A method for connecting a titanium alloy pipe and a dissimilar metal pipe

Abstract

The application discloses a connecting method for titanium alloy pipe and dissimilar metal pipe, and the method comprises the following steps: sealing other end parts of the titanium alloy pipe except the end part to be connected; rolling the end part of the dissimilar metal branch pipe to be connected, and sleeving the end part to the outside of the end part of the titanium alloy pipe to be connected; and in the vacuum furnace under the vacuum and high temperature state, inert gas is introduced into the titanium alloy pipe, and the end part of the titanium alloy pipe to be connected is tightly combined with the inner surface of the dissimilar metal branch pipe under the action of the gas pressure load in the process of hot forming. Since the thermal expansion coefficient of the dissimilar metal branch pipe is greater than the thermal expansion coefficient of the titanium alloy, in the process of cooling, the dissimilar metal branch pipe will extrude the tee end part of the titanium alloy pipe, especially at the rolled part, the diameter is the largest, and the extrusion force is relatively greater than other parts, and the outer surface of the titanium alloy pipe and the inner surface of the dissimilar metal branch pipe can form a reliable linear seal. The application realizes the forming of the end part of the titanium alloy pipe to be connected and the reliable connection of the titanium alloy pipe and the dissimilar metal branch pipe, and has good practicability.

Description

Technical Field

[0001] This invention belongs to the technical field of dissimilar metal tee connection, specifically relating to a method for connecting titanium alloy pipes and dissimilar metal pipes. Background Technology

[0002] Currently, stainless steel pipes are widely used in the hydraulic systems of domestic aircraft. To improve strength and reduce overall system weight, titanium alloy pipes such as TA18 and TA16 can be used. During use, some areas of the titanium alloy pipes need to be connected to stainless steel or high-temperature alloy pipes. However, the existing manufacturing process for tee pipes generally involves laser-cutting or manually trimming the intersection line on the main pipe, then welding it to a straight pipe. This existing method requires trimming the intersection line on the main titanium alloy pipe, welding the titanium alloy branch pipe to the intersection line, and then using a straight connector and outer nut to connect the titanium alloy branch pipe to the stainless steel or high-temperature alloy pipe. This solution is structurally inefficient, and the addition of connectors and outer nuts increases the overall weight of the aircraft. Summary of the Invention

[0003] The purpose of this invention is to provide a method for connecting titanium alloy tubing with dissimilar metal tubing, thereby solving the aforementioned problems.

[0004] This invention is mainly achieved through the following technical solutions: A method for connecting a titanium alloy pipe to a dissimilar metal pipe, comprising a dissimilar metal branch pipe and a titanium alloy pipe, wherein the coefficient of thermal expansion of the dissimilar metal branch pipe is greater than that of the titanium alloy pipe, and includes the following steps: Step S1: Perform corrugation treatment on the ends of the dissimilar metal branch pipes to be connected; Step S2: Seal the ends of the titanium alloy tube except for the end to be connected; Step S3: Weld a titanium alloy connecting pipe, which communicates with the inside of the titanium alloy tube, to one end of the titanium alloy tube. Step S4: Perform an airtightness test on the titanium alloy tube to ensure that there is no air leakage except for the ends to be connected; Step S5: Place the titanium alloy tube and the dissimilar metal branch tube into the forming surface of the upper or lower mold of the forming fixture, respectively, and fit the end of the dissimilar metal branch tube to be connected onto the outside of the end of the titanium alloy tube to be connected; then, insert the mandrel into the dissimilar metal branch tube and abut against and seal the top of the end of the titanium alloy tube to be connected, and fix the position of the mandrel. Step S6: Close the upper and lower molds of the molding fixture and place the entire molding fixture into the vacuum furnace; evacuate the inside of the vacuum furnace to an absolute vacuum degree of 5×10⁻⁶. -3 -1×10 -2 Pa; The furnace cavity of the vacuum furnace is heated to 820-850℃; Step S7: High-pressure inert gas is introduced into the titanium alloy tube through the connecting pipe to form and load the end of the titanium alloy tube to be connected. The loading pressure is increased from 0.1MPa to 1.5-2.0MPa and then maintained at 1.5-2.0MPa. Step S8: Cool the vacuum furnace to 200-300℃, remove the connecting fittings between the titanium alloy tube and the dissimilar metal branch tube, and after cooling, drill holes at the connecting ends of the formed titanium alloy tube to match the flow requirements.

[0005] To better realize the present invention, in step S2, the titanium alloy tube is a three-way tube structure, and titanium alloy plugs are used to seal the ends of the titanium alloy tube respectively; in step S3, a connecting pipe communicating with the inside of the titanium alloy tube is welded to the plug at one end of the titanium alloy tube.

[0006] To better realize the present invention, further, in step S3, a hole is drilled in the plug at one end of the titanium alloy tube. 2- Drill a hole in section 3; then, weld a connecting pipe with a diameter of 6-8 mm and a wall thickness of 1.5-2 mm to the drilled hole in the plug.

[0007] To better realize the present invention, in step S4, the inside of the titanium alloy tube is evacuated. When the vacuum degree reaches 10 kPa, the evacuation is stopped and the change of the vacuum degree inside the titanium alloy tube is observed. If the change of the vacuum degree within 1 minute is less than 5 kPa, it is considered that the titanium alloy tube is not leaking except for the end to be connected.

[0008] To better realize the present invention, in step S5, the coefficient of thermal expansion of the forming tooling is less than the coefficient of thermal expansion of the dissimilar metal branch pipe.

[0009] To better realize the present invention, the molding tooling is further made of quartz material.

[0010] To better realize the present invention, the dissimilar metal branch pipe is further described as a stainless steel pipe or a high-temperature alloy pipe.

[0011] The beneficial effects of this invention are as follows: During the thermoforming process, under pneumatic load, the end of the titanium alloy tube to be connected fits tightly against the inner surface of the dissimilar metal branch pipe. Because the coefficient of thermal expansion of the dissimilar metal branch pipe is greater than that of the titanium alloy, during cooling, the dissimilar metal branch pipe will compress the tee end of the titanium alloy tube, especially at the wavy section where the diameter is largest and the compressive force is relatively greater than in other parts. A reliable line seal is formed between the outer surface of the titanium alloy tube and the inner surface of the dissimilar metal branch pipe. This invention utilizes the significant difference in the coefficients of thermal expansion between titanium alloy and dissimilar metals. During the thermoforming process, through a single pneumatic load application, it achieves the simultaneous forming of the end of the titanium alloy tube to be connected and the reliable connection between the titanium alloy tube and the dissimilar metal branch pipe. The connecting fitting formed by this invention between the titanium alloy tube and the dissimilar metal branch pipe produces neither irregular weld seams nor requires joint connections. It has a compact structure, significantly reduces the overall weight of the aircraft, and has good practicality. This invention is applicable to the connection of titanium alloy tubes with stainless steel branch pipes and titanium alloy tubes with high-temperature alloy branch pipes, effectively improving the integrity and quality stability of the conduit system. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure after the titanium alloy pipe and stainless steel branch pipe are formed. Figure 2 A schematic diagram of the structure after the stainless steel branch pipe end has been corrugated. Figure 3 for Figure 1 A cross-sectional view of the titanium alloy pipe and stainless steel branch pipe after forming. Figure 4 A schematic diagram of the structure for fitting titanium alloy pipes and stainless steel branch pipes into forming fixtures. Figure 5 for Figure 4 AA section view in the image.

[0013] Among them: 1-Titanium alloy tube, 2-Stainless steel tube, 3-Upper mold, 4-Lower mold, 5-Mandrel. Detailed Implementation

[0014] Example 1: A method for connecting a titanium alloy pipe to a dissimilar metal pipe, wherein the coefficient of thermal expansion of the dissimilar metal branch pipe is greater than that of the titanium alloy pipe 1, and the titanium alloy pipe 1 is a tee pipe. The method includes the following steps: A1. Apply a corrugated treatment to the ends of the dissimilar metal branch pipes to be connected, such as... Figure 5 As shown, the outer surface of the rolling wave rear end head must be consistent with the inner surface of the forming tooling; A2. Circular plugs made of titanium plates with the same diameter as the inner diameter of titanium alloy tube 1 are sealed and welded to both ends of titanium alloy tube 1. A3. Drill a hole in the plug at one end of the titanium alloy tube 1. 2- Hole 3; A4. Weld a connecting pipe made of titanium alloy with a diameter of 6-8mm and a wall thickness of 1.5-2mm to the drilled hole of the plug. A5. Perform an airtightness test on titanium alloy tube 1 to ensure that it does not leak. If leakage occurs, repair welding shall be performed. A6. Place the titanium alloy pipe 1 and the dissimilar metal branch pipe on the forming fixture. At this time, the end of the dissimilar metal branch pipe to be connected is sleeved on the outside of the tee end of the titanium alloy pipe 1. Insert the mandrel 5 into the dissimilar metal branch pipe and press it against the titanium alloy pipe 1. Then, fix the mandrel 5 on the fixture. The mandrel 5 is used to limit and fix the dissimilar metal branch pipe and to seal the top of the tee end of the titanium alloy pipe 1.

[0015] A7. Close the upper mold 3 and lower mold 4 of the molding fixture and place the whole mold into the vacuum furnace, and insert a temperature measuring thermocouple into the molding fixture. A8. Evacuate the furnace until the overall absolute vacuum is 5×10-3-1×10-2 Pa; A9. Heat the furnace cavity until the tooling temperature reaches 820-850℃; A10. Through the connecting pipe welded to the plug, high-pressure argon gas is introduced into the titanium alloy tube 1 to be formed for forming loading. The loading pressure is increased from 0.1MPa to 1.5-2.0MPa, and then held at 1.5-2.0MPa for 1 minute. A11. Stop heating inside the furnace and cool the tooling furnace to 200-300℃; A12. Remove the parts and place them in the air to cool. A13. Drill holes at the tee section of the formed titanium alloy tee pipe. The size of the drilled holes can be matched according to the flow rate requirements.

[0016] Preferably, in step A5, the method for the airtightness test is as follows: evacuate the titanium alloy tube 1, and when the vacuum degree reaches 10 kPa, stop evacuating and observe the change in the vacuum degree of the pocket. If the change in the vacuum degree within 1 minute is less than 5 kPa, then it is considered that the titanium alloy tube 1, except for the end to be connected, is airtight.

[0017] Preferably, in step A6, the molding tooling is made of quartz material.

[0018] During the thermoforming process, under the action of pneumatic load, the blank at the tee end of the titanium alloy tube 1 is tightly fitted to the inner surface of the dissimilar metal branch pipe. Because the coefficient of thermal expansion of the dissimilar metal branch pipe is greater than that of the titanium alloy, during the cooling process, the dissimilar metal branch pipe will compress the tee end of the titanium alloy tube 1, especially at the corrugated section, where the diameter is largest and the compressive force is relatively greater than in other parts. At the corrugated section, a reliable line seal is formed between the outer surface of the titanium alloy tube 1 and the inner surface of the dissimilar metal branch pipe. This invention utilizes the significant difference in the coefficients of thermal expansion between titanium alloy and dissimilar metals to achieve a reliable connection between the titanium alloy tube 1 and the dissimilar metal branch pipe simultaneously through a single loading process. Figure 1 and Figure 3 As shown, the combination of titanium alloy tube 1 and dissimilar metal branch tube formed by the present invention does not produce irregular weld seams or require joint connections. It has a compact structure, significantly reduces the overall weight of the aircraft, and has good practicality.

[0019] Example 2: A method for connecting titanium alloy pipes and dissimilar metal pipes is disclosed, aiming to connect titanium alloy pipe 1 and stainless steel pipe 2. Titanium alloy pipe 1 is a tee pipe, made of TA18 steel, with a diameter of 30mm and a wall thickness of 1.5mm; stainless steel pipe 2 is made of 1Cr18Ni9Ti steel, with a diameter of 20mm and a wall thickness of 1.5mm. The method includes the following steps: ① First, such as Figure 2 and Figure 5 As shown, the two ends of the stainless steel pipe are corrugated, and the outer surface of the corrugated end is required to be consistent with the inner surface of the forming tool.

[0020] ② Use circular titanium alloy plugs with the same diameter as the inner diameter of titanium alloy tube 1 to seal and weld them to both ends of titanium alloy tube 1, and drill a hole in the plug at one end of titanium alloy tube 1. 2- Make a hole 3, and weld a connecting pipe made of titanium alloy with a diameter of 6-8mm and a wall thickness of 1.5-2mm to the drilled hole of the plug.

[0021] ③ Perform an airtightness test on titanium alloy tube 1 to ensure it is leak-free. Then, as follows: Figure 4 and Figure 5 As shown, titanium alloy tube 1 and stainless steel tube 2 are placed on the forming fixture respectively, and a mandrel 5 is inserted into stainless steel tube 2 and presses against the tee end of titanium alloy tube 1 to fix the mandrel 5 on the fixture.

[0022] ④ Close the upper mold 3 and lower mold 4 of the molding fixture and place the whole assembly into the vacuum furnace, and insert a temperature measuring thermocouple into the molding fixture. Then, evacuate the furnace until the absolute vacuum degree of the furnace reaches 5×10-3-1×10-2 Pa, and then start heating the furnace cavity until the fixture temperature reaches 820-850℃.

[0023] ⑤ Through the connecting pipe welded to the plug, high-pressure argon gas is introduced into the titanium alloy tube 1 to be formed for forming loading. The loading pressure is increased from 0.1MPa to 1.6MPa. Then, the pressure is maintained at 1.6MPa for 1 minute and the heating in the furnace is stopped. The tooling furnace is cooled to 200-300℃, the parts are taken out and placed in the air to air cool.

[0024] ⑥ During the thermoforming process, under the action of air pressure load, the blank at the tee end of the titanium alloy tube 1 is tightly bonded to the inner surface of the stainless steel tube 2. Since the coefficient of thermal expansion of stainless steel is much greater than that of titanium alloy, during the cooling process, the stainless steel tube 2 will compress the titanium alloy tube 1, especially at the corrugated section where the diameter is largest and the compressive force is relatively greater than in other parts. At the corrugated section, a reliable line seal will be formed between the outer surface of the titanium alloy tube 1 and the inner surface of the stainless steel tube 2. Finally, according to the flow restriction requirements, a hole is drilled at the tee end of the titanium alloy tube 1 to match the flow rate requirements.

[0025] like Figure 1 and Figure 3 As shown, the combination of titanium alloy tube 1 and stainless steel tube 2 formed by the present invention does not produce irregular weld seams or require joint connections. It has a compact structure, significantly reduces the overall weight of the aircraft, and has good practicality.

[0026] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for connecting titanium alloy tubing to dissimilar metal tubing, characterized in that, Including dissimilar metal branch pipes and titanium alloy pipes (1), the thermal expansion coefficient of the dissimilar metal branch pipes is greater than that of the titanium alloy pipes (1), including the following steps: Step S1: Perform corrugation treatment on the ends of the dissimilar metal branch pipes to be connected; Step S2: Seal the ends of the titanium alloy tube (1) except for the end to be connected; Step S3: Weld a titanium alloy connecting pipe that communicates with the inside of the titanium alloy tube (1) to one end of the titanium alloy tube (1); Step S4: Perform an airtightness test on the titanium alloy tube (1) to ensure that the titanium alloy tube (1) is airtight except for the end to be connected; Step S5: Place the titanium alloy tube (1) and the dissimilar metal branch tube into the forming surface of the upper mold (3) or lower mold (4) of the forming fixture respectively, and attach the end of the dissimilar metal branch tube to be connected to the outside of the end of the titanium alloy tube (1) to be connected; then, insert the mandrel (5) into the dissimilar metal branch tube and abut against and seal the top of the end of the titanium alloy tube (1) to be connected, and fix the position of the mandrel (5); Step S6: Close the upper mold (3) and lower mold (4) of the molding fixture, and place the entire molding fixture into the vacuum furnace; evacuate the inside of the vacuum furnace, and the absolute vacuum degree is 5×10 -3 -1×10 -2 Pa; The furnace cavity of the vacuum furnace is heated to 820-850℃; Step S7: High-pressure inert gas is introduced into the titanium alloy tube (1) through the connecting pipe to form the end of the titanium alloy tube (1) to be connected, and the loading pressure is increased from 0.1MPa to 1.5-2.0MPa, and pressure is maintained at 1.5-2.0MPa. Step S8: Cool the vacuum furnace to 200-300℃, remove the connecting fittings between the titanium alloy tube (1) and the dissimilar metal branch tube, and after cooling, drill holes at the connecting end of the formed titanium alloy tube (1) to match the flow requirements.

2. The method for connecting titanium alloy tubing and dissimilar metal tubing according to claim 1, characterized in that, In step S2, the titanium alloy tube (1) is a three-way tube structure, and titanium alloy plugs are used to seal the ends of the titanium alloy tube (1); in step S3, a connecting pipe that communicates with the inside of the titanium alloy tube (1) is welded to the plug at one end of the titanium alloy tube (1).

3. The method for connecting titanium alloy tubing and dissimilar metal tubing according to claim 2, characterized in that, In step S3, a hole is drilled in the plug at one end of the titanium alloy tube (1). 2- Drill a hole in section 3; then, weld a connecting pipe with a diameter of 6-8 mm and a wall thickness of 1.5-2 mm to the drilled hole in the plug.

4. The method for connecting titanium alloy tubing and dissimilar metal tubing according to claim 1, characterized in that, In step S4, the inside of the titanium alloy tube (1) is evacuated. When the vacuum degree reaches 10KPa, the evacuation is stopped and the change in the vacuum degree inside the titanium alloy tube (1) is observed. If the change in the vacuum degree within 1 minute is less than 5KPa, it is considered that the titanium alloy tube (1) is not leaking except for the end to be connected.

5. The method for connecting titanium alloy tubing and dissimilar metal tubing according to claim 1, characterized in that, In step S5, the coefficient of thermal expansion of the forming tooling is less than that of the dissimilar metal branch pipe.

6. The method for connecting titanium alloy tubing and dissimilar metal tubing according to claim 5, characterized in that, The molding tooling is made of quartz material.

7. A method for connecting a titanium alloy pipe and a dissimilar metal pipe according to any one of claims 1-6, characterized in that, The dissimilar metal branch pipe is a stainless steel pipe (2) or a high-temperature alloy pipe.

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