EP0433203B1 - Method and apparatus for drawing conical containers and containers so obtained - Google Patents

Abstract

The deep-drawing device comprises a frustoconical punch 2 and a die 1. The die comprises concentric rings 8, 9, 10 which move in the direction of the displacement of the punch and pressure means 14, 15, 16 for exerting a predetermined force on the said rings in the direction of the punch, each of the frontal annular surfaces 20, 21, 13 of the said rings having a shape complementary to the annular surface 20', 21', 13' of the punch which faces it axially. According to the method of the invention, intended especially for the production in a single pass of a generally frustoconical container, annular zones 32, 33, 34, which are concentric with the blank are deformed in succession by starting with the zone of smallest dimension, each annular zone 32, 33, 34 being held pressed to the punch by a corresponding ring (respectively 10, 9, 8) from the moment when the said zone is in contact with the punch and until the end of the deep drawing, each annular zone being moreover in bearing contact against a corresponding ring as long as the inner adjacent zone is not applied against the punch. <IMAGE>

Description

The invention relates to the manufacture of containers of generally frustoconical shape, by stamping a sheet metal blank, in particular of steel and of small thickness. It relates more particularly to the manufacture of containers with a high taper, that is to say the side wall of which is largely flared on the side of the opening of the container.

According to conventional methods of manufacturing this type of container, several stamping sequences are carried out successively which gradually deform the initial blank until the final product is obtained. These methods, therefore requiring the use of several stamping tools, one per sequence, and several operations for producing a container, entail a significant manufacturing cost.

To reduce these costs, it has already been proposed in document DE-A-1452963 to stamp frustoconical containers in a single pass, using a device according to the preamble of claim 6, comprising a male frustoconical punch, a frustoconical matrix facing it, and a blank holder conventionally used to retain the periphery of the blank while allowing it to slide. However, such methods according to the preamble of claim 1 tend to cause bulging and wrinkling of the conical side wall of the container, due to the large free strand inherent in this type of process. It is recalled that the free strand is the annular area of the blank located between the punch and the die, which is neither in contact with the punch nor in contact with the die during stamping, that is to say , in the case of punch and frustoconical matrix and just before the end of the drawing, practically the entire side wall of the container.

In particular to avoid these folds, it has been proposed, in document US 3302441, to reduce this free strand by using a punch made up of several concentric annular rings and sliding one inside the other. In this case the drawing is conducted so as to deform first by the external annular ring of the punch, a first annular zone of the blank to shape the frustoconical part of larger diameter of the container, that is to say the part closest to the opening of the container, then to deform successively, by means of annular rings of decreasing diameters, corresponding annular areas of the blank to form frustoconical portions of the container of equally decreasing diameters, until the end of the stamping operation, where the entire frustoconical wall of the stamped container is applied to the matrix by the different annular rings of the punch. By this method, the free strand during stamping is in fact considerably reduced, since it consists only of said annular zones whose width is substantially divided, compared to the previous case, by the number of annular rings of the punch.

However, this method has the drawback of greatly limiting, from the start of stamping, the flow of the metal constituting the blank between the die and the outer ring of the punch. Therefore, the subsequent deformations caused by the other decreasing diameter rings cause a significant stretching of the metal in the central area of the blank, which can lead to its rupture, especially in the case of a thin blank. In addition, tearing can occur by significant friction of the deformed area of the blank between the die and the outer ring of the punch.

The object of the present invention is to remedy these problems and to allow the manufacture of containers of generally frustoconical shape by stamping sheet blanks of thin or very thin thickness, in particular of steel.

With these objectives in view, the present invention relates to a method of stamping a sheet blank for the manufacture in one pass of a container of generally frustoconical shape, according to which a stamping tool is used. comprising a male frustoconical force punch and a matrix facing it, the expression frustoconical shape to be understood as relating not only to containers of circular cross-section, but also to containers of cross-section of generally polygonal shape, and of which the cross-section in a plane passing through the center of the container can be generally rectilinear or curvilinear with more or less pronounced concavity or convexity.

According to the invention, this method is characterized in that the matrix comprises, facing the frustoconical surface of the punch, concentric rings movable perpendicular to the plane of the blank, the concentric annular zones of the blank are deformed successively, starting with that of smaller dimension, each annular zone, of frustoconical shape after deformation, being kept pressed towards the punch by a corresponding ring from the moment when said zone is in contact with the punch and until the end of the stamping, each annular zone being by elsewhere by pressing on a corresponding ring as long as the adjacent internal annular zone is not applied to the punch.

Thanks to the invention, it is possible to manufacture, by stamping in a single pass, containers of frustoconical shape from sheet metal of small thickness, practically without risk of breakage of the blank. Indeed, the deformation of the blank occurring first in its central part, close to the bottom of the container, the subsequent successive deformations of the zones of increasing diameter practically do not occur on the already deformed metal of the zones of smaller dimensions, and n therefore do not tend to stretch it excessively, thus avoiding the ruptures which commonly occur as close as possible to the nose of the punch in the procedures according to the prior art. On the other hand, the metal necessary to absorb these deformations is freely, subject to the pressure exerted by the blank holder, brought from the peripheral areas of the blank. It is thus possible to easily control the deformations by stretching the metal by adapting the pressures exerted on the blank drawn by the different rings of the matrix and by the blank holder.

This also results, compared to a stamping in several passes, a gain on the dimensions of the blank, since the stretching of the metal which constitutes it can be controlled and therefore optimized.

According to a particular arrangement of the invention, each annular zone is maintained substantially in the plane of the blank as long as the adjacent internal annular zone is not applied to the punch.

This particular arrangement makes it possible, in addition to permanently containing the free strand by contact of the blank on the annular rings of the die, to keep firmly pressed between punch and die each stamped annular zone before the adjacent zone towards the outside begins. to be deformed by the action of the punch and the corresponding die ring. The influence of the deformation of an annular zone on the adjacent zones towards the interior is then further reduced.

However, the rings can also move slightly, accompanying the area of the blank in free strand, under the effect of less pressure exerted on said rings, this pressure being adapted to the buckling characteristics of the material constituting the blank. It can also be assumed that, during stamping, an annular area of the blank is not fully pressed by the corresponding ring on the punch when the adjacent external annular area begins to be deformed. Even in this case, during stamping, the blank area in free strand gradually decreases, which has the effect of reducing the risks of wrinkling.

However, the sequential blocking of the blank on the punch, caused by the rings of increasing size, creates a stretch all the more important as the free strand decreases, and the thickness of the conical walls is all the more constant.

According to another particular arrangement, the punch has on its conical surface one or more circumferential recesses, and corresponding steps are formed on the wall of the container during stamping between two adjacent annular zones of said wall, successively when brought into contact. an annular zone on the punch by the corresponding ring.

This arrangement makes it possible to produce a container having on its conical side wall steps which, in addition to their aesthetic appearance, constitute reinforcements of the wall. In addition, the formation of these steps creates at the end of the deformation of each annular zone an additional tension of the metal in said annular zone, which participates in the elimination of any wrinkling.

For the same purpose, it is also possible, using a punch comprising steps, to bring each annular zone of the blank in contact with the corresponding zone of the punch during stamping by the corresponding die ring without forming the step, the contact then being only linear on the angle of the step, and simultaneously forming all the steps at the end of stamping by a simultaneous increase in the pressure exerted by the rings of the matrix.

The invention also relates to a stamping device for the implementation of the method described above, comprising a punch of generally frustoconical male shape facing a matrix and a blank holder to retain the periphery of the blank while letting it slide, this device being characterized in that the matrix comprises, opposite the frustoconical surface of the punch, concentric rings movable in the direction of movement of the punch, and pressure means for exerting on each of said rings a predetermined force enough to deforming, during stamping, the corresponding annular zone of the blank in the direction of the punch, each of the front annular surfaces of said rings having a shape complementary to the annular surface of the punch which faces it axially, for, at the end of stamping, press each annular area against the punch.

• les bagues sont retenues par des butées limitant leur déplacement en direction du poinçon ;
• les extrémités des bagues faisant face au poinçon sont toutes sensiblement dans le même plan avant emboutissage ;
• le dispositif comporte entre le serre-flan et le poinçon une bague dans laquelle est réalisée, sur sa face dirigée vers la matrice, une cuvette annulaire, une bague coulissante de la matrice lui faisant face et comportant une prohéminence de profil correspondant à celui de la cuvette annulaire ;
• les moyens de pression comportent des éléments élastiques, tels que des ressorts, déterminés pour exercer sur chaque bague de la matrice un effort fonction de la profondeur de pénétration du poinçon dans la matrice, de manière à exercer sur le flan embouti en cours d'emboutissage, un effort suffisant pour plaquer la zone annulaire correspondante du flan sur le poinçon.

According to specific provisions:

• the rings are retained by stops limiting their movement in the direction of the punch;
• the ends of the rings facing the punch are all substantially in the same plane before stamping;
• the device comprises between the blank holder and the punch a ring in which is made, on its face directed towards the matrix, an annular bowl, a sliding ring of the matrix facing it and comprising a profile prominence corresponding to that of the annular bowl;
• the pressure means comprise elastic elements, such as springs, determined to exert on each ring of the die a force depending on the depth of penetration of the punch into the die, so as to exert on the stamped blank during stamping , sufficient effort to press the corresponding annular area of the blank onto the punch.

Other characteristics and advantages will appear in the description which will be given by way of example of a device and of the implementation method according to the invention, for the manufacture of widely flared containers such as plates, made of sheet steel with a thickness of less than 0.21 mm, for example 0.18 mm.

• les figures 1a à 1f représentent en demi-coupe axiale le dispositif d'emboutissage et le flan lors de différentes phases successives de l'emboutissage d'une assiette à gradins,
• la figure 2 montre une variante du dispositif en fin d'emboutissage d'une autre forme d'assiette,
• la figure 3 montre une autre variante appliquée à l'emboutissage d'assiettes à paroi latérale lisse,
• la figure 4 montre une autre variante encore appliquée à l'emboutissage d'assiettes à paroi latérale de section incurvée.

Reference is made to the appended drawings in which:

• FIGS. 1 a to 1 f show in axial half-section the stamping device and the blank during different successive phases of the stamping of a stepped plate,
• FIG. 2 shows a variant of the device at the end of stamping of another form of plate,
• FIG. 3 shows another variant applied to the stamping of plates with a smooth side wall,
• FIG. 4 shows yet another variant applied to the stamping of plates with a side wall of curved section.

The stamping tool shown in the different figures comprises a die 1, a frustoconical punch 2 and a blank holder 3. The die 1 is linked in a manner known per se to an upper plate 4 of a stamping press. Similarly, the punch is linked to a lower plate 5 of said press. The blank holder 3 is slidably mounted on the lower plate 5, means not shown being provided for exerting pressure on the blank holder 3 in the direction of the die 1. Between the blank holder 3 and the punch 2 is interposed one cutting ring 6, intended in particular to perform at the end of stamping the peripheral cutting of the edge of the container.

The die 1 comprises a fixed ring 7 rigidly fixed to the upper plate 4 of the press, and several concentric rings 8, 9, 10, three in the example shown. The central ring 10 is, in this example, a disc, the face 11 of which faces the punch comprises a flat central zone 12 surrounded by a frustoconical zone 13, this central ring 10 being intended to form the bottom of the container and the part of the side wall thereof adjacent to said bottom.

As will be understood later, this disc could be replaced by an annular ring having a conical surface identical to the surface 13, and a central counter-punch provided for forming, in collaboration with the central part of the punch, the bottom of the container. . The surface of the central zone 12 or of the counter-punch could also be shaped so as to give the bottom of the box a particular relief.

The concentric rings 8, 9, 10 are slidably mounted relative to each other, and permanently pushed towards the punch by pressure means such as springs 14, 15, 16. These rings, including the maximum clearance is determined as a function of the stamping depth, are moreover retained by stops 17, 18, 19 limiting their displacement in the direction of the punch, so that the lower ends of these rings are all substantially in the same plane before the stamping.

Furthermore, said springs are determined for each ring so as to be able to exert sufficient force on the stamped blank to press the annular area of the blank on the punch which is found during stamping opposite said ring.

Each ring has a frustoconical surface 20, 21, 13 of the same conicity as the annular surfaces 20 ', 21', 13 'of the punch located respectively opposite. The external sliding ring 8, that is to say the one having the largest diameter, furthermore comprises a substantially planar surface 22, adjacent to its frustoconical surface 20, situated opposite a surface 22 'of the cutting ring 6, and preferably comprising a protrusion or annular ring 23. An annular cup 23 'of corresponding profile is produced in the cutting ring 6. Said ring 23 and said cup 23' are in particular intended to form on the edge of the container a peripheral rib constituting a heat-sealing track for the subsequent welding of a closure cap for the container. This arrangement also ensures flatness, at the end of stamping, of said heat-sealing track, which guarantees the continuity and therefore the seal, of the weld when the container is closed.

The conical annular surfaces 20 ′, 21 ′, 13 ′ of the punch are also connected by recesses 24, 25, which form, with said annular surfaces, circumferential steps, said recesses being located opposite the guide surfaces between the rings of the matrix.

In connection with FIGS. 1 a to 1 f , representing the different stamping phases, a description will now be given of the method of stamping a sheet blank 30 to form a frustoconical container of high conicity such as a plate.

In the first phase, shown in Figure 1a, the blank 30 is placed between the die and the punch spaced apart from each other, the blank resting on the blank holder 3 and the cutting ring 6, maintained in the high position by the pressurizing means of the blank holder. The sliding rings 8, 9 and 10 are pushed down by the springs 14, 15, 16, the lower ends of these rings and of the fixed ring 7 of the matrix being substantially in the same horizontal plane.

The upper plate 4 of the press is then pushed down, until the fixed ring 7 of the die comes into contact with the blank and presses it against the blank holder 3.

In this second phase shown in FIG. 1b , the periphery of the blank is therefore clamped between the fixed ring 7 of the matrix and the blank holder 3, and the annular zone 31 of the blank located between the outer ring 8 of the matrix and the cutting ring 6 is deformed by the ring 23, the force exerted on said outer ring 8 by the springs 14 being sufficient to prevent or limit its recoil, upwards. In addition to the function described above, of forming the heat-sealing track, the rod 23 associated with the bowl 23 ′ thus participates, in addition to the pressure exerted by the blank holder, in retaining the periphery of the blank, by folding and successive unfolding of this, during the sliding of the blank between the outer ring and the cutting ring, during the following phases of the stamping.

In this second phase, the lower ends of the rings 9 and 10 are just in contact with the blank and therefore participate in maintaining the free strand, as indicated above.

The upper plate 4 continuing to be pushed down, the blank then begins to be stamped in its central part by the interaction of the central ring 10 with the punch 2.

At the end of this third phase, represented in FIG. 1 c , the annular zone 32 of the blank adjacent to the bottom of the container is pressed and pressed between the conical surface 13 of the central ring 10 and the corresponding surface 13 ′ of the punch by the force exerted on said central ring 10 by the springs 16.

It will be noted that during this deformation of the blank, the periphery of the blank has slid radially between the fixed ring 7 of the matrix and the blank holder 3, and between the outer ring 8 and the cutting ring 6, the rod 23 participating in the regularity of this sliding over the entire periphery of the blank.

The descent of the upper plate continues, the punch continues to penetrate into the matrix by pushing, relative to the latter, the central ring 10 upwards and by compressing the springs 16.

During this fourth phase, the blank continues to be deformed, the remaining free strand being supported by the lower end of the sliding ring 9 adjacent to the central ring 10. The force exerted by the springs 15 on this ring 9, hereinafter called the middle ring, is sufficient to avoid its retraction from the outer ring 8, the free strand of the blank then remaining in the original horizontal plane of the blank. A certain retreat from this middle ring can however be accepted insofar as, despite this decline, the deformation of the free strand remains contained by the pressure exerted by the lower end of said middle ring.

At the end of this fourth phase, represented in FIG. 1 d , the annular zone 33 of the blank, adjacent to the annular zone 32, is pressed and pressed, between the conical surface 21 of the middle ring 9 and the corresponding surface 21 'of the punch, by the force exerted on said middle ring 9 by the springs 15. Simultaneously, due to the recess 25 connecting the surfaces 21 'and 13' of the punch, a step 35 is formed between the annular zones 32 and 33 of the blank.

The fifth phase is carried out in a similar manner to the fourth phase, by continuing the descent of the upper plate 4, the continued penetration of the punch into the matrix causing the sliding of the middle ring 9 in the outer ring 8. The annular zone conical 34 of larger diameter is then deformed then clamped between the conical surface 20 of the outer ring 8 and the corresponding surface 20 'of the punch, as shown in Figure 1 e , the step 36 then being formed similarly to the step 35.

It will be noted that, at the end of this fifth phase, the cutting ring 6 is brought into abutment on the lower plate 5 and the upper surfaces 8 ', 9', 10 'of the rings 8, 9 and 10 are located in the same plan.

Therefore, during the sixth and last phase of stamping, these surfaces simultaneously abut on the upper plate 4, as shown in Figure 1 f . This sixth phase is a phase of cutting the periphery of the container, this cutting being carried out, during the final penetration of the punch into the die, by the cutting ring 6 which, being in abutment on the lower plate 5, moves, relative to the fixed ring 7 of the die, simultaneously with the punch, and, in cooperation with this fixed ring 7, shears the edge 37 of the blank.

At the end of this sixth phase, the drawing of the container is finished and it can be removed from the drawing tool, in a manner known per se, after raising the upper plate 4 and returning the different rings to their starting position shown in Figure 1 a .

As has already been indicated, the forming of the steps 35, 36 makes it possible to create an additional tension of the metal of the blank which participates in the elimination of any remaining folds. In the description which has just been made, the steps are formed successively, at the end of the fourth and of the fifth stamping phase. It will easily be understood that the same effect would be obtained if all the steps were formed simultaneously at the end of stamping. This could result from the fact that, voluntarily or not, the pressure exerted on a ring, for example the middle ring 9, was insufficient to form the corresponding step. In this case, moreover, the annular zone 33 of the blank would not be completely pressed between the punch and the ring 9 at the end of the fourth phase. However, it would be held against the punch near the recess 25 during the fourth phase, and near the recess 24 during the fifth phase.

Figures 2, 3 and 4 show in the end of stamping position different variants of the device, each intended for stamping plates of different shapes.

In the variant shown in FIG. 2, the steps 35 ′, 36 ′, instead of being formed by cylindrical recesses such as those described above, are formed by planar recesses in parallel planes. It will be readily understood that the lower ends of the sliding rings are adapted accordingly, and that the method will be carried out in a similar manner to that which has been described above.

It is the same for the variants shown in FIG. 3, where the conical wall 38 of the plate is smooth, without steps, the generatrix of the side wall being rectilinear, and in Figure 4, where the wall 39 consists of several frustoconical zones of increasing taper towards the periphery of the container, the generatrix of the wall then being generally curved.

Of course, the shape of the container wall is not limited to the various configurations shown only by way of example. In particular, the invention also applies to the manufacture of containers of non-circular horizontal section, the shape of the punch and of the various sliding rings being adapted accordingly.

The method and the device according to the invention are particularly suitable for stamping blanks of thin steel sheet, in particular less than 0.2 mm and with high mechanical characteristics (Re> 450 MPa), but can of course be used for stamping thicker or different metal sheets. They allow in particular the manufacture of containers of various shapes, the slope of the walls, the depth of the container, and its dimensions which can vary widely, the shape of the tools and in particular the number of rings being adapted accordingly.

Claims (11)

1. Process for stamping a blank (30) of sheet metal for manufacturing, in a single pass, a container of generally frustoconical shape, according to which use is made of a stamping tool comprising a punch (2) of male frustoconical shape and a die (1) opposite it, characterized in that the die (1) includes, opposite the frustoconical surface of the punch, concentric rings (8, 9, 10) which are movable perpendicularly to the plane of the blank, annular zones (32, 33, 34), concentric with the blank, are deformed successively, beginning with that which is of smallest size, each annular zone (32, 33, 34) being held pressed against the punch by a corresponding ring (10, 9, 8) from the moment when the said zone is in contact with the punch and until the end of the stamping, each annular zone being, moreover, in abutment on a corresponding ring whilst the inner adjacent annular zone is not applied on the punch.
2. Process according to Claim 1, characterized in that each annular zone (32, 33, 34) is held substantially in the plane of the blank (30) while the inner adjacent annular zone is not applied on the punch (2).
3. Process according to Claim 1 or 2, characterized in that the punch (2) includes, on its conical surface, one or more circumferential recesses (24, 25), and corresponding steps (35, 36) are formed on the wall of the container during stamping between two adjacent annular zones (32, 33, 34) of the container, successively during the placing in contact of an annular zone on the punch (2) by the corresponding ring (10, 9, 8).
4. Process according to Claim 1 or 2, characterized in that the punch (2) includes, on its conical surface, circumferential recesses (24, 25) and corresponding steps (35, 36) are formed simultaneously at the end of stamping on the wall of the container.
5. Process according to one of Claims 1 to 4, characterized in that a peripheral rib (31) is formed on a planar peripheral zone of the blank constituting the edge of the stamped container.
6. Stamping device for implementing the process according to one of Claims 1 to 5, including a punch (2) of general male frustoconical shape opposite a die (1) and a blank holder (3) for retaining the periphery of the blank while enabling it to slide, characterized in that the die includes, opposite the frustoconical surface of the punch, concentric rings (8, 9, 10) which are movable in the direction of displacement of the punch, and pressure means (14, 15, 16) for exerting a predetermined force on each of the said rings which is sufficient to deform, during stamping, the corresponding annular zone of the blank in the direction of the punch, each of the front annular surfaces (20', 21', 13) of the said rings having a shape complementing the annular surface (20', 21', 13') of the punch facing it axially in order, at the end of stamping, to press each annular zone against the punch.
7. Device according to Claim 6, characterized in that the rings (8, 9, 10) are retained by stops (17, 18, 19) limiting their displacement in the direction of the punch (2).
8. Device according to Claim 6, characterized in that the ends of the rings (8, 9, 10) facing the punch (2) are all substantially in the same plane before stamping.
9. Device according to Claim 6, characterized in that it includes, between the blank holder (3) and the punch (2), a ring (6) in which is produced, on its face directed towards the die, an annular dish (23'), a sliding ring (8) of the die facing the ring (6) including a protuberance (23) with a profile corresponding to that of the annular dish (23').
10. Device according to Claim 6, characterized in that the said pressure means include elastic elements such as springs (14, 15, 16).
11. Device according to Claim 6, characterized in that the said pressure means are determined for each ring (8, 9, 10) so as to exert, on the stamped blank during stamping, a force which is sufficient to press the corresponding annular zone (32, 33, 34) of the blank (30) on the punch (2).

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