Key Engineering Materials Vols. 359-360

Abstract: In this study, Fe3O4 particles were used as magnetic particles to form Fe3O4 magnetorheological (MR) fluid, and experiments were conducted to polish optical glass using this Fe3O4 MR fluid. The machining characteristics of glass surface with different MR fluids that are added diamond abrasives and short fibres are studied. Experimental results indicate that the tiny-grinding wheel based on the Fe3O4 MR fluid can effectively polish optical glass and that the maximum diameter and depth of machined region increase obviously in the presence of diamond abrasives and short fibres. When both of diamond particles and short fibres are added to the Fe3O4 MR fluid, the removal efficiency of the tiny-grinding wheel is markedly enhanced due to the synergetic effect of diamond abrasives and fibres.

Abstract: At present, crankshafts with larger size are finished mostly by abrasive cloth and manual steel brush, which is not ideal on finishing quality, efficiency and cost, especially cleanness degree does not meet design and use request. So horizontal spindle barrel finishing has been developed and has good finishing effects for crankshafts with small size. But this process has bad uniformity for connecting rod journal of crankshafts with larger size by simulation experiments. Aimed at the size, shape and weight of crankshafts with larger size, theoretic research is done, and main factors for finishing uniformity are analyzed. Finally its finishing project is defined and experiments are done. The research indicates that this process is very effective for crankshafts with larger size, and has also positive influence on efficiency and auto product line.

Abstract: For precision grinding, especially the aspheric grinding, the vibrations of wheel and workpiece have great impact on workpiece accuracy and roughness with special waviness. This paper firstly studies the relationship between grinding parameters and surface quality. Then according to the two kinds of aspheric machining mode: grinding with equal step feeding and grinding with equal angle feeding, the corresponding surface equations and vibration equations after grinding are given in this paper. Moreover, the specific analysis of aspheric surface model and surface waviness are also discussed for parameters optimization. The grinding experiments are done to support the theoretical research. The comparison between theoretical waviness analysis and experimental results shows good matching.

Abstract: Micro abrasive jet machining (MAJM) is a high effective economical technology for three dimensional micro structure fabrications of brittle materials. It is widely used in the fabrication of semiconductors, electronic devices, micro electro-mechanical systems (MEMS), optical-electronic and optical devices, and medical instruments. In this paper, based on the experimental study of MAJM for glass, the influences of the nozzle type/size and abrasive type on the material erosion rate and structure profile are analyzed. The results show that the rectangular nozzle can yield a more accurate and efficient machining performance due to reduced flux effect. By contrast, with round nozzle all the cross section profiles of the machined patterns show rounded V-type shape. The rectangular nozzle is able to produce geometry with flat shape. The machining area is almost independent of the abrasive hardness, and the erosion rate increases with the increase in the hardness of the abrasive grits. The nozzle geometry is of great importance for machining accuracy and the efficiency.

Abstract: Ultrafine grain WC hardmetals were manufactured successfully from mixed powders of nominal composition of WC-6Co-1.5Al(wt%). To manufacture bulk ultrafine grain WC alloys, nanocrystalline WC powders as precursor were prepared for sintering from the mixed commercially available powders by high energy milling of 15 h. Then the electrical current sintering process of the milled powders was further studied. Experimental results showed that the density, hardness and transverse rupture strength of the sintered alloys reached 14.224 g/cm3, HRA 94 and 1660 MPa, respectively, by a appropriate coupling of pulse- and subsequent constant-current sintering and with the total sintering time of 6 min. It seemed difficult to obtain desirable sintered hardmetal by a single type of electric current sintering. However, the application of intensive pulse electric current was favorable to sintering, although it was difficult to achieve good WC alloys only by the pulse electric current sintering. A higher density WC alloy could be prepared by enlarging the electric current when only constant electric current was applied to sinter the milled powders. Unfortunately, the WC grains substantially coarsened concurrently so that the mechanical properties of the as sintered alloy decreased obviously.

Abstract: Ultrasonic vibration can reduce honing forces efficiently. As the honing wheel can be washed by ultrasonic cavitations of cooling liquid, its jams are decreased and the higher honing efficiency has obtained. Therefore, the combination of ultrasonic machining and gear honing is a method for gear fine machining with its wide application future. However, the gears with big diameter and thickness machined by ultrasonic honing are special loads, which influence the machining frequency of vibration system heavily. Hence, the horn and gear must be considered at the same time while designing the vibration system. In this paper, the frequency equations are derived according to stress match, wherein, the gear is considered as a thin disc and catenary horn is adopted. Then the influences of vibration of transformer that consists of horn and gear are investigated with the variety of the horn length and the machining frequency. The theoretical analysis shows that the resonance frequency of the horn and detune frequency of transformer have the different value. The results are proved by FEM, too.

Abstract: A new kind of ultrasonic machining method named ultrasonic machining aided tool rotation is proposed for sintered NdFeB permanent magnet. In the process abrasive slurry enters the machining area through holes in the rotary tool which can assure the grains easily enter the machining surface slurry. Its machining mechanisms are studied and material removal model is developed. Experimental research was carried out on self-made equipment. Experimental results were accordance with the developed model. It is proved that this new kind of ultrasonic machining technology is suitable to machine deep hole for sintered NdFeB material.

Abstract: Rotary ultrasonic machining (RUM) is considered as an effective machining method, which has been utilized to machine hard and brittle materials such as advanced ceramics. In order to improve the hole wall surface quality during RUM, it is important to wash away swarf in the gap between the tool and the workpiece as fast as possible. In this paper, a new machine process – intermittent rotary ultrasonic machining (IRUM) – is introduced for the first time. The cutting force, surface roughness and coolant flow rate in conventional rotary ultrasonic machining (CRUM) process and IRUM process are compared. It is found that compared with CRUM, the output coolant flow rate could be increased significantly by using the IRUM method. It is also found that the surface roughness of workpiece can be improved significantly in IRUM.

Abstract: Based on the machining pattern, mechanics of material removal and theory of micro-indentation, in previous studies the models of material removal rate of hard-brittle materials was discussed through the relatively influencing factors of machining parameters from various aspects, reflecting the research advances on mechanics of material removal of hard-brittle materials. However, those models of material removal rate have limitations, which results from impercipient theory of fracture of new kinks of materials, randomicity of practical machining process, inappropriate assumptions and simplification of the machining conditions and so on. In this work firstly, previous models of material removal rate of hard-brittle materials machining with ultrasonic assistance were reviewed briefly. Subsequently, the models of material removal rate of complex ceramics machining with two-dimensional ultrasonic vibration assistance were established based on fracture theory of micro- indentation in fracture regime and plastic removal mechanics in ductile regime respectively. The material removal rate is affected not only by the properties of material and machining parameters, but also by the character of grinding wheel and parameters of ultrasonic vibration.

Abstract: Ultrasonic-vibration-based hardened-gear honing is creativity technique in the domain of gear finishing. The honing technique is improved by introducing ultrasonic machining to improve the accuracy and surface quality of hardened-gear. With respect to the design and manufacture of ultrasonic-vibration-based gear honing machine, the paper refers to reasonable project and trial-manufacture. The electroforming technique of spur gear CBN honing-wheel is helpful to improve the comprehensive performance of honing-wheel. Finally the characteristic and advantage of ultrasonic vibration based gear-honing technique is described.