Patent Application
20220362876
The invention relates to methods and arrangements for plasma cutting 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.
Various gases are used as the plasma gas—for example, 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 parameters of the plasma jet can be greatly influenced by the design of the nozzle and electrode. These parameters of the plasma jet are, for example, 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 2×106 W/cm2 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 method for cutting electrically conductive materials. Different gases and gas mixtures are used according to 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 flows between them and exits through the nozzle bore. Most commonly, the plasma gas is guided through a gas conduit, which is attached between the electrode and the nozzle, and which can be made to rotate. 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 conduit which is arranged between the nozzle or nozzle cap and the nozzle protection cap.
The nozzle protection cap protects the nozzle and the nozzle cap from the heat or from the ejected molten metal of the workpiece, in particular when the plasma jet pierces the material of the workpiece being 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 as per DIN EN 10027-1, air, oxygen or nitrogen, or a mixture thereof, is usually used as plasma gases. Air, oxygen or nitrogen, or a mixture thereof, is also mostly used as the secondary gas, wherein the composition and volume flows of the plasma gas and the secondary gas are most often different, but can also be the same.
For plasma cutting of high-alloy steels and stainless steels, for example, 1.4301 (X5CrNi10-10) or 1.4541 (X6CrNiTi18-10), the plasma gases used are usually nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen-nitrogen mixture. In principle, air can also be used as a plasma gas, but the oxygen content in the air leads to oxidation of the cut faces and thus to a deterioration in the quality of the cut. Nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen-nitrogen mixture is also commonly used as the secondary gas, wherein the composition and volume flows of the plasma gas and the secondary gas are most often different, but also can be the same.
In plasma cutting, it is necessary to cut and/or cut out a wide variety of contours—for example, small inner contours, large inner contours and outer contours—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, for example, electrical cutting current, plasma torch distance (distance between the plasma torch tip and the 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 workpieces with which the most varied of contours, for example small inner contours, large inner contours and outer contours, can be cut and/or cut out in high quality.
According to a first aspect, this object is achieved by a method for plasma cutting workpieces, in which a plasma cutting torch which has at least one plasma torch body, an electrode, and a nozzle is used for cutting a part from a, in particular, plate-shaped workpiece which has a material thickness, wherein the part of the plasma cutting torch from which a plasma jet emerges from the nozzle forms the plasma torch tip, and in which the plasma cutting torch is guided by means of a guidance system along a contour at a cutting speed v relative to the workpiece surface in the feed direction in such a manner that at least a 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, is/are cut out, and in such a manner that at least one outer contour of the part and/or a large inner contour of the part, the circumference of which is greater than 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, wherein the plasma torch tip is at a cutting distance from the workpiece surface during cutting, wherein at least a small, or a major, portion of the circumference of the small inner contour being cut from the part is cut at a different cutting distance between the plasma torch tip and the workpiece surface than at least a small, or a major, portion of the circumference of the outer contour of the part being cut, and/or at least one large, or a major portion, of the circumference of the large inner contour of the part being cut.
According to a second aspect, this object is achieved by a method for plasma cutting workpieces, in which a plasma cutting torch which has at least one plasma torch body, an electrode, a nozzle and a secondary gas cap is used, 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 guidance system along a contour at a cutting speed (v) relative to the workpiece surface in the feed direction in such a manner that at least a 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 in such a manner that at least one outer contour and/or a large inner contour of the part, the circumference of which is greater than six times the material thickness of the workpiece, or the diameter of which is greater than twice the material thickness of the workpiece, and the plasma torch tip is at a cutting distance ds from the workpiece surface during cutting, wherein at least a small portion, or the major portion, of the circumference of the small inner contour being cut from the part is cut with a different cutting distance ds between the plasma torch tip and the workpiece surface than at least a small, or a major, portion of the circumference of the outer contour being cut from the part, and/or at least a large portion, or a major portion, of the circumference of the large inner contour being cut from the part.
According to a third aspect, this object is achieved by a method for plasma cutting workpieces, in which a plasma cutting torch which has at least one plasma torch body, an electrode, a nozzle and a secondary gas cap is used, 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 guidance 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, wherein 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 hitting the workpiece surface has reached a position on the contour being cut whose distance from a cut edge yet to be traversed is in a range of a maximum of 50%, more preferably a maximum of 25%, of a material thickness of the workpiece, or whose distance from the cut edge yet to be traversed is in a range of a maximum of 15 mm, more preferably a maximum of 7 mm, or in which the plasma jet hitting the workpiece surface contacts the cut edge.
According to a fourth aspect, this object is achieved by a method for plasma cutting workpieces, in which a plasma cutting torch which has at least one plasma torch body, an electrode, a nozzle and a secondary gas cap is used, 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 guidance 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, wherein 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 plasma jet hitting the workpiece surface has reached a position on the contour being cut out
whose distance 502 from the already-traversed cut edge 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 traversed is in the range of a maximum of 7 mm,
or
in which the plasma jet hitting the workpiece surface has passed the cut edge.
In the method according to the first and the second aspect, it can be provided that the cutting distance ds during the cutting of the small inner contour of the part is less than the cutting distance ds during the cutting of 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 during the cutting of the small inner contour is between 40% and 80% of the cutting distance ds during the cutting of 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 during the cutting of the small inner contour of the part is lower than the cutting speed v during the cutting of 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 during the cutting of the small inner contours of the part is between 20% and 80%, preferably between 40% and 80%, of the cutting speed v during the cutting of 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 are cut, and then the outer contour/outer contours of the part are cut.
In the method according to the third and fourth aspect, it can be provided that the cut edge has been created by cutting the same contour.
Air, oxygen, nitrogen, argon, hydrogen, methane or helium, or a mixture thereof, is advantageously used as the secondary gas.
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, 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 implemented 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 in such a manner 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 implemented 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 thereof.
In particular, it can be provided that the composition of the secondary gas is changed in such a way 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, at which the plasma cutting torch is guided relative to the workpiece surface, is changed, at the earliest, when the plasma jet hitting the workpiece surface has reached a position on the contour being cut whose distance from the cut edge yet to be traversed is in the range of a maximum of 50%, more preferably a maximum of 25%, of the material thickness of the workpiece, or whose distance from the cut edge yet to be traversed is in a range of a maximum of 15 mm, more preferably a maximum of 7 mm, or at which the plasma jet hitting the workpiece surface contacts the cut edge.
Advantageously, the cutting speed v, at which the plasma cutting torch is guided relative to the workpiece surface, is changed, at the latest, when the plasma jet hitting the workpiece surface has reached a position on the contour being cut whose distance from the cut edge that has already been traversed is in the range of a maximum of 25% of the workpiece thickness, or whose distance from the cut edge that has already been traversed is in the range of 7 mm, or at which the plasma jet hitting the workpiece surface has passed the cut 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%. Based on investigations, the present invention is based 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 cut qualities are obtained. In particular, the cut quality of the small inner contours deteriorates—in particular, the perpendicularity and inclination tolerance according to DIN ISO 9013—that is, the cut faces are no longer formed essentially 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 inclination 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 total cutting time. The cutting speed of the small contours can be between 20% and 80%, more preferably 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 for 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 cut quality of the inner contours, and the high productivity, cut quality and process reliability for the outer contours and large inner contours on a workpiece are achieved. 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 possible simply 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 purpose, only the time for transmission of the electronic signal, for example, <5 ms, is required; a wait time as in, for example, the case of changing wear parts or changing gas, of >0.1 to 5 seconds, is not necessary. The associated gas losses and gas consumption are also reduced.
Different data sets, for example, for cutting one and the same material, that is, for the same material type and thickness for different contours (small inner contours, large inner contours, outer contours) can be stored in the controller of the guidance system or the plasma cutting system, which data sets are then assigned to the given 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, in at least one particular embodiment, cutting even-smaller inner contours in better quality is made possible. These are contours whose circumferential length is equal to or less than three times the material thickness (or the diameter of which is less than the material thickness itself). For this, the cutting speed is reduced again in order to achieve a high cut quality in these contours as well. 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, and also an outer contour. This is in particular the case 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 kerf. At this point, 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 face of the inner contour.
When the kerf is skipped, a disruptive projection usually remains. When the plasma jet is applied to the already existing cut face, “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 during 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 the relevant issue is 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 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 several embodiments of the present invention are described in detail with reference to the schematic drawings, wherein:
Conventional arrangements for plasma cutting are shown schematically in
The plasma cutting torch 2 substantially 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 consists substantially 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 (for example, copper, silver, alloys thereof), and a high-melting emission insert 2.1.2 with a low work function for electrons (hafnium, zirconium, tungsten). The nozzle 2.2 is made mostly of copper, and constricts the plasma jet 3. A gas conduit 2.6 for the plasma gas PG, which adds a rotary movement to the plasma gas, 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 portions ds and dz mentioned below.
In
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 (for example, 10 A-30 A) and thus low power, for example, by means of an electrical high 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 prepares the path between the plasma cutting torch 2 and the workpiece 4 for the cutting arc by partial ionization. If the pilot arc contacts 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 a generally greater electrical current (for example, 20 A to 900 A), and therefore also with greater power. The switch contact 1.4 is opened and the nozzle 2.2 is connected and isolated by the power source 1.1. This mode of operation is also referred to as the direct mode of operation. The workpiece 4 is exposed to the thermal, kinetic and electrical action of the plasma jet 3. This makes the process very effective, and it is possible to cut metals up to great thicknesses, for example 180 mm at 600 A cutting current, at a cutting speed of 0.2 m/min.
For this purpose, the plasma cutting torch 2 is moved with a guidance system relative to a workpiece 4 or its surface 4.1. This can, for example, be a robot or a CNC-controlled guide machine. The controller of the guidance system (not shown) communicates with the arrangement according to
In the simplest case, it starts and ends the operation of the plasma cutting torch 2. According to the current state of the art, however, a variety of signals and information—for example, about operating conditions—and data can be exchanged.
With plasma cutting, high cutting qualities can be achieved. The criteria for measuring this quality are, for example, tight perpendicularity tolerances and inclination tolerances 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 faces and burr-free edges 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 present, the secondary gas cap 2.4, and in particular its bore, lie on a common axis, in order to obtain the same or at least only slightly different perpendicularity and inclination tolerances at the different cut 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°.
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 this 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, and the circumference U430 is, for example, approx. 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 plurality of parts 400, and also a very 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
As shown in
The small inner contours 430, 450 and 470 are cut in this case, 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, for 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 in this case at 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 of the outer contour 490 is opposite in this example, as can also be seen from
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
Attempts are made to counteract this effect by reducing the feed rate v. However, this leads to washouts 457 in the cut edge or cut face that is already present, particularly in the direction of the lower surface of the workpiece 4, as shown in
The same problem also arises during the cutting of the outer contour 490 when the cut edge 495 formed by the insertion tail 492 is traversed.
As already described under
It is also possible to use nitrogen as the secondary gas. In this case as well, oxygen is added to the secondary gas, and thus the proportion of oxygen is increased in the conditions noted above.
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, for example, 1.4301 (X5CrNi10-10) or 1.4541 (X6CrNiTi18-10), the plasma gas used can be nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen-nitrogen mixture. The secondary gas used is also most commonly nitrogen, argon, an argon-hydrogen mixture, a nitrogen-hydrogen mixture or an argon-hydrogen-nitrogen mixture.
The inner contour 410 in this example is a large inner contour. The inner contours 430, 450 and 470 are small inner contours, for example. Inner contours are small inner contours if the circumference of the contour is equal to or less than six times the thickness 4.3 of the workpiece 4. In this case this 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 of U430 is approximately 47 mm, for example. The inner contour 450 is, for example, square 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 plurality of parts 400, and also a very 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
As shown in
The small inner contours 430, 450 and 470 are cut in this case, 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 in this case at 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
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
An attempt is made to counteract this effect by reducing the feed speed v, but this leads to washouts 457 in the already existing cut edge or cut face, particularly in the direction of the lower surface of the workpiece 4, as shown in
As already described under
In
The point in time of the change in the secondary gas composition is stored in the controller of the guidance system as a function of the profile of the contour being cut, and is emitted as a signal to the plasma cutting system, which then switches the valves.
The different compositions of the secondary gases for the cutting and for the end of the cut when the kerf formed by the insertion tail is traversed are stored in a database.
In some cases it has been shown that the described effects of the remaining protrusion 546 or the washout 457 are reduced if the cutting distance ds of the plasma torch tip 2.8 from the workpiece surface 4.1 in the vicinity of the cut edge 415 or 435 or 455 or 475 or 495 is decreased. By reducing the distance by, for example, 1 mm, the protrusion was reduced.
The point in time when the cutting distance ds is changed is stored in the controller of the guidance system as a function of the profile of the contour being cut, and is emitted to the distance control of the guide machine and/or the plasma cutting torch.
In this case as well, the values for the cutting distance ds for the cutting and for the end of the cut when the kerf formed by the insertion tail is traversed 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 002 825.2 | Apr 2019 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2020/100104 | 2/14/2020 | WO |
