| Titanium alloy drum type blind rivets are high-end fasteners widely used in the aviation field.The essence of its work is to apply tension to the rivet rod through the riveting device,and at the same time transmit it to the thin-walled nail sleeve to compress it to produce a bulge and the end face of the nail sleeve to generate a fastening force.The overall structural dimensional accuracy and mechanical properties of the nail shank are the key to ensure the riveting quality.Therefore,the research on the forming process and properties of the overall structure of the shank is one of the key issues in the development of blind rivets.This topic is supported by the Guizhou Provincial Department of Science and Technology Program(Qiankehe Support [2021] General 281).Taking a certain type of titanium alloy nail shank as the research object,the technological problems of the nail shank roll forming and the microstructure and properties of the nail shank after heat treatment were mainly studied.The specific research contents are as follows:(1)According to the structural characteristics and process requirements of this type of titanium alloy nail shank,combined with the analysis of the metallographic diagram of key parts,a process plan for rolling the fracture groove first,and then rolling the locking groove was formulated.According to the structural characteristics of the multi-ring grooves of the nail rod,the thread rolling board is selected as the rubbing die,and the structure of the thread rolling board is designed in combination with the thread rolling principle and the corresponding setting indicators.Based on the size of the existing blank,the dimensions of the ring groove and the clamping groove in the middle of the nail rod are designed.In the end,the maximum height of the ring groove mold tooth profile in the middle of the thread rolling plate is 15.455 mm,and the minimum height is 15.005 mm.The maximum height of the thread rolling plate clamping groove die tooth profile is 15.374 mm,and the minimum height is 15.174 mm.(2)For the local key parts of the nail shank and the overall rolling,use Deform-3D numerical simulation software and orthogonal experiments to conduct experimental design and complete numerical simulation calculations for the process parameters that have not been optimized and analyzed in the forward direction.The effects of process parameters such as tooth fillet and chamfer,rolling speed,and each pressing angle on the fracture groove width,die wear,die radial load and workpiece temperature rise in the rolling process were simulated and analyzed.And through the range analysis of variance,get the significant conclusion of the influence of each factor on each index.Finally,the optimal combination of process parameters for nail shank rolling is as follows: the radius of the crest fillet of the fracture groove die is 0.08 mm,the chamfer of the tooth side of the fracture groove die is 95°,the rubbing speed is 150mm/s,and the bite angle Kr1 is 1°,the biting angle Kr3 is0.6°,and the biting angle Kr4 is 0.6°.(3)Carry out heat treatment experiments on rolling nail rods,and use the designed fracture test device to conduct mechanical performance tests and section information analysis.The test results show that after the aging heat treatment,the nail shank presents a fracture mechanism of toughness-brittleness as a whole,and the brittleness accounts for a large proportion,and the cross-section is flat to meet the use requirements.Using SEM technology,the microstructure of the fracture surface of the nail shank was deeply analyzed,and the distribution of the microstructure of the titanium alloy nail shank under different heat treatment conditions was discussed by designing the aging temperature and length control group,revealing the microstructure evolution of the nail shank under different control conditions and the relationship between it and the mechanical properties of the shank was analyzed.Finally,the optimal aging process parameters were obtained as 350°C and 8hours. |
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