Research On Crimping And Folding Defects Of Octagonal Bolt Based On DEFORM And Process Optimization

Bolt fasteners,known as "Meters of industry",are widely used in automobile,high-speed train,aircraft,submarine aircraft carrier and other industries.They have a wide variety and different defects in the processing and forming process.The main processing method of domestic bolt products is cold heading,which has high utilization rate of metal materials.The internal metal streamline distribution of the processed bolt products is relatively complete,and has good comprehensive mechanical properties and high fatigue strength.Taking the low-carbon alloy octagonal rod bolt products produced by domestic S standard parts company as the research object,this paper makes an in-depth study on the premature die cracking in the multi station cold heading processing stage,simulates the bolt cold heading processing through finite element simulation,designs and carries out orthogonal experiments,analyzes the influence of cold heading process parameters on bolt processing and forming,and finally optimizes the existing process scheme.The main contents of this paper are as follows:(1)Combined with the metal forming principle and finite element analysis method,the forming simulation of four station cold heading of octagonal rod bolt is carried out through DEFORM simulation platform.Based on the existing product processing scheme,the finite element model of octagonal bar bolt forming is established.By studying the changes of stress and strain,metal streamline and loading force in the forming process of each station,the defect of metal crimping and folding in the step area of bolt head during the final upsetting of octagonal bar bolt is obtained.Through the experimental detection of the product,the real existence of the defect is effectively confirmed.(2)The BP neural network prediction model of bolt cold heading shrinkage is built based on MATLAB.By selecting the process parameters of forming angle a,reduction ratio e,pressing speed v and friction coefficient f as the input eigenvalues and taking the metal accumulation in cold heading as the output value,the forming simulation tests under 64 groups of process schemes are designed,the variation law of metal accumulation in bolt cold heading process is studied,and the prediction model of cold heading process parameters and metal accumulation in bolt forming process is established.(3)The orthogonal experiment of cold upsetting is designed,and the optimization scheme of final upsetting process of octagonal bolt is put forward.By determining the die forming angle a and the reduction ratio ε,The pressing speed v and friction coefficient f are four parameters,and the four factor and four level orthogonal test table is designed L16(44)test,analyze the influence degree of various factors on metal stacking,crimping and folding,and obtain the optimal combination of process parameters.The finite element simulation results show that the crimping and folding problem of octagonal bolt can be eliminated,the metal fluidity is improved,the forming loading force is reduced by 38.6%,and the stress in the cracking area of the upper port of the die is reduced by 40.3%.Finally,through the actual production test,the optimization scheme proposed in this paper is verified,which proves that the metal crimping and folding defect has been solved,and the comprehensive performance of the bolt meets the standard.During mass production,the working life of the die is greatly improved without abnormal damage.