Research On The Cold Heading Microstructure And Properties Of TB9 Titanium Alloy And Finite Element Simulation Analysi

Titanium alloy tensile core rivets are widely used in the aviation field,such as: military aircraft,helicopters,large transport aircraft and large passenger aircraft.TB9 titanium alloy core rod is the key part of the rivet,and its processing quality directly affects the service life and reliability of the rivet.This part is a typical elongated shaft,which is mainly prepared by cold heading forming.In actual production,due to the improper selection of process plan and process parameters,the head of the core rod is easy to produce cracks,holes and other defects.Therefore,reasonable cold heading process scheme and process parameters are of great significance to improve the forming quality of the core rod.The research content of this paper belongs to the sub-project of National Natural Science Foundation of China(51664006)and Guizhou Provincial Natural Science Foundation key project(Guizhou Science basic word [2020]1Z049),mainly aiming at the problems in the manufacturing of TB9 titanium alloy core rod of a company in Guizhou.The research focuses on the upsetting process,parameter optimization,properties and microstructure of the core rod.The specific contents are as follows:(1)The TB9 titanium alloy core rod is mainly made by cold heading forming,and the performance of the core rod is affected by the problems such as stress concentration band,flash edge and crack in the process.Therefore,according to the structure characteristics of core bar and forming quality requirements,the upsetting process of two-die forming is proposed by controlling the amount of upsetting deformation.(2)The upsetting process of the core rod was numerically simulated by DEFORM simulation software.The flow rule of the upsetting material and the stress and strain distribution of different parts of the core rod were studied.The maximum strain value and damage value of the two-die forming scheme are 5.61mm/mm and 0.210,which are lower than the maximum strain value and damage value of the one-die forming scheme,which are6.16mm/mm and 0.315,indicating that the two-die forming scheme is beneficial to the suppression of the defects of the core rod(3)Orthogonal test method and finite element simulation technique were used to optimize the three key parameters of pre-heading deformation,friction coefficient and cold heading velocity.The optimum process parameters were determined by range analysis: the pre-upsetting deformation was 25%;The friction coefficient is 0.15.The cold heading speed is 125mm/s.The process parameters can effectively reduce the maximum forming load,maximum damage value and maximum equivalent strain value.(4)Based on the optimized process parameters,TB9 titanium alloy core rod parts were prepared.The microstructure and properties of the samples were studied by means of optical microscope,scanning electron microscope and Vickers hardness tester.The results show that the sample has good forming quality,no obvious defects,high grain refinement and obvious work hardening at the shear zone.The validity of the upsetting process parameter optimization is proved,which provides technical support for the manufacture of TB9 titanium alloy core rod.