Machining efficiency of powder mixed near dry electrical discharge machining based on different material combinations of tool electrode and workpiece electrode

Powder mixed near dry electrical discharge machining (PMND-EDM) is a novel electrical discharge machining (EDM) process. It is proposed to further improve the machining efficiency of dry EDM. The principle of material removal in PMND-EDM is illustrated and its deionization principle is proposed. The influence of residual heat on MRR is analyzed. The concept of superfluous residual heat is proposed. The material removal rate (MRR), the main index of machining efficiency for PMND-EDM process, is researched. Single factor experiments are performed to get effect of peak current, pulse on time, pulse off time, flow rate, tool rotational speed, air pressure and powder concentration on MRR under different material combinations of tool electrode and workpiece electrode. Thermal phenomena in PMND-EDM are illustrated. Effect of each process parameter on MRR of PMND-EDM is gotten and analyzed based on the deionization principle of PMND-EDM. Differences in MRR under different material combinations are found out. Brass tool electrode and W18Cr4V workpiece gain higher MRR under most of discharge conditions, while the superiority of copper tool electrode and 45 carbon steel workpiece in MRR arise when there is improper heat dissipation. The difference is analyzed based on the deionization principle of PMND-EDM.     

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.     

Study of ultrasonic assisted cryogenically cooled EDM process using sintered (Cu–TiC) tooltip

In most EDM operations, the maximum contribution in the total operation cost is the tool cost. Electrode wear is a major problem in EDM process. Therefore, in this paper, the process performance of sintered copper (Cu)–titanium carbide (TiC) electrode tip in ultrasonic assisted cryogenically cooled electrical discharge machining (UACEDM) has been studied. The performance parameters studied in this paper are electrode wear ratio (EWR), material removal rate (MRR), surface roughness (SR), out of roundness and surface integrity. The process parameters considered in this study are discharge current, pulse on time, duty cycle and gap voltage. Cermet was fabricated, having copper content of 75% and titanium carbide content of 25%, by mixing, pressing, and sintering. The performance of the newly formed cermet electrode tip is compared with conventional copper electrode tip for UACEDM process and analyzed. It has been observed that EWR and out of roundness decreases when cermet electrode tip is used as compared to conventional tooltip. It has also been observed that MRR and SR increase when cermet tooltip is used. The surface cracks density and crack width on workpiece machined by cermet tooltip have been found to be lesser as compared to the specimen machined by conventional tooltip.     

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.     

An Approach to Theoretical Modeling and Simulation of Face Milling Forces

A new approach to theoretical modeling and simulation of face milling forces is presented. The present approach is based on a predictive machining theory in which machining characteristic factors in continuous cutting with a single-point cutting tool can be predicted from the workpiece material properties, tool geometry, and cutting conditions. The action of a milling cutter is considered as the simultaneous work of a number of single-point cutting tools, and the milling forces are predicted from input data of workpiece material properties, cutter parameters and tooth geometry, cutting condition, cutter and workpiece vibration structure parameters, and types of milling. A predictive force model for face milling is developed using this approach. In the model, the workpiece material properties are considered as functions of strain, strain rate, and temperature. The ratio of cutter tooth engagement over milling is taken into account for the determination of temperature in the cutting region. Cutter runout is included in the modeling for the chip load. The relative displacement between the cutter and workpiece due to the cutter and workpiece vibration is also included in the modeling to consider the effect on the undeformed chip thickness. A milling force simulation system has been developed using the model, and face milling experimental tests have been conducted to verify the simulation system. It is shown that the simulation results agree well with experimental results.     

3D numerical investigation of thermally assisted high efficiency ductile machining of nanocrystalline hydroxyapatite

This study investigates the effects of four different variables (initial workpiece temperature, side rake angle, edge radius/feed rate, and nose radius/depth of cut) on ductile regime machining of a bioceramic material known as nanohydroxyapatite (nano-HAP) using 3D numerical simulation. AdvantEdge FEM Version 5.9 is used to conduct turning simulations of the nano-HAP workpiece. Tecplot 360 is used to analyze the results of the simulations. Because the workpiece is thin, the entire workpiece is set to a uniform initial temperature to simulate laser preheating of the material. Initial workpiece temperature, rake angle (side rake angle), edge radius, and nose radius are varied, and the effects of these operating conditions on critical feed are investigated. It is found that critical feed increases as initial workpiece temperature increases, and also as negativity of rake angle increases. For the edge radius, it is concluded that an initial increase causes an increase in critical feed – however, at some value of edge radius, critical feed shows no further increase; for the nose radius, critical feed appears to show no significant dependence.     

Investigating surface roughness,material removal rate and corrosion resistance in PMEDM of γ-TiAl intermetallic

Titanium aluminide intermetallics offer an attractive combination of low density and good oxidation, corrosion and ignition resistance with unique mechanical properties. In this study two series of machining tests are designed. Firstly the powder mixed electrical discharge machining (PMEDM) of γ-TiAl by means of different powders such as aluminum, chrome, silicon carbide, graphite and iron is performed to investigate the output characteristics of surface roughness and topography, material removal rate (MRR), electrochemical corrosion resistance of machined samples and also the machined surfaces are investigated by means of EDS and XRD analyses. Secondly after selection the aluminum powder as the most appropriate kind of powder, the current, pulse on time, powder size and powder concentration are changed in different levels for overall comparison between EDM and PMEDM output characteristics. In the first setting of input machining parameters, aluminum powder improves the surface roughness of TiAl sample about 32% comparing with EDM case and also aluminum particles with the size of 2 μm, in the second setting of input parameters lead to 54% enhancement of MRR comparing with EDM case. The electrochemical corrosion results show that, corrosion resistance of the samples which are machined by graphite and chrome powders respectively are about three and two times more than the sample which is machined without powder.     

Selection of Optimal Superfinishing Parameters

This paper is concerned with the selection of optimal superfinishing conditions. During superfinishing of cylindrical surfaces, an axially oscillating abrasive stone is pressed against a rotating workpiece. Experimental results are presented that show the effect of contact pressure, process kinematics, and grit size on superfinishing behavior. An optimal contact pressure is found at which the removal rate is maximized. The ratio of axial oscillation frequency to workpiece rotational frequency should be selected so as to avoid integer values, which result in low stock removal, and half values, which can lead to lobe formation. Finer grit stones provide smoother surface finishes but less stock removal; therefore, the grit size selected should be only fine enough to generate the required surface roughness.     

Laser tempering based turning process for efficient machining of hardened AISI 52100 steel

Cost-effective machining of hardened steel components such as a large wind turbine bearing has traditionally posed a significant challenge. This paper presents an approach to machine hardened steel parts efficiently at higher material removal rates and lower tooling cost. The approach involves a two-step process consisting of laser tempering of the hardened workpiece surface followed by conventional machining at higher material removal rates with lower cost ceramic tools to efficiently remove the tempered material. The laser scanning parameters that yield the highest depth of tempered layer are obtained from a kinetic phase change model. Machining experiments are performed to demonstrate the possibility of higher material removal rates and improved tool wear behavior compared to the conventional hard turning process. Tool wear performance, cutting forces, and surface finish of Cubic Boron Nitride (CBN) tools as well as low cost ceramic tools are compared in machining of hardened AISI 52100 steel (~63 HRC). In addition, cutting forces and surface finish are compared for the laser tempering based turning and conventional hard turning processes. Experimental results show the potential benefits of the laser tempering based turning process over the conventional hard turning process.     

Macro-level environmental comparison of near-dry machining and flood machining

This paper focuses on investigating several aspects of the machining process from an ecological perspective, the result being a macro-level analysis. The analysis presented here considers not only the environmental impact of the material removal process itself, but also the impact of the associated processes such as the material preparation, and the scrap processing. A macro-level assessment of the comparative life cycle environmental performance of the near-dry machining (NDM) using TiN-coated carbide tools and the flood machining (FM) is performed by a case study referring to the gear milling. The assessment, using the SimaPro 7.1.5 software and the ecoinvent1.5 database, includes combined Life Cycle Assessment (LCA) of the workpiece material, the scrap processing, the use of lubrication, and the energy consumption.     

Abrasive jet machining by means of velocity shear instability in plasma

The material removal within different machining process can be performed in distinct modalities. One of the modality is based on the erosion phenomena. In this paper, theoretical model of abrasive jet machining based on erosion phenomenon is discussed. The material is removed from the surface due to erosion. In abrasive jet machining process, the output parameter is achieved by controlling various input parameters. This paper discusses the effects of various input parameters in abrasive jet machining (AJM) on the material removal rate (as the output parameter). The results presented in the paper are obtained from a theoretical study carried out with the help of mathematical model and computational technique. Theoretical investigation indicates that magnetic field, electric field and inhomogeneity in DC electric field have significant effect on metal removal by abrasive jet machining process.     

Thermo-physical modeling of die-sinking EDM process

This paper reports the development of a thermo-physical model for die-sinking electric discharge machining (EDM) process using finite element method (FEM). Numerical analysis of the single spark operation of EDM process has been carried out considering the two-dimensional axi-symmetric process continuum. The analysis is based on more realistic assumptions such as Gaussian distribution of heat flux, spark radius equation based on discharge current and discharge duration, latent heat of melting, etc., to predict the shape of crater cavity and the material removal rate (MRR). Using the developed model, parametric studies were carried out to study the effect of EDM process parameters such as discharge current, discharge duration, discharge voltage and duty cycle on the process performance. Experimental studies were carried out to study the MRR and crater shapes produced during actual machining. When compared with the reported analytical models, our model was found to predict results closer to the experimental results. The thermo-physical model developed can further be used to carry out exhaustive studies on the EDM process to obtain optimal process conditions.     

海州湾及其临近海域沉积物-水界面的磷形态特征与动力学

对海州湾采集的沉积物样品进行磷形态分析,采用实验室培养法对采集的海州湾取样站位进行磷酸盐沉积物-水界面交换研究。结果表明:海州湾及其临近海域表层沉积物磷呈现出从近海海域向远海海域增大的趋势;Fe-P、F-P、R-P均与S-P显著相关,其中F-P和R-P与S-P相关性最好,达极显著水平,且F-P和R-P显著相关,说明F-P和R-P与陆源污染物排放有关,F-P和R-P在来源上具有一致性;海域中的PO43--P在大部分的站位PO43--P在沉积物-海水界面上的交换量随时间的变化,先增加到最大值后再逐渐减小,表明在培养实验的初期,PO43--P由沉积物向海水中释放,然后海水中的PO43--P向沉积物转移,随着时间的推移,沉积物中的PO43--P向海水中转移,少部分的站位PO43--P在沉积物-海水界面上的交换量随时间的变化,呈现出S型变化;当生物存在时,PO43--P在实验站位点沉积物-海水界面上的交换量都随时间的推移逐渐增大,达到最大值后再逐渐减小;没有生物存在时,PO43--P在实验站位点沉积物-海水界面上的交换量都随时间的增加,呈现出S型增加,说明生物扰动和微生物的分解作用对PO43--P沉积物-海水界面上的交换量有较大影响。     

Tool Path Planning for Avoiding Exit Burrs

Milling exit burrs usually form along the edges of a workpiece when the tool leaves the part while removing stock material. One of the most efficient methods for minimizing exit burrs is to prevent the tool from exiting the workpiece during material removal. This paper describes a systematic framework to generate tool paths that always enter a part, which is not a thin structure, in a planar milling operation. Three distinct tool exit conditions are analyzed for polygonal parts. A test criterion is then proposed to examine the occurrence of tool exits. For each condition, a tool path planning scheme is developed to avoid tool exits. These schemes are proved to be effective using the test criterion. This work is integrated into a networked manufacturing environment as a burr agent. Test parts are cut to demonstrate that this framework enhances edge quality by minimizing tool exits.     

A Study on Torch Path Planning in Laser Cutting Processes Part 1: Calculation of Heat Flow in Contour Laser Beam Cutting

Conductive heat transfer in contour laser beam cutting is analyzed by using a transient, two-dimensional finite difference model, and the result is combined with a simple analytic model. From the calculation results, the correlation is derived between workpiece temperature and opening angles at a corner in contour cutting. As a result, a modified analytic solution is developed to predict if excessive workpiece heating occurs for given cutting contours in a nested plate. The main objective is to use the computation results in the optimization of torch path planning to provide fully automated CNC programming software for laser cutting. To efficiently apply the analytic model in torch path planning, the critical temperature that should be avoided during the cutting sequence is considered. This leads to an improvement of the cutting quality in the automatic cutting process.     

Design and tuning of a fuzzy logic controller for micro-hole electrical discharge machining

The design and tuning of a three-input fuzzy logic controller for electrical discharge machining (EDM) of diesel injector spray holes are presented. The tuning process is based on the variable type and discretization level to balance the data precision and computational time for servo motion updates in the fuzzy logic controller and is performed to improve the micro-hole EDM drilling time. The type and number of input parameters are studied to select the gap voltage, spark ratio, and change of spark ratio as input parameters for the fuzzy logic controller. A gain scheduling controller is used as the baseline and shows excellent drilling time in drilling a 1.14 mm thick workpiece using a 150 μm diameter wire electrode. The tuned fuzzy logic controller is comparable with the gain scheduling controller in drilling time and demonstrates its advantages on different EDM drilling configurations, including deep-hole and small-diameter micro-hole drilling. Analysis of EDM pulse trains reveals insights for controller design and identifies requirements for further improvement.     

粗粒化法处理乳化食用油脂废水的研究

采用W型和H型改性聚丙烯纤维作为粗粒化材料，能有效处理乳化食用油脂废水，某些指标显示H型比W型具有更好的除油性能。废水流速和粗粒化材料填充量，是影响粗粒化除油效果的两个重要工艺操作参数，在最佳流速和适当填充量下，能使粗粒化取得最佳最经济的效果。超过一定浓度的表面活性剂存在，会影响粗粒化除油的效果；废水的温度对粗粒化除油的效果影响不大。实际处理餐饮废水的试验结果表明，采用粗粒化技术能有效降低餐饮废水中的含油量，并能大幅降低COD的浓度，有利于后续的生化处理。     

An Analytical Prediction of Flange Wrinkling in Sheet Metal Forming

Wrinkling is one of the major defects in sheet metal forming. The ability to accurately predict the occurrence of wrinkling is critical to the design of tooling and processing parameters. An analytical approach for predicting the onset of flange wrinkling is presented. This method is based on the wrinkling criterion proposed by Cao and Boyce for predicting the buckling behavior of sheet metal under normal constraint. Using a combination of energy conservation and plastic bending theory, the analysis provides the critical buckling stress and wavelength as functions of normal pressure. The results are in excellent agreement with those obtained from Cao and Boyce's numerical approach, and also match well with the experimental results of a square cup forming. In addition, the effects of material properties on the wrinkling behavior are also discussed. The analytical method significantly reduces computational time and is suitable for direct engineering application.     

电解催化还原-氯氧化无害化去除水中硝酸盐氮

基于对Pd-Me双金属催化还原的机理分析,提出了以NH₄+-N为目标产物,Fe催化还原NO₃--N的理论设想. 结合折点氯化技术,以Ti/Fe为阴极,以Ti/Ir-Ru为阳极,以NaCl为支持电解质组建无隔膜电解体系,开展了水中NO₃--N去除的试验研究. 结果表明,利用电解催化还原-氯氧化法可将模拟水样中NO₃--N转化为N₂去除,其反应历程为阴极催化还原NO₃--N生成NH₄+-N,阳极电解氯氧化NH₄+-N生成N₂. 在ρ(Cl-)为500 mg/L,电流密度为12 mA/cm2,极板距离为9 mm,搅拌强度为450 r/min的试验条件下电解150 min,初始ρ(NO₃--N)为50 mg/L的模拟水样出水ρ(TN)和ρ(NO₃--N)可分别降至2.9和2.8 mg/L,去除率分别达到94.1%和94.3%,NH₄+-N和NO₂--N均未检出. 分析认为,阴极对NO₃--N的催化还原机理为:Fe化学吸附氮氧化合物离子中的O形成固定的N—O键,电解产生的活性还原物质攻击N—O形成N—H新键.      

活性炭滤池中微生物特征及其对溶解性有机碳的去除作用

采用异养菌总数计数（HPC）法检测了北京地区J水厂活性炭滤池中微生物量,并分析了活性炭滤池进出水中有机物的组成、活性炭的吸附作用及微生物作用对溶解性有机碳(DOC)去除的贡献率.结果表明,不同炭龄、不同运行周期活性炭滤池中的微生物量有显著的差异.由于溶解性可生物降解有机碳（BDOC）占溶解性有机碳（DOC）的比例较小,且受微生物数量、活性等因素的影响,微生物对DOC的去除效果极为有限,在1.5年和5年炭龄活性炭滤池中对DOC的去除率仅占总去除率的18.8%和26.4%.此外,微生物对较为敏感的嗅味物质2-MIB和geosmin去除作用也不显著,去除率在15%以下（初始浓度为100ng·L-1）;在使用5年活性炭滤池中,微生物对2-MIB和geosmin去除率为12%和14%,分别占总去除率的32%和29%.因此,北京地区地表水净水厂活性炭滤池中微生物对有机物控制的贡献率较低,对DOC的去除主要以活性炭的吸附为主.