Research On Bulge Of Inhomogeneous Plastic Deformation During Multi-pass Hot Power Backward Spinning Process For 7075 Aluminium Alloy Tube

Large integral high strength aluminum alloy thin-walled tube has been widely used in the areas of aerospace and aviation, because of the high strength, light weight and good corrosion resistance. The multi-pass hot power backward spinning(MHPBS) is one of the main methods for manufacturing this kind of tube. Material undergoes complicated uneven plastic deformation with multi-field, multi-factor coupling interactive effects in MHPBS process. If the process parameters are not controlled properly in the spinning process, it will cause bulge, crack, ovality, etc. and making the forming quality of tube difficult to control. Therefore, inhomogeneous plastic deformation behavior and bulge were studied, which combined numerical simulation mostly with theoretical analysis and experiment, The main results are as follows:1) A 3D-FE model for the MHPBS process of 7075 aluminum alloy tube, which was taken into account realistic and computational efficiency, was built that based on the explicit code ABAQUS/Explicit after solving some key technology problems and its reliability was validated by experiment.2) Based on the finite element model which validated experimentally, the variation characteristics of bulge and inhomogeneous plastic deformation behavior of 7075 aluminum alloy tube were studied systematically during the MHPBS process. The results show that: the highest temperature locates at the spinning zone; there is a temperature gradient in the radial and axial direction, and the internal temperature is slightly higher than the outside; but the internal and external temperature tend to be the same with spinning pass increasing. The maximum equivalent stress appears at the contact position that is between roller and tube, the equivalent stress of radial direction tends to decrease from outside to inner; in the axial direction, the inner wall of tube is affected by pressure stress during formed zone, the materials that locates in front of roller is affected by the tensile stress, and the root of tube is affected by pressure stress; in the tangential direction, the materials under compressive stress appears around the spinning zone and other area is affected by the tensile stress; in the radial direction, the stress of formed zone has bumped along around the zero. The maximum equivalent strain appears at the back of roller, the radial strain and axial strain that locate inner of tube are greater than the outer, the circumferential strain is smaller and the maximum axial strain appears in the root of chamfer. With spinning pass increasing, the bulge appears earlier, and the bulge generally appears in the end of tube and the back of roller, and the bulge is the most serious..3) The influence laws of process parameters on bulge in the MHPBS process were studied, the process parameters include preheating temperature of mandrel, feed speed, rotational speed and friction, the results show that: the bulge’ height decreases firstly and then increases with the increase of the preheating temperature of mandrel. With the feed speed increasing, the bulge’ height increases in second-pass and third-pass process, however, it increases firstly and then decreases in the fourth-pass spinning process. The friction coefficient between rollers and tube affects the bulges’ height slightly in the second-pass and third-pass process, but it has great influence on the bulges’ height during the fourth-pass spinning process. With spinning pass increasing, the friction that bulge’ height is the smallest exists a trend to increase. With the increase of the spindle rotating speed, the bulge’ height don’t change significantly in second-pass and third-pass process, and the bulge’ height increases in the fourth-pass spinning process.