Search

The geometrical precision of cylindrical rollers is a crucial factor influencing the rotation accuracy of the cylindrical roller bearing and limits of the rotation speed, load bearing capacity and serving life of the bearings. A novel lapping method with a circulating system for batch machining of ultraprecision cylindrical rollers is presented based on the principle of precision evolution. The variations of roller diameter and roundness are improved due to the effect of selective material removal. That is, more material is removed at the convex position for a single roller, and also for the balls with larger diameters, because higher stress concentrated in these areas will lead to plastic deformation and failure. Self-rotation of the rollers was realized by the application of electromagnetic force. Batch lapping of cylindrical rollers was carried out on a newly developed lapping system for approximately 500 rollers. After lapping 90 cycles, the variation of roller diameter for the randomly selected ten rollers, roundness and surface roughness were 0.76 µm, 0.4 µm and 14.93 nm, respectively. Additionally, the variation of roller diameter of 100 randomly selected rollers was 0.97 µm. This geometrical accuracy is higher than that of the highest standard class G1. This method realized the machining of ultraprecision rollers without size sorting and provided a solution for machining rollers with higher diameter consistency than that of the normal industrial manufacturing method. Based on the principle of precision evolution, this work provides a novel machining approach for batch machining of high precision cylindrical rollers. [ABSTRACT FROM AUTHOR]

Surface quality of workpiece could be significantly improved by ELID grinding. However, ELID grinding bearing outer ring raceway with small inner diameter has small space, which limits installation of electrode. In this work, ELID grinding bearing outer ring raceway acting as cathode is proposed. But electric spark discharge will occur in ELID grinding with workpiece-cathode, which affects grinding quality. The purpose of this work is to investigate formation mechanism of electric spark discharge and influence of oxide layer on grinding quality. A novel experimental method is proposed to study state of oxide layer (mainly thickness and compactness) in ELID grinding bearing outer ring raceway with workpiece-cathode. Experimental results show that electric spark discharge occurs with thick oxide layer (characterized by control current), resulting in corroded pits on surface of oxide layer and workpiece in ELID grinding with workpiece-cathode. With increased control current, surface of oxide layer becomes smooth. Moreover, grinding force increases with increased control current. When control current is 0.5 A, surface roughness of workpiece is the largest. And surface roughness of workpiece increases with increased control current, as control current is greater than or equal to 1 A. The results are helpful to apply ELID to grind bearing outer ring raceway and improve ELID grinding performance. [ABSTRACT FROM AUTHOR]

Edge surface grinding has been widely applied in achieving functional surfaces and repairing the damage surfaces of carbon fiber-reinforced plastic (CFRP) composites especially with complex three-dimensional features. The conventional surface grinding (CSG) usually generates surface damages, leading to reduced service life and load-carrying capability of the parts. Therefore, there is a critical need to develop a surface grinding process of CFRP composites in a high-quality and high-efficiency way. Rotary ultrasonic machining (RUM) surface grinding has been proven to be such a process. In addition, RUM edge surface grinding can be conducted by up surface grinding or down surface grinding. However, the difference between up surface grinding and down surface grinding with RUM has not been reported. In this paper, the comparison between up surface grinding and down surface grinding with RUM is studied for the first time. The effects of the grinding parameters on machining performance, including cutting force, surface roughness, and surface morphology characteristics, are experimentally studied. The results show that the cutting forces in up grinding are obviously larger than those in down grinding. Lower surface roughness is generated by down grinding when grinding parameters are kept unchanged. The reasons for the differences of cutting forces and surface integrity are discussed. Surface morphologies suggest clearly that brittle fracture is the predominant material removal mode in grinding of CFRP composites. The chip size of the resin, the fracture size of the carbon fiber, and the material removal scale are smaller in down grinding. Furthermore, compared with CSG, the advantages of RUM surface grinding are presented. This investigation will provide useful guidance for surface grinding of CFRP composites. [ABSTRACT FROM AUTHOR]

The machining mechanism of woven ceramic matrix composites is one of the most challenging problems in composite application. To elucidate the grinding mechanism of the woven ceramic matrix composites, a new model material consisting of unidirectional CVI-C/SiC was prepared and ground. The composite was ground in three typical directions and the experimental investigation of the surface grinding process for this composite is described. In addition, the micro structural characteristics and grinding mechanism of the composite were analyzed. The result shows that brittle fracture is the dominant removal mechanism for grinding of the C/SiC composites, and the destroy form of the composites is mainly the syntheses of the matrix cracking, fiber fracture, and interfacial debonding. The grinding force follows the order: Normal > Longitudinal > Transverse, and the surface roughness follows: Longitudinal > Normal > Transverse. The grinding parameters (feed speed, cut depth, grinding speed) have great influence on the grinding force and surface roughness. Based on the findings, the grinding force and surface integrity of the woven ceramic matrix composites can be predicted. Furthermore, it is expected to provide a useful guideline for the design, evaluation and optimal application of the C/SiC composites. [ABSTRACT FROM AUTHOR]

The oxide layer state directly relates to machining quality in electrolytic in-process dressing (ELID) grinding. In this paper, intermittent grinding control strategy was used to monitor and control the state of the oxide layer in interval ELID (ELID II) grinding. Some experiments were implemented based on active control of the oxide layer state. The influence of dressing current, wheel speeds, and grit size on surface roughness and waviness has been discussed in detail with ELID II grinding for bearing steel. The experimental results illustrate that the ELID II method can realize a stable grinding process based on active control of the oxide layer state. The surface roughness (Ra) and waviness (Wa) increase with increase of the dressing current. When the dressing current is constant, Ra and Wa reduce as wheel speed increases and decrease as grain size of wheel decreases. The experimental results also show that sufficient abrasive protrusion can be ensured in ELID II grinding, especially for grinding with a W2.5 super-abrasive wheel which may produce a very smooth surface quality, Ra 0.0166 μm and Wa 0.018 μm. [ABSTRACT FROM AUTHOR]

Abstract: The oxide layer state directly relates to the grinding efficiency and machining quality in electrolytic in-process (ELID) grinding. However, no proper and detailed information has been found about internal grinding by controlling the state of the oxide layer. Therefore, in this investigation, some experiments have been conducted based on the active control of the oxide layer state to study internal grinding performance and ground surface qualities. The experimental comparison with the traditional ELID grinding has been carried out to prove the advantages of the proposed method in dynamic equilibrium. The influences of the grinding and electrical parameters on the workpiece surface quality, force characteristics and material removal rate of internal machining of bearing steel have been investigated in detail. The experimental results show that the new method can realize a stable internal grinding process even with finer abrasive wheels of W10 and W2.5. [Copyright &y& Elsevier]