Abstract
Provided is a method for pretensioning the membrane of a press, including the following steps: a) providing a press having a first pressing tool, a second pressing tool and a membrane. The first pressing tool and the second pressing tool are movable relative to one another, wherein the membrane is connected to one of the pressing tools. A cavity for a working medium is formed between the membrane and the pressing tool connected thereto. The cavity is sealed by at least one seal which presses onto the membrane with a sealing force; b) providing at least one workpiece, wherein the workpiece includes a matrix and fibres embedded therein; c) inserting the workpiece into the press; d) closing the press; e) subjecting the workpiece to pressure and/or to heat by means of the membrane. A cured shaped part is formed from the workpiece; and f) opening the press and removing the shaped part. In order to ensure as smooth as possible a surface of the membrane, it is proposed that the membrane is already pretensioned before step e). Also presented and described is a press for carrying out this method.
Claims
1-10. (canceled)
11. A method for prestressing the membrane of a press, comprising the following steps: a) providing a press having a first pressing tool, a second pressing tool, and a membrane, wherein the first pressing tool and the second pressing tool can be moved relative to one another, wherein the membrane is connected to one of the pressing tools, wherein a cavity for a working medium is formed between the membrane and the pressing tool connected to it, and wherein the cavity is sealed by at least one seal which presses on the membrane with a sealing force, b) providing at least one workpiece, c) inserting the workpiece into the press, d) closing the press, e) applying pressure and/or temperature to the workpiece by means of the membrane, wherein a hardened moulded part is formed from the workpiece, and f) opening the press and removing the moulded part, wherein the membrane is already prestressed before step e), wherein the sealing force is changed during step e), and the workpiece has a matrix and fibres inserted therein.
12. The method according to claim 1, wherein during step e) the pressure and/or the temperature of the working medium in the cavity are changed.
13. The method according to claim 1, wherein in step e), the pressure of the working medium in the cavity is increased to a maximum pressure in the range between 5 bar and 50 bar, in particular between 15 bar and 30 bar.
14. The method according to claim 1, wherein in step e), the temperature of the working medium in the cavity is increased to a maximum temperature in the range between 300° C. and 500° C., in particular between 350° C. and 410° C.
15. The method according to claim 1, wherein the sealing force is changed during step e) by a device for changing the sealing force, in particular by an actuator acting on the seal.
16. The method according to claim 1, wherein the sealing force is changed depending on the pressure and/or the temperature of the working medium in the cavity.
17. The method according to claim 1, wherein at least one first sealing force and one second sealing force different thereto, in particular a greater sealing force, is set.
18. The method according to claim 1, wherein the membrane is manufactured from metal and preferably has a thickness in the range between 0.05 mm and 0.5 mm, in particular between 0.25 mm and 0.4 mm.
19. A press for carrying out the method according to claim 1, comprising: a first pressing tool, a second pressing tool, and a membrane, wherein the first pressing tool and the second pressing tool can be moved relative to one another, wherein the membrane is connected to one of the pressing tools, wherein a cavity for a working medium is formed between the membrane and the pressing tool connected to it, and wherein the cavity is sealed by at least one seal which presses on the membrane with a sealing force, and wherein at least one device for changing the prestressing of the membrane is provided, wherein at least one device for changing the sealing force of the seal, for example comprising an actuator acting on the seal.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The invention will be explained in more detail below with reference to a drawing which simply represents a preferred exemplary embodiment, in which is shown:
[0037] FIG. 1A: a first configuration of a press for carrying out a method according to the invention in the cross-section in the open position without an inserted workpiece,
[0038] FIG. 1B: the press from FIG. 1A in open position with inserted workpiece,
[0039] FIG. 1C: the press from FIG. 1A in closed position,
[0040] FIG. 2A: a partial area of the press from FIG. 1C in enlarged view,
[0041] FIG. 2B: a partial area of the press from FIG. 1C in enlarged view,
[0042] FIG. 3A: a partial area of a second configuration of a press for carrying out a method according to the invention in enlarged view,
[0043] FIG. 3B: a partial area of a second configuration of a press for carrying out a method according to the invention in an enlarged view, and
[0044] FIG. 4: the sequence of a method according to the invention in schematic representation.
DESCRIPTION OF THE INVENTION
[0045] FIG. 1A shows a first configuration of a press 1 for carrying out a method according to the invention in the cross-section in the open position without an inserted workpiece. The press 1 comprises a first, upper pressing tool 2 and a second, lower pressing tool 3. The two pressing tools 2, 3 can be moved relative to one another, for example in the vertical direction (indicated by arrows in FIG. 1). In addition, the press comprises a membrane 4 which is connected to the upper pressing tool 2. As an alternative to the configuration shown in FIG. 1, the membrane 4 could also be connected to the lower pressing tool 3. A cavity 5 for a working medium, for example oil, is formed between the membrane 4 and the upper pressing tool 2 connected to it. The membrane 4 is manufactured from metal and preferably has a thickness in the range between 0.05 mm and 0.5 mm. The cavity 5 can be filled with the working medium via a channel 6. Bores 7 are provided in both the upper pressing tool 2 and the lower pressing tool 3 through which a heating and/or cooling medium can be guided.
[0046] In the configuration of the press 1 shown in FIG. 1A, a working space 8 is provided in the lower pressing tool 3 in which a workpiece (not shown in FIG. 1A) can be inserted. The two pressing tools 2, 3 have a guide 9 which can for example be formed by a protrusion 9A and a recess 9B, wherein the protrusion 9A can be provided on the lower pressing tool 3 and wherein the recess 9B can be provided on the upper pressing tool 2.
[0047] The membrane 4 is connected to the upper pressing tool 2 in the following manner: The upper pressing tool 2 has a circumferential edge element 10, which is screwed to the upper pressing tool 2 (the screw connection is not represented in FIG. 1A). A gap 11 is formed between the upper pressing tool 2 and its edge element 10 through which the membrane 4 is passed. The gap 11 opens into a hollow space 12 in which a clamping device 13 is provided in which the membrane 4 is clamped. The clamping device 13 is connected to a tension anchor 14, which is led out of the upper pressing tool 2 and the edge element 10 through an opening and is pressed outwards there by a spring 15 supporting itself on the outer surface, whereby the membrane 4 is provided with prestressing. In order to seal the cavity 5, a seal 16 is provided in the gap 11, which allows movement of the membrane 4. A device 17 for changing the sealing force F.sub.D is provided adjoining the seal 16. A device 18 for changing the spring force F.sub.F is provided adjoining the spring 15.
[0048] FIG. 1B shows the press 1 from FIG. 1A in open position with inserted workpiece 19. The areas of the press 1 that have already been described are provided in FIG. 1B with corresponding reference numerals. The difference with the position shown in FIG. 1A is that the workpiece 19 has been inserted into the working space 8 of the lower pressing tool 3.
[0049] FIG. 1C shows the press 1 from FIG. 1A in closed position. The areas of the press 1 that have already been described are also provided in FIG. 1C with corresponding reference numerals. The press 1 has been closed by moving the two pressing tools 2, 3 towards one another. In the position shown in FIG. 1C, pressure and temperature are applied to the workpiece 19. Pressurisation is carried out by guiding a working medium, for example oil, through the channel 6 into the cavity 5, whereby the membrane 4 is pressed in the direction of the workpiece 19. The application of temperature can take place in different ways: One possibility is to heat the working medium guided into the cavity 5 through the channel 6 such that the heat is transferred from the working medium in the cavity 5 through the membrane 4 to the workpiece 19. Conversely, the working medium could be cooled in order to cool the workpiece 19. Alternatively or additionally to this, it can be provided that the bores 7 are flowed through by a heating and/or cooling medium, whereby first the two pressing tools 2, 3 and subsequently also the workpiece 19 can be heated or cooled. As a result of the pressure application, the workpiece 19 is compressed in the position shown in FIG. 1C.
[0050] FIG. 2A and FIG. 2B show a partial area of the press from FIG. 1C in enlarged view. The areas of the press 1 that have already been described are also provided in FIG. 2A and in FIG. 2B with corresponding reference numerals. In FIG. 2A and in FIG. 2B, the clamping and sealing of the membrane 4 are particularly easy to see. The cavity 5 is sealed by the seal 16 arranged in the gap 11 pressing on the membrane 4 with a sealing force F.sub.D1 (FIG. 2A) or F.sub.D2 (FIG. 2B). The sealing force F.sub.D1, F.sub.D2 acts vertically on the surface of the membrane 4, i.e. in FIG. 2A and FIG. 2B approximately in the vertical direction. The size of the sealing force F.sub.D1, F.sub.D2 can be changed by the device 17 for changing the sealing force. This can for example take place in that the device 17 for changing the sealing force has an actuator which presses the seal 16 onto the membrane 4 with greater or lesser force. The sealing force F.sub.D1 represented in FIG. 2A is smaller than the sealing force F.sub.D2 represented in FIG. 2B. For example, FIG. 2A shows the state below a certain temperature limit of the working medium in the cavity 5 (e.g. below 250° C., in particular below 200° C.) and FIG. 2B shows the state above a certain temperature limit of the working medium in cavity 5 (e.g. above 250° C.). A greater sealing force results in a more reliable seal, but restricts the mobility of the membrane 4 (even complete “locking” of the membrane 4). Conversely, a lower sealing force improves the mobility of the membrane 4, but leads to a worse seal and the associated risk of leaks. The size of the sealing force F.sub.D1, F.sub.D2 can therefore be set depending on the process parameters (in particular pressure and temperature in the cavity 5) to an optimum value by the device 17 for changing the sealing force.
[0051] The sealing force F.sub.D1, F.sub.D2 represented in FIG. 2A and FIG. 2B leads to a frictional force F.sub.R1, F.sub.R2 when the membrane 4 moves relative to the seal 16. The frictional force F.sub.R1, F.sub.R2 acts parallel to the surface of the membrane 4, i.e. in FIG. 2A and FIG. 2B approximately in the horizontal direction. In addition, the frictional force F.sub.R1, F.sub.R2 is always opposed to the movement of the membrane 4; since the membrane 4 can expand and contract induced by heat, the frictional force F.sub.R1, F.sub.R2 can thus have different directions (represented by double arrows in FIG. 2A and in FIG. 2B). The size of the frictional force F.sub.R1, F.sub.R2 depends on the size of the sealing force F.sub.D1, F.sub.D2 causing it, often within certain limits there is an approximately linear relationship (the ratio between frictional force and contact pressure is also referred to as the “friction coefficient”). Accordingly, the frictional force F.sub.R1 represented in FIG. 2A is smaller than the frictional force F.sub.R2 represented in FIG. 2B.
[0052] In addition, a spring force F.sub.F1, F.sub.F2 is represented in FIG. 2A and FIG. 2B with which the membrane 4 is prestressed. The spring force F.sub.F1, F.sub.F2 acts parallel to the surface of the membrane 4, i.e. in FIG. 2A and FIG. 2B approximately in the horizontal direction. The size of the spring force F.sub.F1, F.sub.F2 can also be set or changed by means of the device 18 for changing the spring force F.sub.F. The setting or changing of the spring force F.sub.F can for example be achieved by a change in the prestressing of the spring 15. The spring force F.sub.F1 (FIG. 2A) is approximately the same size as the spring force F.sub.F2 (FIG. 2B).
[0053] FIG. 3A and FIG. 3B show a partial area of a second configuration of a press 1′ for carrying out a method according to the invention in an enlarged view. The areas of the press 1′ that have already been described are also provided in FIG. 3A and in FIG. 3B with corresponding reference numerals. The main difference to the previously shown and described press 1 is that the press 1′ shown in FIG. 3A and FIG. 3B, in addition to the first seal 16, has a second seal 16′, which is also arranged in the region of the gap 11 in order to act on the membrane 4 there. The second seal 16′ is also provided with a device 17′ for changing the sealing force F.sub.D with which the sealing force F.sub.D1′, F.sub.D2′ can be changed on the second seal 16′ in the manner already described. The sealing force F.sub.D1′, F.sub.D2′ represented in FIG. 3A and FIG. 3B leads to a frictional force F.sub.R1′, F.sub.R2′ when the membrane 4 moves relative to the seal 16′. The frictional force F.sub.R1′, F.sub.R2′ also acts on the second seal 16′ parallel to the surface of the membrane 4, i.e. in FIG. 3A and FIG. 3B approximately in the horizontal direction. In addition, the frictional force F.sub.R1′, F.sub.R2′ is always opposed to the movement of the membrane 4; since the membrane 4 can expand and contract induced by heat, the frictional force F.sub.R1′, F.sub.R2′ can thus have different directions (represented in FIG. 3A and in FIG. 3B by double arrows). The size of the frictional force F.sub.R1′, F.sub.R2′ depends on the size of the sealing force F.sub.D1, F.sub.D2 causing it, often within certain limits there is an approximately linear relationship (the ratio between frictional force and contact pressure is also referred to as the “friction coefficient”). Accordingly, the frictional force F.sub.R1′ represented in FIG. 3A is smaller than the frictional force F.sub.R2′ represented in FIG. 3B.
[0054] In FIG. 3A and FIG. 3B, a hollow space 20 is also discernible, which is arranged in the gap 11 between the two seals 16, 16′. The hollow space serves to collect working medium escaping from the cavity 5 in the event of a leak of the first seal 16 and to drain it through an outlet 21. In this way, a slight leak of the first seal 16 can be accepted. This makes it possible to set the sealing force F.sub.D1, F.sub.D2 on the first seal 16 so low that the frictional force F.sub.R1, F.sub.R2 occurring there is low and the membrane 4 can move as well as possible relative to the first seal 16, in particular can expand and contract induced by heat. A complete sealing of the press 1′ is then carried out by the second seal 16′, which can also be set due to the pressure difference or the pressure drop between the first seal 16 and the second seal 16′ such that the sealing force F.sub.D1′, F.sub.D2′ occurring there and the frictional force F.sub.R1′, F.sub.R2′ caused thereby are so low that the membrane 4 can also move as well as possible relative to the second seal 16′ and no locking or jamming of the membrane 4 is to be feared.
[0055] FIG. 4 lastly shows the sequence of a method 100 according to the invention in a schematic representation. The method 100 comprises the following steps: 101: Providing a press, 102: Providing a workpiece, 103: Inserting the workpiece, 104: Closing the press, 105: Applying pressure and/or temperature to the workpiece, 106: Opening the press.
LIST OF REFERENCE NUMERALS
[0056] 1, 1′: Press [0057] 2: First (upper) pressing tool [0058] 3: Second (lower) pressing tool [0059] 4: Membrane [0060] 5: Cavity [0061] 6: Channel [0062] 7: Bore [0063] 8: Working space [0064] 9: Guide [0065] 9A: Protrusion [0066] 9B: Recess [0067] 10: Edge element [0068] 11: Gap [0069] 12: Hollow space [0070] 13: Clamping device [0071] 14: Tension anchor [0072] 15: Spring [0073] 16, 16′: Seal [0074] 17, 17′: Device (for changing the sealing force F.sub.D) [0075] 18: Device (for changing the spring force F.sub.F) [0076] 19: Workpiece [0077] 20: Hollow space [0078] 21: Outlet [0079] F.sub.D1, F.sub.D2: Sealing force (of the seal 16) [0080] F.sub.D1′, F.sub.D2′: Sealing force (of the seal 16′) [0081] F.sub.R1, F.sub.R2: Frictional force (of the seal 16) [0082] F.sub.R1′, F.sub.R2′: Frictional force (of the seal 16′) [0083] F.sub.F1, F.sub.F2: Spring force (of the spring 15)
