变幅值脉冲可控调节电火花-电解复合加工基础研究

Micro-holes are widely used in the aerospace industry, and their fabrication requires high machining speed and accuracy, as well as good surface quality. In this study, attention has been paid to the fabrication of micro-holes in difficult-to-machine superalloys at high speeds and without recast layers. High-low alternate pulse high-speed electrochemical discharge drilling is proposed as a promising hybrid machining method for the fabrication of micro-holes in difficult-to-machine superalloys. In this process, materials can be removed at a high speed using electrical discharge fast drilling, and an electrochemical reaction also can occur to remove the recast layer generated by electrical discharge erosion. Thus, this machining process achieves both a high machining speed and good surface finish. The main studies and contributions in this project are as followings: The material removal mechanism of electrochemical discharge drilling is studied under high-low pulse voltage. The prediction model of recast layer is established, also the formation and removal processes of recast layer are discussed. Besides, the waveform of high-low pulse voltage is design, and the bi-characteristic working fluid is studied. In narrow inter-electrode gap, uniformity of flow field is analyzed under super-high-pressure interior flushing. And the nonmetal is padded the back of the workpiece to completely remove the recast layer especially in the exit of the hole. Also the low temperature is used to improve the machining performances of high-low pulse voltage high-speed electrochemical discharge drilling. Finally, based on these researches about fundamental scientific problems and key technique, micro-holes can be drilled at high speeds and without recast layers.

微小孔结构在航空发动机核心零部件中有着广泛应用，其高效、高质量加工一直是航空制造业的一项重要难题。本项目聚焦于难加工航空材料微小孔高效、精密、无重铸层加工基本问题，提出变幅值脉冲可控调节电火花-电解复合加工方法，利用脉冲电压的高低幅值变换将管电极电火花高速穿孔技术与电解表面光整技术相结合，充分发挥电火花高速穿孔加工效率高和电解加工无重铸层的优势，实现微小孔的高效、无重铸层加工。本项目将深入探索变幅值脉冲作用下电火花熔融与电化学溶解的交替材料蚀除机理，阐明双性工作介质中电火花放电重铸层形成过程并对所形成重铸层厚度进行预测，探究重铸层的小间隙电化学溶解规律等基础理论问题，突破变幅值脉冲电源波形设计及加工模式优化，双性工作介质研究，微小极间间隙超高压内冲液流场均匀性分析，低熔点非金属反衬方法和低温变幅值脉冲电火花-电解复合加工等关键技术，解决难加工材料微小孔制造难题，提升我国航空制造能力

针对航空工业难加工材料的微小孔高效、无重铸层加工难题，本研究提出了一种变振幅脉冲的电火花-电解复合加工方法。具体开展工作如下：.（1）该方法将电解加工(ECM)和电火花加工(EDM)统一为一个加工过程，采用一组变幅脉冲序列，在一个加工周期内，通过高、低电压波形的高频变换，实现加工过程在电火花加工和电解加工的可控变换，研究获得临界转换电压为40V。.（2）针对工具电极击穿工件后横向加工间隙的工作液减少问题，提出了一种非金属反衬电解扩孔方法。非金属反衬层能够增强出口冲液效果，改善出口制孔效果。研究获得优化工艺参数组合为工作液浓度为1.5g/L，加工电压为60V，电化学扩孔时间为12s。.（3）针对管电极高速电化学放电钻孔(TSECDD)中工具电极的磨损问题，本研究从电化学扩孔、气膜和溅射层三个方面研究了TSECDD中刀具电极的磨损机理。通过实验得出，当工作液电导率为10mS/cm，脉冲宽度为15μs，脉冲间隔为38μs，峰值电流为8A时，工具电极磨损最小。.（4）针对狭小间隙产物排出困难问题，提出螺纹管电极正反转匹配内外冲液方式进行电火花(EDM)-电解(ECM)组合加工方法。利用流场仿真证明螺旋管电极提高了间隙最大流速15.6％。实验验证螺旋管电极可以减小孔锥度至0.008，加工效率提高了25％。最终优化参数为冲液压力4 MPa和电极转速460r/min。.（5）低温环境能够降低电极放电点最高温度、提高材料热导率和热交换效率，能够降低电极损耗。通过实验分析获得低温环境能够使电极损耗相对降低38％，锥度减少了22％。