| Profiled-shape ring rolling process with a closed die structure on the top and bottom of the driven roll, simplified as PRRCDS, is an advanced plastic forming technology, which can decrease the thickness of the ring wall and increase the diameter of the ring by the motions of driven roll rotating about its fixed axis and the mandrel moving towards the driven roll. PRRCDS process has many advantages in saving energies and materials, increasing productive efficiency, and decreasing noises, etc. And the rolled rings often have good comprehensive mechanical properties. Therefore, it is found a wide application in many fields such as aerospace, wind power, nuclear power, drilling mountain machinery, shipbuilding, etc.Compared with commonly seen rectangular ring rolling process, the metal flowing laws in PRRCDS process are more complex. Up to now, systematic studies on PRRCDS process are rarely reported. There exist many problems in realistic PRRCDS process such as instability of rolling process, lower accuracy and poor mechanical properties of rolled ring, seriously damaged dies caused by large rolling force, etc., which to some extent restrict the applications of PRRCDS process in engineering fields. However, in order to solve the mentioned problems it should understand the metal flowing pattern in rolling process, selecting reasonable mandrel feeding strategy and motions controlling methods of rolls, investigate the effects of forming parameters on rolling process, analyze the mechanical properties of rolled ring, reveal the intrinsic links between the mechanical properties and microstructure of rolled ring. Therefore, it is necessary to investigate the modeling methods of PRRCDS process, the feeding strategy that can realize a stable PRRCDS process, and optimal design of forming parameters, etc., reveal the metal deformation mechanisms in rolling process, realize a stable rolling process, optimize the rolling technologies, improve the product performance, provide theoretical guidelines for realistic PRRCDS process.Aiming to investigate typical PRRCDS processes (inner L-shape ring rolling process and conical ring rolling process), the numerical simulation and experimental methods are adopted; the mathematical models for inner L-shape ring rolling process and conical ring rolling process are established, respectively; the feeding strategy that can realize a constant growth rate of ring’s outer radius is proposed; the motions controlling equations of rolls are deduced; the plastic penetration condition and biting-in condition are determined in rolling process; the reasonable value ranges of mandrel feed rate are obtained. Based on this, the FE models of inner L-shape ring rolling process and conical ring rolling process are established, respectively; the changing laws of the equivalent plastic strain and temperature of rolled ring with rolling time are obtained, the effects of the initial temperature of blank, rotational speed of driven roll, mandrel feed rate, radius of driven roll, radius of mandrel, etc. on the changing laws of the equivalent plastic strain and temperature of rolled ring, average rolling force and rolling moment are investigated; a certain inner L-shape ring rolling process is carried out; the intrinsic links between the macro metal streamline and the microstructure of rolled ring are revealed by uniaxial tensile tests at room temperature, impact toughness test at low temperature, SEM and EBSD analysis, etc.; the numerical simulation results of rolled ring are compared with experimental ones; the established FE model of inner L-shape ring rolling process is verified; the metal flowing laws in rolling process is revealed. The main contents and conclusions in this paper are as follows:(1) The mathematical model for inner L-shaped ring rolling process is established, a constant growth rate of ring’s outer radius feeding strategy is proposed to realize a stable inner L-shaped ring rolling process; the motion controlling equations of rolls are deduced; the plastic penetration condition and biting-in condition in rolling process are deduced; the reasonable value ranges for mandrel feed rate is determined; the coupled thermal-mechanical three dimensional finite element model for inner L-shaped ring rolling process is established based on ABAQUS software and then experimentally verified; the equivalent plastic strain, temperature, and equivalent stress distributions of rolled ring are obtained, the changing laws of rolling force and rolling moment with rolling time are analyzed. This study can provide guidelines about the selection of mandrel feed rate in inner L-shaped ring rolling process.(2) Based on the established coupled thermal-mechanical three dimensional finite element model for inner L-shaped ring rolling process, the effects of the initial temperature of ring blank, the rotational speed of the driven roll, the mandrel feed rate, rolls sizes, etc. on the equivalent plastic strain and temperature distributions of rolled rings, and on the rolling force and rolling moment are systematically "studied; the influence rules of forming parameters on the deformation of the ring are revealed; the optimal values of the forming parameters are obtained. This research can lay the foundation for the selection of forming parameters in inner L-shaped ring rolling process.(3) The uniaxial tensile tests at room temperature, impact toughness4 test at low temperature, SEM and EBSD analysis for fracture morphology and microstructure, etc. are carried out to investigate the mechanical properties of rolled ring. The influencing mechanisms that lead to the tensile fracture and ductile fracture at low temperature are revealed, respectively; the changing laws of microstructure such as grain sizes, grain sizes distributions, grain orientations, texture densities, etc. along radial direction(RD), tangential direction(TD), and axial direction(AD), respectively, between the upsetting blank and the rolled ring are analyzed and discussed; the intrinsic links between the macro metal streamline and the microstructure of rolled ring are revealed.(4) The mathematical model for conical ring rolling process is established; a constant growth rate of ring’s outer radius feeding strategy is proposed to realize a stable conical ring rolling process; the plastic penetration condition and biting-in condition in rolling process are deduced; the reasonable value ranges for mandrel feed rate is determined; the coupled thermal-mechanical three dimensional finite element model for conical ring rolling process is established based on ABAQUS software and then verified experimentally; the equivalent plastic strain, temperature, and equivalent stress distributions of rolled ring are obtained; the changing laws of rolling force and rolling moment with rolling time are analyzed. This study can provide guidelines in theory for the selection of mandrel feed rate in conical ring rolling process.(5) Based on the established coupled thermal-mechanical three dimensional finite element model for conical ring rolling process, the effects of mass scaling factor, time scaling factor and remeshing elements times per increment on the simulation time and the volumetric loss of rolled ring are systematically investigated; the effects of the initial temperature of ring blank, the rotational speed of the driven roll, the mandrel feed rate, rolls sizes, etc. on the equivalent plastic strain and temperature distributions of rolled rings, and on the average rolling force and rolling moment are systematically studied; the influence rules of forming parameters on the deformation of rolled ring are revealed; the optimal values of the forming parameters are obtained. |
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