In micro-milling, the diameter of the micro-milling cutter is smaller than tens of microns, making it difficult to achieve precise positioning with the workpiece, which affects the machining accuracy and the safety of the micro-milling cutter. To solve these problems, the coordinate system has been analyzed. A micro-milling precise automatic tool setting technology has been proposed, which based on the micro-energy pulse discharge sensing principle. A tool setting scheme is proposed to determinate the Central coordinates of workpiece, which is realized by repeating automatically the precise sense from four directions. Experiment is carried out to verify the feasibility and correctness of the technology by analyzing the perceived results.
The gap average voltage measurement method is commonly used to detect the discharge state in micro electrical discharge machining (Micro-EDM), which is simple and effective for the discharge states detection of transistor pulse power and relaxation type pulse power. In order to further explore the ultimate machining ability of micro-EDM, a very high frequency (VHF, frequency range 30MHz~300MHz) micro energy pulse generator based on the principle of circuit resonance has been developed in a previous study. It has smaller discharge energy and nanoscale discharge erosion ability compared with the traditional pulse power. Furthermore, defects in micro-EDM such as thermal damage, recast layer and heat affected zone are significantly reduced. A simulation circuit model was established to analyze the effect of the gap average voltage measurement method applied to VHF pulse generator. The results show that the inter-electrode discharge states cannot be distinguished effectively and sensitively by this means. In order to detect the discharge state of VHF pulse generator, a novel method to detect discharge state based on impedance change of inter-electrode channel was presented, which is not affected by the pulse power. Hence, when the detection circuit was fixed, the detection sensitivity and the accuracy of threshold voltage was not varied according to different pulse parameters. Both simulation and experimental studies were undertaken to verify the effectiveness of the proposed method. The results demonstrate that the discharge states of VHF pulse generator can be distinguished by this detection method.
Ultra-high speed photoelectric photographic system is one of the important methods to study the image parameters of ultrafast physical process. This paper proposes a method of combining multi-group prism optical splitter, super shutter selection image intensifier with adjustable delay and CCD picture acquisition. The proposed method solves the problem of the image cutting in the small aperture backlight illumination experiment using the pyramid-type photoelectric camera. Several ultra-high speed photographic systems are developed, which can be used for the shadow photography, and realize ultra high speed photoelectric photographic system with 43 mm-1 spatial resolution, 2x108 images/s speed, and the capability of capturing 8 images continuously (Fig. 1). In order to adapt to the strong electromagnetic interference test environment, the photographic system adopts all optical fiber communication, signal interpretation and locking, unit modularization and other technical schemes to avoid the loss of signal in the image transmission and the system mistriggering problems. The developed camera has good application to such dynamic experiments as plasma physics and the interaction between laser and substance, and satisfactory results have been achieved.
In order to find out the law how the nozzle height influences the removal function in FJP, a mathematical model of the nozzle-rotating removal function is proposed and its correctness has been verified by experiment. Moreover, another model which is able to predict the surfaces processed by different removal functions is established in this paper. The calculation results show the profile of nozzle-rotating removal functions change from W-shaped to single peak Gaussian shaped as the nozzle height increases. Besides, when the removal functions are Gaussian shaped, the best surface roughness is obtained when the removal function is the widest and shallowest one. Which has theoretical significance for the optimization of the process parameters in actual processing.
The slurry of fluid jet polishing mainly consists of deionized water and abrasives. Material removal is mostly regarded as plastic removal by the strike of the abrasives on the workpiece surface. Since jet pressure is relatively low, which result in a low material removal rate and bring a limitation of applying to this processing method. To improve the material removal rate of glass (Fused Silica, UBK7, K9, etc.), alkaline slurry was used to enhance chemical effects during polishing. Firstly, the material removal of conventional neutral slurry (pH≈7) and the new alkaline slurry (pH≈10, 11, 12, 13) were compared and the results showed that alkaline slurry brought an obvious increase in material removal rate. Then, four kinds of slurry of different alkalinity (pH≈10, 11, 12, 13) were used in polishing experiments to make clear the influence of alkaline intensity on the material removal rate. It was found that a larger material removal rate would be obtained with a higher pH slurry. Finally, the surface roughness which were made by slurry with different alkalinity were also compared, the results reached as that slurry with higher pH could bring lower surface roughness. It could be drawn from this study that enhance the chemical effects in fluid jet polishing could be an effective way to enlarge the material removal rate and improve the processing performance.
Fluid jet polishing (FJP) is a versatile method used for polishing small and complex components. The unstable removal function which is caused by the pulsation of turbulent jet is one of the main limitations for FJP. In this paper, this problem is addressed by a novel shear thickening FJP method. The shear thickening fluid (STF) is employed for preparing the polishing slurry instead of conventional Newtonian fluid. The principle of shear thickening FJP is present based on analyzing the behavior of STF under the special shear rate distribution. Then the influence of the shear thickening behavior on the material removal rate and the surface roughness of UBK7 components is investigated. The performance of the shear thickening FJP is verified detail by experiments. It is found that the shear thickening behavior would be beneficial to the surface accuracy of workpiece, owing to its ability of reducing the turbulence intensity in the boundary layers of fluid jet. Compared with normal FJP, the surface roughness of polished parts could be improved more than 40% in shear thickening FJP, while maintaining the material removal rate.
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