Process for compositely forming shape memory alloy pipeline joint through 3D printing and application

Abstract

The invention discloses a process for compositely forming a shape memory alloy pipeline joint through 3D printing and application, belongs to the technical field of material forming, and solves the technical problems that an existing shape memory alloy pipeline joint is high in production and preparation energy consumption, multiple in working procedure, long in process, low in yield, poor in mechanical property and the like. According to the solution, the method comprises the following steps that S1, a shape memory alloy pipeline joint blank is prepared through 3D printing; s2, stress relief annealing is conducted on the pipe joint blank; s3, performing hot rolling on the pipe joint blank to obtain a hot-rolled pipe blank of the pipe joint; s4, machining the hot-rolled pipe blank of the pipeline joint; s5, performing low-temperature bulging and diameter expansion on the pipeline joint sleeve to obtain a shape memory alloy pipeline joint; the prepared shape memory alloy pipeline joint can be used for aviation hydraulic pipeline connection. According to the method, the intrinsic characteristic of inherent defects existing in cast ingot smelting preparation is overcome, and the high-quality, high-performance and high-precision high-quality pipe blank is obtained; and the method has the remarkable characteristics of low forming and manufacturing energy consumption, greenness, environmental friendliness and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of material forming, and specifically relates to a process and application of a 3D printing composite forming shape memory alloy pipe joint. Background Art

[0002] Aviation hydraulic pipeline components are key basic components that play the role of "blood vessel-like" life control lines. However, the pipe joints of pipeline components need to serve in extremely harsh environments such as high stress, high temperature and high pressure, corrosive media, and are prone to "leakage" and other problems. Therefore, achieving high-performance and high-reliability connections for pipeline components has become the key to solving the above problems. Pipe joints made of shape memory alloys have unique functional characteristics of shape memory effect and superelasticity, and have the advantages of good sealing performance and high connection strength, which can meet the requirements of high pressure resistance, high reliability and long life of pipeline components.

[0003] The preparation and processing technology of shape memory alloy pipe joints mainly includes vacuum melting method and powder metallurgy method: 1) Vacuum melting method: vacuum melting method to prepare ingots → hot forging and hot rolling to open the blanks → machining punching to make extruded blanks → annealing → multi-pass rolling → heat treatment → memory alloy pipe forming - cutting processing; 2) Powder metallurgy method: package design → package processing and leak detection → powder is loaded into the package → powder is vibrated → vacuum → hot isostatic pressing memory alloy tube - cutting processing.

[0004] Among them, the ingots prepared by the traditional vacuum melting method have a coarse metallographic structure and poor uniformity, which will lead to difficulties in subsequent rolling deformation, uneven wall thickness of rolled pipes, orange peel and wrinkles on the surface of the pipes, poor surface quality and other problems. The overall forming process is complicated, energy consumption is large and quality is difficult to control. The pipes prepared by powder metallurgy can only be prepared into small pieces with simple shapes due to the poor fluidity of the powder, and have poor strength and toughness, which is difficult to meet industrial needs. In short, the above two preparation methods have a long production cycle and high operating technical difficulty when used to prepare shape memory alloy pipe joints.

[0005] The new preparation processes for memory alloy pipe joints in existing documents or open patents are mostly improvements on conventional preparation and processing processes. The patent document "A blank for memory alloy pipe joints and a preparation method" (authorization announcement: CN112538582B) discloses the use of vacuum induction melting and vacuum consumable melting composite melting method to prepare ingots, followed by hot working method to prepare bar blanks and then cold rolling to prepare pipe joints. The patent document "An iron-based shape memory alloy for stainless steel pipe joints at a specific temperature and a preparation method" (authorization announcement: CN114807783A) still uses the traditional melting and casting method to prepare ingots, which are rolled into round rods after annealing and then extruded to prepare pipes to obtain memory alloy connection parts with good shape memory effect. The patent document "A 4D printing rapid manufacturing method and product of a shape memory alloy pipe joint" (authorization announcement: CN111151756B) discloses the use of 4D printing to prepare a pipe joint with three layers of different alloy components. The process is complex, the operation is difficult, the energy consumption is high, and the differences in composition and structure between layers can easily cause cracks, resulting in a decrease in the mechanical properties of the pipe joint and causing the pipe joint to fail prematurely.

[0006] In summary, it is urgent to explore a short-process, high-performance preparation method for shape memory alloy pipe joints. Summary of the invention

[0007] The main purpose of the present invention is to overcome the shortcomings of the prior art, solve the production problems of the existing shape memory alloy pipe joints, such as high energy consumption, many steps and long process, extremely low yield rate, high cost, and technical problems such as uneven wall thickness, pipe cracking, and poor mechanical properties. The present invention provides a 3D printing composite forming shape memory alloy pipe joint with a short process, low energy consumption, and high quality preparation process method and its application.

[0008] The design concept of the present invention is: taking the coarse ingot structure in the traditional melting and casting process that affects the difficulty of subsequent hot deformation of the pipe and the limitations and poor strength of the powder metallurgy method on the preparation of large components with complex shapes as the starting point, and shortening the process flow as the main line, a technical concept of 3D printing composite rolling forming shape memory alloy pipe joints is proposed, that is, 3D printing (laser selective melting) is used to prepare shape memory alloys with fine structure, uniform composition, no serious segregation, coarse inclusions, and coarse second phases; then a rolling process is used to eliminate casting defects such as holes introduced by 3D printing, reduce local stress concentration of the alloy, and improve the strength of the alloy.

[0009] The present invention is achieved through the following technical solutions: A process for 3D printing composite forming of shape memory alloy pipe joints, comprising the following steps: S1. Preparation of shape memory alloy pipe joint blanks by 3D printing: S1-1. Modeling is performed using CAD computer-aided design software to design the shape and size of the three-dimensional model of the pipe joint and export the STL format file. Then, the STL format file is imported into the additive path planning software provided by the 3D printing device to determine the printing direction, slice the three-dimensional model in layers, and obtain the 2D slices of the pipe joint model. Finally, a laser scanning path is generated based on the 2D slices of the pipe joint model, including the external contour filling path and the internal filling path, and the 3D printing process parameters are set: the laser power is 120W~200W, the scanning speed is 800mm / s~1600mm / s, and the track spacing is 40μm~60μm, and a JOB format printing file is generated. S1-2. Weigh the powder material for 3D printing. The powder material for 3D printing is a NiTi-based shape memory alloy pre-alloyed powder prepared by an aerosol method. The average particle size of the pre-alloyed powder is 15 μm to 35 μm. Then, place the weighed pre-alloyed powder in a vacuum environment at 80°C to 120°C, spread it evenly, and vacuum dry it for 12h to 24h to remove the moisture contained in the pre-alloyed powder for later use. S1-3. Select NiTi shape memory alloy as the substrate, use anhydrous ethanol to repeatedly clean the substrate to keep the substrate surface clean and free of pollution, and then preheat the substrate to 70-150°C for standby use. The substrate preheating is used to reduce the large temperature difference between the substrate and the molded part, thereby reducing the residual thermal stress; S1-4, starting the 3D printing device, and performing 3D printing by spreading powder layer by layer on the surface of the substrate according to the laser scanning path generated in step S1-1 and the selected 3D printing process parameters to obtain a pipe joint blank; S2. Stress relief annealing of pipe joint blanks: the annealing temperature is 500℃~900℃, and the annealing time is 0.5~2h; stress relief annealing can eliminate the residual stress caused by local heating, cooling and uneven composition of the 3D printed tube blanks, improve the strength and plasticity of the tube blanks, and facilitate subsequent rolling processing; S3. Hot rolling of pipe joint blanks: the pipe joint blanks are preheated at 500°C for 10 minutes and then sent to the hot rolling mill for hot rolling. The feeding speed of the pipe joint blanks is 1mm / s~3mm / s, the hot rolling temperature is 750°C~1000°C, the hot rolling passes are 1~4 passes, and the rolling reduction of each pass is 5%~35%. Intermediate annealing is performed between each hot rolling pass, the intermediate annealing temperature is 400°C~700°C, and the holding time is 10min~20min; after the last hot rolling, isothermal annealing is performed, the isothermal annealing temperature is 500°C, the holding time is 2h, and the pipe joint hot-rolled blank is obtained by water cooling to room temperature; S4. Mechanical processing of hot-rolled pipe joint blanks: First, an inner ridge is cut on the inner wall of the round tube-shaped hot-rolled pipe joint blank by turning; then, the inner and outer walls of the round tube-shaped hot-rolled pipe joint blank are polished by mechanical polishing to obtain a shape memory alloy pipe joint.

[0010] Furthermore, in step S1-2, the NiTi-based shape memory alloy pre-alloy powder is NiTi, NiTiNb or NiTiFe.

[0011] Furthermore, in step S1-4, after the 3D printing device is started, the molding cavity is first evacuated and filled with argon protective gas until the oxygen content is no more than 30 ppm. During the 3D printing process, the molding cavity is placed in an argon protective atmosphere to reduce the oxygen content during the preparation process and prevent oxidation of the metal powder.

[0012] Furthermore, in step S4, the inner ridge has a width of 1.2 mm, a height of 0.3 mm, and an inclination angle of 90°.

[0013] Furthermore, in step S4, the length of the shape memory alloy pipe joint is 50 mm to 55 mm, the inner diameter is 19 mm to 21 mm, and the wall thickness is 2.6 mm to 2.8 mm.

[0014] An application of a shape memory alloy pipe joint prepared by the preparation method as described above comprises the following steps: First, the shape memory alloy pipe joint is expanded: the pipe joint sleeve is placed in a high and low temperature environment box, and the pipe joint is expanded uniformly under the temperature condition of -190℃~-30℃, and the expansion rate is 8%; Then, in a high and low temperature environment box, the ends of two aviation hydraulic pipes to be connected are respectively inserted into the head and tail ends of the expanded shape memory alloy pipe joint; Finally, the high and low temperature environment box is heated to 25℃~70℃, and the shape memory alloy pipe joint is restored to its size before expansion. The inner ridge bends inward to press the end of the pipe to be connected, and the two aviation hydraulic pipes are fixedly connected through the shape memory alloy pipe joint.

[0015] Furthermore, the portion of the end of the pipe to be connected extending into the shape memory alloy pipe joint is located at the portion of the shape memory alloy pipe joint where the inner ridge is provided.

[0016] The beneficial effects of the present invention are as follows: the present invention overcomes the inherent deficiencies existing in the ingot smelting preparation, and obtains high-quality, high-performance and high-precision high-quality tube blanks; the process flow is greatly shortened, and the forming manufacturing has the remarkable characteristics of low energy consumption, green, and environmentally friendly. At the same time, the present invention has strong applicability and is almost suitable for the preparation of all metal material tubes by laser additive manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the process flow chart of 3D printing composite forming shape memory alloy pipe joints. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Example 1

[0019] like Figure 1 A process for 3D printing composite forming of a shape memory alloy pipe joint is shown, comprising the following steps: S1. Preparation of shape memory alloy pipe joint blanks by 3D printing: S1-1, CAD computer-aided design software modeling, design the shape and size of the three-dimensional model of the pipe joint. In this embodiment 1, the pipe joint blank is in the shape of a round tube with a length of 25 mm, an outer diameter of 28 mm, and a wall thickness of 6 mm; Export the STL format file; then, import the STL format file into the additive path planning software that comes with the 3D printing device, determine the printing direction, slice the 3D model in layers, and obtain the 2D slices of the pipe joint model; finally, generate the laser scanning path based on the 2D slices of the pipe joint model, including the external contour filling path and the internal filling path, set the 3D printing process parameters: laser power is 160W, scanning speed is 1400mm / s, track spacing is 60μm, and generate a JOB format printing file; S1-2, weighing the powder material for 3D printing, the powder material for 3D printing is a NiTi-based shape memory alloy pre-alloyed powder prepared by an aerosol method, the pre-alloyed powder in this embodiment 1 is an aerosolized spherical NiTi powder (chemical composition is shown in Table 1 below), and the average particle size of the pre-alloyed powder is 35 μm; then, the weighed pre-alloyed powder is placed in a vacuum environment at 100° C. and evenly flattened, vacuum dried for 16 hours, and the moisture contained in the pre-alloyed powder is removed for standby use;

[0020] S1-3. Select NiTi shape memory alloy as the substrate (hot forging state), use anhydrous ethanol to repeatedly clean the substrate to keep the substrate surface clean and free of pollution, and then preheat the substrate to 100°C for standby use; S1-4, start the 3D printing device. After the 3D printing device is started, the molding chamber is first evacuated and filled with argon protective gas until the oxygen content is no more than 30ppm. According to the laser scanning path generated in step S1-1 and the selected 3D printing process parameters, the substrate is layered with powder for 3D printing. The pipe joint blank is separated from the substrate by wire cutting, and ultrasonic cleaning is performed to obtain the pipe joint blank. In this Example 1, the orthogonal experimental method was used to design different process parameter combinations and then print the alloy, and then observe its macroscopic morphology and microstructure, test its mechanical properties and shape memory properties, and determine the process parameter combination with good macroscopic morphology and optimal shape memory properties; S2. Stress relief annealing of pipe joint blank: annealing temperature is 600℃, annealing time is 2h; S3. Hot rolling of pipe joint blank: the pipe joint blank is preheated at 500°C for 10 minutes and then sent to the hot rolling mill for hot rolling. The feeding speed of the pipe joint blank is 1.5 mm / s, the hot rolling temperature is 950°C, the number of hot rolling passes is 3, the rolling reduction in each pass is 20%, and intermediate annealing is performed between each hot rolling pass. The intermediate annealing temperature is 500°C and the holding time is 15 minutes. After the last hot rolling, isothermal annealing is performed at 500°C and the holding time is 2 hours. The pipe joint hot-rolled blank is obtained. The dimensions of the pipe joint hot-rolled blank prepared in Example 1 are: length 55 mm, outer diameter 23 mm, and wall thickness 3.2 mm. The overall recovery rate of the 3D-printed NiTi shape memory alloy pipe joint sleeve is as high as 98% when the strain is 6%, and its strength after rolling is increased by about 30% compared with the 3D-printed state. Compared with traditional processes, material utilization is increased by nearly 4 times and costs are reduced by 40%; S4. Mechanical processing of hot-rolled pipe joint blanks: First, an inner ridge is cut on the inner wall of the round tube-shaped hot-rolled pipe joint blank by turning, and the inner ridge width is 1.2 mm, the height is 0.3 mm, and the inclination angle is 90°; then, the inner and outer walls of the round tube-shaped hot-rolled pipe joint blank are polished by mechanical polishing to obtain a shape memory alloy pipe joint. The shape memory alloy pipe joint has a length of 50 mm, an inner diameter of 19.8 mm, and a wall thickness of 2.8 mm.

[0021] An application of a shape memory alloy pipe joint prepared by the preparation method as described above comprises the following steps: First, the shape memory alloy pipe joint is expanded: the pipe joint sleeve is placed in a high and low temperature environment box, and the expansion is uniformly expanded under the low temperature condition of -90℃~-55℃, and the expansion rate is 8%; the steps of expanding the shape memory alloy pipe joint are as follows: 1) Assembling the expansion device: fix the base on the workbench of the press, adjust the position of the expansion rod for centering test, and insert the expansion rod into the center positioning hole of the base. Place the pad on the base and connect it with bolts, close the expansion valve and place it on the pad, press down the upper plate of the press, adjust the expansion valve to make it centered, then move the press upward, put the prepared shape memory alloy pipe joint on the closed expansion valve, and then fix the baffle plate and the pad with bolts to prevent it from moving with the expansion rod during unloading. At this time, the assembly of the expansion device is completed; 2) Expansion operation: Place the assembled expansion device and shape memory alloy pipe joint in a high and low temperature environment box, start the press to press the upper pressure plate downward to drive the expansion rod downward, the outer cone surface in the middle of the expansion rod contacts the inner cone surface of the expansion valve, the expansion valve opens and moves, driving the shape memory alloy pipe joint to expand and deform as a whole, and expand uniformly under low temperature conditions of -90℃~-55℃, with an expansion rate of 8%; 3) Remove the shape memory alloy pipe joint by disassembling the device: move the upper pressing plate of the press machine upward, remove the expanded shape memory alloy pipe joint from the expansion valve, and complete the expansion of the shape memory alloy pipe joint; Then, in a high and low temperature environment box, the ends of two aviation hydraulic pipes to be connected are respectively inserted into the head and tail ends of the expanded shape memory alloy pipe joint; Finally, the high and low temperature environment box is heated to 70°C to induce the shape memory effect. The shape memory alloy pipe joint returns to its size before expansion. The inner ridge bends inward to press the end of the pipe to be connected, and the two aviation hydraulic pipes are fixedly connected through the shape memory alloy pipe joint. Example 2

[0022] like Figure 1 A process for 3D printing composite forming of a shape memory alloy pipe joint is shown, comprising the following steps: S1. Preparation of shape memory alloy pipe joint blanks by 3D printing: S1-1, CAD computer-aided design software modeling, design the shape and size of the three-dimensional model of the pipe joint. In this embodiment 2, the pipe joint blank is in the shape of a round tube with a length of 27.5 mm, an outer diameter of 30 mm, and a wall thickness of 5 mm; Export the STL format file; then, import the STL format file into the additive path planning software that comes with the 3D printing device, determine the printing direction, slice the 3D model in layers, and obtain the 2D slices of the pipe joint model; finally, generate the laser scanning path based on the 2D slices of the pipe joint model, including the external contour filling path and the internal filling path, set the 3D printing process parameters: laser power is 150W, scanning speed is 800mm / s, track spacing is 60μm, and generate a JOB format printing file; S1-2, weighing the powder material for 3D printing, the powder material for 3D printing is a NiTi-based shape memory alloy pre-alloyed powder prepared by an aerosol method, the pre-alloyed powder in this embodiment 2 is an aerosolized spherical NiTiNb powder (chemical composition is shown in Table 2 below), and the average particle size of the pre-alloyed powder is 35 μm; then, the weighed pre-alloyed powder is placed in a vacuum environment at 100° C. and evenly flattened, vacuum dried for 18 hours, and the moisture contained in the pre-alloyed powder is removed for standby use;

[0023] S1-3. Select NiTi shape memory alloy as the substrate (hot forging state), use anhydrous ethanol to repeatedly clean the substrate to keep the substrate surface clean and free of pollution, and then preheat the substrate to 100°C for standby use; S1-4, start the 3D printing device. After the 3D printing device is started, the molding chamber is first evacuated and filled with argon protective gas until the oxygen content is no more than 30ppm. According to the laser scanning path generated in step S1-1 and the selected 3D printing process parameters, the substrate is layered with powder for 3D printing. The pipe joint blank is separated from the substrate by wire cutting, and ultrasonic cleaning is performed to obtain the pipe joint blank. S2. Stress relief annealing of pipe joint blank: annealing temperature is 600℃, annealing time is 2h; S3. Hot rolling of pipe joint blanks: After preheating at 500℃ for 10min, pipe joint blanks are sent to hot rolling mill for hot rolling. The feeding speed of pipe joint blanks is 1.5mm / s, the hot rolling temperature is 950℃, the hot rolling passes are 3, and the rolling reduction of each pass is 20%. Intermediate annealing is performed between each hot rolling pass, the intermediate annealing temperature is 500℃, and the holding time is 15min; after the last hot rolling pass, isothermal annealing is performed, the isothermal annealing temperature is 500℃, the holding time is 2h, and water cooling is performed to At room temperature, a hot-rolled tube blank for a pipe joint is obtained; the dimensions of the hot-rolled tube blank for a pipe joint prepared in Example 2 are: 53 mm in length, 23 mm in outer diameter, and 3.2 mm in wall thickness; the recovery stress of the 3D-printed NiTiNb shape memory alloy pipe joint sleeve reaches 420 MPa, which is about 55.9% and 15.4% higher than that of the traditional forging state and extrusion state. Compared with the traditional process, the 3D printing method increases the material utilization by nearly 4 times and reduces the cost by 40%; its strength is further improved after rolling; S4. Mechanical processing of hot-rolled pipe joint blanks: First, an inner ridge is cut on the inner wall of the round tube-shaped hot-rolled pipe joint blank by turning, and the inner ridge width is 1.2 mm, the height is 0.3 mm, and the inclination angle is 90°; then, the inner and outer walls of the round tube-shaped hot-rolled pipe joint blank are polished by mechanical polishing to obtain a shape memory alloy pipe joint. The shape memory alloy pipe joint has a length of 50 mm, an inner diameter of 19.8 mm, and a wall thickness of 2.8 mm.

[0024] An application of a shape memory alloy pipe joint prepared by the preparation method as described above comprises the following steps: First, the shape memory alloy pipe joint is expanded: the pipe joint sleeve is placed in a high and low temperature environment box, and the pipe joint is expanded uniformly under the temperature condition of -160℃~-140℃, and the expansion rate is 8%; Then, in a high and low temperature environment box, the ends of two aviation hydraulic pipes to be connected are respectively inserted into the head and tail ends of the expanded shape memory alloy pipe joint; Finally, the high and low temperature environment box is heated to 25°C to induce the shape memory effect. The shape memory alloy pipe joint returns to its size before expansion. The inner ridge bends inward to press the end of the pipe to be connected, and the two aviation hydraulic pipes are fixedly connected through the shape memory alloy pipe joint.

[0025] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A process for 3D printing composite forming of shape memory alloy pipe joints, comprising the following steps: S1. Preparation of shape memory alloy pipe joint blanks by 3D printing: S1-1. Modeling is performed using CAD computer-aided design software to design the shape and size of the three-dimensional model of the pipe joint and export the STL format file. Then, the STL format file is imported into the additive path planning software provided by the 3D printing device to determine the printing direction, slice the three-dimensional model in layers, and obtain the 2D slices of the pipe joint model. Finally, a laser scanning path is generated based on the 2D slices of the pipe joint model, including the external contour filling path and the internal filling path, and the 3D printing process parameters are set: the laser power is 120W~200W, the scanning speed is 800mm / s~1600mm / s, and the track spacing is 40μm~60μm, and a JOB format printing file is generated. S1-2. Weigh the powder material for 3D printing. The powder material for 3D printing is a NiTi-based shape memory alloy pre-alloyed powder prepared by an aerosol method. The average particle size of the pre-alloyed powder is 15 μm to 35 μm. Then, place the weighed pre-alloyed powder in a vacuum environment at 80°C to 120°C, spread it evenly, and vacuum dry it for 12h to 24h to remove the moisture contained in the pre-alloyed powder for later use. S1-3. Select NiTi shape memory alloy as the substrate, use anhydrous ethanol to repeatedly clean the substrate to keep the substrate surface clean and free of pollution, and then preheat the substrate to 70-150°C for standby use; S1-4, starting the 3D printing device, and performing 3D printing by spreading powder layer by layer on the surface of the substrate according to the laser scanning path generated in step S1-1 and the selected 3D printing process parameters, to obtain a pipe joint blank; S2. Stress relief annealing of pipe joint blanks: annealing temperature is 500℃~900℃, annealing time is 0.5~2h; S3. Hot rolling of pipe joint blanks: the pipe joint blanks are preheated at 500°C for 10 minutes and then sent to the hot rolling mill for hot rolling. The feeding speed of the pipe joint blanks is 1mm / s~3mm / s, the hot rolling temperature is 750°C~1000°C, the hot rolling passes are 1~4 passes, the rolling reduction of each pass is 5%~35%, and intermediate annealing is performed between each hot rolling pass. The intermediate annealing temperature is 400°C~700°C and the holding time is 10min~20min. After the last hot rolling, isothermal annealing is performed at 500°C and the holding time is 2h. The pipe joint blanks are water-cooled to room temperature to obtain hot-rolled pipe joint blanks. S4. Mechanical processing of hot-rolled pipe joint blanks: First, an inner ridge is cut on the inner wall of the round tube-shaped hot-rolled pipe joint blank by turning; then, the inner and outer walls of the round tube-shaped hot-rolled pipe joint blank are polished by mechanical polishing to obtain a shape memory alloy pipe joint.

2. The process for 3D printing composite forming of shape memory alloy pipe joints according to claim 1, characterized in that: In the step S1-2, the NiTi-based shape memory alloy pre-alloy powder is NiTi, NiTiNb or NiTiFe.

3. The process for 3D printing composite forming of shape memory alloy pipe joints according to claim 1, characterized in that: In step S1-4, after the 3D printing equipment is started, the molding chamber is first evacuated and filled with argon protective gas until the oxygen content is no higher than 30 ppm.

4. The process for 3D printing composite forming of shape memory alloy pipe joints according to claim 1, characterized in that: In step S4, the inner ridge has a width of 1.2 mm, a height of 0.3 mm, and an inclination angle of 90°.

5. The process for 3D printing composite forming of shape memory alloy pipe joints according to claim 1, characterized in that: In step S4, the length of the shape memory alloy pipe joint is 50 mm to 55 mm, the inner diameter is 19 mm to 21 mm, and the wall thickness is 2.6 mm to 2.8 mm.

6. An application of a shape memory alloy pipe joint made by the process as claimed in claim 1, characterized in that: The following steps are involved: First, the shape memory alloy pipe joint is expanded: the pipe joint sleeve is placed in a high and low temperature environment box, and the pipe joint is expanded uniformly under the temperature condition of -190℃~-30℃, and the expansion rate is 8%; Then, in a high and low temperature environment box, the ends of two aviation hydraulic pipes to be connected are respectively inserted into the head and tail ends of the expanded shape memory alloy pipe joint; Finally, the high and low temperature environment box is heated to 25℃~70℃, and the shape memory alloy pipe joint is restored to its size before expansion. The inner ridge bends inward to press the end of the pipe to be connected, and the two aviation hydraulic pipes are fixedly connected through the shape memory alloy pipe joint.

7. The use according to claim 6, characterized in that: The portion of the end of the pipe to be connected extending into the shape memory alloy pipe joint is located at the portion of the shape memory alloy pipe joint where the inner ridge is arranged.

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