Abstract:
The invention relates to a tool for shaping hollow parts or metal sheets with the aid of a pressurized gas or fluid. Said shaping tool comprises at least two contour blocks which form a cavity. At least one of the contour blocks can be heated. The contour blocks ( 20, 25; 120, 125 ) are disposed in a two-piece tool housing ( 1 ) which is provided with insulation ( 10 ) for the contour blocks ( 20, 25; 120, 125 ). The load distribution plate ( 8,9 ) is connected to the tool housing ( 1 ).

Description:
[0001]    This application is a continuation of PCT Application No. PCT/DE2007/00185, filed Feb. 2, 2007, which claims priority from German application DE 10 2006 015 793.1-14, filed 5 Apr. 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a forming tool for forming hollowware or sheet metal using a pressurized gas or fluid, said forming tool comprising at least two contour blocks forming a cavity, at least one of the contour blocks being heatable. 
         [0004]    2. Description of the Prior Art 
         [0005]    Forming under internal pressure and at increased temperature is sufficiently known in prior art. The reader is referred to the documents WO 2005/092534 A1, EP 0 930 109 B1 and DE 199 44 679 C2, which are cited by way of example only. An advantage is obtained if the contour blocks have a temperature that corresponds approximately to the temperature the body to be formed, such as a hollowware or a sheet metal or a board, is intended to have during forming. For this is the only way to guarantee that the workpiece to be formed substantially keeps its temperature during forming. If cold forming tools and cold contour blocks were used, this would cause the temperature in the workpiece to immediately drop when the heated workpiece to be formed comes into touching contact with the cavity of the forming block, which means that higher pressures are needed for forming on the one side and, what is much more important, that the workpiece would be at risk to burst on the other side since a cooler material is generally less ductile than a heated one. Insofar, the forming temperatures range between 200° C. and 1100° C. depending on the material to be formed. 
         [0006]    The document DE 101 62 438 A1 shows a top part and a bottom part of a tool, the top part of the tool being disposed on a tool holder. The tool holder is a constituent part of the pressworking die, said pressworking die being disposed in the stationary housing, the press housing. It has been found disadvantageous that the heat transfer from the tool top part and from the tool bottom part into the press frame is problematic. Insofar, there is provided that, on opening the tool mould, i.e. when the two tool parts are being driven apart, the actual tool parts are separated from the press frame by spring systems. This means that the object this cited document relies upon is to minimize the heat dissipation from the tool to the tool holder. 
         [0007]    A forming tool is known from DE 101 53 139 A1 wherein there are provided contour blocks, said contour blocks each comprising an insulation for the contour blocks. This document does not teach how to move the contour blocks toward each other nor does it disclose a housing provided for this purpose. 
         [0008]    As already mentioned, it must be made certain that the tool, and here in particular the two contour blocks forming the cavity, provide a temperature that substantially corresponds to the desired forming temperature of the workpiece. 
         [0009]    It is known that whenever there is a workpiece change, the mould has to be opened, which involves heat loss. Moreover, it must be taken into consideration that also cold workpieces may be placed into the cavity. As already mentioned, it must be made certain that the workpiece is formed at the desired forming temperature. Moreover, it must be taken into consideration that the contour blocks themselves also dissipate a considerable amount of heat to the environment, due to their surface. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    In order to limit the amount of lost heat, there is proposed, with reference to a forming tool of the type mentioned herein above, that the contour blocks are disposed in a two-part tool housing, said two-part tool housing comprising an insulation for the contour blocks, a load distribution plate being provided, which is connected to the tool housing. It has been found that such an insulation above the surface of the contour blocks allows for substantially reducing the amount of irradiated heat, this immediately resulting in the fact that the cycle times for changing the workpiece can be increased, this being finally due to the fact that the heating phases can be shortened once the workpiece has been changed. More particularly, this permits to substantially make certain that the workpieces can indeed be shaped at the forming temperature provided therefor. As a result, the formation of cracks or even bursting is substantially excluded. Moreover, the load distribution plate permits to prevent damage to the insulation. 
         [0011]    Is Advantageous variants and features to the invention will become apparent from the dependent claims. 
         [0012]    There is in particular provided that, parallel to the separation plane, there are provided load distribution means between the contour blocks and the insulation. The insulation is thereby accommodated in the tool housing with base plate and walls. With respect to the insulating material, the following is to be noted in this context: 
         [0013]    If insulating material is meant to isolate, it is characterized by poor heat conducting properties. This means that the insulating material comprises the highest possible porosity. This also means that the burst strength of insulating material is limited. It is also known that the two contour blocks forming the cavity tend to swerve outward under pressure during high internal pressure forming using a pressurized gas or fluid. This means that an insulation surrounding the contour blocks must be capable of resisting such a pressure. Thanks to the so-called load distribution means, it is achieved that the pressure forces exerted upon the environment can be distributed over a large area, the size of this area preferably corresponding to the size of the load distribution plate. This means that the size of the insulation and also the insulating material is chosen so that the pressure forces exerted by the load distribution plate upon the insulation are not suited to compress the insulation. 
         [0014]    It should be further noted that the major part of the pressure force is absorbed by what are referred to as spacers, which are provided between the load distribution plate and the base plate of the tool housing. Toward the side also, meaning toward the walls of the tool housing, there is provided an insulation that is retained by a cover which is fastened to the walls of the tool housing. 
         [0015]    According to a particular embodiment, there is provided that the load distribution plate is a constituent part of the contour block, the load distribution plate abutting directly the insulation. It is thereby provided that the load distribution plate itself is connected to the tool housing in order to make certain that it is possible to open and close the cavity when the tool housing is moved apart. 
         [0016]    According to another variant, there is provided that the load distribution plate, in its quality as an independent element, is connected to the tool housing so as to abut the insulation with almost its entire surface, the load distribution plate comprising means for retaining the contour block. As already discussed above the contour blocks are moved apart for inserting the workpiece. Next, the contour blocks are again moved toward each other and held together and it must be made certain that the two superposed contour blocks are flush with each other. Since however tensions occur which are due to the fact that the contour blocks are heated differently on the one side but also to the two-part tool housing on the other side and to the parts connecting them, here in particular to the load distribution plate, which is adapted to be fixed in the corresponding housing half, said tensions preventing alignment of the superimposed contour blocks when they are solidly clamped, there is provided that the one contour block be received by the load distribution plate so as to float. This means that, since the top contour block is advantageously received by the load distribution plate so as to float, the two contour blocks always center themselves with respect to each other by virtue of the one float mounted, advantageously top, contour block. In this context, there is particularly provided that the contour blocks comprise centering means with respect to each other in the region of their separation plane. The centering means can hereby be a nose disposed on the one contour block, said nose mating with a corresponding recess on the other contour block, i.e., that it engages therein. The best orientation of the two contour blocks with respect to each other is achieved if the side flanks of nose and recess are oriented at right angles with respect to each other. It has been found though that in such a case the contour blocks corrode together, meaning that they stick together, which leads to increased wear. For this reason, a clearance could be provided between the contour blocks where such corrosion is expected. 
         [0017]    Insofar, there is provided, in accordance with an advantageous implementation, that the nose and, corresponding thereto the recess, comprise an engagement surface inclined at an angle of 20° for example. Such a meshing between the two contour blocks through the nose and the mating recess is advantageously provided on substantially the entire circumference, meaning on the entire circumference in the separation plate of the contour blocks. This but for the two openings which serve to supply the dies for the hollow body and by means of which gas or fluid is injected under pressure into the hollowware on the one side or also the hollowware can be compressed for feeding further material by moving the dies together. The touching contact must however not occur on the entire circumference in order to avoid tensions for example. Through the circumferential arrangement of the meshing described herein above, there is provided a kind of burst protection ensuring that, if the hollowware to be formed bursts, the meshing slows down the suddenly escaping pressure. 
         [0018]    In accordance with an advantageous embodiment, there is moreover provided in this sense that the tool housing comprises, over substantially the entire circumference, what is referred to as a screen in the region of the separation plane of the contour blocks, said screen serving as an additional burst protection. This screen serving as a burst protection is more specifically provided in the region of the dies for the workpiece since there—as already explained—the two contour blocks do not engage. 
         [0019]    As already discussed above, at least the one contour block of the two contour blocks forming the cavity are mounted in the tool housing so as to float. More specifically, means for retaining the contour block, and in particular for retaining the floating contour block, are located on the load distribution plate. In particular for mounting the tool, there is provided in this context that the load distribution plate is also orientable in the tool housing, namely by lateral set screws allowing for pre-adjusting the location of the load distribution plate. 
         [0020]    As already discussed above, the contour block comprises heating means. The heating means can hereby be configured to be a panel heater or a rod heater. If a panel heater is being used, the panel heater is directly connected, such as screwed, to the contour block to achieve a good heat transfer. This means that the panel heater is located between the contour block on the one side and the load distribution plate on the other side. For receiving rod heaters, the contour block comprises suited openings for insertion thereof. In any case, it must be made certain that the contour blocks and the heaters are prevented from overheating, which can occur more specifically by arranging thermoelements on the contour blocks in connection with a corresponding control. 
         [0021]    In the introductory portion, it is already noted that in particular in the case of high temperatures of up to 1100° C., which are eventually achieved during hot forming, the workpiece change has to occur in quite short cycle times. This means that, as far as practicable, the heat is to be prevented from dissipating to the environment in order not to further increase the anyway occurring and unavoidable heat escape when the tool is being opened. Insofar, there is provided that the contour blocks are mounted in the tool housing so as to be insulated. The quality of insulation substantially depends on the type of insulation. This means that an efficient insulation is soft since it has a corresponding number of pores. A hard insulation is for example in the form of foamed stones, e.g., Poroton stones; the openings in the Poroton stones can be filled with insulating material. Despite of their good insulation, the Poroton stones themselves are quite resistant to pressure e.g., when compared to steel, so that this insulation seems suited for insertion between the tool housing and the load distribution plate. As an alternative, there can be provided that dies are provided between the tool housing and the load distribution plate, said dies being in particular made from a material that is not heat conductive, e.g., from ceramics, and a suitably soft insulation having high insulation efficiency can be provided about the ceramic rods or supports. On any implementation, the insulation itself can consist of several horizontal layers, said layers being configured such that the layers located nearest to the load distribution plate are much more resistant to high temperatures than those that are located farther away. Moreover, the layers can have different density and thickness. 
         [0022]    For forming hollow bodies with the help of a pressurized gas for example, it is necessary to seal the ends of the hollowware. This occurs for example in that a cone is inserted into the hollowware on either end thereof, the gas being supplied through said cone. If the hollowware is additionally compressed by internal gas pressure for feeding further material during forming, it is indicated to use a clamping device as it is known from DE 10 2004 009 485 B3. 
         [0023]    Using such contour blocks, not only hollow bodies can be formed, but also sheet metal or boards. In this context, there is provided that through the contour blocks, the board or the sheet metal are preferably retained by hold down clamps. For this purpose, at least the one contour block comprises a female part that corresponds to the final shape of the sheet metal or the board to be formed. To reduce the volume of fluid/gas in the cavity as such, and here in particular in the space located underneath the board, there is provided that the female part be displaceable onto the other contour block so as to reduce the volume of the cavity. The female part in the other contour block can comprise a surface conforming in shape to the shape of the female part of the one contour block; however this must not be so. The reduction of the volume in the cavity is of interest since on the one side a small volume reduces the risk of persons standing nearby in case of a sudden pressure drop and since on the other side it is more cost-effective. 
         [0024]    The deformation of the board can only occur through gas pressure, but, in parallel thereto, the one female part can also be displaced onto the other female part. For this purpose, a die can be provided in accordance with one variant; according to another variant, the displacement of the female part can also occur through gas pressure. 
         [0025]    The invention will be described in closer detail herein after with respect to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0026]      FIG. 1  shows the forming tool in a sectional side view; 
           [0027]      FIG. 2  shows a detail view according to  FIG. 1 , but rotated 90°; 
           [0028]      FIG. 2   a  shows the detail IIa of  FIG. 2 ; 
           [0029]      FIG. 3  shows a detail view of another kind of insulation between the tool housing and the load distribution plate; 
           [0030]      FIG. 3   a  shows an illustration of another kind of insulation with horizontally running insulation layers of different thickness and density; 
           [0031]      FIG. 4  shows the arrangement of a panel heater directly on a contour block; 
           [0032]      FIG. 5  shows a forming tool according to  FIG. 1 , a board or a sheet metal being inserted in the cavity and being formed by gas pressure; 
           [0033]      FIG. 5   a  shows an illustration according to  FIG. 5 , the one female part being configured to be displaced by a gas cushion; 
           [0034]      FIG. 6  shows a section according to arrow X in  FIG. 1  with a cone for closing the ends of the hollowware to be formed; 
           [0035]      FIG. 7  shows an illustration according to  FIG. 6 , a clamping device for taking hold of the ends of the hollowware to be formed being provided. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    According to  FIG. 1 , the tool housing is indicated generally at  1 . The tool housing includes two base plates  2 ,  3  for connection to the chassis of the machine, side walls  4 ,  5 ,  6  and  7  being respectively provided on the base plate. The walls  4  through  7  are each solidly connected to the respective one of the base plates  2 ,  3 . Between the walls  4  through  7  there are located load distribution plates  8  and  9  that are spaced apart from the base plates  2  and  3 , a spacing being provided between the load distribution plate  8 ,  9  and the base plate  2 ,  3 , said spacing being filled with an insulation  10 . Between the load distribution plate  8 ,  9  and the respective base plate  2 ,  3  there are provided spacers  10   a  in the insulation  10 , which serve to transfer the force. Another insulation  65  is located on the side of the contour block, underneath/above the load distribution plate  8 ,  9 . In order to keep the insulation in place, there are provided covers  65   a  that are disposed on the walls  4 - 7  of the housing. 
         [0037]    On the load distribution plate  8 ,  9  there is located a holding device indicated at  11  and  15  for receiving a respective one of the contour blocks  20 ,  25 . Such a holding device includes an equalization plate  21 ,  26  with two parallel spacer rails  22 ,  27  disposed thereon and with two parallel head jaws  23 ,  28 . The head jaws  23 ,  28  extend beyond the spacer rail  27  so that a guide is provided, the contour blocks  20 ,  25  each comprising a projection  20   a ,  25   a  on either side in the region of this guide. As a result, the two contour blocks  20 ,  25  are retained in a dovetail guide fashion by the holding device generally indicated at  11  and  15 . The implementation of the holding device  11  however differs from the one of holding device  15  by the fact that the contour block  20  is received floating in the holding device  11 . This is particularly noticeable since the contour block  20  is spaced laterally a distance  23   a  from the head jaw  23  and since the lower edge of the head jaw  23  is spaced vertically a distance  23   b  apart from the top side of the web  20   a . This means that the contour block  20  is movable in any direction, which is necessary for the contour block to be capable of centering itself, i.e., to orient itself, on the contour block  25  with respect thereto in spite of possibly occurring differences in heat dilatation. 
         [0038]    The coarse orientation during mounting occurs by orienting the load distribution plate  8 ,  9  using screws  8   a ,  9   a  disposed laterally in the housing  1 . 
         [0039]    For centering ( FIG. 2 ) there is more specifically is provided that the centering block  20  comprises a nose  24  located on the side, this lateral nose  24  projecting into a corresponding recess  29  of the other contour block  25 . What matters here, is that the nose and the recess each comprise an inclined insertion surface  20   a ,  25   a.    
         [0040]    Through this detent connection or meshing, burst protection is ensured as it is necessary if the hollowware  50  placed inside the cavity  40  were to burst under the inner pressure. The meshing at least slows down the then generated pressure wave. 
         [0041]    Further burst protection is obtained insofar as a screen  45  is provided, which is disposed on the one contour block, in the region of the plane separating the two contour blocks. 
         [0042]    Moreover, another external burst protection  46  is obtained, which covers the opening  47  for supplying the dies (not shown) to the hollowware  50 . 
         [0043]    The contour blocks  20 ,  25  further exhibit openings  30 ,  35  for receiving rod-shaped heaters (not shown). The rod-shaped heaters are caused to laterally protrude from the tool housing. In order to make certain that the rod-shaped heater will not shear off when the contour blocks or also the female parts are moving ( FIG. 5 ,  FIG. 5   a ), both the wall  5 ,  7  and the insulation  65  have a clearance about the heater. 
         [0044]      FIG. 3  shows another implementation of the insulation  10 , said insulation  10  comprising supports  12  ensuring the same constant distance between the base plate  2 ,  3  and the load distribution plate  8 ,  9 . The supports  12  can be made for example from a heat insulating ceramic material. 
         [0045]      FIG. 4  shows a panel heater  60  that is disposed on the contour block  20 ,  25  and is screwed to the top side of the contour block  20 ,  25 . 
         [0046]      FIG. 5  shows a variant in which it is not a hollowware that is being formed but a sheet metal or a board  100 . Now the contour blocks indicated at  120  and  125  are not configured to be substantially identical but to be different. In this context it is noted that the contour block  120  comprises a female part  122 , said female part  122  being displaceable pursuant to the arrow  150  by the forming die  130 . For this purpose, the contour block  120  comprises a frame  121  that receives the actual female part  122  for movement or displacement pursuant to the arrow  150 . The board labelled at  100  is kept clamped between the frame  121  serving as a hold down clamp and the lower contour block  125 . The interesting point here is that the female part  122  is displaceable pursuant to the arrow  150 , it being provided that the female part  122  is movable toward the contour block  125  with the female part  126  in order to minimize the volume  140  between the board  100  and the female part  126 . This against the background that the amount of pressurized gas is reduced in case the board bursts. Insofar, there is provided to displace the female part  122  toward the female part  126  in order to then supply the volume  140  with gas through the feed line  160 . The forming die  130  is connected to the female part  122 , also through the insulation  135 . The frame  121  is also float mounted in the holding device  11 , as this has already been discussed above with respect to the contour block  20 . 
         [0047]    The implementation according to  FIG. 5   a  differs from the one in  FIG. 5  by the fact that instead of the die  130 , there is provided a hollow space  128  above the female part  122 , said hollow space  128  being fed with gas or with a fluid through the line  128   a  in order to displace the female part  122  in the same way as the die  130 . 
         [0048]    With respect to the  FIGS. 6 and 7 , the following is to be mentioned: 
         [0049]      FIG. 6  schematically shows a view of the contour block pursuant to arrow X in  FIG. 1 . The hollowware  50  to be formed and the contour block  25  can be seen. To seal the hollowware  50 , there are provided cones  70  that are displaced in the opening at the end of the hollowware. The gas is supplied to the hollowware through said cones. If the hollowware is not only to be sealed at the end but if additional material is also to be fed during forming, the hollow body must not only be sealed at the end, but also clamped. Such a clamping device  75  ( FIG. 7 ) is known from DE 10 2004 009 485. 
         [0050]    In order to prevent welds on the cone, the cone can be cooled during sealing.