Research On Cold Extrusion Forming Process And Forming Quality Of Internal Thread

Cold-extruded internal threads have the advantages of good surface quality,high strength and good fatigue resistance,and are currently used in aerospace,oil drilling,ship transportation and other fields.However,China’s research on internal thread cold extrusion process still lags behind developed countries,and the research progress is slightly behind.In this paper,the cold extrusion forming mechanism of internal thread is studied,the influence of process parameters on the extrusion process is obtained through numerical simulation,the extrusion process parameters are optimized,and the forming quality and mechanical properties of cold extrusion internal thread are analyzed.The specific research content and results of this paper are as follows:（1）The forming process of cold extrusion internal thread and the deformation mechanism of metal are analyzed.The parametric equation of the section profile of the extrusion tap is derived by using the envelope method.Combined with the structural parameters of the extrusion tap and the performance parameters of the metal itself,the theoretical calculation methods of the extrusion angle,extrusion torque and prefabricated bottom hole diameter are deduced.（2）The geometric model of extrusion tap and the finite element model of cold extrusion of internal thread are established.Through the numerical simulation of the cold extrusion process of the internal thread,the influences of the diameter of the prefabricated bottom hole,the extrusion speed and the friction coefficient on the extrusion torque,extrusion temperature and thread height ratio of the internal thread are analyzed.The variation law of the load in three directions of the extrusion tap and the distribution of extrusion stress during the extrusion process were studied.The metal deformation,flow direction and flow velocity of the crest,flank and root of the female thread were obtained by tracking data at different positions in the flank area of the female thread.（3）The process parameters of internal thread cold extrusion were optimized by orthogonal test,and the significant effects of prefabricated bottom hole diameter,extrusion speed and friction coefficient on extrusion torque and extrusion temperature were obtained,and the combination of process parameters was optimized.The extrusion torque and extrusion temperature are effectively reduced,and the forming quality of the internal thread is improved.The GA-BP neural network prediction model is constructed to predict the extrusion torque,extrusion temperature and tooth height rate,which has higher prediction accuracy than the traditional BP neural network.（4）The hardness of cold extruded internal thread and cut internal thread was compared by microhardness measurement,and the forming quality of extruded internal thread and cut internal thread was observed and compared.The difference of the metallographic structure before and after the metal was extruded was obtained through the observation of the metallographic structure,and the reasons for the formation of the hardened layer were analyzed.The failure loads of the extruded internal thread and the cut internal thread under axial tension were compared,and the influence law of the tooth height ratio on the failure load was obtained.