Materials Science Forum Vol. 723

Abstract: TC4-DT is a new damage-tolerant titanium alloy. In the paper, a series of experiments on tool wear and surface integrity in high speed milling of the alloy were carried out. The tool lives of different tool materials were studied and the wear mechanism of cutting tools was also investigated. Then surface integrity, including surface roughness, microhardness and metallurgical structure was studied and analyzed in high speed milling at different tool wear status. Results showed that K10 is the most suitable cutting tool after considering a combination of factors. And good surface integrity could be obtained in high speed milling of TC4-DT under all cutting situations. In addition, even with acutely worn stages, there has been no so-called serious hardening layer (or white layer) according to the study of microhardness and metallurgical structure beneath the machined surface.

Abstract: Tool flank wear has the significant effects on machined surface integrity. The influences of tool flank wear on the cutting forces, surface roughness, microhardness and white layer thickness are investigated in this paper through orthogonal milling experiments. FGH95 powder metallurgy (PM) superalloys are machined with coated cemented carbide tools in the milling experiments. The experiment results show that with the increasing of tool flank wear, cutting force, surface roughness and white layer thickness increase. However, the machined surfaces micro-hardness aggravates with the increase of tool flank wear. It is found that, the machined surface roughness, micro-hardness and white layer increase dramatically especially when the tool flank wear exceeds 0.3mm. A conclusion is then be drawn that, the maximum acceptable tool flank wear land is 0.3mm from the view point of surface integrity when FGH95 PM superalloy is machined with coated cemented carbide tools.

Abstract: Abrasive water jet was utilized to polish the 40CrMnMo7 mold steel and BK7 glass in this experiment designed by Taguchi method. The influence of polishing parameters on the polishing quality, their significance order, and the optimum polishing parameters were analyzed and reported. With the experimental data, the mathematic molds of surface roughness of polished workpieces were created by dimensional analysis, and then they were validated by the test experiment.

Abstract: In this study AISI 1045 steel of different hardness are used in high speed milling. According to Taguchi method, cutting parameters (milling speed, milling depth, feed per tooth) and workpiece hardness for the influence of high speed milling of the surface roughness are optimized. Through this study, not only the optimal cutting parameters of the minimum surface roughness is obtained, but also the main cutting parameters that effect performance in high speed milling is analysed. Researching results can be provided to guide establishment of the high speed milling process.

Abstract: In order to reconcile the contradiction between the ceramic grinding efficiency and surface integrity, high-speed grinding with diamond grinding wheel is supposed to be a solution. In this paper, first of all, a normal grinding force model is proposed based on the consideration of the material property and the grinding process parameters. It can be seen that an elevated grinding wheel velocity in combination of a higher workpiece speed can increase the machining rate while maintaining the desired surface integrity. After a series of grinding tests, a comprehensive measurement has been done to study the surface damage by the surface roughness, the microscope profile and the X-ray diffraction. In particular, the effect of the grinding parameters on the ground surface are analyzed and reported.

Abstract: Residual stresses generated in milling process affect the performance of machined components. Milling residual stresses correlate closely with the cutting parameters. In this paper, the generation and distribution of surface residual stresses in milling of aluminum alloy 7050-T7451 was investigated. The cutting speed changes from 300m/min to 3000m/min. In the experiments, the residual stresses on the surface of specimen are detected by X-ray diffraction technique. The result shows that compressive residual stresses are generated when cutting speed is under 500 m/min. In feed and its orthogonal direction, the effect of cutting speed and feed rate on residual stresses is similar. The formation of the residual stresses can be explained by thermo-mechanical coupling effects.

Abstract: The orthogonal analysis and single factor analysis were used to analyze the roughness of SiCp/Al metal matrix composites (SiCp/Al MMCs) with ultrasonic high-speed milling and high-speed milling. The influences of milling speed, feed and milling depth on the roughness were studied. The research indicates that the roughness in ultrasonic high-speed milling is lower than that in high-speed milling under the same condition, at the same time the optimal parameters of ultrasonic high-speed milling are obtained, this has a guiding significance for finish machining of SiCp/Al composites.

Abstract: A mechanical model of surface roughness is established based on the Kragelskii-Drujanov theory of friction and wear and Hertz elastic contact theory. Effect of material flow stress on remnant height of the machined surface was investigated. Test showed that the machined surface morphology provides the phenomena of the side flow in the vertical direction of ploughing in high-speed machining. The remnant height values on the machined surface of the high-speed machining are obtained by DEFORM-3D simulation. Based on the results it can be concluded that the surface roughness values of the workpiece increase with material flow stress.

Abstract: This paper presents an integrated approach to the design and analysis of an ultra-high speed air bearing spindle, by integrating the structural design, performance analysis and system optimization in a virtual design environment. Firstly, the ultra-high speed air bearing spindle is designed, including grooved hybrid air bearing, helical water cooling channel and built-in motor, etc; Subsequently, pneumatic hammer instability and whirl instability of air bearing are studied; The thermal-structural behaviors of the spindle system at ultra-high speeds are investigated by using structural FEA coupled CFD; Static and dynamic performance of spindle is studied to predict the stiffness, modes and natural frequencies of the spindle; Lastly, system optimizations are conducted to obtain optimal performance and dynamic behaviors of the spindle. The proposed integrated approach can be used to design an optimal ultra-high speed air bearing spindle.

Abstract: TiB₂-(W,Ti)C composites with (Ni,Mo) as sintering additive have been fabricated by hot-pressing technique, and the microstructure and mechanical properties of the composites have been investigated. (Ni,Mo) promotes grain growth of the composites. In the case of 7vol.% (Ni,Mo), the grain size decreases consistently with an increase in the content of (W,Ti)C. When the proper content of (W,Ti)C is added to TiB₂ composites, the growth of matrix grains is inhibited and the mechanical properties of the composites are improved. The best mechanical properties of the composites are 1084.13MPa for three-point flexural strength, 7.80MPa•m ^1/2 for fracture toughness and 17.92GPa for Vickers hardness.