Advanced Materials Research Vols. 53-54

Abstract: We developed a nanoparticle colloid jet machining to fulfill the requirement for ultrasmooth surface in terms of the studying on micro structure of work surface, the high surface energy and intense adsorption of SiO2 nanoparticle. In this paper, three types impact in nanoparticle colloid jet machining have been analysed and the atom removing model has been founded based on the physical chemistry theory of solid surface and interface. The factors which may influence the nanoparticle colloid jet machining quality (such as the diameter of nanoparticle, colloid jet velocity and dynamical viscidity) have been studied to provide theoretical support for further studying in nanoparticle colloid jet machining.

Abstract: The simulation of the gas-solid two phase flow inside the abrasive jet nozzle is studied by the computed dynamic software (CFD)-FLUENT, the velocity field of the two phase flow and the trajectory of the abrasive inside the nozzle are obtained. The Eulerian multiphase model and the DPM model have been used to compute the two-phase flow field. The simulation results express that the velocity of the jet is slow at the inlet, while it will be increased with the area of the section decreasing, the cone angle of the nozzle affects the flow field very much, the flow has low turbulence and the gradient of the velocity is small when the cone angle is small, while the velocity of the flow increased rapidly and the gradient of the velocity is big when the cone angle increasing. The simulation results also express that the arc radius affects the flow field greatly, the flow will move more smoothly when the arc radius is large. The pressure field of the wall expresses that the nozzle will wear rapidly at the corner of the nozzle, the reason is that the pressure is big or changed greatly, the fatigue wear and the blast wear will happen at those place.

Abstract: In this paper we discuss the temperature dependence and its effect on surface roughness. In abrasive flow machining (AFM) process the temperature of media rises drastically due to procedure of being sheared. To examine the effect of media temperature on surface roughness, an experiment system with the functions of controlling, measuring and recording temperature is set up. The variable trend of media temperature is revealed during AFM. Experiments are performed at different temperatures. Experimental results show that the media at high temperature results in less improvement in surface roughness. Therefore the media can have good machining performance in the first few cycles and the media temperature rise rapidly. Finally we conclude that the best workable temperature should be below 25 °C during the AFM.

Abstract: To the processing requirements of high precision small dimension and high surface quality for internal spherical surface with through hole processing, a new technological method of precision turning was proposed in this paper, the processing equipment and control system were designed and developed, the parameters of precision turning technology were given. Through precision turning experiment’s verification, this technological method of precision turning can satisfy processing requirement, and has features of simple, high efficiency, and low processing cost. Some comparative research in various small dimension precision turning technology for internal spherical surface were also made in this paper, and conclusions full of research and processing reference value were drawn.

Abstract: Utilizing gas as the dielectric instead of dielectric liquid has enabled the development of dry wire electrical discharge machining (dry WEDM) technology for finishing cut. Experiment results showed that Low-Speed WEDM (LS-WEDM) in gas offers advantages such as better straightness, and shorter discharge gap. This paper studies on influence of different gas dielectrics, wire winding speed and pulse duration on the WEDMed surface quality (discharge gap, straightness, surface roughness, removal rate) in finishing. New attempt of applying dry WEDM as the 4th cut had been proved feasible in improving conventional multiple cut surface quality of LS-WEDM.

Abstract: A novel abrasion-assisted electroforming technique with the orbital motion of cathode is developed. The related theories are studied and experiments of nickel electroforming are carried out. It is confirmed that the hard particles can effectively remove the hydrogen bubbles and nodules by polishing the mandrel surface. A bright, smooth and compact deposit with the average surface roughness of about 0.12m is produced on a polyhedral mandrel.

Abstract: Heat-resistant steel F91, which has high heat-resistance, is widely used in valve and pipe manufacturing industry, but it is difficult to process due to its high strength and toughness. To investigate the influence of cutting parameters on the machinability of F91, a series of milling experiments based on uniform design were carried out. From the experimental data, an exponential model of milling force was set up. The result of regress analyse showed that the model had a high confidence degree. A group of optimized cutting parameters were obtained from the model for dry cutting with TiAlX coated carbide milling cutter. Cutting with the optimized milling parameters, lower milling force, higher material removal rate and less tool wear could be obtained. The prediction model showed a satisfactory agreement with those obtained from the experiments, so it can be referenced in actual processes for F91.

Abstract: The selection of manufacturing conditions is very important in manufacturing processes as these ones determine the material removal rate (MRR) of the so-obtained parts. So in this paper, based on the brief introduction of the experimental principle and the high-speed small hole EDM drilling system, effects of non-electrical parameters on MRR are discussed in detail. The relationships between MRR and these factors are also analyzed. The conclusion can provide an important reference for production in practice.

Abstract: The flow field characteristics have a significant effect on the machining stability in high-speed small hole EDM drilling. Thus, Lagrangian discrete phase model (DPM) has been developed to simulate the gap liquid-solid two-phase flow field. The numerical calculation is based on the standard k-ε turbulent model, and the SIMPLEC algorithm is used in the simulation. All the governing equations are solved by software Fluent 6.2. Through numerical simulation, the pressure distribution, the velocity distribution of the dielectric liquid, traces of debris particles, and the debris particle concentration were obtained. The flow field characteristics under different pressures and drilling depths were obtained through simulations. Finally, experiments were carried out to investigate the effects of the flush velocity at exit obtained through simulation on material removal rate (MRR).

Abstract: Rotor steel has been widely used in marine engineering and power industry because of its high yield stress and anti-fatigue performance at high temperature. The surface integrity must be guaranteed due to severe working environment. Hence it is worth studying residual stress (RS) for its significant influence on the quality of machined part. In this paper, an effective model is built with the help of finite element method (FEM) to evaluate RS induced by machining of rotor steel 26NiCrMoV145. An adaptive mesh control is introduced in this work to avoid excessive element distortion. Johnson-Cook flow stress model is proposed to model workpiece material. Rolling process is necessary to obtain desired RS according to the performance of form-milling process. In order to validate FEM predictions, both milling and rolling experiments have been carried out. The predicted RS profiles are in reasonable agreement with the experimental ones.