Key Engineering Materials Vols. 407-408

Abstract: The strategies of selection of feedrate are studied in the ball-end machining process. The optimization algorithm utilizes the objective requirements of a line of NC program to set constraints relation between cutting force and feedrate and optimizes feedrate by controlling the variety ranges of the instantaneous cutting force specified in the cutting forces simulation. Off-line feedrate optimization software for complex sculptured is developed. For a line of NC program, the developed software calculates instantaneous cutting force and an optimization algorithm is used to acquire desired feedrate. The machining experimental results show that the proposed algorithms are satisfying in reduction of machining time and improvement of machining quality.

Abstract: The formation of shear localized chips in orthogonal machining of Ti-6Al-4V was investigated. The chips in different cutting velocities were collected and the structure of the adiabatic shear localization was examined by optical microscope and SEM after polishing and eroding. The serrated coefficient, serrated frequency and fibred coefficient were proposed in this paper to characterize the degree of serration and plastic shear flow of the chip quantitatively. Experimental results show that the width of the shear band decreased and the fibred coefficient of the shear band increased as cutting speed increased. The serrated and frequency, the serrated coefficient increased with the increase of cutting speed in the experimental range of cutting speeds.

Abstract: Leaded free-machining steel is used in production industry. However the use of the leaded free-machining steel is limited from an environmental problem. So sulfurized free-machining steel, not include lead, has been researched widely. In order to improve the machining performance of the sulfurized free-machining steel, it is necessary to find out the behavior of inclusion. The experiment was carried out to find out the mechanism of the surfurized inclusion on the machinability, using some kinds of materials which were changed the size of the inclusion. In orthogonal cutting, the deformation behaviors of the sulfurized inclusion in the work materials were observed in the vicinity of tool face. Cutting forces were also measured and finished surfaces were observed. Besides, low speed orthogonal cutting in Scanning Electron Microscope (SEM) which was mounted a small cutting device was carried out in order to observe the deformation behavior more microscopically. As a result, it is clear that some inclusions creates voids around them and some broke to several pieces depending on their conditions. Moreover, in order to investigate the formation and growth of BUE, a quick stop experiment was done during turning. As a result, it is clear that the larger inclusions can reduce the formation of BUE.

Abstract: An explicit dynamic coupled thermal-mechanical Arbitrary Lagrangian Eulerian (ALE) model was established to simulate orthogonal cutting AISI 52100 bearing steel, and its temperature and stress distribution. Based on ABAQUS, The ALE approach effectively simulates plastic flow around round edge of the cutting tool without employing chip separation criteria. The calculation results reveal that cutting speed and cutting depth have great impact on chip morphology, stress and temperature distribution in the finished surface and subsurface, the predicted temperature agrees well with experiment data obtained under the similar cutting conditions as well as the change in chip morphology from continuous to sawtooth as the cutting speed increases.

Abstract: Saw-tooth chip has great effect on the dynamic cutting forces, cutting temperature waviness, PCBN tool life and surface integrity during precision hard part machining. The forming and finish process of saw-tooth chip could be observed through different high frequencies of dynamic cutting forces by wavelet analysis. According to the cutting speed, feed rate, sampling frequency and time, the characteristic parameters of saw-tooth chip type and shear instability could be calculated based on the saw-tooth chip forming frequency formula supported by M.C.Shaw theory. The forming frequency of saw-tooth chip was far smaller than high frequency of cutting forces under the normal cutting parameters during precision hard part machining process, and will be moved similar equal to each other under the high cutting speed. Experimental results and analysis show that the basic characteristics of saw-tooth chip could be calculated through dynamic cutting forces wavelet analysis.

Abstract: In this study, turning of the cemented carbides that their WC particle size was standardized were carried out with the PCD and the cBN tools. The WC particle diameter of cemented carbides was about 2µm and the Co contents were 10, 15, 20 and 25%, respectively. The influence of the WC particle size and Co contents was investigated. Summary of results are shown as follows: (1) In turning with the PCD tool, the more the Co contents increase, the more the tool wear increases. (2) In turning with the cBN tools, the more the Co contents of the work material increase, the more the tool wear decreases. (3) In turning of the cemented carbides contained the larger quantity of Co, the cBN tools are more effective than the PCD tool.

Abstract: Dynamics model on abrasive particles and workpieces during the centrifugal barrel surface finishing process was built by Discrete Element Method (DEM). The motion status of abrasive particles and workpieces was visually simulated and some important process parameters were numerically studied. The influence of planetary transmission ratio on finishing efficiency was analyzed, and finishing efficiency was the highest as the transmission ratio is -1. Finally, the conclusion was validated by experiments. Such economical and precise method could replace lots of finishing tests to optimize process parameters, which would provide theoretic basis for experimental research and efficient means for the finishing mechanism analysis of centrifugal barrel finishing.

Abstract: This investigation aims to develop a quantitative model to estimate the material removal of polycrystalline diamond composites by dynamic friction polishing. The model accounts for not only the polishing parameters that govern the material removal mechanisms, but also the constitutive properties of the diamond composites subjected to polishing. The model prediction was justified by relevant experimental measurements.

Abstract: In the ultra-precision machining, the smaller the undeformed chip thickness is, the more the machined surface integrity is affected by the cutting edge roundness of the cutting tool. In this research, the work hardened surface layer was dealt with as an evaluation of the machined surface integrity and the effect of the mechanical factors on work hardening was investigated experimentally in orthogonal cutting. In the case of a rounded cutting edge, unlike a sharp one, it makes the generation mechanism of the work hardened surface layer complicated. In this research, the mechanical dominant factors were investigated by comparing the effect of the rounded cutting edge on the work hardened surface layer, which counts for much in ultra precision machining involved in small undeformed chip thickness, with that of the sharp cutting edge.

Abstract: Based on large deformation theory and virtual work principle, a coupled three-dimensional (3D) thermo-elastic-plastic finite element model (FEM) was constructed to simulate the high speed cutting process of Al7050-T7451. The mechanical properties of workpiece material under conditions of high temperature and high strain rate were defined in the model. A shear friction model was involved at the interfaces of tool-chip, tool-workpiece. Based on the model, different 3D machining FEM with different inclination angles were established, and distributions of stress, strain and temperature were achieved. Further more, the effects of inclination angle on the chip curling direction, chip flow angle, cutting force and cutting temperature were studied.