极性效应在微细电火花反拷加工中的应用

研究了极性效应对微细电火花加工的影响,讨论了微细电火花加工中碳黑膜的生成条件及其对微细电极的保护作用.针对微细电火花反拷加工中电极损耗较大的问题,采取了粗精结合的加工策略,提高了工件的加工精度和表面质量.     

电火花成形加工工具电极损耗预测

电火花成形加工过程中,极间放电在蚀除工件材料的同时,也会对工具电极带来一定程度的损耗,进而影响工件的尺寸及形状精度,降低加工效率。目前普遍采用更换电极重复加工的方式来获得最终形面,需要消耗大量的工具电极和工时。针对电火花加工的工具电极损耗展开了研究,通过系统地分析所得电极形面特征及进给方向与损耗量之间的关系,建立了实用的电极损耗预测模型。通过实验证明了该模型能准确预测工具电极形面损耗,为电火花加工的电极损耗预测提供了有效方法。     

分流法小孔电火花加工数值模拟及实验

介绍分流法小孔电火花加工数值模拟方法,利用有限元分析软件ANSYS模拟单次脉冲放电温度场和电火花小孔加工放电状态,以等面积分流为原则,分别模拟单电极和双电极小孔电火花加工材料去除过程,分析了材料去除量随时间变化的规律.双电极模拟和试验,获得加工过程稳定且小于单电极临界加工尺寸的小孔.选用紫铜工具电极、奥氏体不锈钢工件进行验证实验,仿真结果与实验验证结果相符,为微小孔电火花加工提供了应用依据.     

微细电火花伺服扫描加工实验研究

进行微细电火花三维扫描加工时,由于电极损耗相对严重,导致形位公差难以保证和加工效率较低。该研究分析了电火花加工常规的电极损耗补偿方法,提出了基于放电间隙伺服控制进行电极损耗实时补偿的微细电火花三维扫描加工方法。辅助以电极电接触感知工件平面和加工原点,三维结构加工实验显示,采用间隙伺服控制进行电极损耗实时补偿有利于提高扫描加工微三维结构的形位精度和加工效率。     

超声振动复合微细电火花加工微小孔试验研究

微小孔加工时的放电间隙较小,排屑、消电离状态差,放电效率低,直接影响加工效率和电极损耗;超声振动可改善排屑、消电离状态,能提高放电效率。将超声引入微细电火花加工,通过工件的超声振动,进行超声功率、小孔孔径、脉冲频率的微小孔电火花加工工艺试验研究,结果表明:加工不同孔径时,超声功率及电源频率都存在一个最佳值;加工条件合适时,超声复合微细电火花加工优于常规微细电火花加工。     

微细电火花加工损耗补偿的研究

针对三维微细结构的微细电火花加工,应用等损耗理论,采用分层加工的方法,建立了单道单层加工时底面形状随电极损耗而变化的轮廓模型,在此基础上,提出电极损耗适时补偿的方法.实验测定了钨电极加工不锈钢的损耗率,应用适时补偿方法加工得到的单层单道窄槽的尺寸精度良好.     

微细电火花加工的底面轮廓模型及定长补偿方法

针对三维金属微细结构的微细电火花加工,应用等损耗理论,采用分层加工的方法,建立了单道加工时底面形状随电极损耗而变化的轮廓模型.在此基础上,提出定长补偿的方法,给出了补偿长度的计算公式.对底面轮廓模型及定长补偿方法进行了仿真分析.实验测定了微细条件下钨打钢的相对体积损耗比,进行了无补偿和定长补偿的实验加工.仿真及实验结果表明无补偿时底面轮廓为一指数曲线,与实验结果相符;定长补偿方法加工出的底面轮廓为一幅值恒定的波动曲线;随着补偿精度le的增大,底面轮廓的波动范围也越大;在符合端面损耗理论的范围内,分层厚度越大,加工相对误差越小;定长补偿方法提高了加工尺寸精度和形状精度,补偿方法可行.     

外加磁场对铁磁材料电火花小孔加工的影响

针对电火花加工中电蚀产物排出困难、加工效率低、电极损耗严重等问题,研究了外加磁场对铁磁性材料电火花小孔加工的影响,分析了铁磁性电蚀微粒在加工区域受外加磁场磁力作用的影响规律,实验研究了在不同电极材质条件下,外加磁场对加工速度、电极损耗的影响。结果表明:采用磁场电火花复合加工方法在铁磁材料工件上加工小孔,其加工速度和电极损耗都比普通电火花加工有明显改善。     

微细电极进给与激振机构及其微细孔电火花加工实验

研制了一种用于微细孔电火花加工的微细电极进给与激振机构,实现了加工过程中微细电极的伺服进给、损耗自动补偿、辅助激振及高精度导向。实验研究了加工过程中电极激振的频率对加工效率、加工孔径的影响。实验结果表明,电极激振振幅为0．6μm,频率位于4．3～4．5kHz范围内时,加工效率和所加工的微细孔尺寸精度同时明显提高。     

去离子水中N型硅的微细电火花加工工艺实验

对去离子水中N型硅的微细电火花加工工艺进行了实验研究,分别在加工效率、电极损耗、表面粗糙度等方面与煤油工作液中N型硅的加工进行了对比.通过大量的实验研究得出：在相同的电参数下,与煤油工作液中加工实验相比,以去离子水为工作液介质时微细电火花加工N型硅的加工效率更高,其工件表面粗糙度值基本相当,且其放电加工过程非常稳定,可知微细电火花加工N型硅时,去离子水是一种较好的工作液介质.     

Tool wear in friction drilling

This study investigates the tool wear in friction drilling, a nontraditional hole-making process. In friction drilling, a rotating conical tool uses the heat generated by friction to soften and penetrate a thin workpiece and create a bushing without generating chips. The wear of a conical tungsten carbide tool used for friction drilling a low carbon steel workpiece is studied. Tool wear characteristics are quantified by measuring its weight change, detecting changes in its shape with a coordinate measuring machine, and making observations of wear damage using scanning electron microscopy. Energy dispersive spectrometry is applied to analyze the change in chemical composition of the tool surface due to drilling. In addition, the thrust force and torque during drilling and the hole size are measured periodically to monitor the effects of tool wear. Results indicate that the carbide tool is durable, showing minimal tool wear after drilling 11,000 holes, but observations also indicate the progressively severe abrasive grooving on the tool tip.     

Virtual EDM simulator: Three-dimensional geometric simulation of micro-EDM milling processes

In this paper a three-dimensional geometric simulation method of micro-EDM milling processes is proposed, which introduces a Z-map algorithm to precisely represent the geometries of a machined workpiece and the evolution of the tool shape caused by tool wear during the machining. The micro-EDM milling process is mathematically and geometrically modeled. In order to verify the performance of the developed simulator, an actual square cavity is machined and compared to the simulation result. The developed EDM simulator can be used for tool path generation for tool wear compensation as well as for prediction of tool wear.     

A new tool wear compensation method based on real-time estimation of material removal volume in micro-EDM

Owing to the reduced tool area and poor flushing conditions in deep holes, tool wear in micro-electrical discharge machining (EDM) is more significant than in macro-EDM. In micro-EDM drilling, the z-axis of the tool position is monitored as machining progresses. However, due to significant electrode wear, the machined hole depth is not identical to the programmed depth of the hole, and thus this will result in geometrical inaccuracy. This paper presents a new micro-EDM drilling method, in which the material removal volume is estimated as machining progresses. Compensation length is calculated and adjustment is made repeatedly along the tool path until the targeted material removal volume is reached. A real-time material removal volume estimator is developed based on the theoretical electro-thermal model, number of discharge pulse and pulse discrimination system. Under various energy input and machining depth settings, the experimental and estimated results are found to be in satisfactory agreement with average error lower than 14.3% for stainless steel, titanium, and nickel alloy work materials. The proposed drilling method can compensate the tool wear and produce more accurate micro-holes as compared to other methods. Experimental work also shows that the proposed method is more reliable as compared to the uniform wear method. In drilling micro-holes of 900 μm depth, the depth error can be reduced to 4% using the proposed method.     

A study on the machining of high-aspect ratio micro-structures using micro-EDM

Micro-electro-discharge machining (micro-EDM or μ-EDM) has been gaining popularity as a new alternative method to fabricate micro-structures. The main advantages of the micro-EDM method are its low set-up cost, high accuracy and large design freedom. Compared to etching or deposition techniques, micro-EDM has the advantage of being able to fabricate complex three-dimensional shapes with high-aspect ratio. However, there are many operating parameters that affect the micro-EDM process. The fabrication of micro-electrodes on the machine is also an important process to remove the clamping error to maintain high accuracy in the machined micro-structures.

In this paper, the machining of micro-structures is divided into two basic processes. One is the on-machine fabrication of the micro-electrodes with high-aspect ratio, and the other is the EDM of the workpiece in micrometer range. An optical sensor has been developed to measure and control the dimension of the thin electrode during the tool fabrication process. Different methods have been investigated to fabricate a thin electrode into the desired dimension without deflection. The performance of the micro-EDM process is evaluated in terms of the material removal rate (MRR), tool wear ratio (TWR), and the stability of the machining. Influences of the various operating parameters of the micro-EDM process, such as the operating voltage, gap control algorithm, and resistance and capacitance values in the R–C spark control circuit, are discussed.     

基于回归正交试验的浅孔钻钻削的有限元仿真

基于回归正交试验法设计钻削模拟方案,利用最小二乘法原理得到钻削力的经验公式;基于有限元软件Deform3D平台,建立了用浅孔钻钻削加工45钢的有限元模型,动态模拟浅孔钻钻削过程,获得了浅孔钻钻削加工过程中工件的等效应力和温度,分析预测了加工过程中硬质合金刀具所受的主切削力、径向力以及两刀片所受的扭矩,并评估刀片的磨损情况。     

型孔电解加工阴极优化试验研究

为解决电解加工型孔的加工稳定性和形状精度等问题,建立了异形孔电解加工稳定过程中加工间隙数学模型,分析了工具阴极结构对加工区域和非加工区域的电场及其均匀性以及其对电流密度与加工效果的影响,通过优化工件结构改善了加工间隙内的电场分布,使工件形状精度显著提高,并进行相关试验对仿真结果进行验证。得出结论:在相同的电解加工参数下,工具电极的结构对工件的形状精度有着显著的影响,通过优化工具电极结构,改善加工间隙内的电场分布与电流密度,让加工间隙内的流场更为稳定,使工件侧壁垂直度提高,提高了电解加工的形状精度与加工稳定性。     

Prediction of anode profile in ECBD and ECDoperations

During electrochemical drilling, use of bit type of tools produce more accurate holes as compared to bare type of tools. But, no model is available to predict anode profiles obtained during electrochemical bit drilling (ECBD). In this paper, models SBFET-11 (one dimensional analysis) and SBFET-22 (two dimensional analysis), based on finite element technique, have been proposed. The models are capable to predict the workpiece shape and size obtained either by bit type of tool or bare type of tool. The models can analyse both types of workpieces, i.e. the workpiece having a predrilled hole and the workpiece without a predrilled hole. Some assumptions made in earlier models regarding zero void fraction, constant electrolyte flow velocity, zero feed rate in transition and side zones etc., have been relaxed. Special attention has been paid on the analysis of anode profile in the transition zone and its effects on the accuracy of the computed anode profile in side zone. Comparison of analytical and experimental anode profiles has revealed a good agreement between the two.     

微细电加工应用技术研究

微细电加工要达到工业应用的目的,需兼顾加工效率和加工精度两方面的要求.以微细孔、微细三维结构的加工为目标,进行了微细孔电火花加工、三维微细结构电火花伺服扫描加工及微细电化学加工技术的研究开发.设计出微细电极的损耗补偿进给和导向机构,开发出三维微细结构的电火花伺服扫描加工工艺,研究了采用阵列微细电极的微细电化学加工方法.微细孔电火花加工可连续加工直径小至100 μm的孔.伺服扫描电火花加工可便捷地在小于1 mm2区域内加工出三维微细结构.提出的微细电化学加工技术路线拟将微细电解加工应用于阵列微细孔和三维微细结构的加工.     

Improvement of hole exit accuracy in electrochemical drilling by applying a potential difference between an auxiliary electrode and the anode

Electrochemical drilling (ECD) is a promising and low-cost process for yielding multiple holes simultaneously in difficult-to-machine materials. In this process, the hole exit accuracy is very sensitive to the electrode feeding depth. In practice, excessive electrode feeding is necessary to ensure that all holes are drilled through simultaneously when there is an error in thickness of the workpiece plate. This results in stray removal at the hole exit and an etched and pitted surface. In the modification of ECD described here, a potential difference is introduced via an insoluble platinum auxiliary electrode that is attached beneath a dielectric perforated plate and arranged opposite to the hole exits to diminish the damage from the stray current and thereby improve the tolerance of the exit accuracy to excessive electrode feeding. Simulation results indicate that an appropriate value of the potential difference concentrates the current at the tool tip and may reverse the current direction on the workpiece surface. Experiments verify that this approach is effective in obtaining holes with good exit accuracy in the case of excessive electrode feeding. Furthermore, it is confirmed that this method is capable of drilling multiple holes with remarkably enhanced exit accuracy and uniformity.