外文翻译---电火花线切割工艺进给率的控制.docx

附 录英文原文Feed rate control of the wire-EDM process1、IntroductionThe CNC wire-EDM machines first appears in the market in the 1970s，Although the wire-EDM process has been playing an important role in the tooling and manufacturing industry，especially for the production of punches and dies，The metal removal process of wire-EDM is very complex with stochastic and time-varying characteristics。 Moreover， many machining conditions such as workpiece properties(material，thickness)，machining settings(wire feed， table feed， flushing pressure，etc。)and power settings(pulse on-time，pulse interval，etc。)have an effect to the machining process。In order to improve the machining efficiency，stability and quality，many efforts have been made by the researchers and manufacturers to develop pulse discrimination and control system。Liao et al。developed a pulse discrimination system to study the characteristics of pulse trains in the wire-EDM process。They also proposed an approximate method for estimating the variation of the average gap width。Wire breakage and unstable machining drastically reduce the machining efficiency and accuracy in wire-EDM。Some adaptive control systems using the fuzzy control strategy employed the sensing parameters detected by the developed pulse discriminating and control system to monitor and control wire rupture suppression as well as maintain stable machining。Although these adaptive control systems can be applied to a wide rangeof machining conditions，they cannot respond to the gap conditions properly when there is an unexpected disturbance such as the condition of machining a stair-shape workpiece。In order to carry out the processing of a workpiece with variable height，Rajurkar et al。 presented an adaptive control system to on-line optimize the sparking frequency by estimating the workpiece height with a multi-input model。 This paper presents a new computer-aided pulse discriminating and control system for process motoring and control in wire-EDM。By means of the pulse discriminating and control system，the relationships between machine settings and sensing parameters are analyzed quantitatively。According to the identified gap states，a control strategy is proposed by adjusting the feed rate in real-time to achieve stable machining。2、Feed rate control and the process parametersThe quality of feed rate control determines the stability of the gap width the machining process。 The following four process variables can be used for feed control：A、Gap voltage This process characteristic is average value of the gap voltage。This mean value depending on the different burning voltage levels of spark and arc as well as on the ignition delay time。The determination of the middle gap voltage and its technical implementation for gap width control isrelatively easy in comparison with other methods。The gap voltage was directly proportional to the working gap width。B、Ignition delay timeThe ignition delay time characterizes the conditions for the voltage breakdown of the gap。The theoretical consideration，that a small gap offers better conditions for a breakdown than a large gap leads therefore to shorter ignition delay times。In this way， the ignition delays time can be used as a controlled variable for the feed rate control。The gap conditions at spark erosion are ideal if the voltage breakdown occurs after a short ignition delay。Longer ignition delays，the danger for occurring arc discharges arises。The measurement of the ignition delay of the dielectric breakdown has the advantage compared to other procedures that critical states the gap before the actual power pulse can be found，In addition，the disturbance afflicted current and voltage measurements are replaces by time measurement。The start of measurement is given by the generator control。 The time interval ends with reaching a reference voltage or a reference current。C、Voltage breakdown The voltage breakdown is characteristic of subsequent discharge because the slope of this breakdown is determined by the dominating mechanism of conducting。D、High-frequency parts of the burning voltage The practical investigations show that the spark voltage has a high-frequency part while the arc burning voltage does not have this one。Using this， process analyses and feed rate controls achieving a sufficiently good machining result were developed。 Today the feed rate control is carried out via the analysis of the above-mentioned process parameters。 There are hardly problems if a sufficiently good process analysis determines the “critical” process states and eliminates them via a process control，the new feed rate controls must be adapted to theses variable conditions at shortest times。3、Pulse discriminating and control systemA new pulse discriminating and control system has been developed for wire-EDM process as shown in Fig.1。Fig.1 The developed pulse discriminating and control system of wire-EDMIn the system，it consists of two parts。Those are gap states examination module and motion control module。 In the Gap states examination module，a high voltage in the gap can be changed into a low voltage by a voltage divider for digital circuits。There are three voltage levels 70，50 and 10V labeled as Vh，Vm and Vl，respectively。A comparator is used produce three different states by comparing the gap voltage signal。A complex programmable logic device(CPLD)，which allows easy modification of the design，clocked by a 4MHz crystal oscillator is not only employed to generate the pulse control signals(i.e.P1 and P2)，it is also used to discriminate the gap states。 A PC is used externally for user interface，data transfer and computation purpose。The user interface was designed under the integrated development environment of Visual C+6.0。 In the Motion control module。The PCI-1240 card connected to the PCI bus and communicated with the Pentium PC through a dual port random access memory(RAM)with the capacity of 8K words is used to count the pulse trains by software written in C language。Based on this architecture，the pulse data can be displayed，recorded and analyzed by the PC simultaneously。 As shown in this Fig.2，Vg is the gap voltage，Ig is the gap current，because the current measurement device is expensive，so the gap current is not considered in the input signal of the discriminating system。P1 is the pulse control signal of the discharge circuit。Ql，Qm and Qh are output states of the comparators。When the gap voltage is higher than Vl， Vm and Vh，respectively。Ql，Qm and Qh is high。tl is a time period between P1 goes high and Ql goes high。tm is a time duration when Qm remains high。When the gap state is an open circuit，tl and tm are measured and their values are recorded and labeled as tls and tms， respectively。As shown in Fig.2，it is difficult to distinguish between an open circuit and a normal spark，and differentiate an arc spark from a short spark only by means of the three voltage levels Vl，Vm and Vh。As it can be seen from Fig.2，tl of a short circuit is the longest time period among that of other gap states。 Besides，tm of a normal spark is visibly shorter than that of an open circuit。Therefore，not only the gap voltage level but also the time periods tl and tm are employed in the discrimination system to identify the gap states。According to the pulse discriminating signals as depicted in Fig.2，Gap states can be differentiated by using the following logical analysis As shown in table .1。There are four kinds of gap states in the Wire-EDM process。These are open circuit，normal spark，arc discharge and short circuit。When the work piece and wire electrode contact with each other， the short circuit happens。Arc discharges and short circuits can be caused by poor flushing，gap contamination and short ionization because the spark debris can not be flushed away and it allow reionization of the dielectric。Arc discharges and short circuits are dangerous to machining process and achieve the stability of the machining process。So it should be avoided。A control strategy is proposed by regulating the feed rate in real-time according to the identified gap states。Fig.3 shows the timing chart of the pulse control signals。Do，Dn，Da and Ds represent the output signal of the discriminating circuit when the gap states are identified as open circuit，normal spark，arc discharge and short circuit，respectively。As shown in Fig.3，the feed rate is controlled at a pre-determined value when the gap state is determined as an open circuit or a normal spark，and at the other pre-determined value when the gap state is determined as an arc discharge or a short circuit，the former feed rate is shorter than the latter。4、ConclusionIn this paper，a wire-EDM pulse discriminating and control system has been developed for the identification of gap states，more precise on-line quantitative pulse train analysis，machining condition monitoring and process control。From the experimental results of process monitoring and control， the following conclusions are observed。 A、Discharge pulses can be classified into four pulse types by combining some of the time periods and gap voltage characteristics。The proportion of short circuits(short ratio)and the sparking frequency can be used to monitor and evaluate the gap condition。 B、For controlling the feed rate while spark erosion machining the four process variables：middle gap voltage，ignition delay time，high-frequency part of the gap voltage and voltage breakdown are suitable as controlled variables。A combination of process variables has to be used for powerful control strategies。C、A feed rate control strategy has been proposed to improve the abnormal machining condition。 Experimental results not only verify the effectiveness of the proposed control method，they also indicate that the developed pulse discriminating and control system is capable of achieving stable machining under the condition where there exists an unexpected disturbance during machining。中文翻译电火花线切割工艺进给率的控制1、 简介数控电火花线切割机在十九世纪七十年代在市场出现。尽管线切割在模具行业与制造业中发挥了重要的作用，尤其是对凸模和凹模的制造。线切割的金属切割工艺是非常复杂的，而且具有随机性，随时间不同而具有不同的特点。而且，很多切削条件如工件性能（材料，厚度），切削装置（送丝，工作台进给，冲压力等）和功率设置（脉冲，脉冲间隔等）对切削工艺有很大影响。为了改进切削效率，稳定性，和质量，研究人员和制造者在开发脉冲识别和控制系统上做了很大努力。廖等人开发了一种脉冲识别系统来研究线切割工艺中脉冲序列的特征。他们也建议一种测量平均距离宽度变化的近似方法。在线切割中金属丝断掉和不稳定的切削条件会严重的减少切削效率和精度。用模糊控制方法控制的一些调适性控制系统利用通过开发的脉冲识别和控制系统检测的传感参数来监视和控制金属丝破裂和保持稳定的切削条件。尽管这些 自适应性控制系统能被应用到很大范围的切削条件，但是当有一个意想不到的干扰时如在切削一个阶梯形的工件时，它们不能对距离条件进行准确的反应。为了运用具有不同高度的工件的加工工艺，Rajurkar等人提出了一种调适性控制系统，即通过运用多输入模型估计工件高度来在线优化电火花频率。这篇论文提出了一种新的计算机辅助脉冲识别和控制系统来监测和控制线切割工艺。通过运用脉冲识别和控制系统，我们可以定量分析切削设置和传感参数。根据以确定的距离状态，提出通过实时调整进给率来达到稳定的切削状态的控制方法被来了。2、 进给率控制和工艺参数进给率的质量控制决定了切削工艺的距离宽度的稳定性。下面四种工艺变量可以用来进行进给控制：A. 缝隙电压 这个工艺特性是缝隙电压的平均值。这个平均值取决于电火花、电弧和燃烧延迟时间的不同燃烧电压水平。中间缝隙电压的确定和距离宽度控制与其他方法相比比较容易控制。缝隙电压与工作距离宽度呈正比例关系。B引燃延迟时间 引燃延迟时间描述了缝隙间的击穿电压情况。理论研究表明，小的缝隙与大的缝隙相比，能提供更好的击穿条件，因此导致更短的引燃延迟时间。用这种方法，引燃延迟时间能作为进给率控制的一个控制变量。如果电压击穿发生在短的引燃延迟之后，电火花侵蚀的缝隙条件是理想的。引燃延迟时间越大，发生电弧放电的危险越大。与其他实际功率脉冲被发现之前的缝隙的临界值相比，介电击穿的引燃延迟的测量有其优点。而且，影响电流和电压测量的干扰可以替换为对时间的测量。通过控制电动机来开始测量。达到一个电压参考值和电流参考值后时间间隔停止。C击穿电压 计算电压是连续放电特点，因为击穿的斜率取决于主控系统。D燃烧电压的高频部分 实际研究表明计算电压有高频部分，而电弧的燃烧电压并没有高频部分，利用这一点工艺分析和进给速率控制取得相当好的切削效果。现在进给速率控制是通过分析上述工艺参数来实现的。一个足够好的工艺分析决定临界工艺状态，通过工艺控制估计上述参数不是问题，新的进给率控制必须在最短的时间内适应这些非稳态。3、脉冲识别与控制系统 为了改进电火花线切割工艺，我国开发了一种新的脉冲识别系统，如图1所示：图1 研制的电火花线切割脉冲识别控制系统这个系统包括两个部分：第一部分是间隙状态检测装置;第二部分是移动控制部分，在间隙状态检测装置，通过数字电路分压器间隙中的高压可以被变成电压，有三个电压值，它们分别是70、50和10（v），分别在标为Vh、Vm、Vl。通过比较间隙电压信号可以对三种不同的状态进行比较，一个复杂的程序逻辑装置（CPLD）(允许对其结构稍作调整，有4MH的晶体振荡器来计时)。这种装置不但用于产生脉冲控制信号（i.e.P1和P2），也用来区别间隙的状态，个人微机常常用来用户对接、数据的传输和计