Papers by Author: Song Zhang

Abstract: Dynamic characteristics of numerical control (NC) machine tools, such as natural frequency and vibration property, directly affect machining efficiency and finished surface quality. In general, low-order natural frequencies of critical components have significant influences on machine tool’s performances. The headstock is the most important component of the machine tool. The reliability, cutting stability, and machining accuracy of a machining center largely depend on the structure and dynamic characteristics of the headstock. First, in order to obtain the natural frequencies and vibration characteristics of the headstock of a vertical machining center, modal test and vibration test in free running and cutting conditions were carried out by means of the dynamic signal collection and analysis system. According to the modal test, the first six natural frequencies of the headstock were obtained, which can not only guide the working speed, but also act as the reference of structural optimization aiming at frequency-shift. Secondly, by means of the vibration test, the vibration characteristics of the headstock were obtained and the main vibration sources were found out. Finally the corresponding vibration reduction plans were proposed in this paper. That provides the reference for improving the performance of the overall unit.

Abstract: Surface roughness has a significant effect on the performance of machined components. In the present study, a total of 49 end milling experiments on AISI H13 steel are conducted. Based on the experimental results, the signal-to-noise (S/N) ratio is employed to study the effects of cutting parameters (axial depth of cut, cutting speed, feed per tooth and radial depth of cut) on surface roughness. An ANN predicting model for surface roughness versus cutting parameters is developed based on the experimental results. The testing results show that the proposed model can be used as a satisfactory prediction for surface roughness.

Abstract: The static and dynamic characteristics of the key components of machine tools should be studied in order to improve quality of work pieces and manufacture efficiency. In this paper, the static and dynamic analyses of the beam in the gantry-type milling machine were conducted with ANSYS Workbench,one of finite analysis software. The static simulated results indicate that the maxiumum deformation appears at the upper guide and the max strain and stress at the position connecting with columns. The modal analysis shows the bending and torsion deformations are the main factors influencing the dynamic performances of the beam when working frequencies are close to the first six natural frequencies; therefore, the selected spindle rotational speed should keep away from the natural frequencies of the beam when planning the cutting parameters.

Abstract: In the present research, a model of the cryogenic oil mist flow field of milling cutters with different interior oil channels was conducted to determine the effects of rotational speed, temperature and flow of cold air. For the milling cutters with single direct hole and double direct holes, the increase of the rotational speed has little effect on the velocity and temperature of the measuring points at different distances along the milling cutters. For the milling cutter with double direct holes the separated streamlines of double direct holes are nearer with the rise of the distance because of the viscidity of cutting fluid. When the distance exceeds 5mm, the separated streamlines combine with each other. For the milling cutter with double helical holes the streamlines of cold air present irregularly. At last, some of the simulated results were validated.

Abstract: In the present research, an attempt has been made to experimentally investigate the cutting forces in hard milling of H13 steel with coated carbide tools under dry, MQL (minimum quantity lubrication) and MQCL (minimum quantity cooling lubrication) cutting conditions. Based on Taguchis method, four-factor (cutting speed, feed per tooth, radial depth of cut, and axial depth of cut) four-level orthogonal experiments were employed. It is found that the periodical fluctuation of the cutting forces caused by the variation of the undeformed chip thickness with the entry/exit of the cutting edge is an essential feature of the hard milling process. The empirical models for cutting forces are established, and ANOVA (analysis of variance) indicates that the quadratic models can well express the relationship between cutting forces and cutting parameters.

Abstract: An investigation of the cryogenic oil mist flow field of nozzle was carried out in this study. A domain of the nozzle jet area was modeled with Pro/ENGINEER. CFD (Computational Fluid Dynamics) analysis was used to state the velocity field of different distances from the outlet of nozzle. The simulating velocity field was verified with the experimental results. Experimental results on velocity were measured by SYT-2000 digital multipurpose wind speed gage. The orthogonal experiment was designed to investigate the main effects parameters on velocity and temperature. It indicates that higher flow of cold air and smaller diameter of nozzle’s outlet will generate higher velocity. The temperature of cold air has most influence on the temperature of measuring point. Finally the optimum structure of the spraying nozzle was proposed.

Abstract: In the present study, an experimental investigation has been carried out in an attempt to monitor tool wear progress in turning Inconel 718 with coated carbide inserts under the wet cutting condition. First, each experimental test was conducted with a new cutting edge and the turning process was stopped at a certain interval of time. Secondly, the indexable insert was removed from the tool holder and the flank wear of the insert was measured using a three-dimensional digital microscopy (VHX-600E); and then the insert was clamped into the tool holder for the next turning experiment. The final failure of tool wear surfaces were examined under a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). It is indicated that significant flank wear was the predominant failure mode, and the abrasive, adhesive and oxidation wear were the most dominant wear mechanisms which directly control the deterioration and final failure of the cutting tools.

Abstract: Surface roughness is one of the most important requirements in the cutting process. In this paper, advantages of Taguchi’s experimental design technique, experimental measurements, and analysis of variance (ANOVA) are integrated to statistically investigate surface roughness in hard milling H13 steel (HRc50±1) with coated round inserts under dry cutting conditions. A 12-parameter cubic regression model for surface roughness is developed, which simultaneously takes into consideration the main effects and the interactions of four cutting parameters. A good correlation is observed between the predictive values and the experimental data.

Abstract: Surface roughness plays a significant role in machining industry for proper planning of process system and optimizing the cutting conditions. In this paper, a back-propagation neural network (BPNN) model has been developed for the prediction of surface roughness in end milling process. A large number of milling experiments were conducted on Ti-6Al-4V alloy using the uncoated carbide tools. Four cutting parameters including cutting speed, feed per tooth, radial depth of cut, and axial depth of cut are used as the inputs to develop the BPNN model, while surface roughness corresponding to these combinations of different cutting parameters is the output of the neural network model. The performance of the trained BPNN model has been verified with the experimental results, and it is found that the BPNN predicted and the experimental values are very close to each other.

Abstract: In this paper, some experiments were conducted to investigate tool wear when end-milling Inconel 718 with the TiAlN-TiN PVD coated carbide inserts. The worn tools were examined thoroughly under scanning electron microscope (SEM) with Energy Dispersive X-ray Spectroscopy and 3D digital microscope to expatiate tool wear morphologies and relevant mechanisms. The flank wear was uniformity in finishing milling process, and the average flank wear were selected as the criterion to study the effects of cutting parameters (cutting speed, feed per tooth, radial depth of cut, and axial depth of cut) on tool wear. Finally, the optimal combination of the cutting parameters for the desired tool life is obtained.