Plant for forming a bipolar plate of a fuel cell and associated forming method

Abstract

The forming plant (10) is configured to form polar plates in series from a strip (12) and includes three presses, each of which includes an actuator (28) that moves a slider in a vertical reciprocating motion. The three presses are - an upstream press (50), - an intermediate press (40) that includes a stamping tool (42) configured to stamp a network of circulation channels onto the strip, and - a downstream press (60). According to the invention, - the strip (12) runs continuously through the three presses, - the forming plant includes a tensioning member that is configured to maintain the portion (16A) of the strip in the press under tension while keeping the portion (26B) of the strip between the presses in a released state, - the actuating device (28) of the intermediate press exerts a pressing force on the stamping tool (42), the pressing force passes through the connection point between the slider and the actuating device, and the pressing force passes through the channel network.

Description

Technical Field

[0001] The present invention relates to a facility for forming a bipolar separator for a fuel cell, and also to a forming method carried out by such a forming plant.

Background Art

[0002] A fuel cell is a device for generating electricity by an electrochemical reaction between a fuel (e.g., hydrogen) and an oxidant (e.g., oxygen contained in air). In this specification, interest lies in a solid electrolyte proton exchange membrane type fuel cell (also called PEMFC), which usually includes a stack of basic cells each forming an electrochemical power generation device.

[0003] Generally, each cell includes two bipolar plates, between which a cathode element and an anode element are arranged, and they are separated by a solid electrolyte in the form of an ion exchange membrane (e.g., made of a sulfonated perfluoropolymer material). Each bipolar plate includes a front surface and a rear surface, the front surface having a central portion in which hydrogen and oxygen circulation channels are provided, and the rear surface being on the opposite side of the front surface. In the cell, the front surface of each bipolar plate is oriented towards the membrane.

[0004] For two adjacent cells, one of the bipolar plates of the two cells will eventually be back-to-back with the bipolar plate of the other cell. The two bipolar plates together form a bipolar separator (also called a bipolar plate). A cooling circuit, in which a cooling liquid such as water containing glycol circulates, is generally arranged between the two bipolar plates of the bipolar separator. Hydrogen, air, and coolant are fluids that are continuously supplied to the fuel cell during its operation. Openings are provided in each bipolar plate around the central portion, enabling the fluid to pass between two adjacent cells. Thereby, each bipolar separator supplies fuel to the cell adjacent to the side on one side and supplies an oxidant to the cell adjacent to the other side on the other side, and the supplies provided by the bipolar separator are carried out in parallel.

[0005] In this specification, there is an interest in metal bipolar plates made from sheet metal. The openings are generally formed by punching, while the channels are made by stamping. To enable the fuel cell to operate properly, the bipolar plates have a very fine thickness and very narrow manufacturing tolerances. As an order of magnitude, the bipolar plates are conventionally made from a 0.1 mm thick sheet, while the channels have a depth of 0.2 mm to 0.3 mm respectively and have a tolerance of less than 0.01 mm.

[0006] To reduce production costs, the bipolar plates are manufactured in series from strips wound in the form of coils. The strips are punched and stamped and finally cut to form each bipolar plate.

[0007] It is known that a large-capacity press including a plurality of tools (which together form a tool set of the press) performs three operations (which may be subdivided into sub-steps in some cases). Such a press generally includes a frame, a slider (which is movable relative to the frame), and a working zone (referred to as a table), where the working zone is stationary relative to the frame and is disposed on the opposite side of the slider. The tools are distributed along the table. During each press operation, the strip is advanced along the table by a fixed pitch and is gradually shaped. On the order of magnitude of size, a polar plate has a width of, for example, 180 mm, while the table has a length included between 1500 mm and 2000 mm, and 8 to 10 tools are typically distributed along the table.

[0008] To ensure each of the operations is satisfied, the press is dimensioned to ensure sufficient force for each operation. Typically, the press is sized to generate a force on the order of 800 tons or more. However, such force leads to deformation of the frame and the table, and the deformation reaches up to 0.04 mm at the center of the table during the stamping operation, which is unacceptable given the tolerances required for the manufacture of the channel.

[0009] U.S. Patent No. 9,821,360, for example, describes a forming plant including three presses that operate in parallel to perform a piercing operation, a stamping operation, and a cutting operation. The strip is wound up after passing through each of the presses and then unwound before passing through the next press, which may damage the channel and reduce the productivity of the forming plant.

[0010] Japanese Patent No. 4464934 and US Patent Application Publication No. 2015 / 280252-A1 each describe another example of a bipolar plate forming plant, where the strip is wound between forming steps. US Patent Application Publication No. 2018 / 223408-A1 describes a facility for forming fins for a vehicle radiator.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0012] More specifically, the present invention seeks to improve such problems by proposing a forming plant that provides good productivity while enabling the production of parts with low geometric tolerances.

Means for Solving the Problems

[0013] For this purpose, the present invention is a bipolar plate forming plant for an electrochemical cell of a fuel cell, - The forming plant is configured to form bipolar plates in series from a metal strip, and each bipolar plate is fabricated as a basic section of the strip, - The forming plant includes three separate presses, each of which · A movable slider disposed on the opposite side of a stationary table, the slider being moved by an actuating device between an upper position and a lower position, the slider and the table together defining the boundary of the working volume of the press, the movable slider, · A forming tool set for forming a strip, each forming tool set including at least one tool with a movable part, the movable part being held by a corresponding slider, the movable part defining the boundary of the working zone of a corresponding press, the forming tool set including, - Each press is configured to pass a strip into a corresponding working volume and includes a feeding device for moving the strip, the feeding device being configured to control the feeding movement of the strip along the table, the feeding movement being a sequential movement, the sequential movement having an increment of feed equal to the length of each basic section measured along the strip and a predetermined feed frequency, the feeding movement defining the downstream direction of each press, and each press being configured to move a corresponding slider to its lower position after each feeding movement, - The press, · An upstream press, the tool set of the upstream press including a primary marking tool configured to form a primary reference mark on the strip when a corresponding slider moves from its upper position to its lower position, the upstream press, · An intermediate press, the tool set of the intermediate press including a stamping tool fastened to a corresponding slider, the stamping tool being configured to relief-stamp a network of channels for fluid circulation on the strip when a corresponding slider moves from its upper position to its lower position, the intermediate press, · A downstream press, the tool set of the downstream press including a cutting tool, the cutting tool being configured to separate respective basic sections from the remaining part of the strip when a corresponding slider moves from its upper position to its lower position, the downstream press and relating to a forming plant including.

[0014] According to the present invention, - An intermediate press is arranged downstream of the upstream press in the feed direction, while the downstream press is arranged downstream of the intermediate press, and under the established operation of the forming plant, the strip is adapted to run continuously through the three presses, each part of the strip received within the working volume of one press being an inner part of the strip, while each part of the strip located between two adjacent presses being an outer part of the strip, - The forming plant includes a tensioning member, the tensioning member being arranged between two adjacent presses, the tensioning member being configured to keep the inner part of the strip taut while keeping the outer part of the strip in a released state, - The operating device for the intermediate press includes a press actuator, the press actuator being connected to the slider by a connection point, the press actuator being configured to move the slider between its upper position and its lower position, the press actuator being configured to exert a press force on the slider when the corresponding slider is in its lower position and the strip is being stamped by a stamping tool, - The press force is oriented along a press axis, the press axis running through the connection point and the press axis running through a network of channels.

[0015] Due to the present invention, the intermediate press is intended for a stamping step and is optimized for such a purpose. The press actuator is arranged perpendicular to the stamping tool, and the deformation of the intermediate press is distributed around the zone of the channel stamped on the strip, thereby reducing the dimensional dispersion of the formed channel. On the other hand, by means of the tensioning member, the strip is released between the presses, which prevents the mechanical forces generated during forming from being transmitted by the strip from one press to another. More specifically, the stamping step tends to pull the strip. Thereby, the forming plant enables the continuous production of polar plates with low geometric tolerances.

[0016] According to an advantageous but not essential aspect of the present invention, such a forming plant can incorporate one or more of the following features, individually or in any technically acceptable combination: - The stamping tool is configured to stamp a network of channels of only one basic section on the strip after each feed movement. - The tool set of the intermediate press does not include strip forming tools other than the stamping tool. - The tool set of the intermediate press includes, in addition to the stamping tool, a secondary marking tool, which is configured to form a secondary marking on the strip while the strip is held clamped in the stamping tool. - The secondary marking tool is configured to form a secondary reference mark on the strip when the slider of the intermediate press is in or near its lower position. - The feed device of the downstream press includes a positioning member, which is configured to cooperate with the secondary reference mark formed on the strip and is adapted to position the strip in the downstream press. - The actuating device of the intermediate press includes a servo motor, which controls the press actuator, and the servo motor is configured to maintain the press force for a predetermined time when the slider is in the lower position. On the other hand, the secondary marking tool includes another actuating device, which is held by the slider, and the other actuating device is triggered while the strip is clamped in the stamping tool and is adapted to form a secondary reference mark on the strip. - The actuating device of the intermediate press consists of only one press actuator. - The actuating device of the intermediate press is configured to generate a nominal press force of less than 4 meganewtons, preferably less than 3 meganewtons, or else preferably less than 2 meganewtons. - The intermediate press table is a solid table.

[0017] According to another aspect, the present invention is a method of forming a polar plate, the forming method being carried out by a forming plant as defined above, the forming method comprising a) moving the slider from its upper position to its lower position while the inner part of the strip is received in the working volume of the intermediate press, and stamping a relief of the network of channels for the circulation of the fluid on the strip; b) using a secondary marking tool to form a secondary reference mark on the strip while the strip is held clamped in the stamping tool and comprising the steps of.

[0018] Such a method leads to the same advantages as those described above with respect to the forming plant of the present invention.

[0019] In light of the following description of an embodiment of a forming plant and an embodiment of a forming method according to the principles thereof, given as a mere example and made with reference to the enclosed stamping, the present invention will be better understood and other advantages of the present invention will become more clearly apparent.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0021] The forming plant 10 is shown in FIG. 1. The forming plant 10 is configured to form a polar plate for an electrochemical cell of a fuel cell. The polar plate 100 is shown in FIG. 2.

[0022] The bipolar plate 100 is made of a metal sheet (e.g., stainless steel). Each bipolar plate 100 has an overall rectangular shape extending along the plate plane P100. The bipolar plate 100 includes a central portion 102, where a network 104 of channels for the circulation of the fluid required for the operation of the fuel cell is provided. The fluid is, for example, one of hydrogen, air, and glycol water. The network 104 of channels is schematically represented by three lines. The center 105 of the channel network 104 is defined as the geometric centroid of the channel network 104. In the illustrated example, while the bipolar plate 100 has a rectangular shape, the center 105 is approximately located at the intersection of the diagonals of the rectangle.

[0023] Also, the bipolar plate 100 includes perforations 106, which are formed in the peripheral portion of the central portion 102, and the perforations 106 are provided for the passage of fluid from one side to the other side of the bipolar plate 100. In the illustrated example, the perforations 106 are divided into two groups of three perforations, and the shape and arrangement of the perforations 106 are not limited.

[0024] The forming plant 10 is configured to form the bipolar plates 100 in series from the strip 12. The strip 12 is a metal strip, and the metal strip is generally transported in a wound-up state in the form of a roll 14. The roll 14 is unwound at the inlet of the forming plant 10, and the strip 12 is shaped in the forming plant 10, i.e., formed and cut in the press of the forming plant 10, to form the bipolar plates 100. Thereby, each bipolar plate 100 is provided within the basic section 13 of the strip 12 and corresponds to the basic section 13 of the strip 12, apart from the material losses and the losses generated during forming.

[0025] The forming plant 10 includes three individual presses 20. Each press 20 includes a frame 22, which has an overall elongated parallelepiped shape and extends along a height axis Z20. When the press 20 is in its operating configuration, the frame 22 is installed above the ground, and the height axis Z20 is orthogonal to the ground. The ground is assumed to be horizontal, and thus the axis height Z20 is assumed to be vertical. The frame 22 includes four peripheral surfaces 23, among which are a front surface 23A, a rear surface 23B opposite the front surface 23A, an upstream surface 23C, and a downstream surface 23D opposite the upstream surface 23C and orthogonal to the front surface 23A and the rear surface 23B. In FIGS. 1 and 5, the press 20 is shown in perspective, with the front surface 23A of each press oriented towards the left of the figure while the downstream surface 23D is oriented towards the right.

[0026] For each press 20, the front surface 23A and the rear surface 23B are orthogonal to the depth axis Y20 of the press, while the upstream surface 23C and the downstream surface 23D are orthogonal to the transverse axis X20 of the press, and the three axes (transverse axis X20, depth axis Y20, and height axis Z20) are oriented to form a direct coordinate system.

[0027] Each press 20 includes a slider 24 movable relative to the frame 22, and the slider 24 is guided to translate relative to the frame 22 along the height axis Z20 by the slider 24, which can be seen in FIG. 5 herein. Each press 20 further includes a table 26, which is stationary relative to the frame 22, and the table 26 is arranged facing the corresponding slider 24, and the slider 24 and the table 26 together define the boundary of the working volume V20 of the press 20. In the operating configuration of the press 20, the table 26 is positioned under the slider 24.

[0028] Each press 20 further includes an actuating device 28 which moves the slider 24 between its lower and upper positions. The slider 24 is closer to the table 26 in its lower position than in its upper position. Further, each press 20 is in a lower configuration or an upper configuration when the corresponding slider 24 is in its lower position or in its upper position, respectively. Each press 20 moves from its upper configuration to its lower configuration when it is so-called triggered and then returns to its upper configuration at the end of a pre-determined time interval.

[0029] Each press 20 is equipped with a tool 30 for shaping the strip 12. As shown in FIGS. 3 and 4, the shaping of the strip 12 is performed in a plurality of consecutive steps, each of which is carried out using a specific tool mounted on one of the presses 20. All the shaping tools mounted on the same press 20 form the tool set 30 of the press 20. Thus, the tool set 30 of each press 20 may include one or more shaping tools in some cases. "Shaping" refers to an operation of deforming the strip (e.g., plastic deformation, cutting, drilling, etc.). Thus, simple elastic deformation, inspection, or cleaning operations are not considered to be shaping.

[0030] The three presses 20 are aligned with each other. More precisely, the transverse axes X20 of the three presses 20 are aligned, and one of the three presses 20 located between the other two presses is called the "intermediate press 40". One of the presses facing the upstream surface 23C of the intermediate press 40 among the presses 20 is called the "upstream press 50", while the third press 20 facing the downstream surface 23D of the intermediate press 40 is called the "downstream press 60".

[0031] In FIG. 5, the intermediate press 40 is shown in a cross-section along a plane orthogonal to the depth axis Y20, revealing the inside of the intermediate press 40. For each press 20, each tool of the press (or rather, each tool set 30) includes a movable part 34 and a fixed part 36. The movable part 34 is held by the corresponding slider 24, and the fixed part 36 is fastened on the opposite side of the movable part 34 on the corresponding table 26. Each movable part 34, together with the associated fixed part 36, defines the boundary of the working zone of the corresponding press 20, and each working zone is configured to receive the basic section 13 of the strip 12.

[0032] Here, the steps of the method for forming the strip 12 will be described in detail. FIG. 3 shows the unwound roll 14 at the input to the forming method, and the strip 12 is gradually fed in, with the feed of the strip 12 shown from left to right and from top to bottom.

[0033] During a first step 200 called "primary marking", a primary reference mark 202 is formed on the strip 12 by a primary marking tool 204 belonging to the forming plant 10. The primary marking tool 204 herein includes two perforating punches, while the primary reference mark 202 herein is formed from two holes, each being arranged along the respective edge of the strip. According to an alternative (not shown), the primary marking tool 204 is obtained, for example, by punching, by plastic deformation of the strip 12. However, the primary reference mark 202 is preferably formed by one or more holes.

[0034] The primary marking tool 204 is mounted herein on the slider 24 of the upstream press 50. Thereby, the primary reference mark 202 is formed on the strip 12 each time the slider 24 of the upstream press 50 passes from its upper position to its lower position, in other words, each time the upstream press 50 is activated and moves from its upper configuration to its lower configuration. Thereby, preferably, the primary reference mark 202 is formed for each basic section 13 of the strip 12.

[0035] Between each trigger of the upstream press 50, when the upstream press 50 returns to its upper configuration, the strip 12 is moved relative to the upstream press 50 in accordance with the feed movement of the strip 12 along the table 26 parallel to the axis X20. The feed movement of the strip 12 is a sequential movement, and the sequential movement has a feed increment equal to the length of each basic section 13 measured along the strip 12 parallel to the axis X20, and a predetermined feed frequency. The feed movement of the strip 12 defines the upstream-downstream direction of the forming plant 10. Generally, the feed frequency is equal to the triggered frequency of the press.

[0036] The upstream press 50 (more generally, each press 20) includes a feed device for the strip 12, which is configured to control the feed movement of the strip 12 along the corresponding table 26. The feed device is not shown. The feed movement of the strip 12 is preferably synchronized with respect to each press 20, and each press 20 is configured to move the corresponding slider 24 to the lower position after each feed movement.

[0037] The upstream press 50 further includes a positioning member 38, which is configured to cooperate with a primary reference mark 202 provided on the strip 12 and is adapted to position the strip 12 relative to the upstream press 50 after each feeding movement of the strip 12. The positioning member 38 is, in the present specification, formed by positioning fingers inserted into the holes of the primary reference mark 202. The positioning fingers are preferably conical in shape. Thereby, precise and repeatable positioning of the strip 12 relative to the tool 30 of the upstream press 50 is achieved. The positioning member 38 can be movable, among other things, along the direction of the axis Z20 and is accompanied by alternating movements having the same frequency as the triggered frequency of the press.

[0038] Subsequently, between the step 210 called the punching step and after the primary marking step 200, the perforations 106 are formed through the strip 12 by a punching tool 121. Thus, the punching step 210 is a forming step. The punching tool 121 in the present specification includes six punches, each of which is configured to form a respective perforation 106. The punches are mounted on the slider 24 of the upstream press 50 and are configured to cooperate with a die fastened to the table 26 of the upstream press 50. The die is not shown.

[0039] During the punching step 210, the positioning member 38 thereby serves for the good alignment of the strip 12 with respect to the punches used to form the perforations 106, or rather with respect to the punching tool 121.

[0040] The primary marking step 200 and the punching step 210 are, for example, two steps each corresponding to an individual trigger of the upstream press 50. The primary marking step 200 and the punching step 210 are, for example, two steps each corresponding to one of two immediately consecutive individual triggers of the upstream press 50.

[0041] Next, after the piercing step 210 and during the so-called stamping step 220, the strip 12 is stamped, that is to say, the strip 12 is plastically deformed, and the network 104 of fluid circulation channels is engraved thereon in relief by a stamping tool fastened to the slider 24 of the corresponding press. Thus, the stamping step 220 is a forming step. Typically, the stamping tool includes two dies of mating shape, which are positioned on both sides of the part to be stamped (here, the strip 12). The stamping step 220 is here carried out by the intermediate press 40, and thus the intermediate press 40 is a stamping press, and its tool 30 includes a stamping tool 42, which includes a movable die 43A fastened to the slider 24 by a fastening device and a mating die 43B supported by the table 26. The fastening device is not shown. Conventionally, the fastening device provides a support zone between the movable die 43A and the slider 24, and the support zone is flat.

[0042] During stamping step 220, strip 12 tends to deform, and thus, the primary reference mark 202 formed on strip 12 moves relative to its original position on strip 12 and can no longer serve as a reference. To overcome such a problem, when the channel network 104 is formed by stamping on strip 12 during stamping step 220, while strip 12 is held clamped within the stamping tool 42 (which corresponds to the fact that the corresponding slider 24 is in or near its lower position), a so-called secondary reference mark 222 is formed on the strip by a secondary marking tool 224 held by the slider 24. In the illustrated example, the secondary marking tool 224 includes two perforating punches, while the secondary reference mark 222 is formed from two holes, each being arranged along a respective edge of strip 12. Generally, the secondary reference mark 222 is preferably formed by one or more holes in strip 12. Preferably, the secondary reference mark 222 is formed for each respective basic section 13 of strip 12.

[0043] The secondary marking tool 224 includes another actuating device (referred to as the secondary actuating device), which is held by the corresponding slider 24, and which moves the piercing punch while the strip is held clamped in the stamping tool 42 so as to form a secondary reference mark 222 on the strip 12. The secondary actuating device is not shown. Thereby, when the slider 24 is in or near its lower position, the secondary marking tool 224 is installed in the working position, and when the strip 12 is held clamped in the stamping tool 42, the secondary actuating device is then activated to form the secondary reference mark 222. Thereby, the secondary reference mark 222 can be formed on the strip 12 at the moment selected by the operator as long as the strip 12 is held clamped in the stamping tool 42.

[0044] The actuating device 28 of the intermediate press 40 includes a press actuator 46 which moves the corresponding slider 24 between its upper and lower positions, and the press actuator 46 is configured to exert a pressing force on the slider 24 when the slider 24 is in its lower position and the strip 12 is being pressed by the press tool. The press actuator 46 in this specification includes a connecting rod which is mounted by its upper end on an eccentric crankshaft 47 that pivots eccentrically about an axis parallel to the depth axis Y20. The press actuator 46 is connected to the slider 24 by a connection point 49. In this example, the press actuator 46 includes a connecting rod which is connected to the slider 24 by a pivot connection or ball joint connection that forms a connection point 49 through which the pressing force passes at its lower end. The actuating device 28 further includes a servo motor 48 which is represented herein by a cylinder protruding from the corresponding rear face 23B, and the servo motor 48 is configured to control the eccentric rotational movement of the eccentric crankshaft 47. In other words, the servo motor 48 is configured to control the press actuator 46 such that the press actuator 46 drives the slider 24 between its upper and lower positions in alternating translational movements along the vertical axis Z20 at a frequency at which the press is triggered. In a simplified manner, the actuating device 28 acts as a crankshaft, the rotation of the crankshaft being controlled by the servo motor, while the eccentric crankshaft 47 drives the slider 24 in a reciprocating motion between its upper and lower positions. Generally, the pressing force is oriented along a press axis A49 which is an axis parallel to the height axis Z20 and which passes through the connection point 49 between the press actuator 46 and the slider 24.Advantageously, the press axis A49 is arranged to pass through the network 104 of channels formed on the strip during the stamping step 220. Preferably, the press axis A49 is aligned with the center 105 of the network 104 of channels. In the example shown, the stamping tool 42 is installed vertically below the press actuator 46, and more particularly, vertically below the connection point 49 of the press actuator 46 with the slider 24.

[0045] According to an example, the stamping tool 42 is installed at the center of the working volume of the intermediate press 40. Thereby, any deformation of the frame 22 during the stamping step is symmetrically distributed around the press axis A49, which contributes to the homogeneity of the press force during the formation of the network 104 of channels and thus to the quality of the stamping.

[0046] For this purpose, the intermediate press 40 advantageously includes an odd number of press actuators 46. More specifically, the intermediate press 40 preferably includes only one press actuator 46. When the intermediate press 40 includes only one press actuator 46, the press actuator 46 is thereby arranged above the working zone and aligned with the center of the working zone along the height axis Z20. When the intermediate press 40 includes a plurality of (for example, three) press actuators 46, the press actuators 46 are distributed along the shaft 47, and one of the press actuators 46 is positioned substantially at the center of the shaft 47 and aligned with the center of the working zone along the height axis Z20.

[0047] Generally, in prior art presses, the table has an opening at its center, which is designed to discharge the material chips generated during the forming operation. However, that opening tends to reduce the rigidity of the table, which tends to bend during the operation of the press, and this bending reduces the accuracy of the stamping operation.

[0048] Preferably, the table 26 of the intermediate press 40 is a so-called solid table, which does not have a central chip discharge opening and is provided, for example, by a solid metal block. Of course, if necessary, tapping holes or equivalent holes are provided in the table for fastening the forming tool.

[0049] During the reciprocating movement of the slider 24 between the upper and lower positions, the slider 24 reaches extreme positions, specifically, the lower position and a higher position. In the case of the stamping step 220, it is understood that while the slider 24 moves from the upper position to the lower position, the strip 12 held between the two movable dies 43A of the stamping tool 42 and the stationary die 43B is clamped between the two dies 43A and 43B before the slider 24 reaches the lower position. As the slider 24 approaches the lower position, the clamping force of the dies 43A and 43B (or rather, the pressing force of the press actuator 46) gradually increases, plastically deforming the strip 12 and engraving the network of channels 104 in relief. The clamping force reaches its 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 elastically relax as the two dies 43A and 43B move away from each other. The clamping force gradually decreases until it is offset. Thereby, the clamping force of the strip 12 by the stamping tool 42 is applied not only when the slider 24 is in the lower position but also for a range of positions around the lower position (which is called the vicinity of the lower position).

[0050] The movement of the slider 24 is controlled by the servo motor 48, which is used, inter alia, to control the speed of the slider's descent, the speed of the slider's ascent, and the time interval during which the strip 12 is held clamped in the stamping tool 42, or, otherwise, the clamping force (or press force) received by the strip 12 during said time interval.

[0051] Preferably, during the stamping step 220, the press force is maintained by the servo motor 48 at a pre-determined value over a pre-determined time interval when the slider 24 is in or near its lower position, and the secondary marking tool 224 is triggered during said time interval to form a secondary reference mark 222 in the strip 12. The pre-determined time interval during which the press force is maintained is called the "holding time", while the pre-determined value of the press force is called the "holding force".

[0052] Thereby, it is ensured that the transient effects of stamping, inter alia, the vibrations of the intermediate press 40 and the elastic return of the strip 12, end before the secondary reference mark 222 is formed on the strip 12. Thereby, the secondary reference mark 222 is placed more accurately on the strip 12.

[0053] The holding time is preferably selected to be greater than 0.2 s (seconds), more preferably greater than 0.3 s, or otherwise preferably greater than 0.4 s, while the holding force is included between 150 kN (kiloNewtons) and 300 kN, preferably between 170 kN and 250 kN, or otherwise preferably between 180 kN and 200 kN.

[0054] Advantageously, provisions can be made to retract the positioning member 38 that cooperates with the primary marking during the holding time in order to prevent abnormal wear and contamination caused by deformation of the strip 12 during the stamping operation 220. The positioning member 38 can, in particular, be re-engaged after the holding time has elapsed, in order to complete the transfer of the strip 12 into the intermediate press 40.

[0055] According to an embodiment, the servo motor 48 is decelerated while the slider 24 approaches its lower position and is adapted to maintain the stamping tool 42 clamped on the strip 12. Of course, the way of controlling the intermediate press 40 depends on the technology used for the press, and an expert will be able to replace the examples described herein with presses of other technologies.

[0056] By comparison, the press force required to pull out the strip 12 (in other words, the stamping force) is on the order of 200 tons, or about 2000 kN. Thereby, good positioning of the secondary reference mark 222 is provided while avoiding excessive stress on the servo motor 48.

[0057] Once the secondary reference mark 222 has been formed on the strip 12, the intermediate press 40 then returns to its higher configuration and the strip 12 is moved in accordance with the feed movement.

[0058] The forming method includes the step 230 of separating the strip 12, which is carried out following the stamping step 220, during which the strip 12 is finally separated, thereby forming the polar plate 100. Thus, separating is a shaping step, which is, in the present document, carried out by the cutting tool 232, which separates each basic section 13 from the strip 12.

[0059] Where appropriate, the forming method includes other forming steps (e.g., a pre-cutting step, a step of reworking the perforation 106, etc.) following the stamping step 220. The forming steps following the stamping step are referred to as "downstream steps" of the forming method, and the cutting step 230 is a specific example of a downstream step. Thereby, the forming method includes at least downstream steps.

[0060] One or more downstream steps 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 a positioning member 238 called a secondary positioning member, the positioning member 238 being mounted on the downstream press 60, and the positioning member 238 is adapted to cooperate with the secondary reference mark 222, in particular by a mating shape, to position the strip 12 relative to the downstream press 60. The secondary positioning member 238 is represented herein by a positioning finger, and the positioning finger is received in the hole of the secondary reference mark.

[0061] Preferably, the secondary reference mark 222 is used to position the strip 12 between each of the downstream steps. As a natural result, only the stamping step 220 is carried out in the intermediate press 40, and the stamping step 220 preferably includes the formation of the secondary reference mark 222. In other words, the tool set of the intermediate press 40 includes a secondary marking tool 224 in addition to the stamping tool 42.

[0062] According to a variant (not shown), the intermediate press 40 does not include a tool for forming the strip 12 other than the stamping tool 42 and does not have a secondary marking tool.

[0063] Generally, during the design of the forming plant 10, each press 20 is designed to exert a maximum press force called the nominal force, which is a function, inter alia, of the maximum force required to perform the task for which the press 20 is intended and of the safety factor.

[0064] In prior-art forming plants, stamping presses generally perform other forming steps (more specifically, piercing operations and cutting operations). Prior-art presses are dimensioned accordingly to exert a nominal press force in the range from 800 tons to 1000 tons, or in the range from 8 MN to 10 MN (mega-newtons).

[0065] In the forming plant 10, while the downstream steps are carried out by the downstream press 60, the steps preceding the stamping step 220 (referred to as the upstream steps) are carried out by the upstream press 50.

[0066] More specifically, the primary marking step 200 is carried out by the upstream press 50, and the primary marking tool 204 is mounted on the slider 24 of the upstream press 50. Similarly, in the example shown, the piercing step 210 is also carried out by the upstream press 50.

[0067] Thereby, in the forming plant 10, the press force of the intermediate press 40 is used only in the stamping step 220. The intermediate press 40 is designed to generate a nominal press force of less than 4 MN (i.e., approximately 400 tons). Preferably, the nominal press force is less than 3 MN, or else, preferably, less than 2 MN. The intermediate press 40 is much less expensive than the presses used in prior-art forming plants.

[0068] While the inner part 16A refers to a part of the strip 12 that is received within the working volume of the press 30, the part of the strip 12 that is positioned between two adjacent presses 30 is the outer part 16B of the strip 12. In FIG. 1, the strip 12 thus includes three inner parts 16A and two outer parts 16B. The forming plant 10 includes a tensioning member that is arranged between two adjacent presses 30 and that is configured to keep the inner part 16A of the strip 12 taut while keeping the outer part 16B of the strip 12 in a released state. The tensioning member is not shown. In practice, it can be a gripper transfer (referred to as a “digital” transfer) that moves along the axis X20 of the value of the basic section 13 by a movement along the axis Z20 of the order of 5 mm.

[0069] According to an example, the tensioning member is combined with a feeding member.

[0070] Since the outer part 16B is released, the transmission of mechanical stress along the strip 12 between two successive presses 30 is prevented. More specifically, since the stamping step 220 tends to “pull” the strip 12, the released outer part 16B eliminates the risk of shifting the strip 12 with respect to the tools of the upstream and downstream steps.

[0071] The above-described embodiments and variations can be combined with each other so as to generate new embodiments of the present invention.

Explanation of Signs

[0072] 10 Forming plant 12 Strip 13 Basic section 14 Roll 16A Inner part 16B Outer part 20 Press 22 Frame 23 Peripheral Surface 23A Front Surface 23B Rear Surface 23C Upstream Surface 23D Downstream Surface 24 Slider 26 Table 28 Actuating Device 30 Tool Set 34 Movable Part 36 Fixed Part 38 Positioning Member 40 Intermediate Press 42 Stamping Tool 43A Movable Die 43B Fitting Die 46 Press Actuator 47 Eccentric Crankshaft 48 Servo Motor 49 Connection Point 50 Upstream Press 100 Polar Plate 102 Central Portion 104 Channel Network 105 Center 106 Perforation Portion 121 Perforating Tool 200 Primary Marking Step 202 Primary Reference Mark 204 Primary Marking Tool 210 Perforation Step 220 Stamping Step 222 Secondary Reference Mark 224 Secondary Marking Tool 230 Cutting Step 232 Cutting Tool 238 Positioning Member A49 Press Axis P100 Plate Plane X20 Transverse Axis Y20 Depth Axis Z20 Height Axis

Claims

1. A forming plant (10) for a bipolar plate (100) of an electrochemical cell of a fuel cell, The forming plant (10) is configured to form the bipolar plates (100) in series from a metal strip (12), and each bipolar plate (100) is provided within a basic section (13) of the strip (12), The forming plant (10) includes three individual presses (30), each of which A movable slider (24) arranged on the opposite side of a stationary table (26), the slider (24) being moved by an actuating device (28) between an upper position and a lower position, the slider (24) and the table (26) defining together the boundary of the working volume of the press, a movable slider (24); A tool set (30) for forming the strip (12), each tool set including at least one tool with a movable part, the movable part being held by the corresponding slider (24), the movable part defining the boundary of the working zone of the corresponding press, a tool set (30); and includes Each press is configured to pass the strip (12) through the corresponding working volume and includes a feeding device for moving the strip (12), the feeding device being configured to control the feeding movement of the strip (12) along the table (26), the feeding movement being a sequential movement having an increment of feed equal to the length of each basic section (13) measured along the strip (12) and a pre-determined feeding frequency, the feeding movement defining the downstream direction of each press, and each press being configured to move the corresponding slider (24) to a lowered position after each feeding movement. The press An upstream press (50), wherein the tool set of the upstream press (50) includes a primary marking tool (204), and the primary marking tool (204) is configured to form a primary reference mark (202) in the strip (12) when the corresponding slider (24) moves from its upper position to its lower position, the upstream press (50); An intermediate press (40), wherein the tool set of the intermediate press (40) includes a stamping tool (42), the stamping tool (42) is fastened to the corresponding slider (24), and the stamping tool (42) is configured to relief stamp a network of channels (104) for fluid circulation onto the strip (12) when the corresponding slider (24) moves from its upper position to its lower position, the intermediate press (40); A downstream press (60), wherein the tool set of the downstream press (60) includes a cutting tool (232), and the cutting tool (232) is configured to separate respective basic sections (13) from the remaining portion of the strip (12) when the corresponding slider (24) moves from its upper position to its lower position, the downstream press (60); In a forming plant (10) comprising; The intermediate press (40) is arranged downstream of the upstream press (50) in the feed direction, while the downstream press (60) is arranged downstream of the intermediate press (40), and under the established operation of the forming plant (10), the strip (12) is adapted to run continuously through the three presses, each portion of the strip (12) received within the working volume of one press being an inner portion (16A) of the strip, while each portion of the strip located between two adjacent presses being an outer portion (16B) of the strip; The forming plant (10) includes a tension applying member, the tension applying member is disposed between two adjacent presses, and the tension applying member is configured to maintain the inner portion (16A) of the strip (12) in a tensioned state while keeping the outer portion (16B) of the strip (12) in a released state. The actuating device (28) of the intermediate press (40) includes a press actuator (46), the press actuator (46) is connected to the slider (24) by a connection point (49), the press actuator (46) moves the slider (24) between its upper position and its lower position, and the press actuator (46) is configured to apply a press force to the slider (24) when the corresponding slider (24) is in its lower position and the strip (12) is being stamped by the stamping tool (42). The press force is oriented along a press axis (A49), the press axis (A49) runs through the connection point, and the press axis (A49) runs through the network (104) of channels. characterized in that forming plant (10).

2. The stamping tool (42) is configured to stamp the network (104) of channels of only one basic section (13) onto the strip (12) after each feed movement. The forming plant (10) according to claim 1.

3. The tool set (30) of the intermediate press (40) does not include a strip forming tool (12) other than the stamping tool (42). The forming plant (10) according to claim 1 or 2.

4. The tool set (30) of the intermediate press (40) includes, in addition to the stamping tool (42), a secondary marking tool (234), and the secondary marking tool (234) is configured to form a secondary reference mark (232) in the strip (12) while the strip (12) is held clamped in the stamping tool (42). The forming plant (10) according to claim 1 or 2.

5. The secondary marking tool (234) is configured to form the secondary reference mark (232) in the strip (12) when the slider (24) of the intermediate press (40) is in or near its lower position. The forming plant (10) according to claim 4.

6. The feeding device of the downstream press (60) includes a positioning member (238), and the positioning member (238) is configured to cooperate with the secondary reference mark (232) provided in the strip (12) and position the strip (12) in the downstream press (60). The forming plant (10) according to claim 4 or 5.

7. The actuating device (28) of the intermediate press (40) includes a servo motor (48), the servo motor (48) controls the press actuator (46), and the servo motor (48) is configured to maintain a press force for a predetermined time when the slider (24) is in the lower position. The secondary marking tool (234) includes another actuating device (28), the other actuating device (28) is held by the slider (24), and the other actuating device (28) is triggered while the strip (12) is held clamped in the stamping tool (42) and is configured to form the secondary reference mark (232) in the strip (12). The forming plant (10) according to any one of claims 4 to 6.

8. The forming plant (10) according to any one of claims 1 to 7, wherein the actuating device (28) of the intermediate press (40) comprises only one press actuator (46).

9. The forming plant (10) according to any one of claims 1 to 8, wherein the actuator (28) of the intermediate press (40) is configured to generate a nominal pressing force of less than 4 meganewtons, preferably less than 3 meganewtons, or else preferably less than 2 meganewtons.

10. The forming plant (10) according to any one of claims 1 to 9, wherein the table (26) of the intermediate press (40) is a solid table.

11. A method of forming a polar plate (100), the forming method being carried out by a forming plant (10) according to any one of claims 4 to 6, the forming method comprising: a) moving the slider (24) from its upper position to its lower position while the inner part (16A) of the strip (12) is received in the working volume of the intermediate press (40), and stamping a relief of a network (104) of channels for fluid circulation onto the strip (12) (step 220); b) using the secondary marking tool (234) to form the secondary mark (232) on the strip (12) while the strip (12) is held tightly in the stamping tool (42). and method.

Images