Method and apparatus for separating and cutting a workpiece part from a plate-shaped workpiece using a thermal cutting process

Abstract

The invention relates to a method for cutting a workpiece part from a plate-shaped workpiece by means of a thermal cutting process, wherein the workpiece part has a length and a width, the length being greater than the width, comprising at least the following process steps: a. In a first process step, an expansion joint is cut out of the plate-shaped workpiece, which has a joint width and a joint length, wherein the joint length is greater than or equal to the width of the workpiece part and the joint width is greater than a cutting gap width of the thermal separation process; b. In a second process step following the first process step, the workpiece part is cut out of the plate-shaped workpiece in such a way that a short edge defining the width of the workpiece part is arranged along the joint length of the expansion joint.

Description

[0001] The invention relates to a method and a device for cutting a workpiece part from a plate-shaped workpiece by means of a thermal cutting process. The invention further relates to a device for cutting a workpiece part from a plate-shaped workpiece by means of a thermal cutting process, in particular a laser cutting device, wherein the workpiece part has a length and a width, the length being greater than the width.

[0002] Thermal cutting processes are used, for example, to cut workpiece parts from flat workpieces, such as sheets, and employ intense heat to separate the workpiece material. This involves introducing a significant amount of heat locally into the material, causing it to melt, burn, or vaporize at the desired location.

[0003] Generally, at least three different thermal cutting processes are known: laser cutting, plasma cutting, and oxyfuel cutting. Laser cutting uses a high-energy laser beam, which can be specifically adjusted to the desired cut using optical parameters such as the focus position. The focused laser beam enables a high energy density to melt, burn, or vaporize the material. Furthermore, the resulting melt can be influenced by the addition of process gases. Common process gases for laser cutting include oxygen, nitrogen, compressed air, and argon. Another adjustable parameter is the laser power. Laser cutting is particularly advantageous for thin and medium-thickness workpieces made of materials such as metals or plastics. It also allows for very precise cuts and fine edges.In plasma cutting, the workpiece material is cut by ionized gas, i.e., a plasma. An electric arc between the cutting nozzle and the material to be cut generates the plasma, which melts and severs the material. Plasma cutting is particularly suitable for thick workpieces, such as metals. Compared to laser cutting, plasma cutting is more cost-effective and allows for faster cutting speeds. In oxyfuel cutting, a combination of oxygen and a fuel gas is used to cut the material. The fuel gas is burned with the addition of oxygen, generating a high temperature. This high temperature melts the material. This cutting method is preferred for processing metals and can cut materials of varying thicknesses.

[0004] A problem with thermal cutting processes is the distortion of the workpiece caused by the significant heat input. This localized heat input leads to a local area becoming considerably hotter than surrounding areas or the underside of the workpiece segment being cut. Particularly with elongated workpiece segments, this heat can cause significant thermal expansion and, due to the surrounding cooler surfaces, warping. The expanding workpiece segment then encounters the supposedly stronger, cooler surfaces of the sheet metal and buckles in one direction. Aside from the fact that warped workpiece segments are undesirable, the warping can also impair the thermal cutting process. For example, if warping occurs during laser cutting, the distance between the cutting nozzle and the workpiece is typically increased automatically to prevent damage to the nozzle.This negatively impacts the cutting process, as the device is no longer correctly adjusted. A controlled and desired cutting process is then no longer possible.

[0005] Against this background, the object of the present invention is to provide a method for the efficient and robust cutting of elongated workpiece parts.

[0006] This problem is solved by a method for cutting a workpiece part from a plate-shaped workpiece using a thermal cutting process, wherein the workpiece part has a length and a width, the length being greater than the width, comprising at least the following process steps: a. In a first process step, an expansion joint is cut out of the plate-shaped workpiece, which has a joint width and a joint length, wherein the joint length is greater than or equal to the width of the workpiece part and the joint width is greater than a cutting gap width of the thermal separation process; b. In a second process step following the first process step, the workpiece part is cut out of the plate-shaped workpiece in such a way that a short edge defining the width of the workpiece part is arranged along the joint length of the expansion joint.

[0007] The inventive method produces an elongated workpiece section, i.e., a workpiece whose length is greater than its width. The expansion joint introduced into the workpiece in the first process step provides a space within the workpiece into which the workpiece section can expand during the cutting process, i.e., in the second process step, thus preventing undesirable warping of the workpiece section during cutting. According to the invention, the width of the expansion joint is greater than the width of the cutting kerf introduced by the thermal process, so that more than a single cut along the short edge of the workpiece section is required to form the expansion joint.Since the expansion joint is located on the short edge of the workpiece, the longitudinal expansion of the workpiece during cutting can be completely accommodated by the expansion joint. Even when larger amounts of heat are applied, the workpiece can expand into the expansion joint, preventing warping. Consequently, warping of the workpiece is avoided, and the thermal cutting process is not affected by such warping. Therefore, a more efficient and robust method for cutting an elongated workpiece from a sheet-like workpiece can be provided.

[0008] The plate-shaped workpiece is preferably a sheet metal part, which can be made of a metal such as aluminum, structural steel, brass, copper, or stainless steel. The thermal cutting process can be laser cutting, plasma cutting, or oxyfuel cutting. Laser cutting is the preferred thermal cutting method.

[0009] The expansion joint is preferably bounded by one or more incisions that define its contour. The expansion joint preferably has a rectangular surface. Alternatively, the expansion joint can have a non-rectangular surface, for example, a surface with a curved contour. An expansion joint with a curved contour can be used when cutting workpiece parts that have a short edge with a curved profile. The joint length and width preferably define an area that is cut out in the first process step using a thermal cutting process. This area can also be referred to as a pocket.

[0010] According to an advantageous embodiment of the invention, the length of the workpiece section is at least three times its width, preferably at least four times its width, and particularly preferably at least five times its width. With an increasing length-to-width ratio, for example, the cut for the length of the workpiece section may require significantly more heat input than the short cut for the width of the workpiece section. This promotes the formation of warping and impairs the cutting result of the thermal cutting process. Thus, the advantage of the expansion joint according to the invention becomes more significant with an increasing length-to-width ratio of the workpiece section.

[0011] According to an advantageous embodiment of the invention, the width of the expansion joint is determined as a function of the length of the workpiece part. This embodiment is based on the understanding that a longer workpiece part requires a wider joint than a shorter one and offers the advantage that the joint width can be tailored to the workpiece part to be cut out, thus avoiding the cutting of expansion joints that are too narrow or too wide.

[0012] According to an advantageous embodiment of the invention, the joint width of the expansion joint is determined, additionally or alternatively, as a function of the maximum expected temperature change during the cutting of the workpiece part in the second process step. The maximum expected temperature change can describe the difference between the temperature of the plate-shaped workpiece part before and during cutting. A greater temperature change is more likely to lead to thermal distortion or warping of the workpiece part than a smaller temperature change. Preferably, the joint width is determined as a function of the length of the workpiece part and the maximum expected temperature change during the cutting of the workpiece part in the second process step.This allows for a more precise determination of the joint width of the expansion joint, so that the determined joint width is more likely to be sufficient to compensate for thermal distortion when cutting out the workpiece part and to minimize the risk of warping.

[0013] According to an advantageous embodiment of the invention, the maximum expected temperature change is determined as the mean temperature change across the entire surface area of ​​the workpiece part to be cut out in the second process step. The temperature change can be determined experimentally, simulated, or estimated. A thermal imaging camera can measure the temperature across the workpiece part in a previous (previous cycle) second process step, so that the mean temperature change across the entire surface area of ​​the workpiece part can be determined based on the measured data.Furthermore, it is conceivable that only the temperature profile across the entire surface of the workpiece is measured using a thermal imaging camera. The temperature of the flat workpiece is then measured shortly before the second processing step, and only then is the maximum expected temperature change determined as the average temperature change across the entire surface of the workpiece to be cut in the second process step. This allows the temperature of the flat workpiece immediately before cutting to be taken into account, resulting in a more precise outcome. Alternatively, the potential temperature profile across the entire surface of the workpiece to be cut can be simulated using a simulation program.Here, shortly before cutting out the workpiece, the actual temperature of the plate-shaped workpiece can be fed into the simulation again to provide the most accurate simulation of the temperature change possible. However, simulations are costly and time-consuming. Finally, the average maximum temperature change can be estimated based on the total surface area of ​​the workpiece to be cut out; this is the simplest method. However, this estimation can be inaccurate, resulting in a joint width that is either too small or far too large. An insufficient width leads to warping in the workpiece, while an excessive width wastes space on the plate-shaped workpiece. The estimate can be based on empirical data, particularly experimental data.

[0014] According to an advantageous embodiment of the invention, the joint width of the expansion joint is determined, alternatively or additionally, as a function of the coefficient of thermal expansion of the plate-shaped workpiece. It has been found that the tendency to form bulges depends on the coefficient of thermal expansion of the plate-shaped workpiece. Preferably, in addition to the length of the workpiece section and / or the maximum expected temperature change across the entire workpiece section to be cut out, the coefficient of thermal expansion of the plate-shaped workpiece section is also used to determine the joint width.

[0015] According to an advantageous embodiment of the invention, it is provided that in the first process step a further expansion joint is cut out of the plate-shaped workpiece, which has a joint width and a joint length, wherein the joint length is greater than or equal to the width of the workpiece part and the joint width is greater than a cutting gap width of the thermal cutting process, wherein a distance between the expansion joint and the further expansion joint corresponds to the length of the workpiece part, and wherein in the second process step the workpiece part is cut out of the plate-shaped workpiece in such a way that the workpiece part is arranged between the expansion joint and the further expansion joint.Preferably, the determined joint width of the expansion joint can be divided into one or more further expansion joints, with a particularly preferred arrangement of only one expansion joint at each short edge defining the width of the workpiece part. For example, a workpiece part can have two or more of these short edges, with an expansion joint being arranged at each of these edges. The further expansion joint can have a joint width and a joint length that are preferably identical to the joint width and joint length of the expansion joint. The distance between the expansion joint and the further expansion joint can correspond to the length of the workpiece part, so that preferably at least one incision in the expansion joint and one in the further expansion joint each represent a incision in the workpiece part.Advantageously, this makes it possible to save two cuts for the respective workpiece part, which can have a positive impact on process economy.

[0016] According to an advantageous embodiment of the invention, several workpiece parts are cut from the plate-shaped workpiece, with the first and second process steps being carried out for each workpiece part. It is conceivable that the first process step is carried out first for the several workpiece parts, followed by the second process step. Alternatively, the inventive method can be carried out cyclically for each of the several workpiece parts.

[0017] According to an advantageous embodiment of the invention, exactly one expansion joint is arranged between adjacent workpiece parts. This advantageously leaves more space on the plate-shaped workpiece for workpiece parts to be cut out, and also requires fewer cuts, which has a particularly positive effect on the efficiency of the process. The expansion joints are preferably divided, so to speak, by adjacent workpiece parts, and it is particularly required that the joint width of the expansion joint is dimensioned such that the expansion joint can accommodate the thermal expansion of both workpiece parts.

[0018] Another object of the present invention is a device for cutting a workpiece part from a plate-shaped workpiece by means of a thermal cutting process, in particular a laser cutting device, wherein the workpiece part has a length and a width, wherein the length is greater than the width, and wherein the device is configured to perform the following process steps: a. In a first process step, an expansion joint is cut out of the plate-shaped workpiece, which has a joint width and a joint length, wherein the joint length is greater than or equal to the width of the workpiece part and the joint width is greater than a cutting gap width of the thermal separation process; b. In a second process step following the first process step, the workpiece part is cut out of the plate-shaped workpiece in such a way that a short edge defining the width of the workpiece part is arranged along the joint length of the expansion joint.

[0019] According to an advantageous embodiment of the invention, the device includes a computing unit, the computing unit being configured to perform the following process steps: a. Determining the joint width of the expansion joint as a function of the length of the workpiece part and / or a maximum expected temperature change during the cutting of the workpiece part in the second process step and / or a coefficient of thermal expansion of the plate-shaped workpiece; and / or b. Laying out the several workpiece parts on the plate-shaped workpiece in such a way that the plate-shaped workpiece can be used optimally.

[0020] The same technical advantages and effects can be achieved with this device as have already been described in connection with the method according to the invention. The preferred embodiments and features explained in connection with the method according to the invention can also be applied individually or in combination to the device according to the invention.

[0021] Further details and advantages of the invention will be explained below with reference to the embodiment shown in the drawing. Fig. Figure 1 shows a schematic embodiment of a laser cutting device. Fig. Figure 2a shows a first workpiece with a workpiece part and an expansion joint to illustrate a first embodiment of the method according to the invention. Fig. Figure 2b shows a second workpiece with a workpiece part and two expansion joints to illustrate a second embodiment of the method according to the invention. Fig. Figure 3 shows a third workpiece with two workpiece parts and three expansion joints to illustrate a third embodiment of the method according to the invention.

[0022] Fig. Figure 1 shows a schematic embodiment of a laser cutting device 10, which is configured to perform the method according to the invention. The laser cutting device 10 can cut out a workpiece part 11 from a plate-shaped workpiece 12, which is arranged on a workpiece support 13, by means of laser cutting. For this purpose, the laser cutting device 10 has a laser beam generator 13, which in the present embodiment is designed as a CO2 laser. Alternatively, the laser beam generator 14 can also be designed as a diode laser or a solid-state laser. Furthermore, the laser cutting device 10 has a cutting head 15, wherein a laser beam 16 generated by the laser beam generator 14 is directed to the cutting head 15. The cutting head 15 can be focused selectively on the plate-shaped workpiece 12 by means of a focusing optic, depending on the application.In the alternative cases where a diode laser or a solid-state laser is used, the laser beam is guided from the laser beam generator 14 to the cutting head 15 via a fiber optic cable.

[0023] Furthermore, the laser cutting device 10 is supplied with process gases 17, wherein in Fig. Oxygen and nitrogen are shown. Alternatively, compressed air and argon can also be used as process gas 17, each process gas 17 having its own advantages. The process gases 17 enter the cutting gas nozzle 18 of the cutting head 15 under pressure control, from which they exit together or separately with the laser beam 16. The laser cutting device 10 can further comprise optical elements, for example, adaptive optics or several lenses of a zoom optic, with which the focus position and focus diameter of the laser beam 16 can be varied or adjusted. Furthermore, the laser cutting device 10 has a machine control 20. The machine control 20 is configured both to move the cutting head 15 together with the cutting gas nozzle 18 relative to the workpiece 12 and to control the optics.

[0024] The machine control 20 is used in the Fig. Figure 1 shows an example of separating the workpiece part 11 from the workpiece 12 by cutting. In particular, the machine control 20 is configured to carry out the methods according to the invention, described in more detail below, on the laser cutting device 10.

[0025] Fig. Figure 2a shows a first workpiece with a workpiece part 11 which can be separated from the plate-shaped workpiece 12 by means of the method according to the invention. This is achieved according to the invention by means of a thermal separation process, wherein, within the scope of the invention, thermal separation processes are understood to include, in particular, laser cutting, plasma cutting and oxyfuel cutting.

[0026] The workpiece part 11 has a length and a width, wherein it consists of Fig. As can be clearly seen in Figure 2a, the length is greater than the width. The width of the workpiece part 11 is defined by a short edge 11b of the workpiece part 11, and the length of the workpiece part 11 is defined by a long edge 11a of the workpiece part 11. The length and width of the workpiece part 11 are in a ratio to each other that is greater than three, preferably greater than four, and particularly preferably greater than five. This can mean that the longer cuts required to trace the length of the workpiece part 11 result in significant temperature differences within the workpiece part 11, and consequently, greater thermal distortion. It is therefore conceivable that with an increasing length-to-width ratio, the probability of thermal distortion in the workpiece part 11 increases, and thus also the risk of warping of the workpiece part 11. In order to completely avoid this probability of warping, or to minimize it,To provide a more robust separation process, in a first process step according to the invention, an expansion joint 1 is cut out of the plate-shaped workpiece part 12. The expansion joint 1 has a joint length 1a and a joint width 1b, wherein the joint length 1a corresponds to the width of the workpiece part 11. Alternatively, the joint length 1a can be greater than the width of the workpiece part 11. According to the invention, the joint width 1b is selected to be greater than the cutting gap width of the thermal process, which advantageously compensates for thermal distortion in the workpiece part 11. Sufficient space can be provided for thermal expansion in the workpiece part 11 so that no warping occurs in the workpiece part 11. A single cutting gap with the cutting gap width of the thermal separation process is not sufficient, especially with such long workpiece parts 11, to prevent warping.

[0027] Only after the expansion joint 1 has been introduced into the plate-shaped workpiece 12 is the workpiece part 11 cut out of the plate-shaped workpiece 12 such that a short edge 11b, defining the width of the workpiece part 11, is arranged along the joint length 1a of the expansion joint 1. Consequently, the workpiece part 11 and the expansion joint 1 share a cut in the plate-shaped workpiece 12, which in particular increases process efficiency.

[0028] The joint width 1b of the expansion joint 1 can be determined, in particular, by means of mathematical calculations. This allows for an estimation of the required joint width 1b of the expansion joint 1 based on specific parameters in order to compensate for the potential, and especially the maximum, thermal distortion of the workpiece part 11 during thermal cutting. Preferably, the joint width 1b of the expansion joint is determined as a function of the length of the workpiece part 11 and / or of a maximum expected temperature change during the cutting of the workpiece part 11 in the second process step and / or of a coefficient of thermal expansion of the plate-shaped workpiece 12.For example, the joint width 1b of the expansion joint can be determined as the product of the length of the workpiece part 11 and the maximum expected temperature change during the cutting of the workpiece part 11 in the second process step and the coefficient of thermal expansion of the plate-shaped workpiece 12.

[0029] To determine the maximum expected temperature change, an average temperature change based on the total area of ​​the workpiece part 11 to be cut out can be used. The temperature change can either be determined experimentally, calculated using simulation data from CAD simulations, or estimated.

[0030] Preferably, the joint width 1b of the expansion joint 1 is determined in a determination step that takes place before the first process step. Particularly preferably, the joint width 1b is determined by a computing unit that is part of the laser cutting device 1.

[0031] Fig. Figure 2b shows a second workpiece to illustrate a second embodiment of the method according to the invention. In the Fig. 2a and Fig. In the embodiments shown in 2b, the same workpiece part 11 is used. Only the expansion joints 1, 2 differ.

[0032] Fig. Figure 2b shows a first expansion joint 1 and a second expansion joint 2. The second expansion joint 2 has a joint length 1a and a joint width 1b, where the joint length 1b corresponds to the width of the workpiece part 11. Alternatively, the joint length 1b can be greater than the width of the workpiece part 11. The joint width 1b is chosen to be greater than the cutting gap width of the thermal cutting process. There is a distance d between the expansion joint 1 and the second expansion joint 2, which corresponds to the length of the workpiece part 11. The second workpiece part 11 is cut from the plate-shaped workpiece 12 after the expansion joint 1 and the second expansion joint 2 have been cut out, with the workpiece part 11 positioned between the expansion joint 1 and the second expansion joint 2. The joint width 1b preferably extends essentially perpendicular to the short edge 11b of the workpiece part 11.The expansion joint 1 and the further expansion joint 2 preferably have a rectangular surface.

[0033] Fig. Figure 3 shows a third workpiece to illustrate a third embodiment of the method according to the invention. The workpiece according to the third embodiment has several workpiece parts 11 – here two – wherein each workpiece part 11 has exactly one first expansion joint 1 and at least one second expansion joint 2. It is evident that adjacent workpiece parts 11 share the first expansion joint 1.

[0034] The method according to the invention can be carried out either cyclically for each individual workpiece 11 or once for all workpieces 11 simultaneously. Accordingly, the first expansion joint 1 and the second expansion joints 2 can be cut out first, and only then can all workpiece parts 11 be cut out. Alternatively, the expansion joints 1, 2 required for a workpiece part 11 can first be cut out of the plate-shaped workpiece 12, and then the respective workpiece part 11, before this cycle is repeated for the next workpiece part 11.

[0035] Preferably, the multiple workpiece parts 11 are arranged by the computing unit on the plate-shaped workpiece part 12 in such a way that the plate-shaped workpiece part 12 is utilized as optimally as possible and the first expansion joint 1 or second expansion joints 2 can be used by multiple workpiece parts 11 simultaneously. Reference symbol list 1 expansion joint 1a Joint length 1b Joint width 2 more expansion joints 10 Laser cutting device 11 workpiece part 11a long edge 11b short edge 12 plate-shaped workpieces 13 Workpiece support 14 laser beam generators 15 cutting head 16 Laser beam 17 process gases 18 Cutting gas nozzle 19 Machine control d distance between one expansion joint and another expansion joint

Claims

[1] Method for cutting a workpiece part (11) from a plate-shaped workpiece (12) by means of a thermal cutting process, wherein the workpiece part (11) has a length and a width, the length being greater than the width, comprising at least the following process steps: a. In a first process step, an expansion joint (1) is cut out of the plate-shaped workpiece (12), which has a joint width (1b) and a joint length (1a), wherein the joint length (1a) is greater than or equal to the width of the workpiece part (11) and the joint width (1b) is greater than a cutting gap width of the thermal separation process; b. In a second process step following the first process step, the workpiece part (11) is cut out of the plate-shaped workpiece (12) in such a way that a short edge (11b) defining the width of the workpiece part (11) is arranged along the joint length (1a) of the expansion joint (1). [2] Method according to claim 1, characterized by that the length of the workpiece part (11) is at least three times the width, preferably at least four times the width, and particularly preferably at least five times the width. [3] Method according to any one of the preceding claims, characterized by , that the joint width (1b) of the expansion joint (1) is determined as a function of the length of the workpiece part (11). [4] Method according to any one of the preceding claims, characterized by, that the joint width (1b) of the expansion joint (1) is determined as a function of a maximum expected temperature change during the cutting out of the workpiece part (11) in the second process step. [5] Method according to claim 4, characterized by , that the maximum expected temperature change is determined as the mean value of a temperature change based on a total area of ​​the workpiece part (11) to be cut out in the second process step. [6] Method according to any one of the preceding claims, characterized by , that the joint width (1b) of the expansion joint (1) is determined as a function of a coefficient of thermal expansion of the plate-shaped workpiece (12). [7] Method according to any one of the preceding claims, characterized by, that in the first process step a further expansion joint (2) is cut out of the plate-shaped workpiece (12), which has a joint width (1b) and a joint length (1a), wherein the joint length (1a) is greater than or equal to the width of the workpiece part (11) and the joint width (1b) is greater than a cutting gap width of the thermal cutting process, wherein a distance (d) between the expansion joint and the further expansion joint corresponds to the length of the workpiece part (11), and wherein in the second process step the workpiece part (11) is cut out of the plate-shaped workpiece (12) such that the workpiece part (11) is arranged between the expansion joint (1) and the further expansion joint (2). [8] Method according to any one of the preceding claims, characterized by, that several workpiece parts (11) are cut out from the plate-shaped workpiece (12), wherein the first and second process steps are carried out for each workpiece part (11). [9] Method according to claim 8, characterized by , that exactly one expansion joint (1, 2) is arranged between adjacent workpiece parts (11). [10] Device for cutting a workpiece part (11) from a plate-shaped workpiece (12) by means of a thermal cutting process, in particular a laser cutting device (10), wherein the workpiece part (11) has a length and a width, wherein the length is greater than the width, wherein the device is configured to perform the following process steps: a. In a first process step, an expansion joint (1) is cut out of the plate-shaped workpiece (12), which has a joint width (1b) and a joint length (1a), wherein the joint length (1a) is greater than or equal to the width of the workpiece part (11) and the joint width (1b) is greater than a cutting gap width of the thermal separation process; b. In a second process step following the first process step, the workpiece part (11) is cut out of the plate-shaped workpiece (12) in such a way that a short edge (11b) defining the width of the workpiece part (11) is arranged along the joint length (1a) of the expansion joint (1).

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