Papers by Author: Yong Zhang

Abstract: This paper puts forward a kind of new technology for metal matrix difficult-to-machine materials based on compound energy field. The new technology combine electrochemical jet machining and abrasive jet machining technology, which obtain the high quality of processing surface and greatly improve processing efficiency. Aiming at the new technology, the experimental device of compound machining is established, a large number of process experiments are carried out. The different process parameters are studied for the influence of the machining efficiency, including the machining gap, voltage and jet pressure. The experimental results show that the compound machining can be applied to machining or polishing complex shape parts of metal matrix structure difficult-to-machine materials, so it has widely application prospects.

Abstract: This paper researches the material erosion mechanisms of high silicon- aluminum (Si-Al) alloy in micro electrical discharge machining (Micro-EDM). By using Quanta 200F environment scanning electron microscope, the microstructure of Al-50wt%Si alloy by spray forming was observed. And a simplified model of high Si-Al alloy was set up. The Al-50wt%Si alloy was machined by using copper electrode and tungsten electrode respectively. And the differences of surface morphologies and element energy spectrum were compared. The process and the material erosion mechanisms of high Si-Al alloy in Micro-EDM were analyzed in detail. The results may provide theoretical basis for Micro-EDM of high Si-Al alloy.

Abstract: Because of the high content of Si, traditional machining can hardly machine micro and small structures. While there is almost no microscopic force in the process of micro-electrical discharge milling (MEDM), so it has great advantages. In the process of MEDM for high silicon aluminum (Si-Al) alloy, the impacts of electrical parameters on processing time, the trend and degree of electrode wear are researched. The Al-50wt%Si alloy made by spray forming (SF) and casting forming (CF) and electrode of copper and tungsten are adopted to do the research. Related processing laws are summarized. A micro-3D structure was made by using appropriate parameters based on the experiment and research.

Abstract: Ultrasonic-magnetorheological combined finishing (UMCF) is a new technique for the ultra precision machining of aspheric surfaces, especially for high quality work pieces with small curvature radius concave surfaces. The goal with UMCF is to minimize surface figure errors by optimizing the dwell time and tool path, and the current approach typically results in low amplitude form errors. However, discrepancies exist between the predicted and observed form errors. The major sources of such errors are machine axes positioning errors and unpredicted variations of the removal function. Errors that can produce discrepancies between actual and predicted removal profiles were modelled. A diagnostic method was developed to determine the residual error induced by two types of error. Their effects were examined with numerical simulations and the simulation result was presented. Finally, UMCF experiments are performed on a variety of optical surfaces. The final residual error after polishing is less than 2.6 nm PV values. The successful figuring results prove the validity and advantages of UMCF.

Abstract: Nanoparticle colloid hydrodynamic cavitation jet polishing (HCJP) is a super-smooth machining technology. This technology utilizes the interface reaction to remove material from the workpiece and uses cavitation effect to improve the processing efficiency. In this paper, the prototype equipment of HCJP is researched. Based on the prototype equipment, the processing experiments of pulsed jet nozzle, swirling jet nozzle and common cone-shaped nozzle have been done and the results of the experiments are compared with each other. The experiment results indicate that the roughness of the surfaces polished by three nozzles has remarkably decreased. The material removal rate of pulsed jet nozzle is the highest among the three types of nozzles. The material removal rate of the swirling jet nozzle is not improved obviously compared with the common cone-shaped nozzle. The processing experiment of monocrystalline silicon by the pulsed jet nozzle has been done and the roughness of processed surface is Ra 0.475 nm.

Abstract: Nanoparticle colloid hydrodynamic cavitation jet polishing (HCJP) is a supersmooth surface machining technology that utilizes the interface reaction to remove material from workpiece, applying the cavitation effect to improve the processing efficiency. In this paper, a plototype equipment of HCJP is introduced and the experiment of HCJP and common jet polishing has been done. The experiment results indicate that in both cases, the processed area presents the orbicular structure of “W” shape when the angle of jet and horizon is 90°; the position that has the best surface quality located on the annulus of processing region where the most material removed. Compared with the common jet polishing, the surface quality processed by HCJP that uses the swirling jet is better. In processing experiment of HCJP, the supersmooth surface with roughness of Ra 0.758nm is obtained.

Abstract: The application of ‘small tool’ based on computer controlled is a breakthrough in modern optical machining technology. The unicursal pseudo-random tool path, called “random path” for short, was schemed to reduce the high-frequency errors left by small polishing tool. The clipping algorithm has been developed to optimize random path, thereby it can be used in polishing workpiece surface of any boundary shape efficiently. The power spectral density (PSD) of surface before and after polishing with random path was analyzed and the result indicated that the high frequency error can be reduced by the application of random path.

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.