An experimental study on micro-EDM in low-resistivity deionized water using short voltage pulses

Deionized water has been used as dielectric fluid for micro-electrical discharge machining (micro-EDM) because it gives higher material removal rate and lower tool wear than hydrocarbon oil. Moreover, it is a relatively low-cost and eco-friendly substance. Therefore, deionized water tends to be more favorable for micro-EDM. However, it causes weak electrochemical reaction during micro-EDM due to its slight conductivity. This leads to the unanticipated additional material removal from the workpiece which affects the machining shape and quality. The study in this paper aims to suppress the electrochemical reaction in die-sinking micro-EDM using deionized water by employing short voltage pulse. Experiments were carried out to fabricate micro-holes using the developed nanosecond pulse circuit. Different pulse parameters were applied to identify the main factor affecting the electrochemical reaction rate. Machining gap was found to be thinner and workpiece surface adjacent to the rim of micro-holes were found to be free of defects caused by material dissolution when pulse duration reached a critical value. Moreover, the influence of pulse parameters on material removal rate and machined shape was also investigated. Besides, energy-dispersive X-ray spectroscopy analysis showed that the machined surface using deionized water was less affected from material migration during micro-EDM process in comparison to hydrocarbon oil.     

Fabrication of different geometry cutting tools and their effect on the vertical micro-grinding of BK7 glass

With the demand for microstructures of not only with diversified shape but also of reduced dimension on glass, fabrication of polycrystalline diamond (PCD) tool/microelectrodes with different shape has become important. However, to date, fabrication of different shapes in single setup is not possible and also needs special indexing attachment. To solve this problem, in this study, a specially designed block containing three v-slots of 60°, 90°, and 120° has been designed and fabricated using wire cut. Thereafter with the help of block electro-discharge machining method and using this specially designed block, different shapes of microelectrodes with symmetrical and non-symmetrical section has been fabricated. This study also investigates the feasibility of using these different geometry PCD tool for micro-grinding of BK7 glass. In this context, a relative study on the micro-grinding performance of four different geometry tools (circular, D-shaped, triangular, and square) has been carried out. It has been observed that among the different shaped tools, D-shaped tool experienced lowest cutting force along x- and y-axes where as triangular tool faced lowest force along z-axis, and highest cutting forces were found to be experienced by square tool. Average and maximum roughness of machined surface was found to be improved from circular to others tool except triangular one. But, it was also observed that side surface started to deteriorate from circular to other tool due to edge wear. In case of tool wear, square and triangular tool experienced more wear than circular and D-shaped tool due to their frequent edge blunting or rounding effect. Finally, among four different geometry tools, D-shaped tool was considered to provide better performance in terms of the achieved surface finish, tool wear, and cutting force analysis.     

基于微纳机械加工的THz单光子探测器及其应用

通过量子阱的子带跃迁光吸收改变自身带电状态来调控另一个量子阱中的二维电子横向输运特性,从而产生可探测的电导变化。这种双量子阱电容耦合的结构具有很高的非线性放大系数,从而具有很高的探测效率,响应波长可以从远红外设计至THz波段。针对器件特性设计增益可调读出电路,进一步研制成工业级微型光谱仪。     

A multi-stage methodology for virtual cell formation oriented agile manufacturing

In recent years, as an emerging concept in industry, agile manufacturing has attracted considerable attention, combining virtual manufacturing cells to construct new manufacturing systems to respond to the changing market needs, especially in nonlinear processes. In this paper, a multi-stage cell formation methodology, which can help select appropriate resources and form the VCs, is presented. First, appropriate resources for completing production tasks are selected by a LP model considering the available capacity and the costs. In order to form VC in a logical mode, parts having alternative product process routings as multi-functional machines are analyzed by a resource element approach. Furthermore, some routing-based heuristic rules are introduced to optimize the candidate VCs in the form of resource elements. Finally a case study is used to illustrate the detailed formation methodology.     

Movement of Entrapped Oil Under Pure Rolling Conditions

This article presents a study on the movement of an oil entrapment (or impact dimple) in a pure rolling elastohydrodynamic lubricated (EHL) contact. The oil entrapment was formed by impacting a steel ball against a lubricated glass disc. The contact was then activated under pure rolling conditions, and the movement of the entrapped oil was visualized by optical interferometry. It was found that during the movement of the dimple within the EHL contact, there exists a critical value for the displacement of dimple core. For the displacement of the dimple core less than the critical value, the dimple moves at the entrainment velocity and the film thickness of dimple core remains almost constant. For displacement beyond the critical value, the dimple slows down and its depth decreases rapidly. The effects of influential factors such as speed, initial dimple depth, load, and initial gap size were theoretically and experimentally investigated.     

Virtual reflected-light microscopy

Research on better methods to digitally represent microscopic specimens has increased over recent decades. Opaque specimens, such as microfossils and metallurgic specimens, are often viewed using reflected light microscopy. Existing 3D surface estimation techniques for reflected light microscopy do not model reflectance, restricting the representation to only one illumination condition and making them an imperfect recreation of the experience of using an actual microscope. This paper introduces a virtual reflected-light microscopy (VRLM) system that estimates both shape and reflectance from a set of specimen images. When coupled with anaglyph creation, the system can depict both depth information and illumination cues under any desired lighting configuration. Digital representations are compact and easily viewed in an online setting. A prototype used to construct VRLM representations is comprised only of a microscope, a digital camera, a motorized stage and software. Such a system automatically acquires VRLM representations of large batches of specimens. VRLM representations are then disseminated in an interactive online environment, which allows users to change the virtual light source direction and type. Experiments demonstrate high quality VRLM representations of 500 microfossils.     

A CFD study of low pressure wet gas metering using slotted orifice meters

Wet gas metering is becoming an increasingly important problem to many industries, in particular the oil and gas industry. Extensive studies have been done in the past on Venturi and standard orifice differential pressure (DP) flow meters to tackle wet gas flow problems. However in recent years, the slotted orifice flow meter has been developed in the attempt to improve the performance of the standard orifice meter. The novel flow meter is shown to be insensitive to the upstream flow profile with lower head loss and faster pressure recovery. This paper describes the numerical studies to establish the effect of different geometrical perforations on the performance of the slotted orifice. Three sets of slotted orifices with varying aspect ratios (1.5≤l/w≤3.0), of rectangular perforations and one slotted orifice with a circular perforation and a β ratio of 0.40 are simulated in a 1.6 m horizontal pipe using the k-ε turbulence model over a range of parameters, i.e. gas volume fraction (GVF) and gas mass flow rate. The commercial CFD code, FLUENT 6.3 was used to model the wet gas flow. Simulation results revealed that the shape of the perforation has no effect on the differential pressure, However, a marginally better pressure recovery was observed with rectangular perforations of l/w=3.0. The relatively higher over-reading values obtained in this work are consistent with the results of Geng et al. (2006) [1] that for a slotted orifice, a low β ratio is more sensitive to the liquid presence in the stream and hence is preferable for wet gas metering. Mass flow prediction by wet gas correlations showed that the homogeneous model, Steven’s and De Leeuw’s correlations had the best performance, with a calculated mean error of 4%-5%.     

Experimental Study on Lubrication Film Thickness Under Different Interface Wettabilities

This paper describes some experimental studies about the effect of interface wettability on hydrodynamic lubrication film thickness by a custom-made slider bearing tester. The lubricated contact pair consists of a fixed-incline slider and a transparent disc, and a thin lubrication film can be generated when the disc rotates. The film thickness was measured by interferometry. The wettability of different slider surfaces was evaluated by the contact angle of the lubricant on them. The relationship of film thickness versus disc speed was measured under different liquid–solid interfaces, and the results showed that slider surfaces with strong wettability to the lubricant could generate higher film thickness. Furthermore, case experiments were carried out to validate the hydrodynamic effect by tailored-slippage. By numerical simulations, the experimental findings were tentatively explained with the phenomenon of wall slippage.     

Comparative authentication of three “snow lotus” herbs by macroscopic and microscopic features

“Snow lotus” is a famous Chinese Materia Medica derived from species of the genus Saussurea (Compositae). To differentiate three representative easily‐confused snow lotus herbs, namely, Saussurea involucrata (Kar. et Kir.) Sch.‐Bip, Saussurea laniceps Hand.‐Mazz., and Saussurea medusa Maxim., macroscopic features of the three herbs were systemically observed, and microscopic features were compared by using ordinary light microscopy, polarized light microscopy and scanning electron microscopy (SEM). The results indicate that, as for macroscopic identification, capitula situation and arrangement, and as for microscopic identification, pollen grains, nonglandular hairs, glandular hairs, and cells of inner surface of the microdiodange can be used to authenticate the three snow lotus herbs. Comprehensive table comparing the characteristics were presented in this study. SEM has been found to provide a number of unique characteristics of pollen grains. Based on the observation of pollen grains, evolution sequence of the three species was speculated. The present method was proven to be efficient, convenient, simple, and reliable, which was successfully applied to the authentication of three snow lotus herbs. Microsc. Res. Tech.1 77:631–641, 2014. © 2014 Wiley Periodicals, Inc.     

Effect of micro-powder suspension and ultrasonic vibration of dielectric fluid in micro-EDM processes—Taguchi approach

Solutions are needed for increasing the material removal rate without degrading surface quality in micro-electrical discharge machining (μ-EDM). This paper presents a new method that consists of suspending micro-MoS₂ powder in dielectric fluid and using ultrasonic vibration during μ-EDM processes. The Taguchi method is adopted to ascertain the optimal process parameters to increase the material removal rate of dielectric fluid containing micro-powder in μ-EDM using a L₁₈ orthogonal array. Pareto analysis of variance is employed to analyze the four machining process parameters: ultrasonic vibration of the dielectric fluid, concentration of micro-powder, tool electrode materials, and workpiece materials. The results show that the introduction of MoS₂ micro-powder in dielectric fluid and using ultrasonic vibration significantly increase the material removal rate and improves surface quality by providing a flat surface free of black carbon spots.