Bipolar plate forming method

Abstract

A method of making a bipolar plate for a fuel cell includes placing a sheet in a bipolar plate forming apparatus, deforming a first region of the sheet between a first die and a first punch in a first stage, the first stage forming one or more walls and one or more vertices, and forming a second region of the sheet between the first die and the first punch. Deforming a second region of the sheet between a second die and a second punch in a second stage, the second region being arranged laterally on either side of the first region, the second stage forming at least one first flat portion and at least one second flat portion on either side of the one or more walls, and deforming, in a third stage, a third region of the sheet between a third die and a third punch, the third region being arranged laterally between the first region and the second region.

Description

[0001] Government funding

[0002] This invention was made with government support under Agreement No. DE-EE0009616 awarded by the Department of Energy for HD Bipolar Plates. The government may have certain rights in this invention.

[0003] introduction

[0004] The information provided in this section is for the purpose of generally presenting the context of the present disclosure. The work of the presently named inventors, to the extent it is described in this section and insofar as it may not qualify as prior art at the time of filing, is neither explicitly nor implicitly admitted as prior art to the present disclosure. Technical Field

[0005] The present disclosure generally relates to a method of forming a bipolar plate, and more particularly, to a method of forming a bipolar plate using a poorly formable material. Background Art

[0006] Typically, bipolar plates for fuel cell systems are made of metal or other conductive materials to form an electrical path between the membrane electrode assembly and the external circuit. Bipolar plates operate in high temperatures and corrosive environments, so conventional metals (such as ordinary carbon steel) may not be suitable for some applications. Alloy metals (such as stainless steel) can be used to form bipolar plates because they have desirable corrosion resistance. For example, stainless steel with a ferrite microstructure (i.e., ferritic stainless steel) generally has good corrosion resistance due to its high chromium content.

[0007] Ferritic stainless steel, as well as other desirable materials, are often susceptible to necking, thinning, and cracking when exposed to conventional stamping or related metal forming operations (e.g., hydroforming). These shortcomings are prevalent in single-step operations or in operations where rapid wall deformation may occur. The shortcomings of existing systems and methods are addressed by one or more aspects of the present disclosure. Summary of the Invention

[0008] In one configuration, a method for preparing a bipolar plate for a fuel cell is provided, the method comprising placing a sheet in a bipolar plate forming apparatus, deforming a first region of the sheet between a first die and a first punch in a first stage, the first stage forming one or more walls and one or more vertices, deforming a second region of the sheet between a second die and a second punch in a second stage, the second region being laterally disposed on either side of the first region, forming at least one first flat portion and at least one second flat portion on either side of the one or more walls in the second stage, and deforming a third region of the sheet between a third die and a third punch in a third stage, the third region being laterally disposed between the first region and the second region, the third stage forming the sheet such that a final draw depth between the at least one first flat portion and the at least one second flat portion is increased.

[0009] The method may include one or more of the following optional features.For example, the sheet material may include one of ferritic stainless steel, austenitic stainless steel, titanium or aluminum.

[0010] According to at least one aspect, the sheet can include a pitch of 0.7 mm to 1.6 mm.

[0011] According to another aspect, the sheet can include a land width of 0.1 mm to 0.5 mm.

[0012] According to at least one example, the sheet can include a channel span of 0.2 mm to 1.1 mm.

[0013] According to another example, the final drawing depth may be 0.26 to 0.6 mm.

[0014] According to at least one aspect, the sheet can include a sheet thickness of about 50 microns to 200 microns. The sheet includes a maximum thinning of about 20-24% of the sheet thickness and a flat length of about 294-300 microns.

[0015] According to another aspect, the sheet may include a maximum thinning of less than 24% of the sheet thickness.The sheet may include a flat length greater than 226 microns.

[0016] In another configuration, a method for preparing a bipolar plate for a fuel cell is provided, the method comprising engaging a substantially planar metal sheet having a certain thickness with a tool and forming the metal sheet using a three-step forming process to form the metal sheet into a substantially non-planar shape, the substantially non-planar shape comprising a surface profile comprising one or more walls, one or more bosses, one or more intersections, and one or more channel bottoms. The three-step forming process comprises a first forming step, wherein the tool forms a first region of the substantially planar metal sheet, the first forming step forming a first drawing depth. The three-step forming process also comprises a second forming step, wherein the tool forms a second region of the substantially planar metal sheet, the second region being laterally arranged on either side of the first region, the second step forming a second drawing depth. The three-step forming process also comprises a third forming step, wherein the tool forms a third region of the substantially planar metal sheet, the third region being laterally arranged between the first region and the second region, the third forming step forming a final drawing depth.

[0017] The method may include one or more of the following optional features.For example, the sheet material may include one of ferritic stainless steel, austenitic stainless steel, titanium or aluminum.

[0018] According to at least one aspect, the sheet comprises a sheet thickness of about 50 microns to 200 microns. The sheet comprises a maximum thinning of about 20-24% of the sheet thickness and a flat length of about 294-300 microns.

[0019] According to another aspect, the sheet may include a maximum thinning of less than 24% of the sheet thickness.The sheet may include a flat length greater than 226 microns.

[0020] In yet another configuration, a fuel cell for a vehicle is provided, comprising a proton exchange member, an anode catalyst layer in contact with one face of the proton exchange member, a cathode catalyst layer in contact with the other face of the proton exchange member, an anode diffusion layer in contact with the anode catalyst layer, a cathode diffusion layer in contact with the cathode catalyst layer, a first bipolar plate engaged with the anode diffusion layer, and a second bipolar plate engaged with the cathode diffusion layer. The first bipolar plate and the second bipolar plate each include a preformed thickness, one or more first flat portions including a first flat portion length greater than 226 microns, one or more second flat portions including a second flat portion length greater than 226 microns, and one or more intersections between the first and second flat portions, the one or more intersections including a reduction of less than 24% of the preformed plate thickness.

[0021] The fuel cell may include one or more of the following optional features: For example, the first flat portion length of the one or more first flat portions may be between 294 microns and 300 microns.

[0022] According to one example, the second flat portion length of the one or more second flat portions can be between 294 microns and 300 microns. The first bipolar plate and the second bipolar plate can each include a preform thickness between approximately 50 microns and 200 microns. The one or more intersections can include a reduction in thickness of 20% to 24% of the preformed plate thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are for illustrative purposes only of selected configurations and are not intended to limit the scope of the present disclosure.

[0024] Figure 1 is a perspective view of a fuel cell stack including one or more fuel cells according to the principles of the present disclosure;

[0025] Figure 2 yes Figure 1 a partial cross-sectional view of a portion of one of the fuel cells;

[0026] Figure 3 is a cross-sectional view of a sheet subjected to a one-step forming process according to the prior art;

[0027] Figure 4A and 4B is a cross-sectional view of a sheet subjected to a two-step forming process according to the prior art;

[0028] Figure 5A 、 Figure 5B and Figure 5C is a cross-sectional view of a sheet subjected to a three-step forming process according to the principles of the present disclosure;

[0029] Figure 6 The results of a one-step molding process, a two-step molding process, and a three-step molding process according to the principles of the present disclosure are shown;

[0030] Figure 7 yes Figure 1 a cross-sectional view of a portion of one of the fuel cells; and

[0031] Figure 8 Various steps used in the incremental formation of a bipolar plate according to the principles of the present disclosure are shown.

[0032] Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0033] Example configurations will now be described more fully with reference to the accompanying drawings. The example configurations are provided so that this disclosure will be thorough and will fully convey the scope of the disclosure to those of ordinary skill in the art. Specific details, such as examples of specific components, devices, and methods, are set forth to provide a thorough understanding of the configurations of the present disclosure. It will be apparent to those of ordinary skill in the art that specific details need not be employed, that the example configurations may be embodied in many different forms, and that the specific details and example configurations should not be construed as limiting the scope of the present disclosure.

[0034] The terms used herein are only used to describe the purpose of specific exemplary configurations and are not intended to be limiting. As used herein, the singular articles "a" and "the" may also be intended to include plural forms, unless the context clearly indicates otherwise. The terms "comprise," "include," and "have" are inclusive and therefore specify the presence of features, steps, operations, elements, and / or parts, but do not exclude the presence or addition of one or more other features, steps, operations, elements, parts, and / or groups thereof. The method steps, processes, and operations described herein should not be interpreted as necessarily requiring them to be performed in the particular order discussed or shown, unless specifically identified as an execution order. Additional or alternative steps may be adopted.

[0035] When an element or layer is referred to as being "on," "engaged to," "connected to," "attached to," or "coupled to" another element or layer, it may be directly on, directly engaged, connected, attached to, or coupled to the other element or layer, or there may be intervening elements or layers. Conversely, when an element is referred to as being "directly on," "directly engaged to," "directly connected to," "directly attached to," or "directly coupled to" another element or layer, there may be no intervening elements or layers. Other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0036] The terms "first", "second", "third" etc. may be used in this article to describe various elements, components, regions, layers and / or parts. These elements, components, regions, layers and / or parts should not be limited by these terms. These terms can only be used to distinguish one element, component, region, layer or part from another region, layer or part. Unless the context clearly indicates, terms such as "first", "second" and other numerical terms do not imply an order or sequence. Therefore, without departing from the teachings of the example configurations, the first element, component, region, layer or part discussed below may be referred to as a second element, component, region, layer or part.

[0037] In this application, including the definitions below, the term "module" may be replaced with the term "circuit". The term "module" may refer to, be part of, or include: an application-specific integrated circuit (ASIC); a digital, analog, or mixed analog / digital discrete circuit; a digital, analog, or mixed analog / digital integrated circuit; a combinational logic circuit; a field-programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; a memory (shared, dedicated, or group) that stores code executed by the processor; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system on a chip.

[0038] The term "code" as used above may include software, firmware and / or microcode, and may refer to programs, routines, functions, classes and / or objects. The term "shared processor" includes a single processor that executes some or all code from multiple modules. The term "group processor" includes a processor that, in combination with additional processors, executes some or all code from one or more modules. The term "shared memory" encompasses a single memory that stores some or all code from multiple modules. The term "group memory" includes memory that, in combination with additional memory, stores some or all code from one or more modules. The term "memory" may be a subset of the term "computer-readable medium". The term "computer-readable medium" does not include transient electrical and electromagnetic signals propagated through the medium, and therefore may be considered to be tangible and non-transitory memory. Non-limiting examples of non-transitory memory include tangible computer-readable media, including non-volatile memory, magnetic storage, and optical storage.

[0039] The apparatus and methods described herein may be implemented in part or in whole by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions stored on at least one non-transitory tangible computer-readable medium. The computer programs may also include and / or rely on stored data.

[0040] A software application (i.e., a software resource) may refer to computer software that enables a computing device to perform tasks. In some examples, a software application may be referred to as an "application," "app," or "program." Example applications include, but are not limited to, system diagnostic applications, system management applications, system maintenance applications, word processing applications, spreadsheet applications, messaging applications, media streaming applications, social networking applications, and gaming applications.

[0041] Non-transitory memory can be a physical device used to temporarily or permanently store programs (e.g., sequences of instructions) or data (e.g., program state information) for use by a computing device. Non-transitory memory can be volatile and / or non-volatile addressable semiconductor memory. Examples of non-volatile memory include, but are not limited to, flash memory and read-only memory (ROM) / programmable read-only memory (PROM) / erasable programmable read-only memory (EPROM) / electrically erasable programmable read-only memory (EEPROM) (e.g., commonly used for firmware, such as bootloaders). Examples of volatile memory include, but are not limited to, random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), phase change memory (PCM), and disk or tape.

[0042] These computer programs (also referred to as programs, software, software applications, or code) include machine instructions for a programmable processor and may be implemented in high-level procedural and / or object-oriented programming languages ​​and / or assembly / machine languages. As used herein, the terms "machine-readable medium" and "computer-readable medium" refer to any computer program product, non-transitory computer-readable medium, apparatus, and / or device (e.g., a disk, optical disk, memory, programmable logic device (PLD)) for providing machine instructions and / or data to a programmable processor, including machine-readable media that receives machine instructions as a machine-readable signal. The term "machine-readable signal" refers to any signal used to provide machine instructions and / or data to a programmable processor.

[0043] Various implementations of the systems and techniques described herein can be implemented in digital electronic and / or optical circuitry, integrated circuits, specially designed ASICs (application-specific integrated circuits), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include implementation in one or more computer programs executable and / or interpretable on a programmable system comprising at least one programmable processor, which can be special purpose or general purpose, coupled to receive data and instructions from and send data and instructions to a storage system, at least one input device, and at least one output device.

[0044] The processes and logic flows described in this specification can be performed by one or more programmable processors (also referred to as data processing hardware) that execute one or more computer programs to perform functions by operating on input data and generating outputs. The processes and logic flows can also be performed by dedicated logic circuits (e.g., FPGAs (field programmable gate arrays) or ASICs (application-specific integrated circuits)). As an example, processors suitable for executing computer programs include both general-purpose and special-purpose microprocessors, as well as any one or more processors of any type of digital computer. Typically, a processor will receive instructions and data from a read-only memory or a random access memory or both. The basic elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Typically, a computer will also include one or more mass storage devices (e.g., magnetic disks, magneto-optical disks, or optical disks) for storing data, or be operably coupled to receive data from it or transmit data to it or both. However, a computer need not have such a device. Computer-readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media, and storage devices, including, for example, semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks or removable disks; magneto-optical disks; and CD ROM and DVD-ROM disks. The processor and memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0045] To provide for interaction with a user, one or more aspects of the present disclosure may be implemented on a computer having a display device (e.g., a CRT (cathode ray tube), an LCD (liquid crystal display) monitor, or a touch screen) for displaying information to the user and, optionally, a keyboard and pointing device (e.g., a mouse or trackball) through which the user can provide input to the computer. Other kinds of devices may also be used to provide for interaction with the user; for example, the feedback provided to the user may be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback; and input from the user may be received in any form, including sound, voice, or tactile input. Additionally, a computer may interact with a user by sending documents to and receiving documents from a device used by the user; for example, by sending a web page to a web browser on a user's client device in response to a request received from the web browser.

[0046] refer to Figure 1 The fuel cell stack 10 includes a stack 12 including one or more power generation units or fuel cells 100 stacked relative to each other. The fuel cell stack 10 can be installed in a vehicle (not shown), such as a fuel cell vehicle or fuel cell electric vehicle, a stationary power station, and / or a mobile charging station.

[0047] refer to Figure 2 , one or more fuel cells 100 include a proton exchange membrane 110, an anode catalyst layer 120 in contact with one surface of the proton exchange membrane 110, and a cathode catalyst layer 130 in contact with the other surface of the proton exchange membrane 110. The proton exchange membrane 110 and the catalyst layers 120, 130 may be referred to as a membrane electrode assembly (MEA) 140. An anode diffusion layer 150 is arranged in contact with the anode catalyst layer 120, while a cathode diffusion layer 160 is arranged in contact with the cathode catalyst layer 130. The diffusion layers 150, 160 may be made into a porous structure to facilitate the passage of gaseous reactants through the catalyst layers 120, 130. The anode catalyst layer 120 and the cathode catalyst layer 130 are referred to as electrodes and may be formed as separate distinct layers as shown, or alternatively, at least partially embedded in the diffusion layers 150, 160, respectively, and partially embedded in the opposite surfaces of the proton exchange membrane 110.

[0048] In addition to providing a substantially porous flow path for the reactant gases to reach the appropriate side of the proton exchange membrane 110, the diffusion layers 150, 160 also provide electrical contact between the electrode catalyst layers 120, 130 and the bipolar plate 170, which in turn serves as a current collector. In addition, due to their porous nature, the diffusion layers 150, 160 also form a conduit for removing the product gases produced at the catalyst layers 120, 130. In addition, the cathode diffusion layer 160 produces a large amount of water vapor in the cathode diffusion layer. This may be desirable to help keep the proton exchange membrane 110 hydrated. For example, water permeation in the diffusion layers 150, 160 can be adjusted by introducing a small amount of polytetrafluoroethylene (PTFE) or related materials.

[0049] Continue to refer Figure 2, the bipolar plate 170 includes a first plate 172A and a second plate 172B. The first plate 172A and the second plate 172B can each be defined by a pre-formed thickness (e.g., 50 microns and 200 microns) (not shown). The first plate 172A and the second plate 172B include opposing surfaces 174A, 174B that separate each MEA 140 and the accompanying diffusion layer 150, 160 from the adjacent MEAs and layers of the stack 12. The first plate 172A is bonded to the anode diffusion layer 150, while the second plate 172B is bonded to the cathode diffusion layer 160. Each plate 172A, 172B (which, when assembled as a whole, will constitute the bipolar plate 170) defines a plurality of reactant gas flow channels 176. The channel 176 can be defined by a three-dimensional (i.e., out-of-plane) structure 178 comprised of wall(s) 178A, boss(es) or first flat portion 178B, and intersections (i.e., bends or radii) 178C that separate adjacent portions of the reactant gas flow channel 176 by protruding toward and in direct contact with the respective diffusion layers 150, 160. The channel 176 can also be defined by a channel floor or second flat portion 178D or a portion of the plates 172A, 172B disposed laterally between each structure 178. Although the plates 172A, 172B are shown as defining a purely rectangular reactant gas flow channel 176 and structure 178, the configuration and shape of the gas flow channel 176 and structure 178 can be further defined and will be discussed in greater detail below.

[0050] In operation, a first gaseous reactant, such as hydrogen, is delivered from plate 172A to the anode 120 side of MEA 140 through channels 176, while a second gaseous reactant, such as oxygen (e.g., air), is delivered from plate 172B to the cathode 130 side of MEA 140 through channels 176. Catalytic reactions occur at anode 120 and cathode 130, respectively, generating protons that migrate across proton exchange membrane 110 and electrons that result in an electrical current that can be transported through diffusion layers 150, 160 and bipolar plate 170 via contacts between boss 178B and layers 150, 160.

[0051] refer to Figure 3 、 Figures 4A-4B and Figures 5A-5C, provides the results of forming ferritic stainless steel sheets (i.e., blanks) 101, 201, 301 into bipolar plates 170, 270, 370 in one step, two steps, and three steps. According to the prior art, sheets 201 and 301 are formed using one-step forming and two-step forming, respectively. According to the principles of the present disclosure, sheet 101 is formed using three-step forming. Sheets 101, 201, 301 can be made of another material, such as austenitic stainless steel, titanium, an alloy, or a material commonly used to form bipolar plates. The thickness of sheets 101, 201, 301 can be between 50 microns and about 200 microns.

[0052] When forming the sheets 101, 201, 301, a generally continuous surface profile is provided consisting of the sidewalls 178A, 278A, 378A, bosses 178B, 278B, 378B, intersections 178C, 278C, 378C, and channel floors 178D, 278D, and 378D. Each sheet 101, 201, 301 includes a unique surface profile depending on each forming process (i.e., one-step forming, two-step forming, or three-step forming). More specifically, depending on which forming process is used, the sheets 101, 201, 301 may experience varying degrees of thinning along the surface profile. For example, referring to Figure 3 , a significant thinning portion 280 (ie, about 46%) occurs at the intersection 278C between the wall 278A of the sheet 201 and the channel floor 278D and / or between the wall 278A of the sheet 201 and the boss 278B. Figure 4B , a significant thinning 380 (i.e., about 33.5%) occurs between the wall 378A and the channel floor 378D and / or at the intersection 378C between the wall 378A and the boss 378B of the sheet 301. In accordance with at least one aspect of the present disclosure, the three-step process of forming the sheet 101 results in only about a 29% thinning at the intersection 178C between the wall 178A and the channel floor 178D and / or between the wall 178A and the boss 178B of the sheet 101. In other words, using three-step forming to gradually form the sheet is desirable to utilize less formable (i.e., less expensive) materials while maintaining a generally uniform thickness along the surface contours of the sheet 101.

[0053] Reference again Figure 3 , the one-step forming of the sheet 201 results in the boss 278B being roughly curved. Figure 4B, the two-step forming of sheet 301 results in bosses 378B being generally curved. In contrast, the three-step forming of sheet 101 results in bosses 178B being generally flat (i.e., planar) rather than curved. For example, it may be desirable to have flatter (i.e., more planar) bosses 178B to improve performance (e.g., reduce contact resistance and voltage drop) between bipolar plates 172A, 172B and diffusion layers 150, 160. According to one aspect of the present disclosure, bosses or first flat portions 178B are generally parallel to the channel bottom surface or second flat portions 178D.

[0054] Reference Figure 8 , a bipolar plate forming apparatus 400 is provided for forming the sheet 101 into the bipolar plate 170. The bipolar plate forming apparatus 400 may include a first stage 402, a second stage 404, and a third stage 406. The first stage 402 includes a first die 402A and a first punch 402B, the second stage 404 includes a second die 404A and a second punch 404B, and the third stage 406 includes a third die 406A and a third punch 406B. The first stage 402 may be configured for a first or deep drawing depth D1, such as Figure 5A For example, the first drawing depth D1 may be 50-100% of the third or final drawing depth D3 ( Figure 5C ). The second stage 406 can be configured for a second or shallow draw depth D2, such as Figure 5B In other words, the second drawing depth D2 can be 30-90% of the final drawing depth D3 ( Figure 5C ).

[0055] Generally speaking, it is desirable to form the sheet 101 in three steps or using a first stage 402, a second stage 404, and a third stage 406 to target and gradually deform a specific area of ​​the sheet 101 at each stage of the forming process. Gradual forming of the sheet 101 is also desirable to provide a generally uniform thickness upon deformation. Deforming the sheet 101 between the first die 402A and the first punch 402B in the first stage 402 may form a first area (I) of the sheet. In other words, as Figure 5A As shown, the first die 402A and the first punch 402B can form one or more vertices, such as the first vertex 175A and the second vertex 175B, between the one or more walls 178A. Deforming the sheet 101 between the second die 404A and the second punch 404B in the second stage 404 can form a second region (II) of the sheet. The second region (II) can be arranged laterally on either side of the first region. In this example, as shown in FIG. Figure 5BAs shown, the second die 404A and the second punch 404B form a portion of the wall 178A to define the boss or first flat portion 178B and the channel bottom or second flat portion 178D. Deforming the sheet 101 between the third die 406A and the third punch 406B in the third stage 406 can form a third region (III) of the sheet 101, which is laterally arranged between the first region (I) and the second region (II). In other words, in the third stage 406, the final draw depth D3 between the first flat portion 178B and the second flat portion 178D can be increased while reducing the width of the second flat portion 178D and / or 178B. Additionally or alternatively, as Figure 5C As shown, the boss or first flat portion 178B may be formed substantially parallel to the channel bottom surface or second flat portion 178D.

[0056] refer to Figure 7 , three-step forming improves the dimensional accuracy of the bipolar plate 170, which can improve the performance of the bipolar plate 170. The pitch 190 can be determined by adding the boss width 192 of the boss 178B and the channel span 194 of the channel 176. When the sheet 101 is formed using a three-step forming process, the pitch 190 can be between 0.7 millimeters (mm) and 1.6 millimeters (mm). The boss width 192 can be between 0.1 mm and 0.5 mm, and the channel span 194 can be between 0.2 mm and 1.1 mm. The depth 196 (i.e., the distance between the boss or first flat portion 178B and the channel bottom surface or second flat portion 178D) can be between 0.26 mm and 0.6 mm.

[0057] refer to Figure 6 , provides the results of forming sheets using a one-step forming process, a two-step forming process, and a three-step forming process according to the principles of the present disclosure. Generally, the three-step forming process can reduce thickness reduction (i.e., thinning) while increasing the flat length of the sheet. The three-step forming process of the sheet results in a maximum thinning of about 20-24% of the sheet thickness and a flat length of about 294-300 microns. In contrast, the one-step forming process of the sheet results in a maximum thinning of about 54-56% and a flat length of about 220-226 microns (e.g., 224 microns). In addition, the two-step forming process of the sheet results in a maximum thinning of 23-27% and a flat length of about 218-222 microns (e.g., 220 microns). Therefore, the three-step forming of the sheet can include a thinning of less than 24% of the sheet thickness and a flat length greater than 226 microns.

[0058] Combine Figure 1 、 2 , 5 and 6 reference Figure 8, a method 500 for forming a bipolar plate by three-step forming is provided. At 510, a substantially planar sheet or blank, such as sheet 101, is prepared for forming. At 520, 530, 540, a series of forming steps are performed using the bipolar plate forming apparatus 400.

[0059] In the first forming step 520, the sheet 101 is positioned in the first stage 402 between the die 402A and the punch 402B and formed in the first region (I). The first forming step can be configured such that the sheet 101 includes one or more walls 178A ( Figure 5A ) and a first vertex 175A and a second vertex 175B between one or more walls 178A.

[0060] In the second forming step 530, the sheet 101 is positioned in the second stage 404 and between the die 404A and the punch 404B and formed in the second region (II). The second forming step 530 can be configured to include a boss or first flat portion 178B and a channel bottom surface or second flat portion 178D, as shown in FIG. Figure 5B shown.

[0061] In the third forming step 540, the sheet 101 is positioned within the third stage 406 and between the die 406A and the punch 406B, and is formed in the third region (III). The third forming step can be configured such that the final draw depth D3 between the first flat portion 178B and the second flat portion 178D can be increased while the widths of the first flat portion 178B and the second flat portion 178D can be reduced. Additionally or alternatively, the third forming step 540 can be configured such that the boss or first flat portion 178B can be formed substantially parallel to the channel bottom surface or second flat portion 178D.

[0062] From these three forming steps, step 550 can be used to form additional bipolar plate features, such as perforations for internal features, port openings, etc. Such perforated features can include head openings to distribute fluids to the completed stack assembly (not shown), while port (i.e., anode and cathode) openings provide a path for reactant fluids to enter or exit each cell. Other features can also be formed, such as openings for creating or supporting reference structures for assembly and other knockouts for facilitating assembly and integration (e.g., for facilitating cell voltage monitoring). Thereafter, additional step 560 can be used to provide cutting, trimming, peripheral perforations, or related separation of excess material to be discarded. For example, the last station corresponding to step 560 can be used to flush out peripheral material to cut the finished bipolar plate 170 from the strip for collection into downstream components.

[0063] A number of embodiments have been described. However, it will be appreciated that various modifications can be made without departing from the spirit and scope of this disclosure. Accordingly, other embodiments are within the scope of the following claims.

[0064] The foregoing description is provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the present disclosure. Individual elements or features of a particular configuration are generally not limited to that particular configuration, but are interchangeable where applicable and can be used in a selected configuration, even if not specifically shown or described. They may also vary in many ways. Such variations should not be considered as departing from the present disclosure, and all such modifications are intended to be included within the scope of the present disclosure.

Claims

1. A method for preparing a bipolar plate for a fuel cell, comprising: placing the sheet in a bipolar plate forming device; deforming a first region of the sheet between a first die and a first punch in a first stage, the first stage forming one or more walls and one or more apexes; deforming a second region of the sheet between a second die and a second punch in a second stage, the second region being disposed laterally on either side of the first region, the second stage forming at least one first flat portion and at least one second flat portion on either side of the one or more walls; as well as In a third stage, a third region of the sheet is deformed between a third die and a third punch, the third region being laterally disposed between the first region and the second region, the third stage forming the sheet such that a final draw depth between the at least one first flat portion and the at least one second flat portion is increased.

2. The method of claim 1, wherein the sheet material comprises one of ferritic stainless steel, austenitic stainless steel, titanium, or aluminum.

3. The method according to claim 1, wherein The sheets comprise a pitch between 0.7 mm and 1.6 mm. The method of claim 3 , wherein the sheet comprises a land width of 0.1 mm to 0.5 mm.

5. The method according to claim 4, wherein The sheet includes a channel span of 0.2 mm to 1.1 mm.

6. The method according to claim 1, wherein The final drawing depth is 0.26 to 0.6 mm.

7. The method of claim 1, wherein the sheet comprises a sheet thickness of about 50 microns to 200 microns.

8. The method of claim 7, wherein the sheet comprises a maximum reduction of about 20-24% of the sheet thickness and a flat length of about 294-300 microns.

9. The method of claim 7, wherein the sheet comprises a maximum thinning of less than 24% of the sheet thickness.

10. The method of claim 9, wherein the sheet comprises a flat length greater than 226 microns.

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