Study On Plane Envelop Grinding Convex Surface With Variable Positioning Circle Method

The large-caliber aspherical surface of hard and brittle material is widely used in weapon equipment system and scientific instrument and plays an key role in such sophisticated systems.Thus the manufacturing technology of large-caliber aspherical surface is the important research contents in the field of modern manufacturing.The manufacturing process of large-caliber aspherical surface usually includes the following steps: blank forming,lighter weight,grinding,lapping,polishing and etc.Especially,polishing efficiency is much lower than grinding.So researchers always hope that materials can be removed as much as possible in grinding process,meanwhile get better machining accuracy and surface quality so as to reduce the time spent on polishing.From the angle of grinding method,this dissertation,which aims to improve efficiency,reduce wear and increase efficiency,presents a new grinding method that is named plane envelop grinding method with Variable Positioning Circle Method which is referred to as VPCM.The end face of cup grinding wheels utilized in this grinding method is divided into several rings,then makes the grinding particles located on these rings participate in grinding process according to its wear law,meanwhile let the end face of grinding wheel always keep tangent contact with the convex surface of work piece,which envelops the surface of work piece.In this way,we can improve efficiency,reduce wear and increase efficiency.Around these contents,the following work is carried out:1.The wear rule of rings on the end face of a grinding wheel is studied by wear experiment,from which,a conclusion is derived that the upward feed rate of the grinding wheel has the most important influence on the wear of the rings mainly,followed by rotation rate.2.Grinding path planning is an important link of NC machining surface,which has directly influence on machining efficiency.In this dissertation,a new tool-path generation algorithm for plane envelope grinding convex surface based on constant scallop height method is presented,which targeting at cup grinding face grinding convex surface.From the view of differential geometry,the process of plane envelop grinding convex surface is described,then a equation is presented to describe plane envelop surface,and the algorithm for searching the points of constant scallop height curves is given,moreover,a proof about the differential geometrical relationship between the constant scallop height curve and its tangent vector is given,based on which,the tool-path generation algorithm is constructed.Compared the tool-path algorithm with which usually used,it is proved that the new tool-path algorithm is more efficient.3.Cup grinding wheel Face grinding is mainly utilized in grinding a plane.In this dissertation,Cup grinding wheel Face grinding is used for grinding convex surface.In the new application,especially united with Five-axis CNC technology,the inherent nonlinear error of Five-axis CNC technology takes on a new form.In this dissertation,the study on nonlinear error in interpolation is carried out in two cases,one is RTCP mode,and the other is non-RTCP mode.From the study,the generation process of nonlinear error,the emerging location of nonlinear error and its distribution law are derived.In RTCP mode,the nonlinear machining error is muchless than the discretization error,and has no influence on the machining error.The nonlinear machining error plays an important role in the machining error when the RTCP function of the five-axis machine tool is closed,in this situation,the peak value of nonlinear machining error occur near the contact point,which far exceeds the allowed machining error.Based on the analysis,a method for compensation the nonlinear machining error is presented.4.On the basis of the experiment data and the analysis,the experiment of plane envelop grinding method with variable positioning circle method is carried out.By comparing the experimental data,it is shown that the grinding method presented in this dissertation can significantly improve the machining accuracy,and enlarge the effective area,and reduce wheel wear.