Papers by Author: Ping Zhao

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: An oscillating-plane lapping method, by which pre-sintered ceramic ball blanks are shaped before full sintering, was proposed to improve the precision of the ceramic ball blanks. For good sphercity and diameter consistency of ceramic ball blanks obtained after this shaping process, much less workmaterial is needed to be removed in the following lapping process of the full sintered ceramic ball blanks. Shaping experiments were carried out on a newly developed oscillating-plane lapping device. Results show that material removal rate of the pre-sintered Si₃N₄ ball blanks with nominal diameter Ø13mm reaches 0.92mm/h in average. The sphericity error is reduced from 0.07-0.196mm to 0.002-0.006mm, and the consistency error of diameter is reduced from 0.309 to 0.019mm after 45min's shaping. Compared with the processing time of the unshaped full-sintered blanks in the following lapping process, it takes just a half time for the shaped full-sintered blanks to be semi-finished in this study. It indicates that the oscillating-plane lapping is a promising high efficient method to improve the precision and consistency of the ceramic ball blanks, and the efficiency of the followed lapping process can be improved notably.

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.

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: The lapping trace distribution on ball surface is one of the key factors during the lapping process, which can affect the sphericity of lapping. The Rotated Dual-Plates lapping mode (RDP lapping mode) can achieve better uniformity of lapping trace distribution on precision ball surface, which ensure the results of forming sphere by lapping. Combining with the basic principle of RDP lapping mode, as well as the analysis of the kinematics of the RDP lapping method, this paper puts forward a basic rule about the material removal at the contact point between the ball and the plate with the material removal rate equation of bearing steel, and the improvement of the sphericity which can be simulated, and is defined as the lapping uniformity according to basic rule equation. The influence caused by the lapping pressure and the speed of the plates are considered in the simulation, the surface of ball is triangle grid divided. The uniformity of lapping is evaluated at different speed ratio, and eventually a better curve of the speed ratio can be got, so the lapping uniformity during the RDP lapping mode can finally be accurately evaluated.

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: To evaluate the characteristics of semi-fixed abrasive plate (SAP), several parameters and relevant measurement methods are developed. The characteristic parameters include shore hardness, compression ratio, resilience ratio and shear strength. Five semi-fixed abrasive plates are manufactured with different bond concentration. The test results of five characteristic parameters of the SAP show the shore hardness, resilience ratio and shear strength increase, and compression ratio decreases with the bond concentration increasing. This test can provide instructive guides to the manufacture of SAP which can fit different occasions by changing the concentration of adhesives.

Abstract: Semi-fixed abrasive is a novel abrasive. It has a ‘trap’ effect on the hard large grains that can prevent defect effectively on the surface of the workpiece which is caused by large grains. In this paper, some relevant experiments towards silicon wafers are carried out under the different processing parameters on the semi-fixed abrasive plates, and 180# SiC is used as large grains. The processed workpieces’ surface roughness Rv are measured. The experimental results show that the surface quality of wafer will be worse because of higher load and faster rotating velocity. And it can make a conclusion that the higher proportion of bond of the plate, the weaker of the ‘trap’ effect it has. Furthermore the wet environment is better than dry for the wafer surface in machining. The practice shows that the ‘trap’ effect is failure when the workpiece is machined by abrasive plate which is 4.5wt% proportion of bond in dry lapping.

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: 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