Patent Application
20060117826
The present invention relates to a press of pressure cell type and a method in such a press. The invention further relates to a tray device.
A press of pressure cell type generally comprises a force-absorbing press body defining a press chamber. In the upper part of the press chamber, a press plate and a diaphragm of rubber or another resilient material are arranged, which together form a pressure cell. The pressure cell communicates with a source of pressure and expands when a pressure medium is supplied. In the lower part of the press chamber, a structural support or a tray is usually arranged, which comprises a bottom plate having a tray frame. The tray supports a forming tool, a workpiece or blank to be machined, and, generally, a mat of rubber or another resilient material covering the forming tool and the blank.
Presses of pressure cell type are used, among other things, when forming sheet-shaped blanks or workpieces, for example sheets of steel or aluminium, to short-series products within the aerospace and automotive industries. The sheet is placed in the press in such manner that one of its sides faces a forming tool. The resilient diaphragm is arranged on the other side of the sheet. A closed space between the diaphragm and the press plate located above the diaphragm constitutes the pressure cell and this space is filled during the forming process with a pressure medium. By pumping additional pressure medium into the pressure cell, the pressure is increased in the pressure cell and the resilient diaphragm is pressed during stretching against the sheet which, in its turn, is formed round or in the forming tool. When the sheet completely fits to the forming tool, the pressure in the pressure cell is released and the diaphragm is removed, following which the formed component can be taken out of the press. It is often desirable to obtain an efficient handling of the production flow and, thus, short cycle times.
One object of the present invention is to provide more efficient operation of a press of pressure cell type.
Another object of the invention is to provide a simple method of operating a press of pressure cell type.
These and other objects, which will be evident from the following description, are achieved by means of a press of pressure cell type and a method, which have the features indicated in the appended claims.
According to one aspect of the invention, a method is provided in a press of pressure cell type comprising a forming tool and, separated therefrom, a diaphragm, which define a forming space in which a blank is inserted for forming thereof against the forming tool by pressing the diaphragm against the blank. According to the method, a blank portion projecting from the forming space is gripped by means of at least one gripping device, and the connection between the blank and the gripping device is shielded from the diaphragm at least when the diaphragm is pressed against the blank.
Thus, the present invention is based on the understanding that the operation of a press of pressure cell type can be rendered more effective compared with existing forming methods by using at least one further measure in the form of shielding the connection between the blank and the gripping device. Incorporating such an additional measure is contrary to the general approach according to which the elimination of measures is what makes the operation less time-consuming and more efficient. Surprisingly, however, it has been found that providing shielding according to the method of the invention may result in an overall saving of time. One reason for this is that, during repeated pressing operations, the diaphragm, even when protected from below by a mat, risks being damaged or worn progressively as it comes in contact with edges and penetrates into slots, thus requiring a time-consuming operation to replace the diaphragm to be carried out. By shielding the connection between the blank and the gripping device, the diaphragm cannot extend to said connection and, thus, does not risk being damaged. Moreover, as will be described below, shielding can be achieved essentially simultaneously with at least one other measure.
According to a further aspect of the present invention, a press of pressure cell type is provided. At least one gripping device is arranged to grip a blank portion projecting from the forming space, and shielding means are arranged to shield the connection between the blank and the gripping device from the diaphragm at least when the diaphragm is pressed against the blank. As will be described below, said shielding means can be effectively incorporated into the press.
In the present application, forming space means the space in which a blank is to be formed between the diaphragm and the forming tool. The connection between the sheet and the gripping device forms the border area in which the sheet enters the gripping device.
It may be appropriate, in particular when forming a sheet-metal blank, to stretch the blank beyond its yield point to obtain a plastic deformation thereof. This is achieved, for example, by arranging the blank between two gripping devices and stretching it by means of said devices before the diaphragm is allowed to press against the blank. Consequently, the blank has one connection to a gripping device and another connection, for example in a second end portion of the blank, to another gripping device. If the distance between these two connections is increased after the blank has been gripped, the blank will be stretched. It should be noted that to stretch the blank it is enough to displace one of the connections, for instance by causing one of the gripping devices to move. According to at least one embodiment of the invention, the stretching operation is carried out essentially simultaneously with the shielding. According to at least one further embodiment of the invention, the connection is shielded after stretching, but before the diaphragm is pressed against or enters into contact with the blank.
Shielding can be achieved, after the blank has been stretched, if applicable, for example by moving two shielding members, one on each side of the blank, towards each other and applying a compressive force to the shielding members in said direction. The compressive force has to be large enough to obtain a sufficiently tight abutment between the shielding members and the blank, i.e. a seal that will resist the pressure of the diaphragm and prevent the diaphragm from extending between the shielding members and the blank to said connection. The shielding members can be brought together even if it is desirable to stretch the blank, as long as they do not prevent the blank from being stretched. For example, they could abut against the blank without any compressive force having yet been applied thereon. Alternatively, the shielding members can be designed, as will be described below, in such manner that it is possible to stretch the blank even if the compressive force is applied.
It should be noted that unlike clamps, pinches or other forms of gripping devices, which are susceptible of receiving both a blank and a diaphragm, the variant of the shielding member described above may be influenced by an applied compressive force, which ensures that the gripping device receives the blank only. As will be shown, even the diaphragm itself may contribute to the application of said force. The compressive force is maintained until there is no longer any risk of the diaphragm penetrating in the connection between the blank and the gripping device.
A lower shielding member is conveniently arranged on the tray bottom, for example adjacent the forming tool, and the blank is then placed above said member and gripped by means of the gripping device and stretched, if applicable. An upper shielding member is lowered and, suitably, pressed against the lower shielding member and the intermediate blank. The compressive force is achieved, for example, by means of hydraulic pistons. In this case, the shielding members, or at least portions thereof, are preferably situated in front of the connection between the blank and the gripping device, i.e. between the connection and the forming tool.
The operation of bringing together the shielding members as described above can also be used in connection with the actual gripping of the blank, thus resulting in a more efficient and time-saving operation. By bringing together not only the shielding members, but simultaneously an upper part and a lower part of the gripping device, the blank can be fixed during this motion.
For instance, fixing can be achieved with the aid of force-exerting means, such as hydraulic pistons. A force is applied to at least one of the shielding members, on both sides of the horizontal extent of the blank and/or gripping device transversely to the stretching direction, said force being directed towards the other shielding member. These forces, which are thus-applied along the periphery of the shielding members, located outside the blank and/or the gripping device in the stretching plane, exert a pressure on the gripping device in such manner that the blank is fixed by said gripping device.
Preferably, the upper shielding member is bent in such manner that its central portion is located vertically lower than peripheral portions to which said forces are applied. When the forces are applied, the upper shielding member is straightened and an evenly distributed pressure will be exerted on the gripping device below.
Suitably, the two shielding members are sufficiently separated in front of the connection of the blank to allow the blank to be stretched, i.e. there is a gap between the front portions of the shielding members that are not in contact with the gripping device. During the actual pressing of the diaphragm, the press load will close the gap enough to prevent the diaphragm from penetrating through it. Preferably, the diaphragm itself is used in this operation by exerting a pressure, during its expansion, on the upper shielding member to reduce the gap.
The upper part of the gripping device is suitably connected to an upper shielding member, so that they are lowered together onto the blank once the blank has been arranged on the lower part of the gripping device. Similarly, the upper part of the gripping device can preferably be lifted together with the upper shielding member, thus allowing quick and easy release of a finished blank.
Preferably, the shielding members are designed in such manner that they, when brought together, enclose the gripping device from above and from below, thus creating a space for the gripping device. Suitably, the space is large enough to allow the gripping device to be moved so that a blank fixed therein can be stretched. The gripping device is suitably moved radially outwards from the forming space. Owing to this encapsulation, the moving parts of the gripping device are thus relatively well protected from other elements also during stretching and, in particular, when the compressive force is applied to the shielding members. Moreover, the encapsulation allows the gripping device to be moved without a gap or a space being formed in which a diaphragm could penetrate.
The upper and the lower shielding member preferably have displacement surfaces, such as sliding surfaces on which respectively the upper and the lower part of the gripping device are slidable. A displacement surface can be achieved in various ways, for example by means of plane surfaces, grooves, ball bearings, etc.
When the gripping device is displaced in the space formed by the shielding member, the upper and the lower part are preferably interconnected and, thus, simultaneously displaced. The interconnection can be achieved, for example, by one of the parts having a bead or boss which fits in a hollow or dent in the other part. If the upper and the lower part of the gripping device are interconnected in the assembled position, then only one of them has to be subjected to a moving force, for example in the form of an external pulling device.
Preferably, a fixed stop is provided in or at said formed space, so that the gripping device cannot be displaced any further than this stop. Such a fixed stop ensures satisfactory repeatability and thereby allows blanks to be equally stretched even if they are stretched at different moments.
According to at least one embodiment of the invention, the forming tool is arranged in a tray device provided in a press, which tray device can be divided into an upper and a lower tray part, the blank being gripped by the upper and the lower tray part being brought together. Suitably, the shielding members are also brought together in connection with such a movement of the tray parts. In this case, the upper shielding member is connected to the upper part of the tray device to allow them to be lifted and/or lowered together.
An upper tray part can comprise, for example, part of a tray side, such as a beam which can be lifted from the rest of the tray. Suitably, two different side beams are liftable, for instance one from either longitudinal side of a tray. The upper shielding member is then connected to these side beams and extends between them. If the short side forms an indivisible piece, or even an integrated portion of said remaining part of the tray, such a short side is provided with a through hole through which the gripping device is accessible to an external pulling device to allow the blank to be stretched.
Instead of lifting only side beams of the tray, a whole annular part of the tray may be liftable and lowerable. Consequently, according to at least one embodiment of the invention, the tray device comprises a tray plate and a tray frame, said tray frame being annularly divisible into at least one upper frame part and one lower frame part. Annularly divisible here means that the parts are annular in cross section, i.e. they have the shape of a closed path around a central hollow space. An annular shape can be, circular, elliptic, straight long sides to semi-circular short sides, etc. Suitably, the upper shielding member is connected to the upper frame part to allow them to be lifted and/or lowered together. Moreover, the blank is preferably clamped or gripped in a corresponding manner. When the upper frame part has been lifted, thus exposing the lower tray part on which the lower part of the gripping device is arranged, an outer portion of the blank is arranged thereon. Then, as the upper frame part is lowered together with the upper part of the gripping device connected thereto, the upper and the lower part of the gripping device will fix the blank between them. At the same time, the entire tray frame is reassembled by the frame parts having been brought together.
When the pressing operation has been completed, the upper and the lower tray part are preferably separated by displacing said parts in relation to one another along the common centre axis direction of the parts, so that a space is formed between them. For instance, an upper frame part is lifted from a lower frame part, so that a processed blank is accessible for removal thereof, and so that, after removal of the processed blank, a new blank can be arranged in the tray device. An alternative to a straight lifting motion can be a turning motion, or a motion similar to opening a hatch, more or less corresponding to the motion of a trouser press.
It will be apparent from the above that a divisible tray device allows rapid fitting of a new blank, and also rapid removal of a finished blank, while at the same time the actual gripping of the blank is achieved in a simple manner. In addition, the displacement of the shielding members can be used advantageously in combination with the divisible tray device.
An efficient process is obtained if the tray device is taken out of the press before it is separated into said parts. A second tray device, in which a blank has already been fitted, can be simultaneously inserted in the press to be formed therein. While said blank is being formed in the press, the finished blank is removed from the tray device that has been taken out and replaced by a new, unprocessed blank. The separated parts of the tray device located outside the press are then brought together so that the device is ready for a new pressing operation.
Although it may be preferred to separate the tray parts outside the press, said parts can alternatively be separated and/or brought together inside the press chamber.
In the tray disposed in presses of pressure cell type, filling elements or end pieces are sometimes provided, for example at the short sides of the tray. In addition, resilient supports that are parallel to the main axis of the press chamber can be arranged adjacent the long sides of the tray. These end pieces and supports are made of a resilient material, such as rubber, and are thus fitted next to the forming tool. The end pieces serve as a support for the forming tool. They also have a protective function, since they protect the tray frame and prolong its service life, which is advantageous in particular in the case of a tray frame that is divisible into at least one upper and one lower frame part, as described above.
Advantageously, end pieces can be used also in connection with the present invention by integrating the shielding members in an end piece. Thus, an end piece can be divisible into an upper and a lower part. While the lower part is intended to remain on the bottom of the tray, in conventional manner, the upper part can be lifted and act as the upper shielding member. The upper part of the gripping device is conveniently arranged in said upper end piece. As described above in connection with the shielding members, the upper and the lower part of the end piece preferably form a space in which the gripping device is movable.
Preferably, use is made of at least two divisible end pieces as described above, said end pieces being arranged at two opposite sides of the inner wall of the tray device and serving as a support for the forming tool. The blank is thus placed over the forming tool and clamped on either side by means of the end pieces and the gripping devices arranged therein. If a smaller forming tool is to be used, the dimension of which is smaller than the available space between the end pieces, one of the end pieces is suitably moved away from the inner wall towards the centre of the tray device to abut against and support the small forming tool.
In the case where use is made of a divisible tray device, as described above, an upper part of each end piece is suitably integrated with or at least connected to the upper tray part. As mentioned above, the upper tray part may consist of either two side beams or an annular upper frame part. When the upper tray part is lifted, so are the upper part of the end pieces and, conveniently, also the upper part of each gripping device.
In the variant involving end pieces, as in other variants, only one of the gripping devices, or the connection of the blank thereto, needs to be movable in order to allow the blank to be stretched. According to at least one preferred embodiment of the present invention, use is made of a hydraulic arrangement comprising a hydraulic piston and a coupling means connected thereto. The coupling means, which can consist of an arm or a plate, is further connected to at least one of the parts of the gripping device, such as the upper or the lower part. The hydraulic piston is adapted to actuate the coupling means and, thus, the gripping device for stretching the fixed blank. In the case where one fixed end piece and one movable end piece are used, the hydraulic arrangement is suitably adapted to actuate the gripping device in the fixed end piece.
It follows from the above that, according to a third aspect of the invention, a tray device is provided for use in a press of pressure cell type, which tray device defines a space adapted to receive a forming tool against which a blank is formable. The tray device is thus characterised by at least one gripping device, which is adapted to grip an end portion of the blank, and shielding members, which are guidable between an open position and a shielding position and which are adapted to at least partially enclose the gripping device in the shielding position.
The above description emphasizes the fact that the gripping device comprises two parts which can be separated and then brought together. However, other alternative embodiments are conceivable. For instance, the gripping device can be provided with a slot which extends from the periphery of the gripping device, for example towards its centre. If the gripping device is circular in cross-section, the slot may extend radially from the periphery towards the centre of the gripping device. The blank portion projecting from the forming space is thus gripped by inserting it through the slot. The slot may optionally be inwardly tapered.
The shield of a gripping device which is circular in cross-section and has a slot that extends inwards from the circumferential surface is preferably rotatable about its centre axis. Such a rotation causes a blank portion inserted in the slot to move and can be compared with an initial wrapping or winding of the blank around the gripping device. Consequently, the blank is stretched when the gripping device is rotated. Moreover, the gripping device can be at least partially enclosed by a wall in tight abutment against the gripping device, said wall having a suitable cross section, which means that after a certain degree of rotation the slot faces the wall and, as a result, the connection between the blank and the gripping device is shielded. In this case, the wall can be considered to make up at least part of a shielding member, and shielding of the connection between the blank and the gripping device is achieved essentially simultaneously with the stretching of the blank.
The present invention is particularly suitable for forming a sheet-shaped blank, such as sheet steel, into a relatively flat object or a large surface object. Objects of this type are, for example, car roofs, hoods, parts of an aircraft wing.
a and 5b illustrate a method of shielding the connection between a blank and a gripping device.
a and 6b illustrate alternative methods for shielding and gripping arrangements.
a and 7b illustrate the handling of an alternative tray device.
a and 9b are cross-sectional views of a gripping and shielding arrangement according to one embodiment of the present invention.
In the space defined by the tray frame, a forming tool 22 is arranged on which a sheet 24 is to be formed. In the basic configuration, the lamellar means 14a, 14b, 14c are brought together in such manner that there is essentially no air gap between them. On the other hand, before a pressing operation, the sheet 24 is clamped between the uppermost lamellar means 14a and the lamellar means 14b located immediately below. The sheet 24 extends above the forming tool 22 across the defined space.
An end piece is arranged between the forming tool 22 and the inner wall on the short side 18 of the tray frame to support the forming tool. The end piece comprises an upper part 26, which is connected to the uppermost lamellar means 14a, and a lower part 28, which rests on the tray plate 12. When brought together, the upper 26 and the lower 28 part of the end piece form a sliding space 30 in which a locking or gripping device is displaceable. The gripping device comprises an upper part 32 and a lower part 34, between which the sheet 24 is clamped. The upper part 32 of the gripping device is connected to the upper part 26 of the end piece, while its lower part 34 abuts against the lower part 28 of the end piece. The gripping device is moved in the space by means of a hydraulic arrangement. The hydraulic arrangement comprises a hydraulic piston 36 which actuates a plate 38 connected to the gripping device. Accordingly, when the plate 38 is caused to move, the gripping device 32, 34 connected thereto will also move, which results in the fixed sheet 24 being stretched.
A protective mat 40, indicated by phantom lines, is arranged to cover the forming tool 22 and the sheet 24 and protects a diaphragm (not shown) to limit the wear thereof. The mat 40 rests on the upper side of the end pieces in the tray device. The diaphragm is located above the protective mat 40 and adapted to expand and press the sheet 24 located underneath against the forming tool 22. The surface of the forming tool is machined and provided with recesses having sharp edges, which act as cutting devices to cut or trim the sheet. Under low pressures, the area around the edge of the sheet is pressed against a first cutting device 42a. This is achieved by a punch 44 arranged above the cutting device 42a forcing the sheet 24 down towards the cutting device. The diaphragm, which is expanded during pressing, then presses the punch 44 against the sheet 24, which is pressed down into the first cutting device 42a, the outer edge of the sheet being cut off. When the pressure increases, a fine trimming takes place in a second cutting device 42b, which is a stepped recess. The sheet 24 is thus cut off at this cutting device 42b, following which the pressure is further increased to a maximum pressure, such as 1400 bar, and the sheet is thus given its final shape, for example that of a car roof.
Thus, in the left part of
It should be noted that the tray frame, i.e. the lamellar means 14a, 14b, 14c, 14d, as shown in
The right part of
In the tray device shown in
A sheet 24 to be formed against the forming tool is arranged in such manner that it also extends through a gap between the projecting portions 62a, 64a on the inside 58 of the end piece and penetrates between an upper 32 and a lower 34 part of the gripping device. The gap between the projecting portions 62a, 64a on the inside 58 of the end piece may typically be as small as about 0.10-0.15 mm, which basically prevents a diaphragm from penetrating through the gap while allowing a thin sheet-metal blank 24 to be stretched. The lower part 34 of the gripping device has a bulge or boss 66 which fits in a hollow 68 or dent in the upper part 32. In the joined position shown, the boss 66 and the hollow 68 form a connection, which allows the parts 32, 34 of the gripping device to be moved simultaneously even if only one of the parts is directly actuated by a moving force, such as an external pulling device. An external pulling device preferably comprises an arm or plate which, in this case, is connected to the gripping device. A pull ram 36 is connected to the plate 38 with the aid of which it can actuate the gripping device 32, 34 causing it to move, thereby allowing the clamped sheet 24 to be stretched beyond its yield point. In this phase, the upper 26 and the lower 28 part of the end pieces are not tightly compressed, but allow the sheet 24 to be stretched. It is not until after this that they are supposed to abut sealingly against the sheet so that its connection 70 to the gripping device, i.e. the side facing the forming tool 22, is shielded from the diaphragm when the latter is being used for forming the sheet 24. Examples of a gripping device and a pulling device will be described in more detail below with reference to
In general, it may be difficult to provide a uniform blocking of the sheet, which is desirable, in particular if the sheet is wide. However, a method will be described below according to which an even distribution of the pressure over the whole clamping area is obtained in a simple manner.
The two forces, indicated by arrows F, typically exert-a load of 20 tons (about 200 kN) each, i.e. a total of 40 tons (about 400 kN) distributed over a typical width of 1.6 m, as illustrated in
Following the application of the forces F, which blocks the sheet, the stretching operation is carried out. This is possible because the projecting portions 62a, 64a (see
a and 6b illustrate alternative methods for shielding and gripping arrangements.
b shows an upper part 100 and a lower part 102 of a gripping device, each provided with a recess 104 and 106, respectively. A sheet 108 projecting from a forming space is disposed on the lower part 102 so that it covers the recess 106 therein. A rotatable cylinder 110 is provided with a radially projecting arm 112 the shape of whose end 114 is complementary to the recesses. The cylinder 110 is further provided with a radially extending protrusion 116, which in turn is articulated to a pulling plate 118. When the pulling plate 118 is pulled in the direction of the arrow, the protrusion 116 is actuated causing the cylinder 110 to rotate. This, in turn, causes the arm 112 to be lowered and the end 114 of the arm, together with the recess 106 in the lower part 102 of the gripping device, to fix the sheet 108. The upper part 100 of the gripping device is then lowered, its recess 104 being fitted to the end 114 of the arm, thereby interconnecting the lower part 102 and the upper part 100. The pulling plate 118, or any optional pulling means, such as a ram, can then pull the gripping device to stretch the sheet 108. This gripping device is conveniently used in combination with a shielding means similar to the end pieces described in connection with the previous figures.
a and 7b illustrate the method of handling an alternative tray device 120. The tray device 120 shown in perspective in
The possibility of movement thus allows forming tools of different sizes to be used without the risk of the diaphragm penetrating in a space between the forming tool and the end piece, which could lead to unnecessary wear of the diaphragm against the edges of these elements.
Although
a and 9b are cross-sectional views of a gripping and shielding arrangement according to one embodiment of the present invention.
With reference to
In addition, an upwardly directed guide pin 174 is fixed to the plate. The diameter of the guide pin 174 is adapted to the diameter of a hole 176 through the upper part 156 of the gripping device. Thus, the upper part 156 of the gripping device is movable along the guide pin 174 by said pin being inserted in the hole 176. The guide pin 174 ensures that the upper part 156 and lower part 158 of the gripping device are correctly aligned relative to one another when brought together. In the position of separation of the gripping device and the shielding members, as shown in
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 0201430-6 | May 2002 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE03/00256 | 2/17/2003 | WO | 7/12/2005 |
