绞合电极丝电火花线切割加工极间流场研究

为了解决电火花线切割加工在高效切割中极间工作介质补充不足的问题,研究开发了一种新型的电火花线切割加工用绞合电极丝。利用Fl uent流体力学软件,计算了绞合电极丝和常规电极丝在切缝中的流场体积流率和速度场。结果表明:绞合电极丝的极间流场体积流率比常规电极丝高约46%,绞合电极丝极间工作液的周向速度分量能促进加工区的工作液补充和蚀除产物排出,所设计的实验也在一定程度上验证了上述结论。     

场致射流微细放电加工实验研究

对场致射流微细放电加工单晶硅进行了工艺实验研究,分析在不同加工极性下的加工机理,发现在正极性加工时,蚀坑在工件表面存在电解液残留是由电火花蚀除和电化学蚀除共同作用的结果,而在充分放电的情形下,是由电火花放电来实现材料蚀除的;在负极性加工时,蚀坑仅仅是由电火花蚀除作用的结果。通过单因素实验获取喷管内径、极间距离、极间电压及工作液浓度对单次放电蚀坑直径的影响曲线,通过优化工艺参数在单晶硅表面加工出宽度为1μm、长度为5μm的微细沟槽。研究结果充分证明了场致射流微细放电加工的加工能力。     

往复走丝线切割复合工作液寿命表征的研究

研究了往复走丝电火花线切割加工过程中切割效率、工件表面形貌、蚀除效率、电导率、工作液折光率及pH值的变化规律,并检测了放电加工波形。分析认为:以往采用切割效率来衡量工作液使用性能的方法缺乏科学性,而采用蚀除效率作为复合工作液寿命的表征指标更加科学,且蚀除效率的变化与加工时的放电脉冲利用率有很大关联性,为建立往复走丝线切割复合工作液寿命的评价体系指明了方向。     

磁场对电火花放电通道的影响研究

放电过程中的横向静磁场可使带电粒子受到洛伦兹力而改变运动轨迹,造成工件上放电点的位置变化,进而引起电蚀坑形貌的变化。利用理论方法推算出磁场作用下的电子运动轨迹,得到工件上放电点的理论偏移值,并通过实验证明洛伦兹力改变了放电点的位置。结果表明:部分电蚀坑出现明显的拉长型畸变,放电点沿洛伦兹力方向移动,放电通道在洛伦兹力与工作液阻力的作用下逐渐发生偏移。电蚀坑被拉长后其深度会变浅,大而浅的电蚀坑将有助于提高电火花加工的表面质量。     

电火花加工中气泡与电蚀产物对阴极场强影响的仿真研究

针对电火花加工中不同放电位置产生的不同电极损耗形状,讨论了极间存在工作液、气泡、电蚀产物的情况下,火花击穿放电前阴极电场强度的分布情况,从而探究气泡对放电发生位置及电极损耗形状的影响。采用Maxwell软件进行电火花放电通道的静电场仿真,得到气泡、电蚀产物对放电发生位置的影响规律。仿真结果表明：气泡对阴极表面具有保护作用,气泡越大,离阴极表面越近,场强越低,保护作用越明显;电蚀产物对阴极场强有增强作用,且随其浓度的增加而增加;气泡周围区域电蚀产物浓度高,放电发生概率最大;静止的气泡可减少放电损耗,运动的气泡对电极损耗的影响取决于高放电概率,气泡的不同分布状态影响电极的损耗形状。     

多次电火花线切割变射流供液技术研究

针对目前高速多次电火花线切割供液扰动电极丝,极间排屑不畅问题。在分析目前线切割极间流场和废屑粒子排除研究状况的基础上,对变射流流场进行了理论研究,探讨了汇聚角和宽径比对射流内外压差的影响。结合多次电火花线切割加工特点,提出了变射流供液技术,并对变射流装置进行了结构设计和仿真,从而实现减小工作液对电极丝扰动,增加进入切缝工作液流量,加速电极丝的冷却和切缝废屑粒子的排出,达到提高多次线切割加工效率和稳定性目的。     

多孔质电极电火花加工极间流场仿真

为研究多孔质电极电火花加工中分布式冲液对加工过程的作用机制,建立了多孔质电极极间流场模型,采用固液两相流数值方法模拟电极间冲液和蚀除产物的两相流动过程,与单孔电极进行了对比研究,并进行了电火花加工实验验证。仿真结果显示:多孔质电极的极间流场流速由于分布式冲液出口的存在而呈现分布式特征,且流场外围流速大于中心流速;采用多孔质电极后,由于分布式冲液出口的存在,能够将固相蚀除产物沿一定的通道有效排出加工区域。与仿真结果相对应,电火花加工实验结果表明:由于冲液对蚀除产物良好的排出作用,多孔质电极能够获得更高的加工效率,且加工速度随加工深度变化不大;但由于冲液影响了炭黑向工具电极的附着行为,导致工具电极相对损耗率增大。     

放电诱导雾化烧蚀深型孔加工技术研究

为提高常规电火花深型孔加工的稳定性及工艺指标,提出了一种新的深型孔加工方法——放电诱导雾化烧蚀加工技术。采用"水基-氧气"高压气雾介质作为放电介质,对烧蚀燃烧反应具有冷却、抑制和分散放电作用,有效降低了烧蚀能量,保证了加工的平稳性。另外,放电间隙中分散的熔融金属与气雾介质的氧气继续充分燃烧,气雾介质吸收释放的能量而迅速气化,产生的爆炸效果对蚀除产物的排出有巨大的促进作用,蚀除产物呈现喷发式排出。因此,放电诱导雾化烧蚀深型孔加工技术不断引入了新的能量,并解决了排屑的难题。在本试验条件下,对于边长为4.4mm的方孔,加工深度可达70 mm以上,材料蚀除率约为内冲液电火花加工的5.45倍,电极质量相对损耗降低了82%。     

基于复合工作液的电火花线切割加工技术研究

从极间放电机理的角度分析了阻碍高速走丝电火花线切割加工(HSWEDM)工艺指标提高以及产生表面黑白交叉条纹的根本原因是工作介质的洗涤性问题,试验证明HSWEDM在使用洗涤性良好的复合工作液后,由于极间冷却状态的改善而使切割工艺指标大幅度提高,切割速度已超过200 mm2/min.并从放电间隙、电极丝的放电能量承受能力及运丝速度等方面进行了HSWEDM更高效率切割的可行性研究,分析了基于复合工作液的电火花线切割加工技术的发展方式.     

基于复合工作液的高压喷液电火花线切割实验分析

阐述了基于复合工作液的高压喷液电火花线切割加工以提高切割效率和加工精度的方法：从理论上分析了电火花线切割加工过程中，工作液在极间的压力分布状况和冷却规律；对比了高压喷液与无高压喷液条件下加工工件的表面形貌；通过检测电流、电压波形反映了极间放电状况；分析了极间状态对加工工件表面形貌的影响。     

Machining characteristics of magnetic force-assisted EDM

The gap conditions of electrical discharge machining (EDM) would significantly affect the stability of machining progress. Thus, the machining performance would be improved by expelling debris from the machining gap fast and easily. In this investigation, magnetic force was added to a conventional EDM machine to form a novel process of magnetic force-assisted EDM. The beneficial effects of this process were evaluated. The main machining parameters such as peak current and pulse duration were chosen to determine the effects on the machining characteristics in terms of material removal rate (MRR), electrode wear rate (EWR), and surface roughness. The surface integrity was also explored by a scanning electron microscope (SEM) to evaluate the effects of the magnetic force-assisted EDM. As the experimental results suggested that the magnetic force-assisted EDM facilitated the process stability. Moreover, a pertinent EDM process with high efficiency and high quality of machined surface could be accomplished to satisfy modern industrial applications.     

Landau理论研究TiNi顺磁合金热/强磁场耦合下的马氏体相变

利用改进后的Landau理论模型研究了顺磁TiNi合金在热/强磁场耦合作用下的马氏体相变行为.利用第一原理计算了TiNi合金在不同相变剪切应变(序参量)下的Flermi面态密度,得到相变过程中磁化率和磁自由能的变化,把磁场效应引入到Landau模型中.结果表明,稳恒强磁场可使顺磁材料的相变温度(M6和T0)出现突变性的升高,这主要是因为相变驱动力随磁场增强而呈二次曲线上升规律.另外,因强磁场下马氏体变体之间的自由能差急剧增大,导致磁场对变体的促进和抑制作用变得明显,出现取向生长现象.在5 T稳恒强磁场下的TiNi合金相变实验中,利用TEM观察到了一些变体以相互垂直的二变体形式出现(即取向生长),证实了模型的结果.     

强磁场对钢中马氏体相变的影响及其研究展望

固态相变中,由于两相之间的磁性差异,外加磁场将改变奥氏体向马氏体的相变过程,同时对马氏体的微观组织产生影响。主要阐述了马氏体相变过程中,强磁场对其产生的影响。相关研究表明,磁场可以提高马氏体的开始转变温度,这主要是由磁场的静磁能效应、高场磁化率效应和磁致伸缩效应导致的。磁场促进了马氏体的形核和长大,从而使其含量增加,但磁场对马氏体的形貌影响不显著。同时介绍了强磁场作用下马氏体相变的最新进展与未来展望。     

Modeling and simulation of cylindrical electro-chemical magnetic abrasive machining of AISI-420 magnetic steel

The objective of the present research is to simulate cylindrical electro-chemical magnetic abrasive machining (C-EMAM) process for magnetic stainless steel (AISI-420). C-EMAM is a new hybrid machining process used for high efficiency finishing of cylindrical jobs made of advanced engineering materials. The material is removed from the workpiece surface due to simultaneous effect of abrasion and electrochemical dissolution. Finite element method is used to calculate the distribution of magnetic field between the magnetic poles in which cylindrical shaped workpiece is placed. The cutting forces responsible for abrasion are calculated from the magnetic forces due to gradient of magnetic field in the working gap. The effect of electrochemical dissolution and abrasion-assisted dissolution are incorporated into the C-EMAM process model using empirical relation for average anodic current. The empirical relation is correlated with the input parameters in the present system based on experimental results. Finally a surface roughness model is developed by considering total volume of material removed with the assumption of triangular surface profile. The simulation results for material removal and surface roughness are validated using experimental results. The simulated results agree with experimental observations.     

脉冲磁场对TC4钛合金析出行为及力学性能的影响

为了探讨脉冲磁场对TC4钛合金析出行为的影响,在其时效过程中施加了脉冲磁场,分别在形核阶段和长大阶段进行观察与分析,利用扫描电镜、透射电镜、拉伸试验机研究脉冲磁场在TC4时效过程中对显微组织、强度和塑性的的影响,并通过经典形核理论及扩散理论分析了脉冲磁场在时效过程中的作用机制。结果表明,由于脉冲磁场的加入,TC4析出速度明显提高,相同时间下析出相的体积分数增加,在保证力学性能的前提下,降低了时效所需的时间。施加脉冲磁场时效2 h相较于未施加脉冲磁场4 h延伸率塑性提高了21.68%,抗拉强度基本一致。在脉冲磁场和温度场耦合作用下时效,可使TC4提前（2h）进入过时效阶段;在拉伸断口方面,施加脉冲磁场在2h前断口形貌为韧窝断口,但当时间增加至2 h后,断口逐渐转变为准解理断口形貌,表明脉冲磁场可以加速时效进程。分析认为,脉冲磁场通过磁吉布斯自由能促进了TC4在时效过程中次生相的析出及长大,是由于降低临界形核功和促进原子扩散的协同效应所致。     

Improving surface quality in BEAM with optimized electrode

Blasting erosion arc machining (BEAM) introduces a high-efficiency and low-cost machining technique in dealing with difficult-to-cut materials. Despite its high machining efficiency, the machined surface is quite rough. It leads to an excessive allowance for subsequent processing. This paper presents an optimized tool electrode design that enables an enhanced hybrid arc breaking mechanism. Both flow field simulation and machining test verify that the optimized electrode can guarantee a much better gap flow field and debris expelling effect. The corresponding machined surface is significantly improved in aspects of surface roughness, smoothness, uniformity, recast layer as well as heat affected zone.     

基于磁场复合和高频、窄脉冲电流电解加工的试验研究

通过磁场复合和高频、窄脉冲电流电解加工工艺,实现了薄壁大面积(10 000mm2)型面铝基材料零件的稳定小间隙加工.试验研究中采用高频、窄脉冲电流,解决了加工间隙流场不均匀的问题;采用磁场复合电解加工工艺方法,解决了试件的表面质量差和杂散腐蚀严重的问题.     

A study on the quality micro-hole machining of tungsten carbide by micro-EDM process using transistor and RC-type pulse generator

Tungsten carbide (WC) is an extremely hard and difficult-to-cut material used extensively in manufacturing because of its superior wear and corrosion resistance. Besides diamond-charged grinding wheels, micro-EDM is an effective method of machining this extremely hard and brittle material. Since micro-EDM is more generally an electro-thermal process, the supplied energy from a pulse generator is an important factor determining the performance of the micro-EDM process. This study investigates the influence of major operating parameters on the performance of micro-EDM of WC with focus in obtaining quality micro-holes in both transistor and RC-type generators. Experimental investigations were conducted with view of obtaining high-quality micro-holes in WC with small spark gap, better dimensional accuracy, good surface finish and circularity. In micro-EDM, the fabrication of micro-parts requires minimization of the pulse energy supplied into the gap which can be fulfilled using the RC-generator. It was observed that the RC-generator can produce better quality micro-holes in WC, with rim free of burr-like recast layer, good dimensional accuracy and fine circularity. Moreover, the smaller debris formed due to low discharge energy in RC-type micro-EDM can be easily flushed away from the machined area resulting in surface free of burr and resolidified molten metal. Therefore, RC-type micro-EDM could be more suitable for fabricating micro-structures in WC, where accuracy and surface finish are of prime importance.     

High Steady Magnetic Field Processing of Functional Magnetic Materials

The materials science community has been enriched for some decades now by the “magneto-science” approach, which consists of applying a magnetic field during material processing. The development of anisotropic properties by applying a steady magnetic field is now a well-established effect in the material processing of magnetic substances, which benefits from the unidirectional and static nature of the field delivered by superconducting magnets. Among other effects, magnetic anisotropy in functional magnetic materials, which arises from the alignment of magnetic moments under external field, can be developed at various structural scales. Magnetic ordering, magnetic patterning, and texturation are at the origin of this anisotropy development. Texture is developed in materials from magnetic orientation due to magnetic forces and torques or from stored energy. In metals and alloys, for instance, this effect can occur either in their liquid state or during solid-state thermomagnetic treatments and can thus impact significantly the material functional magnetic properties. Today’s improved superconducting magnet technology allows higher field intensities to be delivered more easily (1 T up to several tens of Teslas) and enables researchers to gather evidence on magnetic field effects that were formerly thought to be negligible. The magneto-thermodynamic effect is one of them and involves the magnetization energy as an additional parameter to tailor microstructures. Control of functional properties can thus result from magnetic monitoring of the phase transformation, and kinetics can be impacted by the magnetic energy contribution.     

Analysis and performance of slotted tools in electrical discharge drilling

Accumulation of machining debris due to inadequate gap flushing severely limits the material removal rate and impairs the quality of the machined surface in electrical discharge machining. This is particularly pronounced in electrical discharge drilling of holes with a high aspect-ratio, wherein conventional flushing techniques essentially cease to be effective. To this end, this paper proposes the application of novel tool electrodes comprising geometric features specifically designed to promote tool rotation-induced debris egress. The corresponding flow fields are modelled numerically to optimize said designs. Relative to conventional rotating cylindrical tools, removal rate enhancements on the order of 300% are demonstrated.