Numerical Simulation On Hot Spinning Process Of CNG Cylinders

The topic comes from 325, 425 spinning machine R & D projects of a spinning machine factory in Sichuan.Spinning is a forming process during which the hollow billet gets fixed on the basic shaft of the spinning machine, and the spinning roller presses the billet while it rotates with the basic shaft, so that local deformation is induced on the billet. Under the combined effect of the feed movement of the roller and the rotary movement of the blank, the local plastic deformation gradually extends to the entire surface of billet until the desired shape is achieved, when the spinning process is completed. It is an advanced technology with no machining or less, combining of forging, extrusion, tension, bending, ring-rolling and roll-extrusion processes. Spinning technology is a better way to produce the CNG cylinder, in which the defects of traditional welding process on cylinder, such as non-continuous welded seam, lower strength, brittle fracture and tensile stress concentration, can be eliminated, so that the airtightness and pressure resistance of the cylinder are substantially increased, meanwhile, it possesses a number of advantages, such as smaller necessary tonnage of the equipment, lower processing and die cost, wide forming range as well as high-quality products.The material of the CNG cylinders is 34CrMo4, and the stress-strain curves of the material at different temperatures and strain rate was obtained based on the simple tension test, providing reliable basis datum for finite element simulation of the gas cylinders. The paper focuses to research the impact factors of spinning cylinders, such as the shape of the spin roller, the fillet of the roller, temperature, the speed of the spindle, feed rate, etc. In this paper, ABAQUS finite element analysis software was employed to analyze the forming processes, such as bottoming cover, thickening the bottom thickness, and closing in the CNG cylinder, its stress and strain distribution law and trends were obtained, besides, a new structure of bottoming wheel spin, which helps to thicken the bottom thickness, was raised. In addition, contrast of impact on forming between the traditional and the newly developed spinning wheels was made, thereby reliable spinning technology and wheel size were provided for the practical application of technology.