Studies On Single Point Diamond Turning Technology Of Fluoride Optical Elements

With the rapid development and application of Ca F₂,Mg F₂ and Ba F₂ crystals in the field of optical engineering,the optical industry has put forward more strict requirements for the processing accuracy of fluoride crystal elements.Single point diamond turning technology,as the main processing method of optical crystal elements,has been paid more and more attention by the industry because of its high precision,high efficiency and high benefits.At present,there are few studies on the single point diamond turning technology of fluoride optical elements at home and abroad,especially in establishing process system of controlling its high precision surface quality,resulting in the fact that the surface roughness of fluoride elements could not meet the requirements of the optical system.In order to reduce the surface roughness of fluoride elements,this article systematically studied the single point diamond turning technology of fluoride optical elements,and established a set of reliable process scheme.Firstly,both the surface roughness origin and the“brittle-ductile transformation”phenomenon of fluoride elements in ultra-precision turning process were studied,and the main factors affecting the surface quality of fluoride elements in the manufacturing process were deeply analyzed to provide a theoretical basis for the establishment of reliable technological scheme.Secondly,the ultra-precision turning model of fluoride elements were established to obtain the influence of material characteristics,tool geometry characteristics and process parameters on the surface quality of fluoride elements.The mechanical properties of fluoride crystals were studied by indentation test to provid fluoride material property parameters for the ultra-precision turning model.In addition,according to the ductile deformation theory and equivalent crystal theory,the force analysis of"brittle-ductile transition"critical point was carried out,and the critical undeformed chip thickness was predicted.Combined with the characteristics of ultra-precision turning,the critical processing condition of"brittle-ductile coupling"was put forward,and the critical range of process parameters were predicted.Thirdly,the simulation models of ultra-precision turning process of fluoride elements were established,and the influence of tool geometry characteristics and process parameters in the simulation process were analyzed.According to the fracture mechanics theory of fluoride materials,the optimal diamond tool models and reasonable process parameters ranges of the fluoride materials were predicted,and provide guidance for the subsequent optimization experiments of turning process.Finally,Taguchi method is used to optimize the process parameters,design the orthogonal experiments of processing fluoride crystal planar elements,and then the optimal process schemes of fluoride elements have been determined.With the guidance of these optimal process schemes,the surface roughness of Ca F₂,Mg F₂ and Ba F₂ planar elements were obtained to be 2.53nm,3.18nm and 2.05nm,respectively.In addition,the diffraction optical elements of Ca F₂ and Mg F₂ and the harmonic diffraction optical element of Ba F₂were processed,according to the single factor experiments,the reliability of the optimal process schemes were verified.The experimental results show that the surface roughness of the fluoride optical elements with the guidance of the optimal process schemes were the minimum,which are all controlled below 5nm,the surface roughness of the fluoride elements were controlled.