A device and method for electromagnetic preforming and die pressing composite forming of a metal bipolar plate

Abstract

The present invention provides a method and device for electromagnetic preforming - die pressing composite forming of a metal bipolar plate. The method includes: placing a metal blank above a female die, moving the female die below a discharge coil, bringing the discharge coil close to the female die, discharging the discharge coil to electromagnetic preform the metal blank to obtain an electromagnetic preformed blank, wherein micro - grooves are provided on the female die; keeping the electromagnetic preformed blank on the female die, transferring the female die below a male die, micro - protrusions matching the micro - grooves are provided on the male die, closing the male die and the female die, and die pressing the electromagnetic preformed blank to obtain a fuel cell metal bipolar plate. The method for electromagnetic preforming - die pressing composite forming of a metal bipolar plate provided by the present invention can simultaneously improve the forming limit depth, thickness reduction uniformity and dimensional accuracy of the fuel cell metal bipolar plate.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a metal bipolar plate electromagnetic preforming-molding composite forming device and method. Background Art

[0002] As fossil energy such as oil and coal becomes increasingly scarce and environmental pollution becomes increasingly serious, new energy technologies need to be developed to reduce dependence on energy and reduce emissions of greenhouse gases such as carbon dioxide. Hydrogen fuel cells are chemical devices that use hydrogen as a raw material to directly convert the chemical energy in hydrogen and oxidants into electrical energy. They have the advantages of high power generation efficiency and low environmental pollution. They are currently widely used in aerospace and automotive vehicles. As an important component of hydrogen fuel cells, bipolar plates have important functions such as mechanical support, providing fluid channels, and electrical and thermal conductivity. Therefore, bipolar plate materials are required to have high specific strength, excellent corrosion resistance, and excellent electrical and thermal conductivity.

[0003] At present, the materials used to manufacture bipolar plates mainly include graphite, composite materials and metal sheets. Although graphite has low density and good corrosion resistance, its mechanical properties are poor and its manufacturing cost is high, which limits the commercial application of graphite. The contact resistance of composite bipolar plates is high and the thickness is difficult to reduce. Compared with graphite and composite bipolar plates, metal bipolar plates have excellent mechanical properties and electrical conductivity, high density and easy batch production, which are ideal for large-scale application of fuel cells. In the prior art, the commonly used forming methods for metal bipolar plates include stamping and electromagnetic forming. However, the use of stamping can easily lead to severe thinning of the fillet of the metal bipolar plate, and the microchannel depth is shallow, which is difficult to meet the use requirements of fuel cells. As a single-sided mold and high-speed forming technology, the electromagnetic forming method can improve the deformation uniformity of the material, but the bipolar plate prepared by the electromagnetic forming method has poor channel depth uniformity and low dimensional accuracy, which is also difficult to meet the use requirements of fuel cells. Summary of the invention

[0004] The problem solved by the present invention is how to provide a metal bipolar plate electromagnetic preforming-molding composite forming method, which can simultaneously improve the total elongation and forming limit depth of the metal bipolar plate.

[0005] In order to solve at least one aspect of the above problems, the present invention provides a metal bipolar plate electromagnetic preforming-molding composite forming method, comprising the following steps:

[0006] Step S1, placing a metal sheet on top of a die, moving the die to below a discharge coil, placing the discharge coil close to the die, discharging the discharge coil, and electromagnetically preforming the metal sheet to obtain an electromagnetically preformed sheet, wherein micro grooves are provided on the die;

[0007] Step S2: Keep the electromagnetic preformed sheet on the female die, transfer the female die under the male die. The male die is provided with micro - protrusions matching the micro - grooves. Close the male die and the female die to perform die - pressing forming on the electromagnetic preformed sheet to obtain a fuel cell metal bipolar plate.

[0008] Preferably, in step S1, the discharging of the discharge coil includes:

[0009] Set the discharge voltage to 7 - 12 kV and discharge the discharge coil.

[0010] Preferably, in step S2, the die - pressing forming of the electromagnetic preformed sheet includes:

[0011] Set the stamping speed to 0.1 mm / s. After the punching pressure reaches 20 - 40 kN, hold the pressure for 20 - 40 s to perform die - pressing forming on the electromagnetic preformed sheet.

[0012] Preferably, in step S1, the material of the metal sheet includes one of stainless steel, aluminum alloy, titanium alloy and pure titanium.

[0013] The present invention prepares a fuel cell metal bipolar plate by a composite forming method of electromagnetic pre - forming and die - pressing forming. Among them, the electromagnetic pre - forming process can improve the deformation uniformity of the metal sheet, making the thickness reduction of the formed bipolar plate uniform. And the die - pressing forming process can improve the problems such as uneven flow channel depth and difficult filling of fillets in the fuel cell metal bipolar plate when only electromagnetic pre - forming is used. The electromagnetic pre - forming - die - pressing composite forming method for the metal bipolar plate provided by the present invention can, on the one hand, solve the problems of poor flow channel depth uniformity and low dimensional accuracy in the electromagnetic pre - forming process, and on the other hand, solve the problems such as easy cracking of fillets and insufficient flow channel depth in the die - pressing forming process. At the same time, it can improve the forming limit depth, thickness reduction uniformity and dimensional accuracy of the fuel cell metal bipolar plate, and has a good total elongation rate.

[0014] The present invention also provides an electromagnetic pre - forming - die - pressing composite forming device for a metal bipolar plate, including:

[0015] An electromagnetic pre - forming module for electromagnetic pre - forming a metal sheet to obtain an electromagnetic preformed sheet;

[0016] A die - pressing forming module for die - pressing forming the electromagnetic preformed sheet to obtain a fuel cell metal bipolar plate;

[0017] A driving module for driving the electromagnetic pre - forming module and the die - pressing forming module to close the die.

[0018] Preferably, the electromagnetic preforming module includes a charging and discharging sub-module, a discharge coil, and a female die. The charging and discharging sub-module is electrically connected to the discharge coil. The discharge coil is located above the female die, and micro-grooves are provided on the female die.

[0019] Preferably, the charging and discharging sub-module includes a power source, a charging switch, a capacitor bank, and a discharging switch. Among them, the power source, the charging switch, and the capacitor bank form a charging circuit for charging the capacitor bank, and the capacitor bank, the discharging switch, and the discharge coil form a discharging circuit for discharging the discharge coil.

[0020] Preferably, the compression molding module includes a male die and the female die. The male die is located above the female die, and micro-protrusions matching the micro-grooves are provided on the male die. The female die is used to move below the discharge coil and the male die, and respectively form the electromagnetic preforming module and the compression molding module with the discharge coil and the male die.

[0021] Preferably, the metal bipolar plate electromagnetic preforming-compression molding composite forming device further includes an upper template and a lower template. The discharge coil and the male die are fixedly installed on the upper template, and the female die is movably installed on the lower template. A first insulating plate is provided between the discharge coil and the upper template, and a second insulating plate is provided between the female die and the lower template.

[0022] Preferably, guide rails and a telescopic mechanism are provided on the lower template. The lower end surface of the second insulating plate is movably arranged on the guide rails, and the side surface of the second insulating plate is connected to the telescopic mechanism. The telescopic mechanism is used to drive the second insulating plate to move horizontally along the guide rails, so that the female die moves below the discharge coil or the male die.

[0023] The beneficial effects of the metal bipolar plate electromagnetic preforming-compression molding composite forming device provided by the present invention compared with the prior art are the same as those of the metal bipolar plate electromagnetic preforming-compression molding composite forming method, and will not be elaborated here. Description of the Drawings

[0024] Figure 1 It is a flowchart of the metal bipolar plate electromagnetic preforming-compression molding composite forming method in an embodiment of the present invention;

[0025] Figure 2 It is a schematic structural diagram of the metal bipolar plate electromagnetic preforming-compression molding composite forming device in an embodiment of the present invention Figure 1 ;

[0026] Figure 3 It is a schematic structural diagram of the metal bipolar plate electromagnetic preforming-compression molding composite forming device in an embodiment of the present invention Figure 2;

[0027] Figure 4 It is a schematic structural diagram of a guide rail in the electromagnetic preforming - die pressing composite forming device for a metal bipolar plate in an embodiment of the present invention;

[0028] Figure 5 It is a schematic structural diagram of a discharge coil in an embodiment of the present invention;

[0029] Figure 6 It is a schematic structural diagram of an electromagnetic preformed blank after electromagnetic preforming in an embodiment of the present invention;

[0030] Figure 7 It is a schematic structural diagram of a fuel cell metal bipolar plate after composite forming in an embodiment of the present invention;

[0031] Figure 8 It is a schematic dimension structure diagram of micro - grooves in a female die in an embodiment of the present invention;

[0032] Figure 9 It is a diagram of the flow channel depth and flow channel shape under different load conditions during single die pressing forming;

[0033] Figure 10 It is a diagram of the flow channel depth and flow channel shape under different discharge voltage conditions during single electromagnetic forming;

[0034] Figure 11 It is a comparison diagram of the flow channel depth under different discharge voltages during composite forming;

[0035] Figure 12 It is a comparison diagram of the flow channel depth at different positions of different flow channels and the 7th flow channel in Comparative Example 1;

[0036] Figure 13 It is a comparison diagram of the flow channel depth at different positions of different flow channels and the 7th flow channel in Comparative Example 2;

[0037] Figure 14 It is a comparison diagram of the flow channel depth at different positions of different flow channels and the 7th flow channel in Embodiment 3 of the present invention;

[0038] Figure 15 It is a comparison diagram of the measurement results of the flow channel size accuracy of the metal bipolar plate in Embodiment 4 of the present invention and Comparative Examples 3 and 4.

[0039] Explanation of reference numerals:

[0040] 1. Press beam; 2. Base; 3. Upper template; 4. Lower template; 41. Guide rail; 5. Discharge coil; 51. Outer guide frame; 52. First insulating plate; 6. Punch; 61. Blank holder; 62. Punch fixing seat; 7. Die; 71. Die fixing plate; 72. Second insulating plate; 8. Charge and discharge electronic module; 81. Power supply; 82. Charge switch; 83. Capacitor bank; 84. Discharge switch; 9. Telescopic mechanism; 10. Driving motor. Specific embodiments

[0041] To make the above objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below.

[0042] It should be noted that, without conflict, the features in the embodiments of the present invention can be combined with each other. The meanings of the terms "comprising", "including", "containing", and "having" are non-restrictive, that is, other steps and other components that do not affect the result can be added. The above terms cover the terms "consisting of" and "consisting essentially of". Unless otherwise specified, the materials, equipment, and reagents are commercially available.

[0043] An embodiment of the present invention provides a method for electromagnetic preforming and die pressing composite forming of a metal bipolar plate, as Figure 1 shown, including the following steps:

[0044] Step S1: Place the metal blank above the die 7, move the die 7 below the discharge coil 5, bring the discharge coil 5 close to the die 7, discharge the discharge coil 5 to electromagnetic preform the metal blank to obtain an electromagnetic preformed blank, wherein micro-grooves are provided on the die 7;

[0045] Step S2: Keep the electromagnetic preformed blank on the die 7, transfer the die 7 below the punch 6, micro-protrusions matching the micro-grooves are provided on the punch 6, close the punch 6 and the die 7, and perform die pressing on the electromagnetic preformed blank to obtain a fuel cell metal bipolar plate.

[0046] Among them, the material of the metal blank includes stainless steel, aluminum alloy, titanium alloy, and pure titanium, preferably titanium alloy.

[0047] In step S1, when discharging the discharge coil 5, set the discharge voltage to 7 - 12 kV. When the discharge voltage is too low, the forming effect is poor, and when the discharge voltage is too high, it is easy to cause cracks in the fuel cell metal bipolar plate after forming. Setting the discharge voltage at 7 - 12 kV can make the metal blank form well.

[0048] By discharging the discharge coil 5, an electromagnetic interaction is generated between the discharge coil 5 and the metal sheet, imparting a large electromagnetic forming force to the metal sheet. The female die 7 is provided with micro-grooves, so that the metal sheet is laminated under the action of the electromagnetic forming force, the metal sheet is deformed, and micro-channels are generated. The electromagnetic pre-forming method can improve the deformation uniformity of the metal sheet, making the thickness of the formed bipolar plate thinner and more uniform. However, after electromagnetic forming, the uniformity of the flow channel depth of the bipolar plate is poor and the dimensional accuracy is low.

[0049] In step S2, after separating the discharge coil 5 from the female die 7, the electromagnetic pre-formed sheet is kept on the female die 7, the female die 7 and the electromagnetic pre-formed sheet are moved under the male die 6, and the male die 6 and the female die 7 are closed. Since the male die 6 is provided with micro-protrusions matching the micro-grooves, the electromagnetic pre-formed sheet will be molded by pressing. During the molding process, the stamping speed is set to 0.1 mm / s. When the stamping pressure reaches 20 - 40 kN, pressure holding is carried out, and the pressure holding time is 20 - 40 s, then the fuel cell metal bipolar plate can be obtained.

[0050] Based on electromagnetic pre-forming, performing molding by pressing on the electromagnetic pre-formed sheet can solve the problems of poor uniformity of the flow channel depth and low dimensional accuracy during the electromagnetic pre-forming process, and at the same time improve the forming limit depth, thickness reduction uniformity and dimensional accuracy of the fuel cell metal bipolar plate, so that the prepared fuel cell metal bipolar plate has good total elongation and forming limit depth at the same time.

[0051] It should be understood that according to the different materials and sizes of the metal sheet, the discharge voltage during electromagnetic pre-forming, as well as the holding pressure and pressure holding time during molding by pressing are also different. For example, when the material of the metal sheet is aluminum alloy, the discharge voltage and holding pressure are lower and the pressure holding time is shorter, while when the material of the metal sheet is pure titanium or titanium alloy, the discharge voltage and holding pressure are relatively higher and the pressure holding time is longer. For metal sheets of the same material, the larger the size, the higher the discharge voltage and holding pressure, and the longer the pressure holding time.

[0052] As Figure 2 and Figure 3 shown, another embodiment of the present invention provides a fuel cell bipolar plate forming device, including:

[0053] An electromagnetic pre-forming module for electromagnetic pre-forming a metal sheet to obtain an electromagnetic pre-formed sheet;

[0054] A molding by pressing module for molding the electromagnetic pre-formed sheet by pressing to obtain a fuel cell metal bipolar plate;

[0055] A driving module for driving the electromagnetic pre-forming module and the molding by pressing module to close the mold.

[0056] The device can electromagnetic preform a metal sheet through an electromagnetic preforming module to obtain an electromagnetic preformed sheet, and then press-form the electromagnetic preformed sheet through a die pressing forming module to obtain a fuel cell metal bipolar plate.

[0057] Specifically, the electromagnetic preforming module includes a charge and discharge electronic module 8, a discharge coil 5, and a female die 7. The charge and discharge electronic module 8 is electrically connected to the discharge coil 5. The discharge coil 5 is located above the female die 7, and the female die 7 is provided with micro-grooves. The charge and discharge electronic module 8 can discharge the discharge coil 5 to cause an electromagnetic interaction between the discharge coil 5 and the metal sheet. Since the female die 7 is provided with micro-grooves, under the action of the electromagnetic preforming force generated by the discharge coil 5, the metal sheet is molded, the thickness of the metal sheet is reduced, and micro-channels are generated to obtain an electromagnetic preformed sheet. Exemplarily, in some embodiments, the structure of the discharge coil 5 is as Figure 5 shown.

[0058] The charge and discharge electronic module 8 includes a power supply 81, a charging switch 82, a capacitor bank 83, and a discharge switch 84. Among them, the power supply 81, the charging switch 82, and the capacitor bank 83 form a charging circuit for charging the capacitor bank 83. The capacitor bank 83, the discharge switch 84, and the discharge coil 5 form a discharge circuit for discharging the discharge coil 5.

[0059] When charging, the charging switch 82 is closed, the discharge switch 84 is opened, and the capacitor bank 83 is charged through the power supply 81 until the discharge voltage value is reached, and then the charging switch 82 is opened; when discharging, the discharge switch 84 is closed, the charging switch 82 is opened, and the discharge coil 5 is discharged through the capacitor bank 83.

[0060] Furthermore, an outer guide frame 51 is arranged outside the discharge coil 5, and a female die fixing plate 71 is arranged outside the female die 7. When the discharge coil 5 approaches the female die 7, the outer guide frame 51 and the female die fixing plate 71 can clamp and fix the metal sheet between them.

[0061] The compression molding module includes a punch 6 and the die 7. The punch 6 is located above the die 7, and micro - protrusions matching the micro - grooves are provided on the punch 6. The die 7 is used to move below the discharge coil 5 and the punch 6, and respectively form the electromagnetic pre - forming module and the compression molding module with the discharge coil 5 and the punch 6. That is, the electromagnetic pre - forming module and the compression molding module share a die 7. The die 7 can move below the discharge coil 5 and the punch 6. When the die 7 moves below the discharge coil 5, it can form the electromagnetic pre - forming module with the discharge coil 5. When the die 7 moves below the punch 6, it can form the compression molding module with the punch 6. Micro - protrusions matching the micro - grooves are provided on the punch 6. When the punch 6 and the die 7 are closed, the micro - protrusions can be pressed into the micro - grooves to stamp the electromagnetic pre - formed blank, realizing the compression molding of the electromagnetic pre - formed blank. In addition, a blank - holding ring 61 is provided on the periphery of the punch 6. When the punch 6 and the die 7 are closed, the blank - holding ring 61 can press on the die fixing plate 71 to fix the electromagnetic pre - formed blank.

[0062] The electromagnetic pre - forming - compression molding composite forming device for the metal bipolar plate further includes an upper template 3 and a lower template 4. The discharge coil 5 and the punch 6 are fixedly installed on the upper template 3, the die 7 is movably installed on the lower template 4. A first insulating plate 52 is provided between the discharge coil 5 and the upper template 3, a second insulating plate 72 is provided between the die 7 and the lower template 4, and a punch fixing seat 62 is provided between the punch 6 and the upper template 3. The provision of the first insulating plate 52 and the second insulating plate 72 can avoid the influence on the upper template 3 and the lower template 4 when the discharge coil 5 discharges, and improve the electromagnetic forming force.

[0063] As Figure 4 shown, a guide rail 41 and a telescopic mechanism 9 are provided on the lower template 4. The lower end surface of the second insulating plate 72 is movably arranged on the guide rail 41, and the side surface of the second insulating plate 72 is connected to one end of the telescopic mechanism 9. The other end of the telescopic mechanism 9 is fixedly arranged on the lower template 4. The telescopic mechanism 9 can expand and contract in the horizontal direction. The telescopic mechanism 9 is used to drive the second insulating plate 72 to move horizontally along the guide rail 41, so that the die 7 moves below the discharge coil 5 or the punch 6. The automation degree of the device can be improved through the guide rail 41 and the telescopic mechanism 9. By controlling the expansion and contraction of the telescopic mechanism 9, the position transformation of the die 7 can be realized, and electromagnetic pre - forming and compression molding can be achieved. Exemplarily, the telescopic mechanism 9 is an electric cylinder or an electric oil cylinder.

[0064] Furthermore, the upper die plate 3 is fixedly connected to the press crossbeam 1 located above it. A driving motor 10 is provided on the press crossbeam 1, and the driving motor 10 can drive the press crossbeam 1 to move in the vertical direction. When the press crossbeam 1 moves upward, the discharge coil 5 and the punch 6 move away from the die 7. When the press crossbeam 1 moves downward, the discharge coil 5 and the punch 6 move closer to the die 7. A base 2 is provided below the lower die plate 4, and the lower die plate 4 is fixedly arranged on the base 2.

[0065] The process of preparing the fuel cell metal bipolar plate using this metal bipolar plate electromagnetic preforming - die pressing composite forming device will be described below:

[0066] Step T1: As shown in Figure 2 , place the metal sheet on the die 7, control the telescopic mechanism 9 to move the die 7 to directly below the discharge coil 5, start the driving motor 10, drive the press crossbeam 1 to move downward, drive the discharge coil 5 to move closer to the die 7 until the outer guide frame 51 of the discharge coil 5 and the die fixing plate 71 of the die 7 clamp the metal sheet tightly.

[0067] Step T2: Close the charging switch 82 in the charge - discharge electronic module 8, open the discharge switch 84, charge the capacitor bank 83 by the power supply 81 to the discharge voltage, then open the charging switch 82 and close the discharge switch 84 to discharge the capacitor bank 83 to the discharge coil 5. The discharge coil 5 forms the metal sheet through the Lorentz force. After electromagnetic preforming, the shape of the pure titanium sheet is as shown in Figure 6 .

[0068] Step T3: Start the driving motor 10 to move the press crossbeam 1 upward. As shown in Figure 3 , control the telescopic mechanism 9 to move the die 7 to directly below the punch 6.

[0069] Step T4: Start the driving motor 10 to move the press crossbeam 1 downward, drive the punch 6 to move closer to the die 7, and close the die at a certain stamping speed until the preset pressure is reached and hold the pressure for a period of time to complete die pressing forming.

[0070] Step T5: Start the driving motor 10 to drive the press crossbeam 1 upward, and the composite forming of the fuel cell metal bipolar plate is completed, obtaining the fuel cell metal bipolar plate. The shape of the fuel cell metal bipolar plate obtained after composite forming is as shown in Figure 7 .

[0071] It should be noted that when the metal sheet is made of a material with a relatively large resistance such as pure titanium, due to the relatively large resistance of the metal sheet, the induced current during electromagnetic preforming is small, resulting in a small Lorentz force. Therefore, during the electromagnetic preforming process, a pure copper driving plate needs to be placed above the metal sheet to increase the Lorentz force during electromagnetic preforming and facilitate the forming of the metal sheet.

[0072] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are generally carried out according to the conditions recommended by the manufacturer.

[0073] In the following embodiments, unless otherwise specified, it is prepared by using the metal bipolar plate electromagnetic preforming - die pressing composite forming device as shown in Figures 2 - 3 The metal bipolar plate electromagnetic preforming - die pressing composite forming device includes:

[0074] The press beam 1, the upper template 3, the discharge coil 5, the punch 6, the drive motor 10, the die 7, the lower template 4 and the base 2. The upper template 3 is fixedly arranged on the press beam 1. The discharge coil 5 and the punch 6 are fixedly arranged on the upper template 3. The drive motor 10 is used to drive the press beam 1 to lift and lower. The lower template 4 is fixedly arranged on the base 2. The die 7 is movably arranged on the lower template 4. A first insulating plate 52 is arranged between the discharge coil 5 and the upper template 3. An outer guide frame 51 is arranged outside the discharge coil 5. A punch fixing seat 62 is arranged between the punch 6 and the upper template 3. A blank holder 61 is arranged outside the punch 6. A second insulating plate 72 is arranged between the die 7 and the lower template 4. A guide rail 41 is arranged on the lower template 4. A groove matching the guide rail 41 is arranged on the lower end surface of the second insulating plate 72. One end of the telescopic mechanism 9 is connected to the side surface of the second insulating plate 72, and the other end of the telescopic mechanism 9 is fixedly arranged on the lower template 4. The telescopic mechanism 9 is used to drive the second insulating plate 72 and the die 7 located on the second insulating plate 72 to move along the guide rail.

[0075] It further includes a charge - discharge electronic module 8. The charge - discharge electronic module 8 is electrically connected to the discharge coil 5 and includes a power supply 81, a charging switch 82, a capacitor bank 83 and a discharge switch 84. The power supply 81, the charging switch 82 and the capacitor bank 83 form a charging circuit, and the capacitor bank 83, the discharge switch 84 and the discharge coil 5 form a discharging circuit.

[0076] Embodiment 1

[0077] 1.1. Place an aluminum alloy sheet with a thickness of 0.1 mm on the die 7. Control the telescopic mechanism 9 to move the die 7 to directly below the discharge coil 5. Start the drive motor 10 to drive the press beam 1 to move downward, driving the discharge coil 5 closer to the die 7 until the outer guide frame 51 of the discharge coil 5 and the die fixing plate 71 of the die 7 clamp the aluminum alloy sheet tightly, so that the pressure reaches 10 - 20 kN.

[0078] 1.2. Close the charging switch 82 in the closed charging and discharging electronic module 8, open the discharging switch 84, charge the capacitor bank 83 by the power supply 81 to the discharging voltage of 7 - 9 kV, then open the charging switch 82, close the discharging switch 84, and discharge the capacitor bank 83 to the discharging coil 5. The discharging coil 5 forms the aluminum alloy sheet by the Lorentz force;

[0079] 1.3. Start the driving motor 10 to move the press crossbeam 1 upward, and control the telescopic mechanism 9 to move the female die 7 to directly below the male die 6;

[0080] 1.4. Start the driving motor 10 to move the press crossbeam 1 downward, drive the male die 6 to approach the female die 7, close the male die 6 and the female die 7 at the stamping speed of 0.1 mm / s, and keep the pressure for 20 - 30 s after reaching the preset pressure of 20 kN to complete the die pressing forming;

[0081] 1.5. Start the driving motor 10 to drive the press crossbeam 1 upward, and the composite forming of the fuel cell metal bipolar plate is completed, and the fuel cell metal bipolar plate is obtained.

[0082] Example 2

[0083] 2.1. Place the pure titanium sheet with a thickness of 0.1 mm on the female die 7. The flow channel area of the mold is 35 mm × 45 mm, and the size of the pure titanium sheet is 35 mm × 65 mm. Place the pure copper driving plate with a thickness of 0.2 mm above the pure titanium sheet. Control the telescopic mechanism 9 to move the female die 7 to directly below the discharging coil 5. Start the driving motor 10 to drive the press crossbeam 1 downward, drive the discharging coil 5 to approach the female die 7 until the outer guide frame 51 of the discharging coil 5 and the female die fixing plate 71 of the female die 7 clamp the pure titanium sheet tightly to make the pressure reach 10 - 20 kN;

[0084] 2.2. Close the charging switch 82 in the closed charging and discharging electronic module 8, open the discharging switch 84, charge the capacitor bank 83 by the power supply 81 to the discharging voltage of 10 - 11 kV, then open the charging switch 82, close the discharging switch 84, and discharge the capacitor bank 83 to the discharging coil 5. The discharging coil 5 forms the pure titanium sheet by the Lorentz force;

[0085] 2.3. Start the driving motor 10 to move the press crossbeam 1 upward, control the telescopic mechanism 9 to move the female die 7 to directly below the male die 6, and remove the pure copper driving plate;

[0086] 2.4. Start the driving motor 10 to move the press crossbeam 1 downward, drive the male die 6 to approach the female die 7, close the male die 6 and the female die 7 at the stamping speed of 0.1 mm / s, and keep the pressure for 30 - 40 s after reaching the preset pressure of 30 kN to complete the die pressing forming;

[0087] 2.5. Start the drive motor 10 to drive the press beam 1 to move upward, thus completing the composite forming of the fuel cell metal bipolar plate and obtaining the fuel cell metal bipolar plate.

[0088] Example 3

[0089] 3.1. Place a pure titanium blank with a thickness of 103 μm on the female die 7. The mold flow channel area is 35 mm × 45 mm, and the size of the pure titanium blank is 30 mm × 65 mm. Among them, as Figure 8 shown, the bottom width of the female die 7 is 1 mm, the side wall inclination angle is 60°, and the depth is 1 mm. Place a pure copper drive plate with a thickness of 0.2 mm above the pure titanium plate blank. Control the telescopic mechanism 9 to move the female die 7 to directly below the discharge coil 5. Start the drive motor 10 to drive the press beam 1 to move downward, driving the discharge coil 5 closer to the female die 7 until the outer guide frame 51 of the discharge coil 5 and the female die fixing plate 71 of the female die 7 tightly clamp the pure titanium blank, so that the pressure reaches 20 kN;

[0090] 3.2. Close the charging switch 82 in the charge and discharge electronic module 8, open the discharge switch 84, so that the power supply 81 charges the capacitor bank 83 to the discharge voltage of 10 kV. Then open the charging switch 82 and close the discharge switch 84, so that the capacitor bank 83 discharges to the discharge coil 5, and the discharge coil 5 forms the pure titanium blank through the Lorentz force;

[0091] 3.3. Start the drive motor 10 to move the press beam 1 upward, control the telescopic mechanism 9 to move the female die 7 to directly below the male die 6, and remove the pure copper drive plate;

[0092] 3.4. Start the drive motor 10 to move the press beam 1 downward, drive the male die 6 closer to the female die 7, and close the male die 6 and the female die 7 at a stamping speed of 0.1 mm / s until the preset pressure of 27.2 kN is reached and then hold the pressure for 30 - 40 s to complete the die pressing forming;

[0093] 3.5. Start the drive motor 10 to drive the press beam 1 to move upward, thus completing the composite forming of the fuel cell metal bipolar plate and obtaining the fuel cell metal bipolar plate.

[0094] Example 4

[0095] 4.1. Place a pure titanium sheet with a thickness of 75 μm on the female die 7. The flow area of the mold runner is 35 mm × 45 mm, and the size of the pure titanium sheet is 30 mm × 65 mm. Among them, the bottom width of the female die 7 is 1 mm, the side wall inclination angle is 60°, and the depth is 0.45 mm. Place a pure copper driving plate with a thickness of 0.2 mm above the pure titanium sheet. Control the telescopic mechanism 9 to move the female die 7 to directly below the discharge coil 5. Start the driving motor 10, drive the press crossbeam 1 to move downward, drive the discharge coil 5 to approach the female die 7 until the outer guide frame 51 of the discharge coil 5 and the female die fixing plate 71 of the female die 7 clamp the pure titanium sheet tightly, so that the pressure reaches 20 kN;

[0096] 4.2. Close the charging switch 82 in the charge and discharge electronic module 8, open the discharge switch 84, make the power supply 81 charge the capacitor bank 83 to the discharge voltage of 10 kV, then open the charging switch 82, close the discharge switch 84, make the capacitor bank 83 discharge to the discharge coil 5, and the discharge coil 5 forms the pure titanium sheet through the Lorentz force;

[0097] 4.3. Start the driving motor 10 to move the press crossbeam 1 upward, control the telescopic mechanism 9 to move the female die 7 to directly below the male die 6, and remove the pure copper driving plate;

[0098] 4.4. Start the driving motor 10 to move the press crossbeam 1 downward, drive the male die 6 to approach the female die 7, and close the male die 6 and the female die 7 at a stamping speed of 0.1 mm / s until the preset pressure of 25 kN is reached and then hold the pressure for 30 - 40 s to complete the die pressing forming;

[0099] 4.5. Start the driving motor 10 to drive the press crossbeam 1 upward, and the composite forming of the fuel cell metal bipolar plate is completed, and the fuel cell metal bipolar plate is obtained.

[0100] Comparative Example 1

[0101] The difference between this comparative example and Example 3 is that the pure titanium sheet is directly processed by the die pressing forming method without electromagnetic pre - forming treatment. The preset pressure for die pressing forming is 20 kN, and the other conditions are the same as those in Example 3.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 3 is that the pure titanium sheet is directly processed by the electromagnetic forming method without die pressing forming treatment, and the other conditions are the same as those in Example 3.

[0104] Comparative Example 3

[0105] The difference between this comparative example and Example 4 is that the pure titanium sheet is directly processed by the die pressing forming method without electromagnetic pre - forming treatment, and the other conditions are the same as those in Example 4.

[0106] Comparative Example 4

[0107] The difference between this comparative example and Example 4 is that the pure material plate is directly processed by electromagnetic forming. During the electromagnetic forming process, the discharge voltage is 11 - 12 kV, without undergoing die pressing forming treatment, and the other conditions are the same as those in Example 4.

[0108] Experimental Example 1

[0109] Place a pure titanium plate with a thickness of 103 μm on the female die 7. The flow channel area of the mold is 35 mm × 45 mm, and the size of the pure titanium plate is 30 mm × 65 mm. Among them, the bottom width of the female die 7 is 1 mm, the side wall inclination angle is 60°, and the depth is 1 mm. Control the telescopic mechanism 9 to move the female die 7 directly below the male die 6. Start the driving motor 10 to move the press beam 1 downward, drive the male die 6 closer to the female die 7, perform die pressing forming on the pure titanium plate, and gradually increase the die pressing load (i.e., the die pressing pressure) until the pure titanium plate generates microcracks. Record the depth of the pure titanium plate under different load conditions, as well as the flow channel shape of the fuel cell metal bipolar plate after forming. The results are as Figure 9 shown.

[0110] Figure 9 In which, the abscissa Load represents the load (i.e., the die pressing pressure), which are 4 kN, 8 kN, 12 kN, 16 kN, 20 kN, 24 kN, and 25.5 kN respectively, and the ordinate Channel depth represents the flow channel depth. Figure 9 The picture in the upper left corner in is the cross-sectional view of the flow channel shape of the obtained fuel cell metal bipolar plate.

[0111] As Figure 9 shown, as the die pressing load increases, the depth of the pure titanium plate gradually increases. When the die pressing load is 25.5 kN, the depth is 719 μm. According to the cross-sectional shape of the flow channel of the fuel cell metal bipolar plate after forming, it can be seen that the thinning mainly occurs at the rounded corners of the bipolar plate, while the thinning at the bottom of the flow channel is relatively small, indicating that there is a problem of uneven thickness thinning in the fuel cell metal bipolar plate prepared by the die pressing forming method.

[0112] Experimental Example 2

[0113] Place a pure titanium sheet with a thickness of 103 μm on the female die 7. The mold runner area is 35 mm × 45 mm, and the size of the pure titanium sheet is 30 mm × 65 mm. Among them, the bottom width of the female die 7 is 1 mm, the side wall inclination angle is 60°, and the depth is 1 mm. Control the telescopic mechanism 9 to move the female die 7 to directly below the discharge coil 5. Start the drive motor 10 to drive the press beam 1 to move downward, driving the discharge coil 5 closer to the female die 7 until the outer guide frame 51 of the discharge coil 5 and the female die fixing plate 71 of the female die 7 clamp the metal sheet tightly, so that the pressure reaches 20 kN, make the discharge coil 5 discharge, perform electromagnetic forming on the pure titanium sheet, and gradually increase the discharge voltage during the electromagnetic forming process from 7 kV to 12 kV. When the discharge voltage is 12 kV, the bipolar plate ruptures. Record the depth of the pure titanium sheet under different load conditions, as well as the runner shape of the fuel cell metal bipolar plate after forming. The results are as Figure 10 shown.

[0114] Figure 10 In it, the abscissa Discharge voltages represents the discharge voltage, which are 7 kV, 8 kV, 9 kV, 10 kV, 11 kV and 12 kV respectively. The ordinate Average channel depth represents the average channel depth. Figure 10 The picture in the upper left corner in it is the cross-sectional view of the runner shape of the obtained fuel cell metal bipolar plate.

[0115] As Figure 10 shown, with the increase of the discharge voltage, the depth of the formed fuel cell metal bipolar plate also gradually increases. When the discharge voltage is 12 kV, the depth is 711 μm. It can be seen from the cross-sectional shape of the runner of the fuel cell metal bipolar plate that the shape of the runner is arc-shaped, which is quite different from the runner shape of the female die.

[0116] Experimental Example 3

[0117] Adjust the discharge voltage in Example 3 from 7 kV to 11 kV, and record the depth of the pure titanium sheet under different discharge voltage conditions, as Figure 11 shown.

[0118] Figure 11 In it, the abscissa Discharge voltages of EMPB represents the discharge voltage of electromagnetic preforming, which are 7 kV, 8 kV, 9 kV, 10 kV and 11 kV respectively. The ordinate Limit channel depth represents the limit channel depth. 719at QS in the figure means that when using die pressing forming alone, the limit channel depth is 719 μm (Experimental Example 1), and 711at EM means that when using electromagnetic forming alone, the limit channel depth is 711 μm (Experimental Example 2).

[0119] From Figure 11It can be seen that as the discharge voltage increases, the depth of the formed fuel cell metal bipolar plate gradually increases and then decreases. When the discharge voltage is 10 kV, the maximum depth of the fuel cell metal bipolar plate is 879 μm, which is significantly higher than the maximum depths obtained by using only molding and electromagnetic forming alone.

[0120] Experimental Example 4

[0121] The channel depths of different channels of the fuel cell metal bipolar plates obtained in Example 3, Comparative Example 1, and Comparative Example 2, as well as the channel depths at different positions of the 7th channel, were statistically analyzed, as Figures 12 - 14 shown.

[0122] Figure 12 Figure showing the channel depths of different channels of the fuel cell metal bipolar plate in Comparative Example 1 and the channel depths at different positions of the 7th channel Figure 13 Figure showing the channel depths of different channels of the fuel cell metal bipolar plate in Comparative Example 2 and the channel depths at different positions of the 7th channel Figure 14 Figure showing the channel depths of different channels of the fuel cell metal bipolar plate in Example 3 and the channel depths at different positions of the 7th channel Figures 12 - 14 In the following figure, the lower horizontal axis "Channel number" represents different channel numbers, the upper horizontal axis "Positions along 7th channel" represents different positions of the 7th channel, the vertical axis "Chanel depth" represents the channel depth, and "Max deviation" represents the maximum depth deviation.

[0123] From Figure 12 it can be seen that the maximum depth deviation of different channels and different positions of the 7th channel in Comparative Example 1 is only 6 μm, indicating that the fuel cell metal bipolar plate obtained by the molding method has good channel depth uniformity, which is helpful for subsequent welding and assembly.

[0124] From Figure 13 it can be seen that the depth deviation between different channels in Comparative Example 2 reaches 31 μm, and the depth deviation at different positions of the 7th channel reaches 28 μm, which is significantly greater than the depth deviation during molding, indicating that the fuel cell metal bipolar plate obtained by using only the electromagnetic forming method has poor channel depth uniformity.

[0125] As Figure 14 shown, the depth deviation between different channels is 8 μm, and the depth deviation at different positions of the 7th channel is 9 μm, indicating that the fuel cell bipolar plate obtained by the combined forming method of electromagnetic preforming - molding has good channel depth uniformity. This is mainly because after the electromagnetic preformed blank plate is preformed by electromagnetic and then processed by molding, the problem of large depth uniformity in electromagnetic preforming is compensated.

[0126] Experimental Example 5

[0127] The side wall inclination angles of the formed fuel cell metal bipolar plates obtained by using the forming methods of Example 4, Comparative Example 3, and Comparative Example 4 were measured, and the results are as Figure 15 shown.

[0128] Figure 15 Among them, QS stamping represents the fuel cell metal bipolar plate obtained by using the stamping forming method alone (i.e., Comparative Example 3), EM stamping represents the fuel cell metal bipolar plate obtained by using the electromagnetic forming method alone (i.e., Comparative Example 4), and EMPB+QS stamping represents the fuel cell metal bipolar plate obtained by using electromagnetic preforming and then performing composite forming treatment by stamping forming (i.e., Example 4); Sever thinning represents severe thinning, Poor fitability represents poor dimensional accuracy, and Uniform thinning represents uniform thinning.

[0129] From Figure 15 it can be seen that the side wall inclination angle of the formed fuel cell metal bipolar plate obtained by Comparative Example 3 is 53.3°, and the thinning at the rounded corners is severe. The side wall inclination angle of the formed fuel cell metal bipolar plate obtained by Comparative Example 4 is 47°, and the dimensional accuracy is poor. The side wall inclination angle of the formed fuel cell metal bipolar plate obtained by Example 4 is 55.6°, indicating that the composite forming method of Example 4 has higher dimensional accuracy and uniform thinning compared to the fuel cell metal bipolar plates obtained by using the stamping forming and electromagnetic forming methods alone.

[0130] In summary, when using electromagnetic forming alone, the obtained fuel cell metal bipolar plate has uniform thinning, but the uniformity of the flow channel depth is poor and the dimensional accuracy is low. When using stamping forming alone, the obtained fuel cell metal bipolar plate has better uniformity of the flow channel depth, but the thinning is uneven, the rounded corners are prone to cracking, and the flow channel depth is insufficient. The composite forming method of electromagnetic preforming followed by stamping forming can not only increase the limit depth of the fuel cell metal bipolar plate but also avoid the problems existing when using electromagnetic forming and stamping forming alone, and improve the total elongation rate of the fuel cell metal bipolar plate.

[0131] Although the present disclosure is disclosed as above, the scope of protection of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the scope of protection of the present invention.

Claims

1. A method for electromagnetic preforming - die pressing composite forming of a metal bipolar plate, characterized in that, Applied to an electromagnetic preforming - die pressing composite forming device for metal bipolar plates, the electromagnetic preforming - die pressing composite forming device for metal bipolar plates includes: An electromagnetic preforming module for electromagnetic preforming of a metal sheet to obtain an electromagnetically preformed sheet; The electromagnetic preforming module includes a charge - discharge electronic module (8), a discharge coil (5), and a female die (7). The charge - discharge electronic module (8) is electrically connected to the discharge coil (5). The discharge coil (5) is located above the female die (7), and micro - grooves are provided on the female die (7). A die - pressing forming module for die - pressing forming of the electromagnetically preformed sheet to obtain a fuel cell metal bipolar plate; The die - pressing forming module includes a male die (6) and the female die (7). The male die (6) is located above the female die (7), and micro - protrusions matching the micro - grooves are provided on the male die (6). The female die (7) is used to move below the discharge coil (5) and the male die (6) respectively, and together with the discharge coil (5) and the male die (6) form the electromagnetic preforming module and the die - pressing forming module; The die - pressing forming module further includes an upper template (3) and a lower template (4). The discharge coil (5) and the male die (6) are fixedly installed on the upper template (3), and the female die (7) is movably installed on the lower template (4). A first insulating plate (52) is provided between the discharge coil (5) and the upper template (3), and a second insulating plate (72) is provided between the female die (7) and the lower template (4); The lower template (4) is provided with a guide rail (41) and a telescopic mechanism (9). The lower end surface of the second insulating plate (72) is movably arranged on the guide rail (41), and the side surface of the second insulating plate (72) is connected to the telescopic mechanism (9). The telescopic mechanism (9) is used to drive the second insulating plate (72) to move horizontally along the guide rail (41), so that the female die (7) moves below the discharge coil (5) or the male die (6); A driving module for driving the electromagnetic preforming module and the die - pressing forming module to close the die; The electromagnetic preforming - die pressing composite forming method for metal bipolar plates includes the following steps: Step S1: Place a metal sheet above the female die (7), move the female die (7) below the discharge coil (5), bring the discharge coil (5) close to the female die (7), discharge the discharge coil (5) to electromagnetically preform the metal sheet to obtain an electromagnetically preformed sheet. Among them, micro - grooves are provided on the female die (7); Step S2: Keep the electromagnetically preformed sheet on the female die (7), transfer the female die (7) below the male die (6). Micro - protrusions matching the micro - grooves are provided on the male die (6). Close the male die (6) and the female die (7) to perform die - pressing forming on the electromagnetically preformed sheet to obtain a fuel cell metal bipolar plate.

2. The electromagnetic preforming - die pressing composite forming method of the metal bipolar plate according to claim 1, characterized in that, In step S1, the discharging of the discharge coil (5) includes: Set the discharge voltage to 7 - 12 kV and discharge the discharge coil (5).

3. The electromagnetic preforming and die pressing composite forming method of the metal bipolar plate according to claim 1, characterized in that In the step S2, the die pressing of the electromagnetic preformed blank includes: Set the stamping speed to 0.1 mm / s. After the stamping pressure reaches 20 - 40 kN, hold the pressure for 20 - 40 s to perform die pressing on the electromagnetic preformed blank.

4. The electromagnetic preforming and die pressing composite forming method for a metal bipolar plate according to claim 1, characterized in that In the step S1, the material of the metal blank includes one of stainless steel, aluminum alloy, titanium alloy, and pure titanium.

5. The electromagnetic preforming - die pressing composite forming method of the metal bipolar plate according to claim 1, wherein, The charge and discharge electronic module (8) includes a power supply (81), a charging switch (82), a capacitor bank (83), and a discharge switch (84). Among them, the power supply (81), the charging switch (82), and the capacitor bank (83) form a charging circuit for charging the capacitor bank (83), and the capacitor bank (83), the discharge switch (84), and the discharge coil (5) form a discharge circuit for discharging the discharge coil (5).

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