Method of bending

Abstract

The invention relates to a method for performing a bending deformation on a workpiece (4) made of sheet metal using a bending machine (1) and a bending angle measuring device (10, 11) with a light source (13) for projecting a light line (15) onto the workpiece (4) and a camera (14). A control device (18) is designed with an image recognition program (21) and an evaluation program (22), and the evaluation program (22) calculates a value of the bending angle from changes in the generated light line (15) in the images from the camera (14). The light line (15) is projected onto the surface of the workpiece (4), the light line (15) extending to an outer edge (16, 17) of the workpiece (4) that is spaced from the bending edge (7). The evaluation program (22) calculates not only the bending angle but also the spatial position of the end of the light line (15) at the outer edge (16, 17) of the workpiece (4).

Description

[0001] The invention relates to a method for performing a bending deformation on a sheet metal workpiece using a bending machine and a bending angle measuring device.

[0002] During the production of components from bent sheet metal, stretching occurs in the bending zone due to plastic deformation during bending of the material. This extension of the sheet metal blank compared to the stretched length before bending is taken into account in the design as so-called bending shortening. Although there are methods for calculating bending shortening that can be taken into account in the design of a component, due to the type and number of parameters influencing the bending shortening values, it is common practice in practice to create tables with the corresponding values ​​for bending machines based on the results of test bends carried out with the bending machine. Bending shortening is known to depend on the material (strength, microstructure, grain size, ductility), the sheet thickness (ratio of thickness to radius), the position of the bend in relation to the rolling direction, the type of bending (e.g.Die bending, air bending, swivel bending), surface roughness (sheet metal and tool), the presence of lubricant and coatings, the bending radius and the size of the bending angle.

[0003] With regard to measuring the bending angle, it is already known to equip bending machines with an optical bending angle measuring device, which makes it possible to measure the current bending angle during the bending process of a workpiece and thus monitor whether the desired target value of the bending angle has been reached. Such optical bending angle measuring methods are usually based on a light pattern or a light line being projected from an illumination device of the bending angle measuring device onto the undersides of the two legs of the workpiece. Images are captured by a camera positioned obliquely to the plane of the incident light of the light line, and with the help of an image recognition program, the bending angle is calculated from the changed, current position of the light line as it appears in the images.

[0004] The object of the present invention was to overcome the disadvantages of the prior art and to provide a method with which the production of sheet metal workpieces on bending machines can be carried out reliably with even higher precision and quality.

[0005] This object is achieved by a method according to the claims.

[0006] The method according to the invention is designed for performing a bending operation on a sheet metal workpiece using a bending machine with two bending tools suitable for producing a bending edge on the workpiece. The bending machine is designed with at least one bending angle measuring device, which comprises a laser for projecting a light line onto a surface of the workpiece and a camera for recording images of the projected light line. A control device is designed with an image recognition program and an evaluation program, and the evaluation program calculates a value of the bending angle from changes in the light line generated on the surface of the workpiece in the camera images.In a first process step, the workpiece is placed in an undeformed, flat state between the bending tools. The laser then projects the light line onto the surface of the workpiece, extending to an outer edge of the workpiece at a distance from the bending edge. For a current bending angle value, the evaluation program calculates the spatial position of one end of the light line at the outer edge of the workpiece. This has the advantage of significantly expanding the functional scope of the bending angle measuring device.

[0007] According to a preferred method, it is provided that a value of a bending shortening is calculated from the values ​​of the bending angles and the spatial positions of the ends of the light lines on the outer edge of the workpiece at the beginning of the bending and at a time at the end of the bending using the evaluation program.

[0008] An advantageous approach is to use the evaluation program to calculate a springback value from the bending angle values ​​and the spatial positions of the ends of the light lines on the outer edge of the workpiece. This makes it possible, during design or when creating a production program for the bending machine control, to define the target value of the deformation angle of a workpiece to be achieved under load between the bending tools in such a way that the (design) target value of the bending angle is actually achieved.

[0009] According to a particularly preferred method, a measuring cylinder is attached to the outer edge of the workpiece prior to performing the bending process, with a cylinder axis of the measuring cylinder aligned coaxially with the outer edge of the workpiece. This has the advantage that, for the camera detecting the edge of the workpiece, largely unchanged lighting conditions prevail throughout the entire bending process, during which the deformation angle changes. The cylindrical surface of the measuring cylinder offers optically homogeneous conditions, regardless of the workpiece material or its surface texture.

[0010] It is also advantageous if the measuring cylinder includes at least one screw and the measuring cylinder is clamped to the edge of the workpiece by the screw.

[0011] Preferably, a test sheet which is cut rectangularly is used as the workpiece in the method.

[0012] In particular, it proves advantageous if the workpiece dimensions are 200 mm long and 100 mm wide. Rectangular workpieces, especially if the outer edge of the workpiece, which is at a distance from the bending edge, is aligned parallel to the bending edge, have the advantage that the measurement or calculation of the coordinates of the workpiece edge is largely insensitive to deviations in the projected light line.

[0013] It is also advantageous to store the values ​​of the bending angle achieved after bending, the bending shortening, the springback value, the workpiece thickness, along with the type of workpiece material and the type or type of bending tools in a database. This makes it possible to reliably determine the required dimensions of the sheet metal selected for the component during the design process.

[0014] For a better understanding of the invention, it is explained in more detail with reference to the following figures.

[0015] They show in a highly simplified, schematic representation: Fig. 1 shows a bending device represented by its processing area, shown in perspective; Fig. 2 shows a side view of the bending device according to Fig. 1; Fig. 3 a diagram of the control of the bending device; Fig. 4 a bending device according to a further embodiment of the method for forming a workpiece, in side view; Fig. 5 a detail of a leg of the workpiece with a measuring cylinder according to Fig. 4 .

[0016] By way of introduction, it should be noted that in the variously described embodiments, identical parts are provided with identical reference symbols or component designations, whereby the disclosures contained in the entire description can be applied mutatis mutandis to identical parts with identical reference symbols or component designations. Furthermore, the positional information chosen in the description, such as top, bottom, side, etc., refers to the directly described and illustrated figure, and in the event of a change in position, these positional information must be applied mutatis mutandis to the new position.

[0017] Based on the following Fig. 1 to 3A first embodiment of the method for forming a sheet metal workpiece is described.

[0018] The Fig. 1 shows a bending press or a bending device 1 in perspective. Only central parts of the processing area around a lower bending tool 2 and an upper bending tool 3 are shown, representing the entire bending device 1. This means that the illustration of other components of the bending machine 1, such as the machine frame and the drive means for adjusting the bending tools 2, 3 relative to one another, has been omitted for reasons of clarity.

[0019] The relative position of the upper bending tool 3 to the lower bending tool 2 corresponds to the situation at the beginning of the bending of a workpiece 4, which is inserted between the lower bending tool 2 and the upper bending tool 3 for processing. The lower bending tool 2 is attached to a press table or to a lower press beam 5, and the upper bending tool 3 is attached to a vertically adjustable upper press beam 6. By pressing the upper press beam 6 against the workpiece 4, a bending deformation is effected on the workpiece in the manner of air bending. On both sides of the bending tool arrangement formed by the two bending tools 2, 3, a leg of the workpiece 4 protrudes laterally, and these legs are pivoted upwards by a deformation angle 8, 9 during bending, forming a bending edge 7, as shown in the Fig. 2can be seen on the workpiece 4 shown in dashed lines. In order to determine or measure values ​​of the two deformation angles 8, 9 with respect to a bending axis 12 corresponding to the bending edge 7 of the corresponding legs of the workpiece 4, a bending angle measuring device 10, 11 is attached to the lower press beam 5 on both sides of the press table or the lower press beam 5. With the two bending angle measuring devices 10, 11, the deformation angles 8, 9 of the respective legs of the workpiece 4 can be determined without contact and based on the geometry and the relative spatial position of the parts to one another.

[0020] For the sake of completeness, it should be noted at this point that the provision of one bending angle measuring device 10, 11 on each side of the lower press beam 5 is due to the air bending used in this embodiment. If the bending device 1 were designed as a device for swivel bending, in which one leg of the workpiece 4 is held in its spatial position, the provision of only a single bending angle measuring device 10, 11 would be sufficient.

[0021] The bending angle measuring device 10, 11 is designed for contactless, optical measurement of the deformation angle 8, 9 in such a way that it comprises a light source 13 and a camera 14. The light source 13 is designed to emit a narrow, fan-shaped light beam onto the underside of the respective leg of the workpiece 4. A laser is preferably used as the light source 13. This creates a light line 15 on the underside of the leg of the workpiece 4. The planar light beam emitted by the light source 13 is preferably aligned perpendicularly with respect to the bending axis 12 (or the bending edge 7). Furthermore, the camera 14 is offset in the direction of the bending axis 12 by a distance relative to the light source 13, resulting in an oblique viewing direction of the light line 15.In images of the underside of the workpiece 4 recorded by the camera 14, the light line 15 therefore appears at different locations or at different angles depending on the deformation angle θ, 9. This makes it possible to calculate a value for the achieved deformation angle θ, 9 of the respective leg of the workpiece 4 from changes in the light line 15 in the images recorded by the camera 14. Subsequently, the bending angle enclosed by the two legs of the workpiece 4 can be determined from this. This means that the value of the bending angle is calculated as 180° minus the sum of the values ​​of the two deformation angles θ, 9.

[0022] According to the invention, the method also provides for the spatial positions of points on an outer edge 16, 17 of the workpiece 4 to be measured or calculated with the aid of the bending angle measuring device 10, 11 during the bending of the workpiece 4. For this purpose, the workpiece 4 is placed in a still undeformed, flat state between the lower bending tool 2 and the upper bending tool 3. The light source 13 of the bending angle measuring device 10, 11 projects the light onto the two undersides of the workpiece 4 such that the light line 15 extends to the outer edge 16, 17 of the workpiece 4. The light line 15 therefore reaches to the outer edge of the legs of the workpiece 4. During the bending of the workpiece 4, the camera 14 continuously records images of the underside of the workpiece 4 or of the respective light lines 15.The ends of the light lines 15 appearing in the images of the camera 14 thus mark the respective points on the outer edge of the legs of the workpiece 4.

[0023] The Fig. 3 shows a schematic of a control system for bending device 1. Bending device 1 has a control device 18 with a central processing unit 19 and a production program 20 to carry out the bending process. The images from camera 14 are processed using an image recognition program 21 and an evaluation device or an evaluation program 22. From the position or orientation of light line 15 within the field of view or within the image section of camera 14, the respective deformation angles 8, 9 of the two legs of workpiece 4 can be calculated with the aid of image recognition program 21 and evaluation program 22. From this, the current value of the bending angle between the two legs of workpiece 4 can be calculated.

[0024] According to the invention, the evaluation program 22 is designed to calculate the spatial position of the corresponding point on the outer edge 16, 17 of the workpiece 4 from the position of the pixels of the light line 15 on the outer edge 16, 17 of the workpiece 4 in the images recorded by the camera 14. The deformation angles θ, θ thus determined, the bending angle between the legs of the workpiece 4, and the spatial coordinates of points on the outer edges 16, 17 of the workpiece 4 are temporarily stored in a memory 23 of the control device 18. From the values ​​of these variables continuously recorded during the bending process, trajectories of the outer edges 16, 17 of the workpiece 4 can finally be calculated as a function of the bending angle. The bending of the workpiece 4 is carried out until a preselectable target value of the bending angle is reached.Finally, the evaluation program 22 can also calculate a value for the bending shortening of the workpiece 4 by relating the respective values ​​of the spatial positions or the spatial coordinates of the outer edges 16, 17 at the beginning and end of the bending process. Since an elastic recovery or springback of the two legs of the workpiece 4 occurs when the contact pressure of the bending tools 2, 3 is released after the target value of the bending angle has been reached, the corresponding values ​​of the deformation angles θ, θ and the spatial coordinates for the unloaded state of the workpiece 4 are also determined. Even after the applied target value of the bending angle has been reached, the bending angle measuring devices 10, 11 record the deformation angles θ, θ as well as the spatial positions of the outer edges 16, 17 of the workpiece 4.Thus, a bending angle value achieved under load by the bending tools 2, 3 and the bending angle value in the unloaded, force-free state—i.e., the actually achieved bending angle—can be determined. This enables the evaluation program 22 to calculate not only a value of the actually achieved bending angle but also so-called springback values ​​of the workpiece 4. The data thus obtained, such as the material type, the sheet thickness, the achieved bending angle value, the springback value, and also information about the type of bending tools 2, 3 used, are finally stored by the control device 18 or by the evaluation program 22 in a database stored in the memory 23.

[0025] The implementation of the described method can be controlled and monitored by an operator with the aid of an operating terminal 24 and a screen 25, which interact with the control device 18. To do so, the operator selects a suitable production program 20 by making appropriate inputs on the operating terminal 24 and starts the bending process after placing the workpiece 4 between the bending tools 2, 3. In addition, the operator can manually enter information such as the type of material used, the sheet thickness of the workpiece 4 and the type of bending tools 2, 3 used on the operating terminal 24 for inclusion in the database. By using a plurality of similar test sheets as the workpiece 4 to be deformed, other target values ​​orBending deformations of workpiece 4 are performed based on the target values ​​of the bending angle, thereby determining additional data sets to complete the database. The same applies to test series with different sheet thicknesses of workpiece 4, different sheet materials, etc.

[0026] In the bending operations carried out as described above, test sheets with standardized dimensions are used as workpiece 4. Preferably, rectangularly cut or shaped test sheets with side lengths of 200 mm x 100 mm are used as workpiece 4. It proves particularly advantageous if such test sheets used as workpiece 4 are inserted between the lower bending tool 2 and the upper bending tool 3 in such a way that their edges 16, 17 are aligned parallel to the bending axis 12 of the bending tools 2, 3.

[0027] Based on the Fig. 4 and 5A further embodiment of the method for forming a sheet metal workpiece 4 is described below. The same reference symbols or component designations are used for the same parts as in the previous Fig. 1 to 3 To avoid unnecessary repetition, please refer to the detailed description in the previous Fig. 1 to 3 referred to or referred to. The Fig. 4 shows a side view of the bending device 1 according to a viewing direction parallel to the bending axis 12 ( Fig. 1) of the bending tools 2, 3. Here, only the central part of the processing area around the bending tools 2, 3 is shown, again as representative of the entire bending device 1. As in the first exemplary embodiment, a bending deformation in the manner of air bending is carried out on the workpiece 4 by pressing down the upper bending tool 3. In the same way, a bending angle measuring device 10, 11 is arranged on both sides of the press table and the lower press beam 5. In the method according to this exemplary embodiment, it is now provided that a measuring cylinder 26, 27 is fastened to each of the two outer edges 16, 17 of the workpiece 4.

[0028] The Fig. 5 shows a detail of the workpiece 4 with the measuring cylinder 27 according to Fig. 4shown enlarged. In its state attached to the workpiece 4, the measuring cylinder 27 extends along the edge 17 of the workpiece 4. It has, on the one hand, a cylindrical surface 28 and, on the other hand, a concave recess with a first contact side 29 and a second contact side 30. The contact sides 29, 30, which are aligned essentially at right angles to one another, serve for contact with the lower side of the workpiece 4 and the front side of the edge 17. The measuring cylinder 27 or its cylindrical surface 28 and the contact sides 29, 30 are shaped such that a cylinder axis of the cylindrical surface 28 lies coaxially with the lower edge of the edge 17. As in the Fig. 5 As shown, the measuring cylinder 27 can be fastened or clamped to the workpiece 4 by means of one or more screws 31.

[0029] In this embodiment of the method, the measuring cylinders 26, 27 attached to the edges 16, 17 serve as a reference for determining the spatial position or the determination of the coordinates of points on the edges 16, 17 of the workpiece 4. The use of the measuring cylinders 26, 27 facilitates the detection of the edges 16, 17 of the workpiece 4 during bending. This is because, in particular, the surface quality of the cylinder jacket 28 of the measuring cylinders 26, 27 always remains constant and thus an optically homogeneous surface is available for evaluations with the aid of the image recognition program 21 or with the evaluation program 22. In contrast, the angles of incidence of the light rays on the underside of the legs of the workpiece 4 change with the progressive change in the deformation angle 8, 9. The coordinates orThe trajectory determination of the edges 16, 17 of the workpiece 4 can be performed using the measuring cylinders 26, 27, regardless of the material type. Differences in the surface finish of the workpiece 4 thus have no influence on the quality of the measurements.

[0030] The light line 15 generated by the light source 13 on the underside of the leg of the workpiece 4 continues in the shape of a circular arc on the surface of the cylinder surface 28 of the measuring cylinder 26, 27. In an image recorded by the camera 14, such a circular arc line with a radius 32 of the cylinder radius 28 generally appears in the shape of an elliptical arc segment. With a known or preselected value of the radius 32 of the cylinder surface 28, the coordinates of the current position of the edge 16, 17 of the workpiece 4 can be calculated taking into account the known geometric relationships. Potential measurement errors due to stray light or changing surface properties of the workpiece 4 can therefore be avoided by using the measuring cylinders 26, 27.The method according to this exemplary embodiment is characterized in that, before the bending process begins, a measuring cylinder 26, 27 with a preselected radius 32 of the cylinder shell 28 is attached to the edges 16, 17 of the workpiece 4. Furthermore, it is provided that the evaluation program 22 is configured to calculate the spatial coordinates of the edges 16, 17 based on the light line 15 generated on the surface of the cylinder shell 28.

[0031] It should be expressly noted at this point that the method according to this exemplary embodiment, i.e., the method using the measuring cylinders 26, 27, can also be carried out with a bending device 1 designed for swivel bending. In such a case, the arrangement of only a single bending angle measuring device 10, 11 would be sufficient, since one of the legs of the workpiece 4 is held by one of the bending tools 2, 3.

[0032] The embodiments show possible embodiments, whereby it should be noted at this point that the invention is not limited to the specifically illustrated embodiments thereof, but rather various combinations of the individual embodiments with one another are also possible and this possibility of variation lies within the skill of the person skilled in the art in this technical field due to the teaching of technical action by means of the objective invention.

[0033] The scope of protection is determined by the claims. However, the description and drawings must be used to interpret the claims. Individual features or combinations of features from the various embodiments shown and described may represent independent inventive solutions. The problem underlying the independent inventive solutions can be derived from the description.

[0034] All information on value ranges in this description is to be understood as including any and all sub-ranges thereof, e.g. the information 1 to 10 is to be understood as including all sub-ranges starting from the lower limit of 1 and the upper limit of 10, ie all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0035] For the sake of clarity, it should finally be pointed out that, in order to better understand the structure, some elements have been shown out of scale and / or enlarged and / or reduced in size. Reference symbol list 1 Bending device 32 radius 2 lower bending tool 3 upper bending tool 4 workpiece 5 lower press beam 6 upper press beam 7 bending edge 8 Deformation angle 9 Deformation angle 10 Bending angle measuring device 11 Bending angle measuring device 12 Bending axis 13 light source 14 camera 15 Light line 16 edge 17 edge 18 Control device 19 central processing unit 20 Production program 21 Image recognition program 22 Evaluation program 23 memory 24 Operating terminal 25 Screen 26 measuring cylinder 27 measuring cylinder 28 cylinder jacket 29 Investment page 30 Investment page 31 screw

Claims

1. A method for performing a bending deformation on a workpiece (4) made of sheet metal, comprising a bending machine (1) with two bending tools (2, 3) designed to produce a bending edge (7) on the workpiece (4), and with at least one bending angle measuring device (10, 11) comprising a laser (13) for projecting a light line (15) onto a surface of the workpiece (4) and a camera (14) for recording images of the projected light line (15), wherein a control device (18) is designed with an image recognition program (21) and with an evaluation program (22), wherein the evaluation program (22) calculates a value of the bending angle from changes in the light line (15) generated on the surface of the workpiece (4) in the images of the camera (14), characterized in thatin a first method step, the workpiece (4) is placed in an undeformed, flat state between the bending tools (2, 3) and then the laser (13) projects the light line (15) onto the surface of the workpiece (4) so ​​that the light line (15) extends to an outer edge (16, 17) of the workpiece (4) which is at a distance from the bending edge (7), and in that a spatial position of one end of the light line (15) on the outer edge (16, 17) of the workpiece (4) is calculated with the evaluation program (22) for a current value of the bending angle.

2. Method according to claim 1, characterized in that a value of a bending shortening is calculated from the values ​​of the bending angles and the spatial positions of the ends of the light lines (15) on the outer edge (16, 17) of the workpiece (4) at the beginning of the bending and at a time at the end of the bending using the evaluation program (22).

3. Method according to claim 1 or 2, characterized in that a springback value is calculated from the values ​​of the bending angles and the spatial positions of the ends of the light lines (15) on the outer edge (16, 17) of the workpiece (4) using the evaluation program (22).

4. Method according to one of the preceding claims, characterized in that before carrying out the bending deformation, a measuring cylinder (26, 27) is attached to the outer edge (16, 17) of the workpiece (4), wherein a cylinder axis of the measuring cylinder (26, 27) is aligned coaxially to the outer edge (16, 17) of the workpiece (4).

5. Method according to claim 4, characterized in that the measuring cylinder (26, 27) comprises at least one screw (31) and is clamped to the edge (16, 17) of the workpiece (4) by the screw (31).

6. Method according to one of the preceding claims, characterized in that a test sheet cut into a rectangular shape is used as the workpiece (4).

7. Method according to one of the preceding claims, characterized in thatDimensions of the workpiece (4) are 200 mm long and 100 mm wide.

8. Method according to one of the preceding claims, characterized in that Values ​​of the bending angle formed after the bending deformation, the bending shortening, the springback value, a value of a thickness of the workpiece (4) together with a type of material of the workpiece (4) are stored in a database.

9. Method according to one of the preceding claims, characterized in that a planar light beam generating the light line (15) is aligned perpendicularly with respect to the bending edge (7).

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