| The micro-structure surface is a structural feature with high aspect ratio and geometrical characteristics determined on a plane,a cylinder or other free-form surface.The optical film with micro structure is widely used in the fields of optics,bionics,medicine,communication,etc,which have the advantages of lighter weight,smaller size and stronger optical performance.Micro structure requires nanometer-scale surface roughness and micro-or even sub-micron form error accuracy in different applications.Single point diamond turning with slow tool servo can fabricate the required micro-structure parts by one processing to meet the accuracy requirements without any post-processing.At present,the commonly used cylindrical micro-structure machining methods include single point diamond turning with slow tool servo,fast tool servo and special machine tools,which all have high fabrication precision and machining efficiency.In this paper,the theory and technology of micro structure for single point diamond turning on cylindrical surface are investigated.In order to successfully fabricate the designed micro structure,the machining tool directly affects the characteristic machining accuracy whether the geometric parameters are suitable,and avoiding the interference and over cutting between the machining and tool workpieces caused by improper selection of tool parameters.In this paper,the tool clearance angle,the tool nose radius and the tool wrap angle are analyzed.For the characteristics of solid of revolution and solid of non-revolution,the analysis method mainly adopts the generatrix and section curve to optimize tool parameters to ensure the processing smoothly.The existing feature modeling methods mainly include partial area modeling and overall modeling of cylindrical,and the corresponding cylindrical partial area have equal-angle and equal-arc spiral turning trajectories.The overall cylindrical turning trajectory is limited to the axial direction feeding and without radial direction.In this paper,two modeling theories of revolving and non-revolution micro features are studied.The micro structure attached to cylinder is modeled as a whole,which has fluctuating feeding in the radial direction.And the corresponding tool turning trajectory planning method is studied.The tool nose radius compensation method is investigated for revolving and non-revolution micro features.According to the trajectory of the actual machining process to established the mathematical model of the machining error generated during the fabrication process,including the chord error,the scallop height error between the adjacent axial tool contact points and the scallop height error between adjacent straight line in axial direction that are between adjacent tool contact points in cutting direction.The error calculation method is derived after geometric analysis of three kinds of errors,and the machining parameters under the given error value can be calculated.Under the premise of ensuring the machining precision,the machining time is optimized and machining efficiency is improved.Four micro-features software are developed by MATLAB/GUI,in which the relevant parameters can be set directly to display the micro structure model,the machining trajectory,outputting the required tool contact points and Tool location points.Besides,an error calculations software is also developed for one of the micro structure.Under the set of relevant parameters,the three kinds of error images and extreme error values are displayed accordingly to facilitate the modification of the model parameters and obtain the required turning trajectory data.An ultra-precision machine nanoform250 were used to machine the designed cylindrical sine wave groove and cylindrical sinusoidal mesh micro features.The surface roughness of the features was measured by an instrument Talysurf PGI 1240 to obtain the surface data,which is used to analyze for matching the designed and machined feature surface,and calculating the overall deviation,and measure thefeature surface topography using the KEYENCE vhx900.Based on the analyzing of measured data,the cylindrical sine wave groove micro feature surface roughness Ra and PV are 0.1714μm and 1.32μm,the cylindrical sinusoidal mesh micro feature surface roughness Ra and PV are 0.1625μm and 1.8μm. |
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