Fundametal Research On Cold Extrusion Process Of Internal Threads In High Strength Steel Q460

Presently, for the internally threaded parts used in the landing gear, the fatigue life of the landing gear is only one-third of the whole airplane caused by using the traditional cutting methods. Therefore, it is especially important that using advanced anti-fatigue manufacturing process to improve the internal threads fatigue strength, so that the landing gear can have the same life with the airplane body.In this work, the study on the cold extrusion anti-fatigue manufacturing process of internal threads in Q460 high strength steel was carried out. The main work and the results achieved are as follows:1. The cold extrusion forming mechanism of internal threads was studied. The results show that the cold extrusion of internal threads is a process of plastic deformation of metal workpiece caused by repeated extrusion of the tap teeth. After extrusion, the surface microstructure of the internal threads is fiberized and distributed along the tooth profile, and there is a certain degree of work-hardening layer on the thread root surface, which improves the tensile strength and the anti-fatigue property of the internal threads.2. Experimental study on uniaxial stretching in Q460 high strength steel was carried out, and the stress-strain curve of this material was obtained, which lay a good foundation for subsequent finite element numerical simulation. Besides, a series of performance parameters of this material were got, for example, the yield strength is 810MPa, the tensile strength is 925MPa, the elongation is 18.56%, and the reduction of area is 47.3%.3. The numerical simulation on the tooth profile region of the internal threads after extrusion based on ANSYS was performed, and the stress-strain laws were gained. The results show that the root and the lateral parts of the teeth of the internal threads after extrusion are both subjected axial and radial compressive stresses, and the existence of the compressive stresses play an important role in the strengthening of the root and the lateral parts of the teeth. The maximum values of the axial and radial compressive stresses in the tooth root parts are 525MPa and 550MPa respectively. The maximum values of the axial and radial compressive stresses in the tooth lateral parts are 725MPa and 360MPa respectively. The farther away from the root and the lateral parts of the teeth, the smaller the compressive stresses are.4. The study on the cold extrusion forming process of internal threads in Q460 high strength steel was carried out. The results show that the bottom diameter of the workpiece, the workpiece speed and the type of cooling lubricant have great impact on the extrusion torque and temperature generated in the cold extrusion process, and the rational choice of them can reduce the extrusion torque and temperature. It indicates in this work that when the bottom diameter of the workpiece is during 21.24mm~21.26mm, the workpiece speed is during 20r/min～32r/min and the cooling lubricant is PDMS, the internal threads after cold extrusion have higher quality.