EP1160025A1 - Method of bending thick steel plates, and safe made of bent thick steel plate - Google Patents

Abstract

The method of bending thick steel sheet (10) involves gripping the sheet between two jaws (8,9), with a part of the sheet extending beyond the jaws. The sheet is bent to a pre-set angle with the surface of the sheet in contact with a rounded surface (12). The sheet is folded by pivoting around an axis passing through the centre of curvature of the rounded surface. The fold angle can be at least ninety degrees. Claims include a safe made using the method

Description

The present invention relates to the field of heavy sheet metal, especially for the manufacture of safes.

As is known, a safe is a parallelepiped on one side opening. A protective safe from a vending machine banknotes includes five fixed walls, upper, lower, right side, left side, and bottom, and a front wall forming door, some of these faces can be provided with holes necessary for the distribution of tickets. The walls are made of sheet metal thick rolled hard steel to resist burglary.

Each of the five fixed walls is cut from a sheet blank by flame cutting, calibrated by press to reduce possible heat deformation during flame cutting, milled out of the four edges for exact dimensioning, chamfered to allow welding over the entire thickness of the sheet, if necessary drilled, equipped with its accessories, hinges, lock supports, locking square, supports interiors, then assembled with the other walls on a template, welded, and ground in the weld locations. Then we go up the door. We paints the safe. We mount the locks and condition the safe For transport.

The present invention provides a method and a machine for precise bending of thick sheets of high yield strength steel, and a safe with improved appearance and economical manufacturing without notable modification of interior and exterior volumes.

The process of folding heavy steel sheets, according to one aspect of the invention comprises steps of pinching the sheet between two jaws with part of the sheet protruding from said jaws, and folding of said part of the sheet at a predetermined angle. A face of the sheet comes into contact with a convex rounded surface, said part of the sheet being folded by pivoting about an axis passing through the center of curvature of the convex rounded surface. A sheet undergoes two apt folds to give it a U-shaped section, the arms of the U can each be longer than the bottom of the U.

In one embodiment of the invention, the folding angle is equal to 90 °, the sheet being bent at an angle slightly greater than 90 °, then returning by elasticity to the desired angle equal to 90 °.

Advantageously, the sheet is of thickness between 10 and 20 mm.

In one embodiment of the invention, each sheet is folded in the direction of rolling. This avoids the appearance of cracks and cracks harmful to the mechanical properties of the sheet and its aspect.

In one embodiment of the invention, steel sheets with high elastic limit, of tensile strength greater than or equal to 340 N / mm ² , preferably greater than or equal to 690 N / mm ² , are bent, for example manufactured by hot rolling.

In one embodiment of the invention, the U-folded sheet serves template for mounting and welding other sheets.

After folding during which it was pinched between the jaws, the sheet has a satisfactory flatness which avoids the step conventional press calibration necessary to perfect the flatness that the heating caused by flame cutting may have deteriorated. We can go directly to a step of fixing other elements, in particular other sheets on the U-folded sheet.

The present invention also relates to a machine for folding of heavy steel sheets, of the press brake type, comprising a box spring forming a fixed lower jaw, a clamp forming a vertically movable upper jaw provided with a ruler for come into contact with the sheet metal, and a pivoting apron. The rule includes a convex rounded end surface, the pivot axis of the deck passing through the center of curvature of the convex rounded surface. We thanks to this machine obtains folded sheets with a small radius without twisting and whose dimensions and dimensions are very precise.

The present invention also relates to a safe general parallelepiped shape with a top wall, a wall of below, a bottom wall, two side walls, the walls being assembled by welding, and a door capable of closing the front face, the walls being made of strong steel sheet. The safe includes at least one folded monobloc piece provided with two folds giving it a section in U, the arms of the U being each of length greater than that of the bottom of the U.

Advantageously, the sheet is of thickness between 10 and 20 mm.

The folded monobloc piece forms at least three walls, two of which are parallel, for example the side walls.

The safe has an improved exterior appearance due to replacement of ground weld lines with fold lines. This replacement eliminates preparation and machining steps chamfers necessary for welding, assembly, welding and grinding of weld lines. We also reduce the footage of sheet metal in front be cut, in general flame cut, then milled, and we simplify the assembly template which can be adapted to large boxes different. This reduces manufacturing costs. We could however conceive of using other means of cutting sheets.

If necessary, the walls are pierced and the installation of interior fittings such as shelf or equipment supports after folding, hence positioning accuracy increased.

The safe can be made of 12.7 mm (0.5 inch) sheet metal thick with a bending radius of 20 mm and used for protection banknote dispensing machines. The low value of the radius folds to keep the installed interior layout unchanged in the trunk by its user. Of course, the thickness of the sheet and the folding radius are linked. The folding radius can be all the smaller that the sheet is thin. The excellent precision of the dimensions of the one-piece part folded facilitates the arrangement of the other walls to be welded, the part folded monoblock serving, in a way, as a template for others walls.

The method and the machine according to the invention can be used for bending of sheets intended for other purposes, in particular metal framework, engineering structures, overhead cranes, gantries, pylons, boilermaking, shipbuilding, etc.

la figure 1 est une vue schématique en perspective de la construction d'un coffre-fort conforme à l'invention;

la figure 2 est une vue en coupe transversale d'une machine de pliage de tôle conforme à l'invention; et

la figure 3 est une vue de dessus de la machine de pliage de la figure 2.

The present invention will be better understood on studying the detailed description of a particular embodiment taken by way of nonlimiting example and illustrated by the appended drawings, in which:

Figure 1 is a schematic perspective view of the construction of a safe according to the invention;

Figure 2 is a cross-sectional view of a sheet bending machine according to the invention; and

FIG. 3 is a top view of the folding machine of FIG. 2.

As can be seen in Figure 1, the safe shown here during assembly includes a folded monobloc envelope 1 comprising three panels 2, 3 and 4, the panels 2 and 4 being parallel and the panels 2 and 3 and 3 and 4 being respectively perpendicular. The envelope 1 therefore forms a U whose branches are formed by the panels 2 and 4 and the bottom of which is formed by panel 3. Panels 2 and 4 are intended to form the lateral faces of the safe, while the panel 3 is intended to form the rear face.

The safe is completed by a top panel 5, a lower panel 6 and a door 7 forming the front face. The edges of envelope 1 and panels 5 and 6 are milled to obtain precision sufficient dimension less than or equal to 0.5 mm. The edges are also chamfered to allow the welding of different panels on all or part of the thickness of the sheet which can be between 10 and 20 mm, for example equal to 12.7 mm. After fixing panels 5 and 6 on the casing 1, the door 7 can be mounted by means of hinges not represented. Provision may be made for lining the door 7 with lock supports, anti-tear-off edges and any other accessory or security.

Alternatively, one could conceive of using an envelope folded monobloc forming the upper, lower and rear panels, or a folded monobloc envelope forming four panels, upper, lower and lateral.

Up to now, bending of high limit heavy steel sheets elastic was not known due to the size of the folding radii to be used, their imprecision, the imprecision of the bent part which would require subsequent steps to catch up with variations dimensions and the risk of twisting or warping of panels during folding.

The folding machine illustrated in Figures 2 and 3 allows you to overcome these difficulties.

As can be seen in Figure 2, the machine includes a clamp 8 movable vertically with respect to a fixed base 9 and between which a sheet 10 can be arranged. The box spring 9 includes a wedge 11 intended to receive and support the sheet 10 and whose upper surface undergoes ionic nitriding and has a higher hardness or equal to 60 HRC. The wedge 11 has a flat front surface 11a and vertical. The clamp 8 is movable by means of hydraulic cylinders not represented and is provided with a rule 12 intended to come into contact with the sheet 10. The rule 12 is mounted in a longitudinal groove 13 of the clamp 8 and comprises a flat lower surface 12a intended to enter into contact with the sheet 10, an oblique rear surface 12b partially in contact with the groove 13, a flat upper surface 12c, parallel to the lower surface 12a and partially in contact with the groove 13, and a front surface 12d rounded and the center of curvature of which is referenced 14. The center of curvature 14 is arranged in the plane of the front surface 11a of the wedge 11. The front surface 12d is convex and tangent with the surface lower 12a and extends upwards until it is substantially vertical, its upper end being perpendicular to the upper surface 12c. For folding, a flat sheet is advanced so as to present a portion 10a protruding from the wedge 11 and from the rule 12.

The folding machine also includes a movable apron 15 of rectangular cross section and shown in Figure 2, in lines strong in position before folding and in phantom in position after folding. In the position before folding, the apron 15 comprises a folding surface 15a disposed under the sheet 10 in contact with it. Apron 15 includes also a stop surface 15b perpendicular to the folding surface 15a and which is in contact with the end surface 11a of the wedge 11 arranged under rule 12. In this folded position, the surface of folding 15a is horizontal and the abutment surface 15b is vertical. The abutment surface 15b is arranged in the same vertical plane as the center of curvature 14 of the rounded surface 12d of rule 12. The surface lower 12a and the rounded area 12d of rule 12, and the area of folding 15a of the deck 15, are also the subject of a surface treatment such as ion nitriding to obtain surface hardness satisfactory, greater than or equal to 60 HRC, and a lifetime long enough.

Then, we will control the pivoting of the apron 15 around its pivot axis which coincides with the center of curvature 14. At the end folding, the apron 15 is rotated 90 ° counterclockwise relative to its axis. The folding surface 15a is vertical and in contact with the portion of sheet metal 10a. The abutment surface 15b is horizontal in the same horizontal plane as the center of curvature 14.

The folding takes place as follows. The clamp 8 being lifted by compared to the box spring 9, the sheet metal 10 is brought in, generally from the rear to the opposite of the deck 15, on the wedge 11, until a portion 10a of determined length protrudes from the end surface 11a. To facilitate the movement of the sheet 10, the bed base 9 may be provided with rollers or balls with free rotation, not shown, behind the wedge 11 and on which the sheet metal rests. The positioning of the sheet 10 can be facilitated by using positioning stops 16 (FIG. 3) blocking its movement in translation relative to the machine. Then, we just block the sheet 10 in lowering the clamp 8. The sheet 10 is thus taken between the wedge 11 and the rule 12.

The apron 15 is pivoted by the desired angle, generally 90 °, or by a slightly higher angle due to the elasticity of the sheet 10. When pivoting of the deck 15, it is understood that the folding surface 15a remains in contact with the sheet 10 by accompanying its folding along the surface 12d rounding of rule 12. The accuracy of folding is guaranteed by the fact that the pivot axis of the deck 15 and the center of curvature 14 are confused. As a result, the end of the folding surface 15a close of the abutment surface 15b will describe a circle concentric to that of the rounded surface 12d. The sheet 10 is thus not only pinched between the wedge 11 and the rule 12, but also between the folding surface 15a and the rounded surface 12d. This dynamic pinching during folding causes the concave side of the sheet 10 to press on the surface 12d which serves as a matrix and guarantees a constant and determined folding radius while by preventing any parasitic deformation of the sheet metal such as twisting or warping.

In Figure 2, we note that opposite to the portion 10a, the sheet 10 includes a portion 10b already folded. Indeed, the portion 10b has done the object of a prior folding, for example on the same machine. We see that you can easily bend a U-shaped sheet with branches of the U of length greater than the bottom of the U, the length of the bottom being determined by the dimensions of the clamp 8, in particular its length in the plane of section of Figure 2, and the length of the shortest branch being determined by the height over which the clamp 8 is movable to release after folding. We can thus bend sheets in shapes that you couldn't get with classic knife type folding machines mobile in translation.

In Figure 3, we see the folding machine in top view in empty folding end position, without a sheet having been placed. The residual space between the folding surface 15a and the rule 12 corresponds to the thickness of the sheet to be folded.

We understand that a change in thickness of the sheet causes a change in the distance between the bending axis and the bending surface 15a. An apron 15 is therefore provided which is adjustable relative to its axis of pivoting. Likewise, a change in sheet thickness has a influence on the admissible bending radius and can therefore cause change in rule 12 hence a change in the position of the center of radius of curvature. Means will also be provided for adjusting the position. of the pivot axis of the deck 15 relative to the rule 12, so that the pivot axis and the center of curvature 14 are always coincident.

Thanks to the invention, there is a method and a machine for folding for heavy plate, to obtain folded parts with walls planes and dimensions reproducible with precision.

The folding machine and method can be advantageously used for the manufacture of steel safes high yield strength, which removes a number manufacturing steps for the safe, including machining, welding and installation in a template, which leads to a reduction in costs of manufacturing and a better external appearance of the safe without modifying significantly its interior volume thanks to the small radii of curvature that we manage to obtain.

Claims (10)

Method for bending flat, heavy steel sheets, in which the sheet is clamped between two jaws with a part of the sheet projecting from said jaws, and said part of the sheet is bent at a predetermined angle, one side of the sheet coming into contact with a convex rounded surface, said part of the sheet being folded by pivoting about an axis passing through the center of curvature of the convex rounded surface, characterized in that a sheet undergoes two folds suitable for it confer a U-shaped section, the arms of the U each being longer than that of the bottom of the U. Method according to claim 1, characterized in that the folding angle is equal to 90 °. Method according to claim 1 or 2, characterized in that the sheet is between 10 and 20 mm thick. Method according to any one of the preceding claims, characterized in that each sheet is bent in the rolling direction. Method according to any one of the preceding claims, characterized in that steel sheets with high elastic limit, of breaking strength greater than or equal to 340 N / mm ² , preferably greater than or equal to 690 N / are bent mm ² . Method according to any one of the preceding claims, characterized in that the U-folded sheet serves as a template for mounting and welding other sheets. Safe of generally parallelepiped shape with a top wall (5), a bottom wall (6), a bottom wall (3), two side walls (2, 4), the walls being assembled by welding, and a door (7) capable of closing the front face, the walls being made of strong steel sheet, characterized in that it comprises at least one folded monobloc piece (1) provided with two folds giving it a U-shaped section, the arms of the U being each of length greater than that of the bottom of the U. Safe according to claim 7, characterized in that the folded piece is between 10 and 20 mm thick. Safe according to claim 7 or 8, characterized in that said part is made of high elastic limit steel, with a breaking strength greater than or equal to 340 N / mm ² , preferably greater than or equal to 690 N / mm ² . Safe according to any one of Claims 7 to 9, characterized in that the said piece has a thickness of the order of 12.7 mm with a folding radius of the order of 20 mm.

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