A method for designing molds for fuel cell molding graphite plates to mitigate springback effects

Abstract

This invention discloses a method for designing molds for fuel cell molded graphite plates to mitigate the effects of springback. First, a springback characteristic is initially understood using an easily machinable and low-cost aluminum mold. Then, by measuring and calculating the expansion characteristics of flexible graphite, corresponding compensation designs are made for each part of the graphite plate, resulting in the fabrication of the appropriate graphite plate mold. If the fuel cell graphite plate still does not meet tolerance requirements after molding, a method for modifying the mold is also provided. Finally, a graphite plate mold that meets the requirements is designed, solving the problem of large deviations between the actual and design dimensions of existing fuel cell flexible graphite plates after molding.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a method for designing a mold for fuel cell molding graphite plates to mitigate the effects of springback. Background Technology

[0002] In fuel cells, bipolar plates are crucial components, separating fuel and oxidant, providing flow channels for hydrogen and oxygen, and serving as the medium for current conduction. Currently, graphite bipolar plates for proton exchange membrane fuel cells are commonly mass-produced using flexible graphite plate molding. For example, patent application CN112590263A discloses a method for preparing air-cooled molded graphite bipolar plates. This method allows for mass production using multiple first and second molds, effectively improving processing efficiency and reducing manufacturing costs. Furthermore, the resulting bipolar plates exhibit good flexibility, resilience, and plasticity, preventing brittle fracture and facilitating assembly.

[0003] However, because flexible graphite bipolar plates spring back after molding and demolding, the molded graphite plates generally have a larger width in the middle and a smaller width at both ends. The dimensions of the processed graphite plates are prone to exceed the tolerance requirements, which affects the flow channel matching of the cathode and anode plates of the fuel cell stack and the assembly of the fuel cell stack.

[0004] Patent application CN117895008A discloses a flexible graphite bipolar plate and its preparation method. This application describes a process where a graphite preform is immersed in a resin solution for a first vacuum impregnation followed by molding, then cured under heat and pressure, and finally subjected to a second vacuum impregnation after curing. By controlling the conditions of each step, the resulting flexible graphite bipolar plate can be made to prevent springback after demolding, maintaining a warpage between 0.94% and 1.2%. However, conventional flexible graphite plate manufacturing processes still need to address the issue of dimensional springback after demolding. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for designing molds for fuel cell molded graphite plates to mitigate the impact of springback. By fully considering the springback characteristics of expanded graphite during the mold design stage, the method solves the problem of large deviations between the actual and designed dimensions of the molded flexible graphite plates.

[0006] The graphite plate molded by this invention has an overall rectangular plate structure and flow channels on its surface. The mold design method for fuel cell molded graphite plates to reduce the impact of springback provided by this invention includes the following steps:

[0007] (1) A low-cost and easy-to-manufacture aluminum mold is made according to the design dimensions of the fuel cell molded graphite plate, wherein the thickness of the fuel cell molded graphite plate is H, the width is W, the length is L, and the flow channel depth is C.

[0008] (2) Use the aluminum mold made in step (1) to mold the fuel cell molded graphite plate. Select different positions to measure different thickness data and calculate the average thickness H1; select different positions to measure different width data and calculate the average width W1; select different positions to measure different length data and calculate the average length L1; select multiple flow channels to measure the flow channel depth and calculate the average depth C1.

[0009] (3) Calculate the compensation factor and thickness compensation factor S based on the springback characteristics. ΔH1 = (H1-H) / H, Width compensation factor S ΔW1 = (W1-W) / W, length compensation factor S ΔL1 = (L1-L) / L, Flow channel depth compensation factor S Δc1 = (C-C1) / C;

[0010] (4) Based on the compensation factor calculated in step (3), redesign and manufacture a new aluminum mold. The thickness of the fuel cell molded graphite plate corresponding to the new aluminum mold is h1 = H / (1+S). ΔH1 The width is w1 = W / (1 + S). ΔW1 The length is l1 = L / (1 + S). ΔL1 The channel depth is c1 = C / (1-S). ΔC1 );

[0011] (5) Use the new aluminum mold made in step (4) to mold the fuel cell molded graphite plate. Select different positions to measure different thickness data and calculate the average thickness H2; select different positions to measure different width data and calculate the average width W2; select different positions to measure different length data and calculate the average length L2; select multiple flow channels to measure the flow channel depth and calculate the average depth C2.

[0012] (6) Compare the deviations between the values ​​of H2, W2, L2, C2 and the design dimensions H, W, L, C. If they meet the tolerance requirements, use the design dimensions h1, w1, l1, c1 to make a fuel cell molded graphite plate mold that meets the design requirements.

[0013] Furthermore, in step (2), the molding pressure during the molding of fuel cell molded graphite plates is 200-300T (tons), and the vacuum degree is ≤50mbar.

[0014] Furthermore, in steps (2) and (5), the locations selected for measuring and calculating the average thickness are: at least one point at the center of the active area of ​​the graphite plate, at least eight points at the edge of the active area, and at least four points at the edge of the graphite plate. This selection of points can uniformly represent the change in the thickness of the active area, while also taking into account the dimensional rebound at the edge of the graphite plate.

[0015] Furthermore, in steps (2) and (5), the location selected for measuring and calculating the average width is: one point at the center of the active area of ​​the graphite plate, and measurement points are selected symmetrically at equal intervals based on this point, with an interval of no more than 20 mm. This selection of points can more accurately reflect the changes in the width of the graphite plate, and the smaller the interval, the more accurate the average width.

[0016] Furthermore, in steps (2) and (5), the location selected for measuring and calculating the average length is: one point at the center of the active area of ​​the graphite plate, and measurement points are selected symmetrically at equal intervals based on this point, with an interval of no more than 20 mm. This selection of points can more accurately reflect the change in the length of the graphite plate, and the smaller the interval, the more accurate the average length.

[0017] Furthermore, in steps (2) and (5), the locations selected for measuring and calculating the average depth are: at least one point at the center of the active area of ​​the graphite plate and at least eight points at the edge of the active area. This selection of points can uniformly represent the change in the flow channel depth of the active area and more accurately calculate the degree of dimensional springback.

[0018] Furthermore, in step (6), the fuel cell molding graphite plate mold that meets the design requirements is a steel mold that is not easily deformed after heat treatment. Generally, high-precision mold steel Cr12MoV is used, while aluminum molds are used in the design stage to save costs.

[0019] Furthermore, the tolerance requirements in step (6) are: the dimensional tolerances of the graphite plate length and width are less than or equal to 0.5 mm; the dimensional tolerances of the graphite plate thickness and channel depth are less than or equal to 0.05 mm.

[0020] Furthermore, in step (6), if the deviations between the values ​​of H2, W2, L2, and C2 and the design dimensions H, W, L, and C do not meet the tolerance requirements, then the corresponding compensation factor is calculated: thickness compensation factor S. ΔH2 = (H2-H) / H, Width compensation factor S ΔW2 = (W2-W) / W, length compensation factor S ΔL2 = (L2-L) / L, Flow channel depth compensation factor S Δc2 = (C-C2) / C;

[0021] Based on the recalculated compensation factor, a new aluminum mold was redesigned and manufactured. The thickness of the fuel cell molded graphite plate corresponding to the new aluminum mold is h2 = h1 / (1+S). ΔH2 The width is w2 = w1 / (1 + S). ΔW2 The length is l2 = l1 / (1 + S). ΔL2 The channel depth is c2 = c1 / (1-S). ΔC2 Based on the compensation, the mold is repaired or redeveloped. The mold is continuously iterated in this way to finally obtain a fuel cell molded graphite plate mold that meets the design requirements.

[0022] The beneficial effects of this invention are as follows: This invention provides a method for designing molds for fuel cell molded graphite plates to mitigate the effects of springback. First, using an easily machinable and low-cost aluminum mold, the springback characteristics are initially understood. Then, by measuring and calculating the expansion characteristics of flexible graphite, corresponding compensation designs are made for each part of the graphite plate, resulting in the fabrication of the appropriate graphite plate mold. If the fuel cell graphite plate still does not meet tolerance requirements after molding, a method for correcting the mold is also provided. This method ultimately designs a graphite plate mold that meets the requirements, solving the problem of large deviations between the actual and design dimensions of existing fuel cell flexible graphite plates after molding. Attached Figure Description

[0023] Figure 1 A simplified diagram of the design features of a graphite plate is provided in one embodiment of the present invention.

[0024] Figure 2 A simplified diagram of the design features of an aluminum mold is provided in one embodiment of the present invention.

[0025] Figure 3 This invention provides a schematic diagram of a graphite plate molded with an aluminum mold in one embodiment.

[0026] Figure 4 A schematic diagram of a newly designed steel mold cavity is provided in one embodiment of the present invention.

[0027] Figure 5 This is a schematic diagram of the model modification after the next iteration.

[0028] Figure 6 This is a schematic diagram showing the location for measuring the thickness of a graphite plate.

[0029] Figure 7 This is a schematic diagram showing the location for measuring the width of a graphite plate.

[0030] Figure 8 This is a schematic diagram showing the location for measuring the length of a graphite plate.

[0031] Figure 9 This is a schematic diagram showing the location for measuring the depth of a graphite plate. Detailed Implementation

[0032] In practice, the fuel cell molded graphite plate mold design method for mitigating springback provided by this invention specifically includes the following steps:

[0033] (1) An aluminum mold is made according to the design dimensions of the fuel cell molded graphite plate, wherein the thickness of the fuel cell molded graphite plate is H, the width is W, the length is L, and the flow channel depth is C.

[0034] (2) Using the aluminum mold made in step (1), fuel cell molded graphite plates are produced by molding under pressure of 200-300T and vacuum degree ≤50mbar.

[0035] Different thickness data were measured at different locations, and the average thickness H1 was calculated. The selected locations were: at least 1 point at the center of the active area of ​​the graphite plate, at least 8 points at the edge of the active area, and at least 4 points at the edge of the graphite plate.

[0036] Different width data were measured at different locations, and the average width W1 was calculated. The selected location was one point at the center of the active area of ​​the graphite plate, and measurement points were selected symmetrically at equal intervals based on this point, with an interval of no more than 20mm.

[0037] Different lengths of data were measured at different locations, and the average length L1 was calculated. The selected location was one point at the center of the active area of ​​the graphite plate, and measurement points were selected symmetrically at equal intervals based on this point, with an interval of no more than 20 mm.

[0038] Multiple flow channels were selected to measure the flow channel depth, and the average depth C1 was calculated. The selected locations were: at least one point at the center of the active area of ​​the graphite plate and at least eight points at the edge of the active area.

[0039] (3) Calculate the compensation factor and thickness compensation factor S based on the springback characteristics. ΔH1 = (H1-H) / H, Width compensation factor S ΔW1 = (W1-W) / W, length compensation factor S ΔL1 = (L1-L) / L, Flow channel depth compensation factor S Δc1 = (C-C1) / C.

[0040] (4) Based on the compensation factor calculated in step (3), redesign and manufacture a new aluminum mold. The thickness of the fuel cell molded graphite plate corresponding to the new aluminum mold is h1=H / (1+S) ΔH1 The width is w1 = W / (1 + S). ΔW1 The length is l1 = L / (1 + S). ΔL1 The channel depth is c1 = C / (1-S). ΔC1 ).

[0041] (5) Use the new aluminum mold made in step (4) to produce fuel cell molded graphite plates. Select different positions according to the above method, and measure and calculate the average thickness H2, average width W2, average length L2 and average depth C2.

[0042] (6) Compare the deviations of the values ​​of H2, W2, L2, and C2 with the design dimensions H, W, L, and C. If they meet the tolerance requirements (the dimensional tolerances of the graphite plate length and width are less than or equal to 0.5 mm; the dimensional tolerances of the graphite plate thickness and flow channel depth are less than or equal to 0.05 mm), then use the design dimensions h1, w1, l1, and c1 to manufacture a fuel cell molding graphite plate mold that meets the design requirements, while simultaneously constraining the mold.

[0043] If the values ​​of H2, W2, L2, and C2 do not meet the tolerance requirements of the design dimensions H, W, L, and C, then the corresponding compensation factor, thickness compensation factor S, is calculated. ΔH2 = (H2-H) / H, Width compensation factor S ΔW2 = (W2-W) / W, length compensation factor S ΔL2 = (L2-L) / L, Flow channel depth compensation factor S Δc2 = (C-C2) / C.

[0044] Based on the recalculated compensation factor, a new aluminum mold was redesigned and manufactured. The thickness of the fuel cell molded graphite plate corresponding to the new aluminum mold is h2=h1 / (1+S) ΔH2 The width is w2 = w1 / (1 + S). ΔW2 The length is l2 = l1 / (1 + S). ΔL2 The channel depth is c2 = c1 / (1-S). ΔC2 Based on the compensation, the mold is repaired or redeveloped to ultimately obtain a fuel cell molded graphite plate mold that meets the design requirements. The final mold that meets the design requirements is made of heat-treated steel that is not easily deformed.

[0045] Example 1

[0046] Reference Figure 1-9 As shown, this embodiment provides a method for designing a mold for a fuel cell molded graphite plate to mitigate the effects of springback. The method mainly includes the following steps:

[0047] S100. Based on the original design of the graphite plate dimensions: thickness H = 0.8mm, width W = 100mm, length L = 400mm, and runner depth C = 0.4mm, design the basic dimensions of a low-cost and easy-to-manufacture aluminum mold (soft mold). The cavity thickness of this aluminum mold is 0.8mm, the width is 100mm, and the length is 400mm. Since the runner depth of the graphite plate corresponds to the runner ridge height of the mold, the runner ridge height of this aluminum mold is 0.4mm.

[0048] S200, with a density of 70 mg / cm³ 2 The graphite plate was molded using the aluminum mold prepared in step S1 under a pressure of 200T and a vacuum degree of less than 50mbar. The molded graphite plate exhibited a phenomenon of being narrow at both ends and wide in the middle, as shown in the image. Figure 3 As shown.

[0049] like Figure 6 As shown, one point at the center of the active area of ​​the graphite plate, eight points at the edge of the active area, and four points at the edge of the graphite plate were uniformly selected as test points to obtain the average thickness of the graphite plate H1 = 0.85 mm. Due to the rebound characteristics of expanded graphite, this value is greater than the design value of 0.8 mm for the graphite plate, with a deviation of 0.05 mm.

[0050] like Figure 7 As shown, a point is selected at the center of the active area of ​​the graphite plate, and measurement points are selected symmetrically at equal intervals based on this point. The interval between the measurement points is 20mm. The average width of the graphite plate, W1, is obtained as 101.5mm. Due to the rebound characteristics of expanded graphite, this value is greater than the design value of 100mm for the width of the graphite plate, with a deviation of 1.5mm.

[0051] like Figure 8 As shown, a point is selected at the center of the active area of ​​the graphite plate, and measurement points are selected symmetrically at equal intervals based on this point. The interval between the measurement points is 20mm. The average length value of the graphite plate is obtained as L1 = 400.5mm. The deviation of this value from the design length value of 400mm is 0.5mm.

[0052] like Figure 9 As shown, one point at the center of the active area of ​​the graphite plate and eight points at the edge of the active area were selected evenly to measure the depth of the flow channel. The average depth data of the flow channel was obtained as C1 = 0.36 mm. The deviation of this value from the depth design value of 0.4 mm is -0.04 mm.

[0053] S300. Based on the springback characteristics, calculate the compensation factor: thickness compensation factor S. ΔH1 =(H1-H) / H=0.0375, Width compensation factor S ΔW1 = (W1-W) / W = 0.015, length compensation factor S ΔL1= (L1-L) / L = 0.00125, Flow channel depth compensation factor S Δc1 = (C-C1) / C = 0.1.

[0054] S400. Based on the compensation factor calculated in step S3, redesign and manufacture a new aluminum mold. The cavity thickness parameter of the new aluminum mold is designed as h1=H / (1+S ΔH1 ) = 0.771mm, the mold width is designed as w1 = W / (1+S) ΔW1 The diameter of the mold is 98.522 mm, and the mold length is designed as l1 = L / (1+S). ΔL1 =399.501mm, the mold runner ridge height is designed as c1 = C / (1-S) ΔC1 = 0.444 mm.

[0055] S500. Use the redesigned mold to produce graphite plates. Select test points according to the method in S2 to obtain the average thickness H2 = 0.81 mm, the average width W2 = 99.85 mm, the average length L2 = 400.10 mm, and the average channel depth C2 = 0.41 mm.

[0056] S600. Comparing the measured values ​​with the design values, the thickness deviation of the graphite plate after molding with the new mold is H2-H=0.01mm, which is less than the predetermined tolerance of 0.05mm; the width deviation is W2-W=-0.15mm, which is less than the predetermined tolerance of 0.5mm; the length deviation is L2-L=0.1mm, which is less than the predetermined tolerance of 0.5mm; and the runner depth deviation is C-C2=0.01mm, which is less than the predetermined tolerance of 0.05mm. Considering other characteristic requirements, the mold is deemed to meet the requirements, and the dimensional deviations are significantly less than those after the first molding. Therefore, the iterative mold modification is terminated.

[0057] Finally, a steel mold for flexible graphite plates that meets the requirements was obtained, and graphite plates that meet the tolerance requirements were pressed, thus solving the problem of large dimensional deviations caused by springback after molding of flexible graphite plates.

Claims

1. A method for designing a mold for a fuel cell molded graphite plate to mitigate the effect of springback, wherein the fuel cell molded graphite plate is generally a rectangular plate structure with flow channels on its surface, characterized in that... The fuel cell molded graphite plate mold design method includes the following steps: (1) An aluminum mold is made according to the design dimensions of the fuel cell molded graphite plate, wherein the thickness of the fuel cell molded graphite plate is H, the width is W, the length is L, and the flow channel depth is C. (2) Use the aluminum mold made in step (1) to mold the fuel cell molded graphite plate. Select different positions to measure different thickness data and calculate the average thickness H1; select different positions to measure different width data and calculate the average width W1; select different positions to measure different length data and calculate the average length L1; select multiple flow channels to measure the flow channel depth and calculate the average depth C1. (3) Calculate the compensation factor and thickness compensation factor S based on the springback characteristics. ΔH1 = (H1-H) / H, Width compensation factor S ΔW1 = (W1-W) / W, length compensation factor S ΔL1 = (L1-L) / L, Flow channel depth compensation factor S Δc1 = (C-C1) / C; (4) Based on the compensation factor calculated in step (3), redesign and manufacture a new aluminum mold. The thickness of the fuel cell molded graphite plate corresponding to the new aluminum mold is h1 = H / (1+S). ΔH1 The width is w1 = W / (1 + S). ΔW1 The length is l1 = L / (1 + S). ΔL1 The channel depth is c1 = C / (1-S). ΔC1 ); (5) Use the new aluminum mold made in step (4) to mold the fuel cell molded graphite plate. Select different positions to measure different thickness data and calculate the average thickness H2; select different positions to measure different width data and calculate the average width W2; select different positions to measure different length data and calculate the average length L2; select multiple flow channels to measure the flow channel depth and calculate the average depth C2. (6) Compare the deviations between the values ​​of H2, W2, L2, C2 and the design dimensions H, W, L, C. If they meet the tolerance requirements, use the design dimensions h1, w1, l1, c1 to make a fuel cell molded graphite plate mold that meets the design requirements.

2. The fuel cell molded graphite plate mold design method for mitigating springback as described in claim 1, characterized in that, In step (2), the molding pressure during the molding of fuel cell molded graphite plates is 200-300T, and the vacuum degree is ≤50mbar.

3. The fuel cell molded graphite plate mold design method for mitigating springback as described in claim 1, characterized in that, In steps (2) and (5), the locations selected for measuring and calculating the average thickness are: at least one point at the center of the active area of ​​the graphite plate, at least eight points at the edge of the active area, and at least four points at the edge of the graphite plate.

4. The fuel cell molded graphite plate mold design method for mitigating springback as described in claim 1, characterized in that, In steps (2) and (5), the selected position for measuring and calculating the average width is: one point at the center of the active area of ​​the graphite plate, and measurement points are selected symmetrically at equal distances based on this point, with an interval of no more than 20 mm.

5. The fuel cell molded graphite plate mold design method for mitigating springback as described in claim 1, characterized in that, In steps (2) and (5), the location selected for measuring and calculating the average length is: one point at the center of the active area of ​​the graphite plate, and measurement points are selected symmetrically at equal intervals based on this point, with an interval of no more than 20 mm.

6. The fuel cell molded graphite plate mold design method for mitigating springback as described in claim 1, characterized in that, In steps (2) and (5), the locations selected for measuring and calculating the average depth are: at least one point at the center of the active area of ​​the graphite plate and at least eight points at the edge of the active area.

7. The fuel cell molded graphite plate mold design method for mitigating springback as described in claim 1, characterized in that, In step (6), the fuel cell molding graphite plate mold that meets the design requirements is a steel mold.

8. The fuel cell molded graphite plate mold design method for mitigating springback as described in claim 1, characterized in that, The tolerance requirements in step (6) are: the dimensional tolerances of the graphite plate length and width are less than or equal to 0.5 mm; the dimensional tolerances of the graphite plate thickness and channel depth are less than or equal to 0.05 mm.

9. The fuel cell molded graphite plate mold design method for mitigating springback as described in claim 1, characterized in that, In step (6), if the deviations between the values ​​of H2, W2, L2, and C2 and the design dimensions H, W, L, and C do not meet the tolerance requirements, then the corresponding compensation factors are calculated, including the thickness compensation factor S. ΔH2 = (H2-H) / H, Width compensation factor S ΔW2 = (W2-W) / W, length compensation factor S ΔL2 = (L2-L) / L, Flow channel depth compensation factor S Δc2 = (C-C2) / C; Based on the recalculated compensation factor, a new aluminum mold was redesigned and manufactured. The thickness of the fuel cell molded graphite plate corresponding to the new aluminum mold is h2 = h1 / (1+S). ΔH2 The width is w2 = w1 / (1 + S). ΔW2 The length is l2 = l1 / (1 + S). ΔL2 The channel depth is c2 = c1 / (1-S). ΔC2 Based on the compensation, the mold is repaired or redeveloped to finally obtain a fuel cell molded graphite plate mold that meets the design requirements.

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