DE102009049750A1 - Method for cutting of materials using modulated laser beam that cut the material along a desired cutting path through application of laser pulses, comprises freely selecting the pulse length of the laser pulse - Google Patents

Abstract

The method for cutting of materials using modulated laser beam (L) that cut the material along a desired cutting path through application of laser pulses, comprises freely selecting the pulse length of the laser pulse, where the intensity of the laser pulse and/or the interval between two laser pulses and/or the modulation frequency and/or the beam scanning velocity of the modulated laser beam is freely selected as further parameter. The pulse length of the laser pulse is changed during the cutting process and a further parameter is changed during the cutting process. The method for cutting of materials using modulated laser beam (L) that cut the material along a desired cutting path through application of laser pulses, comprises freely selecting the pulse length of the laser pulse, where the intensity of the laser pulse and/or the interval between two laser pulses and/or the modulation frequency and/or the beam scanning velocity of the modulated laser beam is freely selected as further parameter. The pulse length of the laser pulse is changed during the cutting process and a further parameter is changed during the cutting process. One of the parameters is held constant in a time interval during the cutting process. The cutting path repeatedly passes by the modulated laser beam during the cutting process. During passing the cutting path, the beam scanning velocity of the modulated laser beam is changed and/or the start point is provided for a conduit with a variable offset, and/or the interval between the laser pulses is changed in order to receive an offset of laser cutting point caused by the laser pulse on the material to be cut between the individual flow paths. The pulse length of the laser pulse is changed between two individual steps. The cutting process comprises three steps such as a first step for the application of a surface coating on the material to be cut, a second step with a changed pulse length of the laser pulse for cutting ablation of the material to be cut, and a third step with a changed beam scanning velocity of the modulated laser beam for cutting the material. The second and third steps are carried out with a changed parameter during the cutting process. An independent claim is included for a device for cutting of materials such as coated and/or lacquered body panels using modulated laser beam.

Description

The invention relates to a method for cutting material by means of a laser beam. The invention further relates to a device for carrying out the method and a preferred use for the method and / or for the device.

The energy introduced during cutting by means of a laser beam into the material to be cut, in particular in the form of heat, can be undesirably high. In order to keep the energy input low, is in the DE 10 2004 039 023 A1 proposed to use a laser source which emits a pulsed laser beam which cuts the material along a desired cutting path or line of intersection by a juxtaposition of a plurality of laser cutting points, which are generated by the individual laser pulses. It is also proposed that both the energy of the laser pulses and the time interval between two successive laser pulses can be chosen freely, whereby the energy input into the material can be influenced.

The object of the invention is to optimize the cutting of material by means of a laser beam.

This object is achieved by a method according to claim 1. This object is further achieved by a device according to the first independent claim. Advantageous and preferred developments are the subject of the respective dependent claims. The solution of the problem also extends to a use according to the second independent claim.

The inventive method is used for cutting material by means of at least one laser beam which cuts the material to be cut along a desired cutting path by applying a plurality of laser pulses, wherein the laser beam is a modulated laser beam, wherein at least the pulse length or pulse duration of the laser pulses substantially can be chosen freely.

The inventive method is used in particular for cutting a closed or open contour or cutting contour with any geometry.

Preferably, the material to be cut is a plastic material (preferred thickness up to 3.0 mm), a CFRP material (preferred thickness up to 3 mm), a composite material or a leather material.

In particular, the material to be cut is a sheet material and primarily a sheet steel material. The preferred sheet thickness is z. B. 1.0 mm, but especially more than 0.5 mm. It is preferably provided that it is a sheet material coated at least on one side. A coating may, for. B. a corrosion protection coating such. B. be a zinc layer or a paint. The sheet material may be formed as a workpiece or component.

A modulated laser beam is understood to mean a laser beam which is formed from individual laser pulses generated in succession, the individual laser pulses being modulatable, i. H. changeable and thus adjustable. It is provided that at least the temporal pulse length or pulse duration of the laser pulses can be selected substantially freely. The term "essentially" means within the scope of the technically possible. It is preferably provided that all laser pulses are modulated the same within a defined time interval. However, it can also be provided that individual, successive laser pulses are modulated individually and independently of each other.

According to the invention, each individual laser pulse generates a corresponding laser cutting point (dot) on or in the material to be cut. By moving the modulated laser beam along the cutting path, a plurality of laser cutting points are applied to the material to be cut, resulting in a cutting gap as a result. However, according to the invention it is not necessary, although possible, for the laser cutting points of the temporally successive laser pulses to be arranged on the material to be cut, as shown in FIG DE 10 2004 039 023 A1 is described. Alternatively, it is also possible to generate staggered laser cutting points. Moreover, it is otherwise not necessary that the laser cutting points generated by the laser pulses completely penetrate the material to be cut. Alternatively, there is the possibility of a successive cutting process in which, during the cutting operation, the cutting gap is introduced into the material to be cut by successively increasing the cutting depth along the cutting path (for example, spirally). The invention also includes the resulting combination possibilities.

The use of a modulated laser beam offers the possibility of a very precise adjustment of the laser beam power or laser beam intensity. Power is understood in accordance with the general definition of an energy per time or time interval. Under intensity is determined according to the general definition of an energy per time or time interval and area understood (corresponds to a power per area). The laser beam power correlates directly with the resulting cutting performance. However, a significant proportion of the laser beam power or the laser beam energy is converted into heat in the material to be cut, resulting in processing limits. By using a modulated laser beam whose laser beam power can be set very precisely, the energy input, which acts on the material to be cut within a certain section or along a specific processing path of the cutting path and primarily leads to heating there, can be selected or set in this way. that optimal material processing can always be guaranteed. In other words, the energy introduced by the modulated laser beam along the cutting path into the material to be cut can be adapted much better to the respective cutting process. As a result, processing speeds can be increased and processing times can be reduced.

The use of a modulated laser beam also advantageously enables the cutting of coated and / or lacquered sheet materials, as well as the use as a marking laser, as explained in more detail below.

The use of a modulated laser beam also allows a novel design of the cutting process. The so-called sublimation cutting is known from the prior art, in which the material to be cut is sublimated by means of a laser beam along the cutting path to form a cutting gap. The cutting speed is relatively slow and is z. B. 3 mm / sec, which is why the sublimation cutting is not suitable in particular for the production of large-area and / or long cutting contours. The so-called fusion cutting is also known from the prior art, in which the material to be cut is melted by means of a laser beam along the cutting path and z. B. is blown out of the generated cutting gap by means of a separate blowing device. The cutting speed is relatively high and is z. B. 40 mm / sec. A disadvantage of fusion cutting, however, is the sometimes very high energy input into the material to be cut and burr formation on the cut edge as a result of the blowing out of the melt.

The use of a modulated laser beam enables a cutting operation, which can be referred to as "cutting removal". Such Schneidabtragen is particularly suitable for metallic materials and primarily sheet materials. When Schneidabtragen carried out a discharge of the individual laser pulses of the modulated laser beam selectively melted material (melt) from the cutting gap (or from the individual laser cutting points) due to an adjusting expansion pressure of the phase transition of solid or liquid phase into a gaseous phase. As a result, a largely burr-free cutting gap is generated. In addition, a very high cut edge quality is achieved. In the case of cutting abrasion, it is possible to achieve speeds which correspond approximately to those of fusion cutting, but the energy input which acts on the material to be cut within a certain working distance of the cutting path can be kept below a critical level for the material. The cutting speed when Schneidabtragen is z. B. 35-45 mm / sec and preferably 40 mm / sec. This corresponds approximately to 12 times the cutting speed of sublimation cutting. However, the cutting speed at Schneidabtragen can also be below or above this specified range.

The use of a modulated laser beam advantageously allows a very flexible design of the cutting process, in particular also with regard to materials and material combinations that could not previously or not satisfactorily or only very slowly cut by means of a laser beam.

According to a preferred development it is provided that, in addition to the pulse length of the laser pulses, the intensity of the laser pulses and / or the time interval between two successive laser pulses and / or the modulation frequency and / or the beam-guiding speed of the modulated laser beam are also chosen to be substantially free as further parameters can or can. The term "essentially" means within the scope of the technically possible. In this way, an even more precise adjustment of the laser beam power can be made possible, in particular taking into account the energy introduced along the cutting path into the material to be cut.

• – die Pulslänge bzw. Pulsdauer der Laserpulse;
• – die Intensität der Laserpulse;
• – der zeitliche Abstand zwischen zwei aufeinanderfolgenden Laserpulsen;
• – die Modulationsfrequenz; und
• – die Strahlführungsgeschwindigkeit des modulierten Laserstrahls.

The relevant parameters of the modulated laser beam in the sense of the invention are:

• - The pulse length or pulse duration of the laser pulses;
• The intensity of the laser pulses;
• The time interval between two successive laser pulses;
• The modulation frequency; and
• - The beam velocity of the modulated laser beam.

The pulse length of the laser pulses, the intensity of the laser pulses, the time interval between two successive laser pulses and the modulation frequency have a direct influence on the laser beam power. The beam guidance speed can have a significant influence on the energy introduced locally into the material to be cut. In addition, other parameters can exist that have an influence on the laser beam power and / or the energy input into the material to be cut.

The previously named parameters each have a setting, i. H. a concrete value. According to the invention, it is provided that at least the adjustment of the pulse length of the laser pulses is essentially freely selectable, ie. H. changeable and thus adjustable. Preferably, the settings for the other parameters are freely selectable, d. H. changeable and thus adjustable. The time interval between two successive pulses can, for. B. by changing the modulation frequency or alternatively by changing the pulse length at the same modulation frequency. It should be noted that the modulation frequency and the time interval between two consecutive laser pulses can in principle be changed independently of one another. It should also be noted that the beam guidance speed does not have to correspond to the real cutting speed. Rather, the beam steering speed and the cutting speed may also be different.

According to a preferred development it is provided that at least the pulse length of the laser pulses is changed during the cutting process. The change of the pulse length is preset. Likewise, a control loop would be possible, including z. B. the heating and in particular local heating of the material to be cut could be detected.

According to a preferred embodiment, it is provided that, in addition to the pulse length of the laser pulses, at least one further parameter, as indicated above, is changed during the cutting process. This is preferably done by default, whereby a control loop would be conceivable.

According to a preferred development, it is provided that during such a change of at least one parameter during the cutting process of at least one of the parameters, as stated above, is kept constant at least in a time interval. It is preferably provided that the changed parameter itself is kept constant over a time interval.

According to a preferred development, it is provided that during the cutting process, the cutting path is repeatedly traversed or passed through by the modulated laser beam. Ie. The modulated laser beam passes through the cutting path several times. It is preferably provided that the modulated laser beam traverses the cutting path repeatedly exactly. However, for single or a plurality of passes and a track offset is conceivable to z. B. to make a forming cutting gap wider. In this case, it is preferably provided that the laser cutting points are not lined up but offset in the material to be cut.

According to a preferred embodiment, it is provided that in this repeated passage through the cutting path, the beam guidance speed of the modulated laser beam is changed and / or the starting point for a pass or circulation is provided with a variable offset and / or the time interval between the laser pulses is changed, in order to bring about an offset of the laser cutting points caused by the laser pulses on or in the material to be cut between the individual passes. A respective setting preferably applies to a passage of the modulated laser beam. Changing a setting is done by default. Likewise, a control loop would be conceivable.

The idea here is that during a pass of the modulated laser beam, the laser pulses along the cutting path generate mutually spaced laser cutting points and that in a subsequent pass of the modulated laser beam, the laser pulses impinge on other location points of the cutting path than in the previous run and thus generate offset laser cutting points. There are so many passes of the modulated laser beam until the entire cutting path is covered with laser cutting points. Compared to a conventional juxtaposition of laser cutting points along the cutting path, as in the DE 10 2004 039 023 A1 described, despite a very high laser beam power, the energy that is introduced within a certain processing path of the cutting path in the material to be cut, be kept below a critical level. The averaged over the cutting path energy input, which leads to the heating of the material to be cut, falls due to the high laser power overall very high. Locally, however, the energy input remains below a disadvantageous level for the material to be cut.

This succeeds particularly well if the distance between the individual laser cutting points is set as large as possible from one pass to the next, so that cooling can take place in which the heat introduced at a laser cutting point into the material to be cut is diverted into the still cool or again cool material environment which avoids congestion heat and the temperature or the temperature gradient in one permissible range or below a critical level can or can be maintained. The beam guidance speed can be z. B. 5000 mm / sec, this does not correspond to the cutting speed, which can be determined only mathematically as average processing speed and which z. B. in the range of considerable 35-45 mm / sec.

Such a cutting process, in which the laser cutting points are arranged offset during different passes of the modulated laser beam along the cutting path, as explained above, is conceivable without the use of a modulated laser beam. So z. For example, a conventional Q-switched laser can be used. The offset of the generated laser cutting points could then z. B. set by a current beam steering speed. However, the use of a modulated laser beam according to the preceding embodiments offers excellent possibilities for adjusting the laser beam power, taking into account the energy introduced along the cutting path into the material to be cut.

Incidentally, in such a cutting operation in which the laser cutting points are staggered along the cutting path during different passes of the modulated laser beam, it is not necessary for the laser cutting points generated by the laser pulses to completely penetrate the material to be cut. Alternatively, there is the possibility of a "successive cutting process", in which the cutting depth along the cutting path during the cutting process successively increased and thus gradually a cutting gap is introduced into the material to be cut. In this case, it is then provided that individual location points of the cutting path are repeatedly tapped in different passes of the modulated laser beam (with complete or even only partial coverage). For this purpose, a modulated laser beam according to the preceding embodiments is particularly well suited, due to the excellent possibilities already described for setting the laser beam power. When using a modulated laser beam, it is possible in particular to differently modulate the laser pulses impinging on the same location point during different passes of the modulated laser beam, preferably with an at least different pulse length. Such a cutting process appears to be particularly useful with heat-sensitive materials, with large material thicknesses (eg steel sheet materials with a thickness of ≥ 0.5 mm) or multilayer materials, such. B. composite materials.

According to a preferred embodiment, it is provided that the cutting process is designed as a whole as a multi-stage cutting process or cutting process, wherein at least the pulse length of the laser pulses between two individual processing stages (hereinafter referred to as stages) is changed. This preferably relates to a cutting process in which the cutting path is traversed repeatedly by the modulated laser beam, according to the preceding embodiments. A stage preferably comprises at least one pass of the modulated laser beam along the cutting path. In particular, one stage comprises a plurality of passes, wherein the laser cutting points are staggered along the cutting path during the various passes of the modulated laser beam, according to the preceding embodiments. It is also possible to line up the laser cutting points in individual passes. This results in various possible combinations, which allows a flexible design of the cutting process. It is preferably provided that the setting of the pulse length is kept constant within a stage, which, however, does not necessarily have to be the case.

According to a preferred development, it is provided that at least one further parameter, as indicated above, is changed between two individual stages. The relevant parameter can be changed between the same stages, between which the pulse length of the laser pulses is changed, or between other stages. Here, too, it is provided that a setting is kept constant at least within one stage.

According to a preferred embodiment, it is provided that the multi-stage cutting process comprises at least three stages or steps. In particular, these are: a first stage for removing a surface coating (for example a corrosion protection coating or a lacquer coating) on the material to be cut, a second stage having at least one changed pulse length of the laser pulses, preferably an extended pulse length, for cutting removal of the material to be cut, and a third stage with at least one changed beam-guiding speed, preferably a reduced beam-guiding speed, of the modulated laser beam for (final) cutting through or final cutting of the material to be cut. The material to be cut is in particular a metallic material. By "cutting away" is a spreading of the modulated laser beam melted material, in particular metal material, from the cutting gap due to the adjusting pressure of the expansion of the phase transition from solid or liquid phase into the gaseous phase understood (see above in this regard). This can be achieved by adjusting the parameters given above. Such a three-stage cutting process is particularly suitable for cutting a coated and / or painted sheet metal material.

According to a preferred development, it is provided that in the above-described three-stage cutting process during the cutting operation, the second stage and third stage are alternately performed with at least one changed parameter, as stated above. Preferably, a modified setting is determined as a function of the material properties of the material to be cut, its heat flow properties (heat conductivity) or heat storage properties (heat capacity), the contour of the cutting path and / or the position of the material to be cut relative to the modulated laser beam. (This can in principle apply to each setting to be selected).

Alternatively, instead of the previously described three-stage cutting process, it is possible to provide only a two-stage cutting process, which virtually eliminates the third stage and thus only a first stage for removing a surface coating on the material to be cut and a second stage for cutting away the material to be cut includes. Preferably, a method is provided which comprises at least these two stages.

The above statements relating to the method according to the invention also apply mutatis mutandis to the device according to the invention explained below and vice versa. Furthermore, in the context of the invention all further developments and features explained here can be combined, provided that this does not result in a technical contradiction.

• – wenigstens eine Laserquelle, wobei der erzeugte Laserstrahl ein modulierter Laserstrahl ist, bei dem zumindest die Pulslänge der Laserpulse im Wesentlichen frei gewählt werden kann;
• – wenigstens eine Ablenkeinrichtung zur Lenkung und ggf. auch Fokussierung des von der Laserquelle erzeugten modulierten Laserstrahls auf dem zu schneidenden Material; und
• – wenigstens eine Steuereinheit zur verfahrensgemäßen Steuerung der Laserquelle und/oder der Ablenkeinheit.

The device according to the invention serves to carry out the method according to the invention. It includes:

• - At least one laser source, wherein the laser beam generated is a modulated laser beam, wherein at least the pulse length of the laser pulses can be selected substantially freely;
• - At least one deflection device for steering and possibly also focusing the modulated laser beam generated by the laser source on the material to be cut; and
• - At least one control unit for procedural control of the laser source and / or the deflection unit.

The laser beam generated by the laser source is a modulated laser beam, which is formed from individual, successively generated laser pulses, the individual laser pulses are modulated or variable and thus adjustable in such a way that at least the temporal pulse length of the laser pulses in Essentially freely chosen.

The use of a modulated laser beam offers the possibility of a very precise adjustment of the laser beam power, whereby the laser beam power and the associated cutting performance can be increased without the introduced into the material to be cut energy input exceeds a critical level for the material. As a result, the previous processing speeds (based on the sublimation cutting) increased by up to 12 times and the processing times are reduced accordingly. In particular, reference is made to the above relevant comments on the method according to the invention.

The use of a modulated laser beam also offers the possibility to lower the laser beam power so far that the modulated laser beam z. B. could be used for labeling, which opens up opportunities for novel combination applications, as explained in more detail below in connection with the preferred use.

The deflection is z. B. by a mirror system (Galvo scanner system) by means of which the modulated laser beam generated possibly focused and the focus of the laser beam (diameter, eg., 30-40 microns) from a distance or from a particular larger distance over the cutting Material is led. Depending on the configuration of the deflection device, relatively large scanner fields are possible (eg 250 mm × 250 mm). This can be relatively large and / or long cutting contours realize without Geometriebre-ränkung with short processing times.

The distance or the distance between the deflector and the material to be cut is up to several hundred millimeters. The distance is z. B. 350-400 mm, wherein the distance can also be larger or smaller. Because of this distance, the method according to the invention can also be referred to as remote laser cutting and the device according to the invention as a remote laser cutting device. An advantage of remote laser cutting is that a ground connection to the material to be cut is usually not required.

The greater distance between the deflector and the material to be cut is, inter alia, with a relatively large Focusing tolerance accompanied (> ± 0.3 mm and in particular ± 1.5 mm), which contributes to a safe process management. This may possibly be a previously customary distance control omitted, which means a reduced control effort and fewer error influencing variables and which also contributes to a reduction of equipment and operating costs.

The deflection device is preferably a 3D scanner system, which also permits a spatial depth of the scanner field (no restriction on 2D cutting contours and thus also application on shaped materials, that is to say components and workpieces). The scanner volume of such a 3D scanner system is z. B. 250 mm × 250 mm × 20 mm or 250 mm × 250 mm × 40 mm.

It is preferably provided that at least the deflecting device is attached to a robot arm, by means of which a movement and positioning in space and possibly relative to the material to be cut can take place.

The control unit for controlling the laser source and / or the deflection unit according to the invention is preferably a computer device which comprises a special software program.

The device according to the invention has a long service life and a relatively low maintenance, which contributes to a cost reduction over the entire running time.

According to a preferred embodiment, it is provided that the laser source is a fiber laser. Fiber lasers are a special form of solid state lasers and are known as such from the prior art. Fiber lasers have a long service life, whereby z. B. the maintenance costs are relatively low. Another advantage is the ambient temperature independence and the temporal power stability. In particular, it is an ytterbium single-mode fiber laser with a fiber diameter (Feedingfaser) of 14 microns. The generated wavelength of the modulated laser beam is in the infrared range.

According to a preferred development it is provided that the device comprises at least one device for generating a cross flow (crossjet) to the modulated laser beam. The cross flow is used to keep the laser beam path of smoke, and to reduce precipitation on the window of the deflector and / or on the material to be cut. Optionally, such a transverse flow can also be used for cooling the material to be cut. Preferably, the device for generating the transverse flow comprises at least one cross-flow nozzle. Preferably, the means for generating the cross flow is also controlled by the control unit. Preferably, the device for generating the transverse flow or the cross-flow nozzle is attached to the deflection device or possibly the robot arm thereof. Alternatively, an attachment to a separate robot arm may be provided.

The invention also extends to a preferred use of the method according to the invention and / or the device according to the invention for cutting vehicle body panels. In particular, these are coated and / or painted body panels, for example. From a steel sheet material or an aluminum sheet material. However, CFRP materials and plastics can also be cut.

The inventive method and / or the device according to the invention can or can, for. B. for cutting holes or breakthroughs on an at least partially joined and / or painted (or pre-painted) vehicle body can be used, which can serve to adapt to individual requirements ("Late Configuration"). Breakthroughs can z. B. end wall, tunnel or roof openings, such. As a steering column breakthrough on the front wall (adaptation to right / left-hand drive). By means of the deflection device, a large scanner field can be covered to produce large apertures with low processing time. The producible hole diameter be z. B. significantly more than 6.5 mm, the producible Schnittkantenlängen be up to 800 mm and more, with processing times may be less than 30 sec. The cutting of a hole with an area of about 500 mm ² and with an edge length of about 20 mm × 25 mm on a body panel required z. B. 2 sec.

The cutting takes place here without contamination and / or damage to the underlying substructures. The accessibility to the relevant body sites can be accomplished by attaching the deflector to a robotic arm. Compared to a robot-guided laser beam, the accessibility to the material to be cut is also improved by the use of a deflection device, in particular if this is a 3D scanner system. The use of a deflection device, in particular in combination with a modulated laser beam, furthermore offers the advantages that there are essentially no geometry limitations with regard to the contours or sectional contours (ie essentially any geometric shape can be represented) and that this is essential in comparison to a robot-guided laser beam finer geometries with narrower tolerance fields, even with large and / or long cutting contours are possible.

As already explained above, a modulated laser beam can also be used for labeling when the laser beam power is reduced. Thus, the same device in the production line z. B. for the generation of breakthroughs, such as. B. for the steering column, and for introducing or labeling the VIN. This is advantageously supported by the use of a 3D scanner system. An essential advantage of the modulated laser beam is the fast adaptability of its laser beam power to a specific cutting or labeling process.

By means of the method according to the invention and / or by means of the device according to the invention, in particular also lacquered sheet metal materials, primarily also body panels made of a steel material with a higher thickness, can be processed ("lasers according to lacquer"), in which case also large-area and / or long cut contours can be realized. In order to avoid the problem of paint burns and paint delamination (blistering, spalling etc. as a result of energy input or heat input), a multi-stage cutting process is proposed, as explained above, in which first a paint removal with low laser beam power takes place in a first stage. With the method according to the invention and / or with the device according to the invention, steel sheet thicknesses of up to 1.0 mm (or even more) and paint thicknesses or paint constructions of up to 300 μm (or even more) can be processed without difficulty, ie. H. cut and possibly also be labeled.

The invention will be explained in more detail by way of example with reference to the figures. Show it:

1 a device according to the invention in a schematic view;

2 a schematic sectional view through the material to be cut during the cutting process;

3 schematically the introduction of laser cutting points along a cutting path in a plan view;

4 an example of the temperature profile in the material to be cut in a schematic sectional view, which is substantially the sectional view of 2 corresponds;

5 a multi-stage cutting process in an illustrative representation; and

6 Laser pulses of a modulated laser beam in a diagrammatic view (with reference to FIGS 5 ).

1 shows a device according to the invention in a schematic view. The total with 1 designated device is used for cutting (and possibly also labeling) of a material M, which is in particular a sheet material, by means of a modulated laser beam L, as explained in more detail below.

To the device 1 one belongs as a fiber laser 2 trained laser source with a radiation source 21 , such as B. a diode laser device whose generated radiation (eg pump light) in the flexible waveguide or in the fiber 23 is fed. This fiber 23 contains the active medium in which the laser amplification takes place. Such or similar fiber lasers are known in the art.

To the device 1 also includes a designed as a 3D scanner system deflection 3 to which the fiber 23 with her from the beam source 21 tethered end is tethered. The connection is made by means of a coupling (coupling-out optics) 31 , which generates the generated laser radiation in the deflection device 3 continue forwards. The deflection device 3 includes motorized focusing means 32 (Lens system) and motorized deflection means 33 (Mirror system) for the laser radiation. One by means of focusing 32 and deflecting means 33 in the room focusable and steerable laser beam L occurs at a window 34 from the deflector 3 from and hits the remotely located to be cut material M (or workpiece or component). The distance between the deflector 3 and the material M to be cut is indicated by d.

By means of the deflection means 33 For example, the laser beam L on the material M to be cut can describe a cutting path B. By means of focusing means ( 32 ), the laser beam can be focused on the material M to be cut (focus diameter eg 30-40 μm).

The deflection device 3 is on a robotic arm 4 attached, by means of which the deflector 3 in the processing space (x, y, z) can be moved and positioned. During a cutting process typically no movement movements are provided, ie the deflection device 3 remains stationary with respect to the material M to be cut. Alternatively, z. As well as a portal structure conceivable.

To the device 1 also includes a software-based control unit 5 which the fiber laser 2 and in particular the radiation source 21 , as well as the deflection device 3 and in particular their focusing agent 32 and deflecting means 33 controls or if necessary also regulates. The control unit 5 can with a control unit for the robot arm 4 be coupled.

At the deflector 3 or alternatively on the robot arm 4 is also a device for generating a cross flow C by means of a cross-flow nozzle 6 attached, which expels Schmauch from the laser beam path and serves to reduce precipitation. Possibly. the transverse flow C can also serve to cool the material M to be cut, which is not primarily provided. The cross flow C can also be from the control unit 5 be controlled.

The laser beam L is a modulated laser beam which is composed of individual laser pulses generated in succession, wherein the individual laser pulses can be modulated in such a way that at least the temporal pulse length or pulse duration of the laser pulses can be selected substantially freely. This is in the diagram of 6 shown. The abscissa is the progressive time t and the ordinate the pulse intensity i (or pulse power) is removed. Intensity is generally understood to mean an energy per time or time interval and area (corresponds to one power per area). The laser pulses p1 and p2 are formed as rectangles. The laser pulse energy ε of the individual laser pulses corresponds to the respective rectangular area.

The two left, to a first processing stage or stage (as explained in more detail below) belonging laser pulses p1 have a different intensity i and a different temporal pulse length δ, as the two right, belonging to a second stage laser pulses p2. The modulation frequency is constant and is 5 kHz (F = 1 / τ = 1/200 μsec). The pulse length δ of the laser pulses p1 is approximately 50 μsec, which corresponds to approximately ¼ (25%) of the cycle time τ (200 μsec). The pulse length δ of the laser pulses p2 is approximately 100 μsec, which corresponds approximately to half (50%) of the cycle time τ. The intensity i of the laser pulses p1 is approximately ¼ (25%) of the intensity i of the laser pulses p2. The laser beam energy in a defined time interval can be understood as the sum of all individual laser pulse energies ε in this time interval. With the same time lengths of stages I and II, the laser beam energy in the first stage I would thus be lower than in the second stage II. This shows 5 The illustrated rectangular areas correspond to the laser beam energy in the respective stage. Since the laser beam power P or the laser beam intensity I correlated with the laser beam energy (power = energy per time interval) is also true that the laser beam power P in the first stage I is significantly lower than in the second stage II, which is also evident from the 5 results. By modulating the laser pulses p1 and p2, therefore, the laser beam power P of the modulated laser beam L can be set very precisely. The control or regulation of the modulation of the laser pulses p1 and p2 by means of the control unit 5 ,

2 schematically shows a section through the material to be cut M during the cutting process. Preferably, the material M is a metallic material. The laser pulses of the modulated laser beam L strike along a defined cutting path on the material to be cut M and produce individual, in the cross section shown approximately V-shaped laser cutting points (dots), the entirety of a cutting gap S (hereinafter referred to as cutting gap) can form , as explained in more detail below. In the cutting gap S, the material M is melted and partially sublimated by the laser pulse of the modulated laser beam L (direct transition from the solid to the gaseous state of matter). The application of the material M from the cutting gap S is upward (on the side of the incident laser beam L opposite to the direction of impact) due to an adjusting expansion pressure of the phase transition of solid or liquid phase in the gaseous phase, which is shown with arrows a. The effect of this expansion pressure sublimation in the cutting gap S is represented by bubbles G. Such a cutting operation is achieved by appropriate adjustment of the parameters (pulse length or pulse duration of the laser pulses, intensity of the laser pulses, time interval between two successive laser pulses, modulation frequency, and beam guidance speed of the modulated laser beam) and can be referred to as "cutting removal" (see above explanations ).

A small proportion of the molten material can also emerge downwards (on the material side facing away from the incident laser beam L) from the cutting gap S, in particular as the depth of the cutting gap S increases, as shown by the dashed arrows b, and this can lead to undesirable burr formation , This should be prevented or at least minimized essentially by a suitable setting of the parameters given above.

3 shows left in a plan view schematically the introduction of the laser cutting points along a circular cutting path B according to a particularly preferred embodiment of the invention. The modulated laser beam L is detected by means of the deflection device 3 moved in the direction of R along the cutting path B and focused. The individual laser pulses generate laser cutting points S1 and S2, which, due to the movement of movement of the modulated laser beam L, have no circular but an oblong shape, contrary to the illustration. The individual laser cutting points S1 and S2 are not directly lined up here, but introduced with a spacing to each other in the material to be cut M, wherein the modulated laser beam L, the cutting path B repeatedly moves away or runs through.

During a first pass of the modulated laser beam L, the laser cutting points S1 shown filled are introduced at a distance from one another. The heat introduced per laser cutting point S1 into the material to be cut can be dissipated into the still cool material environment. The selected distance between the first laser cutting points S1 is determined z. B. according to the thermal conductivity and / or the heat storage capacity of the material to be cut M.

During a second pass of the modulated laser beam L, offset from the first laser cutting points S1, the second laser cutting points S2 are introduced, which are shown as unfilled dots. This is achieved in that the beam-guiding speed of the modulated laser beam L is changed and / or the starting point for a pass is provided with a variable offset and / or the time interval between the laser pulses is changed.

The distance of the second laser cutting points S2 to the first laser cutting points S1 is set as large as possible, which is ideally given when a second laser cutting point S2 is positioned exactly in the middle between two first laser cutting points S1, as shown. Alternatively, a plurality of second laser cutting points S2 can also be introduced between the first laser cutting points S1 in a subsequent pass. Alternatively, it would also be conceivable to slightly offset the second laser cutting points S2 with respect to the cutting path B in one direction or in both directions with equal or different spacing, so as to form a zigzag arrangement of the second laser cutting points S2 with respect to the first laser cutting points and / or one To obtain zig-zag arrangement of the second laser cutting points S2 to each other. Another aspect is the variation of the size (area with respect to the top view) of the individual laser cutting points S1 and / or S2, which z. B. by the movement of the modulated laser beam and / or its focus is adjustable.

The modulated laser beam L passes through the cutting path B until the entire cutting line is covered by laser cutting points S1, S2, etc. and a closed cutting gap S is formed, as in FIG 3 shown right for a quarter circle. Here, the parameters, as stated above, kept constant or, z. From pass to pass or from step to step, substantially independently of the previously described measures for providing an offset between the laser cutting points from pass to pass. The number n of passes of the modulated laser beam L is up to 80 (preferably, for example, 60). The beam speed of the modulated laser beam can be set very high and is z. B. 5000 mm / sec. To distinguish this is the adjusting cutting speed z. B. may be 35-45 mm / sec.

By placing the laser cutting points offset along the cutting path during different passes of the modulated laser beam, the laser beam power and the associated cutting performance can be increased overall. Here, the averaged over the cutting path heat input into the material to be cut is indeed increased by the higher laser beam power, but remains locally below an adverse level for the material to be cut. This can z. B. the processing time can be shortened. Another advantage is the fact that due to the lower local heating of the material to be cut even more sensitive materials can be cut in particular at a relatively high speed. It is expressly noted that this list of benefits and uses is not exhaustive.

For such an embodiment of the cutting process, in which the laser cutting points are arranged offset during different passes of the modulated laser beam along the cutting path, a modulated laser beam is ideal, due to the many possibilities for setting the laser beam power taking into account the along the cutting path in the material to be cut introduced heat.

According to a likewise particularly preferred development of the invention, it is provided that the cutting operation is designed overall as a multi-stage cutting process or cutting process, wherein the settings of the parameters (ie at least one parameter), between the individual processing stages or

Steps are changed as follows in connection with the 5 and the 6 explained.

In the descriptive, diagram-like representation of 5 is on the abscissa of the time sequence T and on the ordinate the laser beam power P (or laser beam intensity I) removed. The illustrated cutting process comprises five stages or steps I to V, which are shown as rectangles. The laser beam energy of a stage corresponds to the respective rectangular area, wherein a rectangular area corresponds to the sum of all pulse energies ε of the individual laser pulses in the respective stage. Within one stage, the laser beam power P is constant, but this does not necessarily have to be the case. The illustrated cutting process relates to a cutting guide in a steel sheet material, which is provided with a lacquer layer, wherein it is z. B. may be a painted vehicle component. The thickness of the steel sheet material is for example 0.7-0.8 mm and could, for. B. also be 1.0 mm. The thickness of the paint layer is z. B. 300 microns, which may also be a multi-layer paint system. The application of the modulated laser beam takes place on the painted material side.

In the first stage I, the lacquer layer is removed with a low laser beam power P. The settings of the laser pulses of stage I are in 6 reproduced as laser pulses p1, to which reference is also made to the above relevant embodiments. Of course, more than the two exemplary laser pulses p1 are provided. The modulated laser beam L passes through the cutting path B until the paint layer is completely removed. In this case, provision may be made for the laser cutting points brought about by the laser pulses p1 to be arranged directly one after the other along the cutting path (see the above statements in this regard). Preferably, however, it is provided that the laser cutting points are offset from one another in the material to be cut introduced (see above relevant embodiments). This also preferably applies to all subsequent stages (which, however, need not be the case). In addition, a successive removal of the lacquer layer is preferably provided (for which reference is also made to the above statements in this regard). In the case of a multilayer paint system, the first stage I can be subdivided into a plurality of partial stages, preferably with different settings of the parameters (ie at least one parameter).

In the second stage II, which adjoins without interruption to the first stage I, then the cutting removal of the material with changed parameters, which is accompanied by a higher laser beam power P and with a higher laser beam energy (square surface of level II). The settings of the level II laser pulses are in 6 reproduced as laser pulses p2. Both the pulse intensity i and the pulse length δ of the laser pulses p2 are set higher or longer with respect to the first stage I, wherein the time interval between two laser pulses p2 is smaller. Of course, more than the two exemplary laser pulses p2 are provided. It is preferably provided that the laser cutting points brought about by the laser pulses p2 are arranged offset relative to one another along the cutting path (see the above statements in this regard). In the second stage II is beam speed z. B. 5 m / sec and the number of rounds is z. B. up to 60. The modulation frequency for the laser pulses p2 is unchanged at 5000 Hz, as in the first stage I.

In the initial phase of the cutting process, d. H. During the first two stages and II, the energy introduced into the material to be cut, which directly corresponds to the laser beam power or the laser beam energy, can be set to very high, since the material to be cut is still cold and thus initially has a high heat absorption capacity having.

The second stage II is followed by a shorter third stage III with changed parameters and a lower laser beam energy (rectangular area) than the second stage II. The laser beam power P is unchanged from the second stage II, but this need not necessarily be the case. Between the second stage II and the third stage III, a break is provided, in which the material to be cut can cool down and / or in which different temperature fields can equalize. In the third stage III, the cutting removal is continued with changed parameters, for example an altered and in particular reduced beam guidance speed, which serves primarily to keep the energy input low and the heat load of the material to be cut below a critical level.

The third stage III in turn is followed by breaks a shorter time fourth stage IV and a temporally even shorter fifth stage V, in which the Schneidabtragen continues. The laser beam power P is unchanged from the third stage III, but this need not necessarily be the case. The steps IV and V may be repetitions of stages II and III with changed parameters (eg with a changed beam guidance speed), wherein the setting changes depending on the material properties of the material to be cut, its thermal conductivity and heat capacity, the contour of the Cutting path and / or the position of the material to be cut relative to the modulated laser beam can be made, which z. B. could also be done in a control loop. The aim is to keep the energy input low and the heat load of the material to be cut below a critical level. In addition, the expansion pressure of the phase transition of the solid or liquid phase is to be maintained in the gaseous phase and thereby prevented that molten material exits down from the cutting gap (see. 2 ), resulting in a undesirable burring can occur (see above in this regard). At the end of step V, the cutting operation is completed and the material to be cut is severed along the cutting line in a short processing time and with a high cut edge quality.

In stages III to V, a reduction in the beam-guiding speed or a reduction in the number of passes per time interval (corresponding to the time length of one stage) is provided in particular with respect to the respective preceding stage. This serves to create overlaps of the laser cutting points on the material to be cut in order to obtain a smooth, grid-free average. The modulated laser pulses of stages III to V are in the 6 not shown.

As is very good from the presentation in 5 results, the laser beam energy corresponding to the rectangle sizes from the second stage II to the fifth stage V is decreasing, which is required due to the increasing heating due to the heat input into the material to be cut. Of course, the cutting process may include more or less than five stages. In addition, the time length of the individual stage may differ from the illustration shown.

It is envisaged that the parameters are kept substantially constant within a stage. However, this does not rule out that the settings of the parameters can also be changed within one level. The settings for all stages are preferably made manually in advance and stored in the control unit of the device and retrieved during the cutting process. Alternatively or possibly also in addition, the settings may also be made and / or changed in a control loop. Furthermore, a learning control can be provided, in which the results of completed cutting processes are automatically inspected at least randomly and, based thereon, the settings for subsequent cutting operations are changed.

The preceding explanations show that a very flexible design of the cutting process is possible by means of a modulated laser beam.

4 shows an example of the temperature profile in a material to be cut M immediately after introduction of the cutting gap S, in a schematic sectional view, which is substantially the sectional view of 2 equivalent. By way of example, the material M is a sheet steel material which is coated with a lacquer layer U. The local temperature profile shown as a line is denoted by θ. For example, the temperature θ in the cutting gap S is above 2000 ° C and thus above the sublimation point for steel. The essential part of the heat introduced by means of a laser pulse flows into the material M surrounding the cutting gap S, so that an approximately bell-shaped temperature gradient occurs, as shown.

During the first stage I, the lacquer layer can be removed over a large area with respect to the cutting path, in order to prevent unwanted lacquer delamination and / or lacquer burns during the subsequent cutting removal in steps II and following. 4 shows that the edges of the paint layer U are set back from the edges of the cutting gap S by a distance V. Ie. the paint layer is z along the cutting path. B. removed with a larger web width, which z. B. can be realized by the fact that the modulated laser beam during the first stage I passes through several concentric to the cutting path tracks or the laser focus is set larger or a zigzag arrangement of the individual laser cutting points. Incidentally, this is not limited to the use of a modulated laser beam, but could also be realized with a Q-switched laser.

The limit temperature for the lacquer layer, which must not be exceeded during the entire cutting process, is z. B. 140 ° C. In order to ensure that the distance V between the removed lacquer layer U and the cutting gap S is as small as possible, the bell-shaped temperature profile θ should have steep flanks. A steep slope can be brought about in particular by the adjustment of the parameters taking into account the material properties of the material M (thermal conductivity, heat capacity, thickness, etc.).

Optionally, it may be necessary to seal the formed cut edges in a separate step following the cutting operation. This applies in particular to coated and in particular painted sheet materials. In this regard, it also makes sense that a temperature profile θ adjusts with as steep flanks as possible, because then the surfaces to be sealed (along the distances V; 4 ) between the edges of the lacquer layer U and the edges of the cutting gap S can be small.

LIST OF REFERENCE NUMBERS

1

Device (according to the invention)

2

fiber laser

21

radiation source

23

Fiber (waveguide)

3

Deflector

31

Coupling (coupling-out optics)

32

focusing

33

deflecting

34

window

4

robot arm

5

control unit

6

cross jet nozzle

a

Application (from cutting gap)

b

Application (from cutting gap)

d

Distance (deflector, material) Pulse intensity

n

Number of passes

p1, p2

laser pulses

t

Time

x, y, z

spatial directions

B

Cutting path, cutting line

C

crossflow

F

modulation frequency

G

Sublimationsanteil

I

laser beam intensity

L

modulated laser beam

M

Material (workpiece / component)

P

laser beam power

R

Guiding direction of laser beam

S1, S2

Laser cutting points

S

cutting gap

T

schedule

U

Lacquer coating, coating

V

distance

I to V

Stages, processing stages

δ

temporal pulse length

ε

Laser pulse energy

θ

Temperature, temperature profile

τ

Cycle time (cycle length)

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 102004039023 A1 [0002, 0010, 0025]

Claims (15)

Method for cutting material (M) by means of at least one laser beam which cuts the material (M) along a desired cutting path (B) by applying a plurality of laser pulses (p1, p2), characterized in that the laser beam is a modulated laser beam (L ), in which at least the pulse length (δ) of the laser pulses (p1, p2) can be selected substantially freely. Method according to claim 1, characterized in that furthermore the intensity (i) of the laser pulses (p1; p2) and / or the time interval between two successive laser pulses (p1; p2) and / or the modulation frequency (F) and / or the Beam control speed of the modulated laser beam (L) can be selected as other parameters substantially free / can. A method according to claim 1 or 2, characterized in that during the cutting operation at least the pulse length (δ) of the laser pulses (p1, p2) is changed. Method according to claim 3, characterized in that at least one further parameter is changed during the cutting process. A method according to claim 3 or 4, characterized in that during the cutting process at least one of the parameters is kept constant at least in a time interval. Method according to one of the preceding claims, characterized in that the cutting path (B) is repeatedly traversed by the modulated laser beam (L) during the cutting process. A method according to claim 6, characterized in that during repeated passage through the cutting path (B), the beam guiding speed of the modulated laser beam (L) is changed and / or the starting point is provided for a run with a variable offset and / or the time interval between the laser pulses (p1; p2) is changed in order to obtain, between the individual passes, an offset of the laser cutting points (S1; S2) caused by the laser pulses (p1; p2) on the material (M) to be cut. Method according to one of the preceding claims, characterized in that the cutting process comprises a plurality of stages, wherein at least the pulse length of the laser pulses (p1; p2) is changed between two individual stages. Method according to Claim 8, characterized in that at least one further parameter is changed between two individual stages. A method according to claim 8 or 9, characterized in that the multi-stage cutting process comprises at least three stages (I to III): a first stage (I) for removing a surface coating (U) on the material to be cut (M), a second stage ( II) with an altered pulse length of the laser pulses (p2) for cutting removal of the material to be cut (M), and a third stage (III) with a changed beam guiding speed of the modulated laser beam (L) for cutting the material to be cut (M). A method according to claim 10, characterized in that during the cutting operation, the second stage (II) and third stage (III) are carried out alternately with at least one changed parameter. Contraption ( 1 ) for carrying out a method of cutting material (M) according to one of the preceding claims, comprising: a laser source ( 2 ), wherein the generated laser beam is a modulated laser beam (L) in which at least the pulse length of the laser pulses (p1; p2) can be selected substantially freely; a deflection device ( 3 ) for steering the laser source ( 2 ), modulated laser beam (L) on the material to be cut (M); and a control unit ( 5 ) for the control of the laser source according to the method ( 2 ) and / or the deflection unit ( 3 ). Contraption ( 1 ) according to claim 12, characterized in that the laser source ( 2 ) is a fiber laser. Contraption ( 1 ) according to claim 12 or 13, characterized in that further comprises means ( 6 ) for generating a transverse flow (C) to the modulated laser beam (L) is included. Use of a method and / or a device ( 1 ) according to one of the preceding claims for cutting body panels and in particular for cutting coated and / or painted body panels.

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