Materials Science Forum Vols. 626-627

Abstract: In this paper, the principle and impact factors for super-accurate grinding are analyzed and discussed. A comparative test is made to investigate the differences between advanced cubic boron nitride (CBN) slipstone and ordinary CBN abrasive corundum in performance such as grinding force, grinding temperature, metal surface metamorphic layer and so on. Based on these results, we design and manufacture a carding Laura slot super-accurate grinding machine. This new grinding machine is standard in system, compact in structure and perfect in appearance. Its fixture has a high positioning accuracy. The surface roughness of the Laura manufactured on the new grinding machine has reduced to Ra0.01μm. The productivity of the new machine increases by 25 times.

Abstract: A three-dimensional axial symmetrical model of laser cutting is established by adopting N-S equation in the paper, and numerical simulation is put up to analyze the flow field of assist gas in cutting channel. The investigation reveals the law about how channel width affects the dynamic characteristic of gas jet in the cutting process, and the distributions of pressure and velocity of gas jet with different channel widths are shown in the study. The study shows that the intensity of compressed wave and expanded wave in cutting channel declines remarkably with channel width increasing, and the kinetic energy at channel surface drops while the cutting quality is deteriorated. A taper nozzle with cone angle of 30°and a convergence nozzle comprised a parabola equation of are designed for the laser cutting experiment. The experimental results are given at the end of the paper.

Abstract: Titanium alloys are known for their strong chemical reactivity with surrounding gas due to their high chemical affinity, especially in dry machining. This paper describes a study of chip formation characteristics under nitrogen gas media when machining Ti6Al4V alloy with WC-Co cemented carbide cutting tools at high cutting speeds. Based on the experimental study, a finite element model of two-dimensional orthogonal cutting process for Ti6Al4V alloy at different cutting conditions was developed using a commercial finite element software Deform-2D. Saw-tooth chips with adiabatic shear bands were produced in both experiments and simulations. And the enhanced cooling and anti-frictional effects of nitrogen gas upon the high speed cutting process of Ti6Al4V alloy were analyzed. Results of this investigation indicate that the anti-frictional performance of nitrogen gas has a significant effect on chip formation when machining Ti6Al4V alloy at high cutting speeds. Compared to air, Nitrogen gas is more suitable in improving the contact conditions at chip-tool interfaces and in increasing the shear band frequency of chip formation during high speed cutting of Ti6Al4V alloy.

Abstract: High speed milling experiments are performed for hardened H13 die steel by using coated ball end milling cutter, the residual stress of the work-piece surface on the feed and cross feed direction are measured, and the distribution characteristics of residual stress is analyzed. The result shows that the residual stress presents gradient distribution on feed direction, and furthermore, the three-dimensional surface micro topography has no close relation with the residual stress. In addition, the cumulative effect is discussed for explaining the phenomena.

Abstract: TA15 (Ti-6.5Al-2Zr-1Mo-1V) is a close alpha titanium alloy strengthened by solid solution with Al and other component. A series of experiments were carried out on normal and high speed milling of TA15. The recommended tools for many years had been the uncoated tungsten carbide grade K. In this work, the tool life of coated carbide tools used in high speed milling of forging and cast titanium alloy was studied. Additionally, the wear mechanism of cutting tools was also discussed. Finally, surface integrity, including surface roughness, metallograph and work hardening, were examined and analyzed. The result shows that the surface quality of forging and cast machined by carbide cutter is similar, but the tool life of carbide in high speed milling of forging TA15 is longer than that in high speed milling of cast TA15.

Abstract: In the application of brazed diamond tools, residual stress caused by differences in materials properties is an important factor in obtaining good brazing quality. The residual stress in diamond/steel brazed joint is studied by means of finite element method and Raman spectroscopy in this paper. The comparison between the results from the simulations and the measurements shows that a good agreement has been reached. Tensile stress concentration at the diamond edge near interface was observed. High residual stress concentration may cause cracks in diamond. Actually, cracks in diamond caused by brazing residual stress after were observed. The stress concentration of the joint must be reduced to obtain good brazed joint. The change of brazing atmosphere or to adopt the soft brazing alloy will reduce the stress concentration.

Abstract: This paper describes an integrated method to determine optimal cutting parameters for milling pocket based on minimum cutting time. The main constraints entailed in real cutting, such as chatter free, uncut free tool paths, cutter and machine tool limitations, are included into the optimal model. The optimal parameters (depth of cut, width of cut, spindle speed) are inserted into the tool paths generation directly for four kinds of conventional cutting modes (Zig and Zig-Zag parallel cutting mode, inwards and outwards spiral pattern modes). According to the fact that the first cut in every cut level is slotting milling, the milling areas are divided into slotting milling area and general milling area. This dynamically corrected tool paths generation method changes the order of conventional tool paths, so different cutting parameters are used in slotting milling and general milling areas. The case study has demonstrated that the proposed methods can identify the optimal milling conditions and generate tool paths automatically and result in minimum milling time.

Abstract: Based on analyzing the problem of tap worn and broken in the tapping process, the faults in tapping process are classified into four types: tap worn, chips jamming, uneven hardness of material and the tapping process failure; According to the fuzzy theory, this paper describes the torque characteristic of the four types of faults, ascertains the characteristic vector of fault, presents the weight matrix among faults, puts forward the judgment method of system faults and establishes the fuzzy fault diagnosis system in tapping process. The experimental study shows that the fuzzy diagnosis method can effectively identify the four types of faults in tapping process and guard against tap broken.

Abstract: An investigation is reported of the temperatures in the sawing of granite with a circular sawblade under a wide range of machining parameters including cutting fluids and cutting modes. Temperature responses in the sawing contact zone were measured using a foil thermocouple. The measurement was subsequently used to analyze the influence of operating parameters on the sawing temperatures and the energy partition. For either down-cutting or up-cutting, either with cutting fluids or without cutting fluids, the temperatures in the sawing zone were found to increase with depth of cut, sawblade speed, and workpiece speed. The maximum temperature in the sawing without cutting fluids was found to be up to 400°C whereas it was reduced to around 250°C while using cutting fluids. The energy partition conducted to the workpiece is about 7% ~10% in dry sawing and about 2% ~5% in wet sawing.

Abstract: The objective of this study is to experimentally investigate the effect of reinforced SiC particles on the machining of Aluminum/SiC composite (15% volume ratio of SiC particles with average grain size 15m). Aluminum/SiC composite and aluminum metal were milled by a tungsten carbide endmill in this study. Based on the surface observation and surface roughness inspection, it is found that the machining parameters of Aluminum/SiC composite have optimum values, and that the surface roughness of aluminum/SiC composite is smaller than that of aluminum metal. when feedrate and depth of cut are smaller than limited values, satisfactory surface finish can be attainable, however, as the depth of cut and feedrate increases, the microcracks are first initiated at the interface of SiC particles and aluminum matrix, and then periodically macrocracks are formed on the machined surface, The damage mechanism during the machining of aluminum/SiC are discussed in this paper.