An electro-assisted precise forming method for large-sized titanium alloy springs

Abstract

The present invention discloses an electro-assisted precise forming method for large-sized titanium alloy springs. The method includes: First, cutting a titanium alloy bar and coating it with an anti-oxidation insulating coating; Second, performing cold coiling processing using a numerically controlled spring coiling machine to obtain a titanium alloy spring blank; Third, keeping the titanium alloy spring blank in a spring-loaded state and heating it by connecting a DC power supply; Fourth, flat head treatment and heat treatment; Fifth, shot peening treatment to obtain a large-sized titanium alloy spring. The present invention adopts an electro-assisted precise forming method, utilizes the thermal effect after the spring is electrified and the impact of the current on dislocations, quickly improves the high dislocation density caused by cold working, reduces the residual stress in the titanium alloy spring blank, eliminates the springback deformation after the processing of the titanium alloy spring, effectively controls the forming accuracy of the titanium alloy spring, realizes the preparation of large-sized titanium alloy springs, and is applicable to the preparation of high-precision titanium alloy springs in fields such as aerospace, marine ships, and petrochemical industries.

Description

Technical Field

[0001] The present invention belongs to the technical field of spring preparation, and particularly relates to an electro-assisted precise forming method for large-sized titanium alloy springs. Background Art

[0002] With the rapid development of the aerospace industry, rocket launches are becoming increasingly frequent, and the requirements for weight reduction and performance of components in rockets are also getting higher and higher. Compression springs are widely used in rockets. The spring set propulsion mechanism in the rocket launch system still uses steel springs at present, which not only have a large weight but also have a corrosion risk during long-term storage, and cannot meet the requirements of the aerospace field for large-sized springs with light weight and corrosion resistance.

[0003] Titanium alloy springs have many advantages over traditional steel springs in terms of weight, size and performance. In terms of lightweight, the density of titanium alloy is about 60% of that of steel. Titanium alloy springs have a higher deflection, and the shear modulus is about half of that of steel. Fewer effective coils are required in the design, which can save a large amount of space and more than half of the weight without sacrificing performance. Titanium alloy springs require less energy to accelerate and decelerate during movement. The lower mass and energy requirements reduce spring shock, making the movement under load smoother and more controllable. In addition, titanium alloy has high corrosion resistance, especially in harsh environments, which can reduce the complex anti-corrosion treatment process.

[0004] However, due to the large ratio of the yield limit to the elastic modulus of titanium alloy, the springback of titanium alloy springs after forming is very large when unloaded. Especially during the subsequent heat treatment process, the outer diameter of the spring will continue to increase and the spring height will decrease. The existing processing of large-sized titanium alloy springs is prepared by the empirical trial-and-error method, which is time-consuming and laborious, and the dimensional accuracy of the springs cannot be guaranteed. How to effectively control the spring accuracy and ensure that the outer diameter and height are within the tolerance range is the main problem faced by the processing of large-sized titanium alloy springs at present. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an electro-assisted precise forming method for large-sized titanium alloy springs in view of the above-mentioned deficiencies of the prior art. This method adopts an electro-assisted precise forming method, utilizes the thermal effect after the spring is electrified and the impact of current on dislocations, quickly improves the high dislocation density caused by cold working, reduces the residual stress in the titanium alloy spring blank, eliminates the springback deformation after the processing of the titanium alloy spring, effectively controls the forming accuracy of the titanium alloy spring, realizes the preparation of large-sized titanium alloy springs, and solves the problems of time-consuming and laborious of the empirical trial-and-error method and the inability to guarantee the dimensional accuracy of the springs.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: an electro-assisted precise forming method for large-sized titanium alloy springs, characterized in that the method comprises the following steps:

[0007] Step 1: Cut the titanium alloy bar according to the size of the large-sized titanium alloy spring as the target product. Then, coat the anti-oxidation insulation coating on the areas outside 30.0 mm on the surfaces of both ends of the titanium alloy bar, and let it stand until dry to obtain the titanium alloy bar blank to be cold coiled. The diameter of the titanium alloy bar is 8.0 mm to 20.0 mm;

[0008] Step 2: According to the size of the large-sized titanium alloy spring as the target product, cold coil the titanium alloy bar blank obtained in Step 1 on a numerical control spring coiling machine to obtain the titanium alloy spring blank;

[0009] Step 3: Keep the titanium alloy spring blank obtained in Step 2 in a spring-loaded state, connect a DC power supply to both ends of the titanium alloy spring blank, and heat it to 700 °C to 820 °C at a current density of 10 A / mm 2 ~12 A / mm 2 and keep it warm for 1 min to 5 min. Immediately cut off the power supply and cool it after the heat preservation ends;

[0010] Step 4: Use a spring grinding machine to perform flat head treatment on the cooled titanium alloy spring blank in Step 3, and then perform heat treatment in a resistance furnace;

[0011] Step 5: Perform shot peening treatment on the heat-treated titanium alloy spring blank in Step 4 to remove the anti-oxidation insulation coating on the surface, and obtain the large-sized titanium alloy spring. The wire diameter of the large-sized titanium alloy spring is more than 8 mm, the winding ratio is 4 to 10, and the total number of turns is more than 10.

[0012] Currently, the large-sized titanium alloy spring mainly adopts the cold coiling forming method. Because the hot coiling processing and forming method will cause oxide scale to form on the titanium alloy bar during the heating and heat preservation process, thus changing the wire diameter of the titanium alloy spring and seriously affecting the stiffness of the spring. During the cold coiling forming process, the springback of the titanium alloy cannot be controlled; after cold coiling unloading, the outer diameter of the titanium alloy spring will have a springback of about 1 mm to 4 mm. The springback amount is related to factors such as the bar material grade, original tissue morphology, spring wire diameter, spring outer diameter, and spindle speed. And the spring will have springback again after heat treatment, not only the outer diameter will increase, but the spring height will also shorten. The springback amount after heat treatment is related to the heat treatment temperature and time. Due to the influence of various factors, currently, the large-sized titanium alloy spring can only adopt the method of empirical trial and error to estimate the springback amount and improve the process through multiple experiments. This method is not only time-consuming and laborious, but also the dimensional consistency of the springs made of raw materials with different batches is poor due to tissue differences. In addition, when changing the titanium alloy grade or changing the spring size, all processing technologies need to be retried.

[0013] During the cold coiling process of a helical compression spring, a large number of dislocations are generated, and the energy is converted into internal energy and stored in the spring itself. After the cold coiling is unloaded, the internal energy stored in the spring is released, and the spring undergoes a recovery deformation. To precisely control the spring forming, it is necessary to improve the high dislocation density inside the material and eliminate the residual stress in the spring to effectively control the spring accuracy. In the present invention, a DC power supply is connected to both ends of the titanium alloy spring blank formed by cold coiling under a loaded state. By utilizing the thermal effect after the spring is energized and the impact of the current on dislocations, the movement of dislocations is accelerated, the high dislocation density caused by cold working is rapidly improved, the residual stress in the titanium alloy spring blank is reduced, enabling it to quickly enter a low-stress equilibrium state, eliminating the springback deformation after the processing of the titanium alloy spring, effectively controlling the forming accuracy of the titanium alloy spring, and realizing the preparation of large-sized titanium alloy springs.

[0014] In the above-mentioned method for electrically assisted precise forming of a large-sized titanium alloy spring, it is characterized in that the anti-oxidation insulation coating in step one is a KBC-12 titanium alloy anti-oxidation coating, and the coating thickness is 0.2 mm to 0.4 mm. In the present invention, the titanium alloy bar is coated with the above-mentioned anti-oxidation insulation coating before spring forming. On the one hand, it prevents the surface of the titanium alloy from oxidizing during the process of energized heating and heat preservation. On the other hand, it prevents the spring head and tail from being tightly contacted, which may cause current instability during the spring energization process. At the same time, this anti-oxidation insulation coating can also play a certain lubricating role to prevent damage to the spring surface during the cold coiling process of the bar. By controlling the coating thickness, the insulation and anti-oxidation effects of the coating are ensured, and the peeling of the coating during the cold coiling process is avoided due to excessive thickness.

[0015] In the above-mentioned method for electrically assisted precise forming of a large-sized titanium alloy spring, it is characterized in that both the mandrel and the feeding wheel used in the numerically controlled spring coiling machine in step two are made of high-strength insulating materials, and the spindle speed during the cold coiling process is 24 revolutions per minute. The slow deformation of titanium alloy is beneficial to improving the spring surface quality. The spindle speed is set at the slow gear of 24 revolutions per minute, which ensures the uniform deformation of titanium alloy and avoids the peeling of the anti-oxidation insulation coating. At the same time, by controlling the spindle speed, the peeling of the anti-oxidation insulation coating caused by too fast spindle speed, as well as scratches or cross-section deformation on the spring surface due to high stress, are avoided.

[0016] The present invention has the following advantages compared with the prior art:

[0017] 1. The present invention adopts an electrically assisted precise forming method. By utilizing the thermal effect after the spring is energized and the impact of the current on dislocations, the high dislocation density caused by cold working is rapidly improved, the residual stress in the titanium alloy spring blank is reduced, the springback deformation after the processing of the titanium alloy spring is eliminated, the forming accuracy of the titanium alloy spring is effectively controlled, and the preparation of large-sized titanium alloy springs is realized.

[0018] 2. Compared with the current empirical trial-and-error method, the electro-assisted precision forming method adopted by the present invention greatly improves the dimensional accuracy and stability of titanium alloy springs, and is applicable to the preparation of high-precision titanium alloy springs in the fields of aerospace, marine ships, petrochemical industry, etc.

[0019] 3. The titanium alloy spring prepared by the present invention does not rebound after electro-assisted treatment, and the outer diameter and height of the spring are consistent before and after heat treatment, effectively ensuring the accuracy of the titanium alloy spring.

[0020] 4. The preparation method of the present invention is simple to operate and easy to implement, and the titanium alloy spring has good batch stability and is suitable for popularization and application.

[0021] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic installation diagram of the titanium alloy spring blank during the electro-assisted precision forming process of the present invention.

[0023] Figure 2a It is a side physical diagram of the large-sized titanium alloy spring prepared in Example 1 of the present invention.

[0024] Figure 2b It is a top physical diagram of the large-sized titanium alloy spring prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] Example 1

[0026] This embodiment includes the following steps:

[0027] Step 1: Cut the TB9 titanium alloy bar according to the size of the target product, a large-sized TB9 titanium alloy spring, and then coat the areas outside 30.0 mm on the surfaces of both ends of the TB9 titanium alloy bar with a KBC-12 titanium alloy anti-oxidation coating, and the coating thickness is 0.3 mm, and let it stand until dry to obtain a TB9 titanium alloy bar blank to be cold coiled; the diameter of the TB9 titanium alloy bar is 13.4 mm and the length is 4500.0 mm;

[0028] Step 2: According to the size of the target product, a large-sized TB9 titanium alloy spring, cold coil the TB9 titanium alloy bar blank obtained in Step 1 on a numerical control spring coiling machine according to the total number of spring turns of 21 turns to obtain a TB9 titanium alloy spring blank; the mandrel and the feeding wheel used in the numerical control spring coiling machine are both made of high-strength insulating materials, the diameter of the mandrel is 51.0 mm, and the spindle speed during the cold coiling process is 24 revolutions per minute;

[0029] Step 3: As Figure 1As shown, the TB9 titanium alloy spring blank obtained in the second step is still wound around the mandrel and one end is fixed on the feeding wheel, maintaining the spring in a loaded state. A DC power supply is connected to both ends of the TB9 titanium alloy spring blank, and it is heated to 800 °C at a current density of 11.0 A / mm 2 and held for 2 minutes. Immediately after the holding ends, the power is cut off and water cooling is carried out to obtain a water-cooled TB9 titanium alloy spring blank with an outer diameter of 77.8 mm and a height of 621.0 mm;

[0030] Step 4: Use a spring grinding machine to perform flat head treatment on the water-cooled TB9 titanium alloy spring blank obtained in the third step, and then perform aging heat treatment at 520 °C for 10 h using an electric resistance furnace to obtain a heat-treated TB9 titanium alloy spring blank with an outer diameter of 77.8 mm and a height of 621.0 mm;

[0031] Step 5: Perform shot peening treatment on the heat-treated TB9 titanium alloy spring blank obtained in the fourth step to remove the surface anti-oxidation insulation coating, obtaining a TB9 titanium alloy spring with an outer diameter of 77.8 mm, a height of 621.0 mm, and a wire diameter of 13.15 mm.

[0032] Five large-sized TB9 titanium alloy springs were prepared using the process of Example 1 of the present invention. As Figure 2a and Figure 2b shown, the loads of the five large-sized TB9 springs at the working height (366 mm) are shown in Table 1.

[0033] Table 1

[0034] Spring number 1# 2# 3# 4# 5# Load (N) 7013 7174 7052 7081 7100

[0035] It can be calculated from the data in Table 1 that the load error range of the five large-sized TB9 springs is within 3%. This shows that the large-sized TB9 titanium alloy springs prepared by the method of the present invention not only have high precision but also good consistency, and are suitable for the preparation of high-precision titanium alloy springs in fields such as aerospace, marine ships, and petrochemical industries.

[0036] Example 2

[0037] This example includes the following steps:

[0038] Step 1: Cut TC4 titanium alloy bars according to the dimensions of the target product, large-sized TC4 titanium alloy springs. Then, coat the areas outside 30.0 mm on the surfaces of both ends of the TC4 titanium alloy bars with a KBC-12 titanium alloy anti-oxidation coating, and the coating thickness is 0.2 mm. Let it stand until dry to obtain a TC4 titanium alloy bar blank to be cold coiled. The diameter of the TC4 titanium alloy bar is 8.0 mm and the length is 3800.0 mm;

[0039] Step 2: According to the dimensions of the large-sized TC4 titanium alloy spring as the target product, cold-wind the TC4 titanium alloy bar blank obtained in Step 1 on a numerical control spring winder with 14 total turns of the spring to obtain a TC4 titanium alloy spring blank; both the mandrel and the feeding wheel used in the numerical control spring winder are made of high-strength insulating materials, the diameter of the mandrel is 68.0 mm, and the spindle speed during the cold-winding process is 24 revolutions per minute;

[0040] Step 3: As Figure 1 shown, keep the TC4 titanium alloy spring blank obtained in Step 2 still wound on the mandrel and fix one end on the feeding wheel, maintain the spring loading state, connect a DC power supply to both ends of the TC4 titanium alloy spring blank, and heat it to 700 °C at a current density of 10.0 A / mm 2 and keep it warm for 1 min. Immediately cut off the power supply and cool it with water after the heat preservation ends to obtain a water-cooled TC4 titanium alloy spring blank with an outer diameter of 84 mm and a height of 400 mm;

[0041] Step 4: Use a spring grinding machine to perform flat head treatment on the water-cooled TC4 titanium alloy spring blank in Step 3, and then perform aging heat treatment at 750 °C for 10 h in an electric resistance furnace to obtain a heat-treated TC4 titanium alloy spring blank with an outer diameter of 84.0 mm and a height of 400.0 mm;

[0042] Step 5: Perform shot peening treatment on the heat-treated TC4 titanium alloy spring blank in Step 4 to remove the surface anti-oxidation insulating coating to obtain a TC4 titanium alloy spring with an outer diameter of 84.0 mm, a height of 400.0 mm, and a wire diameter of 8.0 mm.

[0043] Example 3

[0044] This example includes the following steps:

[0045] Step 1: Cut the TI-B19 titanium alloy bar according to the dimensions of the large-sized Ti-B19 titanium alloy spring as the target product, and then coat the KBC-12 titanium alloy anti-oxidation coating on the areas beyond 30.0 mm on the surfaces of both ends of the TI-B19 titanium alloy bar, with a coating thickness of 0.4 mm, and let it stand until dry to obtain a TI-B19 titanium alloy bar blank to be cold-wound; the diameter of the TI-B19 titanium alloy bar is 20 mm and the length is 5250.0 mm;

[0046] Step 2: According to the dimensions of the large-sized Ti-B19 titanium alloy spring as the target product, cold wind the Ti-B19 titanium alloy bar blank obtained in Step 1 on a numerical control spring winder for 15 turns to obtain a Ti-B19 titanium alloy spring blank; both the mandrel and the feeding wheel used in the numerical control spring winder are made of high-strength insulating materials, the diameter of the mandrel is 90.0 mm, and the spindle speed during the cold winding process is 24 revolutions per minute;

[0047] Step 3: As shown in Figure 1 , keep the Ti-B19 titanium alloy spring blank obtained in Step 2 still wound on the mandrel and one end fixed on the feeding wheel, maintain the spring loading state, connect a DC power supply to both ends of the Ti-B19 titanium alloy spring blank, and heat it to 820 °C at a current density of 12.0 A / mm 2 , then keep it insulated for 5 minutes. Immediately cut off the power supply and cool it with water after the insulation ends to obtain a water-cooled Ti-B19 titanium alloy spring blank with an outer diameter of 130.0 mm and a height of 520.0 mm;

[0048] Step 4: Use a spring grinding machine to perform a flat head treatment on the water-cooled Ti-B19 titanium alloy spring blank obtained in Step 3, and then perform an aging heat treatment at 500 °C for 8 hours in a resistance furnace to obtain a heat-treated Ti-B19 titanium alloy spring blank with an outer diameter of 130.0 mm and a height of 520.0 mm;

[0049] Step 5: Perform shot peening treatment on the heat-treated Ti-B19 titanium alloy spring blank obtained in Step 4 to remove the surface anti-oxidation insulating coating, and obtain a Ti-B19 titanium alloy spring with an outer diameter of 130.0 mm, a height of 520.0 mm, and a wire diameter of 20.0 mm.

[0050] The above is only a preferred embodiment of the present invention and does not impose any limitation on the present invention. Any simple modification, change, and equivalent change made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. An electro-assisted precise forming method for large-sized titanium alloy springs, characterized in that, The method includes the following steps: Step 1: Cut a titanium alloy bar according to the size of the large-sized titanium alloy spring as the target product. Then, coat an anti-oxidation insulating coating on the areas beyond 30.0 mm on the surfaces of both ends of the titanium alloy bar, and let it stand until dry to obtain a titanium alloy bar blank to be cold coiled. The diameter of the titanium alloy bar is 8.0 mm to 20.0 mm; Step 2: According to the size of the large-sized titanium alloy spring as the target product, cold coil the titanium alloy bar blank obtained in Step 1 on a numerically controlled spring coiling machine to obtain a titanium alloy spring blank; Step 3: Keep the titanium alloy spring blank in a spring-loaded state, connect a DC power supply to both ends of the titanium alloy spring blank, and heat it to 700°C to 820°C at a current density of 10 A / mm 2 ~12 A / mm 2 , hold for 1 min to 5 min, and immediately cut off the power supply for cooling after the holding ends; Step 4: Use a spring grinding machine to perform flat head treatment on the cooled titanium alloy spring blank in Step 3, and then perform heat treatment using an electric resistance furnace; Step 5: Perform shot peening treatment on the heat-treated titanium alloy spring blank in Step 4 to remove the anti-oxidation insulating coating on the surface to obtain a large-sized titanium alloy spring. The wire diameter of the large-sized titanium alloy spring is more than 8 mm, the coil pitch ratio is 4 to 10, and the total number of turns is more than 10.

2. The electro-assisted precise forming method for a large-sized titanium alloy spring according to claim 1, wherein The anti-oxidation insulating coating in Step 1 is a KBC-12 titanium alloy anti-oxidation coating, and the coating thickness is 0.2 mm to 0.4 mm.

3. A method for electrically assisted precise forming of a large-sized titanium alloy spring according to claim 1, characterized in that, Both the mandrel and the feed wheel used in the numerically controlled spring coiling machine in Step 2 are made of high-strength insulating materials, and the spindle speed during the cold coiling process is 24 revolutions per minute.

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