Materials Science Forum Vols. 697-698

Abstract: Based on the analysis of micro electrical discharge machining (micro EDM) principle, the process conditions of micro EDM deposition has been obtained. Micro EDM deposition is a new EDM method, in which the process conditions includes selecting air as working medium, short pulse duration, long pulse interval, low discharge current and setting the tool electrode as anode. In micro EDM deposition experiments, two types pulse generators of transistor type and RC type are applied respectively. The characteristics of discharge waveforms using each type pulse generator are researched. Results show that both two types pulse generators can be applied in the micro EDM deposition process. The transistor type is easy to obtain the same single discharge energy, but short circuit will damage the deposited material. While RC type can adjust discharge energy according to the discharge gap state, which is well used in micro EDM deposition process with the high deposition rate.

Abstract: The interfacial energy and diffusion phenomenon of the Al₂O₃(012)-SiC (011) interface model are studied based on molecular dynamics. The interfacial energy increases firstly until reaches its maximum 0.459J/m² at the temperature of 1500K and then decreases. The relationship of diffusion coefficients for each kind of atoms is C>Si>O>Al. Diffusion coefficients of atoms increase at first and then decrease as the temperature goes up. This indicates the diffusion mechanism has been changed during the temperature rising process.

Abstract: High-speed milling tests were performed on SiC_p/2009Al composites in the speed range of 600-1200m/min using PCD tools to investigate the cutting temperatures and the influence factors. The results showed that the cutting temperature could reach 580°C under the given cutting conditions. Graphitization took place on the PCD tools under the high cutting temperature coupled with the effects of abrasive wear of SiC particles and catalysis of copper in the 2009 aluminum matrix. Cutting parameters, tool materials, workpiece materials and tool wear condition had significant effect on the high speed milling temperature while tool geometries had the minor effect. Among these influence factors, cutting speed was the most significant factor. Reinforcement volume fraction was the less significant factor and followed by radial depth of cut, feed rate and tool materials.

Abstract: Material models in the libraries of commercially available finite element codes often cannot satisfy the needs of some special material property descriptions, such as those of materials under ultra-high-speed cutting. To overcome the difficulty, this paper introduces an efficient explicit algorithm to implement a generalized user-defined model of metal plasticity into the Abaqus/Explicit program. This algorithm makes the computation quite efficient by avoiding updating the tensor of elastic-plastic modulus in each increment.

Abstract: Surface integrity is becoming important to satisfy the increasing requirements service life of machined parts. The purpose of this study is to investigate the effects of cutting speeds on surface integrity of Inconel 718. Experiments are conducted on a CNC machining center under various cutting speeds. The machined surface integrity is evaluated in terms of surface roughness, microhardness and residual stress. Experimental results show that machined surface integrity of Inconel 718 is sensitivity to the variations of cutting speeds. The surface roughness firstly increases with the cutting speeds increasing at the range from 50 m/min to 200 m/min, then decreases with the further increasing of the cutting speeds. For microhardness, it can be seen that work-hardening for the machined surface is serious. The surface residual stresses are tensile ones at the range of the selected cutting speeds from 50 m/min to 3,000 m/min in this research.

Abstract: Based on the high-speed cutting theory, high-speed dry milling processes of spiral bevel gears are studied and mathematical models of milling forces are established in this paper. This paper analyzes variation trend of high-speed cutting force and puts forward the notion of non-constant feed cutting according to specific cutting process, so that the purpose of lowing the maximum main cutting force and reducing the fluctuation of cutting force can be achieved.

Abstract: This research is concerned with the analytical and experimental study on milling of 2024-T351 aluminum alloy with TiAlN coated carbide cutting tools in both low-speed machining and high-speed machining. The results are analyzed in terms of surface roughness and residual stresses of the workpiece. Surface roughness studies indicate that in high-speed milling of 2024-T351 aluminum alloy the surface roughness can maintain a lower value and the workpiece can obtain excellent surface quality compared to the low-speed machining. The high-speed milling was found to be able to enhance the original residual stresses of the workpiece; while the low-speed milling may weaken or undermine the original residual stresses, or even transform the initial compressive stresses into the tensile stresses.

Abstract: The most common tunings for the TMD in the field of vibration suppression are H_∞ and H₂. However, regenerative machine tool chatter is a complex problem with many variations, which therefore requires a new tuning for the optimum chatter suppression. The real part based tuning is investigated numerically by employing the minimax numerical approach, which aims to maximize the minimum real part of the primary structure under the harmonic excitation. The performances of multiple TMDs system are discussed. A face milling case is employed to verify the benefits of multiple TMDs in increasing the chatter free depth of cut. It is concluded that multiple TMDs configuration are more effective than single TMD in chatter control.

Abstract: In the high speed precision machine tools, the thermal deformation of spindle had an important influence in machining accuracy. The data of thermal deformation of spindle was got through measuring test rod in the experiment. However, the system error existing of test rod in running and heat imported led to the difference between the measured values and the actual values. The paper has discussed the deformation of test rod caused by centrifugal force in high speed, Non-uniform thermal field in a stable state, and gravity and the variational elastic modulus. Through analyzing those factors, the main ones and neglectable ones could be confirmed, which laid the theoretical foundation in order to eliminate the interference factors in the measurement values.

Abstract: A plasma sound wave detection method of laser shock processing (LSP) technology is proposed. Speciments of Ni-base superalloy are used in this paper. A convergent lens is used to deliver 1.2 J, 10 ns laser pulses by a Q-switch Nd:YAG laser, operating at 1 Hz. The influence of the laser density to the shock wave is investigated in detail for two different wavelength lasers. Constant amplitude fatigue data are generated in room environment using notch specimens tested at an amplitude of vibration 2.8 mm and first-order flextensional mode. The results show that LSP is an effective surface treatment technique for improving the high cycle fatigue performance of Ni-base superalloys having a factor of 1.62 improvement in fatigue life.