利用新型工作液和改进电极提高电火花加工性能的试验

针对电火花小孔加工中加工速度低、电极损耗严重、工件产生斜度和棱角变钝等缺陷,提出了改进小孔工具电极、研制新型工作液以提高电火花加工性能的具体措施,并在电火花机床上进行了试验。通过大量的试验研究得出:在相同的电参数下,与传统工艺相比,采用新型工作液作为介质并配有改进的电极进行电火花小孔加工时,其加工速度大幅提高、电极损耗与工件锥度有所降低,从而提高了电火花加工性能。     

电火花微小孔加工工艺参数的优化研究

由于目前对电火花放电机理认识的有限性而使参数优化成为电火花加工中的难点之一,特别是多项工艺指标要求下的参数优化问题更是缺乏理论指导和具体应用方法。因此,在用正交试验法研究了电火花微小孔加工中放电参数和非放电参数对加工速度、电极损耗和孔径间隙等各单项工艺指标的影响规律的基础上,采用灰色相关性理论,重点解决了多项工艺指标下的参数优化这一难点问题,简化了优化过程,得出了优化的参数组合方案。     

螺旋电极电火花小孔加工排屑仿真和试验

在电火花小孔加工中,排屑困难一直是困扰加工速度的一个重要问题。通过对工具电极改进,用螺旋电极进行电火花小孔加工,使其改变加工过程中间隙流场的流动状态以及电蚀产物的受力,达到增强小孔加工过程中的排屑能力,进而提高加工速度的目的。利用Gambit软件建立仿真模型,应用Fluent对小孔加工过程中排屑进行仿真,对其压力场和速度场进行分析,研究其加工机理。在D703F高速电火花小孔加工机床上进行了试验研究,结果表明螺旋电极电火花小孔加工速度最大提高了20%。     

微细电火花加工倒凹坑效应的研究

对微细电火花圆柱电极损耗出现倒凹坑效应的影响因素进行研究。通常微细电火花电极损耗稳定后,加工端面为半球形,然而在特定的加工条件下,电极端面呈倒凹形状,微孔底端为山状突起,这种异常损耗会破坏电极形状精度而影响加工零件的尺寸精度。通过改变放电能量与放电间隙流体状态等微细电火花加工工艺参数,对比不同实验条件下电极端面形状损耗的变化情况,经检测,出现倒凹坑效应的微孔底端突起为电极材料沉积。实验研究结果表明:电极熔融沉积是电极损耗倒凹坑效应出现的主要原因。     

压电自适应微细电火花加工系统特性分析

针对微细电火花加工过程中排屑困难,极易产生短路、拉弧等非正常加工现象,进而造成微细电火花加工效率低、电极损耗大等特点,基于压电陶瓷的逆压电效应提出了一种新的加工方法--压电自适应微细电火花加工技术,对其加工原理进行了详细阐述,并结合试验对该加工系统的加工特性进行了详细分析.试验证明该技术在加工过程中能够实现放电间隙与放电状态的自适应调节,促进捧屑,可有效控制短路及拉弧现象的出现,进而提高微细电火花的加工稳定性及加工效率,并能实现超低电压下的微细电火花加工.结合实例说明采用压电自适应微细电火花加工技术进行小孔加工的过程中能实现稳定加工,获得较高的加工效率,并且加工的小孔圆度较好,说明该技术在微小孔加工方面具有广阔的应用前景.     

一种新型卧式微电火花机床的设计与实验研究

针对微电极制作的效率问题,提出了一种快速在线微电极加工成形的方法,设计了一种新型卧式微电火花机床。该机床由金刚石砂轮超精密在线电极磨削、线电极电火花在线电极磨削共同完成微米级电极的高效精密制作,该机床组成部分还包括基于CCD的在线光学尺寸检测与测量系统、精密运动与进给系统、纳秒级独立式脉冲放电电源与放电状态检测反馈系统组成。在该机床上进行了微电极制作、微小孔加工以及微电火花铣削等实验,加工出直径为15μm微细轴和直径为50μm微小孔。     

大深径比微小孔快速电火花加工系统研究

电火花加工因具有宏观作用力小、可控性好等优点,被广泛应用于微小孔加工领域,但对于快速加工大深径比微小孔仍存在散热困难、排屑不畅、电极损耗大及加工过程不易控制等技术难点。为此,在分析电火花加工机理及加工特点的基础上,研发了一台用于快速加工大深径比微小孔的电火花机床。该设备通过采用立式布局,应用电极旋转、工件振动的旋振式机构,实现在加工过程中快速散热和排屑;通过采取工业控制计算机搭载数据采集卡和运动控制器的方式,实现了加工过程的检测控制功能一体化。针对电火花加工过程中放电信号严重畸变以及放电状态不稳定导致加工状态难检测的问题,提出了两级模糊逐级映射放电状态检测方法,同时为了实现机床的快速响应和精确控制,设计了双闭环加工控制系统。实验表明,该机床适合于大深径比微小孔的快速加工,且性能稳定,可靠性高。     

分散剂在电火花小孔加工中的作用机理及试验研究

从研究水分散剂的分散机理入手,分析研究了水分散剂对电火花小孔加工的排屑、加工速度和加工质量的影响。通过电火花小孔加工中采用自来水工作液和分散剂工作液的加工效果对比,发现在电火花小孔加工的水基工作液中加入一定比例的分散剂后,不仅使电火花小孔加工的加工速度提高、电极相对损耗降低,而且有效脉冲数增加,二次放电数明显减少,工具电极作用端和被加工孔的锥度变小,加工质量提高。     

复合PAAS工作液与工件半浸液的深小孔电火花加工工艺

现有电火花小孔机床在加工大深径比小孔时存在加工稳定性差、小孔质量差、相对电极损耗率大等技术难点。深入分析D703F电火花小孔加工机床的原理及特点,实验证明使用一定浓度分散剂聚丙烯酸钠(PAAS)作为工作液可大幅提高小孔加工速度、降低相对电极损耗,但随着加工小孔深径比变大,孔内加工环境变差、散热困难,PAAS工作液会产生碳化现象反而阻碍了正常加工。用PAAS工作液和工件半浸液复合的方法,使工件在加工时能良好散热,减缓PAAS工作液的碳化现象,正常发挥分散作用,从而达到高速加工大深径比小孔的目的。     

电火花加工中减小电极损耗的方法和实验研究

制作一种电火花小孔加工用Cu-Ni复合电极,其原理是基于电镀层和基体材料性能的差异,改变电极材料电蚀性能,保证电极端面和侧面的均匀损耗。在D703F型高速电火花小孔加工机床上,用Cu-Ni电极加工1Cr18Ni9Ti不锈钢材料,与常用的普通铜管电极对比。结果表明:在相同的加工条件下,Cu-Ni复合电极的电极损耗明显降低,同时改善了因电极损耗引起的被加工工件的尺寸精度和形状精度。     

钛合金小孔电火花加工有限元仿真研究

为有效地预测钛合金材料电火花小孔加工的体积去除率,利用有限元法建立了单脉冲电火花加工钛合金小孔的数学模型。模型考虑了诸多因素：高斯热源模型、能量分配率、随放电时间变化的放电半径以及熔融潜热。应用生死单元法模拟出去除体积形貌图,然后计算出单脉冲去除体积。采用K1C高速小孔机加工钛合金小孔,记录加工时间,利用称重法得出加工前后重量,从而算出单脉冲体积去除率。验证实验得出,实际加工单脉冲体积去除率和模拟结果的误差小于10%,结果表明,仿真模型可较准确地预测体积去除率,为指导电火花加工钛合金小孔提供了依据。     

Adaptive control for small-hole EDM process with wavelet transform detecting method

Journal of Mechanical Science and Technology - To achieve an efficient small-hole EDM process, an accurate pulse monitoring strategy and a precise control are both required. In order to improve the...     

Detecting discharge status of small-hole EDM based on wavelet transform

Discharge waveforms contain information representing the gap discharge status of an EDM process. The gap discharge status has a great influence on the machining performance including the machining efficiency, workpiece surface integrity, and tool wear rate in EDM processes. In order to identify the gap discharge status effectively, wavelet transform is used to analyze the discharge waveforms. A data acquisition and processing system based on DSP is developed for high-speed wavelet transforms and related calculations. The wavelet transform result shows that each EDM pulse can be classified by judging the approximation coefficients of the wavelet transform result. Experimental results demonstrate that the wavelet transform detection is capable of capturing the primary features of each single discharge pulse, which are usually unable to be discovered by conventional discharge detection methods such as the average gap voltage detection. By analyzing the local extreme values of approximation coefficients, the numbers of different pulses within a detection time period can be identified. The gap discharge status coefficient, which is a function of the numbers of different pulses, is then calculated and used as a feedback signal to an adaptive EDM process controller. A small-hole machining test demonstrates that, with the online adaptive controller based on the wavelet transform method, the machining efficiency and stability are improved significantly.     

混粉电火花加工中粉末对工件表面的影响

对不同加工条件下混粉电火花加工后工件表面的硅含量进行了对比测量。实验结果表明：当峰值电流小于4A时，混粉电火花加工后的工件表面硅含量随峰值电流的增大而急剧减小，而当峰值电流大于4A时，工件表面硅含量随峰值电流的增大而缓慢增加；混粉电火花加工后的工件表面硅含量随脉宽的增大而增加；在其他加工条件相同的情况下，对于相同的单次放电脉冲能量，混粉电火花加工获得的工件表面硅含量随峰值电流变化的关系呈近似二次曲线。引入熵的概念，对产生上述结论的原因进行了分析，并解释了混粉电火花加工可以改善工件表面质量的机理。     

Optimisation of process parameters for multi-performance characteristics in EDM of Al2O3 ceramic composite

The advantages of electrical discharge machining (EDM) in machining of complex ceramic components have promoted research in the area of EDM of ceramic composites. The recent developments in ceramic composites are focused not only on the improvements of strength and toughness, but also on possibilities for difficult-to-machine shapes using EDM. One such EDM-machinable ceramic composite material (Al₂O₃–SiC_w–TiC) has been developed recently and has been selected in the present study to investigate its EDM machinability. Experiments were conducted using discharge current, pulse-on time, duty cycle and gap voltage as typical process parameters. The grey relational analysis was adopted to obtain grey relational grade for EDM process with multiple characteristics namely material removal rate and surface roughness. Analysis of variance was used to study the significance of process variables on grey relational grade which showed discharge current and duty cycle to be most significant parameters. Other than discharge current and duty cycle, pulse-on time and gap voltage have also been found to be significant. To validate the study, confirmation experiment has been carried out at optimum set of parameters and predicted results have been found to be in good agreement with experimental findings.     

Study of unidirectional conductivity on the electrical discharge machining of semiconductor crystals

This paper investigates the unidirectional conductivity of semiconductor crystals machined by electrical discharge machining (EDM) by analyzing the properties of current–voltage (I–V) curves of the equivalent circuit. The simplified equivalent circuit of a semiconductor EDM consists of reverse-biased diodes and linear resistance. The I–V curve has three typical parameters, namely, conduction angle, breakdown angle, and breakdown point. The values of the conduction angle and the breakdown point are determined by the contact area of the reverse-biased diode, and the breakdown angle is determined by the value of linear resistance. Two diodes exist in the model with two metal electric feeders. To increase the current in this model, the diode with larger contact area should be reverse-biased. If the work piece is connected to anode in semiconductor EDM, the diode in the conduction side is reverse-biased and the avalanche voltage is only 42 V. If the work piece is connected to the cathode in semiconductor EDM, then the arc plasma, which is a termination with a small area, becomes reverse-biased. The temperature in the arc plasma side is high, causing the breakdown voltage to be much higher than the theoretical calculation value 88.5 V. As a result, when the work piece is connected to the cathode, spark production is difficult. Holes are bored on the P-type semiconductor crystals by positive and negative polarity, which could prove that machining with positive polarity is suitable for P-type semiconductor crystals during EDM. When the no-load voltage is set to 150 V, the penetration speed by positive polarity can reach 533 μm/min.     

激光微涂敷层的电火花后处理及其加工性能

分析、测量了不同加工条件下的材料去除率、相对电极损耗和电火花加工表面粗糙度,并研究了表面微裂纹和微硬度分布。实验结果表明,不同的材料具有类似的电火花加工性能,材料去除率随脉冲电流的增加而增加,峰值电流比脉冲宽度对表面粗糙度的影响更显著。研究结果对于选择合适参数进行电火花后处理具有重要意义。     

螺旋电极电解扩孔工艺研究

介绍了螺旋电极电解扩孔，该方法兼有小间隙电解加工和脉冲电流电解加工的优点，用于硬质金属材料导孔的加工是一种行之有效的新的工艺方法，文对其中原理。加工实验研究和基本工艺规律作了综述。     

Investigation of the physical mechanisms in rolling bearings during the passage of electric current

With the increasing use of frequency converters as control units for electric motors, bearing failures caused by the passage of electric current through the bearings are more common. This paper discusses the most relevant parasitic current loops in frequency converter‐driven motors that can lead to damage of bearing raceways or deterioration of lubricants. Electrical stray capacitances, which are inevitably present in any electric motor, in combination with the high‐frequency components of the drive voltages, have been identified as the source of electric discharge machining (EDM) currents. Based on an EDM equivalent electric circuit, the passage of electric current through the rolling contact of a bearing is simulated. A set‐up is introduced to initiate EDM processes in bearings under well‐controlled electrical and mechanical conditions. The effect of EDM currents on bearing elements in the presence of different lubricants is studied. Initial results are presented.     

紫铜小孔振动攻丝扭矩的试验研究

紫铜是塑性很大的纯金属材料。小孔攻丝时。常因切屑不折断而将孔阻塞。致使攻丝无法进行。通过在步进电动机同为振源和主运动源的振动攻丝机上。对紫铜的小孔进行振动攻丝试验。找出了振动频率、振型对攻丝时扭矩的影响规律。通过对振动频率和振型进行优化。使振动攻丝成为紫铜小孔攻丝的有效工艺方法。