EP1961502A2 - Method and device for bending workpieces - Google Patents

Abstract

The method involves determining and storing additionally the leg length and the leg length change of the workpiece (20) for different bending angles and computing and storing on the recorded and computed value of the K-factor for the workpiece. The leg length and the leg length change are computed and stored on the internal bending radius. An independent claim is also included for a bending device for bending the workpiece.

Description

The present invention relates to a method for bending workpieces with a bending punch and a die having a bending device according to the preamble of claim 1 and a bending device for bending workpieces according to the preamble of claim 13.

When bending workpieces by means of a bending die and a die having bending device, the bending angle for known materials and known workpiece thickness by determining the penetration depth of the punch into the die can be determined theoretically accurate. To bend the workpiece, the bending punch moves more or less into the die during so-called air bending, depending on the desired bending angle. In so-called three-point bending, the punch presses into the die until the punch or workpiece comes into contact with the more or less set die bottom.

However, practice shows that, for example, the rolling direction of the workpiece has an influence on its properties. But the thickness of the workpiece is subject to certain tolerances. In addition, the inner bending radius can not be determined exactly. But even the material itself may have different properties such as different moduli of elasticity, so that even within a single batch of material, the final bending angle with identical punch immersion depth vary by a few degrees or may differ from the actual setpoint. However, such differences are in many cases unacceptable and possibly cause a bending of the already finished workpiece.

From the EP 0 341 211 A1 For example, a method of bending sheet metal by means of a bending device is known, which has a bending punch and a die with an adjustable bottom. For a given die opening, the bending angle is determined by the relative position of the die bottom to the die opening certainly. In order to increase the bending accuracy, it is proposed here to determine the effective bending angle as a function of the penetration depth of the punch into the die in a test series with a specific sheet metal quality and to store it as a comparison curve. For subsequent bending operations with equivalent sheets, the angle of the loaded sheet during the bending operation is measured at at least one selected penetration depth and compared with the corresponding angle resulting from the comparison curve. Due to a possibly determined angular difference, the position of the die base is corrected in such a way that at the end of the bending process, the predetermined target angle can be maintained more accurately.

In the further is from the DE 10 2005 012 384 A1 a method for bending of workpieces known in which measured at least after a first bending process, the bending angle achieved and determined during the bending process depending on the process path of the punch the applied bending force and the resulting measurement curve. Thereafter, a correction value for the course of the bending process is determined from the occurring deviation between the predetermined desired bending angle and the achieved bending angle and, based on the detected measurement curve and a model-based calculation of the bending behavior. Subsequent bending operations are then performed taking into account the determined correction values.

Although an increase in the accuracy of the final bending angle can be achieved with the described methods, it would be desirable in many cases if the nominal bending angle could be maintained more precisely.

It is therefore the object of the invention to develop a method for bending workpieces according to the preamble of claim 1 such that even with changing workpiece parameters and / or for different tool combinations, an even higher accuracy in terms of Endbiegewinkels can be achieved.

This object is achieved by the method steps mentioned in the characterizing part of claim 1.

By detecting in a reference bend for different bending angles not only the associated penetration depth of the punch in the die and the bending force, but also for different bending angles additionally the leg length and / or the leg length change of the workpiece is determined and stored, and / or for different bending angle additionally the limb length and / or the leg length change of the workpiece is determined and from the detected and / or calculated values of the k-factor and possibly the inner bending radius for the workpiece calculated and stored, can be used in subsequent bending operations directly or indirectly to these values or These values are also taken into account for determining the immersion depth of the punch, so that ultimately the final bending angle can be maintained more accurately than before, even if individual workpiece parameters should change.

It has been found in practice that by the assignment of the leg length and / or the leg length change to the various bending angles on the one hand, the bending shortening of the workpiece leg or the workpiece leg during the bending process can be accurately determined, which for subsequent bending operations in which these values can no longer be determined, can be of great importance. On the other hand, by assigning the leg length and / or the leg length change to the different bending angles, the k-factor as well as the inner radius of the bend can be determined relatively accurately, which is also of great importance for subsequent bending operations. The knowledge of the k-factor and the bending inner radius is particularly important, if at least similar workpieces with different tool combinations and / or different workpiece thickness must be bent. In any case, in subsequent bending operations, the final bending angle can be maintained very accurately even if neither the bending angle nor the leg length are measured during the bending process, but only several times the bending force and the associated immersion depth measured and compared with the stored reference values. Due to occurring deviations then ultimately for the final bending angle decisive maximum immersion depth of the punch can be set in the die.

This is important because no sensors or measuring devices for measuring the bending angle and / or the leg length are provided for subsequent bending operations. Namely, in conventional bending processes, gauges for measuring the bending angle and / or the leg length are undesirable because they are expensive, interfere with the handling, or even possibly protrude into the area of the workpiece to be bent, thereby limiting the bending capabilities.

It is understood that the data determined during the reference bend and stored in a database can be transferred to other bending devices on which the subsequent bending operations are then carried out. In any case, the reference bend and the subsequent bending operations need not be performed on the same machine.

To determine the leg length and / or the leg length change, the position of the outer edge of the workpiece during the bending process is preferably detected several times.

Preferred developments of the method are described in the dependent claims 3 to 12.

A further object of the invention is to propose a bending device which is particularly suitable for detecting a plurality of parameters necessary for a precise bending angle on the basis of a reference bend.

This object is achieved with a bending device according to claim 13.

Advantageous developments of the bending device are described in the dependent claims 14 to 17.

Fig. 1

einen Querschnitt durch eine schematisch dargestellte Biegevorrichtung in der Ausgangsstellung;

Fig. 2

die Biegevorrichtung gemäss Fig. 1 zusammen mit einem zu biegenden Werkstück;

Fig. 3

die Biegevorrichtung gemäss Fig. 1 in einer Momentaufnahme während des eigentlichen Biegevorgangs.

The inventive method and an embodiment of an apparatus for bending workpieces will be explained in more detail with reference to drawings. In these drawings shows:

Fig. 1

a cross section through a schematically illustrated bending device in the starting position;

Fig. 2

the bending device according to Fig. 1 together with a workpiece to be bent;

Fig. 3

the bending device according to Fig. 1 in a snapshot during the actual bending process.

Based on Fig. 1 which shows a cross section through a schematically illustrated bending device 1 in the starting position, the basic structure of the bending device will be explained. The bending device 1 comprises a movable upper beam 2 and a fixed lower beam 3. At the upper beam 3, a bending punch 5 is fixed, while the immovable lower beam 3 carries a die 13. The underside of the punch 5 is provided with a rounding 6. The die has a V-shaped recess 14 with a fixed opening width and a top side designated 15, on which the workpiece to be bent comes to rest. The upper beam 2 is movably supported on the actual machine frame 4, wherein the means necessary for moving the upper beam 2 are not shown. In the following, an electronic control device 7 can be seen. For detecting the vertical position of the punch 5 relative to the machine frame 4, a displacement sensor 8 is provided, which is connected via an electrical connection line 9 to the control device 7. The control device 7 is provided with an interface 12, via which data and can be read out. In the upper beam 2, at least one sensor 10 is arranged, by means of which the force exerted by the bending punch 5 on the workpiece to be bent force can be detected directly or indirectly. As a sensor 10, for example, a force transducer can be used by means of which directly acting on the upper beam 2 force can be measured. Preferably, two force transducers are provided. Alternatively, for example, a pressure transducer can be used, by means of which the prevailing during hydraulic displacement of the upper beam 2 hydraulic system pressure is detected, which is proportional to the upcoming bending force. Due to this pressure, in any case, the upcoming bending force can be determined. Another variant is that strain gauges are mounted on the machine frame, preferably on a highly stressed point, as sensors, by means of which the bending force can then also be determined.

On the one side of the lower beam 3, a measuring system 16 is arranged, by means of which the bending angle of a workpiece to be bent and the leg length or leg length change can be detected, as will be explained in more detail below. In the present case, a laser measuring device is used as measuring system 16, which emits a linear light beam 17 or laser beam, which is indicated by way of indication. The measuring system 16 is also connected to the control device 7 via an electrical line 18. Possibly. Of course, a measuring system 16 can also be provided on both sides of the lower cheek 3.

The measuring system is positioned such that the longitudinal axis 25 of the light beam 17 emitted by the measuring system encloses an angle α between 30 and 60 ° with the longitudinal axis 26 of the bending punch 5.

The Fig. 2 shows the bending device 1 in the starting position together with a workpiece to be bent 20. The workpiece 20 is in the present example, a plate whose length, ie extension transverse to the intended bending edge is designated by X. The workpiece 20 rests on the upper side of the die 13, the means provided for positioning and possibly fixing the workpiece 20 not are shown in more detail. The measuring system 16 is positioned or set such that only part 17a of the light emitted by the measuring system 16 in the form of the laser line impinges on the workpiece 20, while a part 17c of this light passes laterally past the workpiece 20. A small portion 17b of the emitted light impinges on the end face of the workpiece 20, which is not important for the following consideration. The line of the laser beam projected onto the workpiece 20 by the measuring system 16 runs essentially transversely to the bending axis and forms a line with the length L1 on the workpiece 20. In the present case, the edges of the outer edge of the workpiece 20 are those edges which run parallel or possibly obliquely on both sides to the bending edge which arises during the bending process.

In any case, the measuring system 16 makes it possible to detect the bending angle of the workpiece 20 as well as the position of the outer edge 21 of the workpiece 20 facing the measuring system.

In addition to the actual light source, which may consist of an LED line laser, for example, the measuring system 16 has a receiver device by means of which the laser line projected onto the workpiece 20 can be optically detected or detected and evaluated in such a way that the bending angle as well as the bending angle Position of an outer edge 21 of the workpiece 20 can be detected or calculated. Such a receiver device may for example consist of a so-called CCD camera.

In any case, the length of the laser line projected onto the workpiece 20 can be detected with the receiver device, from which, together with the associated bending angle, a calculation of the absolute leg length and / or the relative leg length change is made possible. In order to determine the leg length change, the measuring system and the workpiece do not even have to be exactly positioned, but it merely has to be ensured that the laser line passes over the outer edge during the entire bending process 21 of the workpiece 20 and the range detected by the detection device also extends at least to the outer edge 21 of the workpiece 20.

Optionally, the position of the edge 21 may also be detected with respect to a reference point defined relative to the receiver device. In any case, the receiver device integrated in the measuring system is able to detect its absolute and / or relative position due to the light-dark transition in the region of the edge 21.

In this case, both the length of the detected line and also the leg length calculated together with the angle information and / or the leg length change can be stored.

In any case, it is advantageous if, for different bending angles, the associated immersion depth of the punch 5, the associated bending force as well as the associated limb length and / or the limb length change are stored. Of course, instead of the leg length, the length of the laser line projected onto the workpiece 20 or a leg may also be stored. It is understood that the parameters mentioned need not necessarily be stored in a directly usable unit, but only a value must be stored in each case, which allows a conclusion on the associated measured variable. In this regard, any variants are possible, which are not all enumerated here. In addition, it should be mentioned that it is not mandatory to record and store all the aforementioned parameters for each bending angle, but that, if necessary, individual parameters are recorded more frequently than others. The recorded values can also be stored in the form of a reference curve.

In addition to the directly recorded data, other variables such as the k-factor and internal bending radius can be calculated and possibly assigned to the bending angle. A correction factor is referred to as the k-factor, which can be used to draw conclusions about the change in length caused by the bending process Workpiece 20 allows. During the bending process, the neutral fiber of the workpiece 20 is moved to the inside, which is equivalent to an extension or extension of the workpiece 20 in the region of the bending line 22. The k-factor and the bending inner radius are important because it important conclusions for the Bending of the same or similar materials but can be drawn with other tool combinations and / or other workpiece thicknesses. In any case, due to the determined parameters, the immersion depth of the punch 5 necessary for reaching a certain angle into the matrix 13 can also be determined very accurately if the properties of the workpiece vary or do not correspond exactly to the desired values.

To perform a reference bend with the workpiece 20, the upper beam 2, as shown in Fig. 3 can be seen in a snapshot, moved down so that the punch 5 penetrates into the die 13 and the workpiece 20 bends along a bending line 22. By bending the workpiece 20, two legs 23, 24 are formed, which pivot upward as the bend increases. Of course, the position of the respective leg 23 with respect to the measuring system 16 changes continuously. When bending up the respective leg 23, on the one hand, the angle at which the laser light 17 strikes the leg 23 changes. On the other hand, the length L2 of the line projected by means of the measuring system 16 on the underside of the leg 23 also changes. The measurement of the bending angle is made by measuring the projection of the line laser on the leg 23 of the workpiece 20. In particular, the position of the line with the camera is measured, which is directed obliquely to the surface of the workpiece 20. Due to the included angle between laser and camera axis, the bending angle can be calculated, as will be explained in more detail below. Although, when the leg 23 is bent upwards, the laser line projected thereon does not undergo a linear change in length, the absolute length of the leg 23 and / or its change in length can be determined precisely on the basis of the measured length of the line and the associated bending angle. In principle, it does not matter whether the leg length or the leg length change of the workpiece 20 is determined or determined Since, in principle, both quantities are to be stored and used directly or indirectly as reference quantities or to be used for a subsequent bending process to determine the k-factor.

Since the die 13 has a fixed opening width, the bending angle is determined exclusively by the insertion depth of the punch 5 into the die 13. As immersion depth of the punch 5 in the die 13, the penetration of the front side of the punch 5 relative to the support surface 15 of the die 13 is referred to. As the bending force, the force exerted on the workpiece 20 to be bent by the punch 5 is referred to in its entirety.

It is understood that the punch 5 need not necessarily be arranged on the upper beam 2 and the die 13 on the lower beam 3, but that very well, a reverse arrangement is possible by the die 13 on the upper beam 2 and the punch on the Under cheek 3 of the bending device 1 are arranged. However, this does not change the fundamental idea of the invention and the method of operation.

Since the inside radius of the bend before the reference measurement is neither known nor can be calculated exactly, but this is crucial for the calculation of the exact immersion depth of the punch, the knowledge of the effective bending inner radius is of great importance. Thus, the bending inner radius changes in particular depending on the opening width and the V-shape of the die, the punch radius, the sheet metal quality and the sheet thickness.

In order to determine the bending inner radius exactly, for example, a bending process can be carried out in cycles, wherein during the bending process several times, for example every 10 °, the calculated angle is compared with the actually measured angle.

If, in this bending process, the workpiece is not relieved during the execution of the respective reference measurement, can be due to the measured Leg length or leg length change and the bending angle of the bending inner radius detached from the springback of the material can be determined. In any case, due to the difference between the calculated and the measured angle, the respective error in the calculation of the inner bending radius can be determined. From this, an "error curve" can be derived, which in each case has validity for the relevant sheet metal parameters such as type of sheet, thickness, etc. as well as a combination of upper and lower tool and can be used for subsequent bending. The data obtained can be stored in the form of a table or "error curve" in such a way that these data can be used directly or indirectly in subsequent bending operations.

Due to the knowledge of the effective bending inner radius, the bottom dead center-maximum insertion depth-of the punch can be determined very accurately, especially since the user only has to correct the actual sheet metal springback. The user can do without the mentioned measuring system for determining the leg length.

As such, sheet metal springback can also be readily determined by stopping the bending operation, relieving the sheet by raising the punch, and measuring the angular change resulting from springback. It is understood that the sheet metal springback can also be measured several times per bending process.

It should be mentioned that the combination of tools is to be understood as the combination of punch and die. In addition, it should be noted that under the bending force is not necessarily the effective applied bending force to understand, but only a parameter that is proportional to the applied bending force.

The Fig. 4 shows a schematic representation of the actively detected by the CCD camera of the measuring system field 28. The thick line 29 symbolizes the projected onto a leg of the workpiece laser line, while the dashed lines shown Line 30 represents the outside of the workpiece or the outer edge extending part of the laser line. The range effectively detected by the camera is larger than the actively detected field 28. However, the software is able to shift the active field 28 within the detection range of the camera so that the horizontal line 31 always coincides with the beginning of the laser beam 29 or the beginning of the laser beam 29 is located on the horizontal line 31.

The CCD camera together with the corresponding evaluation software is able to determine the angle β between the horizontal line 31 of the measuring field and the laser line 29 and to calculate therefrom the bending angle. The angle β is thus a measure of the effective bending angle, wherein the angle detected by the camera does not have to match or coincide with the effective bending angle.

In addition to the bending angle, due to the length L1 of the detected laser line 29 and the angle β, the effective leg length and / or the leg length change can also be calculated. While in the Fig. 4 the situation at a bending angle of 180 °, that is shown in the unbent initial state of the workpiece is in the Fig. 5 the situation is shown at a bending angle of 90 °. As can be seen, the angle β is smaller, while the length L2 of the laser line 29 projected onto the leg of the workpiece is greater. The length L1, L2 of the projected onto the leg of the workpiece laser line 29 can be accurately detected due to the respective light-dark transition, especially since a defined light-dark transition is formed by the outer edge of the workpiece. It is only important that the projected laser line projects laterally beyond the workpiece 20 during the entire bending process, ie over the outer edge 21 (FIG. Fig. 3 ) goes out.

The measured variables and data acquired or determined and / or calculated during the reference measurement are usually assigned to a specific material with a specific thickness and a specific tool combination. Ideally, therefore, for every material, every workpiece thickness and every Tool combination performed at least one reference measurement and stored the corresponding measurement data. Since this is hardly feasible in practice, however, reference data are normally used which come nearest to the material or tool combination to be bent and allow the best results to be expected with respect to the final bending angle. Since in the present case in the reference measurement for different bending angles both the corresponding penetration depth of the punch in the die, as well as the bending force and the leg length and / or the leg length change is measured and stored and possibly also the k-factor and the bending inner radius is determined in practice very good results, even if the material and / or the material thickness and / or the tool combination does not match exactly with that or those of the reference measurement. For this purpose, the measured data and reference values stored in the database can be interpolated. For example, if there are entries for 2 mm and 3 mm thick workpieces from a particular material, the data for 2.5 mm can also be calculated. You can also interpolate up or down. If, for example, the entries for 2 mm, 3 mm and 4 mm thick workpieces are available, the data can also be calculated for a 5 mm thick workpiece. The same applies, for example, for intermediate angle. If, for example, the insertion depth of the punch into the die required for achieving a bending angle of 90 ° and 100 ° is known for a particular material, then the insertion depth necessary to achieve a bending angle of 93.2 °, for example, can also be calculated. Also between different die openings can be interpolated.

Since conventional bending devices usually have no measuring system for detecting the bending angle and / or the leg length of the workpiece, but are generally equipped only with sensors for detecting the depth of immersion of the punch in the die and the associated bending force, in the subsequent bending operations usually only the immersion depth measured the punch in the die and the associated bending force. Of course, in subsequent bending operations, the immersion depth of the punch and the associated bending force can also be measured continuously. However, it has been found in practice that a repeated measurement of the bending force and the associated immersion depth and a comparison with the stored reference values is generally sufficient to exactly the penetration depth of the punch 5 into the matrix 13 necessary for a certain final bending angle -Sollbiegewinkel- calculate that the error in terms of the effective Endbiegewinkel is much smaller than before. In this regard, tests have shown that with a good database and a dynamic measurement of the bending force together with the associated immersion depth and a continuous comparison of the measured with the stored reference values and a dynamic correction of the error in terms of the final bending angle, ie the deviation between the target and actual Angle, is on the order of ± 15 angular minutes and is thus much smaller than in the generic method.

If, for example, it is determined that a higher bending force must be applied for a certain penetration depth of the punch into the die compared to the workpiece used for the reference bend, then it can be concluded that the material used is stiffer. This in turn means that the bending radius is greater at a certain depth of immersion and therefore for a certain bending angle of the stamp must dive slightly less deep into the die.

Conversely, it behaves when the workpiece to be bent is softer. In this case, the bending force applied for a certain penetration depth of the punch into the die compared to the workpiece used for the reference bend is lower and the bend radius correspondingly smaller. Therefore, for a given bending angle of the stamp must therefore dive slightly deeper into the die.

Claims (17)

Method for bending workpieces (20) with a bending device (1) having a bending punch (5) and a die (13), wherein at least one reference bending is carried out, during which different bending angles together with the associated penetration depth of the punch (5 ) are recorded in the die (13) and the associated bending force, and wherein at least a portion of the detected values is stored such that it can be used in subsequent bending operations to the necessary for a certain target bending angle penetration of the punch (5) in the Calculate template (13), characterized in that the limb length and / or the limb length variation of the workpiece (20) is additionally determined and stored for different bending angles, - And / or that for different bending angles in addition the leg length and / or the leg length change of the workpiece (20) is determined and calculated from the detected and / or calculated values of the k-factor for the workpiece (20) and stored. - And / or that for different bending angles additionally the leg length and / or the leg length change of the workpiece (20) is determined and calculated from the detected and / or calculated values of the k-factor and the inner bending radius for the workpiece (20) and stored. A method according to claim 1, characterized in that for determining the leg length and / or the leg length change, the position of the outer edge (21) of the workpiece (20) during the bending operation is detected several times. A method according to claim 2, characterized in that for several bending angles, the position of the outer edge (21) of the workpiece to be bent (20). is detected and stored and that due to the position of the outer edge (21) and the associated bending angle, the leg length and / or the leg length change is calculated. Method according to one of the preceding claims, characterized in that for determining the bending angle, a line-shaped light beam (17) is projected onto the workpiece (20) in such a way that the position of the light beam (17) directed onto the surface of the workpiece (20) is determined by means of a camera. and the bending angle is calculated on the basis of an angle (β) enclosed between the light beam (17) and the camera axis. A method according to claim 2, characterized in that for determining the position of the outer edge (21) of the workpiece (20) during the bending process, a line-shaped light beam (17) is projected onto the workpiece (20) extending over the outer edge (21 ) of the workpiece (20) extends, and that by means of a camera due to a difference in brightness, the position of the outer edge (21) of the workpiece (20) is detected. A method according to claim 4 or 5, characterized in that on the workpiece (20) projected line of the light beam (17) extends substantially transversely to the bending axis (22). Method according to one of the preceding claims, characterized in that at least for a bending angle of the associated bending radius is calculated and stored, wherein the bending radius is calculated on the basis of the measured bending angle and the associated penetration depth of the punch (5) in the die (13). Method according to one of the preceding claims, characterized in that at least for a bending angle, the associated bending shortening of the workpiece leg (23) is calculated and stored. Method according to one of the preceding claims, characterized in that at least part of the detected and / or specific data on a storage medium, in particular in a database of a central computer or a personal computer, are stored. A method according to claim 9, characterized in that the stored data is transmitted to a further bending device, in particular by means of a network or the Internet. A method according to claim 9 or 10, characterized in that at least a part of the detected and / or determined data are transferred to another bending device such that the further bending device can access it for a subsequent bending operation to the necessary for a certain bending angle immersion depth of Calculate punch in the die. Method according to one of claims 8 to 10, characterized in that for at least one tool combination and at least one type of material the different bending angles attributable penetration depth of the punch are transferred to the die together with the associated bending force and the determined k-factor on the further bending device, and that in a subsequent bending operation of a workpiece consisting of an at least similar material on the further bending device, the penetration depth of the punch into the die and the associated bending force are measured several times and compared with the stored values or the stored reference curve, and on the basis of the measured values and any deviations the decisive for the final bending angle maximum immersion depth of the punch into the die is calculated. Bending device (1) for bending workpieces by means of a bending punch (5) penetrating into a die (13), wherein the bending device (1) comprises at least one displacement sensor (8) for detecting the advance of the bending punch (5), at least one sensor (10) for direct or indirect detection of the applied Bending force and an electronic control device (7) for controlling the advancing movement of the punch (5) and for evaluating and / or storing and / or comparing detected measured variables or calculated measured variables, characterized in that the bending device (1) additionally a measuring system ( 16) for measuring the bending angle and the respective associated leg length and / or the leg length change of the workpiece (20) during the bending operation. Bending device (1) according to claim 13, characterized in that the measuring system (16) is designed such that it detects the position of the outer edge (21) of the workpiece (20) during the bending operation several times to determine the leg length and / or the leg length change , Bending device (1) according to claim 14, characterized in that the measuring system (16) has at least one light source and a camera, wherein the light source for determining the bending angle of a linear light beam (17) projected onto the workpiece (20) that by means of a Camera, the position of the obliquely directed onto the surface of the workpiece (20) line is measured and calculated due to the enclosed between light and camera axis angle of the bending angle. Bending device (1) according to claim 15, characterized in that the longitudinal axis (25) of the measuring system (16) emitted light beam (17) forms an angle (α) between 30 and 60 ° with the longitudinal axis (26) of the punch (5) , Bending device (1) according to one of claims 13 to 16, characterized in that the bending device (1) has an interface (12) via which the detected and / or calculated data can be transmitted.

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