EP0166351A2 - Device at a machine for deformation work of sheet metals - Google Patents

Abstract

Mounted on a forming machine for sheet material (2) which has the unwanted property of springback especially in the case of bending, is a device which contains the following components or subassemblies: - during the bending process, a sensor (10, 20, 30, 60) detects the amount and direction of the bending (X, alpha ) of the sheet material (2) and/or, upon retraction of the tool (1, 3, 7) from its set position, the amount and direction of the springback ( DELTA X, DELTA alpha ) of the sheet material (2) relieved from the load of the tool (1, 3, 7); - a downstream conversion member (14, 28, 29, 36, 61) produces electrical signals which correspond to the detected amount and direction of the bending (X, alpha ) and/or springback ( DELTA X, DELTA alpha ); - taking into account the characteristic values of the sheet material (2) and of the tool (1, 3, 7) and the detected bending (X, alpha ) and springback ( DELTA X, DELTA alpha ), a signal for the set position of the tool (1, 3, 7) is produced and stored in an electronic circuit (40) and passed to actuators (50) which move the tool (1, 3, 7) into the set position. <IMAGE>

Description

The invention relates to a device on a machine for forming work on sheet-like materials with springback properties, a tool movable by the machine forming the sheet-like material.

The bending or edging of sheet metal belonging to the forming manufacturing process is used for the production of semi-finished products or end products such as housings, molded parts, joining parts, rods, etc. Increasing automation has recently led to the equipping of forming machines (e.g. bending presses and folding machines) with NC controls. In order to program the NC controls, you need mathematically formulated information about the elastic-plastic deformation behavior of the workpiece material, in particular about the springback.

It was found that the actual geometry of the formed workpiece deviates from the target geometry. This particularly relates to the bending angle, which is adversely affected by the springback. After the bending process, the desired and set bending angle of the workpiece is changed by the springback angle. The change in the bending angle is uncontrolled and cannot be recorded statistically. The exact amount of the springback angle can practically not be predicted, since it depends on many factors, such as material properties (high-strength thin sheets made of micro-alloyed and phosphorus alloyed steel alloys, coated sheets, modulus of elasticity), rolling direction of the sheet, sheet thickness, average bending radius, Tool radius, amount of the desired bending angle, bending process (free bending in the die, swivel bending, pressure bending). Due to this very complex dependency, the springback of the workpiece could only be calculated approximately in advance, so that certain deviations of the bending angle from the TARGET dimension had to be accepted in the finished workpieces. Since the requirements for workpiece accuracy, for example for joining parts, have been increasing more and more recently, the manufacturing effort has been increased. This is done by bending the same workpiece at least twice with the same tool or with a different tool. The tool must be reinserted into the machine for each work process. This is described in more detail in the journal "Industrieanzeiger", number 85, October 22, 1982, pages 22-24, article "Predetermination of the Bending Angle"; in the "VDI-Zeitung", progress reports, row 2, no. 60, VDI-Verlag, Düsseldorf 1983, "Investigations to improve the forming behavior of sheets during bending" and in the publication "Increasing the flexibility when bending sheets with different springback properties" at the DFB conference on October 28, 1983 in Düsseldorf.

The object of the invention is to eliminate the disadvantages of the known NC-controlled forming processes. The deviation of the actual value of the bending angle from its target value should be eliminated. The reproducibility of this zero deviation should also be guaranteed under different conditions, such as different material properties, rolling direction of the sheet, sheet thickness, average bending radius, tool radius, amount of the desired bending angle, bending process (free bending in the die, die bending, swivel bending). The manufacturing effort should be reduced to a minimum. As a result, great flexibility of the forming machine and economical production in particular Small batch sizes are achieved when different material qualities and sheet thicknesses can be processed side by side with the lowest possible tool investments.

The object of the invention is achieved by the features of patent claim 1.

• Figuren 1 und 2 Veranschaulichung der Problemstellung an einem ersten und einem zweiten Beispiel;
• Figuren 3 bis 5 Verschiedene Ausführungen von Sensoren;
• Figur 6 die Steuerschaltung.

Embodiments of the invention are explained in more detail with reference to the drawings. Show it:

• Figures 1 and 2 illustrate the problem on a first and a second example;
• Figures 3 to 5 different versions of sensors;
• Figure 6 shows the control circuit.

FIG. 1 shows a sectional view of a bending rail 1 that bends a sheet 2 in the die or in the die 3 using the free bending method and the die bending method. The bending rail is either only a part or up to the lower point in the die. moved into the die 3. The length of the bending section X depends on the desired bending angle. of the sheet metal 2. In the known bending machines, the relative movement of the bending rail 1 and the die 3 is accomplished by an electrical, hydraulic or pneumatic drive mechanism and moved into the desired position with the desired force. The relative movement can be carried out by moving the bending rail 1 or the die or the die 3. Since the geometry data of the die or die 3 and the bending rail 1 are known, only the specification of the distance X is sufficient to achieve the desired bending angle. The bending distance X indicates how deep the bending rail 1 has to go into the die 3 or die in order to reach the TARGET bending angle ζ of the sheet 2. If the bending rail 1 retracts and the sheet is relieved, the sheet springs back by the distance Δx and thereby changes the bending angle as a result of the springback property 4m of the sheet, which - as already mentioned - depends on a larger number of factors. The spring-back angle Δα, which is designated in the literature and which is drawn in FIG. 2, changes the TARGET bending angle α in an uncontrolled manner. In order to reduce the bending error caused by the springback angle, the bending rail 1 has been moved several times in the direction of the sheet metal 2 with the distance X + Δ X increasing. However, these known methods are imprecise and unsatisfactory since the springback error could not be completely eliminated because it apparently changed its amount from sheet to sheet indiscriminately. Therefore, one with a constant amount k. Δx corrected TARGET bending angle cannot be reproduced. For this reason, a certain deviation of the actual bending angle from the target bending angle has been accepted.

Figure 1 also shows a hold-down device 4, which is slidably mounted on the bending rail 1 and e.g. is moved by spring balancing or a special drive (pneumatic, electromagnetic, electric motor, etc.). This hold-down device 4 serves to fix the sheet metal 2 in the die 3 or in the die 3 when the bending rail 1 moves back. As a result, the sheet metal 2 cannot be displaced after it has been relieved of load, so that the sensor determines the springback path Δ X of the sheet metal 2 that has occurred. This measure of holding down is only necessary for thin sheets. When relieved by the tool, thick sheets remain in the same place without any special hold-down.

In addition, Figure 1 shows a key switch 5, which in Head of the bending rail 1 is arranged and its electrical line 51 are connected to the electronic circuit of Figure 6. The pushbutton switch serves to report the moment the sheet 2 is relieved from the bending rail 1 of the circuit 40 in FIG. Its function will be explained in more detail later in connection with FIG. 6.

The swivel bending process is shown in FIG. Since such machines are known, only the parts directly involved in the bending process were drawn. The sheet 2 is clamped between the upper and lower cheek 6. The bending beam 7 is moved in the direction of arrow 71 until the target bending angle «is reached. The sheet 2 is drawn in dashed lines in this position. After retracting the bending beam 7 in the direction of its starting length, the sheet metal 2 springs back due to its relief by the angle Δζ. The pushbutton switch 5 is arranged in the bending beam 7 and serves to report the moment when the sheet-like material 2 is relieved from the bending beam 7 of the electronic circuit 40 in FIG. In the known pivot bending, the error due to the springback angle Δα cannot be eliminated either. With this method, too, this angle apparently changes indiscriminately from sheet to sheet, so that the target bending angle ζ or the target bending stretch X with a constant value cannot be reproduced. For this reason, a certain deviation in the actual value of the bending angle cK or the bending distance X from its target value was accepted in the swivel bending.

Before the electronic circuit of FIG. 6 is discussed, which ensures the reproducibility of the same amount of the bending angle or the bending path with great precision, the sensors are described with reference to FIGS. 3 to 5, which describe the bending path X springback path ΔX, Detect the bending angle α and the springback angle Δα of the sheet 2 and pass this information on to the electronic circuit of FIG. 6 as electrical signals.

FIG. 3 shows a sensor 10, the plunger 11 of which is slidably provided in the die or in the die 3. The lower part of the plunger is formed as a rack in a _- handle with the gear 12 protrudes, which is connected via shaft 13 to a rotary encoder 14 in conjunction. A coil spring 15, the lower end of which is fastened to the construction piece 16, presses the plunger 11 against the sheet metal 2 with its upper end. The plunger makes the movements of the sheet metal during the bending and the springback caused by the retraction of the bending rail 1. Here, the bending distance X and the springback distance AX are detected. The movements of the plunger 11 reach the rotary encoder 14 via the gear wheel 12 and shaft 13, which converts the movement into electrical, analog or digital signals. The electrical signals contain the information about the amount and the direction of the movement of the plunger 11. These signals are fed via line 37 to the electronic circuit 40 of FIG. 6, so that the bending path X and spring-back path ΔX can be processed therein. Since such rotary encoders 14 are known and commercially available, the generation of the electrical signals is not described in detail. The forming member 14 can be designed as a rotary encoder or linear encoder. The mechanical sensor 10 of FIG. 3 is only used for the free bending and die bending process of FIG. 1.

FIG. 4 shows a further exemplary embodiment of the mechanical sensor 10 with a scanning lever 17 which can be pivoted about its axis 17a and which rests on the sheet metal 2 by means of a spring 18 and which follows all the movements during the forming of the sheet metal. The mechanical deflection of the scanning lever 17 is transmitted via a gear 19 to a shaping element 14 which generates digital or analog electrical signals and outputs them to the circuit of FIG. 6. In the present example, the shaping element 14 is drawn as a rotary encoder. It can also be designed as a slide potentiometer in a suitable mechanical form. With this sensor 10, bending path X and springback path L1 X can be detected.

If linear signal generators are used in place of the rotary encoder in FIGS. 3 and 4, the gears 12, 13 shown in the figures are omitted.

FIG. 5 shows an optical sensor 20 which can be used for the free bending and die bending of FIG. 1 and for the swivel bending of FIG. 2. The optical sensor consists of a light source 21, which is supplied with the necessary current via lines 211, one Collective lens 22, which directs the light rays 23 evenly onto light guides 240-249. These light guides are arranged as optical fibers in a frame 26. In reality, a few hundred light guides are accommodated in the frame 26. The area is as large as the uniform illumination of the light guides 240 - 249 is ensured by the light rays 23 of the point light source 21. If a sheet-like light source is used, the area of the frame 26 for the light guide can be made larger, and the converging lens 23 is then no longer necessary. Bending rail 1, die 3 for free bending or die 3 for die bending according to FIG. 1, or holder 6 and bending cheek 7 for pivot bending according to FIG. 2 are arranged in space 25 of optical sensor 20. The optical sensor of FIG. 5 lies in the drawing plane of FIG. 1 and perpendicular to the drawing plane of FIG. 2, so that the light beams emerging from the light guides 240-249 are bent rail 1, sheet metal 2, die or Ge lower 3, upper and lower beam 6 and bending beam 7 illuminate. At the other end of the room 25, a similar frame 26 is provided with a few hundred light guides 270-279. These light guides receive the light and shadow areas of the bending rail 1 and the sheet metal 2 and guide them to a semiconductor component 28, which receives this optical information from the light guides 270-279 and converts them into electrical signals. Such sensors are known as CCD semiconductor line sensors or CCD semiconductor matrix sensors from Fairchild. Such sensors are also described in the special edition by Ing. Erich Sommer, Frankfurt am Main 1973, article "Reticon line scan camera" by H. Friedberg. These sensors have an extremely high image resolution of 2048 points per CCD line sensor or 185,000 picture elements per CCD matrix sensor. Therefore, the light guides 270 - 279 are strongly bundled. The optical information reaching the semiconductor module 28 contains the bending distance X, the bending angle α, the spring-back distance AX and the spring-back angle Δα with a resolution in the μm range. The semiconductor module 28 transfers the information as fields analogous to the TV scanning principle to the following circuit 29, the register and logic modules of which transmit electrical signals which represent the detected amount and the detected direction of the bend X, α and the springback Δ X, Δα enter the line 37 into the electronic circuit 40 of FIG.

The radiation conductors of the 2nd type 270-279 can also be arranged at the same location as the radiation conductors of the 1st type 240-249. In this case, the rays from the radiation guides 240-249 reach a reflector which reflects them onto the radiation guides 270-279. The radiation conductors of the second type can be arranged coaxially around the radiation conductors of the first type or as receivers next to the radiation conductors of the first type. The reflector is advantageously at the other end of space 25 appropriate.

The radiation conductors 240-249 and 270-279 can be provided such that the lighting device 21, 22 and the optronic components 28, 29 are arranged at a certain distance from the room 25. This prevents the vibrations caused by the forming process from being transmitted to the sensitive components 21, 22, 28, 29.

If a laser or LED is used instead of the punctiform light source 21 in FIG. 5, the converging lens 22 and the light guides 240 - 249 and 270 - 279 are omitted. In this case, the beams reach the semiconductor module 28 directly and are processed there in the same way as already described.

The electronic circuit 40 of FIG. 6 is drawn as a block diagram. The free bending or die bending method according to FIG. 1 was chosen as an example. The sensors 10, 20 of FIGS. 3, 4, 5 are connected to the input lines 37 with their forming members 14, 28, 29. The electrical signals, which contain the information about the amount and the direction of the actual bend (distance X or angle α) or the springback (distance Ax or angle Δα), are given in the evaluator 44 and stored in the memory 41. These signals on lines 37 can be analog or digital. Furthermore, the signals in the evaluator 44 are checked for change speed, change standstill and direction. From this, the values of the springback ΔX or Δα are determined and stored in the computer 45, which, by means of further inputs by the circuits 46, 47, 48, forms the new TARGET value for compensating the springback distance ΔX or the springback angle A.oi. The input circuit 46 contains the TARGET value of the bend X, i. The input circuit 47 contains the properties of the sheet-like material 2 to be bent, such as material properties, modulus of elasticity, rolling direction and thickness. The input circuit 48 contains the data of the tool geometry, such as, for example, the radius of the bending rail 1, the width of the die 3, the position and radius of the upper beam 6, the bending method selected. Before the actual bending process, the above-mentioned data are given into the circuits 46, 47, 48 by the operator or by a predetermined program. The new TARGET value calculated in the computer 45 contains the force or the distance with which the sheet-like material 2 has to be bent a second time. The new TARGET value reaches the actuator 50 via the signal generator 48. The actuator 50 generates the electrical, pneumatic or hydraulic control signals which control the electrical, pneumatic or hydraulic drive of the forming machine according to FIGS. 1 or 2. The bending rail 1 or bending beam 7 now bends the sheet-like material 2 for the second time. After the tool has been moved back, the sheet metal 2 has been bent further around the springback path & X and the angular error due to springback has thus been eliminated; ie the originally desired bending angle has been established.

Since the correction quantity for the bending distance X or for the bending angle ζ is now fixed after this first sheet 2, each subsequent sheet is bent to the correct TARGET bending in a single bending process. This ensures reproducibility of the bend for any number of sheets. The set-up times and dead times of a forming machine are reduced to a minimum.

A sensor 60, a shaping element 61 and a switch 5 are shown in broken lines in FIG. This is intended in the event that the sensor with the relative movement of the bend rail 1 is connected to the die or die 3 or to the axis of rotation of the bending beam 7; that is, sensor 60 and shaping element 61 electrically replace sensors 10, 20 with transducers 14, 28, 29. The sensor 60 detects the relative movement of the bending rail 1 and the die 3, respectively. the pivoting of the bending beam 7 without making a difference between the bending process and the empty movement. Since the electrical signals are only required for the bending distance X or the bending angle α and for the spring-back distance Δ X or the spring-back angle Δα, the switch 5 is provided in the bending rail 1 or in the bending beam 7. Its arrangement for free bending or die bending is shown in FIG. 1. For the pivot bending of Figure 2, the switch 5 is arranged in the bending beam 7. During the bending process, the switch 5 touches the sheet material 2. This closes it. If after the bending process the tool 1, 1 returns, the switch 5 remains closed as the sheet-like material 2 touches the tool. The switch is only opened when the tool separates from the sheet material. As long as the switch 5 is closed, a signal is given via line 51 via the evaluator 44 of the electronic circuit 40 of FIG. During this time, the evaluator 44 causes the actual signals of the sensor 60 and the shaping element 61 to be stored in the memory 41. These signals are processed in the computer 45 in the same way as the signals from the sensors 10, 20. The actuating element 50 receives the signal generator 48 the new values for the next bending process to compensate for the springback distance bkX or the springback angle Δα of the sheet-like material 2. The subsequent sheets are bent to the desired bend in a single bending process, since the springback error has been eliminated. This ensures reproducibility of the bend for any number of sheets. The set-up and dead time for the forming machine of Figures 1 or 2 are reduced to a minimum.

Claims (7)

1. Device on a machine for forming work on sheet metal materials with springback properties, wherein a tool that can be moved by the machine reshapes the sheet material, characterized by the following components of the device: - A sensor (10, 20, 60) detects the amount and direction of the bend (X, ζ) of the sheet material (2) and / or when opening the tool (1, 3, 7) from its TARGET position during the bending process the amount and the direction of the spring-back Δx, Δζ) of the sheet-like material (2) relieved by the tool (1, 3, 7); - A downstream forming element (14; 28, 29; 61) generates electrical signals (B, R) which correspond to the detected amount and the direction of the bend (X, ζ) and / or springback (Δ X, Δ ζ); - In an electronic circuit (40), taking into account the material characteristics of the sheet material (2) and the tool (1, 3, 7) as well as the detected bend (X, c <) and springback (Δ X, Δα), a signal for the TARGET position of the tool (1, 3, 7) is generated and stored and given to actuators (50) which move the tool (1, 3, 7) to the TARGET position. 2. Device according to claim 1, thereby Characterizes that the sensor (10) contains a mechanically movable button (11, 17), which button gives the movements of the sheet material (2) to the forming member (14) for generating electrical signals, which electrical signals the amount and the direction of the Specify the bending distance (X) and / or the amount and the direction of the springback distance (Δ X) of the sheet material (2) relieved by the tool (1, 3). Figures 3, 4). 3. Device according to claim 1, characterized in that the sensor (10) contains a plunger (11) abutting the sheet-like material (2) which, via a gear (12, 13), has a deforming element (14) for generating electrical Signals are connected, which electrical signals indicate the amount and the direction of the bending path (X) and / or the amount and the direction of the spring-back path (AX) of the sheet-like material (2) relieved by the tool (1, 3). (Fig. 3). 4. Device according to claim 1, characterized in that the sensor (20) contains the following components: - A device (21, 22) for generating electromagnetic radiation, the rays (23) of which are distributed uniformly over an area; - Radiation guides of the first type (240 - 249), which receive the beams (23) distributed uniformly over an area and guide them into a space (25) provided for the tool (1, 3, 7) and the sheet-like material (2); - Radiation guides of the second type (270 - 279), which receive and transmit the beams from the room (25) influenced by the tool (1, 3, 7) and sheet-like material (2); - At least one optronic component (28, 29), which receives the beams from the radiation guides of the second type (270 - 279) and converts them into electrical signals, which electrical signals determine the amount and the direction of the bending distance (X) or the bending angle (vt ) of the sheet material (2). (Fig. 5) 5. The device according to claim 1, characterized in that the sensor (20) contains the following components: - A device (21, 22) for generating electromagnetic radiation, the rays (23) of which are distributed uniformly over an area; - Radiation guides of the first type (240 - 249), which receive the beams (23) distributed uniformly over an area and guide them into a space (25) provided for the tool (1, 3, 7) and the sheet-like material (2); - A reflector provided at the other end of the space (25), which directs the rays influenced by tools (1, 3, 7) and sheet-like material (2) onto radiation guides of the second type (270-279); - 2nd type radiation guides (270-279) which are arranged coaxially around the 1st type radiation guides (240-249); - At least one optronic component (28, 29), which receives the beams from the radiation conductors of the second type (270 - 279) and converts them into electrical signals, which electrical signals determine the amount and the direction of the springback distance (Δ X) or the springback angle ( Specify Δα) of the sheet material (2) relieved by the tool (1, 3, 7). 6. The device according to claim 1, characterized in that a sensor (60) with a shaping element (61) is arranged on the tool (1, 3, 7) and and the relative movement of the tool is detected relative to one another, and a switch (5) is provided in a tool part (1, 7) which, as a result of contact with the sheet material (2), switches its state (on / off) during this time via line (51 ) as a signal in the electronic circuit (40) (Fig. 1, 2, 6). 7. Device according to patent claim 1, characterized in that the electronic circuit (40) contains the following circuit parts: - An evaluation circuit (44) and actual amount memory (41) for receiving the signals containing the movement (X, o¿) and / or the feedback information (Δ X, Δα); - A computer (45) with input circuits (46, 47, 48) for entering the SET values of the bend (X, α) and the parameters, the properties of the sheet material (2) to be formed, the selected forming process and, if necessary of the tool (1, 3, 7), the computer (45) from the memory (41) and from the evaluation circuit (44) receiving the signals of the bend (X, ζ) and / or the springback (ΔX, Δζ) and processed with the TARGET values and the parameters from the input circuits (46, 47, 48). (Fig. 6)

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