Forming method of super large size titanium alloy U-shaped section

Abstract

This invention discloses a method for forming ultra-large titanium alloy U-shaped profiles, comprising: 1. Initial heating of titanium alloy sheet using a tracked heating device; 2. Rapid transfer and first bending of the titanium alloy sheet under heat preservation conditions; 3. Second heating and bending of the L-shaped single-sided bent part; 4. Milling the edges of the U-shaped double-sided bent part; 5. Performing steel plate pressing and shaping heat treatment on the milled U-shaped double-sided bent part; 6. Performing surface treatment on the heat-treated U-shaped double-sided bent part to remove surface oxide scale, thereby obtaining the finished titanium alloy U-shaped profile. This invention optimizes the layout of the tracked heating device and bending machine, constructing an L-shaped rapid transfer path, thus solving the cracking problem caused by temperature drop in ultra-large titanium alloy sheet and ensuring the temperature stability of the titanium alloy sheet during bending; the large bogie furnace steel plate pressing and shaping heat treatment process improves the uniformity of the U-shaped double-sided bent part's shaping.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy material processing technology, specifically relating to a method for forming ultra-large titanium alloy U-shaped profiles. Background Technology

[0002] Titanium alloys, due to their high specific strength, excellent corrosion resistance, and good comprehensive mechanical properties, have become indispensable key structural materials in aerospace, military equipment, and new energy vehicles. With the rapid development of modern equipment towards larger size, integration, and lightweight design, higher requirements are being placed on the specifications of titanium alloy structural components, especially the increasingly urgent demand for ultra-large titanium alloy U-shaped profiles with a base plate cross-section width ranging from 200mm to 400mm, a plate thickness ranging from 5mm to 30mm, and a length ranging from 6m to 12m (up to 15m). Currently, the preparation of titanium alloy profiles mainly faces two major technical bottlenecks: "difficulty in forming" and "limited specifications." Common forming technologies and their limitations are as follows: Hot extrusion process: Long-length hot-extruded profiles suffer from severe torsion, making reshaping extremely difficult and unable to meet precision assembly requirements. Limited by the diameter of the extrusion cylinder, the maximum width of the U-shaped profile base plate cross-section that can be produced is usually no more than 200mm. Hot rolling process: For titanium alloys, due to their high resistance to high-temperature deformation, poor fluidity, and high temperature control requirements, they have only been used in small-sized pure titanium profiles, making it difficult to meet the manufacturing needs of ultra-large profiles of medium-strength and high-strength titanium alloys (such as TA18 and TC4). Hot stamping process: Hot stamping is a common method for U-shaped parts. For example, patent CN111054867A discloses a forging method for ultra-large U-shaped titanium alloy integral forgings, which is formed by multiple heating and bending fixtures. Although this method uses sheet metal as the blank, avoiding the blank waste problem of extrusion processes, the hot stamping process is also limited by the length and cross-sectional dimensions of the sheet metal. Due to the need for integral heating and integral stamping, the length of the sheet metal is usually limited to within 4 meters, and the width of the base plate cross-section is less than 200 mm, making it difficult to meet the needs of profiles with a length of more than 6 meters. At the same time, the contact area between the sheet metal and the die is large in the hot stamping process, and the required forming force increases exponentially, requiring extremely high equipment tonnage. Taking a U-shaped profile with a base plate cross-section width of 300mm as an example, the pressure required for hot stamping can reach over 5000 tons, resulting in huge equipment investment and poor economic efficiency. Patent CN114653793A provides a roll bending forming method for titanium alloy profiles, using multiple heated roll bending cycles to slow down deformation. However, this method requires large equipment investment and complex process control, primarily targeting thin-walled profiles with a base plate cross-section width typically less than 200mm, and the length is also limited by the roll bending equipment. Bending process: Cold bending of sheet metal is the most direct and efficient method for producing L-shaped and U-shaped profiles. Steel profiles can usually be formed using cold bending, but titanium alloys, due to their high yield strength ratio, low elastic modulus (only about 50% of steel), and poor room temperature plasticity, are prone to cracking during cold bending, with springback reaching 5°~10°, which is difficult to control. Therefore, traditional cold bending technology is completely unsuitable for titanium alloy profiles with poor formability.Simply heating a titanium sheet and bending it in one step presents a problem of rapid temperature drop: during the transfer of the heated sheet from the furnace to the bending machine, heat is rapidly dissipated; upon contact with the cold die, the temperature drops sharply, leading to reduced material plasticity and making the bent corners highly susceptible to cracking. Simultaneously, springback control is difficult, and the large springback after forming results in poor dimensional accuracy and shape stability. To address the challenges of controlling springback during titanium alloy bending and overcome the technical bottlenecks of heat treatment for shaping, a forming method for ultra-large titanium alloy U-shaped profiles is provided. Summary of the Invention

[0003] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a forming method for ultra-large titanium alloy U-shaped profiles. This method optimizes the layout of the tracked heating equipment and bending machine, enabling the conveyor rollers and conveyor belt to work together to form an L-shaped rapid transfer path. This solves the cracking problem caused by temperature drop in ultra-large titanium alloy sheets and ensures the temperature stability of the titanium alloy sheets during bending. Furthermore, the large bogie furnace steel plate pressing and shaping heat treatment process overcomes the difficulty of uniformly applying pressure on the press. The steel plate's self-weight pressing and high-temperature stress-relieving annealing are carried out simultaneously, ensuring that the shaping force acts uniformly and continuously on the entire U-shaped double-sided bent part, thus improving the uniformity of the U-shaped double-sided bent part's shaping.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for forming ultra-large titanium alloy U-shaped profiles, comprising the following steps: Step 1: Initial heating of the titanium alloy sheet using a tracked heating device: The tracked heating equipment includes a heating device and a conveyor roller conveyor located at one end of the heating device. The tracked heating equipment is closely attached to one side of the conveyor belt of the bending machine. The height of the conveyor roller conveyor of the tracked heating equipment is consistent with the height of the conveyor belt. The conveying direction of the conveyor roller conveyor is perpendicular to the conveying direction of the conveyor belt. The conveyor roller conveyor and the conveyor belt work together to form an L-shaped fast transfer path. The titanium alloy sheet is heated by the heating device in a wrapping manner, and after it is heated to the set heating temperature, it is kept at the temperature for a first set time. Step 2: Rapid transfer and first bending of titanium alloy sheet under heat preservation conditions: Step 201: The titanium alloy sheet in the heat preservation state is quickly transferred to the working area of ​​the bending machine through the L-shaped rapid transfer path. The specific process is as follows: First, heat preservation cotton is covered on the surface of the titanium alloy sheet, then the conveyor roller pushes the titanium alloy sheet into the conveyor belt along the length direction of the titanium alloy sheet, and then the conveyor belt transports the titanium alloy sheet to the working area of ​​the bending machine along the width direction of the titanium alloy sheet. Step 202: The titanium alloy sheet is bent on one side by a bending machine to obtain an L-shaped single-sided bent part, wherein the bending angle is... satisfy ,in, For the target bending angle, This refers to the springback amount during bending. Step 3: Perform a second heating and bending of the L-shaped single-sided bent part: Step 301: The L-shaped single-sided bent part is transferred in reverse through the L-shaped rapid transfer path to the tracked heating equipment, where the L-shaped single-sided bent part is heated a second time. Step 302: The L-shaped single-sided bent part, after secondary heating, is fed back into the bending machine for a second bending via an L-shaped rapid transfer path to obtain a U-shaped double-sided bent part; wherein, the bending angle is... satisfy ,in, For the target bending angle, This refers to the springback amount during bending. Step 4: Milling the edges of the U-shaped double-sided bent part: The U-shaped double-sided bent part after the second bend is fixed on a milling machine, and the end face of the wing plate of the U-shaped double-sided bent part is milled to make the height of the wing plate meet the height requirements of the finished titanium alloy U-shaped profile. Step 5: Perform steel plate pressing and shaping heat treatment on the milled U-shaped double-sided bent parts: Step 501: First, lay a first high-flatness steel plate on the furnace bottom platform of the large bogie furnace. Then, place the milled U-shaped double-sided bent piece on the first high-flatness steel plate and arrange at least two pairs of steel pads on the outside of the two flanges to prevent the flanges from being crushed and deformed during the annealing process. Finally, lay a second high-flatness steel plate on the two flange end faces of the milled U-shaped double-sided bent piece. Step 502: Close the furnace door of the large bogie furnace, heat up to the stress-relieving annealing set temperature, hold for the second set time, slowly cool with the furnace, and then remove from the furnace and air cool. After that, remove the first high flatness steel plate and the second high flatness steel plate. Step 6: Perform surface treatment on the heat-treated U-shaped double-sided bent parts to remove the surface oxide scale and obtain the finished titanium alloy U-shaped profile.

[0005] In the above-mentioned method for forming an ultra-large titanium alloy U-shaped profile, in step one, the thickness of the titanium alloy sheet ranges from 5mm to 30mm, and the length ranges from 6m to 15m. In steps one and three, the set heating temperature is determined according to the titanium alloy grade. Specifically, the set heating temperature range for industrial pure titanium is 200℃~300℃, the set heating temperature range for TA18 titanium alloy is 400℃~500℃, and the set heating temperature range for TC4 alloy is 600℃~800℃. In step one, the first set duration of heat preservation ranges from 5 minutes to 30 minutes.

[0006] In the above-mentioned method for forming ultra-large titanium alloy U-shaped profiles, during steps two and three, when the titanium alloy sheet or L-shaped single-sided bent part is transferred through an L-shaped rapid transfer path, the actual temperature of the titanium alloy sheet or L-shaped single-sided bent part before bending is not lower than 90% of the set heating temperature.

[0007] In the above-mentioned method for forming ultra-large titanium alloy U-shaped profiles, in steps two and three, the bending springback amount... The bending springback is determined based on the titanium alloy grade, sheet thickness, heating temperature, and flange height. For extra-large profiles with flange heights greater than 50mm, the springback is... satisfy ,in, Based on the rebound amount, The value range is 2° to 5°. For high rebound, The value range is 0.5° to 2°; In step three, the width of the bottom plate section of the U-shaped double-sided bending piece shall not be less than 200mm.

[0008] In the above-mentioned method for forming an ultra-large titanium alloy U-shaped profile, in step five, the surface flatness of the first high-flatness steel plate and the second high-flatness steel plate is no greater than 0.5 mm / m. The lengths of the first high-flatness steel plate and the second high-flatness steel plate are both greater than the length of the U-shaped double-sided bending piece, and the difference between the lengths of the first high-flatness steel plate and the second high-flatness steel plate and the length of the U-shaped double-sided bending piece ranges from 200mm to 500mm. The width of the first high flatness steel plate and the width of the second high flatness steel plate are both greater than the width of the U-shaped double-sided bending piece, and the difference between the width of the first high flatness steel plate and the width of the second high flatness steel plate and the width of the U-shaped double-sided bending piece is in the range of 100mm~200mm. The weight of the second high-flatness steel plate ranges from 1 ton to 5 tons, ensuring that the pressure applied to the U-shaped double-sided bend at the annealing temperature is lower than the yield strength of the U-shaped double-sided bend, thus preventing the two flanges of the U-shaped double-sided bend from being crushed and deformed during the annealing process.

[0009] In the above-mentioned method for forming ultra-large titanium alloy U-shaped profiles, in step five, the stress-relieving annealing setting temperature is determined according to the titanium alloy grade. The stress-relieving annealing setting temperature ranges from 500℃ to 600℃ for industrial pure titanium, from 550℃ to 650℃ for TA18 titanium alloy, and from 600℃ to 750℃ for TC4 alloy. The second set holding time ranges from 1 hour to 6 hours, with a longer holding time for thicker plates. The furnace cooling rate is controlled at 4℃ / min to 10℃ / min.

[0010] The above-mentioned method for forming ultra-large titanium alloy U-shaped profiles uses a heating device that is either a flexible ceramic resistance heating blanket or a tracked induction heater. Both the flexible ceramic resistance heating blanket and the tracked induction heater can be wrapped around the outside of the titanium alloy sheet, and the temperature control accuracy is ±5℃.

[0011] Compared with the prior art, the present invention has the following advantages: 1. This invention, by optimizing the layout of the tracked heating equipment and bending machine, and combining it with the heat treatment process of steel plate pressing and shaping in a large bogie furnace, successfully produces ultra-large titanium alloy U-shaped profiles with a base plate cross-section width of 200mm~500mm, a plate thickness range of 5mm~30mm, and a length range of 6m~15m. It breaks through the dual bottlenecks of the length limitation of traditional hot stamping process and the cross-section limitation of hot extrusion / rolling process, and is applicable to medium and high strength titanium alloys such as TA18 and TC4. It solves the limitation that traditional processes can only produce small-sized pure titanium profiles, breaks through the size limit, and fills the gap in the preparation of ultra-large titanium alloy U-shaped profiles.

[0012] 2. In this invention, the tracked heating device is positioned close to one side of the conveyor belt of the bending machine. The height of the conveyor rollers of the tracked heating device is consistent with the height of the conveyor belt, and the conveying direction of the conveyor rollers is perpendicular to the conveying direction of the conveyor belt. The conveyor rollers and the conveyor belt work together to form an L-shaped rapid transfer path. At the same time, insulation cotton is covered during the transfer process, so that the temperature drop of the sheet from the heating device to the completion of bending is controlled within 10%. This fundamentally solves the problem of cracking caused by temperature drop in ultra-large titanium alloy sheets and can further ensure the temperature stability of titanium alloy sheets during the bending process.

[0013] 3. This invention employs a control strategy where the bending angle exceeds the target forming angle to precisely compensate for the springback of titanium alloy sheets after bending. Addressing the characteristics of ultra-large titanium alloy U-shaped profiles with a base plate cross-section width exceeding 200mm and uneven springback, this invention optimizes the springback amount to achieve consistent angle control across the entire length, improving forming accuracy by over 60%. The final angle deviation can be controlled within ±0.5°, solving the industry problem of ensuring dimensional accuracy for ultra-large titanium alloys due to large and uneven springback. Through precise temperature control and springback amount adjustment, a matching plastic processing window and springback compensation strategy are provided for titanium alloys of different strength levels. Whether using pure titanium or high-strength TC4 titanium alloy, ultra-large titanium alloy U-shaped profiles with a base plate cross-section width exceeding 200mm, a plate thickness ≤30mm, and a length of 6m to 15m can be stably produced.

[0014] 4. This invention achieves shaping heat treatment by using a large bogie furnace in conjunction with steel plate pressing. A first high-flatness steel plate is laid on the furnace bottom platform to ensure the flatness of the bottom plate. A second high-flatness steel plate is laid above the flanges to achieve uniform pressure along the entire length using its own weight. At least two pairs of steel pads are arranged on the outer side of the two flanges to prevent the flanges from being crushed and deformed during annealing. For ultra-large titanium alloy U-shaped profiles with a bottom plate cross-section width of more than 200mm and a length of 6 to 15 meters, this invention overcomes the difficulty of limited press worktable surface and difficulty in uniformly applying pressure on the press. The self-weight pressing of the second high-flatness steel plate is carried out simultaneously with high-temperature stress-relieving annealing, so that the shaping force is uniformly and continuously applied to the entire U-shaped double-sided bending part, improving the uniformity of the U-shaped double-sided bending part's shaping. Compared with traditional processes that involve separate heat treatment and mechanical straightening, this method shortens the process flow and avoids the contradictions of "straightening before heat treatment" leading to straightening failure or "heat treatment before straightening" causing new residual stress. By utilizing the self-weight of a second-highest flatness steel plate at high temperature, the creep and stress relaxation characteristics of the metal are fully utilized, improving the residual stress elimination rate and ensuring the straightness and angular tolerances of ultra-large profiles.

[0015] 5. This invention uses a hot bending process for titanium alloy sheets, which has a high material utilization rate. Compared with the traditional hot extrusion process, it significantly reduces material costs and has significant economic benefits. Compared with hot stamping and hot extrusion processes, it does not require large presses or large extrusion equipment. It only requires general bending equipment and does not require special large molds, which greatly reduces equipment investment and facilitates promotion and application.

[0016] In summary, this invention optimizes the layout of the tracked heating equipment and the bending machine, enabling the conveyor rollers and conveyor belt to work together to form an L-shaped rapid transfer path. This solves the cracking problem caused by temperature drop in ultra-large titanium alloy plates and ensures the temperature stability of the titanium alloy plates during the bending process. Furthermore, the large bogie furnace steel plate pressing and shaping heat treatment process overcomes the difficulty of uniformly applying pressure on the press. The steel plate's self-weight pressing and high-temperature stress-relieving annealing are carried out simultaneously, ensuring that the shaping force acts uniformly and continuously on the entire U-shaped double-sided bent part, thus improving the uniformity of the U-shaped double-sided bent part's shaping.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a flowchart of the present invention.

[0019] Figure 2 This is a schematic diagram showing the positional relationship between the tracked heating device and the bending machine of the present invention.

[0020] Figure 3 This is a schematic diagram of the structure of the L-shaped single-sided bending part of the present invention.

[0021] Figure 4 This is a schematic diagram of the structure of the U-shaped double-sided bending component of the present invention.

[0022] Figure 5 This is a schematic diagram of the structure before the second high flatness steel plate of the present invention is placed.

[0023] Figure 6 This is a schematic diagram of the steel plate pressing and shaping structure of the present invention.

[0024] Explanation of reference numerals in the attached figures: 1—Titanium alloy sheet; 2-1—Flexible ceramic resistance heating blanket; 2-2—Conveyor rollers; 3—Bending machine; 3-1—Conveyor belt; 4—L-shaped single-sided bending part; 5—U-shaped double-sided bending component; 6—Furnace bottom platform; 7—First high-flatness steel plate; 8—Steel pad; 9—Second highest flatness steel plate. Detailed Implementation

[0025] The technical solution of the present invention will be described in detail through Embodiments 1 and 2: Example 1 like Figure 1 The method shown is a forming method for an ultra-large titanium alloy U-shaped profile, which includes the following steps: Step 1: Initial heating of titanium alloy sheet 1 using a tracked heating device: like Figure 2 As shown, the tracked heating equipment includes a heating device 2-1 and a conveyor roller 2-2 disposed at one end of the heating device 2-1. The tracked heating equipment is disposed close to one side of the conveyor belt 3-1 of the bending machine 3. The height of the conveyor roller 2-2 of the tracked heating equipment is consistent with the height of the conveyor belt 3-1. The conveying direction of the conveyor roller 2-2 is perpendicular to the conveying direction of the conveyor belt 3-1. The conveyor roller 2-2 and the conveyor belt 3-1 work together to form an L-shaped rapid transfer path. The titanium alloy plate 1 is heated by the heating device 2-1 in a wrapping manner, and after being heated to the set heating temperature, it is kept at the temperature for a first set time. It should be noted that a tracked heating device is set up, which includes a heating device 2-1 and a conveyor roller 2-2. In actual use, the heating device 2-1 is used to heat the titanium alloy sheet 1. Then, the heated titanium alloy sheet 1 is transferred using the conveyor roller 2-2. The conveyor roller 2-2 is located at one end of the heating device 2-1. There is no need for hoisting, or for the sheet to cross workshops or areas. The heated titanium alloy sheet 1 is simply pushed directly onto the conveyor roller 2-2. By optimizing the layout of the tracked heating device and the bending machine 3, firstly, the spatial distance between the heating process and the bending process is shortened, reducing the temperature loss of the heated titanium alloy sheet 1. Secondly, the transfer efficiency of the heated titanium alloy sheet 1 is improved, the transfer cost is reduced, and the safety during the transfer process is ensured. Because this method involves more than one heating and transfer, a second heating and transfer is also required for the L-shaped single-sided bent part. This provides a stable heating and transfer foundation for the forming of ultra-large titanium alloy U-shaped profiles, ensuring the speed and safety of the transfer of titanium alloy sheets between the heating and bending processes.

[0026] Step 2: Rapid transfer and first bending of titanium alloy sheet under heat preservation conditions: like Figure 2 As shown, in step 201, the titanium alloy plate 1 in the heat preservation state is quickly transferred to the working area of ​​the bending machine 3 through the L-shaped rapid transfer path. The specific process is as follows: first, heat preservation cotton is covered on the surface of the titanium alloy plate 1, then the conveyor roller 2-2 pushes it into the conveyor belt 3-1 along the length direction of the titanium alloy plate 1, and then the conveyor belt 3-1 transports it to the working area of ​​the bending machine 3 along the width direction of the titanium alloy plate 1. It should be noted that by setting the tracked heating equipment close to one side of the conveyor belt 3-1 of the bending machine, the height of the conveyor roller 2-2 of the tracked heating equipment is consistent with the height of the conveyor belt 3-1, and the conveying direction of the conveyor roller 2-2 is perpendicular to the conveying direction of the conveyor belt 3-1. The conveyor roller 2-2 and the conveyor belt 3-1 work together to form an L-shaped rapid transfer path. In actual use, the L-shaped rapid transfer path realizes the rapid transfer of the titanium alloy plate 1 in the heat preservation state. First, the conveyor roller 2-2 pushes the titanium alloy plate 1 into the conveyor belt 3-1 along the length direction, and then the conveyor belt 3-1 moves along the width direction of the titanium alloy plate 1. The titanium alloy sheet 1 is transported to the bending machine 3 working area in the 1-degree direction without needing to be turned around or raised, greatly shortening the time consumed in transporting the titanium alloy sheet 1. By covering it with insulation cotton during the transport process, the temperature loss is reduced, ensuring that the temperature drop of the titanium alloy sheet 1 is controlled within 10% from the time it is taken out of the heating device 2-1 until the first bend is completed. This ensures the temperature stability of the titanium alloy sheet during the bending process and fundamentally solves the problem of cracking caused by excessive temperature drop in ultra-large titanium alloy sheets. Furthermore, the titanium alloy sheet does not require hoisting during the transport process, making it safe, reliable, time-saving, and labor-saving.

[0027] like Figure 3 As shown, in step 202, the titanium alloy sheet 1 is bent on one side by the bending machine 3 to obtain an L-shaped single-sided bent part 4, wherein the bending angle is... satisfy ,in, For the target bending angle, This refers to the springback amount during bending. It should be noted that by adopting a bending angle Greater than the target bending angle The control strategy uses "over-bending compensation" to precisely compensate for the bending springback of titanium alloy sheet 1. This ensures the bending angle. The precision is such that there will be no over-bending or under-bending.

[0028] Step 3: Perform a second heating and bending of the L-shaped single-sided bent part: Step 301: The L-shaped single-sided bent part 4 is transferred in reverse to the tracked heating device via the L-shaped rapid transfer path, and the L-shaped single-sided bent part 4 is heated a second time by the tracked heating device. like Figure 4 As shown, in step 302, the L-shaped single-sided bent part 4, after secondary heating, is fed back into the bending machine 3 via an L-shaped rapid transfer path for a second bending, resulting in a U-shaped double-sided bent part 5; wherein, the bending angle... satisfy ,in, For the target bending angle, This refers to the springback amount during bending. It should be noted that in actual use, the titanium alloy sheet 1 needs to be transported in the forward direction once using the L-shaped rapid transfer path, that is, from the tracked heating equipment to the bending machine 3. The L-shaped single-sided bent part 4 needs to be transported in the reverse direction once using the L-shaped rapid transfer path, that is, from the bending machine 3 to the tracked heating equipment. After the second heating, it is transported in the forward direction once more.

[0029] Step 4: Milling the edges of the U-shaped double-sided bent part: The U-shaped double-sided bent part 5 after the second bend is fixed on a milling machine, and the end face of the wing plate of the U-shaped double-sided bent part 5 is milled to make the height of the wing plate meet the height requirements of the finished titanium alloy U-shaped profile. It should be noted that, since the method uses steel plate pressing and straightening heat treatment, that is, the self-weight pressing and straightening of the second high flatness steel plate 9 is carried out simultaneously with high temperature stress relief annealing, before the straightening heat treatment, the end face of the U-shaped double-sided bending part 5 needs to be processed by the milling process. The end face of the wing plate is finely repaired by rough milling and fine milling, so as to provide a straightening basis for pressing the second high flatness steel plate 9 onto the end face of the two wing plates.

[0030] like Figure 5 and Figure 6 As shown, step five involves performing steel plate pressing and reshaping heat treatment on the milled U-shaped double-sided bent part 5: Step 501: First, lay a first high-flatness steel plate 7 on the furnace bottom platform 6 of the large bogie furnace. Then, place the milled U-shaped double-sided bent piece 5 on the first high-flatness steel plate 7 and arrange at least two pairs of steel pads 8 on the outside of the two flanges to prevent the flanges from being crushed and deformed during the annealing process. Finally, lay a second high-flatness steel plate 9 on the two flange end faces of the milled U-shaped double-sided bent piece 5. Step 502: Close the furnace door of the large bogie furnace, heat up to the stress-relieving annealing set temperature, hold for the second set time, slowly cool with the furnace, and then air cool out of the furnace. After that, remove the first high flatness steel plate 7 and the second high flatness steel plate 9. In this embodiment, a large bogie furnace is used in conjunction with steel plate pressing to achieve the shaping heat treatment. A first high-flatness steel plate 7 is laid on the furnace bottom platform 6, which serves to ensure the accuracy of the bottom plate of the U-shaped double-sided bending part 5. A second high-flatness steel plate 9 is laid on the two flange end faces of the U-shaped double-sided bending part 5. The self-weight of the second high-flatness steel plate 9 is used to apply uniform pressure to the U-shaped double-sided bending part 5. By arranging at least two pairs of steel pads 8 on the outer side of the two flanges, the flanges can be prevented from being crushed and deformed during the annealing process. This heat treatment method overcomes the difficulty of uniformly pressing the U-shaped double-sided bending part 5 on the press due to the limited work surface of the press. The self-weight pressing and straightening of the second high-flatness steel plate 9 is carried out simultaneously with the high-temperature stress-relieving annealing, so that the shaping force is applied evenly and continuously to the entire U-shaped double-sided bending part 5, thereby improving the uniformity of the shaping of the U-shaped double-sided bending part 5. Compared with the existing technology that involves separate heat treatment and mechanical straightening, this heat treatment method shortens the process flow, avoids the process contradiction of "straightening before heat treatment" leading to straightening failure or "heat treatment before straightening" causing new residual stress, and makes full use of the creep and stress relaxation characteristics of metals, improving the residual stress elimination rate and ensuring the straightness and angular tolerance of ultra-large titanium alloy U-shaped profiles.

[0031] Step 6: Perform surface treatment on the heat-treated U-shaped double-sided bent part 5 to remove the surface oxide scale and obtain the finished titanium alloy U-shaped profile.

[0032] In this embodiment, by optimizing the layout of the tracked heating equipment and bending machine, and combining it with the large bogie furnace steel plate pressing and shaping heat treatment process, ultra-large titanium alloy U-shaped profiles with a base plate cross-section width of 200mm~500mm, a plate thickness range of 5mm~30mm, and a length range of 6m~15m were successfully produced. This breakthrough overcomes the dual bottlenecks of the traditional hot stamping process's length limitation and the hot extrusion / rolling process's cross-section limitation. It is also applicable to medium and high strength titanium alloys such as TA18 and TC4, solving the limitation that traditional processes can only produce small-sized pure titanium profiles. This breakthrough in size limits fills the gap in the production of ultra-large titanium alloy U-shaped profiles. Moreover, compared with hot extrusion, multi-pass rolling bending, or complex die forging processes, this process has a shorter flow and lower production cost. It only requires two bending operations, one edge milling operation, and one bogie furnace shaping heat treatment operation. The equipment investment is small, and there is no need for special large molds and large presses, which significantly improves production efficiency and reduces manufacturing costs. This provides an economically feasible technical path for the industrial production of large-sized titanium alloy profiles.

[0033] In this embodiment, in step one, the thickness of the titanium alloy plate ranges from 5mm to 30mm, and the length ranges from 6m to 15m. In steps one and three, the set heating temperature is determined according to the titanium alloy grade. Specifically, the set heating temperature range for industrial pure titanium is 200℃~300℃, the set heating temperature range for TA18 titanium alloy is 400℃~500℃, and the set heating temperature range for TC4 alloy is 600℃~800℃. In step one, the first set duration of heat preservation is between 5 min and 30 min.

[0034] In actual use, the first set duration of heat preservation corresponds to the thickness of the titanium alloy plate. For example, when the thickness of titanium alloy plate 1 is 10mm, the first set duration of heat preservation for titanium alloy plate 1 is 10min; when the thickness of titanium alloy plate 1 is 15mm, the first set duration of heat preservation for titanium alloy plate 1 is 15min.

[0035] In this embodiment, during the process of transferring the titanium alloy plate 1 or the L-shaped single-sided bent part 4 through the L-shaped rapid transfer path in steps two and three, the actual temperature of the titanium alloy plate 1 or the L-shaped single-sided bent part 4 before bending is not lower than 90% of the set heating temperature.

[0036] In this embodiment, in steps two and three, the bending springback amount The bending springback is determined based on the titanium alloy grade, sheet thickness, heating temperature, and flange height. For extra-large profiles with flange heights greater than 50mm, the springback is... satisfy ,in, Based on the rebound amount, The value range is 2° to 5°. For high rebound, The value range is 0.5° to 2°; In step three, the width of the bottom plate section of the U-shaped double-sided bending piece 5 shall not be less than 200mm.

[0037] In this embodiment, due to the characteristics of high flange and uneven springback of the ultra-large titanium alloy U-shaped profile, the bending springback amount is optimized to achieve consistent control of the bending angle over the entire length, thereby improving the bending forming accuracy of the ultra-large titanium alloy U-shaped profile and making the bending angle deviation controllable within ±0.5°.

[0038] In this embodiment, in step five, the surface flatness of the first high-flatness steel plate 7 and the second high-flatness steel plate 9 is no greater than 0.5 mm / m; The length of the first high flatness steel plate 7 and the length of the second high flatness steel plate 9 are both greater than the length of the U-shaped double-sided bending piece 5, and the difference between the length of the first high flatness steel plate 7 and the length of the second high flatness steel plate 9 and the length of the U-shaped double-sided bending piece 5 is in the range of 200mm~500mm. The width of the first high flatness steel plate 7 and the width of the second high flatness steel plate 9 are both greater than the width of the U-shaped double-sided bending piece 5, and the difference between the width of the first high flatness steel plate 7 and the width of the second high flatness steel plate 9 and the width of the U-shaped double-sided bending piece 5 is in the range of 100mm~200mm. The weight of the second high flatness steel plate 9 ranges from 1 ton to 5 tons, ensuring that the pressure applied to the U-shaped double-sided bend 5 at the annealing temperature is lower than the yield strength of the U-shaped double-sided bend 5, and preventing the two flanges of the U-shaped double-sided bend 5 from being crushed and deformed during the annealing process.

[0039] In actual use, the dimensions of the first high flatness steel plate 7 and the second high flatness steel plate 9 need to be determined comprehensively based on the titanium alloy grade, the specifications of the U-shaped double-sided bending part 5, and the yield strength of the U-shaped double-sided bending part 5, so as to improve the straightening accuracy of the U-shaped double-sided bending part 5 while ensuring safety.

[0040] In this embodiment, in step five, the stress-relieving annealing setting temperature is determined according to the titanium alloy grade. The stress-relieving annealing setting temperature range for industrial pure titanium is 500℃~600℃, for TA18 titanium alloy it is 550℃~650℃, and for TC4 alloy it is 600℃~750℃. The second set holding time ranges from 1 hour to 6 hours, with a longer holding time for thicker plates. The furnace cooling rate is controlled at 4℃ / min~10℃ / min.

[0041] In this embodiment, the heating device 2-1 is a flexible ceramic resistance heating blanket, which can be wrapped around the outside of the titanium alloy plate 1, and the temperature control accuracy is ±5℃.

[0042] In this embodiment, the titanium alloy plate 1 is made of TA18 titanium alloy. The length of the finished titanium alloy U-shaped profile to be formed is 6 meters, the width of the base plate cross-section is 300mm, the height of the wing plate is 70mm, the plate thickness is 8mm, and the target forming angle is... With a 90° angle, this TA18 titanium alloy U-shaped profile can be used for the longitudinal beam structure of the main chassis of lightweight armored vehicles.

[0043] In step one, TA18 titanium alloy sheet 1 with a thickness of 8mm, a width of 450mm, and a length of 6050mm is selected. The TA18 titanium alloy sheet is completely covered by heating device 2-1, heated to 450℃, and then held at that temperature for 8 minutes with a temperature control accuracy of ±5℃.

[0044] In step two, the titanium alloy plate 1, which is in a heat preservation state, is quickly transferred to the working area of ​​the bending machine 3 through the L-shaped rapid transfer path, and the first bending and forming process takes 23 to 30 seconds. The actual temperature of the titanium alloy plate 1 before the first bending is 435°C, and the temperature drop is only 15°C.

[0045] Based on the springback characteristics of TA18 titanium alloy at 450℃ and the dimensional factors of the flange height, the bending springback amount is determined. =3.5°, where the basic rebound amount =3°, height rebound =0.5°; therefore, during the first bend using bending machine 3, the bending angle is controlled. =93.5°, forming an L-shaped single-sided bent part 4.

[0046] In step three, the U-shaped double-sided bent part 5 obtained after the second bend has a measured bottom plate cross-section width of 302mm, a measured wing plate rough forming height ranging from 73mm to 76mm, and a measured bending angle of 90.3° after unloading.

[0047] In this embodiment, in step four, the U-shaped double-sided bent part 5 is fixed to the worktable of a large gantry milling machine using a special fixture. A 200mm diameter disc milling cutter is used to mill the end faces of the two flanges, with a milling allowance of 5mm. The milling is performed in two feeds: rough milling and finish milling. After finish milling, the flange height is 70±0.2mm, and the surface roughness Ra≤3.2μm.

[0048] In this embodiment, in step five, the first high-flatness steel plate 7 has a thickness of 45mm, a length of 6.5m, a width of 0.5m, and a flatness of ≤0.3mm / m; the second high-flatness steel plate 9 has a thickness of 45mm, a length of 6.5m, a width of 0.5m, and a weight of 1.1 tons to 1.2 tons.

[0049] In step 502, the temperature is raised to 600℃, the stress-relieving annealing temperature of TA18 titanium alloy, and held for 2 hours. Then, it is cooled in the furnace at a rate of 6℃ / min to below 150℃, and then air-cooled after being removed from the furnace.

[0050] After surface treatment, the finished product was inspected. The TA18 titanium alloy U-shaped profile obtained in this embodiment has a base plate cross-section width of 300±2mm, a plate thickness of 8±0.3mm, a wing plate height of 700±0.2mm, a straightness of ≤1.3mm / m, a bending angle of 90.2°±0.3°, no surface cracks, uniform structure, and a residual stress test value of ≤40MPa, which fully meets the requirements of military equipment.

[0051] Example 2 In this embodiment, the difference from Embodiment 1 is: In this embodiment, the titanium alloy plate 1 is made of TC4 titanium alloy. The length of the finished titanium alloy U-shaped profile to be formed is 10 meters, the width of the base plate cross-section is 400mm, the height of the wing plate is 320mm, the plate thickness is 25mm, and the target forming angle is... With a 90° angle, this TC4 titanium alloy U-shaped profile can be used in the chassis frame structure of hydrogen fuel cell heavy-duty trucks.

[0052] In step one, titanium alloy plate 1 is selected from TC4 titanium alloy plates with a thickness of 25mm, a width of 1052mm, and a length of 10050mm. The TC4 titanium alloy plate is heated to 800℃ using a tracked induction heater, and the initial holding time is set to 25 minutes, with a temperature control accuracy of ±5℃.

[0053] The heating device 2-1 is a tracked induction heater, which can be wrapped around the outside of the titanium alloy plate 1. The distance between the tracked induction heater and the conveyor belt 3-1 is 2 meters.

[0054] In step two, the titanium alloy plate 1, which is in a heat preservation state, is quickly transferred to the working area of ​​the bending machine 3 through the L-shaped rapid transfer path, and the first bending and forming process takes 29 to 35 seconds. The actual temperature of the titanium alloy plate 1 before the first bending is 770°C, and the temperature drop is 30°C.

[0055] Based on the springback characteristics of TC4 titanium alloy at 450℃ and the dimensional factors of the flange height, the bending springback amount is determined. =5°, where the basic rebound amount =4°, height rebound =1°; therefore, during the first bend using bending machine 3, the bending angle is controlled. =95°, forming an L-shaped single-sided bent part 4.

[0056] In step three, the U-shaped double-sided bent part 5 obtained after the second bend has a measured bottom plate cross-section width of 402mm, a measured wing plate rough forming height ranging from 326mm to 328mm, and a measured bending angle of 90.4° after unloading.

[0057] In this embodiment, in step four, the U-shaped double-sided bent part 5 is fixed to the worktable of a large gantry milling machine using a special tooling. A disc milling cutter is used to mill the end faces of the two flanges, with a milling allowance of 6mm~8mm. The milling is performed in two feeds: rough milling and finish milling. After finish milling, the flange height is 320±0.2mm.

[0058] In this embodiment, in step five, the first high-flatness steel plate 7 has a thickness of 50mm, a length of 10.5m, a width of 0.6m, and a flatness of ≤0.3mm / m; the second high-flatness steel plate 9 has a thickness of 50mm, a length of 10.5m, a width of 0.6m, and a weight of 2.4 tons to 2.5 tons.

[0059] In step 502, the temperature is raised to 650℃ (TC4 stress-relieving annealing temperature), held for 5 hours, and then cooled in the furnace at a rate of 5℃ / min to below 150℃ before being removed from the furnace and air-cooled.

[0060] After surface sandblasting, the finished product was inspected. The TC4 titanium alloy U-shaped profile obtained in this embodiment has a base plate cross-section width of 401±2mm, a plate thickness of 25±0.3mm, a flange height of 320±0.2mm, a straightness of ≤1.4mm / m, a bending angle of 90.3°±0.4°, no surface cracks, uniform structure, and a residual stress value of ≤70MPa. All performance indicators meet the standards for structural components used in new energy heavy-duty vehicles.

[0061] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for forming ultra-large titanium alloy U-shaped profiles, characterized in that: Includes the following steps: Step 1: Initial heating of titanium alloy sheet (1) using a tracked heating device: The tracked heating equipment includes a heating device (2-1) and a conveyor roller (2-2) disposed at one end of the heating device (2-1). The tracked heating equipment is closely attached to one side of the conveyor belt (3-1) of the bending machine (3). The height of the conveyor roller (2-2) of the tracked heating equipment is consistent with the height of the conveyor belt (3-1). The conveying direction of the conveyor roller (2-2) is perpendicular to the conveying direction of the conveyor belt (3-1). The conveyor roller (2-2) and the conveyor belt (3-1) work together to form an L-shaped fast transfer path. The titanium alloy plate (1) is heated by the heating device (2-1) in a wrapping manner. After the temperature is heated to the set temperature, it is kept warm for a first set time. Step 2: Rapid transfer and first bending of titanium alloy sheet under heat preservation conditions: Step 201: The titanium alloy plate (1) in the heat preservation state is quickly transferred to the working area of ​​the bending machine (3) through the L-shaped rapid transfer path. The specific process is as follows: First, heat preservation cotton is covered on the surface of the titanium alloy plate (1), and then the conveyor roller (2-2) pushes the titanium alloy plate (1) into the conveyor belt (3-1) along the length direction of the titanium alloy plate (1), and then the conveyor belt (3-1) transports the titanium alloy plate (1) to the working area of ​​the bending machine (3) along the width direction of the titanium alloy plate (1). Step 202: The titanium alloy sheet (1) is bent on one side by the bending machine (3) to obtain an L-shaped single-sided bent part (4), wherein the bending angle is... satisfy ,in, For the target bending angle, This refers to the springback amount during bending. Step 3: Perform a second heating and bending of the L-shaped single-sided bent part: Step 301: The L-shaped single-sided bent part (4) is transferred in reverse through the L-shaped rapid transfer path to the tracked heating equipment, and the L-shaped single-sided bent part (4) is heated a second time by the tracked heating equipment. Step 302: The L-shaped single-sided bent part (4) after secondary heating is fed back into the bending machine (3) through an L-shaped rapid transfer path for a second bending to obtain a U-shaped double-sided bent part (5); wherein, the bending angle is... satisfy ,in, For the target bending angle, This refers to the springback amount during bending. Step 4: Milling the edges of the U-shaped double-sided bent part: The U-shaped double-sided bent part (5) after the second bend is fixed on the milling machine, and the end face of the wing plate of the U-shaped double-sided bent part (5) is milled so that the height of the wing plate meets the height requirements of the finished titanium alloy U-shaped profile. Step 5: Perform steel plate pressing and shaping heat treatment on the U-shaped double-sided bent part (5) after milling: Step 501: First, lay a first high flatness steel plate (7) on the furnace bottom platform (6) of the large bogie furnace. Then, place the milled U-shaped double-sided bent piece (5) on the first high flatness steel plate (7) and arrange at least two pairs of steel pads (8) on the outside of the two flanges to prevent the flanges from being crushed and deformed during the annealing process. Finally, lay a second high flatness steel plate (9) on the two flange end faces of the milled U-shaped double-sided bent piece (5). Step 502: Close the furnace door of the large bogie furnace, heat up to the stress relief annealing set temperature, hold for the second set time, cool slowly with the furnace and then air cool out of the furnace. After that, remove the first high flatness steel plate (7) and the second high flatness steel plate (9). Step 6: Perform surface treatment on the heat-treated U-shaped double-sided bent part (5) to remove the surface oxide scale and obtain the finished titanium alloy U-shaped profile.

2. The forming method of an ultra-large titanium alloy U-shaped profile according to claim 1, characterized in that: In step one, the thickness of the titanium alloy sheet ranges from 5mm to 30mm, and the length ranges from 6m to 15m. In steps one and three, the set heating temperature is determined according to the titanium alloy grade. Specifically, the set heating temperature range for industrial pure titanium is 200℃~300℃, the set heating temperature range for TA18 titanium alloy is 400℃~500℃, and the set heating temperature range for TC4 alloy is 600℃~800℃. In step one, the first set duration of heat preservation ranges from 5 minutes to 30 minutes.

3. A method for forming an ultra-large titanium alloy U-shaped profile according to claim 1, characterized in that: In steps two and three, during the process of transferring the titanium alloy sheet (1) or the L-shaped single-sided bent part (4) through the L-shaped rapid transfer path, the actual temperature of the titanium alloy sheet (1) or the L-shaped single-sided bent part (4) before bending is not lower than 90% of the set heating temperature.

4. A method for forming an ultra-large titanium alloy U-shaped profile according to claim 1, characterized in that: In steps two and three, the amount of bending springback The bending springback is determined based on the titanium alloy grade, sheet thickness, heating temperature, and flange height. For extra-large profiles with flange heights greater than 50mm, the springback is... satisfy ,in, Based on the rebound amount, The value range is 2° to 5°. For high rebound, The value range is 0.5° to 2°; In step three, the width of the bottom plate section of the U-shaped double-sided bending piece (5) shall not be less than 200mm.

5. A method for forming an ultra-large titanium alloy U-shaped profile according to claim 1, characterized in that: In step five, the surface flatness of the first high-flatness steel plate (7) and the second high-flatness steel plate (9) is no greater than 0.5 mm / m; The length of the first high flatness steel plate (7) and the length of the second high flatness steel plate (9) are both greater than the length of the U-shaped double-sided bending piece (5), and the difference between the length of the first high flatness steel plate (7) and the length of the second high flatness steel plate (9) and the length of the U-shaped double-sided bending piece (5) is in the range of 200mm~500mm. The width of the first high flatness steel plate (7) and the width of the second high flatness steel plate (9) are both greater than the width of the U-shaped double-sided bending piece (5), and the difference between the width of the first high flatness steel plate (7) and the width of the second high flatness steel plate (9) and the width of the U-shaped double-sided bending piece (5) is in the range of 100mm~200mm. The weight of the second high flatness steel plate (9) ranges from 1 ton to 5 tons, ensuring that the pressure applied to the U-shaped double-sided bending part (5) at the annealing temperature is lower than the yield strength of the U-shaped double-sided bending part (5), and preventing the two flanges of the U-shaped double-sided bending part (5) from being crushed and deformed during the annealing process.

6. A method for forming an ultra-large titanium alloy U-shaped profile according to claim 1, characterized in that: In step five, the stress-relieving annealing setting temperature is determined according to the titanium alloy grade. The stress-relieving annealing setting temperature range for industrial pure titanium is 500℃~600℃, for TA18 titanium alloy it is 550℃~650℃, and for TC4 alloy it is 600℃~750℃. The second set holding time ranges from 1 hour to 6 hours. The larger the plate thickness, the longer the holding time. The furnace cooling rate is controlled at 4℃ / min~10℃ / min.

7. A method for forming an ultra-large titanium alloy U-shaped profile according to claim 1, characterized in that: The heating device (2-1) is a flexible ceramic resistance heating blanket or a tracked induction heater. Both the flexible ceramic resistance heating blanket and the tracked induction heater can be wrapped around the outside of the titanium alloy plate (1), and the temperature control accuracy is ±5℃.

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