Steel Tube Tension Reducing The Diameter Of The Molding Process Simulation And Optimal Pass

Due to its excellent properties such as high strength and good corrosion resistance, the seamless tube is widely used in many fields. Using stretch reducing technique to produce seamless tube, the irregular distribution of thickness is unavoidable when tubes are produced with big ratio of thickness to diameter. The inner shape of final tube tends to be hexagon. Because of this defect, the finished tube becomes useless, which greatly decreases the market competitiveness and wastes a large mount of resource. With the development of computer technology, it is not only economical but also has practical implications to investigate the defect of irregularity of thickness through simulation. Based on demostic and abroad research findings, FEM was put forward to analyze the irregularity of thickness and a lot of concrete work is performed.According to stretch reducing features, hot tensile tests and hot compression tests were designed to investigate deformation behavior of tube material 12CrMoV. The true stress-strain curve was obtained and performed with regression analysis. So the large deformation viscoelastic-plastic constitutive equation of tube material 12CrMoV for simulation was set up.Concentrated on the specific technique in which the initial tube billet ofΦ137×19.5 mm was rolled to the final dimension ofΦ114×20.0 mm, FE model was established in software LS-DYNA and the tube stretch reducing process was simulated. Simulation results showed good accordance with the actual results by comparing the simulated thickness with the measured results. The inner hexagon extent symbol P in simulation is 0.042, while P is 0.056 for the specimen. This approved the validity of simulation.Simulation results showed:due to the roller pass profile, the inner metal moves from roller top to roller gap and accumulates at the slowest position; At roller gap, the friction force direction is the same of rolling direction, forming axial tensile stress on the surface of roller. While at the roller top, the friction force direction is opposite with rolling direction, forming axial compressive stress. This makes the tension is uneven among circumference. In addition, temperature is unevenly distributed along circumference and the metal moves toward higher temperature region, which add up to the uneven thickness.According to the relationship between temperature and thickness, a new type of roller pass profile was designed to improve the irregularity of thickness. Results from simulation showed:the stress, strain and temperature were more evenly distributed after optimization. The biggest thickness difference is reduced from 0.9 mm to 0.42 mm after optimization and the inner hexagon extent symbol P was reduced from 0.042 to 0.019. This showed the irregularity of thickness got great improvement after optimization.