A method of forming a titanium alloy tube by induction current assisted solid granular media bulging

Abstract

This invention discloses a method for forming titanium alloy tubes using induced current-assisted solid granular medium bulging, belonging to the field of titanium alloy tube processing. The method includes: filling a titanium alloy tube blank with a solid granular medium; sealing both ends of the tube blank with punches after placing it into a mold cavity; winding an induction coil around the outside of the mold and covering the area to be bulged for induction heating; continuously heating while driving the punches to move in opposite directions to compress the solid granular medium, utilizing the generated radial bulging force to bulge the tube blank into a shape conforming to the mold cavity under the coupling of electric and force fields; stopping heating and punch movement, maintaining pressure and cooling, and then opening the mold to obtain the titanium alloy tube. This invention uses a solid granular medium instead of gas for force transmission, eliminating the need for gas pressurization and strict sealing, resulting in high forming efficiency; targeted heating with induced current enhances the plastic deformation capacity of the tube blank; axial compression feeding effectively reduces wall thickness reduction, resulting in good forming quality; and the solid granules are recyclable, leading to low cost.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy pipe processing, specifically relating to a method for forming titanium alloy pipes by induced current-assisted solid particle medium expansion. Background Technology

[0002] Titanium alloys possess high specific strength and excellent corrosion resistance, making them widely used in aerospace, medical, and other fields. Particularly in aerospace, titanium alloy tubing is a crucial structural component. However, titanium alloys exhibit poor formability at room temperature, making them prone to springback, cracking, or wrinkling during processing, thus complicating the guarantee of forming accuracy.

[0003] To address the aforementioned issues, thermoforming is currently the most common method. This involves heating the mold to a high temperature while simultaneously introducing a protective gas inside the tube blank. The heat from the mold, residual heat, and gas pressure work together to form the tube. However, this process requires a dedicated gas pressurization system and a strict sealing structure. The assembly process before forming is time-consuming, and the overall steps are numerous, resulting in lower processing efficiency.

[0004] In recent years, current-assisted forming technology has been gradually used in the forming of titanium alloy tubes due to its fast heating and flexible control. Among them, induction current-assisted bulging has also made some progress. Chinese patent CN201510191192.3 discloses an incremental thermal difference bulging device for metal tubes and its usage method. By translating the coil to perform induction heating on the tube blank in sections, the tube can achieve incremental thermal difference bulging, which can alleviate the problems of springback, suppress instability and wrinkling to a certain extent. However, this method requires the coil to move to heat in sections, which is relatively complicated in terms of process control, and there is still room for improvement in forming efficiency.

[0005] In addition, in existing induction current assisted forming technology, the molds are generally made of metal, which can easily shield or interfere with the magnetic field under induction heating conditions, affecting the effective absorption of the induction current by the tube blank and restricting the forming efficiency to a certain extent.

[0006] Therefore, there is still a need for a titanium alloy tube forming method that is relatively simple in steps and has a high forming efficiency, in order to better meet the requirements of aerospace and other fields for the processing efficiency and precision of titanium alloy tubes. Summary of the Invention

[0007] The purpose of this invention is to provide a method for forming titanium alloy tubes by induced current-assisted solid particle medium bulging, so as to solve the problems mentioned in the background art.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for forming titanium alloy tubes using induced current-assisted solid particle dielectric bulging includes the following steps: S1 places the titanium alloy tube blank filled with solid particulate medium into the mold cavity and seals it from both ends of the tube blank with a punch; S2 winds an induction coil around the outside of the mold and covers the area of ​​the tube blank to be expanded, and performs induction heating on the area to be expanded; While continuously heating, S3 drives the punch to move towards each other to compress the solid particle medium, and uses radial expansion force to make the tube blank expand under the coupling effect of electric field and force field until it fits the mold cavity. S4 stops heating and punch movement, holds pressure, cools and opens the mold to obtain titanium alloy tubing.

[0009] Furthermore, in the induction heating step described in S2, the maximum surface temperature of the tube blank to be expanded is controlled at 700~800℃.

[0010] Furthermore, the power of the induction heating in S2 is 15~50kW, and the output frequency is 30~80kHz; the material of the mold is 3Y-TZP zirconia or toughened alumina ceramic.

[0011] Furthermore, during the bulging process under the coupling effect described in S3, by adjusting the induction heating parameters, the magnetic induction intensity of the tube blank to be bulged reaches 0.020~0.029T, and the induced current density reaches 18.6~20.6 A / mm². 2 .

[0012] Furthermore, after the expansion is completed as described in S3, the expansion height of the tube blank expansion area increases by 30-40% relative to the original tube diameter, and the average wall thickness of the expansion area is reduced to 40-50% of the original wall thickness.

[0013] Furthermore, in S3, the speed at which the punches are driven to move towards each other is 1~5 mm / s.

[0014] Furthermore, the pressure holding time described in S4 is 3-5 minutes, and the cooling method is air cooling to room temperature.

[0015] Furthermore, the solid particulate medium is an insulating, non-magnetic, and high-temperature resistant spherical particle with a particle size of 0.05~1mm.

[0016] Furthermore, the solid particulate medium is one of hexagonal boron nitride, silicon dioxide, or ceramic particles.

[0017] Furthermore, the titanium alloy tube blank is made of any one of TC4, TA2, TA9, TA18, TA10, TA7, TA15, TC11, TC18 or TB6.

[0018] Compared with the prior art, the beneficial effects of the present invention are: I. This invention uses solid particulate media instead of gas as the expansion force transmission medium. Radial expansion force is generated by compressing the solid particulate media through a punch to complete the expansion of the tube blank. This method eliminates the need for a dedicated gas pressurization system, reduces the requirements for tube end sealing, simplifies the assembly steps of the forming equipment, and shortens the preparation time before forming, thereby improving the overall forming efficiency of titanium alloy tubes.

[0019] II. This invention utilizes induced current to target and heat the area of ​​the tube blank to be expanded, raising the surface of the tube blank to a softening temperature of 700-800°C within 10 seconds. Simultaneously, it employs an insulating, non-magnetic, and high-temperature-resistant solid particle medium, which does not interfere with the magnetic field distribution in the induction heating environment, ensuring efficient heating of the tube blank by the induced current. Under the coupling effect of the electric field and the radial force field of the solid particles, the plastic deformation capacity of the tube blank's expansion area is significantly improved, with the expansion height reaching 30-40% of the original tube diameter. Furthermore, axial compression feeding effectively reduces the wall thickness reduction in the expansion area, balancing forming efficiency and forming quality.

[0020] Third, the solid particulate medium in this invention can be made of materials such as hexagonal boron nitride, silicon dioxide, or ceramics. These are all non-conductive, non-magnetic, and heat-resistant materials that will not affect the magnetic field distribution in the induction heating environment, thus ensuring the heating efficiency of the induced current on the tube blank. The mold is also made of a non-conductive, non-magnetic ceramic material, thus avoiding the shielding problem of the magnetic field caused by metal molds, and improving the utilization efficiency of the induced current. Furthermore, the solid particulate medium can be recycled and reused after use, reducing operating costs. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the tube forming mold of the present invention; Figure 2 This is a schematic diagram of the internal structure of the tube forming mold of the present invention; Figure 3 The dashed box indicates the bulging area of ​​the pipe fitting of the present invention; Figure 4 This is a schematic diagram of the tube forming process of the present invention.

[0022] In the diagram: 1. Left punch; 2. Upper die; 3. Groove; 4. Induction heating power supply; 5. Circuit switch; 6. Right punch; 7. Lower die; 8. Coil; 9. Vent hole; 10. Titanium alloy tube blank; 11. Solid particulate medium. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] In this embodiment of the invention, the hot deformation behavior of the titanium alloy tube blank under induction heating conditions is described by a modified Johnson-Cook constitutive model, the expression of which is:

[0025] In the formula, The initial yield strength at the reference temperature is 847.752 MPa; k is the strength coefficient, 808.394 MPa. is the equivalent plastic strain; n is the hardening exponent, 0.267; C is the strain rate strengthening coefficient, 0.009; This is the equivalent plastic strain rate; For reference strain rate, 0.234 s. -1 T represents the material temperature. The material reference temperature is 25℃. is the melting point of the material, 1662℃; m is the temperature index, 0.78. Among the thermal parameters, the thermal conductivity is set to 7 W / (m·K); among the electromagnetic parameters, the electrical conductivity is set to 5.88 × 10⁻⁶. 5 The relative permeability is set to 1.0005, and the relative permittivity is set to 5. The simulation calculations for the following embodiments and comparative examples are all based on the above constitutive model and parameters.

[0026] Example 1

[0027] S1 takes a titanium alloy tube blank 10 made of TC4 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; the tube blank is placed in the cavity of the upper mold 2 and the lower mold 7, both of which are made of 3Y-TZP zirconia ceramic; the tube blank is filled with hexagonal boron nitride spherical particles with a particle size of 0.5mm as solid particle medium 11. After filling, the tube blank is sealed and clamped from both ends by the left punch 1 and the right punch 6 made of 718 nickel-based high temperature alloy, and the upper mold 2 and the lower mold 7 are closed by inserting the cylinder into the groove 3 of the external equipment.

[0028] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, and the external power supply voltage is 220V. The power of the induction heating power supply 4 is 30kW, the output frequency is 50kHz, and the no-load current is 50A. The circuit switch 5 is closed, and the induction heating power supply 4 is started to induction heat the area of ​​the tube blank 10 to be expanded. The heating time is 9~10s, and the maximum surface temperature of the area of ​​the tube blank 10 to be expanded is controlled at 734℃. During this process, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded increases from 0.020T to 0.029T, and the induced current density increases from 18.6 A / mm². 2 Increased to 20.6 A / mm 2 .

[0029] Four seconds after the start of induction heating S3, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 1 mm / s, compressing the hexagonal boron nitride solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial bulging force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be bulged undergoes bulging under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11. The punch movement time is 18 seconds, and by the 22nd second, the outer wall of the tube blank 10 is in contact with the mold cavity. After bulging, the bulging height of the bulging area of ​​the tube blank 10 is 22 mm, which is 40% higher than the original tube diameter. The average wall thickness of the bulging area is 0.43 mm, which is reduced to 43% of the original wall thickness.

[0030] S4 disconnects circuit switch 5 at 22s, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 5 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool the tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TC4 titanium alloy tube.

[0031] Example 2

[0032] S1 Take a titanium alloy tube blank 10 made of TA2 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; place the tube blank in the cavity of the upper mold 2 and the lower mold 7, both of which are made of toughened alumina ceramic; fill the tube blank with 0.05mm diameter silica spherical particles as solid particle medium 11. After filling, use the left punch 1 and the right punch 6 made of 718 nickel-based high temperature alloy to seal and clamp the tube blank from both ends, and use the cylinder of the external equipment to insert into the groove 3 to close the upper mold 2 and the lower mold 7.

[0033] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, connected to an external power supply with a voltage of 220V, and the induction heating power supply 4 has a power of 15kW, an output frequency of 30kHz, and a no-load current of 35A. The circuit switch 5 is closed to start the induction heating power supply 4, which induction heats the area of ​​the tube blank 10 to be expanded, controlling the maximum surface temperature of the area of ​​the tube blank 10 to be expanded at 700℃. During this process, by adjusting the induction heating parameters, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded reaches 0.020T, and the induced current density reaches 18.6 A / mm². 2 .

[0034] After S3 induction heating begins, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 1 mm / s, compressing the silica solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial expansion force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be expanded undergoes expansion under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11, until the outer wall of the tube blank 10 fits against the mold cavity. After expansion is completed, the expansion height of the expansion area of ​​the tube blank 10 increases by 30% relative to the original tube diameter, and the average wall thickness of the expansion area is reduced to 50% of the original wall thickness.

[0035] S4 disconnects circuit switch 5, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 3 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool the tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TA2 titanium alloy tube.

[0036] Example 3

[0037] S1 Take a titanium alloy tube blank 10 made of TA9 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; Place the tube blank in the cavity of the upper mold 2 and the lower mold 7, both of which are made of 3Y-TZP zirconia ceramic; Fill the tube blank with ceramic spherical particles with a particle size of 1mm as a solid particle medium 11. After filling, use the left punch 1 and the right punch 6 made of 718 nickel-based high-temperature alloy to seal and clamp the tube blank from both ends, and use the cylinder of the external equipment to insert into the groove 3 to close the upper mold 2 and the lower mold 7.

[0038] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, connected to an external power supply with a voltage of 220V, and the induction heating power supply 4 has a power of 50kW, an output frequency of 80kHz, and a no-load current of 200A. The circuit switch 5 is closed to start the induction heating power supply 4, which induction heats the area of ​​the tube blank 10 to be expanded, controlling the maximum surface temperature of the area of ​​the tube blank 10 to be expanded at 800℃. During this process, by adjusting the induction heating parameters, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded reaches 0.029T, and the induced current density reaches 20.6 A / mm². 2 .

[0039] After S3 induction heating begins, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 5 mm / s, compressing the ceramic solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial expansion force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be expanded undergoes expansion under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11, until the outer wall of the tube blank 10 fits against the mold cavity. After expansion is completed, the expansion height of the expansion area of ​​the tube blank 10 increases by 40% relative to the original tube diameter, and the average wall thickness of the expansion area is reduced to 43% of the original wall thickness.

[0040] S4 disconnects circuit switch 5, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 5 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool the tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TA9 titanium alloy tube.

[0041] Example 4

[0042] S1 Take a titanium alloy tube blank 10 made of TA18 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; place the tube blank in the cavity of the upper mold 2 and the lower mold 7, both of which are made of toughened alumina ceramic; fill the tube blank with hexagonal boron nitride spherical particles with a particle size of 0.05mm as solid particle medium 11. After filling, use the left punch 1 and the right punch 6 made of 718 nickel-based high temperature alloy to seal and clamp the tube blank from both ends, and use the cylinder of the external equipment to insert into the groove 3 to close the upper mold 2 and the lower mold 7.

[0043] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, connected to an external power supply with a voltage of 220V, and the induction heating power supply 4 has a power of 15kW, an output frequency of 30kHz, and a no-load current of 35A. The circuit switch 5 is closed to start the induction heating power supply 4, which induction heats the area of ​​the tube blank 10 to be expanded, controlling the maximum surface temperature of the area of ​​the tube blank 10 to be expanded at 700℃. During this process, by adjusting the induction heating parameters, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded reaches 0.020T, and the induced current density reaches 18.6 A / mm². 2 .

[0044] After S3 induction heating begins, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 1 mm / s, compressing the hexagonal boron nitride solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial bulging force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be bulged bulges under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11 until the outer wall of the tube blank 10 fits against the mold cavity. After bulging is completed, the bulging height of the bulging area of ​​the tube blank 10 increases by 30% relative to the original tube diameter, and the average wall thickness of the bulging area is reduced to 50% of the original wall thickness.

[0045] S4 disconnects circuit switch 5, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 3 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool the tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TA18 titanium alloy tube.

[0046] Example 5

[0047] S1 Take a titanium alloy tube blank 10 made of TA10 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; Place the tube blank in the cavity of the upper mold 2 and the lower mold 7, both of which are made of 3Y-TZP zirconia ceramic; Fill the tube blank with 1mm diameter silica spherical particles as solid particle medium 11. After filling, use the left punch 1 and the right punch 6 made of 718 nickel-based high temperature alloy to seal and clamp the tube blank from both ends, and use the cylinder of the external equipment to insert into the groove 3 to close the upper mold 2 and the lower mold 7.

[0048] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, connected to an external power supply with a voltage of 220V, and the induction heating power supply 4 has a power of 50kW, an output frequency of 80kHz, and a no-load current of 200A. The circuit switch 5 is closed to start the induction heating power supply 4, which induction heats the area of ​​the tube blank 10 to be expanded, controlling the maximum surface temperature of the area of ​​the tube blank 10 to be expanded at 800℃. During this process, by adjusting the induction heating parameters, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded reaches 0.029T, and the induced current density reaches 20.6 A / mm². 2 .

[0049] After S3 induction heating begins, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 5 mm / s, compressing the silica solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial expansion force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be expanded undergoes expansion under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11, until the outer wall of the tube blank 10 fits against the mold cavity. After expansion is completed, the expansion height of the expansion area of ​​the tube blank 10 increases by 40% relative to the original tube diameter, and the average wall thickness of the expansion area is reduced to 43% of the original wall thickness.

[0050] S4 disconnects circuit switch 5, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 5 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TA10 titanium alloy tube.

[0051] Example 6

[0052] S1 Take a titanium alloy tube blank 10 made of TA7 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; Place the tube blank in the cavity of the upper mold 2 and the lower mold 7, both of which are made of toughened alumina ceramic; Fill the tube blank with ceramic spherical particles with a particle size of 0.5mm as solid particle medium 11. After filling, use the left punch 1 and the right punch 6 made of 718 nickel-based high temperature alloy to seal and clamp the tube blank from both ends, and use the cylinder of the external equipment to insert into the groove 3 to close the upper mold 2 and the lower mold 7.

[0053] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, connected to an external power supply with a voltage of 220V, and the induction heating power supply 4 has a power of 30kW, an output frequency of 50kHz, and a no-load current of 50A. The circuit switch 5 is closed to start the induction heating power supply 4, which induction heats the area of ​​the tube blank 10 to be expanded, controlling the maximum surface temperature of the area of ​​the tube blank 10 to be expanded at 750℃. During this process, by adjusting the induction heating parameters, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded reaches 0.025T, and the induced current density reaches 19.5 A / mm². 2 .

[0054] After S3 induction heating begins, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 3 mm / s, compressing the ceramic solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial expansion force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be expanded undergoes expansion under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11, until the outer wall of the tube blank 10 fits against the mold cavity. After expansion is completed, the expansion height of the expansion area of ​​the tube blank 10 increases by 40% relative to the original tube diameter, and the average wall thickness of the expansion area is reduced to 45% of the original wall thickness.

[0055] S4 disconnects circuit switch 5, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 4 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool the tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TA7 titanium alloy tube.

[0056] Example 7

[0057] S1 Take a titanium alloy tube blank 10 made of TA15 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; Place the tube blank in the cavity of the upper mold 2 and the lower mold 7, both of which are made of 3Y-TZP zirconia ceramic; Fill the tube blank with hexagonal boron nitride spherical particles with a particle size of 0.05mm as a solid particle medium 11. After filling, use the left punch 1 and the right punch 6 made of 718 nickel-based high-temperature alloy to seal and clamp the tube blank from both ends, and use the cylinder of the external equipment to insert into the groove 3 to close the upper mold 2 and the lower mold 7.

[0058] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, connected to an external power supply with a voltage of 220V, and the induction heating power supply 4 has a power of 50kW, an output frequency of 80kHz, and a no-load current of 200A. The circuit switch 5 is closed to start the induction heating power supply 4, which induction heats the area of ​​the tube blank 10 to be expanded, controlling the maximum surface temperature of the area of ​​the tube blank 10 to be expanded at 800℃. During this process, by adjusting the induction heating parameters, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded reaches 0.029T, and the induced current density reaches 20.6 A / mm². 2 .

[0059] After S3 induction heating begins, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 1 mm / s, compressing the hexagonal boron nitride solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial bulging force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be bulged bulges under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11 until the outer wall of the tube blank 10 fits against the mold cavity. After bulging is completed, the bulging height of the bulging area of ​​the tube blank 10 increases by 40% relative to the original tube diameter, and the average wall thickness of the bulging area is reduced to 43% of the original wall thickness.

[0060] S4 disconnects circuit switch 5, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 5 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool the tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TA15 titanium alloy tube.

[0061] Example 8

[0062] S1 takes a titanium alloy tube blank 10 made of TC11 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; the tube blank is placed in the cavity of the upper mold 2 and the lower mold 7, both of which are made of toughened alumina ceramic; 1mm diameter silica spherical particles are filled into the tube blank as solid particle medium 11. After filling, the left punch 1 and the right punch 6 made of 718 nickel-based high temperature alloy are used to seal and clamp the tube blank from both ends, and the upper mold 2 and the lower mold 7 are closed by inserting the cylinder into the groove 3 of the external equipment.

[0063] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, connected to an external power supply with a voltage of 220V, and the induction heating power supply 4 has a power of 15kW, an output frequency of 30kHz, and a no-load current of 35A. The circuit switch 5 is closed to start the induction heating power supply 4, which induction heats the area of ​​the tube blank 10 to be expanded, controlling the maximum surface temperature of the area of ​​the tube blank 10 to be expanded at 700℃. During this process, by adjusting the induction heating parameters, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded reaches 0.020T, and the induced current density reaches 18.6 A / mm². 2 .

[0064] After S3 induction heating begins, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 5 mm / s, compressing the silica solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial expansion force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be expanded undergoes expansion under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11, until the outer wall of the tube blank 10 fits against the mold cavity. After expansion is completed, the expansion height of the expansion area of ​​the tube blank 10 increases by 30% relative to the original tube diameter, and the average wall thickness of the expansion area is reduced to 50% of the original wall thickness.

[0065] S4 disconnects circuit switch 5, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 3 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool the tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TC11 titanium alloy tube.

[0066] Example 9

[0067] S1 Take a titanium alloy tube blank 10 made of TC18 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; Place the tube blank in the cavity of the upper mold 2 and the lower mold 7, both of which are made of 3Y-TZP zirconia ceramic; Fill the tube blank with ceramic spherical particles with a particle size of 0.05mm as a solid particle medium 11. After filling, use the left punch 1 and the right punch 6 made of 718 nickel-based high-temperature alloy to seal and clamp the tube blank from both ends, and use the cylinder of the external equipment to insert into the groove 3 to close the upper mold 2 and the lower mold 7.

[0068] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, connected to an external power supply with a voltage of 220V, and the induction heating power supply 4 has a power of 50kW, an output frequency of 80kHz, and a no-load current of 200A. The circuit switch 5 is closed to start the induction heating power supply 4, which induction heats the area of ​​the tube blank 10 to be expanded, controlling the maximum surface temperature of the area of ​​the tube blank 10 to be expanded at 800℃. During this process, by adjusting the induction heating parameters, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded reaches 0.029T, and the induced current density reaches 20.6 A / mm². 2 .

[0069] After S3 induction heating begins, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 1 mm / s, compressing the ceramic solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial expansion force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be expanded undergoes expansion under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11, until the outer wall of the tube blank 10 fits against the mold cavity. After expansion is completed, the expansion height of the expansion area of ​​the tube blank 10 increases by 40% relative to the original tube diameter, and the average wall thickness of the expansion area is reduced to 43% of the original wall thickness.

[0070] S4 disconnects circuit switch 5, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 5 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool the tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TC18 titanium alloy tube.

[0071] Example 10

[0072] S1 takes a titanium alloy tube blank 10 made of TB6 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; the tube blank is placed in the cavity of the upper mold 2 and the lower mold 7, both of which are made of toughened alumina ceramic; the tube blank is filled with hexagonal boron nitride spherical particles with a particle size of 1mm as solid particle medium 11. After filling, the left punch 1 and the right punch 6 made of 718 nickel-based high temperature alloy are used to seal and clamp the tube blank from both ends, and the upper mold 2 and the lower mold 7 are closed by inserting the cylinder into the groove 3 of the external equipment.

[0073] S2 winds the induction coil 8 around the outside of the upper mold 2 and the lower mold 7, so that the coil covers the area of ​​the tube blank 10 to be expanded. The induction coil 8 is made of copper, connected to an external power supply with a voltage of 220V, and the induction heating power supply 4 has a power of 15kW, an output frequency of 30kHz, and a no-load current of 35A. The circuit switch 5 is closed to start the induction heating power supply 4, which induction heats the area of ​​the tube blank 10 to be expanded, controlling the maximum surface temperature of the area of ​​the tube blank 10 to be expanded at 700℃. During this process, by adjusting the induction heating parameters, the magnetic induction intensity of the area of ​​the tube blank 10 to be expanded reaches 0.020T, and the induced current density reaches 18.6 A / mm². 2 .

[0074] After S3 induction heating begins, the axial feeding mechanism is activated, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 5 mm / s, compressing the hexagonal boron nitride solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial bulging force acting on the inner wall of the tube blank 10. While induction heating continues, the area of ​​the tube blank 10 to be bulged bulges under the coupling effect of the electric field generated by the induced current and the radial force field generated by the solid particle medium 11 until the outer wall of the tube blank 10 fits against the mold cavity. After bulging is completed, the bulging height of the bulging area of ​​the tube blank 10 increases by 30% relative to the original tube diameter, and the average wall thickness of the bulging area is reduced to 50% of the original wall thickness.

[0075] S4 disconnects circuit switch 5, stops induction heating and punch movement, keeps left punch 1 and right punch 6 in the same position for pressure holding for 3 minutes; after pressure holding, unload left punch 1 and right punch 6, reset the punch, remove induction coil 8, air cool tube blank 10, and after cooling to room temperature, open upper mold 2 and lower mold 7, take out the expanded tube, and obtain TB6 titanium alloy tube.

[0076] Comparative Example The comparative example does not use induced current assistance.

[0077] S1 takes a titanium alloy tube blank 10 made of TC4 material, with a length of 400mm, an outer diameter of 55mm, and a wall thickness of 1mm; the tube blank is placed in the cavity of the upper mold 2 and the lower mold 7, both of which are made of 3Y-TZP zirconia ceramic; the tube blank is filled with hexagonal boron nitride spherical particles with a particle size of 0.5mm as solid particle medium 11. After filling, the tube blank is sealed and clamped from both ends by the left punch 1 and the right punch 6 made of 718 nickel-based high temperature alloy, and the upper mold 2 and the lower mold 7 are closed by inserting the cylinder into the groove 3 of the external equipment.

[0078] S2 does not have an induction coil 8 and an induction heating power supply 4, and does not perform induction heating on the tube blank 10.

[0079] S3 starts the axial feeding mechanism, driving the left punch 1 and the right punch 6 to move towards each other at a speed of 1 mm / s, compressing the hexagonal boron nitride solid particle medium 11 inside the tube blank. The solid particle medium 11 converts the axial force applied by the punch into a radial bulging force acting on the inner wall of the tube blank 10. Under room temperature conditions, the area to be bulged in the tube blank 10 only bulges under the action of the radial force field generated by the solid particle medium 11, and the punch movement time is 18 s. After bulging, the bulging height of the bulging area of ​​the tube blank 10 is 10.2 mm, the average wall thickness of the bulging area is 0.67 mm, the maximum plastic strain of the bulging area is 0.39, the stress in the bulging area of ​​the tube blank 10 during the bulging process is about 1080 MPa, and the outer wall of the tube blank 10 does not fit the mold cavity.

[0080] S4 stops the punch movement, keeps the left punch 1 and right punch 6 in the same position for pressure holding for 5 minutes; after pressure holding is completed, unload the left punch 1 and right punch 6, reset the punch, open the upper die 2 and lower die 7, take out the expanded tube, and obtain the TC4 titanium alloy tube.

[0081] Examples 1-10 and the comparative examples were compared and tested. The specific test methods are as follows: I. Bulging Height Testing instrument: Digital vernier caliper, accuracy 0.02mm.

[0082] Test Method: After bulging, remove the fitting from the mold and allow it to cool naturally to room temperature. Use the outer diameter of the unbulged areas at both ends of the fitting as the original pipe diameter reference. Measure and record this reference outer diameter using vernier calipers. Then, clamp the outer diameter at the highest point of the bulging area with vernier calipers and read the value. Repeat the measurement three times and take the arithmetic mean. The bulging height is calculated using the following formula:

[0083] II. Maximum Plastic Strain Testing instruments: Tool microscope (magnification 20×~50×) or image measuring instrument, electrochemical etching device or laser marking machine.

[0084] Test method: After the tube blank is processed and before bulging, the outer surface of the area to be bulged is pretreated: a circular grid array is made on the outer surface of the area to be bulged on the tube blank using electrochemical etching or laser marking. The grid diameter is 2 mm, the center-to-center spacing of adjacent grids is 5 mm, and they are evenly arranged along the axial and circumferential directions of the tube blank.

[0085] After bulging, cool the tube to room temperature. Observe the deformed grid shape under a tool microscope or image measuring instrument, and measure the major and minor axis lengths of each grid after deformation. For each grid, the plastic strain is calculated using the following formula:

[0086] In the formula, a is the length of the major axis after mesh deformation, b is the length of the minor axis after mesh deformation, and d is the original mesh diameter of 2mm.

[0087] Traverse all meshes in the bulging region and take the calculated maximum value as the maximum plastic strain.

[0088] III. Stress in the bulging region Testing instrument: X-ray stress analyzer.

[0089] Test method: After bulging, allow the fitting to cool to room temperature. Use an X-ray stress analyzer, with sin... 2 The ψ method is used to measure residual stress on the outer surface of the bulging region of the tube blank. A Cr or Cu target is selected as the X-ray source, and a suitable diffraction plane is chosen, with ψ angles set to 0°, 15°, 30°, and 45°. The position of the diffraction peak is measured at each ψ angle, and the lattice strain is calculated from the diffraction peak displacement, then converted into stress values ​​based on the elastic constants.

[0090] Three measurement sections are uniformly selected along the axial direction of the bulging region, and four measurement points are uniformly selected along the circumference of each section, for a total of 12 measurement points. The interval between the minimum and maximum stress values ​​of all measurement points is taken as the stress of the bulging region.

[0091] If real-time stress during the bulging process is required, it cannot be obtained through manual measurement afterward and must be extracted using Comsol simulation.

[0092] IV. Average Wall Thickness and Wall Thinning Testing instruments: Ultrasonic thickness gauge, accuracy 0.01mm; digital micrometer for sampling verification.

[0093] Test Method: After bulging, the fitting was cooled to room temperature. Five measurement sections were evenly selected axially on the surface of the bulging area of ​​the tube blank. Four measurement points were evenly selected circumferentially on each section (located at 0°, 90°, 180°, and 270°). The wall thickness was measured point by point using an ultrasonic thickness gauge with glycerol as the coupling agent. A total of 20 measurement points were recorded, and the wall thickness value at each measurement point was recorded.

[0094] The average wall thickness is the arithmetic mean of the wall thickness values ​​at the above 20 measurement points.

[0095] Wall thickness reduction is based on the measured average wall thickness and is calculated using the following formula:

[0096] In the formula, t0 is the original wall thickness of the tube blank (1 mm), and t is the measured average wall thickness after bulging.

[0097] During sampling verification, the pipe fitting is cut along the axial direction, and the wall thickness is measured at the corresponding measurement point using a digital micrometer. The result is then compared with the ultrasonic measurement result to confirm the measurement accuracy.

[0098] V. Molding application status Testing instruments: feeler gauges (0.02mm, 0.05mm, 0.10mm, etc.), visual inspection supplemented by touch.

[0099] Test Method: After bulging is completed, the mold is opened and the pipe fitting is removed. First, visually inspect the outer surface of the bulging area of ​​the pipe blank to observe whether there are any recessed areas that do not fit the mold cavity or any parts that are inconsistent with the shape of the mold cavity. Then, put the pipe fitting back into the mold cavity, select at least 3 axial cross-sectional positions in the bulging area, and insert a feeler gauge along the gap between the outer wall of the pipe blank and the inner wall of the mold cavity at each position. The minimum thickness of the feeler gauge is 0.02 mm.

[0100] Judgment criteria: If the gap between the outer wall of the tube blank and the inner wall of the mold cavity is less than 0.05mm, that is, a 0.05mm feeler gauge cannot be inserted, and the shape of the outer wall of the tube blank is consistent with the shape of the mold cavity, then it is judged as being molded; otherwise, it is judged as not being molded.

[0101] The test data is shown in the table below:

[0102] Analysis of the table data yields the following: The test results from Example 1 show that after using induced current-assisted heating, the surface temperature of the tube blank reached 734°C, the bulging height was 22 mm, and the outer wall of the tube blank adhered to the mold cavity. In the comparative example, under the same solid particulate medium and punch loading conditions as Example 1, but without induced current assistance, the tube blank's bulging height at room temperature was only 10.2 mm, the maximum plastic strain was 0.39, the stress in the bulging region was approximately 1080 MPa, and the tube blank failed to adhere to the mold cavity. These comparisons indicate that without induced current assistance, the titanium alloy exhibits high flow stress and insufficient plastic deformation capacity at room temperature, making it difficult to achieve mold-fitting forming solely through the radial bulging force transmitted by the solid particulate medium.

[0103] Examples 2 to 10 used nine titanium alloys: TA2, TA9, TA18, TA10, TA7, TA15, TC11, TC18, and TB6. Three solid particulate media were also tested: hexagonal boron nitride, silicon dioxide, and ceramic. Heating temperatures ranged from 700 to 800°C, punch speeds from 1 to 5 mm / s, and holding times from 3 to 5 minutes. Under these conditions, die-fitting bulging was achieved, with bulging heights reaching 30% to 40% of the original pipe diameter and average wall thickness reductions between 40% and 50%. These results demonstrate that the inductively current-assisted solid particulate media bulging method of this invention can be used with different grades of titanium alloys, exhibiting good process adaptability.

[0104] Based on the above comparisons and analyses, this invention effectively solves the problem of insufficient room-temperature formability of titanium alloys by coupling induced current-assisted heating with solid particle medium bulging. Data from the examples and comparative cases show that induced current-assisted heating can significantly reduce the flow stress of titanium alloys and improve their plastic deformation capacity, which is a necessary condition for achieving solid particle medium bulging. Furthermore, this method is applicable to various titanium alloy materials and has significant advantages in aerospace and other fields where high efficiency and quality in forming titanium alloy tubing are required.

[0105] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for forming titanium alloy tubes by induced current-assisted solid particle dielectric bulging, characterized in that, Includes the following steps: S1 places the titanium alloy tube blank filled with solid particulate medium into the mold cavity and seals it from both ends of the tube blank with a punch; S2 winds an induction coil around the outside of the mold and covers the area of ​​the tube blank to be expanded, and performs induction heating on the area to be expanded; While continuously heating, S3 drives the punch to move towards each other to compress the solid particle medium, and uses radial expansion force to make the tube blank expand under the coupling effect of electric field and force field until it fits the mold cavity. S4 stops heating and punch movement, holds pressure, cools and opens the mold to obtain titanium alloy tubing.

2. The method according to claim 1, characterized in that: During the bulging process under the coupling effect described in S3, the magnetic induction intensity in the bulging area of ​​the billet is adjusted to reach 0.020~0.029T, and the induced current density is adjusted to reach 18.6~20.6 A / mm². 2 .

3. The method according to claim 1, characterized in that: In the induction heating step described in S2, the surface temperature of the tube blank to be expanded is controlled at 700~800℃.

4. The method according to claim 1, characterized in that: The solid particulate medium consists of insulating, non-magnetic, and high-temperature resistant spherical particles with a particle size of 0.05~1mm.

5. The method according to claim 4, characterized in that: The solid particulate medium is one of hexagonal boron nitride, silicon dioxide, or ceramic particles.

6. The method according to claim 1, characterized in that: After the expansion is completed as described in S3, the expansion height of the tube blank expansion area increases by 30-40% relative to the original tube diameter, and the average wall thickness of the expansion area is reduced to 40-50% of the original wall thickness.

7. The method according to claim 1, characterized in that: The speed at which the punches move towards each other in S3 is 1~5 mm / s.

8. The method according to claim 1, characterized in that: The pressure holding time described in S4 is 3~5 minutes, and the cooling method is air cooling to room temperature.

9. The method according to claim 1, characterized in that: The power supply for induction heating in S2 is 15~50kW, and the output frequency is 30~80kHz; the material of the mold is 3Y-TZP zirconia or toughened alumina ceramic.

10. The method according to any one of claims 1 to 9, characterized in that, The titanium alloy tube blank is made of any one of TC4, TA2, TA9, TA18, TA10, TA7, TA15, TC11, TC18 or TB6.

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