Papers by Author: Ju Long Yuan

Abstract: The semi-fixed abrasive tool (SFAT) is a new tool used in the ultra-precision machining. Based on the theory of particle flow code (PFC), the abrasive particle motion characteristics of SFAT are studied in SFAT processing which is divided to workpiece pressing progress and workpiece tangential moving progress. It is conclusion that the particles are fallen out the tool surface due to the fracture of bonds under the normal force of workpiece point in the workpiece pressing progress; the particles contacting the workpiece are moved on every hand while some particles fall out the surface at the edge of abrasive tool in the workpiece tangential moving progress, and the maximum value of binding agent holding force is computed.

Abstract: In order to improve the efficiency of ultra-precision processing, the semi-fixed abrasive plate (SFAP) is developed to reduce or eliminate the surface and subsurface defects and improve the process efficiency. The interaction of the semi-fixed abrasive plate-workpiece is the key factor for the processing. The complex plate-workpiece interaction is taken into consideration in the generation of the semi-fixed abrasive surface in this paper. A numerical model which allows describing the elastic-plastic contact load of the isotropic fractal surface and the real contact area of plate-workpiece is developed for the semi-fixed abrasive plate. The results shows that the real contact area is only a part of the workpiece and it changed with the contact load alteration, it is useful to determine the processing parameter of SFAP lapping.

Abstract: In order to kinematic simulate the lapping process with the semi-fixed abrasive plate; a fractal modeling of the semi-fixed abrasive lapping abrasive plate’s surface topography is presented in this paper. A numerical procedure for effectively generating the semi-fixed abrasive lapping abrasive plate surface topography is suggested. The procedure is based on the fractal characteristic of the semi-fixed abrasive plate and the fractal dimension was obtained from the measured structure function of the abrasive plate surface used the Digital Microscope Resources Center. Numerical examples are used to illustrate the viability of the approach. It would be powerful to describe the complex interaction of the abrasive plate and workpiece.

Abstract: In recent years, optical manipulators based on forces exerted by enhanced evanescent field close to near-field optical probes have provided the access to nonintrusive manipulation of nanometric particles. However, the manipulation capability is restricted to the intensity enhancement of the probe tip due to low emitting efficiency. Here a near-field optical trapping scheme using the combination of an optical fiber probe and an AFM metallic probe is developed theoretically. Calculations are made to analyze the field distributions including tip interaction and the trapping forces in the near-field region by applying a direct calculation of Maxwell stress tensor using three-dimensional FDTD. The results show that the scheme is able to trap particle at the nanoscale with lower laser intensity than that required by conventional near-field optical tweezers.

Abstract: The solid-phase reaction experiment and principle were introduced. 1000# SiO₂ micromist and CaO powder were used polishing sapphire, with polishing pressure 7.5kPa，polishing speed 60r/min and 40r/min. The process of polishing was separated every 120 minutes. The surface appearance and roughness will be survey in each part. Non-surface-scratch will be achieved after 600min of polishing. The roughness (Ra) was decreased from 395nm to 7nm. Rmax was decreased from 2.98μm to 0.05μm. Rt was decreased from 3.34μm to 0.05μm. Through the analysis of the experimental data of XRD, kyanite phase map and diffraction pattern fitting degree. The fact that quality of sapphire’s surface was improved by using this approach has been proved.

Abstract: Based on the detailed analysis of the one-side milling theory of the spatial cam, an error comprehensive prediction model of the contour normal deviation is proposed in this paper by applying the spatial meshing theory, the rotation transformation of tensor and Newton’s iteration. A computer simulation example is presented, and the results show the error prediction model can disclosure and predict the law of influence effectively, that the tool and installation inaccuracy produce the contour normal error during the one-side processing of the spatial cam. Consequently, a scientific proof has been supplied to improve the precision and quality of the one-side milling of the globoidal indexing cam.

Abstract: In order to obtain low surface damage and high machining efficiency for advanced ceramics, overcome clogging and dressing difficulties of traditional metal bonded super-hard abrasive, a novel fine super-hard abrasive with porous self-generating ability is proposed in this paper. And the matching of filler and dissolvent in abrasive are studied. Soluble filler is a key technology of porous self-generating fine super-hard abrasive. In this paper, metal, metal oxide and non-metallic oxide are respectively used as soluble fillers. Results of the experimental shows: In metal bonded super-hard abrasive, metal, metal oxide and non-metallic oxide as soluble filler are feasible, correspondingly, FeCl3 solution, aqueous solution and weak alkaline solution are used as dressing dissolvent, respectively. It can be met the requirement of high precision machining for advanced ceramic materials, hard and brittle machining materials.

Abstract: To improve the machining efficiency as well as surface roughness, a series of experiments employed fixed abrasive tools are carried out for stainless steel substrate, and influences of properties of fixed abrasive tool on the lapping process are studied. It is found that the resin is the best bonding material in this study. The surface roughness under different concentration of bonding material is similar, and the material removal rate (MRR) increases as the concentration of bonding material decreases from 50% to 20%. But too little of bonding material results into low bond strength that causing low material removal rate. It is also found that higher shear strength, lower wear rate, and the shear strength of the tool with 35% bonding material is the highest. It is obvious that the surface roughness and material removal rate decline as the grit size decreases. The roughness of surface lapped with resin bonded 4000# SiC abrasive tool comes to 18nm, and the material removal rate is 0.63μm/min.

Abstract: In order to reduce or eliminate the surface defects caused by abrasive grains and improve the efficiency of ultra-precision processing, the technique of semi-fixed machining has been proposed for machining advanced ceramics. A semi-fixed abrasive tool (SFAT) has been manufactured; it has performances of semi-fixed machining technique. This document demonstrates wear characteristics of SFAT through experiments of machining silicon wafer. It showed that wet status or dry status of SFAT has greatly influenced wear characteristics of SFAT. Wear characteristic of SFAT presented mostly blockage and little grain-off occurred in dry status; mostly grain-off and little blockage presented in wet status.

Abstract: A three-dimensional hydrodynamic lubrication model for chemical-mechanical polishing is presented based on the Reynolds equation and Reynolds boundary condition. By solving the Reynolds equation, the slurry film pressure distribution has been obtained. The effects of minimum film thickness and the wafer tile angle on the film pressure are analyzed, and the influence of the polishing applied load and rotation speed on slurry film thickness and tilt angle are discussed. At last, by experiment, it is found that the simulation results are similar to experiment results which film thickness is increasing with the increasing of rotation speed, decreasing of the applied load. It is proved that the simulation is reliable.