在微细电火花铣削中介质对电极损耗的影响

在微细电火花加工（EDM）中电极损耗是不可避免的,而针对电极损耗的研究大都是在油工作液中,很少针对气中放电时的电极损耗进行研究．气中电火花加工普遍采用管状电极,所以为了获得尺寸更小的工件,通过反拷块可磨削出微米级的实心电极,并采用外部充气的方式,可实现微米级三维结构的气中电火花加工．实验考虑了影响气中放电电极损耗的各种因素．通过观察微细电火花三维铣削放电现象与结果,可得到气中放电的规律．由于电火花加工中电极损耗是不可避免的,所以在三维铣削加工中对电极进行在线检测并补偿,工件成形精度大大提高．对刀具路径进行合理规划,可以缩短加工时间．与油中电火花铣削相比,气中电火花加工时电极损耗更低,加工表面质量更好．     

三维微细电火花伺服扫描加工工艺

为提高三维微细电火花加工的加工效率,从而达到工业应用目的,采用放电间隙伺服控制实时补偿电极损耗的技术路线,提出了三维微细电火花伺服扫描加工方法．基础实验验证了伺服扫描加工每层加工深度的一致性,研究了横向扫描加工速度对加工深度的影响规律．在小于1mm2加工区域内的三维结构加工实验结果显示,伺服扫描加工可以便捷地实现三维微小结构的加工成型．进一步在工件与电极之间附加激振,可大幅度地提高放电脉冲的有效利用率以及加工效率．采用φ100μm的钨丝电极,在铜试件上加工深度300μm的典型三维形状,加工时间小于50min．     

一种三维金属微型腔的组合加工方法

为了制作局部为三维结构的金属模具微型腔,实验研究了一种组合加工新工艺,即先用紫外线光刻和电铸成形（准LIGA）技术在模具基底上制作二维金属微型腔,再用微细电火花成形加工（EDM）技术对微型腔的局部进行修形,得到局部为三维结构的微型腔,电火花修形的位置根据微型腔结构的设计要求而定．以制作聚合物微流控芯片用的金属模具为试件,以微细电火花成形加工中影响工件表面粗糙度的因素分析为理论指导,应用该方法制作了局部侧壁倾斜的三维微型腔．根据测量结果,两边侧壁与水平方向的夹角分别为49．6°和46．4°,倾斜侧壁的表面粗糙度Rs为0．391μm．     

P20钢电火花成形加工表层的组织结构和性能

在不同脉冲电流条件下对模具钢P20进行电火花成形加工,研究了脉冲电流对试样表层的微观组织结构的影响,以及微观组织结构对表面性能的影响。结果表明,电火花成形加工后试样的表面分为烧蚀层、熔化凝固层和热影响层。随着脉冲电流的增大,熔化凝固层和热影响层的厚度增大;在加工过程中元素的扩散和迁移使熔化凝固层外侧碳元素和氧元素的浓度较高。电火花成形加工过程相当于热处理过程,从熔化凝固层到热影响层、基体,显微硬度快速降低。有限元模拟计算表明,在熔化凝固层内的垂直与界面微裂纹主要是加工放热过程中的残余应力引起的。     

面向精密加工的仿真技术研究及应用

详细阐述了计算机仿真技术在精密加工领域中应用的两个方面——加工过程动态仿真和加工过程物理特性仿真;建立了微细电火花加工仿真系统,实现微细电火花放电通道仿真,建立并分析了电火花加工的热学模型,分析了表面粗糙度与工艺参数的关系。系统在实际中得到验证,加工出微三维结构。通过电火花仿真系统,说明计算机仿真技术在精密加工研究方面的可行性和优越性。     

微细材料细晶处理方法及其研究发展

近些年微成形技术的研究热度不断增高,金属薄板、箔材及丝材等可直接用于微型件制造的微细材料缺少专门性研究,微细材料的微观结构与性能直接影响微型件的成形质量。综合评述了大塑性变形细晶方法、电流辅助工艺和微观结构调控等方面的相关研究,着重介绍了适合于微细材料的反复折弯压直和限制模压变形2种反复折弯形变细晶的方法。分析了微细材料细晶处理存在的问题,提出了适合用于微细材料的细晶及增塑处理的研究方法,展望了微细材料电流辅助形变工艺和微观结构调控的研究方向。开展了微成形用微细材料预处理方法与相关技术研究,对促进微成形技术的发展具有重要的理论意义和应用价值。     

高技术、高附加值、高利润的新产品微细电磁线生产项目

随着电子元器件“轻、薄”的方向发展,而要求的微细电磁线材料,其线径细、薄,要求极限制造。高科技产品直径0．05～0．02mm,微细电磁线是微特精密电子,电机,继电器,电子变压器,电磁线绕组线的关键基础材料,广泛用于航空、仪器、仪表、电子计算机、数码产品,平板电视,3G手机,IC卡等,微小型电子元器件的生产。应用范围自然拓展,用量大、国内外市场紧销,附加值高,市场潜力巨大。     

电磁缩径中集磁器参数和铝合金管件参数对变形的影响

管件电磁缩径是高端智能制造的一个新方向，缩径成形质量好坏主要与集磁器线圈参数、管件自身参数和放电能量大小有关，研究集磁器和管件工艺参数对电磁力和成形性能的影响尤为重要。针对3003和6063铝合金管件，本文结合实验研究和数值仿真方法，讨论了集磁器结构和管件参数等对电磁力的影响，研究了放电电压、管件金属材料类型、管件长度对最终管件成形的影响规律，并探究了影响管件成形均匀性的原因，可为合理制定管件电磁成形工艺方案提供一定技术参考。研究结果表明：集磁器内斜面角度变化对磁场力有明显影响，且角度为40°比较合理；3003铝合金管成形性较好，最大缩径率31.2%，塑性变形影响区域长度7.0 mm～15.5 mm，在5000 V～6000 V放电电压时成形均匀度φ≦18%，但是放电电压达到6500 V时出现失稳现象；6063铝合金管强度较高，最大缩径率16.2%，塑性变形影响区域长度5.3 mm～9.4 mm，管件变形均匀φ<14%。     

基于微PCD刀具的微结构成型制造与应用

本文提出一种基于微聚晶金刚石(PCD)刀具的微结构快速车削成型制造方法.首先利用电火花线切割加工(WEDM)放电蚀除技术实现了微PCD刀具的精密切割成型制造.在WEDM过程中对线切割丝的运动轨迹、电火花加工间隙及加工能量进行了研究分析以提高微切削刀具的制造精度.随后将微PCD刀具安装到精密车削系统,通过铝合金的微车削实验验证了本文所提出的微结构快速成型制造方法的可行性.最后对微刀具的磨损形态进行了实验分析.在微车削过程中,刀具切削刃无明显磨损和破坏,而工件材料粘结于刀具前刀面是造成微结构加工精度降低的主要因素.本文所提出的微细制造技术有望成为微结构快速、大批量生产的潜在工业应用.     

大批量微细刀具HFCVD涂层制备的温度场仿真与试验分析

采用热丝化学气相沉积法制备金刚石涂层微细刀具的过程中,刀具表面温度场分布的均匀性与稳定性对金刚石涂层的质量具有决定性的作用。本文采用有限容积法,对微细刀具表面沉积金刚石涂层过程中的温度场分布进行了仿真研究,采用Taguchi正交试验法考察了热丝直径d、热丝高度H、热丝间距D以及热丝长度L对温度场均匀性的影响,并获得了最优参数组合,即d=0.65mm,H=12mm,D=27mm以及L=160mm。对比仿真与实际测温试验结果,发现两者之间的偏差不超过4%,验证了仿真模型具有较高精度。采用仿真获得最优参数进行的沉积实验结果表明,放置在沉积区域不同位置的微细刀具表面均被涂覆了一层厚度均匀、组织结构良好的金刚石涂层,从而验证仿真结果的正确性。     

Electrode wear phenomenon and its compensation in micro electrical discharge milling: A review

Micro electrical discharge machining (µEDM) is playing a significant role in the world of miniaturization, especially in micro electro mechanical systems, biomedical devices, micro die/molds, etc. Micro electrical discharge milling (µED-milling) is a variant of µEDM used for producing complex 3D features with a simple shaped tool. The material removal mechanism of µEDM depends on electro-thermal energy between the tool electrode and workpiece. µEDM inherently being a non-contact machining process, leads to produce miniaturized features in hard to machine materials. Besides erosion of the workpiece material, intrinsic feature of the process leads to tool wear (TW) and introduces dimensional inaccuracy in the micro features. Thus, it is essential to know the factors influencing the TW, and thereby compensate the TW to achieve dimensional stability of the machined features. The critical factors affecting the wear phenomenon of a tool and various techniques applied to compensate TW in µED-milling along with future trends of their application are presented. The key issues of µED-milling and challenges faced in implementing a TW compensation technique are highlighted. The concept of intentional wear of tool electrode and associated advantages in EDM is also demonstrated.     

Effect of Cryogenic Cooling of Tool Electrode on Machining Titanium Alloy (Ti–6Al–4V) during EDM

The discharge characteristics and discharge gap of machining Ti–6Al–4V titanium alloy by cryogenically cooled tool electrode electrical discharge machining (EDM) in distilled water were investigated in this study using the monopulse discharge method. The influence of the cryogenically cooled tool electrode on the discharge gap and the initial maintaining voltage between the electrode and workpiece were analyzed under various temperatures. Test results showed the initial maintaining voltage of the cryogenically cooled tool electrode EDM was lower than that of conventional EDM. The discharge gap of the cryogenically cooled tool electrode EDM was also smaller than that of conventional EDM, which improved the copying accuracy of die-sinking EDM. A comparative experiment of machining Ti–6Al–4V titanium alloy was carried out by using cryogenically cooled tool electrode EDM and conventional EDM, lower electrode wear, higher material removal ratio, and higher corner size machining accuracy was obtained by using cryogenically cooled tool electrode EDM.     

采用疏水材料侧壁绝缘电极的微细电解加工实验

微细电解加工中工具电极和工件之间的加工间隙是影响加工效果的核心因素.工具电极侧壁施加绝缘膜的工艺方法,可显著改变侧面加工间隙内的电场分布,提高加工精度,同时保持原有的加工效率,有着良好的应用前景.本文基于仿真方法,分析了绝缘膜对端面加工间隙和侧面加工间隙的影响规律,研究了绝缘膜疏水性质对电解加工中产生的氢气泡运动的吸附作用对微细电解加工的影响.在直径为数十到数百微米的钨丝侧壁制备出可用于微细电解加工的几微米厚的硅胶疏水材料侧壁绝缘薄膜.在硝酸钠电解液中,实现了不锈钢材料上将微气泡附着于电极前端与绝缘膜结合处、保护绝缘膜和约束杂散腐蚀的微细电解端面分层扫描加工效果.     

基于多功能加工平台的微细电解加工

电解加工在加工过程中因难以控制加工形状而很少应用在微细加工领域,为了对微细电解加工可行性进行探索,设计了多功能微细加工平台,利用多功能微细加工平台可为微细电解加工在线制作电极,采用低加工电压、低浓度的钝化电解液、高频窄脉冲电源和高速旋转的微细电极,进行了微细电解加工实验,取得了很好的工艺效果,加工间隙是影响加工精度的关键因素,设计了一个加工间隙控制伺服系统,以保证微小的加工间隙,在厚为100μm的不锈钢薄片上用微细电解打孔加工出直径为65μm的微小孔,利用微细电解加工时电极无损耗,提出采用简单圆柱微细电极进行微细电解铣削,加工出较高精度的微结构,取得了较好的工艺效果,从而验证了该微细电解加工装置的微细加工能力和方法的可行性。     

Effect of tool wear on microrods fabrication using reverse μEDM

Arrayed microrods are used to drill array of microholes in workpieces by Micro electrical discharge machining (μEDM). In comparison to a single microrod, the use of an array of microrods enables drilling of multiple microholes in lesser time, and hence it offers a higher productivity. The present work focuses on the effect of tool wear on the dimensions of the machined array of microrods through reverse micro electrical discharge machining (R-μEDM). The effects of the input parameters such as voltage, capacitance and feed rate on the obtained length and diameter of the microrods have been investigated. This study introduces a simple analytical model to evaluate the amount of tool wear and material removal from a bulk rod. As the levels of voltage and capacitance increase from lower to higher, the tool wear increases by 574%. At lower levels of voltage and capacitance, a straight array of microrods with a longer length of about 1.961?mm is obtained. On the other hand, at higher levels of voltage and capacitance, the obtained microrods are found to have a shorter length of 1.725?mm but with taper. Scanning electron microscope (SEM) and optical microscope images are also analyzed for describing the effects of tool wear on the shape and size of the fabricated microrods.     

The Effects of Electrode Force on the Mechanical Behaviour of Resistance Spot‐Welded 5083‐O Aluminium Alloy Joints

Abstract: In this study, the effects of electrode force on the static and fatigue strength of spot welded joints of 5083‐O aluminium alloy sheets were investigated. The thickness of the sheet joints was 1.5 mm. Tensile‐shear joints with one spot weld were considered and three different load levels for electrode force were selected as 2500 N, 3000 N and 3500 N while the welding time and electric current were fixed during resistance spot welding process. Also, micro‐structures and micro‐hardness of cross‐sectional area of the test samples were investigated. The results show that increasing the electrode force from 2500 N to 3000 N has no major impact on the nugget size and fatigue strength of the specimens, but increasing the electrode force from 3000 N to 3500 N, despite reducing in the diameter of the nuggets, increases the fatigue life of the joints significantly. The results also indicate that increasing the electrode force increases the life associated with the crack initiation phase of total fatigue lifetime.     

Plasma-applied machining of a narrow and deep hole in a metal using a dielectric-encased wire electrode

Electro discharge machining (EDM) utilizing transferred arc plasma is widely accepted for the drilling or the molding of metals. In the present study, a new type of EDM system employing a composite electrode fabricated a narrow and deep hole (diameter: 0.70 mm, depth: 150 mm) in a steel block. The composite electrode consisted of a metal rod encased in a dielectric pipe jacket. The dielectric jacket prevents secondary discharges occurring between the sidewalls of the rod electrode and the fabricated hole, enabling fabrication of a deep and narrow hole. The system design and set-up, operation, and machining performance of the new system are described here.     

Electrical Discharge Machining (EDM) Characteristics Associated with Electrical Discharge Energy on Machining of Cemented Tungsten Carbide

In this investigation, cemented tungsten carbides graded K10 and P10 were machined by electrical discharge machining (EDM) using an electrolytic copper electrode. The machining parameters of EDM were varied to explore the effects of electrical discharge energy on the machining characteristics, such as material removal rate (MRR), electrode wear rate (EWR), and surface roughness. Moreover, the effects of the electrical discharge energy on heat-affected layers, surface cracks and machining debris were also determined. The experimental results show that the MRR increased with the density of the electrical discharge energy; the EWR and diameter of the machining debris were also related to the density of the electrical discharge energy. When the amount of electrical discharge energy was set to a high level, serious surface cracks on the machined surface of the cemented tungsten carbides caused by EDM were evident.     

Machining of Engineering Ceramics by Ultrasonic Vibration Assisted EDM Method

Ultrasonic vibration assisted EDM was performed by using an ultrasonic machine tool with a d.c. power supply, with its positive and negative poles connected to the workpiece and the tool electrode, respectively. The pulse discharge is produced by the relative motion between the tool electrode and the workpiece. In the working process of this combined technology, ultrasonic machining and EDM are complementary techniques. Experimental results show that the material removal rate is a little more than just the sum of ultrasonic machining and EDM, while surface roughness is about the same as that for ultrasonic machining.     

Electrical Discharge Machining of Functionally Graded 15-35 Vol% SiCp/Al Composites

A functionally Graded 15-35 volume% silicon carbide particulate (SiC_p) reinforced Al359 metal matrix composite (SiC_p/Al MMC) was drilled by electrical discharge machining (EDM) to assess the machinability and workpiece quality. The machining conditions were identified for both the machining performance and workpiece quality of the EDM process, including some aspects of material removal mechanisms, material removal rate (MRR), electrode tool wear, and subsequent drilled hole quality including surface texture and roundness by using surface profilometry, coordinate measuring machine (CMM), and scanning electron microscopy (SEM). It was observed that the material removal rate increases with increasing peak current and pulse-on-time up to the optimal points and drops drastically thereafter. Higher peak current and/or pulse-on-time result in both the greater tool wear and the larger average diameter error. As the percentage of the SiC particles increases, MRR was increased and electrode wear was found to be decreased. At the EDM machined subsurface layer, the fragmented and melted SiC particles were observed under the SEM and EDX-ray examination.