微小孔冰层反衬电火花—电解复合加工方法及试验研究

发布时间：2018-03-19 18:20

本文选题：冰层反衬　切入点：电火花-电解复合加工　出处：《南京航空航天大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着航空工业的发展,航空发动机关键零部件上出现了大量微小孔结构,这些孔的孔径一般在0.3~2mm之间,由于航空发动机关键零部件的材料一般为高强度、高硬度的难加工材料,如高温合金、钛合金、金属间化合物等,而且这些微小孔还要求加工表面无再铸层、无微裂纹、无热影响区等,所以传统的加工方法已经很难满足要求。电火花-电解复合穿孔加工结合了电火花加工与电解加工各自的优势,既能通过电火花快速蚀除材料保证较高的穿孔效率,又能通过电解溶解作用去除电火花加工产生的再铸层、热影响区等缺陷,有望成为无再铸层气膜冷却孔有效的加工方法。但这种方法在小孔穿透后工作液会流失,造成加工间隙中缺液,出口处孔壁电解不充分,可能会有再铸层残留。因此需要找到一种反衬材料填充在工件背面,既能在小孔穿透后提供充足稳定的反向冲液,又能方便的填充到诸如涡轮叶片这种结构复杂腔体中,而且要求去除方便、经济、环保等。本文提出了冰层反衬层电火花-电解复合穿孔加工方法。即在工件背面填充冰层,利用液氮制冷,保持加工过程中反衬冰层一直存在,理论上反衬冰层在小孔穿透后可以提供充足稳定的反向冲液,同时管电极中的常温高压工作液会将冰层局部融化,不会对管电极继续进给造成阻碍,可以保证管电极对孔壁的电解作用持续稳定的进行。另一方面,反衬冰层也降低了加工区域的温度,尤其降低了工件的温度。本文搭建了冰层反衬电火花-电解复合穿孔试验平台,研究了低温环境对复合穿孔加工过程中的影响,以及反衬冰层对小孔复合加工质量的影响。论文主要研究内容如下:(1)提出了冰层反衬电火花-电解复合穿孔加工新方法,并详细阐述其加工原理,从理论上分析了反衬冰层对穿孔加工工作液流场的影响。设计并搭建冰层反衬电火花-电解复合加工试验平台,通过监测加工过程中工具电极与工件电极之间的电压、电流波形,验证反衬冰层在小孔穿透后的反向冲液效果。通过观察加工后反衬冰层的融化情况,研究了不同底部停顿时间对冰层融化程度的影响。进行工件在常温和低温环境下电火花加工产生再铸层厚度对比试验,研究工件温度对电火花加工产生再铸层的影响。(2)进行工件在常温与低温环境下电火花-电解复合加工对比试验,借助加工过程中电压、电流波形以及温度等参数的监测,分析工件在低温状态下电解加工过程的电压、电流波形与常温环境下的异同点。对比常温和低温两种加工环境下复合加工效率,从加工过程中电解、短路、放电所占的时间比例以及单个脉冲蚀除量的角度,分析了工件在低温状态下复合加工材料去除率略微降低的原因。研究了工件在常温和低温环境下不同工作液浓度对工具电极损耗的影响,得到了工件在低温环境下加工可以减小工具电极相对损耗的结论。(3)进行冰层反衬电火花-电解复合穿孔加工试验。研究了工作液浓度、冰层溶液浓度以及底部停顿时间对小孔出入口孔径、孔形、锥度以及孔壁再铸层去除效果的影响。最后进行45°斜小孔复合加工试验,分析了无反衬、石蜡反衬以及冰层反衬三种情况下,斜小孔穿透后工作液流场的不同变化,研究了冰层反衬复合加工对斜小孔出入口孔形的影响,并对斜小孔穿透后孔壁及出入口工件表面进行了电场仿真,从电流密度的分布解释了斜小孔出入口产生倒圆现象的原因。最后研究了底部停顿时间对斜小孔孔壁再铸层去除效果的影响。
[Abstract]:With the development of aviation industry, the emergence of a large number of micro pore structure of key parts of the aeroengine, the aperture hole is generally between 0.3~2mm, as the key parts of the aeroengine materials for high strength, high hardness of hard processing materials, such as high-temperature alloy, titanium alloy, intermetallic compounds, and these tiny holes also required the surface no recast layer, no cracks, no heat affected zone, so the traditional processing method has been difficult to meet the requirements of electrical discharge electrolysis combined perforation process combines the advantages of EDM and ECM respectively, both by electric spark rapid erosion material to ensure high efficiency and perforation. Produce EDM recast layer removal by electrolytic dissolution, defects in the heat affected zone, is expected to become the processing without re cast layer of film cooling holes effectively. But this method in wear Through working fluid will be lost, resulting in lack of liquid in the machining gap, the outlet hole wall of electrolysis is not sufficient, there may be recast layer residues. So we need to find a contrast material filled in the back of the workpiece, which can penetrate the holes in the reverse to provide adequate and stable flushing, and convenient filling such as turbine this leaves the complex structure of the cavity, and easy to remove, economy, environmental protection and so on. This paper proposes the ice layer contrast electrical discharge electrolysis combined perforation processing method. The ice is filled in the back of the workpiece, using liquid nitrogen refrigeration, keep in the process of contrasting ice has always existed, contrast theory can provide adequate and stable ice reverse flushing in keyhole penetration, while tube at room temperature high pressure working fluid in the electrode will not hinder the local ice melt, to continue to feed tube electrode, can ensure continuous electrolysis tube electrode on the hole wall Stable. On the other hand, making ice also reduces the temperature of the cutting area, especially reduce the temperature of the workpiece. This paper built the ice foil electrical discharge electrolysis combined perforation test platform, to study the influence of composite perforation in the process of low temperature environment, and the influence of compound contrast of ice. The machining quality of the hole the main research contents are as follows: (1) proposed ice contrast electrical discharge electrolysis combined perforation method processing, and describes the working principle, and analyzes the influence of perforation fluid ice contrast processing flow. To design and build ice contrast EDM combined electrochemical machining test platform, through the voltage between the tool the monitoring process of the electrode and the workpiece electrode current waveform, verify the contrast effect in reverse flushing ice after penetrating holes. By melting ice processing after contrast observation. Study on the influence of different conditions, the bottom of the ice melting degree of the pause time. The workpiece is recast layer thickness contrast test under normal and low temperature environment of EDM, workpiece temperature recast layer have influence on EDM. (2) of the workpiece at room temperature and low temperature environment for electrical discharge electrolysis composite processing contrast test, with the help of voltage in the process of monitoring parameters of current waveform and the temperature of the workpiece in the machining process analysis of voltage in the low temperature and normal temperature environment, current waveform similarities and differences. Compared to normal temperature and low temperature environment of two kinds of processing compound processing efficiency, from the process of electrolysis, short circuit ratio time for a single pulse discharge and the erosion angle, analyzes the causes of the workpiece in the composite materials processing under low temperature removal rate decreased slightly. The workpiece at normal temperature and low temperature ring Effect of different concentration under the environment of tool electrode, the workpiece in a low temperature environment can reduce the tool electrode relative wear conclusions. (3) of the ice foil electrical discharge electrolysis combined machining experiment concentration, solution concentration and the ice at the bottom of the hole entrance aperture pause time the hole shape, taper, and hole wall recast layer influence the removal efficiency. Finally, 45 degree oblique hole machining test, analysis of the contrast, contrast and contrast of three kinds of paraffin ice under the condition of different changes in the inclined hole after penetrating fluid flow field, on the contrast effect of ice composite processing entrance hole on the inclined hole, and the inclined hole after penetrating the hole wall and entrance surface electric field simulation, from the distribution of the current density explains why the inclined hole round phenomenon. In the end of the entrance The effect of the bottom pause time on the removal efficiency of the recasting layer of the slanted hole wall.

【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG66

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