Deformation Mechanisms And Optimization Of Processing Parameters Of Cold Rotary Forging Of Bevel Gears

Bevel gears,as an indispensable element for momentum transfer between intersection axes, have been widely applied in aeronautical and astronautical, automotive, mechanical, marine and chemical industries owing to their high contact ratio, smooth transmission and excellent carrying capacity. Utilizing cold rotary forging (CRF) for fabrication of bevel gears is an innovative metal plastic precision forming technology, in comparison with the conventional forging technology, with the predominant advantages such as minimum material waste, high dimensional accuracy, lower level of noise and vibration, good surface finish, better mechanical properties of products. However, it is also a cpmplex incremental metal forming process under coupled effects of multi-factors. Additionally, in consideration of the non-linear features of geometrical model, material model and contact conditions integrated in CRF, it is difficult for the experimental and analytical methods to obtain the material flow characteristics and interior field variable distributions. Therefore, finite element (FE) based numerical simulation is an effective tool to investigate this complicated metal forming processes.In this paper,20CrMnTi alloy after isothermal spheroidization is taken as investigating material of bevel gears, and its material properties including basic mechanical properties and stress-strain constitutive equation are first determined based on standard tensile tests at room temperature. Furthermore, the friction conditions of 20CrMnTi alloy with different lubricants in bulk forming are determined via a series of ring compression tests coupled with FE simulations. The research results obtained provide the precision material model and the realistic friction boundary conditions for constructing the precision FE model of cold rotary forging of 20CrMnTi alloy bevel gears.The sound 3D rigid-plastic FE models of cold rotary forging of spur bevel gears and spiral bevel gears are established under the DEFORM-3D platform by solving several key modeling techniques such as geometrical and material models, meshing and boundary conditions. Based on the precision FE models, the entire cold rotary forging simulation process of 20CrMnTi alloy bevel gears are actualized. Through a great quantity of numerical simulations, the optimised workpiece geometries are first recommended and then the deformation mechanism of cold rotary forging of bevel gears including the laws of metal flow, the evolution of forming load and the distribution laws of different field-variables are thoroughly revealed.Furthermore, CRF is an extremely complex metal forming process under coupled effects of multi-factors, such as configurations of dies and blank, materials properties, forming process parameters, etc. Among these factors, forming process parameters may be of primary significance because it not only determines the stable forming of CRF but also markedly influence the formability, metal flow, and forming quality individually and synergistically. Consequently, in this paper, aimed at revealing the effect laws of various interrelated process parameters on CRF of complicated bevel gears, the effect laws of four important process parameters, namely rotational speed of the upper die n, feed rate of the lower die v, inclination angle of the upper die y and friction factor between the workpiece and dies m, on the force and power parameters, die filling and damage factor, all of which are able to well represent the formability, metal flow, and forming quality respectively, have been comprehensively explored by employing the foregoing 3D FE models. The research results not only show the importance of controlling and choosing key process parameters and their interactions, but also provide useful guidance on the selection and optimization of process parameters in CRF of bevel gears.