| Shaft parts are commonly used as important basic parts.Hollow shaft has the advantages of weight reduction,material saving and energy conservation.It is an important way to realize the lightweight structure of torque-transfer parts.At present,hollow shaft parts are mostly produced by remanufacturing solid shafts,which has low production efficiency and high material consumption.Moreover,the manufacturing difficulty and high cost of deep hole drilling limit the application of hollow shafts.In this paper,a new forming process of cross wedge rolling(CWR)based on mandrel control was proposed for manufacturing hollow parts,which has the advantages of high production efficiency,low cost and good product quality.Stress-strain curves of 40MnBH under unidirectional compression at different strain rates and deformation temperatures were obtained by Gleeble-1500D thermal simulator.The effect of deformation temperature,strain rate and strain on austenite grain refinement of 40MnBH during unidirectional compression deformation were studied.The effect of heating temperature and holding time on austenite grain growth of 40MnBH was studied by static grain growth experiment.A unified viscoplastic constitutive model of 40MnBH was established based on dislocation theory and internal variable method.The material constants in the model were solved by genetic algorithm combined with thermal simulation experiments and grain growth experiments data.By comparing and analyzing the predicted results and experimental results of the micro structural model,it is shown that the established microstructural model can accurately express the viscoplastic flow characteristics and microstructural evolution of 40MnBH during unidirectional compression deformation.The numerical analysis of CWR hollow shafts was conducted by using Deform-3D.The mechanism of mandrel control of CWR hollow shafts was studied and the variation of contact state between mandrel and hole during rolling was analyzed.The influence of mandrel size on the contact shape,contact area and contact load between mandrel and hole was studied,and the influence of mandrel size on the stress and strain field,temperature field and metal flow was investigated.In this paper,the forming dimension of inner hole in CWR hollow shaft with mandrel was analyzed by combining experimental and numerical results.The fluctuation mechanism of the inner hole size was revealed,and the influence of process parameters on the fluctuation of inner hole size was analyzed.The method of combining wedge corner and mandrel compensation was proposed to improve the fluctuation of inner hole size.The formation mechanism of spiral marks of inner hole was revealed and the influence of mandrel size on spiral marks of inner hole was analyzed.A finite element model for CWR of 40MnBH hollow shaft coupling thermo-mechanical field and microstructure evolution was established based on the secondary development of Deform-3D.The evolution of microstructure during CWR hollow shaft was simulated and analyzed.The influence of relative mandrel diameter,temperature and relative wall thickness of workpiece on microstructure evolution of CWR hollow shafts was revealed.The experimental and numerical grain size was compared.The result shows good consistency,which indicates that the evolution of 40MnBH microstructures during cross wedge rolling can be accurately predicted.The rolling experiment with reduced proportion of hollow axle sleeve with variable inner diameter was carried out.The results show that it is feasible to use mandrel to control the inner hole size in CWR hollow axle.The research results are of great significance for perfecting the theory of CWR hollow shaft with mandrel,and lay a foundation for efficient and economical production of hollow parts with variable inner diameter by CWR. |
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