ANALYSIS OF SPARK PROFILES DURING EDM PROCESS

Abstract

A fundamental study of electro discharge machining (EDM) based on the physics of an arc and heat transfer theory has been carried out. The field equations for electric potential and temperature in the spark region are simultaneously solved by employing the finite element method. Using the criterion of constant current at any cross section of a spark, the arc radii at different cross sections are corrected until convergence. The final spark shape obtained is noncylindrical, and has different radii at different cross sections. Also, the percent of heat input absorbed by cathode, anode, and dielectric has been calculated. The computed relative electrode wear has been compared with experimental results.     

ANALYSIS OF SPARK ERODED CRATER FORMED UNDER GROWING PLASMA CHANNEL IN ELECTRO-DISCHARGE MACHINING

In electro-discharge machining, the occurrence of sparks cause material removal in the form of craters. These craters are due to melting and vaporization of workpiece over a localized area under the spark, which acts as the heat source. The crater under a single spark has been predicted by theoretical models adopting different approaches in solving the transient heat conduction equation, considering suitable assumptions with appropriate initial and boundary conditions. In the present work, a transient thermal model for a very large solid cylinder has been used to predict the size of the crater obtained under a single spark by determining the melting isotherm in both the axial and radial directions. An analytical study of the effect of plasma channel radius, heat flux, and pulse duration on the size of the crater has been made. Experiments are conducted using a commercial electro-discharge machine. The craters are measured under microscope and a comparison with theoretical results is presented. Subsequently, the nature of variation of crater diameter, crater depth and volume of material removed with respect to different machining parameters such as 'ON' time, 'OFF' time, and current have been explained by the theoretical results and it has been concluded that the plasma channel grows with respect to pulse duration such that at the end of the pulse the plasma channel radius becomes equal to the crater radius.     

复杂航天筒体结构件的焊接应力应变演变规律

采用有限元分析手段对复杂航天筒体结构件的纵向和环向焊缝温度场和应力场进行模拟。航天筒体焊接采用变极性等离子弧焊工艺,根据变极性等离子弧焊工艺特点使用面高斯热源和圆柱热源的组合热源模型作为变极性等离子弧焊的热源。采用ANSYS软件中ANSYS参数化设计语言(ANSYS parametric design language, APDL)编写程序,实现变极性等离子弧焊接热源在筒体结构上加载和移动,完成四道纵缝和两道环缝的焊接热力过程仿真。通过对模拟结果分析,解释复杂筒体焊接应力应变的演变过程。发现在焊接过程中纵缝两端有明显的应力-应变释放,交叉部位的变形直接影响到结构整体的尺寸精度。     

用于电弧发射光谱的数字化自动引弧电路设计

转盘电极发射光谱分析技术在油液成分检测中有重要应用,研究表明,电弧光源的稳定性对光谱分析的结果有重要影响,传统的电弧发生器多使用火花放电器作为引弧电路的核心器件,在油液成分分析中引弧的稳定性和可靠性难以保证.文章提出了一种用于电弧光源激发的数字化自动引弧电路,建立了高频引弧电路拓扑结构模型,使用双路可控硅代替火花放电器...     

TEMPERATURE DISTRIBUTION DURING ELECTRO-DISCHARGE ABRASIVE GRINDING

The objective of this work is to develop a finite element method (FEM) based mathematical model to simulate the hybrid machining process of grinding and electric discharge machining (EDM), named as Electro-discharge abrasive grinding (EDAG), for temperature distribution in the workpiece. Two different finite element codes have been developed to calculate the temperature distribution due to grinding heat source and EDM heat source separately. The transient temperature field within workpiece due to cut-off grinding is determined due to moving rectangular heat source. Gaussian heat distribution of power within a spark has been considered in the calculation of temperature distribution due to EDM. Temperature distribution in the workpiece due to combined process is obtained by using superposition. The simulation shows a sudden rise in temperature at the spark location. The predicted results can be used for calculation of thermal stresses, which play a major role as far as high-quality product requirements are concerned.     

TEMPERATURE DISTRIBUTION DURING ELECTRO-DISCHARGE ABRASIVE GRINDING

The objective of this work is to develop a finite element method (FEM) based mathematical model to simulate the hybrid machining process of grinding and electric discharge machining (EDM), named as Electro-discharge abrasive grinding (EDAG), for temperature distribution in the workpiece. Two different finite element codes have been developed to calculate the temperature distribution due to grinding heat source and EDM heat source separately. The transient temperature field within workpiece due to cut-off grinding is determined due to moving rectangular heat source. Gaussian heat distribution of power within a spark has been considered in the calculation of temperature distribution due to EDM. Temperature distribution in the workpiece due to combined process is obtained by using superposition. The simulation shows a sudden rise in temperature at the spark location. The predicted results can be used for calculation of thermal stresses, which play a major role as far as high-quality product requirements are concerned.     

热交换器布置方式对家用空调器噪声影响的理论分析

从理论上分析了热交换器布置方式对家用分体式空调器室内机所用横流风机系统的流场和声场的影响，说明了圆弧形为理想的布置方式；并对三种具有不同热交换器布置方式的横流风机系统的流场进行了二维数值模拟，结果与理论分析相吻合，较好的预测了家用分体式空调的内部流场。     

Finite element prediction of material removal rate due to traveling wire electrochemical spark machining

Manufacturing engineers are facing new challenges during machining of electrically nonconducting or partially conducting materials such as glass, quartz, ceramics, and composites. Traveling wire electrochemical spark machining (TW-ECSM), a largely unknown technology, has been applied successfully for cutting these types of materials. However, hardly any theoretical work has been reported related to machining performance of TW-ECSM process. The present work is an attempt in this direction. In the present work, a 3-D finite element transient thermal model has been developed to estimate the temperature field and material removal rate (MRR) due to Gaussian distributed input heat flux of a spark during TW-ECSM. First, the developed code calculates the temperature field in the workpiece and then MRR is calculated using this temperature field. The calculated MRR has been compared with the experimental MRR for verifying the approach. Computational experiments have been performed for the determination of energy partition and spark radius of a single spark. The effects of various process parameters such as energy partition, duty factor, spark radius, and ejection efficiency on MRR have been reported. It has been found that MRR increases with increase in energy partition, duty factor, and ejection efficiency but decreases with increase in spark radius.     

平面四杆机构的定性和定位轨迹综合

提出一种直接按轨迹定性要求中的曲率半径误差和直线度误差、圆弧段或直线段长短等定量要求进行定性综合的新方法。将舍有直观几何特性的轨迹曲线斜率角和曲率半径共同作为特征参数建立平面四杆机构连杆曲线的计算机数值轨迹图谱，设计了轨迹的圆弧度和直线度的评价模型，使不必增加附加坐标点即能根据所需的直线或圆弧要求直接进行定性综合，提出了根据斜率角反求轨迹曲线及结合最小二乘法进行间接的定位轨迹综合。两类综合都具有较高的综合速度．     

Three-electrode gas switches with electrodynamical acceleration of a discharge channel

High voltage, high current, and high Coulomb transfer closing switches are required for many high power pulsed systems. There are a few alternatives for closing switches, for example, ignitrons, vacuum switches, solid-state switches, high pressure gas switches (spark gaps), and some others. The most popular closing switches up to date are spark gaps due to relatively simple design, robustness, easily field maintenance, and repair. Main drawback of spark gaps is limited lifetime, which is related directly or indirectly to erosion of the electrodes. Multichannel switches and switches with moving arc have been proposed to prevent the electrodes erosion. This study investigates switches, where a spark channel is initiated in a three-electrode layout and then the spark accelerates due to electrodynamic force and moves along the extended electrodes. At a given current amplitude, the diameter of the extended electrodes allows to control the spark velocity and hence, the erosion of the electrodes providing the required lifetime. The first switch is designed for 24 kV charging voltage and approximately 4 C total charge transfer. This spark gap was tested at 25 kA peak current in 40 000 shots in a single polarity discharge and in 20 000 shots in bipolar discharge. Second spark gap is designed for 24 kV charging voltage and approximately 70 C total charge transfer. It was tested in 22 000 shots, at a current of 250 kA with a pulse length of 360 mus. In this paper, we present design of these spark gaps and trigger generator, describe the test bed, and present the results of the tests.     

带状电极窄间隙MAG焊

为解决窄间隙焊接中普遍存在的侧壁和焊缝根部熔合不良的问题,基于减小间隙宽度让电弧直接加热间隙侧壁的思路,提出采用矩形截面的带状电极代替常规的圆形焊丝作为熔化极伸入到间隙中进行焊接,利用特殊形状的带状电极在间隙中自动形成的摆动电弧来改善对间隙侧壁和根部的加热,实现窄间隙焊接。研制专用的焊枪,研究间隙宽度、电弧电压和送带速度对间隙中带极端部电弧行为的影响。试验发现,电弧在间隙中的摆动受间隙宽度、电弧电压和送带速度的影响程度依次降低。间隙宽度对电弧的摆动具有决定性作用,间隙太宽电弧不能摆动;电弧电压过高导致电弧沿侧壁攀升得不到抑制,而送带速度主要与电弧电压搭配,保证焊接过程的稳定性,二者对间隙中电弧的摆动行为影响较小。结果表明,合理匹配间隙宽度、电弧电压和送带速度可以实现稳定的摆动电弧,获得侧壁和焊缝根部熔合良好的窄间隙焊缝。     

某液冷冷板换热特性实验研究

针对电子设备冷却用液冷冷板设计,选用了3种新型的锯齿型翅片作为冷板内芯。为了验证新型冷板的换热特性,应用稳态电加热法,分别对内芯为矩形、梯形和侧向梯形锯齿型翅片的3种冷板以蒸馏水为介质的换热特性进行了实验研究,分别获得了在一定雷诺数范围内的换热无量纲准则式,并对液冷冷板的换热特性进行了比较。结果表明,在小流量区域,3种冷板换热系数差别不大;随着流量增大,侧向梯形锯齿型翅片对冷板通道内的扰动更强,换热性能更好。本实验为液冷冷板设计提供了参考。     

钢带并联机器人力学失稳机理

为了发展新的并联机构形式,提出一种以圆弧弯曲截面钢带作为运动支链的6自由度钢带并联机器人机构形式。简要阐述钢带并联机器人结构组成与工作原理。采用基于变分原理的有限元静力学理论和线性屈曲分析理论建立求解钢带失稳临界力的屈曲方程。利用有限元软件ANSYS对不同结构参数的截面由圆弧弯曲形状过渡到平直形状的钢带进行失稳分析,得到钢带能承受的失稳力与结构参数的关系,并进行试验验证。对钢带并联机器人在平移运动位姿下的整机失稳机理进行系统研究,得到不同位姿参数与钢带并联机器人失稳临界力的关系。研究结果表明：弯曲截面结构的钢带能承受一定的压力,钢带失稳力随钢带圆弧截面中心角、钢带厚度增大而增大,随钢带长度增大而减小。对于机器人动平台作上升运动,在500 mm的高度,失稳临界力最大。而对于沿Y轴平动或沿=60平动且100 mm200 mm的范围,对于沿极径=500 mm平动且1020的范围,失稳临界力均比较大。研究成果能用于优化钢带并联机器人的结构设计及确定刚度工作空间。     

A study on micro machining of e-glass–fibre–epoxy composite by ECSM process

The paper presents the result of an experimental investigation on the micro machining of electrically non-conductive e-glass–fibre–epoxy composite during electrochemical spark machining using specially designed square cross section with centrally micro hole brass tool and different diameter round-shaped micro tools made of IS-3748 steel. A micro electrochemical spark machining (ECSM) setup has been designed, fabricated and used for conducting the experiments. According to the Taguchi method-based design, the specific numbers of experiments have been carried out to investigate the influence of the fabricated ECSM parameters on the material removal rate and overcut on generated hole radius. Test results show that the material removal rate is maximum when machining was performed at higher setting value of D.C. supply voltage (e.g. 70?V), moderate setting value of electrolytic concentration (e.g. 80?g/l) and 180-mm gap between electrodes. Taking significant machining parameters into consideration and using multiple linear regression, mathematical modes for material removal rate and overcut on hole radius are established to investigate the influence of cutting parameters during micro-ECSM. The influence of machining parameters on machined hole and special shape contour quality are also analysed through different scanning electron micrographs. Confirmation test results established the fact that the developed mathematical models are appropriate for effectively representing the machining performance criteria.     

Hybrid heat source model designing and parameter prediction on tandem submerged arc welding

In submerged arc welding simulation, the heat source parameters are always decided by experience, and it usually leads to a high simulation error. This work is aimed to develop a methodology for the estimation of the heat source in submerged arc welding. A hybrid heat source model was applied on submerged arc welding simulation. The new heat source model was combined by a surface heat source model and the double ellipsoid heat source model. The surface heat source model was designed based on the Gaussian heat source model. The width and penetration of the weld pool were simulated and compared with the measurement results, and the width at 2?mm depth from the top surface was also considered to describe the shape of the weld pool more accurately. In order to reduce the simulation complexity, the sensitivity of heat source parameters was discussed. The heat source parameter corresponding to different experimental processes was obtained by modified pattern search method. The artificial neural network algorithm and the support vector machine algorithm were applied to predict the relationship between all possible process and the heat source parameters. The validation experiment showed that the prediction model was accurate.     

Effects of inlet radius and bell mouth radius on flow rate and sound quality of centrifugal blower

The effect of inlet radius and bell mouth radius on flow rate of centrifugal blower were numerically simulated using a commercial CFD program, FLUENT. In this research, a total of eight numerical models were prepared by combining different values of bell mouth radii and inlet radii (the cross section of bell mouth was chosen as a circular arc in this research). The frozen rotor method combined with a realizable k-epsilon turbulence model and non-equilibrium wall function was used to simulate the three-dimensional flow inside the centrifugal blowers. The inlet radius was then revealed to have significant impact on flow rate with the maximum difference between analyzed models was about 4.5% while the bell mouth radius had about 3% impact on flow rate. Parallel experiments were carried out to confirm the results of CFD analysis. The CFD results were thereafter validated owning to the good agreement between CFD results and the parallel experiment results. In addition to performance analysis, noise experiments were carried out to analyze the dependence of sound quality on inlet radius and bell mouth radius with different flow rate. The noise experiment results showed that the loudness and sharpness value of different models were quite similar, which mean the inlet radius and the bell mouth radius didn’t have a clear impact on sound quality of centrifugal blower.     

Analysis of deformation textures of asymmetrically rolled steel sheets

Asymmetric rolling has been studied to obtain the shear deformation texture of bcc steels through the thickness. Asymmetric rolling in which the circumferential velocities of two working rolls are different can be achieved by different roll radii at the same rotation rates, different roll speeds at the same roll radii and single roll drive. The deformation of steel sheets in the three different asymmetric rolling methods was analyzed by FEM. The deformation was used to calculate crystal rotation by full constraints Taylor model to predict the deformation textures. The texture evolution during the asymmetric rolling was measured and analyzed with the emphasis on the effect of shear reversions.     

TIG-MIG双面对称焊焊缝成形机理研究

就纯铝中薄板,通过单面TIG、MIG和TIG-MIG双面对称焊工艺试验对比,利用ANSYS有限元计算软件进行了TIG-MIG双面对称焊熔池的数值模拟,研究了TIG-MIG双面对称焊的熔池特征及焊缝成形规律。研究表明,TIG-MIG双面对称焊的热源静态累积效应和动态热阻效应使得此焊接方法熔深大大增加,TIG、MIG熔池在焊接过程中发生交汇并在电弧力、熔池表面张力和重力等作用下达到平衡,并由此形成焊缝反面成形。TIG-MIG交汇熔池的稳定性决定焊缝的反面成形特征。     

高比转数蜗壳式混流泵的设计与试验

采用线性分布的轴面流线速度环量和叶片角度变化规律来设计叶轮,采用圆弧翼型进行固定导叶的设计,蜗壳断面采用非对称断面,进而设计了一叶片可调比转数为564.3的蜗壳式混流泵。应用FLUENT对该泵的内部流动进行了数值模拟并根据模拟结果进行了能量性能预测。内流模拟结果显示该泵内部流动均匀,性能预测结果表明该泵可以满足设计要求。真机性能测试表明该泵在叶片角度为0°时最高运行效率达85.76%,在设计点运行效率要比设计要求高约3%。研究结果对于更高比转数蜗壳式混流泵的设计具有比较重要的指导作用。     

火花放电制备微纳空心球粉的工艺研究及分析

初步研究了火花放电制备微纳空心球粉的工艺,对不同的工艺参数下制得的微纳镍粉的表面形貌、空心状况和粒度进行分析,推断出大电流、小脉冲的电参数有利于空心球的成形,初步分析了空心球的成形机理.对未来的研究方向进行了展望.