DE102022118281A1 - Laser cutting process with oscillating laser beam and optimized cutting gas supply - Google Patents

Abstract

The invention relates to a laser cutting method in which a laser beam 24 strikes a workpiece 12 together with a gas jet of cutting gas. A cyclically repeated secondary movement 34 is superimposed on a primary feed movement 32 along a cutting contour. The cutting gas forms a pressure cushion 40 on the workpiece surface 38, the extent of which 44, 50 is significantly larger than an area detected by the laser beam 24 through the secondary movement 34.

Description

Field of invention

The present invention relates to a method for cutting metallic, in particular plate-shaped, workpieces using a laser beam, in which the laser beam carries out a secondary movement within the cutting nozzle, from which the laser beam emerges together with a process gas jet.

State of the art

Such processes are also known as “scanner cutting”.

For example from the DE102008053397A1 It is known that the degree of absorption of the laser radiation on the cutting front surface can be increased by a pendulum movement of the laser beam during laser cutting. For a given laser power, a significant increase in the melt film surface temperature and thus better expulsion of the melt from the cutting gap can be achieved. This enables an increase in the maximum possible cutting feed and an improvement in the cutting edge quality by minimizing the number and size of solidified melt drops adhering to the underside of the sheet (reduced burr formation).

In the prior art, for example in JPS60210384A, JPS63177991A, JPH06234090A, JPH07185856A, JPH07236987A, JP2005279730A , JP2010162561A , WO2020008833A1 or WO2020008827A1 , cutting methods have therefore been proposed in which the laser beam is oscillated in the cutting direction, transversely to the cutting direction or in different scan figures (circle, zigzag, figure eight). However, if the laser beam is to be guided along a curved path in the proposed method, then complex planning of the scanner movement and an adjustment of the scanning speed and the scanning amplitude are necessary, especially in the curves of the path, as e.g JP2014417875A , WO2019176431A1 , WO2019176631A1 , WO2019176632A1 or WO200085073A1 is described.

The present invention is based on the object of further improving the process of scanner cutting compared to the prior art, in particular in order to reduce the complexity of the scanner movement and to achieve higher cutting speeds while maintaining good cutting edge quality.

The invention

This task is solved by a laser cutting method according to claim 1 and a laser cutting system according to claim 12. The respective subclaims specify advantageous variants or embodiments.

To solve the problem underlying the invention, a method for cutting metallic, in particular plate-shaped, workpieces is provided using a laser beam, in which the laser beam is directed together with a cutting gas jet from a cutting nozzle onto the workpiece to be cut, with a primary feed movement of the cutting nozzle along a A cyclically repeating secondary movement of the laser beam within the cutting nozzle is superimposed on the cutting contour. The primary feed movement of the cutting nozzle is understood to be a relative movement to the workpiece surface, whereby the nozzle and/or the workpiece can be moved to generate the relative movement. The secondary movement of the laser beam has a movement component longitudinally and/or a movement component transversely to the primary feed movement (i.e. to the cutting direction or cutting contour). Furthermore, in the method, the cutting gas blown onto the workpiece forms a pressure cushion on the workpiece surface, the extent of which along the primary feed movement is at least 10 times as large as the area on the workpiece surface irradiated by the laser beam due to the secondary movement of the laser beam primary feed movement.

In a broader sense, the pressure cushion can include the area in which a dynamic pressure of the cutting gas generated by the cutting gas jet is significantly greater than the ambient pressure. The dynamic pressure of the cutting gas in the area of the pressure cushion is preferably at least 1 bar, particularly preferably at least 2 bar, very particularly preferably at least 4 bar, greater than the ambient pressure. The expansion of the pressure cushion can therefore be defined by the minimum excess pressure of the cutting gas relative to the ambient atmosphere. Alternatively, the pressure cushion can be defined by the amount of dynamic pressure. In the pressure cushion, the dynamic pressure of the cutting gas on the workpiece surface can be at least 5 bar, preferably at least 7 bar, particularly preferably at least 10 bar.

In a narrower sense, the term “pressure cushion” is to be understood in particular as meaning the area on the workpiece surface in which the dynamic pressure of the cutting gas generated by the cutting gas jet is essentially constant. The dynamic pressure is “essentially constant”. a maximum deviation of the pressure minimum of less than 30%, preferably less than 20%, particularly preferably less than 10% from the pressure maximum. The expansion of the pressure cushion can therefore be defined by the pressure drop relative to the pressure maximum. For example, with a maximum pressure of the cutting gas of 8 bar on the workpiece surface, the minimum pressure in the pressure cushion may be 5.6 bar (deviation of 2.4 bar or 30%), preferably 6.4 bar (deviation of 1.6 bar or . 20%), more preferably 7.2 bar (deviation of 0.8 bar or 10%). When forming the pressure cushion, the absolute value of the pressure is less important. What is more important is the constancy of the pressure over the area covered by the pressure pad.

The inventors have recognized that there are limits to increasing cutting speed and cutting edge quality by solely influencing the cutting front length and cutting gap width by adjusting the secondary movement of the laser beam. The inventors' experiments have shown that by creating a sufficiently large pressure cushion, the feed speed can be increased without significant losses in the quality of the cut edges. Complicated path planning of the secondary movement is not necessary.

• • Beleuchtung eines ausreichend langen Teils der Schnittfront durch eine Komponente der Sekundärbewegung in Längsrichtung des Schnittspalts, um eine flachere Neigung der Schnittfront und dadurch eine Erhöhung der Absorption der auf die Schnittfront einwirkenden Laserleistung zu erreichen.
• • Erzeugung eines ausreichend breiten Schnittspaltes durch eine Komponente der Sekundärbewegung quer zum Schnittspalt, um den Austrieb der Schmelze zu verbessern.

When cutting metallic materials with the help of a laser beam set into a secondary movement (“scanner cutting”), the laser beam is moved back and forth in the longitudinal direction and/or transversely to the cutting gap, for example by means of one or more scanner mirrors. This secondary movement is superimposed on a feed movement of the laser cutting head, from which the laser beam emerges in the direction of the workpiece surface. The shape and amplitude of the secondary movement are essentially chosen to achieve the following two optimization goals as simultaneously as possible:

• • Illumination of a sufficiently long part of the cutting front by a component of the secondary movement in the longitudinal direction of the cutting gap in order to achieve a flatter inclination of the cutting front and thereby increasing the absorption of the laser power acting on the cutting front.
• • Creation of a sufficiently wide cutting gap through a component of the secondary movement transverse to the cutting gap in order to improve the expulsion of the melt.

An adequate adaptation of the length of the illuminated part of the cutting front to the available power of the laser beam enables an increase in the cutting speed, especially when melt cutting with inert cutting gases under high pressure, and also makes a positive contribution to the quality of the cut edges produced. Due to the flatter inclination of the cutting front and the improved absorption of the laser power, the melt film surface temperature is increased, thus minimizing the viscosity and surface tension of the melt and improving the expulsion of the melt. In this way, burr adhesion is reduced.

The acceleration and expulsion of the melt can also be improved by increasing the cutting gap width. This increases the quality of the cut edges produced, particularly with regard to the adhesion of solidified melt to the underside of the workpiece (“burr formation”).

According to the invention, it was recognized that for further process improvements in scanner cutting, a targeted influence on the gas flow of the cutting gas is necessary.

When laser cutting metal workpieces, the resulting melt is usually expelled from the cutting gap using a gas jet. The gas jet emerges from a cylindrically shaped nozzle mouth of the nozzle arranged on the cutting head under a typical boiler pressure of between 1 bar and 30 bar. As it continues to spread, due to its compressibility, this cutting gas jet experiences an expansion that scales with the boiler pressure, the shape of which corresponds to the inner contour of a Laval nozzle in the first millimeters after emerging from the nozzle mouth. If the cutting gas jet hits the surface of the cutting front (cutting front) of the cutting gap as it continues to propagate in the cutting gap, it bounces off of it due to its elastic compressibility and thereby changes its direction of propagation away from the cutting front into the cutting gap that has already been formed.

The frictional forces acting on the cutting gas jet in contact with the cutting gap surfaces slow it down along the cutting front and therefore additionally tilt the direction of propagation of the cutting gas jet away from the cutting front into the already formed cutting gap. These effects scale with the square of the gas flow velocity, which in turn results from the vessel pressure inside the cutting gas nozzle.

As a result of these two effects, in methods according to the prior art, the cutting gas jet loses direct contact with the cutting front surface from a certain depth of penetration into the cutting gap. This position on the cut front surface is called the separation point. The inventors have recognized that the depth of its position in the cutting gap increases with the expansion of the gas pressure cushion on the workpiece surface and with the maximum cutting gas speed achieved in the cutting gap, which in turn scales with the boiler pressure used in the nozzle mouth. Below the release point, the wall friction forces between the cutting gas jet and the melt film surface are significantly reduced, as a result of which the melt on the cutting front surface below the release point is only insufficiently accelerated or blown out of the cutting gap. As a result, part of the melt adheres to the underside of the workpiece and solidifies there as a visible and noticeable ridge.

In addition to the nozzle diameter and the vessel pressure of the cutting gas, the inclination of the cutting front also determines the position of the release point on it: as the inclination of the cutting front decreases, the release point moves towards the workpiece surface. A cutting front that is flatter due to the secondary movement of the laser beam results in the same disadvantageous effect on the propagation properties of the cutting gas jet in the cutting gap as a narrowing of the cutting gap.

According to the state of the art, both effects would have to be responded to by increasing the cutting gas pressure for a given nozzle diameter in order to compensate for a decline in the cutting edge quality.

However, when using a small nozzle diameter, increasing the cutting gas pressure leads to significantly higher speeds of the cutting gas jet when it emerges from the nozzle opening. Increasingly high speeds of the cutting gas jet as it enters the cutting gap increase the angle of inclination of the cutting front at its upper end. In extreme cases (an angle of 90°), almost no laser power is absorbed on the vertical area of the cutting front, which results in a strong cooling of the molten metal flowing from the workpiece surface into the cutting gap. If the melt film builds up increasingly as the cutting front progresses due to this cooling, this can result in a further shift of the release point towards the sheet metal surface, despite an increase in the cutting gas pressure. The result of such a shift would be - despite an increase in the cutting gas pressure - a decrease in the possible cutting speed with a simultaneous increase in burr formation. For these reasons, the position of the release point of the gas flow in the cutting gap during scanner cutting cannot be improved simply by increasing the gas pressure.

According to the invention, it was recognized that in order to optimally utilize the potential for increasing process efficiency through a reduced inclination of the cutting front, it is necessary to generate an extensive cutting gas pressure cushion on the workpiece surface. Its large expansion in the feed direction makes it possible, despite a significant reduction in the cutting front inclination (from approx. 88° - 87° without secondary movement of the laser beam to up to 80° by using a secondary movement parallel to the feed), to still have a position of the detachment point below the underside of the workpiece, i.e. outside of the cutting gap.

• • Maximale geometrische Schnittspaltüberdeckung durch das Schneidgas in Vorschubrichtung: Daraus resultiert ein minimiertes „Auffächern““ des Schneidgasstrahls im Schnittspalt und ein hoher nach unten gerichteter Anteil der Schneidgasströmung. Ein Ablösen der Schneidgasströmung von der Schnittfrontoberfläche wird verhindert und eine Oxidation der beiden Schnittkanten oder eine Gratanhaftung wird minimiert.
• • Der erforderliche Schneidgasdruck wird verringert: Daraus resultiert eine geringere Strömungsgeschwindigkeit des Gasstrahls beim Eintritt in den Schnittspalt und damit eine größere Schnittfrontneigung. Der Absorptionsgrad der Laserstrahlung auf der Schnittfrontoberfläche wird erhöht und damit ebenso die Temperatur der Schmelzfilmoberfläche, während Viskosität und Oberflächenspannung der Schmelze sinken. Es wird ein verbesserter Schmelzaustrieb, d. h. eine geringere Wellen- oder Tropfenbildung auf der Schmelzfilmoberfläche und eine kleinere Rauigkeit der Schnittkantenoberfläche, kleinere Größe der Schmelzetropfen und reduzierte Gratanhaftung erreicht.

The creation of the largest possible gas pressure cushion on the workpiece surface brings about the following advantageous effects in particular:

• • Maximum geometric cutting gap coverage by the cutting gas in the feed direction: This results in a minimized “fanning out” of the cutting gas jet in the cutting gap and a high downward proportion of the cutting gas flow. Detachment of the cutting gas flow from the cutting front surface is prevented and oxidation of the two cutting edges or burr adhesion is minimized.
• • The required cutting gas pressure is reduced: This results in a lower flow speed of the gas jet when it enters the cutting gap and thus a greater inclination of the cutting front. The degree of absorption of the laser radiation on the cut front surface is increased and with it the temperature of the melt film surface, while the viscosity and surface tension of the melt decrease. Improved melt expulsion is achieved, ie less wave or drop formation on the melt film surface and a smaller roughness of the cut edge surface, smaller size of the melt drops and reduced burr adhesion.

The cutting gas can exit the cutting nozzle with a boiler pressure of at least 1 bar, preferably at least 3 bar, particularly preferably at least 5 bar, and/or at most 25 bar, preferably at most 15 bar, particularly preferably at most 10 bar.

The advantages of the method according to the invention are particularly evident when cutting curves (so-called “curving”). A radius of curvature of the cutting contour can be at most 100 mm, preferably at most 50 mm, particularly preferably at most 30 mm. The feed rate of the primary Feed movement when driving through the curve can be at least 5 m/min, preferably at least 10 m/min, particularly preferably at least 15 m/min.

The shape of the cutting front surface, which can be described as a (simply viewed) linear half-cylinder when driving straight ahead, changes into a sinuous shape during a change in the cutting direction (i.e. when driving around a curve or corner), which can be clearly described as a section of a spiral.

The cutting gas jet flows in the cutting gap during a change in the feed direction (curving), following its inertia, increasingly along the outer cutting gap surface. Depending on the curve radius, in extreme cases the cutting gas jet detaches completely from the surface of the inner cutting gap surface in the previously common scanner cutting processes.

A consequence of these fluid mechanical effects can, in addition to the reduced melt expulsion on the inner cutting gap surface, also be the suction of ambient atmosphere into the cutting gap, which can lead to oxidation of the inner cutting edge surface depending on the curve radius. If the change in direction of the cutting process follows ever smaller curve radii, the increasingly weakening, expelling effect of the cutting gas jet on the melt on the inner surface of the cutting gap in the area of the change of direction also leads to increased adhesion of the melt to the lower end of the cutting edge (“burr formation”).

A countermeasure to be carried out according to the state of the art from a fluid mechanics point of view is, for a given mouth diameter of the nozzle and a given cutting gas pressure, a widening of the cutting gap by increasing the pendulum amplitude transverse to the cutting gap. This reduces the flow resistance which acts on the gas jet in the cutting gap, thereby reducing the gas jet remains in contact with the cutting front at higher speed and over a larger area of the cutting front. A larger proportion of the cutting gas jet flows through the cutting gap parallel to the cutting front surface, resulting in more efficient melt expulsion with less burr formation.

The previous reaction to the fluid mechanical requirements of cornering has been to increase the amplitude of the pendulum movement transversely to the feed direction. However, if the pendulum movement is switched digitally, this results in a visible step in the surface of the cutting edge, which is generally viewed as poor quality of the cutting edge surface and should therefore be avoided.

Widening the cutting gap also directly increases the volume of material that has to be melted by the laser beam and expelled by the gas jet per unit of time. At the same time, the average laser beam intensity on the cut front surface decreases and as a result the temperature of the melt film also decreases. In order to be able to keep the temperature of the melt film sufficiently high and thus the viscosity sufficiently low for a given laser power despite the widened cutting gap, the cutting speed must also be reduced at the same time in order to allow the limited laser power the longer interaction time required to heat the larger volume of material.

At a feed speed of 10 m/min, which is typical for processing medium-sized sheet metal thicknesses, the laser beam covers a distance of 166.7 mm per second on the sheet surface. The transmission of digital signals between the various participants in the control architecture required to operate a laser material processing system takes place in fixed cycles with typical cycle times of approx. 3 - 9 ms. If e.g. For example, if the path control (NC) of the laser cutting system sends the command to execute new operating parameters to both the scanner control and the laser control at the same time, it is possible that the scanner and laser will implement the change in their operating parameters requested by the NC (pendulum figure, Laser power) with a time offset of the order of 3 ms to 9 ms from each other. In relation to the unaffected movement of the cutting gas nozzle over the workpiece surface, this would result in scanners or lasers only beginning to actually implement the new operating parameters at path points that are up to 1.5 mm apart. The result of such a delayed implementation of digital information would be an area up to 1.5 mm long along the cutting edge in which there was no correct coordination between path speed, pendulum figure or laser power, which typically results in a visible negative change in the cutting edge quality in this area has.

All of these negative effects can be avoided if an extensive gas pressure cushion is created on the workpiece surface: This means that it is not necessary to change the scanning amplitude across the cutting gap while cornering.

According to a variant, the cutting nozzle has a nozzle sleeve which is mounted displaceably in the direction of a nozzle longitudinal axis relative to a base body of the cutting nozzle and protrudes beyond the workpiece-side end of the base body, the nozzle sleeve being designed to limit the pressure pad laterally. Preferably, the nozzle sleeve can be brought into contact with the workpiece surface during cutting. In this way, the nozzle sleeve forms a pressure chamber below the nozzle mouth and together with the workpiece surface, within which the pressure cushion builds up. In other words, the nozzle sleeve simplifies the formation of a pressure cushion, the extent of which corresponds to the internal dimensions of the nozzle sleeve. The nozzle sleeve is arranged on the cutting nozzle (or on its base body) in such a way that it surrounds a nozzle opening from which the cutting gas emerges during cutting. The displaceable nozzle sleeve prevents the cutting gas from flowing laterally parallel to the workpiece surface, so that the gas pressure cushion is sufficiently formed at a comparatively low boiler pressure of the cutting gas. For further features of the cutting gas nozzle with the nozzle sleeve see DE102015208157B4 referred.

The nozzle sleeve can have an inner diameter of 10 mm to 15 mm, preferably about 12 mm. In the case of an elongated hole opening, the dimension of the inner diameter refers to the length of the opening, i.e. the extent of the elongated hole opening along the primary feed movement. This allows a correspondingly large pressure cushion to be set up.

According to an alternative variant, the cutting nozzle can have an opening with an opening diameter of at least 6 mm, preferably at least 7 mm, with a distance between the workpiece-side nozzle end face and the workpiece surface being at most 0.7 mm, preferably at most 0.5 mm. When using a cutting nozzle with an elongated hole opening, the dimension of the opening diameter refers to the length of the opening, i.e. the extent of the elongated hole opening along the primary feed movement. With a nozzle diameter of 10 mm and a cutting gas pressure of 8 bar, using this variant can create a pressure cushion with a maximum pressure of over 7 bar.

According to a further alternative variant, the cutting nozzle can have an opening with an opening diameter of less than 3 mm and a distance between the workpiece-side nozzle end face and the workpiece surface can be at least 4 mm. Here too, the dimension of the opening diameter refers to the extent of the opening along the primary feed movement. In this variant, the boiler pressure of the cutting gas can be at least 16 bar. In this way, the natural expansion of the gas jet after exiting the nozzle mouth creates a pressure cushion on the workpiece surface with an expansion of the cutting gas jet that is approximately twice as large as in the nozzle mouth.

Preferably, the pressure pad has an extent transverse to the cutting direction that is at least 10 times as large as the area on the workpiece surface irradiated by the laser beam transverse to the primary feed movement. The advantageous effects described above then become particularly clear, particularly when cutting curved contours.

The process may be a melt cutting process. Nitrogen or a nitrogen-oxygen mixture, in particular compressed air, is preferably used as the cutting gas.

Preferably, the pressure cushion is kept unchanged when the primary feed movement changes, in particular when the direction of the primary feed movement changes (i.e. when cornering). If the pressure cushion has different dimensions along and across the primary feed movement, the pressure cushion is rotated as it were when cornering. This can ensure that the pressure pad always lies in the desired manner relative to the primary feed movement.

Alternatively or additionally, the secondary movement can be kept unchanged when the primary feed movement changes. This can initially apply to the form of the secondary movement. Preferably, the amplitude or speed of the secondary movement is also kept unchanged. In particular, the secondary movement can be rotated when the direction of the primary feed movement changes. This ensures that the components of the secondary movement are maintained in the desired manner along and transversely to the primary feed movement.

A laser power of the laser beam can be at least 0.5 kW, preferably at least 1 kW, and/or at most 16 kW, preferably at most 12 kW.

The feed speed of the primary feed movement can be at least 5 m/min, preferably at least 10 m/min, particularly preferably at least 15 m/min. Basically, the feed speed of the primary feed Push speed is in the range of 0.1 m/min and 80 m/min.

An amplitude of the secondary movement along the primary feed movement can be at least 0.1 mm, preferably at least 0.5 mm, and/or at most 3 mm, preferably at most 2 mm. A speed of the secondary movement on the workpiece surface can preferably be at least 0.5 m/s, in particular at least 1 m/s and/or at most 2 m/s, in particular at most 1 m/s.

Also within the scope of the present invention is a laser cutting system which is set up to carry out a method according to the invention described above. The laser cutting system thus enables the method according to the invention to be carried out, so that its advantages are realized.

The laser cutting system in particular has a laser processing head with a cutting nozzle that can be moved relative to a workpiece support. The laser cutting system is set up to move the cutting nozzle with a primary feed movement along a cutting contour relative to the workpiece support. The laser cutting system is further set up to move the laser beam within the cutting nozzle with a secondary movement, which has a movement component longitudinally and/or a movement component transversely to the primary feed movement. Furthermore, the laser cutting system is set up to blow the cutting gas onto a workpiece held on the workpiece support in such a way that a pressure cushion is formed on the workpiece surface, the extent of which along the primary feed movement is at least 10 times as large as that of the laser beam due to the Secondary movement irradiated area on the workpiece surface along the feed movement.

A control device can be programmed to correspondingly control the processing head, a laser beam source and a gas supply device.

The laser cutting system preferably has a scanner device in order to move the laser beam within the cutting nozzle. The scanner device simplifies the generation of the secondary movement. The scanner device can be arranged in the laser processing head. The control device is preferably programmed to control the scanner device so that the laser beam carries out the secondary movement.

Further features and advantages of the invention result from the description, the claims and the drawing. According to the invention, the above-mentioned features and those further detailed can be used individually or in groups in any desired, practical combinations. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary character for describing the invention.

Examples of embodiments

The following description of preferred exemplary embodiments serves to explain the invention in more detail in conjunction with the drawings.

• 1 eine erfindungsgemäße Laserschneidanlage zur Durchführung eines erfindungsgemäßen Laserschneidverfahrens, in einer schematischen Perspektivansicht;
• 2 eine erste Schneiddüse für die Erfindung, in einer schematischen Schnittansicht;
• 3 eine schematische Aufsicht auf ein Werkstück während eines erfindungsgemäßen Laserschneidverfahrens;
• 4 eine zweite Schneiddüse für die Erfindung, in einer schematischen Schnittansicht;
• 5 eine dritte Düse für die Erfindung, wobei die Schneiddüse eine an einem Düsenkörper geführte Düsenhülse zur Auflage auf einem Werkstück aufweist, in einer schematischen Schnittansicht.

Show it:

• 1 a laser cutting system according to the invention for carrying out a laser cutting method according to the invention, in a schematic perspective view;
• 2 a first cutting nozzle for the invention, in a schematic sectional view;
• 3 a schematic top view of a workpiece during a laser cutting process according to the invention;
• 4 a second cutting nozzle for the invention, in a schematic sectional view;
• 5 a third nozzle for the invention, wherein the cutting nozzle has a nozzle sleeve guided on a nozzle body for resting on a workpiece, in a schematic sectional view.

1 shows a laser cutting system 10 cutting a workpiece 12, which is formed here by a metal sheet. The workpiece 12 is held on a workpiece support 14 of the laser cutting system 10.

The laser cutting system 10 has a laser beam source 16. A laser beam generated by the laser beam source 16 is guided through a beam guide 18 to a processing head 20. The machining head 20 is moved relative to the workpiece 12 for cutting the workpiece 12 along a cutting contour 22. The cutting contour 22 can have one or more curves 23, the radius of curvature of which can be less than, for example, 30 mm.

The laser beam 24 emerges together with a cutting gas jet 26 through a nozzle opening 27 of a cutting nozzle 28 of the processing head 20, compare 2 . Cutting gas of the cutting gas jet 26 is supplied to the cutting nozzle 28 from a gas supply device 30 with a boiler Pressure of, for example, 15 bar is supplied. The cutting gas can be a mixture of nitrogen and oxygen; it can therefore be a pain-cutting procedure.

When cutting the workpiece 12, the processing head 20 is guided over the workpiece 12 with a primary feed movement 32 along the cutting contour 22, see also 3 . At the same time, the laser beam 24 is moved cyclically back and forth within the cutting nozzle 28 with a secondary movement 34. The movement of the laser beam 24 relative to the workpiece 12 therefore arises from the superimposition of the primary feed movement 32 of the processing head 20 and the periodically repeating secondary movement 34 of the laser beam 24 relative to the processing head 20. The secondary movement 34 can, as in 3 shown, have a movement component along the primary feed movement 32. Additionally or alternatively, the secondary movement 34 could have a movement component transverse to the primary feed movement 32 (not shown in detail).

In order to impart the secondary movement 34 to the laser beam 24, a scanner device (not shown) can be provided in the processing head 20. A control device 36 of the laser cutting system 10 is used to control the cutting process. The control device 36 controls in particular the movement of the processing head 24 as part of the primary movement 32, the cyclical deflection of the laser beam 24 as part of the secondary movement 34 and the cutting gas jet 26.

The cutting gas flowing out of the cutting nozzle 28 forms a pressure cushion 40 on a workpiece surface 38 facing the processing head 20. The cutting gas of the pressure cushion 40 supports the expulsion of the melted material of the workpiece 12 from a cutting gap 42.

The pressure pad 40 is oval in the present case. An extent (length) 44 of the pressure pad 40 in the direction of the primary feed movement 32 is more than 10 times as large as the area 46 irradiated by the laser beam 24 due to the secondary movement 34 along the primary feed movement 32. This is irradiated by the laser beam 24 due to the secondary movement 34 irradiated area along the primary feed movement 32 corresponds here to the diameter of the laser beam 24 at the point of impact on the workpiece surface 38 plus twice the amplitude of the secondary movement 34 in the direction of the primary feed movement 32.

An extent (width) 48 of the pressure pad 40 transverse to the direction of the primary feed movement 32 is here more than 10 times as large as the area 50 irradiated by the laser beam 24 due to the secondary movement 34 transverse to the primary feed movement 32. Since in the exemplary embodiment of 3 the secondary movement 34 has no component transverse to the primary feed movement 32, the area irradiated by the laser beam 24 due to the secondary movement 34 corresponds transversely to the primary feed movement 32 to the diameter of the laser beam 24 and approximately a width 52 of the cutting gap 42.

When driving through curve 23, compare 1 , both the pressure cushion 40 and the secondary movement 34 can remain unchanged relative to the primary feed movement 32. In particular, the movement components of the secondary movement 34 can remain the same in magnitude but can be carried out in relation to the current direction of the primary feed movement 32.

In the embodiment of 3 an opening diameter 54 of the nozzle opening 27 on a workpiece-side nozzle face 56 is less than 3 mm, for example 2.5 mm. A distance A of the workpiece-side nozzle face 56 from the workpiece surface 38 is here more than 4 mm, for example 6 mm.

4 shows a second cutting nozzle 28 for the invention. An opening diameter 55 of an opening of the cutting nozzle is here more than 7 mm, for example 8 mm. A distance A' of a workpiece-side nozzle face 56 from the workpiece surface 38 is here less than 0.7 mm, for example 0.5 mm. A pressure pad 40 (see 3 ) are generated, which is significantly larger in all directions over the workpiece surface 38 than the area 46, 50 irradiated by the laser beam 24 due to the secondary movement 32.

5 shows a third cutting nozzle 28 for the invention. The cutting nozzle 28 from 5 has a nozzle sleeve 58, which is slidably guided on a nozzle base body 60. The nozzle sleeve 58 can be made of plastic. During laser cutting, the nozzle sleeve 58 rests on the workpiece surface 38. The nozzle sleeve 58 and the nozzle base body 60 thus enclose a space in which a pressure cushion 40 is formed. The extent of the pressure pad 40 perpendicular to the laser beam corresponds to an inner diameter 62 of the nozzle sleeve 58. The inner diameter 62 can be between 10 mm and 15 mm, for example 12 mm.

In summary, the invention relates to a laser cutting method in which a laser beam 24 strikes a workpiece 12 together with a cutting gas jet 26. A cyclically repeated secondary movement 34 is superimposed on a primary feed movement 32 along a cutting contour 22. The cutting gas forms a pressure cushion 40 on the workpiece surface 38, the extent of which 44, 48 is significantly larger than, in particular more than 10 times as large as, an area detected by the laser beam due to the secondary movement.

Reference symbol list

10

Laser cutting system

12

workpiece

14

Workpiece support

16

Laser beam source

18

Beam guidance

20

machining head

22

cutting contour

23

Curve

24

laser beam

26

cutting gas jet

27

nozzle opening

28

cutting nozzle

30

Gas supply facility

32

primary feed movement

34

Secondary movement

36

Control device

38

workpiece surface

40

Pressure pad

42

cutting gap

44

Expansion (length) of the pressure pad 40

46

Irradiated area along the primary feed movement 32

48

Expansion (width) of the pressure pad 40

80

Irradiated area transverse to the primary feed movement 32

50

Width of the cutting gap 42

54; 55

Opening diameter

56

nozzle face surface

58

nozzle sleeve

60

Nozzle base body

62

Inner diameter

A; A'

Distance

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was 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 102008053397 A1 [0003]
• JP 2005279730 A [0004]
• JP 2010162561 A [0004]
• WO 2020008833 A1 [0004]
• WO 2020008827 A1 [0004]
• JP 2014417875 A [0004]
• WO 2019176431 A1 [0004]
• WO 2019176631 A1 [0004]
• WO 2019176632 A1 [0004]
• WO 200085073 A1 [0004]
• DE 102015208157 B4 [0033]

Claims (13)

Method for cutting a metallic, in particular plate-shaped, workpiece (12) by means of a laser beam (24), in which the laser beam (24) is directed onto the workpiece (12) together with a cutting gas jet (26) from a cutting nozzle (28), wherein a primary feed movement (32) of the cutting nozzle (28) along a cutting contour (22) is superimposed on a cyclically repeating secondary movement (34) of the laser beam (24) within the cutting nozzle (28); wherein the secondary movement (34) of the laser beam (24) has a movement component longitudinal and/or a movement component transverse to the primary feed movement (32); and wherein the cutting gas blown onto the workpiece (12) forms a pressure cushion (40) on the workpiece surface (38), the extent (44) of which along the primary feed movement (32) is at least 10 times as large as that of the laser beam (24 ) irradiated area (46) on the workpiece surface (38) due to the secondary movement (34) along the primary feed movement (32). Procedure according to Claim 1 , wherein the cutting nozzle (28) has a nozzle sleeve (58) which is mounted so that it can move in the direction of a nozzle longitudinal axis relative to a base body (60) of the cutting nozzle (28) and protrudes beyond the workpiece-side end of the base body (60), wherein the nozzle sleeve (58 ) is designed to limit the pressure pad (40) laterally. Procedure according to Claim 2 , wherein the nozzle sleeve (58) has an inner diameter (62) of 10 mm to 15 mm, preferably about 12 mm. Procedure according to Claim 1 , wherein the cutting nozzle (28) has an opening with an opening diameter (55) of at least 7 mm and a distance (A ') of the workpiece-side nozzle end face (56) to the workpiece surface (38) is at most 0.7 mm. Procedure according to Claim 1 , wherein the cutting nozzle (28) has an opening with an opening diameter (54) of less than 3 mm and a distance (A) of the workpiece-side nozzle end face (56) to the workpiece surface (38) is at least 4 mm. Method according to one of the preceding claims, wherein the pressure pad (40) has an extent (48) transverse to the primary feed movement (32) which is at least 10 times as large as the area (50) irradiated by the laser beam (24). the workpiece surface (38) transverse to the primary feed movement (32). Method according to one of the preceding claims, wherein the method is a melt cutting process and nitrogen or a nitrogen-oxygen mixture, in particular compressed air, is used as the cutting gas. Method according to one of the preceding claims, wherein the pressure pad (40) is kept unchanged when the primary feed movement (32) changes. Method according to one of the preceding claims, wherein the secondary movement (34) is kept unchanged when the primary feed movement (32) changes. Method according to one of the preceding claims, characterized in that in the pressure cushion (40) a dynamic pressure of the cutting gas on the workpiece surface (38) is at least 5 bar, preferably at least 7 bar, particularly preferably at least 10 bar. Method according to one of the preceding claims, characterized in that the cutting contour (22) has a curve (23) with a radius of curvature of at most 100 mm, preferably at most 50 mm, particularly preferably at most 30 mm. Laser cutting system (10) set up to carry out a method according to one of the preceding claims. Laser cutting system (10). Claim 12 , wherein a scanner device is provided to move the laser beam (24) within the cutting nozzle (28).

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