Papers by Author: Fei Hu Zhang

Abstract: Ultrasonic-magnetorheological combined (UMC) finishing is a new technique for the ultra precision machining of aspheric surfaces, especially for high quality workpieces with small-radius concave surfaces or freeform surfaces. The characteristic of UMC finishing is discussed, and an experimental equipment for UMC finishing with 5 axes is developed. According to requirements of deterministic removal in UMC finishing and the experimental equipment, post processing algorithm for aspheric surfaces is researched. The derivation process and computer simulation result of the algorithm is presented. The error analysis is conducted and the error control method is also proposed. A series of experiments have been conducted, and experimental results show that high quality surfaces can be achieved by the post processing algorithm.

Abstract: Ultrasonic- magnetorheological combined finishing (UMC) is a new technique for the ultraprecision machining of aspheric surfaces, especially for high quality workpieces with small curvature radius concave surfaces. According to the characteristics of UMC finishing, material removal model has been developed. Several types of tool path planning algorithm have been discussed. Two kinds of polyline dwell time algorithm are presented. Polyline Dwell time algorithm based on two-dimensional discrete convolution is a new dwell time algorithm, and the dwell time on the endpoints which compose the tool path can be solved by the algorithm directly. Every polyline dwell time is the mean value of dwell time of two endpoints, therefore, the polyline dwell time of every type of tool path can be solved efficiently by the algorithm. The simulation of two dwell time algorithms has been conducted with same removal function and original error distribution, and the pv convergence rate is improved from 0.939 to 0.973 by using new algorithm. Figure error PV values reduced to 29.4 nm from 1.67μm after UMC finishing. The efficiency of the polyline dwell algorithm is proved by computer simulation and experimental results.

Abstract: Concave aspheric surface with small curvature radius is difficult to fabricate by most of existing technologies. Ultrasonic- magnetorheological combined finishing (UMC) is a new technique for the ultraprecision machining of aspheric surfaces, especially for the ultrasmooth surfaces machining of small-radiuses concave surfaces and freeform surfaces. According to the characteristics of rotary symmetrical aspheric surface, path algorithms for UMC finishing have been developed. Propose and compare two kinds of polishing dwell time algorithms, and the derivation process and computer simulation result of the algorithms was also presented. The experiments using the control algorithm have been conducted, and the efficiency of algorithm is proved by experimental results.

Abstract: The traditional ELID Grinding Technology has many limitations in grinding small diameter hole and spherical face. As a solution, a new method for ELID grinding - the fourth generation ELID Grinding Technology, ELID IV, is presented in the recent research. To serve the industrialized application of ELID IV, a series of experiments were performed to reveal principle of ELID IV. Results of these experiments indicated that: (1) electrolyse function is enhanced obviously when the workpiece is connected to the positive pole of the power supply using 45 steel as the material of test piece; (2) the relationship between the effect of electrolysis and the electrode gap is studied by using the 120 # Rail Based grinding wheel on the cemented specimens carbide for electrolytic grinding, and 1mm is determined the best electrode gap.

Abstract: A computational fluid dynamic (CFD) model for submersion jet has been developed to investigate the hydrodynamics in nanoparticle colloid jet machining with small diameter nozzle about 0.21mm. With this model, the fluid field characteristics and pressure distributions in the system are computed under the condition of vertical injection and aslant injection when jet pressure is 4MPa. The corresponding material removal experiments in nanoparticle colloid jet machining have been done to validate the rationality of the CFD model. And the simulated data are in good agreements with the experimental results.

Abstract: Colloid jet polishing (CJP) is a new technique for the ultraprecision machining of aspheric surfaces, especially for the ultrasmooth surfaces machining of small-radiused concave surfaces and freeform surfaces. In this paper, a colloid jet polishing equipment with 5 axes, four of which perform linkage movement was developed. According to characteristic of colloid jet polishing, NC interpolation algorithm for rotary symmetric aspheric based on this equipment was researched. The derivation process and computer simulation result of the algorithm was also presented. The interpolation error of this algorithm was analyzed and the calculation formula was also proposed. According to the result of analysis, the precision of the interpolation algorithm is high and the algorithm is very useful. Experiments show that high quality ultrasmooth surface can be achieved using this method and surface roughness Ra less than 1nm for K9 glass can be obtained stably.

Abstract: 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.

Abstract: This paper describes the current situation of spherical grinding for carbide material. The experiment of Concave spherical ELID grinding of generating method for carbide is conducted. Because dressing electrode can’t be installed in limited space due to the small space of concave spherical surfaces and carbide material has good conductivity, the workpiece material was used as dressing electrode in the ELID grinding experiment. According to negative effect of spark discharge in the process of grinding to surface roughness, two methods "ELIDⅡ" and "ELID Ⅲ" were designed. Comparing and analyzing the experimental results, it is confirmed preliminary that the spherical error and surface roughness of the workpiece after "ELIDⅡ" grinding were better than those after the "ELID Ⅲ" grinding. The ELID grinding method using micro diamond powder wheel and using carbide workpiece as dressing electrode is an effective way for spherical ultra-precision grinding for carbide.

Abstract: 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.

Abstract: 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.