Research On Precision Forming Of Large-size, High-strength And High-fatigue-resistant Fasteners For High-speed Trains

Hexagon head bolts are widely used in the connection of high-speed train brake discs,which need to meet high-strength performance requirements,conventional experience processing solutions are prone to quality defects such as cracks and folding during processing,and it is difficult to meet their quality requirements,therefore,designing and optimizing the processing scheme and process parameters is of great significance to improve the qualification rate of the hexagonal head bolt forming process.In this paper,A286 superalloy hexagon head bolt for brake disc of high-speed train produced by a manufacturer is taken as the research object,and its forming scheme,processing technology and other contents are studied,the work completed and the results obtained are as follows:?1?The forming scheme of A286 superalloy hexagon head bolt was studied.According to the structural characteristics and quality requirements of the bolt and the material characteristics of A286 superalloy,the precision forming process of hexagon head bolt is analyzed and studied,and the forming scheme of the bolt is designed,it is determined that the head is processed by the hot upsetting process and the thread is processed by the cold rolling process.?2?Optimal design of hot upsetting process parameters for the head of hexagon head bolts.The hot upsetting process parameters have a great influence on the quality of the head,the study selected DEFORM-3D software,combined with metal forming theory and finite element analysis method,to conduct a numerical simulation analysis of the hot upsetting process of the hexagon head bolt head,and studied the possible quality defects in the hot upsetting process;in this paper,the influence of three process parameters,namely heating temperature,upsetting speed and friction coefficient,on the four target parameters,namely,equivalent stress,equivalent strain,damage value and forming load,is discussed by means of orthogonal test and numerical simulation;based on the analysis of the results of the orthogonal test by the maximum range method,the multi-objective optimization of the process parameters of the hot upsetting is completed,the optimal processing parameters are obtained as follows:heating temperature 1050?,hot upsetting speed60mm·s^-1,friction coefficient 0.3.The analysis of the numerical simulation results before and after optimization shows that each target parameter has been improved,the optimized hot upsetting process parameter combination is used for production test,the results show that the bolt head has a good molding effect and meets the quality requirements of the process.?3?Design of cold rolling forming process for the thread of hexagon head bolts.The thread cold rolling forming process is complicated and has many process parameters,the research has analyzed the cold rolling process of the thread of the hexagon head bolt through theoretical analysis and combined with the actual production,calculated the blank diameter of the thread cold rolling process,and proposed two adjustment methods for the installation of the rolling wheel,the axial movement method and the counterclockwise rotation method,the cold rolling processing scheme of thread with 80k N rolling pressure,32r/min spindle speed,0.05mm/r rolling feed rate and 0.693mm/s radial feed rate of the rolling wheel is determined,the sum of the final thread finishing time and thread forming time is 1.43s.It can be known from the test verification that the quality of the thread rolled according to this processing scheme meets the requirements.?4?Test verification and analysis.According to the technological plan and processing parameters obtained from the study,A286 superalloy hexagon head bolts were tested and produced,and the test pieces were subjected to the appearance and size verification,metallographic structure test and mechanical property test and analysis.The results show that the quality test results of the test pieces all meet the product design standards,it shows that the design of the processing scheme and process parameters in this paper is reasonable,and it solves the key technical problems of the research and development of the precision forming process of A286 superalloy hexagon head bolts,the research results have important theoretical significance and practical application value.