Reciprocating spinning strengthening method for titanium alloy thin-walled cylindrical part

Abstract

This invention discloses a reciprocating spinning strengthening method for thin-walled cylindrical titanium alloy parts, belonging to the field of metal material plastic forming. This invention addresses the problem that while heat treatment can control texture through phase transformation, its effect is limited, and it easily eliminates the flow lines generated during spinning. Furthermore, the added steps increase time costs and reduce economic efficiency. This invention changes the metal flow direction during forming by altering the clamping direction of the billet relative to the mandrel after each forming pass, thereby achieving a reciprocating change of the spinning forming path, thus weakening the texture and improving mechanical properties. Controlling the loading path during spinning forming by changing the relative flow direction has advantages such as low operational difficulty and high efficiency.

Description

Technical Field

[0001] This invention belongs to the field of plastic forming of metallic materials. Specifically, it relates to a method for reciprocating spinning strengthening of thin-walled cylindrical parts of titanium alloys, which is particularly suitable for performance strengthening of thin-walled cylindrical parts of near-α titanium alloys and duplex titanium alloys. Background Technology

[0002] Titanium alloy thin-walled cylindrical components are key load-bearing members widely used in defense fields such as aerospace and weaponry. During service, these components often bear complex axial tensile and compressive loads combined with circumferential internal pressure, thus placing extremely stringent requirements on the material's comprehensive mechanical properties, especially axial (longitudinal) yield strength and circumferential tensile strength. Traditional spinning forming processes can achieve continuous streamlines; however, after unidirectional cumulative large plastic deformation, a strong basal texture is formed in the wall thickness direction. While this texture improves the strength in the wall thickness direction, it does not meet the high axial and circumferential performance requirements under service conditions. Therefore, controlling the texture plays a positive role in meeting the component's performance requirements. Heat treatment can control the texture through phase transformation; however, its effect is limited, and it easily eliminates the streamlines generated by spinning. Furthermore, the added process increases time costs and reduces economic efficiency. Summary of the Invention

[0003] This invention provides a method for reciprocating spinning strengthening of thin-walled cylindrical titanium alloy parts. By changing the loading path during spinning to control the strain components, the strength of the base surface texture can be effectively weakened, enhancing the axial and circumferential mechanical properties of the spun cylindrical parts. To further improve the mechanical properties of the cylindrical parts after high-strength spinning, the blank flow direction is changed after each spinning pass, achieving variation of the spinning trajectory for different passes.

[0004] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a method for reciprocating spinning strengthening of thin-walled cylindrical titanium alloy parts, characterized by the following steps: Step 1: Spray graphite lubricant evenly on the surface of the mandrel and preheat it to 300~400℃. Preheat the rotating wheel to 150~250℃. Spray high-temperature anti-oxidant evenly on the surface of the titanium alloy cylindrical part and heat it evenly to 500~600℃. Place the heated titanium alloy cylindrical part on the mandrel and make it contact the thrust plate. Step 2: Start the spinning machine and heat the titanium alloy cylindrical part. Perform the first forming according to the set process parameters. During the forming process, maintain the temperature of the deformed zone at 650~850℃ and stabilize the temperature of the undeformed zone at 400~500℃. After the spinning wheel passes the blank by a distance x, it feeds radially until the metal at that position reaches the set thinning rate. Then it feeds axially until the distance from the other end of the blank is also x. After the first forming is completed, the spinning wheel retracts and the heating stops. Step 3: Use the pusher to eject the titanium alloy cylindrical part, swap its two ends and place it back on the mandrel, and make it contact the thrust plate. The end point of the rotating wheel's motion trajectory is the same as the first pass. The axial feed distance is determined according to the elongation of the billet after this pass. The remaining process parameters are the same as in Step 2. Step 4: Repeat step 3 until the desired cumulative thinning rate is achieved.

[0005] Furthermore, the titanium alloy type is specified as near-α titanium alloy or duplex titanium alloy, where the α phase has a large proportion, making it easier to produce a strong texture during spinning. Preferably, the initial state of the billet is a post-forging annealed state. The spinning temperature is 100-150°C below the phase transformation point to avoid significant β phase transformation that weakens the strengthening effect.

[0006] To further specify, in step 1, the material used for the spinning wheel is 3Cr2W8V hot work die steel, and the shape is a double-cone angle spindle.

[0007] Further specifying, in step 1, the material used for the mandrel is 5CrNiMo hot work die steel; the heating method for the mandrel is induction coil heating or oxygen-acetylene flame heating.

[0008] 4. The method according to claim 1, wherein in step 1, the fit between the titanium alloy cylindrical part and the mandrel is a clearance fit.

[0009] Further specifying, in step 2, the heating method of the deformed area is induction coil or oxygen-acetylene flame heating, and the width of the hot zone is about 50~80 mm, while the heating method of the undeformed area is oxygen-acetylene flame heating.

[0010] Further specifying, in step 2, the spinning forming method is high-pressure spinning, and it is reverse spinning.

[0011] Further specifying, in step 2, the thinning rate of the first pass of spinning is 15% to 30%.

[0012] Further specifying, in step 2, the distance x is 10~30 mm, and both ends of the billet retain this part of metal so that it does not deform during spinning.

[0013] Further specifying, in step 2, the spindle speed is 70~120 rpm and the feed ratio is 0.5~1.5 mm / r.

[0014] Another object of the present invention is to provide a titanium alloy thin-walled cylindrical part processed by any of the above methods.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention alters the metal flow direction during spinning by changing the clamping direction of the billet relative to the mandrel after each forming pass, thereby achieving reciprocating changes in the spinning path, which in turn weakens the texture and improves mechanical properties. Controlling the loading path during spinning by changing the relative flow direction offers advantages such as low operational difficulty and high efficiency.

[0016] This invention controls the thinning rate per pass within a small range (between 15-25%) to increase the number of reciprocating spinning cycles. The 6-8 pass (cumulative thinning rate of 70%~85%) reciprocating spinning process (cumulative reciprocating cycle count of 3-4 times) can effectively improve the strength of titanium alloy cylindrical parts. Compared with the traditional spinning method, the strength of TC4 titanium alloy is increased by 38.5 MPa.

[0017] In this invention, each pass of the reciprocating spinning process adopts a reverse spinning method. When forming, the spinning machine's rollers need to retain a fixed-length (10-30mm) non-deformation zone at both ends of the blank to ensure sufficient metal transmission of mandrel torque after the blank ends are exchanged between passes.

[0018] By changing the relative flow direction of the metal during the powerful spinning process of titanium alloy thin-walled cylindrical parts, the limitation of traditional spinning processes that easily form base surface textures is broken. Under the action of the reciprocating path, the weakening of texture reduces the anisotropic effect and effectively improves the axial and circumferential properties of titanium alloy thin-walled cylindrical parts.

[0019] While keeping the other process parameters of the high-strength spinning of titanium alloy unchanged, the complex forming path is achieved by simply swapping the two ends of the billet between passes, which is easy to implement and simple to operate.

[0020] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0021] Figure 1(a) is a schematic diagram of reciprocating spinning forming with an odd number of passes; Figure 1(b) is a schematic diagram of reciprocating spinning forming with an even number of passes; In the diagram, 1-mandrel, 2-titanium alloy billet, 3-heating equipment, 4-push plate, 5-spinning machine spindle, 6-spinning wheel; Figure 2 The comparison shows the spinning texture of TC4 titanium alloy: (a) traditional process; (b) reciprocating spinning process. Detailed Implementation The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0022] Example The original billet was selected as TC4 titanium alloy, heat-treated to a forged and annealed state. The billet dimensions were Φ99×9×150mm, and the exposed section of the mandrel was Φ100×800mm. The mandrel material was 5CrNiMo hot work die steel, and the spinning forming equipment was a horizontal double-roller spinning mill. The specific process flow is as follows: (1) The titanium alloy billet is cut to Φ100×8×150 mm by machining. The billet and the mandrel are in clearance fit at room temperature. (2) Spray graphite lubricant evenly on the surface of the mandrel, spray high-temperature glass water evenly on the surface of the blank, preheat the mandrel to 300~400 ℃ using an induction coil, preheat the rotating wheel to 150~250 ℃ using an oxygen-acetylene cutting torch, and after preheating, heat the blank to 600~700 ℃ using an oxygen-acetylene cutting torch and push it onto the mandrel; (3) Push the billet to contact the pusher plate, start the spinning machine, and spin forming in a counter-rotating manner. After the spinning wheel passes the end of the billet by 20 mm, it forms the billet by radial feed. Process parameters: thinning rate per pass is 20%, mandrel speed is 100 rpm, spinning wheel feed rate is 70 mm / min, and heating power of induction coil is 10 kW. During this period, use an oxygen-acetylene torch to continuously heat the spinning wheel and mandrel to keep the temperature consistent with the final temperature of the preheating stage. After forming, stop the spindle rotation, output the induction coil, retract the spinning wheel, use the pusher plate to push the billet out until it is completely separated from the mandrel, change the two ends of the billet and push it back onto the mandrel; (4) Repeat step (3) until the six-pass forming is completed, and finally obtain a TC4 titanium alloy cylindrical part with a cumulative thinning rate of about 78% and a wall thickness of about 2.2 mm. Keep the mandrel rotating at a low speed and wait for the temperature to cool evenly to room temperature before taking off the workpiece for observation.

[0023] After sampling and testing, the strength of the TC4 titanium alloy cylindrical part is 1199.2 MPa, which is higher than the strength (1160.8 MPa) of the traditional multi-pass high-strength spinning process (without changing the feed direction of the spinning wheel relative to the billet) under the same cumulative thinning rate. Furthermore, the {0002} crystal plane is deflected from the wall thickness direction towards the circumferential direction (see...). Figure 2 The basal texture is weakened.

[0024] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the technical solutions of the present invention.

Claims

1. A method for reciprocating spinning strengthening of thin-walled cylindrical titanium alloy parts, characterized in that, Includes the following steps: Step 1: Spray graphite lubricant evenly on the surface of the mandrel and preheat it to 300~400℃. Preheat the rotating wheel to 150~250℃. Spray high-temperature anti-oxidant evenly on the surface of the titanium alloy cylindrical part and heat it evenly to 500~600℃. Place the heated titanium alloy cylindrical part on the mandrel and make it contact the thrust plate. Step 2: Start the spinning machine and heat the titanium alloy cylindrical part. Perform the first forming according to the set process parameters. During the forming process, maintain the temperature of the deformed zone at 650~850℃ and stabilize the temperature of the undeformed zone at 400~500℃. After the spinning wheel passes the blank by a distance x, it feeds radially until the metal at that position reaches the set thinning rate. Then it feeds axially until the distance from the other end of the blank is also x. After the first forming is completed, the spinning wheel retracts and the heating stops. Step 3: Use the pusher to eject the titanium alloy cylindrical part, swap its two ends and place it back on the mandrel, and make it contact the thrust plate. The end point of the rotating wheel's motion trajectory is the same as the first pass. The axial feed distance is determined according to the elongation of the billet after this pass. The remaining process parameters are the same as in Step 2. Step 4: Repeat step 3 until the desired cumulative thinning rate is achieved.

2. The method according to claim 1, characterized in that, In step 1, the material used for the spinning wheel is 3Cr2W8V hot work die steel, and its shape is a double-cone angle spindle.

3. The method according to claim 1, characterized in that, In step 1, the mandrel is made of 5CrNiMo hot work die steel; the mandrel is heated by induction coil heating or oxygen-acetylene flame heating.

4. The method according to claim 1, characterized in that, In step 1, the fit between the titanium alloy cylindrical part and the mandrel is a clearance fit.

5. The method according to claim 1, characterized in that, In step 2, the heating method for the deformed area is induction coil or oxygen-acetylene flame heating, and the width of the heated area is about 50~80 mm. The heating method for the undeformed area is oxygen-acetylene flame heating.

6. The method according to claim 1, characterized in that, In step 2, the spinning forming method is high-pressure spinning, and it is reverse spinning.

7. The method according to claim 1, characterized in that, In step 2, the thinning rate is 15%~30%.

8. The method according to claim 1, characterized in that, In step 2, the distance x is 10~30 mm.

9. The method according to claim 1, characterized in that, In step 2, the spindle speed is 70~120 rpm and the feed ratio is 0.5~1.5 mm / r.

10. A titanium alloy thin-walled cylindrical part processed by the method of any one of claims 1-9.

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