Study On The Key Technologies Of Tank Body Forming For Railway Tank Cars

The structure parts of tank body for railway tank car are the key load bearing components, the quality of manufacturing of the parts directly affects the running safety and reliability of the tank car. The heads and shell sections are the two main impoertant parts of the tank. The manufacturing of the tank body mainly includes the plastic forming process such as the head stamping and shell section rolling, and the welding process in blank preparation and tank body assembly. Because of the large size and thickness of the tank body, the traditional manufacturing crafts that according to the experience and experiments are adopted for the forming of the heads and shell sections, and tank body welding. The traditional process leads to the high cost and inefficiency of the prduct development. And the tank body defects and the influence on operation safty can not been forecast and controlled using the traditional crafts. Therefore, it is very necessary to apply the advanced research methods to tank body manufacturing process. Based on the theoretic analysis of tank body forming, a systematical and profound study on tank body manufacturing process is undertaken using the combine method of the finite element simulations and experiments. The main research contents and conclusions are listed as follows.(1) The material properties of Q345R that used for tank body were studied. The Q345R is the material commonly used for tank car body and also is the special steel for pressure vessel. The experiments including tension test, bending test and impact test were implemented for the material property of Q345R. The experiments indicated that the Q345R material has good stamping formability.(2) The contrast experiments were implemented to study the stamping process for the ellipsoidal heads of tank car. Because of the large profile dimension and large thickness, it has some difficulties on the stamping process of tank body heads. In order to ensure the heads stamping quality, the forming experiments include cold stamping process, hot stamping process and spinning process were implemented. The experiments indicated that the heads can be conveniently formed with the hot stamping process, but the heads shape changed greatly after stamping, and heating equipment were needed for this process. The experiment also showed that the heads which formed with spinning process had poor surface quality and formed inefficiently. Thus the spinning process is only suitable to trial-producing of single head. The heads formed with cold stamping process had good dimensional stability and excellent product quality, but the stamping load was higher. The experiments and analysis indicated that cold stamping process can assure the quality and safety of the tank car, therefore, the cold stamping process was applied to heads stamping.(3) The cold stamping process of ellipsoidal heads was simulated with the finite element method. The spring-back of ellipsoid surface and crinkles are the main forming defects during the large heads drawing processing. While the draw-bead is the important and effective technical measures to avoid the forming defects. Thus the round draw-bead and rectangular draw-bead were designed based on the shape of the ellipsoidal heads, and the simulations were carried out for this drawing process. Then these simulation results were compared with the simulation results of no bead stamping process, which indicated that the rectangular draw-bead can effectively assure the stamping quality of the heads.(4) The main process parameters of drawing forming have great influence on the heads stamping process. The influences of process parameters have been studied. The process parameters consist of frictional coefficient, blank holding force, clearance between punch and die, and so on. The process parameters should ensure product quality and reduce forging equipment and energy usage. The study shows that the blank holding force and the clearance have significant effect on product quality. The small clearance can cause the forming load rising up rapidly, while the defects of wrinkles and blowups do not appear. The small blank holder force can cause wrinkles appearing and the forming load rising up rapidly because the material can not flow easily. According to the study results, the reasonable blank holding force and the clearance have been drafted for heads stamping.(5) The shell sections rolling process have been analyzed by using the numerical simulation method. The incremental forming process of the shell sections rolling was studied using the finite element method. The study shows that the frictional coefficient has great effect on the shell section rolling process.(6) The wear analysis of the drawing die was conducted. The wear at the die surface, especially at the little round surface is the main factor affecting the tools life. The stresses and the wear of tools were analyzed. The study indicates that the reasonable process parameters can prolong tools’life and reduce the product processing cost.(7) The welding process of tank body manufacturing was analyzed. The welding process during the tank body manufacturing includes the butt welding of thick blank plate, the butt welding of shell sections after rolling and the butt welding between shell sections and heads. The butt welding of heads blank, especially welding residual stresses directly affect the subsequent stamping process. The butt welding of shell sections after rolling also has some effects on its’adjustment process. Hence, the welding process was analyzed with numerical simulation technology. The study indicates that the high residual stress zone is distributed at the weld metal zone and the residual stress can be reduced by the aging treatment and annealing. The high welding residual stress of tank body assembly is also distributed at the weld metal zone and which has some influence on the distortion after welding. Therefore, the reasonable welding sequence could be drafted to reduce the welding residual stress and distortion.