Laser destressing method for bipolar plate of titanium alloy fuel cell
The high-density and high-energy laser scanning of the metal bipolar plates is solved by laser destressing method, which solves the problem of internal stress concentration in the manufacturing process, achieves efficient stress removal, and improves mechanical properties and usage performance.
Patent Information
- Application Number
- CN202510054743.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-14
- Publication Date
- 2025-04-15
AI Technical Summary
During the manufacturing process, the internal stress concentration of metal bipolar plates is affected by mechanical force and uneven heat input, which affects its mechanical properties and performance. Existing stress removal methods such as vibration stress removal, thermal aging and process control methods have problems such as high cost, low efficiency or complex process.
The laser stress removal method is used to scan the surface of the metal bipolar plate by a high-density and high-energy laser beam to generate local high temperatures to weaken or eliminate internal stress. The method includes pretreatment steps such as phosphating treatment and pretreatment, laser scanning steps, and flatness and residual stress detection.
It can effectively reduce or eliminate the internal stress of the metal bipolar plate, improve its mechanical properties and performance, and the process is relatively simple and cost is low.
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of metal bipolar plate manufacturing, in particular to a laser stress relief method for a titanium alloy fuel cell bipolar plate. Background Art
[0002] Metal bipolar plates are important components of fuel cells. Their specific functions are to provide gas flow channels, prevent hydrogen and oxygen in the gas chamber from communicating with each other, and establish a current path between the positive and negative electrodes connected in series.
[0003] During the machining stage, the metal bipolar plate generates internal stress due to the influence of mechanical forces such as cutting force and friction, or during the welding forming stage, the metal bipolar plate is subjected to local stress concentration and local thermoplastic deformation due to uneven heat input, which in turn causes internal stress concentration. The existence of internal stress will seriously affect the mechanical properties and performance of the metal bipolar plate. Due to the existence of internal stress, the metal bipolar plate is very prone to bending and deformation in specific applications, which will affect the regularity of the gas flow channel structure.
[0004] As far as the current industry status is concerned, the following solutions are usually adopted to eliminate the internal stress of metal bipolar plates, specifically:
[0005] 1) Vibration stress relief method. By applying periodic dynamic stress and superimposing it on the residual stress inside the metal bipolar plate, local plastic deformation occurs, thereby releasing the internal stress. The vibration stress relief method can release the internal stress of the metal bipolar plate in a short time with less damage to it. However, the purchase cost of ultrasonic stress relief equipment is high and it is difficult to maintain;
[0006] 2) Thermal aging method. Heat the metal bipolar plate to the elastic-plastic transition temperature and keep it for a certain period of time to release its internal stress, then slowly lower the temperature so that the cooled metal bipolar plate can be maintained in a low stress state. There is a temperature difference between different areas of the furnace chamber, and the temperature difference is the main reason for the formation of internal stress. Therefore, the actual stress relief effect is not ideal, and the total aging time generally takes more than 8 hours;
[0007] 3) Process control method. In the blanking and forming stage, the traditional one-time forming process is abandoned, and the continuous die stamping forming process is adopted to minimize the adverse effects of cutting force and friction on the metal bipolar plate. In the welding and forming stage, the welding current is reduced, and preheating before and after welding is performed to reduce the impact of unbalanced heat input on the internal structure of the metal bipolar plate. The stress relief effect is better, however, the process route is complex and cumbersome, and it places extremely high demands on workshop equipment and worker experience, which leads to high manufacturing costs.
[0008] Therefore, technical personnel are urgently needed to solve the above problems. Summary of the invention
[0009] Therefore, in view of the above-mentioned existing problems and defects, the research and development team of the present invention collected relevant information, conducted multiple evaluations and considerations, and after continuous experiments and modifications by the research and development team members, finally launched the laser destressing method for titanium alloy fuel cell bipolar plates.
[0010] In order to solve the above technical problems, the present invention relates to a laser stress relief method for titanium alloy fuel cell bipolar plates, comprising the following steps:
[0011] S1. Pre-treating the metal bipolar plate, which includes the following sub-steps:
[0012] S11. Perform phosphating treatment on the metal bipolar plate, and the thickness of the phosphating film is controlled at 6-8g / m 2 ;
[0013] S12, immersing the metal bipolar plate in the pretreatment solution and retaining it for 8-10 minutes;
[0014] S13, transferring the metal bipolar plate to a curing station to form a dark coating on the surface;
[0015] S2, transferring the metal bipolar plate to the profiling workbench and completing the positioning;
[0016] The profiling workbench has a profiling structure formed on the table surface that matches the back features of the blueprint standard design metal bipolar plate;
[0017] S3. Use a laser scanner to perform energy impact on the front of the metal bipolar plate; the laser scanner power is controlled at 1800-2000W; the spot power density is controlled at 500-650W / cm 2 ; The scanning speed is controlled at 60-80mm / min; the beam incident angle is controlled at 0-90°; the light speed swing width is controlled at 10-20mm;
[0018] S4, flip the metal bipolar plate 180 degrees and place it on the air flotation platform, so that the metal bipolar plate is suspended;
[0019] S5. Use a laser scanner to perform energy impact on the back of the metal bipolar plate; the laser scanner power is controlled at 800-1200W; the spot power density is controlled at 300-350W / cm 2 ; The scanning speed is controlled at 150-200mm / min; the beam incident angle is controlled at 30-45°; the light speed swing width is controlled at 10-20mm;
[0020] S6. The metal bipolar plate is transferred to the quality inspection station to test its flatness and residual stress; if the flatness test results and the residual stress test results meet the quality inspection standards, it is transferred to the next process; if either the flatness test results or the residual stress test results do not meet the quality inspection standards, steps S2-S5 are repeated.
[0021] As a further improvement of the technical solution disclosed in the present invention, in step S12, the formula of the pretreatment solution is as follows, by weight: 100 parts of graphite powder; 10-20 parts of acrylic resin; 5-8 parts of mica powder; 3-5 parts of zinc phosphate; 7-12 parts of diacetone alcohol; 2-6 parts of ethanolamine; 0-20 parts of coupling agent; 800-1000 parts of organic solvent; the retention time of the metal bipolar plate after being immersed in the pretreatment solution is controlled to be 8-10 minutes.
[0022] As a further improvement of the technical solution disclosed in the present invention, in step S2, the profiling workbench uses the negative pressure effect to achieve adsorption and fixation of the metal bipolar plate. A plurality of vents are formed on the profiling workbench at the periphery of the profiling structure forming area to cooperate in adsorbing and fixing the metal bipolar plate.
[0023] In practical applications, the titanium alloy fuel cell bipolar plate laser stress relief method disclosed in the present invention can achieve at least the following beneficial technical effects, specifically:
[0024] 1) By using a high-density, high-energy laser beam to scan the surface of the metal bipolar plate, local stress is concentrated and high temperature is generated locally. When the peak value of the stress wave induced by the laser energy exceeds the dynamic yield limit of the material, the metal bipolar plate will undergo plastic deformation, and the internal stress will be weakened or eliminated. At the same time, beneficial residual compressive stress is generated in the forming area;
[0025] 2) During the laser shock stress relief process, no heat-affected zone is generated, and the laser has the advantages of high energy efficiency and strong controllability, which is conducive to reasonably adjusting the laser parameters according to the different types of metal bipolar plates in actual operation;
[0026] 3) Before the laser shock operation is performed, a phosphating film needs to be generated on the surface of the metal bipolar plate, and a dark coating is formed based on the phosphating film. The dark coating has a good absorption capacity for lasers and a relatively high thermal conductivity. It can quickly transfer the absorbed laser energy to the metal bipolar plate, so that the metal bipolar plate can achieve the design purpose of rapid heating. The phosphating film serves as a connection transition between the metal bipolar plate and the dark coating, which helps to improve the bonding strength of the dark coating.
[0027] 4) The profiling structure formed on the profiling workbench is basically consistent with the back features of the metal bipolar plate, which is conducive to improving the positioning accuracy of the metal bipolar plate and effectively increasing the reliability of the limit, avoiding the occurrence of bulging and arching problems of the metal bipolar plate due to uneven heating during the laser impact process. Furthermore, thanks to the profiling structure design, multiple independent insulation cavities can be formed on the back of the metal bipolar plate. During the laser impact process, part of the laser heat energy that penetrates the metal bipolar plate is retained in the insulation cavity instead of being quickly dissipated, and is used to perform immediate post-heat treatment on the metal bipolar plate after the laser impact. The temperature gradient curve along the thickness direction of the metal bipolar plate can be optimized, which is conducive to fully releasing internal stress;
[0028] 5) During the low-energy laser shock process, the metal bipolar plate is kept in a suspended state to minimize the adverse effects of external restraining forces on the full release of its internal stress. DETAILED DESCRIPTION
[0029] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with the examples, which are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention. The methods described are all conventional methods unless otherwise specified.
[0030] A method for laser stress relief of titanium alloy fuel cell bipolar plates, comprising the following steps:
[0031] S1. Pre-treating the metal bipolar plate, which includes the following sub-steps:
[0032] S11. Perform phosphating treatment on the metal bipolar plate, and the thickness of the phosphating film is controlled at 6-8g / m 2 ;
[0033] S12, immersing the metal bipolar plate in the pretreatment solution and retaining it for 8-10 minutes;
[0034] S13, transferring the metal bipolar plate to a curing station to form a dark coating on the surface;
[0035] S2, transferring the metal bipolar plate to the profiling workbench and completing the positioning;
[0036] The profiling workbench has a profiling structure formed on the table surface that matches the back features of the blueprint standard design metal bipolar plate;
[0037] S3. Use a laser scanner to perform energy impact on the front of the metal bipolar plate; the laser scanner power is controlled at 1800-2000W; the spot power density is controlled at 500-650W / cm 2; The scanning speed is controlled at 60-80mm / min; the beam incident angle is controlled at 0-90°; the light speed swing width is controlled at 10-20mm;
[0038] Note: The working parameters of the laser scanner need to be adaptively adjusted according to the model and specifications of the metal bipolar plate, and the instantaneous temperature should not exceed the phase change temperature of the metal bipolar plate, while ensuring that the internal stress can be released;
[0039] S4, flip the metal bipolar plate 180 degrees and place it on the air flotation platform, so that the metal bipolar plate is suspended;
[0040] S5. Use a laser scanner to perform energy impact on the back of the metal bipolar plate; the laser scanner power is controlled at 800-1200W; the spot power density is controlled at 300-350W / cm 2 ; The scanning speed is controlled at 150-200mm / min; the beam incident angle is controlled at 0-90°; the light speed swing width is controlled at 10-20mm;
[0041] Note: The working parameters of the laser scanner need to be adaptively adjusted according to the model and specifications of the metal bipolar plate, and the instantaneous temperature should not exceed the phase change temperature of the metal bipolar plate, while ensuring that the internal stress can be released;
[0042] S6. The metal bipolar plate is transferred to the quality inspection station to test its flatness and residual stress; if the flatness test results and the residual stress test results meet the quality inspection standards, it is transferred to the next process; if either the flatness test results or the residual stress test results do not meet the quality inspection standards, steps S2-S5 are repeated.
[0043] In practical applications, the titanium alloy fuel cell bipolar plate laser stress relief method disclosed in the present invention can achieve at least the following beneficial technical effects, specifically:
[0044] 1) By using a high-density, high-energy laser beam to scan the surface of the metal bipolar plate, local stress is concentrated and high temperature is generated locally. When the peak value of the stress wave induced by the laser energy exceeds the dynamic yield limit of the material, the metal bipolar plate will undergo plastic deformation, and the internal stress will be weakened or eliminated. At the same time, beneficial residual compressive stress is generated in the forming area;
[0045] 2) During the laser shock stress relief process, no heat-affected zone is generated, and the laser has the advantages of high energy efficiency and strong controllability, which is conducive to reasonably adjusting the laser parameters according to the different types of metal bipolar plates in actual operation;
[0046] 3) Before the laser shock operation is performed, a phosphating film needs to be generated on the surface of the metal bipolar plate, and a dark coating is formed based on the phosphating film. The dark coating has a good absorption capacity for lasers and a relatively high thermal conductivity. It can quickly transfer the absorbed laser energy to the metal bipolar plate, so that the metal bipolar plate can achieve the design purpose of rapid heating. The phosphating film serves as a connection transition between the metal bipolar plate and the dark coating, which helps to improve the bonding strength of the dark coating.
[0047] 4) During the low-energy laser shock process, the metal bipolar plate is kept in a suspended state to minimize the adverse effects of external restraining forces on the full release of its internal stress.
[0048] Here, it should be emphasized that the profiling structure formed on the profiling workbench is basically consistent with the back features of the metal bipolar plate, which is conducive to improving the positioning accuracy of the metal bipolar plate, and effectively increases the reliability of the limit, avoiding the occurrence of bulging and arching problems of the metal bipolar plate due to uneven heating during the laser impact process. Furthermore, thanks to the design of the profiling structure, multiple independent insulation cavities can be formed on the back of the metal bipolar plate. During the laser impact process, part of the laser heat energy that penetrates the metal bipolar plate is retained in the insulation cavity instead of being quickly dissipated, and is used to perform immediate post-heat treatment on the metal bipolar plate after the laser impact. The temperature gradient curve along the thickness direction of the metal bipolar plate can be optimized, which is conducive to fully releasing the internal stress.
[0049] As a further optimization of the above technical solution, in step S2, the profiling workbench uses the negative pressure effect to achieve the adsorption and fixation of the metal bipolar plate. On the periphery of the profiling structure forming area, a plurality of vents are formed on the profiling workbench to cooperate in the adsorption and fixation of the metal bipolar plate. In this way, on the one hand, the positioning and position locking of the metal bipolar plate are quickly achieved, and it is not easy to cause damage to the metal bipolar plate; on the other hand, only the periphery of the metal bipolar plate is vacuum adsorbed, and the middle area is supported by the profiling structure, so as to avoid the adverse effects of the clamping operation on the internal stress release process as much as possible.
[0050] In addition, a pretreatment solution formula is also disclosed in this embodiment, specifically: by weight, 100 parts of graphite powder; 10-20 parts of acrylic resin; 5-8 parts of mica powder; 3-5 parts of zinc phosphate; 7-12 parts of diacetone alcohol; 2-6 parts of ethanolamine; 0-20 parts of coupling agent; 800-1000 parts of organic solvent; the retention time of the metal bipolar plate after being immersed in the pretreatment solution is controlled to be 8-10 minutes. In this way, on the one hand, the prepared pretreatment solution has good fluidity and excellent affinity, which is conducive to the rapid infiltration of the phosphating mold; on the other hand, the cured dark coating has good mechanical properties, weather resistance, and better thermal stability, and will not completely decompose or peel off even if subjected to instantaneous high temperature.
[0051] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest range of convergences with the principles and novel features disclosed herein.
Claims
1. A method for laser stress relief of titanium alloy fuel cell bipolar plates, comprising the following steps: S1. Pre-treating the metal bipolar plate, including the following sub-steps: S11. Perform phosphating treatment on the metal bipolar plate, and the thickness of the phosphating film is controlled at 6-8g / m 2 ; S12, immersing the metal bipolar plate in the pretreatment solution and retaining it for 8-10 minutes; S13, transferring the metal bipolar plate to a curing station to form a dark coating on the surface; S2, transferring the metal bipolar plate to the profiling workbench and completing the positioning; The profiling workbench has a profiling structure formed on the table surface that matches the back features of the blueprint standard design metal bipolar plate; S3. Use a laser scanner to perform energy impact on the front of the metal bipolar plate; the laser scanner power is controlled at 1800-2000W; the spot power density is controlled at 500-650W / cm 2 ; The scanning speed is controlled at 60-80mm / min; the beam incident angle is controlled at 0-90°; the light speed swing width is controlled at 10-20mm; S4, flip the metal bipolar plate 180 degrees and place it on the air flotation platform, so that the metal bipolar plate is suspended; S5. Use a laser scanner to perform energy impact on the back of the metal bipolar plate; the laser scanner power is controlled at 800-1200W; the spot power density is controlled at 300-350W / cm 2 ; The scanning speed is controlled at 150-200mm / min; the beam incident angle is controlled at 30-45°; the light speed swing width is controlled at 10-20mm; S6. The metal bipolar plate is transferred to the quality inspection station to test its flatness and residual stress; if the flatness test results and the residual stress test results meet the quality inspection standards, it is transferred to the next process; if either the flatness test results or the residual stress test results do not meet the quality inspection standards, steps S2-S5 are repeated.
2. The method for laser stress relief of titanium alloy fuel cell bipolar plates according to claim 1, characterized in that: In step S12, the formula of the pretreatment solution is as follows by weight: 100 parts of graphite powder; 10-20 parts of acrylic resin; 5-8 parts of mica powder; 3-5 parts of zinc phosphate; 7-12 parts of diacetone alcohol; 2-6 parts of ethanolamine; 0-20 parts of coupling agent; 800-1000 parts of organic solvent; the retention time of the metal bipolar plate after being immersed in the pretreatment solution is controlled to be 8-10 minutes.
3. The method for laser stress relief of titanium alloy fuel cell bipolar plates according to claim 1, characterized in that: In step S2, the profiling workbench utilizes the negative pressure effect to achieve adsorption and fixation of the metal bipolar plate; a plurality of vent holes that cooperate to adsorb and fix the metal bipolar plate are formed on the profiling workbench at the periphery of the profiling structure forming area.