Abstract:
A method for locally increasing pressing pressure on a press tool having an abutment surface for being clamped onto a clamping surface in a press comprises providing a power unit smaller than the abutment surface and having an internal space, positioning the power unit between the clamping surface and the abutment surface, pressing the clamping surface against the abutment surface, connecting the internal space to a source of pressurized hydraulic fluid, and supplying the pressurized hydraulic fluid to the internal space thereby causing the power unit to expand and to exert a local pressure on the abutment surface.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 10/582,591, filed Apr. 17, 2007, entitled APPARATUS AND METHOD FOR COMPENSATING FOR STRESS DEFORMATIONS IN A PRESS. 
     
    
     BACKGROUND 
       [0002]    (1) Field of the Invention 
         [0003]    The present invention relates to an apparatus for compensating for such deformations as occur in first and second clamping surfaces intended for a tool in a press, the clamping surfaces being reciprocally moveable towards and away from one another for moving a first and a second part of the tool towards and away from each other, respectively, such deformations generating an uneven pressure in at least one area of contact between the tool and the clamping surfaces. 
         [0004]    (2) Prior Art 
         [0005]    In hydraulic presses, tools are positioned by means of which different objects are compression moulded to the desired configuration and appearance. Hydraulic presses operate at high pressure, which results in the parts in the hydraulic press, as well as the tool placed in the hydraulic press, being subjected to extreme stresses. These stresses are so great that the parts of the hydraulic press and the tool are deformed. This deformation results in the pressure distribution in those tools which are to impart to the final product its configuration and appearance becoming uneven. For example, the pressure will be lower in the centre of the tool and greater in its periphery. This will have as a result that the end product will be unevenly formed and will have an unacceptable quality. 
         [0006]    In order to compensate for this deformation and distribute the pressure more evenly in presses, use has hitherto been made of shims, a form of interlay placed in between tools and the work surfaces of the hydraulic press. Cambering or crowning are also previously known methods for compensating for deformations. Cambering or crowning implies that those surfaces which are deformed during the pressing operation are arched so as to compensate for the deformation so that the compression pressure is distributed more evenly. 
         [0007]    The drawbacks inherent in prior art technology are numerous. In the utilisation of shims, there is, granted, obtained a compensation for the deformation, but accurate setting is required and, this not withstanding, the compensation will be incomplete and above all not constant, but the compensation itself must be repeated at regular intervals. This results in unnecessary time loss for the compensation which lowers production capacity for the press. Another drawback inherent in shims is further that the thickness of the shims is given and not variable. Accuracy using shims is also difficult to achieve, which has a negative effect on the quality of the product produced using the tool in the press. 
         [0008]    The drawback inherent in cambering or crowning is that the arching which is created is difficult to change in a simple manner if required. This lack of flexibility also results in considerable time loss when a new tool is to be positioned in a press. A cambering or crowning of the work surfaces of the press customised for the tool must then be utilised. Hence, cambering or crowning shows a low level of flexibility. 
         [0009]    That which has hitherto been lacking in the art is an apparatus which is flexible and which can assume a thickness which fits a given situation in order to compensate for deformation in a press. In addition, there has been a lack of an apparatus which simply and rapidly can be adapted to a new tool disposed in a press. An apparatus for compensation of deformation which has a short adjustment time for a new tool and which thereby increases productivity in a press has long been sought for in the art. Further, a compensation apparatus which can compensate by bulging outwards has also been called for. 
       SUMMARY OF THE INVENTION 
       [0010]    The object of the present invention is to obviate or at least minimize the above-outlined drawbacks, the object being attained by means of an apparatus which is characterised in that there is disposed, at least in a contact region between a clamping surface and an abutment surface, a power unit which, on activation, is operative to urge, away from the clamping surface located in the contact region, at least a part of the abutment surface of the tool located there. 
         [0011]    The object of the present invention is to realise an apparatus which is flexible and which can compensate for deformations by bulging outwards and thereby realising a compensation for deformations so that a more uniform compression depth is attained in a tool which is placed in a press in which the present invention has been disposed. 
         [0012]    The present invention enjoys the following advantages. The apparatus according to the present invention may be formed and given a thickness which is sufficiently great where required and sufficiently thin where required over a surface in a press, in order thereby to compensate for deformations which occur. The high level of flexibility of the invention makes it easier to compensate for a new tool which is placed in the press, which results in shorter retooling time and higher production capacity in the press. Thus, the apparatus according to the invention enjoys the advantage that its thickness is variable. 
     
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         [0013]    The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings: 
           [0014]      FIG. 1  is a side elevation of a hydraulic press in which a tool has been placed, in which tool a product may be pressed to the desired appearance; 
           [0015]      FIG. 2  is a side elevation showing how the tool is disposed between an upper slide and a lower work table and how both the slide and the work table are deformed during pressing; 
           [0016]      FIG. 3  is a perspective cross sectional view in which the cross section is in both the X and Y directions and shows how the apparatus according to the present invention is disposed between the upper side of the tool and the underside of the slide; 
           [0017]      FIG. 4  shows the perspective cross sectional view of  FIG. 3  where the apparatus according to the invention has been caused to expand further in order thereby to compensate further for the deformations and increase the compression force in the centre of the tool; 
           [0018]      FIG. 5  is a plan view showing an upper part of the apparatus according to the present invention; 
           [0019]      FIG. 6  is a plan view showing the underside of the upper part of the apparatus; 
           [0020]      FIG. 7  is a plan view showing a second part of the apparatus; 
           [0021]      FIG. 8  is a side elevation in cross section through the apparatus according to the present invention; 
           [0022]      FIG. 9  is a detailed view of the apparatus of  FIG. 8 ; and 
           [0023]      FIG. 10  shows the upper side of the tool and how the downward bending if distributed in the tool when an apparatus according to the present invention is disposed between the slide and the tool. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  shows a hydraulic press  1  in which two large press cylinders  2 ,  3  together with four smaller press cylinders  4 ,  5 ,  6  and  7  act on a slide  8 . Beneath the slide, a tool  9  is disposed which rests on a work table  10 . The lower part  11  of the hydraulic press is disposed beneath the work table  10 . 
         [0025]    The tool  9  is of dual construction and has an upper part which is fixed in the slide  8  and a lower part which is fixed on the work table  10 . 
         [0026]    The illustrated type of hydraulic press  1  operates as follows. Between the slide  8  and the work table  10 , the tool  9  is positioned. In this tool  9 , there is placed a work piece (blank) which is to be formed by this tool. When the work piece is in place in the tool  9 , the slide  8  presses the tool  9  against the work table  10  with the aid of the press cylinders  2 ,  3 ,  4 ,  5 ,  6  and  7 . Once these press cylinders have acted for a given time interval which is sufficiently long for the work piece placed in the tool  9  to have achieved the desired configuration, the compression force of the press cylinders is reduced so that the ready-pressed work piece can be removed from the tool  9 . There is further marked in  FIG. 1  a first clamping surface  52  on the slide  8 , as well as a second clamping surface  53  on the work table  10 . The first clamping surface  52  on the slide  8  extends over the slide and abuts against a first abutment surface  54  on the tool  9 . The second clamping surface  53  extends over the entire work table  10  and abuts against a second abutment surface  55  on the tool  9 . A contact region  56  thereby occurs between the first clamping surface  52  on the slide  8  and the first abutment surface  54  on the tool  9 . A further contact region  57  occurs between the second clamping surface  53  on the work table  10  and the second abutment surface  55  on the tool  9 . It is in the contact regions  56 ,  57  that the compression pressure from the press cylinders  2 ,  3 ,  4 ,  5 ,  6  and  7  is transferred between the slide  8  and the tool  9 , as well as between the tool  9  and the work table  10 . The abutment surfaces  54  and  55  extend out to an outer contour which defines each respective abutment surface. 
         [0027]      FIG. 2  shows how both the slide  8  and the work table  10  are deformed when the hydraulic press operates. This deformation results in the compression pressure being distributed unevenly over both the slide  8 , the tool  9  and also over the work table  10 . It is this uneven distribution of the compression pressure which the present invention is intended to compensate for. 
         [0028]    In one preferred embodiment of the present invention, the slide  8  and the work table  10  are manufactured of metal. At the elevated pressures at which a hydraulic press works, the metal may be likened to flexible rubber which bends when being subjected to the compression pressure. The result as far as the slide  8  is concerned will be that the outer parts  12 ,  13  of the slide  8  will be bent downwards, while a central part  14  is bent upwards. 
         [0029]    The work table  10  is also bent when the compression force acts in the hydraulic press. The outer parts  15 ,  16  of the work table  10  are bent upwards, while a central area  17  of the work table  10  is bent downwards. That the central area  14  of the slide  8  is bent upwards and the central area  17  of the work table  10  is bent downwards will have as a consequence that a central part  18  in the tool  9  will have an insufficient compression pressure. A work piece which is placed in the tool  9  will be subjected to a compression pressure which varies over a press surface in the tool. In an outer portion  19 , the compression pressure will be sufficiently great to form a work piece in a desired manner, i.e. the work piece will have the desired appearance and the desired compression depth. In a central area  18  of the tool  9 , the compression pressure will, on the other hand, be too low which leads to the work piece not having the desired appearance and press depth. This is obviously unacceptable and the problem has been subject to various solutions, for example using shims or crowning. The present invention offers an apparatus whose purpose is to compensate for the deformation so that the difference between the compression pressure in the outer portion  19  and in the central area  18  will be as slight as possible in the tool  9 . 
         [0030]      FIG. 3  shows how an apparatus  20  according to the present invention has been disposed in the underside  21  of the slide  8 . The apparatus according to the present invention is placed in the central area  14  of the slide and above the central area  18  of the tool  9 .  FIG. 3 , which is a perspective cross sectional view along a centre plane in both the longitudinal direction and the transverse direction of the slide  8 , the tool  9  and the work table  10 , shows how a first part  22  and a second part  23  are separated by an interspace  24  which is filled with a suitable liquid which, in the present embodiment, consists of oil. In that the interspace  24  may be increased or reduced throughout the entire surface where the apparatus is placed, with the aid of the pressure in the oil, a satisfactory compensation for the deformation in the slide  8  can be obtained. 
         [0031]      FIG. 3  schematically shows how the compression pressure varies in the illustrated areas of the tool  9 . In  FIG. 3  is shown schematically how much material in the areas a, b in the slide  8  and an area c in the tool  9  move in the vertical direction. This change in the vertical direction corresponds to an increase of the compression pressure in the areas a, b, c. In the area a, the change in the vertical direction will be great as a result of the action of the apparatus  20  in the central area  14  of the slide  8 . In the area b, the change will be somewhat less than in the area a, but also in this area the action from the apparatus  20  can be noted. In the area c, the action from the apparatus  20  can also be noted. Also in this area c, a change is realised in the vertical direction, which gives a compression pressure in the central area  18  of the tool  9 . 
         [0032]      FIG. 4  is a similar view to  FIG. 3 , but in  FIG. 4 , the oil pressure in the interspace  24  in the apparatus  20  has been increased further, whereby the first part  22  is pressed harder against the underside  21  of the slide  8  and the second part  23  presses harder against an upper part  25  on the tool  9 . By such means, the compression force in the central area  18  in the tool  9  increases. In  FIG. 4 , the increased pressure is shown in that the areas a, b, c have expanded. By the action from the apparatus  20 , it will be apparent how the change in the vertical direction in the area c takes up a larger part of the central area  18  in the tool  9  in  FIG. 4  than in  FIG. 3 . In  FIG. 4 , it may also be seen that this change in the vertical direction, i.e. an increase of the compression pressure, is propagated down also into the work table  10 . By the action of the apparatus  20 , the vertical change in the area a and the area b will also be greater in that the apparatus  20  has expanded. The illustrated areas a, b, c are shown schematically. 
         [0033]      FIG. 5  shows in plan view the apparatus  20  for compensating for deformations. The apparatus  20  may be likened to a membrane which, from its initial appearance, can expand and act in this expanded state and thereafter return to its initial appearance when desired. The membrane  20  comprises a centrally disposed rectangular first part  22  which is surrounded by a frame section  26  which is welded together to the first part  22  along an upper welded joint. The upper welded joint extends all the way between the frame section  26  and the first part  22 . The first membrane part  22  has rounded corners  28 ,  29 ,  30 ,  31 . In the frame section  26 , through-going holes  32  are provided through which, for example, screws may be passed for securing the membrane  20 , for example on the clamping surface  21  ( FIGS. 3 and 4 ) on a slide. Centrally in the rectangular first part  22  with rounded corners, a through-going hole  33  is provided. 
         [0034]    The frame section  26  follows the appearance of the first part  22  and also has rounded corners. 
         [0035]      FIG. 6  shows in plan view a lower side of the first part  22  which the apparatus  20  includes, as well as the frame section  26  in cross section. The through-going hole is provided in the centre of the first part  22 . About the hole  33 , a circular recess  34  is provided. From this circular recess  34  extend grooves  35  out over the underside of the first part  22 . In the illustrated embodiment of the invention, two grooves  35 ,  36  extend out from the circular recess  34 . Each respective groove  35 ,  36  branches in a T curve to grooves  37 ,  38  and  39 ,  40 , respectively which lead out to the outer edge of the first part  22 . The through-going hole  33 , the recess  34  and the grooves  35 ,  36 ,  37 ,  38 ,  39 ,  40  are designed so that the liquid, e.g. oil, will be capable of being fed into the membrane  20 . It is naturally conceivable to design the pattern of grooves in many different ways. The grooves  37 ,  38 ,  39 ,  40  discharge in a circumferential groove  41  which is provided in the frame section  26 . The circumferential groove  41  extends around the whole of the frame section. 
         [0036]      FIG. 7  shows a plan view of the membrane  20  and also shows a second part  23  which is fixedly welded in the frame section  26  with a lower welded joint  42 . The second part  23  is also a rectangular plate with rounded corners  43 ,  44 ,  45 ,  46 . The frame section  26  surrounds the whole of the second part  23  and also has rounded corners which are in association with the rounded corners of the second part  23 . In the frame section  26 , holes  32  are provided and surrounded by a depression  47  which is to accommodate the head of a screw which is utilised for fixing the membrane  20  in, for example, the slide. 
         [0037]      FIG. 8  shows the membrane  20  in cross section along the plane A-A as shown in  FIG. 5 . In the figure, it is apparent how the first part  22  rests against the second part  23  and how the parts are disposed in relation to the frame section  26 . Further, the figure shows the through-going hole  33  in the first part  22 , as well as the circumferential groove  41  which is provided by recessing from the frame section  26 . 
         [0038]      FIG. 9  is a detailed view of the area around the anchorage between the first part  22  and second part  23 , respectively, and the frame section  26 . The formation of this area is of crucial importance and affects how the membrane  20  can move and compensate for deformations. In order to cater for the extreme stresses that occur when the tool is working in a hydraulic press, great emphasis has been placed on mechanical strength properties in the formation of the upper welded joint  27  and the lower welded joint  42 , as well as the circumferential groove  41 . The circumferential groove  41  enters horizontally into the frame section  26  and has well rounded corners  48 ,  49  so that the forces are distributed uniformly around the surface of the groove. In addition, the inner surface of the groove is highly polished in order to minimize unevenness where fracture in the material may occur. By placing the upper welded joint  27  and the lower welded joint  42  above one another in a vertical plane which constitutes an abutment surface between the first part  22  and the second part  23 , respectively and the frame section  26 , superior mechanical strength will be obtained in the welded joints. The major part of the strain in the material of which the frame section  26  consists is taken up in connection with the circumferential groove  41 . 
         [0039]      FIG. 10  shows the tool  9  and how the apparatus according to the present invention realises a downward depression of the central part of the tool  9 .  FIG. 10  shows the tool  9  in perspective view. The tool  9  consists of a first tool part  50  and a second tool part  51 . The first tool part  50  and the second tool part  51  may be distanced from one another and the blank which is to be formed in the tool  9  is placed in between these two tool parts  50 ,  51 . As a result of the increased compression pressure on the central area of the tool on the upper side of the tool, the blank which is placed between the tool part  50  and the tool part  51  will receive a more even stamping throughout its entire surface when the hydraulic press acts on the tool  9 . The areas c, d, e are visible in the figure. The areas c, d, e show areas of different pressure which the apparatus according to the present invention gives rise to when it acts on the tool  9 . In the central area c of the tool  9 , a compression pressure occurs which is greatest. This compression pressure declines outwardly, and so the area d shows a compression pressure which is less than the area c, and area e shows a compression pressure which is less than area d. The areas are shown schematically in this figure. The change in the vertical direction corresponds to the compression pressure, i.e. the change in the vertical direction of the material in the tool  9  is greatest in area c and less in area d and e. Thus, areas c, d, e show that where most change in the vertical direction is needed for realising a higher compression pressure, i.e. centrally in the tool  9 , the apparatus according to the present invention also gives rise to the greatest change and compression pressure. If the apparatus according to the present invention had not been placed between the tool  9  and the slide, a more uneven distribution of the compression pressure would have been obtained in the tool  9 , which would have resulted in the blank placed between the tool part  50  and part  51  would have been stamped more unevenly. The stamping action would have been greater at the edges and less in the central areas of the blank. 
         [0040]    The embodiment of the present invention described in the foregoing may be varied in numerous different ways. It will readily be perceived by the skilled reader that the positioning of the apparatus  20  shown in  FIG. 3  may be varied. For example, additional apparatuses  20  may be placed on the underside  21  if necessary. In the foregoing description, we have spoken about placing the apparatus  20  or several apparatuses of the type  20  between the slide  8  and the tool  9 , in other words in the contact area  56  which is shown in  FIG. 1 . It is also conceivable to place one or more apparatuses  20  on the second clamping surface  55  on the work table  10 . The apparatuses  20  then act in the contact area  57  between the second clamping surface  53  on the work table  10  and the second abutment surface  55  on the tool  9 . By such means, additional compensation can be attained for improving the results on pressing in the tool  9 . 
         [0041]    The configuration of the apparatus shown in  FIGS. 5 ,  6 ,  7  and  8  may be varied. The size of the apparatus may also be varied. Thus, it is conceivable to provide, for example, totally square configuration, triangular configuration, circular configuration, as well as a configuration with more than four edges, for example a hexagonal or octagonal configuration. All of this is with a view to achieving the best possible compensation in the press. Thus, the configuration of the apparatus  20  is completely free and it may be designed in the manner which best suits any given practical application. 
         [0042]      FIG. 7  shows the holes  32  which are intended for the screw which is to secure the membrane  20  in, for example, the slide  8  or the work table  10 . Since extremely high forces act on the membrane in the press, the securement of the membrane must be made slightly resilient in order to prevent the anchorage screw from breaking. This somewhat resilient securing can, for example, be realised with the aid of a spring washer which is placed between the membrane and the fixing screw in order to compensate for the configurational change which takes place when the membrane is working. It is also conceivable to provide different types of springs which permit a certain resilient springing in order to protect the fixing screws from breaking. 
         [0043]    The present invention is not restricted to the embodiment described in the foregoing, but may be varied without departing from the scope of the appended Claims.