混粉电火花加工温度场的计算与分析

火花放电时形成的放电蚀坑的大小与形状对电火花加工表面粗糙度有重要影响,而放电蚀坑的形成又与放电时在工件表层产生的温度有关。本文通过对火花放电时在工件表层形成的温度场的计算,分析了影响放电蚀坑深度的因素及影响规律,并利用该规律对混粉电火花加工的机理进行了解释。     

混粉电火花加工机理的分析

论述了混粉电火花加工的发展概况 ,并以实验为基础对其机理进行了分析 ,认为加工表面粗糙度的迅速降低主要是放电通道对熔融金属平整作用的结果。对于这一工艺的加工效率进行了剖析 ,认为从改善表面质量的角度来看 ,混粉电火花加工具有很高的加工效率。通过对电极损耗情况的观察 ,发现电极损耗特性也有一临界点 ,这一点与普通电火花加工相似     

单脉冲气中电火花线切割电蚀坑形貌仿真分析

为研究气中电火花线切割加工机制,建立Cr12Mo V模具钢温度场的数学模型。基于ABAQUS软件对单脉冲放电过程中Cr12Mo V模具钢的温度场进行仿真分析,得出Cr12Mo V模具钢的温度场分布规律,测量出不同峰值电流和脉冲宽度下工件表面电蚀坑的半径和深度并进行了修正,进而计算出电蚀坑的体积。获得了单脉冲放电后工件表面电蚀坑半径、深度、体积以及深径比随峰值电流与脉冲宽度的变化规律,进而预测出电火花线切割加工效率与工件的表面质量。     

粉末特性对混粉电火花镜面加工的影响

用实验方法研究了粉末粒度、形状及导电性对混粉电火花镜面加工表面粗糙度的影响,同时对混粉电火花加工表面的耐磨性和耐蚀性进行了研究。结果表明,粉末粒度和导电性对混粉电火花加工表面粗糙度有较大的影响;混粉电火花镜面加工不但能改善加工表面粗糙度,且能提高加工表面的耐磨性和耐蚀性。     

混粉电火花加工技术在粗加工中的应用研究

在对混粉电火花加工机理进行系统研究的基础上，对混粉电火花粗加工中的加工效率和加工表面粗糙度进行了实验研究。结果表明，通过合理选择放电参数，混粉电火花加工在相近加工表面粗糙度时，能显著提高加工效率，从而为混粉电火花加工技术在粗加工中应用提供依据。     

混粉准干式电火花精密加工技术研究

提出了一种混粉准干式电火花加工技术,其加工介质是气液固三相流混合物。研究了其单脉冲放电过程,一次放电过程可分为电离、击穿放电、抛出电蚀物及消电离4个阶段。并对比了气中放电、准干式电火花加工、混粉准干式电火花加工的材料去除率和表面粗糙度。实验结果表明,这3种加工方法材料去除率依次升高,表面粗糙度值依次降低。     

超声辅助线切割加工超声参数对表面粗糙度的影响

为提高超声振动与电火花线切割复合加工难切削金属的加工质量,通过理论分析、数值模拟和试验验证,对超声振动与电火花线切割复合加工作用下不同振幅和频率对表面粗糙度的影响规律进行深入研究。基于超声振动的电火花线切割复合加工构建物理模型和数学模型,推导基于超声振动的移动高斯热源热流密度公式,建立了完整的温度场仿真模型。通过ANSYS有限元复合加工过程温度场的模拟分析,构建基于温度场数值模拟的表面粗糙度理论计算模型。通过单因素试验对表面粗糙度的理论计算模型进行了验证,结果表明：随着振幅和频率的增大,被蚀除电蚀坑体积减小,表面质量变高;试验结果与理论及仿真模型的变化规律具有较好的一致性,最小偏差7.717%,最大偏差16.708%。     

移动热源作用下气中电火花线切割加工仿真分析

为了快速有效地提高气中电火花线切割加工Cr12MoV模具钢的表面质量,通过有限元法计算并分析了单脉冲气中火花放电条件下工件的温度场分布规律,获得了移动热源作用下工件表面电蚀坑形貌为半双椭球形,这与理想条件下电蚀坑形貌为半球形不同,进而探讨了移动热源作用下不同脉冲宽度对工件表面电蚀坑几何形貌的影响,并与试验结果进行了对比分析。结果表明,修正后电蚀坑深度与工件表面最大粗糙度变化趋势基本相同且数值非常接近,并得出修正前后电蚀坑的长度、宽度及深度随着脉冲宽度的增加不断增大的规律,然而电蚀坑尺寸增加使得电蚀坑体积不断增大,从而提高了气中电火花线切割加工效率,但降低了工件的表面质量。     

新型混粉电火花机床液体搅拌装置的研究

研究了在混粉电火花加工过程中,混粉颗粒的沉降状况,在总结国内混粉电火花机床液体搅拌装置结构特点及现有优缺点的基础上,对其进行改良。提出了新型混粉电火花机床液体搅拌装置的结构方案。此液体搅拌装置可通过机械升降装置调节出油管道喷嘴的高度,使其与工作台上工件表面高度相平,并运用水平及45°方向循环射流方式对液体进行搅拌,促使粉末均匀化,提高加工工件表面质量。将新型液体搅拌装置加工的工件表面与普通机械液体搅拌装置加工的工件表面进行对比,结果表明:新型液体搅拌装置可显著降低加工工件的表面粗糙度值。     

基于神经网络的混粉电火花加工效果的预测模型

针对混粉电火花加工的工艺特点及其复杂性,提出了一个基于径向基函数（RBF）神经网络的混粉电火花加工效果的预测模型,并通过该模型对混粉电火花加工试验研究的工件表面粗糙度进行了预测,预测结果与实际试验结果有较好的一致性,说明RBF神经网络对混粉电火花加工效果的预测是有效的.     

Improvement of surface finish on SKD steel using electro-discharge machining with aluminum and surfactant added dielectric

Electrical discharge machining (EDM) process is widely used to process hard materials in the industry. Electrical discharge distribution effects can be achieved by the addition of Al powder in the dielectric. A fine surface roughness value of the workpiece is thus obtained. However, the electrostatic force among fine Al particles is found to agglomerate the Al powders in the dielectric. A surfactant can be adopted to separate the Al powder in the dielectric homogenously. A better surface even the mirror-like quality of the EDMed workpiece is thus desired. In the study, the effect of surfactant and Al powders added in the dielectric on the surface status of the workpiece after EDM is investigated.It is observed the best distribution effect is found when the concentrations of the Al powder and surfactant in the dielectric are 0.1 and 0.25 g/L, respectively. An optimal surface roughness (Ra) value of 0.172 μm is achieved under the following parameter—positive polarity, discharge current 0.3 A, pulse duration time 1.5 μs, open circuit potential 140 V, gap voltage 90 V and surfactant concentration 0.25 g/L.The surface roughness status of the workpiece has been improved up to 60% as compared to that EDMed under pure dielectric with high surface roughness Ra of 0.434 μm.     

Electrical discharge machining using simple and powder-mixed dielectric: The effect of the electrode area in the surface roughness and topography

Electrical discharge machining (EDM) is one of the most widely disseminated manufacturing technologies, in particular as regards the generation of accurate and complex geometrical shapes on hard metallic components. Nevertheless current EDM technologies have major limitations when dealing with fine surface finish over large process area. Indeed this is one reason that explains the need of final manual polishing of mould cavities performed by EDM. Recently EDM with powder-mixed dielectric (PMD-EDM) has been a focus of an intense research work in order to overcome these technological performance barriers. This paper presents a research work within the objective to acquire deep knowledge on EDM technology with powder mixed dielectric and to compare its performance to the conventional EDM when dealing with the generation of high-quality surfaces. In particular the analysis of the effect of the electrode area in the surface quality measured by the surface roughness and craters morphology was carried out for both technologies. The results achieved evidenced a linear relationship between the electrode area and the surface quality measures as well as a significant performance improvement when the powder mixed dielectric is used.     

TC4钛合金混粉电火花表面改性研究

目的通过混粉电火花加工方法,分别使用紫铜和石墨作为工具电极,获得综合性能较好的TC4钛合金表面。方法利用手持式TR200粗糙度仪对工件表面的粗糙度进行测量,用扫描电子显微镜(SEM)、X射线衍射仪对工件组织形貌和物相结构进行分析,用FM800型显微硬度计对工件表面进行显微硬度测量。结果在相同电参数下,紫铜电极加工的工件较石墨电极加工的工件表面粗糙度要低,硬度也相对低。当I=4.5A、tON=30?s时,紫铜电极加工的工件表面平均粗糙度值Ra=2.223?m,表面硬度约为600HV;石墨电极加工的工件表面平均粗糙度值Ra=2.796?m,表面硬度约为700HV。当I=9 A、tON=30?s时,紫铜电极加工的工件表面平均粗糙度值Ra=2.748?m,表面硬度约为650HV;石墨电极加工的工件表面平均粗糙度值Ra=3.705?m,表面硬度约为750HV。结论在不同电极条件下混粉电火花加工后,TC4钛合金工件表面都达到了强化的效果。     

空气介质中电火花表面强化的温度场有限元模拟分析

通过选取合适的热源模型、边界条件,建立了空气介质中电火花表面强化的热传导模型;通过分析其温度场的特点,建立了空气介质中电火花表面强化的二维温度场模型;借助ANSYS有限元分析软件对空气介质中电火花表面强化的温度场进行了模拟,分析了工件在不同时间、不同位置的热流密度矢量和随温度矢量的变化规律,以及电火花强化时温度随深度方向的变化历程。结果显示:电火花表面强化层的放电凹坑主要是由于热量在材料中不同方向的热传导存在差异引起的;电火花表面强化具有骤冷骤热的特点;在相同的加工速度下,节点的温度随着离表面距离的增大而减小。     

短电弧加工不同直径电极间隙流场研究

在短电弧加工过程中,利用流体软件Fluent对不同的电极直径加工间隙流场进行仿真,通过极间流场中的压力场与速度场间接得出加工屑排除的变化规律,并通过实验进行验证。结果发现:电极直径的增大可以促进加工屑从加工间隙排出,减少因间隙颗粒的堆积而产生的短路现象,从而避免“二次放电”;当加工深度不变时,电极直径的大小与工件材料的去除率呈正相关,证明短电弧加工过程中存在“面积效应”;电极直径的相对变化对工件表面质量没有明显的改善,即对表面粗糙度的影响不大。     

A numerical model of the EDM process considering the effect of multiple discharges

The electrical discharge machining (EDM) process is, by far, the most popular amongst the non-conventional machining processes. The technology is optimum for accurate machining of complex geometries in hard materials, as those required in the tooling industry. However, although a large number of EDM machines are sold every year, scientific knowledge of the process is still limited. The complex nature of the process involves simultaneous interaction of thermal, mechanical, chemical and electrical phenomena, which makes process modelling very difficult. In this paper a new contribution to the simulation and modelling of the EDM process is presented. Temperature fields within the workpiece generated by the superposition of multiple discharges, as it happens during an actual EDM operation, are numerically calculated using a finite difference schema. The characteristics of the discharge for a given operation, namely energy transferred onto the workpiece, diameter of the discharge channel and material removal efficiency can be estimated using inverse identification from the results of the numerical model. The model has been validated through industrial EDM tests, showing that it can efficiently predict material removal rate and surface roughness with errors below 6%.     

电火花加工镍基合金的热影响层研究

为去除电火花加工后的镍基合金热影响层,进行了大量镍基合金的电火花加工实验.通过对电火花加工后的镍基合金亚表面合金颗粒的金相观察发现,长时间非正常放电加工的样品亚表面出现了明显的晶粒细化,而正常放电加工的亚表面晶粒与基体晶粒尺寸相仿.根据热传导理论,通过模型仿真了在电火花放电后的工件亚表面温度场分布,估算出热影响层的厚度...     

The use of the orthogonal array with grey relational analysis to optimize the electrical discharge machining process with multiple performance characteristics

In this paper a new approach for the optimization of the electrical discharge machining (EDM) process with multiple performance characteristics based on the orthogonal array with the grey relational analysis has been studied. A grey relational grade obtained from the grey relational analysis is used to solve the EDM process with the multiple performance characteristics. Optimal machining parameters can then be determined by the grey relational grade as the performance index. In this study, the machining parameters, namely workpiece polarity, pulse on time, duty factor, open discharge voltage, discharge current, and dielectric fluid are optimized with considerations of multiple performance characteristics including material removal rate, surface roughness, and electrode wear ratio. Experimental results have shown that machining performance in the EDM process can be improved effectively through this approach.     

Analysis of the electrochemical behaviors of WC–Co alloy for micro ECM

Micro electrochemical machining (ECM) of tungsten carbide with cobalt binder (WC–Co) was studied using ultrashort pulses. In ECM, the machining characteristics were investigated according to machining conditions such as electrolyte, workpiece potential, and applied voltage pulse. Using a mixture of sulfuric acid and nitric acid, microstructures with a sharp edge and good surface quality were machined on tungsten carbide alloy. The potentials of workpiece electrode and tool electrode were determined by considering the machining rate, machining stability, and surface quality of products. With the negative potential of the workpiece electrode, oxide formation was successfully prevented and shape with good surface quality in the range from R_a 0.069 μm to 0.075 μm were obtained by electrochemical machining. Moreover, the performance of ECM, which includes machining gap, tapering, surface roughness, and machining time, without tool wear was compared with that of electrical discharge machining (EDM). Microstructures of WC–Co with a sharp edge and good surface quality were obtained by electrochemical milling and electrochemical drilling. Micro electrochemical turning was also introduced to fabricate micro shafts.