Papers by Author: Ju Long Yuan

Abstract: Silicon nitride ceramic balls are successfully applied in advanced bearings. In order to improve the performance and precision for ball bearings, the research about the material properties of Si3N4 ball is shown in this paper. For the Si3N4 ball, the material properties can be described by the following factors: density, hardness, apparent porosity, crushing load and fracture toughness. In this paper, Si3N4 balls from three different manufacturers are tested to reveal the inherent correlations of the material properties, and the correlation coefficients are calculated. The results indicate that with the increasing of ball diameter, its crushing load increases correspondingly. The higher hardness contributes to the lower crushing load of the Si3N4 ball. Apparent porosity has a greater influence on the crushing load than hardness and the density. Hardness has the closest relevance with fracture toughness among the material characteristics, with the increasing of the hardness, the fracture toughness of Si3N4 ball becomes lower.

Abstract: A new polishing method by using fixed soft abrasive film is proposed to polish the end-face of the optic fiber connector. In order to study the wear property of the fixed soft abrasive film, the Particle Flow Code program was employed to simulate the interaction of surface topography. The discrete element model of the optic fiber connector and the fixed soft abrasive film were established. Through the interaction of the surface of two models, the process of contact and friction between the fixed soft abrasive film and the end-face of the optic fiber connector could be simulated. Simulation results showed that the main factors affecting the wear of the fixed soft abrasive film were pressure and speed, which mainly affected the normal stress and the tangential stress respectively. And the wear of the surface was mainly related to pressure and speed. The greater the speed and pressure were, the more serious wear of the fixed soft abrasive film was.

Abstract: To achieve the components of the highest quality in terms of shape, dimension, surface integrity and high efficiency in the course of processing difficult-to-cut material, the concept of self-sharpening fine super-hard abrasive tool as machining tool is put forward, this method not only improves the dressing performance of the abrasive tool, but also ensures the accuracy and durability of the abrasive tool, self-sharpening fine super-hard abrasive tool lapping technology is developed by using Zn as abrasive fillers and using FeCl₃ solution as lapping liquid, the wear form of the self-sharpening fine super-hard abrasive tool and the influence of abrasive wear on the material removal form is studied, research shows that the wear of the self-sharpening fine super-hard abrasive tool is mainly in breakage wear, which has a good self-sharpening performance, and the material removal form is mainly in two-body material removal mode., which means this method has good holding force of abrasives.

Abstract: The rolling element is the most important component of rolling bearings. Its geometric accuracy and consistency affect greatly the performance and working life of bearings. In this paper, a standard Taguchi L9(34) orthogonal array(oa) is designed to analyse how abrasive size, rotating speed of plates, deflection angle of carrier holes and other factors impacting on precision of cylindrical roller process and achieved the optimized parameters combination by adopting evaluation of Signal-to-Noise ratio and ANOVA analysis(analysis of variance). Under the optimized lapping condition, the roundness,pand s can reach , and respectively.

Abstract: The Quartz substrates are widely used in various fields, and the requirement for the surface quality of quartz substrate is higher than ever before. This paper focuses on the ultra-precision polishing technology for the quartz substrates, and the material removal mechanism in the process of ultra-precision polishing is discussed. The results showed that an extremely smooth surface of quartz substrate was obtained in the ultra-precision polishing process, and the best surface roughness reached Ra 0.82nm. Meanwhile, the thickness can be controlled very well.

Abstract: As a typical multi-functional single crystal material, Lithium tantalate (LiTaO₃ or LT) exhibits its excellent electro-optical, pyroelectric and piezoelectric properties, and has now been widely applied into many applications, especially in the telecommunication field. However, the most critical issue in the process is its pyroelectric effect and piezoelectric effect which potentially leads to crack initiation during grinding. Because it is rich in plasticity, LT demands larger specific energy for material removal. As the most machining energy is eventually converted into heat, LT undergoes a rapid rise in temperature during the grinding process, thus highly risks in thermal shock. In order to clarify the thermal influence on the grinding process of LiTaO_3, the effects of coolant temperature, diamond grinding wheel geometry and material of substrate are investigated in this research. The experimental results show that the increasing rate of grinding torque (or force) and surface roughness are two major factors dominating the crack initiation during grinding of LT wafers. Via a DOE (design of experiment) analysis, coolant temperature and wheel type stand out as the main factors influencing on the increasing rate and wafer surface roughness.

Abstract: In order to improve the efficiency of ultra-precision processing, the self-sharpening fine super-hard abrasive tool is presented to reduce or eliminate the surface and subsurface defects and improve the process efficiency. In the study of efficient experimental research of self-sharpening fine super-hard abrasive tool, base on single factor experiments such as additives composition, grinding speed, grinding pressure and processing liquid. The results showed that the wear rate of the self-sharpening fine super-hard abrasive tool can reach appropriate rate when the additive concentration 30wt%, grinding pressure 45N, grinding speed 60rpm and processing liquid 1wt%.

Abstract: This paper represents a dual-plane polishing method for ceramics ball. Compared with traditional ball polishing method, its upper and lower plate are all flat and easy to use soft pad to polish, so it can largely reduce the surface mechanical damage and obtain high quality processing surface. This paper analyzes surface polishing trajectory by calculation and simulation to test the polishing trajectory uniformity. A mathematics model of polishing process is established to disintegrate the process of a balls movement. Experiment is operated in dual-plane planetary polishing machine. The result shows that perfect polishing surface and spherical error can be obtained under the proper process parameters, the surface roughness achieves 4nm and the spherical error can reach 0.217μm.

Abstract: The dynamic characteristics of a hydrostatic and hydrodynamic journal bearing with two arrays of eight holes have been investigated theoretically by the three-dimensional Computational Fluid Dynamics (CFD) models with respect to equilibrium position. The various dynamic coefficients for design parameters, such as orifice diameter, length to diameter ratio, eccentricity ratio, supply pressure, and rotational speed, are analyzed systematically under the action of displacement disturbance and velocity disturbance which are considered by the User Definition Function (UDF) programs. Results show that the dynamic coefficients greatly affected by design parameters. The cross stiffness coefficients increase rapidly more than direct stiffness with an increase of length to diameter ratio and rotational speed. Conversely, the direct stiffness coefficients are larger than cross stiffness with an increase of supply pressure and eccentricity ratio. It indicates that the journal bearing with two arrays of eight holes is suitable for their applications to small diameter grinding spindle by the means of optimizing the operating parameters and the structural parameters in order to obtain a better dynamic characteristic.

Abstract: Abrasive machining is an important process for the manufacturing of advanced ceramics. The demand for advanced ceramics with better quality and higher efficiency presents tremendous challenges for abrasive tools in the advanced ceramics industry. The concept of semi-fixed abrasive machining with a newly developed semi-fixed abrasive tool (SFAT) as machining tool is put forward. This paper presents an experimental investigation for SFAT wear into course of machining single crystal silicon with SFAT. Process parameters (water flow, load and velocity) influencing the SFAT wear are analyzed. Influencing factor of SFAT wear in processing course has been clearly demonstrated.