Upsetting forming method for head structure of ultrahigh-strength titanium alloy fastener

Abstract

The invention discloses an ultra-high-strength titanium alloy fastener head structure upsetting forming method which comprises the following steps that firstly, an ultra-high-strength titanium alloy straight bar is cut off after being subjected to surface treatment, and an ultra-high-strength titanium alloy blank is obtained; secondly, the to-be-deformed area of the ultrahigh-strength titanium alloy blank obtained in the first step is heated, then the to-be-deformed area is transferred into an upsetting die to be subjected to upsetting forming, and a fastener head structure is obtained; the heating temperature ranges from 700 DEG C to 730 DEG C. According to the method, the to-be-deformed area of the ultrahigh-strength titanium alloy blank is heated to 700-730 DEG C before upsetting, the temperature is lower than the solution treatment temperature of the ultrahigh-strength titanium alloy material, it is ensured that the to-be-deformed area has good machinability and metal fluidity for upsetting forming, and the method is suitable for the technical field of fastener preparation.

Description

Technical Field

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

[0002] With the development of aerospace industry, the connection technology level used in new aircraft and spacecraft is constantly improving. In the future, high-performance aviation fasteners will put forward higher strength and higher fatigue performance requirements for the titanium alloy materials used to manufacture them. At present, high-strength titanium alloys such as TB3, TB8, and TB9 used as aviation fasteners usually use strength levels not exceeding 1300MPa, and their processing technology has been well solved. In the future, as a development trend in the field of aviation fasteners worldwide, the manufacturing of 1300MPa-level ultra-high strength titanium alloy fasteners is very difficult, and there are still a lot of problems in the manufacturing process, mainly manifested in the difficulty of hot upsetting, severe deformation during processing, and factors that affect the test results in performance tests.

[0003] In order to ensure the good fatigue and durability mechanical properties of fasteners, the fastener-related standards clearly stipulate that the heads of certain fasteners cannot be formed by cutting and can only be formed by upsetting. As the first step in fastener processing, head mold upsetting plays a key role in product quality. Ultra-high strength titanium alloys have a high degree of alloying, a variety of alloying elements, a complex microstructure control mechanism during thermal deformation, and a relatively narrow forging temperature range. Although fasteners are not prone to cracking during hot upsetting, they are prone to defects such as folding and insufficient cavity filling, which reduces the quality of fastener forming and restricts the application of fastener products in the aviation field. 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 upsetting the head structure of an ultra-high strength titanium alloy fastener. The head structure upsetting method heats the area to be deformed of the ultra-high strength titanium alloy billet to 700°C to 730°C before upsetting, which is lower than the solution treatment temperature of the ultra-high strength titanium alloy material, to ensure that the area to be deformed has good machinability and metal fluidity for upsetting, thereby solving the problem of low forming quality of the head of the ultra-high strength titanium alloy fastener.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for upsetting the head structure of an ultra-high strength titanium alloy fastener, characterized in that the method comprises the following steps:

[0006] Step 1: Cutting the ultra-high strength titanium alloy straight bar after surface treatment to obtain an ultra-high strength titanium alloy blank;

[0007] Step 2: heating the area to be deformed of the ultra-high strength titanium alloy blank obtained in step 1, and then transferring the area to be deformed into an upsetting die for upsetting to obtain a fastener head structure; the heating temperature is 700°C to 730°C.

[0008] The above-mentioned method for upsetting the head structure of an ultra-high strength titanium alloy fastener is characterized in that the ultra-high strength titanium alloy straight bar material in step one is a hot-processed bar material.

[0009] In the prior art, the delivery state of bars for fasteners is usually annealed (M state) or solid solution state (ST state), wherein the annealed state is to eliminate the processing stress of the bars and uniform the structure, and the solid solution state makes the alloy have a lower rheological stress, which is conducive to upsetting. However, the performance of ultra-high-strength titanium alloys is sensitive to heat treatment, and fasteners need to be subjected to solid solution + aging treatment after upsetting and before thread rolling. The annealing or solid solution treatment of the bars in the early stage will have an adverse effect on the performance after the later solid solution + aging treatment, especially it will reduce the plasticity of the bars, which is not conducive to the subsequent thread rolling process; therefore, the present invention uses hot-processed bars as raw materials to prepare fasteners.

[0010] The above-mentioned method for upsetting the head structure of an ultra-high strength titanium alloy fastener is characterized in that the strength grade of the ultra-high strength titanium alloy in step one is not less than 1300 MPa.

[0011] The above-mentioned method for upsetting the head structure of an ultra-high strength titanium alloy fastener is characterized in that the heating in step 2 is performed by induction coil heating, and the heating time is 3s to 5s.

[0012] By setting the heating time, the present invention can ensure that the temperature of the entire area to be deformed meets the requirements for one-time stamping and can effectively control the heat-affected zone of the rod.

[0013] The above-mentioned method for upsetting the head structure of an ultra-high strength titanium alloy fastener is characterized in that the transfer time in step 2 does not exceed 2 seconds.

[0014] The present invention transfers the area to be deformed to an upsetting die quickly after heating for upsetting, thereby reducing the risk of cooling the area to be deformed during the transfer process.

[0015] The above-mentioned method for upsetting the head structure of an ultra-high strength titanium alloy fastener is characterized in that the upsetting forming in step 2 is a one-time stamping forming, and the stamping speed of the upsetting forming is 4mm / s to 5mm / s.

[0016] The present invention can ensure the integrity of the head streamline by adopting one-time stamping, and complete the head upsetting when the area to be deformed has good processability by controlling the stamping speed to 4mm / s-5mm / s, thereby avoiding defects such as folding and insufficient cavity filling.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. The present invention heats the area to be deformed of the ultra-high strength titanium alloy billet to 700°C to 730°C before upsetting. This temperature is lower than the solution treatment temperature of the ultra-high strength titanium alloy material, which can ensure that the area to be deformed has good machinability and metal fluidity for upsetting and forging, avoiding defects such as folding of the head and insufficient filling of the cavity; at the same time, this temperature does not affect the subsequent heat treatment to improve the performance of the fastener, and can ensure that the overall structure and performance of the fastener are uniform, thereby improving the forming quality of the fastener.

[0019] 2. The present invention performs upsetting molding by adopting the method of short-time heating by induction coil and heating the deformation area of ​​the material separately, which fully considers the effectiveness of material heating, and can ensure that the head structure meets the surface and internal organization requirements, while ensuring that the rod is not affected by the heating temperature, thereby reducing the impact on the performance of the fastener rod.

[0020] 3. The present invention can be produced on an ordinary warm heading machine, and there is no need to design special equipment and molds for ultra-high strength titanium alloys, which can reduce production costs. In addition, the forming method is simple and easy to promote.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is an appearance diagram of the fastener head structure prepared in Example 1 of the present invention.

[0023] Figure 2 This is a microstructure diagram of the fastener head structure prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] Example 1

[0025] The method of this embodiment includes the following steps:

[0026] Step 1: Surface-treat a hot-processed Ti-1500 straight bar with a diameter of 8.5 mm and then cut it to obtain an ultra-high-strength titanium alloy blank; the ultra-high-strength titanium alloy Ti-1500 has a strength grade of not less than 1500 MPa;

[0027] Step 2: Use an induction coil to heat the area to be deformed of the ultra-high strength titanium alloy billet obtained in step 1 for 5 seconds, heating it to 730°C, and then transfer the area to be deformed to the upsetting die within 2 seconds, and perform one-time upsetting molding at a stamping speed of 5 mm / s to obtain a 100° countersunk head structure of the fastener.

[0028] like Figure 1 As shown in FIG. 1 , the 100° countersunk head structure of the fastener prepared in this embodiment has good macroscopic surface quality, and no defects such as flash, folding, cracking, and incomplete filling of the cavity are found; the 100° countersunk head structure of the fastener is cut open along the longitudinal axis to observe the microstructure, as shown in FIG. Figure 2 As shown, the flow lines under the head of the 100° countersunk head structure of the fastener are continuous and dense, and there is no adiabatic shear band and overheating in the structure, which will not affect the consistency of subsequent structure and fastener performance.

[0029] Example 2

[0030] The method of this embodiment includes the following steps:

[0031] Step 1: Surface-treat a hot-processed Ti-1300 straight bar with a diameter of 12.5 mm and then cut it to obtain an ultra-high-strength titanium alloy blank; the ultra-high-strength titanium alloy Ti-1300 has a strength grade of not less than 1300 MPa;

[0032] Step 2: Use an induction coil to heat the area to be deformed of the ultra-high strength titanium alloy billet obtained in step 1 for 8 seconds, heating it to 700°C, and then transfer the area to be deformed to the upsetting die within 2 seconds, and perform one-time upsetting molding at a stamping speed of 4 mm / s to obtain a 100° countersunk head structure of the fastener.

[0033] The 100° countersunk head structure prepared in this embodiment has a good macroscopic surface, and no defects such as flash, folding, cracking, and incomplete filling of the cavity were found; the 100° countersunk head structure was cut open along the longitudinal axis to observe the microstructure. There were no adiabatic shear bands and overheating and overburning in the structure, which would not affect the consistency of subsequent structure and fastener performance.

[0034] Example 3

[0035] The method of this embodiment includes the following steps:

[0036] Step 1: Surface-treat a hot-processed Ti-1300 straight bar with a diameter of 10.5 mm and then cut it to obtain an ultra-high-strength titanium alloy blank; the strength grade of the ultra-high-strength titanium alloy Ti-1300 is not less than 1300 MPa;

[0037] Step 2: Use an induction coil to heat the area to be deformed of the ultra-high strength titanium alloy billet obtained in step 1 for 4 seconds, heating it to 720°C, and then transfer the area to be deformed to the upsetting die within 2 seconds, and perform one-time upsetting molding at a stamping speed of 4.5 mm / s to obtain the hexagonal head structure of the fastener.

[0038] The macroscopic surface of the hexagonal head structure prepared in this embodiment is good, and no defects such as flash, folding, cracking, and incomplete filling of the cavity are found; the hexagonal head structure is cut open along the longitudinal axis to observe the microstructure. There are no adiabatic shear bands and overheating and overburning in the structure, which will not affect the consistency of subsequent structure and fastener performance.

[0039] Example 4

[0040] The method of this embodiment includes the following steps:

[0041] Step 1: Surface-treat a hot-processed Ti-1500 straight bar with a diameter of 10.5 mm and then cut it to obtain an ultra-high-strength titanium alloy billet; the ultra-high-strength titanium alloy Ti-1500 has a strength grade of not less than 1500 MPa;

[0042] Step 2: Use an induction coil to heat the area to be deformed of the ultra-high strength titanium alloy billet obtained in step 1 for 4 seconds, heating it to 730°C, and then transfer the area to be deformed to the upsetting die within 2 seconds, and perform one-time upsetting molding at a stamping speed of 4 mm / s to obtain a hexagonal head structure of the fastener.

[0043] The macroscopic surface of the hexagonal head structure prepared in this embodiment is good, and no defects such as flash, folding, cracking, and incomplete filling of the cavity are found; the hexagonal head structure is cut open along the longitudinal axis to observe the microstructure. There are no adiabatic shear bands and overheating and overburning in the structure, which will not affect the consistency of subsequent structure and fastener performance.

[0044] 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 upsetting the head structure of an ultra-high strength titanium alloy fastener, characterized in that: The method comprises the following steps: Step 1: Cutting the ultra-high strength titanium alloy straight bar after surface treatment to obtain an ultra-high strength titanium alloy blank; Step 2: heating the area to be deformed of the ultra-high strength titanium alloy blank obtained in step 1, and then transferring the area to be deformed to an upsetting die for upsetting to obtain a fastener head structure; the heating temperature is 700°C to 730°C.

2. The method for upsetting the head structure of an ultra-high strength titanium alloy fastener according to claim 1, characterized in that: The ultra-high strength titanium alloy straight bar material described in step 1 is a hot-processed bar material.

3. The method for upsetting the head structure of an ultra-high strength titanium alloy fastener according to claim 2, characterized in that: The strength grade of the ultra-high strength titanium alloy described in step 1 is not less than 1300 MPa.

4. The method for upsetting the head structure of an ultra-high strength titanium alloy fastener according to claim 1, characterized in that: The heating in step 2 is performed by induction coil heating, and the heating time is 3s to 5s.

5. The method for upsetting the head structure 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 upsetting the head structure of an ultra-high strength titanium alloy fastener according to claim 1, characterized in that: The upsetting forming in step 2 is a one-time stamping forming, and the stamping speed of the upsetting forming is 4 mm / s to 5 mm / s.

Images