Research On Three-dimensional Surface Parts Rolling Based On Variable-section Curved Rollers

The 3D curved parts rolling technology based on variable-section curved rollers is a new type of plastic forming method for 3D curved surface parts.In this method,a pair of variablesection rollers whose generatrixes are arcs are used as forming tools to form unevenly distributed roll gaps.,so that the sheet metal produces uneven thickness reduction during the rolling process.The sheet metal produces transversal bending deformation in the roll gap and uneven longitudinal elongation at the same time,and the additional stress causes the sheet metal to produce 3D bending deformation.Through reasonable design of the rollers,3D curved parts such as convex surface parts and saddle-shaped parts can be formed by this method.In addition,the longitudinal curvature of the formed 3D curved parts can be changed by small adjustments of the rolling reduction.Due to the line contact forming method,the required forming force is small,the equipment structure is simple,the production cost is low,continuous rapid forming can be realized,and the production efficiency is high.At present,the process is still in the laboratory research stage.This paper studies the influence of several process parameters on the rolled 3D curved parts;based on the characteristics of the surface rolling forming process,a method to effectively improve the stability of the forming process is proposed;and it is found that this process can form different types of curved parts by adjusting the rolling reduction without changing the rollers.The main research contents of this paper are as follows:1.The principle and forming process of 3D curved surface rolling based on variablesection curved rollers are discussed.The longitudinal bending deformation mechanism of sheet metal is analyzed,and based on the law of invariance of volume,the calculation method of longitudinal bending deformation of formed curved parts under ideal conditions is deduced.The relationship between roll gap distribution rule and generatrix radius of the rollers and the distance between the rollers is discussed in detail.It is found that when the generatrix radius of the convex roller is smaller than that of the concave roller,the distribution rule of the roll gap can be changed by adjusting the distance between the rollers.2.Based on the rolling process of 3D curved parts and the finite element modeling method of flexible rolling and multi-point forming process,a finite element model of 3D curved parts rolling based on arc-shaped rollers is established.The key model parameters such as contact and friction conditions and boundary conditions involved in the forming process are determined.Through the comparison of experimental results and finite element numerical simulation results,the reliability of the finite element model is verified.3.The effects of rolling reduction,sheet width,center section diameter of rollers and friction coefficient on the rolled convex surface parts and saddle-shaped parts are studied by finite element numerical simulation.The results show that the longitudinal bending deformation of convex surface parts increases with the increase of the rolling reduction and the friction coefficient,decreases with the increase of the sheet width,and first increases and then decreases with the increase of the center section diameter of rollers;The transverse bending deformation of convex surface parts decreases slightly with the increase of the rolling reduction,and increases slightly with the increase of the sheet width,and is basically not affected by the center section diameter of the rollers and the friction coefficient.The longitudinal bending deformation of saddle-shaped parts increases firstly and then decreases with the increase of the rolling reduction,increases with the increase of the sheet width,and decreases with the increase of the center section diameter of the rollers and the friction coefficient;The transverse bending deformation of saddle-shaped parts is basically not affected by the rolling reduction,the sheet width,the central section diameter of the rollers and the friction coefficient.4.Aiming at the problem that the swing of the sheet during the rolling process has a greater impact on the shape accuracy of the formed 3D curved parts.The influence of the shape and size of the deformation zone,the tangential linear velocity of the rollers and the friction force of the sheet metal on the stability of the 3D curved parts rolling process during the rolling process is analyzed.The analysis results show that,except for the special case that the speed of the convex roller is greater than that of the concave roller,the frictional force on the sheet during the rolling process makes the sheet tail always have a downward swinging tendency.Therefore,it is proposed to restrain the sheet tail swinging downward with a auxiliary support device,so that the sheet is bitten into the roll gap at a consistent angle,and effectively improving the stability of the forming process.And the reliability of this method has been proved by finite element numerical simulation.5.Developed a method to form different types of curved parts without changing rigid rollers.According to the characteristic that the distribution rule of the uneven roll gap could be changed with the change of the distance between the rollers,a method for rolling different types of curved parts(saddle-shaped and convex surface parts)by adjustment in rolling reduction without changing the rollers is proposed.And the feasibility of this method is verified by finite element numerical simulation.According to the phenomenon that the critical reduction is less than the theoretical analysis value,it is found that the 3D curved parts rolling has a local asynchronous rolling phenomenon when the rolling reduction is relatively large.Based on the phenomenon,a method of forming different types of curved parts by larger adjustment in rolling reduction,with an uneven roll gap which is big in the middle and small in the edge,is proposed.The feasibility of this method is proved by finite element numerical simulations.6.The rolling equipment of 3D curved parts and the measuring equipment for the formed3 D curved parts are introduced.The transition zone of the curved surface part rolled by the variable-section arc roll is studied.The effect of sheet size on the transition zone of the formed curved part and the sheet utilization rate was studied by rolling experiments.It is proved that under the condition that other process parameters remain unchanged,the sheet utilization rate of formed curved parts is positively correlated with sheet length,but negatively correlated with sheet width and thickness.