Papers by Author: Ju Long Yuan

Abstract: Multi-array hole-entry hybrid journal bearings have been widely applied to support the high speed precision machine tool spindle with small diameter used in high efficient inner grinding, due to their prominent properties of high rotation accuracy, high dynamic stiffness, high vibration damping and long life. But the imperfection of the hybrid bearing is the significant temperature rising in the oil film on the condition of high speed operation, which brings about the sharp decreasing of load capacity and the larger thermal deformation of the bushing that cause the bearing failure immediately. In this paper, CFD analysis of the temperature fields of the multi-array hole-entry hybrid journal bearing with various bearing construction parameters and operation parameters are presented. According to the simulation results, the temperature rising in the oil film can be controlled efficiently by optimizing the matching of the bearing construction parameters and operation parameters and excellent characteristics of load capacity and static stiffness have been obtained simultaneously.

Abstract: ‘Trap’ effect of the newly developed semi-fixed abrasive tool (SFAT) plays key role in decreasing the surface damages of advanced ceramics caused by the undesirable large particles emerging in machining area. Influences of characteristics of the large particle, such as size, shape and concentration, on the ‘trap’ effect of SFAT are studied with Particle Flow Code (PFC) simulation and lapping experiments. A normalized normal force is defined to evaluate the ‘trap’ effect in PFC simulation, and surface roughness is taken as an indicator in lapping experiments. The results show that the change of surface roughness is according to the one of normalized normal force. Bigger normalized normal force is better for ‘trap’ effect and surface roughness. ‘Trap’ effect works well when the large particle is in small size, sharp shape, and low concentration. In this study, the followed characteristics of the large particle are good for ‘trap’ effect of SFAT made of 1000# SiC abrasive: size <17µm, corner angle < 60°, and concentration <18 particles per mm2.

Abstract: Multi-wire sawing is a novel method for slicing silicon. The tension control of wire is a vital factor that has impaction on the slicing process. Along with the modern wind machine developing to higher speed and precision, tension control technology becomes more important. This paper introduces a closed-loop tension control system with the digital signal processor (DSP) with function modules as its control kernel, the alternating current (AC) servo motor as execute element and the radius-following device to accomplish the real-time radius compensation. The mechanism of the tension control system is analyzed and the numerical model is set up. The compensation technique of the radius of the scroll is analyzed. Experimental results show that the system is well qualified with high control precision and high reaction speed.

Abstract: A novel control strategy for on-line polishing wheel wearing compensation in a polyhedral glass grinding machine is proposed, which is mainly consisted of hybrid feed-forward feed-backward control scheme and adaptive wearing prediction algorithm. It has advantage of eliminating the size excursion of polishing roller during long term operation, while the implementation of high accuracy diameter measurement is unnecessary. Hence it greatly reduces the demand for precise sensor and complicated calculation algorithm. Consequently, surface polishing quality and flexibility of the grinding machine was enhanced greatly. Theoretical analysis and experiment result obtained from a laboratory prototype shows good agreement, which indicates that the proposed control strategy has good performance in polishing wheel diameter compensation applications.

Abstract: The deflection of cutting wire on multi-wire saw is determined by cutting wire tension, diameter ingot feed force and some other factors, and it affects the quality of silicon wafers greatly. In this paper, the initial stage of cutting process is analyzed and modeled with three ODEs. Then the numerical solutions are solved by finding out the BVPs of each ODE. The numerical solutions showed the relationship between the deflection and the cutting parameters such as cutting wire tension, diameter and ingot feed force. This method is helpful for the further research of modeling the entire cutting process.

Abstract: Water-lubricated hybrid journal bearings have been developed to support the ultra-precision machine tool spindles, due to the prominent properties of high load capacity and stiffness, high rotational accuracy, excellent thermal stability, low power consuming and environmental friendliness. Quasi-analytical procedures are deduced to present a relatively easy and rapid method for estimating of the parameters of the water-lubricated hybrid bearings without resorting to complex full numerical calculation. The procedures are based on the lumped resistance method, which have been extended to the situation dominated by the turbulence and inertia effects. The results show good agreement with the full numerical solution, especially when the bearing operating at moderate eccentricities. The procedures can be taken as a real time analytical tool for parametric study and preliminary engineering design of water-lubricated hybrid journal bearings.

Abstract: Electrical and magnetic characteristics of motorized spindles have a great effect on machining quality of ultra-precision machine tools. Bad characteristics will result in significant heat losses, low efficiency and large vibration. Study on optimizing electrical and magnetic characteristics of an inverter-fed induction motor is presented in this paper. A method of optimization design of an inverter-fed induction motor is given. The method is used to design a motor used for an ultra-precision machine tool motorized spindle. By comparing the optimal design with the traditional one, it shows that the total electrical and magnetic heat losses are obviously decreased and the efficiency can be improved.

Abstract: Studies on chemical mechanical polishing (CMP) for silicon nitride (Si3N4) balls with CeO2 abrasive carried to investigate the mechanism of chemo-mechanical action between silicon nitride and CeO2. It is found that CeO2 is more effective to obtain smooth Si3N4 balls than other abrasives, and extremely smooth Si3N4 balls with surface Ra 4nm were obtained after polishing. XRD test is used to detect the reaction resultants on the ball surface, and the results show that SiO2 is the main resultant of the chemical reaction between Si3N4 and CeO2, and the test results confirm the correctness of thermodynamic analysis based on Gibb’s free energy of formation. It is also found that water play as a key factor in CMP.

Abstract: With increasing trend toward automatic manufacture and demands for improved quality, position of ultra-precision machining processes is considered as more and more important. As the main processes of ultra-precision machining, abrasive machining processes can be chiefly divided into free abrasive processes and fixed abrasive processes. Typical techniques such as chemicalmechanical polishing, ELID, Flat Honing and so on have been reviewed and compared with each other in preliminary aspects such as surface quality, finish accuracy and finish efficiency. The development trend of ultra-precision abrasive machining will have great efforts on realizing the integration with high accuracy, high efficiency and low cost.

Abstract: Lapping plate wear is of great influence on shape precision of workpiece. Investigation on the wear uniformity of uncertain eccentricity plane lapping was carried out in this research. The relative velocity function of the plate to the workpiece is obtained through kinematic analyses in the mode of uncertain eccentricity plane lapping, and material removal rate (MRR) function and wear uniformity function were deduced based on Preston equation. Effects of the ratio and eccentricities on the wear uniformity are discussed in detail through MATLAB simulation. Theoretical analysis and simulation results show that the ratio k1 of workpiece revolution speed to lapping plate is the key to decide whether the lapping plate is lapped uniformly. Theoretically, when k1<0, the greater |k1| is, the better the lapped uniformly of lapping plate can be. The ratio k2 of workpiece rotation speed to lapping plate has great influence on the lapped uniformly when k1 approximate 1, and k2 has little influence on the lapped uniformly when k1<0 or k1>1, Besides, a bit bigger eccentricity e1 is propitious to the lapping uniformly of the lapping plate, and bigger eccentricity e2 are also helpful to lapping uniformly of the lapping plate. And the conclusion could be extended to single-side plane lapping and double-side plane lapping process.