Preforming die and forming method for bipolar plate of fuel cell stack

Abstract

The invention provides a pre-forming die and a forming method for a bipolar plate of a fuel cell stack. The pre-forming die includes an upper die portion and a lower die portion. The lower end face of the upper die part comprises a first convex arc part and a second concave arc part, and the first arc part and the second arc part are alternately connected to form the lower end face. The upper end face of the lower die part comprises a third concave arc part and a fourth convex arc part, and the third arc part and the fourth arc part are alternately connected to form the upper end face. The central angles of the first arc part, the second arc part, the third arc part and the fourth arc part are equal, the third arc part is configured to be matched with the first arc part, and the fourth arc part is configured to be matched with the second arc part. According to the preforming die and the forming method for the bipolar plate of the fuel cell stack, the risks of necking, local thinning and even cracking of the formed bipolar plate can be effectively avoided.

Description

Technical Field

[0001] The present disclosure relates to a bipolar plate for a fuel cell stack, and more particularly to a preforming mold and a forming method for a bipolar plate for a fuel cell stack. Background Art

[0002] Bipolar plates (also known as flow field plates) are important components of fuel cell stacks. They are arranged on both sides of each cell to provide a flow path for the reaction gas and physically and electrically connect the cathode of one cell to the anode of an adjacent cell. Metal materials are often used to manufacture bipolar plates for reasons of conductivity, air tightness, structural strength, thermal conductivity, corrosion resistance, and cost effectiveness. In this case, stamping dies are usually used to produce bipolar plates.

[0003] In order to ensure good battery stack performance, the dimensional accuracy of the bipolar plate is crucial. However, high dimensional accuracy requirements will inevitably bring greater processing difficulties. Figure 1 As shown, in the currently manufactured bipolar plates, the problem of material thinning in the fillet area of ​​the gas flow channel formed by the bipolar plate (as indicated by the circle in the figure) is very significant. Figure 2 As shown, the prior art CN103887534A discloses a unique preforming design for two-step forming of stainless steel fuel cell bipolar plates. In which a V-shaped die is used to preform the bipolar plate. During the preforming process, stress is continuously concentrated at one point, i.e., the apex of the V-shape, so there is a risk of local necking / thinning.

[0004] The present invention is designed based on the above background. Summary of the invention

[0005] In order to solve one or more problems existing in the prior art, the present disclosure proposes a pre-forming mold for a bipolar plate of a fuel cell stack, the pre-forming mold comprising an upper mold part and a lower mold part corresponding to the upper mold part, wherein the lower end surface of the upper mold part comprises at least one convex first arc portion and at least one concave second arc portion, the first arc portion and the second arc portion are alternately connected to form the lower end surface, and the upper end surface of the lower mold part comprises at least one concave third arc portion and at least one convex fourth arc portion, the third arc portion and the fourth arc portion are alternately connected to form the upper end surface, wherein the central angles of the first arc portion, the second arc portion, the third arc portion and the fourth arc portion are equal, and wherein the third arc portion is configured to cooperate with the first arc portion, and the fourth arc portion is configured to cooperate with the second arc portion.

[0006] In one embodiment, the first arc portion and the second arc portion transition smoothly in a tangential manner at a connection point, and the third arc portion and the fourth arc portion transition smoothly in a tangential manner at a connection point.

[0007] In one embodiment, central angles of the first arc portion, the second arc portion, the third arc portion, and the fourth arc portion are 130° to 160°.

[0008] In one embodiment, the radius R3 of the third arc portion is equal to the radius R2 of the second arc portion, the radius R4 of the fourth arc portion is equal to the radius R1 of the first arc portion, and wherein the radius R3 of the third arc portion and the radius R2 of the second arc portion are greater than the radius R4 of the fourth arc portion and the radius R1 of the first arc portion.

[0009] In one embodiment, the lower end surface of the upper mold part includes a plurality of the first arc portions and a plurality of the second arc portions, and the upper end surface of the lower mold part includes a plurality of the third arc portions and a plurality of the fourth arc portions corresponding to the plurality of the first arc portions and the plurality of the second arc portions, respectively.

[0010] In one embodiment, the left side of the lower end surface of the upper mold part terminates at one-half of the second arc portion, and the right side terminates at one-half of the first arc portion, and the left side of the upper end surface of the lower mold part terminates at one-half of the fourth arc portion, and the right side terminates at one-half of the third arc portion.

[0011] The present disclosure also proposes a forming method for a bipolar plate for a fuel cell stack, the forming method comprising a preforming step, in which a preforming mold as described above is used to form a blank into a preformed plate, wherein the preformed plate comprises a circular arc-shaped channel cross-section.

[0012] In one embodiment, the forming method further comprises a second forming step, in which the arc-shaped channel cross section is formed into a trapezoidal cross section with rounded corners.

[0013] In one embodiment, the length of the cross-section of the preformed sheet formed in the preforming step is equal to the designed length of the cross-section of the bipolar plate, and the second forming step only includes pressing out the trapezoidal cross-section at the arc-shaped channel cross-section, but does not include adjusting the length of the cross-section of the preformed sheet.

[0014] In one embodiment, the length of the cross-section of the preformed sheet formed in the preforming step is greater than the designed length of the cross-section of the bipolar plate, and the second forming step includes pressing out the trapezoidal cross-section at the arc-shaped channel cross-section, and adjusting the length of the cross-section of the preformed sheet to the designed length of the cross-section of the bipolar plate.

[0015] The preforming mold and forming method of the bipolar plate for a fuel cell stack according to the present disclosure can effectively avoid the risk of necking, local thinning or even rupture of the formed bipolar plate.

[0016] The above summary of the invention briefly summarizes some embodiments of the present disclosure to provide a basic understanding of some aspects discussed herein. This summary of the invention is not intended to provide a broad overview of the present disclosure, nor is it intended to delimit the scope of the present disclosure. The sole purpose of this summary of the invention is to present some concepts in a simplified form as an introduction to the detailed description presented below. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate specific embodiments of the present disclosure and, together with the general description of the present disclosure given above and the detailed description of the embodiments given below, serve to explain the present disclosure.

[0018] Figure 1 is a cross-sectional view schematically illustrating a prior art bipolar plate, wherein the material in the fillet region of the gas flow channel formed by the bipolar plate is thinned;

[0019] Figure 2 is a cross-sectional view schematically illustrating a preforming step of a bipolar plate in the prior art;

[0020] Figure 3A and Figure 3B is a cross-sectional view schematically illustrating a preforming step of a bipolar plate according to one embodiment of the present disclosure;

[0021] Figure 4 It is a schematic diagram Figure 3A and Figure 3B A cross-sectional view of a detail of the pre-forming die shown in;

[0022] FIG. 5A to FIG. 5D is a cross-sectional view schematically illustrating a second forming step of a bipolar plate according to one embodiment of the present disclosure; and

[0023] FIG. 6A to FIG. 6D is a cross-sectional view schematically illustrating a second forming step of a bipolar plate according to another embodiment of the present disclosure.

[0024] It should be understood that the attached drawings only provide a somewhat simplified representation of various features of the basic principles of the present disclosure. The specific design features disclosed herein (including, for example, the specific size, orientation, location and shape of the various illustrated components) may be determined in part by the specific intended application and use environment. DETAILED DESCRIPTION

[0025] The present disclosure is described below by specific embodiments. It should be understood that specific embodiments are provided only for the purpose of facilitating a thorough understanding of the present disclosure, and are not intended to limit the present disclosure. Therefore, the following embodiments are merely exemplary, and the scope of protection of the present disclosure is limited only by the appended claims.

[0026] The present disclosure adopts a two-step (i.e., a first forming step and a second forming step) forming process to form the bipolar plate of the fuel cell stack. Among them, the first forming step can also be called a pre-forming step, during which the blank is processed into a transition state, which can also be called an intermediate state. Subsequently, in the second forming step, the blank in the transition state is further processed and formed to form a bipolar plate with cathode and anode flow field channels. Compared with the one-time forming process, the forming process of the present disclosure can effectively reduce the stress concentration in the fillet area of ​​the bipolar plate, thereby reducing the risk of necking and rupture. In addition, compared with the multi-step (more than two steps) forming process, the forming process of the present disclosure can reduce the number of stretching processes, thereby improving positioning accuracy and reducing mold costs.

[0027] Hereinafter, a preforming mold and a forming method of a bipolar plate for a fuel cell stack according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

[0028] Figure 3A , Figure 3B and Figure 4 FIG. 1 illustrates a preform mold for a bipolar plate of a fuel cell stack according to an embodiment of the present disclosure. Figure 3A and Figure 3B As shown, the mold 10 includes an upper mold part 101 and a lower mold part 102. Figure 3A In the process, the upper mold part 101 and the lower mold part 102 sandwich the planar blank 20 to prepare for the preforming step. Subsequently, by means of the relative movement of the upper mold part 101 and the lower mold part 102 approaching each other, the planar blank 20 is squeezed or stamped to form a wavy, uneven preformed plate (such as Figure 3BAs shown), for subsequent formation of bipolar plates. The protrusions and recesses in the preformed plate will be used to form airflow channels. The above relative movement can be that the upper mold part 101 remains stationary and the lower mold part 102 moves toward the upper mold part 101; or the lower mold part 102 remains stationary and the upper mold part 101 moves toward the lower mold part 102; or the upper mold part 101 and the lower mold part 102 move toward each other at the same time, which is not limited by the present disclosure.

[0029] Specifically, Figure 4 As shown, the upper mold part 101 is block-shaped as a whole and includes a lower end surface for preforming, that is, a lower end surface for contacting the blank 20. Figure 4 It can be seen from the cross section shown that the lower end surface includes a plurality of first arc portions 101a and a plurality of second arc portions 101b. Among them, the first arc portion 101a is a convex arc portion (i.e., an arc portion protruding toward the outside of the upper mold portion 101), and the second arc portion 101b is a concave arc portion (i.e., an arc portion recessed toward the inside of the upper mold portion 101). In addition, the center angle α of the first arc portion 101a is the same as the center angle α of the second arc portion 101b, while the radius R1 of the first arc portion 101a is different from the radius R2 of the second arc portion 101b, so as to be used for pre-forming bipolar plates with various groove-ridge ratios. Figure 4 In the illustrated embodiment, the radius R1 of the first arc portion 101a is smaller than the radius R2 of the second arc portion 101b. The plurality of first arc portions 101a and the plurality of second arc portions 101b are alternately connected and smoothly transition in a tangential manner at the connection points to form a smooth wavy, undulating profile. Figure 4 In the illustrated embodiment, the left side of the lower end surface ends at one-half of the second arc portion 101 b, and the right side ends at one-half of the first arc portion 101 a. However, the present disclosure is not limited thereto.

[0030] Correspondingly, if Figure 4 As shown, the lower die portion 102 is also block-shaped as a whole and includes an upper end surface for preforming, that is, an upper end surface for contacting the blank 20. Figure 4It can be seen from the cross section shown that the upper end surface includes a plurality of third arc portions 102a and a plurality of fourth arc portions 102b. Among them, the third arc portion 102a is a concave arc portion (i.e., an arc portion that is recessed toward the interior of the lower mold portion 102), and the fourth arc portion 102b is a convex arc portion (i.e., an arc portion that protrudes toward the exterior of the lower mold portion 102). In addition, the center angle α of the third arc portion 102a is the same as the center angle α of the fourth arc portion 102b, while the radius R3 of the third arc portion 102a is different from the radius R4 of the fourth arc portion 102b, so as to be used to form bipolar plates with various groove-ridge ratios. Figure 4 In the illustrated embodiment, the radius R3 of the third arc portion 102a is greater than the radius R4 of the fourth arc portion 102b. Similarly, the third arc portions 102a and the fourth arc portions 102b are alternately connected and smoothly transitioned in a tangential manner at the connection points to form a smooth wavy, undulating profile. Similarly, Figure 4 In the illustrated embodiment, the left side of the upper end surface ends at one-half of the fourth arc portion 102b, and the right side ends at one-half of the third arc portion 102a. However, the present disclosure is not limited thereto.

[0031] When the upper mold part 101 and the lower mold part 102 are arranged relative to each other, the first arc portion 101a is configured to cooperate with the third arc portion 102a, and the second arc portion 101b is configured to cooperate with the fourth arc portion 102b. Since the lower end surface of the upper mold part 101 and the upper end surface of the lower mold part 102 are both formed by the arc portions 101a, 101b, 102a, 102b, the mold 10 can pre-form the blank 20 with a reduced risk of necking and local thinning. Specifically, in Figure 3A After the moment shown, as the upper mold portion 101 and the lower mold portion 102 gradually approach each other, the upper mold portion 101 and the lower mold portion 102 transition from point contact to line contact with the blank 20 (from a three-dimensional perspective, it can also be understood as transitioning from line contact to surface contact). As a result, the stress concentration point of the blank 20 will gradually move from the center to both sides, so that pressure can be evenly applied to the blank 20 to make it uniformly thinner. In addition, the arc portion of the above-mentioned mold 10 is easier for the material of the metal blank 20 to flow and can avoid necking. Finally, as Figure 3B As shown, the die 10 is capable of forming a preformed panel without necking and local thinning.

[0032] Preferably, the radius R3 of the third arc portion 102a of the lower die portion 102 is equal to the radius R2 of the second arc portion 101b, and the radius R4 of the fourth arc portion 102b is equal to the radius R1 of the first arc portion 101a. Thus, the die 10 can preform the blank 20 with a substantially uniform thickness. The substantially uniform thickness is equal to the radius of the concave arc portion minus the radius of the convex arc portion (R2-R1), and therefore, the radii of the concave arc portion and the convex arc portion can be selected based on the thickness of the preformed plate to be formed.

[0033] Those skilled in the art will understand that the number of the first arc portion 101a, the second arc portion 101b, the third arc portion 102a and the fourth arc portion 102b included in the upper mold portion 101 and the lower mold portion 102 can be adjusted according to actual needs. For example, the upper mold portion 101 can include only one first arc portion 101a and one second arc portion 101b, and the lower mold portion 102 can also include only one third arc portion 102a and one fourth arc portion 102b, and the present disclosure is not limited to this.

[0034] Preferably, the center angle α of the first to fourth arc portions 101a, 101b, 102a, 102b is 130° to 160°. Experiments show that using the center angle within the above range is more conducive to material flow and can effectively avoid necking.

[0035] FIG. 3A to FIG. 6D The method for forming a bipolar plate for a fuel cell stack according to an embodiment of the present disclosure is illustrated. As described above, the method includes a preforming step and a second forming step. In the preforming step (e.g. Figure 3A and Figure 3B As shown), the blank 20 is formed into a corrugated preformed panel using the die 10 described in detail above.

[0036] In the second forming step, the preformed plate is processed using a further mold (hereinafter referred to as the second forming mold), the main purpose of which is to reshape the channel cross-sectional shape so as to form the arc-shaped channel cross-sectional shape into a trapezoidal cross-sectional shape with rounded corners. The second forming mold is a forming mold commonly used in the art, which includes an upper mold part and a lower mold part corresponding to the upper mold part. The upper mold part and the lower mold part include features for forming a trapezoidal cross-sectional shape with rounded corners. In order to unnecessarily obscure the focus of the present disclosure, a detailed description of the second forming mold will be omitted in the specification.

[0037] FIG. 5A to FIG. 5D is a cross-sectional view schematically illustrating a second forming step of a bipolar plate according to one embodiment of the present disclosure; and FIG. 6A to FIG. 6Dis a cross-sectional view schematically illustrating a second forming step of a bipolar plate according to another embodiment of the present disclosure.

[0038] exist FIG. 5A to FIG. 5D In one embodiment shown, after the preforming step, the actual length L_true (i.e. Figure 5A The length of the curve of the wavy preformed plate shown in FIG. 1 is substantially equal to the design length L_design of the cross section of the bipolar plate (i.e., the desired length of the cross section of the bipolar plate to be finally formed). Therefore, in the second forming step of this embodiment, as shown in FIG. FIG. 5B to FIG. 5D As shown, it is only necessary to reshape the shape of the channel cross section, that is, to apply pressure through the mold to gradually press out the rounded corner part and the flat part of the trapezoidal cross section shape at the arc part, without adjusting the length of the channel cross section. Therefore, it is only necessary to generate stress in a local area to achieve forming. Therefore, the second forming step according to this embodiment can reduce the rebound effect.

[0039] exist FIG. 6A to FIG. 6D In another embodiment shown, after the preforming step, the actual length L_true (i.e. Fig. 6A The curve length of the wavy preformed plate shown in FIG. 1 is greater than the design length L_design of the cross section of the bipolar plate (i.e., the desired length of the cross section of the bipolar plate to be finally formed). Therefore, in the second forming step of this embodiment, as shown in FIG. FIG. 6B to FIG. 6D As shown, a reverse compressive force is gradually applied to the preformed plate through the mold, so that the preformed plate is subjected to a certain degree of compressive stress at all positions to enter a plastic deformation state. In this process, while reshaping the cross-sectional shape of the channel, that is, pressing out the rounded corners and the plane part of the trapezoidal cross-sectional shape at the arc part, the thickness of the preformed plate increases. Finally, the length of the cross section of the plate is made equal to the designed length of the cross section of the bipolar plate. The second forming step according to this embodiment can reduce the risk of material rebound and thinning, thereby avoiding the warping deformation of the bipolar plate finally formed.

[0040] That is to say, in the preforming step, the blank is processed so that the length of the cross section of the formed preformed plate is not less than the designed length of the cross section of the bipolar plate. Thus, further stretching of the preformed plate in the second forming step can be avoided, thereby avoiding the formation of cracks in the plate, necking / thinning, etc.

[0041] The purpose of the terms used herein is only to describe specific embodiments and is not intended to limit the embodiments of the present disclosure. As used herein, the singular forms of "one", "an" and "said" are intended to include singular and plural forms, and the terms "and" and "or" are each intended to include substitutions and combinations, unless the context otherwise indicates. It can be further understood that the terms "include" or "comprise" are used in this specification to specify the presence of the features, integers, actions, steps, operations, elements or components, but do not exclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components or groups thereof. In addition, when the terms "include", "have", "have", "consist of" or their variants are used in the detailed description or claims, these terms are intended to be inclusive in a manner similar to the term "comprise".

[0042] Although all disclosures have been illustrated by the description of various embodiments, and although these embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such details. Additional advantages and modifications will be readily apparent to those skilled in the art. Therefore, the present disclosure in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Therefore, departures may be made from these details without departing from the spirit or scope of the applicant's general inventive concept.

Claims

1. A preforming mold (10) for a bipolar plate of a fuel cell stack, the preforming mold (10) comprising an upper mold part (101) and a lower mold part (102) corresponding to the upper mold part (101), characterized in that: The lower end surface of the upper mold part (101) includes at least one convex first arc portion (101a) and at least one concave second arc portion (101b), wherein the first arc portion (101a) and the second arc portion (101b) are alternately connected to form the lower end surface, and The upper end surface of the lower mold part (102) includes at least one concave third arc portion (102a) and at least one convex fourth arc portion (102b), and the third arc portion (102a) and the fourth arc portion (102b) are alternately connected to form the upper end surface. The central angles of the first circular arc portion (101a), the second circular arc portion (101b), the third circular arc portion (102a) and the fourth circular arc portion (102b) are equal, and the third circular arc portion (102a) is configured to cooperate with the first circular arc portion (101a), and the fourth circular arc portion (102b) is configured to cooperate with the second circular arc portion (101b).

2. The preforming mold (10) for a bipolar plate of a fuel cell stack according to claim 1, characterized in that: The first arc portion (101a) and the second arc portion (101b) are smoothly transitioned in a tangential manner at a connection point, and the third arc portion (102a) and the fourth arc portion (102b) are smoothly transitioned in a tangential manner at a connection point.

3. The preforming mold (10) for the bipolar plate of a fuel cell stack according to claim 1 or claim 2, characterized in that: The center angles of the first circular arc portion (101a), the second circular arc portion (101b), the third circular arc portion (102a) and the fourth circular arc portion (102b) are in a range of 130° to 160°.

4. The preforming mold (10) for a bipolar plate of a fuel cell stack according to claim 1 or claim 2, characterized in that: The radius R3 of the third circular arc portion (102a) is equal to the radius R2 of the second circular arc portion (101b), and the radius R4 of the fourth circular arc portion (102b) is equal to the radius R1 of the first circular arc portion (101a), and wherein the radius R3 of the third circular arc portion (102a) and the radius R2 of the second circular arc portion (101b) are greater than the radius R4 of the fourth circular arc portion (102b) and the radius R1 of the first circular arc portion (101a).

5. The preforming mold (10) for the bipolar plate of a fuel cell stack according to claim 1 or claim 2, characterized in that: The lower end surface of the upper mold part (101) includes a plurality of the first circular arc parts (101a) and a plurality of the second circular arc parts (101b), and the upper end surface of the lower mold part (102) includes a plurality of the third circular arc parts (102a) and a plurality of the fourth circular arc parts (102b) corresponding to the plurality of the first circular arc parts (101a) and the plurality of the second circular arc parts (101b), respectively.

6. The preforming mold (10) for a bipolar plate of a fuel cell stack according to claim 5, characterized in that: The lower end surface of the upper mold part (101) terminates at one-half of the second arc portion (101b) on the left side and terminates at one-half of the first arc portion (101a) on the right side, and the upper end surface of the lower mold part (102) terminates at one-half of the fourth arc portion (102b) on the left side and terminates at one-half of the third arc portion (102a) on the right side.

7. A method for forming a bipolar plate for a fuel cell stack, the method comprising a preforming step, characterized in that: In the preforming step, the blank (20) is formed into a preformed panel using a preforming die (10) according to any one of claims 1 to 6, wherein the preformed panel comprises a circular arc-shaped channel cross section.

8. The method for forming a bipolar plate for a fuel cell stack according to claim 7, characterized in that: The forming method further comprises a second forming step, in which the arc-shaped channel cross section is formed into a trapezoidal cross section with rounded corners.

9. The method for forming a bipolar plate for a fuel cell stack according to claim 8, characterized in that: The length of the cross section of the preformed plate formed in the preforming step is equal to the designed length of the cross section of the bipolar plate, and The second forming step only includes pressing out the trapezoidal cross section at the arc-shaped channel cross section, but does not include adjusting the length of the cross section of the preformed plate.

10. The method for forming a bipolar plate for a fuel cell stack according to claim 8, characterized in that: The length of the cross section of the preformed plate formed in the preforming step is greater than the designed length of the cross section of the bipolar plate, and The second forming step includes pressing out the trapezoidal cross section at the arc-shaped channel cross section, and adjusting the length of the cross section of the preformed plate to the designed length of the cross section of the bipolar plate.

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