NL2004385A

NL2004385A - A press brake for bending sheets.

Info

Publication number: NL2004385A
Application number: NL2004385A
Authority: NL
Inventors: Bjarne Hansen
Original assignee: Amada Europ
Priority date: 2009-03-13
Filing date: 2010-03-12
Publication date: 2010-09-14
Also published as: FI20105240A0; FI20105240A; GB201004075D0; GB2468591A; SE534092C2; DE102010015920A1; IT1398894B1; ES2382282A1; TW201039938A; JP2010214469A; ITTO20100188A1; AT507944A2; FR2942981B1; AT507944B1; AT507944A3; NL2004385C2; CH700556A2; CH700556B1; US20100229619A1; RU2429096C1

Description

A PRESS BRAKE FOR BENDING SHEETS

The present invention relates to a bending press or"press brake" having tables with controlled deformation.

Bending presses are machine tools of a type that isitself well known. As shown in accompanying Figure 1,the machine tool comprises a lower table 12 and an uppertable 14 that is movable relative to the lower table 12.Usually, the lower table 12 is stationary and the uppertable 14 is suitable for being moved towards the lowertable 12 under drive from actuators Vx and V2 that act onthe ends 14a and 14b of the upper table 14. Usually, thelower table 12 has its free edge 12a fitted with fastenermeans 16 for fastening bending matrices 18. In the sameway, the edge 14c of the upper table 14 is fitted withfastener means 20 for fastening bending punches 22.

A metal sheet or lamination F is placed on thebending matrices 18 of the lower table 12. The sheet Fmay be of a length that varies widely depending on thecircumstances. Under drive from the pistons of theactuators Vi and V2, the punches 22 mounted on the uppertable 14 move towards the sheet placed on the matrices ofthe lower table. As soon as the punch 22 comes intocontact with the sheet F, force begins to increase withinthe sheet as the punch penetrates therein, initially inthe elastic range and subseguently in the plastic range,thereby enabling the sheet to be bent permanently.

Because the force is applied to the upper table bythe actuators Vi and V2 acting on the ends of the table,the linear load distributed between the two ends of thetables corresponds to the upper table being deformedalong a line in the form of a concave arc withdeformation maximas close to the midplane of the table.This means that, for bending purposes, at the end ofbending, the central portions of the punches havepenetrated into the sheet less than have the endportions. If bending were to be performed on a matrixthat, itself, were to remain perfectly straight during bending, then the result would be that a workpiece wouldbe obtained having a bend angle that was wider in its central portion than at its ends. Such a result isnaturally unacceptable.

In order to remedy that drawback, various solutionshave been proposed for the purpose of controlling thesedeformations at the edges of the tables by using variousmeans in order to obtain a bend that is substantiallyidentical over the entire length of the bent workpiece.

Conventionally, these solutions involve providingslots, such as the slots 24 and 26 shown in Figure 1,that are formed in the lower table 12 symmetrically aboutthe midplane P'P of the press. These slots 24, 26 thendefine a central zone 28 of the lower table 12 that isslot-free and that presents a length b, each of the twoslots 24 and 26 being of length a.

With slots 24 and 26 of conventional type, i.e. thatleave between them a slot-free portion 28 of length b,substantially parallel deformations are obtained for theedges of the upper and lower tables 14 and 12. Thisensures that proper bending is achieved. Nevertheless,this result is obtained only when the metal lamination orsheet F for bending has a length that is substantiallyequal to the total length of the lower or upper tables 12or 14. In contrast, when the length of the sheet F isless than the total length of the lower or upper table 12or 14, both of the deformations of the lower and uppertables 12 and 14 are concave.

In addition to the difficulty of proposing a bendingpress that is suitable for enabling the metal laminationor sheet F for bending to be deformed substantiallyuniformly over the entire length of said lamination orsheet F, regardless of whether its length is shortcompared with the length of the tables 12, 14 of thepress or, on the contrary, is equal to the length of thetables 12, 14 of the press, there exists an additionaldifficulty related to the top edges 24", 26" of the slots 24, 26 deforming while the bending force of the movingtable 14 is being applied to the stationary table 12, andsaid force is being taken up on the bottom edges 24', 26'of the slots 24, 26.

An object of the present invention is to remedythese two problems by proposing to dispose at least onestopper in each of the slots 24, 26, which stopper ismade up of two elements or wedges that have firstsurfaces fastened to respective ones of the edges of theslots, and second surfaces adapted for localized mutualcontact substantially in the centers of the wedges, in amanner such as to ensure excellent transmission of thebending force from the top edges of the slots to thebottom edges of the slots.

The invention thus provides a press brake forbending at least one metal sheet, said press brakecomprising: • an upper table having a bottom edge carrying firstbending tools, and a lower table having a top edgecarrying second bending tools, the two tables beingmovable relative to each other to exert a bending forceon the sheet; said press brake presenting a vertical midplane, oneof said tables having, through its entire thickness, twoslots disposed symmetrically about the midplane, eachslot having a first edge and a second edge, and an openfirst end opening out in a side edge of the table, aswell as a closed end; said press brake being characterized in that: at least one stopper is disposed in each slot, eachstopper comprising a first wedge having a first endsecured to the first slot edge and a second end forming afirst surface, and a second wedge having a first endsecured to the second slot edge and a second end forminga first surface; and in that the first surface of at least one of thefirst and second wedges has a central portion that is domed or protuberant relative to the other portions ofsaid surface so that the contact between the first andthe second wedges is established essentially over saidcentral portion.

The expression "secured to the first/second edge" isused to mean that the wedge in question is connected tothe first or second edge, it being understood that saidwedge may be movable relative to said edge of the slot.

Other characteristics of the press brake of theinvention are indicated below: • advantageously, the first surface of the firstwedge and the first surface of the second wedge both haverespective central portions that are domed or protuberantrelative to the other portions of said first surfaces; in an embodiment, the first surface of the firstwedge and/or the first surface of the second wedge is aconvex surface; • in an embodiment of the invention, the firstsurface of one of the wedges presents a concave surfacewhile the first surface of the other wedge presents aconvex surface; • in an embodiment of the invention, the firstsurface of at least the first wedge and/or of the secondwedge is a spherical surface portion; • advantageously, at least in the zone of thestoppers, the slots present constant height so that thefirst edge and the second edge are parallel, in theabsence of bending force for bending the metal sheet F; • advantageously, the first surfaces of the wedgesare inclined relative to the parallel edges of the slots; • preferably, the first surfaces of the wedges areinclined at a slope lying in the range 1% to 40% andpreferably in the range 5% to 10%, relative to an axis ora plane that is parallel to the edges of the slots; • in an embodiment of the invention, the firstsurface of at least the first wedge or of the second wedge presents a plurality of inclined plane peripheralportions connecting to the central portion; • the central portion presents a height orprotrusion lying in the range 0.05 millimeters (mm) to0.25 mm relative to the other portions of the firstsurface for a wedge of length substantially equal to 80mm; • advantageously, the wedges are mounted on supportsconnected to respective ones of the edges of the slots;at least one of the supports is movable laterally, i.e.along an axis parallel to the parallel edges of the sloton which it is mounted; in a possibility offered by the invention, the twowedges are offset relative to each other laterally, i.e.along an axis parallel to the parallel edges of the slot; • in a possibility offered by the invention, in theabsence of bending force for bending the metal sheet F,the first and second wedges present clearance betweenthem; and • advantageously, the press brake of the inventionhas a plurality of stoppers disposed in respective onesof the slots symmetrically about the midplane P'P.

Other characteristics and advantages of theinvention appear more clearly on reading the followingdescription of preferred embodiments of the inventiongiven by way of non-limiting example. The descriptionrefers to the accompanying drawings, in which: • Figure 1 shows a press brake having two slotssituated on respective sides of the midplane P'P andextending from opposite sides; • Figure 2 is a diagrammatic view showing anembodiment of a stopper that is made up of two wedges ofthe invention, one of the wedges being fastened to thetop edge of a slot 24 or 26, and the other being fastenedto the bottom edge of the slot 24 or 26; • Figure 3 is a diagrammatic view of two stoppersprovided with a motor-driven control system for controlling the value of the clearance associated withthe stoppers; • Figures 4 to 7 are diagrammatic views ofembodiments of a stopper of the invention, made up of twowedges that are initially in mutual contact; • Figure 8 is a side view of a stopper wedge of the invention; • Figures 9 to 12 show various embodiments of thefirst surface or contact surface of a stopper wedge ofthe invention; • Figure 13 diagrammatically shows the force fieldsor pressure fields passing through the wedges of astopper of the invention, when a bending force is appliedto the metal sheet F causing contact and a force F0between the wedges; • Figure 14 is a perspective view of a wedge whosefirst surface or contact surface is made up of threeportions; and • Figure 15 is a side view in section of two wedges,one below the other, that are identical to the wedge ofFigure 14.

Figure 2 is a section view of two wedges 28, 29 of astopper 27 of the invention. The two wedges 28, 29 haverespective contact first surfaces 28', 29' that, prior toapplication of a bending force F0, present clearance j_between them, as also shown in Figures 5 and 15.

Each of the wedges 28, 29 is mounted on a respectivesupport 40, 41 connected to a respective edge 24', 26' or24", 26" of a respective one of the slots 24 and 26. Thefunction of each wedge 28, 28', 29, 29' / stopper 27 isto control the extent to which the edges 24', 24" and26', 26" of each slot 24, 26 move towards each other whenthe bending force is applied. By controlling the extentto which the edges 24', 24" and 26', 26" of the slot 24or 26 move towards each other, it is possible to controlthe deformation of the top edge 24", 26" of the slot 24, 26, and therefore the deformation of the top edge 12a ofthe lower table 12.

At least one of the supports 40 or 41, andoptionally both of the supports 40 and 41 is/are mountedto move laterally, i.e. along an axis parallel to theparallel edges 24', 26' and 24", 26" of the slots 24, 26on which it is mounted. In the example shown toillustrate the invention in Figures 2 and 3, only thesupports 40 are suitable for being moved by means of theset of actuators 60, the supports 41 being fastened tothe slot edges 24", 26" of the lower table 12. Saidsupports 40 are moved by means of a set of actuators 60,shown m Figure 3, which set is connected via link arms61 to the moving supports 10. The set of actuators 60 iscontrolled by a remote control unit (not shown in theaccompanying figures). The motor-driven movement of thesupports 40, and thus of the wedges 29, makes it possibleto adjust the position of at least one of the wedges 29relative to the wedge 28, with a view to applying thebending force F0. This adjustment defines the value ofthe clearance j_, it being understood that the initialadjustment of the relative positions of the wedges 28, 29(before the bending force F3) is applied may also not makeprovision for any clearance, so that the wedges 28, 29are in abutment with each other. The clearance j_ betweenthe wedges 28, 29 or the relative position of the wedges28, 29 can be adjusted to within one hundredth of amillimeter by means of the set of actuators 60.

Naturally, it is possible to make provision for theset of actuators 60, or for a distinct drive mechanism,also to enable the supports 41 and thus the wedges 28 tomove. By way of example, Figure 8 shows a wedge 28, 29in which tapped orifices 71, 72, 73 can be seen (theorifices 71, 72 are seen end-on, while the orifice 73,situated in an adjacent face, is shown in dashed lines inthe thickness of the wedge), the orifices being designedto enable the wedge 28 or 29 to be fastened to a moving support 40 or to a stationary support 41 by conventionalmechanical means, such as a screw or a threaded rod.

In order to allow only limited lateral movement, thesupports 40 are provided with windows or notches 62 thatextend linearly to define the axes along which the movingsupports 40 move, inside which guide pins 63 are disposedthat are adapted to fit said windows 62. The movement ofthe supports 40 and of the wedges 29 is ideally parallelto the edges 24', 26' of the slots 24, 26. It should benoted that, advantageously, the edges 24', 24", and 26',26" of each of the slots 24, 26 are parallel, at least atthe wedges 28, 29 / stoppers 27.

The first surface 28', 29' of each of the wedges 28,29 advantageously has an inclination relative to the axesor to the planes of the parallel edges 24', 26' and 24",26" of the slots 24, 26. This inclination of the firstsurface 28', 29' of each of the wedges 28, 29 lies in therange 1% to 30%, as a function of the material formingthe wedges 28, 29, or more exactly of the coefficient offriction of the materials used to constitute the contactsurface 28', 29' of each of the wedges 28, 29. Thus, byway of example, it can be noted that the inclination ofeach of the wedges 28, 29 shown in Figures 2 and 3 liesin the range 2% to 10% while said inclination lies in therange 10% to 30% for the wedges 28, 29 shown, forexample, in Figures 6, 13, or 14. It should also benoted that the inclinations of the wedges 28, 29 cominginto abutment with each other may be the same or slightlydifferent.

In an essential aspect of the invention, at leastone of the first surfaces, or contact surfaces, 28', 29'of the respective wedges 28, 29 is provided with a domedor protuberant central portion 30, 31 so that the contactbetween the first and the second wedges 28 and 29 isestablished essentially over said central portion 30 or31.

This domed or protuberant central portion 30, 31 maybe of various shapes and may be present on one of the twowedges 28 or 29 only, or on both of the wedges 28, 29.

In addition, as explained below through the variousembodiments, due to the shape of the domed or protuberantportion 30, 31 of each of the first surfaces 28', 29' ofthe wedges 28, 29, the contact between the wedges 28, 29may consist of contact at a point or substantially at apoint, of contact along a line, or of contact over anarea.

In Figure 4, each of the wedges 28 and 29 has adomed or protuberant central portion 30, 31, whichportions form the contact zone of the two wedges 28, 29.In this example, the bottom wedge 29 is situated closerto the open end 26a of the slot 26 than is the top wedge28 so that there is a slight lateral offset between thetwo wedges 28, 29. In this example, the first surface28', 29' of each of the two wedges 28, 29 consists of aspherical surface, but the vertex S of the sphericalsurface of each of the two wedges 28, 29 is not situatedexactly in the center of the first surface 28' or 29'.That is why the two wedges 28, 29 are offset slightlylaterally relative to each other so that the contactbetween the two wedges, initially and/or while thebending force F0 for bending the sheet F is being applied,makes contact possible at the central portions 30, 31.

Naturally, this manner of arranging the wedges 28, 29 relative to each other is a function of the spherical surfaces of the two first surfaces 28', 29' of the wedges 28, 29, but it is also a function of the flexing of thetop portion 12c of the lower table 12, and thus of theextent to which the top wedge 28 itself moves.

In general, it should be noted that, by convention,the vertex of the domed or protuberant central portion30, 31 is considered relative to a plane P0 joining twoopposite edges 80, 81 of the wedge 28 or 29, which planePc corresponds to the inclination of the wedge 28, 29.

The vertex S is the point of the domed or protuberantcentral portion 30, 31 that is at the furthest distance("protrusion") from the plane P0. This plane Po is shownin Figures 14 and 15 that show a last embodiment of theinvention. As can be seen in Figure 14, the plane P0 isthe plane joining the two opposite edges 80, 81. Thevertex S of the domed or protuberant central portion 30, 31 may be located at one end of said portion, as shown inFigure 14. The maximum height of the vertex S isreferenced h. In Figure 15, it can be noted thatsubstantially the entire domed or protuberant centralportion 30, 31 is at the height h relative to the planePc. It can also be understood that, due to theinclination of the first surfaces 28', 29' of the wedges28, 29, the vertex S of the protuberant portion 30, 31does not necessarily coincide with the point of the firstsurface 28', 29' that is furthest away from the slot edge26', 26" to which the wedge 28, 29 is fastened.

Figure 5 shows a variant of Figure 4. In thisexample, the bottom wedge 29 is situated further awayfrom the open end 26a than is the top wedge 28, so that,once again, there is a slight lateral offset between thetwo wedges 28 and 29, but the offset is the reverse ofthe lateral offset of the wedges 28, 29 shown inFigure 4. In addition, in the initial state, in theabsence of any force exerted by the actuators Vi, V2, thefirst surfaces 28', 29' present clearance j_ between them.In the embodiment of Figure 5, as in the embodiment ofFigure 4, the arrangement of the domed central portion30, 31 of each of the first surfaces 28', 29' of each ofthe wedges 28, 29 and the relative lateral offset of thetwo wedges 28, 29 are chosen so that, while the bendingforce is being applied to the metal sheet F, the twowedges 28, 29 are in contact over their respective domedor protuberant central portions 30, 31.

Figures 6 and 7 show the bending force F0 for bendingthe metal sheet F that essentially causes the top portion 12c of the lower table 12 to flex so that the top edge26" of the slot 26 moves closer to the bottom edge 26' ofthe same slot 26.

Once again, in these two Figures 6 and 7, the wedges28 and 29 are offset laterally relative to each other.

In the embodiment of Figure 6, only wedge 29 has a firstsurface 29' with a domed or protuberant central portion31, e.g. a spherical surface or a plane protuberantsurface. The contact between the two wedges 28, 29 takesplace, for the wedge 29, over its domed or protuberantportion 31. It should be noted that, when only one ofthe two wedges 28 or 29 has a domed or protuberantcentral portion 30, 31, it is advantageous for the wedgethat is provided with the central portion 31 to be thebottom wedge 29 that is fastened to the bottom edge 26'of the slot 26. The wedges 28, 29 with their protuberantcentral portions 30 and/or 31 and their relative lateraloffset are designed to compensate for the non-parallelismof the edges 24', 24" and 26', 26" of the slots 24 and26.

The embodiment of Figure 7 is analogous to theembodiment shown in Figure 4, but Figure 7 shows the topportion 12c of the lower table flexing while the bendingforce Fo is being applied, and said force beingtransmitted to the lower table 12.

In addition to the tapped orifices 71, 72, and 73serving to fasten the wedge 28 or 29 to a support 40, 41,Figure 8 shows a first surface 28', 29' seen from theside, on which surface it is difficult to see with thenaked eye that there is a domed or protuberant centralportion 30, 31. This is because the first surface 28',29' of the wedge 28, 29 is a spherical surface that has aradius of curvature that is extremely large relative tothe length of the wedge 28, 29. By way of example, thewedge 28, 29 of Figure 8 has a length lying in the range60 mm to 80 mm and the radius of curvature of each of thefirst surfaces 28', 29' lies in the range 7000 mm (or 7 meters) to 9000 mm (or 9 meters). The protrusion, i.e.the maximum height of the central portion 30, 31 relativeto the plane surface of the first surface, which planesurface is defined by the straight line joining theopposite ends 80, 81 of the first surface 28', 29', liesapproximately in the range 0.05 mm to 0.25 mm. The domedor protuberant portion 30, 31 thus has a maximum heightor protrusion lying in the range 0.05% of the length(longest surface dimension) of the first surface 28', 29'to 0.4% of said length (when the inclination of the firstsurface is not too large, it can be considered, byapproximation, that the length of each of the wedges isequal to the length of its first surface), said maximumheight or protrusion preferably lying in the range 0.1%of the length of the first surface 28', 29' of the wedge28, 29 to 0.3% of said length. It can be understood thatthe difference in height of the domed or protuberantcentral portion 30, 31 is often not perceptible with thenaked eye, and that the accompanying figuresintentionally magnify the central portion 30, 31 forreasons of simplification and of understanding.

Figure 9 shows a wedge 28, 29 having a first surface28', 29' that is substantially cylindrical and dished.

In this example, the first surface 28', 29' of the wedge28, 29 is provided with a dome constituting the domed orprotuberant central portion 30, 31 of the wedge 28, 29.This dome may consist of a spherical surface that isprotuberant relative to the first surface 28', 29'presenting a section of substantially cylindrical shape.

The wedge 28, 29 shown in Figure 10 has an inclinedcylindrical first surface 28', 29'. The center 0 of thesphere, of which the first surface 28', 29' of the wedge28 or 29 forms a portion, is offset relative to thevertical V starting from the center C of the firstsurface 28', 29' (this vertical V intersects the bottomplane formed by the first end secured to the first edgeof the slot 24' or 26'). In this example, the centre C

of the first surface 28' or 29' of the wedge 28 or 29constitutes the point of contact with the first surface28' or 29' of the other wedge 28 or 29. Thus, when thefirst surface 28' or 29' has a spherical surface, thecontact with the first surface 28', 29' of the otherwedge 28 or 29, regardless of the shape thereof, iscontact at a point or substantially at a point. The areaof contact 28', 29' between the two wedges 28, 29 is thusvery small and, taking account of the manufacturingtolerances for the wedges 28, 29, and of the materialsused, it represents about 1 square millimeter (mirk) . Ingeneral manner, this point or substantially point contactbetween the two wedges 28, 29 may optionally take placeat the center C of each of the first surfaces 28', 29' ofthe wedges 28, 29 but, as explained above, the contactbetween the two wedges 28, 29 depends on their respectiveinclinations and on their relative offset, as well as onthe movement of the top wedge 28 while the bending forceFc for bending the metal sheet F is being applied.

Figure 11 shows a variant embodiment of the firstsurface 28', 29' of the wedge 28, 29. In thisembodiment, the central portion 30, 31 consists of aplane surface. This central portion 30, 31 is in theform of a rectangular or square surface representing inthe range 5% of the total area of the first surface 28',29' to 25% of said total area, and preferably in therange 10% of said total area to 15% thereof. In thisexample, the first surface 28', 29' of the wedge 28, 29has four inclined plane peripheral portions 33, 34, 35,and 36 extending from respective ones of the four edgesof the first surface 28', 29' to the central portion 30,31. In this example in which the central portion 30, 31is a plane surface, the contact with the first surface28', 29' of the other wedge 28, 29, presenting a planecontact surface (optionally the first surface 28', 29' ofsaid other wedge 28, 29 is identical to the first surface of the wedge 28, 29 shown in Figure 11), is area contactbetween the two wedges 28 and 29.

Figures 14 and 15 also show an embodiment in whichthe contact between the first two surfaces 28', 29' ofthe two wedges 28, 29 is area contact. As shown in thesefigures, the first contact surface 28', 29' issubstantially an inclined surface, i.e. the oppositeedges 80, 81 have different heights. In addition, thefirst surface 28', 29' of the wedges 28, 29 has threesuccessive segments 40, 30 or 31, and 42, extending overthe entire width of the wedge 28, 29, and each having adifferent inclination; the inclinations of the segments40, 30/31, and 42 increasing going from the segment 40 tothe segment 42. The intermediate or central segmentconstitutes the central or protuberant portion 30, 31.Relative to the plane or the axis 50 joining the oppositeedges 80, 81 of the wedge 28, 29, the central portion 30,31 presents a maximum height h of about 0.1 mm. As canbe seen in Figure 15, the two wedges 28, 29 that areoffset slightly relative to each other are identical butthe orientations of their respective first surfaces 28',29' are opposite so that only the central portions 30, 31face each other and are substantially parallel. Becauseof the offset between the two wedges 28, 29, only aportion of each of the central portions 30, 31 comes intocontact, of the area contact type, with the respectiveportion of the other central portion. It should be notedthat, in this example, the two wedges 28, 29 presentclearance j_ in the initial state.

Figure 12 shows the third possible mode of contactbetween the two wedges 28, 29, namely linear contact, thefirst two modes being point or substantially pointcontact, and area contact. In this example that ischosen to illustrate this third type of contact, only thewedge 28 has a protuberant central portion 31. In thisexample, the first surfaces 28', 29' of the wedges 28, 29are cylindrical surfaces, but while the first surface 28' lies on the inside of a cylinder so that the firstsurface 28' is protuberant relative to the plane/axisjoining the opposite edges of the wedge 28, the firstsurface 29' lies on the outside of a cylinder so that thefirst surface 29' forms a recess relative to theplane/axis joining the opposite edges 80, 81.

In addition, the center Oi of the cylinder on whichthe first surface 28' lies is closer to said surface 28'than the center 02 of the cylinder on which the firstsurface 29' lies. Thus, the radius of the cylinder ofwhich the first surface 28' forms a portion is smallerthan the radius of the cylinder of which the firstsurface 29' forms a portion. That is why only the vertexof the central portion 30 of the first surface 28' comesinto contact over the entire width of the first surface29' of the wedge 29, so that the contact between the twowedges 28, 29 is linear contact.

Figure 13 shows the force lines that are exertedwhile the bending force Fc for bending the metal sheet Fis being applied. The force lines converge or areconcentrated from the first end of the wedge 28 that isfastened to the edge 26" of the slot 26 towards theprotuberant central portion 30 of the first surface 28'of the wedge 28 that is in contact with the protuberantcentral portion 31 of the first surface 29' of the wedge29; these force lines then spread out over the entirewidth of the wedge 29. In this example, the firstsurfaces 28', 29' of the wedges 28, 29 present sphericalor cylindrical surfaces so that the contact isrespectively point contact, substantially point contact,or linear contact. The wedges 28, 29 may be made ofhardened steel while the lower table 12 may be made ofmild steel, thereby, in the absence of plasticdeformation, making it possible for stress to be highbetween the wedges 28, 29 but low between the wedges 28,29 and the lower table 12.

Naturally, the contact between the first surfaces28', 29' that is described as being point contact orlinear contact is the first contact during or at thebeginning of application of the force Fc, because, afterthis point or linear contact, the pressure from the topwedge 28 on the bottom wedge 29 is such that the firstsurfaces 28', 29' of the wedges 28, 29 enter at least anelastic deformation stage so that a contact zone that islarger is reached. While the force F0, e.g. a force of200 kilonewtons (kN), is being applied, the contact zoneis preferably approximately in the range 20% of the totalarea of each of the first surfaces 28', 29' of the wedges28, 29 to 50% of said total area.

In accordance with a characteristic of theinvention, the domed or protuberant central portion 30, 31 may include the center C of the first surface 28', 29'as the center of said central portion 30, 31 so that theprotrusion of the domed portion 30, 31 coincides with thegeometrical center of the first surface 28', 29' of thewedge 28, 29, but it is also possible to make provisionfor said domed or protuberant central portion 30, 31 tobe offset slightly relative to the center C of the firstsurface 28', 29': such an embodiment is, for example,shown in Figure 7 in which the domed or protuberantcentral portion 31 is offset slightly relative to thecenter C of the first surface 28', 29' of each of thewedges 28, 29, so that the protrusion or maximum heightof the central portion 30, 31 does not coincide exactlywith the geometrical center C of the first surface 28',29' of each of the wedges 28, 29. This offset or thiseccentricity of the protrusion of the domed portion 30, 31 relative to the center C of each of the first surfaces28', 29' is relatively small and, by way of example, liesin the range 2 mm to 10 mm for a wedge of length 80 mm.This eccentricity or offset of the protrusion of thedomed or protuberant central portion 30, 31 relative tothe center C of the first surface 28', 29' may thus lie in the range 0% of the length of the wedge 28, 29 to 40%of the length thereof.

In a possible embodiment of the invention, thewedges 28, 29 are identical, i.e. their dimensions aremutually equal and their first surfaces 28', 29' aremutually identical, both in shape and in size.

However, it is also quite possible, as described forthe various accompanying figures, for the two wedges 28,29 not to be identical, i.e. essentially for their firstsurfaces 28', 29' not to be the same, and optionally foronly one of the first surfaces 28', 29' of said wedges28, 29 to have a domed or protuberant central portion 30,31.

Claims

A bending press for bending at least one metal plate (F), the bending press comprising: an upper work surface (14) with a lower edge (14c) bearing first bending tools, and a lower work surface (12) with an upper edge (12a) which carries second bending tools, wherein the two work surfaces are movable relative to each other for exerting a bending force on the plate (F); the bending press having a vertical center plane (P'P), one of the worktops (12, 14) having through its entire thickness two slots (24, 26) disposed symmetrically with respect to the center plane (P'P), each slot (24, 26) a first edge (24 ', 24 ") and a second edge (26', 26"), and an open first end (24a, 26a) which opens into a side edge of the worktop, as well as a closed end ( 24b, 26b); wherein the press is characterized in that: at least one stopper (27) is placed in each slot (24, 26), each stopper (27) comprising a first wedge (28), with a first end attached to the first slot edge (24 'or 26 ') and a second end that forms a first surface (28'), and a second wedge (29) with a first end attached to the second slot edge (24 "or 26") and a second end that forms a second surface (29 ') ; and in that the first surface (28 'or 29') of at least one of the first and second wedges (28, 29) has a central portion (30 or 31) that is dome-shaped or protruding with respect to the other portions of the surface (28 ', 29 '), so that the contact between the first and the second wedges (28 and 29) is effected mainly on the central portion (30 or 31).

Bending press according to claim 1, characterized in that the first surface (28 ') of the first wedge (28) and the first surface (29') of the second wedge (29) both have corresponding central portions (30, 31 ') that are dome-shaped or protruding from the other portions of the first surfaces (28 ', 29').

Bending press according to claim 1 or claim 2, characterized in that the first surface (28 ') of the first wedge (28) and / or the first surface (29') of the second wedge (29) is a convex surface.

Bending press according to one of claims 1 to 3, characterized in that the first surface (28 ', 29') of one of the wedges (28 or 29) comprises a concave surface, the first surface (28 ', 29) ') of the other wedge (28 or 29) comprises a convex surface.

Bending press according to one of claims 1 to 4, characterized in that the first surface (28 ', 29') of at least the first wedge (28) and / or of the second wedge (29) is a spherical surface portion.

Bending press according to one of the preceding claims, characterized in that, at least in the area of the stoppers (27), the slots (24, 26) have a constant height (H) so that the first edge (24 ', 26') and the second edge (24 ", 26"), in the absence of a bending force for bending the metal plate (F), are parallel.

Bending press according to claim 6, characterized in that the first surfaces (28 ', 29') of the wedges (28, 29) are inclined with respect to the parallel edges (24 ', 26' and 24 ", 26") of the slots (24, 26).

Bending press according to claim 7, characterized in that the first surfaces (28 ', 29') of the wedges (28, 29) are inclined with respect to an axis parallel to the edges (24 ', 26' and 24 ", 26 ") of the slots (24, 26), with a slope that is in the range of 1% to 40% and preferably in the range of 5% to 10%.

Bending press according to one of the preceding claims, characterized in that the first surface (28 ', 29') of at least the first wedge (28) or of the second wedge (29) has a multiple number of inclined flat peripheral sections (33,34, 35, 36, or 40, 42) connected to the central portions (30 or 31).

Bending press according to one of claims 1 to 9, characterized in that, for a wedge (28, 29) with a length substantially equal to 80 mm, the central part (30, 31) has a height or protrusion lying in the range from 0.05 mm to 0.25 mm relative to the other portions of the first surface (28 ', 29').

Bending press according to one of the preceding claims, characterized in that the wedges (28, 29) are mounted on supports (40, 41) connected to corresponding edges (24 ', 26' and 24 ", 26") of the slots (24) , 26).

Bending press according to claim 11, characterized in that at least one of the supports (40) is movable laterally, i.e. along an axis parallel to the parallel edges (24 ', 26', and 24 ", 26") of the slot (24, 26) to which it is attached.

Bending press according to one of claims 1 to 12, characterized in that the two wedges (28, 29) are spaced laterally apart, i.e. along an axis parallel to the parallel edges (24 ', 26' and 24 ", 26") of the slot (24, 26).

Bending press according to one of the preceding claims, characterized in that, in the absence of a bending force for bending the metal plate (F), there is clearance (45) between the first and second wedges (28, 29).

Bending press according to one of the preceding claims, characterized in that it has a plurality of stoppers (27) that are placed in corresponding slots (24, 26) symmetrically with respect to the center plane (P, P ").