Plant for forming a bipolar plate of a fuel cell and related forming plant

Abstract

The method for forming the polar plate (100) comprises - a stamping step (220), · The stamping step (220) is performed by a stamping press (40), which includes a stamping tool (43A) mounted on a slider that is moved by a reciprocating movement in the vertical direction. · During the stamping step (220), a network of channels (104) for circulating fluid is stamped onto the strip. the stamping step (220), - a downstream step (230) performed by a downstream press (60) following the stamping step and includes. According to the present invention, - When the channel network (104) is stamped onto the strip (12), while the strip (12) is held clamped in the stamping tool (43A), a reference mark (222) is formed on the strip by a marking tool (224) held by the slider. - During the downstream step (230), the strip is positioned relative to the downstream press (60) by a positioning member (238), which is mounted on the downstream press and cooperates with the reference mark (222).

Description

Technical Field

[0001] The present invention relates to a method for forming a bipolar separator for a fuel cell and to a forming plant for carrying out such a method.

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). Herein, interest lies in solid electrolyte proton exchange membrane type fuel cells (also referred to as PEMFCs), which typically include 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 disposed, and they are separated by a solid electrolyte in the form of an ion exchange membrane (e.g., made from a sulfonated perfluoropolymer material). Each bipolar plate includes a front face and a rear face, the front face having a central portion in which hydrogen and oxygen circulation channels are provided, and the rear face being on the opposite side of the front face. In the cell, the front face of each bipolar plate is oriented towards the membrane.

[0004] For two adjacent cells, one of the bipolar plates of the two cells will ultimately 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 disposed 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 to enable 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 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 work properly, the bipolar plates have a very fine thickness and very narrow manufacturing tolerances. As an order of magnitude of the size, conventionally, the bipolar plates are made from a 0.1 mm thick sheet, while the channels each have a depth of 0.2 mm to 0.3 mm 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, the 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 satisfactorily perform each of the operations, centering holes are provided in the strip at regular intervals. On the other hand, the press includes pins configured to be received into the centering holes and to align the tools mounted on the press with the strip. The centering holes are formed in the peripheral portion of the central part.

[0009] However, the stamping operation significantly deforms the strip toward the center of each central part, which results in an offset of the centering holes. Such random offsets can reach 0.15 mm or more, which leads to a reduction in the quality of the operations following stamping, especially cutting operations.

[0010] U.S. Patent Application Publication No. 2018 / 223408-A1, U.S. Patent Application Publication No. 2015 / 280252-A1, EP-39519645-A1, and U.S. Patent Application Publication No. 2021 / 305614-A1 each describe a prior art forming method.

Prior Art Documents

Patent Document

[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 intends to overcome such problems by proposing a more precise method for forming a bipolar plate.

Means for Solving the Problems

[0013] For this purpose, the present invention is a method for forming a bipolar plate for an electrochemical cell of a fuel cell, the method being implemented by a forming plant comprising at least one stamping press, the stamping press being configured to form bipolar plates in series from a metal strip, each bipolar plate being provided within a basic section of the strip, and the stamping press comprising: - 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 stamping tool, the stamping tool being fastened to a slider, the stamping tool being configured to relief-stamp a network of channels for fluid circulation onto a strip as the slider moves from its upper position to its lower position, the stamping tool and comprising - The forming method includes a so-called stamping step and a so-called downstream step, the downstream step following the stamping step and being carried out by a so-called downstream press, the downstream press belonging to a forming plant and being separate from the stamping press, - During the stamping step, with the strip being received in the working volume of the stamping press, the slider moves from its upper position to its lower position, stamping a network of circulation channels for the fluid onto the strip, relates to a method.

[0014] According to the present invention, - When the channel network is stamped onto the strip, while the strip is held clamped in the stamping tool, a reference mark is formed on the strip using a marking tool held by the slider, - During the downstream step, the strip is positioned relative to the downstream press by a positioning member, the positioning member being mounted on the downstream press and cooperating with the reference mark.

[0015] Due to the present invention, the reference mark formed during the stamping step is positioned after the strip has been deformed by the stamping tool. During the downstream step, the strip is positioned using the reference mark, and thus the shaping carried out during the downstream step is positioned with higher accuracy relative to the network of channels. Thereby, the overall quality of the polar plate is improved, particularly from the viewpoint of dimensional accuracy.

[0016] According to an advantageous but non-essential aspect of the invention, such a forming method can incorporate one or more of the following features, individually or in any technically acceptable combination: - The reference mark is formed on the strip while the slider is held in the lower position for a predetermined time interval while the stamping tool exerts a predetermined force on the strip. - The predetermined time interval is greater than 0.2 s, preferably greater than 0.3 s, more preferably greater than 0.4 s. - The predetermined force is included between 150 kN and 300 kN, preferably between 170 kN and 250 kN, or preferably between 180 kN and 200 kN. - The forming method includes an upstream step that precedes the stamping step. During the upstream step, a primary mark is formed on the strip by a primary marking tool belonging to the forming plant. During the stamping step, the strip is positioned relative to the stamping press by a positioning member that is mounted on the stamping press and cooperates with the primary reference mark. - The primary marking tool is mounted on the slider of the upstream press, which is part of the forming plant and is separate from the stamping press.

[0017] The invention further relates to a forming plant for bipolar plates, the forming plant being configured to perform a forming method according to that described above, comprising a plurality of presses, the presses including at least one stamping press and a downstream press, the stamping press being configured to perform a stamping step, and the downstream press being configured to perform a downstream step following the stamping step. - Each press includes a movable slider disposed on the opposite side of a stationary table. The slider is moved by an actuating device between an upper position and a lower position. The slider and the table together define the boundary of the working volume of the corresponding press. - The stamping press · A stamping tool, which is fastened to the corresponding slider. The stamping tool is configured to relief-stamp a network of channels for fluid circulation onto the strip when the slider moves from its upper position to its lower position. · A marking tool, which is held by the slider. The marking tool is configured to form a reference mark on the strip while the strip is held clamped in the stamping tool after the channel network has been printed onto the strip. including - The downstream press includes a positioning member, which is mounted on the downstream press and is configured to cooperate with the reference mark formed on the strip to position the strip relative to the downstream press. Regarding the forming plant.

[0018] 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 by way of mere example and made with reference to 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

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0020] The forming plant 10 is shown in FIG. 1. The forming plant 10 is configured to form a bipolar plate for an electrochemical cell of a fuel cell. The bipolar plate 100 is shown in FIG. 2.

[0021] The bipolar plate 100 is made of a metal sheet (for example, 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, in which a network 104 of channels for the circulation of 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 example shown, while the bipolar plate 100 has a rectangular shape, the center 105 is schematically located at the intersection of the diagonals of the rectangle.

[0022] 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 portion to the other side portion of the bipolar plate 100. In the example shown, the perforations 106 are divided into two groups of three perforations, and the shape and arrangement of the perforations 106 are not limited.

[0023] The forming plant 10 is configured to form the polar 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 to form the polar plates 100, i.e., shaped and cut in the press of the forming plant 10. Thereby, each polar 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 incurred during shaping.

[0024] The forming plant 10 includes three individual presses 20. Each press 20 includes a frame 22, and the frame 22 has an overall elongated parallelepiped shape, which extends along the height axis Z20. When the press 20 is in the 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.

[0025] 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.

[0026] Each press 20 includes a slider 24 movable relative to a frame 22, and the slider 24 is translated and guided relative to the frame 22 along a height axis Z20 by a slider 24 that can be seen in FIG. 5 herein. Each press 20 further includes a table 26, the table 26 being stationary relative to the frame 22, the table 26 being disposed 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 below the slider 24.

[0027] Each press 20 further includes an actuating device 28, and the actuating device 28 moves the slider 24 between its lower position and its upper position. The slider 24 is closer to the table 26 in the lower position than in the 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 predetermined time interval.

[0028] 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, and each of the steps 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 (such as plastic deformation, cutting, drilling, etc.). Thus, simple elastic deformation, inspection, or cleaning operations are not considered to be shaping.

[0029] 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 20 facing the upstream surface 23C of the intermediate press 40 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".

[0030] 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 (more precisely, 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.

[0031] Here, the steps of the method for forming the strip 12 will be described in detail. FIG. 3 shows the unrolled roll 14 at the input to the forming method, and the strip 12 is gradually fed in, with the feeding of the strip 12 shown from left to right and from top to bottom.

[0032] 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 a 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.

[0033] 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.

[0034] 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.

[0035] The upstream press 50 (more generally, each press 20) includes a feeding device for the strip 12, which is configured to control the feeding movement of the strip 12 along the corresponding table 26. The feeding device is not shown. The feeding 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 feeding movement.

[0036] 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 with respect to the upstream press 50 after each feeding movement of the strip 12. The positioning member 38 is formed, in the present specification, by a positioning finger that is inserted into the hole of the primary reference mark 202. The positioning finger is preferably conical in shape. Thereby, precise and repeatable positioning of the strip 12 with respect 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 involves alternating movements having the same frequency as the triggered frequency of the press.

[0037] Then, after the primary marking step 200 and during a step 210 called the punching step, the perforations 106 are formed through the strip 12 by the 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.

[0038] During the piercing step 210, the positioning member 38 thereby serves for the good alignment of the strip 12 with respect to the punch used to form the piercing portion 106, and more specifically with respect to the piercing tool 121.

[0039] The primary marking step 200 and the piercing 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 piercing step 210 are, for example, two steps each corresponding to one of two immediately consecutive individual triggers of the upstream press 50.

[0040] Then, after the piercing step 210, during the so-called stamping step 220, the strip 12 is stamped, in other words, 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, the tool 30 of which 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.

[0041] During the stamping step 220, the strip 12 tends to deform, and thus the primary reference mark 202 formed on the strip 12 moves relative to its original position on the strip 12 and can no longer serve as its reference. To overcome such a problem, when the network of channels 104 is formed by stamping on the strip 12 during the stamping step 220, while the strip 12 is held clamped in 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 the strip 12. Generally, the secondary reference mark 222 is preferably formed by one or more holes in the strip 12. Preferably, the secondary reference mark 222 is formed for each respective basic section 13 of the strip 12.

[0042] The secondary marking tool 224 includes another actuation device (referred to as the secondary actuation device), which is held by the corresponding slider 24 and is adapted to move the piercing punch and form a secondary reference mark 222 on the strip 12 while the strip is held clamped in the stamping tool 42. The secondary actuation device is not shown. Thereby, when the slider 24 is in or near its lower position, the secondary marking tool 224 is placed in the working position, and when the strip 12 is held clamped in the stamping tool 42, the secondary actuation 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.

[0043] The actuating device 28 of the intermediate press 40 includes a press actuator 46, and the press actuator 46 moves the corresponding slider 24 between its upper position and its lower position. 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 the present specification includes a connecting rod, and the connecting rod 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, and the connecting rod is connected to the slider 24 at its lower end by a pivot connection or a ball joint connection that forms a connection point 49 through which the pressing force passes. The actuating device 28 further includes a servo motor 48, and the servo motor 48 is represented herein by a cylinder protruding from the corresponding rear surface 23B. 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, and the press actuator 46 drives the slider 24 between its upper position and its lower position in an alternating translational movement 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 is controlled by the servo motor, while the eccentric crankshaft 47 drives the slider 24 in a reciprocating motion between its upper position and its lower position. Generally speaking, the pressing force is oriented along a press axis A49, the press axis A49 is an axis parallel to the height axis Z20, and the press axis A49 runs 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 in particular, vertically below the connection point 49 of the press actuator 46 with the slider 24.

[0044] 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 stamping.

[0045] 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 (for example, three) of 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.

[0046] Generally, in prior art presses, the table has an opening in 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.

[0047] 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.

[0048] 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, 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 understood to be 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 (more precisely, 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 apart 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).

[0049] The movement of the slider 24 is controlled by the servo motor 48, which is used, inter alia, to control the speed of descent of the slider, the speed of ascent of the slider, and the time interval during which the strip 12 is held clamped in the stamping tool 42, or, alternatively, the clamping force (or pressing force) exerted by the strip 12 during said time interval.

[0050] Preferably, during the stamping step 220, the pressing 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 pressing force is maintained is referred to as the "holding time", while the pre-determined value of the pressing force is referred to as the "holding force".

[0051] Thereby, it is ensured that the transient effects of stamping, in particular 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.

[0052] The holding time is preferably selected to be greater than 0.2 s (seconds), more preferably greater than 0.3 s, or alternatively, more 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 alternatively, preferably between 180 kN and 200 kN.

[0053] 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 be re-engaged after the holding time has elapsed, inter alia, for the end of the transfer of the strip 12 into the intermediate press 40.

[0054] 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 the expert will be able to replace the examples described herein with presses of other technologies.

[0055] 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.

[0056] Once the secondary reference mark 222 is formed on the strip 12, the intermediate press 40 then returns to its higher configuration and the strip 12 is moved according to the feed movement.

[0057] 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 forming step, which is carried out herein by the cutting tool 232, which separates each basic section 13 from the strip 12.

[0058] Where appropriate, the forming method includes other forming steps (such as 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 called "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.

[0059] 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 is mounted on the downstream press 60, and the positioning member 238 cooperates with the secondary reference mark 222, in particular by means of a mating shape, so as 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.

[0060] 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.

[0061] 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 carry out the task for which the press 20 is intended and a safety factor.

[0062] In a forming plant according to the prior art, the stamping press generally performs other forming steps (more specifically, a piercing operation and a cutting operation). The prior art presses are dimensioned to exert a nominal press force in the range of 800 tons to 1000 tons, or in the range of 8 MN to 10 MN (mega newtons).

[0063] In the forming plant 10, while the downstream steps are performed by the downstream press 60, the steps before the stamping step 220 (referred to as upstream steps) are performed by the upstream press 50.

[0064] More specifically, the primary marking step 200 is performed 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 illustrated example, the piercing step 210 is also performed by the upstream press 50.

[0065] 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.

[0066] 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 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), which moves along the axis X20 of the value of the basic section 13 by a movement along the axis Z20 on the order of 5 mm.

[0067] According to an example, the tensioning member is combined with a feeding member.

[0068] Since the outer part 16B is released, the transmission of mechanical stress along the strip 12 between two consecutive 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.

[0069] The above-described embodiments and variations can be combined with each other so as to give rise to new embodiments of the present invention.

Explanation of reference numerals

[0070] 10 Forming plant 12 Strip 13 Basic section 14 Roll 16A Inner part 16B Outer part 20 Press 22 Frame Peripheral surface 23 Front surface 23A Rear surface 23B Upstream surface 23C Downstream surface 23D Slider 24 Table 26 Actuating device 28 Tool set 30 Movable part 34 Fixed part 36 Positioning member 38 Intermediate press 40 Stamping tool 42 Movable die 43A Fitting die 43B Press actuator 46 Eccentric crankshaft 47 Servo motor 48 Connection point 49 Upstream press 50 Polar plate 100 Central part 102 Channel network 104 Center 105 Perforation part 106 Perforating tool 121 Primary marking step 200 Primary reference mark 202 Primary marking tool 204 Perforation step 210 Stamping step 220 Secondary reference mark 222 Secondary marking tool 224 Cutting step 230 Cutting tool 232 Positioning member 238 Press axis A49 Plate plane P100 Transverse axis X20 Depth axis Y20 Height axis Z20

Claims

【Claim 1】 A method of forming a bipolar plate (100) for an electrochemical cell of a fuel cell, the method being carried out by a forming plant (10) comprising at least one stamping press (40), the stamping press (40) being configured to form the bipolar plates in series from a metal strip (12), each bipolar plate being provided within a basic section (13) of the strip, the stamping press comprising: A movable slider (24) disposed opposite a stationary table (26), the slider being moved by an actuating device (28) 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 (24); A stamping tool (42), the stamping tool (42) being connected to the slider and configured to relief stamp a network of channels (104) for fluid circulation onto the strip as the slider moves from its upper position to its lower position, the stamping tool (42); Including; The forming method includes a so-called stamping step (220) and a so-called downstream step (230), the downstream step (230) following the stamping step and being carried out by a so-called downstream press (60), the downstream press (60) belonging to the forming plant (10) and being separate from the stamping press (40), During the stamping step, with the strip (12) received within the working volume of the stamping press, the slider (24) moves from its upper position to its lower position, stamping a network of circulation channels for fluid circulation onto the strip, The forming method includes When the channel network (104) is stamped onto the strip (12), a reference mark (222) is formed on the strip by a marking tool (224) held by the slider while the strip (12) is held clamped within the stamping tool (42), and During the downstream step (230), the strip is positioned relative to the downstream press (60) by a positioning member (238), the positioning member (238) being mounted on the downstream press and cooperating with the reference mark characterized in that method. **Claim 2** The forming method according to claim 1, wherein the reference mark (222) is formed on the strip (12) while the slider (24) is held in the lower position for a predetermined time interval while the stamping tool (42) exerts a predetermined force on the strip. **Claim 3** The forming method according to claim 2, wherein the predetermined time interval is greater than 0.2 seconds, preferably greater than 0.3 seconds, or else preferably greater than 0.4 seconds. **Claim 4** The forming method according to claim 2 or 3, wherein the predetermined force is comprised between 150 kN and 300 kN, preferably between 170 kN and 250 kN, or else preferably between 180 kN and 200 kN. **Claim 5** The forming method includes a so-called upstream step (200) preceding the stamping step (220), during which a primary reference mark (202) is formed on the strip (12) using a primary marking tool (204) belonging to the forming plant (10). During the stamping step (220), the strip (12) is positioned relative to the stamping press (40) by a positioning member (38), the positioning member (38) being mounted on the stamping press and cooperating with the primary reference mark, the forming method according to any one of claims 1 to 4. **Claim 6** The forming method according to claim 5, wherein the primary marking tool (204) is mounted on the slider (24) of an upstream press (50), the upstream press (50) being part of the forming plant (10) and separate from the stamping press (40). **Claim 7** A forming plant (10) for a bipolar plate (100), said forming plant being configured to carry out the forming method according to any one of claims 1 to 6, comprising a plurality of presses (30), said presses comprising at least one stamping press (40) and a downstream press (60), said stamping press (40) being configured to carry out a stamping step (220), said downstream press (60) being configured to carry out a downstream step following said stamping step, Each press comprises a movable slider (24) arranged on the opposite side of a stationary table (26), said slider being moved by an actuating device (28) between an upper position and a lower position, said slider and said table together defining the boundary of the working volume of the corresponding press, Said stamping press (40) A stamping tool (42), said stamping tool (42) being connected to the corresponding slider, said stamping tool (42) being configured to relief stamp a network of channels (104) for fluid circulation onto said strip (12) when said slider moves from its said upper position to its said lower position, a stamping tool (42), A marking tool (224), said marking tool (224) being held by said slider (24), said marking tool (224) being configured to form a reference mark (222) on said strip while said strip (12) is held clamped in said stamping tool (42) after said network channels have been printed onto said strip, comprising Said downstream press (60) comprises a positioning member (238), said positioning member (238) being mounted on said downstream press and being configured to cooperate with a reference mark (222) formed on said strip and to position said strip with respect to said downstream press. Forming plant (10).

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