With the enlargement of the application field and the increase of the quality requirement of the copper tubes, it is of great significance to research the rolling process of the copper tubes. The continuous casting & planetary rolling method is an advanced technology for the manufacture of the copper tubes, and three-roll planetary rolling is the key process in this method. Three-roll planetary rolling is a one-pass rolling process with large deformation. In this process, the temperature rises quickly and the microstructure evolves sharply, so the deformation field, the temperature field and the microstructure field should be studied systematically and entirely. The systematic research has important value in theoretical investigation and practical applications. The entire deformation process of copper tubes on three-roll planetary rolling was researched systematically and thoroughly in this dissertation.
This dissertation builds the kinematic models of the three-roll planetary rolling firstly. It gives the theoretical derivation about the coordinate transformation of the structure, the modelling and the locating of the roller. The equation of meshing was used to calculate the contact profile between the rollers and the tube billet. The calculation method of the velocity of the contact profile was built. Based on these results, the parameterization design and FE modelling software for the three-roll planetary rolling was developed. This software provides the basic model for engineering design, theoretical calculation and simulation analysis.
To ensure the accuracy of the finite element simulation of three-roll planetary rolling, the material mechanical properties, the physical parameters and the coefficient of contact heat transfer were measured and analyzed. The constitutive equations of plastic deformation during high temperature were built, which provided the accurate material parameters for FE simulation. The methods to deal with the key problems in FE modelling of three-roll planetary rolling were proposed, and the simulation analysis for three-roll planetary rolling was realized.
The characteristics of three-roll planetary rolling such as the quick deformation rate, large deformation and rapid rising of temperature of the tube billet were fully analyzed. The calculation methods of internal heat resources were put forward, which included the plastic deformation heat and the friction heat, and the reasonable heat boundary models were given. Then a temperature forecast theoretical system of the rolling was built. With the coupled simulation analysis of the temperature and the large deformation, heat accumulation in the contact zone can be clearly revealed. At the same time, the friction heat accumulation leads to a rapid temperature rise and the copper billet temperature rises rapidly in a short time. The temperature analysis provides a theoretical basis for the accurate prediction about the deformation behavior and the microstructure evolution.
The characteristics of the rolling process were analyzed and summarized emphatically. Bases on the analysis of simulation, the deformation rule of triangular effect in the cross-section of the billet was revealed, which can be described as: the shape of the cross-section was from the original circle shape to triangle-like shape as the deformation proceeds，then turns to a circle shape again finally. Artificial neural network was used to predict the rolling force, a new forecast method of rolling force was established, and then the software which can calculate and analysis the rolling force was developed.
Based on the simulation results and the experimental analysis, the evolution rules of the microstructure of copper tube billet were acquired, and the mathematical models concerning dynamical recrystallization and grain growth during three-roll planetary rolling were established and integrated into the finite element software--MSC.Marc by secondary programming. Microstructure evolution during rolling process can be well predicted. The simulation results of microstructure were also analyzed and predicted by artificial neural network method, and the processing parameters were optimized. The results obtained by the metallographic observation proved the evolutional models of the microstructure simulation of copper tube billet. The simulation results of the microstructure show agreement with the experimental results, which are verified by the measurements of hardness and the velocity field of the rolled tube. The practical observations prove the important value of the microstructure simulation prediction in improving the properties of copper tubes.
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