Research On The Microstructural Prediction And Evolution Laws Of Helical Gear During Hot Precision Forging Process

Helical gear is widely used in the automotive,energy,aerospace,heavy industry and other industries because of its well-known advantages of smooth transmission,low noise and good bearing capacity and transmission performance.The traditional metal cutting methods of gear parts have some disadvantages,severe waste of materials and energy consumption,and the most important is the metal flow lines are cut through and no longer parallel to the external surface,thus there is a strong demand for high performance gear.However,the hot precision forging technology of helical gear is favored by more and more scholars and enterprises because of its well-known advantages compared with conventional cutting methods,such as high material utilization ratio and productivity,low production cost and the excellent mechanical properties.Microstructural structure will be improved during hot deformation process,which significant affects the properties of the formed parts.Thus,it is meaningful to study the microstructural evolution laws of helical gear during hot forming process and establish the control method of microstructure and properties,which can be used to optimize the hot forging forming process and form the helical gear forgings with refined and uniform microstructures and good mechanical properties.Firstly,with the requirement of the research on hot workability characteristics and the optimization of processing parameters of 20 CrMnTiH steel,the hot processing maps were established under various processing conditions,and the"safety” zone and "instability" zone of processing parameters of the hot deformation process were obtained.In combination with microstructural observation under optical microscope and scanning electron microscopy,the optimized hot processing window with refined and uniform recrystallized microstructure were obtained,which verify the reliability of hot working window.Secondly,the hot upsetting finite element models with deformtion-heat transmission-microstructural evolution were established by DEFORM-3D software.The distribution and evolution rules of microstructures under various processing conditions were revealed.The hot upsetting experiments were conducted based on the results of finite element analysis,and observed microstructural distribution of upsetting specimens,the agreement in numerical simulation result corresponding to the experiment process with the experiment data under different processing conditions verify the microstructural finite element model can be used to simulate and predict the evolution law and distribution of microstructure during hot deformation.Then,the deformation-heat transmission-microstructural evolution coupled finite element model of helical gear were established by using DFORM-3D based on the characteristics of hot precision forging technology,the microstructural behaviors of helical gear during hot forging forming process with various aspect ratio cylindrical billet and preheating temperature were analyzed,the microstructural evolution and distribution laws were obtained of the tooth region,and the influence mechanism of various aspect ratio and preheating temperature on microstructural evolution were reaveled.Finally,combined with the response surface method and the finite element simulation technology,the response surface prediction model were established between the forming process parameters and the microstructure of the tooth area,and the effect laws of significant processing parameters and its interaction on the microstructural evolution were revealed,then the optimized combination of processing parameter with full DRX and uniform and fine recrystallized microstructures were obtained by controlling the microstructure of the tooth area based the response surface method,which provide the theoretical and technical basis for hot forging forming helical gear of 20 CrMnTiH steel.