A method of welding during forming of a contact

Abstract

This invention discloses a welding method in the contact forming process, comprising the following steps: S1, powder preparation: sequentially placing conductive component and silver-based electrical contact powder into a mold to obtain a flash-firing mold; S2, flash-firing: placing the flash-firing mold into a sintering furnace for a single flash-firing to obtain the contact assembly; S3, machining: machining the contact assembly obtained in step S2; This invention connects the contact powder and conductive component together during the powder forming process to form a contact conductive component, which is suitable for fixing the contact onto the conductive component without affecting subsequent welding or performance. It can avoid solder creep in the contact metal coating and allows gas to be discharged during welding. This welding structure can overcome problems such as poor venting, insufficient contact area, and reduced welding complexity in the current welding process.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically to a welding method in the forming process of a contact. Background Technology

[0002] Silver-based electrical contacts have a brazing composite material layer sintered on the welding surface of the silver-based electrical contact body. The brazing composite material includes brazing alloy powder, flux, adhesive and curing agent, etc. Different processes have different requirements. Finally, it is sintered and cured under inert gas protection. This method has a certain yield.

[0003] The existing technical solution for contact molding is as follows: a) Mix the components of the brazing composite material according to the specified ratio and stir until a paste-like fluid is formed; b) Print the resulting paste-like fluid onto the welding surface of the silver-based electrical contact using a dispensing machine; c) Sinter and cure the silver-based electrical contact with the printed paste-like fluid under an inert gas protection.

[0004] The above technical solution has the disadvantages of poor venting and insufficient contact area in the current welding process, which are caused by the easy occurrence of solder creep during the contact welding process. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a welding method in the forming process of contacts.

[0006] The technical solution of this invention is: a welding method in the forming process of a contact, comprising the following steps:

[0007] S1. Preparing the powder:

[0008] Prepare contact powder for silver-based electrical contacts, and then place the conductive components and contact powder into a mold in sequence to obtain a flash-fired mold;

[0009] S2, Flash Burn:

[0010] The flash-fired mold is placed in a sintering furnace and heated to the sintering temperature at a heating rate of 95-105℃ / min. The sintering temperature is 10% lower than the melting point of the silver-based electrical contact. The pressure is 115-125MPa. The sintering time is 9-11 minutes to complete one flash-fire. After the first flash-fire, the temperature and pressure are maintained for 9-11 minutes to obtain the entire contact.

[0011] S3, Processing:

[0012] The contact obtained in step S2 is machined to obtain a welded contact.

[0013] Furthermore, the silver-based electrical contact is AgWC, wherein the mass ratio of Ag to WC is 3:2.

[0014] Note: Silver tungsten carbide electrical contacts have good electrical conductivity, excellent thermal conductivity, low and stable contact resistance, high corrosion resistance, and strong resistance to welding.

[0015] Furthermore, the C content in the WC is <4%.

[0016] Note: When the carbon content is too high, the hardness and brittleness of tungsten carbide will increase, while the toughness will decrease, thus affecting its mechanical properties and processing performance. When the carbon content is too low, unreacted tungsten or subcarbide may be present in the tungsten carbide, which will lead to a decrease in hardness and wear resistance, thereby affecting the performance of tungsten carbide.

[0017] Furthermore, the particle size of the contact powder is <10μm.

[0018] Note: If the contact powder particle size is too large, the contact powder flowability is often poor, making it difficult to mix and compress evenly during processing; if the contact powder particle size is too small, it will increase the density of the contact powder, making processing more difficult.

[0019] Furthermore, the conductive component is made of copper alloy.

[0020] Note: Copper alloys have a certain degree of corrosion resistance, which can increase the corrosion resistance of conductive components; copper alloy materials have high electrical conductivity, which can provide good electrical conductivity for conductive components.

[0021] Furthermore, in step S1, after placing the conductive component, the solder sheet is placed first and then the contact powder is placed; in step S2, after the first flash burn is completed and the temperature and pressure are maintained, a second flash burn is performed, and the parameters of the second flash burn are the same as those of the first flash burn.

[0022] Note: When the size of the conductive component is too large to directly form a contact whole with the contact powder, a solder pad is added to weld the solder pad to the contact powder to obtain a contact with the solder pad. Then, the contact is flash-welded to the conductive component to form a contact whole.

[0023] Furthermore, the solder pad is AgCu, wherein the mass ratio of Ag to Cu is 1:4.

[0024] Note: AgCu has the same Ag element as the contact and the same Cu element as the conductive part, so it can be used as a solder pad to connect the two.

[0025] Furthermore, the contact assembly obtained in step S2 can be divided into three layers: a contact powder layer, a bonding layer between the contact powder and the conductive element, and a conductive element layer. After the first flash firing and heat preservation and pressure holding are completed, the contact assembly is subjected to layered directional cooling, as follows:

[0026] 1) First, immerse the entire contact in a coolant at a temperature of 15-25℃ for 30-40 minutes to cool it down.

[0027] 2) Then remove the entire contact and immerse the conductive layer in a coolant at a temperature of 0 to 5°C and the contact powder layer in a coolant at a temperature of -5 to 0°C, and cool them simultaneously for 50 to 60 minutes.

[0028] 3) Stop cooling the conductive layer and the contact powder layer, and immerse the bonding layer in a coolant at a temperature of -15 to -10°C for 40 to 50 minutes.

[0029] Note: Due to the high power of the overall flash burn-in process, water cooling cannot meet the heat dissipation requirements, resulting in a slow heat dissipation rate and failing to achieve the effect of grain refinement. Therefore, coolant is chosen for cooling, which can reduce the temperature of the silver-based contact layer, reduce its thermal conduction effect, and extend its service life. The bonding layer between the silver-based contact and the copper conductive component is the key layer connecting the two. Cooling can reduce the temperature of the bonding layer, reduce the impact of thermal expansion on the bonding layer, and improve electrical contact performance and stability. Cooling the copper alloy conductive component layer can protect the copper conductive component from the effects of high temperature, delay its aging and oxidation process, and play an important role in improving the conductivity and stability of the conductive component.

[0030] Silver-based electrical contacts have higher thermal and electrical conductivity, so they require lower cooling temperatures to achieve good conductivity at lower temperatures. If the cooling temperature of the bonding layer is too high, it may increase the difference in thermal expansion coefficients between the bonding layer and the materials on both sides, thereby generating thermal stress, which may lead to material damage or performance degradation. It may also cause material loss or oxidation in the bonding layer, thus affecting the performance and stability of the contact.

[0031] Further, the coolant is water: ethylene glycol in a mass ratio of 4:1:0.5:0.06-0.09.

[0032] Disodium hydrogen phosphate: 4-vinylpyridine.

[0033] Note: Ethylene glycol is affordable, has low corrosiveness, strong antifreeze ability, high safety, and a high boiling point that makes it difficult to evaporate. However, ethylene glycol antifreeze is prone to generating acidic substances during use, which can corrode metals. Therefore, an appropriate amount of disodium hydrogen phosphate is added to prevent corrosion, and 4-vinylpyridine is added to improve the overall cooling effect of ethylene glycol on the outlet.

[0034] The beneficial effects of this invention are:

[0035] (1) This invention discloses that, according to different actual needs, conductive components and contact powder are added to the mold; during the powder forming process, they are connected together with the conductive components to form a contact conductive component, which is suitable for fixing the contact on the conductive component without affecting subsequent welding or performance. It can avoid solder creep in the metal coating of the contact and exhaust gas to the outside during welding. This welding structure can overcome the problems of poor venting in the current welding process, insufficient contact area, and reduced welding complexity.

[0036] (2) The welding method of the present invention can be used for contacts and conductive parts with the same metal composition, or for materials that can form alloys, thereby improving the product preparation cycle and stability. Detailed Implementation

[0037] The present invention will now be described in more detail with reference to specific embodiments, so as to better demonstrate the advantages of the present invention.

[0038] Example 1

[0039] A welding method in the forming process of a contact includes the following steps:

[0040] S1. Preparing the powder:

[0041] A contact powder for preparing silver-based electrical contacts is prepared, wherein the particle size of the contact powder is 8-9 μm, and the conductive element and the contact powder are sequentially placed into a mold to obtain a flash-firing mold; the silver-based electrical contacts are AgWC, wherein the mass ratio of Ag:WC is 3:2, and the C content in the WC is 2%; the conductive element is a CuCr1 alloy.

[0042] S2, Flash Burn:

[0043] The flash-fired mold is placed in a sintering furnace and heated to the sintering temperature at a heating rate of 100℃ / min. The sintering temperature is 10% lower than the melting point of AgWC, i.e., 850℃. The pressure is 110MPa. Sintering is carried out for 10 minutes to complete one flash-fire. After the first flash-fire, the temperature and pressure are maintained for 10 minutes to obtain the entire contact.

[0044] S3, Processing:

[0045] After the contact obtained in step S2 is cooled to room temperature, it is machined to obtain a welded contact.

[0046] Example 2

[0047] The difference between this embodiment and embodiment 1 is that in step S2, the temperature is increased to the sintering temperature at a heating rate of 95℃ / min. The sintering temperature is 10% lower than the melting point of the silver-based electrical contact, the pressure is 115MPa, and the sintering time is 9 minutes to complete one flash firing. After the flash firing is completed, the temperature and pressure are maintained for 9 minutes.

[0048] Example 3

[0049] The difference between this embodiment and embodiment 1 is that in step S2, the temperature is increased to the sintering temperature at a heating rate of 105℃ / min. The sintering temperature is 10% lower than the melting point of the silver-based electrical contact, the pressure is 125MPa, and the sintering time is 11 minutes to complete one flash firing. After the flash firing is completed, the temperature and pressure are maintained for 11 minutes.

[0050] Example 4

[0051] The difference between this embodiment and embodiment 1 is that in step S1, after placing the conductive component, the solder sheet is placed first and then the contact powder is placed. The solder sheet is AgCu, and the mass ratio of Ag to Cu is 1:4. In step S2, after the first flash firing is completed and the temperature and pressure are maintained, a second flash firing is performed, and the parameters of the second flash firing are the same as those of the first flash firing.

[0052] Example 5

[0053] The difference between this embodiment and Embodiment 1 is that the contact obtained in step S2 can be divided into three layers: a contact powder layer, a bonding layer between the contact powder and the conductive element, and a conductive element layer. After the first flash firing and heat preservation and pressure holding are completed, the contact is subjected to layered directional cooling, as follows:

[0054] 1) First, immerse the entire contact in a coolant at a temperature of 20°C for 35 minutes to cool it down.

[0055] 2) Then remove the entire contact and immerse the conductive layer in a coolant at 3°C ​​and the contact powder layer in a coolant at -3°C for 55 minutes to cool simultaneously.

[0056] 3) Stop cooling the conductive layer and the contact powder layer, and immerse the bonding layer in a coolant at -12℃ for 45 minutes to cool it separately.

[0057] The coolant is composed of water, ethylene glycol, disodium hydrogen phosphate, and 4-vinylpyridine in a mass ratio of 4:1:0.5:0.08.

[0058] Example 6

[0059] The difference between this embodiment and embodiment 5 is that: 1) the entire contact is first immersed in a coolant at a temperature of 25°C for 30 minutes to cool it down.

[0060] Example 7

[0061] The difference between this embodiment and embodiment 5 is that: 1) the entire contact is first immersed in a coolant at a temperature of 15°C for 40 minutes to cool it down.

[0062] Example 8

[0063] The difference between this embodiment and embodiment 5 is that, 2) the entire contact is then removed and the conductive layer is immersed in a coolant at a temperature of 5°C, and the contact powder layer is immersed in a coolant at a temperature of 0°C for 50 minutes to cool simultaneously.

[0064] Example 9

[0065] The difference between this embodiment and embodiment 5 is that, 2) the entire contact is then removed and the conductive layer is immersed in a coolant at a temperature of 0°C, and the contact powder layer is immersed in a coolant at a temperature of -5°C for 60 minutes to cool simultaneously.

[0066] Example 10

[0067] The difference between this embodiment and embodiment 5 is that, 3) the cooling of the conductive layer and the contact powder layer is stopped, and the bonding layer is immersed in a cooling liquid at a temperature of -10°C for 40 minutes to cool it separately.

[0068] Example 11

[0069] The difference between this embodiment and embodiment 5 is that, 3) the cooling of the conductive layer and the contact powder layer is stopped, and the bonding layer is immersed in a cooling liquid at a temperature of -15°C for 50 minutes to cool it separately.

[0070] Example 12

[0071] The difference between this embodiment and Embodiment 5 is that the coolant is water: ethylene glycol: disodium hydrogen phosphate: 4-vinylpyridine in a mass ratio of 4:1:0.5:0.06.

[0072] Example 13

[0073] The difference between this embodiment and Embodiment 5 is that the coolant is water, ethylene glycol, disodium hydrogen phosphate, and 4-vinylpyridine in a mass ratio of 4:1:0.5:0.09.

[0074] Experimental Example

[0075] For the contacts prepared in each embodiment, five samples from each embodiment were taken to test the performance of the contacts. The average performance measurement results of the five samples in each embodiment were taken as the performance measurement result of that embodiment. The specific investigation is as follows:

[0076] 1. Investigate the effects of flash burning parameters on contact hardness and conductivity.

[0077] Table 1 shows the effects of Examples 1-3 and Control Example 1 on contact hardness (HB), conductivity (MS / m), and preparation time (h).

[0078] hardness 180 170 173 187 235 electrical conductivity 23.5 23.3 23.4 23.7 20.2 Preparation time 1 1.4 1.2 2.1h 8h

[0079] The difference between Comparative Example 1 and Example 1 is that the contact was prepared by welding after infiltration;

[0080] As shown in Table 1, although the overall hardness of the contact was higher when the contact was prepared by melt infiltration in Example 1, the electrical conductivity was lower than that of the flash firing process used in Examples 1-4. Moreover, the preparation time required for melt infiltration was 6-7 hours longer than that of the present invention. Therefore, the flash firing process used in the present invention not only improved the mechanical properties of the contact, but also shortened the preparation time of the contact.

[0081] Furthermore, comparing Examples 1 to 3, it can be seen that if the flash burning parameters are too small or too large, the hardness and conductivity of the contacts will be reduced. Comparing Examples 1 to 3 with Example 4, it can be seen that the contacts obtained by the second flash burning are harder, and the internal oxidation treatment during the interval between the first and second flash burning can significantly improve the hardness and conductivity of the contacts. Therefore, the flash burning parameters of Example 1 are relatively optimal.

[0082] 2. Investigate the effect of the overall cooling process on the contact hardness and conductivity.

[0083] Table 2 shows the effects of Examples 4-13 and Comparative Examples 2-3 on contact hardness (HB) and conductivity (MS / m).

[0084] hardness 216 205 211 203 207 electrical conductivity 24.5 24.1 24.2 23.9 24.0 Group Example 10 Example 11 Example 12 Example 13 Compare with Example 2 hardness 210 204 206 212 193 electrical conductivity 24.3 24.2 24.1 24.2 23.8

[0085] The difference between Comparative Example 3 and Example 5 is that the coolant does not contain 4-vinylpyridine;

[0086] As shown in Table 1, the coolant in Control Example 3 lacked 4-vinylpyridine, resulting in a decrease in both hardness and conductivity compared to Examples 5-13, with a greater decrease in hardness. Therefore, Examples 5-13 exhibited superior processing performance.

[0087] Comparing Examples 1 and 5-13, it can be seen that Example 1 lacks layered directional cooling, and the hardness and conductivity of the contact obtained by overall cooling are lower than those of Examples 5-13. Therefore, layered directional cooling improves the hardness and conductivity of the contact to a certain extent.

[0088] Comparing Examples 5-13, it can be seen that if the overall cooling parameters of the contact are too small or too large, the cooling parameters of the conductive layer and the contact powder layer are too small or too large, the cooling parameters of the bonding layer are too small or too large, and the proportion of 4-vinylpyridine in the coolant is too small or too large, the improvement in contact hardness and conductivity will be reduced.

[0089] Therefore, in summary, the process and parameters of Example 5 are the most effective.

Claims

1. A welding method in the forming process of a contact, characterized in that, Includes the following steps: S1. Preparing the powder: A silver-based electrical contact powder is prepared, and conductive components and contact powder are sequentially placed into a mold. After placing the conductive components, a solder sheet is placed first, followed by the contact powder, to obtain a flash-burning mold. The silver-based electrical contact is AgWC, wherein the mass ratio of Ag to WC is 3:2, and the C content in WC is <4%. The solder sheet is AgCu, wherein the mass ratio of Ag to Cu is 1:

4. S2, Flash Burn: The flash-fired mold is placed in a sintering furnace and heated to the sintering temperature at a heating rate of 95~105℃ / min. The sintering temperature is 10% lower than the melting point of the silver-based electrical contact. The pressure is 115~125MPa. Sintering takes 9~11 minutes to complete the first flash firing. After the first flash firing, the temperature and pressure are maintained for 9~11 minutes, and then a second flash firing is performed. The parameters of the second flash firing are the same as those of the first flash firing to obtain the entire contact. The material after one flash firing is divided into three layers: a contact powder layer, a bonding layer between the contact powder and the conductive component, and a conductive component layer. These layers are then subjected to directional cooling, as follows: 1) After the first flash firing, immerse the material in a coolant at a temperature of 15~25℃ for 30~40 minutes to cool it as a whole; 2) Take out the material after the flash burning is completed again and immerse the conductive layer in a coolant at a temperature of 0~5℃, and immerse the contact powder layer in a coolant at a temperature of -5~0℃ for 50~60 minutes to cool simultaneously. 3) Stop cooling the conductive layer and the contact powder layer, and immerse the bonding layer in a coolant at a temperature of -15~-10℃ for 40~50 minutes to cool it separately. The coolant is water, ethylene glycol, disodium hydrogen phosphate, and 4-vinylpyridine in a mass ratio of 4:1:0.5:0.06~0.

09. S3, Processing: The contact obtained in step S2 is machined to obtain a welded contact.

2. The welding method in the contact forming process according to claim 1, characterized in that, The particle size of the contact powder is <10μm.

3. The welding method in the contact forming process according to claim 1, characterized in that, The conductive component is made of copper alloy.