Thread rolling forming method for ultrahigh-strength titanium alloy fastener

Abstract

The invention discloses an ultra-high-strength titanium alloy fastener thread roll forming method which comprises the following steps: step 1, carrying out solution aging heat treatment on an ultra-high-strength titanium alloy subjected to head upsetting, carrying out finish machining on a thread blank rod according to the target thread size of an ultra-high-strength titanium alloy fastener, and carrying out rolling forming on the thread blank rod; a semi-finished product of the ultrahigh-strength titanium alloy fastener is obtained; and secondly, the threaded blank rod of the semi-finished product of the ultrahigh-strength titanium alloy fastener is heated to 350-400 DEG C and then transferred to a movable thread rolling machine to be rolled and formed, and the ultrahigh-strength titanium alloy fastener thread is obtained. According to the forming method, according to the characteristics that the ultrahigh-strength titanium alloy is extremely high in strength and low in plasticity, the small thread blank rod diameter is designed, then warm rolling is carried out at the temperature of 350-400 DEG C, threads with full thread forms and good surface quality are obtained, and the forming method is suitable for the technical field of titanium alloy fastener thread forming.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy fastener thread forming, and in particular relates to a thread rolling forming method for an ultra-high strength titanium alloy fastener. Background Art

[0002] Titanium alloy fasteners have comprehensive properties such as light weight, high specific strength, corrosion resistance, and good fatigue performance. They can meet the requirements of aircraft in terms of weight reduction, corrosion resistance, and fatigue resistance, and therefore have been widely used. Titanium alloy fasteners are currently the best connectors for key structures of composite materials. At present, high-strength titanium alloys such as TB3, TB8, and TB9, which are widely used as aviation fasteners, usually use strength levels not exceeding 1300MPa, and their processing technology has been well solved. However, the manufacture of 1500MPa-level ultra-high strength titanium alloy fasteners is still difficult.

[0003] Currently, the high-strength titanium alloy thread rolling used in aerospace is carried out in the aging state, while the ultra-high-strength titanium alloy material has a strength of more than 1500MPa after solid solution aging heat treatment, and the plasticity is only 8% to 10%, which makes it difficult to deform. The thread rolling process can easily cause the rolling wheel to break and reverse the teeth, and the rolled threads may have defects such as cracks and folds, which cannot meet the technical requirements. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a method for rolling forming threads of ultra-high strength titanium alloy fasteners. The forming method designs a smaller thread blank rod diameter according to the characteristics of ultra-high strength titanium alloy with extremely high strength and low plasticity, and then warm-rolls at a temperature of 350°C to 400°C to obtain threads with full tooth profile and good surface quality, thus solving the problem of defects that are easily generated when rolling ultra-high strength titanium alloys above 1500MPa in the prior art.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for rolling forming threads of ultra-high strength titanium alloy fasteners, characterized in that the method comprises the following steps:

[0006] Step 1: performing a solution aging heat treatment on the ultra-high strength titanium alloy that has completed head upsetting, and performing finish machining of the thread blank rod according to the target thread size of the ultra-high strength titanium alloy fastener to obtain a semi-finished ultra-high strength titanium alloy fastener;

[0007] Step 2: Heat the thread blank of the semi-finished ultra-high strength titanium alloy fastener obtained in step 1 to 350° C. to 400° C., and then transfer it to a mobile thread rolling machine for rolling forming to obtain the thread of the ultra-high strength titanium alloy fastener.

[0008] The above-mentioned method for rolling thread forming of ultra-high strength titanium alloy fasteners is characterized in that the tensile strength of the ultra-high strength titanium alloy after the solid solution aging heat treatment in step one is greater than 1500 MPa and the elongation is greater than 10%.

[0009] The above-mentioned method for rolling forming threads of ultra-high strength titanium alloy fasteners is characterized in that the diameter of the thread blank rod in step 1 is calculated as follows:

[0010] d = D - (0.68 ~ 0.7) × P;

[0011] Among them, d is the diameter of the thread blank rod, in mm; D is the nominal diameter in the target thread size, in mm; P is the pitch in the target thread size, in mm.

[0012] The above-mentioned method for rolling forming threads of ultra-high strength titanium alloy fasteners is characterized in that the thread blank rod in step 2 is heated by an induction coil, and the heating time of the induction coil is 3s to 5s.

[0013] The above-mentioned method for rolling thread forming of ultra-high strength titanium alloy fasteners is characterized in that the transfer time in step 2 does not exceed 2s.

[0014] The above-mentioned method for rolling forming threads of ultra-high strength titanium alloy fasteners is characterized in that the rolling forming in step 2 is a one-time rolling forming, the rolling forming pressure is 40kN~42kN, and the rolling wheel speed of the rolling forming is 32r / min~37r / min.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. According to the characteristics of ultra-high strength titanium alloy with extremely high strength and low plasticity, the present invention designs a smaller thread blank rod diameter, and performs warm rolling at a temperature of 350°C to 400°C. At this temperature, the ultra-high strength titanium alloy has a certain plastic deformation ability without reducing the strength, and can obtain a thread with full tooth profile and good surface quality, which breaks through the fastener screw preparation technology of ultra-high strength titanium alloy above 1500MPa level.

[0017] 2. The present invention adopts the method of warm rolling thread to prepare fastener threads. Although the warm rolling process reduces the compressive stress on the thread surface after rolling to a certain extent compared with cold rolling, warm rolling can significantly reduce the occurrence of thread defects. The residual compressive stress after rolling combined with good thread quality can enable the fastener product to obtain good fatigue performance.

[0018] 3. The present invention can produce ultra-high strength titanium alloy fastener threads above 1500MPa on a conventional warm rolling machine without the need to improve the equipment, and the prepared ultra-high strength titanium alloy fastener threads have stable and reliable overall quality, simple preparation process and low production cost.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a microstructure diagram of the thread of the ultra-high strength titanium alloy fastener prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The ultra-high strength titanium alloys in Examples 1 to 3 are all ultra-high strength titanium alloys described in the Chinese invention patent "An Ultra-High Strength Titanium Alloy for Aviation Structural Parts" (Announcement No. CN115772616B).

[0022] Example 1

[0023] The method of this embodiment includes the following steps:

[0024] Step 1: The ultra-high strength titanium alloy is subjected to head upsetting, solution aging heat treatment, and fine processing of a small diameter thread blank rod according to the target thread size of the ultra-high strength titanium alloy fastener in sequence, so as to obtain a semi-finished ultra-high strength titanium alloy fastener with a thread blank rod diameter of 10.98 mm; the process of the solution aging heat treatment is: heating to 770°C and keeping it for 1 hour, then air cooling, and then heating to 510°C and keeping it for 4 hours, and then water quenching and cooling; the tensile strength of the ultra-high strength titanium alloy after the solution aging heat treatment is 1550MPa, and the elongation is 10.5%;

[0025] Step 2: Heat the threaded blank rod of the semi-finished ultra-high strength titanium alloy fastener obtained in step 1 to 350°C for 5 seconds, then transfer it to a mobile thread rolling machine within 2 seconds, perform a rolling forming operation at a pressure of 42kN and a thread rolling wheel speed of 35r / min to obtain the ultra-high strength titanium alloy fastener thread.

[0026] The fatigue strength test of the ultra-high strength titanium alloy fastener obtained in this embodiment is carried out, and the fatigue life exceeds 130,000 times; the thread of the ultra-high strength titanium alloy fastener prepared in this embodiment is a flat-top round-bottom tooth type. After testing, the nominal diameter of the thread of the ultra-high strength titanium alloy fastener is 12mm and the pitch is 1.5mm. The size of the thread of the ultra-high strength titanium alloy fastener is qualified; the thread of the ultra-high strength titanium alloy fastener prepared in this embodiment is photographed microscopically, as shown in FIG. Figure 1 As shown, the threads of the ultra-high strength titanium alloy fasteners are free of defects such as cracks, folds, and rotten teeth. The thread shape is smooth and the quality is stable and reliable.

[0027] Example 2

[0028] The method of this embodiment includes the following steps:

[0029] Step 1: The ultra-high strength titanium alloy is subjected to head upsetting, solution aging heat treatment, and fine processing of a small diameter thread blank rod according to the target thread size of the ultra-high strength titanium alloy fastener in sequence, so as to obtain a semi-finished ultra-high strength titanium alloy fastener with a thread blank rod diameter of 11.14 mm; the process of the solution aging heat treatment is: heating to 760°C and keeping it for 1 hour, then air cooling, and then heating to 510°C and keeping it for 4 hours, and then water quenching and cooling; the tensile strength of the ultra-high strength titanium alloy after the solution aging heat treatment is 1520MPa, and the elongation is 12.5%;

[0030] Step 2: Heat the threaded blank rod of the semi-finished ultra-high strength titanium alloy fastener obtained in step 1 to 400°C for 3 seconds, then transfer it to a mobile thread rolling machine within 2 seconds, and perform one rolling forming at a pressure of 40kN and a rolling wheel speed of 35r / min to obtain the ultra-high strength titanium alloy fastener thread.

[0031] The ultra-high strength titanium alloy fastener obtained in this embodiment was subjected to a fatigue strength test, and the fatigue life exceeded 130,000 times; the thread of the ultra-high strength titanium alloy fastener prepared in this embodiment is a flat-top round-bottom tooth type. After testing, the nominal diameter of the thread of the ultra-high strength titanium alloy fastener is 12mm and the pitch is 1.25mm. The size of the thread of the ultra-high strength titanium alloy fastener is qualified, and there are no defects such as cracks, folding, and rotten teeth. The thread quality is stable and reliable.

[0032] Example 3

[0033] The method of this embodiment includes the following steps:

[0034] Step 1: The ultra-high strength titanium alloy is subjected to head upsetting, solution aging heat treatment, and fine processing of a small diameter thread blank rod according to the target thread size of the ultra-high strength titanium alloy fastener in sequence, so as to obtain a semi-finished ultra-high strength titanium alloy fastener with a thread blank rod diameter of 11.14 mm; the process of the solution aging heat treatment is: heating to 770°C and keeping it for 1 hour, then air cooling, and then heating to 510°C and keeping it for 4 hours, then air cooling; the tensile strength of the ultra-high strength titanium alloy after the solution aging heat treatment is 1530 MPa, and the elongation is 11.0%;

[0035] Step 2: Heat the threaded blank rod of the semi-finished ultra-high strength titanium alloy fastener obtained in step 1 to 380°C for 4 seconds, then transfer it to a mobile thread rolling machine within 2 seconds, and perform one rolling forming at a pressure of 41kN and a rolling wheel speed of 35r / min to obtain the ultra-high strength titanium alloy fastener thread.

[0036] The ultra-high strength titanium alloy fastener obtained in this embodiment was subjected to a fatigue strength test, and the fatigue life exceeded 130,000 times; the thread of the ultra-high strength titanium alloy fastener prepared in this embodiment is a flat-top round-bottom tooth type. After testing, the nominal diameter of the thread of the ultra-high strength titanium alloy fastener is 12mm and the pitch is 1.25mm. The size of the thread of the ultra-high strength titanium alloy fastener is qualified, and there are no defects such as cracks, folding, and rotten teeth. The thread quality is stable and reliable.

[0037] Example 4

[0038] The difference between this embodiment and embodiment 3 is that: the diameter of the thread blank rod of the semi-finished ultra-high strength titanium alloy fastener in step 1 is 11.125 mm; the speed of the rolling wheel for rolling forming in step 2 is 32 r / min.

[0039] The ultra-high strength titanium alloy fastener obtained in this embodiment was subjected to a fatigue strength test, and the fatigue life exceeded 130,000 times; the thread of the ultra-high strength titanium alloy fastener prepared in this embodiment is a flat-top round-bottom tooth type. After testing, the nominal diameter of the thread of the ultra-high strength titanium alloy fastener is 12mm and the pitch is 1.25mm. The size of the thread of the ultra-high strength titanium alloy fastener is qualified, and there are no defects such as cracks, folding, and rotten teeth. The thread quality is stable and reliable.

[0040] Example 5

[0041] The difference between this embodiment and embodiment 3 is that the speed of the thread rolling wheel for rolling forming in step 2 is 37 r / min.

[0042] The ultra-high strength titanium alloy fastener obtained in this embodiment was subjected to a fatigue strength test, and the fatigue life exceeded 130,000 times; the thread of the ultra-high strength titanium alloy fastener prepared in this embodiment is a flat-top round-bottom tooth type. After testing, the nominal diameter of the thread of the ultra-high strength titanium alloy fastener is 12mm and the pitch is 1.25mm. The size of the thread of the ultra-high strength titanium alloy fastener is qualified, and there are no defects such as cracks, folding, and rotten teeth. The thread quality is stable and reliable.

[0043] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for rolling and forming threads of ultra-high strength titanium alloy fasteners, characterized in that: The method comprises the following steps: Step 1: performing a solution aging heat treatment on the ultra-high strength titanium alloy that has completed head upsetting, and performing finish machining of the thread blank rod according to the target thread size of the ultra-high strength titanium alloy fastener to obtain a semi-finished ultra-high strength titanium alloy fastener; Step 2: Heat the thread blank of the semi-finished ultra-high strength titanium alloy fastener obtained in step 1 to 350° C. to 400° C., and then transfer it to a mobile thread rolling machine for rolling forming to obtain the thread of the ultra-high strength titanium alloy fastener.

2. The method for rolling forming a thread of an ultra-high strength titanium alloy fastener according to claim 1, characterized in that: The tensile strength of the ultra-high strength titanium alloy after the solution aging heat treatment in step 1 is greater than 1500 MPa and the elongation is greater than 10%.

3. The method for rolling forming a thread of an ultra-high strength titanium alloy fastener according to claim 1, characterized in that: The calculation method of the diameter of the thread blank rod described in step 1 is as follows: d = D - (0.68 ~ 0.7) × P; Among them, d is the diameter of the thread blank rod, in mm; D is the nominal diameter in the target thread size, in mm; P is the pitch in the target thread size, in mm.

4. The method for rolling forming a thread of an ultra-high strength titanium alloy fastener according to claim 1, characterized in that: In step 2, the thread blank rod is heated by an induction coil, and the heating time of the induction coil is 3s to 5s.

5. The method for rolling forming a thread of an ultra-high strength titanium alloy fastener according to claim 1, characterized in that: The transfer time in step 2 does not exceed 2 seconds.

6. The method for rolling forming a thread of an ultra-high strength titanium alloy fastener according to claim 1, characterized in that: The rolling forming in step 2 is a one-time rolling forming, the rolling forming pressure is 40kN to 42kN, and the rolling wheel speed of the rolling forming is 32r / min to 37r / min.

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