Abstract:

On the basis of formation mechanism of plasma channel in WEDM, a novel heat conduction model with a circular truncated cone shape was put forward for the first time by studying the velocity difference of electrons and ions in plasma channel. Based on this heat conduction model a finite element analysis was conducted considering the typical machining conditions of aeronautical material-Inconel 718 in WEDM to research its the machining mechanism. The influences of discharge energy on maximum temperature of plasma channel and depth of discharge crater were studied systematically. A verification experiment was carried out,which firstly employed acoustic emission testing technology to monitor the machined surface roughness. It shows that the simulation results are in good agreement with measured Rt values of surface roughness. The analysis results of acoustic emission signals collected during the machining process of WEDM reveal that the intensity of acoustic emission signals get stronger with the increase of discharge energy and get weaker as the changing rate of maximum temperature of discharge channel becomes slower. A regression analysis of value of surface roughness and root-mean-square (RMS) value yields a mathematical prediction model with high precision, the error is less than 4.40%.

Key words: Inconel 718, wire electrical discharge machining(WEDM), truncated cone-shaped thermal conduction model, finite element, acoustic emission, regression analysis

摘要：

基于放电通道中等离子体的形成机理，根据慢走丝线切割在短脉冲放电加工时放电通道中电子流与离子流散射速度的差异，提出了圆台形热传导模型。采用基于圆台形热传导模型的有限单元法对航空材料Inconel 718的典型工况进行了仿真计算，系统地分析了放电能量对放电通道温度以及放电蚀坑深度的影响规律，并采用声发射检测技术在线监测慢走丝线切割的加工表面粗糙度。通过仿真结果与试验测得工件表面粗糙度Rt值的对比，再结合试验测得的声发射信号波形图特征及声发射信号均方根值发现：仿真计算得到的放电蚀坑深度与表面粗糙度Rt值吻合较好；声发射信号的强度随着放电能量的增加而增强，声发射信号强度随着放电温度变化速率的变小而减弱。最后回归分析得到材料表面粗糙度与声发射信号均方根值的数学预测模型，预测结果与测得的表面粗糙度误差仅为4.4%。

关键词: Inconel 718, 线切割, 圆台形热传导模型, 有限元, 声发射, 回归分析