OPTIMIZATION OF ELECTRO-CHEMICAL MACHINING PROCESS PARAMETERS USING GENETIC ALGORITHMS

ECM and ECM-based processes (derived and hybrid processes) are one of the most widely used advanced machining processes (AMPs) to make complicated shapes of varying sizes in the products made of electrically conducting but difficult-to-machine materials such as superalloys, Ti-alloys, alloy steel, tool steel, stainless steel, etc. These materials are extensively used in aerospace, automobile, space, nuclear, defense, cutting tools, dies and mold making applications. ECM offers some unique advantages over other conventional and advanced machining processes but its use incurs relatively higher initial investment cost, operating cost, tooling cost, and maintenance cost. Use of optimum ECM process parameters can significantly reduce the ECM operating, tooling, and maintenance cost and will produce components of higher accuracy which is very important in some critical areas such as aerospace, space, defense, nuclear applications. Therefore, choice of optimum process parameters is essential to ensure the most cost-effective, efficient, and economic utilization of ECM process potentials. This paper describes optimization of three most important ECM process parameters namely tool feed rate, electrolyte flow velocity, and applied voltage with an objective to minimize geometrical inaccuracy subjected to temperature, choking, and passivity constraints using real-coded genetic algorithms. Comparison of the obtained optimization results with the results of past work in this direction shows an improvement in terms of geometrical accuracy.     

数控火焰切割机割缝补偿的实现

分析了火焰切割加工工艺的特点,及由此引起的割缝补偿的特定要求,论述了割缝补偿的计算和实现过程.该补偿模块可用于其他热切割机的补偿.     

Numerical investigation of the combined effects of slip and texture on tribological performance of bearing

Slider bearings are used in many applications. An increase in the load support may allow for saving of energy. In this work, in order to enhance the load support and decrease the friction force, a combined textured surface bearing using boundary slip is discussed. A modified Reynolds equation with slip is adopted. With the main goal of evaluating the effects of slip and texture, a parametric analysis is performed. For the given operating conditions, texturing features as well as slip pattern are analysed in detail. The numerical analysis is undertaken under the condition of different gap ratio values and the slip-textured area. The results show that combined techniques of slip and texture have a significant effect on the improvement of the tribological performance of bearing, that is, a high load support but low friction force. The gap ratio of the bearing is shown to have a significant effect on the lubrication behaviour. It is found that even with a smallest gap ratio (parallel gap), a high load support can be produced. However, it is also shown that the gap ratio appears to contribute to the generated friction force and the volume flow rate more than the boundary slip. Further analysis indicates that the optimum slip-text zones for certain gap ratio are highlighted. These findings may provide references for designing hydrodynamic-textured slider bearing considering boundary slip.     

Enhanced structural and optical properties of ZnO nanopowder with tailored visible luminescence as a function of sodium hydroxide to zinc sulfate mass ratio

ZnO nanopowders of tailored particle sizes were synthesized using a simple wet chemical method, by controlling the mass ratio of the precursors. The physical properties were investigated as a function of OH^?/Zn²⁺ mass ratio (x). The structural properties of the synthesized nanoparticles (NPs) are studied using X-ray diffraction (XRD). XRD patterns show pure wurtzite structure. Microstructural parameters dependence on x ratio was studied based on Williamson-Hall model. We notice an increase in crystallite size (17–24?nm) and a decrease in strain values when the x ratio increases (0.5–1.4). The best crystallinity corresponds to the higher mass ratio. Indeed, for x?=?1.4 we obtain the largest crystallite size, the lowest strain and stacking faults. The TEM images support the XRD results. Raman spectra confirm the purity of the synthesized ZnO powder. Furthermore, the optical properties were examined by UV–vis and Photoluminescence as a function of precursor’s ratio. Absorption data show a band gap red-shift of the ZnO-NPs with increase in particle’s size. Moreover, we found that the ZnO-NPs luminescence in the visible range can be engineered by changes of x ratio. This constitutes an advantage for the use of ZnO-NPs in different wavelength areas in optoelectronic applications covering UV-Blue-Green domain for the LED design, sensors…     

基于Moodle和PhoneGap的移动学习客户端的设计与应用研究

本文将结合用户移动学习现状及偏好,确定移动学习客户端的系统需求,进而基于Moodle和PhoneGap平台,实现对移动学习客户端的设计,并将移动学习客户端应用到实际教学过程中,确定应用成效。     

Improving electrical discharging machining efficiency by using a Kalman filter for estimating gap voltages

Gap voltage can be used as an indicator on the direction of the electrode movement along a desired tool path in electrical discharging machining (EDM) processes. However, due to the noise induced by electrical discharges, the estimation of gap voltages is difficult due to the lack of an appropriate state space model. In this paper, gap voltage signals are considered to be generated as a summation of colored noise through a linear filter and measurement noise. Obtained by the Yule–Walker auto-covariance method, the transfer function of the linear filter can be converted into a state space model. The composite process noise and the composite measurement noise are defined to derive the composite noise covariance matrices. A Kalman filter can thus be designed based on the state space model and the noise covariance matrices. Experimental results showed that, as compared with the traditional 10-point moving average filter, the Kalman filter can decrease the average machining time as well as improve the discharging gap status.     

“轻”的南京明城墙前湖段缺口连接体设计--2015年中国建筑院校境外交流优秀作业方案简介

在“南京明城墙前湖段缺口连接体设计”的概念方案中,采用了“轻”作为方案构思的切入点,从建筑轻的形态、轻的建造、轻的形式,轻与光的共生这几主要个方面来解决明城墙在南京前湖公园内的缺口的问题。     

The Social News Gap: How News Reading and News Sharing Diverge

This article seeks to explain variation in news sharing patterns on social media. It finds that news editors have considerable power to shape the social media agenda through the use of “story importance cues” but also shows that there are some areas of news reporting (such as those related to crime and disasters) where this power does not apply. This highlights the existence of a social “news gap” where social media filters out certain types of news, producing a social media news agenda which has important differences from its traditional counterpart. The discussion suggests that this may be consequential for perceptions of crime and engagement with politics; it might even stimulate a partial reversal of the tabloidization of news outlets.     

转塔式双头圆盘剪分析及应用

简要介绍转塔式双头圆盘剪的工作原理及结构特点,对圆盘剪的各个部件机构进行分析说明,针对某钢厂连续酸洗机组中圆盘剪的使用实例进行设计参数选择的探讨,为以后同样的设计提供参考依据。     

环缝洗涤工艺在包钢5#高炉煤气清洗中的应用

文章针对环缝洗涤工艺在包钢5#号高炉煤气清洗中的应用进行了过程和特点描述,在获取部分重要设计参数的条件下进行了工程设计,并对工程设计进行了实验验证.