Metal deforming – By application of fluent medium – or energy field – With actuated tool engaging work
Reexamination Certificate
2001-03-23
2003-02-18
Jones, David (Department: 3725)
Metal deforming
By application of fluent medium, or energy field
With actuated tool engaging work
C072S060000, C029S421100
Reexamination Certificate
active
06519992
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of operating a metal forming press in which in a rigid press frame a workpiece is preloaded against a tool by means of a hold-down force, with at least one ram tool applying a ram force in parallel with the hold-down force, and closing cylinder forces being applied opposite to the ram force and the hold-down force, and a water chamber die being formed in the tool, whereby water chamber die forces can act on the workpiece.
BACKGROUND OF THE INVENTION
A metal forming press of the above-described type is already known from German patent application 195 13 444.
Said metal forming press is inter alia characterized by the decisive advantage that for both internal high-pressure metal forming and external high-pressure metal forming it is possible to lock both the ram tool and the hold-down devices and to apply the necessary further metal-forming forces by means of a multitude of closing cylinders. Said closing cylinders can be controlled in a selective way and can act on the most different portions of the workpiece owing to their arrangement. Large forces can thus be applied at short piston travels of the cylinders.
However, it has been found out in the operation of the above-described metal forming press that the necessary hold-down forces cannot be realized or can only be realized in an inadequate manner for specific workpieces.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a method of the above-mentioned type which is simple and can be carried out easily and permits the application of exact hold-down forces and is also applicable to the most different workpieces.
According to the invention this object is achieved by the features of the main claim; the subclaims show further advantageous developments of the invention.
Thus, according to the invention, the disturbing force resulting from the application of the ram force is determined and compensated by a change in the closing cylinder forces.
The method according to the invention is characterized by a number of considerable advantages.
It is possible with the procedure according to the invention to compensate the disturbing force which occurs in the whole system due to the application of the ram force. It has been found that the closing cylinders react at least in part like elastic elements and deform upon application of a ram force and/or a water chamber die force. This deformation, in turn, together with the elasticity of the tool, has the effect that the hold-down forces are changing. These are either higher or lower, depending on the corresponding deformation. As a consequence, the metal forming parameters change, resulting in flaws (excessively strong or weak feed flow of the material of the workpiece).
The above-described problems are avoided by the method of the invention.
In sheet-like workpieces the hold-down force controls the sheet movement and produces a sufficient surface pressure on the tool to seal the water chamber die at the pressures arising. The hold-down force is adapted to the necessary water chamber die pressure, ideally in response to the ram travel, and varies over the whole flange area of the workpiece to compensate for locally different metal forming degrees.
In a metal forming press of the above-described type the pressure prevailing in the water chamber die is initially only a few bar and then rises to a few hundred bar in the finishing shaping process of the workpiece.
According to an advantageous development of the invention, the disturbing force is measured by a change in the hold-down force. It is here possible to use the hold-down cylinders as pressure sensors, so that additional measuring means, such as pressure cells, can be dispensed with. This simplifies the structure of the metal forming press quite considerably. Similarly, in an advantageous development of the invention, the change in the hold-down force can be determined by a change in pressure in the respective hold-down cylinders.
The disturbing force is advantageously compensated by locally different closing cylinder forces. Since in the metal forming press according to the invention the closing cylinders can be arranged in variable order to position the same such that they are adapted to the geometry of the workpiece and the arising forces, it is also possible to act on individual ones of the closing cylinders at different pressures. Thus, according to the invention individual closing cylinders can be acted upon by pressure more strongly than other closing cylinders. The elastic deformation of the tool can be compensated such that the desired hold-down forces are maintained. According to the invention the pressure of individual closing cylinders can thus be changed advantageously in different ways.
For the determination of the necessary parameters and for performing an optimum metal forming process it is particularly advantageous when the sum of the closing cylinder forces is constant for a respective phase of a metal forming process. This means that the sum of the individual closing cylinder forces, i.e. the total closing-cylinder force is distributed over individual control circuits of the individual closing cylinders. The distribution may preferably be in percent, so that a value of 100% is obtained for the total closing-cylinder force. This distribution of the total closing-cylinder force in percent takes into account a hold-down force curve as a reference variable which inter alia depends on the hold-down path and the ram travel and the ram force, respectively. The hold-down force curve is measured via the pressure of the hold-down cylinders, multiplied by the active area. For the individual phases of a metal forming operation deviations from said desired value of the hold-down force or from the predetermined hold-down force curve are then corrected according to a control scheme to be still described. It is thus possible to determine, either empirically or mathematically, both the number of the individual closing cylinders and their control circuits as well as their load carrying capacity in percent. For instance, at the beginning of an optimizing process a uniform load carrying capacity may be assumed. Possible flaws in the tool can thus be compensated or avoided by locally changing the hold-down force. Said local changes in the respective local hold-down forces are effected by changes in the individual closing-cylinder forces. When the individual force of a closing cylinder is increased or decreased, the respective force of the remaining closing cylinders will also change in accordance with the predetermined distribution key in percentage. Such a compensation in percentage is preferably carried out fully automatically within the scope of the present invention.
To achieve an optimum metal-forming result, it may be advantageous that the hold-down force that is respectively optimum in time and location is determined at the beginning and that the change in the closing cylinder forces is varied for maintaining said hold-down force. An optimum curve of the hold-down force at locally very different places can thus be realized by means of the press control.
It is particularly advantageous when for each metal forming process the necessary hold-down forces are divided into individual zone-like areas of the workpiece and determined with respect to their respective value and the individual closing cylinder forces are adapted to the respective areas.
For the determination of the necessary hold-down forces the metal forming operation is preferably divided into individual phases, and the hold-down forces are determined for said phases by means of finite element methods both locally and in time and according to the value. The respective closing cylinder forces can thus be applied to be assigned locally and in time to the hold-down forces.
It is particularly advantageous when the closing cylinder forces are chosen to have a value greater than the closing cylinder forces which are each mathematically predetermined locally and in time.
This yields a closi
Jones David
Shinjyu Global IP Counselors, LLP
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