EP2158982B1 - 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 ,
Such a method and such a device are for example in DE-A-10252625 disclosed.

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 a device 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 counter-holder and / or the ring point 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 cushion pressure P1, the cushion pressure P1 acts on the working space 5 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)

1. Method for controlling the synchronization of piston/cylinder units for counterforce rams and/or vee rings and for reducing pressure peaks during the fineblanking and/or forming of workpieces on a fineblanking and/or stamping press equipped with at least one tool, in which the piston/cylinder unit is subjected to control pressure of a hydraulic fluid and the press ram is driven mechanically or hydraulically, characterized in that first of all the piston/cylinder unit is continuously maintained at a preadjustable cushion pressure (F1) by means of a first accumulator supplied from a low-pressure source and that the piston/cylinder unit is then subjected to a preadjustable displacement pressure (P2) from a connectable high-pressure source, with said pressure being set to a pressure (PU) varying between cushion pressure (P1) and pressure for forming and/or blanking by supplying a separate control oil quantity to a second accumulator via a central control unit, whereby a rise in pressure caused by the impact between the tool and the workpiece is regulated, independently of quantity, from of the pressure (P3) in the second accumulator to a permissible set pressure by discharging a significant part of the pressure pulse into a separate tank, and that the available cushion pressure allows ejection of the workpiece to be synchronized with retraction of the press ram.
2. Method according to claim 1, characterized by the following process steps

   a) Charging the first accumulator during rapid traverse of the plunger to the cushion pressure (P1) corresponding to the clamping force of the workpiece in the die of the tool, which is equal to the ejection force of the counterforce ram;

   b) Charging of the second accumulator operating independently of the first accumulator by means of a separate control oil quantity to the displacement pressure (P3) which must be delivered by the counterforce ram and/or vee ring during forming;

   c) Extension of the counterforce ram with low pressure;

   d) Connection of the hydraulic high-pressure source and charging of the counterforce ram and/or the vee ring to the displacement pressure (P2);

   e) Discharge of the pressure peaks resulting from the impact between the punch and the workpieces to a set pressure defined as being permissible (SP) into the separate tank;

   f) Displacement of the counterforce ram and/or vee ring and pressure relief of the cylinders of the counterforce ram and/or vee ring to the pressure (P1) in accordance with step a);

   g) Synchronized ejection of the counterforce ram on retraction of the press ram, whereby the return speed of the press ram is set to a value that is equal to the ejection speed of the counterforce ram.
3. Method according to claims 1 and 2, characterized in that the pressure (P1) in the first accumulator is adjusted by a proportional pressure valve, which can be programmed by a central control unit.
4. Method according to claims 1 and 2, characterized in that the displacement pressure (P3) in the second accumulator is adjusted by a further proportional valve (Y2) which is pilot-operated by a piston valve (Y4).
5. Method according to claims 1, 2 and 4, characterized in that the set pressure (SP) is adjusted during the impact between the tool and the workpiece by a 4-way piston valve.
6. Method according to claim 5, characterized in that a proportional way valve is used as 4-way piston valve (Y4) to regulate the rise in pressure to the predefined set pressure during the impact between the tool and the workpiece, with the result that the pressure (P3) remains more or less constant.
7. Method according to claim 1, characterized in that the high-pressure hydraulic source is connected by a two-way valve (Y3) once the pressure (P1) has been reached in the first accumulator.
8. Method according to claim 1, characterized in that bladder accumulators are used as accumulators.
9. Device for controlling a piston/cylinder unit for the counterforce ram and vee ring and for reducing pressure peaks during the fineblanking of workpieces for implementation of the method according to claim 1, with a fineblanking or stamping press, which is equipped with at least one tool consisting of an upper section and a lower section, which is allocated at least one piston/cylinder unit of the press for at least one counterforce ram and/or vee ring of the tool in addition to one press ram, and with a hydraulic system connected to the piston/cylinder unit, which comprises an accumulator for the storage of hydraulic fluid, hydraulic lines for the inlet and outlet of the hydraulic fluid to and from the piston/cylinder unit, controllable actuators for opening and closing the hydraulic lines and a control unit for activation of the actuators, whereby the press ram us either incorporated in the hydraulic system or connected to a separate drive system, characterized in that the piston/cylinder unit (1) is connected with a low-pressure source (8) via a first proportional pressure valve (9), which can be programmed by a control unit (12), to a first accumulator (10) for the generation of a cushion pressure (P1) continuously present at the piston/cylinder unit (1), which is specified by the proportional pressure valve (9), via a two-way valve (14) which connects the piston/cylinder unit (1) with a disconnectable high-pressure source (13) for charging of the piston/cylinder unit (1) to a displacement pressure (P2), and that the piston/cylinder unit (1) is connected via a proportional pressure valve (17), pilot-operated to the set pressure (SP) by a 4-way piston valve (16) which can be programmed by a the control unit 12, to a second accumulator (19) for the generation of a displacement pressure (P3) acting on the counterforce ram/vee ring, whereby the 4-way-piston valve (16) is connected to a separate tank (22) for discharge of the pressure peaks resulting from the impact between tool and the workpiece, and that the second accumulator (19) with the available displacement pressure (P2) is connected by the two-way valve (14) so it can be cut in to the piston/cylinder unit (1) subject to cushion pressure (P1), whereby a check valve (11) separates the first accumulator (10) from the high-pressure source (13)
10. Device according to claim 9, characterized in that the accumulators (10;19) are bladder accumulators.

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