Key Engineering Materials Vols. 304-305

Abstract: In order to obtain higher ground surface quality of silicon wafers, it is essential to better understand the grinding mechanism. This study investigates the phase transformations in ground silicon wafer surface with the aid of Raman microspectroscopy. On the surface ground by #325 grinding wheel, the characteristic Raman peak of pristine Si (Si-I) is predominant and very small amount amorphous silicon (α-Si) is observed. It shows that short-range disorder or residual strains in the Si lattice are not caused, the material was removed by brittle mode. But the Raman spectra of surface ground by #600 and #2000 wheel demonstrate the presence of the α-Si and high-pressure phases (Si-III and Si-XII). It is confirmed that the Si momentarily exists in the metallic phase Si-II during grinding process. The Si-II is ductile and easily removed by ductile mode. The transformed phases of all ground wafers disappear after chemical etching. In general, the material can be removed by ductile or brittle mode. Which mode dominates is determined by the grinding condition.

Abstract: The theory model of the indent experiment of the brittle material was established, its specific energy was analyzed, and the calculation expression of the total specific energy for a single grain was given. Experiment process and results were given. Ultra-high speed grinding experiment was done, and its results were obtained. After the results were analyzed, the conclusions were gained that brittle materials could produce ductile-regime grinding under ultra-high speed shock. The model of mechanism of chip-formation due to shock in quasi-fluid phase on super-high speed grinding was established, and the chip formation hypothesis for the chip formation mechanism on ultra high speed grinding was produced.

Abstract: This paper puts forward an intelligent single-plane biaxial balance monitor system, which is used in ultra-precision grinding. It adopts the method of single-plane balance correction for the vibration of wheel and workpiece. And this system can also be used for integral balance. For ultra-precision grinding, caused by the mutual influence of the vibration of wheel and workpiece, there will be a ripple on the workpiece surface, which is mainly influenced by the frequency ratio of wheel to workpiece, the feed rate and the vibration of wheel and workpiece. This system can improve the machining accuracy, reduce the surface error of workpiece and appraise the integrated machining result, by analyzing the vibration data of wheel and workpiece and adjusting machining parameters.

Abstract: A new method is proposed for machinability comprehensive evaluation of engineering ceramic materials based on digraph theory. Machinability attributes of the materials are taken as the nodes and the correlations between attributes are taken as the edges. The digraph model for machinability evaluation of ceramics is set up. According to the diagraph model, the machinability attribute matrix was constituted. Then machinability indexes of ceramic materials were calculated with permanent function and machinabilities of the ceramics were evaluated. In this paper, mechanical property parameters of ceramic materials, including hardness, fracture toughness and elastic modulus, were selected as machinability attributes. Machinability of four typical engineering ceramics were evaluated and ranked with machinability indexes. The grinding experiments give further proof of evaluation results.

Abstract: SiC-particle-reinforced aluminum-based metal matrix composite is one of the important composites among the metal matrix composites, for their various advantages such as lightweight, high specific modulus, specific strength, wear resistance and high temperature resistance. The precision machining of these advanced materials will not be possible without the solution of the grindability problem, which resists wide spread engineering application of PRAlMMCs as precise parts. This paper investigates the grinding performance and burn mechanism of SiC-particle-reinforced aluminum-based MMCs through thesystematical grinding experiments. Grinding characteristics of these MMCs including grinding force, grinding temperature, morphology of ground surface, surface roughness, residual stress, and chemical composition of the surface layer are obtained and analyzed by the various advanced measuring method. Experiment results reveal the varieties of grinding force, grinding temperature and surface integrity with the onset of grinding burn. The grinding burn mechanism can be unveiled by the varieties of grinding properties. Grinding experiments are conducted under different grinding conditions so as to explore the appropriate grinding parameters to obtain good surface integrity. The research results are of great significance for high efficiency and precision grinding of MMCs, thus promote the wide application of these advanced materials on the precise and wearable components.

Abstract: Green machining fluids of oil-filmed water-droplets (OW) can be produced by means of combined mist-jet with cooled air, minimum naturally dissoluble oils (botanic or ester oils) and little water, which are beneficial to realize zero-emission machining and thoroughly eliminate the influences of the conventional water-miscible machining fluids on the operators’ health and the eco-environments as well as save energy consumption and lower in production costs. In this study, grinding performances and mechanism analyses of green machining fluids are investigated by comparison to the conventional ones such as emulsion flood coolant on the plane NC grinder. The investigations have further shown that green machining fluids can improve grinding quality in comparison with emulsion flood coolant due to good lubrication and cooling effects, which are applicable to many situations of machining processes.

Abstract: Ceramic is prone to engender surface/subsurface crack damage layer because of great grinding force and high brittle. Prediction of crack damage of ground ceramic is important for design and assessment of grinding process. In this paper, an investigation for surface/subsurface crack damage of ground ceramic is introduced. Depth of crack damage layer can predicted by calculating crack propagation balance size and a predicting model of crack damage layer depth is obtained.

Abstract: Surface microgrinding of the nanostructured WC/12Co coatings have been undertaken with diamond wheels under various conditions. Nondestructive and destructive approaches were utilized to assess damage in ground nanostructured coatings. Different surface and subsurface configurations were observed by scanning electron microscopy. This paper investigates the effects of microgrinding conditions on damage formation in the surface and subsurface layers of the ground nanostructured WC/12Co coatings. And the material-removal mechanism has been discussed.

Abstract: During the process of plunge grinding, a test piece can be axially grooved with thermocouple embedded, thermo-electromotive force will be conducted through collecting ring and then after A/D converting, data will be digitally acquired and online test will be realized. Based on the thermal theories, this paper presents a simple model to calculate the workpiece’s contact zone temperature during plunge grinding process. This model can be used to predict and calculate the grinding temperature easily. An empirical formula calculating the temperature of the grinding contact surface had been obtained through multivariate linear regression analysis experiments. The thermometric system showed in this paper had solved the knotty problem that the grinding temperature was very difficult to measure for plunge grinding. Compared with traditional method, the testing method adopted by the author will give more accurate result and more closely represent the test piece situation. The results of the computer simulation and the experiments proved the exactitude of the thermal model and the feasibility of the thermometric system.

Abstract: Molecular dynamics (MD) simulation is carried out to analyze the effects of abrasive ngrain size and cut depth on monocrystal silicon grinding process. Tersoff potential is used to describe the interactions of diamond and silicon atoms. Based on classical Newtonian mechanics law, the motion equations of atoms are established and the trajectory of each atom in phase space is obtained with the aid of Velocity Verlet algorithm. Debye model is introduced to convert between kinetic energy and temperature of an atom. The grinding processes of by single grain with different size and different cut depth are investigated in atomic space. Through comparing shearing force and potential energy in the single grain grinding process, the effects of cut depth and grain size on the grinding process are discussed. From the results of MD simulation, it is revealed that when the cut depth increases, both the shearing force in silicon crystal and potential energy between the silicon atoms rise, deformation and dislocations in the silicon lattices increase. As a result, all theses lead to^more severe surface and subsurface damage. With the decreasing of grain size in the same cut-depth nanometric grinding processes, the shearing force in silicon crystal and potential energy between the silicon atoms become larger, deformation and dislocations in the silicon lattices increase.