Fei Hu Zhang

Magnetorheological Finishing of Glass Ceramic

Glass ceramic is a kind of important material, which has been widely used in modern optics industry. Magnetorheological Finishing (MRF) is a newly developed technology, which eliminates subsurface damage, reduces micro roughness, and corrects surface errors. In the present study, glass ceramic was polished using Magnetorheological Finishing (MRF). The finished surface was tested with an AFM. The result shows that the workpiece has good surface quality. The flexibility of MRF makes it effective for ultra-precision machining of glass ceramic.

High efficiency ELID grinding of garnet ferrite

Abstract Hard and brittle materials such as ferrite, optical glass and ceramics have been used in many fields and still gain increasing attention. They are difficult to machine and it is hard to obtain good surface quality. Some workpieces of large batch production have large machining allowances and the machining efficiency is low with the usual grinding method. Thus it is of great importance to research the high efficiency grinding technology of hard and brittle materials. In this paper a cast iron bond diamond wheel and ELID (electrolytic in-process dressing) grinding technology are used on a surface grinder to research the high efficiency grinding technique. ELID grinding has been used previously in precision grinding with a fine abrasive wheel. In this study, the feasibility of ELID grinding for high efficiency deep-cut grinding has been researched. Garnet ferrite (YAG) has been machined both by the new method and by using a resin bond diamond wheel. The grinding force of the cast iron bond diamond wheel with ELID technology is apparently smaller than that of the other method. Under the same conditions, it is about 2/5–3/5 of the force using the resin bond diamond wheel. The result indicates that the grinding efficiency of garnet ferrite can be highly improved and good surface quality ensured by applying ELID grinding technology and adopting a large grinding depth.

Research on Deliquescent Polishing Fluid for KDP Crystals

The characteristics and principle of deliquescent polishing technology for potassium dihydrogen phosphate (KDP) crystals are introduced, and the performance requirements of deliquescent polishing fluid for KDP crystals are proposed. The main components of the deliquescent polishing fluid for KDP crystals were selected according to these performance requirements. Through uniformity experiment, stability experiment and fluidity experiment, uniformity, stability and fluidity of deliquescent polishing fluid for KDP crystals prepared using the selected components were tested. Through deliquescent polishing experiment of KDP crystal, polishing performance of deliquescent polishing fluid compounded using the selected components was tested. The material removal rate of the KDP crystal in the deliquescent polishing experiment was 6.03μm/min, and the surface roughness of the KDP crystal after deliquescent polishing was 4.857nm. The experimental results show that the compounded deliquescent polishing fluid for KDP crystals has good polishing performance and can reach the requirements.

Factors Influencing the Surface Quality during Ultra-Precision Grinding of Brittle Materials in Ductile Mode

The factors influencing surface quality for brittle materials is theoretically analyzed during ultra-precision grinding. Grinding experiments of brittle materials are carried out. The results show that the average abrasive grain size of the diamond wheel has a main influence on the surface quality, and the influence of the wheel speed and feed rate is secondary. In the case of s=1200m/min, f=0-20 μm/rev, and ap=0.1-10μm, only when the average abrasive grain size of the diamond wheel is less than 10μm, the super-smooth surface, for which Ra is 6.200nm and rms is 8.201 nm, can be obtained under grinding in the ductile mode. Introduction With the development of science and technology, high quality products of brittle materials play more and more important roles in many key instruments, such as various optical glasses, single crystal silicon, microcrystalline glass and ceramic bearing are very widely applied in space-flight and military equipment, and the requirement for surface quality of the workpiece is very high. In ultra-precision grinding, in order to obtain a super smooth surface of brittle materials, how to improve the surface roughness is hot theoretic direction of many countries [1-2]. But there are very few relative literatures on analysis and experimental study of effecting factors to surface roughness for brittle material. During grinding brittle material, the removal mode of the material at the workpiece surface affects the surface quality obviously [3-5]. In the paper, firstly the main influence factors of the surface quality are studied by dynamic grinding theoretically in the ductile mode. Afterwards some grinding experiments of brittle materials are carried out, and an Atomic Force Microscope (AFM) is used to characterize the machined surface. Experimental results show that theoretic analysis in this paper is correct. Critical Condition of the BrittleDuctile Transition of the Brittle Materials The critical condition of the brittle-ductile transition (the critical cutting of brittle materials) can be obtained by [6] 2 0 0 0 2 ) 2 cot( = H K a K a ld gc , (1) where H is the micro-hardness of the material, is the geometry factor of the indenter, =1.8854, 0 is the integrative factor, 0=(1.0 1.6)×10, Kld is the dynamic fracture toughness of the material and K0 is the affecting coefficient to brittle-ductile transition of the coolant. From theoretic analysis and experimental study, such a conclusion can be drawn concluded whether the grinding of brittle materials is in the ductile mode depends on the maximum cutting depth of single abrasive grain. The maximum cutting depth (agmax) of single abrasive grain is obtained by Key Engineering Materials Online: 2004-02-15 ISSN: 1662-9795, Vols. 257-258, pp 201-206 doi:10.4028/www.scientific.net/KEM.257-258.201

Effect on surface roughness of zerodur material in atmospheric pressure plasma jet processing

Zerodur material is considered as the ideal material in the high performance optic systems because of its excellent thermal stability characteristics. This paper deals with the impacting factors on the zerodur material surface roughness during atmospheric pressure plasma jet(APPJ) processing. At first, based on multiphase and multi-component in zerodur material, the effect on the zerodur surface chemical components and surface roughness is studied when the element contained Si is etched during the chemical machining process. The change of surface microcosmic topography is observed, it is proved that the technology of atmospheric pressure plasma jet can modify the surface roughness of zerodur material. Moreover, in consideration of the re-deposition phenomenon in the machining process, the composition of the re-deposition are studied and the genesis of the re-deposition were analysed. Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray spectrometry (EDX) were utilized to obtain the elemental composition of the sample powder residuum on zerodur surface. The relationship between substrate roughness and the process parameters is established based on the experimental results. Experimental results indicate that it is beneficial to add certain amount O2 to modify the surface roughness of zerodur material. This finding provides an important basis for the improvement of surface roughness in APPJ of zerodur material.

Research on the Material Removal Mechanism in Deliquescent Polishing of KDP Crystals

A new ultraprecision machining technology for KDP crystals, deliquescent polishing technology for KDP crystals, is presented. On the basis of analyzing the definitions of deliquescence, the dissolution experiment of KDP crystal’s surface was conducted. Through the experiment, the material removal mechanism in deliquescent polishing of KDP crystals is proposed, and the deliquescent polishing device for KDP crystals is described. Based on the material removal mechanism in deliquescent polishing of KDP crystals, the deliquescent polishing experiment of KDP crystal was carried out, the experimental result has verified the validity, feasibility and effectiveness of the material removal mechanism.

Polishing of Ultra Smooth Surface with Nanoparticle Colloid Jet

A nanoparticle colloid jet machining system has been developed for polishing ultra smooth surface of brittle materials. Interaction between nanoparticles and work surface in nanoparticle colloid jet machining has been given, and the theoretical dependence of the material removal rate with various important process parameters of the nanoparticle colloid jet machining have been investigated through material removal experiments. Some material removal results of nanoparticle colloid jet machining show that it is possible to obtain removal rates of one nanometer level per minute for glass surfaces with appropriate machining process parameters. A K9 glass surface was polished for obtaining ultra smooth surface. The surface roughness value of atomic force microscopy (AFM) observations is under 1nm Rms.

Ultra-Precision Shaping and Ultra-Smooth Polishing Investigation of High-Purity Quartz Glass in Nanoparticle Colloid Jet Machining

In this paper, ultra-precision shaping and ultra-smooth polishing investigations have been done upon a high-purity quartz glass substrate with an aspheric surface in nanoparticle colloid jet machining, which is an ultra smooth surface processing technique utilizing surface chemical reaction between work surface atoms and nanoparticles to remove the uppermost surface atoms. The shaping and polishing characters of high-purity quartz glass in nanoparticle colloid jet machining has been researched. The surface profile of the high-purity quartz glass workpiece before and after shaping has been measured by surface profilometer. And the surface microscopic morphological characteristics of high-purity quartz glass surface polished by nanoparticle colloid jet machining have been observed by atomic force microscopy (AFM). The measurement results indicate that nanoparticle colloid jet machining has good shaping ability for surface shape correction in ultra-precision machining. And the AFM observation results show that the roughness of the high-purity quartz glass surface has been reduced from 1.919 nm RMS to 0.784 nm RMS by nanoparticle colloid jet machining.

Research on Minimum Mechanism of Roughness of ELID Grinding

ELID grinding technology is used widely in the precision grinding of hard and brittle materials. The nature of passivating film play an important role in ELID mirror grinding. Spring’s stiffness of passivating film was researched from theory and simulation and experiment. And the theory of the dynamic stiffness of spring was proposed, based on this theory minimum mechanism of roughness of ELID grinding was proposed further, and experimental verification was done. Results show, the spring stiffness of passivating film is change with the grinding paramenter, and when implementing the precision grinding, the elastic deformation of oxide film reduces the exposure and grinding depth of the grinding grains, accordingly, ameliorating the grinding surface quality.

Experimental Study on Polishing Characteristics of Ultrasonic- Magnetorheological Compound Finishing

Concave aspheric surface with small radius is difficult to be fabricated by most of existing technologies for optical manufacture. Ultrasonic- magnetorheological compound finishing (UMC finishing) is a new technology for the ultra-precision machining of concave aspheric surface with small radius and freeform surface. The principle and experimental deviece used in UMC finishing are introduced. Main technological parameters in UMC finishing include the magnetic flux density, the gap between the polishing tool head and the workpiece, the rotational speed of polishing tool head and so on. The technology experiment of UMC finishing for optical glass K9 is conducted, and the influence of main technological parameters on the material removal rate has been studied by analysis of experimental results. The analysis of removal profile curve of UMC finishing spots prove that the material removal function of UMC finishing meet the surface error convergence requiement in computer control precise optical surface machining. The part surfaces after UMC finishing are measured by an Atomic Force Microscopy (AFM), and the surface roughness Ra is 1.591 nm after polishing for 10 min. It is demonstrated that the polishing capability of the technology is excellent.