Apparatus and method for compensating for stress deformations in a press

An apparatus is provided for compensating for such deformations as occur in operation in first and second clamping surfaces intended for a tool in a press. The clamping surfaces are reciprocally moveable towards and away from one another in order to move a first and second part of the tool towards and away from one another, and the first and second tool parts have a first and second abutment surface for abutment against the first and second clamping surfaces and the deformations cause uneven pressure in at least one contact region between the tool and the clamping surfaces. According to the present invention, there is disposed, in at least one contact region between a clamping surface and an abutment surface, a power unit which, on activation, is operative to press, away from the clamping surface located in the contact region at least a part of the abutment surface of the tool located there.

BACKGROUND

(1) Field of the Invention

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.

(2) Prior Art

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.

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.

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.

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.

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

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.

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.

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.

DETAILED DESCRIPTION

FIG. 1shows a hydraulic press1in which two large press cylinders2,3together with four smaller press cylinders4,5,6and7act on a slide8. Beneath the slide, a tool9is disposed which rests on a work table10. The lower part11of the hydraulic press is disposed beneath the work table10.

The tool9is of dual construction and has an upper part which is fixed in the slide8and a lower part which is fixed on the work table10.

The illustrated type of hydraulic press1operates as follows. Between the slide8and the work table10, the tool9is positioned. In this tool9, there is placed a work piece (blank) which is to be formed by this tool. When the work piece is in place in the tool9, the slide8presses the tool9against the work table10with the aid of the press cylinders2,3,4,5,6and7. Once these press cylinders have acted for a given time interval which is sufficiently long for the work piece placed in the tool9to 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 tool9. There is further marked inFIG. 1a first clamping surface52on the slide8, as well as a second clamping surface53on the work table10. The first clamping surface52on the slide8extends over the slide and abuts against a first abutment surface54on the tool9. The second clamping surface53extends over the entire work table10and abuts against a second abutment surface55on the tool9. A contact region56thereby occurs between the first clamping surface52on the slide8and the first abutment surface54on the tool9. A further contact region57occurs between the second clamping surface53on the work table10and the second abutment surface55on the tool9. It is in the contact regions56,57that the compression pressure from the press cylinders2,3,4,5,6and7is transferred between the slide8and the tool9, as well as between the tool9and the work table10. The abutment surfaces54and55extend out to an outer contour which defines each respective abutment surface.

FIG. 2shows how both the slide8and the work table10are deformed when the hydraulic press operates. This deformation results in the compression pressure being distributed unevenly over both the slide8, the tool9and also over the work table10. It is this uneven distribution of the compression pressure which the present invention is intended to compensate for.

In one preferred embodiment of the present invention, the slide8and the work table10are 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 slide8is concerned will be that the outer parts12,13of the slide8will be bent downwards, while a central part14is bent upwards.

The work table10is also bent when the compression force acts in the hydraulic press. The outer parts15,16of the work table10are bent upwards, while a central area17of the work table10is bent downwards. That the central area14of the slide8is bent upwards and the central area17of the work table10is bent downwards will have as a consequence that a central part18in the tool9will have an insufficient compression pressure. A work piece which is placed in the tool9will be subjected to a compression pressure which varies over a press surface in the tool. In an outer portion19, 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 area18of the tool9, 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 portion19and in the central area18will be as slight as possible in the tool9.

FIG. 3shows how an apparatus20according to the present invention has been disposed in the underside21of the slide8. The apparatus according to the present invention is placed in the central area14of the slide and above the central area18of the tool9.FIG. 3, which is a perspective cross sectional view along a centre plane in both the longitudinal direction and the transverse direction of the slide8, the tool9and the work table10, shows how a first part22and a second part23are separated by an interspace24which is filled with a suitable liquid which, in the present embodiment, consists of oil. In that the interspace24may 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 slide8can be obtained.

FIG. 3schematically shows how the compression pressure varies in the illustrated areas of the tool9. InFIG. 3is shown schematically how much material in the areas a, b in the slide8and an area c in the tool9move 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 apparatus20in the central area14of the slide8. In the area b, the change will be somewhat less than in the area a, but also in this area the action from the apparatus20can be noted. In the area c, the action from the apparatus20can also be noted. Also in this area c, a change is realised in the vertical direction, which gives a compression pressure in the central area18of the tool9.

FIG. 4is a similar view toFIG. 3, but inFIG. 4, the oil pressure in the interspace24in the apparatus20has been increased further, whereby the first part22is pressed harder against the underside21of the slide8and the second part23presses harder against an upper part25on the tool9. By such means, the compression force in the central area18in the tool9increases. InFIG. 4, the increased pressure is shown in that the areas a, b, c have expanded. By the action from the apparatus20, it will be apparent how the change in the vertical direction in the area c takes up a larger part of the central area18in the tool9inFIG. 4than inFIG. 3. InFIG. 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 table10. By the action of the apparatus20, the vertical change in the area a and the area b will also be greater in that the apparatus20has expanded. The illustrated areas a, b, c are shown schematically.

FIG. 5shows in plan view the apparatus20for compensating for deformations. The apparatus20may 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 membrane20comprises a centrally disposed rectangular first part22which is surrounded by a frame section26which is welded together to the first part22along an upper welded joint. The upper welded joint extends all the way between the frame section26and the first part22. The first membrane part22has rounded corners28,29,30,31. In the frame section26, through-going holes32are provided through which, for example, screws may be passed for securing the membrane20, for example on the clamping surface21(FIGS. 3 and 4) on a slide. Centrally in the rectangular first part22with rounded corners, a through-going hole33is provided.

The frame section26follows the appearance of the first part22and also has rounded corners.

FIG. 6shows in plan view a lower side of the first part22which the apparatus20includes, as well as the frame section26in cross section. The through-going hole is provided in the centre of the first part22. About the hole33, a circular recess34is provided. From this circular recess34extend grooves35out over the underside of the first part22. In the illustrated embodiment of the invention, two grooves35,36extend out from the circular recess34. Each respective groove35,36branches in a T curve to grooves37,38and39,40, respectively which lead out to the outer edge of the first part22. The through-going hole33, the recess34and the grooves35,36,37,38,39,40are designed so that the liquid, e.g. oil, will be capable of being fed into the membrane20. It is naturally conceivable to design the pattern of grooves in many different ways. The grooves37,38,39,40discharge in a circumferential groove41which is provided in the frame section26. The circumferential groove41extends around the whole of the frame section.

FIG. 7shows a plan view of the membrane20and also shows a second part23which is fixedly welded in the frame section26with a lower welded joint42. The second part23is also a rectangular plate with rounded corners43,44,45,46. The frame section26surrounds the whole of the second part23and also has rounded corners which are in association with the rounded corners of the second part23. In the frame section26, holes32are provided and surrounded by a depression47which is to accommodate the head of a screw which is utilised for fixing the membrane20in, for example, the slide.

FIG. 8shows the membrane20in cross section along the plane A-A as shown inFIG. 5. In the figure, it is apparent how the first part22rests against the second part23and how the parts are disposed in relation to the frame section26. Further, the figure shows the through-going hole33in the first part22, as well as the circumferential groove41which is provided by recessing from the frame section26.

FIG. 9is a detailed view of the area around the anchorage between the first part22and second part23, respectively, and the frame section26. The formation of this area is of crucial importance and affects how the membrane20can 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 joint27and the lower welded joint42, as well as the circumferential groove41. The circumferential groove41enters horizontally into the frame section26and has well rounded corners48,49so 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 joint27and the lower welded joint42above one another in a vertical plane which constitutes an abutment surface between the first part22and the second part23, respectively and the frame section26, superior mechanical strength will be obtained in the welded joints. The major part of the strain in the material of which the frame section26consists is taken up in connection with the circumferential groove41.

FIG. 10shows the tool9and how the apparatus according to the present invention realizes a downward depression of the central part of the tool9.FIG. 10shows the tool9in perspective view. The tool9consists of a first tool part50and a second tool part51. The first tool part50and the second tool part51may be distanced from one another and the blank which is to be formed in the tool9is placed in between these two tool parts50,51. 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 part50and the tool part51will receive a more even stamping throughout its entire surface when the hydraulic press acts on the tool9. 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 tool9. In the central area c of the tool9, 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 tool9is 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 tool9, 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 tool9and the slide, a more uneven distribution of the compression pressure would have been obtained in the tool9, which would have resulted in the blank placed between the tool part50and part51would have been stamped more unevenly. The stamping action would have been greater at the edges and less in the central areas of the blank.

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 apparatus20shown inFIG. 3may be varied. For example, additional apparatuses20may be placed on the underside21if necessary. In the foregoing description, we have spoken about placing the apparatus20or several apparatuses of the type20between the slide8and the tool9, in other words in the contact area56which is shown inFIG. 1. It is also conceivable to place one or more apparatuses20on the second clamping surface55on the work table10. The apparatuses20then act in the contact area57between the second clamping surface53on the work table10and the second abutment surface55on the tool9. By such means, additional compensation can be attained for improving the results on pressing in the tool9.

The configuration of the apparatus shown inFIGS. 5,6,7and8may 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 apparatus20is completely free and it may be designed in the manner which best suits any given practical application.

FIG. 7shows the holes32which are intended for the screw which is to secure the membrane20in, for example, the slide8or the work table10. 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.

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.