An ultrasonic welding method for a metal bipolar plate for a fuel cell

Abstract

The application discloses an ultrasonic welding method for a metal bipolar plate of a fuel cell. The metal bipolar plate of the fuel cell comprises a first metal plate and a second metal plate stacked in an up-down mode. The ultrasonic welding method comprises the following steps: (1) cleaning and drying the first metal plate and the second metal plate; and (2) ultrasonic welding after stacking the first metal plate and the second metal plate in the up-down mode. When the metal bipolar plate is welded, the first metal plate and the second metal plate are stacked together, and a welding seam is formed between the first metal plate and the second metal plate. The outer surfaces of the two sides of the metal bipolar plate are complete without welding slag, and the damage to the pre-coating layer is avoided, so that the batch production of the pre-coating bipolar plate is facilitated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fuel cells, and particularly relates to an ultrasonic welding method of a metal bipolar plate for a fuel cell. BACKGROUND

[0002] Under the background of energy saving and emission reduction, fuel cell technology with green energy characteristics has attracted people's attention and has obvious advantages in inhibiting carbon dioxide emissions. At present, fuel cells are in the technology introduction period, and fuel cell buses, logistics vehicles, engineering vehicles, unmanned aerial vehicles and other application scenarios have been demonstrated on a large scale. However, the current fuel cell still faces many problems, such as high manufacturing cost, short service life, large volume, complex system and the like.

[0003] The metal bipolar plate is one of the core components of the fuel cell. The metal bipolar plate is composed of two single plates with flow channels on the surface, and the two single plates are fixed together to form a two-plate three-cavity structure. The bipolar plate usually adopts two processes of welding first and coating later or coating first and welding later. The existing process adopts a laser welding machine for laser welding, and the laser is melted from the upper part to weld with the lower bipolar plate. This welding method is easy to cause the upper bipolar plate to be excessively melted, form welding slag on the upper surface, damage the pre-coating layer, or cause the subsequent coating layer to be prepared on the welding line to have poor bonding force, forming a weak point. Especially in the spot welding reinforcement point of the flow field area, corrosion is more likely to occur, causing irreversible damage to the bipolar plate and the membrane electrode. At the same time, more heat in the welding process will also cause the stress to increase during the welding process, affecting the contact resistance and assembly stability.

[0004] For example, the invention with the publication number CN108637476A discloses a laser welding electromagnetic adsorption clamping device for a fuel cell bipolar plate, which comprises a welding rack, a welding base, a welding auxiliary cover plate, a welding cover plate and a welding fixed plate. A guide conveying device is arranged on the welding rack to guide the bipolar plate placed on the welding base to the lower side of the welding position on the welding rack. A lifting device is arranged below the welding position, and the lifting device cooperates with the welding auxiliary cover plate to provide mechanical clamping on the outside of the welding path. A first electromagnetic force generating device is arranged on the welding base, and the first electromagnetic force generating device electromagnetically adsorbs the first magnet on the welding cover plate to electromagnetically adsorb and clamp the inside of the welding path.

[0005] Ultrasonic welding does not need flux and external heating, does not deform due to heating, has no residual stress, and has low requirements for the surface treatment of the welding parts. It can be used to weld similar metals and dissimilar metals. It can be used to weld thin sheets or filaments on thick plates. Ultrasonic welding of good conductors requires much less energy than current welding, and is often used to weld the leads of transistors or integrated circuits. It is suitable for nickel-hydrogen battery nickel mesh and nickel sheet intermelting, nickel sheet intermelting, lithium battery, polymer battery copper foil and nickel sheet intermelting, aluminum foil and aluminum sheet intermelting, wire intermelting, partial joint intermelting, multi-joint intermelting, wire and various electronic components, contacts, connectors, and the like.

[0006] The ultrasonic metal welding machine has poor "openness", the extension size is strictly limited within the range allowed by welding, and the welding form is still limited to lap joints, and long-distance continuous welding cannot be performed. SUMMARY

[0007] The present application aims at the technical problems existing in the prior art, and provides an ultrasonic welding method for a metal bipolar plate of a fuel cell.

[0008] An ultrasonic welding method for a metal bipolar plate of a fuel cell, the metal bipolar plate of the fuel cell comprises a first metal plate and a second metal plate stacked in an up-down manner, and the ultrasonic welding method comprises the following steps:

[0009] (1) cleaning and drying the first metal plate and the second metal plate;

[0010] (2) stacking the first metal plate and the second metal plate in an up-down manner and then performing ultrasonic welding.

[0011] Preferably, in step (1), the cleaning is first oil removal cleaning, and after the oil removal cleaning is completed, ultrasonic cleaning is performed in pure water; then the first metal plate and the second metal plate are placed in ethanol for ultrasonic cleaning, and then placed in pure water for ultrasonic cleaning, and then dried. The oil removal cleaning uses pure alkali or caustic soda with a mass-volume concentration of 5% to 30% or uses pure hydrocarbon cleaning agent for oil removal cleaning.

[0012] Preferably, in step (2), the ultrasonic welding head remains unchanged during the welding process, and the metal bipolar plate is moved for continuous welding.

[0013] In order to further reduce the welds in the welding process, the ultrasonic welding head adopts a conical horn.

[0014] Preferably, the ultrasonic frequency of the ultrasonic welding is 15 to 40 KHz. More preferably, the ultrasonic frequency of the ultrasonic welding is 20 KHz.

[0015] Preferably, the ultrasonic welding speed is 50-400 mm / min. More preferably, the ultrasonic welding speed is 200 mm / min.

[0016] The fuel cell metal bipolar plate comprises a middle flow field region and inlet and outlet regions on both sides in the length direction,

[0017] The ultrasonic welding is wave-propagation welding, which welds one side in the length direction of the fuel cell metal bipolar plate first, then welds both sides in the width direction, then welds the flow field region, and finally welds the other side in the length direction. Using this welding method can wave-propagation weld, which means welding adjacent points one by one according to preset welding points in the spot welding process, reducing the deformation and internal stress accumulation between the two plates during welding.

[0018] The ultrasonic welding is performed under the protection of inert atmosphere. The inert atmosphere can be nitrogen or helium.

[0019] The present application has the following advantages:

[0020] The present application adopts ultrasonic welding of metal bipolar plates. When the metal is ultrasonic welded, no current is transmitted to the workpiece, and no high-temperature heat source is applied to the workpiece. Only the linear frame vibration energy is converted into friction work, deformation energy and limited temperature rise between the workpieces under static pressure. The metallurgical bonding between the joints is a solid-state welding without melting of the base material. When the metal bipolar plate is welded, the first metal plate and the second metal plate are stacked together, and a weld is formed between the first metal plate and the second metal plate. The outer surfaces of the metal bipolar plate on both sides are complete without welding slag, which will not damage the pre-coating layer, and is convenient for batch production of the pre-coating bipolar plate. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a schematic diagram of laser welding and ultrasonic welding of metal bipolar plates.

[0022] Figure 2 It is a schematic diagram of the structure of the metal bipolar plate.

[0023] Figure 3 It is a wave-type welding zoning diagram of the bipolar plate.

[0024] Figure 4 It is a schematic diagram of the welding line position of the metal bipolar plate except the flow field region. DETAILED DESCRIPTION

[0025] Figure 1The comparison of laser welding and ultrasonic welding of metal bipolar plate is shown. It can be seen that when laser welding is used, the energy received by the side of the metal bipolar plate facing the laser welding device (i.e. the upper surface of the metal bipolar plate) is greater, and slag is formed on the upper surface; while when ultrasonic welding is used, a weld is formed between the upper and lower layers of the metal bipolar plate, and the outer surfaces of the two sides of the metal bipolar plate are intact without slag, and the damage to the pre-coating is avoided.

[0026] As shown in Figure 2 The structure of the metal bipolar plate is shown. The overall shape of the metal bipolar plate is a rectangular thin plate structure formed by stacking two metal plates and ultrasonic welding. The upper and lower outer surfaces are used to form the hydrogen flow field and the air flow field, respectively, and the middle of the two metal plates is a cooling channel. The metal bipolar plate includes a flow field region in the middle and an inlet region and an outlet region on both sides in the length direction. When ultrasonic welding is performed, one side of the metal bipolar plate in the length direction is welded first, then the two sides in the width direction are welded in turn, then the flow field region is welded, and finally the other side in the length direction is welded. As shown in Figure 3 The metal bipolar plate is divided into regions, where the A region and the E region are on both sides in the length direction of the metal bipolar plate, the B region and the C region are on both sides in the width direction of the metal bipolar plate, and the D region is the flow field region. The welding can be performed in the order of A region → B region → C region → D region → E region, and the order of the A region and the E region can be interchanged, and the order of the B region and the C region can also be interchanged. Figure 4 The welding line position diagram of the metal bipolar plate except for the flow field region is shown.

[0027] Before ultrasonic welding, the two metal plates are cleaned and dried. The cleaning is first performed by oil removal cleaning, which uses pure soda or caustic soda with a mass-volume concentration of 5% to 30% or pure carbon hydrogen cleaning agent for oil removal cleaning. After oil removal cleaning, ultrasonic cleaning is performed; then the two metal plates are placed in ethanol for ultrasonic cleaning, and then placed in pure water for ultrasonic cleaning, and then dried.

[0028] During ultrasonic welding, the ultrasonic welding head remains unchanged, and the metal bipolar plate is moved for continuous welding. A conical horn is used for ultrasonic welding to further reduce the weld during welding. The ultrasonic frequency of ultrasonic welding is 15 to 40 kHz, and the speed of ultrasonic welding is 10 to 1000 mm / min.

[0029] During ultrasonic welding, the welding is performed under the protection of an inert atmosphere. The inert atmosphere can be nitrogen or helium.

[0030] Example 1

[0031] Two pieces of 316L coated stainless steel metal monopolar plates with the size of 20mmx100mmx0.1mm (two pieces stacked to form a bipolar plate), the coated metal monopolar plates were first subjected to oil removal cleaning for 10 minutes, and the oil removal cleaning used pure soda with a mass-volume concentration of 5%. After the oil removal was completed, the substrate was subjected to ultrasonic water washing, and then was placed into ethanol for ultrasonic cleaning, and then was placed into pure water for ultrasonic cleaning, and then was dried.

[0032] The two pieces of cleaned stainless steel plates for preparing metal bipolar plates were stacked and fixed on the ultrasonic welding machine clamp. The bipolar plate and its clamp were fixed on the guide rail driven by a servo motor. According to the established welding route, the bipolar plate was moved and welded along the guide rail, and during ultrasonic welding, the ultrasonic welding machine was turned on, nitrogen was passed, the cooling water was turned on, the ultrasonic frequency was set to 20 KHZ, the welding speed was set to 200 mm / min, and the welding was performed in the order of A zone→B zone→C zone→D zone→E zone. After the welding was completed, the gas tightness detection was performed, and the water cavity had no leakage, the hydrogen cavity had no leakage, and the oxygen cavity had no leakage. After the welding was completed, the gas tightness detection was performed, and the water cavity had no leakage, the hydrogen cavity had no leakage, and the oxygen cavity had no leakage. The contact resistance test of the bipolar plate was 2 mΩ·cm 2 .

[0033] Example 2

[0034] Two pieces of 316L coated stainless steel metal monopolar plates with the size of 20mmx100mmx0.1mm (two pieces stacked to form a bipolar plate), and the remaining steps were the same as the method of Example 1, and the ultrasonic frequency was set to 20 KHZ, and the welding speed was set to 50 mm / min for welding. After the welding was completed, the contact resistance test was 2.3 mΩ·cm 2 .

[0035] Example 3

[0036] Two pieces of 316L coated stainless steel metal monopolar plates with the size of 20mmx100mmx0.1mm (two pieces stacked to form a bipolar plate), and the remaining steps were the same as the method of Example 1, and the ultrasonic frequency was set to 20 KHZ, and the welding speed was set to 400 mm / min for welding. After the welding was completed, the contact resistance test was 2.3 mΩ·cm 2 .

[0037] Example 4

[0038] Two pieces of 316L coated stainless steel metal monopolar plates with the size of 20mmx100mmx0.1mm (two pieces stacked to form a bipolar plate), and the remaining steps were the same as the method of Example 1, and the ultrasonic frequency was set to 15 KHZ, and the welding speed was set to 200 mm / min for welding. After the welding was completed, the contact resistance test was 3.1 mΩ·cm 2 .

[0039] Example 5

[0040] Two pieces of 316L coated stainless steel metal monopolar plates with a size of 20mm x 100mm x 0.1mm (two pieces stacked to form a bipolar plate), the rest of the steps are the same as the method of Example 1, set the ultrasonic frequency to 40KHZ, and the welding speed to 200mm / min for welding. After welding, the contact resistance test is 3.8mΩ·cm 2 .

[0041] Comparative Example 1

[0042] Two pieces of 316L coated stainless steel metal monopolar plates with a size of 20mm x 100mm x 0.1mm (two pieces stacked to form a bipolar plate), the coated metal bipolar plate is first cleaned for 10 minutes, and the cleaning uses pure soda with a mass-volume concentration of 5%. After cleaning, the substrate is ultrasonically washed with water, then placed in ethanol for ultrasonic cleaning, and then placed in pure water for ultrasonic cleaning, and then dried.

[0043] Stack the two layers of monopolar plates, place them in the fixture and fix them. Turn on the bipolar laser welding machine, set the laser welding machine power to 35w, the welding speed to 20mm / s, and perform laser welding according to the pouring welding path. After welding, the gas tightness test shows that the water cavity has no leakage, the hydrogen cavity has no leakage, and the oxygen cavity has no leakage, and the contact resistance test of the bipolar plate is 8.5mΩ·cm 2 .

[0044] As can be seen from the data of Examples 1-5 and Comparative Example 1, the contact resistance of the bipolar plate prepared using the ultrasonic welding method of the present application is smaller than that of the bipolar plate prepared by conventional laser welding. The ultrasonic frequency and the welding speed are not faster or slower, but have better results under the most suitable conditions.

[0045] Example 6

[0046] Two pieces of 316L coated stainless steel metal plates with a size of 20mm x 100mm x 0.1mm (not pressed flow channel, used for testing tensile strength after ultrasonic welding), the cleaning method is the same as Example 1.

[0047] Stack the two layers of metal plates at the head 1 / 4 part and place them on the ultrasonic welding machine fixture for fixation. The bipolar plate and its fixture are fixed on the guide rail driven by a servo motor. According to the established welding route, the bipolar plate moves along with the guide rail while welding. When ultrasonic welding, turn on the ultrasonic welding machine, pass nitrogen, turn on the cooling water, set the ultrasonic frequency to 20KHZ, and the welding speed to 50mm / min for cross welding.

[0048] After the welding, the tensile test was carried out on the universal testing machine, and the tensile strength was 82 MPa.

[0049] Example 7

[0050] The remaining steps were the same as the method of Example 6, and the ultrasonic frequency was set to 20 KHZ, and the welding speed was 400 mm / min for cross welding. After the welding, the tensile test was carried out on the universal testing machine, and the tensile strength was 74 MPa.

[0051] Example 8

[0052] The remaining steps were the same as the method of Example 6, and the ultrasonic frequency was set to 15 KHZ, and the welding speed was 200 mm / min for cross welding. After the welding, the tensile test was carried out on the universal testing machine, and the tensile strength was 65 MPa.

[0053] Example 9

[0054] The remaining steps were the same as the method of Example 6, and the ultrasonic frequency was set to 40 KHZ, and the welding speed was 200 mm / min for cross welding. After the welding, the tensile test was carried out on the universal testing machine, and the tensile strength was 80 MPa.

[0055] From the data of Examples 6-9, it can be seen that the tensile strength of the metal bipolar plate obtained by using the ultrasonic welding method is higher, and the ultrasonic frequency and the welding speed are not the faster the better or the slower the better, but have better effect under the most suitable conditions.

Claims

1. An ultrasonic welding method of a metal bipolar plate for a fuel cell, the metal bipolar plate for a fuel cell including a first metal plate and a second metal plate stacked in an upper and lower relationship, characterized by, The ultrasonic welding method comprises the following steps: (1) cleaning and drying the first metal plate and the second metal plate; (2) stacking the first metal plate and the second metal plate upside down and then performing ultrasonic welding; The ultrasonic welding frequency is 15-40 KHz; the ultrasonic welding speed is 50-400 mm / min; The metal bipolar plate for fuel cells comprises a middle flow field area and inlet and outlet areas on both sides along the length direction, The ultrasonic welding is wave recursion welding, which first welds one side of the metal bipolar plate for fuel cells along the length direction, then welds both sides along the width direction in sequence, then welds the flow field area, and finally welds the other side along the length direction; In step (2), the ultrasonic welding head remains unchanged during the welding process, and the metal bipolar plate is moved for continuous welding; the ultrasonic welding head adopts a conical horn; the ultrasonic welding is performed under the protection of an inert atmosphere.

2. The ultrasonic welding method of a metal bipolar plate for a fuel cell according to claim 1, characterized by, In step (1), the oil removal cleaning is first performed during the cleaning, ultrasonic cleaning in pure water is then performed after the oil removal cleaning is completed, the first metal plate and the second metal plate are then placed in ethanol for ultrasonic cleaning, and then placed in pure water for ultrasonic cleaning, and finally dried.

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