Study On The Metal Flow And Stability Of The Planetary Rolling Process

At present, a planetary mill has been widely used in the processing industry of copper tube with the application and promotion of the cast-rolling method, but the materials and sizes of finished tube are still limited, which is confined to the production of small-diameter thick-wall TP2 copper tube. The reason is that with the increase of tube diameter and the decrease wall thickness, there are some problems in the planetary rolling process such as the twist of rolled-piece, serious triangle effects and collapse of wall due to instability. Based on current market demand, it is very important to develop the planetary mill of large-diameter thin-wall copper tube. The further study of the rolling mechanism of planetary mill and rolling instability situation in the planetary rolling process becomes very important.In this paper, there is the finite element simulation analysis of the planetary rolling process. Then the effect of the rolling process parameters, the coefficient of friction and new forms of roll structure on the rolling planetary rolling process is studied. The spatial location relationship between rollers and rolled-piece is analysized, and on the basis the further study is metal flow process of the planetary rolling process and the rolling force. Respectively, the instability relation of planetary rolling process is studied by the tangential elastoplastic instability, the plastic hinge instability and torsional buckling. The theoretical help is provided in this paper to the design and manufacture of planetary mill. The main contents and achievements are as follows:1) Combining the actual production and experiment data, the 3-D thermal-mechanical coupling simulation model of the three-roll planetary rolling process of copper tube was established by large-scale nonlinear finite element software ABAQUS. The ALE function of Explicit solves mesh distortion in planetary rolling simulation that caused computing termination, which achieve the finite element analysis simulation of the whole process of a rolled-piece from biting to stable rolling.2) According to the simulation results, a detailed analysis about the metal flow velocity of the rolling process, temperature distribution of the rolled-piece and the rolling force were carried out. In addition, based on the simulation analysis the impact of the rolling process parameters, friction conditions of different regions and roller structure on planetary rolling process was studied. This provided a theoretical reference for further study of the mechanism of planetary rolling process.3) On the basis of the conventional defined spatial relationships of three-roll planetary mill, the contact point between rollers and rolled-piece would be found out correctly. Then the feed angle and jarring angle of three-roll planetary mill were redefined, the calculation method of the location of the contact point, rolling radius, roll speed and other parameters were obtained. The rolling raius was compared with the results calculated by finite element simulation to verify the correctness of the amended definition, so there was the foundation for the subsequent calculation of rolling force and sliding coefficient.4) According to the spatial geometry relationship in the three-roll planetary rolling mill, the rolling forces and the rolling velocity of three-roll planetary rolling process were analysised. Thus, the geometry parameters, motion parameters and force parameters of the rolling process could be obtained by using the theoretical calculation method, and a accurate simple engineering application could be provided for the calculation of metal flow and rolling force.5) By adjusting the free distance and deflection angle of the mill, rolling entrances axial velocity and rotation speed, dimensions of the finished roll and pitch would be tested out in case of different hole sizes and different materials. Comparing test results with theoretical calculations, the correctness of the theoretical analysis has been verified. By measuring the deformation of rolling head support ring, the rolling force would be tested indirectly. The error between tested rolling force and finite element simulation results was small, the theory calculation method of the metal flow was proved once again.6) Three different analytical methods including energy method, plastic hinges instability and elastoplastic buckling theory were used to analyze the tangential instability and torsional buckling in three-roll planetary rolling process. Elastoplastic instability of simplified rolled-piece was studied, and rolling instability conditions by different research methods has been obtained. By comparison with the actual situation, the stable rolling conditions of planetary rolling process got by elastoplastic instability theory was much more in line with the actual situation, and could be used in the rolling formulation of a planetary rolling mill.