EP2077167A2 - Method for energy efficient operation of a hydraulic press and an energy efficient and low maintenance press - Google Patents

Abstract

The method involves opening a release valve (9), and discharging a hydraulic medium from a pusher annular cylinder chamber (7) by a displacement unit (15) e.g. motor, for lowering a pusher (1). The valve is closed, and a pusher cylinder chamber (5) is subjected with the medium, after conjunction of the pusher and a drawing cushion (2). Hydraulic pressure in a drawing cushion cylinder chamber and blank holding force of the cushion are simultaneously regulated. The pusher and cushion are moved to a top dead center after finishing metal forming.

Description

The invention relates to a method for energy-saving operation of a hydraulic press according to the preamble of claim 1 and an energy-saving and low-maintenance hydraulic press according to the preamble of claim. 6

Energy-saving processes and production facilities are currently a topic for sales negotiations at the present time and the associated climate discussion and will play a greater role in future with rising energy prices and scarcer raw materials for energy production.

Nevertheless, energy-saving applications and presses have been the subject of patent literature for many years. For example, from the 1980s, the energy-saving drive for flywheel drives in hydraulic presses is from the DE 32 16 563 C1 or the DD 204 067 known. The flywheel drives are becoming energy efficient or power peak avoiding application, preferably continuously charged, wherein the charging times are arranged opposite cyclic to the load times of the press.

With DE 42 18 952 A1 is a hydraulic drive of a press, in particular for a sheet metal forming press has become known, in which the Rückhubzylinderkammer the plunger is connected to a hydraulic machine. It should be emphasized that the hydraulic circuit of the plunger and the plate holder or the lower table are basically separated and a first hydraulic machine is connected with its second output to a hydraulic accumulator. The hydraulic accumulator is charged in an energy-saving way and releases its charged energy when needed during the press play.
The same revealed DE 42 18 953 A1 shows a similar hydraulic drive of a press, wherein the kinetic energy of the downwardly moving plunger is used to support the pump drive, which supplies the pressing cylinder chamber with pressure. It is known to arrange one or more displacement units or hydraulic pumps and to control them differently depending on the needs. The circuit complexity and the necessary open and closed-loop control are very cumbersome and affect the availability of the press. Also here is in the foreground only to avoid the power peaks of energy intake, which is associated with high circuit and plant technical complexity.

Overall, the state of the art lacks an energy-saving application and at the same time simple construction of the entire hydraulic system. The possibility of optimizing a press was supported in the time of departure from machine-controlled to electronically controlled systems unilaterally on other machine elements (pump / motor combinations, power circuits, memory elements), which could be easily integrated control and control technology in a press. In addition, at that time, it was not the overall electricity demand that represented the cost-intensive problem, but the performance peaks consumed by a press during operation.
More recently, the problem of high electricity costs has been added, which has meanwhile significantly increased the price of each piece of work produced. The industry not only demands from the plant manufacturer an energy-saving and low-power plant, but also a low-maintenance and low-cost plant for the production of mass and consumer goods. The global climate and environmental debate has also led to a massive increase in the cost of the necessary hydraulic oil, so that the plant manufacturer is required to extend the maintenance intervals and to minimize the wear of oils as in the auto industry.
Meanwhile, the replacement of hydraulic oil in a hydraulic press quite a significant cost factor. At the same time as small as possible number of switching elements in the hydraulic system with short hydraulic paths (lines) can be realized by pressure gradient in the Hydraulic lines and to minimize the necessary valves. Of course, there are possible advantages such as a favorable noise behavior by avoiding the usual control and regulation mechanisms (valves, throttles, etc.). Particularly throttle valves, which have hitherto taken over the control of the downward movement in terms of acceleration, speed and braking behavior of die cushion or plunger, are characterized by a high noise level but also by the resulting Öllerwärmung. The latter must be broken down again with high energy expenditure. In addition, oil heating and hydraulic throttling are mainly responsible for the tribological wear of the hydraulic medium.

Object of the present invention is to provide a method for energy-saving and low-maintenance operation of a hydraulic press, which is used in a simple manner, the kinetic energy of a plunger of a press during the forming process to provide the blank holder force of the counter-acting die cushion and adjustable to design, wherein the excess kinetic energy can be used during the forming process in an advantageous manner with the least possible load on the hydraulic medium. Next, an independent functioning and usable press is to be created, which is also able to implement the method according to the invention and at the same time an energy-saving and simplified control of the kinetic energy of the plunger and the force of the sheet metal holder allows significantly gentler use of the hydraulic medium, at the same time accompanied by a reduced increase in temperature of the hydraulic medium.

• zur Absenkung des Stößels wird das Freigabeventil geöffnet und das Hydraulikmedium aus dem Stößelringzylinderraum über die Verdrängereinheit abgeführt, welche über eine Momentenkupplung einen Asynchron- oder Gleichstrommotor oder andere geeignete Verbraucher antreibt; nach Zusammentreffen von Stößel und Ziehkissen wird das Freigabeventil geschlossen und der Stößelzylinderraum mit Hydraulikmedium über das Stellventil aus der Hydraulikpumpe beaufschlagt, wobei gleichzeitig die Freigabeventile des Ziehkissens geöffnet und das Hydraulikmedium aus dem Ziehkissenzylinderraum über die Verdrängereinheit abgeführt werden, welche über eine Momentenkupplung einen Asynchron- oder Gleichstrommotor oder andere geeignete Verbraucher antreibt und gleichzeitig wird über Änderung des Schwenkwinkels in der Verdrängereinheit oder über das abgegebene Moment an der Verdrängereinheit der Hydraulikdruck im Ziehkissenzylinderraum und
• damit die Blechhaltekraft geregelt, und nach Abschluss der Umformung werden der Stößel und das Ziehkissen durch die Versorgung über die Hydraulikpumpe wieder in die Ausgangsstellung, dem oberen Umkehrpunkt verfahren.

The solution to the method consists in the course of the following process steps shown, when in the initial position of the plunger and the die cushion are in the upper reversal point:

• to lower the plunger, the release valve is opened and the hydraulic medium discharged from the plunger ring cylinder space via the displacer unit which drives an asynchronous or DC motor or other suitable consumers via a torque clutch; after the ram and die cushion collide, the release valve is closed and the plunger cylinder chamber is acted upon by hydraulic fluid via the control valve from the hydraulic pump, while the release valves of the die cushion are opened and the hydraulic medium is removed from the die cushion cylinder space via the displacer unit, which via an torque clutch is an asynchronous or DC motor or other suitable consumers drives and at the same time is on changing the swivel angle in the displacer unit or on the output torque to the displacer unit, the hydraulic pressure in Ziehkissenzylinderraum and
• so that the sheet holding force regulated, and after completion of the forming of the plunger and the die are moved by the supply via the hydraulic pump back to the starting position, the upper reversal point.

The solution for an independently functioning press and also for a press for carrying out the method is that for lowering the plunger, the plunger ring cylinder space via a release valve with a displacer unit and / or for lowering the die cushion of Ziehkissenzylinderraum via at least one release valve with a displacer unit for Hydraulic medium is connectable,
wherein the displacer unit has a torque coupling to an asynchronous motor, a DC motor or other suitable consumer.

No cited patent literature in the prior art treatise has suggested using the potential energy of the plunger to control the blank holder force with simple and direct introduction of energy into the die cushion via the effluent hydraulic medium with only one displacer unit, either a displacer unit with constant outflow Volume and a corresponding torque control or a displacer unit with variable outflowing volume is used.
This creates the possibility, depending on the displacement unit used to control the speed of the departing plunger or the blank holder force of the counteracting die cushion on a single machine element, the displacer unit, and regulate. This is advantageously done in an energy-saving or -rückgewinnender manner. One goes to a gentle application of the hydraulic medium, which extends the life of the Hydraulic medium significantly extended and avoids an otherwise energy-destroying cooling of the hydraulic medium.

• Es werden keine Drosselelemente im regulären Betrieb der Presse verwendet und eine unnötige Belastung bzw. ein unnötiger tribologischer Verschleiß des Hydraulikmediums wird vermieden.
• Einher gehen eine Verlängerung des möglichen Wartungsintervalls der Presse und eine Verlängerung der Lebensdauer des Hydraulikmediums.
• Die Geschwindigkeit- bzw. Krafteinstellung erfolgt in einfacher Weise durch die Verstellung des Schwenkwinkels bzw. über die Drehzahl der Verdrängereinheit mit konstantem Verdrängungsvolumen,
• es erfolgt eine Verringerung des Energiebedarfs und der Spitzenleistung der Presse und
• eine Verringerung der notwendigen Kühlleistung für das Hydraulikmedium.
• Zusätzlich zu den obigen Punkten erfolgt eine Verringerung der verbrauchten Energie und notwendiger Anlagenkosten je produziertes Werkstück und damit eine Verringerung der Herstellungskosten eines Werkstückes.

Unnecessary friction and heat losses via the hydraulic medium are avoided. This results in a clear overview of the following advantages:

• No throttle elements are used in regular operation of the press and unnecessary stress or unnecessary tribological wear of the hydraulic medium is avoided.
• An extension of the possible maintenance interval of the press and an extension of the service life of the hydraulic medium are included.
• The speed or force adjustment takes place in a simple manner by the adjustment of the swivel angle or via the rotational speed of the displacer unit with a constant displacement volume,
• There is a reduction in energy consumption and the peak performance of the press and
• a reduction of the necessary cooling capacity for the hydraulic medium.
• In addition to the above points, there is a reduction in the consumed energy and necessary equipment costs per produced workpiece and thus a reduction in the manufacturing cost of a workpiece.

The relatively high initial costs for the energy-saving or energy-recovering system components can be as with most amortize energy-saving investments over a short period of time and represent a rather secondary point of view with regard to the decision to invest. In addition, when buying or installing several presses, it is possible to use individual necessary parts of the system (power supply, conversion) by means of corresponding connections by means of several presses.
Even if the amortization costs are still too high for the energy recovery despite rising energy prices, yet other consumers can be driven via the displacer unit and the associated torque coupling in a simple manner, for example, a cooling unit for hydraulic cooling or the like.

The displacer units or hydraulic motors described are gear motors for one or both directions of rotation generally known to the person skilled in the art. In this case, a driven on the shaft gear motor operates as a pump and can generate a torque at the shaft when supplying pressure oil and work in this state as a motor. Axial piston pumps have the ability to adjust the volume from the outside, depending on the setting of the angle more or less hydraulic medium per shaft revolution is promoted or the shaft is driven.

Further advantageous measures and embodiments of the subject matter of the invention will become apparent from the dependent claims and the following description with the drawing.

Show it:

FIG. 1

a known prior art press drive for a press with known control of the kinetic energy of the plunger and the blank holder force by throttling the hydraulic medium in a schematic representation,

FIG. 2

Press drive and press control for a press with control of the plunger kinetic energy and the blank holder force by directing the displaced hydraulic medium through a variable displacement displacer unit with coupled asynchronous motor for energy recovery,

FIG. 3

Press drive and press control for a press with control of the plunger kinetic energy and the blank holder force by routing the displaced hydraulic medium through a constant displacement displaced volume unit and coupled asynchronous motor for energy recovery via a regenerative unit and frequency converters and

FIG. 4

Press drive and press control for a press with control of ram kinetic energy and blankholder force by directing the displaced hydraulic medium through a constant displacement displacer unit and coupled DC motor for energy recovery via a 4-quadrant power converter.

In FIG. 1 the hitherto known state of the art is shown. In conventional hydraulic presses, for example, for metal forming, in a press frame, a movable plunger 1 and a movable, usually designed as a counter-holder movable die cushion 2, arranged. Tappet 1 is operated via a hydraulic cylinder system, which is systematically divided from a plunger cylinder chamber 5, a tappet ring cylinder chamber 7 and the two chambers separating plunger 3. The die cushion 2 is symmetrically constructed from a die cushion piston 4, the Ziehkissenzylinderraum 6 and the Ziehkissenringzylinderraum 8. In order to move the plunger 1, either the plunger cylinder space 5 or the plunger ring cylinder space 7 is acted upon by the hydraulic pump 10 driven by the drive 11 with hydraulic medium. Analogously, the same again applies to the movement of the die cushion 2, wherein usually a separate hydraulic pump 12 is used. It is far not decisive whether each hydraulic pump 10, 12 has its own drive 11 or these are coupled via a drive 11 as shown 11.
Before the start of a forming process, the control valves 18 and 19 and the safety valves 17 are closed. The plunger 1 and the die cushion 2 are both at the upper reversal point and have by their respective mass and the arrangement at the upper reversal point a potential energy.
At the beginning of the forming process, the safety valves 17 and the release valve 9 are opened. The plunger 1 accelerates due to the inherent potential energy and displaces the hydraulic medium from the ram ring cylinder space 7. By a controlled control on Release valve 9 prevents impermissible acceleration of the plunger 1 and limits the downward speed to an appropriate value. By throttling, on the one hand kinetic energy is converted into heat, which in the further course has to be withdrawn again from the hydraulic medium and at the same time ensures high wear on the hydraulic medium. On the other hand, the remaining kinetic energy is simply released into the cooling and treatment tank (not shown) of the hydraulic medium. If the plunger 1 reaches the die cushion 2, a damped deceleration of the plunger 1 can take place and the forming process of the workpiece begins. To neatly fix the workpiece, the hydraulic medium from the Ziehkissenzylinderraum 6 is not abruptly displaced as Blechhaltefunktion, but throttled drained via the drain valve 13. Again, there is a loss of heat and potential energy, the heat in the hydraulic medium must be withdrawn consuming again later by means of cooling.
To further clarify a possible construction of a press, the following control and regulating elements are to be named. The switching valve 31 closes the die cushion cylinder space 6 and the die cushion ring cylinder space 8 for a short time and enables a reduction of the volume flow. The switching valves 32 and 33 conduct volume flow to the cylinder of the die cushion 2 and have safety-related functions. The pressure sensors 34 and 35 detect the prevailing pressure in the cylinder of the plunger 1 and the die cushion 2 and report this to the press control for the initiation of the necessary control and regulation measures during a Press cycle. The pressure limiting valve 38 secures the plunger cylinder space 5 and the pressure limiting valve 36 secures the plunger ring cylinder space 7 from. The pressure relief valve 37 acts after the end of the rapid traverse movement and supports the mass of the plunger. 1

In FIG. 2 Now, a preferred embodiment of a press for metal forming is shown, can be used to save energy at a variable displacement volume.
For this purpose, the outlets of the release valve 9 and the Ziehkissenzylinderraums 6 are connected to a hydraulic displacer unit 15. Again in the starting position, the release valve 9 is opened and the plunger 1 moves in the direction of die cushion 2. The speed of the plunger 1 is adjusted by the adjustment of the pivot angle of the displacer unit 15, which generates a torque in this time. The torque is supplied via a torque coupling 16 to an asynchronous motor 14. As a result of the asynchronous motor 14, either the hydraulic pump 10 is now driven via a torque coupling 16 as required or the existing mechanical energy is converted into electrical energy and fed back into the power grid 24. Of course, a correspondingly controlled combination is possible. When the plunger 1 reaches the die cushion 2, the forming process starts and the plunger is driven by the hydraulic pump 10. The release valve 9 is closed and the asynchronous motor 14 takes, if necessary, electrical energy from the power supply 24 to drive the hydraulic pump 10.

During the forming process, the pressurized hydraulic medium is controlled discharged from the Ziehkissenzylinderraum 4 via the now open release valves 20 and fed to the displacer unit 15, which in turn is used to drive the hydraulic pump 10 or the return of energy into the power grid 24. The blank holder force or the opposing force which exerts the die cushion 2 on the plunger 1 can be controlled and regulated again via the adjustment of the pivoting angle of the displacer unit 15.
The exact arrangement of the circuit valves in the plunger block 26, designed as a steel block (not shown) with the necessary mounting holes or Anflanschflächen for the plunger valves shown in the drawing for plunger control is as follows: The pressure relief valve 27 secures the plunger cylinder chamber 5 and the pressure relief valve 28 secures the ram ring cylinder space 7 from. The pressure relief valve 29 acts after the end of the rapid traverse movement and supports the mass of the plunger 1 from. Outside the ram block 26 währ still mention that on the tappet 1 opposite side, the switching valve 30 closes the Ziehkissenzylinderraum 6 and the Ziehkissenringzylinderraum 8 short if necessary. In this case, the die cushion 2 extends in differential circuit and there is a meaningful reduction of the required volume flow of the hydraulic medium.

In FIG. 3 Now, another preferred embodiment of a press for metal forming is shown, can be used to save energy at a constant displacement volume. In contrast to FIG. 2 now no double torque coupling 16 between displacer unit 15 and hydraulic pump 10 takes place more. Instead, the pump 10 has its own drive 11. For the asynchronous motor 14 is coupled only via the torque coupling 16 with the displacer unit 15 and feeds in lowering the plunger 1 or the die cushion 2, the mechanical energy of the displaced hydraulic medium after conversion via a regenerative unit 22 and a frequency converter 21 in the power grid 24 a.

In FIG. 4 Now, a third preferred embodiment of a press for metal forming is shown, can be used to save energy at a constant displacement volume. In contrast to the preceding embodiments, a DC motor 25 is now used here for converting the mechanical energy, which feeds the energy into the power network 24 via a 4-quadrant current converter 23.

In the Figures 3 and 4 are used as displacement units 15 constant pumps / - motors that regulate the flow rate over the speed. The released kinetic energy is converted into electrical energy and fed back into the electric power grid 24. It is again pointed out that, compared with the known prior art, it should be emphasized that the plunger-side hydraulic circuit (plunger block 26) are connected directly to the draw cushion-side hydraulic circuit via the release valve 9 and an associated hydraulic line. Between the two hydraulic circuits or areas is the Displacer unit 15 is arranged, which can be operated either as a motor or as a pump. Just this direct connection causes in their simplicity and effectiveness, a realization of the aforementioned advantages and avoiding the disadvantages. As already described, the hydraulic press according to the invention can be used for carrying out the method, but it can also be used independently of the prior art without the direct implementation of the method.

List of Reference Numerals: DP1351 EP

1.

tappet

Second

cushion

Third

ram piston

4th

Cushion plunger

5th

Ram cylinder chamber

6th

Die cushion cylinder chamber

7th

Plunger ring cylinder space

8th.

Cushion ring cylinder space

9th

release valve

10th

hydraulic pump

11th

Drive for 10

12th

Hydraulic pump (2)

13th

drain valve

14th

asynchronous

15th

displacement unit

16th

moment coupling

17th

Safety valves (1)

18th

Control valve on

19th

Control valve off

20th

Safety valves (2)

21st

frequency converter

22nd

Feedback unit

23rd

4-quadrant power converter

24th

power grid

25th

DC motor

26th

follower block

27th

Pressure relief valve (for 5)

28th

Pressure relief valve (for 7)

29th

Pressure relief valve (for 1)

30th

switching valve

31st

switching valve

32nd

switching valve

33rd

switching valve

34th

Pressure transducer

35th

Pressure transducer

36th

Pressure relief valve

37th

Pressure relief valve

38th

Pressure relief valve

Claims (10)

A method for energy-saving operation of a hydraulic press with a top in a press frame arranged ram (1) for the forming operation and lower die cushion (2) for applying a blank holder force on the workpiece to be formed with a drive (11) for at least one hydraulic pump (10) for lifting and lowering the plunger (1) and the die cushion (2),
characterized in that in the initial position of the plunger (1) and the die cushion (2) are in the upper reversal point and the following method steps are carried out: 1.1 for lowering the plunger (1), the release valve (9) is opened and the hydraulic medium from the tappet ring cylinder space (7) via the displacer unit (15) dissipated, which via a torque clutch (16) an asynchronous (14) or DC motor (25) or other suitable consumers, 1.2 after collision of plunger (1) and die cushion (2), the release valve (9) is closed and the plunger cylinder space (5) with hydraulic medium via the control valve (19) from the hydraulic pump (10) acted upon 1.3 simultaneously the release valves (20) of the die cushion (2) are opened and the hydraulic medium from the Ziehkissenzylinderraum (6) via the displacer unit (15) dissipated, which via a torque clutch (16) an asynchronous (14) or DC motor (25) or drives other suitable consumers, 1.4 at the same time is controlled by changing the pivot angle in the displacer unit (15) or via the output torque of the displacer unit (15) of the hydraulic pressure in Ziehkissenzylinderraum (6) and thus the Blechhaltekraft, 1.5 after completion of the forming, the plunger (1) and the die cushion (2) are moved back to the starting position, the upper reversal point, by the supply via the hydraulic pump (10). A method according to claim 1, characterized in that the displacer unit (15) drives an asynchronous motor (14) via a torque coupling (16) with a variable displacement volume, which via a torque coupling (16) if required Hydraulic pump (10) drives and otherwise in generator mode electrical energy into the power grid (24) feeds. A method according to claim 1, characterized in that the displacer unit (15) via an instantaneous coupling (16) at constant displacement volume drives an asynchronous motor (14) in the generator operation electrical energy via a regenerative unit (22) and a frequency converter (21) in the power grid (24) feeds A method according to claim 1, characterized in that the displacer unit (15) via a torque coupling (16) at constant displacement volume drives a DC motor (14) in generator mode electrical energy via a 4-quadrant power converter (23) in the power grid (24 ) feeds. A method according to claim 1, characterized in that the displacer unit (15) as a consumer drives a cooling unit for cooling the hydraulic medium. Hydraulic press with an energy-saving and low-maintenance drive with a ram arranged at the top in a press frame (1) for the forming operation and underlying die cushion (2) for applying a blank holder force to the workpiece to be formed with a drive (11) for at least one hydraulic pump (10) for raising and lowering the plunger (1) and the die cushion (2), characterized in that
for lowering the plunger (1), the plunger ring cylinder space (7) via a release valve (9) with a displacer unit (15) and / or
for lowering the die cushion (2), the die cushion cylinder space (6) can be connected via at least one release valve (20) to a displacer unit (15) for the hydraulic medium,
wherein the displacer unit comprises a torque coupling (16) to an asynchronous motor (14), a DC motor (25) or another suitable consumer. Hydraulic press according to claim 6,
characterized in that
the asynchronous motor (14) has a further torque coupling for driving a hydraulic pump (10) and / or an electrically conductive connection to the power supply (24). Hydraulic press according to claim 6,
characterized in that between
Asynchronous motor (14) and power grid (24) a frequency converter (21) and a parallel-connected feedback unit (22) is arranged. Hydraulic press according to claim 6,
characterized in that between the DC motor (25) and the power grid (24), a 4-quadrant power converter (23) is arranged. Hydraulic press according to claim 6,
characterized in that as other suitable consumers a cooling unit or similar heat exchangers are driven.

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