Key Engineering Materials Vol. 329

Abstract: Self-propelled rotary tools are being rediscovered for their applications in machining of ‘difficult-to-machine’ materials or for general improvement in the productivity of machining operations. The vibration characteristic and the occurrence of chatter during high speed cutting will induce the deterioration of precision and machining surface, tool wear and tool life. This paper deals with the identification of the vibration in SPRT cutting system with AR time series model. The experiment and deduction method provide a sound foundation for improving the structure with high antivibration strength, which could reduce the relative vibration between tool and workpiece in the alloweable scope.

Abstract: Deposition processes of conventional diamond films and smooth fine-grained diamond films on cemented tungsten carbide inserts (SCMT120408-HR, 6wt. %Co) in the hot filament chemical vapor deposition (HFCVD) apparatus were investigated. A novel combined pretreatment of Murakami’s reagent, acid etching and microwave plasma decarburization in Ar-H2 gas was carried out. The adhesive strength of the films to the substrates, diamond-coated tool wear and surface roughness of the workpiece were further studied by turning glass fiber reinforced plastics (GFRP) cylindrical bars. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and Raman spectroscopy were employed to characterize the substrates and diamond films subjected to different pretreatments and deposition processes. Optical microscope and surface scanning profilometer were utilized to monitor the evolution of tool wear and surface roughness of the workpiece respectively during the cutting test. The experimental results showed that the novel combined pretreatment was more effective in enhancing the adhesive strength of diamond films to the substrate. Fine WC interlayer generated during the initial stage of the diamond film deposition played an important role in improving the adhesion. Diamond coated tools subjected to such pretreatment demonstrated up to 6 times longer tool life than uncoated ones. Varied parameter deposition process produced smooth fine-grained diamond films, which led to remarkably lower surface roughness of the workpiece in turning GFRP

Abstract: At present, a commercially available magnetic barrel machine equipped with permanent magnets has some faults arising from constructional reason. That is, grinding or finishing ability is different from place to place in the machining region, resulting in the limitation on the region we can use in the container of workpieces. Therefore, in this research, authors made the new magnetic barrel machine equipped with three dimensional (3D) magnet arrangement to overcome these faults. The grinding ability of the new 3D magnetic barrel machine converted was experimentally examined, and compared with that of the traditional magnetic barrel machine. As a result, it was shown that we can use much broader region in the new 3D machine. It was also shown that the grinding ability became higher. The distribution of barrel media in action was recorded by means of a high speed video camera. It was clarified that the media rose up higher and were distributed more uniformly in the container by the effect of the magnet block newly set up. It was supposed that this must be the reason for the above-mentioned improvement of grinding ability.

Abstract: In this article, modal experiments were used to analysis the dynamics characteristics of the grinding machine. Static modal testing has validated the nature frequency and the critical speeds were also recognized by dynamic racing experiment. In grinding experiment, the surface roughness was investigated in different speed of workpiece spindle. The way to reduce vibration that caused to bad surface roughness of workpiece was also discussed. This experiment laid a foundation to optimize the structure parameter to improve the dynamic character of the grinding machine.

Abstract: Grinding machine condition monitoring is very important during the manufacturing process. Vibration analysis is usually used to its pattern recognition. But traditional signal analysis method limits the accuracy of recognition because of non-stationary and nonlinear characteristics. In this paper, a novel approach is presented in detail for grinding machine fault diagnosis. The method is based on the new developed Hilbert Marginal Spectrum and wavelet transform, named as wavelet-Hilbert marginal spectrum (WHMS). A rolling bearing’s pattern recognition of grinding machine is used to testify the effectiveness of this method, which can accurately detect flaw of the rolling bearing in early stage. Thus, it can be concluded that this promising method will contribute the development of grinding machine condition monitoring.

Abstract: Due to the complexity of machine tool thermal errors affected by various factors, a new combining prediction model, based on the theory of gery system GM (1,1) model, is applied to the trend prediction of machine tool thermal errors. The degree of smoothness of primary data sequence is first improved by function transform method and sequentially grey system GM (1,1) model is established; second, time series analysis model is established by remnant sequence of GM (1,1) model to amend the precision of grey system GM (1,1) model. Thus, the precision of combining prediction model is further improved. Through the prediction study on thermal error modeling in a spot NC turning center, testing results showed that combining prediction model can highly improve machine tool’s prediction precision and make it more effective for real-time compensation of machine tool thermal error.

Abstract: In order to improve the floating nozzle method, a new coolant supply method using a coolant flow guided flexible sheet has been developed. In this paper, basic properties of the coolant supply when the coolant flow guided flexible sheet method is used are investigated. At first, the phenomenon of automatic adherence of the flexible sheet to the wheel surface is observed with a high-speed camera. Next, the effect of the clearance between the sheet and the wheel surface is experimentally investigated. It is found that the thickness of the coolant flow in this clearance is very small as about 0.1mm, and can be controlled to some extent by controlling the coolant flow rate and wheel rotation speed. Furthermore, it is clarified that the influence of the flexible sheet on the electric power consumption of the main spindle motor is small.

Abstract: For micro-positioning systems using piezoelectric actuators for precision grinding process control, sinusoidal command signals will be used and will give additional problems in comparison with the commonly used step signals due to the hysteresis effects, which require a good modeling approach. In order to avoid the discontinuity problem in obtaining the values of the piezoelectric constant, a new approach of direct mapping with polynomial fit is proposed. Theoretical and experimental studies are conducted and comparative studies are made. Compared with the single polynomial approach, the proposed method of direct mapping with polynomial fit is able to reduce the modeling error to 12.5%, which is 6.5% lower, and the problems in obtaining the values of the piezoelectric constant are avoided. The proposed approach is shown advantageous. Further studies are necessary to significantly reduce the modeling error.