Advanced Materials Research Vols. 102-104

Abstract: Mechanical strength and service life of the coatings manufactured by plasma spray forming are significantly reduced by residual stresses. A 2D finite element model constructed for temperature and residual stress simulation of a single stainless steel splat solidifying and cooling on the carbon steel substrate is presented in this paper. Simulated results show that the temperature of the splat rim is higher than that of the central part during the initial stage of solidification, and the temperature difference between the two parts reverse thereafter. The minimum residual stress locates at the rim of the top surface of the splat, and the maximum residual stress, which decreases when the substrate is preheated to a higher temperature, situates at the rim of the interface. Stresses appear as tensile stresses within the splat and compressive stresses within the substrate. The research can provide quantitative understanding of the temperature and residual stress states at the splat level.

Abstract: Studying the surface characteristics of polishing pad helps to understand and analyze the chemical mechanical polishing (CMP) mechanism and optimize the microscopic structure of polishing pad. The surface roughness, organizational structure, porosity, depth and diameter of micro-pore, distribution of asperity and profile bearing rate of IC1000/Suba IV polishing pad were studied with the profilometer ZYGO 5022, AFM and SEM. The results of measurement and calculation show that the surface roughness is 6.8μm , the root mean square ( RMS ) roughness is 9.4μm, the surface porosity is 56 % , the micro-pore average diameter is 36μm , the micro-pore average depth is 20μm , the micro-pore average spacing is 43μm , the micro-pore average volume is 550/mm2 and the asperity height obeys Gaussian distribution.

Abstract: The Composites are difficult machining materials which widely used in aerospace industry due to their excellent mechanical properties. Tool wear and delamination are considered the major concern in manufacture the parts and assembly. The thrust force and torque affect the tool life and delamination mostly. This paper investigated the drilling force and torque of carbon fibred composite with carbide drilling tools and half core drilling tool. The experiments were carried out under air cooling cutting conditions and the drilling force using carbide tool and half core tool were compared and the experimental results indicated that the drilling forces using half core drill were smaller than that of using carbide tool.

Abstract: On the basis of the cylindrical grinding-hardening test, the influences of the grinding parameters on surface hardened layer were studied. The result shows that when ap≤0.2mm, there is an unhardened area exist in cylindrical grinding hardened workpiece. When ap＞0.2mm, there is a tempered area exist in cylindrical grinding hardened workpiece due to the action of grinding heat during cut-in and cut-out of grinding wheel. When depth of cut increases, or feed speed decreases, the hardened layer depth increases accordingly. In the practical application, the satisfactory quality of the cylindrical grinding hardened layer can be obtained through reasonable combination of ap and vw.

Abstract: This paper proposed a new approach to control the micro-quality of sapphire substrate, in order to grow GaN on substrate. The main factors that influence macro-quality are the method of slicing, grinding and polishing. Thread speed of slicing is less than 0.5m/s. Ductile mode grinding of substrate is achieved by #3000 diamond wheel and feed of 1μm/r. The suitable polishing conditions are that the SiO2 grain size is less than 10nm, the concentration SiO2 is 3％, pH value of polishing liquid is 10.5 and polishing stress is 190Pa. The undamaged substrates have been obtained steadily. The surface roughness RMS is less than 0.4 nm.

Abstract: Ceramic materials are widely used in the fields of aviation, chemical industry, military, machinery, electronics, so there are so many researches on ceramic materials. This article is mainly about ceramic sample preparation by polishing process for nano-indentation, taking Alumina ceramic and Zirconia ceramic for example. As we know, nano-indentation test is an effective mean to study materials. It is concluded that after polishing, the ceramic surface roughness can reach Ra<10nm and maximum scratches<1nm, flatness<1μm, we can get good quality surface, that well meets the surface requirements in nano-indentation.

Abstract: Magnetorheological Finishing(MRF) is an advanced optical manufacturing technology, It is a kind of deterministic process. It conquers the defections such as low-efficiency and low-grade surface quality of the traditional method. Deduced from the hydrodynamic lubrication theory of the Bingham plastic flow, the material removal model of MRF is established. The reliability of the model is verified by the experiment. finally, we get the mean Preston coefficient by the theoretical curve and the actual measured curves, the value will be applied to optical components of the computer-controlled MRF operation. Through the magnetorheological finishing experiments , the results that compared with the experimental results in good agreement prove that our proposed model is reasonable.

Abstract: Magnetorheological finishing technology is a new generation of high-precision optical accessory polishing and processing methods. It presents a MRF dwell time algorithm that can quickly calculate the resident time during magnetorheological processing of the rotational optical parts. A magnetorheological forming polishing experiment on a prototype has been carried out on BK9 glass parts of 20mm rotary symmetrical face shape. The algorithm can improve the surface shape precision of the workpiece from 6.5um to 0.61um. Emulational and experimental results show that the surface shape error of a spherical polished workpiece is convergent by this method, which is also, applies to magneto-rheological finishing of non-spherical and planar workpiece.

Abstract: 5-axis milling operations are used in industries such as aerospace, automotive and mold for free-form surface machining. In these process, surface quality and material removal rate are of very important. Conservative cutting parameters have been mostly used since there was a lack of physical models and optimization tools. Part and tool deflections under high cutting forces may result in unacceptable part quality. The overall goal of this research is the integration of geometric and mechanistic models for cutting process simulation and feedrate optimization. The extracted cutter workpiece engagements are used as input to a force prediction model. The model predictions for cutting forces and feedrate optimization are compared and verified by experimental results.

Abstract: In the process of high-speed cutting Ni-base superalloy, some precarious factors such as environment media, cutter wear and so on have great influences on the processed surface roughness, and are not easy to control. According to the microscopic cutter wear and surface roughness generated in the experiments of using different media (such as: cold wind oil-mist, cold wind and normal temperature oil-mist) to cut the alloy, the influences of different media cutting conditions on cutter wear and the surface roughness of a workpiece in the high-speed cutting Ni-base superalloy are studied, and the rule to improve the quality of surface processing of Ni-base superalloy under the condition of the cold wind high-speed cutting is revealed.