WO2018219860A1 - Method and device for monitoring a laser machining process - Google Patents

Abstract

In a known method for monitoring a laser machining process, a laser beam is directed at a workpiece, laser light that is scattered is detected as stray light and a change in the state of the laser machining process is identified on the basis of the detected stray light intensity. In order to provide a laser machining method, developed from the known method, which uses scattered laser radiation to identify the current process state during laser machining and which guarantees reliable process control, in particular for identifying penetration, according to the invention scattered light is detected below the workpiece and is evaluated in order to identify the change in state.

Description

 METHOD AND DEVICE FOR MONITORING

 A LASER PROCESSING PROCESS Description

Technical area

The present invention relates to a method for monitoring a laser processing process, in particular for puncture detection, wherein a laser beam directed at a workpiece, detected scattered laser light as scattered light, and a change in state of the laser processing process based on the detected scattered light intensity is identified.

Furthermore, the present invention relates to a device for monitoring a laser processing process, in particular for puncture detection, with a laser cutting head for focusing a laser beam on a workpiece, with an optical sensor for detecting scattered laser light as scattered light, and with an evaluation and control unit, by means of the Scattered light intensity evaluated and depending on a state change of the laser processing process is identifiable.

The laser-assisted thermal cutting of workpieces is generally carried out by combined use of a focused laser beam and a

Gas jet. Here, a distinction is made between laser beam fusion cutting, laser beam evaporation cutting or laser cutting. High-power lasers, in particular CO ₂ , fiber, disc and diode lasers are used, predominantly circularly polarized or unpolarized laser radiation being used in order to avoid a directional dependence in the absorption behavior in contour cuts.

The laser beam emitted by the laser beam is guided by means of optics or by means of optical fibers, which are bundled in a fiber cable, to a laser processing head. He is optionally parallelized by a collimator optics and fed to a focusing optics, which the parallel laser beam on the

Workpiece focused. When cutting the workpiece, the laser machining moved along a predetermined cutting contour relative to the arranged in a working plane workpiece.

State of the art

Before the actual laser cutting process, a first hole is produced in the workpiece in a so-called piercing or piercing process. Problematic is the detection of the puncture. In a manually programmed piercing process, the piercing parameters including the typical piercing time are stored in a database for each specific constellation of workpiece type and thickness. However, due to unforeseeable material deviations and changes in the process, the puncturing time must be provided with a time safety buffer which prolongs the total time for processing and unnecessarily introduces further process energy into the workpiece despite the puncturing process actually being completed.

This disadvantage is avoided by means for automatic detection of the puncture that has occurred. These devices have thermal or photosensitive sensors in the beam path above the cutting nozzle. In this case, the process light emitted by the piercing site during the piercing process or the laser light which is reflected by the piercing site is measured. If the measured light intensity exceeds a threshold value, this is interpreted, for example, as the completion of the plunge process.

These measurement data can also provide information about the quality of the processing and the current state of other characteristic parameters of the laser processing process and can therefore be used for monitoring and controlling the cutting process. In addition to the determination of the actual puncturing time, such further parameters are, for example, the power control during the plunge process, the edge detection, the recognition of a cut-off or plasma formation or the continuity (quality) of the kerf.

Thus, for example, US Pat. No. 9,427,823 B2, from which an apparatus and a laser processing method according to the aforementioned type are known, for controlling the quality of cut by the laser cutting process detected by the processing point of the workpiece backscattered laser radiation by means of an optical sensor and is evaluated for the control of the cutting process. The measured intensity of the backscattered light is less when the cut passes completely through the workpiece. In order to optimize the removal of slag, the frequency or the pressure of gas pulses used in the cutting process are adjusted by means of a control device so that the measured intensity of the backscattered light assumes a minimum value. The optical sensor is housed in a housing mounted laterally on the laser cutting head, which has an opening to the laser beam path, by means of which the backscattered laser light is deflected onto the sensor.

Technical task

The installation of such optical sensors requires a certain amount of space. In addition, the sensors are either arranged in the vicinity of the workpiece, so that under cutting conditions they are exposed to high thermal stresses or contamination, for example due to the piercing process, or they are arranged at a considerable distance from the separation process, which leads to an unfavorable signal-to-noise ratio. so that the signal of the sensor usually needs to be amplified. Furthermore, optical sensors have the disadvantage that there are influencing factors in the beam path which change the sensor signal, for example the nozzle diameter. Optionally, the apertures in the laser processing head must be made larger than otherwise necessary. These devices are complex, delicate and expensive.

The thicker the workpiece, the more difficult and unreliable the monitoring of the piercing process and the kerf quality, since the

Engraving hole or the kerf are deeper and less process light or laser radiation reaches the top of the sensor.

The invention is therefore based on the object of specifying a method for laser processing that uses scattered laser light to identify the current process state during laser processing, but does not use the above-described invention. reduced parts and ensures a reliable process control, especially for puncture detection.

Furthermore, the invention has for its object to provide a simple constructive little expensive and yet reliable device for performing the method.

General description of the invention

With regard to the method, this object is achieved on the basis of a method of the type mentioned in the present invention that scattered light is detected below the workpiece and evaluated to identify the change in state.

In the method according to the invention scattered light is detected below the workpiece to be machined, and optionally below any workpiece support, and the there determined scattered light intensity or its temporal change is used for the identification of a change in state in the laser processing process. In this case, not only the laser light scattered directly on the workpiece is detected, but also, in particular, the laser light which initially passes unaffected a puncture hole, a continuous kerf or a workpiece edge and is then scattered in a working area below the workpiece, for example in a so-called "work table". A sensor required for detecting the scattered light is not assigned directly to the laser cutting head or integrated therein, so that this measure is also referred to below as "external scattered light detection". In contrast, in the case of the "internal scattered light detection" known from the prior art, the measurement of reflected or scattered laser light takes place above the workpiece and a possible workpiece support.

The external stray light detection replaces or supplements the internal stray light detection. In the supplementary case, measurement and evaluation of reflected or scattered laser light above the workpiece can be done with less equipment. In the replacement case, this effort is completely eliminated. Since the external scattered light detection can be done by means of a sensor that is not integrated directly into the laser cutting head, this sensor is less subject to the above mentioned limitations and loads in terms of size, measuring distance, pollution and temperature, which can lead to a favorable signal / noise ratio. In addition, the measurement result in the external scattered light detection is not subject to a direct influence of guided or reflected laser radiation in the beam path, so that the optics in the laser processing head can be dimensioned comparatively small.

In the method according to the invention, the scattered light detection area is below the workpiece. There the scattered light is recorded continuously, at regular intervals or as required. In this case, a gradual drift of the scattered light intensity or a rapid change can be detected. In both cases, when a predetermined upper limit is exceeded or when a predetermined lower limit is exceeded (both are also summarized below under the term "threshold value detection"), it is assumed that a specific process state correlated with the scattered light intensity has occurred instead of or in addition For the scattered light intensity, a measured quantity derived therefrom can also be determined or evaluated, such as the temporal change, a mathematical derivation of the temporal course of the intensity signal or the difference between the current intensity signal and a permanently updated, time-averaged intensity value On the basis of such derived measured variables in particular allows a faster and more accurate detection of suddenly occurring events, such as a puncture or the meeting of the laser beam at a workpiece edge.

The laser processing process according to the invention is, for example, the process phase for producing a puncture in the workpiece to be machined. The generated puncture results in the state change to be identified.

In the case of a recognized puncture, for example, the energy input into the puncture crater is changed or stopped. The detected change of state can lead to an operator message in order to visually or acoustically display the changed conditions to the operating personnel so that a manual interpretation can be intervened in case of a misinterpretation. Thereafter, the actual laser cutting process begins, in which the movement direction and / or the movement speed of the laser cutting head relative to the workpiece surface and the laser Energy and gas parameters are adapted to the cutting process. ,

Since scattered light can penetrate the workpiece only after a puncture has taken place, a rapid increase in the scattered light intensity in the area below the workpiece is detected, so that a clear, reproducible relationship is established between the measured course of the scattered light intensity and the puncture. The evaluation signal thus obtained has a good signal-to-noise ratio, which also makes it possible, for example, to detect a puncture at an early stage, preferably even in its formation.

Since the change with time of the scattered light intensity when the puncture is carried out is almost independent of the type of material and the thickness of the workpiece, the method according to the invention can also be used without restriction for workpieces having larger material thicknesses of, for example, more than 10 mm.

Apart from the puncture detection, the method according to the invention can also be advantageously used for other phases of the laser processing process in which there is a gradual and in particular a sudden change of the scattered light in the area below the workpiece to be machined. As an example, the detection of a cut-off or the detection of material edges may be mentioned. In the former case, the demolition of the cutting beam is the state change to be identified, and in the latter case, it is the positioning of the scanning laser beam for edge detection outside the workpiece contour.

The detection of the scattered light in the region below the workpiece to be machined by means of a scattered light detection device or by means of multiple scattered light detection devices. Each of the detection devices is equipped with at least one photosensitive optical sensor. The scattered light can impinge directly on the sensor when it is arranged in the detection region for the scattered laser light below the workpiece to be machined. However, the scattered light can also be transmitted via optical guiding means, such as an optical fiber, an optical fiber cable or imaging optics, to a sensor, which may optionally be arranged inside or outside the detection area. In order to minimize interference from ambient light and process radiation, the following measures have been which can be realized individually or preferably in any combination with each other:

1 . The scattered below the workpiece support laser light is detected by at least one optically largely shielded detection device. That is, the scattered light detecting means is largely optically shielded in the stray light detection area, for example, by being housed in a chamber having only a single light opening to the stray light detection area.

2. The scattered light intensity is detected in a wavelength range which comprises the wavelength λ of the laser beam narrow band, preferably in the band range between λ +/- 100 nm.

This can be done, for example, in that the photosensitive element of the optical sensor is such that its maximum sensitivity lies within the wavelength range in which the expected wavelength of the scattered light lies. This corresponds essentially to the wavelength λ of the working radiation of the laser.

Or alternatively or additionally, by the fact that the scattered light detection device is equipped with an optical filter which is transparent to radiation having a wavelength λ of the working radiation of the laser and substantially blocks radiation of other wavelength ranges.

The at least one scattered light detection device is arranged stationary or movable in the scattered light detection range. In the case of a fixed arrangement, preferably a plurality of scattered light detection devices are distributed in the scattered light detection area. In a particularly preferred variant of the method, at least one detection device for the scattered light is tracked along a movement axis of the laser beam. In this case, the laser beam is generated by means of a laser cutting head, which is moved by means of a machine portal, and wherein the at least one detection device is moved synchronously to the movement of the machine portal. The detection device is mounted for this purpose, for example, on the machine portal. Due to the uniaxial, reversing tracking of the scattered light detection device, the distance between the laser beam and the detection device can be kept as low as possible. This ensures that the detected scattered light intensity is influenced as little as possible by this distance.

The method according to the invention is also particularly well-suited for a phase of the laser processing process referred to as "edge detection." In this case, the laser beam is generated by means of a laser cutting head, which is moved by means of a machine portal, and wherein the laser processing process comprises a process phase of detection of a workpiece edge.

In edge detection or edge detection, the laser beam is moved over a workpiece edge. The movement is essentially perpendicular to the edge of the workpiece. In order to injure the workpiece as little as possible and in the best case leave little or no marking marks, work is done with the lowest possible effective laser power. The low effective power is still well recognized by the scattered light detection device. The rise or fall of the measurement signal shows according to the correlating machine coordinate, the position of the workpiece edge and thus, when measuring several points, the position and position of the workpiece.

In addition, the method according to the invention is particularly well suited for a phase of the laser processing process in which the quality of the kerf generated by the laser beam and any disruption of the laser beam is monitored. In this case, the laser beam is generated by means of a laser cutting head, which is moved along a predetermined cutting contour and thereby in the sectional contour of a

Produces kerf, wherein the laser processing process comprises a process phase, during which the movement speed and / or the energy input is adjusted in the kerf in dependence on the detected stray light intensity. The manipulated variable of the process control in this phase of the laser processing process is thus the movement speed, laser power, focus position, distance stood between laser head and workpiece, the gas pressure and / or the energy input into the kerf depending on the detected scattered light intensity.

In the simplest case, the laser cutting process is stopped and a message is issued. The cutting contour can also be repeatedly overrun at the position of the cut-off, or the speed is reduced for a short time.

With regard to the device, the abovementioned object is achieved on the basis of a device of the type mentioned in the introduction by providing at least one optical device for detecting stray light below the workpiece, which is connected to the evaluation and control unit.

The device according to the invention is designed for "external scattered light detection", as described above with reference to the method according to the invention, The device is particularly well suited for carrying out this method.

In the case of the external scattered light detection, the scattered light is detected below the workpiece or below a workpiece support, and the scattered light intensity determined there or its temporal change or a measured variable correlated therewith is transmitted to the evaluation and control unit. Based on the scattered light intensity measurement, a state change of the laser processing process is identified continuously, at regular intervals or as needed.

The external stray light detection replaces or supplements the internal stray light detection. In the supplementary case, measurement and evaluation of reflected or scattered laser light above the workpiece can be done with less equipment. In the replacement case, this effort is completely eliminated. Since the external stray-light detection can be done by means of a sensor that is not directly integrated into the laser cutting head, this sensor is less subject to the above-mentioned restrictions and loads in terms of size, measurement distance, contamination and temperature, which can lead to a favorable signal / noise ratio. In addition, the measurement result in the external scattered light detection is not a direct influence of guided or reflected laser radiation in the beam path, so that the optics in the laser processing head can be dimensioned comparatively small. In the case of the external scattered light detection, the scattered light detection area is generally below a workpiece support, for example a so-called cutting grid. In this case, a gradual drift of the scattered light intensity or a rapid change can be detected. In both cases, when a predetermined upper limit is exceeded or when a predetermined lower limit is exceeded, it is assumed that a certain change in a process state correlated with the scattered light intensity has occurred.

Optionally, the control unit may respond thereto by changing a parameter or storing a characteristic parameter value, such as the detected position value of a workpiece edge.

For example, in the case of a recognized puncture, the energy input into the puncture crater is changed or stopped or the movement direction and / or the movement speed of the laser cutting head relative to the workpiece surface are changed. The energy input into the puncture crater is changed, for example, by changing the focus position, pulse frequency, power and / or pulse duty factor of the laser. Since scattered light can only penetrate the workpiece after a puncture has taken place, a rapid increase in the scattered light intensity in the area below the workpiece is possibly detected, so that a clear, reproducible relationship between the measured course of the scattered light intensity and the puncture is given. The evaluation signal thus obtained has a good signal-to-noise ratio, which also makes it possible, for example, to detect a puncture at an early stage, preferably even in its formation.

The temporal change in the scattered light intensity when the puncture is carried out is almost independent of the type of material and the workpiece thickness, so that the device according to the invention can also be used without restriction for cutting workpieces having larger material thicknesses of, for example, more than 10 mm.

Apart from the puncture detection, the device according to the invention can also be used advantageously for other phases of the laser processing process, in which there is a gradual and in particular a sudden change in the scattered light in the area below the workpiece to be machined can come. As an example, the detection of a cut-off or the detection of material edges may be mentioned.

The detection of the scattered light in the region below the workpiece to be machined by means of a scattered light detection device or by means of multiple scattered light detection devices. Each of the detectors is equipped with at least one photosensitive optical sensor. The scattered light can impinge directly on the sensor when it is arranged in the detection region for the scattered laser light below the workpiece to be machined. However, the scattered light can also be transmitted via optical guiding means, such as a fiber optic cable, an optical fiber cable or imaging optics, to a sensor, which may optionally be arranged inside or outside the detection area. In this case, the scattered light detection device is that component which is arranged in the scattered light detection region and on which the scattered light impinges directly. In order to minimize disturbances caused by ambient light and process radiation, the following embodiments have proved successful, which can be implemented individually or preferably in any desired combination with one another:

1 . To detect the laser light scattered below the workpiece support, at least one optically extensively shielded detection device is preferably provided. The scattered light detecting means is largely optically shielded in the scattered light detection area, for example, by being housed in a chamber having only a single light opening to the scattered light detection area.

2. The scattered light detection device is designed to detect the scattered light intensity in a wavelength range which comprises the wavelength λ of the laser radiation narrow band, preferably in the band range between λ +/- 100 nm.

This can be done, for example, in that the photosensitive element of the optical sensor is such that its maximum sensitivity is within the wavelength range in which the expected wavelength of the scattered light is located. This corresponds essentially to the wavelength λ of the working radiation of the laser. Or alternatively or additionally, that the scattered light detection device is equipped with an optical filter which is transparent to radiation having a wavelength λ of the working radiation of the laser and substantially blocks radiation of other wavelength ranges. The device according to the invention enables, for example, early and reliable detection of the imminent or completed puncture, the locating of a workpiece edge and the detection of a so-called cut-off, ie a suspension of the laser beam.

EXEMPLARY EMBODIMENT The invention will be described in more detail below on the basis of exemplary embodiments and a drawing. In detail shows:

Figure 1 shows a construction diagram of a device according to the invention for puncture detection in a schematic representation

2 shows an embodiment of a scattered light sensor for use in the device according to the invention in a schematic representation,

Figure 3 is a schematic of a laser processing machine with moving unit and cutting table in a plan view

4 shows a diagram for explaining the puncture recognition and the subsequently continued laser cutting process in a sectional contour with inner section and outer section on the basis of the time profile of the measured scattered light intensity

5 shows a diagram for explaining the reproducibility of the puncture recognition in the case of a narrow workpiece strip on the basis of the time profile of the measured scattered light intensity in five consecutive puncture attempts, FIG.

6 shows a diagram for explaining the reproducibility of the puncture detection when using sensors in different areas of a cutting trough on the basis of the time course of the measured scattered light intensity in a puncture test, and 7 shows a diagram with signal responses during the puncture with different laser beam parameters on the basis of the time profile of the measured scattered light intensity in a plurality of puncture attempts.

The puncture recognition device 1 shown schematically in FIG. 1 is part of a laser cutting machine and is used in the thermal processing of a workpiece 2 for monitoring a puncturing operation in the workpiece 2 and for driving the laser cutting machine during the puncturing operation. The laser cutting machine comprises a laser processing unit which can be moved in all directions in space (shown schematically in FIG. 3)

10 a laser cutting head (FIG. 3, reference numerals 4 and 5) by means of which a laser beam 3 is focused on the workpiece 2 via a collimator and a focusing lens 4 and a cutting nozzle 5. The workpiece 2 rests on a cutting grid 7 and this on a cutting trough 8. The cutting tray space below the workpiece 2 is designated by the reference numeral 10. In the case of the laser,

15 is a fiber laser and the laser beam has a working wavelength of about 1070 nm.

To set a predetermined distance of the laser cutting head to the workpiece surface and to control its movement along the predetermined cutting contour and the laser parameters, a machine control 6 20 is provided. With the machine control unit 6, a plurality of scattered-light sensors 9 are connected, which are mounted at a distance of 100 cm in a stationary manner inside the cutting-tub interior 1 1 below the cutting grid 7. The scattered light sensors 9 are used to measure scattered radiation 10, which in the laser cutting process due to different events in the cutting tub interior

25 1 1 passes, and this more or less homogeneously fills due to multiple reflections and diffuse scattering, which is indicated in Figure 1 optically by the same shading of the laser beam 3 and inner edge of the trough 1 1.

FIG. 2 schematically shows such a scattered light sensor 9 in a longitudinal section. In the inner bore of a metal tube 21 are starting from a

30, a protective glass 23 against the ingress of dust into the inner bore, an optical filter 24 for passage of infrared radiation in Wel- lenlängebereich from 1050 to 1 1 10 nm and a photosensitive member 25 having a main absorption wavelength in this wavelength range, which is connected to an evaluation of the machine control 6.

 FIG. 3 shows that the laser cutting head (4, 5) is mounted on a machine portal 31. The machine portal 31 is mounted on guide rails 32 along which it can be moved longitudinally in the x-direction (directional arrow 33). The laser cutting head (4; 5) itself can be reversibly moved back and forth reversibly on the machine gantry 31 along a y-axis of movement (directional arrow 34). Between the guide rails 32, the cutting trough 8, which is divided into a plurality of spatially separated segments 38 extends. Either a scattered light sensor 9 is arranged in each of the segments 38, or alternatively (as in the embodiment of the device according to the invention shown in FIG. 3), a scattered light sensor 39 is provided which is mounted on the machine gantry 31. This stray light sensor 39 performs the same longitudinal movements along the x-movement axis as the machine gantry 31 and the laser cutting head (4; 5). In this embodiment, the scattered light sensor 39 is thus always in synchronism with the laser cutting head (4, 5), both in terms of the longitudinal position and the movement speed of the longitudinal movement of the laser cutting head (4, 5); it receives the scattered laser radiation from the cutting trough interior 1 1 from each of the laser cutting head attacked segment 38. Therefore, sufficient in this embodiment, a single scattered light sensor 39 for detecting the scattered light.

The method according to the invention will be explained below with reference to the figures. In the diagrams of FIGS. 4 to 7, the scattered light intensity I (curves A) and the laser power L (curves B), both in relative units, are plotted against the time t in seconds on the y-axis.

 Figure 4 shows the time course of the measured scattered light intensity when cutting a square with an internal bore of a workpiece made of 15 mm thick structural steel. About 4 seconds after the start of the piercing operation 40 results in a rapid increase in the scattered light intensity 41, which was a successful

Punctuation indicates. The measuring signal of the scattered light intensity A is raised approximately to a higher level, and remains with the laser beam on this- sem level 41. After the puncture, the laser beam is switched off for a short time and the signal of the scattered light intensity A falls off.

Both the production of the inner contour (round hole; 43) and the outer contour (square; 44) is preceded by such a piercing process (40; 41), which is referred to in the figure as "piercing." Then the actual cutting process begins Generation of the inner bore or for cutting out the square, which is indicated by the scattered light intensity profile in the respective intensity ranges 43 and 44. This process phase is referred to in the figure as "cutting". When cutting the edges of the square, significant stray light changes occur when reaching the corners, as indicated by the reference numerals 45. The beginning and end of the contour cutting can also be recognized by a marked increase in the scattered light intensity.

In a further preliminary test several puncture holes were made in a 1 cm wide strip of structural steel. The challenge here is that the narrow strip of workpieces can cover the opening of the cutting trough 8 only to a fraction, so that in addition to the actual stray radiation, stray radiation in the form of ambient light and process radiation impinges on the scattered light sensor 9 to a high degree. This problem can be synonymous with

Cutting contours near workpiece edges occur. It should be clarified whether the scattered light sensor 9 is sufficiently selective with respect to the interference radiation. FIG. 5 shows the scattered light intensity profile in the case of five consecutive puncture tests in the workpiece strip. An influence of interfering radiation is not recognizable. The outlier 51 at one of the averages is due to an explosive ejection of the workpiece material due to a workpiece fault or non-optimal piercing parameters.

FIG. 6 shows the scattered light intensity profile in the case of a triple-bridged puncture test, wherein the scattered light intensity signal has been evaluated by a sensor 9 which is located in a segment 38 (see FIG

Cutting trough 8 is located, which is not directly below the cutting position, but in a neighboring segment. Although the respective segments are optically largely shielded by sheets and Insofar as separate chambers form within the cutting trough 8, a similar scattered light intensity signal arises in all of the puncture tests, which speaks for the reproducibility of the method. The elevations in the intensity signal in the grooves 2 and 3 are due to an explosive slag ejection due to a non-optimal puncture.

The diagram of FIG. 7 shows the result of a further preliminary experiment in which the laser pulse frequency is set to 10 Hz, 50 Hz and 100 Hz in three steps, and then the duty cycle (pulse duration / period duration) of the laser parameters is also set in three steps of 10% and 30 % has been increased to 50%. The fact that a clear puncture signal can be recognized in all cases demonstrates that the puncture can be identified essentially independently of the puncture parameters used by means of the method according to the invention.

Claims

claims 1 . Method for monitoring a laser processing process, in particular for puncture detection, wherein a laser beam (3) on a workpiece (2) directed, scattered laser light detected as scattered light (10), and a state change of the laser processing process based on the detected scattered light intensity is identified, characterized in that scattered light (10) below the workpiece (2) detected and to identify the change of state is evaluated. 2. The method according to claim 1, characterized in that the below the workpiece support (7) scattered light (10) by means of at least one optically largely shielded detection means (9, 39) is detected. 3. The method according to claim 2, characterized in that a plurality of stationary detection means (9) are used. 4. The method according to claim 2, characterized in that the laser beam (3) is produced by means of a laser cutting head (4; 5) which is moved by means of a machine gantry (31), and in that the at least one detecting device (39) is moved synchronously with the movement of the machine gantry (31). 5. The method according to any one of the preceding claims, characterized in that the scattered light intensity is detected in a wavelength range narrowband the wavelength λ of the laser radiation, preferably in the band range between λ +/- 100 nm. 6. The method according to any one of the preceding claims, characterized in that the laser beam (3) by means of a laser cutting head (4; 5) is generated, which is moved by means of a machine portal (31), and that the laser processing process comprises a process phase of the detection of a workpiece edge , 7. The method according to any one of claims 1 to 5, characterized in that the laser beam (3) by means of a laser cutting head (4; 5) is generated, which is moved along a predetermined cutting contour and thereby generates a kerf in the sectional contour, and that of Laserbearbei- Processing process includes a process phase during which the movement speed and / or the energy input is set in the kerf depending on the detected scattered light intensity. 8. Apparatus for monitoring a laser processing process, in particular for puncture detection, with a laser cutting head (4; 5) for focusing a laser beam (3) on a workpiece (2), with an optical sensor (9; 39) for detecting scattered laser light as litter - Light (10), and with an evaluation and control unit (6) by means of which the scattered light intensity is evaluated and in dependence thereon a state change of the laser processing process is identifiable, characterized in that at least one optical device (9; 39) for detecting scattered light (10) below the workpiece (2) is provided, which is connected to the evaluation and control unit (6). 9. Apparatus according to claim 8, characterized in that a workpiece support (7) is provided which comprises a cutting grid. 10. Apparatus according to claim 8 or 9, characterized in that for detecting stray light (10) below the workpiece (2) at least one optically largely shielded detection means (9, 39) is provided. 1 1 .Vorrichtung according to claim 10, characterized in that a plurality of stationary optical detection means (9) are provided. 12. Device according to one of claims 8 to 1 1, characterized in that the laser cutting head (4; 5) by means of a machine portal (31) is movable, and that the at least one optical detection means (39) synchronously with the movement of the machine portal (31) is movable 13. Device according to one of claims 8 to 12, characterized in that the optical detection means (9) for detecting the scattered light intensity is designed in a wavelength range of narrowband the wavelength λ of the laser radiation, preferably in the band range between λ +/- 100th nm.