Method and holding device for forming workpieces in a percussive forming machine

Abstract

The invention relates to a method for forming a heated workpiece (1) in a percussive forming machine, comprising the following steps: a) picking up and clamping the workpiece (1) between two holding mandrels (3) which are held by at least one handling device (6), b) introducing the workpiece (1) in the held state into a working area of ​​a percussive forming machine between two forming die tools (24, 25) of a die (23), c) maintaining the clamped state during a forming step in which the die tools (24, 25) are moved relative to one another and the workpiece (1) is formed between the die tools (24, 25).

Description

[0001] The present invention relates to a method for forming workpieces in an impact forming machine, a holding device for holding a heated workpiece and a use of this device in an impact forming machine.

[0002] For the industrial forging of workpieces in impact forming machines, such as forging hammers or forging presses, it is known to use manipulators or (industrial) robots, for example, screw presses or crank presses. These robots insert the workpiece into the forming machine, hold it, and remove it from the forming machine after the forming process. The manipulators or industrial robots grip the workpiece at two opposite ends using gripping tongs.

[0003] The forged part must be securely controlled, but also have a certain degree of freedom so that it can be positioned within the die and thus be properly formed. During the forming stroke, the die and the forged part form a solid unit.

[0004] For example, DE 42 20 796 A1 and DE 100 60 709 A1 disclose gripping devices designed to prevent the high impact forces and resulting impulses that occur in an impact forming machine from stressing or damaging the gripping device during the gripping process with the gripping tongs. Impulse decoupling to the robot or manipulator is proposed.

[0005] The disadvantage of using pliers is that they account for up to 10% of the material used in the part. This negatively impacts material costs as well as the energy consumption associated with, among other things, the heating of the workpiece.

[0006] It is therefore an object of the invention to reduce the use of materials during the forming or industrial forging of workpieces in an impact forming machine.

[0007] This object is achieved by a method for forming workpieces in an impact forming machine having the features of claim 1, a holding device for holding a heated workpiece having the features of claim 6 and by a use of this holding device in an impact forming machine having the features of claim 11.

[0008] Accordingly, a method for forming a workpiece in a percussive forming machine, in particular a forging hammer or forging press, is provided, comprising the following steps: a) Picking up and clamping a workpiece between two holding mandrels which are held by at least one handling device, b) Inserting the workpiece in the held state into a working area of ​​a percussive forming machine between two forming die tools of a die, c) Maintaining the clamped state during a forming step in which the die tools are moved relative to one another and the workpiece is formed between the die tools.

[0009] By clamping the workpiece between two holding mandrels, the material previously required for the clamp end can be eliminated. Furthermore, by eliminating clamp ends, the energy required for the creation, forming, and recycling of the material is saved.

[0010] It is particularly advantageous if the holding mandrels are located at least partially between the two die tools (also called die halves) and are at least partially concealed by an upper die tool when viewed from above. Preferably, the tip of the holding mandrel is located between the two engraving areas before the forming step to ensure optimal material utilization and minimize burrs.

[0011] Preferably, the holding mandrels are part of a holding device and the holding mandrels are held directly or indirectly in a guide element of the holding device so that they can move away from each other during the forming step and the holding device remains spatially fixed. This ensures that the holding mandrels maintain contact with the workpiece without being destroyed during the forming process. The longitudinal growth of the workpiece during forming is compensated for by the mechanics in the holding device. The manipulator or robot does not move. Impact pulses occurring during the forging process are decoupled from the manipulator or robot and are therefore not transmitted. Nevertheless, the holding mandrels enable the forged part to be held securely and in a controlled manner throughout the entire forming process.

[0012] Preferably, the holding mandrels are mounted in the guide element so that they can pivot directly or indirectly, allowing them to follow the movement of the workpiece in the engraving during impact. The workpiece can find its way into the engraving itself due to the freedom of movement.

[0013] In an advantageous embodiment, the retaining pins are releasably held in a piston that is slidably and pivotably mounted in the guide element. The retaining pins can thus be replaced easily and quickly.

[0014] When gripping the workpiece between the holding mandrels, the mandrels are preferably driven into the end faces of the workpiece, creating a positive connection. It is advantageous if the tip of the holding mandrel allows for pivoting in the bearing location in the workpiece. It may also be advantageous if the tip is shaped to allow torque transmission.

[0015] In this process, steps b) and c) can be performed repeatedly in one or different dies. The workpiece remains clamped.

[0016] Furthermore, a holding device for holding a workpiece heated for a forging process is provided, comprising two holding mandrels designed to firmly clamp the workpiece. The holding mandrels are held directly or indirectly in a guide element of the holding device and can be displaced into the guide element by applying force against a spring, in particular a tension spring. The holding mandrels are mounted so as to be pivotable, directly or indirectly. This results in the aforementioned advantages.

[0017] It is advantageous if the holding mandrels are made of hard metal or sintered metal in order to be able to withstand the high temperatures.

[0018] An embodiment of the holding device with a master-slave principle is advantageous. A first part of the holding device has a first holding mandrel, a first guide element, and at least one first spring, and a second part of the holding device has a second holding mandrel, a second guide element, and at least one second spring, wherein the spring force of the at least one second spring of the second part is lower than the spring force of the at least one first spring of the first part. The ratio of the spring forces is preferably 1 to 0.8. The first part can therefore perform the general positioning, and the second part clamps the workpiece. Any longitudinal growth occurring during impact is preferably compensated by both parts, so that the position of a center axis of the workpiece remains unchanged relative to the die.

[0019] The pivoting is preferably carried out by means of cardanic bearings.

[0020] To ensure that the tool remains securely clamped even during impact, the first part preferably has a backstop or brake that directly or indirectly blocks the movement of the holding mandrel toward the second part and directly or indirectly allows the holding mandrel to move away from the second part. The backstop or brake preferably acts on the piston.

[0021] Furthermore, the use of the holding device described above for holding a workpiece in a percussive forming machine is provided. The described method is preferably carried out.

[0022] The workpiece is preferably substantially cylindrical, in particular circular-cylindrical, before the first forming step, and has a bearing point on each end face, in each of which a holding mandrel is positively received. The holding mandrels and bearing points are preferably designed such that a torque can be transmitted from the holding mandrels to the workpiece.

[0023] The holding device is preferably held by at least one handling device, and the handling device is preferably an industrial robot. It is also conceivable for each part to be held by a handling device, in particular an industrial robot.

[0024] In a preferred embodiment, the forming machine comprises die tools that have die pockets that extend outwardly from the die surfaces toward the front. The die pockets are designed such that the material flow generated during forming is directed into the die pockets, causing the bearing points in the workpiece to migrate outward along the longitudinal axis. The bearing points thus retain their shape.

[0025] During the forming process in the forming machine, the holding mandrels are preferably located at least partially between the two die tools and, when viewed from above, are at least partially concealed by an upper die tool. This allows material to be saved and burrs to be reduced.

[0026] The length of the workpiece (blank) is preferably matched to the die such that the burr formed during forming, with its bearing point, is located outside the engraving area in the area of ​​the die pockets after the first impact. Before the first impact, the tip of the holding mandrel 3 is still positioned within the die surfaces or the engraving area. Due to the impact forming and the increase in length, the tip of the holding mandrel is pushed outward into the die pockets.

[0027] A preferred embodiment of the invention is explained in more detail below with reference to the drawings. Similar or equivalent components are designated by the same reference numerals in the figures. They show: Fig. 1: a schematic view of a holding device of a workpiece heated for a percussive forming process, Fig. 2: a detailed view of a holding mandrel tip driven into the workpiece, Fig. 3: a schematic representation of a forging process, Fig. 4: a schematic representation of the placement of the workpiece in a die by means of the holding device at three different times during processing, Figure 4a: a spatial representation of a lower die, Fig. 5: a spatial view of an embodiment of a holding device with a U-shaped frame, and Figure 5a: a longitudinal section through an arrangement with three dies and the holding device from Figure 5 .

[0028] In the Figure 1a workpiece 1 is shown which is a forged part and is held by a holding device 2. The workpiece 1 is heated to a temperature adapted to the material for the forging process. For steel the temperature is between 800°C and 1250°C, for aluminum 300°C to 400°C, for stainless steel between 800°C and 1250°C and for special metals up to 1400°C. The holding device 2 comprises two holding mandrels 3, 4 which are arranged at opposite ends or front sides of the approximately circular cylindrical workpiece 1. To hold the workpiece 1 the holding mandrels 3, 4 are inserted into the front side of the workpiece 1, preferably driven in. It is advantageous if the holding mandrels 3, 4 are each placed in the center of the approximately circular cylindrical base area. The holding mandrel 3, 4 is held in an exchangeable manner in a holder (not shown). The holder is part of a movably mounted piston 5.The forces acting on the workpiece 1 and the holding mandrels 3, 4 during an impact forming process are not transmitted to the piston 5, so that impulse decoupling can prevent damage to the device 2 and impulses from being transmitted to the robot or manipulator. The holding device 2 is carried by one or more handling devices. A manipulator or robot can be used as the handling device. Preferably, one or two industrial robots with six degrees of freedom are used. In the illustrated embodiment, one part of the holding device is held by an industrial robot 6.

[0029] The longitudinally movable piston 5 is guided in a guide element 7 fixed to the handling device. The piston 5 has a stop 8, which strikes the guide element 7 in an extended end position. The piston 5 can be retracted into a housing 9 of the holding device 2 to a retracted end position.

[0030] In the schematically illustrated embodiment, a first part 2' of the holding device (left side) has a master function and a second part 2" of the holding device has a slave function. Each part 2', 2" comprises a housing 9 and arranged therein the guide element 7 fixed to the housing, the piston 5 and a holding mandrel 3. A spring 10 is arranged between the respective guide element 7 and the stop 8 movable with the piston 5, i.e. the piston 5 carrying the holding mandrel 3 is moved into the housing 9 against the spring force. The spring force of the second part 2" with slave function is lower than that of the first part 2' with master function. The two parts 2', 2" of the holding device carry out the axial positioning of the workpiece 1. During the forming process, the workpiece 1 is held centered in a die (not shown) and the handling device is spatially fixed.To ensure that the holding mandrels 3 always maintain contact with the workpiece 1 during the forging process, the pistons 5 and, with them, the holding mandrels 2 move relative to the housing 9 of the holding device 2. During the forming process, for example, the workpiece 1 changes in length, whereby material is displaced outwards, so that the holding mandrels 3 must be able to move away from one another. This movement in the axial direction is permitted by the movably mounted pistons 5, which move against the spring force of the springs 10. In order to allow pivoting in addition to axial displacement, a cardanic bearing 11 of the pistons 5 can be provided, for example, so that when struck in a forging hammer, the holding mandrels 3 can follow the movement of the workpiece 1 without losing contact.

[0031] Figure 2shows an embodiment of a tip of a holding mandrel 3. The tip 12 is, for example, spherical, as shown, and is received in the workpiece 1 with a form-fitting fit. The spherical tip 12 adjoins a conical region 13, in which the holding mandrel 3 tapers towards the tip 12. This allows the holding mandrel 3 to move in the bearing point 14 in the workpiece 1 within a predetermined angular range 15 (pivot angle) and without losing contact with the workpiece when pivoting. It is conceivable that the bearing point 12 is formed by driving the holding mandrel into the workpiece 1 or by previously inserting it into the end faces. It is also possible to provide a recess on each end face, and for the holding mandrel 3 to be driven into this recess. For driving in, a percussion piston integrated into the holding device can be provided, which acts on the piston.However, it is also conceivable to perform the insertion using a separate device. It may be necessary to re-insert the retaining pins during the forming process. During the forming process, it is important that the bearing location is outside the engraving area to prevent the retaining pin from being forged into the bearing. Furthermore, it is important to ensure that the bearing location is dimensionally stable to ensure secure storage.

[0032] If the workpiece 1 must be rotated while held by the handling device, the tip 12 of the holding mandrel 3 must allow torque transmission. In other words, the tip 12 must be non-circular. For example, the cross-section of the tip 12 may be cruciform, have a slot, a polygon, or the like. The tip or its envelope preferably has a diameter of 2 to 4 mm.

[0033] The holding mandrel 3 is preferably made of hard metal or a sintered metal, so that it is relatively heat-resistant.

[0034] The holding mandrel 3 has a low mass (mass inertia) so that it can easily follow the impulses or movements of the workpiece (forging part). Figure 3 shows a chronological sequence of a forging process with a flattening stroke and the insertion and forming of the workpiece 1 in an engraving 16. The workpiece 1 is held by two holding mandrels 3 as described above. In a first step, the workpiece 1 is picked up by the two holding mandrels 3. The pistons 5 with the holding mandrels 3 of both parts 2', 2" are completely extended out of the respective guide element 7 up to the stop and are in the extended end position.

[0035] The first part 2' of the holding device with master function specifies the longitudinal position of the workpiece 1 throughout the entire forging process. To clamp the holding device 2, the second part 2", which assumes the slave function, slides towards the first part 2'. The first part 2' of the holding device 2 (master) has a backstop 17 to prevent the piston 5 holding the holding mandrel 3 from moving toward the opposite part 2" of the holding device 2 when clamped. The backstop 17 thus serves to fix the piston position or the workpiece, but allows the piston 5 to move away from the center of the holding device 2.The backstop 17 can have wedge surfaces 18 firmly connected to the piston 5 or a conical surface which, when the piston 5 moves toward the center of the holding device, bears against corresponding surfaces 19 or a surface formed on the guide element 7, so that the piston 5 clamps in the guide element 7. When the piston 5 moves away from the center, the clamping is released and movement is permitted. The conical surface can also be split and formed, for example, by three jaws with a partially conical shape on the outside. It is also conceivable to provide another type of fixation.

[0036] As shown in the middle illustration, the holding mandrels 3 engage in a die 20 provided for the forming process. In other words, during the forming process, the holding mandrels 3 are located, at least in the area of ​​the tips 12, between the upper die 21 and the lower die 22 and, in a top view of the upper die 21, are covered by the latter. In contrast, in conventional gripping of pliers ends, the pliers ends lie outside the die.

[0037] First, a flattening operation is performed, as schematically shown in the center. This flattening operation is optional. The workpiece can also be placed directly into the engraving. For this purpose, the essentially circular-cylindrical workpiece 1 is flattened by a hammer (not shown) in the area of ​​the die 20 with flat die plates 21, 22 (without engraving). During impact forming, the workpiece grows x1 in the longitudinal direction 100. The pistons 5 of both parts 2', 2" of the holding device move outward against the spring force of the springs 10, so that the holding mandrels 3 deflect and are not damaged, yet still maintain contact with the workpiece 1. During the entire forming process, the center axis 200 of the workpiece 1 and the congruent center axis of the die 20 are spatially fixed, as is the position of the manipulator or robot. The holder of the workpiece 1 and the bearing points are located within the die 20.

[0038] The holding mandrel 3 of the first part 2' is pushed away from the center by the longitudinal growth against the force of the springs 10. The position of the piston 5 or the holding mandrel 3 is fixed by the backstop. The holding mandrel 3 of the second part 2" with slave function is also displaced by the longitudinal growth, but its position is not fixed, so that the holding mandrels 3 firmly hold the workpiece 1. This process is repeated from stroke to stroke.

[0039] Next, the workpiece 1 is formed by one or more blows in one or more engravings.

[0040] The second die 23 has an engraving in each of the upper and lower die halves 24, 25. During impact forming in the second die, the workpiece increases in length x2 in the longitudinal direction 100°. With each impact, the hammer springs in an impulse-like manner; due to the deformation of the workpiece (material flow in the engraving), the workpiece lengthens by an amount of approximately 5-10 mm at each end. This is compensated for by the movable pistons. As can be seen from the illustration, the guide element remains spatially fixed.

[0041] In the Figure 4 A die 23 with upper die 24 and lower die 25 and engraving 16 is shown in detail at three different times. The lower die 25 is spatially in Figure 4a shown.

[0042] The die 23 has a die surface 26 in each of the upper die 24 and the lower die 25, which spatially surrounds an engraving area 26'. The die surfaces 26 are flat surfaces that are preferably perpendicular to the hammer movement. The burr 1' forms between the two die surfaces 26 (die surface of the upper die and die surface of the lower die) during the forging operation. The engraving area is the negative form of the forged part. In addition, so-called die pockets 27 are formed in the die 23. These die pockets 27 are recesses on the respective inner side of the upper die 24 and the lower die 27 (the respective die surface), which are located centrally in the transverse direction and in the longitudinal direction in the respective end region of the upper and lower parts of the die 23.They extend longitudinally from the end faces 28 of the die halves 24, 25 inwards to the vicinity of the engraving area 26' and thus form an enlarged opening 29 into which a holding mandrel 3 can engage in the die 23 or can be pushed back during the forging process without coming between the die surfaces 26 during forming and becoming damaged. The die pocket and the engraving area are spaced apart in the longitudinal direction. In other words, the die surface 26 lies between the die pocket 27 and the engraving area 26'. The die surface 26 can be minimal in this area. Care must be taken to ensure that the die strength is maintained. Preferably, the die pocket 27 is wedge-shaped in longitudinal section and / or cross-section, with the wedge opening towards the end face 28 of the die. It is also conceivable to design the recess in a partially conical shape.Preferably, the die pocket 27 is formed symmetrically to the position of the bearing point of the workpiece in the die, so that during forming it can be ensured that the bearing point moves outwards on the longitudinal axis.

[0043] The middle image shows a first forming stroke, and the bottom image shows a second forming stroke. A third forming stroke may follow.

[0044] During forming, the material of the workpiece 1 is forced between the die surfaces 26 and into the die pockets 27. Due to the material flow determined by the die pockets 27, the bearing point 14 in the workpiece 1, at which the holding mandrel 3 engages, is always kept centered, thereby ensuring that the holding mandrel 3 always holds the workpiece 1 securely and reliably.

[0045] The length of the workpiece 1 (blank) is matched to the die 23 such that the burr formed during forming, with its bearing point 14, is located outside the die surfaces 26 in the area of ​​the die pockets 27 after the first impact. Before the first impact, the tip 12 of the holding mandrel 3 is still located between the engraving areas. Due to the impact forming and the increase in length, the tip 12 of the holding mandrel 3 is pushed outwards into the die pockets 27. The position of the holding mandrel of the first part (master part) is fixed. The piston deflects against the spring force. The increase in length is compensated for by the mechanics in the holding device. The manipulator or robot does not move.

[0046] During the second impact, the burr increases in size and the bearing point 14 with the retaining mandrel 3 accommodated therein shifts further outwards.

[0047] It is conceivable to provide different dies, for example, with pre- and final engraving, which are preferably installed side by side in the hammer. A rotation of the workpiece by 180° around its longitudinal axis may be necessary for process reasons.

[0048] The die halves preferably each have a dimension in width in a range of 150 mm to 250 mm, in height of 150 mm to 250 mm and in length of 350 mm to 450 mm, in particular the die halves are 200 mm wide, 200 mm high and 400 mm long.

[0049] At the end of the forging process (not shown), the workpiece is set down and the holding device releases it. The second part of the holding device retracts, and in the first part, the piston or holding mandrel is moved back to its initial position (extended end position) by releasing the locking mechanism.

[0050] The longitudinal length of the workpiece (blank) can be up to 400 mm. When using a single manipulator or robot supporting both parts of the fixture, the workpiece length can be up to 300 mm.

[0051] The Figures 5 and 5a show, by way of example, a substantially U-shaped connecting element 30 which connects both parts 2', 2" of the holding device 2 to one another. A clamping device 31 is provided for clamping a workpiece 1 between the two parts 2', 2". The entire holding device 2 can be attached as a tool to a manipulator or to one end of a robot arm.

[0052] In order to be able to perform multiple forming steps, three dies 23 are provided in the example shown. The dies 23 are arranged in a row and have longitudinal recesses 32 in the die surface 26, each of which extends over the entire length in the longitudinal direction and into which the connecting element 30 is received during the forming process. The manipulator or robot can thus move the workpiece 1 from the first die 23 to the second die 23 and finally to the third die 23 in a targeted manner between the forming steps by raising and lowering the holding device 2.

Claims

1. Method for forming a heated workpiece (1) in a percussive forming machine, with the following steps: a) picking up and clamping the workpiece (1) between two holding mandrels (3) which are held by at least one handling device (6), b) introducing the workpiece (1) in the held state into a working area of ​​a percussive forming machine between two forming die tools (24, 25) of a die (23), c) maintaining the clamped state during a forming step in which the die tools (24, 25) are moved relative to one another and the workpiece (1) is formed between the die tools (24, 25).

2. Method according to claim 1, characterized in thatthe holding mandrels (3) are part of a holding device (2) and the holding mandrels (3) are held directly or indirectly movable in a guide element (7) of the holding device (2), so that during the forming step the holding mandrels (3) move away from one another and the holding device (2) remains spatially fixed.

3. Method according to claim 2, characterized in that the holding mandrels (3) are held in the guide element (7) so as to be directly or indirectly pivotable.

4. Method according to one of the preceding claims, characterized in that When picking up between the holding mandrels (3), the holding mandrels (3) are driven into the end faces of the workpiece (1) in order to form a positive connection.

5. Method according to one of the preceding claims, characterized in that steps b) and c) are carried out repeatedly one after the other in one or different dies (23).

6. Holding device (2) for holding a workpiece (1) heated for a forging process, comprising two holding mandrels (3) which are designed to firmly clamp the workpiece (1), wherein the holding mandrels (3) are each held directly or indirectly in a guide element (7) of the holding device (2) and can be moved into the guide element (7) by applying force against a spring (10), and wherein the holding mandrels (3) are mounted directly or indirectly in a pivotable manner.

7. Holding device according to claim 6, characterized in that the holding mandrels (3) are made of hard metal or sintered metal.

8. Holding device according to claim 6 or 7, characterized in thata first part (2') of the holding device (2) has a first holding mandrel, a first guide element and at least one first spring, and a second part (2") of the holding device (2) has a second holding mandrel, a second guide element and at least one second spring, wherein the spring force of the at least one second spring of the second part (2") is lower than the spring force of the at least one first spring of the first part (2').

9. Holding device according to one of claims 6 to 8, characterized in that the pivoting is achieved by means of cardanic bearings.

10. Holding device according to one of claims 6 to 9, characterized in that the first part (2') has a backstop or brake which blocks the movement of the first holding mandrel directly or indirectly in the direction of the second part (2") and releases a movement of the first holding mandrel directly or indirectly away from the second part (2").

11. Use of the holding device (2) according to one of claims 6 to 10 for holding a workpiece (1) in an impact forming machine.

12. Use according to claim 11, characterized in that the workpiece (1) is substantially cylindrical and has a bearing point (14) on each of the end faces, in each of which a tip (12) of the holding mandrel (3) is positively received.

13. Use according to claim 11 or 12, characterized in that the holding device (2) is held by at least one handling device (6) and the handling device (6) is an industrial robot.

14. Use according to one of the preceding claims 12 to 13, characterized in thatthe forming machine comprises die tools (24, 25) which have die pockets (27) adjacent to the die surfaces (26), wherein the die pockets (27) are designed such that material flowing outwards during forming is guided into the die pockets (27) such that the bearing point (14) in the workpiece (1) migrates outwards along the longitudinal axis.

15. Use according to claim 14, characterized in that the holding mandrels (3) are located at least partially between the two die tools (24, 25) during the forming process in the forming machine and are at least partially concealed by an upper die tool (24) in a plan view.

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