DE102021005500B4 - Process for plasma cutting of valuable items - Google Patents

Abstract

Method for plasma cutting of workpieces, in which at least one plasma cutting torch (2) with at least one plasma torch body (2.7), an electrode (2.1) and a nozzle (2.2), through the nozzle opening (2.2.1) of which at least one plasma gas (PG) or plasma gas mixture flows and which constricts the plasma jet (3), is used, the method comprising: - positioning the plasma cutting torch (2) in relation to a workpiece (4), - igniting a pilot arc between the electrode (2.1) and the nozzle (2.2) of the plasma cutting torch (2) and generating a transferred plasma arc between the electrode (2.1) of the plasma cutting torch (2) and the workpiece (4), - piercing the plasma jet (3) into the workpiece (4) until the plasma jet (3) has passed through the workpiece (4), and - then cutting the workpiece (4) by guiding the plasma cutting torch (2) at a feed rate v4 in a plasma torch distance d4 from the workpiece (4) at a cutting current I4, so that a cutting gap (450) with a cutting gap width (452) is created, wherein before the plasma jet (3) penetrates into and through the workpiece (4), a flushing (410) is formed by exposing the workpiece (4) from the workpiece surface (4.1) to the plasma jet (3) at least for a time period t2 in such a way that material of the workpiece (4) is removed from the workpiece surface (4.1) and the flushing (410) is created, characterized in that the smallest distance (411) between a contour (430) described by the plasma cutting torch (2) and an edge (413) of the resulting flushing (410) is smaller than the smallest distance (412) of the contour (430) described by the plasma cutting torch (2)

Description

The invention relates to a method for plasma cutting of workpieces, in particular for hole cutting.

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

The plasma jet's parameters can be greatly influenced by the design of the nozzle and electrode. These parameters of the plasma jet include the jet diameter, temperature, energy density and the flow velocity of the gas.

In plasma cutting, for example, the plasma is constricted by a nozzle that can be gas or water cooled. The nozzle has a nozzle hole through which the plasma jet flows. This allows energy densities of up to 2 × 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 speed of the gas, enable 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 have a plasma torch body in which an electrode and a nozzle are attached. The plasma gas flows between them and exits through the nozzle bore. The plasma gas is usually 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 supply for a secondary medium, either a gas or a liquid. The nozzle is then surrounded by a secondary gas cap. The nozzle is particularly protected in liquid-cooled plasma torches by a nozzle cap, such as in DE 10 2004 049 445 A1 described, fixed. 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 secondary gas cap and exits from the bore of the secondary gas cap. It influences the plasma jet formed by the arc and the plasma gas. It can be set in rotation by a gas guide that is arranged between the nozzle or nozzle cap and the secondary gas cap.

The secondary gas cap protects the nozzle and nozzle cap from the heat or molten metal splashing out of the workpiece, especially when the plasma jet penetrates the material of the workpiece to be cut. It also creates a defined atmosphere around the plasma jet during cutting.

For plasma cutting of unalloyed and low-alloyed steels, also known as structural steels, e.g. 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 usually used as secondary gases, whereby the composition and volume flows of the plasma gas and the secondary gas are usually different, but can also be the same.

For plasma cutting of high-alloy steels and stainless steels, e.g. 1.4301 (X5CrNi10-10) or 1.4541 (X6CrNiTi18-10), nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen-nitrogen mixture are usually used as plasma gases. In principle, the use of air as a plasma gas is also possible, but the oxygen content in the air leads to oxidation of the cutting surfaces and thus to a deterioration in the cutting quality. Nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen-nitrogen mixture are also usually used as secondary gases, whereby the composition and volume flows of the plasma gas and the secondary gas are usually different, but can also be the same.

The problem underlying the present invention is described below.

Here, the feed rate v refers to the speed at which a plasma torch is moved relative to and parallel to a workpiece surface. This is usually done by a guidance system, e.g. a CNC-controlled coordinate guidance machine or a robot.

Common arrangements for plasma cutting are shown in the 1 and 2 shown schematically as an example. An electrical cutting current flows from a power source 1.1 of a plasma cutting system 1 via a line 5.1 to a plasma cutting torch 2 via its electrode 2.1, a plasma jet 3 constricted by a nozzle 2.2 and a nozzle opening 2.2.1 to a workpiece 4 and then via a line 5.3 back to the 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. The plasma cutting system 1 contains a high-voltage ignition device 1.3, a pilot resistor 1.2, a power source 1.1 and a switching contact 1.4 and their control device (not shown). Valves for controlling the gases can also be present, but these are not shown here.

The plasma cutting torch 2 essentially consists of a plasma torch body 2.7 with a beam generation system comprising the electrode 2.1, the nozzle 2.2 and a gas supply 2.3 for plasma gas PG. The plasma torch body 2.7 also accommodates the supply of the media (gas, cooling water and electric current).

The electrode 2.1 of the plasma cutting torch 2 is usually 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 with good electrical and thermal conductivity (e.g. copper, silver, alloys thereof), and a high-melting emission insert 2.1.2 with a low electron work function (such as hafnium, zirconium, tungsten). The nozzle 2.2 is usually made of copper and constricts the plasma jet 3. A gas guide 2.6 for the plasma gas PG, which causes the plasma gas to rotate, 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 exits 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 designated by d.

In 2 In addition, a secondary gas cap 2.4 is attached around the nozzle 2.2 of the plasma cutting torch 2 for supplying a secondary medium, e.g. a secondary gas SG. The combination of secondary gas cap 2.4 and secondary gas SG protects the nozzle 2.2 from damage when the plasma jet 3 penetrates 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 SG in rotation. In this exemplary embodiment, the point on 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 designated d.

For the cutting process, a pilot arc is first ignited, which burns between the electrode 2.1 and 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 line 5.1 to the electrode 2.1 and from the nozzle 2.2 through the line 5.2 via the switching contact 1.4 and the electrical resistance 1.2 to the power source 1.1 and is limited by the electrical resistance 1.2. This low-energy pilot arc prepares the path between the plasma torch tip 2.8 and the workpiece 4 for the cutting arc by partial ionization. If the pilot arc touches the workpiece 4, the electrical potential difference between the nozzle 2.2 and the workpiece 4, generated by the electrical resistance 1.2, causes the cutting arc to form. This then burns between the electrode 2.1 and the workpiece 4 with a generally higher electrical current (e.g. 20 A to 900 A) and thus also with greater power. The switching contact 1.4 is opened and the nozzle 2.2 is switched to a potential-free state by 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, can be cut.

For this purpose, the plasma cutting torch 2 is moved relative to a workpiece 4 or its surface 4.1 using a guide system (not shown). This can be done, for example, by a robot or a CNC-controlled guide. The control device of the guidance system communicates with the arrangement according to 1 or 2 .

In the simplest case, the control device of the guidance system starts and stops 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. about operating states and data, can be exchanged as just ON and OFF between the control device of the guidance system and the plasma cutting system.

High cutting qualities can be achieved with plasma cutting. Criteria for this include, for example, a low squareness and inclination tolerance according to DIN ISO 9013. By maintaining the optimal cutting parameters, which include the electrical cutting current, the cutting speed, the distance between the plasma cutting torch and the workpiece and the gas pressure, smooth cutting surfaces and burr-free edges can be achieved.

A typical cutting task for plasma cutting is cutting out one or more contours from a workpiece. To do this, the workpiece 4 must be pierced and penetrated before the contour is cut. The plasma cutting torch 2 is used for this purpose, as shown in 3 shown as an example, with a distance d1 between the torch tip 2.8 and the workpiece surface 4.1 and the pilot arc 3.1, as in 4 shown as an example. d1 must usually be selected so that the pilot arc reaches the workpiece surface and the arc can "translate" from the nozzle to the workpiece and the plasma jet can form towards the workpiece.

When piercing, in 5 As shown by way of example, in and through the workpiece 4, in contrast to starting at the workpiece edge, the entire workpiece thickness 4.3 must be "pierced". In the process, the material 418 melted by the effect of the plasma jet 3 sprays upwards in the direction of the plasma cutting torch 2, in particular against the nozzle 2.2 or the secondary gas cap 2.4 and the plasma torch tip 2.8, and can damage them. According to the prior art, attempts are made to keep the material 418 melted and spraying up during piercing away from the nozzle 2.2, the secondary gas cap 2.4 and plasma torch tip 2.8 and from the plasma torch 2 by means of a larger plasma torch distance d2. Due to the larger plasma torch distance d2, part of the molten material 418 of the workpiece 4 sprays past the nozzle 2.2, the secondary gas cap 2.4 and plasma torch tip 2.8 or the plasma cutting torch 2. Nevertheless, some of the splashing material remains, which splashes against the components mentioned, particularly in the case of thicker sheet metal, and damages them. Attempts are also made to guide the plasma cutting torch 2 in the direction of the contour to be cut out, parallel to the workpiece surface 4.1, at a lower speed than the cutting speed, in order to keep the splashing material away from the plasma cutting torch and the components mentioned.

After piercing the workpiece 4, the molten material sprays out of the workpiece underside 4.5 and it can be cut.

For example, when plasma cutting with a cutting current of 300 A, it is usually possible to cut a maximum workpiece thickness of 80 mm and to pierce a maximum workpiece thickness of 50 mm.

As soon as the workpiece thickness 4.3 is 40 mm or more, material 418 spraying up from the melted workpiece 4 comes into contact with the plasma torch tip 2.8, the nozzle 2.2 and nozzle tip or the secondary gas cap 2.4 and the secondary gas cap tip and damages them due to its high temperature. After this, it is often no longer possible to cut a component from the workpiece in good quality because the nozzle opening 2.2.1 that forms the cutting arc or the plasma jet 3 and/or the secondary gas cap bore are damaged and no longer round. It can even happen that the nozzle 2.2 or the secondary gas cap 2.4 are actually destroyed if a parasitic so-called secondary arc forms, which burns from the electrode to the nozzle and/or secondary gas cap and to the workpiece.

When piercing even thicker material, there is a high probability of damage to the nozzle and/or the secondary gas cap, and often even damage to the plasma torch.

EP 2 939 782 A1 discloses a method for plasma cutting of workpieces, in which at least one plasma cutting torch with at least one plasma torch body, an electrode and a nozzle, through the nozzle opening of which at least one plasma gas or plasma gas mixture flows and which beam constricts, is used. The method comprises positioning the plasma cutting torch in relation to a workpiece, and then a pilot arc is ignited between the electrode and the nozzle of the plasma cutting torch and a transferred plasma arc is generated between the electrode of the plasma cutting torch and the workpiece. Furthermore, the plasma jet is pierced into the workpiece until the plasma jet has passed through the workpiece, and then the workpiece is cut by guiding the plasma cutting torch at a feed rate at a plasma torch distance from the workpiece with a cutting current, so that a kerf with a kerf width is created. Furthermore, before the plasma jet is pierced into and through the workpiece, a flushing is formed by exposing the workpiece from the workpiece surface to the plasma jet for at least a period of time in such a way that material of the workpiece is removed from the workpiece surface and the flushing is created.

The present invention is therefore based on the object of avoiding, or at least reducing, damage to a plasma torch, a plasma torch tip, in particular a nozzle, a nozzle opening and/or a secondary gas cap when piercing a workpiece due to splashing molten hot material, in order to be able to pierce safely, in particular, even into larger sheet thicknesses.

According to the invention, this object is achieved by a method according to claim 1. The flushing can also be referred to as a trough or depression.

The subclaims relate to advantageous further developments thereof.

The present invention is based on the surprising finding that by producing a flush on a workpiece surface before piercing into and through the workpiece, for example by using parameters that differ from those used for cutting, with which the plasma cutting torch is operated or moved, piercing into and through material that is thicker than the prior art can be carried out safely.

• 1 eine Anordnung zum Plasmaschneiden gemäß dem Stand der Technik;
• 2 eine weitere Anordnung zum Plasmaschneiden gemäß dem Stand der Technik;
• 3 beispielhaft den Vorgang des Positionierens eines Plasmaschneidbrenners beim Plasmaschneiden;
• 4 beispielhaft den Vorgang des Zündens eines Pilotbogens im Rahmen des Plasmaschneidens;
• 5 beispielhaft den Vorgang des Einstechens eines Plasmastrahls beim Plasmaschneiden;
• 6 bis 13 Einzelheiten eines Verfahrens zum Plasmaschneiden von Werkstücken gemäß einer besonderen Ausführungsform der vorliegenden Erfindung;
• 14 zeitliche Verläufe von Plasmabrennerabstand und Vorschubgeschwindigkeit gemäß einer besonderen Ausführungsform der vorliegenden Erfindung; und
• Fig. 15zeitliche Verläufe von Plasmabrennerabstand und Vorschubgeschwindigkeit gemäß einer weiteren besonderen Ausführungsform der vorliegenden Erfindung.

Further features and advantages of the invention emerge from the appended claims and the following description, in which several embodiments are explained with reference to the schematic drawings.

• 1 a plasma cutting arrangement according to the prior art;
• 2 another arrangement for plasma cutting according to the prior art;
• 3 example of the process of positioning a plasma cutting torch during plasma cutting;
• 4 example of the process of igniting a pilot arc during plasma cutting;
• 5 an example of the process of piercing a plasma jet during plasma cutting;
• 6 to 13 Details of a method for plasma cutting workpieces according to a particular embodiment of the present invention;
• 14 temporal courses of plasma torch distance and feed rate according to a particular embodiment of the present invention; and
• Fig. 15 Time courses of plasma torch distance and feed rate according to another particular embodiment of the present invention.

For this purpose, the piercing process up to the final piercing into and through the workpiece for structural steel with a material thickness 4.3 of, for example, 60 mm and a cutting current I4 of, for example, 300 A is explained as an example. When cutting, the feed speed v4 of the plasma cutting torch 2 is, for example, 300 mm/min and the plasma torch distance d4 is, for example, 7 mm. When cutting, oxygen is used as the plasma gas PG and air is used as the secondary gas SG. The kerf width 452 of the kerf 450 created during cutting is approximately 6.5 mm.

The piercing process can essentially be divided into 4 phases.
Phase 1: Positioning the plasma torch, igniting the pilot arc and initiating the main arc
Phase 2: Rinsing the workpiece from the workpiece surface
Phase 3: Piercing into and through the workpiece
Phase 4: Cutting

The phases can merge directly into one another and even partially overlap. However, transition processes between the phases and, in principle, additional and/or alternative phases are also possible.

6 shows, by way of example, how a plasma torch 2 with a plasma torch distance d1 of, for example, 9 mm is positioned between a plasma torch tip 2.8 and a workpiece surface 4.1 (phase 1). d1 must usually be selected so that the pilot arc reaches the workpiece surface and the arc can "translate" from the nozzle to the workpiece and the plasma jet can form towards the workpiece.

7 shows that a pilot arc 3.1 has been ignited. This initially burns between an electrode 2.1 and a nozzle 2.2 (not shown here, see 1 and 2 ) with e.g. 25 A (phase 1).

After ignition of the pilot arc 3.1, the anodic starting point moves from the nozzle 2.2 to the workpiece 4, a plasma jet 3 is formed and the plasma torch distance d is increased from d1 to d2 = 25 mm, as in 8 shown (Phase 2).

The current is increased to the cutting current of, for example, 300 A. The feed rate v, with which the plasma cutting torch 2 is moved relative to the workpiece surface 4.1 in the feed direction 10, is increased from v1 of, for example, 0 mm/min to v2 of, for example, 2,800 mm/min. This is advantageously significantly greater than the feed rate v4 during cutting (phase 4). The shape of the contour 430, which the plasma torch 2 describes relative to the workpiece surface 4.1, viewed from above on the workpiece surface 4.1, with the feed rate v2, is in this case an oval contour 430 with a size of, for example, approximately 48 mm × 8 mm ( 9b) . The feed rate v2 and the plasma torch distance d2 are so large that the molten material 418 spraying up from the workpiece surface 4.1 sprays away to the side in such a way that it does not touch the plasma cutting torch 2, the nozzle 2.2, a secondary gas cap 2.4 and the plasma torch tip 2.8 or only to such a small extent that they are not damaged, as in 9a shown (phase 2). In this example, this is achieved in particular by combining the described parameters v2 and d2. Only material is removed. The plasma cutting torch is advantageously moved so quickly (v2) and is sufficiently far away (d2) that the molten material sprays away to the side. You can also imagine that the rapid movement deflects the plasma jet against the feed direction. The molten material then sprays in this direction.

Overall, one could also say that the energy input into the surface per unit length (mm) is advantageously smaller than when cutting.

The 9b shows a top view of the workpiece surface 4.1 of the oval contour 430 described by the plasma cutting torch 2. This is here, for example, circumscribed twice and the flushing 410 is created, also shown, with a maximum length 419 of, for example, approximately 57 mm and a width 420 of, for example, 17 mm. The flushing 410 has an oval shape 415 with a peripheral edge 413 at the transition between the flushing 410 and the workpiece surface 4.1. The distance 417 of the lowest point of the flushing 410, measured perpendicularly (ie according to the rectangular coordinate system in the z direction shown in the figures) to the workpiece surface 4.1, is here, for example, 25 mm (phase 2).

The smallest distance 411 between the edge 413 of the resulting flushing 410 and the oval contour 430 described by the plasma cutting torch 2 is, for example, approximately 4.5 mm, the distance 412 of the longitudinal edges of the oval contour 430 described by the plasma cutting torch 2 is, for example, 8 mm. In this example, the distance 411 is therefore smaller than the distance 412 and the distance 412 is smaller than twice the distance 411.

The 10 shows the plasma cutting torch 2 shortly after leaving the contour 430. It has been moved in the direction of the edge 413 of the flushing area 410 for approximately 2 mm, for example, and positioned such that the plasma jet 3 at least partially hits the edge 413 and/or the slope 421 of the flushing area 410.

So it squirts now when piercing, like 10 shown, in and through the workpiece 4, hot material 418 is directed laterally away, especially in the direction of the flushing 410, so that it does not touch the plasma cutting torch 2 and its components, the nozzle 2.2, torch tip 2.8, secondary gas cap 2.4, or only to a very small extent. During piercing (phase 3), in 10 shown, in and through the workpiece 4, the feed rate v of the plasma cutting torch 2 can be v3 = 0 m/min or between 0 and the feed rate v4 with which the workpiece 4 is cut. The feed rate v3 is advantageously significantly lower than the feed rate v2 during removal. The length 419 of the flushing 410 is so large that the material 418 spraying up to the piercing point can spray away through the flushing 410 in the opposite direction to the cutting direction 10 in such a way that it does not touch the plasma cutting torch 2, the plasma torch tip 2.8, the nozzle 2.2 and/or the secondary gas cap 2.4 or does not touch it for the most part. In other words, the flushing 410 should advantageously be large enough that the molten material 418 spraying up sideways due to the high feed rate v2 can "fly through" between the plasma cutting torch 2 and its components (nozzle 2.2, secondary gas cap 2.4, plasma torch tip 2.8) and the edge 413 and the slope 421 of the flushing 410. If the flushing is too small, the spraying material hits the opposite part of the edge 413 and the slope 421 of the flushing 410 and can be diverted or redirected in the direction of the plasma cutting torch 2.

In the example, the feed rate is v3 = 0 m/min. In phase 3, the plasma torch distance d3 is set at 25 mm, equal to the plasma torch distance d2 during removal. The plasma torch distance d3 is greater than the plasma torch distance d4 during cutting (phase 4).

After the workpiece 4 has been pierced as in 11 , 12 and 13 As shown, the feed speed v4 and the plasma torch distance d4 selected for cutting, for example, 60 mm mild steel can be adjusted to perform the cutting process which produces a kerf 450 with a kerf width 452 (Phase 4).

The 11 the plasma cutting torch 2 immediately after piercing the workpiece, the 12 the plasma cutting torch during cutting and the 13 the top view of the workpiece surface 4.1 and the cutting gap 450 and flushing 410 produced by the plasma cutting torch 2 (illustration without plasma cutting torch 2). Here the molten material 423 sprays out of the workpiece underside 4.5.

In the 14 and 15 The schematic sequence of the plasma torch distance (d, d1, d2, d3, d4) and the feed rate (v, v1, v2, v3, v4) of the plasma cutting torch 2 during the time phases 1, 2, 3 and 4 is shown as an example. 15 shows in addition that between phases 1, 2, 3, and 4 there can be at least one further phase. This can also be just the transition between two parameters, e.g. v1 and v2, v2 and v3, v3 and v4 and/or d1 and d2, d2 and d3, d3 and d4. In practice this will usually be the case because it is the 14 There are no "abrupt" transitions shown. However, there may also be additional, longer phases intentionally included.

For example, in particular between phase 3 and phase 4, a further phase 5 with a time t5 can be provided, during which the plasma torch distance d5 and/or the feed speed d5 differs from those of phases 3 and 4.

$$\text{d}3<=\text{d}5>\text{d}4$$

This is particularly useful if there is a portion of melted material on the workpiece surface, then the following applies: $$\text{<figure-callout id="3" label="v" filenames="DE102021005500B4\_0003.png,DE102021005500B4\_0004.png" state="{{state}}">v</figure-callout>}3<\text{<figure-callout id="5" label="v" filenames="DE102021005500B4\_0003.png,DE102021005500B4\_0004.png" state="{{state}}">v</figure-callout>}5<\text{<figure-callout id="4" label="v" filenames="DE102021005500B4\_0003.png,DE102021005500B4\_0004.png" state="{{state}}">v</figure-callout>}4\text{and}/\text{or}$$

$$\text{<figure-callout id="3" label="d" filenames="DE102021005500B4\_0003.png,DE102021005500B4\_0004.png" state="{{state}}">d</figure-callout>}3<=\text{<figure-callout id="5" label="d" filenames="DE102021005500B4\_0003.png,DE102021005500B4\_0004.png" state="{{state}}">d</figure-callout>}5>\text{<figure-callout id="4" label="d" filenames="DE102021005500B4\_0003.png,DE102021005500B4\_0004.png" state="{{state}}">d</figure-callout>}4$$

It is also possible to insert pauses between the phases or at least two phases, for example to allow the workpiece 4 or the plasma cutting torch 2 to cool down or to remove splashes of the melted workpiece 4 on the workpiece surface 4.1. During pauses, the current I can be "0", for example.

In every phase, the vector of the feed rate can in principle be a component parallel to the workpiece surface, i.e. in the rectangular coordinate system shown in the figures, of which the y-axis runs into the plane of the drawing (perpendicular), in the xy-plane, also still have a component perpendicular to the workpiece surface (z-component). This would then cause the change in the parameter d.

At least in the transitions between the phases, d changes in examples. Thus, there is the vertical component of v.

In the example described, a higher feed rate v2 than the feed rate v4 during cutting and a higher plasma torch distance d2 than the plasma torch distance d4 during cutting (phase 4) were selected for the removal or generation of the flushing 410 (phase 2). The current I2 here advantageously has the same size as the cutting current I4 during cutting.

However, other combinations of the parameters are also possible, for example according to claims 3 to 9. In this case, it is particularly important to combine them in such a way that the molten material 418 spraying up from the workpiece surface 4.1 sprays away to the side in such a way that it does not touch the plasma torch 2, in particular its nozzle 2.2 or its secondary gas cap or its plasma torch tip 2.8, or only touches it to a small extent and thus does not damage it.

• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und/oder
• - mit einem geringeren Strom I2 als I4 und/oder
• - mit einem größeren Plasmabrennerabstand d2 als d4 und/oder
• - mit einem geringeren Druck p12 des Plasmagases PG als p14 und/oder
• - mit einem geringeren Volumen- und/oder Massestrom m12 der Plasmagases als m14 und/oder
• - mit einem geringeren Druck p22 des Sekundärgases SG als p24 und/oder
• - mit einem geringeren Volumen- und/oder Massestrom m12 der Sekundärgases als m24 und/oder
• - mit einer Zusammensetzung des Plasmagases oder Plasmagasgemisches, das einen geringeren oxidierenden Anteil während der Phase 2 aufweist, und/oder
• - mit einer Zusammensetzung des Plasmagases oder Plasmagasgemisches, das einen geringeren reduzierenden Anteil während der Phase 2 aufweist, und/oder
• - mit einer Zusammensetzung des Sekundärgases oder Sekundärgasgemisches, das einen geringeren oxidierenden Anteil während der Phase 2 aufweist, und/oder
• - mit einer Zusammensetzung des Sekundärgases oder Sekundärgasgemisches, das einen geringeren reduzierenden Anteil während der Phase 2 aufweist.

For example, during phase 2 of removal and rinsing, it is possible to work with the following modified parameters compared to cutting (phase 4):

• - With a higher feed rate v2 than v4 and/or
• - with a lower current I2 than I4 and/or
• - with a larger plasma torch distance d2 than d4 and/or
• - with a lower pressure p12 of the plasma gas PG than p14 and/or
• - with a lower volume and/or mass flow m12 of the plasma gas than m14 and/or
• - with a lower pressure p22 of the secondary gas SG than p24 and/or
• - with a lower volume and/or mass flow m12 of the secondary gas than m24 and/or
• - with a composition of the plasma gas or plasma gas mixture which has a lower oxidising content during phase 2, and/or
• - with a composition of the plasma gas or plasma gas mixture which has a lower reducing content during phase 2, and/or
• - with a composition of the secondary gas or secondary gas mixture that has a lower oxidising content during phase 2, and/or
• - with a composition of the secondary gas or secondary gas mixture which has a lower reducing content during phase 2.

Different combinations of parameters are also possible.

For a particularly simple implementation, it is advisable not to change the removal or rinsing with all of the parameters listed that have been changed compared to the cutting, but to use only three, or better still only two, changed parameters.

• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und einem größeren Plasmabrennerabstand d2 als d4.
• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und einem geringeren Druck p12 des Plasmagases PG als p14.
• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und einem geringeren Volumen- und/oder Massestrom m12 des Plasmagases als m14.
• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und einem geringeren Druck p22 des Sekundärgases SG als p24.
• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und einem geringeren Volumen- und/oder Massestrom m12 der Sekundärgases als m24.
• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und einer Zusammensetzung des Plasmagases oder Plasmagasgemisches, das einen geringeren reduzierenden Anteil aufweist.
• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und des Plasmagases oder Plasmagasgemisches, das einen geringeren reduzierenden Anteil aufweist.
• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und einer Zusammensetzung des Sekundärgases oder Sekundärgasgemisches, das einen geringeren oxidierenden Anteil aufweist.
• - Mit einer höheren Vorschubgeschwindigkeit v2 als v4 und einer Zusammensetzung des Sekundärgases oder Sekundärgasgemisches, das einen geringeren reduzierenden Anteil aufweist.
• - Mit einem größeren Plasmabrennerabstand d2 als d4 und einem geringeren Druck p12 des Plasmagases PG als p14.
• - Mit einem größeren Plasmabrennerabstand d2 als d4 und einem geringeren Volumen- und/oder Massestrom m12 der Plasmagases als m14.
• - Mit einem größeren Plasmabrennerabstand d2 als d4 und einem geringeren Druck p22 des Sekundärgases SG als p24.
• - Mit einem größeren Plasmabrennerabstand d2 als d4 und einem geringeren Volumen- und/oder Massestrom m12 der Sekundärgases als m24.
• - Mit einem größeren Plasmabrennerabstand d2 als d4 und einer Zusammensetzung des Plasmagases oder Plasmagasgemisches, das einen geringeren reduzierenden Anteil während der Phase 2 aufweist.
• - Mit einem größeren Plasmabrennerabstand d2 als d4 des Plasmagases oder Plasmagasgemisches, das einen geringeren reduzierenden Anteil während der Phase 2 aufweist.
• - Mit einem größeren Plasmabrennerabstand d2 als d4 und einer Zusammensetzung des Sekundärgases oder Sekundärgasgemisches, das einen geringeren oxidierenden Anteil während der Phase 2 aufweist.
• - Mit einem größeren Plasmabrennerabstand d2 als d4 und einer Zusammensetzung des Sekundärgases oder Sekundärgasgemisches, das einen geringeren reduzierenden Anteil während der Phase 2 aufweist.

The following combinations are given as examples for a better understanding:

• - With a higher feed rate v2 than v4 and a larger plasma torch distance d2 than d4.
• - With a higher feed rate v2 than v4 and a lower pressure p12 of the plasma gas PG than p14.
• - With a higher feed rate v2 than v4 and a lower volume and/or mass flow m12 of the plasma gas than m14.
• - With a higher feed rate v2 than v4 and a lower pressure p22 of the secondary gas SG than p24.
• - With a higher feed rate v2 than v4 and a lower volume and/or mass flow m12 of the secondary gas than m24.
• - With a higher feed rate v2 than v4 and a composition of the plasma gas or plasma gas mixture that has a lower reducing content.
• - With a higher feed rate v2 than v4 and the plasma gas or plasma gas mixture having a lower reducing content.
• - With a higher feed rate v2 than v4 and a composition of the secondary gas or secondary gas mixture that has a lower oxidizing content.
• - With a higher feed rate v2 than v4 and a composition of the secondary gas or secondary gas mixture that has a lower reducing content.
• - With a larger plasma torch distance d2 than d4 and a lower pressure p12 of the plasma gas PG than p14.
• - With a larger plasma torch distance d2 than d4 and a lower volume and/or mass flow m12 of the plasma gas than m14.
• - With a larger plasma torch distance d2 than d4 and a lower pressure p22 of the secondary gas SG than p24.
• - With a larger plasma torch distance d2 than d4 and a lower volume and/or mass flow m12 of the secondary gas than m24.
• - With a larger plasma torch distance d2 than d4 and a composition of the plasma gas or plasma gas mixture which has a lower reducing content during phase 2.
• - With a larger plasma torch distance d2 than d4 of the plasma gas or plasma gas mixture which has a lower reducing content during phase 2.
• - With a larger plasma torch distance d2 than d4 and a composition of the secondary gas or secondary gas mixture which has a lower oxidising content during phase 2.
• - With a larger plasma torch distance d2 than d4 and a composition of the secondary gas or secondary gas mixture which has a lower reducing content during phase 2.

However, other combinations are also possible.

The oxidizing portion is the proportion in volume percent of oxidizing gas, e.g. oxygen or carbon dioxide, in the plasma gas or secondary gas. The reducing portion is the proportion in volume percent of reducing gas, e.g. hydrogen or methane, in the plasma gas or secondary gas.

Advantageous parameters are given below as examples. The following table shows the relationship between the parameters and the corresponding reference symbols. parameter Unit Phase 1 Phase 2 Phase 3 Phase 4 plasma torch distance d mm d1 d2 d3 d4 feed rate v mm/min v1 v2 v3 v4 Electricity A I1 I2 I3 I4 time t ms t1 t2 t3 cutting time (1) plasma gas pressure p1 bear p11 p12 p13 p14 secondary gas pressure p2 bear p21 p22 p23 p24
(1) This time depends on the size of the component to be cut out.

Example 1

Material: low-alloy steel (structural steel) S235 Material thickness: 40 mm Cutting speed v4: 500 mm/min Cutting current I4: 150 A plasma gas: oxygen Secondary gas: Air Shape and size (length × width) of the contour430 with which the plasma cutting torch 2 is moved for flushing in phase 2: Oval, 35 mm × 6 mm, 2x circle Shape and size (max. length 419 × width 420) of the resulting washout 410: Oval, approx. 43 mm × 14 mm parameter Unit Phase 1 Phase 2 Phase 3 Phase 4 plasma torch distance d mm 6 20 12 5 feed rate v mm/min 0 2,800 0 300 current I A 0 ... 150 150 150 150 time t ms 500 3,500 5,000 cutting time plasma gas pressure p1 bear 8.0 8.0 8.0 8.0 secondary gas pressure p2 bear 4.0 4.0 4.0 4.0

Example 2

Material: low-alloy steel (structural steel) S235 Material thickness: 60 mm Cutting speed v4: 300 mm/min Cutting current I4: 300 A Plasma gas: oxygen Secondary gas: Air Shape and size (length × width) of the contour 430 with which the plasma cutting torch 2 is moved for flushing in phase 2: Oval, 48 mm × 8 mm, 2x circle Shape and size (max. length 419 × width 420) of the resulting washout 410: Oval, approx. 57 mm × 17 mm parameter Unit Phase 1 Phase 2 Phase 3 Phase 4 plasma torch distance d mm 9 25 25 7 feed rate v mm/min 0 2,800 0 300 current I A 0...300 300 300 300 time t ms 500 4,500 10,000 cutting time plasma gas pressure p1 bear 6.5 6.5 6.5 6.5 secondary gas pressure p2 bear 3.5 3.5 3.5 3.5

Example 3

Material: low-alloy steel (structural steel) S235 Material thickness: 70 mm Cutting speed v4: 170 mm/min Cutting current I4: 300 A Plasma gas: oxygen Secondary gas: Air Shape and size (length × width) of the contour 430 with which the plasma cutting torch 2 is moved for flushing in phase 2: Oval, 48 mm × 8 mm, 2x circle Shape and size (max. length 419 × width 420) of the resulting washout 410: Oval, approx. 57 mm × 17 mm parameter Unit Phase 1 Phase 2 Phase 3 Phase 4 plasma torch distance d mm 9 30 20 9 feed rate v mm/min 0 2,800 0 170 current I A 0...300 300 300 300 time t ms 500 4,800 5,000 cutting time plasma gas pressure p1 bear 6.5 6.5 6.5 6.5 secondary gas pressure p2 bear 2.5 2.5 2.5 2.5

Example 4

Material: High-alloy steel (stainless steel) 1.4301 Material thickness: 40 mm Cutting speed v4: 250 mm/min Cutting current I4: 150 A Plasma gas: argon-hydrogen mixture Secondary gas: Nitrogen Shape and size (length × width) of the contour 430 with which the plasma cutting torch 2 is moved for flushing in phase 2: Oval, 40 mm × 6 mm, 2x circle Shape and size (max. length 419 × width 420) of the resulting washout 410: Oval, approx. 45 mm × 11 mm parameter Unit Phase 1 Phase 2 Phase 3 Phase 4 plasma torch distance d mm 8 20 12 5 feed rate v mm/min 0 2,800 0 250 current I A 0 ... 150 150 150 150 time t ms 500 3,000 5,000 cutting time plasma gas pressure p1 bear 6.5 6.5 6.5 6.5 secondary gas pressure p2 bear 2.0 2.0 2.0 2.0

Example 5

Material: High-alloy steel (stainless steel) 1.4301 Material thickness: 50 mm Cutting current I4: 150 A Cutting speed v4: 170mm/min Plasma gas: argon-hydrogen mixture Secondary gas: Nitrogen Shape and size (length × width) of the contour 430 with which the plasma cutting torch 2 is moved for flushing in phase 2: Oval, 60 mm × 6 mm, 3x circle Shape and size (max. length 419 × width 420) of the resulting washout 410: Oval, approx. 65 mm × 11 mm parameter Unit Phase 1 Phase 2 Phase 3 Phase 4 plasma torch distance d mm 8 20 12 5 feed rate v mm/min 0 2,800 0 170 current I A 0 ... 150 150 150 150 time t ms 500 8,500 8,500 cutting time plasma gas pressure p1 bear 6.5 6.5 6.5 6.5 secondary gas pressure p2 bear 2.0 2.0 2.0 2.0

Example 6

Material: High-alloy steel (stainless steel) 1.4301 Material thickness: 60 mm Cutting current I4: 300 A Cutting speed v4: 410 mm/min Plasma gas: argon-hydrogen mixture Secondary gas: Nitrogen Shape and size (length × width) of the contour 430 with which the plasma cutting torch 2 is moved for flushing in phase 2: Oval, 40 mm × 6 mm, 1x circle Shape and size (max. length 419 × width 420) of the resulting washout 410: Oval, approx. 50 mm × 15 mm parameter Unit Phase 1 Phase 2 Phase 3 Phase 4 plasma torch distance d mm 9 30 20 7 feed rate v mm/min 0 2,800 0 410 current I A 0...300 300 300 300 time t ms 500 2,000 5,000 cutting time plasma gas pressure p1 bear 6.5 6.5 6.5 6.5 secondary gas pressure p2 bear 5.0 5.0 5.0 5.0

Example 7

Material: aluminum AIMg3 Material thickness: 50 mm Cutting current I4: 150 A Cutting speed v4: 300 mm/min Plasma gas: argon-hydrogen mixture Secondary gas: Nitrogen Shape and size (length × width) of the contour 430 with which the plasma cutting torch 2 is moved for flushing in phase 2: Oval, 60 mm × 6 mm, 1x circle Shape and size (max. length 419 × width 420) of the resulting washout 410: Oval, approx. 62 mm × 8 mm parameter Unit Phase 1 Phase 2 Phase 3 Phase 4 plasma torch distance d mm 8 20 15 3 feed rate v mm/min 0 2,800 0 300 current I A 0 ... 150 150 150 150 time t ms 500 2,900 5,000 cutting time plasma gas pressure p1 bear 8.0 8.0 8.0 8.0 secondary gas pressure p2 bear 7.5 7.5 7.5 7.5

Example 8

Material: aluminum AIMg3 Material thickness: 60 mm Cutting current I4: 300 A Cutting speed v4: 700 mm/min Plasma gas: argon-hydrogen mixture Secondary gas: Nitrogen Shape and size (length × width) of the contour 430 with which the plasma cutting torch 2 is moved for flushing in phase 2: Oval, 60 mm × 8 mm, 1x circle Shape and size (length 419 × width 420) of the resulting washout 410: Oval, approx. 66 mm × 14 mm parameter Unit Phase 1 Phase 2 Phase 3 Phase 4 plasma torch distance d mm 9 30 20 5 feed rate v mm/min 0 2,800 0 700 current I A 0...300 300 300 300 time t ms 500 2,800 1,000 cutting time plasma gas pressure p1 bear 8.0 8.0 8.0 8.0 secondary gas pressure p2 bear 7.5 7.5 7.5 7.5

list of reference symbols

1

plasma cutting system

1.1

power source

1.2

pilot resistor

1.3

high-voltage igniter

1.4

switching contact

2

plasma cutting torch

2.1

electrode

2.1.1

electrode holder

2.1.2

emissions use

2.2

nozzle

2.2.1

nozzle opening

2.3

gas supply plasma gas

2.4

secondary gas cap

2.5

secondary gas supply secondary gas

2.6

gas supply for plasma gas

2.7

plasma torch body

2.8

plasma torch tip

2.9

gas supply for secondary gas

3

plasma jet

3.1

pilot arc

4

workpiece

4.1

workpiece surface

4.3

workpiece thickness

4.5

underside of the workpiece

5

supply lines

5.1

cutting current line

5.2

pilot current line

5.3

Workpiece - Plasma Cutting System Management

5.4

plasma gas line

5.5

secondary gas line 1

6

gas supply

10

feed direction of the plasma cutting torch

410

flushing

411

Distance between contour 430 and edge 413 of flushing 410

412

Distance between the longitudinal edges of the contour 430

413

edge of the flush

415

Contour of the flushing on the workpiece surface

417

depth of the washout

418

molten, splashing material from the workpiece

419

maximum length of the flushing 410 along the workpiece surface

420

Width of the flushing along the workpiece surface

421

slope of the flushing towards the edge

423

molten material spraying out from the underside of the workpiece

430

Contour with which the plasma torch is guided relative to the workpiece surface

450

kerf

452

kerf width

d

Plasma torch distance, distance plasma torch tip - workpiece surface

d1

Plasma torch distance, distance plasma torch tip - workpiece surface in phase 1

d2

Plasma torch distance, distance plasma torch tip - workpiece surface in phase 2

d3

Plasma torch distance in phase 3

d4

Plasma torch distance, distance plasma torch tip - workpiece surface during cutting in phase 4

d5

Plasma torch distance in phase 5

I1

electricity in phase 1

I2

electricity in phase 2

I3

electricity in phase 3

I4

current in phase 4, (cutting current)

m

mass flow

m1

mass flow of plasma gas

m11

Mass flow of plasma gas in phase 1

m12

Mass flow of plasma gas in phase 2

m13

Mass flow of plasma gas in phase 3

m14

Mass flow of plasma gas in phase 4

m2

mass flow of secondary gas

m21

mass flow of secondary gas in phase 1

m22

mass flow of secondary gas in phase 2

m23

mass flow of secondary gas in phase 3

m24

mass flow of secondary gas in phase 4

PG

plasma gas

p1

plasma gas pressure

p11

plasma gas pressure in phase 1

p12

plasma gas pressure in phase 2

p13

plasma gas pressure in phase 3

p14

plasma gas pressure in phase 4

p2

secondary gas pressure

p21

secondary gas pressure in phase 1

p22

secondary gas pressure in phase 2

p23

secondary gas pressure in phase 3

p24

secondary gas pressure in phase 4

SG

secondary gas

v

feed rate

v1

feed rate in phase 1

v2

feed rate in phase 2

v3

feed rate in phase 3

v4

feed rate during cutting (in phase 4)

v5

feed rate in phase 5

Claims (26)

Method for plasma cutting of workpieces, in which at least one plasma cutting torch (2) with at least one plasma torch body (2.7), an electrode (2.1) and a nozzle (2.2), through the nozzle opening (2.2.1) of which at least one plasma gas (PG) or plasma gas mixture flows and which constricts the plasma jet (3), is used, the method comprising: - positioning the plasma cutting torch (2) in relation to a workpiece (4), - igniting a pilot arc between the electrode (2.1) and the nozzle (2.2) of the plasma cutting torch (2) and generating a transferred plasma arc between the electrode (2.1) of the plasma cutting torch (2) and the workpiece (4), - piercing the plasma jet (3) into the workpiece (4) until the plasma jet (3) has passed through the workpiece (4), and - then cutting the workpiece (4) by guiding the plasma cutting torch (2) at a feed rate v4 in a plasma torch distance d4 from the workpiece (4) at a cutting current I4, so that a cutting gap (450) with a cutting gap width (452) is created, wherein before the plasma jet (3) penetrates into and through the workpiece (4), a flushing (410) is formed by exposing the workpiece (4) from the workpiece surface (4.1) to the plasma jet (3) at least for a time period t2 in such a way that material of the workpiece (4) is removed from the workpiece surface (4.1) and the flushing (410) is created, characterized in that the smallest distance (411) between a contour (430) described by the plasma cutting torch (2) and an edge (413) of the resulting flushing (410) is smaller than the smallest distance (412) of the contour (430) described by the plasma cutting torch (2) procedure according to claim 1 , wherein the method comprises at least the following phases: phase 1 with a time duration t1, which comprises positioning the plasma cutting torch (2) and igniting the pilot arc and generating the transferred plasma arc, phase 2 with a time duration t2, which comprises forming the flushing (410), phase 3 with a time duration t3, which comprises piercing into and through the workpiece (4), and phase 4 with a time duration t4, which comprises cutting. procedure according to claim 1 or 2 , wherein during the time period t2 - the plasma cutting torch (2) is guided at a feed rate v2 which differs from the feed rate v4 of the plasma cutting torch (2) during cutting, and/or - the plasma cutting torch (2) is operated with a current I2 which differs from the cutting current I4 during cutting, and/or - the plasma cutting torch (2) is positioned at a plasma torch distance d2 which differs from the plasma torch distance d4 during cutting and/or - the pressure p12 and/or the volume flow and/or the mass flow m12 of the plasma gas PG or of the plasma gas mixture differs from the pressure p14 and/or the volume flow and/or the mass flow m14 of the plasma gas PG during cutting and/or - the composition of the plasma gas and/or of the plasma gas mixture is different from that during cutting. procedure according to claim 3 , wherein during the time period t2: - the feed rate v2 of the plasma cutting torch (2) is greater than the feed rate v4 of the plasma cutting torch (2) during cutting and/or - the current I2 is smaller than the cutting current I4 during cutting and/or - the plasma torch distance d2 is greater than the plasma torch distance d4 during cutting and/or - the pressure p12 and/or the volume flow and/or the mass flow m12 of the plasma gas PG or the plasma gas mixture is/are lower than the pressure p14 and/or the volume flow m14 during cutting and/or - the composition of the plasma gas and/or the plasma gas mixture has a lower proportion of oxidizing and/or reducing gas than during cutting. procedure according to claim 4 , wherein during the time period t2 or at least part of the time period t2: - the feed rate v2 of the plasma cutting torch (2) is at least one and a half times, better at least twice, even better at least four times, best at least eight times the feed rate v4 during cutting and/or - the current I2 is at most 85%, better at most 70%, best at most 50% of the cutting current I4 during cutting and/or - the plasma torch distance d2 is at least 1.5 times, better at least twice, best at least 2.5 times the plasma torch distance d4 during cutting and/or - the pressure p12 and/or volume flow and/or mass flow m12 of the plasma gas PG or the plasma gas mixture is at most 90%, better at most 80%, best at most 70% of the pressure p14 and/or the volume flow and/or the mass flow m14 during cutting and/or - the composition of the plasma gas and/or the plasma gas mixture has a proportion of oxidising and/or reducing gas that is at least 15 vol.%, better by at least 30 vol.%, most preferably by at least 50 vol.% lower than the composition of the plasma gas and/or the plasma gas mixture during cutting. Method according to one of the preceding claims, wherein the plasma cutting torch (2) additionally has a secondary gas cap (2.4) which at least partially encloses the nozzle (2.2) and a secondary gas (SG) flows between the secondary gas cap (2.4) and the nozzle (2.2). procedure according to claim 6 , wherein during the time period t2 - the pressure p22 and/or volume flow and/or mass flow m22 of the secondary gas SG or of the secondary gas mixture is/are lower than the pressure p24 and/or the volume flow and/or mass flow m24 of the secondary gas PG or of the secondary gas mixture during cutting and/or - the secondary gas SG and/or the secondary gas mixture has a different composition than the secondary gas SG and/or the secondary gas mixture during cutting. procedure according to claim 7 , whereby during the time period t2 - the pressure p22 and/or volume flow and/or mass flow m22 of the secondary gas SG or of the secondary gas mixture is at most 90%, better at most 80%, most preferably at most 70% of the pressure p24 and/or the volume flow and/or mass flow m24 of the secondary gas and/or the secondary gas mixture during cutting and/or - the composition of the secondary gas and/or the secondary gas mixture has a proportion of oxidizing and/or reducing gas that is at least 15 vol.%, better by at least 30 vol.%, most preferably by at least 50 vol.% lower than the composition of the secondary gas and/or the secondary gas mixture during cutting. Method according to one of the preceding claims, wherein during the time period t2 the feed rate v2 of the plasma cutting torch (2) and/or the current I2 of the plasma cutting torch (2) and/or the plasma torch distance d2 of the plasma cutting torch (2) and/or the pressure p22 and/or the volume flow and/or the mass flow m22 of the plasma gas PG or of the plasma gas mixture and/or the composition of the plasma gas and/or of the plasma gas mixture are selected such that at least the largest part of the melted, high-spraying material (418) of the workpiece (4) does not touch the plasma cutting torch (2) and/or the plasma torch tip (2.8) and/or the nozzle (2.2) and/or the secondary gas cap (2.4). Method according to one of the preceding claims, wherein the flushing (410) on the workpiece surface (4.1) has a length (419) such that the molten material (418) spraying up until piercing through the workpiece (4) can spray away through the flushing 410 in the opposite direction to the cutting direction (10) such that it does not touch the plasma cutting torch (2), the plasma torch tip (2.8), the nozzle (2.2) and/or the secondary gas cap (2.4) or does not touch it for the most part. Procedure according to the claim 9 and 10 , whereby the largest part means at least 90%, better at least 95%, even better 99% and most preferably 100% of the molten high-spray material (418). Method according to one of the preceding claims, wherein the flushing (410) has a maximum depth (417) of at least 15% of the workpiece thickness (4.3) and/or at least 10 mm, measured perpendicularly from the workpiece surface (4.1). Method according to one of the preceding claims, wherein the flushing (410) on the workpiece surface (4.1) has a length (419) of at least 40% of the workpiece thickness (4.3) and/or at least 20 mm. Method according to one of the preceding claims, wherein the smallest distance (412) of the contour (430) described by the plasma cutting torch (2) is smaller than or equal to twice the smallest distance (411) between the contour (430) described by the plasma cutting torch (2) and the edge (413) of the resulting flushing (410). Method according to one of the Claims 2 until 14 , wherein the plasma cutting torch (2) is positioned after the formation of the flushing (410) and before cutting for the time period t3 such that the plasma jet (3) strikes the edge (413) and/or a slope (421) of the flushing (410) at the start of piercing into and through the workpiece. Method according to one of the Claims 2 until 15 , wherein after the formation of the flushing (410) and before cutting, for the time period t3, a feed rate v3 for piercing into and through the workpiece (4) is smaller than the feed rate v2 during the formation of the flushing (410) or 0. procedure according to claim 16 , whereby the feed rate v3 is at most half, preferably at most a quarter, even better at most an eighth of the feed rate v2. Method according to one of the Claims 2 until 17 , wherein after the formation of the flushing (410) and before cutting, for the time period t3, the feed rate v3 for piercing into and through the workpiece (4) is smaller than the feed rate v4 during cutting or 0. Method according to one of the Claims 15 until 17 , whereby a plasma torch distance d3 for piercing during the time period t3 in and through the workpiece is greater than the plasma torch distance d4 during cutting. Method according to one of the Claims 14 until 17 , wherein the plasma torch distance d3 for piercing into and through the workpiece (4) is less than or equal to the plasma torch distance d2 when forming the protuberance (410). Method according to one of the Claims 2 until 20 , wherein during the time period t1 the plasma torch distance d1 is smaller than the plasma torch distance d2 during the time period t2 and/or smaller than the plasma torch distance d3 during the time period t3 and/or greater than the plasma torch distance d4 during cutting. Method according to one of the Claims 2 until 21 , wherein during the time period t1 the feed speed v1 of the plasma cutting torch (2) is smaller than the feed speed v2 during the time period t2 and/or smaller than the feed speed v4 during cutting. Method according to one of the Claims 2 until 22 , wherein between phase 3 and phase 4 there is at least one further phase in which the plasma torch distance d is less than or equal to the plasma torch distance d3 and greater than the plasma torch distance d4 during cutting. Method according to one of the Claims 2 until 23 , wherein between phase 3 and phase 4 there is at least one further phase in which the feed speed v of the plasma cutting torch (2) is greater than the feed speed v3 and less than the feed speed v4 during cutting. Method according to one of the Claims 2 until 24 , with further phases between phases 1, 2, 3 and 4. procedure according to claim 25 characterized in that between phases 1, 2, 3 and 4 the feed rate v and/or the current I and/or the plasma torch distance d and/or the pressure p1 and/or the volume flow and/or the mass flow m1 of the plasma gas PG or the plasma gas mixture and/or the composition of the plasma gas and/or the plasma gas mixture and/or the pressure p2 and/or the volume flow and/or the mass flow m2 of the secondary gas SG and/or the composition of the secondary gas SG and/or the secondary gas mixture change/change.

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