Plant for forming a polar plate of a fuel cell, and associated forming method

Abstract

Said forming plant (10) is configured to form polar plates in series from a strip (12) and comprises three presses, each of which comprises an actuating device (28) moving a slide in a reciprocating vertical movement and which include: - an upstream press (50), - an intermediate press (40) comprising an embossing tool (42) configured to relief-emboss a network of flow channels on the strip, and - a downstream press (60). According to the invention: - the strip (12) passes continuously through the three presses, - the forming plant comprises tensioning members configured to keep portions (16A) of the strip located in the presses under tension while keeping the portions (26B) of the strip located between the presses slack, - the actuating device (28) of the intermediate press exerts, on the embossing tool (42), a pressing force which extends through a connection point between the slide and the actuating device and which penetrates the network of channels.

Description

[0001] TITLE: Fuel cell polar plate forming installation and associated forming method

[0002] The present invention relates to a forming installation for a polar plate for a bipolar fuel cell separator, as well as to a forming method implemented using such a forming installation.

[0003] A fuel cell is a device for generating electricity by an electrochemical reaction between a fuel, for example hydrogen, and an oxidizer, for example oxygen contained in the air. We are interested here in fuel cells of the solid electrolyte proton exchange membrane type - also known as PEMFC in English - which usually comprise a stack of elementary cells, each constituting an electrochemical generator.

[0004] Schematically, each cell comprises two polar plates, between which are arranged a cathode element and an anodic element, which are separated by a solid electrolyte in the form of an ion exchange membrane, made for example of a perfluorinated sulfide polymer material. Each polar plate comprises a front face, with a central portion in which channels for the circulation of hydrogen and oxygen are arranged, and a back, opposite the front face. In a cell, the front face of each polar plate is oriented towards the membrane side.

[0005] For two neighboring cells, a polar plate of one of the two cells is back-to-back with a polar plate of the other cell. These two polar plates together form a bipolar separator, also called a bipolar plate. A cooling circuit, in which a coolant such as glycol water circulates, is generally arranged between the two polar plates of the bipolar separator. Hydrogen, air and coolant are fluids that are continuously supplied to the fuel cell during operation. Openings are made in each polar plate around the central portion to allow fluids to pass between two neighboring cells.Thus, each bipolar separator ensures on one side the fuel supply to the cell adjacent to this side and on the other side the oxidant supply to the cell adjacent to this other side, the supplies provided by the bipolar separators being done in parallel.

[0006] We are interested here in the metal polar plates, which are made from sheet metal. The openings are generally made by perforation, while the channels are made by stamping. For proper operation of the fuel cell, the polar plates have very thin thicknesses and very tight manufacturing tolerances. As an order of magnitude, a polar plate is typically made from a 0.1 mm thick sheet metal, while the channels each have a depth of 0.2 mm to 0.3 mm, with a tolerance of less than 0.01 mm.

[0007] To reduce production costs, polar plates are mass-produced from a strip rolled into a coil, the strip being perforated and stamped and finally cut to form each polar plate.

[0008] It is known to carry out these three operations, possibly subdivided into sub-steps, with a large capacity press comprising several tools, which together form a tooling of this press. Such a press generally comprises a frame, a slide, which is movable relative to the frame, and a working area, called a table, which is fixed relative to the frame and which is arranged opposite the slide. The tools are distributed along the table. Between each press operation, the strip is advanced by a fixed step along the table, so as to shape it progressively. As an order of magnitude, a polar plate has for example a width of 180 mm, while the table has a length of between 1500 mm and 2000 mm, eight to ten tools being typically distributed along the table.

[0009] To ensure each operation is performed satisfactorily, the press is generally sized to provide sufficient force for each operation. Typically, a press is sized to generate a force of around 800 tonnes or more. However, such forces cause deformations of the frame and the table, which can reach up to 0.04 mm in the center of the table during stamping operations, which is unacceptable given the tolerances required for channel manufacturing.

[0010] US-B-9821360 describes, for example, a forming installation comprising three presses, which operate in parallel to carry out the perforation, stamping and cutting operations. The strip is wound after passing through each of the presses and then unwound before passing into the next press, which risks damaging the channels and reduces the productivity of the forming installation.

[0011] J P-4 464934- B2 and US-2015 / 280252-A1 each describe other examples of polar plate forming installations in which the strip is wound between the forming steps. US-2018 / 223408-A1 describes, for its part, an installation for forming automobile radiator fins.

[0012] It is these problems that the invention more particularly intends to address, by proposing a forming installation which offers good productivity while allowing the production of parts with low geometric tolerances. To this end, the invention relates to an installation for forming polar plates for electrochemical cells of a fuel cell, in which: the forming installation is configured to form the polar plates in series from a metal strip, each polar plate being arranged in an elementary section of the strip, the forming installation comprises three separate presses, each of which comprises:

[0013] • a movable slide arranged opposite a fixed table, the slide being moved by an actuating device between a high position and a low position, the slide and the table together delimiting a working volume of the press,

[0014] • a strip shaping tool, each tool comprising at least one tool with a movable portion, which is carried by the corresponding slide and which delimits a working area of ​​the corresponding press,

[0015] - each press is configured to be traversed by the strip in the corresponding working volume and comprises a strip advancement device, configured to control an advancement movement of the strip along the table, the advancement movement being a sequential movement, with an advancement increment equal to a length of each elementary section measured along the strip, and a predetermined advancement frequency, the advancement movement defining a downstream direction of each press, each press being configured to move the corresponding slide to the low position after each advancement movement,

[0016] - presses include:

[0017] • an upstream press, the tooling of which includes a primary marking tool, which is configured to form a primary mark in the strip when the corresponding slide moves from its high position to its low position,

[0018] • an intermediate press, the tooling of which includes a stamping tool, which is fixed to the corresponding slide and which is configured to stamp in relief on the strip, when the corresponding slide moves from its high position to its low position, a network of fluid circulation channels,

[0019] • a downstream press, the tooling of which includes a cutting tool, configured to separate each elementary section from the rest of the strip, when the corresponding slide passes from its high position to its low position. According to the invention: the intermediate press is arranged, in the direction of advance, downstream of the upstream press, while the downstream press is arranged downstream of the intermediate press, so that in established operation of the forming installation, the strip continuously passes through the three presses, each portion of the strip received in the working volume of a press being an internal portion of the strip, while each portion of the strip located between two neighboring presses is an external portion of the strip, the forming installation comprises tensioning members, which are arranged between two neighboring presses and which are configured to keep the internal portions of the strip taut,while keeping the outer portions of the strip released, the intermediate press actuating device comprises a pressing actuator, which is connected to the slide by a connection point and which moves the slide between its high and low positions and which is configured to exert a pressing force on the slide when the corresponding slide is in its low position and the strip is stamped by the stamping tool, and the pressing force is oriented along a pressing axis, which passes through the connection point and which crosses the network of channels.,

[0020] Thanks to the invention, the intermediate press is dedicated to the stamping step and optimized for this purpose, with a pressing actuator arranged vertically to the stamping tool, so as to distribute the deformations of the intermediate press around the channel zone stamped on the strip, reducing the dimensional dispersion of the channels thus formed. On the other hand, thanks to the tensioning members, the strip is relaxed between the presses, which avoids transmitting from one press to the other, by the strip, mechanical forces generated during shaping. In particular, the stamping step tends to pull on the strip. The forming installation thus allows continuous production of the polar plates, with low geometric tolerances.

[0021] According to advantageous but not mandatory aspects of the invention, such a forming installation may incorporate one or more of the following features taken in isolation or in any technically admissible combination:

[0022] The stamping tool is configured to stamp the channel network of a single elementary section onto the strip after each forward movement.

[0023] The intermediate press tooling does not include any tool for shaping the strip other than the stamping tool. The intermediate press tooling includes, in addition to the stamping tool, a secondary registration tool, configured to form a secondary registration mark in the strip while the strip is held clamped in the stamping tool.

[0024] The secondary register tool is configured to form the secondary register in the strip when the intermediate press ram is in the down position or near its down position.

[0025] The advancement device of the downstream press comprises positioning members, which are configured to cooperate with the secondary mark provided in the strip, so as to position the strip in the downstream press. The actuating device of the intermediate press comprises a servomotor, which controls the pressing actuator and which is configured to maintain a pressing force for a predetermined time when the slide is in the low position, while the secondary marking tool comprises another actuating device, which is carried by the slide and which is triggered while the strip is held clamped in the stamping tool, so as to form the secondary mark in the strip.

[0026] The intermediate press actuating device consists of only one pressing actuator.

[0027] The intermediate press actuating device is configured to generate a nominal pressing force of less than 4 Mega Newtons, preferably less than 3 Mega Newtons, more preferably less than 2 Mega Newtons.

[0028] The intermediate press table is a solid table.

[0029] According to another aspect, the invention relates to a method for forming a polar plate, the forming method being implemented by means of a forming installation as defined above, the forming method comprising the steps of: a) while an internal portion of the strip is received in the working volume of the intermediate press, moving the slide from its high position to its low position, and embossing the network of fluid circulation channels on the strip, b) while the strip is held clamped in the stamping tool, implementing the secondary marking tool and forming the secondary mark in the strip. This method induces the same advantages as those mentioned above with regard to the forming installation of the invention.

[0030] The invention will be better understood, and other advantages thereof will appear more clearly in the light of the following description of an embodiment of a forming installation and of a forming method, in accordance with its principle, given solely by way of example and with reference to the appended drawings, in which:

[0031] - [Fig 1] Figure 1 is a perspective view of a polar plate forming installation;

[0032] - [Fig 2] Figure 2 is a perspective view of a polar plate, shown schematically;

[0033] - [Fig 3] Figure 3 is a schematic representation of steps of a forming process implemented with the forming installation of Figure 1;

[0034] - [Fig 4] Figure 4 represents on a larger scale, on three inserts a) to c), frames IVa, IVb and IVc in Figure 3, and

[0035] - [Fig 5] Figure 5 is a perspective section of a press of the forming installation of Figure 1.

[0036] A forming installation 10 is shown in Figure 1. The forming installation 10 is configured to form pole plates for electrochemical cells of a fuel cell. A pole plate 100 is shown in Figure 2.

[0037] The polar plate 100 is made from a metal sheet, for example stainless steel. The polar plate 100 has a generally rectangular shape and extends along a plate plane P100. The polar plate 100 comprises a central portion 102, in which is arranged a network of channels 104 for circulating a fluid necessary for the operation of the fuel cell. This fluid is for example one of hydrogen, air, and glycolated water. The network of channels 104 is represented schematically by three lines. A center 105 of the network of channels 104 is defined as being a geometric barycenter of the network of channels 104. In the example illustrated, the polar plate 100 has a rectangular shape, while the center 105 is located, schematically, at the intersection of the diagonals of this rectangle.

[0038] The polar plate 100 also comprises perforations 106, which are arranged on the periphery of the central portion 102 and which are provided for the passage of fluids from one side to the other of the polar plate 100. In the example illustrated, the perforations 106 are divided into two groups of three perforations, the shape and arrangement of the perforations 106 not being limiting.

[0039] The forming installation 10 is configured to form the polar plates 100 in series from a strip 12. The strip 12 is a metal strip, which is generally transported wound, in the form of a roll 14. The roll 14 is unwound at the inlet of the forming installation 10, the strip 12 being shaped in the forming installation 10, that is to say shaped and cut in the presses of the forming installation 10, to form the polar plates 100. Each polar plate 100 is thus arranged in an elementary section 13 of the strip 12 and corresponds, apart from the material scraps and losses generated during shaping, to an elementary section 13 of the strip 12.

[0040] The forming installation 10 comprises three separate presses 20. Each press 20 comprises a frame 22, which generally has the shape of an elongated parallelepiped, which extends along a height axis Z20. When the press 20 is in the operating configuration, the frame 22 is placed on a floor, the height axis Z20 being orthogonal to the floor. The floor is assumed to be horizontal, so the height axis Z20 is assumed to be vertical. The frame 22 comprises four peripheral faces 12, including a front face 23A, a rear face 23B opposite the front face 23A, an upstream face 23C and a downstream face 23D, opposite the upstream face 23C and orthogonal to the front 23A and rear 23B faces. In Figures 1 and 5, the presses 20 are shown in perspective, the front face 23A of each press being oriented towards the left of the figures, while the downstream face 23D is oriented towards the right.

[0041] For each press 20, the front 23A and rear 23B faces are orthogonal to a depth axis Y20 of the press, while the upstream 23C and downstream 23D faces are orthogonal to a transverse axis X20 of the press, the three transverse axes X20, depth Y20 and height Z20 being oriented to form a direct reference.

[0042] Each press 20 comprises a slide 24, which is movable relative to the frame 22, the slide 24 being guided in translation relative to the frame 22 along the height axis Z20, here by means of slides 25 which are visible in Figure 5. Each press 20 also comprises a table 26, which is fixed relative to the frame 22 and which is arranged opposite the corresponding slide 24, the slide 24 and the table 26 together delimiting a working volume V20 of the press 20. In the operating configuration of the press 20, the table 26 is located under the slide 24.

[0043] Each press 20 also includes an actuating device 28, which moves the slider 24 between its high and low positions. The slider 24 is closer to the table 26 in the low position than in the high position. By extension, each press 20 is in a low configuration, respectively in a high configuration, when the corresponding slider 24 is in its low position, respectively in its high position. Each press 20 moves from its high configuration to its low configuration when it is said to be triggered, and then returns to its high configuration after a predetermined time interval.

[0044] Each press 20 is equipped with a tool 30 for shaping the strip 12. As illustrated in FIGS. 3 and 4, the shaping of the strip 12 is carried out in several successive steps, each of these steps being carried out using a specific tool, mounted on one of the presses 20. All of the shaping tools mounted on the same press 20 constitute a tool 30 of this press 20. The tool 30 of each press 20 therefore comprises, depending on the case, one or more shaping tools. By "shaping", we mean an operation which deforms the strip, for example plastic deformation, cutting, drilling, etc. Simple elastic deformation, an inspection or cleaning operation are therefore not considered as shaping.

[0045] The three presses 20 are aligned with respect to each other, more precisely the transverse axes X20 of the three presses 30 are aligned, that of the three presses 20 which is located between the other two being called “intermediate press 40”. That of the presses 20 arranged opposite the upstream face 23C of the intermediate press 40 is called “upstream press 50”, while the third press 20, which is arranged opposite the downstream face 23D of the intermediate press 40, is called “downstream press 60”.

[0046] In Figure 5, the intermediate press 40 is shown in section along a plane orthogonal to the depth axis Y20, revealing the interior of the intermediate press 40. For each press 20, each tool - and by extension each tool 30 - of this press comprises a movable portion 34, which is carried by the corresponding slide 24, and a fixed portion 36, fixed opposite the movable portion 32 on the corresponding table 26. Each movable portion 34 delimits, with the associated fixed portion 36, a working area of ​​the corresponding press 20, each working area being configured to receive an elementary section 13 of the strip 12.

[0047] We now detail the steps of the process for forming the strip 12. In Figure 3, there is, at the input of the forming process, a roll 14, which is unwound, the strip 12 advancing progressively, the advance of the strip 12 being represented from left to right and from top to bottom.

[0048] During a first step 200 called “primary marking”, a primary mark 202 is formed in the strip 12, using a primary marking tool 204 belonging to the forming installation 10. The primary marking tool 204 here comprises two perforation punches, while the primary mark 202 is here formed of two holes, each arranged along a respective edge of the strip. According to an alternative not shown, the primary mark 204 is obtained by plastic deformation of the strip 12, for example by punching. However, the primary mark 202 is preferably formed of one or more holes.

[0049] The primary marking tool 204 is here mounted on the slide 24 of the upstream press 50. The primary mark 202 is thus formed on the strip 12 each time the slide 24 of the upstream press 50 moves from its high position to its low position, in other words each time the upstream press 50 is activated and moves from its high configuration to its low configuration. Thus, preferably, a primary mark 202 is formed for each elementary section 13 of the strip 12.

[0050] Between each triggering of the upstream press 50, once the upstream press 50 has returned to its high configuration, the strip 12 is moved relative to the upstream press 50 according to an advancement movement of the strip 12 along the table 26, parallel to the axis X20. The advancement movement of the strip 12 is a sequential movement, with an advancement increment equal to a length of each elementary section 13 measured along the strip 12, parallel to the axis X20, and a predetermined advancement frequency. The advancement movement of the strip 12 defines an upstream-downstream direction of the forming installation 10. Generally, the advancement frequency is equal to the triggering frequency of the press.

[0051] The upstream press 50, and more generally each press 20, comprises a strip advancement device 12, configured to control an advancement movement of the strip 12 along the corresponding table 26. The advancement device is not shown. The advancement movement of the strip 12 is preferably synchronized for each press 20, each press 20 being configured to move the corresponding slide 24 to the low position after each advancement movement.

[0052] The upstream press 50 also comprises positioning members 38, which are configured to cooperate with the primary marker 202 formed in the strip 12 so as to position the strip 12 relative to the upstream press 50, after each advancement movement of the strip 12. The positioning members 38 are here produced by positioning fingers, which are inserted into the holes of the primary markers 202. The positioning fingers are preferably conical. This provides precise and repeatable positioning of the strip 12 relative to the tools 30 of the upstream press 50. The positioning members 38 may be movable, in particular in the direction of the axis Z20, with an alternating movement having the same frequency as the triggering frequency of the press.

[0053] Then, after the primary marking step 200, during a step 210 called perforation, the perforations 106 are formed through the strip 12, by means of a perforation tool 121. The perforation step 210 is therefore a shaping step. The perforation tool 121 here comprises six punches, which are each configured to form a respective perforation 106. The punches are mounted on the slide 24 of the upstream press 50 and are configured to cooperate with a die fixed to the table 26 of the upstream press 26. The die is not shown. During the perforation step 210, the positioning members 38 thus allow good alignment of the strip 12 relative to the punches used to form the perforations 106, and by extension relative to the perforation tool 121.

[0054] The primary marking step 200 and the perforation step 210 are, for example, two steps which each correspond to a distinct triggering of the upstream press 50. The primary marking step 200 and the perforation step 210 are, for example, two steps which each correspond to one of two immediately successive distinct triggerings of the upstream press 50.

[0055] Then, after the perforation step 210, during a so-called stamping step 220, the strip 12 is stamped, in other words the strip 12 is plastically deformed, so as to print in relief the network of channels 104 for the circulation of the fluids, by means of a stamping tool fixed to the slide 24 of the corresponding press. The stamping step 220 is therefore a shaping step. Typically, the stamping tool comprises two complementary shaped dies, which are positioned on either side of the part to be stamped, here the strip 12. The stamping step 220 is here implemented by the intermediate press 40, which is therefore a stamping press, the tools 30 of which include a stamping tool 42, which comprises a movable die 43A, which is fixed to the slide 24 by a fixing device, and a complementary die 43B carried by the table 26. The fixing device is not shown.Conventionally, the fixing device provides a support zone between the mobile die 43A and the slide 24, this support zone being flat.

[0056] During the stamping step 220, the strip 12 tends to deform, so the primary marker 202, formed on the strip 12, moves relative to its original position on the strip 12 and can no longer fulfill its reference role. To overcome this problem, during the stamping step 220, once the network of channels 104 is formed by stamping on the strip 12, while the strip 12 is held clamped in the stamping tool 42, which corresponds to the fact that the corresponding slide 24 is in the low position or close to its low position, a so-called secondary mark 222 is formed in the strip, using a secondary marking tool 224 carried by this slide 24. In the example illustrated, the secondary marking tool 224 comprises two perforation punches, while the secondary mark 222 is formed by two holes, each arranged along a respective edge of the strip 12.Generally, the secondary marker 222 is preferably formed from one or more holes in the strip 12. Preferably, a secondary marker 222 is formed for each elementary section 13 of the strip 12.

[0057] The secondary marking tool 224 comprises another actuating device, called secondary, which is carried by the corresponding slide 24 and which moves the perforation punches while the strip is held clamped in the stamping tool 42, so as to form the secondary mark 222 in the strip 12. The secondary actuating device is not shown. Thus the secondary marking tool 224 is placed in a working position when the slide 24 is in the low position or close to its low position, when the strip 12 is held clamped in the stamping tool 42, the secondary actuating device then being activated to form the secondary mark 222. The secondary mark 222 can thus be formed on the strip 12 at the time chosen by the operator, as long as the strip 12 is held clamped in the stamping tool 42.

[0058] The actuating device 28 of the intermediate press 40 comprises a pressing actuator 46, which moves the corresponding slide 24 between its high and low positions and which is configured to exert a pressing force on this slide 24 when this slide 24 is in its low position and the strip 12 is stamped by the stamping tool 42. The pressing actuator 46 here comprises a connecting rod, which is mounted by an upper end on an eccentric crank shaft 47 pivoting eccentrically about an axis parallel to the depth axis Y20. The pressing actuator 46 is connected to the slide 24 by a connection point 49. In the example, the pressing actuator 46 comprises a connecting rod, which is connected, at its lower end, to the slide 24 by a pivot or ball joint forming the connection point 49 through which the pressing force passes.The actuating device 28 also comprises a servomotor 48, which is represented here by a cylinder protruding from the corresponding rear face 23B and which is configured to control the eccentric rotational movements of the eccentric crank shaft 47. In other words, the servomotor 48 is configured to control the pressing actuator 46 so that it drives the slide 24 in an alternating translational movement along the vertical axis Z20, between its high position and its low position, at a frequency which is the triggering frequency of the press. In simplified manner, the actuating device 28 operates like a crankshaft whose rotation is controlled by the servomotor, while the eccentric crank shaft 47 drives the slide 24 in a reciprocating movement between its high and low positions.Schematically, the pressing force is oriented along a pressing axis A49 which is an axis parallel to the height axis Z20 and which passes through the connection point 49 between the pressing actuator 46 and the slide 24. Advantageously, the pressing axis A49 is arranged so as to pass through, during the stamping step 220, the network of channels 104 formed on the strip. Preferably, the pressing axis A49 is aligned with the center 105 of the network of channels 104. In the example illustrated, the stamping tool 42 is placed vertically below the pressing actuator 46, in particular vertically below the connection point 49 of the pressing actuator 46 with the slide 24.

[0059] According to examples, the stamping tool 42 is placed in the center of the working volume of the intermediate press 40. Thus, any deformations of the frame 22 during the stamping step are distributed symmetrically around the pressing axis A49, which contributes to the homogeneity of the pressing force during the formation of the network of channels 104, and therefore contributes to the quality of the stamping.

[0060] For this purpose, the intermediate press 40 advantageously comprises an odd number of pressing actuators 46. In particular, the intermediate press 40 preferably comprises a single pressing actuator 46. When the intermediate press 40 comprises a single pressing actuator 46, this pressing actuator 46 is thus arranged above the working area, aligned with the middle of the working area along the height axis Z20. When the intermediate press 40 comprises several pressing actuators 46, for example three, the pressing actuators 46 are distributed along the shaft 47, one of the pressing actuators 46 being substantially located in the middle of the shaft 47 and being aligned with the middle of the working area along the height axis Z20.

[0061] Generally speaking, in the presses of the prior art, the table has an opening in its center, intended to evacuate the chips of material generated during the shaping operations. However, this opening tends to reduce the stiffness of the table, which tends to flex during operation of the press, this flexing reducing the precision of the stamping operation.

[0062] Preferably, the table 26 of the intermediate press 40 is a so-called solid table, without a central chip evacuation opening, for example formed in a solid metal block. Of course, if necessary, tapped holes or equivalent are formed in the table for fixing the shaping tools.

[0063] During the back and forth movement of the slide 24 between its high and low positions, the slide 24 reaches extreme positions, specifically reaches a low position and a high position. In the case of the stamping step 220, while the slide 24 moves from the high position to the low position, it is understood that the strip 12, taken between the two movable dies 43A and fixed 43B of the stamping tool 42, is clamped between these two dies 43A and 43B before the slide 24 reaches the low position. As the slider 24 approaches the lower position, the clamping force of the dies 43A and 43B - and by extension the pressing force of the pressing actuator 46 - gradually increases, plastically deforming the strip 12 so as to emboss the network of channels 104. The clamping force reaches a maximum when the slider 24 reaches its lower position. Then, the slider 24 begins to rise.The strip 12, clamped between the two dies 43A and 43B, begins to relax elastically as the two dies 43A and 43B move away from each other. The clamping force gradually decreases, until it is zero. Thus, the clamping force of the strip 12 by the stamping tool 42 is applied not only when the slide 24 is in the low position, but for a range of positions around this low position, which are said to be close to the low position.

[0064] The movements of the slide 24 being controlled by the servomotor 48, it is understood that the servomotor 48 makes it possible to control in particular the speed of descent of the slide, the speed of ascent of the slide, as well as the time interval during which the strip 12 is kept clamped in the stamping tool 42 or even the clamping - or pressing - force undergone by the strip 12 during this time interval.

[0065] Preferably, during the stamping step 220, the pressing force is maintained, by the servomotor 48, for a predetermined time interval, and at a predetermined value, when the slide 24 is in the low position or close to its low position, the secondary marking tool 224 being triggered during this time interval, so as to form the secondary mark 222 in the strip 12. The predetermined time interval during which the pressing force is maintained is called the “holding time”, while the predetermined value of the pressing force is called the “holding force”.

[0066] This ensures that the transient effects of stamping, in particular the vibrations of the intermediate press 40 and the elastic return of the strip 12, are completed before forming the secondary mark 222 on the strip 12. The secondary mark 222 is thus placed more precisely on the strip 12.

[0067] The holding time is chosen to be greater than 0.2 s (second), preferably greater than 0.3 s, more preferably greater than 0.4 s, while the holding force is between 150 kN (kilo Newton) and 300 kN, preferably between 170 and 250 kN, more preferably between 180 and 200 kN.

[0068] It is advantageous to provide for the positioning members 38 which cooperate with the primary marking to be retracted during the holding time, in order to avoid abnormal wear and pollution generated by the deformation of the strip 12 during the stamping operation 220. The positioning members 38 can be reengaged after the expiry of the holding time, in particular for the end of the transfer of the strip 12 into the intermediate press 40.

[0069] According to embodiments, the servomotor 48 is slowed down as the slide 24 approaches its low position, so as to keep the stamping tool 42 clamped on the strip 12. Of course, the mode of control of the intermediate press 40 depends on the technology used for this press, and the specialist will know how to transpose the example described here to presses of other technologies.

[0070] For comparison, the pressing force required to stamp the strip 12, in other words the stamping force, is of the order of 200 tonnes, or approximately 2000 kN. This guarantees good positioning of the secondary marker 222, while avoiding excessive stress on the servomotor 48.

[0071] Then, once the secondary mark 222 is formed on the strip 12, the intermediate press 40 resumes its high configuration, and the strip 12 is moved according to the forward movement.

[0072] The forming method comprises a step 230 of cutting the strip 12, which is subsequent to the stamping step 220 and during which the strip 12 is finally cut, thus forming the polar plate 100. The cutting is therefore a shaping step, which is carried out here using a cutting tool 232, which separates each elementary section 13 from the strip 12.

[0073] Where appropriate, the forming method comprises other shaping steps subsequent to the stamping step 220, for example pre-cutting steps, reworking of the perforations 106, etc. The shaping steps subsequent to the stamping step are called “downstream steps” of the forming method, the stamping step 230 being a particular example of a downstream step. Thus the forming method comprises at least one downstream step.

[0074] The downstream step(s) are preferably carried out in the downstream press 60. Advantageously, during at least one downstream step, the strip 12 is positioned relative to the downstream press 60 by means of so-called secondary positioning members 238, which are mounted on the downstream press 60 and which cooperate with the secondary marker 222, in particular by complementarity of shape, so as to position the strip 12 relative to the downstream press 60. The secondary positioning members 238 are here represented by positioning fingers, which are received in the holes of the secondary marker.

[0075] Preferably, the secondary marker 222 is used to position the strip 12 during each of the downstream steps. As a corollary, only the stamping step 220 is carried out in the intermediate press 40, the stamping step 220 preferably including the forming of the secondary marker 222. In other words, the tooling of the intermediate press 40 includes, in addition to the stamping tool 42, the secondary marking tool 224. According to a variant not shown, the intermediate press 40 does not include any other tool for shaping the strip 12 than the stamping tool 42, without the secondary marking tool.

[0076] Generally, when designing the forming installation 10, each press 20 is designed to exert a maximum pressing force, called nominal force, which is a function in particular of the maximum force necessary to carry out the task for which this press 20 is intended and of a safety coefficient.

[0077] In prior art forming installations, the stamping press generally carries out other shaping steps, in particular punching and cutting operations. These prior art presses are thus sized to exert a nominal pressing force ranging from 800 to 1000 tonnes, or from 8 to 10 MN (Mega Newton).

[0078] In the forming installation 10, the downstream steps are carried out by the downstream press 60, while the steps prior to the stamping step 220, called upstream steps, are carried out by the upstream press 50.

[0079] In particular, the primary marking step 200 is carried out by the upstream press 50, the primary marking tool 204 being mounted on the slide 24 of the upstream press 50. Similarly, in the example illustrated, the perforation step 210 is also carried out by the upstream press 50.

[0080] Thus, in the forming installation 10, the pressing force of the downstream press 40 is only used for the stamping step 220. The intermediate press 40 is designed to generate a nominal pressing force of less than 4 MN, or approximately 400 tonnes. Preferably, the nominal pressing force is less than 3 MN, more preferably less than 2 MN. The intermediate press 40 is much less expensive than a press used in a forming installation of the prior art.

[0081] An internal portion 16A is a portion of the strip 12 which is received in the working volume of a press 30, while a portion of the strip 12 located between two neighboring presses 30 is an external portion 16B of the strip 12. In FIG. 1, the strip 12 therefore comprises three internal portions 16A and two external portions 16B. The forming installation 10 comprises tensioning members, which are arranged between two neighboring presses 30 and which are configured to keep the internal portions 16A of the strip 12 taut, while keeping the external portions 16B of the strip 12 relaxed. The tensioning members are not shown. In practice, these may be clamp transfers, called "digital", moving in the X20 axis by the value of the elementary section 13 with a movement in the Z20 axis of the order of 5 mm. According to examples, the tensioning members are combined with the advancement members.

[0082] The external portions 16B being relaxed, the transmission of mechanical stresses along the strip 12 between two consecutive presses 30 is avoided. In particular, since the stamping step 220 tends to “pull” on the strip 12, the relaxed external portions 16B eliminate the risk of shifting the strip 12 relative to the tools of the upstream and downstream steps.

[0083] The embodiments and variations mentioned above can be combined with each other to generate new embodiments of the invention.

Claims

DEMANDS 1. A forming installation (10) for pole plates (100) for electrochemical cells of a fuel cell, wherein: the forming installation (10) is configured to form the pole plates (100) in series from a metal strip (12), each pole plate (100) being formed from an elementary section (13) of the strip (12), the forming installation (10) comprises three separate presses (30), each of which comprises: • a movable slide (24) arranged opposite a fixed table (26), the slide (24) being moved by an actuation device (28) between a high position and a low position, the slide (24) and the table (26) together defining a working volume of the press, • a tooling (30) for shaping the strip (12), each tooling comprising at least one tool with a movable portion, which is carried by the corresponding slide (24) and which delimits a working area of ​​the corresponding press, each press is configured to allow the strip (12) to pass through the corresponding working volume and includes a strip advance device (12), configured to control an advance movement of the strip (12) along the table (26), the advance movement being sequential, with an advance increment equal to the length of each elementary section (13) measured along the strip (12), and a predetermined advance frequency, the advance movement defining a downstream direction of each press, each press being configured to move the corresponding slide (24) to the lowered position after each advance movement, the presses include: • an upstream press (50), the tooling of which includes a primary locating tool (204), which is configured to form a primary locating mark (202) in the strip (12) when the corresponding slide (24) moves from its upper position to its lower position, • an intermediate press (40), the tooling of which includes a stamping tool (42), which is fixed to the corresponding slide (24) and which is configured to stamp in relief on the strip (12), when the slide (24) correspondingly moves from its upper position to its lower position, a network of fluid circulation channels (104), • a downstream press (60), the tooling of which includes a cutting tool (232), configured to separate each elementary section (13) from the rest of the strip (12), when the corresponding slide (24) moves from its upper position to its lower position, characterized in that: the intermediate press (40) is arranged, according to the direction of travel, downstream of the upstream press (50), while the downstream press (60) is arranged downstream of the intermediate press (40), so that in steady operation of the forming installation (10), the strip (12) continuously passes through the three presses, each portion of the strip (12) received into the working volume of a press being an internal portion (16A) of the strip, while each portion of the strip located between two adjacent presses is an external portion (16B) of the strip, the forming installation (10) includes tensioning devices,which are arranged between two adjacent presses and which are configured to keep the inner portions (16A) of the strip (12) taut, while keeping the outer portions (16B) of the strip (12) slack, the actuation device (28) of the intermediate press (40) includes a pressing actuator (46), which is connected to the slide (24) by a connection point (49) and which moves the slide (24) between its upper and lower positions and which is configured to exert a pressing force on the slide (24) when the corresponding slide (24) is in its lower position and the strip (12) is being pressed by the pressing tool (42), and the pressing force is oriented along a pressing axis (A49), which passes through the connection point and through the channel network (104).

2. Forming installation (10) according to claim 1, in which the stamping tool (42) is configured to stamp on the strip (12), after each advance movement, the channel network (104) of a single elementary section (13).

3. Forming installation (10) according to any one of claims 1 or 2, wherein the tooling (30) of the intermediate press (40) does not include any other strip forming tool (12) than the stamping tool (42).

4. Forming installation (10) according to any one of claims 1 or 2, wherein the tooling (30) of the intermediate press (40) includes, in addition to the stamping tool (42), a secondary locating tool (234), configured to form in the strip (12) a secondary locating tool (232) while the strip (12) is held tight in the stamping tool (42).

5. Forming installation (10) according to claim 4, wherein the secondary locating tool (234) is configured to form in the strip (12) the secondary locating tool (232) when the slide (24) of the intermediate press (40) is in the lower position or close to its lower position.

6. Forming installation (10) according to any one of claims 4 or 5, wherein the downstream press advancement device (60) includes positioning members (238), which are configured to cooperate with the secondary marker (232) provided in the strip (12), so as to position the strip (12) in the downstream press (60).

7. Forming installation (10) according to any one of claims 4 to 6, wherein the actuation device (28) of the intermediate press (40) comprises a servomotor (48), which controls the pressing actuator (46) and which is configured to maintain a pressing force for a predetermined time when the slide (24) is in the lower position, while the secondary registering tool (234) comprises another actuation device (28), which is carried by the slide (24) and which is triggered while the strip (12) is held tight in the stamping tool (42), so as to form the secondary register (232) in the strip (12).

8. Forming installation (10) according to any one of the preceding claims, wherein the actuation device (28) of the intermediate press (40) comprises only one pressing actuator (46).

9. Forming installation (10) according to any one of the preceding claims, wherein the actuation device (28) of the intermediate press (40) is configured to generate a nominal pressing force of less than 4 Mega Newtons, preferably less than 3 Mega Newtons, preferably still less than 2 Mega Newtons.

10. Forming installation (10) according to any one of the preceding claims, wherein the table (26) of the intermediate press (40) is a solid table.

11. Method for forming a polar plate (100), the forming method being carried out by means of a forming installation (10) according to any one of claims 4 to 6, the forming method comprising the steps of: a) while an internal portion (16A) of the strip (12) is received in the working volume of the intermediate press (40), moving the slide (24) from its upper position to its lower position, and embossing (220) in relief on the strip (12) the network of channels (104) for fluid circulation, b) while the strip (12) is held tightly in the stamping tool (42), implementing the secondary locating tool (234) and forming the secondary locating tool (232) in the strip (12).

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