EP0417753B1 - Mechanical or hydraulic press with drawing or pressing station for multiple stage press - Google Patents

Description

The invention relates to a mechanical or hydraulic press with a pulling device or drawing step of a step press according to the preamble of claim 1.

To form drawn parts, it is necessary to hold the workpiece placed on a lower tool, for which purpose the workpiece is clamped between a special sheet metal counterholder and the lower tool that moves down. The force exerted by the plunger during the decline must counteract a counterforce via a yielding cushion. For this purpose, the counterforce is applied to the sheet metal counterholder by an underlying pulling device - also known as a pressure cushion or drawing cushion.

During the working stroke of the press ram, the sheet to be drawn is therefore pressed against the by the upper part of the tool Pressed sheet metal counterholder and moved it against the force of the die cushion. Here, it is deformed by the drawing die fixed on the press table.

When the upper tool hits the sheet metal counterholder, there is always a relatively hard blow with subsequent vibrations, which is associated with a correspondingly large amount of noise. At the same time, the sheet metal counterholder has to be accelerated suddenly to the speed of the press ram, which generates an increased energy requirement.

From EP-A-0 074 421 A1 it is known to counter the sheet metal counterholder before the press ram strikes with the aid of a hydraulic cylinder additionally arranged in the extension of the lower piston rod and a proportional valve which operates via the machine control and which is arranged between a separate hydraulic pump and the hydraulic cylinder is to put a downward movement in advance. However, this movement is only time-controlled in the pre-acceleration phase of the sheet metal counterholder, with no targeted and metered amount of hydraulic oil reaching the hydraulic cylinder.

From DE-A-36 40 788 Al it is also known to set the sheet metal counter-holder in motion with the aid of an additional hydraulic cylinder arranged in the extension of the lower piston rod and an associated pre-acceleration cylinder with a specifically specified hydraulic quantity, the quantity supplied by a Proportional valve is controlled. This movement is also in the pre-acceleration phase of the Sheet counterholder time-controlled and requires a respective adaptation of the control to possibly different stroke numbers and working pressures, whereby the speed of the drawing device with different stroke numbers and working pressures is not always analogous to the speed of the press ram.

From DD-A-242 355 Al (& De-A-3619109), which is considered to be the closest prior art, a device of the generic type for pre-accelerating the movable cushion masses in drawing presses has become known. A gradual acceleration of the die cushion from zero to almost ram speed is achieved. This is done by means of a complicated telescopic cylinder in a control line system, with a telescopic ring piston which is moved by means of a plunger which can be actuated via the press ram. The ring pistons are acted upon one after the other and thus displace pressure medium for the pre-acceleration of the die cushion movement in a step-like manner and thus path-dependent. The number of telescopic pistons determines the degree of pre-acceleration of the movable cushion masses. Different stroke rates of the drawing press and working pressures can be achieved in this known device by adjusting the starting position of the punch connected to the press ram. The path-dependent control measures are then implemented hydraulically via the step-shaped annular pistons. A disadvantage of this known device is the complicated structure of the piston-cylinder unit with the step-shaped annular piston integrated therein. The gradation of the ring pistons results in a fixed gradation of the hydraulic pressures that build up for the pre-acceleration of the sheet metal counter-holder, which is a very inflexible solution.

Advantages of the invention:

The press according to the invention with the characterizing features of claim 1 has the advantage that it contains a pulling device, by means of which the impact noise that occurs when the upper tool hits the sheet metal counterholder can be considerably reduced by accelerating the die cushion mass beforehand, with very simple circuitry and structural measures be used. The pre-acceleration process largely takes place without complicated and delayed valve control, i. H. valve controls are kept to a minimum. Nevertheless, it is possible to influence the process to a large extent if the initial requirements change, whereby the reproducibility of the processing process is guaranteed due to the absence of extensive control mechanisms. Similar to the DD 242 355 A1, the pre-acceleration process of the sheet metal counterholder is to be carried out with separate hydraulic cylinders in the present invention, which are coupled to the movement of the press ram. An optimal effect of this process is achieved by a path and time recording of the individual movement processes as well as by a targeted hydraulic control of the pressure medium causing the pre-acceleration. The device can run in the manner of an individually set positive control.

Further advantageous measures and supplements for the further development of the press according to the invention are specified in the subclaims.

Fig. 1

eine Presse mit Zieheinrichtung mit am Pressenständer angeordneten Kolben-Zylindereinheiten, deren Kolben vom Pressenstößel angetrieben werden,

Fig. 2

in einer schematischen Teilschnittansicht die Zieheinrichtung gemäß Fig. 1 mit den pneumatischen und hydraulischen Steuer- und Regelkomponenten,

Fig. 3

ein Diagramm von Stößelweg und Ziehkissenweg,

Fig. 4

eine Presse mit Zieheinrichtung mit einer Kolben-Zylindereinheit, deren Hydraulikzylinder am Pressenstößel befestigt ist und mit einem am Pressenständer vorgesehenen Verstellmechanismus für die Kolbenstange,

Fig. 5

eine Ansicht Y nach Fig. 4 und

Fig. 6

eine Presse mit Zieheinrichtung gemäß Fig. 4 mit den pneumatischen und hydraulischen Steuer- und Regelkomponenten.

Further details and advantages of the invention which are essential to the invention are given in the following description of the invention using various exemplary embodiments with reference to drawings. Show it

Fig. 1

a press with a pulling device with piston-cylinder units arranged on the press stand, the pistons of which are driven by the press ram,

Fig. 2

1 with the pneumatic and hydraulic control and regulating components,

Fig. 3

a diagram of the ram path and die cushion path,

Fig. 4

a press with a pulling device with a piston-cylinder unit, the hydraulic cylinder of which is attached to the press ram and with an adjustment mechanism for the piston rod provided on the press stand,

Fig. 5

a view Y of FIG. 4 and

Fig. 6

a press with a pulling device according to FIG. 4 with the pneumatic and hydraulic control and regulating components.

The presses with drawing devices shown in FIGS. 1 and 4 are first described in the corresponding features as follows.

The press 1 with the pulling device 2 in FIGS. 1 and 4 consists of a stationary lower press table 3 with a table support designed as a sliding table 4 for receiving a lower tool 5 for producing a workpiece, represented by a board 6 that has not yet been machined. The board 6 is placed on a sheet metal counterholder 7, which is guided in the lower tool 5 with a punch 5 '. The upper tool 8 is connected to a press ram 9. The sheet metal counterholder 7 is supported on a pressure cheek 11 by means of pressure bolts 10. The pressure cheek 11 is supported by an underlying, central piston-cylinder unit 12, which is pneumatically operated and acts like a spring that presses upwards. A further piston-cylinder unit 13 is provided below the piston-cylinder unit 12 in operative connection with the same piston rod 19 and serves as a hydraulic damping cylinder for damping the upward-directed piston movement of the piston-cylinder unit 12 above. The piston-cylinder units 12 and 13 are shown again in more detail in their circuit arrangement in FIGS. 2 and 6. The piston-cylinder unit 12, known per se - hereinafter referred to as pneumatic cylinder 12 - consists of a cylinder housing 14 with an upper 15 and a lower 16 pressure chamber, through which a piston 17, 18, which can be acted upon on one side, passes. A piston rod 19 passing through the entire cylinder housing 14 connects the upper and lower pistons 17, 18 and protrudes from the cylinder housing 14 in the upper and lower regions. The upwardly projecting area 19 'of the piston rod 19 supports the pressure cheek 11, which is only indicated in FIGS. 2 and 6. The lower area 19''of the piston rod 19 protrudes from the lower area of the cylinder housing 14 and opens into the piston-cylinder unit 13 below. called in the further damping cylinder 13 -. In this area, the piston rod 19 '' is included provided with a piston 20 which runs within the damping cylinder 13. Around the damping cylinder 13, an oil tank 21 preloaded with air is arranged. A throttle bore 22 with a downstream hydraulic circuit 23 is used to actuate the damping cylinder 13. For this purpose, a 2/2-way valve 24 with a downstream 3/2-way valve 25 is provided, which on the one hand with the throttle bore 22 and on the other hand with a feed bore 26 to the damping cylinder 13 with the upper pressure chamber 46. The control circuit provides a further access 27 to the oil container 21.

The pressure spaces 15, 16 of the pneumatic cylinder 12 arranged above the damping cylinder 13 are provided with pressure medium from a pneumatic accumulator 29 via a pressure line 28, the pressure of which can be adjusted continuously.

According to the representation in FIG. 1, hydraulic cylinders 33 are provided on the stand 32 of the press 2, the respective piston rod 34 of which is firmly connected to the press ram 9 via a calotte 35. A piston 36, which can be acted upon from both sides, runs in the hydraulic cylinder 33, the upper piston rod 34 being extended downwards with the same diameter, so that an upper pressure chamber 37 and lower pressure chamber 38 which have a constant cross section are established. As shown in more detail in FIG. 2, the two upper pressure chambers 37 of the two hydraulic cylinders 33 arranged laterally in the stator area are connected to one another via a pressure line 39 and connected to a hydraulic pump 40. Furthermore, a memory 41 is connected to the upper pressure spaces 37. The lower pressure chambers 38 of the two hydraulic cylinders 33 are also connected to one another via a further pressure line 42 connected, wherein an adjustable proportional valve 43 connects the upper 39 and lower pressure line 42 and thus the upper 37 and lower 38 pressure chambers.

Via a further pressure line 44, the pressure line 42 connecting the lower pressure spaces 38 is connected via a 2/2-way valve 45 to the pressure space 46 provided above the piston 20 of the damping cylinder 13. A first distance meter 47 for determining the press ram travel 9 is provided on the press ram 9. The movement of the puller, i.e. H. the movement of the pressure cheek 11 is detected via the movement of the piston rod 19. For this purpose, a further odometer 48 is attached to the piston 20 of the damping cylinder 13.

The mode of operation of the press according to FIG. 1 is described in connection with the illustration according to FIGS. 2 and 3 as follows.

The operating cycle of the press with the pulling device begins in accordance with the starting position shown in FIG. H. with the press ram 9 raised. While the press ram 9 with the upper tool 8 attached to it moves downward, the proportional valve 43 shown in FIG. 2 is opened, so that when the piston 36 moves downward, the pressure medium located in the lower pressure chamber 38 of the hydraulic cylinder 33 is above the pressure line 42, the proportional valve 43, the upper pressure lines 39 is displaced into the upper pressure chamber 37. The path of the press ram 9 is detected via the path measuring device 47.

Shortly before the upper tool 8 hits the sheet-metal counterholder 7, the proportional valve 43 closed, whereby the oil displaced in the lower pressure chamber 38 is no longer conveyed into the upper pressure chamber 37 but via the line 44 and the valve 45 into the upper pressure chamber 46 of the damping cylinder 13. The proportional valve 43 is triggered by the travel meter 47 and closed in a ramp-controlled manner, ie according to a predetermined, preferably linear shut-off characteristic. In Fig. 3, the sequence of movements of the pulling device in dependence on the set ramp is shown in principle. The X-axis shows the angle of rotation of the mechanically driven rotating plunger drive, the Y-axis the plunger stroke. Curve 49 shows the path of the press ram 9, the bottom dead center being identified by UT. The path of the pressure cheek 11 and thus the sheet metal counterholder 7 is shown with reference number 50. Already at point 51 at the angle of rotation X 1, the pre-acceleration process of the sheet metal counter-holder 7 begins, ie the proportional valve 43 begins to close the passage of the pressure medium. According to the representation in Fig. 3, the pre-acceleration of the sheet-metal counter-holder 7 from point 51 to point 52 takes place over the distance "a" before the upper tool 8 touches the sheet-metal counter-holder 7 at point 52 at the angle of rotation X₂. From this point in time, the sheet metal counterholder with die cushion between points 52 (X₂) and 53 (X₃) corresponds to curve 54 in the same way as the upper tool. After passing through the bottom dead center UT, the press ram 9 together with the sheet metal counterholder 7 again moves up to the point 53, the pneumatic cushion 12 bringing about the upward movement of the die cushion and thus the sheet metal counterholder. From the point 53 (angle of rotation X₃) press ram 9 and sheet metal counterpart 7 separate by the action of the damping.

The pre-acceleration shown in FIG. 3 by the amount "a" from point 51 to point 52 significantly dampens the impact of the upper tool on the sheet metal counterholder.

By the area ratio of the effective area of the hydraulic cylinder 33 and the damping cylinder 13, i. H. the relative speed of the pistons 36 to the piston 20 relative to one another is determined by the ratio of the effective piston areas of the two pistons 36 of the hydraulic cylinders 33 to the effective upper surface of the piston 20 of the damping cylinder 13. The area ratio is chosen so that during the acceleration phase of the sheet-metal counterholder 7, this runs more slowly than the press ram 9, whereby the upper tool 8 overtakes the sheet-metal counterholder 7 in a certain way and places it on the pulling device. This is recognized by a drop in pressure at the pressure sensor 55.

The distance traveled by the pulling device until the upper tool 8 is placed on the sheet-metal counterholder 7 can be checked on the basis of the travel meter 48. After the pre-acceleration has been completed, the proportional valve 43 is opened again, the damping cylinder 13 absorbing the required oil volume via a check valve 56 after the valve 45 has been closed.

After reaching the bottom dead center UT, the 2/2-way valve 24 and the valve 25 are opened so that the pulling device, following the press ram 9, can move up again. The upward movement is braked by the throttle bore 22 and, in particular, an impact impact in the upper end position of the sheet metal counter-holder is avoided.

The damping cylinder 13 is therefore used both to dampen the upward movement of the pneumatic cylinder 12 acting as a spring and to generate the previously described pre-acceleration of the die cushion with sheet metal counterholder 7. After the pulling process, the 2/2-way valve 24 is closed again.

The press according to the invention shown in FIGS. 4 to 6 is basically constructed in the same way as the press described above with the following differences in construction and mode of operation:

As can be seen from FIG. 4, the hydraulic cylinders 33 provided in this embodiment are attached directly to the press ram 9, the piston rod 34 of the piston 36, which can be acted on from both sides, being connected via a calotte 35 to an adjusting device 57, which in turn is firmly attached to the stand 32. The adjusting device 57 provides a variable height adjustment of the piston rod 34 via an adjusting screw 58, i. H. the starting position of the piston 36 can be varied in height.

As shown in the right part of FIG. 4 and in FIG. 6, the wall of the hydraulic cylinder 33 contains an upper through bore 59, a lower through bore 60 analogously to the illustration in FIG. 2. In addition, a through bore 62 is provided in the middle height range of the hydraulic cylinder, which serves as a control well. 5 shows the view of this control bore from the direction Y in FIG. 4 in more detail.

The press according to Figures 4 to 6 works as follows: The starting position of the piston 36 is determined by the Height adjustment device 57, 58 predetermined depending on the application and mode of operation of the device. During the downward movement of the press ram 9, the hydraulic cylinder 33 moves downward, as a result of which the piston 36 moves upward in the cylinder space of the hydraulic cylinder 33 and the pressure medium located in the upper pressure space 37 via the central through bore 62 and a bypass line 63 in the housing wall of the hydraulic cylinder 33 and the lower bore 60 is conveyed into the lower pressure chamber 38. The upper through bore 59 remains closed during this overflow from the upper 37 to the lower 38 pressure chamber via the valve 43.

Shortly before the upper tool 8 strikes the sheet metal counterholder 7, the piston 36 gradually closes the bore 62, caused by the downward movement of the hydraulic cylinder 33, as a result of which the hydraulic medium in the upper pressure chamber 37 is displaced through the through bore 59 into the pressure line 39, 44. The pressure medium is then fed via the valve 45 to the damping cylinder 13 in order to generate the path-dependent pre-acceleration. The process takes place analogously to that described in FIGS. 1 and 2.

The position of the piston 36 can be positioned with the adjusting device 58 to determine the start of acceleration. In addition, this also adjusts to different tool heights. After the upper tool 8 has been placed on the sheet-metal counterholder 7, which in turn is recognized by the pressure drop by the pressure sensor 55, the distance traveled can again be checked on the travel meter 48. After pre-acceleration, valve 43 is opened and valve 45 is closed. This allows the rest of the drawing process the pressure medium from the upper pressure chamber 37 via the valve 43 into the lower pressure chamber 38 through the through holes 59, 60 in the hydraulic cylinder 33. The required amount of the hydraulic medium for the damping cylinder 13 is removed from the oil container 21. This applies both to the exemplary embodiment according to FIGS. 1 and 4.

In the subsequent upward movement, the process of the device according to FIG. 4 proceeds analogously to that described in FIGS. 1 and 2.

In the press according to the invention with a pulling device according to the figures shown, one or more and in particular two hydraulic cylinders 33 are accordingly arranged laterally in the region of the press ram 9 on the stand 32 of the press, the press ram 9 moving the respective piston rods or the cylinder housing. The hydraulic medium displaced in the cylinder space or pressure space is preferably displaced into a damping cylinder 13 with the aid of a proportional valve 43 in conjunction with position measuring devices 47, 48, as a result of which the pulling device is set in motion before the upper tool 8 hits the sheet metal counterholder 7. The speed of the die cushion is chosen to be lower than that of the press ram; however, it runs analogously and in the same direction as the ram movement. As a result, the upper tool can be placed gently on the sheet metal counterholder according to a predetermined path.

In a special embodiment, one or more hydraulic cylinders 33 are arranged directly on the press ram 9, their piston rods 34 being connected to the stand 32 via adjustment mechanisms 57, 58. The Hydraulic cylinders 33 have special openings 62 in the walls, which are arranged in a triangular shape (see FIG. 5), which are gradually closed by the piston 36 when the press ram 9 drops shortly before the press ram hits the pulling device, as a result of which in the damping cylinders 13 displaced oil volume flow increases more and more and results in an acceleration of the pulling device or the sheet metal counter-holder. The effective area of the sum of the pistons 36 of the hydraulic cylinder 33 is smaller than that of the piston 20 of the damping cylinder 13, so that the press ram 9 catches up with the sheet metal counterholder 7, the speed of which is analogous to the ram speed, in a certain way.

Claims (7)

1. Mechanical or hydraulic press (1) comprising drawing device (2) for drawing operations or drawing stage of a transfer press, wherein the plate holding of a plate counter-holder (7) is clamped by a pressure fluid by means of a draw cushioning device with pressure frame (11), the movement of a pressing plunger (9) being transmitted to a first piston-cylinder unit (33), the pressure fluid of which acts time-dependently and/or displacement-dependently upon a second piston-cylinder unit (13), connected to the pressure frame (11), in the sense of an accelerating downward movement of the draw cushion and thus of the plate counter-holder (7), wherein on account of the selected pressure area ratios, the plunger velocity of the pressing plunger (9) is higher than the draw cushion velocity in the same direction, and wherein, furthermore, the pressure fluid of the first piston-cylinder unit (33) is supplied to the second piston-cylinder unit (13), connected to the draw cushion, in the sense of a defined downward movement of the draw cushion only just before the upper mould (8) meets the counter-holder (7), characterized in that the first piston-cylinder unit (33) is constructed as a double-acting hydraulic cylinder (33) with piston rod (34) extending on both sides of its piston (36), that the upper (37) and lower (38) pressure chambers of the first piston-cylinder unit (33) are connected together via a pressure line (39, 42) or via a bypass line (63), by which, in the downward movement of the pressing plunger (9), a pressure balancing between the upper and lower pressure chambers (37, 38) takes place and that, just before the upper mould (8) meets the plate counter-holder (7), the bypass flow is stopped and the further expelled pressure fluid from the upper pressure chamber (37) of the first piston-cylinder unit (33) is supplied in controlled or positively controlled manner to the second piston-cylinder unit (13) in the sense of a downward acceleration of the associated piston (20) and thus of the draw cushion, so that the upper mould (8) comes down gently onto the plate counter-holder (7) after a previously determined travel distance.
2. Press according to Claim 1, characterized in that the upper (37) and lower (38) pressure chambers of the first piston-cylinder unit (33) are connected via a pressure line (39, 42) with integrated proportional valve (43) connected between them, wherein the displacement of the pressure plunger (9) is preferably detectable by a displacement measuring device (47) and can be supplied to the control of the proportional valve (43).
3. Press according to Claim 1 or 2, characterized in that the upper (37) and lower (38) pressure chambers of the first piston-cylinder unit (33) are connected via a closable bypass line (63), wherein, for the purpose of initiating the prior acceleration of the draw cushion, the upper opening (62) of the bypass line (63) can be closed by the piston (36) of the first piston-cylinder unit (33), so that the hydraulic medium further expelled from the upper pressure chamber (37) can thereafter be supplied to the second piston-cylinder unit (13).
4. Press according to Claim 3, characterized in that the cylinder casing of the first piston-cylinder unit (33) is connected directly to the pressing plunger (9) and the associated piston rod (34) is stationarily fixed in its lower region to the press frame (32), that in the cylinder wall of the hydraulic cylinder (33) an upper (59), a middle (62) and a lower (60) through bore are provided, the middle and lower through bores (62, 60) being connected together by a bypass line (63), and that just before the upper mould (8) meets the plate counter-holder (7) the middle through bore (62) can be closed by the piston (36) of the hydraulic cylinder (33), with the result that the pressure fluid further expelled from the upper pressure chamber (37) can be supplied to the second piston-cylinder unit (13) in the sense of a prior acceleration of the draw cushion (11).
5. Press according to one of Claims 1 to 4, characterized in that the second piston-cylinder unit is constructed as a damping cylinder (13) of known type, which is situated underneath a pneumatic clamping device (12), and the piston (20) of which with piston rod (19'') is in rigid operational connection with the piston rod (19) of the pneumatic clamping device (12) and thus of the draw cushion (11), wherein the annular pressure chamber (46), disposed above the piston (20), of the damping cylinder (13) can be loaded with pressure medium from the hydraulic cylinder (33) in the sense of a downward movement of the piston (20).
6. Press according to one of the preceding Claims, characterized in that two hydraulic cylinders (33) are disposed laterally on the pressing plunger (9), which cylinders are connected hydraulically in parallel by pressure lines (39, 42).
7. Press according to one of the preceding Claims, characterized in that the active surface of the two cylinder units (33) is smaller than the active surface of the damping cylinder (13), in such a manner that the pressing plunger (9) or upper tool (8) catches up the draw cushion (11) or the plate counter-holder (7) respectively, the velocity of which acts in analogous manner to the velocity of the plunger, after a certain distance of travel.

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