阅读说明：本技术 混合成形方法以及对应的成形装置 (Hybrid molding method and corresponding molding device ) 是由 吉莱斯·阿弗里劳德 法布里塞·贝久埃特 于 2020-02-11 设计创作，主要内容包括：公开了一种用于使材料坯料成形的混合方法,其中：待变形的所述材料坯料(2)放置于模具(6)与坯料固持器(4)之间,通过使用至少一个冲头(26、32)冲压使所述材料坯料(2)变形,以便获得预先冲压的材料坯料(2),用液体填充腔体,其中定位一方面具有预先冲压的所述材料坯料(2)的所述至少一个冲头(26、32)以及另一方面至少一对电极(36),所述预先冲压的材料坯料(2)放置成与所述腔体的所述液体接触,以及在至少一对电极(36)之间产生至少一次放电,以这种方式使所述预先冲压的材料坯料(2)抵靠着所述模具(6)变形。(A mixing method for shaping a material blank is disclosed, wherein: -placing the material blank (2) to be deformed between a die (6) and a blank holder (4), -deforming the material blank (2) by punching with at least one punch (26, 32) so as to obtain a pre-punched material blank (2), -filling a cavity with a liquid, wherein-on the one hand-the at least one punch (26, 32) with the pre-punched material blank (2) and on the other hand-at least one pair of electrodes (36) are positioned, -the pre-punched material blank (2) is placed in contact with the liquid of the cavity, and-at least one electric discharge is generated between at least one pair of electrodes (36), in such a way that the pre-punched material blank (2) is deformed against the die (6).)

1. A mixing method for shaping a blank of material, wherein:

-a blank (2) of material to be deformed is placed between the die (6) and the blank holder (4),

-deforming the material blank (2) by stamping using at least one punch (26, 32) so as to obtain a pre-stamped material blank (2),

it is characterized in that

-filling a cavity with a liquid, wherein the at least one punch (26, 32) with the pre-punched material blank (2) on the one hand and at least one pair of electrodes (36) on the other hand are positioned,

-the pre-punched material blank (2) is placed in contact with the liquid of the cavity, and

-generating at least one electric discharge between at least one pair of electrodes (36) in such a way as to deform the pre-punched blank of material (2) against the die (6).

2. Mixing method according to claim 1, characterized in that the relative travel of each punch (26, 32) with respect to the die (6) is limited in such a way that the material blank (2) does not contact the die (6) when pushed by the punch.

3. Mixing method according to claim 1, characterized in that the material blank (2) contacts the die (6) when pushed by at least one punch (26, 32) in such a way that the latter travels relatively to the die (6).

4. Mixing method according to one of claims 1 to 3, characterized in that it further comprises the following steps: -pressurizing a liquid in contact with the material blank (2) during said step to deform the pre-punched material blank (2).

5. Mixing method according to one of claims 1 to 4, characterized in that a vacuum is formed between the material blank (2) and the mould (6).

6. Mixing method according to one of claims 1 to 5, characterized in that the at least one punch (26, 32) is moved away from the die (6) only after at least one discharge has been performed.

7. A hybrid forming device for a blank of material, comprising:

-a die (6) cooperating with a blank holder (4), said die (6) being movable relative to said blank holder (4) between a so-called open position, in which a blank of material (2) can be located between said die (6) and said blank holder (4) and removed therefrom, and another so-called closed position, in which said blank holder (4) cooperates with said die (6) to hold in a controlled manner an edge, preferably all of the edge, of a blank of material (2) to be deformed,

a trough (10) defining a cavity that can be filled with a liquid,

-at least two electrodes (36) placed in the cavity,

it is characterized in that

-said slot (10) comprises at least one movable punch (26, 32) with respect to the assembly formed by said billet holder (4) and said die (6), said die being in said closed position between a so-called distal position, in which the free end of said punch is at a distance from said die (6), and a so-called proximal position, in which the distance of the free end of said punch from said die (6) is smaller than its ranging distance in said distal position.

8. Hybrid forming device according to claim 7, characterized in that the assembly formed by the blank holder (4) and the mould (6) in the closed position is movable relative to the tank (10) which remains fixed.

9. Hybrid forming device according to one of the claims 7 or 8, characterized in that the tank (10) has a bottom (24) and a peripheral wall (26), and wherein the free edge of the peripheral wall (26) forms a punch.

10. Hybrid shaping device according to one of claims 7 to 9, characterized in that the tank (10) has a bottom (24) and a peripheral wall (26),

wherein at least one punch is produced on a free edge of a wall (30) extending through the slot (10) by dividing the slot (10) into at least two compartments (34), and wherein at least one pair of electrodes (36) is located in each of the two compartments (34).

11. Hybrid forming device according to one of the claims 7 to 10, characterized in that the blank holder (4) is attached to a vertical support (8), wherein the die (6) is translationally movably mounted with respect to the blank holder (4) on the side opposite to the support (8), wherein the slot (10) comprises a bottom and a peripheral wall (26), and wherein the slot (10) is fixedly mounted while the support (8) slides with respect to the slot (10).

Technical Field

The present invention relates to a mixing method for shaping sheet material and a corresponding shaping device.

Background

There are a number of methods for shaping sheet materials to have more or less complex shapes. It is possible to bend, roll, stamp sheets, etc., for example. The invention herein relates to forming complex shaped parts from sheet material using a combination of known methods.

By means of methods of deforming a sheet, electro-hydroforming is known which deforms the sheet against a die by applying dynamic pressure. For this purpose, an electric discharge is generated between at least two electrodes in a cavity filled with a liquid (e.g. water). An electric arc is then formed between the two electrodes, thereby inducing a high temperature gradient and vaporization of the liquid. The pressure wave, also commonly referred to as a "shock wave", moves at high speed and presses the sheet against the mold. Electro-hydraulic forming is particularly advantageous compared to other forming methods because it can reduce elastic spring back and achieve enhanced etch type detail and/or square edge and/or elongation before the part to be formed breaks.

In some cases, in particular when the part to be formed is particularly deep, several successive discharges may be carried out. In order to reduce the number of successive discharges required and thus limit the forming time of the part, it has been proposed to perform the hydroforming step prior to the electro-hydraulic forming of the part. To this end, the cavity is filled with a pressurized liquid, as described for example in document US 7802457B 2. When the liquid pressure is sufficient, the sheet is partially deformed against the mould. An electrical discharge is then generated to initiate the shock wave and complete the forming of the part until the desired shape is achieved.

Preforming of the part by applying quasi-static pressure may facilitate the lowering of the sheet in the mould, thus reducing the material deformation that will be performed by electro-hydraulic forming and thus reducing the forming time if it is necessary to recharge the high-voltage electric pulse generator between discharges, or reducing the size of the generator if it is sought to make successive discharges without having to wait for the generator to recharge between discharges.

However, it is difficult to produce parts with vertical walls, i.e. walls extending perpendicular to the plane of the sheet before deformation of the sheet, by these methods. In order to be able to create such vertical walls, extremely high pressures should be used.

Document US2011/0088442 relates to a hydromechanical forming tool that may contain an electro-hydraulic forming cavity, wherein an electrical discharge may be induced by an electrode to improve the level of detail that may be produced in the die.

Document DE 10019594 relates to a method and a device for the hydro-mechanical deformation of a plastically deformable sheet material, in particular for producing motor body parts, wherein the sheet material is placed between a forming tool and a liquid buffer, and wherein the sheet material is pressed against the forming tool under the effect of the static pressure generated in the liquid buffer. While applying the static pressure, a shock wave generator disposed in the liquid buffer is activated to locally generate an increasing pressure directed toward the sheet region.

Document US2012/103045 shows, as such, a system for electro-hydroforming a sheet in an electro-hydraulic forming machine.

It is therefore an object of the present invention to provide a method and a corresponding device that can simply produce a vertical wall using electro-hydraulic forming.

Disclosure of Invention

To this end, the invention proposes a mixing method for shaping a material blank, in which:

-a blank of material to be deformed is placed between the die and the blank holder,

-deforming the material blank by stamping using at least one punch in order to obtain a pre-stamped material blank.

According to the invention, the following steps are also provided:

filling the cavity with a liquid, wherein the at least one punch on the one hand and the at least one pair of electrodes on the other hand are positioned,

-the pre-punched material blank is placed in liquid contact with the cavity, and

-generating at least one electric discharge between at least one pair of electrodes in such a way as to deform the material blank against the die.

This method can facilitate the lowering of material into the die while providing the possibility of using a punch to create what is known as a vertical wall and also having a high quality finish of the part due to electro-hydraulic forming.

According to a first alternative embodiment, the relative travel of each punch with respect to the die is limited in such a way that the material blank does not contact the die when pushed by the punch.

According to another alternative embodiment, the relative travel of the at least one punch with respect to the die is such that the material blank contacts the die when pushed by the at least one punch.

In order to further enhance the polishing quality of the produced part and to facilitate the adjustment of the tool by limiting the manual reworking of the punch, the mixing method described above may further comprise a step during which the liquid in contact with the material blank is pressurized to deform the previously punched material blank. A hydroforming step is then performed, preferably after deformation by the punch and before electro-hydraulic forming.

In order not to be hindered by air remaining between the material blank and the die, it may advantageously be arranged to create a negative pressure between the material blank and the die.

In order to concentrate the shock wave generated by the electrical discharge, it has been observed that the punch is preferably brought into relatively large proximity with the material blank during the electro-hydroforming. It is therefore preferably arranged that the at least one punch is removed from the die only after the at least one discharge has been performed.

The invention also proposes a device for implementing the hybrid forming method described above. Accordingly, the present invention provides a mixed material blank forming apparatus comprising:

-a die cooperating with a blank holder, said die being movable relative to the blank holder between a so-called open position, in which a material blank can be located between the die and the blank holder and removed therefrom, and another so-called closed position, in which the blank holder cooperates with the die to hold in a controlled manner all the edges of the material blank to be deformed,

-a trough defining a cavity that can be filled with a liquid,

-at least two electrodes placed in the cavity,

wherein

The slot contains at least one movable punch relative to the assembly formed by the blank holder and the die, the die being in a closed position between a so-called distal position in which the free end of the punch is at a distance from the die and a so-called proximal position in which the free end of the punch is at a distance from the die that is less than its distance in the distal position.

In this configuration, the die may define the final shape of the sheet to be deformed. The punch is arranged to be placed in the cavity and to deform the sheet in the direction of the die by contacting the sheet and by deforming the sheet.

In a preferred alternative embodiment of such a hybrid forming device, the assembly formed by the billet holder and the die in the closed position is movable relative to the trough which remains stationary.

In such a hybrid forming device it may also be arranged that the trough has a bottom and a peripheral wall, and that the free edge of the peripheral wall forms the punch. Here, the slot and the at least one punch are preferably a single piece.

In the case of a slot having a bottom and a peripheral wall, it may then be arranged to produce at least one punch on the free edge of the wall extending through the slot by dividing the slot into at least two compartments, with at least one pair of electrodes located in each of the two compartments.

A preferred alternative embodiment of the device described above provides that the blank holder is attached to a vertical support, that the die is mounted translationally movably relative to the blank holder on the side opposite the support, that the slot comprises a bottom and a peripheral wall, and that the slot is fixedly mounted while the support slides relative to the slot. For example, the supports may be mounted on a hydraulic buffer. These supports can also be formed, for example, by gas springs, hydraulic cylinders or the like.

Drawings

The details and advantages of the invention will appear more clearly from the following description, with reference to the accompanying schematic drawings, in which:

FIG. 1 shows a schematic view of a

Fig. 1 shows a first step of a mixing method for shaping a sheet, said method being carried out with a mixing and shaping device;

FIG. 2

Fig. 2 shows a second step of the mixing method for shaping a sheet, said method being carried out with a mixing and shaping device;

FIG. 3

Fig. 3 shows a third step of a hybrid method for shaping sheets, said method being implemented with a hybrid shaping device;

FIG. 4

Fig. 4 shows a fourth step of the mixing method for shaping a sheet, said method being implemented with a mixing and shaping device; and

FIG. 5

Fig. 5 shows a fifth step of the mixing method for shaping a sheet, which method is carried out with a mixing and shaping device.

Detailed Description

The drawings and the description below substantially contain elements of a particular nature. They may thus be used not only to better explain the invention, but also to facilitate its definition where appropriate.

Fig. 1 shows a device for shaping a material blank in longitudinal section through a vertical plane. In the following description it is assumed that the material blank to be deformed is a sheet 2 made of steel or of an alloy based on steel, or indeed of another metal or metal alloy. Initially (fig. 1), this sheet 2 has a given shape, for example planar as illustrated in fig. 1. For example, a sheet in the form of a cap is also conceivable.

The sheet 2 to be deformed is here placed between the blank holder 4 and the die 6. The blank holder 4 is carried by a support 8 which is guided in a housing formed in a bottom frame which rests on a ground which is assumed to be horizontal and to which a trough 10 is firmly mounted.

It is assumed in the description below that the supports 8 extend vertically and that they support the blank holder 4 which is thus located above the supports 8. In this way, a top-down orientation is defined. It will be retained in the rest of the description.

The blank holder 4 is here disposed below the sheet 2. The blank holder is formed by an annular portion having a top edge 14 adapted to the die 6 and to the shape to be taken by the sheet 2 after the first deformation (optional preforming operation described below).

Around the top edge 14, the blank holder 4 has an outer edge 16 acting as a support for a compensation device 18 intended to cooperate with the die 6 to control the clamping force exerted by the die 6 and the blank holder 4 on the sheet 2.

In the preferred embodiment illustrated in the drawings, the blank holder 4 has a vertical-axis cylindrical surface 20 with a cross-section adapted to the shape of the groove 10. As explained below, this cylindrical surface 20 may form a seal between the billet holder 4 and the groove 10.

The blank holder 4 further has a bottom base 22 resting on the support 8. The latter for supporting the blank holder 4. They may also help to guide the blank holder 4 relative to the groove 10. These supports may be gas springs or hydraulic cylinders, for example. They may consist of rods mounted on hydraulic buffers. In order to guide the assembly formed by the blank holder 4, the die 6 and the sheet 2 are preferably provided clamped between these two elements (external guide means not shown for the sake of simplicity of the drawing) which translate with respect to the slot 10.

The die 6 is the main part of the device that determines the final shape of the sheet 2 after deformation. The bottom surface of the die 6, i.e. the bottom surface facing the blank holder 4, is intended to provide the final shape of the sheet 2 after deformation. In the forming method, the sheet 2 will be pushed against the mould 6, more specifically against the bottom surface of the mould 6, to plastically deform the sheet and mould its shape.

The bottom surface of the die 6 also comprises an annular area disposed opposite the top edge 14 of the blank holder 4, said bottom surface corresponding to the face of the die 6 positioned facing the blank holder 4 on the one hand and the slot 10 on the other hand. The edge of the sheet 2 will be held between the top edge of the blank holder 4 and the above-mentioned annular area of the bottom surface of the die 6 during the forming method.

In the illustrated embodiment, in which the slot 10 is considered to be fixed, the die 6 is movable in a vertical translational movement so as to be able to move towards and away from the blank holder 4 intended to remain fixed. The blank holder 4 remains fixed and the die 6 moves between a first position, or open position, in which the free space between the blank holder 4 and the die 6 is sufficient for inserting the sheet 2 before deformation and removing it after deformation, and a second position, or closed position, in which the die clamps the peripheral edge of the sheet 2 to be deformed between its annular region and the top edge 14 of the blank holder 4. The compensation device 18 provides a constant gap between the die 6 and the blank holder 4, which corresponds to the thickness of the sheet 2 plus or minus an adjustment value.

For the sake of simplicity, the figures do not show the means for moving the mould 6. For example, such components are known to those of ordinary skill in the conventional stamping art.

In this preferred embodiment, the channel 10 here fulfils the dual function of a container for containing a liquid, preferably water, and a punch. It is hereinafter referred to as a "slot", but may also be referred to as a "punch". Alternatively, the two functions may be separated, with a separate punch, for example, associated with the slot. In the illustrated embodiment, this slot 10 has a floor 24 from which a peripheral wall 26 extends. The bottom plate 24 forms the bottom of the trough 10.

The peripheral wall 26 extends vertically and defines, with the floor 24 (which extends substantially horizontally), a cavity that can be filled with a liquid, typically water. The outer surface of the peripheral wall 26 cooperates with the cylindrical surface 20 of the blank holder to provide sealing during the vertical translational movement of the blank holder 4 around the peripheral wall 26, for example using a seal 28. Certain means (e.g. guide posts not shown) preferably provide guidance during the translational movement of the blank holder 4 relative to the slot 10. It is noted that the cylindrical surface 20 may form the top edge of the cavity defined by the groove 10 and thus extend this cavity depending on the relative position of the blank holder 4 with respect to the groove 10.

In the illustrated embodiment, the top portion of the slot 10, as mentioned above, at least partially forms the top surface of the punch. First, the free edge of the peripheral wall 26 (opposite the base plate 24) has a shape profile suitable for seeking the deformations applied to the sheet 2. Thus, this free edge may comprise a protruding and/or hollow part. The substantially vertical wall 30 is then seated in the tank 10 inside the peripheral wall 26. This wall 30 starts from the bottom plate 24 and extends vertically towards the mould 6. The free ends of the walls 30 form heads 32 which are machined according to the shape to be provided to the sheet 2.

The wall 30 preferably divides the interior cavity of the trough into compartments 34. The compartments may be sealed with respect to each other, but may provide communication (passage) therebetween.

Obviously, several walls 30 may be provided in the groove, depending on the final shape to be provided to the sheet 2. The walls may be parallel, perpendicular or according to any angle relative to each other, and more generally have any shape: straight, curved, wavy, etc.

In each compartment 34, or at least in at least some of its compartments, a pair of electrodes 36 is arranged, which are powered, for example, by the bottom plate 24 (connections and insulators not shown).

It is observed in the drawings that there is a DH stop 38, i.e. a die height stop, which accurately limits the end of travel of the die 6 (and the assembly formed by the blank holder and the sheet 2 actuated by the die 6 during its movement) in a manner known to those of ordinary skill in the art. The DH stop is seated around the peripheral wall 26 on a fixed surface, here for example the top surface of the bottom frame of the support trough 10, and between this floor plate 24 and the bottom surface of the mould 6. They may also cooperate with the bottom base 22 of the blank holder 4.

Fig. 1 shows the hybrid forming device in a position corresponding to the first step of the forming method. In this position, the die 6 is in the open position, i.e. its position furthest from the blank holder 4 (and from the slot 10 containing the punches 26, 32). As mentioned above, the blank holder 4 and the die 6 are then spaced far apart from each other to specifically enable the insertion of the sheet 2 therebetween. Fig. 1 illustrates the positioning of this sheet 2, which positioning is suggested by the arrow 40 on the left side of this fig. 1.

In the position in fig. 1, the blank holder 4 is in a high position, i.e. a position in which the blank holder 4 supporting the sheet 2 is positioned in such a way that the top part of the slot 10 forming the punch cannot come into contact with the sheet 2. Water may already be present in the compartment 34 of the tank 10. A mold 6 is disposed over the sheet 2.

Fig. 2 illustrates the subsequent steps. With respect to fig. 1, the mould 6 is lowered, as indicated by arrow 42. The peripheral edge of the sheet 2 is clamped between the annular region of the die 6 and the top edge of the blank holder 4. The clamping force between the die 6 and the blank holder 4 is set by a compensation device 18 disposed between the outer edge 16 of the blank holder 4 and the edge of the die 6 (also taking into account the force compensation that can be implemented at the level of each of the supports 8). In the method illustrated in the figures, no deformation of the sheet 2 is provided during this step. The contact areas between sheet 2 and die 6 on the one hand and sheet 2 and blank holder 4 on the other hand are preferably parallel.

Alternatively, the clamping of the mould 6 on the sheet 2 may be used in order to perform a first preforming of the sheet 2, for example to bend the sheet and/or mould its edges. A first deformation on sheet 2 can thus be induced (optionally). Furthermore, the clamping of the die 6 on the blank holder 4 may ensure water tightness between the sheet 2 and the blank holder 4. A peripheral bar may also optionally be formed on sheet 2 between die 6 and blank holder 4 to ensure a satisfactory seal between sheet 2 and blank holder 4. Elastomeric seals may also fulfill this sealing function.

The water then fills the entire space delimited by the inner side of the groove 10, the sheet 2, the cylindrical surface 20 of the blank holder 4 and the seal 28. The aim of filling with water is to fill the cavity in such a way that the liquid is brought into contact with the optionally preformed sheet 2. This may be performed, for example, by sucking in air located under the sheet 2. Simultaneous air suction over the sheet 2 is also performed to maintain substantially the same pressure on both sides of the sheet 2. Air suction between sheet 2 and mold 6 is preferably maintained throughout the deformation process to prevent air located in this space from impeding the deformation of sheet 2. Alternatively, it may be arranged to vent air through a vent hole at a high point of the blank holder 4 as water rises in the cavity. During this stage, if the sheet has a concave shape, the pressurized air may be used to keep the sheet concave, thus restricting the air bubbles below it. The blank holder 4 remains in the same position as in fig. 1 during this filling.

Subsequently (fig. 3), the die 6 continues to descend towards the slot 10 and the blank holder 4 is induced to descend-arrow 44 relative to the slot 10. The punch formed by the slot 10, more specifically by the top peripheral edge of the peripheral wall 26 and the head 32, is then brought into contact with the sheet 2 and plastically deforms the sheet by stretching. During this movement, the punch exerts a force pushing the sheet 2 towards the die 6. The sheet 2 held between the blank holder 4 and the die 6 is disposed between the punch and the die 6. The punch and/or the slot 10 acts as a male part cooperating with the die 6, here with a housing to receive a punch female part formed by the top part of the slot 10. The compensating device 18 is here used to adjust the tension at the edge of the sheet 2 and to allow the material to move from the sheet 2 towards the inside of the system (if required).

Here the second deformation step of the sheet 2 is performed (the optional preforming mentioned above is the first deformation step). The second deformation step here consists of a stamping step. During this deformation step, it is preferably, but not compulsorily, sought to ensure that sheet 2 does not contact mould 6 in its central region, i.e. in the region located facing the inner side of peripheral wall 26. However, in some cases, it is possible to provide a "complete" deformation of the sheet 2 at certain positions during this punching operation. This may avoid having to provide electrodes to "cover" the entire surface of the sheet 2.

Fig. 4 illustrates an advantageous, but optional step of the hybrid forming process. Here, a step of quasi-static hydroforming with a sheet 2 is proposed, during which this sheet 2 is once again close to the die 6 and can be brought into local contact therewith. This deformation of sheet 2 is then obtained by pressurizing the water located in tank 10, for example by acting on die 6 (arrow 42). Thus, the sheet 2 is at least partially separated from the punch formed by the top portion of the slot 10 and adopts an intermediate position between the die 6 and the head 32 and the top edge of the peripheral wall 26 forming the punch.

It has been observed by those skilled in the art that the drawings are diagrammatic and explanatory only. The deformations and details are not drawn to scale.

Fig. 5 illustrates a subsequent step of the method for shaping the sheet 2. Here electro-hydroforming is schematically shown. Here the discharge chamber is formed and completely filled with water. The discharge chamber comprises a cavity inside the groove and extending to the deformed sheet 2 and the seal formed between the groove and the blank holder 4. The pair of electrodes 36 disposed in the discharge chamber is then powered by a strong current discharged from the capacitor. In a known manner, this electric discharge generates an explosion in the liquid (water) contained in the tank 10 and in contact with the sheet 2 (it is important to have a satisfactory filling of water in the tank 10, so that the water is in fact in contact with the sheet 2 for this electro-hydroforming step), generating a shock wave that propagates towards the sheet 2. The wall 30 and the peripheral wall 26 guide the shock wave and thus serve to achieve satisfactory deformation of the sheet 2 against the die 6.

In this method, a single discharge in the pair of electrodes 36 is generally sufficient to obtain the sought deformation, due to the previous deformation of the sheet 2 prior to the electro-hydroforming step.

The drawings do not show the final step associated with removing the part formed from sheet 2, in which the mould is opened and the groove is lowered again to the position illustrated in figure 1.

Thus, the methods described herein may produce parts with reduced cycle times because a single electro-hydraulic forming step is required. The drawing pattern and optionally the hydroforming operation are performed almost within the masking time.

The great advantage of the method described here is that the sheet after deformation can have vertical walls (within the clearance angle that enables separation of the sheet formed by the die 6 at the end of the process), in other words, the part obtained by deforming the sheet can have a face that is substantially perpendicular to the orientation of the sheet before deformation. In the example illustrated in the drawings, the sheet is initially in a horizontal plane. After deformation, the sheet then has a quasi-vertical face (before removing the part from the system).

The forming method and hybrid forming apparatus proposed herein can obtain parts with quasi-vertical walls with reduced cycle time by electro-hydraulic forming. Thus, the cost price of such parts may be limited.

According to an alternative embodiment, the walls in the slots (punches) may for example form a honeycomb-type honeycomb structure.

The peripheral wall arranged as a groove in the illustrated embodiment is part of a punch intended to deform the sheet material by punching. This obviously depends on the sought shape to be provided to the sheet. The peripheral wall of the slot need not be part of the punch. For example, it may be arranged in fig. 3 that the blank holder is flush with the top edge of the peripheral wall of the pocket.

In the illustrated arrangement, it has been assumed that the slot is fixed. This is the preferred embodiment, but it is possible to have a fixed mold. Those of ordinary skill in the art will appreciate that what is important is the relative movement between the various components of the system.

The invention is not limited to the different embodiments described and illustrated and to the alternative embodiments mentioned, but it also relates to embodiments that can be understood by a person skilled in the art within the scope of the appended claims.