EP0586028B1 - Press of making dimensionally stable pressed articles - Google Patents

Abstract

The invention relates to a press for making dimensionally stable stacked pressed articles from a powdered material. The said press has a lower (16) and an upper pressing ram hammer with a basic body (1) which is fixedly supported in the press and in which there are arranged hydraulic annular piston systems (2, 3, 4) which are arranged one above the other. According to the invention, the basic body (1) is formed from a plurality of levels (1a, b, c) which are arranged so as to be situated at a distance from one another, and one above the other, while being fixed with respect to one another, each level containing at least one of the coaxial hydraulic annular piston systems (2, 3, 4). <IMAGE>

Description

The invention relates to a press for producing stepped, dimensionally stable pressed bodies made of powdery material, in particular metal powder, according to the preamble of patent claim 1.

A generic press is described in DE-G 90 12 752.8. This press is equipped with a tool adapter, in which the die and the lower and upper punches for the manufacture of the pressing bodies are installed as an exchangeable unit. The tool adapter has a base body (base plate) which is firmly supported in the press and contains two hydraulic ring piston systems arranged coaxially one above the other. The piston rods of these ring piston systems protrude upwards out of the base plate and slide into one another in a coaxial manner. On the upper end faces, the two piston rods have fastening surfaces for the attachment of two lower punches, which can be moved hydraulically with the annular piston systems. A die holding plate for receiving a die is connected via column guides to a lower coupling plate to form a framework which can be connected to and moved with the lower bear of the press by means of the lower coupling plate.

The upper punch or dies required for the production of pressed bodies are connected to an upper coupling plate which is guided relative to the die holding plate via further column guides and is coupled to the upper bear of the press and can be moved with it. In addition to the two movable lower punches, the tool adapter can have a fixed lower punch supported on the base plate and a central pin which can be moved from the lower bar or from the lower coupling plate.

This known construction can have fixed stops for fixing the press end position of the movable lower punch. However, it is also possible to ensure that the press end position of the movable lower rams is reached only by hydraulic means by means of a corresponding positioning control of the machine control. No further details have been given in DE-G 90 12 752.8 about the hydraulic effort required for this. The ring piston systems for the movement of the lower punches have comparatively large effective piston areas and are therefore able to apply the counter-pressing forces to the pressing forces exerted by the upper punches when there are no fixed stops. Since the large piston areas are practically equivalent to large cylinder volumes and a high hydraulic pressure is required in the press end position, a high-pressure pump unit must be available for the pressure supply, which must have a relatively high delivery capacity if short cycle times (high travel speeds of the lower punches) are guaranteed should. High-pressure pumps with a high delivery rate are very expensive.

The known solution of using annular piston systems for moving the lower punches has the disadvantage that practically no more than two movable lower punches are possible.

The hydraulic connections for the cylinder chambers of the annular piston systems and the attachment of electronic measuring systems, which are necessary for the positioning control, can no longer be realized or can only be implemented with great effort in the case of more than two nested annular piston systems.

This problem does not exist in the press with tool adapter known from DE 31 42 126 C2, since the (for example more than two) movable lower punches are each fastened there on punch carrier plates, each of which can be moved from the base plate via its own hydraulic cylinder pairs. Since the press end positions of the stamp carrier plates are fixed by adjustable fixed stops of the base plate and thus the pressing forces applied by the upper punches are mainly absorbed by these fixed stops, the hydraulic cylinder pairs can be kept relatively small and operated with relatively low pressures. A single hydraulic pump with medium pressure (eg 100 - 120 bar) and medium volume capacity (eg 70 - 80 l / min with additional hydraulic pressure accumulator) is usually sufficient to supply several hydraulic cylinder pairs. Electronic position measuring systems can easily be attached to the stamp carrier plates, which are accessible from the outside. A disadvantage of this type of construction is not only that, because of the space required for the hydraulic cylinder pairs and the required fixed stops, tool adapters with more than three movable lower punches can hardly be realized. In particular, however, it is not possible to work for the molding of the compacts produced in accordance with the, in some cases, more advantageous deduction process, since the lower punches cannot be moved downward because of the fixed stops; instead, the lower punches must inevitably be raised in the sense of the ejection process.

In addition, the stops still have to be set by hand, although the other machine functions can be influenced purely digitally by the CNC control of the machine.

From US 2 608 826 a press for the production of compacts from pulverulent masses is known, in which two lower and upper punches can be moved by pressing technology by double-acting hydraulic cylinder / piston systems designed as ring piston systems. The cylinder / piston systems of the lower punches, like the upper punches, are not only arranged coaxially with one another, but are also nested in pairs, so that the piston rods can be telescoped. Therefore, the inner cylinder piston system must inevitably participate in all movements of the respective outer cylinder piston system and cannot be moved independently of these. The interior cylinder rooms are not freely accessible from the outside. This document also does not consider integrating this hydraulic drive into an exchangeable tool adapter.

The object of the invention is to further develop a generic press in such a way that it also allows the production of more complicated pressing bodies which require more than two movable lower punches, the pressing position of the pressing punches being to be guaranteed without fixed stops solely by means of control technology. The effort required for this should be kept as low as possible.

This object is achieved according to the invention by the characterizing features of patent claim 1. Advantageous further developments of the invention are characterized in the subclaims 2 to 6.

Based on the knowledge that large-volume ring piston systems (large effective piston areas) are able to apply the forces required for the press end position, an essential basic idea of the invention is to dissolve the basic body of the tool adapter, which was previously designed as a monolithic plate, into several individual plates that are rigid are stacked one above the other in the form of individual floors. The individual floors are designed, for example, as individual plates and are firmly supported on one another via spacer blocks. At least one annular piston system is arranged on each floor, each of which can accommodate and move a lower punch. All ring piston systems are arranged coaxially with each other. Due to the distance between the levels, there is sufficient space available to be able to attach the hydraulic connections and the electronic measuring systems. It is possible, as is known from the generic DE-G 90 12 752.8, to accommodate two annular piston systems arranged one above the other on one floor in order to achieve an even more compact design. In order to be able to represent the required holding forces for the final press position well, the hydraulic ring piston systems should be designed for the application of high pressure in the range of at least 200 bar, preferably at least 300 bar. The pressure medium supply for the ring piston systems is preferably designed independently of the pressure medium supply for the hydraulically operated press bears (upper and lower bear). The latter have high-pressure hydraulic pumps with high delivery capacity (eg in a 250t press each 250 l / min at 315 bar) to achieve high driving speeds, so they require relatively expensive units. In a further development of the invention, it is provided that each ring piston system for actuating a lower punch preferably has its own high-pressure pump with a significantly lower delivery line (for example 5-20 l / min), which drastically reduces the costs and simplifies the control, and moreover a common pressure medium source for everyone Ring piston systems available to provide, this pressure medium source can deliver large quantities of hydraulic fluid (eg 250 l / min) at low pressure (eg 20 - 40 bar) in a short time. In general, the volume capacity of the pressure medium source for the low pressure will be at least 5 times, preferably 10 to 20 times the volume capacity of the high pressure supply for the ring piston systems. An appropriately large-volume low-pressure pump is suitable as a low-pressure source, which is combined, if possible, with a hydraulic pressure accumulator for peak demand. In many cases it is also possible to dispense with a high-pressure supply for one of the ring piston systems, since one of the lower punches can often be supplied with sufficient pressing force by the low-pressure system alone.

The fact that the use of high-pressure hydraulic pumps with a high delivery capacity to supply the annular piston systems is dispensed with in the invention is based on the knowledge that the requirements for high volume outputs and high pressures practically do not occur simultaneously within a press cycle: during the phases in which the lower punches have a relatively high pressure Speed should be traversed, i.e. in the initial phase of the compaction process (powder transfer within the mold cavity of the die), when molding the compact and especially when moving to the respective filling position, the forces to be applied by the lower punches are relatively low, so that a low hydraulic pressure is sufficient; On the other hand, in the final phase of the pressing process, ie in the phase in which the actual compression work has to be carried out, and in the final pressing position, only very small amounts of hydraulic fluid are required at high pressure. The invention takes advantage of this fact and achieves that the construction costs for the press remain low and the energy consumption during operation is hardly higher than when using a press with a tool adapter with mechanical fixed stops.

In particular, however, the area of application of the press expands considerably, since the extrusion or ejection process or a combination of both processes can be used to mold the pressed body, so that the requirements of even the most complicated parts can be met. Adjustment work for any fixed stops is completely eliminated, so that the press operation with a CNC control can be done completely in digital form without manual adjustment work. The electronic position measuring systems required for CNC operation can easily be coupled with the ring piston systems. Securing the ring piston systems against twisting is also possible in a simple manner due to the good accessibility.

The invention is described in more detail below with reference to the exemplary embodiment of a press according to the invention with three movable lower punches shown in FIGS. 1 and 2. 1 in the right-hand half of the figure, some of the individual parts shown in the left-hand half of the figure have been omitted or are shown at a different height in accordance with another phase in the pressing cycle.

A base body 1 is exchangeably supported on a receiving device 15 which is firmly connected to the press frame (not shown in more detail in FIG. 1). The base body 1 is made up of three floors 1a, b, c. These each consist of solid plate-shaped bodies which are spaced apart from one another by spacing blocks and which are supported on one another. The levels 1a, b, c of the base body 1 are crossed by at least two columns 10 in corresponding sliding or rolling guides, which connect a die holding plate 9 and a lower coupling plate 11 to form a frame. The die holding plate 9 is equipped with a die 14 which peripherally surrounds the press body 8 to be produced. The lower clutch plate 11 is preferably on the hydraulically operated sub-bears 16 coupled to the press, so that it can move the die holding plate 9 up and down. A further pair of columns 13 is arranged on the upper side of the die-holding plate 9, on which an upper coupling plate 12 is slidably guided. The coupling plate 12 is used for coupling to the upper bears of the press and for receiving one or more upper rams for compressing the pressing body 8. One of three hydraulic ring piston systems 2, 3, 4 is arranged in each of the three levels 1a, b, c. The piston rods of the three ring piston systems 2, 3, 4 are hollow and aligned coaxially with each other. The outside and inside diameters of the piston rods and the sleeve-shaped piston rod extensions 18, 19, 20 placed on them, which are very thick-walled and therefore very stiff, are matched to one another in such a way that the piston rods or their extensions 18, 19, 20 slide are brought together. Due to the distances created between floors 1a, b, c, the hydraulic connections (not shown in FIG. 1) for the annular piston systems 2, 3, 4 and the electronic measuring systems (also not shown) for their positioning can be easily attached, for example by mechanical coupling of displacement sensors to the part of the piston rods led downward from the respective cylinder chamber. By using thick-walled extensions 18, 19, 20 of the piston rods of the annular piston systems 2, 3, 4, it is possible to make the effective overall lengths of the comparatively thin-walled and thus more compressible press rams 5, 6, 7 very short. The press rams 5, 6, 7 are placed on the extensions 18, 19, 20, but could of course also be connected directly to the end faces of the piston rods. To create an axial bore in the pressing body 8, a center pin 17 is provided in a manner known per se, which can be moved hydraulically from the lower coupling plate 11 or from the lower bear 16. The effective piston areas of the ring piston systems 2, 3, 4, in comparison to a construction according to DE 31 42 126 C2 are considerably larger, and the level of the hydraulic pressure applied in the associated cylinder chambers are so matched to the maximum compression forces applied by the upper punches that the moving lower punches 5, 6, 7 are held securely in their final press position can be (position control by the CNC machine control) without the need for any fixed stops. For molding the press body 8 shown in FIG. 1, after removing the die to the level of the outer ram 5, the pressing surface of which is the lowest, the middle ram 6 can optionally be pulled off to the level of the outer ram 5 or can be used to eject the outer and the inner lower punch 5, 7 can be raised synchronously to the level of the middle upper punch 6. The center pin 17 can be pulled off together with the die, for example. Further process variants are easily conceivable by combining process steps of the pull-off and the ejection process. In addition to the three movable lower stamps shown in FIG. 1, a fixed lower stamp could be provided, which would be supported directly on the top floor 1c. This would result in a very advantageous, extremely short overall length for this lower punch. In the construction according to DE 31 42 126 C2, on the other hand, a fixed lower punch inevitably turns out to be extremely long, since it has to be supported on the base plate and passed through all stamp carrier plates.

FIG. 2 shows the hydraulic diagram for the supply of pressure medium to the annular piston systems 2, 3, 4, the circuit for the inner, deepest arranged annular piston system 2 being exemplarily described. A low pressure supply system (for example 40 bar) is provided in the form of a hydraulic pressure accumulator 21 which is protected by a pressure relief valve 22. The low pressure pump for filling of the pressure accumulator 21 is not shown. Hydraulic fluid can be conveyed from the pressure accumulator 21 through the lines 23, 24 and 27 or 28 in a controlled manner through a servo valve 26 into the upper or lower cylinder space of the annular piston system 2. As soon as a higher pressure is required in the pressing cycle, the line 28 is decoupled from the low-pressure supply system and connected to a high-pressure supply system while the valve 26 is in the right switching position. This is provided in the form of a high-pressure pump 30 (for example 315 bar), which is protected by a pressure relief valve 31. The high-pressure pump 30 feeds into a line 34, in which a check valve 32 is installed and which leads to a 3/2-way valve 29. In the right switching position of the valve 29, the line 34 is connected to the line 35, which connects to the line 24 immediately behind a check valve 25. Due to the higher pressure in line 35, the check valve 25 decouples the low-pressure supply system. If the valve 29 is in its left switching position in the manner shown, the line 34 is connected to a line 36 which opens directly into the line 23, so that there is a connection from the high-pressure pump 30 to the pressure accumulator 21 of the low-pressure supply system. In this way, it is possible to temporarily use the high-pressure pump 30 in addition to the low-pressure pump to fill the pressure accumulator 21. Under certain conditions (press cycle, volume output of the high-pressure pump), the use of a low-pressure pump could even be dispensed with entirely if the filling of the pressure accumulator 21 can be guaranteed by the high-pressure pump 30 in an acceptable time.

The two ring piston systems 3 and 4 are connected via line 33, which branches off from line 23, to the low-pressure supply system in a corresponding manner (not in detail shown). As a rule, a separate high-pressure supply system (not shown) is provided for each of the two ring piston systems 3, 4, which can be designed as in the case of the ring piston system 2. As already mentioned above, it could also be advantageous in individual cases to assign two ring piston systems to a common high-pressure supply system; this depends on the amount of high-pressure hydraulic fluid required over time.

example

In the case of a 250t press with a tool adapter with three moving lower punches, when using fixed stops (construction, for example, in accordance with DE 31 42 126 C2), a pressure medium pump of 120 bar operating pressure with a delivery rate of 71 l / min is generally sufficient to supply one To enable press operation with short cycle times if an additional hydraulic pressure accumulator is available to cover the quantitative peak demand for hydraulic fluid. In order to be able to operate a corresponding tool adapter in the embodiment according to the invention with ring piston systems without fixed stops with the same cycle times, a pressure medium supply of, for example, 315 bar operating pressure would have to be available, which is provided by a high-pressure pump with a delivery capacity of 250 l / min in conjunction with an additional hydraulic pressure accumulator would be representable for the peak demand. In a further development of the invention, this pressure medium supply could, however, be easily implemented with a significantly reduced construction effort by a hydraulic pump of only 40 bar operating pressure and a delivery rate of 250 l / min and a hydraulic pressure accumulator for the peak demand if three high-pressure pumps of 315 bar with a Flow rates of only 15 l / min are available. In most cases, even that is enough Use of only two small high-pressure pumps, since usually one of the lower punches can still be held securely in position in the press end position with the low-pressure pump of 40 bar. This possibility of reducing the system outlay in the hydraulic system also leads to corresponding reductions in energy expenditure during operation, so that this is only insignificantly higher than in the case of a construction with fixed stops for the press end position.

Claims (6)

1. A press for the production from pulverulent material of graduated pressed articles (8) which are true to size, with a lower (16) and an upper press ram, with a base body (1) firmly supported in the press, in which at least two coaxially arranged hydraulic ring piston systems (2, 3, 4), independent of each other, are arranged one above the other, the piston rods or piston rod extensions (18, 19, 20) of which are guided in a sliding manner into each other and are able to be equipped in each case with a lower die (5, 6, 7), with a matrix holding plate (9), which is connected to a frame with a lower coupling plate (11) connectable to the lower press ram (16) by columns (10) which cross the base body (1), and with an upper coupling plate (12), connectable to the upper press ram, which coupling plate (12), is guided via further columns (13) in the matrix holding plate (9) and is able to be equipped with one or more upper dies,
   characterised in that
   the base body (1) is formed from a plurality of stages (1a, b, c) arranged at a distance one over the other and rigidly with respect to each other, in which each stage (1a, b, c) contains at least one of the coaxial hydraulic ring piston systems (2, 3, 4).
2. A press according to Claim 1,
   characterised in that
   at least three stages (1a, b, c) are provided, which in each case contain precisely one ring piston system (2, 3, 4).
3. A press according to Claim 1,
   characterised in that
   in at least one stage two ring piston systems are arranged coaxially to each other.
4. A press according to one of Claims 1 to 3,
   characterised in that
   the ring piston systems (2, 3, 4) are designed for an operation with high pressure of at least 200 bar, preferably of at least 300 bar.
5. A press according to one of Claims 1 to 4,
   characterised in that
   a high pressure hydraulic pump unit is associated with each ring piston system (2, 3, 4), the volume performance of which is distinctly less than the volume performance of the high pressure hydraulic units for the hydraulically driven press rams, in particular less than 0.1 to 0.2 times this volume performance, and that the ring piston systems (2, 3, 4) are able to be connected with a common lower pressure supply system , in particular with a hydraulic pressure reservoir, in which this low pressure supply system delivers hydraulic fluid with a pressure which in particular only amounts to up to 40 bar, in which the volume performance amounts to at least 5 times, preferably 10 to 20 times the volume performance of the high pressure hydraulic pump units for the ring piston systems (2, 3, 4).
6. A press according to one of Claims 1 to 5,
   characterised in that
   an electronic distance measurement system is associated with each ring piston system (2, 3, 4) and the press end positions of the press die (5, 6, 7) are met and held by the electronic control of the press only by positioning away without mechanical stops.

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