A bending method and device for a titanium alloy tube with a rectangular cross-section

Abstract

The present invention provides a method and device for bending a titanium alloy tube with a rectangular cross-section, belonging to the technical field of tube bending. It solves the problems that when a tube with a non-circular cross-sectional shape is bent, bursting may occur in the outer section of the bending radius or the wall thickness tolerance cannot meet the requirements. The method for bending the titanium alloy tube with a rectangular cross-section comprises the following steps: Step a, bending the original tube blank with a circular cross-section into an intermediate tube blank at a required angle; Step b, performing pre-static deformation on the intermediate tube blank in a pre-static deformation die to obtain a pre-static deformation tube blank with a specified rectangular cross-section; Step c, finally forming the pre-static deformation tube blank with a specified rectangular cross-section by electro-hydraulic pulse in an electro-hydraulic forming device. It can reduce the wall thickness reduction value of the dangerous cross-section of the titanium alloy tube with a rectangular cross-section; store sufficient plasticity without intermediate annealing and directly enter the next two electro-hydraulic forming processes; the fillets of the finished pipe fittings are filled plumply and the wall thickness is relatively uniform.

Description

Technical Field

[0001] The present invention belongs to the field of mechanical manufacturing technologies and processes, and relates to a method and device for bending a titanium alloy tube with a rectangular cross-section. Background Art

[0002] In recent years, with the rapid development of the aerospace field and the demands for lightweight, high strength and toughness, and high functional efficiency applications, such as thin-walled and acutely bent tubes used in fighter planes and the refrigeration industry, and acutely bent waveguides used in the radio industry, especially titanium tubes used in the military industry, which have high forming resistance, poor plasticity, and are prone to diameter shrinkage and wrinkling. Currently, only small-diameter titanium tubes with large bending radii can be produced. Therefore, for the production of thin-walled, large-diameter and small-bending-radius bent pipe fittings, especially when the cross-sectional shape of the pipe fitting is a non-circular cross-section, bursting will occur at the outer section of the bending radius or the wall thickness tolerance cannot meet the requirements, and there is an urgent need to solve the technical problems.

[0003] According to the current methods and processes for manufacturing thin-walled tubes with complex shapes, they can be divided into two types: The first method is to weld according to the planar axial cross-section, but grinding the weld seams and detecting their airtightness, the heavy workload of the complex welding process makes the manufacturing cost unbearable; The second method is to integrally manufacture parts by using the tube bending method, and the cross-sectional shape is the shape required for the pipe fitting. This method has relatively simple technology and is more convenient to operate. Summary of the Invention

[0004] The purpose of the present invention is to address the above problems existing in the current technology, and propose a method and device for bending a titanium alloy tube with a rectangular cross-section.

[0005] The purpose of the present invention can be achieved by the following technical solutions: A method for bending a titanium alloy tube with a rectangular cross-section, characterized by comprising the following steps:

[0006] Step a: Bend the original tube blank with a circular cross-section into an intermediate tube blank at a required angle.

[0007] Step b: Perform pre-static deformation on the intermediate tube blank in a pre-static deformation die to obtain a pre-static deformation tube blank with a specified rectangular cross-section.

[0008] Step c: Finally form the pre-static deformation tube blank with a specified rectangular cross-section in an electro-hydraulic forming device by using electro-hydraulic pulses.

[0009] In the above method for bending a titanium alloy tube with a rectangular cross-section, in step a, a rolling bending method with a gap Z is adopted. First, fill the original tube blank with dry rosin filler, rigidly fix one end of the original tube blank, and then the rolling roller located above the original tube blank and having a distance Z from the original tube blank gradually descends in an arc after passing through the straight section of the original tube blank. After the rolling roller contacts the original tube blank, apply a bending force until an intermediate tube blank at a required angle is obtained.

[0010] In the above-mentioned bending method of the titanium alloy tube with a rectangular cross-section, in step a, the original tube blank is first filled with dry rosin filler, and one end of the tube blank is rigidly fixed. There is a raceway groove between the rolling roller and the original tube blank. The thickness of the raceway is Z, and the fitting radian of the raceway groove with the outer diameter of the original tube blank is 30°. After passing through the straight section of the original tube blank, the rolling roller gradually descends in an arc to the intermediate tube blank at the required angle.

[0011] In the above-mentioned bending method of the titanium alloy tube with a rectangular cross-section, the tube length L in step a m and the bending radius R of the tube blank 中 satisfy the relationship: L m = πR 中 / 2 + 2 = 116.35 mm, Δ is the length of the straight sections of the tube blank at both ends of the tube blank, and R 中 is the radius of the bending neutral axis.

[0012] In the above-mentioned bending method of the titanium alloy tube with a rectangular cross-section, when the outer diameter R of the tube 外 satisfies 15 mm ≤ R 外 ≤ 50 mm, Z / R 中 = 9% - 10%.

[0013] In the above-mentioned bending method of the titanium alloy tube with a rectangular cross-section, in step c, a two-step forming method is adopted, and deformation is achieved through two discharges. The first discharge is carried out in the electrohydraulic forming device with voltage V1 and discharge energy E1, and the second discharge is carried out in the electrohydraulic forming device with voltage V2 and discharge energy E2. V2 > V1 and E2 > E1.

[0014] In the above-mentioned bending method of the titanium alloy tube with a rectangular cross-section, it includes an electrohydraulic forming upper die, an electrohydraulic forming lower die, and an electrode system. The electrode system includes two groups of electrode assemblies. The electrode assembly includes an electrode, an electrode joint, insulator one, and insulator two. Insulator one and insulator two are wrapped around the electrode. The electrode includes a straight section and an arc section. Insulator two is wrapped around the connection part of the electrode and the electrode joint, and insulator one is wrapped around the electrode. The end of the electrode is exposed from insulator one. Electrohydraulic forming is a manufacturing technology that instantaneously releases the electrical energy stored in a storage capacitor between electrodes, obtains a strong shock wave load through the plasma explosion process in the liquid, and the liquid medium transmits the shock wave and causes plastic deformation of the workpiece.

[0015] In the above-mentioned bending method of the titanium alloy tube with a rectangular cross-section, both the electrohydraulic forming upper die and the electrohydraulic forming lower die have a tube bending die cavity, and the electrohydraulic forming upper die and the electrohydraulic forming lower die are positioned and guided by dowel pins. When electrohydraulic pulse forming is carried out, the press compresses the electrohydraulic forming upper die and the electrohydraulic forming lower die.

[0016] In the above-mentioned method for bending a titanium alloy tube with a rectangular cross-section, the electrode system further includes a stainless steel tube. The electrode joint is located inside the stainless steel tube, the electrode penetrates through the stainless steel tube, and the second insulator has a groove communicating with the cavity of the bending die cavity.

[0017] In the above-mentioned method for bending a titanium alloy tube with a rectangular cross-section, a filler is provided between the cavity of the bending die and the electrode system.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The method for bending a titanium alloy tube with a rectangular cross-section according to the present invention can reduce the wall thickness value by 10-11% less in the dangerous cross-section of the bent rectangular cross-section titanium alloy tube compared with the current method, that is, reduce the defects such as bursting or wall thickness tolerance not meeting the requirements in the outer section of the bending radius of the pipe fittings with a non-circular cross-section, and improve the yield rate and bending accuracy;

[0020] The method for bending a titanium alloy tube with a rectangular cross-section according to the present invention can store sufficient plasticity during the pre-bending of the titanium alloy tube with a circular cross-section without intermediate annealing and directly enter the next two electro-hydraulic forming processes;

[0021] The method for bending a titanium alloy tube with a rectangular cross-section according to the present invention adopts a two-step forming method, which can greatly reduce springback and make the fillet at the pipe corner filled plumply, and the wall thickness is also relatively uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the rolling bending method with a gap Z according to the present invention.

[0023] Figure 2 is a schematic diagram of the bending method using a groove according to the present invention.

[0024] Figure 3 is a comparative schematic diagram of the pre-deformation distribution of the longitudinal section thickness after the pipe is bent according to the present invention.

[0025] Figure 4 is Figure 3 the schematic diagram of the cross-sectional shapes of 1-1, 5-5, 2-2, 4-4, 3-3 in

[0026] Figure 5 is a schematic diagram of the original state of the pre-static deformation of the pipe according to the present invention.

[0027] Figure 6 is a schematic diagram of the final state of the pre-static deformation of the pipe according to the present invention.

[0028] Figure 7 is the schematic diagram of the electro-hydraulic pulse device in the present invention Figure 1 .

[0029] Figure 8Schematic diagram of the electro-hydraulic pulse device in the present invention Figure 2 。

[0030] Figure 9 Schematic diagram of the fillet radius of the inner and outer bending radii R of the cross-section along the tube during bending in the present invention

[0031] Figure 10 is Figure 9 the radius table of the fillet radius in

[0032] In the figure, 1. Fixed roller; 2. Rolling roller; 3. Raceway groove; 4. Original tube blank; 5. Intermediate tube blank; 6. Upper half die of electro-hydraulic forming for pre-deformation die; 7. Upper half die of electro-hydraulic forming for pre-deformation die; 8. Tube blank after pre-deformation; 9. Electrode; 10. Filler; 11. Insulator I; 12. Insulator II; 13. Groove; 14. Working liquid; 15. Stud; 16. Upper half die of electro-hydraulic forming; 17. Lower half die of electro-hydraulic forming; 18. Electrode joint; 19. Stainless steel shell. Specific implementation method

[0033] The following are specific embodiments of the present invention and in combination with the accompanying drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

[0034] Refer to Figures 1 - 10 , the original tube blank 4 used in this embodiment is a standard titanium alloy TA18 tube with an outer diameter D = 28.57 mm and a wall thickness S0 = 0.87 mm, meeting GJB3423-1998. In the annealed state, ≥620 MPa, δ 50 ≥15. The tube length L m = πR 中 / 2 + 2Δ = 116.35 mm, where Δ = 15 mm - the straight section length at both ends of the original tube blank 4, using L m = 117 mm.

[0035] During the bending in this embodiment, it consists of the following steps:

[0036] Step a: Bend the original tube blank with a standard thin wall of circular cross-section to an intermediate tube blank at the required angle;

[0037] Step b: Install the die on the HCF5MN workbench of the hydraulic press, start the press, and perform pre-static deformation on the intermediate tube blank to reach the size of the pre-static deformation tube blank with a specified rectangular cross-section;

[0038] Step c: Finally form the pre-static deformation tube blank with a specified rectangular cross-section in the electro-hydraulic forming device by electro-hydraulic pulse.

[0039] Among them, for step a, the following two bending methods can be adopted.

[0040] The first method is as Figure 1 shown. First, fill the original tube blank 4 with dry rosin filler, rigidly fix one end of the original tube blank 4, and then gradually lower the rolling roller 2 located above the original tube blank 4 and spaced from the original tube blank 4 by Z = 5 mm in an arc shape after passing through the straight section (AB section) of the original tube blank 4. That is, after passing through point B, the rolling roller 2 gradually descends. When it reaches point C and the angle between OC and OB is about 20º, the rolling roller 2 contacts the original tube blank 4 to apply a bending force until the intermediate tube blank 5 with the required angle is obtained after reaching the end point E.

[0041] The second method is as Figure 2 shown. First, fill the original tube blank 4 with dry rosin filler, rigidly fix one end of the original tube blank 4, and install a raceway groove 3 between the rolling roller 2 at the starting position and the original tube blank 4. The arc of the raceway groove 3 fitting the outer diameter of the original tube blank 4 is 30 º

[0042] Then, gradually lower the rolling roller 2 located above the original tube blank 4 and spaced from the original tube blank 4 by Z = 5 mm in an arc shape after passing through the straight section (AB section) of the original tube blank 4. That is, after passing through point B, the rolling roller 2 gradually descends. When it reaches point C and the angle between OC and OB is about 20º, the rolling roller 2 contacts the original tube blank 4 to apply a bending force until the intermediate tube blank 5 with the required angle is obtained after reaching the end point E.

[0043] In the above two bending methods, the tube length L m and the bending radius R of the tube blank 中 satisfy the relationship: L m = πR 中 / 2 + 2Δ = 116.35 mm, where Δ is the length of the straight section of the tube blank at the end of the tube blank, and R 中 is the radius of the bending neutral axis. When the outer diameter R of the tube 外 satisfies 15 mm ≤ R 外 ≤ 50 mm, Z / R 中 = 9% - 10%. The calculation of the tube blank deformation degree ε s is: ε s = ln S / S0, where S0 is the thickness of the original tube blank and S is the thickness of the intermediate tube blank. For specific values, refer to Figure 3 , Figure 3 The pre-deformation degree ε s without clearance is -0.28, while the pre-deformation with clearance ε s = –0.25, which can confirm that using the rolling gap bending method and the groove bending method of this embodiment reduces the wall thickness value by 10-11% at the dangerous section; at the same time, sufficient plasticity is stored without annealing and directly enters the next two processes.

[0044] In step b, a mold is installed on the table of the hydraulic press HCF5MN. In the electrohydraulic forming upper half die 6 and the electrohydraulic forming lower half die 7 of the pre-deformation die, the intermediate tube blank is statically deformed to achieve a shape close to the specified cross-section of the finished pipe fitting (see Figure 6 the annotation 8 in the figure). The straight-line length Δ = 15 mm at both ends of the intermediate tube blank 5, and the wall thickness change S along the cross-sectional perimeter is 0.825…0.895 mm. After the deformation of the intermediate tube blank 5, it is observed that the rectangular cross-section of the pre-deformed tube blank is a uniform and equal-value cross-sectional profile with an equal-value fillet radius r. The maximum wall thickness change εs of the intermediate tube blank 5 is ±0.006, which confirms that the cross-sectional wall thickness change of the intermediate tube blank 5 during pre-deformation is negligible. The width of the rectangular cross-section of the pre-formed tube blank is 1 mm smaller than that of the corresponding electrohydraulic forming die to facilitate placement into the electrohydraulic die.

[0045] In step c, an electro-hydraulic forming device of EMF20 type is adopted, with a rated capacitance of 200 μF and a rated voltage of 20 kV. During the electro-hydraulic forming process, the pre-deformed tube blank 8 obtained in the pre-deformation stage is placed at the center of the upper and lower half-molds, between the electro-hydraulic forming upper half-mold 16 and the electro-hydraulic forming lower half-mold 17. The cavity of the half-mold elbow die cavity is manufactured according to the vertical axial section. The electro-hydraulic forming upper half-mold 16 and the electro-hydraulic forming lower half-mold 17 are positioned and guided by the dowel pins 15. A pure aluminum wire electrode system is inserted into the blank cavity. The electrode system includes an electrode 9, an electrode joint 18, a filler 10, an insulator 11, and an insulator 12 with grooves 13. The insulator 11 and the insulator 12 are wrapped around the electrode 9. The electrode 9 includes a straight section and an arc section. The insulator 12 is wrapped around the connection part of the electrode 9 and the electrode joint 18. The insulator 11 is wrapped around the electrode 9, and the end of the electrode 9 exposes the insulator 11. The working liquid 14 for electro-hydraulic forming is introduced through the grooves 13. The filler 10 is a sealant, which is used to wrap and fix the grooves 13 and block the cavity of the elbow die cavity to prevent the working liquid from leaking. The diameter of the electrode 9 is φ0.6 mm through tests, and the electrode spacing L = 19 mm. The press presses the electro-hydraulic forming upper half-mold 16 and the electro-hydraulic forming lower half-mold 17 with a force P. After the electrode system presses towards the half-mold with a force Q, the working liquid 14 is injected into the cavity of the pre-deformed tube blank 8. For the forming of small-round-corner rectangular-section pipe fittings, the key lies in the forming at the corners. The wall thickness at the round-corner transition zone is prone to excessive thinning and cracking. At the same time, it is difficult for the metal to fill and deform towards the corners, and it is difficult to ensure complete die-fitting at the corners in one forming. To solve the above problems, in this embodiment, a two-step forming method is adopted, and deformation is achieved by two discharges: the first time, a voltage of 9.5 kV and a discharge energy of 1.6 kj are used in the electro-hydraulic forming device. After the discharge, there are still some local positions of the tube blank at the corners that do not fit tightly with the die. The second time, a voltage of 12 kV and a discharge energy of 2.6 kj are used. Compared with single electro-hydraulic forming at a relatively high voltage, in order to completely evaluate whether the tube blank is finally formed at the cross-sections 1–1 to 5–5 after electro-hydraulic forming, measure Figure 9 the shown fillet radii r1 to r4, and their values are as Figure 10 shown. In this embodiment, a micrometer with scale display for measuring the inner and outer diameters is used to measure the wall thickness of the tube; a tool microscope with a magnification of 100×50 is used to observe the fillet radius of the cross-section of the semi-finished tube blank. It can be seen from the above figures and tables that the two-step forming method adopted in this embodiment can greatly reduce springback and make the fillets at the tube corners filled plumply, and the wall thickness is also relatively uniform.

[0046] The selection of the electrode parameters in this embodiment mainly refers to the research of Yu Haiping and others, "Experimental Study on Electro-Hydraulic Forming of Aluminum Alloy Tube Blanks", Forging & Stamping Technology, 2016, 41(3): 37-43.

[0047] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains may make various modifications or supplements to the described specific embodiments or use similar means for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A bending method for a titanium alloy tube with a rectangular cross-section, characterized in that, It consists of the following steps, Step a: First, fill the original tube blank with dry rosin filler, rigidly fix one end of the tube blank, and then bend the original tube blank with a circular cross-section into an intermediate tube blank at the required angle; Step b: Perform pre-static deformation on the intermediate tube blank in a pre-static deformation die to obtain a pre-static deformation tube blank with a specified rectangular cross-section; Step c: Finally form the pre-static deformation tube blank with a specified rectangular cross-section in an electro-hydraulic forming device by electro-hydraulic pulses, In step a, a rolling bending method with a gap Z is adopted. First, the rolling roller located above the original tube blank and spaced Z from the original tube blank gradually descends in an arc after passing through the straight section of the original tube blank. After the rolling roller contacts the original tube blank, a bending force is applied until an intermediate tube blank at the required angle is obtained.

2. The bending method of the titanium alloy tube with a rectangular cross-section according to claim 1, characterized in that In step a, there is a raceway groove between the rolling roller and the original tube blank. The thickness of the raceway is Z, and the arc of the raceway groove fitting the outer diameter of the original tube blank is 30°. The rolling roller gradually descends in an arc to an intermediate tube blank at the required angle after passing through the straight section of the original tube blank.

3. The method for bending a titanium alloy tube with a rectangular cross-section according to claim 2, wherein The tube length L in step a m and R 中 are related as follows: L m = πR 中 / 2 + 2Δ = 116.35 mm, where Δ is the straight section length of the tube blank at both ends of the tube blank, and R 中 is the radius of the bending neutral axis of the tube blank.

4. The bending method of the titanium alloy tube with a rectangular cross-section according to claim 3, characterized in that, When the outer diameter of the tube is R 外 satisfies 15 mm ≤ R 外 ≤ 50 mm, Z / R 中 = 9% to 10%.

5. The bending method of the titanium alloy tube with a rectangular cross-section according to any one of claims 1-4, characterized in that, In step c, a two-step forming method is adopted, and deformation is achieved through two discharges. The first discharge is carried out in the electro-hydraulic forming device with a voltage V1 and a discharge energy E1, and the second discharge is carried out in the electro-hydraulic forming device with a voltage V2 and a discharge energy E2, where V2 > V1 and E2 > E1.

6. The bending method of the titanium alloy tube with a rectangular cross-section according to any one of claims 1-4, characterized in that, It includes an electro-hydraulic forming upper die, an electro-hydraulic forming lower die, and an electrode system. The electrode system includes two groups of electrode assemblies. The electrode assembly includes an electrode, an electrode joint, an insulator one, and an insulator two. The insulator one and the insulator two are wrapped around the electrode. The electrode includes a straight section and an arc section. The insulator two is wrapped around the connection part of the electrode and the electrode joint. The insulator one is wrapped around the electrode, and the end of the electrode is exposed from the insulator one.

7. The bending method of the titanium alloy tube with a rectangular cross-section according to claim 6, characterized in that, Both the electro-hydraulic forming upper die and the electro-hydraulic forming lower die have a bent tube die cavity, and the electro-hydraulic forming upper die and the electro-hydraulic forming lower die are positioned and guided by dowel pins. Before electro-hydraulic pulse forming, the press compresses the electro-hydraulic forming upper die and the electro-hydraulic forming lower die.

8. The method for bending a titanium alloy tube with a rectangular cross-section according to claim 7, characterized in that, The electrode system also includes a stainless steel shell. The electrode joint is located inside the stainless steel shell. The electrode penetrates through the stainless steel shell. The insulator two has a groove communicating with the bent tube die cavity.

9. The bending method of the titanium alloy tube with rectangular cross-section according to claim 8, characterized in that, A filler is arranged between the bent tube die cavity and the electrode system, and the filler is a sealant.

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