Materials Science Forum Vol. 723

Abstract: Based on the System Engineering theory, the main factors that lead to the vibration in high-speed cutting were presented, which were the structure of the high-speed machine tool, the component of the tool system, the characters of the workpiece material, the choosing of the cutting parameters and the machining environment conditions. The forming mechanism of the vibration in high-speed machining was discussed, according to the characters of controlling each part of the high-speed machining system. The main controlling strategy and improving paths of the active vibration control in high-speed machining were brought forward.

Abstract: Spherical chip appears frequently in high speed grinding of metals. It is attributed to the melt or oxidation of the small chips in grinding. Spherical chip in machining of steels is observed when the cutting speed is high enough. To clarify the formation mechanism of spherical chip in metal cutting, high speed machining of AerMet100 at cutting speeds from 40 m/min to 3000m/min was investigated. Spherical chip of AerMet100 was obtained at cutting speed range 2000-3000m/min. Optical and SEM (Scanning Electron Microscope) observations of the spherical chip was carried out. The chemical composition of the spherical ship was analyzed through X-ray energy dispersive spectroscopy (XEDS) analysis. The formation mechanism of the spherical chip was proposed. The results showed that the spherical shape of chip is due to the intense reaction between Fe of workpiece and O2 in the air accompanying which large mount of heat is released to melt the oxide into small spheres. The formation of the spherical chip is highly influenced by cutting speed and the size of the chip (surface-volume ratio).

Abstract: As a new type of green manufacturing technology, high speed dry cutting technology to implement human sustainable development strategy has important significance. The research reviews the features and advantages of the high speed dry cutting technology, and analyzes the key technologies (including machine tools, cutting tool and coating technology to achieve high-speed dry cutting).

Abstract: In the present study, face milling of AISI H13 steel (46-47 HRC) with CBN tools was conducted. Cutting speeds 389 and 1592 m/min were adopted in order to identify the characteristics of cutting force and tool wear at low and high cutting speeds. For each cutting speed, the metal removal rate and axial depth of cut were set to be invariable, and different combinations of radial depth of cut and feed per tooth were selected. The optimum combination of radial depth of cut and feed per tooth for each cutting speed was distinguished. For different cutting speeds, the cutting force changed in varying ways with different combinations of cutting parameters. At the cutting speed of 389 m/min, after the initial cutting stage, the tool wear rate was low even at the end of tool life. When the cutting speed was 1592 m/min, the tool wear increased rapidly, and the tool wear rate changed little in the whole tool life span. Adhesion and abrasion were the main wear mechanisms of the tool faces at the cutting speed of 389 m/min. While at the cutting speed of 1592 m/min, fracture contributed greatly to the final tool failure.

Abstract: Meshing cylindrical surface always bears the alternating stress in the practical application. It will bring fatigue failure and fracture phenomena if the alternating stress is uncontroled, seriously affect the service life of the mechanical devices. The fatigue strength of the workpiece will be improved to boost the surface quality and surface strength and use the way of controling the workpiece surface residual stress brought by metal cutting to compressive stress. High-speed milling technology can greatly enhance the surface strength and surface quality of the workpiece surface, it can also change the cutting parameters to control the residual stress of the workpiece surface, so that it can greatly improve the fatigue strength of the workpiece.

Abstract: Numerical controlled milling is widely used in the manufacturing industry because of its high productivity and workpiece surface quality. The aim of this work is to establish a methodology to evaluate the rough machining time and to predict optimal values of cutting speed to minimise machining time of circular cavity, during high speed milling. The circular cavity is divided into volumes distributed according to the real radial depth. The obtained results show that the proposed method is consistent with the actual situation.

Abstract: Since metal matrix composites (MMCs) have increasing applications in industries, this paper presents an experimental investigation on machinability of SiC_p reinforced aluminium metal matrix composites. 14 wt.% of SiC_p reinforcement addition composite was studied in end milling using CVD coated carbide tools under different cutting parameters. By experimental results, the relationships of cutting force and surface roughness with cutting speed and feed were discussed. Some defects concerning surface topography such as ploughed furrow, pits, matrix tearing, etc. were examined by SEM.

Abstract: In this paper, some high speed cutting experiments of hardened 45 steel are carried out. The effects of cutting parameters on the width and space of adiabatic shear band, the frequency and degree of sawtooth are investigated by metallographic observation and theoretical calculation. The results show that the space of adiabatic shear band decreases with the increase of cutting speed and rake angle, but increases with the increase of cutting depth. The width of adiabatic shear band decreases with the increase of cutting speed and cutting depth, however, increases with the increase of rake angle. The frequency of sawtooth increases with the increases of cutting speed, decreases with the increase of rake angle, and has no obvious relationship with cutting depth. The degree of sawtooth increases with the increase of cutting speed and cutting depth, but decreases with the increase of rake angle.

Abstract: It is known that diamond is not suitable for cutting of ferrous metals, ascribed to serious tool wear occurred in machining process. For the sake of studying the tool wear mechanism further, this paper presents thermal analysis method to discuss the chemical transformation of diamond with Fe catalysis. Raman scattering experiment was performed to identify the transformation of crystal structure of the diamond specimens. The surface wear morphology of workpiece was detected by scanning electron microscopy, and energy dispersive X-ray analysis was used to study the change of chemical composition. Experimental results revealed the law of graphitization and diffusion of single crystal diamond at elevated temperature in different gas environment.

Abstract: Minimum quantity lubrication (MQL) is a new cooling technology used in machining process, which is friendly to environment and lower cost. This paper applied computational fluid dynamics (CFD) to analyze flow field of MQL in thread turning. Comprehensively applying droplet breakup method and capillary method, flow field of MQL in cutting zone were analyzed in detail. The results showed that oil mist could enter into cutting zone from sides of chip. And two vortexes existed around cutting zone which could reduce cutting temperature by accelerating heat exchange. Furthermore, flow rate of compressed air had great influence on velocity and diameter of droplets, velocity and pressure distribution of flow field. The effects of different flow rates indicated the larger flow rate was benefit for entering into cutting zone of oil mist.