Papers by Author: Ju Long Yuan

Abstract: This paper presents a finite element (FE) modeling of the nanoindentation test of sapphire, in which the finite element method was employed to study the mechanical characteristic of sapphire under the nanoindentation process. The results demonstrated that the nanoindentation FE models were able to simulate the indentation loading-unloading curves of the sapphire. The load and unload displacement curves of the simulation and experiment results can match with each other well, and then the properties used in the simulation should be the actual properties of the sapphire. The Mises stress field distribution of the sapphire sample was calculated to reveal the alteration from elastic region to plastic region, which are useful for indentifying the ductile to brittle change in the sapphire abrasive process.

Abstract: Ceramic balls have become an important component in advanced bearings, and the sphericity of balls is a key qualification focused in lapping process. An investigation on the effect of dynamic behavior of ball support system on the performance of ball lapping in rotated dual-plates lapping method is carried out. Sinusoidal waveform in terms of Fourier analysis is employed to express the shape error of the ball surface, and a dynamic model for support is setup. It is found with numerical calculation that the variation of lapping load lags behind the variation of the shape error for the damping of support. A lower natural frequency of the support system, higher spin speed of balls and a larger value of spin angle in RDP lapping are better to rectify the shape error of balls and reduce the lagged effect. It is concluded that dynamics of lapping system must be taken into consideration in order to understand comprehensively the spherical surface generation mechanism.

Abstract: This paper analyzes the property parameters influences of semi-fixed abrasive plate on the ‘trap’ effect with discrete element simulation by Particle Flow Code (PFC). The effects of the property parameters such as porosity, hardness and size of the abrasive particles, friction coefficient between the abrasive particles and the bonding agent concentration are simulated. The simulation results show that porosity, friction coefficient, bonding agent concentration has great influences on the ‘trap’ effect, while hardness and size of the abrasive particles almost have no effect. Grey incidence analysis is carried to determine the influence degree of porosity, friction coefficient, bonding agent concentration, and the results show that the most important factor is the porosity, followed by the friction coefficient, and then the bonding agent concentration.

Abstract: Dual-lapping was a process to planarize the surface of the sapphire wafer, the nature of surface&subsurface damage and the surface uniformity was depended on the material removal mode and materials removal ratio. Material removal mode was studied in this paper, and the model of material removal was set up too. The SEM was used to scan the processed sapphire surface and the different removal style (two body and three body) were discovered. This research provided valuable insights into the material removal ratio and the dependence of lapping-induced damage on dual-lapping conditions, the asymmetry of abrasive granularity brought on the different materials removal mode and the surface asymmetry. The model was set up to qualitative analysis the material removal ratio in dual-lapping of sapphire, obtain the reasonable MMR and optimize the surface quality and the planarization result.

Abstract: In plane lapping, workpiece material removal and lapping wheel wear has been influenced each other and should be evenly distributed. Only required a flat lapping wheel, it could be obtained with flat workpieces and small thickness deviations. Therefore, the choice of the truing operation has an important effect on the quality of the lapping wheel and on the flatness of product. This is a way that using truing ring to true lapping wheel in certain eccentricity plane lapping system　to acquire the flatness. The kinematics of certain eccentricity plane lapping for uniformity of processing is analyzed in this paper firstly. Then different sizes and locations of truing ring that influences truing on the flatness of lapping wheel has evaluated and simulated. Lastly, a suitable truing operation of certain eccentricity plane lapping is proposed.

Abstract: This work aims to obtain fine surface of silicon wafer during precision and ultra precision machining, and presents a new method called semibonded abrasive machining. A semibonded abrasive grinding plate is used in the semibonded abrasive machining. Abrasive particle of 1000# Green SiC and bond named SSB are adopted in the manufacture of the plate. Four plates with different concentration of bond which are 1.5%, 2.5%, 3.5%, 4.5% respectively are made. The paper studies the effect of concentration of bond, the control parameters which include the lapping time, the load, and the rotating velocity of the plate on the surface roughness. Experimental results indicate each plate with different concentration of bond can obtain fine surface roughness. When the load or the rotating velocity increases, there is little effect on the surface roughness, but the material removal rate increases correspondingly. The initial roughness of the silicon wafer surface lapping by the plate could be improved from Ra 0.2μm to Ra 0.02μm in 9 min.

Abstract: The semibonded abrasive machining technique is expected to get high surface integrity and processing efficiency attributed to the „trap‟ effect which can reduce or even eliminate the surface damage induced by the larger particles. The goal of the work is to validate the „trap‟ effect by the experiments of semibonded and loose abrasive machining under the conditions of adding and not adding the larger particles. Free surface damage monocrystal silicon wafers after polishing are adopted as workpieces, and 1000# SiC as abrasive particles while 180# SiC as the larger particles. The cast iron plate is used as grinding plate in the loose abrasive machining and different bond concentration semibonded abrasive grinding plate SSB-1 and SSB-2 are used as grinding plates in semibonded abrasive machining. The roughness Rv and SEM photos of workpieces surface are tested to evaluate the extent of „trap‟ effect. The result shows that the semibonded abrasive grinding plate has the „trap‟ effect. The shore hardness value of the semibonded abrasive grinding plate can be used to be one parameter to evaluate the degree of the ‟trap‟ effect of the semibonded abrasive grinding plate.

Abstract: To study the sphere-shaping mechanism under dual rotating plates (DRP) lapping mode for ceramic balls, the uniformity of lapping trace distribution is focused in this paper. Methods for simulation and evaluation of the lapping trace uniformity are proposed, and the effect of velocity parameters on the lapping uniformity of ball under DRP lapping mode is analyzed. It is found that the lapping uniformity is dependent not only on the variation range of spin angle θ, but also on the spin angle speed ωb and on the variation form of θ. The analysis results indicate that the effect of amplitude of the speed ratio function on the lapping uniformity is much greater than the effect of phase on that. When the ratio of the inner plate speed to the outer varies from 0 to2, the best lapping uniformity is obtained under the conditions demanded by this paper.

Abstract: The amorphous Ni-Pd-P alloy films with superior property have good heat conductivity and wear performance. They are widely used in the protecting coating. Copper has been chosen to be a substrate material of the produce of amorphous Ni-Pd-P alloy films with its unique electrical properties. The precision lapping technology for the copper substrate using semi-bonded abrasive grinding plate is studied in this paper. The influences of the different lapping parameters on the surface roughness, material removal rate on copper substrate surface formation in the precision lapping process are both discussed. Experimental results indicate that the copper substrate can be efficiently processed by 800# SiC semi-bonded abrasive grinding plate of, and the initial roughness of a machined surface could be improved from 0.553μm Ra to 0.28μm in 10min, yielding a ideal rarely scratch surface.

Abstract: Silicon nitride ceramics materials have excellent properties such as small density, high rigidity, high Young's modulus, high wearability, good thermal stability and chemical stability, which make it become one of the most appropriate materials for rollers of high precision bearing. Chemical Mechanical Polishing (CMP) technology is employed to have an ultra-precision machining process for silicon nitride ceramics materials workpiece and the effects of workpiece surface roughness in different abrasive are discussed in this research. The XRD and SEM technology are used to take phase analysis and surface profile detection for the finishing workpiece polished with CeO2 abrasive. The chemical reaction mechanism and the material remove mechanism of silicon nitride ceramics materials in CMP process with CeO2 abrasive are both analysed and discussed in this paper. The research result shows that an extremely smooth surface of silicon nitride ceramics materials workpiece with roughness 5nm Ra is obtained after CMP process with polyurethane polishing pad and CeO2 abrasive.