 mm by a laser beam used in pulse mode, with oxygen (O ₂ ) being used as the working gas. Advantageous cutting parameters are: pulsed average laser power (pulse frequency 10 Hz): 400 W, pulse peak power: 4000 W, feed: 0.7 m/min, distance between jet nozzle and upper workpiece surface (A): 0.7 mm, gas pressure of the working gas: 17 bar, focus diameter: 210 µm.

As is apparent from the foregoing, the present invention provides a novel method for laser beam machining of a workpiece, in which counterbored holes can be efficiently formed in a workpiece with high precision and quality in a simple and inexpensive manner. The melt formed during the creation of the countersink can be expelled very well downwards out of the workpiece through the pre-drilled hole. Any slag adhering to the walls of the pilot hole and to the lower surface of the workpiece in the area of the pilot hole is automatically removed when the pilot hole is widened, resulting in a burr-free end hole with a burr-free cutting edge. There is no need for time-consuming mechanical post-processing to machine countersinks and remove burrs on the cut edges. An implementation of the method according to the invention in already existing laser beam processing devices is possible in a simple manner without having to provide complex technical measures for this purpose. Rather, a desired laser beam processing of a workpiece can be realized by the method according to the invention simply by intervening in the machine control.

Reference List

1

Laser beam processing device

2

jet cutting device

3

jet head

4

work table

5

workpiece support

6

cross member

7

guide carriage

8th

laser beam source

9

workpiece

10

upper workpiece surface

11

lower workpiece surface

12

control device

13

jet nozzle

14

laser beam

15

working gas jet

16

prehole

17

end hole

18

lowering

19

beam axis

20

upper pre-hole cutting edge

21

lower pre-hole cutting edge

21

pre-hole cutting line

22

end hole cutting line

23

pre-hole wall

24

end hole wall

25

upper end hole cutting edge

26

bottom end hole cut edge

27

outer countersink

28

inner countersink edge

29

subsidence generation line

30

flank

31

center axis

32

ridge

33

nozzle tip

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2020225448 A1 [0004]
• US 8716625 B2 [0078]

Claims (15)

Method for laser beam machining of a workpiece (9) that is planar at least in sections with a focused laser beam (14), in which the laser beam (14) is used in a mode that cuts or does not cut the workpiece (9) by changing the path energy of the laser beam (14). can, with the following steps in this order: - guiding the laser beam (14) in the cutting mode along a closed pre-hole cutting line (21), whereby a pre-hole (16) is produced in the workpiece (9), - One or more guiding of the laser beam (14) in the non-cutting mode along at least one closed countersink generation line (29), the countersink generation line (29) being arranged in relation to the pre-hole cutting line (21) such that a pre-hole (16) surrounds Countersinking (18) is produced, which opens into the pilot hole (16), - Guiding the laser beam (14) in the cutting mode along a closed end-hole cutting line (22), the end-hole cutting line (22) being arranged in relation to the pre-hole cutting line (21) in such a way that the pre-hole (16) is used to produce a final hole ( 17) is widened, the end hole (17) being located inside the countersink (18) when viewed perpendicularly through the workpiece (9). Method for laser beam machining of a workpiece (9) that is planar at least in sections claim 1 , In which the laser beam (14) is guided along a circular pre-hole cutting line. Method for laser beam machining of a workpiece (9) that is planar at least in sections claim 1 or 2 In which the laser beam (14) is guided one or more times along at least one circular or spiral countersink generation line (29), the countersink generation line (29) being arranged in particular concentrically and at a radial distance from a circular pre-hole cutting line (21). Method for laser beam machining of a workpiece (9) that is planar at least in sections according to one of Claims 1 until 3 In which the laser beam (14) is guided along a circular end hole cutting line (22), the end hole cutting line (22) being arranged in particular concentrically and at a radial distance from a circular pre-hole cutting line (21). Method for laser beam machining of a workpiece (9) according to one of Claims 1 until 4 , in which during the enlargement of the preliminary hole (16) a nozzle tip (33) of a jet nozzle (13), from which the laser beam (14) emerges, within the countersink (18) and below a workpiece surface facing the jet nozzle (13). (10) defined level is located. Method for laser beam machining of a workpiece (9) according to one of Claims 1 until 5 , in which the enlargement of the preliminary hole (16) takes place with a pulsed laser beam (14). Method for laser beam machining of a workpiece (9) according to one of Claims 1 until 6 , in which the pilot hole (16) and the countersink (18) are each produced with a laser beam (14) in the continuous wave. Method for laser beam machining of a workpiece (9) according to one of Claims 1 until 7 , in which the pilot hole (16) is actively cooled by contact with a fluid cooling medium before the enlargement of the pilot hole (16). Method for laser beam machining of a workpiece (9). claim 8 , in which for the active cooling of the pilot hole (16) a working gas jet (15) of compressed working gas, which interacts with the laser beam (14) in the cutting and non-cutting mode, is directed onto the workpiece (9). Method for laser beam machining of a workpiece (9) according to one of Claims 1 until 9 , in which a plurality of reduction generation lines (29) are provided for generating the reduction (18), two immediately adjacent reduction generation lines (29) always having a distance other than zero, in particular a radial distance. Method for laser beam machining of a workpiece (9) according to one of Claims 1 until 10 , In which the laser beam (14) for producing the countersink (18) is guided several times along the at least one countersink production line (29), in particular several times along each of a plurality of countersink production lines (29). Method for laser beam machining of a workpiece (9) according to one of Claims 1 until 11 , In which before the laser beam (14) is guided along the pre-hole cutting line (21), a slug to be cut out to produce the pre-hole (16) is divided by the laser beam (14) in the cutting mode. Laser beam machining device (1) with a laser beam (14) guided by a beam head (3), which has an electronic control device (12) for controlling the laser beam machining of a workpiece (9), which is used for conduct of the procedure according to one of Claims 1 until 12 is set up programmatically. Program code for an electronic control device suitable for data processing for a laser beam machining device (1) according to Claim 13 , Which contains control commands that the control device (12) for carrying out the method according to one of Claims 1 until 12 cause. Computer program product with a stored program code for an electronic control device suitable for data processing for a laser beam machining device (1) according to Claim 13 , Which contains control commands that the control device (12) for carrying out the method according to one of Claims 1 until 12 cause.

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