Abstract
A method for production of molded parts, in particular parts consisting of a fiber composite material, is illustrated and described. In order to reduce the load on the membrane, the membrane according to the invention can be slipped past the seal and the membrane can at least in part be slipped past the seal as a result of the expansion force.
Claims
1. A method for manufacturing moulded parts, in particular from fibre composite material, comprising the following steps: a) providing a device comprising: a first pressing tool, a second pressing tool, at least one membrane, and at least one seal, wherein the first pressing tool and the second pressing tool can be moved relative to one another between an open position and a closed position, wherein a working space for a workpiece is formed between the first pressing tool and the second pressing tool, wherein the membrane is arranged at least in sections between the first pressing tool and the second pressing tool, wherein the membrane is arranged at least in sections in the working space, wherein at least one cavity for a working medium is formed between the membrane and the first pressing tool and/or the second pressing tool at least in the closed position, wherein the cavity can be sealed by the seal least in sections at least in the closed position, wherein, in order to seal the cavity, a sealing force (F.sub.D) can be applied to the membrane by means of the seal, and wherein the membrane and the first pressing tool and/or the second pressing tool have different thermal expansion coefficients, b) applying a sealing force (F.sub.D) by means of the seal to the membrane, wherein the cavity is sealed at least in sections by applying the sealing force (F.sub.D) to the membrane, and wherein a frictional force; (F.sub.R) is applied between the membrane and the seal by the sealing force (F.sub.D), c) applying pressure and/or temperature to the membrane, preferably by means of a working medium in the cavity, wherein the membrane extends at least in sections at least in the working space, preferably more strongly than the first pressing tool and/or the second pressing tool, wherein pressure is applied to the membrane, preferably by means of the working medium in the cavity, wherein the pressure counteracts an expansion of the membrane into the cavity and thereby effects an expansion force (F.sub.A) along the membrane surface, and wherein the expansion force (F.sub.A) counteracts the frictional force (F.sub.R) between the membrane and the seal at least adjoining the seal, wherein the membrane can be passed by the seal and in that in step c), the membrane is passed by the seal at least in sections due to the expansion force (F.sub.A).
2. The method for manufacturing moulded parts according to claim 1, wherein step b) and step c) overlap at least in time.
3. The method for manufacturing moulded parts according to claim 1, wherein the expansion force (F.sub.A) is greater than the frictional force (F.sub.R) between the membrane and the seal.
4. The method for manufacturing moulded parts according to claim 1, comprising the following steps, which take place after step a) and preferably before step b) and/or before step c): a1) providing at least one workpiece, a2) inserting the workpiece into the device, in particular into the working space, and a3) moving the first pressing tool and/or the second pressing tool into the closed position.
5. The method for manufacturing moulded parts according to claim 1, wherein the device provided in step a) comprises at least one device for changing the pretension of the membrane.
6. The method for manufacturing moulded parts according to claim 5, comprising the following step, which takes place after step a) and, preferably, before step b) and/or before step c): a4) pretensioning the membrane by means of the device for changing the pretension.
7. The method for manufacturing moulded parts according to claim 6, wherein a pretension force (F.sub.V) is applied to the membrane through the pretensioning of the membrane according to step a4) and, preferably in that the pretension force (F.sub.V), in particular during step b) and/or during step c), is smaller than the frictional force (F.sub.R) between the membrane and the seal.
8. The method for manufacturing moulded parts according to claim 7, wherein during step b) and/or during step c), the pretension force (F.sub.V) applied to the membrane is changed, in particular reduced, by the device for changing the pretension.
9. The method for manufacturing moulded parts according to claim 7, wherein the sum of expansion force (F.sub.A) and pretension force (F.sub.V), in particular during step b) and/or during step c), is greater than the frictional force (F.sub.R) between the membrane and the seal.
10. The method for manufacturing moulded parts according to claim 1, wherein during step b) and/or during step c), the pressure and/or the temperature of the working medium in the cavity are changed.
11. The method for manufacturing moulded parts according to claim 1, wherein the device provided in step a) comprises at least one device for changing the sealing force, preferably adjoining the seal.
12. The method for manufacturing moulded parts according to claim 1, wherein the device provided in step a) comprises at least one second membrane, wherein at least one second cavity for a working medium is formed between the at least second membrane and the first pressing tool and/or the second pressing tool at least in the closed position, wherein, in order to seal the second cavity, a sealing force can be applied to the second membrane by means of at least one second seal, and wherein the second membrane can be passed by the second seal.
13. The method for manufacturing moulded parts according to claim 1, wherein in step b) and/or in step c), the pressure of the working medium located in the cavity is raised at least to 1.2 bar, in particular to 2 bar, and preferably in that in step b) and/or in step c), the pressure of the working medium located in the cavity is raised up to a maximum pressure in the range of between 10 bar and 50 bar, in particular of between 15 bar and 30 bar.
14. The method for manufacturing moulded parts according to claim 1, wherein in step b) and/or in step c), the temperature of the working medium located in the cavity is raised to a maximum temperature in the range of between 280? C. and 500? C., in particular of between 310? C. and 410? C.
15. The method for manufacturing moulded parts according to claim 1, comprising the following step, which takes place after step b) and/or after step c): c) opening the device and removing the workpiece.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] The invention will be explained in greater detail below on the basis of a drawing merely depicting preferred exemplary embodiments, in which is shown:
[0055] FIG. 1A: a first configuration of a device for carrying out a method according to the invention in cross-section in an open position without an inserted workpiece,
[0056] FIG. 1B: the device from FIG. 1A in an open position with an inserted workpiece,
[0057] FIG. 1C: the device from FIG. 1A in a closed position with an inserted workpiece,
[0058] FIG. 2: a partial region of the device from FIG. 1C in enlarged view,
[0059] FIG. 3: a section of the device from FIG. 1C in enlarged view,
[0060] FIG. 4A: a second configuration of a device for carrying out a method according to the invention in cross-section in the open position without an inserted workpiece,
[0061] FIG. 4B: the device from FIG. 4A in an open position with an inserted workpiece,
[0062] FIG. 4C: the device from FIG. 4A in a closed position with an inserted workpiece, and
[0063] FIG. 5: a section of the device from FIG. 4C in enlarged view.
DESCRIPTION OF THE INVENTION
[0064] FIG. 1A shows a first configuration of a device 1 for carrying out a method according to the invention in cross-section in an open position without an inserted workpiece. The device 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. 1A). The two pressing tools 2, 3 can thereby be moved relative to one another between an open position and a closed position. In addition, the press comprises a membrane 4, which is arranged at least in sections between the first pressing tool 2 and the second pressing tool 3. In the present case, the membrane 4 is connected to the first pressing tool 2. As an alternative to the configuration shown in FIG. 1, the membrane 4 could also be connected to the second pressing tool 3. A cavity 5 for a working medium, for example oil, is formed between the membrane 4 and the first pressing tool 2. The membrane 4 is manufactured from metal and preferably has a thickness in the range of between 0.2 mm and 3.5 mm. The cavity 5 can be filled with the working medium via a channel 6. Bores 7 are provided both in the upper pressing tool 2 and the lower pressing tool 3 through which a heating and/or cooling medium can be guided.
[0065] In the configuration of the device 1 shown in FIG. 1A, a working space 8 is formed between the first pressing tool 2 and the second pressing tool 3 into which a workpiece (not shown in FIG. 1A) can be inserted. In the present configuration, the working space 8 comprises in particular a recess 8a in the second pressing tool 3. 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 second pressing tool 3 and wherein the recess 9B can be provided on the first pressing tool 2.
[0066] The membrane 4 is connected to the first pressing tool 2 in the following manner: The first pressing tool 2 has a circumferential edge element 10, which is screwed to the first pressing tool 2 (the screw connection is not represented in FIG. 1A). A gap 11, through which the membrane 4 is guided, is formed between the first pressing tool 2 and its edge element 10. 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 first 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 can be provided with a pretension, in particular a pretension force F.sub.V. In order to seal the cavity 5, a seal 16 is provided in the gap 11, which allows a movement of the membrane 4. The membrane 4 can thus be passed by the seal 16. A device 17 for changing the sealing force is provided adjoining the seal 16. A device for changing the pretension 18 is also provided adjoining the spring 15.
[0067] FIG. 1B shows the device 1 from FIG. 1A in an open position with an inserted workpiece 19. The regions of the device 1, which 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, in particular the recess 8A of the second pressing tool 3.
[0068] FIG. 1C shows the device 1 from FIG. 1A in a closed position. The regions of the device 1, which have already been described, are also provided in FIG. 1C with corresponding reference numerals. The device 1 has been closed by moving the two pressing tools 2, 3 towards one another into the closed position. In the position shown in FIG. 1C, pressure and/or temperature are applied to the workpiece 19. Pressure is applied by a working medium, for example oil, being guided through the channel 6 into the cavity 5, whereby the membrane 4 is pressed in the direction of the workpiece 19. Temperature can be applied in different ways: One possibility is to heat the working medium guided through the channel 6 into the cavity 5 such that the heat is transferred from the working medium located 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 then also the membrane 4 and the workpiece 19 can be heated or cooled. Pressure and/or temperature can be applied to the membrane 4, the first pressing tool 2 and/or the second pressing tool 3 in the same way. As a result of the pressure action, the workpiece 19 is compressed in the position shown in FIG. 1C.
[0069] FIG. 2 shows a partial region of the device 1 from FIG. 1C in enlarged view. The regions of the device 1, which have already been described, are also shown in FIG. 2 with corresponding reference numerals. In FIG. 2A, the clamping and sealing of the membrane 4 are particularly easy to see. The cavity 5 is sealed at least in sections by the seal 16 applying a sealing force F.sub.D to the membrane 4, preferably by the seal 16 pressing on the membrane 4 with the sealing force F D. The sealing force F.sub.D acts perpendicularly on the surface of the membrane 4, i.e. in FIG. 2A approximately in the vertical direction. The size of the sealing force F.sub.D 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 smaller force. A greater sealing force F.sub.D results in a more reliable seal, but restricts the mobility of the membrane 4. Conversely, a smaller sealing force F.sub.D 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.D can therefore be set depending on the process parameters (in particular pressure and/or temperature in the cavity 5) to an optimum value by the device 17 for changing the sealing force.
[0070] The sealing force F.sub.D represented in FIG. 2 leads to a frictional force F.sub.R between the membrane and the seal. The frictional force F.sub.R acts along the membrane surface and thus parallel to the surface of the membrane 4, i.e. in FIG. 2 approximately in the horizontal direction. The frictional force F.sub.R is always directed against the movement of the membrane 4; since the membrane 4 can expand and contract, in particular thermally induced, the frictional force F.sub.R can therefore have different directions (represented by a double arrow in FIG. 2). For example, in the case of an expansion of the membrane 4 in the working space 8, the frictional force F.sub.R counteracts a movement of the membrane 4 out of the working space 8. In the case of a contraction of the membrane 4 in the working space 8, the frictional force F.sub.R counteracts a movement of the membrane 4 into the working space 8. The size of the frictional force F.sub.R depends on the size of the sealing force F.sub.D 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).
[0071] In addition, a pretension force F.sub.V is represented in FIG. 2 with which the membrane 4 is pretensioned. The pretension force F.sub.V acts along the membrane surface and thus parallel to the surface of the membrane 4, i.e. in FIG. 2 approximately in the horizontal direction. The size of the pretension force F.sub.V can also be set or changed, namely by way of the device for changing the pretension 18. The setting or changing of the pretension force F.sub.V can for example be achieved by a change in the pretension of the spring 15.
[0072] FIG. 3 shows a section of the device 1 from FIG. 1C in enlarged view. The two pressing tools 2, 3 are located in the closed position. Pressure and/or temperature are applied to the membrane 4 such that pressure and/or temperature can also be applied to the workpiece 19 by means of the membrane. In order to achieve a uniform application of pressure and/or temperature to the workpiece 19, the membrane 4 should bear substantially continuously against the workpiece 4. However, due to the application of pressure and/or temperature to the membrane 4, there may be an expansion of the membrane 4, in particular thermally induced. The two pressing tools 2, 3 can also expand due to the application of pressure and/or temperature, in particular thermally induced. The expansion of the membrane 4 is usually greater than the expansion of the pressing tools 2, 3. This is due to the fact that the membrane 4 is usually manufactured from a material which has a lower thermal expansion coefficient than the material or materials from which the pressing tools 2, 3 are manufactured. The pressing tools 2, 3 are, for example, manufactured from invar. Due to the expansion of the membrane 4, the membrane surface of the membrane 4 is enlarged and/or the membrane 4 is elongated, whereby there is the danger that the expanding membrane 4 expands into the cavity 5, in particular bulges into the cavity 5. An expansion of the membrane 4 into the cavity 5 is represented in FIG. 3 using dashed lines as an example. An expansion of the membrane 4 into the cavity 5 would have the consequence that the membrane 4 detaches from the workpiece 19, thus no longer bears substantially continuously against the workpiece 19 and pressure and/or temperature cannot be uniformly applied to the workpiece 19 by means of the membrane 4. In order to counteract an expansion of the membrane 4 into the cavity 5, pressure is therefore applied to the membrane 4, in particular by means of the working medium in the cavity 5. This application of pressure can in particular be the previously explained application of pressure and/or temperature to the membrane 4, in particular by means of the working medium in the cavity 5. The pressure applied to the membrane 4 must thereby be at least equal, preferably greater than the pressure with which the membrane 4 expands in the direction of the cavity 5.
[0073] An expansion force F.sub.A is effected along the membrane surface of the membrane 4 by the application of pressure to the membrane 4. The expansion force F.sub.A is thereby preferably effected in that the pressure applied to the membrane 4 is at least partially dissipated along the membrane surface of the membrane 4. By applying pressure to the membrane 4, the membrane 4 is also pressed at least in sections against the workpiece 19 to be machined or manufactured. As a result, the membrane is clamped at least in sections between the workpiece 19 and the pressure applied to the membrane 4 (represented by arrows in FIG. 3). Due to this clamping, the membrane 4 can only expand substantially along the membrane surface of the membrane 4, which also contributes to effecting the expansion force F.sub.A along the membrane surface of the membrane 4.
[0074] In order that the expanding or expanded membrane 4 does not detach from the workpiece 19, but rather bears substantially continuously against the workpiece 19, the surface or the section by which the membrane surface of the membrane 4 has enlarged and/or the membrane 4 has elongated must also be guided out of the working space 8. Otherwise, the membrane could unfold adjoining the pressing tools 2, 3, in particular adjoining the gap 11. In order to lead the membrane 4 out of the working space 8 at least in sections, the membrane 4 must be passed by the seal 16. Passing the membrane 4 by the seal 16 is thereby effected by the expansion force F A, which acts along the membrane surface of the membrane 4. However, the frictional force F.sub.R counteracts the passage of the membrane 4 by the seal 16 and is applied between the membrane 4 and the seal 16 due to the sealing force F D. The expansion force F.sub.A therefore counteracts the frictional force F.sub.R at least adjoining the seal 16. In order for the membrane 4 to pass by the seal 16, the sum of the forces acting along the membrane surface of the membrane 4, which counteract the frictional force F.sub.R between the membrane 4 and the seal 16 and act adjoining the seal 16, must preferably be greater than the frictional force F.sub.R between the membrane 4 and the seal 16. The sum of the forces acting along the membrane surface of the membrane 4, which counteract the frictional force F.sub.R between membrane 4 and seal 16 and act adjoining the seal 16, thereby comprises at least the expansion force F.sub.A adjoining the seal 16. Preferably, the expansion force F.sub.A is greater than the frictional force F.sub.R, then no additional forces are necessary to pass the membrane 4 by the seal 16. In addition, however, the pretension force F.sub.V, which can be applied to the membrane 4 by means of the device for changing the pretension, can also help to pass the membrane 4 by the seal 16. The sum of the expansion force F.sub.A adjoining the seal 16 and the pretension force F v, which acts in the same direction as the expansion force F A, must in this case be greater than the frictional force F.sub.R between the membrane 4 and the seal 16, which acts against the expansion force F A. In order to simplify the passage of the membrane 4 by the seal 16, it can therefore be provided that the sealing force F.sub.D is reduced by the device 17 for changing the sealing force during the application of pressure and/or temperature to the membrane.
[0075] After pressure and/or temperature has been sufficiently applied to the workpiece 19, the two pressing tools 2, 3 can be moved back into the open position, as shown in FIGS. 1A and 1B. The workpiece can then be removed from the device 1.
[0076] FIG. 4A shows a second configuration of a device 1 for carrying out a method according to the invention in cross-section in an open position without an inserted workpiece. The device 1 differs from the device 1 from FIG. 1A to FIG. 3 substantially in that the device 1 comprises a second membrane 4B. However, the functioning of the two devices 1, 1 is basically the same. In the present case, therefore, detail will in particular be given on the differences between the two devices 1, 1.
[0077] The device 1 shown in FIG. 4A 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 between an open position and a closed position, for example in a vertical direction (indicated by arrows in FIG. 4A). In addition, the device 1 comprises a first, upper membrane 4A and a second, lower membrane 4B, wherein the first membrane 4A is connected to the first pressing tool 2 and wherein the second membrane 4B is connected to the second pressing tool 3. A first cavity 5A for a working medium is formed between the first membrane 4A and the first pressing tool 2 connected thereto and a second cavity 5B for a working medium is formed between the second membrane 4B and the second pressing tool 3 connected thereto, wherein the working medium can for example be oil. The membrane 4A, 4B is manufactured from metal and preferably has a thickness in the range of between 0.2 mm and 3.5 mm. The cavities 5A, 5B can each be filled with the working medium via a channel 6. Bores 7 are provided both in the first pressing tool 2 and the second pressing tool 3 through which a heating and/or cooling medium can be guided.
[0078] The device 1 shown in FIG. 4A also has a working space 8 in which a workpiece (not shown in FIG. 4A) can be inserted. The working space 8 extends partially into the first pressing tool 2 and partially into the second pressing tool 3. 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 second pressing tool 3 and wherein the recess 9B can be provided on the first pressing tool 2.
[0079] The first membrane 4A is connected to the first pressing tool 2 in the following manner (the same applies to the second membrane 4B and the second pressing tool 3): the first pressing tool 2 has a gap 11 in its edge region through which the first membrane 4A is guided. The gap 11 opens into a hollow space 12 in which a clamping device 13 is provided into which the first membrane 4A is clamped. The clamping device 13 is connected to a tension anchor 14, which is led out of the first pressing tool 2 through an opening and is pressed outwards there by a spring 15 supporting itself on the outer surface, whereby the first membrane 4A can be provided with pretension, in particular pretension force F.sub.V. Adjoining the spring 15, a device for changing the pretension 18 is also provided by means of which the pretension, in particular the pretension force F v, can be changed. In order to seal the first cavity 5A, a seal 16 is provided in the gap 11, which allows a movement of the first membrane 4A. Adjoining the seal 16, a device 17 for changing the sealing force is also provided.
[0080] FIG. 4B shows the device 1 from FIG. 4A in an open position with an inserted workpiece 19. The regions of the device 1, which have already been described, are provided in FIG. 4B with corresponding reference numerals. The difference with the position shown in FIG. 4A is that the workpiece 19 has been inserted into the working space 8 of the second pressing tool 3. In addition to the workpiece 19, two further workpieces 19A are inserted into the working space 8 of the device 1, wherein the workpieces 19A can for example be already prefabricated reinforcement elements with Z-shaped cross-section (e.g. stringers of an aircraft fuselage). The workpieces 19A should be connected to the workpiece 19 in the subsequent production step. In order to enable a uniform pressure distribution despite the complex geometry of the workpieces 19A, a plurality of cores 20 are inserted into the working space, the shape of which is adapted to the shape of the working space 8 and to the shape of the workpieces 19, 19A.
[0081] FIG. 4C shows the device 1 from FIG. 4A in a closed position. The regions of the device 1, which have already been described, are also provided in FIG. 4C with corresponding reference numerals. The device 1 has been closed by moving the two pressing tools 2, 3 towards one another into the closed position. In the closed position shown in FIG. 4C, pressure and/or temperature are applied to the workpiece 19. The application of pressure and/or temperature takes place according to the approach described in connection with the first configuration of a device 1 for carrying out the method. In the present second embodiment, the two cavities 5A, 5B can be filled with working medium independently of one another, however, the two cavities 5A, 5B are preferably filled uniformly with working medium. Pressure and/or temperature can also be applied to the working medium in the two cavities 5A, 5B and/or the two membranes 4A, 4B independently of one another. Alternatively or additionally, pressure and/or temperature is uniformly applied to the working medium in the two cavities 5A, 5B and/or the two membranes 4A, 4B.
[0082] FIG. 5 shows a section of the device 1 from FIG. 4C in enlarged view. The two pressing tools 2, 3 are located in the closed position. Pressure and/or temperature are applied to the two membranes 4A, 4B so that pressure and/or temperature can also be applied to the workpiece 19 by means of the membranes 4A, 4B. The cavities 5A, 5B are also sealed at least in sections by the seals 16 applying a sealing force F.sub.D to the respective membrane 4A, 4B, preferably by the respective seal 16 pressing on the respective membrane 4A, 4B with a sealing force F.sub.D. The sealing force F.sub.D acts perpendicularly on the surface of the respective membrane 4A, 4B, i.e. in FIG. 5 approximately in the vertical direction. The size of the sealing force F.sub.D can be changed by the respective device 17 for changing the sealing force, wherein each device 17 for changing the sealing force can independently change the respective sealing force F.sub.D.
[0083] However, the devices 17 for changing the sealing force preferably uniformly change the respective sealing force F.sub.D. As already explained for the first configuration of the device 1 for carrying out the method, the respective sealing forces F.sub.D lead to a respective frictional force F.sub.R between the respective membrane 4A, 4B and the respective seal 16. The frictional force F.sub.R thereby acts along the membrane surface of the respective membrane 4A, 4B and thus parallel to the surface of the respective membrane 4A, 4B.
[0084] The problem also arises in this second configuration of the device 1 that due to the application of pressure and/or temperature to the membranes 4A, 4B, this can lead to, in particular thermal expansion of the membranes 4A, 4B. The two pressing tools 2, 3 can also expand through the application of pressure and/or temperature, in particular thermally, wherein the expansion of the membranes 4A, 4B is usually stronger than the expansion of the pressing tools 2, 3. As already explained for the first configuration of the device 1, the respective membrane surfaces of the membranes 4A, 4B are enlarged and/or the membrane 4A, 4B are elongated, whereby there is a danger that the expanding membranes 4A, 4B expand into the respective adjoining cavity 5A, 5B. An expansion of the membranes 4A, 4B into the respective cavity 5A, 5B is represented in FIG. 5 using dashed lines as an example. In order to counteract an expansion of the membranes 4A, 4B into the respective cavity 5A, 5B, in this configuration of the device 1, pressure is also applied to the membranes 4A, 4B, in particular by means of the working medium in the respective cavities 5A, 5B. This application of pressure can in particular be the previously explained application of pressure and/or temperature to the membranes 4A, 4B, in particular by means of the working medium in the respective cavities 5A, 5B. The pressure applied to the membranes 4A, 4B must thereby in each case be at least equal, preferably greater than the pressure with which the respective membrane 4A, 4B expands in the direction of the respective adjoining cavity 5A, 5B. Pressure can thereby in each case be applied to the membranes 4A, 4B independently of one another or uniformly. The application of pressure to the membranes 4A, 4B effects a respective expansion force F.sub.A along the membrane surface of the respective membrane 4A, 4B.
[0085] As already explained for the first configuration of the device 1, the respective membrane 4A, 4B can pass by the seal counter to the respective frictional force F R due to the expansion force F A. The sum of the forces acting along the membrane surface of the respective membrane 4A, 4B, which counteract the respective frictional force F.sub.R between the respective membrane 4A, 4B and the respective seal 16 and act adjoining the respective seal 16, must preferably be greater than the respective frictional force F.sub.R between the respective membrane 4A, 4B and the respective seal 16. In the present case, it can be provided that this sum of the forces per membrane 4A, 4B can be different or equal in size. In addition, the expansion force F.sub.A adjoining the respective seal per membrane 4A, 4B can be different or equal in size. The pretension force F.sub.V, which can be applied to the respective membrane 4A, 4B by means of the respective devices for changing the pretension 18 and which acts in the same direction as the respective expansion force F.sub.A, per membrane 4A, 4B, can also be different or equal in size. The sum of the expansion force F.sub.A adjoining the seal 16 and the pretension force F.sub.V, which acts in the same direction as the expansion force F.sub.A, can also be different or equal in size per membrane 4A, 4B. Similarly, the change in the sealing force F.sub.D can take place independently of one another or uniformly by the devices 17 for changing the sealing force per membrane 4A, 4B.
LIST OF REFERENCE NUMERALS
[0086] 1, 1: Device [0087] 2, 2: First (upper) pressing tool [0088] 3, 3: Second (lower) pressing tool [0089] 4, 4A, 4B: Membrane [0090] 5, 5A, 5B: Cavity [0091] 6, 6: Channel [0092] 7, 7: Bore [0093] 8, 8: Working space [0094] 8A: Recess [0095] 9, 9: Guide [0096] 9A, 9A Protrusion [0097] 9B, 9B Recess [0098] 10: Edge element [0099] 11, 11: Gap [0100] 12, 12: Hollow space [0101] 13, 13: Clamping device [0102] 14, 14: Tension anchor [0103] 15, 15: Spring [0104] 16, 16: Seal [0105] 17, 17: Device for changing the sealing force [0106] 18, 18: Device for changing the pretension [0107] 19, 19, 19A: Workpiece [0108] 20: Core [0109] F.sub.A: Expansion force [0110] F.sub.D: Sealing force [0111] F.sub.R: Frictional force [0112] F.sub.V: Pretension force
