Method for laser cutting plate-like workpieces, and associated computer program product

Abstract

The invention relates to a method for laser cutting an, in particular plate-like, workpiece (6), along a trajectory (K) by means of a laser beam (5), at least one nano-joint (14a, 14b) having a height (d) less than the workpiece thickness (D) and being formed on a portion of the trajectory (K) that equals the length (L) of the nano-joint (14a, 14b), characterised in that in order to form the nano-joint (14a, 14b), a) a relative movement of the workpiece (6) and a laser beam (5) is stopped and at least one cutting parameter is changed from a first parameter value suitable for cutting through the workpiece (6) to a second parameter value which is not sufficient for cutting through the workpiece (6), or b) the gas pressure and / or the focus position is changed from a first parameter value suitable for cutting through the workpiece (6) to a second parameter value which is not sufficient for cutting through the workpiece (6).

Description

[0001] Method for laser cutting plate-shaped workpieces and associated computer program product

[0002] The invention relates to a method for laser cutting a workpiece, in particular a plate-shaped workpiece, along a trajectory curve by means of a laser beam, wherein at least one nanojoint with a lower height than the workpiece thickness is formed on a section of the trajectory curve corresponding to the length of the nanojoint.

[0003] Such a laser cutting process has become known, for example, from DE 10 2017 213 394 Al.

[0004] When laser cutting plate-shaped workpieces, it is important that the slag created during cutting can escape unhindered downwards from the cutting gap. To ensure this, the workpiece support in laser cutting machines for plate-shaped workpieces usually consists of several support bars that are inserted into a frame. The support bars have a serrated shape so that there is only point-like contact with the workpiece. Depending on the size and position of a workpiece part on the support bars, the effect of the cutting gas pressure can cause the workpiece part to tilt when the workpiece part is cut free. The workpiece part then becomes wedged between the support bars and stands up, which can lead to a collision between the laser processing head or the cutting gas nozzle and the workpiece part. In addition, the random position makes automated removal of the workpiece parts difficult or even impossible.If positioned unfavourably, smaller workpiece parts can fall into the gaps between the support bars and thus end up on the slag conveyor belt arranged beneath the workpiece support or in the slag collecting container.

[0005] To solve this problem, it is known to fix the workpiece parts in the remaining workpiece with the help of so-called microjoints, i.e. by means of connecting webs that remain in the cutting gap between the workpiece part and the surrounding remaining workpiece, so that tilting is prevented. The use of microjoints does, however, have some disadvantages: Microjoints usually extend over the entire workpiece thickness, so that in the case of workpieces with a thickness of more than 5 mm, it is very difficult or even impossible to remove the workpiece parts from the remaining workpiece by hand. After the workpiece parts have been removed, residues of the microjoints remain on the cutting edge and must be removed by complex rework. In addition, microjoints are typically set at the end of the cut. However, if more than one microjoint is required in a workpiece contour, this can only be created by additional grooving and approach to the contour.This reduces the productivity of the cutting process.

[0006] From DE 10 2017 213 394 A1 a method for laser cutting a workpiece, in particular a plate-shaped workpiece, along a trajectory curve by means of a laser beam is known, wherein in order to produce a microjoint which is not located at the end of the trajectory curve and has a lower height than the workpiece thickness during laser cutting of the workpiece, the laser power of the laser beam is reduced on a section of the trajectory curve corresponding to the length of the microjoint from a higher laser power sufficient to cut through the workpiece to a lower laser power which is insufficient to cut through the workpiece completely and is then increased again to the higher laser power.

[0007] In the following, microjoints that have a lower height than the workpiece thickness are called nanojoints.

[0008] The object of the present invention is to provide a simplified and reliable method for forming nanojoints. This object is achieved according to the invention by a method for laser cutting a workpiece, in particular a plate-shaped workpiece, along a trajectory curve using a laser beam, wherein at least one nanojoint with a height less than the workpiece thickness is formed on a portion of the trajectory curve corresponding to the length of the nanojoint.To form the nanojoint, a) a relative movement of the workpiece and a laser beam is stopped and at least one cutting parameter is changed from a first parameter value suitable for cutting through the workpiece to a second parameter value insufficient for cutting through the workpiece or b) the gas pressure and / or the focus position is changed from a first parameter value suitable for cutting through the workpiece to a second parameter value insufficient for cutting through the workpiece.

[0009] In this case, a relative movement that is stopped does not mean a relative movement of the laser processing head and the workpiece perpendicular to a workpiece support or in the direction of the laser beam, but rather a relative movement of the laser beam or laser processing head and the workpiece along the trajectory or parallel to a plane containing the trajectory—in particular, a relative movement parallel to a workpiece support. This stopped relative movement is also referred to as an axis stop.

[0010] The parameter change provided for in alternative a) can occur after the axis stop or simultaneously. In particular, parameter values ​​can be specifically set after the axis stop to prevent the workpiece from being completely cut through. The axis stop ensures that the nanojoint has a small thickness even at its beginning and that the nanojoint maintains a constant thickness, particularly along its length. This facilitates the removal of the workpiece part (good part).

[0011] By changing the gas pressure and / or focus position, it is possible to ensure that less energy is directed into the workpiece, particularly without changing the laser power, and to prevent complete cutting. Gas pressure and / or focus position can also be changed when an axis stop is performed.

[0012] Before the nanojoint begins to form, the laser beam can be turned off. This can occur simultaneously with the axis stop. To create the nanojoint, the laser beam can be turned on again at the same power as used to cut through the workpiece, especially if other cutting parameters are changed, or at a lower power.

[0013] It's also conceivable to leave the laser beam switched on during an axis stop. Depending on which cutting parameter(s) are being varied, this can offer advantages.

[0014] To create a nanojoint, several cutting parameters can be changed from a first parameter value suitable for cutting through the workpiece to a second parameter value that is insufficient for cutting through the workpiece. This allows a particularly favorable combination of parameter values ​​to be set for the formation of a nanojoint.

[0015] To form the nanojoint, the cutting speed can be increased compared to the cutting speed required to cut through the workpiece, in particular by at least 10%. If the cutting speed, i.e., the relative movement of the laser beam and the workpiece parallel to the workpiece support, is increased, less energy is introduced into the workpiece, thus preventing complete cutting through the workpiece.

[0016] To form the nanojoint, the gas pressure, especially of the cutting gas, can be reduced compared to the gas pressure required for cutting through the workpiece, in particular by at least 20%. For example, the gas pressure can be reduced to values ​​in the range of 2-6 bar. To form the nanojoint, the focus position can be adjusted away from the machining head and toward the workpiece, relative to the focus position required for cutting through the workpiece. This allows the power density in the workpiece to be reduced. In particular, the focus can be shifted from the surface of the workpiece into the workpiece.

[0017] According to one method variant, the cutting parameter(s) can be changed from parameter values ​​suitable for cutting through the workpiece to parameter values ​​unsuitable for cutting through the workpiece via a gradient. For example, at the beginning of the nanojoint, the laser power, the nozzle-workpiece distance, and the focus position can be adjusted via a ramp, in particular linearly.

[0018] Furthermore, it can be specified that the formation of the nanojoint only begins when a predefined event has occurred after the relative movement has stopped (axis stop). For example, it can be monitored whether one or more cutting parameters have reached parameter values ​​that are not suitable for complete cutting, or a predefined time can be waited for. The predefined event would then be the reaching of one or more predefined parameter values ​​or the expiration of the predefined time.

[0019] The process can be accelerated if at least one cutting parameter is changed abruptly from a first to a second parameter value.

[0020] After the nanojoint has been formed, the relative movement of the workpiece and the laser beam can be stopped. An axis stop can be provided at the end of the nanojoint. This allows the cutting parameters to be adjusted again for cutting through the workpiece.

[0021] After forming a nanojoint at the end of the trajectory, the laser beam can be turned off, and / or after forming a nanojoint that is not at the end of the trajectory, the cutting parameters can be changed back to the values ​​prior to the formation of the nanojoint. This can be done abruptly or via a gradient. Furthermore, it can be done with or without an axis stop.

[0022] Finally, the invention also relates to a computer program product which has code means adapted to carry out all steps of the method according to the invention when the program runs on a controller of a laser processing machine.

[0023] Further advantages and advantageous embodiments of the subject matter of the invention will become apparent from the description, the claims, and the drawings. Likewise, the above-mentioned and further listed features can be used individually or in combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather as examples for describing the invention.

[0024] They show:

[0025] Fig. 1 shows a laser cutting machine suitable for carrying out the laser cutting method according to the invention;

[0026] Figs. 2a, 2b show a workpiece part laser-cut from a workpiece, which is held in the remaining workpiece by nanojoints, in a plan view (Fig. 2a) and in a sectional view (Fig. 2b) corresponding to Ilb-IIb in Fig. 2a;

[0027] The laser cutting machine 1 shown in perspective in Fig. 1 has, for example, a CO2 laser, diode laser, or solid-state laser as the laser beam generator 2, a movable (laser) processing head 3, and a workpiece support 4. A laser beam 5 is generated in the laser beam generator 2 and guided from the laser beam generator 2 to the processing head 3 by means of a fiber optic cable (not shown) or deflecting mirrors (not shown). A plate-shaped workpiece 6 is arranged on the workpiece support 4. The laser beam 5 is directed onto the workpiece 6 by means of focusing optics arranged in the processing head 3. The laser cutting machine 1 is also supplied with cutting gases 7, for example oxygen and nitrogen. The use of the respective cutting gas 7 depends on the workpiece material and the quality requirements for the cut edges.Furthermore, an extraction device 8 is provided, which is connected to an extraction channel 9 located beneath the workpiece support 4. The cutting gas 7 is fed to a cutting gas nozzle 10 of the processing head 3, from which it exits together with the laser beam 5.

[0028] During laser cutting, the workpiece 6 is cut along a desired trajectory K using a laser beam 5 with cutting parameter values ​​suitable for cutting through the workpiece 6. In this case, the laser beam 5, or alternatively or additionally the workpiece 6, is moved. To do this, the workpiece 6 must first be pierced at a point S on or adjacent to the trajectory K to be cut, as shown in Fig. 2a.

[0029] As shown in Figs. 2a, 2b, during laser cutting of the workpiece 6, connecting webs or nanojoints 14a, 14b are left in the cutting gap 11 between a laser-cut workpiece part 12 and the remaining workpiece 13, which fix the workpiece part 12 in the remaining workpiece 13 and thus prevent tilting relative to the remaining workpiece 13. As shown in Fig. 2b, the nanojoint 14a, 14b does not extend over the entire workpiece thickness D, but only in the lower third of the workpiece thickness, thus having a lower height d than the workpiece thickness D. The nanojoint 14a is located at the end of the cut, i.e. is created shortly before the beginning of the self-contained trajectory K is reached again. The nanojoint 14b, on the other hand, is not located at the end of the cut, but at any desired section of the trajectory K.

[0030] The method according to the invention is described below using the example of varying the focus position. In this embodiment of the method, the nanojoints 14a, 14b are generated solely by targeted adjustment of the focus position during the cutting process, which is predetermined by a controller 15 of the laser cutting machine 1 shown in Fig. 1 depending on the workpiece material. The controller 15 also controls the movement of the processing head 3 relative to the workpiece 6. Due to the changed focus position, which is shifted in particular into the workpiece 6, the cutting process no longer has the power density required for a complete cut, so that the workpiece material is not melted across the entire workpiece thickness D and a nanojoint 14a, 14b remains in the lower region of the cutting gap 11 or the cutting edge between the laser-cut workpiece part 6 and the remaining workpiece 13.In addition to the focus position, further cutting parameters of the laser cutting can be changed for the creation of the nanojoint 14a, 14b, for example the laser power, the distance of the cutting gas nozzle 10 to the workpiece surface, the cutting gas pressure and / or the cutting speed.

[0031] Before the nanojoint 14a, 14b is created, an axis stop can be performed, meaning the cutting speed can be reduced to 0 m / s. During the axis stop, cutting parameters can be set to the values ​​required to create the nanojoint 14a, 14b. After the nanojoint 14b is created, cutting continues with the default parameters. Before continuing cutting with default parameters suitable for cutting through the workpiece 6, an axis stop can be performed again, and the default parameters can be set. After the nanojoint 14a is created, the laser beam 5 is switched off. An axis stop can also be performed.

[0032] In order to produce the nanojoint 14b which is not located at the end of the trajectory K and has a height d which is smaller than the workpiece thickness D, during laser cutting of the workpiece 6 the focus position of the laser beam 5 is changed on a section of the trajectory K corresponding to the length L of the nanojoint 14b from the focus position suitable for cutting through the workpiece 6 to a focus position which is not suitable for completely cutting through the workpiece 6 and is then set back to the original focus position.

Claims

Patent claims Method for laser cutting a particularly plate-shaped workpiece (6) along a trajectory curve (K) by means of a laser beam (5), wherein at least one nanojoint (14a, 14b) with a lower height (d) than the workpiece thickness (D) is formed on one of the lengths (L) of the nanojoint (14a, 14b) corresponding section of the trajectory curve (K) is formed, characterized in that to form the nanojoint (14a, 14b) a) a relative movement of the workpiece (6) and a laser beam (5) is stopped and at least one cutting parameter is changed from a first parameter value suitable for cutting through the workpiece (6) to a second parameter value insufficient for cutting through the workpiece (6), or b) the gas pressure and / or the focus position is changed from a first parameter value suitable for cutting through the workpiece (6) to a second parameter value insufficient for cutting through the workpiece (6). Method according to claim 1, characterized in that the laser beam (5) is switched off before the start of the formation of the nanojoint (14a, 14b).Method according to one of the preceding claims, characterized in that, to form the nanojoint (14a, 14b), several cutting parameters are changed from a first parameter value suitable for cutting through the workpiece (6) to a second parameter value insufficient for cutting through the workpiece (6). Method according to one of the preceding claims, characterized in that, to form the nanojoint (14a, 14b), the cutting speed is increased compared to the cutting speed for cutting through the workpiece (6), in particular by at least 10%. Method according to one of the preceding claims, characterized in that, to form the nanojoint (14a, 14b), the gas pressure is reduced compared to the gas pressure for cutting through the workpiece (6), in particular is reduced by at least 20%. Method according to one of the preceding claims, characterized in that, to form the nanojoint (14a, 14b), the focus position is adjusted away from the processing head (3) in the direction of the workpiece (6) compared to the focus position for cutting through the workpiece (6). Method according to one of the preceding claims, characterized in that the cutting parameter(s) are changed from parameter values ​​suitable for cutting through the workpiece (6) to parameter values ​​unsuitable for cutting through the workpiece (6) via a gradient.Method according to one of the preceding claims, characterized in that the formation of the nanojoint (14a, 14b) does not begin until a predetermined event has occurred after the relative movement has stopped. Method according to one of the preceding claims, characterized in that at least one cutting parameter is changed abruptly from a first to a second parameter value. Method according to one of the preceding claims, characterized in that after the formation of the nanojoint (14a, 14b), a relative movement of the workpiece (6) and the laser beam (5) is stopped. Method according to one of the preceding claims, characterized in that after the formation of a nanojoint (14a) located at the end of the trajectory curve (K), the laser beam (5) is switched off. and / or after the formation of a nanojoint (14a) not located at the end of the trajectory curve (K), the parameter values ​​of the cutting parameters are changed back to the parameter values ​​present before the formation of the nanojoint (14a, 14b). A computer program product comprising code means adapted to carry out all steps of the method according to one of the preceding claims when the program is executed on a controller (15) of a laser cutting machine (1).

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