Key Engineering Materials Vols. 359-360

Abstract: The laser honing technique is a new surface texturing technique. As the piston ring at the top or lower oil attachment point works under worse lubrication condition, its wear increases severely, laser texturing was used to the piston ring/liner, lineary extending grooves and regular arranged dimples with predetermined parameters was well-matched with the needs of lubrication. The effects of different dimple shapes, such as sphere coronal, combined sphere coronal ,columnar, hexahedral, and trapezoidal dimples was analyzed by the theory of hydrodynamic lubrication. It was deduced that trapezoidal dimples are fit for only single running orientation and sphere coronal and combined sphere coronal dimples are fit for double running orientations. The experimental researches show that laser texturing not only can reduce the oil consumption and the cost of engine but also can prolong its work life.

Abstract: Surface microstructure of nano-composite ceramics prepared by mixed coherence system and machined by two-dimensional ultrasonic precision grinding was researched using TEM, SEM, XRD detector and other equipments. Structure, formation mechanism and characteristic of metamorphic layer of ground surface of nano-composite ceramics were researched. The experiment shows micro deformation mechanism of ceramic material in two-dimensional ultrasound grinding is twin grain boundary and grain-boundary sliding for Al2O3, and it is crystal dislocation of enhanced phase, matrix grain boundary sliding, coordination deformation of intergranular second phase as well as its deformation mechanism for nano-composite ceramics. The fracture surfaces of nano-composite materials with different microscopic structure were observed using TEM and SEM. Research shows that ZrO2 plays an important influence on the generation and expansion of crack, and enhances the strength of grain boundaries. When grain boundaries is rich in the ZrO2 particles, the crack produced in grinding process will be prevented, and the surface with plastic deformation will be smooth. The results shows nanoparticles dispersed in grain boundary prevents crack propagation and makes materials fracture transgranularly which makes the processed surface fine.

Abstract: To obtain the amorphous alloy films with superior properties by method of electrochemical deposition, the accuracy requirement for the copper substrates for Alloy Films is extraordinarily strict. The ultraprecision lapping technology for the copper substrate employing polyurethane polishing pad and flannel pad is studied in this paper, surface roughness, material removal rate and change process of surface construction of copper substrates are discussed. The influences of the different lapping parameters on the surface roughness, material removal rate and the influences of lapping load on copper substrate surface formation in the ultraprecision lapping process of copper substrate are both discussed. Experiment results show that the surface scratch will disappear by employing polyurethane polishing pad and flannel pad, and an extremely smooth surface of copper substrate with roughness 6nm Ra is obtained in the final finishing lapping process.

Abstract: Ultrasonic aided high speed lapping with solid abrasive material was put forward aimed at the precision finishing of nano ZTA engineering ceramic. Through theoretical analysis and contrast lapping experiments, the influences of ultrasonic assistance on the surface machining quality were clarified. Research results show that the maximum undeformed chip thickness in ultrasonic aided lapping is smaller than that in conventional lapping under the same conditions; ultrasonic assistance is beneficial to enlarging the range of ductile lapping regime and improving the surface quality of nano ZTA ceramic; with the application of ultrasonic vibration, smaller surface roughness and more regular surface profile can be obtained.

Abstract: The electro discharge machining (EDM) process is widely applied to produces surfaces of difficult-to-machine materials that require some form of grinding or finishing operation. This is conducted so as to improve the surface texture and appearance of the component’s surface. However, it is also desirable to remove the white uppermost recast layer or damaged surface layer (produced by the EDM process) in order to improve the functional performance of the surface. The finishing of the surface by traditional manual methods, especially in the operation of small and long internal cylinder surface, is both tedious and time-consuming. A novel electrically conductive diamond mounted point electrochemical grinding (DMP-ECG) process is being developed for hard passive alloys unclosed internal cylinder surface grinding. The process mechanism of DMP-ECG is introduced; the influence parameters of the surface roughness, machining accuracy, and diamond tool wear are investigated experimentally for nickel-based super alloys materials. An application of the DMP-ECG to aircraft engine component is verified in term of the optimized process parameters.

Abstract: Magnetic abrasive finishing (MAF) is a kind of method for polishing the surfaces and the edges. The investigation for the technique of MAF and the development of the ferromagnetic poles lay a theoretical foundation for developing a new method for finishing the curved surfaces automatically under the numerical control. In the paper, the performance parameters of the developed magneto poles, which are used for finishing the plane surfaces and the curved ones, have been tested. The curvature of the finished surface, the sloping angle of the machined surface and the rotation speed of the poles, which affect the surface roughness, are studied theoretically. What mentioned above supply references to the practical uses of the MAF, especially in the mould manufacturing.

Abstract: Ultrasonic machining is a practical process for advanced ceramic machining. Usually, ceramics with complex surfaces are machined with two common ultrasonic assisted contour machining methods, which may be classified as surface/point contact machining mode. While these methods are not suitable to machine some complex surfaces such as blade surface, so an ultrasonic assisted contour machining method using a simple shaped diamond grinding wheel to machine ceramic blade surface is presented, which is named as Numerical Control-Contour Evolution Ultrasonic Assisted Grinding (NC-CEUAG) method. In the NC-CEUAG process, the contour evolution motion of the grinding wheel is controlled by the NC system and the blade surface is the enveloping surface formed by the grinding wheel’ cutting edges when they cut into the ceramic specimen. In this paper, the relative motion between the grinding wheel and the specimen in the process of NC-CEUAG ceramic blade surface is analyzed. The mathematical models of ruled surfaces are constructed. The ceramic blades with ruled surface are machined with selected machining parameters on the retrofitting NC-CEUAG machine tool.

Abstract: The EDM can machined some superhard conducting material that cannot be handled by the traditional method, such as carbide alloy, tool steel and engineering materials etc., however, it is also accompanied with slow material removal rate(MRR) and poor surface quality (surface roughness). For some fine machining having rigorous criterion on size and surface roughness, the EDM cannot meet the demand. Some researches indicate that the MRR of small hole by electrical discharge machining combined with ultrasonic vibration (UEDM) can increase in certain range, but the surface quality is still poor. Although there are lots of the researches on the UEDM, some debates on machining mechanism and applied scope existed, and technology of UEDM needs the further study. After small hole machined by the UEDM, it is polished by ultrasonic vibrating. Two steps are includes in this technology. In the first place, on a high velocity electro discharge small hole machine with high-pressure dielectric liquid and hollow electrode, a transducer and horn are attached between the spindle and the electrode. The ultrasonic vibration of the tool electrode is implemented by connecting the horn and the tool electrode together with a chucking appliance. The second, after the small hole is complete, with the same machine tool and tool electrode the process of polishing the inwall of the small hole is carried out by accompanying the ultrasonic vibration, revolution and feed of the tool electrode with the abrasive material. In the experiments, the reference point for UEDM is found and the new theory is proposed to explain the increase of the MRR and the decrease of the surface roughness value .The polish with the ultrasonic vibration can improve further the surface roughness. The ultrasonic vibrating polish after the hole by UEDM is an economical and effective technology, which realizes machining of two procedures in one machine tool. So the process for changing machine tool and tool is not needed any more and the efficiency is further improved.

Abstract: Hard-brittle materials have been popular used in manufacture experience because of their excellent performances. However the low plasticity, frangibility and non-conduction make the machining very difficult, especially in ultra-precise surface fabrication. Therefore, ultrasonic vibration is introduced to conventional lapping for the purpose of proper lapping force, higher removal rate and fine surface quality. Through conventional and ultrasonic lapping experiment of hard-brittle materials with different lapping parameters and different vibration models, the empirical formula of lapping force in ultrasonic lapping is deduced by orthogonal regression analysis, the optimum lapping parameters are put forward and the primary and secondary influencing sequence of parameters on lapping force is presented. Moreover, the influencing rule of different lapping parameters such as rotational speed, feed speed, oilstone grit and lapping depth etc. on lapping force is carried out. Experimental results show that ultrasonic vibration lapping is a high efficient processing method adapting to hard-brittle materials.

Abstract: According to the sharp rheological characteristics of magnetorheological fluid in the magnetic field, the principle and mechanism of magnetorheological finishing is analyzed. Based on the Preston equation, the Reynolds equation and its boundary conditions, the two-dimensional material removal model is built and simulated. Furthermore, a series of MRF experiments are carried out, and the influence of the immersed depth and material kinds on material removal rate are clarified respectively. The experimental results are compared with the modeling results of material removal rate to confirm the mechanistic model validity.