Press with compensation for ram tilting

Abstract

The present invention relates to a press (1) comprising a press frame (2) which has at least four ram guides (3) on which a ram (4) is guided via guides. The ram (4) is driven by means of an eccentric shaft (16) and at least two connecting rods (5, 6), each of the connecting rods (5, 6) being connected to the ram (4) via a ball screw (7), and each of the ball screws (7) having a spindle adjustment mechanism with drives (8) that can vary the length of the connecting rods. According to the invention, at least three ram guides (3) are each provided with a displacement measuring system for detecting the distance (x, y) of the ram (4) from the press table (9), wherein an evaluation unit compares the measured distances (x, y) with one another and thus detects any tilting of the ram (4) at the bottom dead centre. Depending on this tilting, the drives (8) of the spindle adjustment mechanisms are controlled so that the length of the connecting rods (5, 6) is adjusted so as to compensate for or reduce the tilting of the ram (4) at the bottom dead centre in subsequent strokes. The present invention also relates to a method for reducing ram tilting in a press (1).

Description

[0001] PRESS WITH COMPENSATION OF SLIDE TILT

[0002] The subject matter of this invention is a press with a press frame having at least four ram guides on which a ram is guided via guides, the ram being driven via an eccentric shaft and at least two connecting rods. The connecting rods are each connected to the ram via a ball screw and have a spindle adjustment by means of which the connecting rod length can be changed. The subject matter of the invention also relates to a method for compensating ram tilting in a press or in an automatic punching machine.

[0003] The ram of a press should be aligned as parallel as possible to the press bed throughout its entire stroke. However, if the workpiece to be machined is not centered on the press bed, or if there are varying loads across the surface of the press bed, the ram may tilt at bottom dead center. Particularly in the production of bipolar plates, very high demands are placed on the press. On the one hand, the sheets to be machined are very thin, and on the other, the embossed channels must be as precise as possible.

[0004] Frequently, several bipolar plates located on the press table are processed simultaneously in one stroke. For example, in a first area on the press table the plate is punched out of a sheet metal strip (separated). In a second area adjacent to this, the openings of another plate are cut out at the same time. In a third area the channels are pre-stamped and in a fourth area the channels are finally finished stamped. Between strokes the individual bipolar plates are transported from the first to the fourth area by appropriate transport equipment until the finished stamped bipolar plates leave the press. The finish stamping of the plates requires higher pressing forces and therefore causes greater stress than, for example, pre-stamping or singling. This means that different loads and pressing forces occur in the different areas of the press table.This force imbalance leads to tilting of the ram during the working stroke, especially at bottom dead center. This tilting places additional stress on the press because it transmits forming forces into the press ram guides. This causes the guides to wear more quickly. The tilting also causes the press tools to wear more quickly, resulting in poorer forming quality. The precision requirements are particularly high for presses used to produce bipolar plates.

[0005] Figure 4 of DE 202007007144 U1 shows an eccentric press with two connecting rods that drive a two-part ram with spindle drives that adjust the distance between the upper and lower ram sections. This adjustment is performed using two measuring sensors. This allows the position of the tool to be aligned, particularly horizontally.

[0006] EP 1308268 A1 shows an eccentric press with two connecting rods that drive a ram, and with guide columns, with position measuring devices provided in two opposing guide columns. Based on these measurement signals, an adjusting device is actuated to change the ram reversal position. US 2021046722 A1 relates to a crank press with four guide columns and two connecting rods that act on a ram. Adjusting devices with position measuring devices are provided in three guide columns, with which the ram position can be aligned before the press is put into operation.

[0007] The object of the invention is therefore to provide a press in which the ram tilting is at least partially compensated.

[0008] This object is achieved by a press according to claim 1. According to the invention, a position measuring system is provided on at least three ram guides, each of which detects the distance between the ram and the press table. These detected distances are fed to an evaluation unit, which compares the measured distances and thus determines the tilting of the ram at bottom dead center. The drives for the spindle adjustments in the connecting rods are then controlled as a function of this tilting, so that the length of the connecting rods is adjusted in such a way that the tilting of the ram at bottom dead center is compensated for or reduced in the subsequent strokes.

[0009] This measure reduces the load on the ram guides and the pressing tools and increases the precision of the forming process.

[0010] The press can, for example, be an automatic punching press, in particular an automatic punching press for producing bipolar plates. Preferably, position measuring systems for detecting the ram tilt are arranged in all four ram guides.

[0011] It is advantageous if force sensors are provided in at least two connecting rods to measure the pressing force in each connecting rod. The measured pressing forces can then also be fed to the evaluation unit and taken into account for spindle adjustment. This ensures that the maximum permissible pressing forces in the press are not exceeded.

[0012] It is also conceivable that more than two connecting rods, preferably three or four connecting rods, are provided, all of which have a spindle adjustment to compensate for the tappet tilting at bottom dead center.

[0013] The subject of this invention also forms a method for compensating or partially compensating the tappet tilting at the bottom dead center.

[0014] A position measuring system is provided on at least three guide columns, with which the respective distance of the ram from the press table in the area of ​​the ram guide is measured. The measured distances are compared in an evaluation unit so that tilting of the ram at bottom dead center can be determined. Depending on this tilting, the drives for the spindle adjustments are then controlled so that the length of the connecting rods is adjusted in such a way that the tilting of the ram at bottom dead center is compensated or reduced in the subsequent strokes. An embodiment of the invention is described below with reference to drawings. In the drawings:

[0015] Fig. 1 is a schematic side view of a press 1 in force equilibrium;

[0016] Fig. 2 shows the press 1 from Fig. 1 in force imbalance;

[0017] Fig. 3 a press according to the invention with compensation of the ram tilting;

[0018] Fig. 4 the spindle adjustment of the press from Fig. 3;

[0019] Fig. 1 shows a press 1 with a press frame 2, a ram guide 3, and a ram 4. The ram 4 is driven by an eccentric shaft 16 and two connecting rods 5, 6. The upper tool part 10 is attached to the ram 4, and the lower tool part 11 is located on the press table 9. The workpiece is formed or punched between the upper tool part 10 and the lower tool part 11.

[0020] Press 1 in Fig. 1 is in force equilibrium here. This means that the pressing force 12 in the left connecting rod 5 and the pressing force 13 in the right connecting rod 6 are equal; likewise, the resulting tool force 14 on the left and the resulting tool force 15 on the right are equal.

[0021] Fig. 2 now shows the press from Fig. 1 with an imbalance of forces. The resulting tool force 15 on the right is greater than the resulting tool force 14 on the left. This can occur, for example, if different punching or forming operations are carried out in the left area of ​​the press 1 and in the right area of ​​the press, which require different press forces. For example, if a punching operation is carried out in the left area of ​​the press 1 and a forming operation is carried out in the right area. The different resulting tool forces 14, 15 in the left and right areas of the press 1 lead to a tilting of the ram 4.

[0022] According to the invention, a position measuring system is provided on each of the ram guides 3, which detects the distance x, y of the ram 4 from the press table 9. In the present example, the distance of the ram 4 from the press table 9 is greater on the right (y) than on the left (x).

[0023] An evaluation unit then compares the measured distances and thus determines the tilt of the tappet 4 at bottom dead center. The drives 8 (see Fig. 4) of the spindle adjustments in the connecting rods 5, 6 are then controlled as a function of this tilt, so that the length of the connecting rods 5, 6 is adjusted in such a way that the tilt of the tappet 4 at bottom dead center is compensated or reduced in the subsequent strokes. The drives 8 are preferably servo drives. In the present example, the length of the right-hand connecting rod 6 is therefore slightly extended.

[0024] With press 1 adjusted in this way, the specified forming process is then repeated. This is shown in Fig. 3.

[0025] By adjusting the connecting rod length, the tappet tilt at bottom dead center is now compensated, although the resulting tool force 15 on the right is greater than the resulting tool force 14 on the left. Reference symbol

[0026] 1 press (punching machine)

[0027] 2 press frames

[0028] 3 tappet guide

[0029] 4 pestles

[0030] 5 left connecting rod

[0031] 6 right connecting rod

[0032] 7 ball screw

[0033] 8 Drive

[0034] 9 Press table

[0035] 10 upper tool part

[0036] 11 Tool base

[0037] 12 Press force in the left connecting rod 5

[0038] 13 Press force in the right connecting rod 6

[0039] 14 resulting tool force left

[0040] 15 resulting tool force right

[0041] 16 Eccentric shaft

[0042] X Distance of the ram from the press table (left)

[0043] Y Distance of the ram from the press table (right)

Claims

Patent claims 1. Press (1) with a press frame (2) having at least four ram guides (3) on which a ram (4) is guided via guides, wherein the ram (4) is drivable via an eccentric shaft (16) and at least two connecting rods (5, 6), wherein the at least two connecting rods (5, 6) are each connected to the ram (4) via a ball screw (7) and the ball screws (7) each have a spindle adjustment with drives (8) via which the connecting rod length can be changed, characterized in that a distance measuring system is provided on at least three ram guides (3) for the respective detection of the distance (x, y) of the ram (4) from the press table (9), and wherein an evaluation unit compares the measured distances (x, y) with one another and thus determines a tilting of the ram (4) at the bottom dead center, wherein the drives (8) of the spindle adjustments can be controlled so that the length of the connecting rods (5, 6) is adjusted in such a way,that the tilting of the tappet (4) at bottom dead center is compensated or reduced in the subsequent strokes.

2. Press (1) according to claim 1, characterized in that in all four ram guides (3) position measuring systems for detecting the ram tilting are arranged.

3. Press (1) according to claim 1 or 2, characterized in that force sensors for detecting the pressing force (12, 13) in the respective connecting rod (5, 6) are provided in the at least two connecting rods (5, 6), the detected pressing forces (12, 13) being transmitted to the evaluation unit can be fed and are taken into account for the spindle adjustment.

4. Press (1) according to one of claims 1 to 3, characterized in that more than two connecting rods (5, 6), preferably three or four connecting rods, are provided, all of which have a spindle adjustment to compensate for the ram tilting at the bottom dead center.

5. Method for compensating a tilting of a ram (4) in a press (1) with a press frame (2) which has at least four ram guides (3) on which the ram (4) is guided via guides, wherein the ram (4) is driven via an eccentric shaft (16) and at least two connecting rods (5, 6), wherein the at least two connecting rods (5, 6) are each connected to the ram (4) via a ball screw (7) and the ball screws (7) each have a spindle adjustment with a drive (8) via which the connecting rod length can be changed, characterized in that a distance measuring system is provided on at least three guide columns (3) with which the respective distance (x, y) of the ram from the press table (9) is measured, wherein the measured distances (x, y) are compared with one another in an evaluation unit, so that a tilting of the ram (4) in the bottom dead center can be determined,wherein, depending on this tilting, the drives (8) of the spindle adjustments are controlled so that the length of the connecting rods (5, 6) is adjusted in such a way that the tilting of the tappet (4) at bottom dead center is compensated or reduced in the subsequent strokes.

6. Method according to claim 5, characterized in that the distances (x, y) of the ram (4) from the press table (9) are determined on all four ram guides (3) and these measured values ​​are used to compensate for the ram tilting.

7. Method according to claim 5 or 6, characterized in that force sensors for detecting the pressing force (12, 13) in the respective connecting rod (5, 6) are provided in the at least two connecting rods (5, 6), and these values ​​are taken into account for controlling the spindle adjustment, so that it is ensured that a predetermined maximum pressing force in the individual connecting rods (5, 6) is not exceeded.

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