Study On Two-dimensional Elliptical Vibration-assisted Freeform Surface Diamond Turning Apparatus And Tool Path Planning

Freeform surfaces have been widely used in various fields,such as aerospace,new energy,and biomedical engineering.Slow slide servo(SSS)and fast tool servo(FTS)based diamond turning have been considered to be the most efficient technologies for freeform surface generating,whereas they cannot machine freeform surfaces of difficult-to-cut materials very effectively.Because of the excellent machining performance in material processing,elliptical vibration cutting(EVC)has been widely used in the machining of difficult-to-cut materials.Nevertheless,it is unable to generate freeform surfaces very successfully.On the other hand,micro/nano textures can significantly improve the optical,mechanical and biological properties of textured surfaces,which enables the surfaces to create special functions.Textured surfaces have been widely used as engineered surfaces,and these surfaces are generally textured flat surfaces or cylindrical surfaces.Compared with flat surfaces and traditional rotationally symmetric surfaces,freeform surfaces have a more extensive application.Therefore,generating micro/nano textures on freeform surfaces can enable the freeform surfaces to achieve special functions,which can significantly expanding the application fields of freeform surfaces.EVC has been used in the machining of textured flat and cylindrical surfaces.This dissertation studies for diamond turning of freeform surfaces of difficult-to-cut materials,and textured freeform surfaces.The research contents mainly include processing methods,device design,tool path planning and surface topography prediction.(1)Double-frequency elliptical vibration cutting(DFEVC)methodThis dissertation proposes the DFEVC method for freeform surface diamond machining on difficult-to-cut materials.This method outputs the high-frequency elliptical vibration to improve the machinability in material removal and the low-frequency reciprocating movements for the freeform surface profile generation.For the application of the DFEVC method in diamond turning,this dissertation proposes a new tool path generation method,and constructs a new surface topography model.Three typical freeform surfaces are machined on die steel,which verifies the feasibility of the developed tool path generation strategy.In addition,the experimental results agree well with the surface topography predictions,which validates the effectiveness of the topography model.(2)DFEVC deviceThis dissertation develops a DFEVC device,which combines FTS and EVC in principle.The device is designed to be a flexure hinge structure and driven by two piezoelectric actuators to generate tool motions.The device performs well in testing experiments.In addition,two freeform surfaces are generated on die steel with the device,and the surface machined by DFEVC shows much better surface integrity and form accuracy than the surface machined by FTS,which validates the principle and the developed apparatus.(3)Diamond turning using DFEVC method with non-zero rake angle toolFor the diamond turning process using the DFEVC method with non-zero rake angle tool,this dissertation proposes a new tool path generation method based on coordinate transformation,and constructs the surface topography model for the machining process.Using the surface topography prediction,the influences of some machining parameters,such as vibration frequency,rake angle on the machined surface quality are discussed.(4)Diamond turning using DFEVC method with variable-frequency vibrationsOn the basis of the DFEVC method,this dissertation develops the double-frequency elliptical vibration diamond turning method with variable-frequency vibrations.In this method,the variable-frequency elliptical vibration is utilized to generate uniform micro/nano textures on the surface during the diamond turning process of freeform surfaces to achieve the textured freeform surface.For this diamond turning process,this dissertation proposes a constant-texture wavelength tool path generation method.A typical freeform surface is textured on die steel,and the textures of constant wavelength can be measured at different locations of the textured freeform surface,which verifies the feasibility of the proposed tool path generation method.To improve the topography prediction accuracy of the textured freeform surface,this dissertation proposes an analytical surface topography prediction approach based on the tool surface profiles.Different from the conventional surface topography model based on the ideal tool cutting edge with zero cutting edge radius,this method includes the rake face,the flank face and the cutting edge surface with actual non-zero cutting edge radius in the tool model,and analytically describes the tool surfaces during the machining process.Compared with the topography prediction results based on the ideal cutting edge,the results considering the tool surfaces show improved prediction accuracy,and are closer to the experimental results,which validates the proposed topography prediction approach.