Theoretical And Technological Research On Micro-structure Optical Surface Of Slow Tool Serve For Single Point Diamond Turning

Compared with traditional optical elements,optical freeform surface elements can obviously make the structure of optical system simple,reduce costs and improve the performance of optical system.However,the optical freeform surface has high demand for the form accuracy PV and surface roughness Ra,the surface roughness Ra needs to reach nano-scale and the form accuracy PV needs to reach micron or submicron in the practical applications.The method of single point diamond ultraprecision turning(SPDT)can obtain high surface quality only by one processing,which could require the PV and Ra demands of optical elements in optical system;so it is widely used in machining the optical elements.The method of slow tool serve owns fine acceleration and deceleration performance and large feed travel,therefore,the optical freeform surface with a large amplitude and a large variable curvature can be machined by the method.In this paper,some theories of slow tool serve for single point diamond turning is analyzed and investigated.In the process of single point diamond ultra-precision turning,because of inappropriate geometric dimension of the diamond tool,some interference may occur between tool and workpiece,which may damage the machining surface and even damage the diamond tool.In this paper,one parameter of the freeform surface is treated as certain,so the equation of the surface can be converted into a space curve.Then,the analysis about clearance angle,included angle and tool radius of the diamond tool can be done to ensure that no interference would occur in the machining process.The traditional cutting tool path planning methods for freeform surface are increasing the numbers of spiral and cutting points,however,it is hard to predict the form accuracy,which increase the machining blindness.In this paper,a new cutting tool path planning method is proposed,which can do the cutting tool path planning based on the requirement of the form accuracy PV value.Along with the cutting direction,the Non-Uniform Rational B-Splines(NURBS)interpolation theory is adopted to control the chord error between two adjacent cutting points.By using the NURBS fitting theory,the error of chord height of traditional cutting tool path strategy is predicted.Along with the feeding direction,the scallop height can be predicted caused by the two adjacent machining cycles.The error theory caused only by trajectory planning in freeform surface ultra-precision turning is studied.And the mathematical model of form accuracy PV is established,which is influenced by the errors caused by the two direction in the tool path planning process.Therefore,the form accuracy PV can be predicted before machining,which can ensure the machining qualification and increase the machining efficiency at the same time.A software,used the GUI part of MATLAB,is designed,which is used to generate the cutting location points of freeform surface.The software can be used to set the parameters of the freeform surface,the workpiece and the cutting tool,choose the primary generate points method,set the constrained value of chord error,show the interpolation error along with feeding direction and cutting direction,generate the machining trajectory,show the data information of cutting location points,and so on.The ultra-precision turning machine tool Nanoform250 is used to machining the complex freeform surface,and Talysurf PGI 1240 is used to measure the surface roughness Ra.The KEYENCE VR-3200 was used to measure the surface topography and the PV deviation of the whole surface was obtained by matching the design surface with measured data.The surface roughness Ra for complex sinusoidal wavy surface is 55.2nm and for complex sinusoidal grid surface is 89 nm.The de-noising form accuracy for complex sinusoidal wavy surface and complex sinusoidal grid surface are 3.7?m and 4.25?m,respectively.