FR3031052A1 - NEW ENCLOSURE ARCHITECTURE FOR ELECTRO-HYDRAULIC FORMING - Google Patents

Abstract

The invention relates to an electro-hydroforming enclosure (10) for the simultaneous forming of a plurality of parts (50) comprising: - a discharge frame (20) comprising: i. a first portion (211a) having a first inner wall (2111a), ii. a second portion (211b) having a second inner wall (2111b), said first and second inner walls defining a discharge chamber (22) for receiving a fluid, the first inner wall (211a) having a polygonal section and having N faces (212a), N> 2, each side face (212a) having a die (30) comprising a forming chamber (32), - an electro-hydraulic discharge system (40) with two electrodes (41), each die being positioned equidistant from the two electrodes.

Description

FIELD OF THE INVENTION The present invention relates to the field of forming, and more particularly to the field of electro-hydraulic forming. The present invention relates to a novel electro-hydroforming enclosure architecture, particularly for the simultaneous forming of multiple parts. State of the art Hydroforming processes are generally used as manufacturing processes, especially for parts of complex shapes. They consist in using the pressure of a fluid, preferably a liquid, to achieve the plastic deformation of a sheet held in a mold. The fluid then acts on the sheet to make it fit the shape of the mold. This fluid can be pressurized in various ways. Among the existing hydroforming processes, mention may be made of the electro-hydroforming process, known as the EHF process (from the Anglo-Saxon Electro Hydraulic Forming). This method is a very high-speed deformation forming process which is based on an electrical discharge of a high energy stored in capacitors either between two electrodes placed in a chamber filled with fluid, or in an explosive wire placed in a chamber filled with fluid. When an electric discharge is created in the fluid, a shock wave is generated in said fluid, it propagates and projects the sheet against the mold. The dynamic pressure thus generated on the sheet allows the high-speed deformation of the constituent material which is projected against the mold, thus allowing its shaping. This method allows the shaping of sheets but also other parts made of a plastically deformable material. It is widely used for the production of large parts, that is to say parts whose characteristic length is significantly greater than a distance between the two electrodes. Such a method has many advantages, in particular obtaining very fine details on the parts, such as, for example, engravings, the absence of springback, or even low manufacturing costs. However, one of the main drawbacks lies in the cycle time required for forming a part, as indicated in US Pat. No. 5,749,378. In fact, in a known manner, a forming cycle via the EHF process is decomposed into several parts. steps: - introduction of the part to be formed in an electrohydroforming chamber, - filling of a hollow chamber in the electro-hydroforming enclosure with a fluid, - electro-hydraulic discharge in the fluid contained in the hollow chamber, - emptying of the hollow chamber, - removal of the formed part.

In view of the dimensions of the parts to be formed, it is clear that the filling and emptying steps of the hollow chamber represent the most time consuming stages. SUMMARY OF THE INVENTION The present invention aims in particular to provide an effective solution for forming parts, while reducing the cycle time and ensuring an equivalent result. The invention thus relates to a new electro-hydroforming enclosure architecture. The electro-hydroforming chamber comprises: a discharge frame comprising: a first part comprising a first internal wall, a second part comprising a second internal wall, said first and second internal walls delimiting a discharge chamber intended to to receive a volume of fluid, - an electro-hydraulic discharge system with two electrodes. According to the invention, the first inner wall has a polygonal section and has N lateral faces, N> 2, each lateral face comprising a matrix comprising a forming chamber having an imprint intended to be complementary to the shape that must take a piece after deformation.

Such an electro-hydroforming enclosure, because of the shape of the inner wall advantageously allows the forming of a plurality of parts simultaneously. The parts are intended to be positioned, each respectively between the discharge chamber and a forming chamber 10 before an activation of said electro-hydraulic discharge system, the activation of said electro-hydraulic discharge system causing the projection and the deformation of each piece against the impression of the associated forming chamber. By activation is meant the creation, via the electro-hydraulic discharge system, of an electric discharge in the fluid to create a shock wave that propagates in the fluid. This electric shock occurs between the two electrodes. The discharge frame is preferably made of a high-strength material, for example a metallic material such as steel, to contain the high pressures generated upon activation of the electro-hydraulic discharge system. According to the invention, each matrix is positioned equidistant from the two electrodes, when said electrodes are in position in the electro-hydroforming enclosure, ready to be activated. With such relative positioning of the dies and electrodes, a pressure of the same strength is applied to all the parts during the electro-hydraulic discharge, deforming them identically. Such an electro-hydroforming enclosure is thus advantageous in that it allows, during a forming process, the forming of a plurality of parts in a single cycle, while guaranteeing a level of forming of identical quality. for each piece. The production rate is therefore greatly increased.

Such an electro-hydroforming enclosure is also particularly suitable for producing small-sized parts, such as, for example, a USB key body, embellished for example with fine engravings.

According to preferred embodiments, the invention furthermore satisfies the following characteristics, implemented separately or in each of their technically operative combinations. According to preferred embodiments, the first inner wall with a polygonal section has a substantially cylindrical general shape.

According to preferred embodiments, the first inner wall of polygonal section has a generally conical or frustoconical general shape. Such a discharge chamber configuration, by virtue of the shape of the first internal wall, makes it possible to minimize the volume of fluid, with respect to a generally cylindrical general shape, necessary for its filling, and thus to reduce the filling time. emptying the discharge chamber. This configuration thus contributes to reducing the cycle time and the production rate. Such a configuration, because of its oblique lateral faces, also allows said lateral faces to serve as a reflector for the shock wave. Thus, the forming of the parts will be realized, on the one hand, by direct waves coming from the electro-hydraulic discharge propagating and coming directly to strike the piece to be formed, and on the other hand, by indirect waves reflected by the others. lateral faces before coming to strike the piece to form. This configuration also eliminates blank greenhouse for the maintenance of parts in the dies. According to preferred embodiments, to increase the number of parts to be formed in a single forming cycle, the second inner wall 30 also has a polygonal section and has N side faces, N> 2, each side face having a matrix comprising a forming chamber having an impression intended to be complementary to the shape that a part must assume after deformation. According to preferred embodiments, at least one matrix is housed in the discharge chamber, preferably against a lateral face.

According to preferred embodiments, at least one die is housed outside the discharge chamber, with the forming chamber opening at a side face. According to preferred embodiments, each matrix is positioned at a center of gravity of a side face.

The invention also relates to an electro-hydroforming machine comprising an electro-hydroforming enclosure according to one of its embodiments and an electrical energy storage unit connected to the electro-hydraulic discharge system. . The invention also relates to an electro-hydraulic forming process for the simultaneous forming of a plurality of parts, comprising the steps of: placing the parts to be formed in the electrohydroforming enclosure according to the invention; one of its embodiments, - filling of the discharge chamber with a fluid, 20 - electro-hydraulic discharge in the fluid contained in the discharge chamber, - emptying of the discharge chamber, - removal of formed parts. With such a forming process, the parts are projected simultaneously against the impression of the forming chamber. The cycle time is significantly reduced. DESCRIPTION OF THE FIGURES The characteristics and advantages of the invention will emerge more clearly in the light of the following examples of implementation, provided for illustrative purposes only and in no way limitative of the invention, with the support of FIGS. 1 to 4. , in which: FIG. 1 represents a sectional view of an electrohydroforming enclosure according to a particular embodiment of the invention; FIG. 2 illustrates a perspective view of a portion of the enclosure of FIG. electro-hydroforming according to said embodiment, Figures 3a and 3b respectively illustrate a perspective view and a sectional view of a portion of an electro-hydroforming enclosure according to another embodiment of the invention, FIG. 4 represents a sectional view of an electrohydroforming enclosure according to another embodiment of the invention.

DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION An electro-hydroforming enclosure 10 according to the invention allows the simultaneous forming of a plurality of parts 50. The parts to be formed may be of flat shape, or alternatively , of tubular form. The pieces can also be preformed by conventional stamping techniques.

This electro-hydroforming enclosure is used in the context of a conventional forming process which will be recalled later. The electro-hydroforming chamber 10 is made in two parts. The electro-hydroforming enclosure 10 comprises a first part, called the lower base 21a, representing a lower part of the electroforming enclosure (according to the orientation of the figures) and a second part, called the upper base 21b. , representing an upper part of the electrohydroforming enclosure (according to the orientation of the figures). Also as a variant, the first part may represent a left part of the electrohydroforming enclosure (according to the orientation of the figures) and the second part may represent a right part of the electro-hydroforming enclosure (according to FIG. orientation of the figures) or vice versa. The lower 21a and upper 21b bases together form a discharge frame 20. The lower base 21a has a first inner wall 211a and the upper base 21b has a second inner wall 211b. These first and second inner walls together define a discharge chamber 22.

The lower base 21a and the upper base 21b are removable relative to each other so as to allow insertion and removal, in the discharge chamber, of the parts 50 to be formed. The discharge frame 20 is preferably made of a metallic material, for example steel, in order to have a structural resistance of the discharge chamber 22 and to contain the high pressures generated at the time of an electro-hydraulic discharge, during the Indeed, the voltage during an electro-hydraulic discharge can reach several tens of kilovolts.

In a non-limiting example of the invention, the discharge frame 20 has a substantially cylindrical geometric shape. The discharge chamber 22 is intended to be filled with an incompressible fluid, preferably a liquid, for example water. A water supply duct (not shown) is provided in the discharge frame 20 to allow the discharge chamber 22 to be connected to a tank (not shown) containing water and to supply said discharge chamber 20 in water. A water discharge conduit (not shown) is provided in the discharge frame 20 to allow the discharge chamber 22 to be connected to a vessel and to drain water from said discharge chamber into the vessel. . In an alternative embodiment, the water supply duct 23 and the water discharge duct are one and the same duct allowing the supply and the emptying of the water in / out of the discharge chamber 25 to / from a single vessel. In an exemplary embodiment, illustrated in Figures 1 and 2, the second inner wall 211b has a generally flat shape. The first inner wall 211a has in turn a generally conical (or pyramidal), triangular section. The first inner wall 211a thus has three lateral faces 212a, intersecting at a point, called an apex, located opposite the second inner wall 211b. In other words, the discharge chamber 22 has a pyramidal shape having the polygonal base, the second inner wall 211b and triangular faces, the three lateral faces 212a. Each side face 212a has a die 30 for receiving a workpiece. Each die 30 has a forming chamber 32. Each workpiece is arranged in a die such that, once in position, it separates the discharge chamber from the forming chamber from said die. Each forming chamber 32 has, facing the workpiece to be formed, an imprint corresponding to the shape that the workpiece must take after deformation. In this exemplary embodiment, the electrohydroforming enclosure 10 thus produced may allow the simultaneous forming of three parts.

Each die is, in one embodiment, housed in the discharge chamber, as illustrated in FIGS. 1 and 2, against a side face. Alternatively, each matrix may be housed outside the discharge chamber with the forming chamber opening at a side face.

Preferably, the first inner wall 211a and the die are made in one piece for sealing and stiffness. The dies 30 are preferably made of a metallic material, for example steel, in order to present a structural resistance of the forming chambers 32 and to contain the high pressures generated at the time of an electro-hydraulic discharge during the forming process. . The forming chamber 32 is in turn preferably under vacuum. A conduit (not shown) is provided in the die 30 to allow the forming chamber 32 to be connected to a vacuum pump (not shown). However, as a variant or in the absence of means for producing this vacuum, it will also be possible to leave the forming chamber 32 under atmosphere and to provide vents enabling the air to be evacuated during the forming process. Such an electro-hydroforming enclosure 10, because of the conical shape of the discharge chamber, advantageously makes it possible to reduce the dimensions of the discharge chamber and consequently to minimize the volume of water necessary for its filling. As a result, the cycle time required to perform a forming process using such an electro-hydroforming chamber is greatly reduced and the production rate is greatly increased.

The electro-hydroforming enclosure 10 further comprises an electro-hydraulic discharge system 40. In a preferred embodiment, illustrated in FIG. 1, the electro-hydraulic discharge system 40 comprises two distinct electrodes 41.

Each electrode 41 passes through the discharge frame 20. A first electrode passes through the upper base, at the second inner wall 211b while a second electrode passes through the lower base at the first inner wall 211a, preferably substantially at the apex.

A first end 42 of each electrode is positioned in the discharge chamber 22. A second end 43 of each electrode, placed outside the discharge frame 20, is connected, via a power cable, to a charging unit. electrical energy storage (not shown). Each electrode 41 is preferably covered with a jacket 44 of electrically insulating material in order to electrically isolate them from the metallic material constituting the discharge frame 20. The electrodes 41 are disposed in the electrohydroforming enclosure 10 so as to create a distance inter-electrode dl, between the first ends 42 of the two electrodes 41. In known manner, this inter-electrode distance dl makes it possible to define the power of a shock wave 60 generated during the electro-hydraulic discharge, in terms of amplitude and duration.

Depending on the complexity of the shape to be obtained for the part to be formed and / or the material constituting the part to be formed, the inter-electrode distance d1 is increased or reduced, which modulates the energy reached during the electro-discharge. hydraulic and influences the power of the shock wave 60.

In one embodiment, the inter-electrode distance d1 can be adjusted by conventional setting means (not shown), such as, for example, a nut system, since the setting operations do not damage the electrodes 41. The dies 30, and therefore each piece, are preferably positioned on each lateral face 212a, equidistant from the inter-electrode distance d1. Thus, a pressure of the same force is applied to all the parts during the electro-hydraulic discharge, causing identical deformation of the parts. In an exemplary embodiment, the dies are positioned substantially at a center of gravity of the associated lateral faces. The electrical energy storage unit, to which the two electrodes 41 are connected, comprises among others at least one capacitor. The various components of the electrical energy storage unit are known to those skilled in the art in their form and operation and are not described in more detail in this specification. The electro-hydroforming enclosure assembly and the electrical energy storage unit form an electro-hydroforming machine. The first inner wall 211a of the lower base 21a of the discharge frame 20 may partly have a non-metallic coating. Each electrode 41 passes through the discharge frame 20 at the non-metallic coating of the first inner wall 211a or the second inner wall 211b. Preferably, the entire first inner wall 211a and the second inner wall 211b are covered with a non-metallic coating.

Preferably, the coating is selected to have a thickness sufficient to eliminate the risk of breakdown between the first end 42 of an electrode 41 and the metal discharge frame. In a preferred embodiment, to reduce its thickness, the nonmetallic coating is made of an electrically insulating material. The present invention is not limited to the preferred embodiments described above by way of non-limiting examples and the variants mentioned. It also relates to the embodiments within the scope of the skilled person.

In particular, although the first conical inner wall is illustrated in Figures 1 and 2 and described with three side faces, the number of these side faces is not limited to that described and illustrated. Thus, it is possible, without departing from the scope of the invention, to provide a first inner wall with four, five or more side faces.

In another variant embodiment, the first inner wall 211a may have a frustoconical (or truncated pyramidal) shape with a polygonal section and comprise N lateral faces, N> 2. Such a variant advantageously makes it possible to further reduce the dimensions of the discharge chamber with respect to a frustoconical shape with identical section.

In the example of FIGS. 3a and 3b, the first inner wall 211a has a frustoconical shape with a pentagonal section, that is to say with five lateral faces. In another alternative embodiment, the first inner wall 211a may have a cylindrical shape with a polygonal section and include N 25 side faces, N> 2. In the example of Figure 4, the first inner wall 211a has a cylindrical shape with a square section, that is to say four lateral faces. In another variant embodiment, the second inner wall 211b may also have a generally cylindrical, conical or frustoconical shape with a polygonal cross section, and comprise N lateral faces, N> 2.

Such a variant advantageously makes it possible to increase the number of parts to be formed in a single electro-hydraulic discharge. Preferably, the first and second inner walls have the same general shape and the same polygonal section.

An example of an electro-hydraulic forming process from the electro-hydroforming enclosure 10 is now described. To simultaneously form a plurality of parts 50 by electro-hydroforming, the method comprises a first step of positioning, in the electro-hydroforming enclosure 10, the parts to be formed.

The lower base and the upper base are disengaged to allow insertion of the parts into the discharge chamber. The pieces 50, for example initially flat, are each arranged in the matrices of the electro-hydroforming enclosure 10 so as to face an impression and to separate the discharge chamber 22 from each other. a forming chamber 32. The parts are each held in position in the electro-hydroforming chamber, so as to seal the water forming chamber associated with the discharge chamber. The lower and upper bases are then assembled and joined together. The method then comprises a step of filling the discharge chamber with water. Water is introduced into the discharge chamber via the water supply conduit 23 until it is filled.

The method then comprises an electrohydraulic discharge step in the fluid contained in the discharge chamber. One way to accomplish this step is to quickly discharge the at least one capacitor from the electrical energy storage unit. When the electro-hydraulic discharge system is activated, an electric arc is created between the electrodes, creating a bubble in the water. This bubble collapses and releases its energy in the form of a shock wave 60, which propagates in the water and projects each piece against the impression of the forming chamber associated with very high speed (several hundred m / s), causing their deformation and their forming by stamping. The voltage reached during the discharge is of the order of a few tens of kV.

In the case of tubular shaped parts, the parts are deformed by radial expansion, instead of being deformed by stamping. With such a forming process, the parts are projected simultaneously against the impression of the forming chamber. At the end of this step, the pieces are formed.

The process then comprises a step of emptying the discharge chamber. Water is pumped from the discharge chamber to the tank via the water drain. The lower and upper bases are then disengaged, releasing access to the forming chambers, from which the formed parts are extracted. The simultaneous forming of a plurality of parts advantageously allows a reduction of the cycle time. The foregoing description clearly illustrates that by its different features and advantages, the present invention achieves the objectives it has set for itself. In particular, it proposes an electro-hydroforming chamber adapted to the simultaneous forming of a plurality of parts while guaranteeing a formation of identical quality for all the parts. The production rate is thus increased.

Claims (9)

REVENDICATIONS1. Electro-hydroforming chamber (10) for the simultaneous forming of a plurality of parts (50) characterized in that it comprises: a discharge frame (20) comprising: i. a first portion (21a) having a first inner wall (211a), ii. a second portion (21b) having a second inner wall (211b), said first (211a) and second (211b) inner walls delimiting a discharge chamber (22) for receiving a volume of fluid, the first inner wall (211a) having a polygonal section and having N side faces (212a), N> 2, each side face (212a) having a matrix (30) comprising a forming chamber (32) having a fingerprint intended to be complementary to the shape to be taken a deformed part, an electrohydraulic discharge system (40) with two electrodes (41), the parts (50) being intended to be positioned each between the discharge chamber (22) and a forming chamber (32) before an activation of said electro-hydraulic discharge system, the activation of said electro-hydraulic discharge system causing the projection and the deformation of each piece (50) against the cavity of the chamber of f ormage (32) associated, and each matrix being positioned equidistant from the two electrodes. 2. Electro-hydroforming chamber (10) according to claim 1 wherein the first inner wall (211a) polygonal section has a substantially cylindrical general shape. The electroforming enclosure (10) of claim 1 wherein the first inner wall (211a) of polygonal section has a generally conical or frustoconical general shape. 4. electro-hydroforming chamber (10) according to one of the preceding claims wherein the second inner wall (211b) has a polygonal section and has N side faces, N> 2, each side face 5 having a matrix comprising a chamber forming a cavity intended to be complementary to the shape that must take a piece after deformation. 5. electro-hydroforming chamber (10) according to one of the preceding claims wherein at least one die (30) is housed in the discharge chamber (22). 6. Electro-hydroforming chamber (10) according to one of the preceding claims wherein at least one die (30) is housed outside the discharge chamber (22), with the forming chamber opening at a face lateral. 15 7. Electro-hydroforming chamber (10) according to one of the preceding claims wherein each matrix is positioned at a center of gravity of a side face (212a). 8. Electro-hydroforming machine comprising an electrohydroforming enclosure (10) according to one of claims 1 to 7 and an electrical energy storage unit connected to the electro-hydraulic discharge system. 9. An electro-hydraulic forming process for the simultaneous forming of a plurality of parts (50), comprising the steps of: placing the parts to be formed in an electroforming enclosure (10) according to the invention; one of claims 1 to 7, - filling of the discharge chamber (22) with a fluid, - electro-hydraulic discharge in the fluid contained in the discharge chamber (22), - emptying of the discharge chamber (22) , 30 - removal of formed parts.