Effect of process parameters on the performance of EDM process with ultrasonic assisted cryogenically cooled electrode

In this work the parametric study on EDM process using ultrasonic assisted cryogenically cooled copper electrode (UACEDM) during machining of M2 grade high speed steel has been performed. Electrode wear ratio (EWR), material removal rate (MRR) and surface roughness (SR) was the three parameters observed. Discharge current, pulse on time, duty cycle and gap voltage were the controllable process variables. The effect of process variables on EWR, MRR and SR has been analyzed. The MRR, EWR and SR obtained in EDM process with normal electrode, cryogenically cooled electrode and ultrasonic assisted cryogenically cooled electrode have been compared. EWR and SR were found to be lower in UACEDM process as compared to conventional EDM for the same set of process parameters, while MRR was at par with conventional EDM process. The surface integrity of work piece machined by UACEDM process has been found to be better as compared to conventional EDM process. The shape of the electrode has also been measured and it was found that the shape retention was better in UACEDM process as compared to conventional EDM process. Thus in the present work UACEDM process has been established to be better than conventional EDM process due to better tool life, tool shape retention ability and better surface integrity.     

造纸废水处理过程的高斯过程回归软测量建模

针对造纸废水处理系统的时变性、非线性和复杂性等特点,本文提出一种基于高斯过程回归的软测量模型.基于平方指数协方差、线性协方差和周期性协方差函数组合构建了7种高斯过程回归模型,分别对出水化学需氧量和出水悬浮固形物浓度进行回归预测.此外,还对比了多元线性回归模型、主成分回归模型、偏最小二乘模型、人工神经网络模型和高斯回归模型的预测效果.对比计算结果表明无论是对输出变量的训练拟合还是预测,高斯过程回归模型的拟合效果均优于非高斯过程回归模型.高斯过程回归模型的预测结果表明：对于出水化学需氧量,线性协方差函数与周期性协方差函数的组合模型可以取得最好的预测结果;对于出水悬浮固形物,平方指数协方差函数与线性协方差函数组合模型可以取得最好的预测结果.     

生物处理动力学参数测定研究

结构化的废水生物处理过程模型引入了较多的模型参数。参数估值是关系到模型实用性的重要课题。本文介绍了利用批量反应器试验技术测定模型参数YH、bH、μ_max和K_hs的原理、方法以及对城市污水处理厂活性污泥的测定结果。采用所设计的试验程序,通过对OUR或DO动态变化的测定、分析和计算,即可得到有关的参数值,方法简便易行。     

大面积镜面电火花加工的实验研究

介绍了大面积镜面电火花加工法现状.通过改变混粉工作液中微粉的种类、浓度、加工参数以及加工面积进行了工艺试验.验证了混粉电火花加工的确能改善表面粗糙度.     

Hot extrusion process modeling using a coupled upper bound-finite element method

A thermo-mechanical model has been developed for modeling of hot extrusion processes. Accordingly, an admissible velocity field was first proposed by means of stream function method and then, extrusion pressure as well as temperature variations within the metal and the die were predicted employing a combined upper bound and Petrov–Galerkin finite element analysis. In order to evaluate the model predictions, hot extrusion of AA6061-10%SiC_p was considered under both isothermal and non-isothermal conditions and the predicted force–displacement diagrams under various extrusion conditions were compared with the experimental ones and reasonable consistency was found between the two sets of results.     

Surface clogging process modeling of suspended solids during urban stormwater aquifer recharge

Aquifer recharge,which uses urban stormwater,is an effective technique to control the negative effects of groundwater overexploitation,while clogging problems in infiltration systems remain the key restricting factor in broadening its practice.Quantitative understanding of the clogging process is still very poor.A laboratory study was conducted to understand surface physical clogging processes,with the primary aim of developing a model for predicting suspended solid clogging processes before aquifer recharge projects start.The experiments investigated the clogging characteristics of different suspended solid sizes in recharge water by using a series of one-dimensional fine quartz sand columns.The results showed that the smaller the suspended particles in recharge water,the farther the distance of movement and the larger the scope of clogging in porous media.Clogging extents in fine sand were 1 cm,for suspended particle size ranging from 0.075 to 0.0385 mm,and 2 cm,for particles less than 0.0385 mm.In addition,clogging development occurred more rapidly for smaller suspended solid particles.It took 48,42,and 36 hr respectively,for large-,medium-,and small-sized particles to reach pre-determined clogging standards.An empirical formula and iteration model for the surface clogging evolution process were derived.The verification results obtained from stormwater recharge into fine sand demonstrated that the model could reflect the real laws of the surface clogging process.     

Scale-up modeling of the twin roll casting process for AZ31 magnesium alloy

In the present study, a 2-D finite-element method (FEM) thermal-fluid-stress model has been developed and validated for the twin roll casting (TRC) of AZ31 magnesium alloy. The model was then used to quantify how the thermo-mechanical history experienced by the strip during TRC would change as the equipment was scaled up from a laboratory size (roll diameter = 355 mm) to a pilot scale (roll diameter = 600 mm) and to an industrial scale (roll diameter = 1150 mm) machine. The model predictions showed that the thermal history and solidification cooling rate experienced by the strip are not affected significantly by caster scale-up. However, the mechanical history experienced by the strip did change remarkably depending on the roll diameters. Casting with bigger rolls led to the development of higher stress levels at the strip surface. The roll separating force/mm width of strip was also predicted to increase significantly when the TRC was scaled to larger sizes. Using the model predicted results, the effect of both casting speed and roll diameter was integrated into an empirical equation to predict the exit temperature and the roll separating force for AZ31. Using this approach, a TRC process map was generated for AZ31 which included roll diameter and casting speed.     

ZrO2掺杂对La2Ce2O7力学和热物理性能 影响的研究

目的提高La_2Ce_2O_7(LC)陶瓷材料的断裂韧性。方法采用固相反应方法合成Y_2O_3稳定ZrO_2(YSZ)掺杂的La_2Ce_2O_7(LC)陶瓷材料(LCZ),研究LCZ块材的弹性模量、断裂韧性等力学性能,以及热膨胀系数、热传导率等热物理性能。结果 10%YSZ摩尔分数掺杂的LCZ块材的断裂韧性约为1.4 MPa·m1/2,比LC提高了近10%。YSZ掺杂有效地抑制了LC在200～400℃温度区间热膨胀系数下降的现象。在200～1200℃温度范围内,LCZ块材的热膨胀系数为10×10-6～12×10-6K-1,在1200℃的热导率约为0.75W/(m·K),比YSZ降低了50%以上,显示了优异的隔热性能。结论 YSZ的掺杂使LC中部分Zr4+取代了La3+,降低了晶格中的O空位浓度,原子的横向剪切运动被削弱,有效地抑制了LC在200～400℃温度区间热膨胀系数下降的现象。由于t-ZrO_2→m-ZrO_2的相变对微裂纹的愈合作用,10%YSZ掺杂使LC块材的断裂韧性得到有效提高。     

Effects of magnetic field and rotary tool on EDM performance

In this work, the effects of tool rotation and various intensities of external magnetic field on electrical discharge machining (EDM) performance have been studied. Experimental trials divided into three regimes of low energy regime, middle energy regime and high energy regime. The influences of process parameters were investigated on main outputs of material removal rate (MRR) and surface roughness (SR). In order to correlate the input parameters and output values two mathematical models were developed to predict the MRR and SR according to variations of discharge energy, magnetic field intensity and tool rotational speed. Results indicated that the applying a rotational magnetic field around the machining gap improves the MRR and SR. Combination of rotational magnetic field and rotary electrode increases the machining performance, in comparison of previous conditions. This is due to better flushing debris from machining gap. This work introduces a new method for improving the machining performance, in cost and time points of view.     

Cost-performance analysis of nutrient removal in a full-scale oxidation ditch process based on kinetic modeling

A full-scale oxidation ditch process for treating sewage was simulated with the ASM2d model and optimized for minimal cost with acceptable performance in terms of ammonium and phosphorus removal. A unified index was introduced by integrating operational costs (aeration energy and sludge production) with effluent violations for performance evaluation. Scenario analysis showed that,in comparison with the baseline (all of the 9 aerators activated), the strategy of activating 5 aerators could save aeration energy significantly with an ammonium violation below 10%. Sludge discharge scenario analysis showed that a sludge discharge flow of 250–300 m3/day (solid retention time (SRT), 13–15 days) was appropriate for the enhancement of phosphorus removal without excessive sludge production. The proposed optimal control strategy was: activating 5 rotating disks operated with a mode of "111100100" ( "1"represents activation and "0" represents inactivation) for aeration and sludge discharge flow of 200 m3/day (SRT, 19 days). Compared with the baseline, this strategy could achieve ammonium violation below 10% and TP violation below 30% with substantial reduction of aeration energy cost (46%) and minimal increment of sludge production (< 2%). This study provides a useful approach for the optimization of process operation and control.     

基于EDM的农业节水技术补偿

实现农业节水,必须建立有效的农业节水补偿机制对农民进行补偿。文章采用经典EDM模型,分析了农业节水技术投入对生产者、消费者及社会福利的影响。研究认为,农业节水技术投入使得生产者剩余、消费者剩余以及社会总剩余全面增加;政策实施带来社会福利变化在产品市场上的消费者与生产者之间分配,缺乏弹性的一方受到的影响往往大于富有弹性的一方;根据投入产出及"谁受益、谁补偿"的补偿原则,由消费者剩余变化及生产者剩余变化分别占社会总福利变化的比重,即可制定消费者及生产者对农业节水项目的投资付费标准以及补偿标准;建立水权交易市场,使农民通过出售节约的水资源而获益,可有效地激发其投入节水事业的积极性。     

电极直接驱动的小型电火花加工装置的研究现状

概括了目前典型的电极直接驱动的小型电火花加工装置——椭圆驱动装置、冲击式驱动装置和蠕动式驱动装置的发展现状,介绍了这些装置的结构和工作原理,分析了其存在的不足,提出了改进措施.最后指出了电极直接驱动的小型电火花加工装置的发展趋势及其应用前景,并首次提出了电火花加工机器人的新概念.     

Surface modification of die steel materials by EDM method using tungsten powder-mixed dielectric

Surface modification by material transfer during electrical discharge machining (EDM) has emerged as a key research area in the last decade. Material may be provided to the machined surface of the workpiece by the eroding tool electrode or by using powder-mixed dielectric. Breakdown of the hydrocarbon dielectric contributes carbon to the plasma channel which may also cause surface modification. The present work has investigated the response of three die steel materials to surface modification by EDM method with tungsten powder mixed in the dielectric medium. Taguchi experimental design technique was used to conduct the experiments on each work material independently. Peak current, pulse on-time and pulse off-time were taken as variable factors and micro-hardness of the machined surface was taken as the response parameter. X-ray diffraction (XRD) and spectrometric analysis show substantial transfer of tungsten and carbon to the workpiece surface and an improvement of more than 100% in micro-hardness for all the three die steels. Presence of tungsten carbide (WC and W₂C) indicates that its formation is taking place in the plasma channel. Machining parameters for the best value of micro-hardness for each work material were found to be the same.     

Effect of Silicon Powder Mixed EDM on Machining Rate of AISI D2 Die Steel

In this paper, the effect of silicon powder mixing into the dielectric fluid of EDM on machining characteristics of AISI D2 (a variant of high carbon high chrome) die steel has been studied. Six process parameters, namely peak current, pulse-on time, pulse-off time, concentration of powder, gain, and nozzle flushing have been considered. The process performance is measured in terms of machining rate (MR). The research outcome will identify the important parameters and their effect on MR of AISI D2 in the presence of suspended silicon powder in a kerosene dielectric of EDM. The study indicated that all the selected parameters except nozzle flushing have a significant effect on the mean and variation in MR (S/N ratio). Optimization to maximize MR has also been undertaken using the Taguchi method. The ANOVA analysis indicates that the percentage contribution of peak current and powder concentration toward MR is maximum among all the parameters. The confirmation runs showed that the setting of peak current at a high level (16 A), pulse-on time at a medium level (100 μs), pulse-off time at a low level (15 μs), powder concentration at a high level (4 g/l), and gain at a low level (0.83 mm/s) produced optimum MR from AISI D2 surfaces when machined by silicon powder mixed EDM.     

衡量模具加工精度的一个重要的尺度——电火花电源的低电极损耗

高精度模具加工除了与机床本身精度有关外电火花电源起重要作用。电极损耗性能与生产率、粗糙度等性能相比更起关键作用。此文论述了在保证同样的电极损耗下,性能优良的电极损耗将使粗糙度更细、放电间隙更小、生产率更高。在例举若干较高的电极损耗指标后提出了评审某电源的电极损耗性能高低的标准。     

Receptor modeling of the Antwerp aerosol

Receptor modeling, using factor analysis, was applied for the source identification and source apportionment of air particulate samples which were collected during two sampling campaigns in Antwerp, Belgium, and analyzed by particle-induced X-ray emission (PIXE) analysis. In a summer campaign (July 1986), 16 12-h samples of total aerosol were taken using conventional low volume filter equipment. In a winter campaign (February–March 1987) 120 24-h samples, consisting of 40 coarse, 40 fine and 40 total aerosol samples, were collected using a stacked filter unit and a total filter sampler. In both campaigns between three and five sources were discerned, most of which could be attributed to existing urban sources of air particulate matter. For each source, source profiles and absolute elemental contributions were calculated.     

Dispersion modeling using personal computers

The widespread availability of personal computers and PC versions of models for these computers is changing the way dispersion modeling is performed. Research scientists, environmental engineers and meteorologists, whether associated with institutes, industry or regulatory agencies, can use screening models to determine the effect of proposed changes, and when more complicated studies are warranted. As model use becomes more egalitarian, better use of intellectual talent among modelers will occur. Scientists can focus on more difficult problems while industry and agency personnel can focus on more routine issues. Moreover, the presently available models enable nearly anyone with some scientific training to perform modeling and make reasonable estimates of air quality changes.     

Water jet guided laser as an alternative to EDM for micro-drilling of fuel injector nozzles: A comparison of machined surfaces

To characterize the inner surface of the fuel injector nozzle holes drilled by EDM and water jet guided laser drilling (Laser Micro-Jet) a specifically conceived scanning probe microscopy technique with true non-contact operating mode was used. A difference in morphology of the drilled surfaces is evident from the acquired surface topography along the hole axis for the two compared drilling techniques. Results showed that the surface texture can be characterized by (i) maximum peak-to-valley distance and (ii) periodicity. Acquired maps confirm that electro-eroded surfaces are an envelope of craters randomly distributed with total excursion up to 1.7 μm with a crater size of 15 μm. While, the efficient melt expulsion and immediate cooling of water jet guided laser generates a peak to valley distance of 800 nm with a periodicity of 18 μm. Average R_q derived from the measured cylindrical surfaces was 450 nm and 150 nm for EDM and Laser Micro-Jet, respectively. Water jet guided laser drilling has proved to be a reliable alternative to EDM from the point of view of repeatability of the results and surface quality to facilitate the atomization of the fuel jet.     

Comparison of some atmospheric chemical modeling schemes

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