EP3953095A1

EP3953095A1 - Plasma cutting method

Info

Publication number: EP3953095A1
Application number: EP20711040.4A
Authority: EP
Inventors: René Nogowski; Volker Krink; André PÖTSCH; Thomas Steudtner
Original assignee: Kjellberg Stiftung
Current assignee: Kjellberg Stiftung
Priority date: 2019-04-11
Filing date: 2020-02-14
Publication date: 2022-02-16
Also published as: WO2020207522A1; CN113966257B; CN113966257A; US20220362876A1

Abstract

The invention relates to a method for plasma cutting workpieces, using a plasma torch that has at least one plasma torch main part, an electrode and a nozzle.

Description

Plasma cutting process

The invention relates to methods and arrangements for plasma cutting of workpieces.

Plasma is a thermally highly heated, electrically conductive gas that consists of positive and negative ions, electrons, and excited and neutral atoms and molecules.

Different gases, e.g. the monatomic argon or helium and / or the diatomic gases hydrogen, nitrogen, oxygen or air are used. These gases ionize and dissociate through the energy of the plasma arc.

The parameters of the plasma jet can be greatly influenced by the design of the nozzle and electrode. These parameters of the plasma jet are e.g. B. the beam diameter, the temperature, energy density and the flow rate of the gas.

In plasma cutting, for example, the plasma is constricted by a nozzle, which can be gas or water-cooled. For this purpose, the nozzle has a nozzle bore through which the plasma jet flows. This enables energy densities of up to 2 x 10 ⁶ W / cm ^{2 to be} achieved. Temperatures of up to 30,000 ° C occur in the plasma jet, which, in conjunction with the high flow rate of the gas, achieve very high cutting speeds on all electrically conductive materials. Plasma cutting is now an established process for cutting electrically conductive materials, with different gases and gas mixtures being used depending on the cutting task.

Plasma torches usually consist of a plasma torch head and a plasma torch shaft. An electrode and a nozzle are attached to the plasma torch head. The plasma gas, which exits through the nozzle bore, flows between them. Most of the time, the plasma gas is guided through a gas guide that is attached between the electrode and the nozzle and can be set in rotation. Modern plasma torches also have a feed for a secondary medium, either a gas or a liquid. The nozzle is then surrounded by a nozzle protection cap (also called a secondary gas cap). In particular in the case of liquid-cooled plasma torches, the nozzle is fixed by a nozzle cap, as described, for example, in DE 10 2004 049 445 A1. The cooling medium then flows between the nozzle cap and the nozzle. The secondary medium then flows between the nozzle or the nozzle cap and the nozzle protection cap and emerges from the bore of the nozzle protection cap. It affects the plasma jet formed by the arc and the plasma gas. It can be set in rotation by a gas duct which is arranged between the nozzle or nozzle cap and nozzle protection cap.

The nozzle protection cap protects the nozzle and the nozzle cap from the heat or the molten metal of the workpiece spurting out, in particular when the plasma jet pierces the material of the workpiece to be cut. In addition, it creates a defined atmosphere around the plasma jet when cutting.

For plasma cutting of unalloyed and low-alloy steels, also called structural steels, for example S235 and S355 according to DIN EN 10027-1, air, oxygen or nitrogen or a mixture thereof are usually used as plasma gases. Air, oxygen or nitrogen or a mixture thereof are also mostly used as secondary gases, the composition and volume flows of the plasma gas and the secondary gas mostly being different, but they can also be the same. For plasma cutting of high-alloy steels and stainless steels, e.g. 1.4301 (X5CrNiio-io) or 1.4541 (X6CrNiTii8-io), the plasma gases used are usually nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen -Nitrogen mixture used. In principle, air can also be used as a plasma gas, but the oxygen content in the air leads to oxidation of the cut surfaces and thus to a deterioration in the quality of the cut. The secondary gas also mostly used is nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen-nitrogen mixture, the composition and volume flows of the plasma gas and the secondary gas mostly being different, but also can be the same.

In plasma cutting there is a requirement to use a wide variety of contours, e.g. B. small inner contours, large inner contours and outer contours to cut or cut in the highest possible quality.

Small contours have a circumferential length that is equal to or less than six times the material thickness and / or a diameter that is equal to or less than twice the material thickness. Large contours have a circumferential length that is more than six times the material thickness, and / or a diameter that is more than twice the material thickness.

In a CNC-controlled guidance system, at least the essential cutting parameters for cutting a material (material type and material thickness) are stored in a database, such as B. electrical cutting current, plasma torch distance (distance between plasma torch tip and workpiece surface), cutting speed, plasma gas, secondary gas, electrode, nozzle.

The present invention is therefore based on the object of providing a method for plasma cutting of workpieces with the most varied of methods

Contours, for example small inner contours, large inner contours and outer contours, can be cut or cut out in high quality. According to a first aspect, this object is achieved by a method for plasma cutting of workpieces, in which a plasma cutting torch with at least one plasma torch body, an electrode and a nozzle is used for cutting a part from an in particular plate-shaped workpiece with a material thickness, the part of the plasma cutting torch , from which a plasma jet emerges from the nozzle, which forms the plasma torch tip, and in which the plasma cutting torch is guided by means of a guide system along a contour with a cutting speed v relative to the workpiece surface in the feed direction so that at least a small inner contour of the part, its circumference, or . Less than or equal to six times the material thickness of the workpiece or whose diameter is less than or equal to twice the material thickness of the workpiece, and that at least one outer contour of the part and / or a large inner contour of the part whose circumference is greater than al s is six times the material thickness of the workpiece or the diameter of which is greater than twice the material thickness of the workpiece, is / are cut out, the plasma torch tip being at a cutting distance of from the workpiece surface during cutting, with at least a small or a large part of the circumference of the Small inner contour to be cut of the part with a different cutting distance that is cut between the plasma torch tip and the workpiece surface than at least a small or a major part of the circumference of the outer contour of the part to be cut and / or at least a large or a major part of the circumference of the part to be cut large inner contour of the part.

According to a second aspect, this object is achieved by a method for plasma cutting of workpieces, in which a plasma cutting torch with at least one plasma torch body, an electrode, a nozzle and a secondary gas cap is used, the part of the plasma cutting torch from which the plasma jet emerges from the secondary gas cap , which forms the plasma torch tip, and in which the plasma cutting torch is guided by means of a guide system along a contour at a cutting speed (v) relative to the workpiece surface in the feed direction so that at least one small inner contour of the part, the circumference of which is less than or equal to six times the material thickness of the Workpiece or the diameter of which is less than or equal to twice the material thickness of the workpiece, and that at least one outer contour and / or a large inner contour of the part, whose circumference is greater than six times the material thickness of the workpiece or whose diameter is greater than twice the material thickness of the workpiece, and the plasma torch tip has a cutting distance ds to the workpiece surface during cutting, at least a small part or the largest part of the circumference of the The small inner contour of the part to be cut is cut with a different cutting distance ds between the plasma torch tip and the workpiece surface than at least a small or a large part of the circumference of the outer contour of the part to be cut and / or at least a large part or a large part of the circumference of the to cutting large inner contour of the part.

According to a third aspect, this object is achieved by a method for plasma cutting of workpieces, in which a plasma cutting torch with at least one plasma torch body, an electrode, a nozzle and a secondary gas cap is used, the part of the plasma cutting torch from which the plasma jet emerges from the secondary gas cap , which forms the plasma torch tip, and in which the plasma cutting torch is guided by means of a guide system along a contour at a cutting speed v relative to the workpiece surface in the feed direction and cuts a part from a, in particular plate-shaped, workpiece, the composition and / or the volume flow and / or the mass flow and / or the pressure of a secondary gas SG flowing out of the secondary gas cap or the cutting distance ds between the plasma torch tip and the workpiece surface is / are changed at the earliest when a plasma jet strikes the workpiece surface has reached a position on the contour to be cut whose distance from a cutting edge to be traversed is in a range of a maximum of 50%, better a maximum of 25% of a material thickness of the workpiece, or whose distance from the cutting edge to be traversed is in a range of a maximum of 15 mm, better a maximum of 7 mm, or where the plasma jet striking the workpiece surface touches the cutting edge.

According to a fourth aspect, this object is achieved by a method for

Plasma cutting of workpieces using a plasma cutting torch with at least one plasma torch body, an electrode, a nozzle and a secondary gas cap, wherein the part of the plasma cutting torch from which the plasma jet emerges from the secondary gas cap, forms the plasma torch tip, and in which the plasma cutting torch is guided by means of a guide system along a contour at a cutting speed v relative to the workpiece surface in the feed direction and a part consists of a, in particular plate-shaped, workpiece cuts, the composition and / or the volume flow and / or the mass flow and / or the pressure of the secondary gas SG flowing out of the secondary gas cap and / or the cutting distance ds between the plasma torch tip and the workpiece surface is changed at the latest when the one strikes the workpiece surface Plasma jet has reached a position on the contour to be cut, the distance 502 of which from the cut edge that has already been traversed is in a range of a maximum of 25% of the workpiece thickness, or whose distance 502 from the cut edge that has already been passed is in the range of at most 7 mm, or where the plasma jet hitting the workpiece surface has passed the cutting edge.

In the method according to the first and second aspects, it can be provided that the cutting distance ds when cutting the small inner contour of the part is smaller than the cutting distance ds when cutting the outer contour of the part and / or the large inner contour of the part. In particular, it can be provided that the cutting distance ds when cutting the small inner contour is between 40% and 80% of the cutting distance ds when cutting the outer contour of the part and / or the large inner contour of the part.

According to a further special embodiment, the cutting speed at which the plasma cutting torch is guided relative to the workpiece surface in the feed direction when cutting the small inner contour of the part is lower than the cutting speed v when cutting the outer contour of the part and / or the large inner contour of the part.

In particular, it can be provided that the cutting speed at which the plasma cutting torch is guided relative to the workpiece surface when cutting the small inner contours of the part is between 20% and 80%, preferably between 40% and 80% of the cutting speed v when cutting the outer contour of the part and / or the large inner contour of the part.

Advantageously, the small inner contour / small inner contours are cut first, then the large inner contour / large inner contours and then the outer contour / outer contours of the part.

In the method according to the third and fourth aspect, it can be provided that the cutting edge is created by cutting the same contour.

The secondary gas is advantageously air, oxygen, nitrogen, argon,

Hydrogen, methane or helium or a mixture thereof is used.

In particular, it can be provided that the mixture consists of oxygen and / or nitrogen and / or air and / or argon and / or helium or of argon and / or nitrogen and / or hydrogen and / or methane and / or helium.

According to a particular embodiment / are the composition and / or the volume flow and / or the mass flow and / or the pressure of the the secondary gas SG flowing out of the secondary gas cap is realized by connecting and / or increasing the volume flow and / or increasing the mass flow and / or increasing the pressure of an oxidizing gas or gas mixture and / or a reducing gas or gas mixture.

In particular, it can be provided that the composition of the secondary gas is changed so that the increase in the proportion of the oxidizing gas or gas mixture and / or the reducing gas or gas mixture in the secondary gas is at least 10% by volume.

Alternatively, it can be provided that the increase in the volume flow, the mass flow or the pressure of the oxidizing gas or gas mixture and / or the reducing gas or gas mixture in the secondary gas is at least 10%.

The oxidizing gas or gas mixture advantageously contains oxygen and / or air.

In particular, it can be provided that the oxidizing gas is oxygen.

Furthermore, it can be provided that the reducing gas or gas mixture contains hydrogen and / or methane.

In particular, it can be provided that the reducing gas is hydrogen.

According to a particular embodiment, the composition and / or the volume flow and / or the mass flow and / or the pressure of the secondary gas SG flowing out of the secondary gas cap is / are by switching off and / or reducing the volume flow and / or reducing the mass flow and / or reducing the Pressure of nitrogen, argon, air, helium or the mixture realized. In particular, it can be provided that the composition of the secondary gas is changed so that the reduction in the volume flow, the mass flow or the pressure of the gases or the gas mixture in the secondary gas is at least 10%.

Alternatively, it can be provided that the reduction in the volume flow, the mass flow or the pressure of the gases or the gas mixture in the secondary gas is at least 10%.

The cutting distance ds between the plasma torch tip and the workpiece surface is expediently reduced.

The cutting distance ds is advantageously reduced by at least 25% and / or at least 1 mm.

According to a further special embodiment, it can be provided that the cutting speed v, with which the plasma cutting torch is guided relative to the workpiece surface, is changed at the earliest when the plasma jet striking the workpiece surface has reached a position on the contour to be cut whose distance from the still The cutting edge to be traversed is in the range of a maximum of 50%, better a maximum of 25% of the material thickness of the workpiece, or the distance from the cutting edge to be traversed is in a range of a maximum of 15 mm, better a maximum of 7 mm, or where the on the workpiece surface impinging plasma jet touches the cutting edge.

Advantageously, the cutting speed v, with which the plasma cutting torch is guided relative to the workpiece surface, is changed at the latest when the plasma jet striking the workpiece surface has reached a position on the contour to be cut whose distance from the cutting edge that has already been passed is in the range of a maximum of 25% of the Workpiece thickness, or its distance from the cut edge already traversed in the range of 7 mm or where the plasma jet hitting the workpiece surface has passed the cutting edge.

In particular, it can be provided that the cutting speed v is increased.

Finally, it can be provided in particular that the cutting speed v is increased by at least 10%. The present invention is based on investigations on the following knowledge:

If the different types of contours, such as small inner contours, large inner contours and outer contours, are cut with the same parameters, different cutting qualities are obtained. In particular, the cutting quality of the small inner contours deteriorates and here especially the perpendicularity and inclination tolerance according to DIN ISO 9013, i.e. H. the cut surfaces are no longer formed almost at right angles to the workpiece surface. It was surprisingly found that by changing, in particular reducing, the plasma torch distance (cutting distance) when cutting small inner contours compared to the outer contours or large inner contours, a significant improvement in the quality of the cut is achieved. In particular, the perpendicularity and slope tolerance improves. A further improvement is achieved if the cutting speed for cutting the small inner contours is also reduced. Since the inner contours are small, this has only a minor effect on the entire cutting time. The cutting speed of the small contours can be between 20% and 80%, better still between 40% and 80% of the cutting speed of the outer contours or large inner contours.

Another advantage of using different plasma torch distances (cutting distances), especially with the larger plasma torch distances with large inner and outer contours, is that the cutting process is less susceptible to interference than with small cutting distances. Here, contamination of the workpiece surface, for example from slag splashes that the plasma torch tip could “hit”, is less of a problem. In this way, the high cutting quality of the inner contours and the high productivity, cutting quality and process reliability for the outer contours and large inner contours on a workpiece. It is not necessary to change the wearing parts of the plasma torch. It is also not necessary to change the plasma gas or the secondary gas between the different contours. It is advantageous that it is only possible to cut with a different plasma torch distance (cutting distance) and / or a different cutting speed, since this change can take place very quickly. For this only the time for transmission of the electronic signal, e.g. <5ms, is necessary, a waiting time, such as. B. when changing wear parts or when changing gas> 0.1 to 5 seconds is not necessary. The associated gas losses and gas consumption are also reduced.

In the control of the guidance system or the plasma cutting system, for example, different data sets for cutting one and the same material, i.e. H. for the same material type and thickness for different contours (small inner contours, large inner contours, outer contours), which are then assigned to the respective cutting task. It is also possible to set a fixed or variable reduction in the plasma torch distance (cutting distance) and / or the cutting speed for small contours.

Furthermore, at least in one particular embodiment, it is possible to cut even smaller inner contours in better quality. These are contours whose circumferential length is equal to or less than three times the material thickness (or whose diameter is less than the material thickness itself). For this, the cutting speed is reduced again in order to achieve a high cutting quality also in these contours. The reduced cutting speed can be between 40% and 80% of the cutting speed of the large contours.

The end of the cut is particularly critical for the quality of an inner contour, but also an outer contour. Especially when the plasma jet reaches the point where it re-enters the kerf that has already been created by the same cut and passes over the workpiece edge of this joint. Here the workpiece edge can be "skipped", the scrap part can "fall out" of the contour and the plasma jet can be applied to the already existing cut surface of the inner contour. When skipping the joint, an annoying projection usually remains. When the plasma jet is applied to the already existing cut surface, "washouts" occur, which also have a negative impact on the quality of the cut. An attempt is made to reduce the projection by reducing the cutting speed. However, this in turn increases the washout.

It is known to change the composition of the secondary gas between the individual cutting processes in order to first cut small holes and then large contours. Switching takes place in the period in which there is no cutting and has the disadvantage that it takes time.

In the method according to claim 8, it should be clear that it depends on the composition of the secondary gas when it emerges from the bore of the secondary gas cap or when it hits the plasma jet and not on where the change in composition occurs through valves in or in front of the plasma torch shaft.

Further features and advantages of the invention emerge from the appended claims and from the following description in which with reference to FIG

schematic drawings of several embodiments of the present

Inception will be described in detail. It shows:

1 shows a schematic diagram of an arrangement for plasma cutting according to the prior art;

2 shows a schematic diagram of a further arrangement for plasma cutting according to the prior art;

Figure 3 is a plan view of a part to be cut out of a workpiece;

FIG. 4 shows a detailed view of FIG. 3, in the cutting paths for cutting out

an inner contour are shown; FIG. 4a shows a side view of a plasma cutting torch over the workpiece shown in FIG. 3 during ignition; FIG.

4b is a side view similar to FIG. 4a, but with the

Plasma cutting torch is shown at a time in cutting after ignition;

FIG. 5 shows a detailed view similar to FIG. 3, but in which cutting paths to the

Cut out a further inner contour are shown;

FIG. 6 shows a detailed view similar to FIG. 3, but in which cutting paths to

Cut out a further inner contour are shown;

Fig. 7 is a detailed view similar to FIG. 3, but in which cutting paths to

Cut out a further inner contour are shown;

8 shows a plan view of the part from FIG. 3 after the inner contours shown in FIGS. 5 to 7 have been cut out, in which the cutting paths for cutting out an outer contour are drawn;

Fig. 9 is a detailed view of Fig. 5 for a more precise representation of the end of the

Cutting process of the inner contour;

9a shows a further detailed view similar to FIG. 9, but in a later view

Stage of the end of the cutting process;

Fig. 9b is a sectional view A-A of Fig. 9a;

FIG. 9c shows a further detailed view similar to FIG. 9a, but in one more

later stage of the end of the cutting process;

Fig. 9d is a sectional view B-B of Fig. 9c;

9e resulting from cutting on a cut surface of the workpiece

Grooves and their wakes caused by the deflection of the plasma jet; Fig. 10 is a plan view of a part to be cut from a workpiece made of a different material from the workpiece shown in Fig. 3;

FIG. 1 shows a detailed view of FIG. 10, in which cutting paths for cutting out an inner contour are drawn; FIG.

FIG. Na is a side view of a plasma cutting torch above that in FIG

11 shown workpiece during ignition;

Fig. Nb a side view similar to FIG. 11a, but with the

Plasma cutting torch is shown at a time in cutting after ignition;

FIG. 12 shows a detailed view similar to FIG. 10, but in which cutting paths to the

Cut out a further inner contour are shown;

FIG. 13 shows a detailed view similar to FIG. 10, but in which cutting paths to the

Cut out a further inner contour are shown;

FIG. 14 shows a detailed view similar to FIG. 10, but in which cutting paths to the

Cut out a further inner contour are shown;

15 shows a plan view of the part from FIG. 10 after the cutting out of the inner contours shown in FIGS. 12 to 14, in which the cutting paths for cutting out an outer contour are drawn;

FIG. 16 is a detailed view of FIG. 12 for a more precise illustration of the end of the

Cutting process of the inner contour;

16a shows a further detailed view similar to FIG. 16, but in a later view

Stage of the end of the cutting process;

16b shows a sectional view AA from FIG. 16a; 16c shows a further detailed view similar to FIG. 16a, but in an even later stage of the end of the cutting process;

Fig. 16d is a sectional view B-B of Fig. 16c; and

FIG. 17 shows a schematic diagram of an arrangement for plasma cutting according to FIG

a particular embodiment of the present invention for performing a method for plasma cutting of workpieces according to a particular embodiment of the present invention.

Usual arrangements for plasma cutting are shown schematically in FIGS. 1 and 2. An electrical cutting current flows from a power source 1.1 of the plasma cutting system 1 via an electrical line 5.1 to a plasma cutting torch 2 via an electrode 2.1 of the plasma cutting torch 2 a plasma jet 3 constricted by a nozzle 2.2 and a nozzle bore 2.2.1 to a workpiece 4 and then via a electrical line 5.3 back to a power source 1.1. The gas supply to the plasma cutting torch 2 takes place via lines 5.4 and 5.5 from a gas supply 6 to the plasma cutting torch 2. In the plasma cutting system 1 there is a high-voltage ignition device 1.3, a pilot resistor 1.2, the power source 1.1 and a switching contact 1.4 and their control. Valves for controlling the gases can also be provided. However, these are not shown here.

The plasma cutting torch 2 essentially comprises a plasma torch head with a beam generation system, comprising the electrode 2.1, the nozzle 2.2, a gas supply 2.3 for plasma gas PG and a plasma torch body 2.7, which supplies the media (gas, cooling water and electrical current) and accommodates the beam generation system . The electrode 2.1 of the plasma cutting torch 2 is a non-consumable electrode 2.1, which essentially consists of a high-temperature material such as tungsten, zirconium or hafnium and therefore has a very long service life. The electrode 2.1 often consists of two parts connected to one another, an electrode holder 2.1.1, which is made of a material that conducts electricity and heat well (e.g. copper, silver, alloys thereof), and a high-melting emission insert 2.1.2 with low Electron work function (hafnium, zirconium, tungsten). The nozzle 2.2 consists mostly of copper and constricts the plasma jet 3. A gas guide 2.6 for the plasma gas PG, which sets the plasma gas in rotation, can be arranged between the electrode 2.1 and the nozzle 2.2. In this embodiment, the part of the plasma cutting torch 2 from which the plasma jet 3 emerges from the nozzle 2.2 is referred to as the plasma torch tip 2.8. The distance between the plasma torch tip 2.8 and the workpiece surface 4.1 is denoted by d. In this example, this distance corresponds to the distance between the nozzle 2.2 and the workpiece surface 4.1. The same applies to the cutting and ignition sections ds and dz mentioned below.

In Figure 2, around the nozzle 2.2 of the plasma cutting torch 2 there is additionally a secondary gas cap 2.4 (nozzle protection cap) for supplying a secondary medium, e.g. a secondary gas SG attached. The combination of secondary gas cap 2.4 and secondary gas SG protects the nozzle 2.2 from damage when the plasma jet 3 pierces the workpiece 4 and creates a defined atmosphere around the plasma jet 3. Between the nozzle 2.2 and the secondary gas cap 4 there is a gas guide 2.9 which can set the secondary gas in rotation. In this embodiment, the point of the plasma cutting torch 2 from which the plasma jet 3 emerges from the secondary gas cap 2.4 is referred to as the plasma torch tip 2.8. The distance between the plasma torch tip 2.8 and the workpiece surface 4.1 is also denoted by d. In this example, this distance d corresponds to the distance between the secondary gas cap 2.4 and the workpiece surface 4.1. The same applies to the cutting and ignition distances ds and dz mentioned below.

For the cutting process, a pilot arc is first ignited, which burns between the electrode 2.1 and the nozzle 2.2 with a low electrical current (e.g. 10 A - 30 A) and thus low power, e.g. by means of high electrical voltage generated by the high voltage ignition device 1.3. The current (pilot current) of the pilot arc flows through the electrical line 5.2 from the nozzle 2.2 via the switching contact 1.4 and the electrical resistor 1.2 to the power source 1.1 and is limited by the pilot resistor (electrical resistor) 1.2. This low-energy pilot arc uses partial ionization to prepare the path between the Plasma cutting torch 2 and the workpiece 4 for the cutting arc. If the pilot arc touches the workpiece 4, the electrical potential difference generated by the pilot resistor 1.2 between the nozzle 2.2 and the workpiece 4 leads to the formation of the cutting arc. This then burns between the electrode

2.1 and the workpiece 4 with mostly higher electrical current (e.g. 20 A to 900 A) and thus also with higher power. The switching contact 1.4 is opened and the nozzle 2.2 is switched potential-free from the power source 1.1. This operating mode is also referred to as direct operating mode. The workpiece 4 is exposed to the thermal, kinetic and electrical effects of the plasma jet 3. This makes the process very effective and metals up to great thicknesses, e.g. 180 mm at 600 A cutting current with a cutting speed of 0.2 m / min.

For this purpose, the plasma cutting torch 2 is moved with a guide system relative to a workpiece 4 or its surface 4.1. This can e.g. B. be a robot or a CNC-controlled guide machine. The control of the guidance system (not shown) communicates with the arrangement according to FIG. 1 or 2.

In the simplest case, it starts and ends the operation of the plasma cutting torch 2. However, according to the current state of the art, a large number of signals and information, e.g. B. about operating conditions and data are exchanged.

With plasma cutting, high cutting qualities can be achieved. Criteria for this are, for example, a low perpendicularity and inclination tolerance according to DIN ISO 9013. If the optimal cutting parameters are adhered to, including the electrical cutting current, the cutting speed, the distance between the plasma cutting torch and the workpiece and the gas pressure, smooth cut surfaces and beard-free edges can be achieved can be achieved.

For the quality of the cut, it is also important that the electrode 2.1, in particular its emission insert 2.1.2 and the nozzle 2.2, in particular its nozzle bore

2.2.1 and, if available, the secondary gas cap 2.4 and especially its Bore lie on a common axis in order to obtain the same or at least only slightly different perpendicularity and inclination tolerance at the different cutting edges in every direction of movement of the plasma cutting torch 2 relative to the workpiece.

In plasma cutting, perpendicularity and inclination tolerances of quality 2 to 4 according to DIN ISO 9013 are state of the art. This corresponds to an angle of up to 3 ⁰ .

FIG. 3 shows, by way of example, a top view of a part 400 which is to be cut out of a workpiece 4. The part 400 to be cut has, for example, four inner contours 410, 430, 450 and 470 and, for example, an outer contour 490. In this example, the workpiece is made of structural steel, that is to say of unalloyed or low-alloy steel, e.g. B. S235 or S355 according to DIN EN 10 027-1. The material thickness 4.3 of the workpiece 4 is 10 mm here, for example. Oxygen is used, for example, as the plasma gas and air, for example, as the secondary gas. There is also the possibility of e.g. to use a mixture of air and oxygen as the secondary gas. In certain material thickness ranges this leads to smoother, more vertical cut edges.

The inner contour 410 is, for example, a large inner contour, while the inner contours 430, 450 and 470 are, for example, small inner contours. Inner contours are small inner contours if the circumference of the contour is equal to or less than six times the thickness of the workpiece. In this case that is a length of 60 mm, since the workpiece thickness is 10 mm.

The circular inner contour 430 has a diameter D430 of, for example, 10 mm, the circumference U430 is, for example, approximately 31 mm. The square inner contour 450 has, for example, a side length S450 of 10 mm each and thus a circumference U430 of 40 mm. The inner contour 470 is, for example, an equilateral triangle and has, for example, a side length S470 of 10 mm each and thus a circumference U470 of 30 mm. The inner contour 410 is square in this example and has a side length S410 of 50 mm each, for example, and thus a circumference U410 of 200 mm.

The outer contour is, for example, a square with a side length S490 of, for example, 100 mm and a circumference U490 of 400 mm. A multiplicity of parts 400, but also a wide variety of other parts, can be cut out of the workpiece 4.

In this example, first the small inner contours 430, 450, 470 of a part 400, then the large inner contour 410 and finally the outer contour 490 are cut out. This is shown by way of example in FIGS. 4, 4a and 4b for the inner contour 430, in FIG. 5 for the inner contour 450, in FIG. 6 for the inner contour 470, in FIG. 7 for the inner contour 410 and in FIG. 8 for the outer contour 490 .

As shown in FIG. 4a, the plasma torch tip 2.8 of the plasma cutting torch 2 is positioned at a starting point 411 or 431 or 451 or 471 with a defined distance, the ignition distance dz, here 4 mm as an example, above the workpiece surface 4.1. The cutting process is started by an ON signal from the guidance system to the plasma cutting system 1 and the cutting arc or plasma jet 3 is initiated as described under FIGS. 1 and 2. With the ignition distance dz, the workpiece 4 to be cut is pierced by the plasma jet 3 (piercing) and after a defined time at a different distance, as shown for example in Figure 4b, positioned above the workpiece surface 4.1, the cutting distance ds, and the cutting is carried out in the feed direction 10 performed with the cutting speed v relative to the workpiece surface 4.1. The cutting distance ds is smaller than the ignition distance dz. As shown in FIGS. 4, 5, 6 and 7, a kerf 414 or 434 or 454 or 474 is created. The piercing takes place on a waste part and the plasma cutting torch 2 is guided over a short section, the so-called piercing lug 412 or 432 or 452 or 472 or 492, that is the kerf on the waste part, to the contour that is ultimately to be cut out. The plasma jet 3 has, depending on its flow and diameter of the nozzle bore 2.2.1 through which it emerges, a diameter that corresponds to a certain joint width B414 or B434 or B454 or B474 and B494 the kerfs 414 or 434 or 454 or 474 and 494 leads. For this reason, the plasma cutting torch 2 is guided during cutting with a distance running parallel to the workpiece surface 4.1 between the longitudinal axis L running through the center of the nozzle bore 2.2.1 of the nozzle 2.2 and the desired contour, the so-called joint offset or joint compensation. As a rule, the cutting distance ds, with which the best cutting quality can ultimately be achieved, is reached at the latest when the contour 410, 430, 450, 470, 490 to be cut is reached. The contour has essentially been cut by traversing the cutting edge 415 or 435 or 455 or 475 or 495, which was formed by the kerf of the piercing lug 412 or 432 or 452 or 472 or 492. The contour is ultimately formed by the cutting edges 413, 433, 453, 473, 493.

The small inner contours 430, 450 and 470 are cut here by way of example with a current of 100 A, a cutting distance ds of, for example, 1.5 mm and a cutting speed v of, for example, 1.4 m / min. The large inner contour 410 and the outer contour 490 are cut by way of example with a current of 100 A, a cutting distance of ds = 3 mm and a cutting speed v of 2.5 m / min. The small inner contours 430, 450 and 470 are cut here with a smaller cutting distance ds and a lower cutting speed v than the large inner contour 410 and the outer contour 490. The circumferential direction (feed direction 10) of the small and large inner contours is the same in this example The direction of travel around the outer contour 490 is opposite in this example, as can also be seen from FIGS. 4 to 8.

FIG. 9 and the following show the view of the workpiece 4. The end of the cutting process of the inner contour 450 can be seen in more detail. The following descriptions also apply to the other inner contours 410, 430 and 470 and the outer contour 490. The plasma jet 3 of the plasma cutting torch 2 has cut part of the kerf 454 and is immediately passed over the cut edge 455, which is formed by the kerf of the plunging lug 452 . The plasma jet 3 usually follows in the opposite direction to its feed direction 10, as shown in FIG. 4b. So it's distracted. A slight deflection of the plasma jet leads to Beard-free or beard-free cuts and high productivity at the same time. In FIG. Ge, the grooves b which arise during the cutting on the cut surface 4.2 and which follow due to the deflection of the plasma jet are shown. The greatest distance between two points of a cutting groove in the cutting direction is called groove trail n according to DIN ISO 9013.

The problem that can occur when cutting at the end of an inner contour, namely a protrusion 456 that arises or remains when the cut edge 455 is traversed, as shown in FIG. 9a, has already been described. This is caused by the sudden loss of the material to be cut in the feed direction 10 when the cutting edge 455 of the plunger 452 is passed over the cutting edge 455. The plasma jet 3 jumps, so to speak, in the feed direction 10 along the cutting edge of the kerf and the trail suddenly becomes smaller. This creates the projection 456, which is usually more pronounced on the underside of the workpiece 4, i.e. on the exit side of the plasma jet 3 from the workpiece 4, than on the workpiece surface 4.1, at which the plasma jet 3 enters the workpiece. This can be seen in FIG. 9b in section A-A through the kerf 454 in the area of the projection 456.

An attempt is made to counteract this effect by reducing the feed rate v. However, this leads to washouts 457 in the already existing cutting edge or cutting surface, particularly in the direction of the lower surface of the workpiece 4, as shown in FIG. 9c. FIG. 9d shows the section B-B through the kerf 454 in the area of the washout 457.

The same problem also arises when cutting the outer contour 490 when driving over the cutting edge 495 formed by the piercing lug 492.

As already described under Figure 3, structural steel is cut here as an example. Oxygen is used as the plasma gas and air as the secondary gas. By adding oxygen to the air of the secondary gas when the plasma jet 3 passes over the cutting edge 455, the formation of the projection 456 is reduced. Since the cutting speed v does not have to be reduced, the formation of the Flushing 457 reduced or even prevented. The cut surface was further improved when the oxygen content in the secondary gas at the outlet of the secondary gas cap and the cutting speed are increased. The cutting speed v should preferably only be increased when the oxygen content of the secondary gas emerging from the secondary gas cap is increased. The increase in the proportion of oxygen should preferably be at least 10% of the volume flow or 10% by volume of the total secondary gas during most of the time of cutting the contour. This can be achieved, for example, by increasing the pressure and / or the volume and / or mass flow of the oxygen in the secondary gas. There is also the possibility of reducing the proportion of the other gas, for example air or nitrogen, for example by reducing the pressure and / or the volume and / or mass flow and thus increasing the oxygen proportion. After passing over the cutting edge 455 and reaching the already cut kerf 454 after passing at least a part or the entire plunging flag, the cutting current is initially reduced and ultimately switched off.

In FIG. 9, the distance 500 in front of or from the cutting edge 455 that is still to be traversed is exemplified, in which the composition, the volume flow and / or the pressure of the secondary gas flowing out of the secondary gas cap 2.4 and / or the cutting distance ds between the plasma torch tip and the workpiece surface can / can be changed, shown. It is here, for example, 10mm and thus corresponds to the workpiece thickness in this example.

In Figure 9c, the distance 502 after or from the already traversed cutting edge 455, in which the composition, the volume flow and / or the pressure of the secondary gas flowing out of the secondary gas cap and / or the distance between the plasma torch tip and the workpiece surface can be changed / can, shown. It is 7mm here, for example.

It is also possible to use nitrogen as the secondary gas. Here too, as in 0. g. Conditions Oxygen is added to the secondary gas, thus increasing the proportion of oxygen. The oxygen content in the secondary gas can also be up to 100%, preferably a maximum of 80% of the volume flow or mass flow.

When cutting high-alloy steels, e.g. 1.4301 (XsCrNiio-io) or 1.4541 (X6CrNiTii8-io), nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen-nitrogen can be used as the plasma gas -Mixture can be used. The secondary gas used is also mostly nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen-nitrogen mixture.

FIG. 10 shows, by way of example, the top view of a part 400 that is to be cut out of a workpiece 4. The part 400 to be cut has four inner contours 410, 430, 450 and 470 and an outer contour 490. The workpiece is made of structural steel, that is, of unalloyed or low-alloy steel, e.g. B. 1.4301 (XsCrNiio-io) or 1.4541 (X6CrNiTii8-io) 1. The thickness of the workpiece 4 is 10 mm here as an example. An argon-hydrogen mixture is used as the plasma gas, for example, and nitrogen is used as the secondary gas. Among other things, there is also the option of using a mixture of nitrogen and hydrogen as the secondary gas. In certain material thickness ranges this leads to smoother, more vertical cut edges.

In this example, the inner contour 410 is a large inner contour. The inner contours 430, 450 and 470 are small inner contours, for example. Inner contours are small inner contours when the circumference of the contour is equal to or less than six times the thickness 4.3 of the workpiece 4. In this case that is a length of 60 mm, since the workpiece thickness is 10 mm.

The circular inner contour 430 has a diameter D430 of 15 mm, for example. The circumference U430 is approximately 47 mm, for example. The inner contour 450 is square, for example, and has a side length S450 of, for example, 14 mm each and thus a circumference U430 of 56 mm. The inner contour 470 is, for example, an equilateral triangle and has a side length S470 of 15 mm each, for example, and thus a circumference U470 of 45 mm. The inner contour 410 is square, for example, and has a side length S410 of 50 mm each, for example, and thus a circumference U410 of 200 mm.

In this example, the outer contour 490 is a square with a side length S490 of, for example, 100 mm and thus has a circumference of 400 mm. A multiplicity of parts 400, but also a wide variety of other parts, can be cut out of the workpiece 4.

In this example, first the inner contours 430, 450, 470 of a part 400, then the large inner contour 410 and finally the outer contour 490 are cut out. This is shown by way of example in FIGS. 11, 11a and 11b for the inner contour 430, in FIG. 12 for the inner contour 450, in FIG. 13 for the inner contour 470, in FIG. 14 for the inner contour 410 and in FIG. 15 for the outer contour 490 .

As shown in Figure 11a, the plasma torch tip 2.8 of the

Plasma cutting torch 2 is positioned at a starting point 411 or 431 or 451 or 471 or 491 with a defined distance, the ignition distance dz, here for example 5 mm, above the workpiece surface 4.1. The cutting process is started by an ON signal from the guidance system to the plasma cutting system 1 and the cutting arc or plasma jet 3 is initiated as described under FIGS. 1 and 2. With the ignition distance dz, the workpiece 4 to be cut is pierced by the plasma jet 3 (piercing) and after a defined time at a different distance, as shown in Figure 11b, positioned above the workpiece surface 4.1, the cutting distance ds, and the cutting is carried out in the feed direction 10 performed at the cutting speed v relative to the workpiece surface 4.1. The cutting distance ds is smaller than the ignition distance dz. As shown in FIGS. 11, 12, 13 and 14, the kerf 414 or 434 or 454 or 474 or 494 is created. The piercing takes place on a scrap part and the plasma cutting torch 2 is guided over a short section, the so-called piercing lug 412 or 432 or 452 or 472 or 492, that is the kerf on the waste part, to the contour to be ultimately cut out. The plasma jet 3 has, depending on its flow and diameter of the nozzle bore 2.2.1 through which it emerges, a diameter which leads to a certain joint width B414 or B434 or B454 or B474 or B494 of the kerfs 414 or 434 or 454 or 474 or 494. For this reason, the plasma cutting torch 2 is guided during cutting with a distance running parallel to the workpiece surface 4.1 between the longitudinal axis L running through the center of the nozzle bore 2.2.1 of the nozzle 2.2 and the desired contour, the so-called joint offset or joint compensation. As a rule, the cutting distance ds, with which the best cutting quality can ultimately be achieved, is reached at the latest when the contour 410 or 430 or 450 or 470 or 490 to be cut is reached. The contour has essentially been cut by traversing the cutting edge 415 or 435 or 455 or 475 or 495, which was formed by the kerf of the piercing lug 412 or 432 or 452 or 472 or 492. The contour is ultimately formed by the cut edges 413 or 433 or 453 or 473 or 493.

The small inner contours 430, 450 and 470 are cut here by way of example with a current of 130 A, a cutting distance ds of, for example, 2.0 mm and a cutting speed v of, for example, 1.0 m / min. The large inner contour 410 and the outer contour 490 are cut with a current of, for example, 130 A, a cutting distance of, for example, ds = 3 mm and a cutting speed v of, for example, 1.4 m / min. The small inner contours 430, 450 and 470 are cut here with a smaller cutting distance ds and a lower cutting speed v than the large inner contour 410 and the outer contour 490.

The direction of travel (feed direction 10) of the small and large inner contours is the same in this example. The direction of travel around the outer contour 490 is opposite in this example, as can also be seen from FIGS. 11 to 15.

FIG. 16 and the following show the view of the workpiece 4. The end of the cutting process of the inner contour 450 can be seen in more detail. The following descriptions also apply to the other inner contours 410, 430 and 470. The plasma jet 3 of the plasma cutting torch 2 has cut part of the kerf 454 and becomes the same as the cut edge 455, which passes through the kerf of the Piercing lug 452 is formed, overrun. Most of the time, the plasma jet 3 runs in the opposite direction to its feed direction 10, as shown in FIG. 9, so it is deflected. A slight deflection of the plasma jet leads to low-beard or beard-free cuts and at the same time to high productivity. FIG. 9a shows the grooves b which arise during the cutting on the cut surface 4.2 and which follow due to the deflection of the plasma jet. The greatest distance between two points of a cutting groove in the cutting direction is called groove trail n according to DIN ISO 9013.

The problem that can occur when cutting at the end of an inner contour, namely a protrusion 456 that arises or remains when the cut edge 455 is traversed, as shown in FIG. 16a, has already been described. This is caused by the sudden loss of the material to be cut in the feed direction 10 when the cutting edge 455 of the plunger 452 is passed over the cutting edge 455. The plasma jet 3 jumps, so to speak, in the feed direction 10 along the cutting edge of the kerf and the trail suddenly becomes smaller. This creates the projection 456, which is usually more pronounced on the underside of the workpiece 4, i.e. on the exit side of the plasma jet 3 from the workpiece 4, than on the workpiece surface 4.1, at which the plasma jet 3 enters the workpiece. This can be seen in FIG. 16b in section A-A through the kerf 454 in the area of the projection 456.

Attempts are made to counteract this effect by reducing the feed speed v, but this leads to flushing 457 in the already existing cutting edge or cutting surface, particularly in the direction of the lower surface of the workpiece 4, as shown in FIG. 15c. FIG. 16d shows the section B-B through the kerf 454 in the area of the washout 457.

As already described under FIG. 10, high-alloy steel is cut here by way of example, an argon-hydrogen mixture is used as the plasma gas and nitrogen is used as the secondary gas. By adding hydrogen to the nitrogen of the secondary gas when the plasma jet 3 passes over the cutting edge 455, the formation of the projection 456 is reduced. Since the cutting speed does not have to be reduced, the formation of the washout 457 is also reduced or even prevented. The cut surface was further improved when the Hydrogen content in the secondary gas at the outlet of the secondary gas cap and the cutting speed can be increased. The cutting speed should preferably only be increased when the hydrogen content of the secondary gas emerging at the secondary gas cap is increased. The increase in the hydrogen content should preferably be at least 10% of the volume flow or 10% by volume of the total secondary gas during most of the time the contour is cut. This can be achieved, for example, by increasing the pressure and / or the volume and / or mass flow or also by switching on the hydrogen in the secondary gas. There is also the possibility of reducing the proportion of the other gas, for example nitrogen, for example by reducing the pressure and / or the volume and / or mass flow or also switching off and thus increasing the hydrogen proportion. After passing over the cutting edge 455 and reaching the already cut kerf 454 after passing at least a part or the entire plunging flag, the cutting current is initially reduced and ultimately switched off.

In FIG. 16, the distance 500 in front of or from the cutting edge 455 that has yet to be traversed is exemplified, in which the composition, the volume flow and / or the pressure of the secondary gas flowing out of the secondary gas cap 2.4 and / or the cutting distance ds between the plasma torch tip and the workpiece surface can / can be changed, shown. It is here, for example, 10mm and thus corresponds to the workpiece thickness in this example.

In Figure 16c, the distance 502 after or from the already traversed cutting edge 455, in which the composition, the volume flow and / or the pressure of the secondary gas flowing out of the secondary gas cap and / or the distance between the plasma torch tip and the workpiece surface can be changed / can, shown. It is 7mm here, for example.

FIG. 17 shows an arrangement in accordance with a particular embodiment of the present invention, with which a method in accordance with a particular embodiment of the present invention can be implemented and which is essentially based on FIGS. 1 and 2. The plasma torch 2, however a first and a second secondary gas SGi and SG2 are supplied via lines 5.5 and 5.6. Solenoid valves Yi and Y2 are located in the plasma torch body 2.7 and switch the secondary gases SGi and SG2. The secondary gas 1, e.g. B. nitrogen or air is fed to the plasma jet 3 during cutting by opening the solenoid valve Yi. When the cut edge 415 or 435 or 455 or 475 or 495 formed by the piercing lug 412 or 432 or 352 or 472 or 492 is passed, either the solenoid valve Y2 for the secondary gas SG2, for example oxygen, is opened and the secondary gas 1 mixed. It is also possible to switch off the secondary gas 1 by switching off the solenoid valve Yi and to allow only the secondary gas 2, for example oxygen, to flow to the plasma jet as the secondary gas.

The point in time at which the secondary gas composition is changed is stored in the control of the guidance system as a function of the course of the contour to be cut and is sent as a signal to the plasma cutting system, which then switches the valves.

The different compositions of the secondary gases for cutting and the end of the cut when passing over the kerf formed by the plunger flag are stored in a database.

In some cases it has been shown that the described effects of the permanent projection 546 or the flushing 457 are reduced if the cutting distance ds of the plasma torch tip 2.8 to the workpiece surface 4.1 is in the vicinity of the cutting edge 415 or 435 or 455 or 475 or 495 is decreased. By reducing the distance by, for example, 1 mm, the projection was reduced.

The time at which the cutting distance ds is changed is stored in the control of the guide system as a function of the course of the contour to be cut and is given to the distance control of the guide machine or the plasma cutting torch. Here, too, the values for the cutting distance ds for cutting and the end of the cut when crossing the kerf formed by the plunge flag are stored in a database.

The features of the invention disclosed in the above description, in the drawings and in the claims can be essential both individually and in any combination for the implementation of the invention in its various embodiments.

List of reference symbols

1 plasma cutting system

1.1 Power source

1.2 pilot resistance

1.3 High voltage ignitor

1.4 Switching contact

2 plasma cutting torches

2.1 electrode

2.1.1 Electrode holder

2.1.2 Use of emissions

2.2 nozzle

2.2.1 Nozzle hole

2.3 Plasma gas supply

2.4 Secondary gas cap

2.5 Secondary gas supply, secondary gas

2.5.1 Secondary gas supply, secondary gas 1

2.5.2 Secondary gas supply Secondary gas 2 Gas guide for plasma gas

Plasma torch body

Plasma torch tip

Gas routing for secondary gas

Plasma jet

workpiece

Workpiece surface

Cut surface

Material thickness

Supply lines

electrical line cutting current

electrical line pilot current

electrical line workpiece - plasma cutting system line plasma gas

Secondary gas line 1

Secondary gas line 2

Gas supply

Direction of advance of the plasma cutting torch part to be cut

large inner contour

Starting point, piercing point

Grooving flag

Cut edge

Kerf

Cutting edge of the grooving flag

small inner contour 431 Starting point, piercing point

432 grooving flag

433 cut edge

434 kerf

435 cutting edge of the plunge flag

450 small inner contour

451 Starting point, piercing point

452 piercing flag

453 cut edge

454 kerf

455 Cutting edge of the plunge flag

456 head start

457 washouts

470 small inner contour

471 Starting point, piercing point

472 grooving flag

473 cutting edge

474 kerf

475 Cutting edge of the plunge flag

490 outer contour

492 plunging flag

493 cut edge

495 Cutting edge of the grooving flag

500 Distance from the cutting edge to be crossed

502 Distance from cut edge already traversed b groove B414 joint width

B434 joint width

B454 joint width

B474 joint width

B494 joint width

D430 diameter small inner contour

d Distance between plasma torch tip and workpiece surface ds Cutting distance between plasma torch tip and workpiece surface dz Ignition distance between plasma torch tip and workpiece surface

L longitudinal axis

n groove lag

PG plasma gas

SG secondary gas

SGi secondary gas 1

SG2 secondary gas 2

S410 side length large inner contour

S450 side length small inner contour

S470 side length small inner contour

S490 side length outer contour

U410 circumference large inner contour

U440 Circumference small inner contour

U450 circumference small inner contour

U470 Circumference small inner contour

U490 circumference outer contour

v cutting speed

Yi solenoid valve secondary gas 1 Y2 solenoid valve secondary gas 2

Claims

Claims l. Method for plasma cutting of workpieces, in which a plasma cutting torch (2) with at least one plasma torch body (2.7), an electrode (1) and a nozzle (2.2) for cutting a part (400) from an in particular plate-shaped workpiece (4) with a material thickness (4.3) is used, the part of the plasma cutting torch (2) from which a plasma jet (3) emerges from the nozzle (2.2) forms the plasma torch tip (2.8), and in which the plasma cutting torch (2) by means of a guide system along a Contour is guided at a cutting speed v relative to the workpiece surface (4.1) in the feed direction (10) so that at least a small inner contour (430, 450, 470) of the part (400), whose circumference (U430, U450 or U470) is smaller than or equal to six times the material thickness (4.3) of the workpiece (4) or whose diameter (D430) is less than or equal to twice the material thickness (4.3) of the workpiece (4), and that at least one outer contour (490) of the part (400) and / or a large inner contour (410) of the part (400) whose circumference (U410) is greater than six times the material thickness (4.3) of the workpiece (4) or whose diameter is greater than twice the material thickness (4.3) of the workpiece (4) is / are cut out, the plasma torch tip (2.8) having a cutting distance ds to the workpiece surface (4.1) during cutting, with at least a small or a large part of the circumference (U430, U450 , U470) of the small inner contour (430, 450, 470) to be cut of the part (400) with a different cutting distance ds between the plasma torch tip (2.8) and the workpiece surface (4.1) is cut than at least one small or a large part of the circumference (U490) of the outer contour to be cut (490) of the part (400) and / or at least a large or a large part of the circumference (U410) of the large inner contour (410) to be cut of the part (400) .

2. A method for plasma cutting of workpieces in which a plasma cutting torch (2) with at least one plasma torch body, an electrode (1), a nozzle (2.2) and a secondary gas cap (2.4) is used, the part of the plasma cutting torch (2) being used in which the plasma jet (3) exits the secondary gas cap (2.4), forms the plasma torch tip (2.8), and in which the plasma cutting torch (2) by means of a guide system along a contour with a cutting speed (v) relative to the workpiece surface (4.1) in the feed direction ( 10) is guided in such a way that at least one small inner contour (430, 450, 470) of the part (400), whose circumference (U430 or U450 or U470) is less than or equal to six times the material thickness (4.3) of the workpiece (4 ) or whose diameter (D430) is smaller than or equal to twice the material thickness (4.3) of the workpiece (4), and that at least one outer contour (490) and / or a large inner contour (410) of the part (400), their The circumference (U410) is greater than six times the material thickness (4.3) of the workpiece (4) or whose diameter is greater than twice the material thickness (4.3) of the workpiece (4), and the plasma torch tip (2.8) a cutting distance ds to

Workpiece surface (4.1) during cutting, with at least a small part or the largest part of the circumference (U430, U450, U470) of the small inner contour (430, 450, 470) to be cut of the part (400) with a different cutting distance ds between the plasma torch tip (2.8) and the workpiece surface (4.1) is cut as at least a small or a large part of the circumference (U490) of the outer contour (490) to be cut of the part (400) and / or at least a large part or a large part of the Perimeter (U410) of the large inner contour to be cut (410) of the part (400).

3. The method according to any one of the preceding claims, characterized in that the cutting distance ds when cutting the small inner contour (430, 450, 470) of the part (400) is smaller than the cutting distance ds when cutting the outer contour (490) of the part (400 ) and / or the large inner contour (410) of the part (400).

4. The method according to claim 3, characterized in that the cutting distance ds when cutting the small inner contour (430, 450, 470) between 40% and 80% of the cutting distance ds when cutting the outer contour (490) of the part (400) and / or the large inner contour (410) of the part (400).

5. The method according to any one of the preceding claims, characterized in that the cutting speed v at which the plasma cutting torch (2) is guided relative to the workpiece surface (4.1) in the feed direction (10) when cutting the small inner contour (430, 450, 470) of the part (400) is less than the cutting speed v when cutting the outer contour (490) of the part (400) and / or the large inner contour (410) of the part (400).

6. The method according to claim 5, wherein the cutting speed v at which the plasma cutting torch (2) is guided relative to the workpiece surface (4.1) when cutting the small inner contours (430, 450, 470) of the part (400) between 20% and 80 %, preferably between 40% and 80% of the cutting speed v when cutting the outer contour (490) of the part (400) and / or the large inner contour (410) of the part (400).

7. The method according to any one of the preceding claims, characterized in that first the small inner contour / small inner contours (430, 450, 470), then the large inner contour / large inner contours (410) and then the outer contour / outer contours (490) of the part ( 400) can be cut.

8. A method for plasma cutting of workpieces in which a plasma cutting torch (2) with at least one plasma torch body (2.7), an electrode (2.1), a nozzle (2.2) and a secondary gas cap (2.4) is used, the part of the plasma cutting torch (2 ), from which the plasma jet (3) emerges from the secondary gas cap (2.4), forms the plasma torch tip (2.8), and in which the plasma cutting torch (2) is advanced by means of a guide system along a contour with a cutting speed v relative to the workpiece surface (4.1) direction is guided and a part (400) cuts from a, in particular plate-shaped, workpiece (4), the composition and / or the volume flow and / or the mass flow and / or the pressure of a secondary gas SG and flowing out of the secondary gas cap (2.4) / or the cutting distance ds between the plasma torch tip (2.8) and the workpiece surface (4.1) is / are changed at the earliest when an on the workpiece surface che (4.1) impinging plasma jet (3) has reached a position on the contour to be cut out, whose distance 500 from a cutting edge (415, 435, 455, 475, 495) that is still to be traversed is in a range of a maximum of 50%, better still a maximum of 25% of a material thickness (4.3) of the workpiece (4), or whose distance 500 from the The cutting edge (415, 435, 455, 475, 495) still to be traversed lies in an area of a maximum of 15 mm, better still a maximum of 7 mm, or in which the plasma jet (3) striking the workpiece surface (4.1) touches the cutting edge (415, 435 , 455, 475, 495).

9. A method for plasma cutting of workpieces, in which a plasma cutting torch (2) with at least one plasma torch body (2.7), an electrode (2.1), a nozzle (2.2) and a secondary gas cap (2.4) is used, the part of the plasma cutting torch (2 ), from which the plasma jet (3) emerges from the secondary gas cap (2.4), forms the plasma torch tip (2.8), and in which the plasma cutting torch (2) is advanced by means of a guide system along a contour with a cutting speed v relative to the workpiece surface (4.1) direction is guided and a part (400) cuts from a, in particular plate-shaped, workpiece (4), the composition and / or the volume flow and / or the mass flow and / or the pressure of the secondary gas SG and flowing out of the secondary gas cap (2.4) / or the cutting distance ds between the plasma torch tip (2.8) and the workpiece surface 4.1 is changed at the latest when the on the workpiece surface (4.1) a the incident plasma jet (3) has reached a position on the contour to be cut out, whose distance 502 from the cut edge (415, 435, 455, 475, 495) that has already been passed is in a range of a maximum of 25% of the workpiece thickness (4.3), or whose distance 502 from the cut edge that has already been passed (415, 435, 455, 475 , 495) is in the range of a maximum of 7 mm, or in which the plasma jet (3) impinging on the workpiece surface (4.1) has passed the cutting edge (415, 435, 455, 475, 495).

10. The method according to claim 8 and 9, characterized in that the cutting edge (415, 435, 455, 475, 495) was created by cutting the same contour.

11. The method according to any one of claims 8 to 10, characterized in that air, oxygen, nitrogen, argon, hydrogen, methane or helium or a mixture thereof is used as the secondary gas.

12. The method according to claim 11, characterized in that the mixture of oxygen and / or nitrogen and / or air and / or argon and / or helium or of argon and / or nitrogen and / or hydrogen and / or methane and / or helium consists.

13. The method according to any one of claims 8 to 12, characterized in that the composition and / or the volume flow and / or the mass flow and / or the pressure of the secondary gas SG flowing out of the secondary gas cap (2.4) through Switching on and / or

Increase the volume flow and / or

Increasing the mass flow and / or

Increasing the pressure of an oxidizing gas or gas mixture and / or a reducing gas or gas mixture is / are realized.

14. The method according to claim 13, characterized in that the composition of the secondary gas is changed so that the increase in the proportion of the oxidizing gas or gas mixture and / or the reducing gas or gas mixture in the secondary gas is at least 10% by volume.

15. The method according to claim 13, characterized in that the increase in the volume flow, the mass flow or the pressure of the oxidizing gas or gas mixture and / or the reducing gas or gas mixture in the secondary gas is at least 10%.

16. The method according to any one of claims 13 to 15, characterized in that the oxidizing gas or gas mixture contains oxygen and / or air.

17. The method according to claim 16, characterized in that the oxidizing gas is oxygen.

18. The method according to any one of claims 13 to 15, characterized in that the reducing gas or gas mixture contains hydrogen and / or methane.

19. The method according to claim 18, characterized in that the reducing gas is hydrogen.

20. The method according to any one of claims 8 to 12, characterized in that the composition and / or the volume flow and / or the mass flow and / or the pressure of the secondary gas SG flowing out of the secondary gas cap (2.4) through

Switch off and / or

Reducing the volume flow and / or

Reducing the mass flow and / or

Reducing the pressure of nitrogen, argon, air, helium or the mixture is / are realized.

21. The method according to claim 20, characterized in that the composition of the secondary gas is changed so that the reduction in the proportion of gases or the gas mixture in the secondary gas is at least 10% by volume.

22. The method according to claim 20, characterized in that the reduction in the volume flow, the mass flow or the pressure of the gases or the gas mixture in the secondary gas is at least 10%.

23. The method according to any one of claims 8 to 10, characterized in that the cutting distance ds between the plasma torch tip (2.8) and the workpiece surface (4.1) is reduced.

24. The method according to claim 20, characterized in that the cutting distance ds is reduced by at least 25% and / or at least imm.

25. The method according to any one of claims 8 to 24, characterized in that the cutting speed v at which the plasma cutting torch (2) is guided relative to the workpiece surface (4.1) is changed at the earliest when the plasma jet striking the workpiece surface (4.1) (3) has reached a position on the contour to be cut, the distance of which from the cutting edge (415, 435, 455, 475, 495) to be traversed in the range of a maximum of 50%, better a maximum of 25% of the material thickness (4.3) of the workpiece 4) or the distance from the cutting edge (415, 435, 455, 475, 495) to be crossed in a range of a maximum of 15 mm, better a maximum of 7 mm, or at which the plasma jet hitting the workpiece surface (4.1) (3) touches the cut edge (415, 435, 455, 475, 495).

26. The method according to any one of claims 8 to 24, characterized in that the cutting speed v at which the plasma cutting torch (2) is guided relative to the workpiece surface (4.1) is changed at the latest when the plasma beam impinging on the workpiece surface (4.1) (3) has reached a position on the contour to be cut out, whose distance from the cut edge that has already been driven over (415, 435, 455, 475, 495) is in the range of a maximum of 25% of the workpiece thickness (4.3), or its distance from the cut edge that has already been driven over (415, 435, 455, 475, 495) is in the range of 7 mm, or in which the plasma jet (3) impinging on the workpiece surface (4.1) has passed the cutting edge (415, 435, 455, 475, 495).

27. The method according to any one of claims 25 and 26, characterized in that the cutting speed v is increased.

28. The method according to claim 27, characterized in that the cutting speed v is increased by at least 10%.