Papers by Author: Jia Jin Zheng

Abstract: The correction process of balls roundness error during lapping is discussed qualitatively. Dynamic analysis for rotated dual-plates lapping mode of ceramic balls is performed, under the assumption of a fluid loading system. The effect of the damping of the loading system on the correction of balls roundness error is discussed. And the result shows large damp causes an increase of magnification of load, and improves the correction of roundness error of balls.

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: Polishing pad plays a key role in determining polish rate and planarity of a chemical mechanical planarization (CMP). The properties of the pad would deteriorate during polishing because of pad surface grazing, which results in reduced removal rates and poorer planarity of wafer surface. Pad conditioning and its influence on pad surface structure and CMP process is introduced and discussed in this paper. The study shows that the surface structure can be regenerated by breaking up the glazed areas with conditioner, MRR(Material Removal Rate) can be maintained at high level with proper pad conditioning, and UN(Non-uniformity)can also improved. Orthogonal experiments design is employed in this study to determine the best conditioning parameters.

Abstract: The pad is one of the key factors in the chemical-mechanical planarization (CMP) process. To ensure the machining capability and the quality of workpieces, the pad must be conditioned in the process. It will cause the pad thiner, and be replaced by a new one for losing the machining capability finally. For this reason, a new method of CMP by using the continuous composite electroplating on the polishing disc is introduced. In this process, the machining ability of the pad can be ensured due to the continuous Sn-SiO2 composite electroplating. The effect of cathode current density and time of plating on the characteristics of composite coating and silica wafer are investigated. The experiment indicates that the continuous composite electroplating polishing (CCEP) is an efficiency method for polishing silicon wafer, and the surface roughness of the silicon wafer is 0.005μm

Abstract: Cesium Lithium Borate (CsLiB6O10 or CLBO) is the most effective non-linear crystal which generates ultraviolet harmonics of the Nd:YAG fundamental laser wavelength. In order to enhance the damage threshold, low CLBO surface roughness, by ultra-precision machining, is needed. Because the CLBO crystal has easy hydroscopic reaction and micro scratches in machining, ultra-precise machining of the CLBO crystal is a difficult technical problem. In this paper, the new lapping slurry and polishing slurry are introduced. And the deliquescence degree of CLBO is fallen to lowest. A new working technology is also adopted. After rough polishing, the concentration of ultra-precision polishing slurry is increased properly. So does the ultra-precision polishing speed, and the wiping speed is faster than the deliquescence speed. The CLBO crystal surface roughness can achieve 1nm and keep the surface quality well.

Abstract: It is of high importance to avoid scratches in lapping process. A Grain Size Sensitivity (GSS) model is put forward in this paper. The GSS is a relative parameter which defines the relative change of the depth of cutting, influenced by the change of the size of grain powders, by which it is possible to evaluate quantificationally the capability of lapping machines in avoiding scratches. It is useful for designing and using lapping machines. The simulating of lapping processes based on GSS model is carried out. The transferring of error is also discussed and a new structure of lapping plate with spring cells developed by the authors is introduced.

Abstract: A novel lapping mode is developed on the base of present eccentric v-grooves lapping mode for precise balls. The kinematics analysis shows that the ball spin axis can wiggle up to 180° under the developed mode, so the lapping trace will be dispersed onto the whole surface of the ball. The effect of offsetting and groove radius on the lapping uniformity in the developed eccentric v-grooves, the present eccentric v-grooves and the traditional v-grooves lapping mode are compared, and the advantage of the developed mode is that the impact offsetting is less while the groove radius has no impact.

Abstract: Crack width is a significant parameter for assessing service life of reinforced concrete structures in chloride-laden environments. Corrosion-induced concrete cracking is a predominant causal factor influencing premature degradation of reinforced concrete structures, incurring considerable costs for repairs and inconvenience to the public due to interruptions. This gives rise to the need for accurate prediction of crack width in order to achieve cost-effectiveness in maintaining serviceability of concrete structures. It is in this regard that the present paper attempts to develop a quasi-brittle mechanical model to predict crack width of chloride contaminated concrete structures. Assuming that cracks be smeared uniformly in all directions and concrete be a quasi-brittle material, the displacement and stress in a concrete cover, before and after surface cracking, were derived respectively in an analytical manner. Crack width, as a function of the cover depth, steel bar diameter, corrosion rate and time, was then determined. Finally, the analysis results were verified by comparing the solution with the experimental results. The effects of the cover depth, steel bar diameter and corrosion rate on the service life were discussed in detail.

Abstract: A three-phase composite circle model is presented in this paper to assess the effect of interfacial transition zone (ITZ) on the chloride diffusion coefficient of concrete. Firstly, the distribution of circular aggregate particles was simulated in a square concrete element. Based on the simulated concrete mesostructure, the Monte Carlo algorithm was adopted to numerically evaluate the ITZ area fraction for different concrete mixes. A parametric study was then conducted to quantify the effects of the largest aggregate diameter, ITZ thickness and aggregate gradation on the ITZ area fraction. Secondly, the ITZ was modeled as a thin-wall annular plate located between a circular aggregate particle and a thick-wall cement paste annular plate. With the three-phase composite circle model, an analytical solution was derived for the chloride diffusion coefficient of concrete. Finally, the derived solution was verified by experimental results obtained from the research literature and a quantitative relationship between the thickness and chloride diffusion coefficient of ITZ was established.