冷电极电火花加工温度控制及蚀除机理研究

发布时间：2018-06-16 11:00

本文选题：电火花加工 + 温度控制　；参考：《南京航空航天大学》2017年硕士论文

【摘要】：电火花加工是一种不存在宏观力的特种加工方法,可以加工各种难加工材料、复杂形状零件和有特殊要求的零件。但是电火花加工也存在电极损耗大、加工过程不稳定、仿形精度低和加工表面质量差等缺点,尤其是加工比强度高、热导率低的难加工材料如钛合金时,缺点更明显。针对常规电火花加工过程中存在的问题,本文提出一种在工具电极上加装强制散热系统的冷电极温度控制加工方法,通过两极间不对称散热控制电极处于较低温度,使极间快速消电离,降低电弧放电概率,达到改善加工稳定性,降低电极损耗,提高仿形精度和表面加工质量的目的。本文主要研究内容如下:(1)设计冷电极结构和温度控制系统,设计搭建单脉冲放电试验平台。对热管型冷电极和半导体制冷片型冷电极装置进行性能分析,最终选择半导体制冷片型冷电极组成电极冷却装置。设计了电极温度控制系统,能够对电极温度进行有效控制。设计搭建了基于放电电流检测的单脉冲试验平台,为研究冷电极电火花加工材料蚀除机理奠定了良好的基础。(2)分析了电极温度对极间放电特性的影响。从理论上分析了电极温度对放电通道半径、电蚀坑半径和极间电子发射电流密度的影响,解释了冷电极对放电通道的压缩作用和冷电极低损耗和小间隙的特性。(3)仿真分析电极温度对极间温度场的影响,并通过单脉冲试验验证仿真结果。建立了电火花极间放电模型,利用ANSYS软件对不同电极温度下电火花放电极间温度场进行有限元分析。分析了电极温度对电火花加工材料蚀除的影响,仿真结果验证了冷电极低损耗特性。利用单脉冲试验平台进行不同电极温度下单脉冲放电试验,研究了电极温度对电蚀坑形貌的影响。(4)研究了电极温度对放电间隙的影响。利用单脉冲装置对极间放电间隙进行检测,并通过冷电极与常规电极成型加工对比试验,表明了降低电极温度可以使放电间隙变小,进而提高仿形精度。(5)对冷电极电火花加工的工艺性能进行对比分析。进行了冷电极与常规电极加工钛合金工艺性能对比试验,对放电波形、电极损耗、材料去除率、加工表面粗糙度和表面裂纹进行了对比分析,验证了冷电极加工具有电极损耗较低、加工稳定性较好、材料去除率较高和表面加工质量较好的特性。通过冷电极加工航空螺旋锥齿轮试验,验证了冷电极具有较高精度的复杂曲面加工能力。
[Abstract]:EDM is a kind of special machining method without macroscopic force. It can process all kinds of difficult materials, complicated shape parts and parts with special requirements. However, EDM also has some disadvantages, such as large electrode loss, unstable machining process, low copying accuracy and poor surface quality, especially when machining materials with high specific strength and low thermal conductivity, such as titanium alloy. In view of the problems existing in conventional EDM, this paper presents a method of controlling the temperature of cold electrode by adding a forced cooling system to the tool electrode, which is controlled by asymmetric heat dissipation between the two poles at a lower temperature. It can quickly deionization between electrodes, reduce the probability of arc discharge, improve the stability of machining, reduce the loss of electrode, and improve the copying accuracy and surface machining quality. The main contents of this paper are as follows: (1) the cold electrode structure and temperature control system are designed and the monopulse discharge test platform is built. The performance of heat tube cold electrode and semiconductor cooling plate cold electrode device is analyzed. Finally, the semiconductor refrigeration sheet cold electrode type is selected to make up the electrode cooling device. The electrode temperature control system is designed, which can effectively control the electrode temperature. A monopulse test platform based on the detection of discharge current is designed and built, which lays a good foundation for studying the erosion mechanism of cold electrode EDM materials. (2) the influence of electrode temperature on the discharge characteristics between electrodes is analyzed. The effects of electrode temperature on discharge channel radius, electroetching pit radius and electron emission current density between electrodes are analyzed theoretically. The effect of cold electrode on discharge channel compression and the characteristics of cold electrode with low loss and small gap are explained. The effect of electrode temperature on the temperature field between electrodes is simulated and the simulation results are verified by monopulse test. The model of discharge between electrodes is established and the finite element analysis of the temperature field between electrodes at different electrode temperature is carried out by ANSYS software. The effect of electrode temperature on EDM material erosion is analyzed. The simulation results verify the low loss characteristics of cold electrode. The influence of electrode temperature on the morphology of electroetching pit was studied by using single pulse test platform. The effect of electrode temperature on discharge gap was studied. By using monopulse device to detect the discharge gap between electrodes, and by comparing the cold electrode with the conventional electrode, it is shown that the discharge gap can be reduced by lowering the electrode temperature. Furthermore, the process performance of cold electrode EDM is compared and analyzed by improving the copying accuracy. The technological properties of titanium alloy processed by cold electrode and conventional electrode were compared and analyzed. The discharge waveform, electrode loss, material removal rate, surface roughness and surface crack were compared and analyzed. The results show that cold electrode machining has lower electrode loss, better processing stability, higher material removal rate and better surface processing quality. The experiments of cold electrode machining of spiral bevel gear show that the cold electrode has high precision and complex curved surface machining ability.
【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】：TG661

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