Research On Cross Wedge Rolling Of Cone-shaped Shaft Parts Based On Numerical Simulation

Cross wedge rolling technology began in the 60's of the 20th century.It has many characteristics such as high production efficiency,saving of raw materials and good quality of parts.After 40 years of development,it has been widely applied in the area of parts rolling,such as automobiles,tractors,motorcycles,engines and hardware tools.As the force subjected in the forming process is very complex,which is a complex non-linear problem combined geometry,physics and boundary conditions together,meanwhile,it is limited by the material forming limit,so it is more difficult to achieve higher product quality ,higher productivity,lower energy and resource consumption,while ensuring the shape.Cone-shaped shaft parts or shaft parts with a tapered part are applied widely in the current rapidly developed industry,such as the textile spindle rod,hardware tools,automobile intermediate shaft and door stand.The shape is different from the other shaft parts,of which the change of reduction of crosssection area is continuous,so it also has a certain distinction in the forming process and mold designing with other shaft parts.There is no broadening stage in the cross wedge rolling process of cone-shaped shaft parts,but only roller-entering and flattening stages. The technological parameters that largely affect the forming of rolled parts mainly involve the largest reduction of cross-section and the angle of cone surface obliquity.So in this paper,the metal flowing,stress,strain and generated disabilities are analysed and compared from the perspective of the two technological parameters.With complex three-dimensional deformation,the deformation mechanism of cross wedge rolling is very complicated,and many factors have influence on the rolling process.In the meantime,the theoretical system is not mature and complete,and many problems are still in explored,such as metal flowing principle,deformation principle of rolled parts and the optimization of process parameters.Previously,study on cross wedge rolling mainly adopted traditional experimental methods,because of the limit of experimental conditions.Only a few quantitative information can be achieved,with long term and low efficiency.The emergence of numerical simulation method provides a good way for resolution of these issues.Compare with other methods,many complex problems of plastic forming,like cross wedge rolling,can be soluted by numerical simulation method. With the gradual development of computer technology and improvement of software technology,numerical simulation technology are widely applied in the plastic forming increasingly.Today,numerical simulation technology play an important role in the study of cross wedge rolling.Through the use of finite element numerical simulation analysis,many informations can be achieved in the rolling process,such as the distribution of inner stress and strain of rolled parts,the load distribution and the shape change of the deformed zone.This will provide a reference for reasonable choice of process parameters and the optimization of mold performance,and an efficient method is also provided for the further exploration and research on the theory of cross wedge rolling.Numerical simulation method is one of the most powerful tools of non-linear analysis presently,so in this paper,it is used to study on the cross wedge rolling process for cone-shaped shaft parts.In numerical simulation method,the materials deformation process is simulated,using relative software,in order to achieve some useful results for research.Currently many kinds of professional software for numerical simulation are used in the market,with different funcitons and characteristics.Compared with other numerical simulation software,DEFORM-3D is easy to use,with good material deformation.So in this paper,DEFORM-3D is chosen to simulate the cross wedge rolling process.Before the simulation,the models of rolled parts and rollers must be established first,but DEFORM-3D doesn't has the modeling function.So in this paper,the three-dimensional geometric models of molds and pieces are established in Pro-E,then the models are imported into DEFORM-3D through integrated interface.After determining the simulation parameters and initial conditons,such as material model,meshing,contact,restriction and loading,the case is simulated and soluted,finally the simulation results are analysed. During researching on deformation of cross wedge rolling by numerical simulation method,a few simplifications and assumptions about the rolling situation are made to ensure efficiency and rationality,out of consideration of actual situation.(1)The total pressure of rolling is not very large,as a result,elastic deformation of rollers and local flattening deformation of mold are neglected,and the rollers and molds are rigid bodies.(2)The heat transfer and exchange between the rolled parts and the mold and the air,are neglected,and it is believed that the temperature of the rolled parts keeps constant during rolling.(3)The contact part between the molds and rolled parts is Coulomb friction,and the friction coefficient is constant.(4)There is no contact between the rolled part and guide plate,in other words,the rolling conditions between the rolled part and the two molds are fully symmetrical. After the simulation is completed,the results achieved are processed,and the achieved data are listed and drawed to analyse.Using the post-processing function of DEFORM-3D,the rolled pieces are part are dissected,and the strain field,the stress field and the deformation on the cross-section and the longitudinal section of rolled pieces are achieved.All the distribution characteristics of the horizontal,vertical,axial and equivalent strain and stress are analysed.The stress and strain datas of a point on the rolled pieces at different time are output,and drawn into comparative diagram.The effects of reduction of crosssection area and the angle of cone surface obliquity on the the stress and strain are also analysed.Through numerical simulation analysis on cross wedge rolling of cone-shaped shaft parts at different woking conditions,it is achieved that if the largest reduction of cross-section area(ψ) and the angle of cone surface obliquity (θ) are different,the internal stress and strain of the rolled pieces are also different.When the reduction of cross-section increases,the stress and strain will also increase.When the angle of cone surface obliquity increases,the internal stress will reduce.The effect of the angle on the stress is smaller,and the overall trend is that with angleθincreases,the stess reduces. After cross wedge rolling,there will be shrinkage defects in the center area of rolled pieces.When the reduction of cross-section increases,the diameter of the maximum shrinkage will also increase.Rolling will refine the grain of roller pieces,and the refined degree will be different with different reduction of cross-section.The grain sizes of the rolled pieces,whose reductions of cross-section are between 40% and 60%,are the smallest.Through the analysis combined numerical simulation with experiments on cross wedge rolling process,the effects of process parameters on the internal stress,strain and central shrinkage of cone-shaped shaft parts are achieved.And the feasibility using cross wedge rolling process to form shaft parts with different process parameters is also confirmed.These have important theoretical significance and application value for in-depth understanding of the changing principle of the internal stress,strain and central shrinkage of the rolled pieces,and for reasonable selection of process parameters and improvement of the theory on cross wedge rolling.