Papers by Author: Mei Zhan

Abstract: With the requirement of aviation and aerospace fields for high-strength Ti-3Al-2.5V titanium alloy bent tubes with high-performance, it is great significance to research the plastic deformation of Ti-3Al-2.5V tubes under compression to obtain desired flow stress curves. A finite element (FE) model of axial compression of Ti-3Al-2.5V tubes was established in this study. Using this model, deformation behaviors of Φ12 mm × t0.9 mm Ti-3Al-2.5V tubes with different ratios of thickness to height (t/h) compressed under different frictions were analyzed. It is shown that the non-uniform deformation degree of the tubes increases with the decrease of t/h and the increase of friction coefficient. This means that a large t/h value and small friction can help to attain a uniaxial compression condition to obtain desired flow stress curves. Such compression conditions for the Φ12 mm × t0.9 mm Ti-3Al-2.5V tube is that, t/h is not less than 0.6 and the friction coefficient is not greater than 0.05

Abstract: In order to improve the limits of wall thickness reduction of 30CrMnSiA steel in process of spinning, realize multi-pass continuous spinning process, and furthermore improve the forming efficiency and shape accuracy of thin-walled shell of 30CrMnSiA steel in spinning process, the influence of traditional annealing and austenization plus spheroidal annealing on the structure performance of 30CrMnSiA steel and the spun performance of 30CrMnSiA steel are studied. Process parameters of traditional anneal and austenize plus spheroidal annealing are optimized to obtain higher plastic performance and lower ratio of yield strength to tensile strength. Spinning experiments of the workpieces that have been heattreated by the optimized traditional annealing process and austenization plus spheroidal process are completed. The result shows that the optimized austenization plus spheroidal annealing is beneficial to achieve a large thinning rate for flow spinning process, and can meet the demands of low cost and high efficiency of batch production.

Abstract: The significant die unfittingness and springback, occuring during the numerically controlled (NC) bending process of large diameter thin-walled CT20 titanium alloy tube, has an obvious influence on the shape and the geometrical precision of the bent tube, furthermore on the assembly precision and the sealing capability. The changing rules of die fittingness and springback of large diameter thin-walled CT20 titanium alloy tube under different bending parameters were investigated and the mechanism was analysed using finite element method (FEM) in this paper. The result shows that the springback of large diameter thin-walled CT20 titanium alloy tube is more significant than that of aluminum alloy and stainless steel tubes with the same specification. The die fittingness has a connection with the tangent compressive stress on the intrados of the tube before springback, the larger the tangent compressive stress, the worse is the die fittingness.The results may provide a significant guide to the control of bending radius and bending angle for large diameter thin-walled titanium alloy tube NC bending.

Abstract: This study introduces the current states and progress of the overseas digitization manufacture technology of airplane ducts, and analyzes the problems about manufacture technology of bent tubes in airplane production in China. Thus, instead of the full pattern, the three-dimensional models are proposed to conduct the NC(Numerical Controling) bending and examine the bending quality, and the integrated digitization manufacture technology of airplane ducts is developed. The key problems are solved including standardization modeling of ducts, 3D data transfering, virtual processing analysis, digital modular fixture design/manufacturing, and NC bending/manufacturing/inspection of ducts. The technology has been successfully applied into the digital forming manufacturing of airplan ducts.

Abstract: In order to disclose the mechanism of the mandrel on the thickness and profile of shear spun parts, the spinning processes with a mandrel or not were analyzed, and the distribution and variation of strain and stress were also investigated by experiment and finite element method. The results show that the thickness without mandrel is larger than that with mandrel on the whole. From bottom to top of spun part, the thickness with mandrel decreases gradually, while that without mandrel decreases at first and then increases. The linearity of part spun with mandrel is better than that without mandrel, but the tendency of the flange keeping backward and wrinkling of the former is larger than that of the latter. There is little difference in shear strain between parts with mandrel and mandrelless. In the midst and final stage, radial tensile strain and axial compression strain of part spun with mandrel increase sharply, while radial tensile strain without mandrel increases a little. So the wall of part spun with mandrel is thinner than that without mandrel. It’s feasible to spin without mandrel for the part with a thicker wall at opening end and no high demand for the linearity, or the linearity of the part can be improved by subsequent spinning.

Abstract: In this paper, a reasonable 3D FE model for power spinning of ellipsoidal heads with variable thickness has been established under ABAQUS/Explicit and validated. Then the variation of stress, strain and wall thickness during the process are obtained. Furthermore, the influence of the springback on stress, strain and wall thickness are gained with ABAQUS/Standard. The results show the following: (1) In the beginning, large stress, large strain and the thinning zone of wall thickness localize at the small contact zone below the roller; Then the zone extends into a ring and moves towards the position behind the roller; In the end, the ring transfers to the contact zone below the roller again and becomes uneven. The thinning zone is gradually impelled along the generatrix direction, and wall thickness is getting smaller and smaller. (2) The distribution of stress becomes more even after the springback, while the springback has little effect on the distribution of strain and wall thickness.

Abstract: The advent of high-strength and high-precision thin-walled parts with inner ribs adapts to the increasing demand of aerospace industry, astronautics industry, military industry, and so on. For a new metal forming technology, how to determine the reasonable blank is a key problem required solved firstly in the research of power spinning process of parts with transverse inner rib. In this paper, based on the platform ABAQUS/Explicit, a reasonable 3D FE model for power spinning of parts with transverse inner rib has been established, the power spinning process of parts with transverse inner rib has been simulated under conditions of four typical blanks and the reasonable blanks for different forming processes have been obtained. The results show the following:(1) Blank with equal half-cone angle is the best selection to deform workpiece with proper height rib; (2) while for the workpiece with excessive height rib which exceed the forming limit, blank with rib is the exclusive selection, although it is difficult to be prepared comparing with non-rib blank.

Abstract: Based on the 3D FE model of conventional spinning, the influence of curvature radius of roller-trace on the conventional spinning process has been studied. It is found that when the curvature radius of roller-trace is smaller, the maximum of thinning rate and hoop compressive stress increases dramatically with the increasing of the radius, and curvature radius does little effect on the forming process when it is up to a critical value. To obtain a more reasonable selection criterion of curvature radius of roller-trace, a new index named flange width has been put forward， which represents the comprehensive effect of workpiece diameter and mandrel diameter in the forming process of conventional spinning. Further research has been done and the selection criterion of curvature radius is obtained: the smaller the flange width is or the larger the workpiece thickness or the entry tangential angle is, the larger the range of reasonable curvature radius is.

Abstract: Cone spinning is an advanced but complex metal forming process under coupled effects of multi-factors. Understanding the deformation mechanism, i.e., the stresses, strains, and metal flow in the deformation zone during the process is of great significance for optimizing the spinning process and controlling the product quality. In this paper, based on ABAQUS/Explicit, a reasonable FEM model for cone spinning with a single roller has been established, and the features of stress, strain and wall thickness during the process have been obtained. The results show the following: (1) In the beginning, large stress, large strain and the acute thinning of wall thickness localize at the small region below the roller, then the region extends into a small ring, further it becomes a large ring, and finally the ring will become uneven if the wrinkling occurs in the flange. (2) After spinning, the acute thinning region locates at the midst of the wall near the bottom of the workpiece. (3) At earlier stage of cone spinning, as a result of the acute thinning of wall thickness in the wall zone, the unevenness of wall thickness increases sharply to a value, then it almost keeps the value at the stable stage, and finally it will slowly increase again if the wrinkling appears in the flange. The results are helpful for determination and optimization of process parameters of cone spinning.

Abstract: A simple and efficient method has been proposed in order to determine the dynamic speed boundary condition caused by the guide rolls for developing the 3D-FE model of cold ring rolling process rapidly. The concept of the motion track of guide rolls has been put forward firstly and an optimal motion track and track type are given by simulation. Meanwhile, an effect of the guide rolls on the ring tilting and ring circularity was simulated and analyzed. The result shows that the simulation results are in good agreement with experiment results from the literature.