FR2698027A1 - Metal sheet perforation method - uses die and matrix which makes two cuts in metal and bends over portion between cuts into semi-cylinder - Google Patents

Abstract

The method uses a perforator consisting of a die (30) and a matrix (41). The die has a projecting tip (33) with a semi-cylindrical recess (28) and two cutting edges (37), and the matrix a matching convex semi-cylindrical surface (45) with recesses (42) on either side of it to receive the cutting edges of the matrix. When a sheet of metal is placed between the die and matrix plates and the die is forced downwards against the matrix, two cuts are made in the metal and the piece of metal between the cuts is bent over into a semi-cylindrical shape. USE/ADVANTAGE - Reduced stretching of metal sheet during perforation; suitable for acoustic absorption surfaces.

Description

 The present invention relates to a method and to an apparatus for obtaining a perforated sheet having parallel cuts or notches, the material of the sheet being pushed cylindrically along an edge of each of these cuts.

 The present invention also relates to such a sheet, having particularities which result from its process for obtaining.

 In patent application FR-A-2,264,6O7, a method has been described for obtaining sheets of the type indicated above, according to which a full sheet is passed between two sets of rollers of suitable shape carried by two parallel shafts. Certain rollers of the first tree are provided with teeth whose crown surface is cylindrical, and which have a certain circumferential development. These teeth have a sharp angle edge, which cooperates with a sharp angle edge of a roller of the second shaft to shear the sheet over a certain length. For this, each tooth is limited on one side by a flat surface perpendicular to the axis of the roller which carries it, and the corresponding matrix roller also has a flat surface perpendicular to the axis. The opposite side of each tooth is constituted by a frustoconical surface which comes opposite a surface in the form of a torus fraction of a shaping roller carried by the second shaft. The reciprocal arrangement of the rollers is adapted so that the sheared sheet is clamped between the inclined edge of the tooth and the rounded edge of the shaping roller, which generates a portion of cylinder whose generatrices are parallel to the direction of cutting and to sheet metal plane.

 This technique makes it possible to obtain perforated sheets which are satisfactory, in particular for constituting acoustic absorption surfaces.

However, it appeared possible to obtain certain improvements on the following points
When the sheet passes between the rollers, it is not maintained in its plane, and slight variations in the nature of the metal, or the degree of wear of the shearing means, can cause the sheet to curve slightly in the direction the first or second tree that carries pebbles. This can result in imperfect flatness, detrimental to the general appearance. To improve this, and avoid having sheets having an overall curvature, which cannot be satisfactorily assembled with other sheets, it is customary to bend the edges of the sheet obtained at right angles. , which complicates the process, and increases its price.

 On the other hand, in the vicinity of the end of each cut, the material of the sheet has undergone a relatively large stretch, which can act on its physical or chemical or crystallographic properties, and cause, for example, in certain cases, a local variation in corrosion resistance.

 This stretching can go, in case the edge of the cylinder portion is very far from the overall plane of the sheet, to a tearing of the material. The appearance of this tear is not regular, which only appears on close examination, but the variation in mechanical characteristics due to stretching remains.

 It has long been known, see for example US-A-3,018,010, to obtain a perforated sheet of the type indicated at the start by pressing between two press plates. One of the plates carries at least one punch provided with a cutting edge bounded on one side by a surface perpendicular to the overall plane of the plate, and on the other side by an oblique, flat or concave surface.

The other plate carries projecting counterparts, one edge of which is limited by a surface perpendicular to the overall plane of the plate, which cooperates with the punch to cut the sheet. When the two plates approach, the cutting edge of the punch enters the sheet, which is retained by the counter-piece. After the formation of the cut, the material of the sheet which is on the edge of the cut opposite the counter-piece is pushed back by the oblique surface of the punch, and curves in the form of a portion of cylinder.

 This technique does not ensure better flatness of the perforated sheet than the previous one, because, during shearing, the sheet is not maintained continuously.

 In addition, the curving of the cut part of the sheet is made in an uncontrolled manner, which further adds to the appearance defects.

 In the vicinity of the ends of the cuts, the deformation of the sheet material is substantially the same as that which was mentioned above.

 The present invention aims to provide a perforated sheet of the type indicated above, which can be obtained with perfect flatness, and with reduced deterioration of the structure of the material in the vicinity of the ends of the cuts.

To obtain this result, the invention provides a process for obtaining a perforated sheet comprising incisions, the sheet being pushed cylindrically along an edge of each of the cuts, according to which a continuous flat sheet is placed between two plates Press,
- A first of the plates carrying at least one projecting punch, having the general shape of a portion of prism with edges parallel to the plane of the sheet, with a first lateral face, perpendicular to the plane of the plate, terminated by a main cutting edge , parallel to the plane of the plate, a second face which ends on the main cutting edge, and two end faces perpendicular to the main cutting edge,
- And the second of the plates comprising a first side wall, perpendicular to the plane of the plate, and the intersection of which with the external surface of the plate defines a main cutting edge, of length, position and orientation calculated to cooperate with main cutting edge to create an incision,
- and we bring together the press plates to create the incision (s) and push back the sheet,
this process having the particularity that
1) a tool is used in which
- the first and second plates carry, around each punch and each die, parallel flat surfaces,
- the intersection of each end face of the punch with the front face is designed to constitute a secondary cutting edge,
- The second plate has a cavity intended to receive each punch, bounded by said side wall, and by two side walls, making an angle, preferably of 90, with said main counter-edge, the intersection of said side wall and end walls with the outer surface of the plate defining said main cutting edge and auxiliary cutting edges,
- And said cavity is further limited by a second side wall, opposite to the first side wall and at least part of which has the shape of a part of a convex cylinder arranged to clamp a folded part of the sheet between it and the second face lateral of the punch at the end of a perforated sheet forming operation, and
2) the sheet is clamped between the flat surfaces carried by the two plates at least at the end of the forming operation.

 The fact that, during the operation, the sheet is clamped around each forming region allows excellent flatness to be obtained, without the need to resort to the device consisting of folding the edges. In addition, the presence of secondary edges and secondary counter cutting edges has the effect that the sheet is sheared along three cutting lines which intersect to form a U-shaped incision with sharp angles. There is therefore no stretching of the sheet material at the ends of the main cutting line, but formation of a perpendicular cutting initiator, with shearing.

 As a result, the surface of the sheet remains flat until this cutting initiation, hence a sharper and more pleasant appearance than that of perforated sheets according to the prior art, where the stretching of the material, that there whether or not it tears, causes localized warping of the sheet near the ends of the sheared parts. Even if a warping extends over a distance of the order of a millimeter, it has been observed that its disappearance resulting from the use of the method of the invention, produces a change in appearance which is detectable at several meters distance.

 It will be observed that the secondary cutting edge does not necessarily act over the entire width of the cut and folded part. It is sufficient that it constitutes a well pronounced cutting initiation. The cutting can continue in a substantially straight line under the effect of the stresses exerted by the second lateral face of the punch. The movement stops when the cut part of the sheet is clamped between this second side face and the second side wall of the cavity, which causes the end of the movement of the punch.

 In the foregoing, we have spoken of a cylindrical shape of the repelled part of the sheet, and of the corresponding forming surfaces. Those skilled in the art will understand that it is not only a cylindrical shape with a section in an arc. The section of the repelled part can also have a shape with variable curvature, possibly with one or more flats, and, ultimately, a polygonal shape, the cylinder then being rather a prism, without departing from the invention.

 Note that it is not possible to obtain the above result in a process using rollers rotating about an axis, since the end faces of the punch and the end walls of the cavity would behave like the teeth of a gear, and those skilled in the art know that a gear cannot function if the cooperating faces of the teeth are all in planes passing through the axis of the corresponding pinion.

The present invention will now be explained in more detail with the aid of practical examples, among which
FIG. 1 shows, in perspective, a fragment of perforated sheet in accordance with the prior art,
Figure 2 shows, in enlarged view, a "punctured" of Figure 1,
FIG. 3 shows a perspective view corresponding to FIG. 1, of a part of a sheet according to the invention, and
Figure 4 is an enlargement of Figure 3, similar to Figure 2.

 Figure 5 is a partial perspective view of a tool for implementing the method of the invention.

 FIG. 1 shows the staggered arrangement of five punctures 1 arranged on a flat sheet metal plate 2.

 Figure 2 shows, in enlarged view, an enlargement of one of these punctures.

 As shown in Figure 2, the sheet 2, flat as a whole, has, at the location of the puncture, a repelled part 3, of generally cylindrical shape, which is connected to the flat part 2 of the sheet by a zone 4 , relatively little deformed. This zone 4 is extended by two connection zones 5, where the material of the sheet is stretched to compensate for the difference between the zone 6 of the repelled part 3 which deviates from the plane 2 of the sheet. The repelled part 3 is limited by two parallel edges 7, which are spaced from the plane 2 of the sheet, and define with the shear line 8 of this sheet an orifice 9, of generally roughly trapezoidal shape, but whose edges d end 10 are curved to correspond to the stretched part 5.

 Figures 3 and 4 describe a sheet obtained according to a method according to the invention. In these figures, the elements identical to those of Figures 1 and 2 have the same references, increased by 10. The relative staggered arrangement of the punctures 11 on the flat part of the sheet 12 is the same as in the prior art.

 The repelled part 13 is of generally cylindrical shape, with little difference from the repelled part 3 of the prior art. It is connected to the flat part 12 of the sheet by a slightly deformed area 14, but it can be seen that the stretched area 5 of the prior art has disappeared. In fact, the zone 16 which is part of the repelled part 13 and which is furthest from the plane of the sheet 12 ends, in the direction of the generatrices of the cylindrical surface, by a line with a sharp edge 21, which constitutes the intersection of this cylindrical surface with a surface 22, substantially planar and perpendicular to the generatrices of said cylindrical surface. The edges 17 of the zone 16 which are parallel to the generatrices are unchanged with respect to those of the prior art, but they form a right angle with the end line 21 which has just been mentioned. The incision line 18 which was formed in the flat sheet 12 is connected, at each of its ends, to a perpendicular incision 22, which is perpendicular to it and which is directed towards the central part 14 of the edge of the puncture.

 It can therefore be seen that the opening 19 between the flat part of the sheet and the stamped part of the latter has been enlarged at its ends and that the highly stretched zones 5, which are more susceptible to corrosion than the rest of the sheet , have been, if not completely removed, at least considerably reduced.

 FIG. 5 shows, in perspective, the part of the tool which makes it possible to make a single punch, such as those described in FIGS. 3 and 4. It is understood that, for the execution of a perforated sheet, a press plate carries a plurality of punches of the type which will be described below, while the other press plate comprises a series of corresponding dies, so as to allow the formation of a plurality of punctures in a single operation .

 The active part of the punch 30 has the shape of a prism with rectangular section, bounded by two lateral faces 31, two end faces 32 and a front face 33. The front face 33 has a longitudinal groove 34, with an arc section of circle, close to a semicircle, which extends from one end face 32 to the other. On each side of the groove 34, the front face 33 has two longitudinal flats 35, which each connect to a lateral face 31 by a main cutting edge 36. The flats 35 are connected to the lateral surfaces 31 by a short cutting line secondary 37, which extends from the main cutting edge 36 to the edge of the groove 34. The groove 34 ends, on the end face 32 by an edge 38 with smooth edges.

 The active part of the punch can slide for the formation of the puncture, with little play, through a passage 39 provided in a support plate P1, the free surface of which is flat, and which is supported by a support structure S.

 The matrix has a cavity 40, in reality a series of cavities, passing through a support piece P2, the free surface 41 of which is flat and parallel to the free surface of the support plate P1. The cavity 40 is of rectangular section, and is limited by two lateral faces 42, and two end faces 43, which correspond to the lateral faces 31 and end 32 of the punch. The bottom of the cavity is occupied by a piece of shape 44, the front surface of which has a rib 45, of section in an arc of a circle, of radius equal to that of groove 34, reduced by the thickness of the sheet to be conformed. . The rib 45 extends from one transverse end to the other of the cavity. It is connected, on its longitudinal edges, to two flats 46, which extend to the lateral end faces 43 of the cavity. The shaped part 44 can slide inside the cavity 40, for adaptation to variations in the thickness of the sheet, then for the ejection of the shaped sheet. In the working position, the top of the rib 45 extends in the direction of the upper surface 41 of the support piece P2, up to # #t a distance from the plane of this surface 41 which corresponds to the thickness of prison. The edges 48, 49 by which the lateral surfaces 42 and end 43 of the cavity 40 are connected to the surface 47 of the plate 41 are counter cutting edges, which cooperate with the cutting edges 36, 37 of the punch .

 The implementation of the apparatus described is obvious: after placing the sheet to be drilled on the support piece P2, the support plate P1 is moved so as to come and clamp the sheet between said support plate P1 and the support piece P2, the free surfaces of which face each other.

 Then, the punch is advanced through the passage 39, then into the cavity 40. The sheet is cut first along the cutting edges 36, 37 of the punch, then the depression of the latter continuing, it is shear cutting along the sharp edges 38 of the groove 34, cooperating with the end cutting edges 49 of the die, until the displaced shear stress becomes less than the breaking load of the material.

 It then suffices to remove the punch, then to move aside the support plate P1 from the support piece P2, and finally to move the piece 44 in the cavity so as to expel the punctured from the cavity and release the plate from sheet thus formed.

 It will be observed that the cutting edges of the punch (s) do not necessarily have parallel orientations, provided of course that the counter-edges of the die have corresponding orientations.

This allows for new decorative effects, which were impossible to obtain with the process of FR-A-2,264,607.

Claims (7)

 1. Method for obtaining a perforated sheet having incisions along which the sheet is pushed cylindrically, process according to which a continuous flat sheet is placed between two press plates,  - A first of the plates carrying at least one projecting punch (30), having the general shape of a prism portion with edges parallel to the plane of the sheet, with a side face (31), perpendicular to the plane of the plate, completed by a main cutting edge, parallel to the plane of the plate, a front face (33), which ends on the main cutting edge, and two end faces (32) making an angle with the main compact edge,  - And the second of the plates comprising a matrix having a lateral wall (42), perpendicular to the plane of the plate, and whose intersection with the external surface of the plate defines a main cutting edge (48), of length, position and orientation calculated to cooperate with the other main cutting edge to create an incision,  and we bring together the press plates to create the incision (s) and push back the sheet,  characterized in that  1) a tool is used in which  - the first and second plates carry, around each punch and each die, parallel flat surfaces,  the intersection of each end face (32) of the punch with the front face (33) is designed to constitute a secondary cutting edge (37),  - The second plate has a flat surface (41), into which opens a cavity (40) intended to receive each punch, limited by said side wall (42), and by two end walls (43), perpendicular to said surface planar and at an angle with said main counter edge, the intersection of said side wall and end walls with the outer surface of the plate defining said main cutting edge (48) and secondary cutting edges (49 ),  - And said cavity is further limited by a bottom wall, opposite to the front wall of the punch and at least one part (45) in the form of a portion of convex cylinder arranged to clamp a folded part of the sheet between it and the front face of the punch at the end of a operation for forming the perforated sheet, and  2) the sheet is clamped between the flat surfaces carried by the two plates at least at the end of the forming operation, then the punch is advanced into the cavity of the die while maintaining the tightening of the sheet.  2. Method according to claim 1, characterized in that the front wall (33) of the punch has a cylindrical part of shape conjugate with that of the bottom wall of the die.  3. Method according to claim 1 or 2, characterized in that the end faces of the punch, and the end walls of the cavity are perpendicular to the direction of the main cutting edge.  4. Perforated sheet comprising at least one incision (8, 18), a part of the sheet which is adjacent to an incision being pushed back in the shape of a cylinder portion (3, 13), obtained according to the method of one of claims 1 to 3,  characterized in that the part of the sheet which is pushed into the shape of a cylinder portion is limited, in a direction parallel to the incision, by a line (21) situated substantially in a plane perpendicular to the direction of the incision and which connects at a sharp angle to the repelled surface in the form of a cylinder on most of the edge of this surface.  5. Sheet according to claim 4, characterized in that said substantially planar surface mainly has a metallographic structure corresponding to a shear cut, a part of this surface possibly having a structure corresponding to a crack propagation.  6. Sheet according to claim 4 or 5, characterized in that it has two parallel incisions between which a part of the sheet is pushed back in the form of a cylinder portion.  7. Sheet according to one of claims 4 to 6, characterized in that it comprises several incisions of different orientations.