EP2158982A1 - Method and device for controlling the synchronism of cylinder/piston units and for reducing peak pressure during forming and/or fine blanking in presses - Google Patents

Abstract

The method involves maintaining a cylinder/piston unit (1) at a preadjustable cushion pressure (P1) by an accumulator (10) e.g. bladder accumulator. The unit is subjected to a preadjustable displacement pressure. A rise in pressure in the form of a pressure pulse caused by impact between a tool e.g. punch, and a workpiece is regulated, independently of quantity of control oil, from a displacement pressure (P3) in another accumulator (19) to a permissible set pressure, where available cushion pressure allows synchronization of ejection of the workpiece with retraction of a press ram. An independent claim is also included for an apparatus for controlling a piston/cylinder unit for a counterforce ram or vee ring and for reducing pressure peaks during fineblanking or forming of workpieces on a fineblanking or stamping press.

Description

The invention relates to a method for controlling the synchronization of cylinder / piston units for counter-holder and / or ring teeth and for pressure peak reduction during fine blanking and / or forming of workpieces on a equipped with at least one tool press, wherein the cylinder / piston unit with the control pressure of a hydraulic fluid acted upon and the press ram is driven mechanically or hydraulically.

The invention further relates to a device for controlling a piston / cylinder unit for counter-holder and ring teeth and for pressure peak reduction in the fine blanking of workpieces for carrying out the method with a press, with at least one of Upper part and lower part existing tool is equipped, the at least one piston / cylinder unit of the press for at least one counter-holder and / or serration of the tool and a plunger of the press are assigned, and connected to the piston / cylinder unit hydraulic system having a memory for the storage of Hydraulic fluid, hydraulic lines for supplying and discharging the hydraulic fluid to and from the piston / cylinder unit, controllable control means for opening and closing the hydraulic lines and a control unit for driving the control means, wherein the press ram is either integrated into the hydraulic system or connected to a separate drive system ,

State of the art

As is well known, fine-blanking presses are characterized by the fact that counter-holders and ring teeth function as controlled axes and reach their limits in terms of process technology at high speeds and at high speeds.
The higher the number of cycles and speeds are, the faster the discharge of the high-pressure cylinder / piston units must be carried out, so that due to the quantitative dependence of the discharge process increasingly synonymous between the main ram of the press and the counter-holder and ring-jaw cylinder is impaired ( DE 2148618A1 ).
The occurrence of pressure peaks when punching or cutting on presses is also known. Pressure surges occur, for example, in the so-called cutting stroke, which always occurs when the cutting punch from the workpiece emerges and the resistance of the material suddenly disappears, or on impact of the cutting punch on the clamped between the upper part and lower part of the tool workpiece.

From the prior art, a variety of different solutions are known, which try to cut the cutting by damping ( DE 1 427 403 A . DE 26 21 726 A1 . DE 28 12 973 A1 . DE 31 12 393 C2 . DE 41 25 992 A1 ) to reduce.
From the DE 1 427 403 A1 is a schnittschlagdämpfendes back pressure system in a press, in particular in a hydraulic press, known, which consists of a filled with hydraulic fluid back pressure chamber in at least one of piston and cylinder working unit and at least one associated outflow throttle.
Although this known prior art dampens the pressure surge of the cutting stroke by the counterpressure system and the discharge of the pressure pulse via the throttle point in a tank, but can not detect the pressure surge that reaches the workpiece to values of up to twice the set force upon impact of the cutting punch , This leads to unwanted deformations, loss of quality and increased tool wear on the parts.
The DE 26 21 726 A1 describes a device for preventing the cutting blow on cutting presses with at least one cylinder-piston unit which is arranged between a tool base plate and a press ram with adjustable height of an impact surface for the press ram, wherein the stroke of the piston on the one hand by a provided on the cylinder collar and on the other hand by the end face of the piston opposite inner end wall of the cylinder is limited, and wherein the pressure medium space between the end face of the piston and the end wall of the cylinder in the inlet direction is connected via a check valve with a high-pressure fluid source and in the outlet direction of a pressure relief valve is connected. The pressure limiting valve is provided with a control chamber, which is in communication with the high-pressure fluid source, wherein the pressure in the control chamber via a control line by means of a central pressure control valve adjustable. Also, this known prior art is not suitable to reduce or prevent the pressure surge when hitting punch on the workpiece, so that the disadvantages described above also occur in this known solution.

All of these known solutions for reducing pressure peaks work depending on the quantity, which leads to different speeds, but also as a function of the oil temperature to pressure differences in the cylinder chambers of the cylinder / piston units.

From the DE 23 60 821 A1 is a synchronization control for hydraulic presses with a plurality of plunger and a between the high pressure fluid source and the pressure chambers of the plunger interposed driver known. The primary side of the driver, the working space is fed at a given operating speed of the plunger with a constant flow of uncontrolled working fluid and controlled by a controlled shut-off valve. This known solution is used in particular for forging machines used, which is not transferable to the fine blanking.

task

In this prior art, the present invention seeks to provide a method and apparatus for controlling the synchronism of cylinder / piston units and at least one main tappet and for pressure peak reduction during forming and / or fine blanking for presses, the recoil due to the impact of cutting punch on the workpiece independently derived from the regulation of the working pressure of the hydraulic fluid and the synchronous characteristics of the cylinder / piston units and the main plunger are significantly improved by a constant pressure curve in the hydraulic system even at high cycle times and speeds.

This object is achieved by a method of the type mentioned above with the features of claim 1 and by an apparatus having the features of claim 9.

Advantageous embodiments of the method and the device are the dependent claims.

The method according to the invention is characterized in that initially the cylinder / piston units are constantly kept under a presettable pad pressure by a first pressure accumulator supplied by a low pressure source, and then the cylinder / piston units are switched by a selectable high pressure source under a presettable positive pressure are set, which is set to a varying between padding pressure and pressure for forming and / or cutting pressure by supplying a separate amount of control oil in a second memory via a central control unit, wherein a pressure increase upon impact of tool and workpiece by deriving a substantial part of Pressure pulse is compensated in a separate tank volume independent of the pressure to a permissible target pressure, and that is carried out by the applied cushioning pressure ejection of the workpiece in synchronism with the retraction of the plunger.

According to the method of the invention, the first accumulator is first charged in rapid traverse of the plunger to the upholstery pressure corresponding to the clamping force of the workpiece in the die of the tool, which is equal to the ejector force of the counterholder. This constantly affects the cylinder / piston unit. Subsequently, the cylinder / piston unit is charged by a high pressure source to the displacement pressure, the height of which is predetermined by a proportional pressure valve.
An independent of the first memory second memory is then charged by a separate amount of control oil to a pressure that must apply the counter-holder and / or the ring teeth during forming. The anvil and / or the ring point proceed with the low pressure from the accumulator.
After the counter-holder and / or ratchet has been extended, the hydraulic high-pressure source is switched on and the counter-holder and / or the rag are charged to the displacement pressure.
Once the punch hits the workpiece, the resulting pressure peaks in a separate tank up to a preselected set pressure presumed. The counter-holder and / or the ring point are displaced and the cylinder / piston unit of the counter-holder and / or the ring point relieved to the pad pressure. Upon retraction of the plunger, the synchronous ejection of the counter-holder and / or the annular prong takes place, wherein the return speed of the plunger has a value which is equal to the ejector speed of the counter-holder.
The method according to the invention has the particular advantage that the counter-holder and / or ring-shaped teeth can move synchronously with or against the tappet profile, without causing a break-off or an increase in the force exerted by the piston.
The control is quantity-independent, which leads to more constant pressure profiles even under different conditions. Especially at high displacement pressures and / or long hydraulic lines, the displacement pressure remains stable, ie, despite a decrease in the pressure in the memory, the control pressure in the displacement valve remains constant due to the external control oil supply. The control pressure supply from the separate circuit makes it possible to provide the maximum displacement force for the anvil and / or the ring buffer even at low press force preselection. Another advantage is that the method according to the invention is equally suitable for both hydraulically and mechanically driven presses.

The inventive device is simple and compact and has the great advantage that the cylinder / piston unit is connected to two independent hydraulic circuits. In other words, the cylinder / piston unit is connected on the one hand with a held by a low pressure source under low pressure pad pressure circuit and on the other hand connected to a high-pressure displacement circuit switched. The cushion pressure circuit constantly sets the cylinder / piston unit under a pressure equal to the ejector force of the counter-holder, and the displacement circuit exerts a force on the counter-holder and / or the ring point with a pressure which is substantially constant. The cylinder / piston unit is connected to the low pressure source via a programmable by a control unit first proportional valve to a first memory for generating a predetermined by the proportional valve, constantly applied to the piston / cylinder unit cushioning pressure. The high pressure source is connected to the piston / cylinder unit via a proportional valve pilot operated by the control unit and a second accumulator for generating pressure for the anvil and / or the tine, the proportional directional valve communicating with a separate tank for discharging pressure spikes stands. The second reservoir is connected to a pilot oil pump which delivers hydraulic fluid to the second reservoir to maintain the pressure in the second reservoir constant. By a two-way valve, the cushion pressure circuit or the positive displacement pressure circuit can be switched to the cylinder / piston unit, wherein a check valve separates the cushion pressure circuit from the Verdrängerdruckkreislauf.

The inventive method and the Device according to the invention are characterized by an extensive synchronization of the cylinder / piston units with the plunger of the press, so that high cycle numbers and speeds can be achieved. In addition, the sensitivity to pressure spikes when hitting the tool on the workpiece is massively reduced, so that deformation, quality degradation and tool wear can be significantly minimized even at the higher speeds.

Further advantages and details will become apparent from the following description with reference to the accompanying drawings.

embodiment

The invention will be explained in more detail below using an exemplary embodiment.

It show the

Fig. 1 a schematic representation of the process step "pad pressure",

Fig.2 a schematic representation of the process step "supercharger pressure charging",

Fig. 3 a schematic representation of the "process step fine blanking / forming ,,

Fig. 4 a schematic representation of the process step "displacement at top dead center" and

Fig. 5 a schematic representation of the process step "synchronous ejection".

The Fig. 1 shows the basic structure of the device according to the invention, with which the method according to the invention on a press for forming / fine blanking of parts to be executed. The cylinder / piston unit 1 has, for example, a piston 3 arranged in a counter-holding cylinder 2. The working space 5 of the cylinder / piston unit 1 is connected by a hydraulic line 7 to a low-pressure source 8.
Viewed from the low-pressure source 8, the hydraulic line 7 leads via a proportional pressure valve 9, a first reservoir 10 and a check valve 11 to the cylinder / piston unit 1. The proportional pressure valve 9 is also connected to a central control unit 12, with which the proportional pressure valve 9 to a corresponding pad pressure P1 is programmed. The piston 3 of the counter-holding cylinder 2 of the press, not shown, is in rapid traverse, ie the piston initially moves from bottom dead center UT in the direction of top dead center TDC. Low-pressure source 8, proportional pressure valve 9, memory 10, check valve 11 and the associated hydraulic line 7 form the hydraulic pad pressure circuit A for the cylinder / piston unit first
The working space 5 cylinder / piston unit 1 is also connected to a high-pressure source 13 via a two-way valve 14 through a hydraulic line 15. With the two-way valve 14, the high-pressure source 13 can be switched to the working space 5. The hydraulic line 7 is blocked in this case by the check valve 11, so that the Low pressure source 8 is safely separated from the high pressure source 13.
The hydraulic line 7 leads upstream to a 4-way piston valve 16, for example, proportional directional valve, which pre-controls a second proportional pressure valve 17 to a certain allowable setpoint pressure SP. The proportional pressure valve 17 is connected on the input side via a hydraulic line 18 to a second memory 19, which is supplied by a separate control oil pump 20 with control oil.
On the outlet side, the 4-way piston valve 16 is connected via a hydraulic line 21 to a separate tank 22, which receives the displaced by the pressure peaks hydraulic fluid.
High-pressure source 13, two-way valve 14, 4-way piston valve 16, proportional pressure valve 17, second memory 19 and the associated hydraulic lines 18 form the hydraulic Verdrängerdruckkreislauf B for the cylinder / piston unit. 1
The memories 10 and 19 are designed as bladder memories.

The inventive method runs in the following in Fig. 1 to 4 shown steps as follows.
The plunger of the cylinder / piston unit 1 is located near the bottom dead center and is in rapid traverse. In the first step, the first reservoir 10 is charged via the low-pressure source 8 to a cushioning pressure P1 corresponding to the clamping force of the workpiece, which is equal to the ejector force of the counter-holder.
After the first memory 1 has reached the pad pressure P1, the pile pressure P1 acts on the working space 3 of the counter-holding cylinder and the counter-holder moves under the pending low pressure in the top dead center OT. Simultaneously with the extension of the counter-holder into the top dead center OT, the second reservoir 19 is charged to the displacer pressure P2, which is predetermined via the proportional pressure valve 17. The programming of the proportional pressure valve 17 to different displacement pressures via the central control unit 12th

In the second step, referring to the Fig. 2 the high-pressure hydraulic fluid of the high-pressure source 13 is switched to the working space 3 by switching the two-way valve 14, which is in the closed position in the first step. It begins charging the working chamber 5 to the predetermined by the proportional pressure valve 17 displacement pressure P2. The proportional pressure valve 17 is adjusted by the central control unit 12 accordingly. The anvil is thus under the action of the positive pressure P2. The two-way valve 14 closes by a corresponding command of the control unit 12th

The Fig. 3 schematically illustrates the third step of the method. The two-way valve 14 has separated the high pressure source 13 by switching. In a sense, the positive pressure P2 acting on the anvil is in hydraulic equilibrium with the pressure generated in the second reservoir 19 and may assume values between the cushion pressure and the pressure PU required for forming or fine blanking.
At the beginning of forming or fine blanking, the tool, for example the punch, strikes the workpiece, for example a strip material. When striking creates a pressure peak that can reach values up to twice the set force during forming / cutting. The pressure pulse produced by the pressure peak passes via the hydraulic line 7 to the 4-way piston valve 16, which regulates the pressure pulse to a permissible desired pressure SP and via the hydraulic line 21 into the tank 21. The effect of the resulting pressure peak on the workpiece is thereby reduced. The pressure in the second reservoir 19 is kept substantially constant by supplying a corresponding amount of control oil by means of the control oil pump 20 from a separate control oil source.

As in Fig. 4 is shown, is the plunger of the anvil cylinder 2 of the cylinder / piston unit 1 in the fourth step in the top dead center TDC. The counterpart is displaced.
The discharge of the working space 5 or 6 from the positive pressure P2 is possible only up to the still applied pad pressure P1 from the first memory 10. The cushion pressure P1 thus constantly acts on the working space 5. The cylinder / piston unit 1 behaves like a mechanical spring, so that it can move against or in the direction of the plunger movement.

The fifth process step is in Fig. 5 shown. With the retraction of the plunger of the counter-holder is ejected synchronously by the applied pad pressure P1. In this case, the ejector speed of the counter-holder must be set so that the return speed of the plunger is equal to the ejector speed. The Auswerferkraft must further the holding force of the Workpiece in the die correspond. If the ejector speed is too low, the workpiece moves away from the strip of material because the ejector force is set too low. If, on the other hand, the ejector speed is too high, the workpiece is pressed into the strip and thereby damaged, because the ejector force is set too large. Therefore, for the ejection synchronous with the retraction of the plunger, the precise adjustment of the cushion pressure P1 is of primary importance. This means that the proportional pressure valve 9 must be preset by central control unit 12 accordingly.

The above statements apply equally to the cylinder / piston unit of the ring tine.

LIST OF REFERENCE NUMBERS

Cylinder / piston unit

1

Counter-holder cylinder

2

piston

3

workrooms

5

hydraulic line

7

Low pressure source

8th

Proportional pressure valve in

Padded pressure circuit A

9

First store

10

check valve

11

Central control unit

12

High pressure source

13

Two-way valve

14

hydraulic line

15

4-way piston valve

16

Proportional pressure valve in

Displacement pressure circuit B

17

hydraulic line

18

Second memory

19

Control oil pump

20

hydraulic line

21

tank

22

Cushion pressure circuit

A

Verdrängerdruckkreislauf

B

Top Dead Center

OT

Bottom dead center

UT

cushion pressure

P1

Displacement pressure in the working space 5

P2

Displacer pressure in the second memory

P3

Pressure for forming / fine blanking

PU

set pressure

SP

Claims (10)

Method for controlling the synchronization of cylinder / piston units for counter-holder and / or ring teeth and for pressure peak reduction during fine blanking and / or forming of workpieces on a stocked with at least one tool press, wherein the cylinder / piston unit subjected to the control pressure of a hydraulic fluid and the press ram is mechanically or hydraulically driven, characterized in that first the cylinder / piston unit of a first, supplied by a low pressure source pressure accumulator constantly under a presettable pad pressure (P1) and then the cylinder / piston unit of a switchable high pressure source at a presettable displacement pressure (P2) set to a pressure varying between padding pressure (P1) and pressure for forming and / or cutting (PU) by supplying a separate amount of control oil to a second memory via a central control unit, wherein a resulting pressure on the impact of tool and workpiece pressure increase by deriving a substantial portion of the pressure pulse in a separate tank volume independent of the pressure (P3) in the second memory is corrected to a permissible target pressure, and that by the applied pad pressure ejection of the workpiece synchronously with the Returning the ram is performed. The method of claim 1, characterized by the following steps a) charging the first memory in rapid traverse of the plunger the cushion pressure P1 equal to the clamping force of the workpiece in the die of the tool equal to the ejection force of the counter-holder; b) charging the second accumulator, which is independent of the first accumulator, by means of a separate control oil pump to the displacer pressure (P3) which the counterholder or the annular serration must apply during forming; c) extension of the counter-holder with low pressure; d) connecting the hydraulic high-pressure source and charging the counter-holder or the annular tine to the positive-pressure (P2); e) deriving the pressure peaks arising on impact of the punch on the workpiece in the separate tank except for the setpoint pressure (PS) specified as permissible; f) displacing the counter-holder or ring-shaped teeth and relieving the cylinders of the counter-holder or ring-shaped teeth up to the pressure P1 according to step a); g) synchronous ejection of the counter-holder during retraction of the plunger, wherein the return speed of the plunger is set to a value which is equal to the ejector speed of the counter-holder. Method according to claims 1 and 2, characterized in that the pressure (P1) in the first reservoir is adjusted by a proportional pressure valve programmable by a central control unit. A method according to claim 1 and 2, characterized in that the displacement pressure (P3) in the second memory by another of a piston valve (Y4) pilot-operated proportional valve (Y2) is set. A method according to claim 1, 2 and 4, characterized in that the target pressure (PS) is set when striking the tool on the workpiece by a 4-way piston valve. A method according to claim 5, characterized in that as a 4-piston valve (Y4), a proportional directional control valve is used, which corrects the pressure increase on impact of the tool on the workpiece to the preset target pressure, so that the pressure (P3) remains substantially constant. Method according to Claim 1, characterized in that the high-pressure hydraulic source is switched on by means of a two-way valve (Y3), after which the pressure P1 in the first reservoir is reached. A method according to claim 1, characterized in that are used as memory bladder memory. Apparatus for controlling a piston / cylinder unit for anvil and ring teeth and for pressure peak reduction in the fine blanking of workpieces for carrying out the method according to claim 1, with a fine blanking press, which is equipped with at least one consisting of upper part and lower part tool, the at least one piston / cylinder unit of Press for at least one Associated with the piston / cylinder unit hydraulic system having a memory for storing hydraulic fluid, hydraulic lines for supplying and discharging the hydraulic fluid to and from the piston / cylinder unit, controllable control means for opening and closing the hydraulic lines and a control unit for controlling the control means, wherein the press ram is connected either in the hydraulic system or with a separate drive system, characterized in that the cylinder / piston unit (1) with a low pressure source (8) via a first proportional pressure valve (9) programmable by a control unit (12) to a first accumulator (10) for generating a cushion pressure (P1) applied by the proportional pressure valve (9) and constantly applied to the piston / cylinder unit (1) via a two-way valve ( 14) is connected, the the cylinder / piston unit (1) with a lockable high pressure source (13) for charging the cylinder / piston unit (1) to a positive pressure (P2), and that the piston / cylinder unit (1) via a programmable by the control unit (12), from a 4-way piston valve (16) to proportional pressure (SP) pilot-operated proportional pressure valve (17) with a second memory (19) for generating a counter-ratchet pressure acting (P3) is connected, wherein the 4-way piston valve ( 16) is in communication with a separate tank (22) for discharging pressure peaks resulting from the impact of tool on workpiece, and that the second reservoir (19) with the applied positive pressure (P2) through the two-way valve (14) to the under cushion pressure (P1) standing piston / cylinder unit (1) is connected switchable, wherein a check valve (11) separates the first reservoir (10) from the high pressure source (13). Apparatus according to claim 9, characterized in that the reservoirs (10; 19) are bubble reservoirs.

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