Solid oxide fuel cell bipolar plate forming process optimization method

Abstract

The invention discloses a solid oxide fuel cell bipolar plate forming process optimization method, and belongs to the technical field of fuel cell bipolar plate process optimization. The method comprises the following steps: establishing a bipolar plate stress-strain constitutive model based on a scale effect generated by plate thickness and grain size change; establishing a bipolar plate stamping finite element model, and setting structural parameters, material attribute parameters and grain parameters of the bipolar plate to obtain a bipolar plate stamping forming prediction model based on a scale effect generated by plate thickness and grain size changes; on the basis of the established bipolar plate stamping forming prediction model, numerical simulation is conducted on the bipolar plate stamping forming process, the influence rule of stamping process parameters and bipolar plate mold parameters on the filling depth and the thinning rate is analyzed, and the parameter range capable of enabling the filling depth to meet the requirement and avoiding tearing in the forming process is obtained. The bipolar plate stamping forming prediction model can accurately simulate the real stamping process so as to optimize the bipolar plate forming process.

Description

Technical Field

[0001] The present invention relates to the technical field of solid oxide fuel cell bipolar plate forming, and in particular to a method for optimizing the forming process of a solid oxide fuel cell bipolar plate. Background Art

[0002] Solid oxide fuel cell (SOFC) can directly convert chemical energy into electrical energy, and its energy conversion efficiency is high. The power generation efficiency can reach up to 74%, which is far higher than proton membrane fuel cell (45~55%) and phosphoric acid fuel cell (37~42%). At the same time, the reaction product is water, without CO2 and NO. x The metal bipolar plate is one of the core components of SOFC, which plays the role of connecting battery cells in series and parallel, isolating fuel gas and air, and supporting. It accounts for 60% of the volume and is the key to ensuring the functionality of the battery stack. Bipolar plate manufacturing is a high-precision forming process from ultra-thin metal plates (0.05~0.1mm) to complex multi-channel structures. Among them, stamping is more competitive in terms of cost, productivity, and bipolar plate forming effect. The factors affecting stamping forming mainly include the following two aspects: First, the complex and changeable internal stress in the stamping forming process leads to defects such as springback, wall thickness reduction, and dimensional error in the metal bipolar plate, which is an important reason for the frequent failure accidents such as corrosion, high-temperature creep and fatigue of the bipolar plate during service, and becomes a key link in the quality control of the bipolar plate; especially for the ultra-thin metal plate formed by rolling, that is, the thickness of the plate does not exceed 0.1mm, and there are often only dozens of grains in the thickness direction. The difference in grain size and orientation leads to anisotropy, which aggravates the complexity of the internal stress of the ultra-thin plate; second, the stamping process parameters and stamping die parameters directly affect the bipolar plate forming process. If the parameters do not match, it is easy to cause tearing during the stamping process. At present, before the bipolar plate is stamped, a numerical simulation method is usually used to simulate the stamping deformation process of the bipolar plate model to guide the bipolar plate structure design. Among them, the material stress-strain constitutive equation can better describe the deformation behavior in the finite element simulation, but the existing stress-strain constitutive model does not consider the influence of the scale effect caused by the thickness and grain size changes of the ultra-thin plate, which often leads to excessive stress in the numerical simulation process, affecting the accuracy of the numerical simulation of stamping.

[0003] Based on this, the present invention proposes a calculation method for the stress-strain constitutive model of ultra-thin plates that takes into account the scale effects caused by changes in plate thickness and grain size, and optimizes the solid oxide fuel cell bipolar plate forming process based on the established stress-strain constitutive model that takes into account the scale effects caused by changes in plate thickness and grain size. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for optimizing the forming process of a solid oxide fuel cell bipolar plate, and optimizes the forming process of a solid oxide fuel cell bipolar plate based on an established stress-strain constitutive model that considers the scale effect caused by changes in plate thickness and grain size.

[0005] The technical solution adopted by the present invention is: The present invention provides a method for optimizing a forming process of a bipolar plate for a solid oxide fuel cell, comprising the steps of: S1. Establish a stress-strain constitutive model of bipolar plates based on the scale effect caused by changes in plate thickness and grain size; S2. Using finite element software to establish a bipolar plate stamping finite element model, introducing the stress-strain constitutive model of the bipolar plate established in step S1, and setting the structural parameters, material property parameters and grain parameters of the bipolar plate, to obtain a bipolar plate stamping prediction model based on the scale effect caused by changes in plate thickness and grain size; S3. Based on the bipolar plate stamping forming prediction model established in step S2, the bipolar plate stamping forming process is numerically simulated, and the influence of the stamping process parameters and the bipolar plate mold parameters on the filling depth and thinning rate of the bipolar plate is analyzed to obtain the parameter range that can make the channel depth meet the requirements and no tearing occurs during the forming process.

[0006] Furthermore, the step S1 is specifically as follows: S11. Based on the composite model, the flow stress of a single grain is divided into two parts: the grain interior and the grain boundary. and grain boundary flow stress The flow stress of a single grain ; S12. Based on the surface layer model, the flow stress of the bipolar plate material is divided into two parts: the internal part and the surface part. and surface flow stress Flow stress of bipolar plate materials ; S13. Considering the influence of the scale effect caused by the change of plate thickness and grain size on the internal stress of the bipolar plate material, the flow stress of the bipolar plate material is Divided into flow stress dominated by plate thickness and grain size-dominated flow stress , a stress-strain constitutive model of bipolar plates is established based on the scale effect caused by changes in plate thickness and grain size.

[0007] Furthermore, the flow stress of the grains in step S11 The calculation formula is: ; The flow stress of the bipolar plate material in step S12 The calculation formula is: ; Right now: ; in: ; ; ; That is, we get: ; In the formula, is the flow stress of a single grain, is the intragranular flow stress of a single grain, is the grain boundary flow stress of a single grain, is the volume fraction inside the grain, is the flow stress of the bipolar plate material, is the internal flow stress of the bipolar plate material, is the surface flow stress of the bipolar plate material, is the ratio of the number of grains inside the bipolar plate material, is the grain boundary layer thickness; is the average grain size, is the number of grains inside the bipolar plate material, is the number of grains on the surface of the bipolar plate material, and is a constant for a specific material.

[0008] Furthermore, the bipolar plate stress-strain constitutive model based on the scale effect caused by the change of plate thickness and grain size established in step S13 is: ; in: ; ; ; ; ; ; ; In the formula, is the flow stress dominated by the grain size, is the flow stress dominated by the plate thickness, is the proportional factor of grain size in the scale effect caused by the change of grain size and plate thickness, and They represent the influencing factors of the scale effect caused by the change of grain size and plate thickness, , are the intragranular flow stress and grain boundary flow stress of a single grain dominated by grain size, , are the intragranular flow stress and grain boundary flow stress of a single grain dominated by plate thickness, is the yield strength dominated by the grain size, is the yield strength dominated by plate thickness, is the average grain size, is the bipolar plate thickness, , , , is the fitting parameter, is the ratio of the number of grains inside the bipolar plate material, and is a constant for a specific material.

[0009] Furthermore, the intragranular flow stress of a single grain is dominated by the grain size. and grain boundary flow stress By substituting the data in the true stress-strain curves Ⅰ-1 and Ⅰ-2 of two bipolar plate samples with the same plate thickness and different average grain sizes into the flow stress of the bipolar plate material in step S12, The calculation formula of is solved together to obtain; Intragranular flow stress of a single grain dominated by plate thickness and grain boundary flow stress By substituting the data in the true stress-strain curves II-1 and II-2 of two bipolar plate samples with the same average grain size and different plate thickness into the flow stress of the bipolar plate material in step S12, The calculation formula of is solved jointly to obtain it.

[0010] Furthermore, the material property parameters in step S2 include elastic modulus, yield strength, and Poisson's ratio, and the elastic modulus and yield strength are obtained through a uniaxial tensile test.

[0011] Furthermore, the grain parameters in step S2 include an average grain size, and the grain parameters are obtained by testing the bipolar plate material using an EBSD electron microscope.

[0012] Furthermore, in step S3, the geometric parameters of the bipolar plate mold include draft angle, fillet radius, channel width, channel depth, and rib width.

[0013] Furthermore, the stamping process parameters in step S3 include stamping speed and stamping pressure.

[0014] The beneficial effects of the present invention are: The present invention first establishes an ultra-thin plate stress-strain constitutive model that takes into account the scale effect caused by changes in plate thickness and grain size, and then optimizes the solid oxide fuel cell bipolar plate forming process based on the established stress-strain constitutive model that takes into account the scale effect caused by changes in plate thickness and grain size. The present invention can more accurately simulate the bipolar plate stamping process, obtain more accurate bipolar plate mold structure parameter range and stamping process parameter range, and provide theoretical guidance for bipolar plate stamping. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 is a flow chart of the present invention; Figure 2 It is a stress cloud diagram of numerically simulating a uniaxial tensile test using a traditional stress-strain constitutive model and a stress-strain constitutive model established by the present invention; Figure 3 The stress-strain curve obtained by numerically simulating a uniaxial tensile test using a conventional stress-strain constitutive model and the stress-strain constitutive model established by the present invention, and the real stress-strain curve obtained by a real uniaxial tensile test; Figure 4 It is a three-channel two-dimensional model of a bipolar plate established in finite element software; Figure 5 Response surface diagram of different bipolar plate mold geometric parameters on thinning rate; (a) is the response surface of draft angle and fillet radius on thinning rate, (b) is the response surface of channel depth and draft angle on thinning rate, (c) is the response surface of channel depth and channel width on thinning rate, (d) is the response surface of channel depth and fillet radius on thinning rate, (e) is the response surface of rib width and fillet radius on thinning rate; Figure 6 Response surface diagram of different bipolar plate mold geometric parameters to filling depth; (a) is the response surface of fillet radius and draft angle to filling depth; (b) is the response surface of fillet radius and channel width to filling depth; (c) is the response surface of fillet radius and rib width to channel depth; Figure 7It is the pressure load curve of the upper surface of the bipolar plate during the stamping process at different stamping speeds. DETAILED DESCRIPTION

[0017] The present invention provides a method for optimizing the forming process of a bipolar plate for a solid oxide fuel cell. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] The present invention is described in detail below with reference to the accompanying drawings.

[0019] Reference Figure 1 This embodiment provides a method for optimizing the forming process of a solid oxide fuel cell bipolar plate, comprising the steps of: S1. Establish a stress-strain constitutive model of bipolar plates based on the scale effect caused by changes in plate thickness and grain size; S2. Using finite element software to establish a bipolar plate stamping finite element model, introducing the stress-strain constitutive model of the bipolar plate established in step S1, and setting the structural parameters, material property parameters and grain parameters of the bipolar plate, to obtain a bipolar plate stamping prediction model based on the scale effect caused by changes in plate thickness and grain size; S3. Based on the bipolar plate stamping forming prediction model established in step S2, the bipolar plate stamping forming process is numerically simulated, and the influence of the stamping process parameters and the bipolar plate mold parameters on the filling depth and thinning rate of the bipolar plate is analyzed to obtain the parameter range that can make the channel depth meet the requirements and no tearing occurs during the forming process.

[0020] Specifically, the above step S1 includes the following steps: S11. Based on the composite model, the flow stress of a single grain is divided into two parts: the grain interior and the grain boundary. and grain boundary flow stress Flow stress of the grains ; S12. Based on the surface layer model, the flow stress of the bipolar plate material is divided into two parts: the internal part and the surface part. and surface flow stress Flow stress of bipolar plate materials , and the internal flow stress of the bipolar plate material Equal to the flow stress of the grain , bipolar plate material surface flow stress Equal to the flow stress inside the grain ; S13. Considering the influence of the scale effect caused by the change of plate thickness and grain size on the internal stress of the bipolar plate material, the flow stress of the bipolar plate material is Divided into flow stress dominated by plate thickness and grain size-dominated flow stress , and the stress-strain constitutive model of the bipolar plate based on the scale effect caused by the changes in plate thickness and grain size is obtained.

[0021] More specifically, the calculation process of the bipolar plate stress-strain constitutive model based on the scale effect caused by the change of plate thickness and grain size obtained in the above step S1 is: First, a composite model is introduced to assume that a single grain consists of a hard grain boundary region and a soft grain interior region, and the flow stress of a single grain is It is expressed as: (1); In the formula, is the flow stress of a single grain, is the intragranular flow stress of a single grain, is the grain boundary flow stress of a single grain, is the volume fraction inside the grain; Assuming the average grain size is The thickness of the grain boundary layer is , the relationship between the two is described as follows: (2); In the formula, and are constants of specific materials. In this embodiment, they are material constants of stainless steel 304 used for the bipolar plate, and are 0.133 and 0.7 respectively; Using an equivalent sphere to replace the grain, the grain size is equal to the equivalent sphere diameter, and the volume of a single grain can be obtained as: (3); have to for: (4); The flow stress of the grain It can be expressed as: (5); Secondly, the surface model is introduced to assume that the material is composed of internal grains and surface grains, and the flow stress of the material is divided into two parts: internal and surface, namely: (6); In the formula, is the flow stress of the bipolar plate material, is the internal flow stress of the bipolar plate material, is the surface flow stress of the bipolar plate material, is the ratio of the number of grains inside the bipolar plate material; Internal flow stress of the above bipolar plate materials Available Indicates that the surface grain boundary strengthening effect is ignored at this time; the surface flow stress of the bipolar plate material Equal to the flow stress inside the grain, it can be used It means that: (7); Since the bipolar plate material used is a plate-shaped sample, its overall volume is obtained as: (8); In the formula, is the length of the short side, is the length of the long side, is the plate thickness; The surface of the bipolar plate material is approximated to half of the average grain size of the material, and the grains are evenly arranged spheres. The number of surface grains can be calculated as: (9); (10); (11); (12); (13); In the formula, , , are the approximate number of grains on the three types of surfaces of the bipolar plate material (i.e., upper and lower surfaces, left and right surfaces, and front and back surfaces), is the number of grains on the surface of the bipolar plate material; The number of grains inside the bipolar plate material is: (14); (15); In the formula, is the number of grains inside the bipolar plate material, is the volume of the bipolar plate material after removing the surface layer; Calculated by the number of grains, the ratio of the number of grains inside the bipolar plate material can be obtained as: (16); Substituting formula (4) into formula (7), we get: (17); Substituting equation (2) into equation (17), the flow stress of the bipolar plate material is obtained as follows: (18).

[0022] In order to more comprehensively consider the influence of the size relationship between grains and plate thickness on the internal stress of the bipolar plate, the true stress-strain curves Ⅰ-1 and Ⅰ-2 of two bipolar plate specimens with the same plate thickness and different average grain sizes, as well as the true stress-strain curves Ⅱ-1 and Ⅱ-2 of two bipolar plate specimens with the same average grain size and different plate thicknesses are obtained through uniaxial tensile tests. Then, the data of the plastic stage and strengthening stage of the true stress-strain curves Ⅰ-1 and Ⅰ-2 are substituted into formula (18) and a set of and , that is, the intragranular flow stress and grain boundary flow stress of a single grain dominated by grain size. Substituting the data of the plastic stage, strengthening stage and fracture stage of the true stress-strain curves Ⅱ-1 and Ⅱ-2 into formula (18), a set of and , that is, the intragranular flow stress and grain boundary flow stress of a single grain dominated by plate thickness, that is, two sets of and .

[0023] It should be noted that in the above solution process, it is assumed that two bipolar plate samples with basically the same average grain size and different plate thickness undergo the same strain. Under the same strain, the intragranular flow stress of a single grain and the grain boundary flow stress of a single grain of the two samples are the same; the two bipolar plate samples with different average grain sizes and the same plate thickness are Under the condition of , the intragranular flow stress of a single grain and the grain boundary flow stress of a single grain of the two specimens are the same.

[0024] Through the above calculations, we get two groups and The known formula (18) can be divided into the formula (19) for a constant plate thickness but a variable grain size and the formula (20) for a constant average grain size but a variable plate thickness, that is, the calculation formula (19) for the flow stress dominated by the grain size and the calculation formula (20) for the flow stress dominated by the plate thickness are obtained: (19); (20).

[0025] In actual calculations, only using formula (19) or (20) will result in inaccurate data. Therefore, the effects of grain size and plate thickness on stress are further introduced to obtain the overall stress of the bipolar plate: (twenty one); The above formula (21) is the stress-strain constitutive model of the bipolar plate based on the scale effect caused by the change of plate thickness and grain size; in: (twenty two); (twenty three); (twenty four); (25); (26); In the formula, is the flow stress dominated by the grain size, is the flow stress dominated by the plate thickness, is the proportional factor of grain size in the scale effect caused by the change of grain size and plate thickness, and They represent the influencing factors of the scale effect caused by the change of grain size and plate thickness, is the yield strength dominated by the grain size, is the yield strength dominated by plate thickness, , , , is the fitting parameter.

[0026] The above formulas (25) and (26) are based on the law that the flow stress of the material increases with the increase of plate thickness and increases with the decrease of grain size under micro / meso conditions, and can be approximated as a linear relationship. The linear univariate equation related to the yield strength is established with respect to the plate thickness and grain size.

[0027] The parameters in the above formulas (25) and (26) are , , , Specifically, the true stress-strain curves of several bipolar plate samples with different average grain sizes and the same plate thickness are obtained through uniaxial tensile tests, and the yield strength of each sample is calculated and fitted with the grain size to obtain the parameter , ; The true stress-strain curves of several bipolar plate samples with basically the same average grain size and different plate thicknesses were obtained through uniaxial tensile tests, and the yield strength of each sample was calculated and fitted with the plate thickness to obtain the parameters , .

[0028] In order to verify the accuracy of the bipolar plate stress-strain constitutive model based on the scale effect caused by the change of plate thickness and grain size established by the present invention, and to compare it with the traditional method, the traditional method refers to the traditional stress-strain constitutive model that does not consider the scale effect caused by the change of plate thickness and grain size. In this embodiment, SUS304 stainless steel is used for uniaxial tensile test to obtain the true stress-strain curve, and the traditional stress-strain constitutive model provided by ABAQUS is used for simulation calculation. At the same time, the bipolar plate stress-strain constitutive model based on the scale effect caused by the change of plate thickness and grain size of the present invention is applied to the VUMAT subroutine of ABAQUS for simulation calculation. Specifically, the specimens used in the real uniaxial tensile test and the simulation test are 0.1mm thick SUS304 stainless steel, and the stretching rate is 1mm / min. The simulations are performed respectively by the traditional stress-strain constitutive model and the stress-strain constitutive model of the present invention, and the simulated stress cloud diagrams are as shown below. Figure 2 As shown, Figure 2 (a) is the simulation result under the stress-strain constitutive model of the present invention, and (b) is the simulation result under the traditional stress-strain constitutive model; Figure 2 It can be seen that the stress cloud maps obtained by the two simulations have obvious differences in distribution. The stress concentration area in the stress cloud map simulated by the traditional method is too large and does not conform to the actual situation. The stress concentration area in the stress cloud map simulated by the method of the present invention is mainly concentrated in the middle area, which is close to the fracture position in the actual test. In addition, the corresponding simulated real stress-strain curve is also obtained in the above simulation process, such as Figure 3 As shown in the figure, and compared with the real stress-strain curve of the real uniaxial tensile test, it can be seen that the result simulated by the method of the present invention is closer to the real stress-strain curve obtained from the real uniaxial tensile test, while the calculated stress in the result simulated by the traditional method is obviously too high. This is because the traditional method does not fully consider the influence of the scale effect, which leads to such a result.

[0029] Specifically, the above step S2 is specifically as follows: S21. The bipolar plate is set as a three-channel structure, and the three-channel two-dimensional model of the bipolar plate is established using ABAQUS finite element software, that is, the bipolar plate stamping forming prediction model, such as Figure 4 As shown; S22, compiling the stress-strain constitutive model of the bipolar plate established in step S1 into a VUMAT subroutine, and introducing it into ABAQUS finite element software; S23. In the ABAQUS finite element software, the thickness of the bipolar plate structure is set to 0.1 mm, the length is 12 mm, the width is assumed to be 50 mm, the bipolar plate material is 304 stainless steel, the physical parameters of the bipolar plate material including elastic modulus, yield strength, and Poisson's ratio are set, and the grain parameters including the average grain size are set, wherein the elastic modulus and yield strength can be obtained by uniaxial tensile test, and the average grain size can be obtained by EBSD electron microscopy; S24. Create periodic boundary conditions and mutual contact, and perform meshing. Since the stamping process is a quasi-static process, the explicit smoothing analysis step is used for simulation.

[0030] Specifically, the above step S3 is specifically as follows: In the ABAQUS finite element software, the bipolar plate stamping forming prediction model established in step S2 is used to numerically simulate the bipolar plate stamping forming process under different bipolar plate mold geometric parameters and different stamping process parameters to obtain the corresponding filling depth and thinning rate, and analyze the influence of the bipolar plate mold geometric parameters and stamping process parameters on the filling depth and thinning rate, so as to obtain the parameter range that can make the channel depth meet the requirements and no tearing occurs during the forming process.

[0031] It should be noted that the filling depth mainly affects the depth of the channel formed, and the thinning rate is mainly used to determine whether tearing occurs in the bipolar plate during the forming process. Usually, tearing occurs when the thinning rate exceeds 33.4%.

[0032] First, step S3 studies the influence of the geometric parameters of the bipolar plate mold on the filling depth and thinning rate. The geometric parameters of the bipolar plate mold mainly include the draft angle α, the fillet radius R, the channel width W, the channel depth h, and the rib width S. The draft angle α is set to a value range of 5~25°, the fillet radius R is set to a value range of 0.1~0.3mm, the channel width W is set to a value range of 1.2~1.5mm, the channel depth h is set to a value range of 0.45~0.65mm, and the rib width S is set to 0.7~1.2mm. The above five mold parameters are designed as 45 groups of data with different value combinations for numerical simulation, and the filling depth and thinning rate corresponding to each numerical simulation are obtained.

[0033] A variance analysis was conducted on the effects of five mold parameters, namely, draft angle α, fillet radius R, channel width W, channel depth h, and rib width S, and their combination on the thinning rate, as shown in Table 1.

[0034] Table 1 Variance analysis results of mold parameters on thinning rate

[0035] It can be seen from Table 1 that for the thinning rate, the contribution rates of the fillet radius R and the channel depth h are large, among which the contribution rate of the fillet radius R is the most prominent.

[0036] A variance analysis was conducted on the effects of four mold parameters, namely, draft angle α, fillet radius R, channel width W, and rib width S, on filling depth, as shown in Table 2.

[0037] Table 2 Variance analysis results of mold parameters on filling depth

[0038] It can be seen from Table 2 above that for the filling depth, the contribution rate of the fillet radius R is the largest, and the influence of other parameters can be ignored.

[0039] In addition, according to the above simulation results, this embodiment uses the response surface method to analyze the influence of different bipolar plate mold geometric parameters on the thinning rate, such as Figure 5 As shown. Among them, Figure 5 (a) is the response surface of draft angle and fillet radius on thinning rate, (b) is the response surface of channel depth and draft angle on thinning rate, (c) is the response surface of channel depth and channel width on thinning rate, (d) is the response surface of channel depth and fillet radius on thinning rate, and (e) is the response surface of rib width and fillet radius on thinning rate. Figure 5 It can be seen that increasing the draft angle, fillet radius, and channel width will lead to a decrease in the thinning rate; while increasing the channel depth and rib width will increase the thinning rate. Therefore, if a deeper channel depth needs to be designed, it is necessary to prevent tearing by increasing the draft angle, fillet radius, channel width, and reducing the rib width.

[0040] According to the above simulation results, this embodiment also uses the response surface method to analyze the influence of different bipolar plate mold geometric parameters on the filling depth. Figure 6 As shown. Among them, Figure 6 (a) is the response surface of fillet radius and draft angle to filling depth; (b) is the response surface of fillet radius and channel width to filling depth; (c) is the response surface of fillet radius and rib width to channel depth. Figure 6 It can be seen that the fillet radius has a great influence on the filling depth. When the fillet radius increases, it helps to improve the filling depth; while the draft angle, channel width and rib width have basically no effect on the filling depth.

[0041] Within the range of geometric parameters of the bipolar plate mold set in this embodiment, after numerical simulation and analysis of the results, the preferred range of each parameter is determined as follows: when a channel depth of more than 0.5 mm is required, the draft angle α ≥ 15°, the fillet radius R ≥ 0.2 mm, the channel width W ≥ 1.4 mm, and the rib width S ≤ 1 mm.

[0042] Secondly, step S3 also studies the influence of stamping process parameters on filling depth and thinning rate. The stamping process parameters mainly include stamping speed and stamping pressure. Under the preferred range of bipolar plate mold geometric parameters determined above, the specific values ​​of each parameter are determined as follows: draft angle α is 15°, fillet radius R is 0.3mm, channel depth is 0.65mm, channel width W is 1.5mm, and rib width S is 1mm. Under the bipolar plate mold geometric parameters, the influence of stamping process parameters on filling depth and thinning rate is studied.

[0043] For the stamping speed, the stamping speed is controlled by the analysis step time of the punch pressing process. The analysis step time is set to 8~12s. Numerical simulation is performed to obtain the pressure load on the upper surface of the bipolar plate during the stamping process at different stamping speeds and the corresponding filling depth and thinning rate. Among them, the pressure load curves on the upper surface of the bipolar plate during the stamping process at different stamping speeds are shown in the figure. Figure 7 As shown, the filling depth and thinning rate are shown in Table 3 below.

[0044] Table 3 Filling depth and thinning rate at different punching speeds

[0045] pass Figure 7 From Table 3, it can be seen that the fluctuation of the stamping speed has little effect on the pressure load on the surface of the bipolar plate, and the changes in the filling depth and thinning rate are also small.

[0046] For the stamping pressure, when the analysis step time of the punch pressing process is set to 10s, the punch pressure load is adjusted to 400~750MPa, and numerical simulation is performed to obtain the filling depth and thinning rate under different stamping pressures, as shown in Table 4 below.

[0047] Table 4 Filling depth and thinning rate under different stamping pressures

[0048] From Table 4, we can see that when the stamping pressure is 400~500Mpa, the filling depth is relatively small and the thinning rate is also small; when the stamping pressure is 600~700Mpa, the filling depth is relatively large and the thinning rate is still small; and when the stamping pressure reaches 750Mpa, although the filling depth is large, the thinning rate is too large at this time, and there is a great risk of fracture. Therefore, if a channel depth of 0.65mm is required, a stamping pressure of 700Mpa is the most appropriate.

[0049] This embodiment first establishes an ultra-thin plate stress-strain constitutive model that takes into account the scale effect caused by changes in plate thickness and grain size, and then optimizes the solid oxide fuel cell bipolar plate forming process based on the established stress-strain constitutive model that takes into account the scale effect caused by changes in plate thickness and grain size. This can more accurately simulate the bipolar plate stamping process, obtain a more accurate bipolar plate optimal structural parameter range and stamping process parameter range, and provide theoretical guidance for bipolar plate stamping.

[0050] It should be noted that some parts not described in the present invention can be implemented by adopting or drawing on existing technologies.

[0051] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for optimizing the forming process of a solid oxide fuel cell bipolar plate, characterized in that: Includes steps: S1. Establish a stress-strain constitutive model of bipolar plates based on the scale effect caused by changes in plate thickness and grain size; S2. Using finite element software to establish a bipolar plate stamping finite element model, introducing the bipolar plate stress-strain constitutive model established in step S1, and setting the structural parameters, material property parameters and grain parameters of the bipolar plate, to obtain a bipolar plate stamping prediction model based on the scale effect caused by changes in plate thickness and grain size; S3. Based on the bipolar plate stamping forming prediction model established in step S2, the bipolar plate stamping forming process is numerically simulated, and the influence of the stamping process parameters and the bipolar plate mold parameters on the filling depth and thinning rate of the bipolar plate is analyzed to obtain the parameter range that can make the filling depth meet the requirements and no tearing occurs during the forming process.

2. The method for optimizing the forming process of a solid oxide fuel cell bipolar plate according to claim 1, characterized in that: The step S1 is specifically as follows: S11. Based on the composite model, the flow stress of a single grain is divided into two parts: the grain interior and the grain boundary. and grain boundary flow stress The flow stress of a single grain ; S12. Based on the surface layer model, the flow stress of the bipolar plate material is divided into two parts: the internal part and the surface part. and surface flow stress Flow stress of bipolar plate materials ; S13. Considering the influence of the scale effect caused by the change of plate thickness and grain size on the internal stress of the bipolar plate material, the flow stress of the bipolar plate material is Grain size dominated flow stress and thickness-dominated flow stress , a stress-strain constitutive model of bipolar plates is established based on the scale effect caused by changes in plate thickness and grain size.

3. A solid oxide fuel cell bipolar plate forming process optimization method according to claim 2, characterized in that: The flow stress of the grains in step S11 The calculation formula is: ； The flow stress of the bipolar plate material in step S12 The calculation formula is: ； Right now: ； in: ； ； ； That is, we get: ； In the formula, is the flow stress of a single grain, is the intragranular flow stress of a single grain, is the grain boundary flow stress of a single grain, is the volume fraction inside the grain, is the flow stress of the bipolar plate material, is the internal flow stress of the bipolar plate material, is the surface flow stress of the bipolar plate material, is the ratio of the number of grains inside the bipolar plate material, is the grain boundary layer thickness; is the average grain size, is the number of grains inside the bipolar plate material, is the number of grains on the surface of the bipolar plate material, and is a constant for a specific material.

4. A method for optimizing a solid oxide fuel cell bipolar plate forming process according to claim 3, characterized in that: The stress-strain constitutive model of the bipolar plate based on the scale effect caused by the change of plate thickness and grain size established in step S13 is: ； in: ； ； ； ； ； ； ； In the formula, is the flow stress dominated by the grain size, is the flow stress dominated by the plate thickness, is the proportional factor of grain size in the scale effect caused by the change of grain size and plate thickness, and Respectively represent the influencing factors of the scale effect caused by the change of grain size and plate thickness, , are the intragranular flow stress and grain boundary flow stress of a single grain dominated by grain size, , are the intragranular flow stress and grain boundary flow stress of a single grain dominated by plate thickness, is the yield strength dominated by the grain size, is the yield strength dominated by plate thickness, is the average grain size, is the bipolar plate thickness, , , , is the fitting parameter, is the ratio of the number of grains inside the bipolar plate material, and is a constant for a specific material.

5. A method for optimizing a solid oxide fuel cell bipolar plate forming process according to claim 4, characterized in that: Grain size dominates the intragranular flow stress of a single grain and grain boundary flow stress By substituting the data in the true stress-strain curves Ⅰ-1 and Ⅰ-2 of two bipolar plate samples with the same plate thickness and different average grain sizes into the flow stress of the bipolar plate material in step S12, The calculation formula of is solved together to obtain; Intragranular flow stress of a single grain dominated by plate thickness and grain boundary flow stress By substituting the data in the true stress-strain curves II-1 and II-2 of two bipolar plate samples with the same average grain size and different plate thickness into the flow stress of the bipolar plate material in step S12, The calculation formula of is solved jointly to obtain it.

6. The method for optimizing the forming process of a solid oxide fuel cell bipolar plate according to claim 1, characterized in that: The material property parameters in step S2 include elastic modulus, yield strength, and Poisson's ratio, and the elastic modulus and yield strength are obtained through a uniaxial tensile test.

7. The method for optimizing the forming process of a solid oxide fuel cell bipolar plate according to claim 1, characterized in that: The grain parameters in step S2 include an average grain size, and the grain parameters are obtained by testing the bipolar plate material using an EBSD electron microscope.

8. The method for optimizing the forming process of a solid oxide fuel cell bipolar plate according to claim 1, characterized in that: The geometric parameters of the bipolar plate mold in step S3 include draft angle, fillet radius, channel width, channel depth, and rib width.

9. The method for optimizing the forming process of a solid oxide fuel cell bipolar plate according to claim 1, characterized in that: The stamping process parameters in step S3 include stamping speed and stamping pressure.

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