Laser processing method

Abstract

A method for laser processing of a metal workpiece (2), comprising at least the following steps: a) directing a laser beam (5) onto the workpiece (2) at a working area (7) of the workpiece (2) in order to perform cutting and / or piercing; b) performing a relative movement between the laser beam (5) and the workpiece (2) at a determined speed; c) acquiring a plurality of acquired images (9) of the working area (7); d) determining the time course (9) of at least one characteristic parameter from the acquired images (9); e) calculating at least one statistical parameter from the time course of the characteristic parameter; f) establishing a quality value based on the statistical parameter; g) controlling one or more process parameters based on the quality value, in particular at least the intensity of the laser beam (5) and / or the laser frequency of the laser beam (5) and / or the focal position of the laser beam (5) and / or the determined speed and / or the gas jet and / or the gas pressure of the gas jet.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims the benefit of Italian Patent Application No. 102019000025093, filed on December 20, 2019, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a laser processing method for cutting and / or piercing a workpiece. In particular, the present invention relates to a laser processing method in a continuous mode and performing closed-loop control of the cutting or piercing quality during the cutting or piercing step, and more particularly to a process control method for ensuring a predetermined processing quality.

[0004] The present invention also relates to a laser processing machine configured to perform a laser method for cutting and / or piercing a workpiece. In particular, the present invention relates to a laser processing machine configured to perform a laser processing method in a continuous mode and to perform closed-loop control of the cutting or piercing quality during the cutting or piercing step, and more particularly to closed-loop control of the process to ensure a predetermined processing quality. Background Art

[0005] Laser processing machines are commonly used to cut and / or penetrate workpieces. A typical laser processing machine includes: a laser beam emission source; a support member for the workpiece; an optical system for controlling the focus position of the laser beam; a generating device configured to generate a gas jet for directing compounds generated during workpiece processing away from the workpiece itself; and a moving device for performing relative movement between the laser beam and the workpiece.

[0006] In use, the resulting quality of cutting or piercing a workpiece depends on, for example, the intensity of the laser beam, the pressure of the gas jet or the speed of the relative movement between the laser beam and the workpiece.

[0007] For example, it is known that dross forms at the lower edge of a cut or pierced portion of a workpiece.

[0008] Theoretically, it is conceivable to set the corresponding parameters in such a way that the maximum achievable quality is achieved (ie, for example, the absence of dross). However, in order to achieve such a result, the process parameters need to be controlled so that the productivity is reduced at the same time.

[0009] Therefore, it is necessary to obtain information, for example through simulations or actual estimations or measurements, in order to optimize the parameters in such a way as to maximize the process productivity while thereby ensuring the process quality. It should be noted that the optimization of the parameters results in the determination of a set of optimized parameters, which, however, is static, i.e., they do not change during the processing of the workpiece. This means that, in some cases, this set of optimized parameters may result in a process that is not optimal in terms of productivity or quality.

[0010] It should be noted that processing machines are known that are equipped with devices capable of obtaining a rough estimate of the amount of dross generated during cutting and / or piercing from the analysis of certain process measurements. Specifically, these estimates are typically based on discrete thresholds and categorize dross as, for example, "absent" or "present," but are unable to estimate a continuous value representative of the dross actually present on the cut piece. Furthermore, in the absence of control (particularly closed-loop control), process parameters that guarantee the absence of dross are often empirically calibrated, resulting in suboptimal operating conditions in terms of productivity.

[0011] In this context, it is known, for example, to use photodiodes to monitor the progress of a process.

[0012] However, the use of photodiodes, for example, does not allow reliable information to be obtained about scum formation.

[0013] Therefore, in this field, there is a need for further improvements in laser processing methods and / or laser processing machines for cutting and / or piercing workpieces in a manner that makes it possible to monitor and adjust the processing quality, in particular in a continuous mode and on-line, more particularly, on continuously estimated variables obtained on-line. Summary of the Invention

[0014] The object of the present invention is to achieve a laser processing method for cutting and / or piercing and a laser processing machine which allow overcoming at least one of the above-mentioned disadvantages in a simple and economical manner.

[0015] In particular, the object of the present invention is to realize a laser processing method for cutting and / or piercing and a laser processing machine which allow quality control and control of the process parameters of the machine according to the quality obtained.

[0016] The above objectives are achieved through the present invention.

[0017] According to one aspect of the present invention, a method for laser processing of a metal workpiece is provided, which comprises at least the following steps:

[0018] a) directing a laser beam onto a workpiece at a working area of the workpiece in order to perform cutting and / or piercing;

[0019] b) performing relative movement between the laser beam and the workpiece at a determined speed;

[0020] c) acquiring a plurality of acquired images of the working area;

[0021] d) determining a time course of at least one characteristic parameter from said acquired images;

[0022] e) calculating at least one statistical parameter from said time course of said characteristic parameter;

[0023] f) establishing a quality value based on the statistical parameters;

[0024] g) controlling one or more process parameters, in particular at least the intensity of the laser beam and / or the laser frequency of the laser beam and / or the focus position of the laser beam and / or a determined speed and / or the gas jet and / or the gas pressure of the gas jet, as a function of the quality value,

[0025] wherein during step e) a probability distribution is determined from the time course of the characteristic parameter, and the statistical parameter is determined from the probability distribution, the statistical parameter being selected from the group consisting of a corresponding mean value, a corresponding variance and a corresponding skewness of the probability distribution,

[0026] wherein each acquired image includes a high-intensity region,

[0027] wherein the characteristic parameter is defined by the width and / or length and / or intensity of the high-intensity region,

[0028] Therein, the quality value indicates the quality of the cutting and / or piercing.

[0029] Advantageously, the above method further comprises at least one h) repetition step, during which at least steps c) to f), in particular steps a) to f), are repeated.

[0030] Advantageously, during said step d), said time course is determined for a certain time.

[0031] Advantageously, the determined time is constant.

[0032] Advantageously, said statistical parameter and said quality value are characteristic of the presence and / or formation and / or amount of dross.

[0033] Advantageously, further comprising the step of defining a desired quality value;

[0034] Therein, during the controlling step, the process parameter is controlled according to the quality value and the desired quality value.

[0035] Advantageously, during said step g), said process parameters are controlled in such a way as to obtain a quality value equal to said desired quality value.

[0036] Advantageously, each acquired image is a thermal image.

[0037] Advantageously, during said step d), a thresholding sub-phase is performed during which each acquired image is segmented in order to obtain a corresponding transformed image.

[0038] Advantageously, the high strength zone has a main portion and one or more elongate portions extending from the main portion.

[0039] Advantageously, during said step f), said quality value is obtained from said statistical parameter, said statistical parameter resulting from a linear function or a non-linear function.

[0040] Advantageously, during step c), said acquired images are acquired at a rate of at least 1000 frames per second, in particular at a rate of at least 1500 frames per second.

[0041] Advantageously, during step c), said acquired images are acquired at a rate of at least 1500 frames per second.

[0042] Advantageously, during step g), at least the intensity of the laser beam, and / or the laser frequency of the laser beam, and / or the focus position of the laser beam, and / or said determined speed, and / or the gas jet are controlled depending on said quality value.

[0043] Advantageously, controlling the gas jet in dependence on the mass value comprises controlling a gas pressure of the gas jet in dependence on the mass value.

[0044] The present invention further relates to a laser processing machine configured to cut and / or pierce a workpiece, wherein the laser processing machine comprises a control unit configured to perform the method as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Further features and advantages of the present invention will become apparent from the following detailed description given by way of non-limiting example with reference to the accompanying drawings, in which:

[0046] Figure 1 The laser processing machine according to the invention is shown in a schematic and partial manner;

[0047] Figure 2a Shown in Figure 1 Examples of images obtained during actuation of the processing machine;

[0048] Figure 2b and Figure 2c Shown Figure 2a The analysis steps of the control image;

[0049] Figure 3 shows a time course of characteristic parameters obtained from analysis of a plurality of acquired images; and

[0050] Figure 4 It shows that under two different conditions, Figure 1 The distribution of characteristic parameters obtained from respective time courses of the characteristic parameters during actuation of the processing machine. DETAILED DESCRIPTION

[0051] exist Figure 1 1 generally denotes a laser processing machine configured to cut and / or pierce a workpiece 2 .

[0052] Preferably, the workpiece 2 is made of a metal material. Specifically, the workpiece 2 has a planar shape and / or a tubular shape.

[0053] In more detail, the laser processing machine 1 includes:

[0054] a control unit 3 for controlling the actuation of the laser processing machine 1;

[0055] an emission source 4 of the laser beam 5 , which is operatively connected to the control unit 3 and is configured to emit the laser beam 5 ;

[0056] an optical group 6 (operably connected to the control unit 3 ) for controlling the laser beam 5 , in particular for directing the laser beam 5 along the optical axis A onto the workpiece 2 and at the working area 7 ;

[0057] Movement means, which are operatively connected to the control unit 3 and are configured to perform a relative movement between the laser beam 5 and the workpiece 2 at a determined speed, in particular to define a cutting and / or piercing shape.

[0058] In particular, it should be noted that the working zone 7 is the area of the workpiece 2 which is exposed to the laser beam 5 and thereby cut and / or pierced during use. Due to the relative movement between the laser beam 5 and the workpiece 2, it is dynamic during use.

[0059] Preferably, the laser processing machine 1 further includes:

[0060] Generating means (not shown and known per se) are operatively connected to the control unit 3 and are configured to generate a gas jet to direct the compound generated during cutting and / or piercing of the workpiece 2 away from the workpiece 2 .

[0061] According to some preferred non-limiting embodiments, the control unit 3 is configured to control the process parameters of the laser processing machine 1, in particular the intensity of the laser beam 5 and / or the laser frequency of the laser beam 5 and / or the focus position of the laser beam 5 and / or a determined speed of the relative movement between the laser beam 5 and the workpiece 2 and / or the gas jet and / or the gas pressure of the gas jet.

[0062] Preferably, the control unit 3 is configured to control the process parameters in a feedback mode.

[0063] It should be noted that process parameters are (substantially) all parameters which define the actuation of the laser processing machine 1 .

[0064] Advantageously, the laser processing machine 1 further comprises a monitoring device 8, which is configured to monitor the processing process, in particular the cutting and / or piercing process. In particular, the monitoring device 8 is configured to acquire a plurality of acquired images 9 of the working area 7 (in Figure 2a An exemplary acquired image is shown in FIG).

[0065] In particular, the monitoring device 8 is operatively connected to the control unit 3 , which is configured to control the actuation of the laser processing machine 1 at least as a function of information extracted and / or obtained from the acquired images 9 .

[0066] In particular, the monitoring device 8 is configured to acquire images 9 acquired during actuation of the laser processing machine 1 (in other words, the monitoring device 8 is configured to operate in an online mode).

[0067] According to some preferred non-limiting embodiments, the monitoring device 8 is configured to acquire process emissions, ie thermal emissions of the heat present at the working zone 7 .

[0068] Preferably, the emission source 4 comprises an ND:YAG laser or a CO2 laser, in particular of the fiber type.

[0069] In more detail, the optical group 6 is configured to direct the laser beam 5 onto the workpiece 2 and to determine the focus of the laser beam 5 .

[0070] Preferably, the optical group 6 is configured to define an optical path P from the emission source 4 to the workpiece 2, the optical path P comprising a first transverse portion P1, in particular perpendicular to the optical axis A, and a second portion P2 coaxial with the optical axis A. In other words, the laser beam 5 propagates along the portion P1 and the portion P2, respectively, wherein P1 is perpendicular to P2, and wherein the portion P2 preferably coincides with the optical axis A.

[0071] Preferably, the optical group 6 comprises at least one focusing lens 14 , which is configured to determine the focus of the laser beam 5 . Specifically, the focusing lens 14 is arranged in the portion P2 .

[0072] More particularly, the optical group 6 further comprises a collimating lens 15 and a dichroic mirror 16 configured to deflect the laser beam 5 from the portion P1 to the portion P2. In particular, the collimating lens 15 is arranged in the portion P1.

[0073] Preferably, the dichroic mirror 16 is arranged in such a way that the laser beam 5 is deflected from propagation along the first portion P1 to propagation along the second portion P2 .

[0074] In more detail, the moving device is configured to control the movement of the laser beam 5 relative to the workpiece 2 in the relative advancing direction D1 .

[0075] Preferably, the movement device comprises a support (not shown and known per se) configured for supporting the workpiece 2 , in particular the support being movable to be set in motion to obtain a relative movement between the laser beam 5 and the workpiece 2 .

[0076] Alternatively or additionally, at least a portion of the movement means is integrated in the support and / or associated with the support in order to move the workpiece 2 in order to obtain a relative movement between the laser beam 5 and the workpiece 2 .

[0077] Alternatively or additionally, the movement means comprise a movable support base carrying the emission source 4 and / or the optical group 6 and / or a part of the optical group 6 for moving the laser beam 5 .

[0078] In more detail, the monitoring device 8 comprises at least one camera 17, for example a CCD or CMOS type camera, which is configured to acquire the acquired images 9. In particular, the camera 17 is configured to continuously acquire the acquired images 9 in order to obtain a time sequence of acquired images 9. Even more particularly, the camera 17 is configured to acquire the acquired images 9 at a frequency of at least 1000 frames per second, in particular at least 1500 frames per second.

[0079] In particular, the camera 17 is configured to acquire a light beam 18 originating from the working area 7 , which light beam 18 propagates in use along a third direction (opposite to the second direction P2 ).

[0080] More particularly, the light beam 18 corresponds to a process emission at the working zone 7 .

[0081] Preferably, the light beam 18 passes through at least a portion of the optical group 6 , in particular the focusing lens 14 and the dichroic mirror 16 .

[0082] Preferably, the camera 17 is arranged coaxially with the optical axis A. In particular, the light beam 18 propagates parallel to the portion P2.

[0083] In more detail, the monitoring device 8 further comprises a filter set 19 configured to ensure that the camera 17 receives light within a defined wavelength band. In particular, the filter set 19 operates in the near infrared (it is a near infrared filter).

[0084] In particular, the filter group 19 is arranged upstream of the camera 17 with respect to the third direction.

[0085] In particular, the filter set 19 comprises a low-band filter (eg at 750 nm) and a low-pass filter (eg at 1000 nm).

[0086] It should be noted that during activation of the laser processing machine 1, the laser beam 5 cuts material from the workpiece 2 at the working zone 7, in particular by heating it, thereby forming a groove extending along the entire thickness of the workpiece 2. In particular, the laser beam 5 cuts the workpiece 2 from a first surface 20 of the workpiece 2 to a second surface 21 of the workpiece 2 opposite the first surface 20. Even more particularly, a first edge of the groove at the surface 20 and a second edge of the groove at the surface 21 opposite the first edge are formed.

[0087] It is also known that the gas jet should remove and / or displace the compounds generated during the cutting and / or piercing of the workpiece 2 at the working zone 7 before they cool down.

[0088] Furthermore, it is known that dross may form at the second edge during processing of the workpiece 2. This is due, inter alia, to the fact that the material removed by the laser beam 5 cools down and therefore stops before being removed from the workpiece 2, thereby generating dross.

[0089] In particular, the generation of dross is dependent on one or more process parameters, such as the intensity of the laser beam 5 and / or the laser frequency of the laser beam 5 and / or the position of the focus of the laser beam 5 and / or a determined speed of the relative movement between the laser beam 5 and the workpiece 2 and / or the gas jet and / or the gas pressure of the gas jet.

[0090] The process parameters are usually controlled in such a way that dross formation is substantially suppressed. However, this results in a reduction in productivity and may also lead to increased costs.

[0091] Applicants have recognized that dross formation need not be suppressed, but its tolerable presence and amount depends on the specific application.

[0092] To this end, as described below, firstly, the laser processing machine 1 is equipped with means for controlling the cutting and / or piercing quality and / or the presence and amount of dross (quantitatively and continuously in terms of time and amount of dross produced).

[0093] Advantageously, the control unit 3 is configured to determine a quality value from the acquired image 9 , in particular from an analysis of the acquired image 9 .

[0094] In particular, the quality value indicates the quality of the cutting and / or piercing.Even more particularly, the quality value describes the presence and / or amount of dross formed at the working area 7.

[0095] According to some preferred non-limiting embodiments, the control unit 3 is configured to determine the quality value continuously (in particular in terms of time and amount of dross produced) during the activation of the laser processing machine 1. In this way, the control of the cutting and / or piercing quality is guaranteed throughout the activation of the laser processing machine 1.

[0096] Preferably, the control unit 3 comprises an analyzing unit 22 which is configured to analyze and / or determine a quality value from the acquired image 9 .

[0097] In particular, the analysis group 22 is configured to determine at least one characteristic parameter from each acquired image 9 (see Figure 2c ), preferably determining a plurality of characteristic parameters.

[0098] Taking into account the fact that the acquired images 9 are determined at different moments in time, the analysis group 22 is further configured to determine the respective time course of one or more characteristic parameters of the acquired images 9 (see e.g. Figure 3 ).

[0099] The analysis group 22 is preferably further configured to calculate at least one statistical parameter, preferably a plurality of statistical parameters, from the characteristic parameter or the corresponding time course of the characteristic parameter, and to establish the quality value starting from the one or more statistical parameters. In particular, each time course is considered for a defined time, in particular, the defined time being constant.

[0100] In more detail, the analysis group 22 is configured to transform each acquired image 9 (independent of the other images) into a transformed image 23 (cf. Figure 2b ) to obtain the corresponding binary image.

[0101] Preferably, each transformed image 23 (binary image) comprises a first color (eg white) and a second color (eg black).

[0102] It should be taken into account that each acquired image 9 is characterized by information about the intensity of the process emission. In particular, a first color and a second color are associated with a respective region of each transformed image 23, which correspond to a respective region of the respective transformed image 23 whose intensity is respectively equal to or greater than a determined intensity threshold.

[0103] According to some preferred embodiments, each acquired image 9, and therefore the corresponding transformed image 23, comprises a respective high-intensity region 24, which in turn has a respective main portion 25, which can in particular be approximated and / or described by a circular shape, and one or more respective elongated portions 26, which extend from the respective main portion 25, in particular in a direction D2 parallel to the relative direction of advancement D1. In particular, each high-intensity region 24 (and therefore also the respective main portion 25 and the respective elongated portions 26) is defined by regions of the respective acquired image 9, the intensity of which is greater than or equal to a determined intensity threshold.

[0104] Special References Figure 2c , each characteristic parameter is defined by or according to the width w and / or length l and / or strength of the corresponding high-strength zone 24, in particular by or according to the width w and / or length l and / or strength of the corresponding main part 24 and the corresponding slender part 26.

[0105] In particular, the analysis group 22 is configured to determine from each acquired image 9 and / or from each transformed image 23 , preferably from each transformed image 23 , a respective width w and / or a respective length l and / or a respective intensity.

[0106] In particular, the respective width w of each high-strength zone 24 is defined by the maximum extension of the high-strength zone 24 in a direction D3 perpendicular to the relative advancement direction D1 .

[0107] More specifically, the maximum extension in direction D3 corresponds to the maximum extension of the respective main portion 24 in direction D3 .

[0108] In particular, the respective length l of each high-strength region 24 is defined as the maximum extension of the high-strength region 24 in the direction D2 from the center of gravity c of the high-strength region 24. In particular, the respective length l corresponds to the maximum extension of the respective elongated portion 26 furthest from the center of gravity c.

[0109] It should be noted that each characteristic parameter can be defined not only by the corresponding length l, by the corresponding width w or by the corresponding intensity, but also by a combination thereof and / or its corresponding time derivative.

[0110] In more detail, the analysis group 22 is further configured to determine a corresponding probability distribution from the corresponding time course of each characteristic parameter (see Figure 4 ), and determining a statistical parameter from the corresponding probability distribution. In particular, the corresponding statistical parameter is selected from the group consisting of a corresponding mean, a corresponding variance, and a corresponding skewness of the probability distribution.

[0111] In particular, Figure 4Two examples are shown of probability distributions determined during cutting of respective workpieces 2. The dashed probability distribution results from a laser cut with a higher quality than the probability distribution drawn with a solid line.

[0112] Obviously, the differences shown by the probability distributions shown can be described by corresponding medium values, corresponding variances and corresponding different skewnesses.

[0113] In more detail, the analysis group 22 is configured to determine the quality value based on statistical parameters from a nonlinear or linear function, in particular a nonlinear function. Preferably, the nonlinear function is approximated by a neural network which, in use, receives the statistical parameters to determine the quality value.

[0114] Preferably, analysis group 22 is configured to operate in a continuous mode (particularly in terms of time and quantity) to determine the temporal progression of quality values. In particular, analysis group 22 is configured such that, to determine each quality value, a plurality of acquired images 9 acquired consecutively and with a defined time period therebetween are analyzed. More particularly, analysis group 22 is configured to analyze a first plurality of acquired images 9 and a second plurality of acquired images 9 to determine a first quality value and a second quality value subsequent to the first quality value, respectively; and the first plurality of acquired images 9 and the second plurality of acquired images 9 at least partially overlap.

[0115] Preferably, the second plurality of acquired images 9 includes the same number of acquired images 9 as the first plurality of acquired images 9. The second plurality of acquired images 9 includes a defined number of additional acquired images 9 that have been acquired (with respect to the time course) after the acquired images 9 of the first plurality of acquired images 9 (in other words, the defined number of acquired images 9 follows the last acquired image 9 of the first plurality of acquired images 9 in the time course). Furthermore, the second plurality of acquired images 9 does not include the same defined number of acquired images 9 of the first plurality of acquired images 9 that were acquired before the other acquired images (i.e., the oldest acquired image 9 of the first plurality of acquired images 9 is not included in the second plurality of acquired images 9). In particular, the defined number is equal to or greater than one.

[0116] In other words, the first plurality of acquired images 9 and the second plurality of acquired images 9 cover the same time span, in particular equal to a defined time. The sequence of the first plurality of acquired images 9 comprises acquired images 9 acquired before all other images, while the second plurality of acquired images 9 comprises a sequence of acquired images 9, wherein at least one acquired image 9 was acquired after all other images of the first plurality of acquired images 9.

[0117] More specifically, the control unit 3 is further configured to receive and / or allow definition of a desired quality value, for example, via a human-machine interface of the laser processing machine 1. The desired quality value indicates a desired cutting and / or piercing quality. For example, the desired quality value indicates the presence and / or amount of dross. In particular, the desired quality value describes the permissible amount of dross.

[0118] Preferably, the control unit 3 is configured to control the process parameters depending on the determined one or more quality values and the desired quality value, in particular to obtain a quality value (substantially) equal to the desired quality value during the continuation of the cutting and / or piercing.

[0119] It should be noted that in the context of this specification the term "quality value" describes the quality level achieved.

[0120] It should also be noted that, in the context of this specification, the term "desired quality value" means that the desired quality value can be selected and / or controlled, for example, by an operator. The desired quality value can also be selected to obtain the highest quality cut and / or piercing (for example, to minimize or even avoid dross formation), however, the laser processing machine 1 and its actuation allow for control and / or arbitrary selection of the desired quality value.

[0121] In particular, the desired quality value describes the desired quality level, ie the quality level to be achieved by cutting and / or piercing.

[0122] In use, the laser processing machine 1 cuts and / or penetrates the workpiece 2 .

[0123] In particular, the activation of the laser processing machine 1 comprises at least the following steps:

[0124] a) directing a laser beam 5 onto a workpiece 2 at a working region 7 of the workpiece 2 in order to perform cutting and / or piercing;

[0125] b) performing a relative movement between the laser beam 5 and the workpiece 2 at a determined speed, in particular for defining the shape of the cut and / or piercing;

[0126] c) acquiring a plurality of acquired images 9 of the working area 7;

[0127] d) determining the time course of one or more characteristic parameters from the acquired images 9;

[0128] e) calculating at least one corresponding statistical parameter from the time course of each characteristic parameter;

[0129] f) establish quality values based on statistical parameters; and

[0130] g) controlling one or more process parameters (of the laser processing machine 1 ), such as the intensity of the laser beam 5 , the laser frequency of the laser beam 5 , the focus position of the laser beam 5 , a specific speed of the relative movement between the laser beam 5 and the workpiece 2 , the gas jet or the gas pressure of the gas jet, in particular in feedback as a function of the quality value.

[0131] Preferably, the activation of the laser processing machine 1 comprises one or more repetitive steps, during which at least steps c) to f), preferably steps a) to f), are repeated.

[0132] Preferably, steps c) to g) are performed during the following steps a) and b).

[0133] In more detail, during the step of directing the laser beam 5 onto the workpiece 2, the emission source 4 emits the laser beam 5, and the optical unit 6 directs the laser beam 5 onto the workpiece 2. In particular, the control unit 2 controls the focus of the laser beam 5 by means of controlling the optical group 6 (in particular the focusing lens).

[0134] Preferably, during step b), the workpiece 2 and / or the laser beam 5 are moved. In particular, during step b), the support carrying the workpiece 2 and / or the support base carrying the emission source 4 and / or the optical group 6 are moved. More preferably, only the support is manipulated to move only the workpiece 2.

[0135] Preferably, during step b), a relative movement is also performed between the monitoring device 8 and the workpiece 2. In particular, no relative movement is performed between the laser beam 5 and the monitoring device 8.

[0136] It should be noted that due to the relative movement between the laser beam 5 and the workpiece 2 , the working area 7 also changes with respect to the workpiece 2 over time.

[0137] In more detail, during step c), the acquired image 9 is determined by the monitoring device 8 , in particular by the camera 17 .

[0138] In particular, during step c), the camera 17 acquires process emissions (ie heat).

[0139] In particular, during step c), each acquired image 9 is acquired at a different time than the other images. Therefore, each acquired image 9 also corresponds to a different working area 7.

[0140] Preferably, during step c), the acquired images 9 are acquired, in particular by the monitoring device 8 , more particularly by the camera 17 , at a frequency of at least 1000 frames per second, in particular at least 1500 frames per second.

[0141] In more detail, during step d), the time course of each characteristic parameter is determined for a defined time, in particular a defined and constant time (in other words, the number of acquired images 9 for determining each characteristic parameter is constant and predetermined).

[0142] Preferably, during step d), a transformation sub-step is performed during which each acquired image 9 is transformed into a corresponding transformed image 23 . Thereafter, each characteristic parameter is obtained from the transformed image 23 .

[0143] In particular, this transformation step is a thresholding sub-phase during which each acquired image 9 is segmented in order to obtain a corresponding binary image (transformed image 23 ).

[0144] In particular and with particular reference Figure 2b During the thresholding sub-phase, a first color (e.g. white) is associated with respective regions of each transformed image 23 (binary image) corresponding to respective regions of the respective acquired image 9 whose intensity is respectively equal to or greater than the determined intensity threshold, and a second color (e.g. black) (binary image) is associated with respective regions of the respective acquired image 9 having an intensity respectively below the determined intensity threshold.

[0145] In particular, during the thresholding sub-phase, each pixel of the respective acquired image 9 is associated with a first color or a second color, based on the determined intensity threshold, to obtain the respective transformed image 23. The first color is associated with pixels having an intensity equal to or greater than the determined intensity threshold, and the second color is associated with pixels having an intensity below the determined intensity threshold.

[0146] Preferably, during step d), each transformed image 23 (binary image) is analyzed to determine one or more characteristic parameters defined by or depending on the width and / or length and / or intensity of the high-intensity areas 24 .

[0147] In particular, during step d), the respective width w of each high-strength zone 24 is determined by the maximum extension of the high-strength zone 24 (in particular of the respective main portion 25 ) in the direction D3 .

[0148] In particular, during step d), the respective length l of each high-strength zone 24 is determined by the maximum extension of the high-strength zone 24 (in particular the elongated portion) in the direction D2 from the center of gravity c of the high-strength zone 24 .

[0149] In more detail, during step e), a corresponding probability distribution is determined from the time course of each characteristic parameter (cf. Figure 4 ), and a statistical parameter is determined from the corresponding probability distribution. In particular, each statistical parameter is selected from the group consisting of a corresponding mean, a corresponding variance, and a corresponding skewness of the corresponding probability distribution.

[0150] In more detail, during step f), a quality value is obtained from a statistical parameter coming from a non-linear or linear function, preferably from a non-linear function.

[0151] In particular, the nonlinear function is approximated by means of an artificial neural network which receives one or more statistical parameters as parameters.

[0152] According to a preferred, non-limiting embodiment, the statistical parameter and the quality value characterize the presence and / or formation and / or amount of dross.

[0153] Preferably, the activation of the laser processing machine 1 also includes a step of defining a desired quality value. This desired quality value defines the desired cutting and / or piercing quality. In particular, during this step, the user is given the possibility to define a cutting and / or piercing quality sufficient for a specific purpose and to optimize the quality-price ratio.

[0154] In more detail, during step g), the process parameters are checked according to the determined quality values and the expected quality values.

[0155] Preferably, during step g), the process parameters are controlled in such a way that a quality value substantially equal to the desired quality value is obtained.

[0156] By examining the characteristics of the laser processing machine 1 and the method of actuation thereof according to the invention, the advantages it allows to obtain are evident.

[0157] In particular, the laser processing machine 1 and its actuation allow continuous monitoring of the cutting or piercing quality, in particular in terms of time and quantity, and control of the actuation according to the quality, which is manifested in a quantitative manner according to the determined quality value.

[0158] Another advantage lies in the use of statistical parameters obtained from processing the time course of the characteristic parameters. This allows obtaining non-discrete information determined only for a specific location and a specific moment, but also information reflecting a larger data set. This increases the accuracy of the determination.

[0159] Another advantage is that it is possible to determine the desired quality value. In this way, the operator is given the possibility to optimize the quality-price ratio of the workpiece 2.

[0160] Finally, it is obvious that modifications and variations may be made to the laser processing machine 1 and the actuation method described and illustrated herein, without departing from the scope of protection defined by the claims.

Claims

1. A method for laser processing a metal workpiece (2), comprising at least the following steps: a) directing a laser beam (5) onto a workpiece (2) at a working area (7) of the workpiece (2) in order to perform cutting and / or piercing; b) performing relative movement between the laser beam (5) and the workpiece (2) at a determined speed; c) acquiring a plurality of acquired images (9) of the working area (7); d) determining a time course of at least one characteristic parameter from the acquired images (9); e) calculating at least one statistical parameter from said time course of said characteristic parameter; f) establishing a quality value based on the statistical parameters; g) controlling one or more process parameters based on said quality value, wherein during step e) a probability distribution is determined from the time course of the characteristic parameter, and the statistical parameter is determined from the probability distribution, the statistical parameter being selected from the group consisting of a corresponding mean value, a corresponding variance and a corresponding skewness of the probability distribution, wherein each acquired image (9) comprises a high intensity region (24), wherein the characteristic parameter is defined by the width and / or length and / or intensity of the high-strength region (24), Therein, the quality value indicates the quality of the cutting and / or piercing. 2 . The method according to claim 1 , further comprising at least one h) repeating step, during which at least steps c) to f) are repeated. 3 . The method according to claim 2 , wherein during the repeating step, steps a) to f) are repeated.

4. The method according to claim 1, wherein During step d), the time course is determined for a specific time. The method according to claim 4 , wherein the determined time is constant.

6. The method according to claim 1, wherein The statistical parameter and the quality value characterize the presence and / or formation and / or amount of dross.

7. The method according to claim 1, further comprising the step of defining a desired quality value; in, During the controlling step, the process parameter is controlled depending on the quality value and the desired quality value. 8 . The method according to claim 7 , wherein during step g) the process parameters are controlled in such a way that a quality value equal to the desired quality value is obtained.

9. The method according to claim 1, wherein Each acquired image (9) is a thermal image.

10. The method according to claim 1, wherein During said step d), a thresholding sub-phase is performed during which each acquired image (9) is segmented in order to obtain a corresponding transformed image (23).

11. The method according to claim 1, wherein The high-strength region has a main portion (25) and one or more elongated portions (26) extending from the main portion (25).

12. The method according to claim 1, wherein During said step f), said quality value is obtained from said statistical parameter, said statistical parameter being derived from a linear function or a non-linear function.

13. The method according to claim 1, wherein During step c), the acquired images (9) are acquired at a rate of at least 1000 frames per second.

14. The method according to claim 1, wherein During step c), the acquired images (9) are acquired at a rate of at least 1500 frames per second.

15. The method according to claim 1, wherein During step g), at least the intensity of the laser beam (5), and / or the laser frequency of the laser beam (5), and / or the focus position of the laser beam (5), and / or the determined speed, and / or the gas jet are controlled depending on the quality value.

16. The method according to claim 15, wherein Controlling the gas jet according to the mass value includes controlling a gas pressure of the gas jet according to the mass value.

17. A laser processing machine (1) configured to cut and / or pierce a workpiece (2), comprising a control unit (3) configured to perform the method according to claim 1.

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