Papers by Keyword: Grinding

Abstract: The grinding process has particular interest in that contact temperatures have great significance for quality and integrity of machined surfaces. Hardened surfaces may be damaged by softening and or being stressed, being hardened or re-hardened, burned or cracked. It is important in grinding for the fluid to remove heat from the grinding contact zone to avoid thermal damage to the workpiece surface and/or sub-surface layers. The cooling effect of grinding fluid can be quantified by the convective heat transfer coefficient (CHTC) acting in the grinding zone. This paper presents values of the CHTC based on measured grinding temperatures. The paper also presents a new convective heat transfer model based on principles of applied fluid dynamics and heat transfer. Predicted values for the CHTC calculated from the model are compared with results from experiment obtained under a range of grinding conditions and with experimental data. The results demonstrate that the new CHTC model improves the accuracy of prediction and helps explain the variation in the value of CHTC under varying process conditions. Results also show that convection efficiency strongly depends on the grinding wheel speed, grinding arc length and fluid properties.

Abstract: Two dimensional ultrasonic vibration assisted grinding (TDUVG) is analyzed based on theoretical analysis of the cutting trace of a grain in the finished surface, and it gives the kinematical model of single grit during TDUVG, and the condition of the separate cutting is established, so two dimensional ultrasonic vibration are introduced into the system, which helps to form good machining way. Then TDUVG is applied in the ultra-precise machining of nanoZrO₂ ceramics, and grinding experiments on surface quality of nanoZrO₂ ceramics were carried out using diamond grinding both with and without ultrasonic vibration. Experimental results show that the surface quality after two dimensional ultrasonic assisted grinding is superior to that of diamond grinding. As a result, it is suitable for the ultra-precise machining of ceramics.

Abstract: A molecular dynamics simulation considered of chip deformation and force analysis for grinding process of Mg-Al alloy is presented. Hybrid potentials including embedded atom method (EAM) potential and Morse potential are applied in this model. The activities among atoms of Mg-Al Alloy material is described by EAM potential which is very suitable for metal materials. Morse potential is used to realize the interaction between Mg-Al alloy and abrasive grain made of diamond. Simulations of Different depths of cut (0.6nm, 0.8nm and 1.0nm) and different cut speeds (50m/s, 100m/s and 200m/s) are given. The experience result shows that with the same nanometric depth of cut, there is a little difference of ratio of the cut potential to the cutting speed. Moreover, with the same cutting speed, the cut potential is increased linearly with the depth of cut while reaching to stable cutting regime.

Abstract: Using MATLAB for development tools,we has developed a set of end mills CNC grinding programming system by analysis the end mills grinding craft ,research on cutter location trajectory calculation and post-processing technology. Meanwhile, build a five-axis tool grinder grinding simulation processing by VERICUT(a kind of CNC machining simulation software), through the edge grinding simulation , we confirm the cutter location trajectory and the NC code is errorless.

Abstract: This paper studies of the relationship between mineralogical characteristics and beneficiation of a copper ore in terms of process mineralogy.The study shows that the copper ore embraces little sulfide,its gangue minerals are deficient of ferrum and calcium,gangue minerals and copper minerals embedded micro-fine cloth, Fully grinding mill can make the mineral cleavage, and thus get good separation of minerals.

Abstract: The conventional machining method for silicon nitride ceramics has low machining efficiency, prone to cracking, chipping and other defects. In this paper, the author carried out a study on the influence of ultrasonic vibration grinding on surface quality of silicon nitride ceramic, and carried out ultrasonic vibration grinding process test for silicon nitride ceramic and conducted the analysis of influence of this machining process on surface quality with orthogonal test. The test results showed that the influence on surface roughness decreased in the order of spindle speed, feed rate, cutting depth, and amplitude of vibration.

Abstract: The susceptibility of non sensitized 304L stainless steel (SS) components towards stress corrosion cracking (SCC) has been studied here in the light of the significant role played by surface working operations. The plant experience shows that the fracture surfaces of non sensitized 304L stainless steel components have no signs of carbide precipitation. However, heavy plastic deformation has been evidenced in the form of high density of slip bands on the surface up to a depth of about 100 μm with high tensile residual stresses near the surface. The present study has established that the primary cause of the increase in SCC susceptibility is the heavy plastic deformation near the surface and high magnitude of tensile residual stresses which is a consequence of the surface finishing operations like machining and grinding. In this study, solution annealed 304L stainless steel has been subjected to a) surface working operations like machining and grinding and b) bulk deformation operations such as 10 % cold rolling operation. The materials in different conditions where then subjected to detailed a) microstructural characterisation, b) electrochemical characterisation and c) tests for determining the stress corrosion cracking susceptibility. The distinct differences in the micro structure as a result of bulk deformation vs. surface deformation of 304L austenitic stainless steel were highlighted and correlated to the susceptibility towards stress corrosion cracking. The effect of surface working on the nature and composition of high temperature (300 °C and 10 MPa) oxide formed on 304L stainless steel has been studied in-situ by contact electric resistance (CER) and electrochemical impedance spectroscopy measurements using controlled distance electrochemistry technique in high purity water (conductivity < 0.1 μScm^-1) at 300 °C and 10 MPa in an autoclave connected to a recirculation loop system. The results highlighted the distinct differences in the oxidation behaviour of surface worked material as compared to solution annealed material in terms of specific resistivity and low frequency Warburg impedance.

Abstract: Ilmenite phase is complex in Shaanxi.There are mainly magnetite, limonite and ilmenite, and associated with extremely small amount of rutile. According to the occurrence iron and titanium in the ilmenite ore。Paper discussed comprehensive recycling of the ilmenite using wet low-intensity magnetic separation by stage grinding process . The results show that it obtains better mineral processing indexes。The productivity of ilmenite concentrate was 28.83%, the grade of iron in concentrate was 62.05%, the content of titanium was 13.11%, iron recovery was 61.73%, titanium recovery was 43.40%.

Abstract: The effect of grinding on the photocatalytic activity of commercial ZnO powder was explored using methyl orange as a model pollutant and the corresponding mechanism was discussed tentatively. The results indicate that the photocatalytic activity of the ZnO powder grinded decreases obviously in comprison with that of the ZnO powder untreated. This phoenomenon might be ascribed to the decrease of surface defects of ZnO induced by grinding, suggesting that the further treatment leading to the change of surface states of ZnO powder as a photocatalyst ought to be avoided.

Abstract: Heat flux distribution has an important influence on grinding thermal field, therefore an accurate heat flux distribution model must be established in order to precisely simulate the grinding process. A new heat flux distribution model was developed by theoretical derivation in this paper. In order to simulate the transient grinding thermal field, finite element models were created, applied with the new, uniform and triangular heat flux models respectively. Comparisons between the distributions of temperatures and temperature histories calculated from numerical simulations using the three different models were also made in this paper.