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 is itself well known. As shown in accompanying
A metal sheet or lamination F is placed on the bending matrices 18 of the lower table 12. The sheet F may be of a length L that varies widely depending on circumstances. Under drive from the pistons of the actuators V1 and V2, the punches 22 mounted on the upper table move towards the sheet F placed on the matrices of the lower table. As soon as the punch comes into contact with the sheet, force begins to increase within the metal lamination or sheet F as the punch penetrates therein, initially in the elastic range and subsequently in the plastic range, thereby enabling the sheet to be bent permanently.
Because the force is applied to the upper table by the actuators V1 and V2 acting on the ends of the table, the linear load distributed between the two ends of the tables corresponds the upper table being deformed along a line in the form of a concave arc with deformation maximas close to the midplane of the table. This means that for bending purposes, at the end of bending, the central portions of the punches have penetrated into the sheet less than have the end portions. If bending were to be performed on a matrix that, itself, were to remain perfectly straight during bending, then a metal lamination or sheet F would be obtained having a bend angle that was wider in its central portion than at its ends. Such a result would naturally be unacceptable.
In reality, the matrices carried by the lower table, or more precisely by the free edge of the lower table, are in fact subjected to deformation during bending, which deformation is likewise concave with its maximum in the central portion. The result of these two deformations is that, in reality, the bending obtained in the sheet is very open in the middle portion of the press and very closed at its ends. In reality, the difference may reach an angle of several degrees, e.g. 93° at the midplane of the tables and 90° at its ends. The resulting sheet thus presents poor accuracy concerning the linearity of its bend, thus giving it a so-called “boat” shape.
In order to remedy that drawback, various solutions have been proposed for the purpose of controlling these deformations at the edges of the tables by using various means in order to obtain a bend that is substantially identical over the entire length of the bent metal lamination or sheet F.
Usually, these solutions involve providing slots, such as the slots 24 and 26 shown in
With slots 24 and 26 of conventional type, i.e. that leave between them a slot-free portion 28 of long length l0, substantially parallel deformations D1 and D2 are indeed obtained for the edges of the upper and lower tables 14 and 12, as shown in
In European patent EP 1 112 130, there is proposed a solution of fitting each slot of the lower table with a mover member connecting together the free top portion and the stationary bottom portion of the lower table so as to cause the top wall of the slot to approach the bottom wall thereof, assuming the bottom wall is stationary. This enables the curvature of the deformation of the free top portion of the lower table carrying the matrices to be modified in controlled manner, in the absence of any stress being applied to the tables. The drawback of that solution is that it requires a complex hydraulic control installation to be put into place.
Similar solutions are disclosed in documents JP 2001-71033, JP 2000-343125, and WO 01/43896.
An object of the present invention is to provide a bending press including a system for correcting the deformation of the edges of the tables, which system remedies the above-mentioned drawbacks, and in particular makes it possible to obtain substantially parallel deformation of the edges of the upper and lower tables over a range of lengths of metal sheet for bending that is very wide compared with the length of the tables of the press, and regardless of whether the metal sheet for bending is positioned the symmetrically or asymmetrically relative to the midplane of the press, for a given adjustment of the machine; and/or makes it possible to obtain very high bending accuracy even for sheets of very great length and made of materials that have the reputation of being difficult to bend.
To achieve this object, in a first aspect of the invention, the bending press for bending metal sheets comprises:
said press presenting a vertical midplane, one of said tables presenting two slots through its entire thickness and disposed symmetrically relative to the midplane, each slot having an open first end opening out in a side edge of the table and a closed end, the closed ends defining a slot-free table portion of length l0; wherein said press:
also includes an even number of stoppers, each stopper being disposed in one of the slots at a fixed distance from the closed ends, and the stoppers being disposed symmetrically about the midplane, said stoppers presenting a predetermined coefficient of elasticity;
each stopper defining in the zone of the slot in which it is located, a possibility of controlled approach of the two edges of the slot under the effect of the load applied to the table including the slots, said approach resulting from at least one of two parameters consisting in clearance j initially provided by said stopper in the slot in the absence of an applied load and the elastic deformation of said stopper, the possibility of approach created by a stopper closer to the closed end being smaller than that of any stopper closer to the open end;
the possibilities of approach of the edges of the slot corresponding to the stoppers and their positions in the slots being determined in such a manner that, at the end of application of the bending force by the movable table against the other table via the sheet, the curves of the edges of the tables are substantially parallel to each other.
The invention is applicable to all types of bending press regardless of whether the movable table is the upper table or the lower table. Likewise, the correcting slots may be formed in the upper table or in the lower table.
Nevertheless, the most common configuration is that in which the upper table is the moving table and the slots are formed in the lower table.
It should be understood, that because of the presence of the stopper(s) in each slot, substantially parallel deformation of the edges of the upper and lower tables is obtained when working on metal sheets of great length (i.e. extending not only through the slot-free portion of the table, but also over substantial fractions of the slots). This is because, given the initial clearance that is provided (in the absence of stress being applied to the table) and/or given the elastic deformation of the stoppers, the stress that is applied to the table including the slots gives rise progressively to a controlled approach of the edges of the slot. By appropriately adapting firstly the position(s) of the stopper(s) in each slot and secondly the clearance created by each stopper and/or the capacity of the stopper itself for elastic deformation, it is indeed possible to obtain parallel deformation of the edges of the upper and lower tables, even when the length of the metal sheet for bending is long and even if the sheet is off-center relative to the midplane P′P of the press.
Provision may be made for at least some of the stoppers to be placed without significant clearance in their respective slots in the absence of any applied load, with the deformation of the slot then being associated solely with the deformation capacity of the stopper. It is also possible to make provision for such clearance to be present, with the slot then deforming freely to begin with, followed by deformation of the stopper.
In one embodiment, the force applied to the movable table is applied to both ends thereof in such a manner that the same travel stroke is applied to both ends, and two symmetrical stoppers present the same possibility of controlled approach.
This embodiment is particularly well adapted to circumstances in which the metal sheet for bending occupies a symmetrical position relative to the midplane of the press.
In an embodiment of the first aspect of the invention, the force applied to the movable table is applied to both ends thereof in such a manner that different travel strokes are applied to both ends and two symmetrical stoppers present the same possibility of controlled approach.
According to one possibility made available by the invention, two symmetrical stoppers present different possibilities of controlled approach.
This embodiment is well adapted to circumstances in which the metal sheet occupies a position that is asymmetrical relative to the midplane P′P of the press. This is because the asymmetrical nature of the position of the sheet is then compensated by the different travel lengths of the two ends of the movable table.
More preferably, the press has four stoppers, with two stoppers being provided in each slot. The stoppers may define clearances j that are controllable.
This disposition enables the deformation of the table to be controlled at two distinct points within the slot. It is therefore particularly well adapted to tables of great length, typically presenting lengths of 2.5 meters (m), 3 m, or longer.
The initial adjustment of the positions of the stoppers in the slots is appropriate for a very large number of bending situations. Nevertheless, in certain circumstances, it may be necessary to modify these adjustments, so it is advantageous for the stoppers to enable the clearances they define to be modified easily.
According to one possibility, at least one of the stoppers defines clearance that is equal to zero. Preferably, the stoppers define clearance that is less than 1 millimeter (mm). In most circumstances, the clearance will in fact be less than 0.3 mm.
In a preferred embodiment, it is possible to make provision for the stoppers to be capable of occupying positions in a controllable manner as a function of the particular length of a sheet for bending, while nevertheless presenting positions that are stationary while the press is in use. The positions to be occupied by the stoppers as a function of the sheet for bending may be determined with the help of three-dimensional mathematical models.
In a preferred embodiment of the bending press, in accordance with the first aspect of the invention, each stopper comprises:
A bending press of a second aspect of the invention comprises an upper table provided with a fastener for top tools and a lower table provided with a fastener for bottom tools, the two tables being placed edge-to-edge in the vertical direction, and one of the tables being movable relative to the other in the vertical direction, one of the tables presenting slots disposed symmetrically relative to the midplane, each slot having an open outside end; wherein each of said slots comprises a first slot portion and a second slot portion that is situated on the inside relative to the first slot portion and that is connected thereto, the shapes of said slot portions being such that the stiffness of the portion of the table situated between the slot and the tool fastener is greater between the first slot portion and the tool fastener than it is between the second slot portion and the tool fastener, and wherein at least one element for adjusting the flexing of said table is disposed in the first slot portion.
As can be understood on reading of the detailed description, these characteristics make it possible to obtain high bending accuracy, both with sheets of great width, comparable to the length of the tables, and with sheets of smaller width, by ensuring that the edges of the lower and upper tables deform substantially in parallel.
Advantageously, the vertical distance between the inside end of the first slot portion whereby the first slot portion is connected to the second slot portion, and the tool fastener, is greater than the vertical distance between the inside end of the second slot portion and the tool fastener.
Advantageously, the first and second slot portions are inclined relative to each other. Under such circumstances, and advantageously, the first slot portion presents, over at least a segment of said first portion, a general direction that is horizontal, while at least the inside end of the second slot portion, remote from the first slot portion, is oriented towards the tool fastener. It is then also advantageous for the second slot portion to be inclined towards the tool fastener.
Furthermore, and advantageously, the second slot portion presents a curved shape with its concave side directed towards the tool fastener.
Advantageously, the second slot portion presents a staircase shape.
Advantageously, the first slot portion presents a general direction that is horizontal, and the inside end of the second slot portion is oriented substantially horizontally towards the vertical midplane of the table.
Advantageously, the second slot portion presents at least one portion that is flared going away from the first slot portion.
Advantageously, the first slot portion includes an outer slot portion that is inclined so as to be closer to the tool fastener than is an inner portion of the first slot portion.
Advantageously, at least one of the slot portions presents a width, as measured vertically, that varies along the zone of said slot portion in which the width is measured.
Advantageously, the inner ends of the first slot portions are positioned in such a manner that while bending a sheet, of width substantially equal to the length of the upper or lower table, the difference in height between the upward convex flexing peak in the middle of the lower table and the two side ends of the lower table remains within a predetermined tolerance.
Advantageously, the inner ends of the second slot portions are positioned in such a manner that while bending a sheet placed in the middle of the length of the tables, and of width shorter than the length of the upper or lower table, the difference in height between the upward convex flexing peak in the middle of the lower table and the portions of the lower table in contact with the side edges of the sheet remains within a predetermined tolerance.
Advantageously, the length l0 is defined so that the portion of the table between the closed ends of the slots is suitable for absorbing any stress substantially equal to the maximum stress applied during bending of the sheet without giving rise to elastic deformation of the table provided with the slots. The term “maximum stress” should be understood as a limit stress for which the bending press is dimensioned and that does not give rise to any plastic deformation.
Preferably, the length l0 between the ends of the slots is less than 35% of the length L of the table including said slots. More preferably, said length l0 is substantially equal to 20%±15%, and preferably 20%±5%, of the length L of the table including said slots.
This particular length for the slot-free portion of the table makes it possible on average to obtain effectively no deformation between the center of the sheet and in its ends, for metal sheets for machining and that are of shorter length, close to the length l0.
Preferably, said length l0 is equal to about 80% of the length of a sheet centered on the press for which the deformation curve under the action of the movable table is substantially negligible.
Other characteristics and advantages of the invention appear better on reading the following description of several embodiments of invention given as non-limiting examples. The description refers to the accompanying figures, in which:
With reference initially to
In
Naturally, the edges 30a and 32a of the tables 30 and 32 are fitted with the tool carriers shown in
The slots 34 and 36 are preferably parallel to the free edge 32a. They are disposed symmetrically about the midplane P′P of the press, this plane being orthogonal to the length of the tables 30 and 32. The slots 34 and 36 thus define top edges 34c and 36c, and bottom edges 36d and 34d.
According to the invention, stoppers 44, 46, 48, and 50 are mounted in each of the slots 34 and 36, and they are disposed symmetrically about the midplane P′P. There is thus necessarily an even number of stoppers. In the example shown in
To finish off describing the general definition of the system for stabilizing deformation of the upper and lower tables 30 and 32, it should be added that the length l0 of the engagement zone 38 between the two slots 34 and 36 is considerably shorter than the length of the same zone in previously-known devices.
The engagement zone 38 has a length l0 that is short, but nevertheless sufficient to absorb the maximum stress that is applied while bending a sheet.
Preferably, the length l0 is less than 90% of the total length of the table 30 or 32 that includes the slots 34 and 36, generally the lower table 32. Naturally, this length l0 depends on the thickness of the table in the direction orthogonal to the plane of the figures. More preferably, the length l0 lies in the range 15% to 25% of the total length of the table 32. It can also be readily understood that for presses of short length, e.g. of length shorter than 2 m, the percentage should be towards the high end of the range.
Also preferably, the length l0 may be defined as follows:
the length l0 corresponds to at least 80% of the length of a metal sheet or lamination that, while being bent over its entire length, gives rise to no significant deformation of the free edges 30a and 32a of the upper and lower tables 30 and 32, providing the metal sheet or lamination is centered on the midplane P′P. From a practical point of view, the width of such a sheet or lamination is about 80 centimeters (cm) such that the length l0 is of the order of 65 cm for upper and lower tables 30 and 32 that present a total length equal to 3 m, which corresponds to a standard length for a bending press.
Thus, as explained above, the function of each stopper 44, 46, 48, and 50 is to control the approach of the edges 34c and 36c of each slot 34 and 36 while the bending force is being applied. By controlling the approach of the edges 34c and 34d or 36c and 36d of the slot 34 or 36, the deformation of the top edge 34c or 36c of the slot 34 or 36 is controlled, and consequently the deformation of the top edge 32a of the lower table 32 is controlled, assuming that it is the lower table that is provided with the slots 34 and 36.
This approach is controlled with the help of the stoppers 44, 46, 48, and 50 as a result either of initial clearance j as defined by the stopper, or of the elastic deformation of the stopper under the effect of the stress, or indeed of a combination of both. By acting on these two parameters, it is thus possible to obtain great accuracy in the deformation of the lower table for a very wide variety of lengths of metal sheet.
Tests that have been performed show that suitable initial clearance j, if any, is less than 1 mm, even for bending presses of great length, typically 6 m. With presses of more standard length, of the order of 3 m, this clearance, if any, is found to be less than 0.8 mm.
Tests performed with a bending press of the above-described type show that regardless of the length of the sheet, and to some extent regardless of the way it is centered relative to the midplane P′P, substantially parallel deformations are obtained of the free edges 30a, 32a of the upper and lower tables 30 and 32 because of the way the stoppers 44, 46, 48, and 50 act, because of their correct positioning li and l2 in the slots 34 and 36, and because of the initial clearance j provided.
As shown in
As shown in
Tests performed using a machine of the above-described type show that when there is a need to bend a part that needs to be off-center relative to the midplane P′P of the press, a mode of operation is obtained that is very similar to that described above, and that corresponds to the sheets for bending being in positions that are centered.
In the above-described preferred embodiments, the upper table 30 is movable while the lower table 32 is stationary. Naturally, the inverse configuration would not go beyond the invention, i.e. the configuration in which the upper table is stationary while the lower table is movable.
In the same manner, the slots 34 and 36 are made in the lower table 32. Naturally, these slots 34 and 36 could be made in the upper table 30, regardless of whether it is movable or stationary, providing the same rules are applied for placing the stoppers 44, 46, 48, 50, or 59 and for defining the engagement zone 38 between the closed ends 34b and 36b of the two slots 34 and 36.
In the preceding figures, the slots 34 and 36 are shown as being substantially parallel to the edge 32a of the lower table 32, and of width that is substantially constant. Nevertheless, it may be advantageous to provide slots of a different shape, in particular in order to reduce stresses in the table that has the slots, preferably the lower table 32, under the action of forces on the other table 30. This is what is shown in
In the figure, there can be seen the top portion 40 of the lower table 32 and the bottom portion 42 of the table 32. In the figure, the slot is given reference 80.
In this embodiment, the slot 80 has a first portion 82 opening out into the side of the table 32, a middle portion 84, and a third portion 86 terminating at the closed end 88 of the slot 80.
The first portion 82 of the slot is substantially rectilinear, of height that is substantially constant, and inclined relative to the edge 32a of the table by an angle α. This serves to reduce the second moment of area of the end of the top portion 40 of the lower table 32.
The intermediate portion 84 is essentially determined to facilitate positioning and assembling the stopper(s), e.g. the stoppers 44 and 46. For this purpose, its height is greater than the height of the portion 82.
The third portion 86 presents the closed end 88 in the form of a portion of a circle of radius that is determined so as to decrease stresses. The remainder 80 of the third portion 86 is preferably defined by two curved zones C1 and C2 that also serve to limit stresses.
The adjustments of the stoppers, i.e. their capacities for controlling the approach of the edges of the slot by means of the initial clearance and/or by means of elastic deformation, are particularly well adapted to circumstances in which the sheet for bending is placed symmetrically relative to the midplane of the press. Under such circumstances, the adjustments of symmetrical stoppers are identical. When the sheet is positioned in slightly asymmetrical manner, the symmetrical adjustments of the stoppers may suffice.
If there is a large amount of asymmetry, different adjustments may be provided for stoppers disposed symmetrically about the midplane. Another solution consists in providing identical adjustments for symmetrical stoppers and in providing different amounts of movement for the two ends of the movable table, usually the upper table. This result may be obtained by applying different controls to the actuators V1 and V2 so that, at the ends of their strokes, the movements of the ends of the movable table are different.
It is naturally possible to combine different initial adjustments for symmetrical stoppers and different amounts of movement for the two ends of the movable table.
There follows a description of
The respective outside ends 134a and 136a of the slots 134 and 136 are open.
It can be seen that adjustment elements 180 are disposed in the slots 134 and 136. For example, each adjustment element may be constituted by a wedge, and as in the example described above, in particular with reference to
It should be understood that the adjustment elements 180 may be of a configuration other than that described above. Any determined combination of bottom and top wedge elements may be involved.
It should be observed that each of the slots 134 and 136 has a respective first slot portion 135a and 137a, and a respective second slot portion 135b and 137b. For each slot, the respective second portion 135b or 137b is the portion that is situated on the inside (closer to the midplane P′P) relative to the first slot portion. For each slot, the second slot portion is connected to the first slot portion. More precisely, each first slot portion, respectively 135a and 137a, is connected via its inside end, respectively 135′a and 137′a, to the second slot portion, respectively 135b and 137b. It can be seen that the vertical distance D1 between the bottom ends respectively 135′a and 137′a of the first slot portions and the tool fastener 132a of the table 132 is greater than the vertical distance D2 between the inside ends, respectively 135′b and 137′b, of the second slot portions and said tool fastener 132a.
It can be seen that the first and second slot portions are inclined relative to each other.
More precisely, the first slot portions, respectively 135a and 137a present a general direction that is horizontal, while the second slot portions, respectively 135b and 137b are inclined towards the tool fastener 132a. In the example shown, the second slot portions, respectively 135b and 137b, are in the form of rectilinear segments that are inclined at an angle α of about 45° relative to the horizontal direction of the first slot portions. By way of example, the angle α may lie in the range 10° to 60°.
The above-mentioned adjustment elements 180 are situated in the first slot portions, respectively 135a and 137a.
There follows a description of
It can be seen that the wedging elements 280 are situated in the segments 235c and 237c of the first slot portions that extend in a generally horizontal direction.
It can be seen that the vertically-measured width E of each slot differs depending on the zone of the slot in which the width is measured. In this respect, the slot 234 is described in greater detail. At least one of the slot portions 235a and 235b presents a width that varies depending on the zone of said portion in which the width is measured. Specifically, the width E is at a minimum and is substantially constant in the segment 235c of the first slot portion 235a that extends in a generally horizontal direction. In contrast, the width varies both in the outer slot portion 235d and in the second slot portion 235b. Specifically, it can be seen that the width E increases regularly in the outer slot portion 235d on going outwards away from the segment 235c. Specifically, the top and bottom edges, respectively 234c and 234d, of the slot 234 present, in the outer slot portion and 235d, the shape of non-parallel sloping planes that diverge towards the outside.
Similarly, the second slot portion 235b presents at least one portion that is flared going away from the first slot portion 235a. It can thus be seen that the width E is greater beside the inside end of said second slot portion 235b than beside its outer end, corresponding to the inside end 235′a of the first slot portion 235a. Specifically, the top and bottom edges 234c and 234d of the slot 234 present, in the second slot portion 235b, the shape of non-parallel planes diverging towards the midplane P′P, all the way to the inner end portion 235e, which is in the form of a portion of a ball.
Naturally, the slot 236 is symmetrical to the slot 234 about the midplane P′P.
With reference to
In
The slot 534 shown in
With reference to
For all of the tests shown in
For the curves of
The curve LT shows the flexing of the lower tables respectively 632 for the press PA (
In the figures, it can be seen that for bending a sheet W of width L that is less than the distance C between the inside ends of the slots of the bending press PI, there is no significant difference between the bending press PA and the bending press PI.
The behavior of these two presses is somewhat more similar with sheets of width 6L, as shown in
The above-described comparative tests make it possible to understand that the bending behavior is much more uniform on sheets of a wide variety of widths using a bending press in accordance with the invention, in particular for one as shown in
For the bending press shown in
In general, in the invention, the bending press is made so that the stiffness of the table having the slots is greater in the regions of the slots that correspond to the first slot portions (in any event for the substantially horizontal segments of said first slot portions) than in the regions that correspond to the second slot portions. The presence of the wedging elements 180 or 280 suitably positioned in the first slot portions serves to further increase this stiffness.
It should be observed that the first slot portions could be of shapes that are slightly inclined or undulating. Nevertheless, these shapes should be selected so that the first slot portions confer on the corresponding region of the table stiffness that is greater than the stiffness of the region of the table that corresponds to the second slot portions. The length of the second slot portion, measured perpendicularly to the midplane P′P advantageously lies between about one third and about half the total length of the slot. The selected length depends in particular on the shape and/or the dimensions of the tables, and/or the tolerance range acceptable for deformation of the table that has the slots, and/or the accuracy desired for bending the part. It should be understood that by determining the shape of the slots and their length, and by suitably selecting the wedging elements and their positions, it can be ensured that the difference in height between the upward convex flexing peak in the middle of the lower table and the two lateral ends of the lower table remains within some predetermined tolerance. This is equally applicable when the width of the sheet that is being bent by means of the bending press is substantially equal to the length of the upper or lower table and when the width of said sheet is less than the length of the upper or lower table.
In the bending presses of
Number | Date | Country | Kind |
---|---|---|---|
0951609 | Mar 2009 | FR | national |
0955130 | Jul 2009 | FR | national |