Research on high strength bolt processing technology

Industrial Technology High-strength Bolt Machining Process Research Shen Xinyu He Dongmin Xing Lijun (Shenyang Liming Aero Engine (Group) Co., Ltd., Shenyang 110043, Liaoning Province) The method of combining the phases, doing a lot of experimental work, seriously plagued the double-hex head high-strength bolt processing The performance problem has been broken through, and the research on the double-hex head high-strength bolt technology with challenging difficulty in the fastener industry has been completed, which has effectively improved the mechanical properties of the bolt. This paper studies the following problems: the blanking technology of high-strength bolts; Heat treatment technology; rolling technology; mechanical properties test and analysis provide an effective process basis for new product development and processing of similar parts, filling the technical gap in high-strength bolt processing.

With the development of high-strength bolt processing industry, the use of high-strength bolts in these complex environments is increasing. High-strength bolt processing is very important in the fastener industry, and it is also a topic of concern in the domestic industry.

Because high-strength bolts are used in the field of aircraft, the occasion is special. The size and performance requirements of the parts are strict. Although it seems that the structure is not complicated, how to meet the performance requirements in the double-hex head high-strength bolt processing It is a problem, which is briefly introduced below.

1Structural characteristics of high-strength bolts The load distribution on the bolts of the bolts is very uneven. In the elastic range, the load of the first stitch near the nut bearing surface is the largest, and the load of the remaining screw threads is gradually smaller. . The bottom of the thread should be rounded, and the radius of the arc of the root should not be less than 0.1 pitch. A triangular cusp or flat bottom should not be used. The undercut between the thread and the screw should be smooth and excessive, and the radius R of the arc is 0.3 thread diameter.

There should be a transition fillet between the bolt head and the screw. The perpendicularity of the end face of the fine thread and the axis of the thread is not more than 0.08. 2 High-strength bolt processing technology The high-strength bolt material is mostly difficult to process nickel-base superalloy or high-temperature anti-corrosion alloy. Due to the high Ni content of the part, the machine is difficult to add. The following difficulties exist; 2.1.1 High-strength bolt thread rolling technology with extremely high Ni content.

Processing Process Parts Tanning - Heat Treatment - Processing Inspection Hardness Test Pieces - Rolling Processing - Cleaning - Fluorescence Inspection - Inspection - Mechanical Property Testing - Final Inspection - Storage, Part Structure Drawings are as follows: 3.1 High-strength bolts have better performance requirements for materials Good resistance to slack, so that the bolt under a pre-tightening stress, after a design run time, its residual tight stress is still higher than the minimum sealing stress. Good fit between strength and plasticity, creep creep sensitivity is small. The tissue is stable and the tendency of hot brittleness is small. Good anti-oxidation performance, preventing bolt and nut seizure due to thread oxidation after long-term operation.

The material of the high-strength bolt is in the manufacture of high-strength bolts, and the material of the parts is a nickel-based superalloy. The design requires that the head should be hot or cold-formed. We use cold heading. Cold heading steel is a highly interchangeable nickel-based tantalum billet produced by cold heading. It is metal-plastic processing at room temperature. Forming, each part has a large amount of deformation and a high deformation speed. Therefore, the performance requirements of the raw materials of the parts are also very strict.

The head of the high-strength bolt is processed by cold heading. Compared with the cutting process, the metal streamline is continuous along the shape of the part without cutting in the middle, which improves the strength of the part and has excellent mechanical properties.

The cold head forming process includes cutting and forming. The cold heading machine is carried out in several forming concave molds respectively. The processing characteristics of the original blank used in the multi-station automatic cold heading machine are determined by the size of the wire rod steel wire. The shaping can meet the process requirements (the design meets the blank). The out-of-roundness of the cold-dash wire used in the manufacture of high-strength fasteners on automatic cold heading machines should be within the diameter tolerance. The precision that can be achieved by cold heading is also the same as the selection of the forming method and the process used. In addition, it depends on the structural characteristics of the equipment used, the process characteristics and its state, life and wear.

High-strength bolts are heat-treated according to technical requirements before partial rolling. Heat treatment is to improve the comprehensive mechanical properties of the fasteners to meet the tensile strength and fatigue strength specified by the bolts. Therefore, in order to produce high-quality high-strength fasteners, advanced heat treatment technology must be provided. Due to the large production volume of high-strength bolts, the threaded parts are relatively fine and precise structures. Therefore, the heat treatment equipment must have the ability of large production capacity, high degree of automation and good heat treatment quality. It is required to ensure uniform heating temperature during the whole part processing, and an automatic temperature controller and data logger should be provided.

There are many methods for threading, and the rolling thread method is one of the effective means to improve the thread performance.

The partial rolling processing strengthening process has become an important means to improve the competitiveness of high-strength bolts. The life of high-strength bolts can be increased by about 70% after partial rolling. Rolling thread is a process of no-remaining and shrinking deformation of the part, but the change of the material flow line of the part, resulting in cold work hardening, so that the surface material has residual compressive stress, etc., which improves the wear resistance and fatigue strength of the part. Has a significant effect.

The high-strength bolt material is a nickel-based superalloy with high strength and hardness, strong plastic deformation ability, and it is difficult to roll. It is necessary to produce large plastic deformation during the rolling process to meet the shape, size and surface quality requirements of the part, which increases the difficulty of rolling.

The local rolling process of high-strength bolts is complicated, and it has a close relationship with the bolt structure and the elongation of materials. It is the result of various factors. In actual production, only through the process test, select the appropriate material and specification of the rolling wheel, adjust the correct pallet height and the speed of the guide wheel and cutting wheel, the feed of the driving wheel, the tooth modification time and other reasonable process parameters. , curing parameters to properly guide production.

Tested to meet the performance requirements of double hexagonal high-strength bolts: hardness, ultimate tensile strength at room temperature, ultimate tensile strength at a certain temperature, fatigue strength.

Due to the bolts used in special environments, it should have excellent anti-relaxation and creep resistance, long-lasting performance and stress corrosion resistance. Therefore, high-strength bolts must meet the following requirements: the thread surface should be smooth and smooth, and there should be no dents or cracks. , rusting edema and other defects that cause stress concentration. Coloring or fluoroscopy: No cracks are allowed. 100% spectral test chemical composition. 100% hardness check. Check the wool material sheet should have a certificate of low-fold tissue inspection. Mechanical performance check. 100% ultrasonic flaw detection.

Based on the research of high-strength bolt technology, combined with on-site conditions, and using effective methods to improve the strength of high-strength bolts, the paper completed the manufacturing process of double-hex head high-strength bolts and solved the guarantee of mechanical properties of bolts under high strength. problem. Research and experiments show that the high-strength bolt technology meets the requirements of design drawings, technical conditions and performance, and successfully completes the research topic of double-hex head high-strength bolt technology.

The high-strength bolts completed the first trial production on July 20, 2009. The successful trial production of this piece has enabled us to accumulate processing experience in high-strength bolt processing. At the same time, we have accumulated an effective process to improve the strength of high-strength bolts through a large number of tests, and completed the research on the process of high-hardness and high-strength bolts. The improvement of the manufacturing technology level is of great significance.

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