EP0376808A1 - Method and device for deep-drawing sheet materials with a stamp deformable underneath a plunger - Google Patents

Abstract

Method for stamping sheet materials, in particular sheet metal, on a press using a cushion (12) made of an elastic material, according to which a sheet blank (20) is arranged to be formed on a support, the peripheral part forms a lower hold-down (2) and the central part of which constitutes a matrix (3), an upper hold-down (9) is applied, under the action of an external slide (21), to the part sheet metal blank (20), then a punch (11) is applied under the effect of a plunger, characterized in that, during a first step, under the action of the plunger, the elastic cushion (12) on the sheet blank (20) for preforming said blank so as to give it a surface substantially equal to the surface of the finished part to be obtained, then, during a second step, we continue , always under the action of the plunger, the descent of the elastic cushion (12) and simultaneously we move all or part the bottom of the die (3) to effect the final shaping of the part.

Description

The subject of the present invention is a method and a device for stamping sheet materials, in particular extra-thin sheet blanks of large dimensions usable for example in the automotive industry, and / or comprising complex shapes, with deformable punch. under diver.

The stamping of large and complex parts is generally done with double effect presses. These machines essentially comprise a fixed table which receives a matrix and two independent slides: an external slide carrying a blank holder and a central slide called a plunger carrying a punch. First of all, the external slide and the blank holder go down and maintain a tightening of the sheet blank, then the punch, under the action of the central slide, goes down quickly until it comes into contact with the sheet blank and continues its descent during the stamping phase, and finally the central slide and the external slide go up practically at the same time.

This classic process does not allow stamping of extra thin sheets, for example of a thickness less than 45/100 mm, because the rigidity of the die and the punch as well as the tightening of the sheet by the blank holder generate non-homogeneous deformations resulting in certain areas by elongations likely to cause excessive thinning given the small initial thickness of the sheet and in other areas by shrinking tending to cause thickening of the sheet blank, which lead to the formation of folds.

In addition, for steels with high elastic limit, this classic drawing technique To avoid the formation of folds under the blank holder, it requires a very high pressure on the sheet blank which most machines cannot provide.

There is also known a process called "Guerin process" according to which a sheet of sheet metal resting on a mass of elastomer is formed by means of a punch. The punch is forced into the matrix elastomer which presses the sheet blank against the punch. The functional role of the elastomer is therefore that of a matrix. The main drawback of this method is that it consumes a great deal of energy and, moreover, this method does not prevent the formation of folds. Indeed, the pressure gradients caused by the deformation of the elastomer decrease as one approaches the upper surface of the elastomer mass, especially for the production of angular shapes, the sheet blank being insufficiently held at its periphery.

There is also known a forming process using a pressurized fluid to form simple shapes of the hemispherical type and / or of revolution. However, this technique can only be used for parts of revolution or axisymmetric shape.

Finally, in FR-A-2,564,339 and FR-A-2,590,814, a drawing process is known on an elastic cushion. According to this method, the sheet blank to be formed is placed on an elastic cushion, an external slider supporting a blank holder is applied to the peripheral part of the sheet blank so as to cause the mass of the elastic cushion to creep to deform the central part of the sheet blank by giving it at the end of the preforming step a surface substantially equal to the surface of the finished part to obtain, then apply with a central slide a punch on the central part of the sheet blank to permanently shape the part.

This method however presents constraints which can be solved in an original way by the method according to the present invention.

In fact, when the elastic cushion returns to a state of equilibrium, that is to say at the time of the ascent of the plunger and the blank holder, a suction effect of said elastic cushion on the formed part which can cause the part to collapse, in particular in the case of large parts. In addition, it should be noted that the return to the initial state of the elastic cushion takes place from the center towards the periphery, which increases the suction effect.

Also known from US-A-2,859,719 is a drawing process which simultaneously implements drawing on elastomer and drawing under fluid pressure. The elastomer element, placed above the sheet blank, is not only made of an elastomer mass, but also comprises a fluid-inflatable bladder, which resembles a technique hydroforming. In addition, this method does not include a first preform step in which the preformed sheet blank acquires a surface substantially equal to the surface of the finished part to be obtained.

The present invention aims to present a new process which, while preserving the efficiency and longevity of the cushion of elastic material, makes it possible to obtain deep-drawn parts of medium depth, but of large surface area, such as automobile parts, the parts of which are only practiced hardly ever forms of revolution, but represent complex forms which cannot be developed, without the problem of suction and incorporating other advantages which will be developed below.

The subject of the invention is therefore a process for stamping sheet materials, in particular sheets, on a press using a cushion of elastic material, according to which a sheet blank is placed to form on a support. whose peripheral part forms a lower blank holder and whose central part constitutes a matrix, an upper blank holder is applied, under the action of an external slide, to the peripheral part of the sheet blank, then a punch under the effect of a plunger, characterized in that, during a first step, the elastic cushion forming a deformable punch is applied to the sheet metal blank under the action of the plunger to preform said blank so as to give it a surface substantially equal to the surface of the finished part to be obtained, then, during a second step, the elastic cushion is lowered, still under the action of the plunger, and simultaneously we move all or part of the die bottom to perform the final shaping of the part.

According to another characteristic of the invention, during the action of the upper peripheral blank holder on the sheet blank, the edges of said sheet blank are dropped in localized areas.

The invention also relates to a device for stamping sheet materials, in particular sheet blanks, comprising a cushion of elastic material, a support for the sheet blank to be formed, the peripheral part of which forms a lower blank holder laughing and whose central part constitutes a matrix, means for preforming the sheet blank consisting of an external slide carrying an upper blank holder and means for definitive forming of said sheet blank consisting of a plunger acting on a punch, characterized in that the cushion made of an elastic material is placed above the sheet blank and secured to the vertically movable punch.

According to other characteristics of the invention:
- the elastic cushion has a constant volume and consists of a deformable and incompressible material placed in an envelope,
the matrix comprises a fixed part and a vertically movable core cooperating with a member for regulating the movement of said core to achieve the final conformation of the part,
the matrix comprises a fixed core and a vertically movable part cooperating with a member for regulating the movement of said movable part to achieve the final conformation of the part,
- The whole of the matrix is movable vertically and cooperates with a member for regulating the movement of said matrix to achieve the final conformation of the part.

• - La figure 1 est une vue en perspective éclatée montrant les différents éléments constituant le dispositif d'emboutissage selon l'invention ;
• - la figure 2 est une vue schématique en perspective de la matrice, montrant le positionnement du flan de tôle sur cette matrice avant emboutissage ;
• - les figures 3 à 6 sont des vues schémati­ques en coupe selon la ligne 3-3 de la figure 1, au cours des étapes successives de formage d'une pièce ;
• - la figure 7 est une vue en perspective éclatée d'une première variante du dispositif d'embou­tissage selon l'invention ;
• - les figures 8 à 10 sont des vues schéma­tiques en coupe selon la ligne 8-8 de la figure 7, au cours des étapes successives de formage d'une pièce ;
• - la figure 11 est une vue en coupe d'une seconde variante du dispositif d'emboutissage selon l'invention ;
• - la figure 12 est une vue en coupe d'une troisième variante du dispositif d'emboutissage selon l'invention ;
• - la figure 13 est un diagramme montrant un cycle du dispositif selon l'invention, pendant le préformage et la conformation de la pièce.

The invention will be better understood with the aid of the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

• - Figure 1 is an exploded perspective view showing the different elements constituting the stamping device according to the invention;
• - Figure 2 is a schematic perspective view of the die, showing the positioning of the sheet blank on this die before stamping;
• - Figures 3 to 6 are schematic sectional views along line 3-3 of Figure 1, during the successive stages of forming a part;
• - Figure 7 is an exploded perspective view of a first variant of the stamping device according to the invention;
• - Figures 8 to 10 are schematic sectional views along line 8-8 of Figure 7, during the successive stages of forming a part;
• - Figure 11 is a sectional view of a second variant of the stamping device according to the invention;
• - Figure 12 is a sectional view of a third variant of the stamping device according to the invention;
• - Figure 13 is a diagram showing a cycle of the device according to the invention, during the preforming and the shaping of the part.

The stamping device shown in FIG. 1 comprises a base 1, the central part of which constitutes a housing for a matrix 3 possibly made in one piece with the base 1 and which comprises on its upper part an imprint corresponding to the profile of the finished part to get.

The base 1 comprises on the one hand an internal part forming a blank holder 2 situated at a level higher than the imprint of the matrix 3 and on the other hand an upper part constituting an area 2a for falling from the edge of the sheet blank 20.

Furthermore, the matrix 3 includes a cavity 4 into which a sliding core 5 penetrates. in the latter and whose upper face completes the imprint of the matrix 3 to obtain the profile of the finished part.

According to the first embodiment shown in Figure 1, the core 5 is movable and cooperates with a member 6 for regulating the movement of said core which can be constituted for example by a multi-blade brake, a spring or even a jack, or any other appropriate system.

Above the base 1, the stamping device comprises a body 7, the lower part of which constitutes an upper peripheral blank holder 9.

The upper peripheral blank holder 9 has external dimensions smaller than those practiced on the base 1, so that said upper blank holder 9 can penetrate into said base to reach the lower blank holder 2.

The body 7 comprises a well 10 into which a punch 11 penetrates. This punch 11 comprises a cushion 12 made of elastic material and has a plate 13 at its upper part. Furthermore, the body 7 is provided on its periphery with two superimposed flanges, 14 and 15 respectively.

The first flange 14 supports jacks 16, each rod of which passes through the second flange 15 through orifices 17 and cooperates with the plate 13 of the punch 11 to constitute a system for raising the punch at the end of the shaping step and optionally adjusting the pressure of the upper blank holder 9.

The sheet blank 20 has in localized areas cutouts forming horns 20a which, when the blank is positioned on the upper face of the base 1, rest on the determined areas 2a of edge falling, as shown in FIG. 2. The edge falling is therefore carried out in limited areas of the peripheral edge of the sheet blank corresponding to areas 2a of the upper part of the base 1 as will be seen later.

The sheet blank 20 is formed in the following manner.

First, the sheet blank 20 is placed on the upper face of the base 1 which rests via the horns 20a only on the zones 2a (FIG. 3). The core 5 protrudes above the imprint of the matrix 3 and the member 6 for regulating the displacement of said core is locked by a suitable device not shown.

Initially, an external slide 21 of the press (Figure 4), supporting via the flange 15 the body 7, gradually descends so that the upper blank holder 9 causes in the areas where the blank sheet 20 rests on zones 2a, the falling of the edge of the sheet blank which folds back.

Consequently, during this first step, the localized zones of the peripheral part of the sheet blank 20, which would be subjected to a strong constriction, under conditions other than those of the present invention, are maintained between the determined zones 2a and the blank holder 9, in order to achieve in these areas the falling of the edge of the sheet blank, thus making it possible to retain the metal to be shrunk.

Then, a plunger 22 of the press comes into contact with the plate 13 of the punch 11 and causes the descent of the elastic cushion 12, the working face of which comes into contact with the sheet blank 20.

During this descent, the core 5 protruding (Figure 5), the elastic cushion 12 is compressed and, under the effect of this compression action, causes the deformation of the sheet blank 20 so as to perform the preforming of said blank and give it a surface substantially equal to that of the finished part to be obtained.

FIG. 6 represents the stage of final shaping of the part. The plunger 22 descends to its low position and causes, via the elastic cushion 12, the final shaping of the preformed part during the first part of the descent.

Simultaneously with the descent of the central plunger 22 and the punch 11, the member 6 is unlocked so that the movable core 5 retracts so as to release the developed surfaces of sheet metal necessary for the conformation of the finished part.

The compressive stresses due to the support of the sheet metal blank 20 on the matrix 3 by the elastic cushion 12 are transformed by the action of said elastic cushion, into tensile stresses exerted on the entire surface of the sheet metal blank, and cause the displacement of this blank throughout the available volume.

As the elastic cushion descends, during the preforming and shaping steps, the edges of the sheet blank 20 are held while sliding between the lower blank clamp 2 and the upper blank clamp 9, and the height of the fallen edges of said blank in the localized zones 2a decreases.

On the other hand, during these steps, the plate 13 of the punch 11 compresses the jacks 16, which also has the effect of adjusting the force of the upper blank holder 9 on the peripheral edge of the sheet blank 20.

The step of releasing the formed part is first carried out by raising the plunger 22, which releases the punch 11. Under the effect of the jacks 16, the punch 11 rises, driving the elastic cushion 12. The detachment of the elastic cushion 12 of the formed part takes place from the periphery towards the center, so that the air penetrates between the part and the external face of the cushion, thus avoiding the effects of suction.

Then, the external slide 21 rises and drives the body 7 by definitively releasing the formed part which can have a shape as shown in FIG. 1.

According to a variant illustrated in Figures 7 to 10, the base 1 carrying the matrix 3 is vertically movable and, for this purpose, rests on a sole 30 which cooperates with a member 31 for regulating the movement of said base, consisting for example of a multi-blade brake, a spring, a jack or any other suitable system.

As in the previous variant, the matrix 3 comprises a cavity 4 into which a core 32 penetrates, the upper face of which completes the imprint of the matrix 3 to obtain the finished part. In this variant, the core 32 is fixed.

The descent and adjustment of the force of the body 7 under the effect of the external slide 21 is effected by means of springs 33 guided by columns 34 interposed between the external slide and the body.

The operations of dropping the peripheral edge of the sheet blank in localized areas (FIG. 8) and of preforming said blank (FIG. 9) are carried out in the same way as in the preceding variant. te, by successive descents of the upper blank holder 9 and the punch 11, the member for regulating the movement of the base 1 being locked.

On the other hand, simultaneously with the shaping operation (FIG. 10), the member 31 for regulating the movement of the base 1 is unlocked so as to release the developed surfaces of sheet metal, by lowering the matrix 3 during this shaping operation.

According to a second variant illustrated in FIG. 11, the base 1 is fixed and it is the whole of the matrix 3 which is movable vertically. The matrix 3 cooperates with a member 31 for regulating the movement of said matrix, consisting for example of a multi-blade brake, a spring, a jack or any other suitable system. The part is formed identically to the previous variants.

According to yet another variant illustrated in FIG. 12, the stamping device comprises means for absorbing the excess volume of the elastic cushion 12 relative to that determined by the surface of the finished part to be obtained. In fact, during the preforming step, the descent of the elastic cushion 12 deforms the central part of the sheet blank, while giving it, at the end of the preforming step, a surface substantially equal to the surface of the part. finished getting. Continued descent of the elastic cushion 12 for the final shaping of the sheet blank causes an increase in pressure in the cushion and, depending on the part to be produced, possibly a difference in volume of said cushion between the preforming step and the 'conformation step.

For this, the punch 11 (Figure 12) has an upper part 11a and a lower part 11b between which are interposed springs 40 or any other equivalent system. These springs 40 compress above a certain pressure to absorb the excess volume of the elastic cushion.

The means for absorbing the excess volume of the elastic cushion can also be arranged in the vicinity of said cushion, as for example in the side walls of the body 7.

In the diagram of FIG. 13, curve I represents the cycle of the external slide 21 and curve II represents the cycle of the plunger 22. The travel of the external slide 21 takes place over a distance A and the travel of the plunger 22 over a distance distance B.

On this diagram, we find for each cycle, in C the falling of the edge of the sheet blank on localized areas, in D the holding of the sheet blank in D, the holding of the peripheral edge of the sheet blank, in E l preforming operation and at F the shaping operation of the part.

The combination of edge falling in localized areas and the use of the elastic cushion makes it possible to obtain parts of complex shapes which cannot be developed with sheets with low deformation capacity and thin thickness.

The elastic cushion has a constant volume and can be constituted by a deformable and incompressible material possibly placed in an envelope. This material can be an elastomer or any product meeting these conditions.

Although the description has been made with reference to the forming of sheet blanks, i.e. generally metallic thin plates, it should be understood however that the method according to the present invention is in no way limited to this application. The method according to the present invention can be implemented with thin plates, in particular of plastic.

Thus in the present description, the term "sheet" must be given a general meaning of a thin plate of sheet material without wanting to limit its scope to metal products.

An advantage of the method and the device of the present invention lies in the increase, on the same double-acting press, of the possible dimensions of the finished stamped part, compared with the stamping solution on elastic cushion developed in the FR-A -2,564,339 and FR-A-2,590,814.

It can also be noted that the volume of the elastic cushion is smaller than in the solutions mentioned above.

Furthermore, the spatial presentation of the finished part is similar to that encountered in conventional stamping and allows mechanization of subsequent operations requiring no change of equipment.

Claims (11)

1.- Method for stamping sheet materials, in particular sheet metal, on a press using a cushion (12) made of an elastic material, according to which a sheet blank (20) to be formed is formed on a support whose peripheral part forms a lower blank holder (2) and whose central part constitutes a matrix (3), an upper blank holder (9) is applied, under the action of an external slide (21) on the peripheral part of the sheet blank (20), then a punch (11) is applied under the effect of a plunger (22), characterized in that, during a first step, under action of the plunger (22), the elastic cushion (12) forming a deformable punch on the sheet blank (20) to preform said blank so as to give it a surface substantially equal to the surface of the finished part to be obtained, then, during a second step, the elastic cushion is lowered (still under the action of the plunger (22)) ( 12) and simultaneously moving all or part of the bottom of the die (3) to effect the final shaping of the part. 2.- Method according to claim 1, characterized in that, during the action of the upper blank holder (9) on the sheet blank (20), is carried out in localized areas (2a) a falling edge of said sheet blank. 3.- Device for stamping sheet materials, in particular sheet blanks, comprising a cushion (12) made of an elastic material, a support for the sheet blank to be formed, the peripheral part of which forms a lower blank holder (2) and the central part of which constitutes a matrix (3), means for preforming the sheet blank (20) constituted by a grout outer bucket (21) carrying an upper blank holder (9) and means for definitive forming of said sheet blank consisting of a plunger (22) acting on a punch (11), characterized in that the cushion (12) in one elastic material is disposed above the sheet blank (20) and secured to the vertically movable punch (11). 4.- Device according to claim 3, characterized in that the elastic cushion (12) has a constant volume and consists of a deformable and incompressible material placed in an envelope. 5.- Device according to claim 3, characterized in that the matrix (3) comprises a fixed part and a core (5) movable vertically cooperating with a member (6) for regulating the movement of said core to achieve the final conformation of the room. 6.- Device according to claim 3, characterized in that the matrix (3) comprises a fixed core (32) and a vertically movable part cooperating with a member (31) for regulating the movement of said movable part to achieve the final conformation of the room. 7.- Device according to claim 3, characterized in that the whole of the matrix (3) is vertically movable and cooperates with a member (31) for regulating the movement of said matrix to achieve the final conformation of the part. 8.- Device according to one of claims 3 to 7, characterized in that it comprises means (16, 33) for adjusting the tightening of the upper blank holder (9) on the peripheral zone of the sheet blank (20 ). 9.- Device according to one of claims 3 to 8, characterized in that it comprises means (40) for absorbing the excess volume of the elastic cushion (12) relative to that determined by the surface of the finished part to obtain. 10.- Device according to claim 9, characterized in that the means (40) for absorbing the excess volume of the elastic cushion are arranged in the punch (11). 11.- Device according to claim 9, characterized in that the means (40) for absorbing the excess volume of the elastic cushion are arranged in the vicinity of said elastic cushion (12).

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