Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Reexamination Certificate
1999-07-14
2002-04-16
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
C060S419000
Reexamination Certificate
active
06370873
ABSTRACT:
this application claims the benefit of German Application No. 198 31 624.0, filed in Germany on Jul. 15, 1998.
FIELD OF THE INVENTION
The present invention relates to a hydraulic drive for a press, and more particularly, to a hydraulic drive using a hydraulic transformed.
DISCUSSION OF THE RELATED ART
Depending on the type of drive, a distinction is made between mechanical and hydraulic presses. In so-called progressive or transfer presses, the workpiece is produced by a plurality of working operations. The shaping of upper tool and lower tool in the respective stage determines the progress of the machining operation. The same applies to so-called progressive presses for large parts, in which tool size and transport steps generally turn out to be larger than in normal progressive or transfer presses. All the ram movements are effected in a synchronized manner from a central main drive via a press drive mechanism located in the head piece of the press. In this case, the longitudinal and/or transverse movements, controlled via cam mechanisms, and any stroke movements of the transport device for the workpiece transport are derived from the main drive and are thus synchronized with the ram movement. As a result, the movements of such progressive or transfer presses or presses for large parts are geometrically fixed with regard to the forming path within the stage and with regard to the transport operation between the stages. Such presses are designed, for example, as eccentric or crank presses. The kinematics of the slider-crank mechanism determine the movement of the working ram, the respective crank angle determining the forming force. In this case, the energy is obtained from a flywheel, which drives the crankshaft. Furthermore, the ram speed is directly related to the crank angle, and a rigid process sequence is thus obtained. Mechanical presses have a high efficiency and may be operated with a high stroke rate, since only as much energy as required for the press movement and the operating cycle is removed from the flywheel.
Hydraulically actuated presses work according to the hydrostatic principle with a uniform propagation of pressure in a fluid, the pressure producing a force on a piston area of a cylinder/piston system, this force being proportional to the pressure. As a result, a hydraulically driven ram can develop a force up to the level of the rated force of the press at any point of the ram stroke and thus independently of the tool position. Hydraulic presses are therefore preferred in those fields of metal-forming technology in which the force has to be constant along the ram path or has to be controlled due to the process and also where a large forming path is necessary.
The drive of the cylinder/piston systems of hydraulic presses and thus the drive of the ram movement are effected either directly by fixed-displacement pumps (gear or screw pumps) or, in larger machines, by adjustable axial—or radial-piston pumps. In the process, operating pressures of, for example, 200-300 bar are produced.
The drive of a hydraulic press with accumulator drive is unlike such a direct pump drive. The pump in the direct drive acts directly on the cylinder/piston system during each operating cycle, whereas the pump in the pressure-accumulator drive pressurizes a high-pressure accumulator, from which the working cylinder is then fed with rated pressure via a proportional valve or servo valve. In the direct pump drive, therefore, the pump and the drive motor must be designed for the greatest instantaneous power requirement of the press. Via an adjustment of the delivery quantity of the high-pressure pump, the ram speed is thus usually infinitely variable. In contrast, the speed of the ram in the pressure-accumulator drive is only influenced indirectly by the pump output, so that the pump output may be designed for an average energy requirement and may thus be of smaller proportions. The energy capability in the accumulator drive is then limited to the energy stored in the high-pressure accumulator for these reasons hydraulic presses can be used more flexibly in their mode of operation than mechanical presses.
It is also possible, and known per se, to reproduce the motion and force characteristic of a mechanical press on a hydraulic press. This possibility is utilized when, during a planned changeover in production, other parts or new parts are to be produced on a press for large parts.
To incorporate and optimize these tools for use on a press for large parts, and a hydraulic press on which the individual forming stages of the press for large parts are simulated is then used.
The considerably more expensive press for large parts is thus not blocked by the coordination of tool sets and is thus fully available for the production process.
On account of the tool sets optimized in the hydraulic press, the press for large parts, after tool change has been effected, can continue the production without considerable interruption.
The applicability of such known simulation presses is very restricted on account of the mode of operation. The hydraulic pressure accumulators always have to be charged to the maximum potential of the rated pressure and deliver this maximum pressure during every operating cycle. Excess energy is dissipated via chokes, which leads to a high energy loss. The accumulators must always be re-charged to rated pressure, which has an adverse effect on the efficiency. The stroke rate, at, for example, 1-2 strokes/min, also turns out to be very low in such simulation presses, so that they are more likely to work inefficiently. However, this is not of importance for pure simulation operation, i.e. for a trial phase.
SUMMARY OF THE INVENTION
The object of the invention is to extend the range of use of such hydraulic simulation presses. In particular, such that a hydraulic simulation press may also be used for pilot lots or small lots. At the same time, the efficiency is to be substantially improved.
This object is achieved by the features of the claimed invention.
The basic idea underlying the invention is that a conventional hydraulic simulation press is constructionally extended by virtue of the fact that a certain production operation for the production of pilot lots or small lots is also possible with this press. This is done by supplementing the conventional hydraulic press with a type of “hydraulic transformer”, by means of which the mode of operation can be changed from a simulation operation to a production operation without problem. In this case, the so-called “hydraulic transformer” is formed by an arrangement of several hydraulic devices adjustable in angular travel, as known in principle as so-called hydraulic motors and hydraulic pumps. To this end, reference is made, for example, to DE 44 29 782 A1 of the applicant, in which a corresponding arrangement of hydraulic devices, adjustable in angular travel, for the drive of a cylinder/piston unit is shown. By means of such devices, a hydraulic press can be changed over from a simulation operation to a production operation. In this case, the so-called hydraulic transformer is switched off during the simulation operation and is switched on during the production operation. The ram speed can be reduced during the production operation to, for example, 30-60 mm/sec, depending on the size of the transformer, 4-6 strokes/min permitting a higher output of parts. By the additional connection of the hydraulic transformer, the efficiency is increased to 60-75%, in which case working strokes of about 150 mm at an overall stroke of about 700 mm can be set without problem. The cycle times are in the order of magnitude of <10 seconds. In accordance with this data, pilot lots or small lots can therefore be run efficiently, so that such a hydraulic press is given substantially extended applicability. This leads to a considerably enlarged range of use of such special presses. It may be used both as a simulation press for setting-up work, e.g. of a press for large parts, and as a production press for small lots.
REFERENCES:
patent: 402
Beyer Joachim
Schaich Guenther
Leslie Michael
Look Edward K.
Morgan & Lewis & Bockius, LLP
Mueller-Weingarten AG
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