Integrated Virtual 3-Dimensional Fem Simulation System With Coupled Thermomechanical For Stretch Reducing Process Of Tube

Approximately 50 million tons of steel tube and pipe products are consumed in the world annually. Development of the innovative tube processing technology has always been one of the key focuses in the steel industry in the world. Due to the complex of metal flow during tube reducing process, it's difficult to control the process of metal flow in a precise fashion. Without accurate and systematic studies, roll profile and process parameters have to be designed through trial and error approach in the practical operation of tube making. As the results, the high production cost and long lead-time are common and it's difficult to develop the new products and so on. It shows the important significance both in developing theory and in improving practical operation to study deformation mechanism, temperature profile and microstructural evolution during tube stretch reducing process systematically. The research works in this dissertation are based on above considerations. A novel 3-dimensional rigid-plastic finite-element program with coupled thermal, deformation and microstructural evolution analysis was developed for simulation of tube stretch reducing and sinking processes. The model for the description of complex curvature of the roll profile and the model for the obliquely constraint boundary were introduced, and the criterion for the contact between roll and tube surface was established. The coupled thermal-mechanical models for the continuous tube stretch-reducing process were developed. The thermal-mechanical coupled simulation of the continuous tube stretch-reducing process was carried out.The stretch-reducing process is considered as the combination of series of single stands with deformation zone and heat transfer zone. By applying Eulerian method, the continuous rolling model on the single pass is established. A finite-element analysis model of the stretch reducing for two rolls and three rolls are constituted. The subroutines of the symmetry model and asymmetry model are developed for saving computer system resources. The microstructural evolution model of the material during hot forming process is introduced into the finite element program to simulate the microstructural evolution during tube reducing process. Through the study of tension distribution using the stretch reducing mill model developed, the author found that the tension distribution is highly dependent on the hardening and softening behaviors of the material in the continuous rolling process. A process design system for tube reducing process has been developed to determine the roll speeds and tension coefficients at individual rolling stands. In the simulation, the changes of the tension force and its distribution through the iteration in the program can be automatically updated without the needs of making assumptions on material behaviors ahead of the time. Based on the OPENGL graphic standard, and Visual Basic programming language, the integrated virtual simulation system including an user friendly graphics interface and a rigid-plastic finite-element analysis program with coupled thermal-mechanical and microstructural evolution analysis has been developed. The system has been employed to simulate the actual tube stretch reducing processes at different tube mills. Comparison of the simulation results from the integrated virtual simulation system and the measurements from the production samples at the steel tube mills shows good agreements. The system developed has been in use at Timken Company daily for the improvement of tube reducing mill rolling processes.The work in the dissertation has built the solid foundation for the further development of the virtual production system that covers the all of in tube making processes. The integrated system introduced in the dissertation can be extended to simulate the bar rolling processes and the structural section steel rolling processes.