关于电火花加工的类型的翻译.doc

课程 特种加工课程 特种加工 电火花加工电火花加工 ELECTRICAL DISCHARGE MACHINING 译 曾云龙 学号 200807024133 2 History In 1770 English physicist Joseph Priestley studied the erosive effect of electrical discharges Furthering Priestley s research the EDM process was invented by two Russian scientists Dr B R Lazarenko and Dr N I Lazarenko in 1943 In their efforts to exploit the destructive effects of an electrical discharge they developed a controlled process for machining of metals Their initial process used a spark machining process named after the succession of sparks electrical discharges that took place between two electrical conductors immersed in a dielectric fluid The discharge generator effect used by this machine known as the Lazarenko circuit was used for many years in the construction of generators for electrical discharge Additional researchers entered the field and contributed many fundamental characteristics of the machining method we know today In 1952 the manufacturer Charmilles created the first machine using the spark machining process and was presented for the first time at the European Machine Tool Exhibition in 1955 In 1969 Agie launched the world s first numerically controlled wire cut EDM machine Seibu developed the first CNC wire EDM machine 1972 and the first system manufactured in Japan Types Sinker EDM Sinker EDM also called cavity type EDM or volume EDM consists of an electrode and workpiece submerged in an insulating liquid such as more typically oil or less frequently other dielectric fluids The electrode and workpiece are connected to a suitable power supply The power supply generates an electrical potential between the two parts As the electrode approaches the workpiece dielectric breakdown occurs in the fluid forming a plasma channel and a small spark jumps These sparks usually strike one at a time because it is very unlikely that different locations in the inter electrode space have the identical local electrical characteristics which would enable a spark to occur simultaneously in all such locations These sparks happen in huge numbers at seemingly random locations between the electrode and the workpiece As the base metal is eroded and the spark gap subsequently increased the electrode is lowered automatically by the machine so that the process can continue uninterrupted Several hundred thousand sparks occur per second with the actual duty cycle carefully controlled by the setup parameters These controlling cycles are sometimes known as on time and off time which are more formally defined in the literature The on time setting determines the length or duration of the spark Hence a longer on time produces a deeper cavity for that spark and all subsequent sparks for that cycle creating a rougher finish on the workpiece The reverse is true for a shorter on time Off time is the period of time that one spark is replaced by another A longer off time for example allows the flushing of 3 dielectric fluid through a nozzle to clean out the eroded debris thereby avoiding a short circuit These settings can be maintained in micro seconds The typical part geometry is a complex 3D shape often with small or odd shaped angles Vertical orbital vectorial directional helical conical rotational spin and indexing machining cycles are also used Wire EDM In wire electrical discharge machining WEDM also known as wire cut EDM and wire cutting a thin single strand metal wire usually brass is fed through the workpiece submerged in a tank of dielectric fluid typically deionized water Wire cut EDM is typically used to cut plates as thick as 300mm and to make punches tools and dies from hard metals that are difficult to machine with other methods The wire which is constantly fed from a spool is held between upper and lower diamond guides The guides usually CNC controlled move in the x y plane On most machines the upper guide can also move independently in the z u v axis giving rise to the ability to cut tapered and transitioning shapes circle on the bottom square at the top for example The upper guide can control axis movements in x y u v i j k l This allows the wire cut EDM to be programmed to cut very intricate and delicate shapes The upper and lower diamond guides are usually accurate to 0 004 mm and can have a cutting path or kerf as small as 0 12 mm using 0 1 mm wire though the average cutting kerf that achieves the best economic cost and machining time is 0 335 mm using 0 25 brass wire The reason that the cutting width is greater than the width of the wire is because sparking occurs from the sides of the wire to the work piece causing erosion This overcut is necessary for many applications it is adequately predictable and therefore can be compensated for for instance in micro EDM this is not often the case Spools of wire are long an 8 kg spool of 0 25 mm wire is just over 19 kilometers in length Wire diameter can be as small as 20 micrometres and the geometry precision is not far from 1 micrometre The wire cut process uses water as its dielectric fluid controlling its resistivity and other electrical properties with filters and de ionizer units The water flushes the cut debris away from the cutting zone Flushing is an important factor in determining the maximum feed rate for a given material thickness Along with tighter tolerances multiaxis EDM wire cutting machining center have added features such as multiheads for cutting two parts at the same time controls for preventing wire breakage automatic self threading features in case of wire breakage and programmable machining strategies to optimize the operation Wire cutting EDM is commonly used when low residual stresses are desired because it does not require high cutting forces for removal of material If the energy power per pulse is relatively low as in finishing operations little change in the mechanical properties of a material is expected due to these low residual stresses although material that hasn t been stress relieved can distort in the machining process 4 The workpiece may undergo a significant thermal cycle its severity depending on the technological parameters used Such thermal cycles may cause formation of a recast layer on the part and residual tensile stresses on the workpiece 译文 历历史史 1779 年 英国物理学家 Joseph Priestley 研究了电气放电的腐蚀的影响 通过 Priestley 的深入研究 1943 年两个俄国科学家 B R Lazarenko 和 N I Lazarenko 发明了电火花成型的方法 通过他们的努力他们发现了放电的破坏性 他们开发 了一种控制过程来进行金属切削加工 他们的最初过程用到了一个电火花加工 过程 他们以发生在两个导电体沉浸在介电质流体中的火花效果命名 这台机器 发生放电发生器的电路被称为 Lazarenko 电路 这个电路在发电机的放电结构上 运用了许多年 更多的研究人员加入到这个领域中来 并且贡献了许多如今天我们所知的基本 特征的加工方法 1952 年 制造商 Charmilles 制造了第一台用可以使用电火花加 工工艺的机器 并在 1955 年的欧洲机床展上展出 1969 年 Agie 启动了世界上第一台电火花线切割机床 1972 年在日本 Seibu 制 造了第一个 CNC 电火花制造系统 电电火花成型加工火花成型加工 电火花成型加工也叫做腔式电火花成型加工或者体积电火花加工 电极和工件 5 淹没在绝缘体的液体中 典型的有 油或者频繁少量的加入另一种介质液体 电 极和工件被接在适当的电源上 为了让电极在绝缘介质中击穿工件 需要产生流 体 形成一种等离子通道和一个小的火花跳跃 这些电火花通常是同时工作的 在相同时间击打同一个点一般是不可能的 因为 不同的位置都是有想同的电气特性 这使得火花在这些地方同时发生 这些火花 看似都发生在工件和电极之间随机的一大片位置 随着基础金属的侵蚀 火化间 的间隙随之增加 机器自动降低电极使得整个工作过程能够继续 每秒钟有数以 万计的火花产生 设置参数是为了小心的控制实际工作周期 这些周期控制有时 候也被叫做 On time 和 Off time 这些控制周期在文献中被更准确的定义 On time的设定决定了电火花的长度和持续时间 因此 在用那样的火花和随后的 所有火花生产一个深腔的过程中 在这个工件上增加一个粗选槽来完成这个工 件 与事实相反 这个时间很短 Off time是一个火花代替另一个火花的一段时间 一个较长的Off time 例如 允许电解质流体通过喷头冲洗清除被侵蚀的碎片 从 而避免短路现象 这些设置可以维持在微秒 典型的部分几何学是一个复杂的3D 形状 里面常常有小的或者奇数的角 垂直 轨道 矢量 定向 螺旋圆锥 旋转 旋转和索引的加工周期也经常被使用 电电火花火花线线切割加工切割加工 在丝电火花加工机 电火花线切割机 也称为线切割机和线切割电火花机 用一层 很薄的单链金属线材 通常是黄铜 通过把工件淹没在一个充满典型的去离子水 6 介质流体池子中 线切割电火花机常常被用来切割厚度 30