Finite Element Simulation Research Of Thin-walled Steel Tube Rotary-draw Bending Forming Process

The thin-walled tube NC bending technic has been attracting more and moreapplications in aerospace, aviation, automobile and various other high technologyindustries, due to its high forming precision. It has become one of frontier fields inthe research and development of advanced plastic forming technology. However, dueto the tube hollow and thin-walled feature, there usually occurs some defects such asover thinning (cracking), cross-section distortion and wrinkling during the rotarydraw bending, which seriously affect the tube quality. Simple experimental ortheoretical analysis is difficult to accurately and efficiently solve the practicalproblems of rotary draw bending. In this paper, the numerical simulation methodcombining with some experiments was used to study the impact of process parameterson the rotary draw bending forming. The main research contents and results are asfollows:Based on the geometrical parameters of pipes and mold，mandrel parameterswere determined. The basic mechanical properties of the materials were obtainedthrough the uniaxial tensile test. The power exponent hardening models were used todescribe the flow stress behavior of the material. Based on HyperMesh and LS-DYNAsoftware platform, a three-dimensional finite element model for thin-walled tuberotary draw bending forming was established.Use the established thin-walled tube bending finite element model to research thebending process with or without mandrel support, and analyze equivalent stress andstrain distribution. The research find a smaller shift of the stress layer neutral andstrain neutral layer with the supporting of the mandrel pipe, which has a goodinhibitory effect of wrinkling and cross-section distortion, we also deeply analyzedthe variation of compressive deformation zone, and found compression deformationzone mainly lay in the30degree angle of the curved point, and finally the authenticityof the model is verified by experiments.Using FEM simulation and experiments, the effects of materials, formingprocesses, boundary conditions on wall thinning, cross-section distribution andwrinkling during the forming process were systematically studied. It was found thatthe SUS304pipe is much more possible for wrinkling and cross section distortionthan Q235A, but the lateral crack weakened. Ball number is the most important factor of cross-section deformation, while mandrel extension length has a significant impacton the outer wall thinning and inside wrinkling. Using boost can obviously improvethe quality of the wall. Change the clearance and friction between pipe and mold willinfluence the stress state of plastic deformation, which affects the quality of the tubebending, mandrel/tube clearance, wiper/tube clearance and mandrel/tube friction isthe most significant influences on the forming quality.