Method for introducing separating cuts into panel-shaped workpieces

Abstract

The invention relates to a method for introducing separating cuts into panel-shaped workpieces with a laser processing head of a laser cutting machine, in which, at least as the separating cut approaches an edge (12) of the workpiece, the distance (10) of the laser processing head from the workpiece is monitored and the stray light (11) arising during the cutting process is detected and, when there is an abrupt change (10.1) in the distance (10) between the laser head and the workpiece and when there is a simultaneous abrupt change (11.2) in the intensity of the detected stray light (11), it is recognized that the edge (12) of the workpiece has been reached and the laser of the laser processing machine is switched off.

Description

[0001] Method for making separating cuts in sheet-shaped workpieces

[0002] The invention relates to a method for making separating cuts in panel-shaped workpieces using a laser processing head of a laser cutting machine.

[0003] When laser cutting large sheet metal panels, separating the cut-out pieces and disposing of the remaining skeleton as waste is difficult. To simplify these tasks, separating cuts are programmed that divide the sheet metal panel across its entire width and / or length. It often happens that the sheet metal panels actually being cut are larger than the ordered panel sizes, as the rolling mill can only produce the panel dimensions within a certain tolerance range. When programming separating cuts in the laser cutting machine, however, the ordered panel size is usually used, which often results in separating cuts that are too short, leaving the skeleton connected for several millimeters at the end of the panel separating cut. This connection point on the skeleton must then be manually separated in a separate step.

[0004] However, if the cut is programmed to be longer than the target sheet dimension, the laser beam may damage the machine's workpiece support if the laser beam is not switched off after reaching the workpiece edge. Furthermore, any control of the distance between the laser processing head and the workpiece must be switched off to a target value before reaching the workpiece edge to prevent the laser processing head from lowering onto the workpiece support if the cut is longer than the sheet dimension.

[0005] The invention is based on the object of providing a method for making separating cuts in panel-shaped workpieces, with which a complete separation of the workpiece and a reliable shutdown of the laser when the workpiece edge is reached is possible.

[0006] This object is achieved according to the invention by a method for making separating cuts in panel-shaped workpieces with a laser processing head of a laser cutting machine, which is characterized in that at least when the separating cut approaches an edge of the workpiece, the distance of the laser processing head to the workpiece is monitored and the scattered light generated during the cutting process is detected and in the event of an abrupt change in the distance between the laser head and the workpiece and a simultaneous abrupt change in the intensity of the detected scattered light, reaching the edge of the workpiece is detected and the laser of the laser processing machine is switched off.

[0007] The subclaims relate to preferred embodiments of the method.

[0008] To detect the workpiece edge, the distance between the machine's laser processing head and the workpiece is monitored. At the end of a sheet, the distance signal undergoes an abrupt change.

[0009] If the distance signal alone is evaluated to switch off the laser, this can lead to incorrect triggering of the laser switch-off, particularly with thinner sheets, due to vibration of the sheet or rounded sheet edges.

[0010] According to the method according to the invention, the plausibility of the distance signal for workpiece edge detection is therefore checked using a second measurement signal, in this case an optical measurement signal caused by scattered light. This signal drops sharply when the workpiece edge is reached. The evaluation of the scattered light signal alone could also lead to incorrect laser shutdowns if the laser moves over a support ridge of the workpiece support after reaching the workpiece edge. In this case, the scattered light signal would only drop after moving over the ridge, triggering laser shutdown, and not upon reaching the workpiece edge.

[0011] According to the invention, both measurement signals are therefore evaluated. If the distance monitoring signal indicates that a workpiece edge has been reached due to an abrupt increase in value, the scattered light signal is evaluated simultaneously. Only if both signals experience an abrupt change is the laser shut off. This largely prevents false triggering of the laser shutdown caused by a vibrating sheet, rounded workpiece edges, or other interference. The evaluation of both measurement signals ensures the required process reliability of the inventive method.

[0012] The feed rate of the laser processing head can preferably be reduced as the cutting edge approaches the workpiece edge to facilitate the evaluation of the measurement signals and the triggering of the laser shutdown. Furthermore, reducing the feed rate generates more scattered light, i.e., the optical signal is amplified before it abruptly drops when the cutting edge reaches the workpiece edge.

[0013] The laser power can also be reduced as the cut approaches an edge of the workpiece. If the laser is switched off with a slight delay, damage to the base of the laser cutting machine is significantly reduced or can even be avoided altogether due to the lower laser power.

[0014] Preferably, the laser power and the feed rate can be reduced simultaneously and linearly when approaching a workpiece edge.

[0015] There are various options for measuring the distance between the laser processing head and the workpiece. Preferably, the distance between the laser processing head and the workpiece can be measured capacitively. In this case, a surface on the processing head and an opposite surface on the workpiece form a capacitor whose capacitance changes with the distance between these surfaces.

[0016] The scattered light can preferably be detected using a photodiode.

[0017] To ensure that the workpiece is completely cut through, it is advisable to program the length of the cutting cut to be greater than the nominal dimension of the workpiece in the direction of the cutting cut before machining the workpiece.

[0018] The invention also relates to a laser cutting machine with a laser processing head for processing panel-shaped workpieces, which is characterized in that it is equipped with a sensor device for measuring the distance of the laser processing head to the workpiece and has an optical sensor device for detecting scattered light and is designed to carry out a method according to the invention.

[0019] The sensor device for measuring the distance between the machining head and a workpiece can be a capacitive sensor device.

[0020] The optical sensor device may comprise at least one photodiode.

[0021] Both sensor devices are connected to a control unit of the laser cutting machine so that their signals can be evaluated there and trigger a shutdown of the laser.

[0022] Further features and advantages of the invention will become apparent from the description, the claims, and the drawings. According to the invention, the above-mentioned and further-described features can be used individually or in combination in any convenient way. The embodiments shown and described are not intended to be exhaustive, but rather are exemplary in nature for describing the invention.

[0023] Detailed description of the invention and drawing

[0024] Fig. 1 shows a diagram with a distance measurement signal and a scattered light measurement signal in an end section of a separating cut.

[0025] Fig. 1 shows a measurement signal 10 from a distance sensor of a laser cutting machine during the movement of a laser processing head of the machine for performing a severing cut in a sheet-shaped workpiece as the head approaches an edge of the workpiece. The laser processing head moves across the workpiece in the x-direction.

[0026] In addition to the distance measurement signal, the diagram shows a measurement signal 11 from a photodiode for detecting scattered light during machining of the workpiece.

[0027] Shortly before the laser processing head reaches an edge 12 of the workpiece, the distance signal 10 experiences a rise (10.1). The scattered light signal 11 also experiences a rise (11.1) here, before dropping steeply upon reaching the edge 12 (11.2). The coincidence of the rise (10.1) of the distance signal 10 and the fall (11.2) of the scattered light signal 11 reliably indicates that the edge 12 of the workpiece has been reached. At this point, the laser can be switched off. The workpiece is safely cut through. Damage to the base of the laser cutting machine caused by a laser remaining active for too long can be avoided.

Claims

Patent claims 1 . Method for making separating cuts in panel-shaped workpieces with a laser processing head of a laser cutting machine, characterized in that at least when the separating cut approaches an edge (12) of the workpiece, the distance (10) of the laser processing head to the workpiece is monitored and the scattered light (11) generated during the cutting process is detected and in the event of an abrupt change (10.1) in the distance (10) between the laser head and the workpiece and a simultaneous abrupt change (11.2) in the intensity of the detected scattered light (11), reaching the edge (12) of the workpiece is detected and the laser of the laser processing machine is switched off.

2. Method according to claim 1, characterized in that the speed of the feed of the laser processing head is reduced as the separating cut approaches an edge (12) of the workpiece.

3. Method according to claim 1 or 2, characterized in that the laser power is reduced as the separating cut approaches an edge (12) of the workpiece.

4. Method according to claim 2 and 3, characterized in that the laser power and the feed rate are reduced simultaneously and linearly as the separating cut approaches a workpiece edge (12).

5. Method according to one of the preceding claims, characterized in that the distance (10) between the laser processing head and the workpiece is measured capacitively.

6. Method according to one of the preceding claims, characterized in that the scattered light (11) is detected by means of a photodiode.

7. Method according to one of the preceding claims, characterized in that before machining the workpiece, the length of the separating cut is programmed to be greater than the nominal dimension of the workpiece in the direction of the separating cut.

8. Laser cutting machine with a laser processing head for processing panel-shaped workpieces, characterized in that it is equipped with a sensor device for measuring the distance (10) of the laser processing head to the workpiece and has an optical sensor device for detecting scattered light (11) and is designed to carry out a method according to one of claims 1 to 7.

9. Laser cutting machine according to claim 8, characterized in that the sensor device for measuring the distance (10) of the processing head to a workpiece is a capacitive sensor device.

10. Laser cutting machine according to claim 8 or 9, characterized in that the optical sensor device has at least one photodiode.

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