Materials Science Forum Vols. 532-533

Abstract: The fabrication of a large Al-4.5wt%Cu-0.5wt%Mn wheel with 670mm diameter by indirect squeeze casting process was studied. The casting system including modified hydraulic press and die structure was introduced, and the casting procedures was designed and described. The filling behavior of the casting process was simulated with software Flow3D. It was found that while flowing from spoke to rim, turbulence flow of liquid melt in the vicinity of free surface was found, and that at the end of the filling, the unwanted solidification might occur. To reduce the turbulent flow and the unwanted solidification, a modified injection condition was proposed. The simulation results with the modified injection indicated that the turbulence was prevented and the unwanted solidification during the filling was reduced as well. The squeeze wheel castings were fabricated with the modified injection condition. Cross sections of the castings were checked. A number of specimens were obtained from different parts of the castings to evaluate microstructure of the wheel, and both high density and fine grain microstructures were found in the specimens. Mechanical properties of the tensile samples from the wheels with T5 heat treatment were measured. The average tensile strength and elongation were 390 MPa and 10%, respectively.

Abstract: To investigate the effect of tool geometry on single-crystal silicon nano-cutting, parallel molecular dynamics (MD) simulations are carried out with different tool rake angles. In this study, a parallel arithmetic based on mechanism of spatial decomposition together with MD is applied to simulate nano-cutting processes of single-crystal silicon (100) plane by using a single-crystal diamond tool. The simulation results show that tool rake angle has great effects on cutting forces and subsurface stress, and the effect of tool rake angle variation on work-piece potential energy is not evident while cutting single-crystal Silicon (100) plane. Moreover, the analysis of cutting forces and potential energy show that there is not evident dislocation in the nano-cutting.

Abstract: Rotary ultrasonic machining (RUM) is one of the cost-effective machining methods for advanced ceramics, which is a hybrid machining process that combines the material removal mechanisms of diamond grinding and ultrasonic machining (USM). This paper presents an overview of the investigations on RUM of advanced ceramics. The issues about the material removal mechanisms, process modeling, material removal rate, and tool wear in RUM are reviewed. Directions of future research on RUM are also presented.

Abstract: Chatter during boring process is one of the main adverse factors influenced on the machining accuracy of precision hole, surface quality and working efficiency. In order to suppress chatter, an innovative controlling means of MR-intelligent-boring-bar with self-chatter-suppression is proposed, which is composed of MR fluid, shell structure, excitation coil and boring bar. The MR fluid’s mechanical characteristic can be adjusted by changing the intensity of magnetic field, thus the system stiffness and damping will be modified, and then the boring chatter can be suppressed. Otherwise, the dynamic model of MR-intelligent-boring-bar with self-chatter-suppression is built. Lastly, the experimental system of MR-intelligent-boring-bar is established, and the experiments of chatter suppression during boring process are performed. The results of experiments show that the new means of chatter suppression is effective.

Abstract: Air cooling is a near dry machining method, which cools cutting area and evacuates chip using low temperature wind instead of cutting liquid. It can decrease tool wear, improve tool life, reduce cost and produce no chemical pollution. In this paper, air cooling system is established, in which vortex tube is used for cooling. Air cooling test was carried on, in which high hardness bear steel GCr15 is machined by PCBN tool. Experiment results indicated that cold air from vortex tube has a significant effect on cutting force, cutting temperature and chip formation process. Cutting force and cutting temperature were simulated using Marc. Change rules that analysis results indicated are in accordance with experiment results. This paper’s conclusions have a great reference value for the practical application of air cooling technology.

Abstract: Although the porous metal bonded diamond grinding wheel, which has recently been developed, had an excellent grinding performance for hard-brittle materials, its applications were only in precision grinding in past study. A new method for fabricating the new porous metal bonded diamond grinding wheel by Ni-Cr alloy as bond and vacuum loose powder sintering was proposed in this paper. The morphology of cross section of the segments and microstructure of interface between diamond grits and bond were analyzed. The wetting mechanism between Ni-Cr alloy bond and diamond is reacting wetting. Machining performance experiments about grinding ratio and surface roughness have been carried out. The testing results show that the porous Ni-Cr alloy bonded diamond grinding wheel has certainly fine machining performance in high grinding force occasion, and the maximal grinding ratio and best surface roughness were 6660 and 1.08
m, respectively.

Abstract: An experimental study on induction brazing diamond grinding wheel with Ni-Cr filler alloy was carried out. Brazing trial was conducted at the temperature range of 1020-1080 oC and the brazing time were 10, 20, 30 and 40 seconds in a flowing argon environment with a flow rate of 5000cm3/min. The scanning electron microscopic (SEM) results indicate that good wetting existed between the brazing alloy and diamond. The element distribution of C, Cr, Si and Ni were examined by energy dispersive spectrometer (EDS), the results demonstrated an intermediate layer rich in the chromium formed between the filler metal and diamond. Kinds of compounds formed in the interface were detected by means of x-ray diffraction (XRD), and the graphitization of the brazed diamond grits was determined by Raman spectroscopy. The monolayer induction brazing diamond grinding wheels were used in grinding of nature granite, experimental results show that induction brazing wheels performed better than vacuum brazing diamond wheels, and no pullout of diamond grits or peeling of the filler metal layer took place.

Abstract: A kind of brazed monolayer diamond grinding wheel was developed with a relatively regular distribution of grains on the wheel surface. Grinding performances of this kind of brazed wheel in the surface grinding of cemented carbide were studied. The experiment results show that the grinding forces ratio becomes higher with the increasing of the maximum undeformed chip thickness and the specific energy falls with the material removal rate during grinding cemented carbide process. Under certain grinding conditions, the material was removed almost through plastic deformation and good surface quality is gained. Furthermore, the grits of the brazed diamond grinding wheel fail mainly in attritious wear modes other than pull-out ones in conventional electroplated and sintered diamond tools, which indicates that the strong retention of brazing alloy to the diamond grits and longer service life of this kind of wheel.

Abstract: An investigation is reported of the effects of three different coatings onto diamonds in the composites for the beads of wire saws. The matrix of the composites contained 80% (w/w) cobalt. Ti, W, and W-Co were coated onto diamond surfaces respectively and then incorporated into the matrix. The mixed powders were hot-pressed to form the specimens for bending tests. Coupled with the results of bending tests and the strength of coated diamonds, the coatings of W were found to be best among the three coatings. Further experiments indicated that the thickness of W-coatings onto the diamonds should be controlled around 10(m in order to obtain an excellent retention of diamonds.

Abstract: The measuring temperature and force experiments of cutting heat-resistance steel (3Cr-1Mo-1/4V alloy and 1Cr18Ni9 alloy) by plane milling insert and milling insert with complex groove that invented by ourselves has been done, meanwhile, the falling process of sticking-welding chip when milling insert cut-in and cut-out has been observed by high-speed photograph. Mechanical-thermal coupled field has been analyzed using ANSYS, and equivalent complex stress of the coupled field is larger than the stress of single field distinctly, it shows that they have a relation of direct proportion. The results of test and analysis show that the main reasons of adhesion failure are heat that produced in cutting process and the change of temperature grads during cut-in or cut-out and alternate tension stress and stress impact during cut-in or cut-out., which provides technical support and experimental data for the groove's optimization and reconstruction of milling insert with 3D complex groove.