Key Engineering Materials Vols. 359-360

Abstract: The machining performance of porous NiTi shape memory alloys prepared using powder metallurgical production technique has been investigated experimentally in the grinding operation. Grinding force ratio, specific grinding energy, surface characteristics were detected. The result reveals that, much difference of grinding characteristics exists among three kinds of NiTi alloy because of the pore rate and the mechanical performance induced by TiH2. Under the experimental conditions, the integrated effects of predominant plastic flow and slight brittle fracture were taken for porous NiTi alloy during grinding. Additionally, the grinding parameters should be chosen carefully, otherwise the surface quality deteriorates and even the microcrack perhaps appears.

Abstract: The temperature, time and cooling rate are key factors in the hardening process using the grinding heat instead of the high frequency induction heat source. Thus, this paper established the mathematical model estimating the grind-hardening temperature, experimentally determined the grinding temperature and the cooling rate of different grinding parameters for 48MnV microalloyed steel using the conventional aluminum grinding wheel on a surface grinder, and investigated the grind-hardening effects and the forming mechanism of grind-hardening layer. The results show that the estimating temperatures are comparatively close to the measuring ones and hence the model could be utilized to optimize the processing parameters, and the satisfactory grind-hardening temperature and cooling rate could be achieved under the optimized processing parameters. The microstructure of the grind-hardening layer, the fine needlelike martensite in the entirely hardened zone, the martensite and ferrite in the transitional region is similar to that acquired through the high frequency induction technique. Especially, the average hardness of the entirely hardened zone is 740HV and the depth of the hardened layer is adjacent to 1.5mm, which indicate that the grind-hardening effects are very excellent. Different from the forming mechanism of the high frequency induction hardened layer, higher grind-hardening temperature is needed to compensate shorter time austenitization, and because of thermo-mechanical loading induced during grinding, from surface to inside, the morphology of martensite changes from fine to thicker, then to finer, other than from thick to finer.

Abstract: An experimental study was carried out to investigate the force in drilling of engineering ceramic with a brazed diamond tool. The drilling forces and protrusion heights of diamond grains were measured. The results showed that the variation of cutting forces, increasing with the cutting time, was divided into three phases for a drilled hole. For each phase, the variation of cutting forces was different. The drilling forces also increased with the numbers of drilled holes due to the wear of diamond grits. The distance values of the cutting force between the end of first phase and the end of second phase approximately kept constant.

Abstract: 9Cr18 is a type of martensite stainless steel. It has high hardness, chemical stability, fine anticorrosion, wearable and quench stability. It has been used in different areas with high-anticorrosion and high polishing surface as mirror. So it requires for the high level surface quality after lapping and polishing. In this paper, the surface quality (surface roughness and flatness) of 9Cr18 is discussed with lapping parameters which include velocity, load and time distribution of two lapping steps(rough lapping and Ultra-precision lapping). In order to optimize those parameters, an optimization experiment for lapping 9Cr18 with Al2O3 was designed by Taguchi method. Finally, the optimum condition of each factor can be determined that speed: 80rpm, load:3.0kPa, and time distribution: rough lapping time=15min, Ultra-precision lapping time＝45min are the optimum conditions for both Ra and Wt.

Abstract: Because of the high precision in roundness, straightness and roughness, it is very difficult to machining the inner surface of injection nozzle. Honing machine is the main equipment for machining the injection nozzle. The key honing control techniques and honing test for injection nozzle on the developed high precision vertical honing machine are analyzed. The quantitative expansion，which is one of the most important feeding styles in honing process, is discussed in detail. Some machining tests on the developed honing machine are made and the work pieces of injection nozzles with inner surface Φ11mm are honed successfully with roundness tolerance less than 0.4μm, straightness tolerance less than 1μm and roughness tolerance less than 0.04μm.

Abstract: A two-dimensional mathematical model is developed to simulate laser truing and dressing of bronze-bonded diamond grinding wheel. Based on the model, the ablation depth produced on bond and diamond abrasives by an acousto-optic Q-switched YAG pulsed laser under different parameters as well as the temperature field on grinding wheel surface produced in the laser ablation process are numerically simulated. An experimental study on laser truing and dressing of grinding wheel is also conducted. In the study, the wheel surface is ablated by the single-pulsed laser and measured with a measurement device for surface topographic information. Both the theoretical analysis and the experimental results indicate that the truing and dressing processes can be simultaneously realized with the laser ablation as a single process.

Abstract: In oil drilling the failures of PDC drill bits are exhibited as erosive wear, dropping and breaking of cutters, so the erosion and corrosion resistance of the matrix is one of the key factors affecting the quality of PDC bits. In order to understand the degradation mechanism of matrix materials for drill bits, a kind of loop recirculation rig is adopted to measure total mass loss TML, mass loss E by pure mechanical erosion, and then through calculation the mass loss C+S by corrosion and synergy is obtained. The tested and calculated results show that TML of matrix materials is not only caused by pure mechanical erosion, but also by corrosion and their synergy of mechanical erosion and corrosion. In the discussed scope of this paper the volume loss produced by corrosion and synergy is 24.16% of the total volume loss (TVL) at most, which tells us that the corrosion resistance of matrix materials should be considered carefully besides their erosive resistance in the design and selection of PDC drill bits used in the corrosive drilling muds.

Abstract: This paper researches the theory of multi-probes EST (Error Separation Technique) further. The computer simulation on the three-probes EST is also carried out. Several contrastive experiments of the on-line measurement are carried out in a grinding machine (MB1332A). The workpieces used in the experiments had been measured by TALYROND 262 Geometrical Error Measurement Instrument. The results of these experiments successfully verify that the theory and mathematical models of this paper are correct. The contrast of the measuring results in these experiments proves that the three-probes method can realize the complete separation of all kinds of errors basically and this method is applicable to on-line measurement of a workpiece and it can also make the measurement accuracy very high.

Abstract: The accurate calculation and the approximate calculations of the cylinder cam’s curve enveloping surface in single-tool-position-compensation are compared. It is proved that the approximate formula is enough precision for engineering purpose. Based on the analyses for the approximate formula, the calculating method of the least feeding times of the multi-tool-position-compensation is proposed. This method provides theoretical foundation for complex surface’s high efficiency and great precision grinding as well as optimal machining control.

Abstract: The investigation of the experiment method on airflow field around super-high grinding wheel by PIV (Particle Image of Velocity, PIV) instrument was introduced in the paper. The measure system and scheme were designed for the experiment with PIV applied in the super-high speed grinding wheel for the airflow. The processing method of experimental data was discussed and the experiment result validated the feasibility of the experiment method.