Research On Forming Mechanism Of Multi-Pass Conventional Spinning Process And Influence Of Roller-trace On The Process

Multi-pass conventional spinning, used as an advanced plastic forming technology, has been widely applied to many fields , such as Aeronautics, Astronautics and Weaponry, etc. However, forming mechanism of multi-pass conventional spinning is complex, and especially the roller-trace has an important influence on spinning forming law, forming quality and processing efficiency. Up to now, the research on forming theory of multi-pass conventional spinning and the influence of roller-trace lags behind obviously, and the selection of roller-trace still depends on trial-and-error. Considering the above, a systematical and thorough investigation into forming mechanism of multi-pass conventional spinning process and influence of roller-trace on the forming process has been carried out using the FEM numerical simulation in combination with theoretical analysis and experiment in this dissertation. The main achievements of the project are as following:According to the forming feature of multi-pass conventional spinning process, a reasonable mechanical model of multi-pass conventional spinning is established, and the key techniques are studied systemically and thoroughly and solved effectively, including continuous loading, material hardening, boundary condition, remesh, etc. And then based on elasto-plastic FEM theory, a multi-pass conventional spinning FEM simulation system (abbr. MPCS) is developed, which is suitable for the FEM simulation of multi-pass conventional spinning, and which has advantages of friendly GUI, perfect function, better pertinency, rapid computation and running credibility, etc.The forming mechanism is studied systematically for multi-pass conventional spinning under three loading modes including spinning of not profiling and one-way moving of roller, profiling and one-way moving of roller and two-way moving ofroller by using the MPCS system developed, then mesh deformation and distribution of stress and strain of the blank are obtained. The results show: (1) materials with different hardening exponent have little effects on the trend of distribution of stress and strain during multi-process conventional spinning, and deformation of materials with large hardening exponent is uniform relatively. (2) The deformation in linear zones under three modes are similar. Therein, the strain in the thickness direction of the blank in close mandrel area under profiling and one-way moving of roller is great, and the deformation of this area is severe; the blank deformation under two-way moving of roller is the most homogeneous, but work-hardening phenomenon of the blank is heavy. (3) The deformation of the outer zone contacting with roller is larger; the blank just adjacent to roller deforms under each feed of roller , and suffers the tensible stress in the inner and the compressive stress in the outer along the radial direction, and suffers compressive stress in the circumferential direction. (4) With the increase in the pass number, the stress and strain of deforming blank become large.With the MPCS system developed, the influence of the curvature radius of roller-trace on the maximal radial stress, the maximal circumferential stress and the maximal strain along the thickness direction is researched throughly, thus it shows the influence of the curvature radius of roller-trace on forming of multi-pass conventional spinning. The results are as the following: (1) the effect of the curvature radius of roller-trace on the maximal stress and strain are almost identical for the blanks with different diameter and different thickness, that is, the maximal stress and strain increases with an increase in the curvature radius of roller-trace; but the curvature radius of roller-trace has little effect on the maximal stress and strain after the curvature radius exceeds some value; and the stress and strain under a straight line mode are the largest. And the maximal stress and strain increases with an increase in the blank diameter. (2) With an increase in the entry tangential angle of roller, the influence of the curvature radius of roller-trace on the maximal stress and strain becomes more obviously. (3) The curvature radius of roller-trace has a greater effect on the maximal stress and strain with the increase in the pass number.The concept of relative curvature radius of roller-trace has been put forward. Then the effect of relative curvature radius on the maximal radial stress, the maximal circumferential stress and the maximal strain along the thickness direction is investigated thoroughly using the MPCS system developed. For the purpose of decreasing the inhomogeneous deformation degree, research on determiningroller-trace during multi-process conventional spinning processing is carried out, then the foundation of the reasonable selection of roller-trace is obtained. And a method of determination of relative curvature radius of roller-trace according to different deforming zones is proposed. The results are as the following: (1) when the entry tangential angle of roller is smaller, the relative curvature radius should be selected in a smaller value, but it should be increased gradually from inner to outer. (2) If the entry tangential angle is larger, 1.5-2 may be feasible relative radius curvature for the deformation area near mandrel filleting; about 1.5 is suitable for middle deformation area; relative curvature radius of roller-trace for the edge deformation area should be just larger than that of middle one. (3) The relative curvature radius of roller-trace increases with an increase in the pass number based on (1) and (2). And the above results can serve as a significant guide to improving the spinning quality by computer numerical control of roller-trace.