深窄槽电火花加工顺应式排屑方法研究

EDM (Electrical Discharge Machining) is able to copy the shape of soft tools to hard workpieces, and it is ideal for deep slotting. However, most machines for EDM of deep slots are built with vertical structures. As a result, the debris is apt to gather and concentrate on the bottom of the slot and is very hard to be evacuated. The machining becomes more and more difficult as the depth increases or even fails. This project attempts to find the answers to the following two fundamental questions: (1) What is the law of motion for debris and the bubbles in the narrow, deep and diverse gap flow field? (2) Is it possible to improve the debris evacuation by means of its gravity in deep slot EDM in a more effective way of motion? On the bases of above investigation, this project will focus on the following issues: (1) Direct observation and analysis onto the debris and bubble movement during deep slot EDM with different poses; (2) Modeling and simulation of the distribution and movement of debris and bubbles in the gap flow field under different machining poses to predict and optimize the machining pose adjustment which enhances the debris evacuation more naturally; (3) Validation of proposed "conjugate motion" for adjusting the tool electrode pose and the workpiece pose synchronously to evacuate debris and bubbles naturally in an alternate manner. The ultimate goal of this research is providing a better technical solution to improve the machining performance of deep slot EDM. The outcome of this research will contribute to the improvement of the manufacturing capability of high-value parts of tire molds, die-casting molds, and aircraft engines as well.

电火花加工以其以柔克刚、对工件直接拷贝成形等特点，非常适用于深窄槽加工。然而，目前深窄槽电火花加工所采用的机床多为立式结构布局，使得加工屑极易聚集并沉淀于深窄槽的底部难以排出，随着深度的增加加工变得越来越困难，甚至导致加工失败。本项目尝试寻求如下两个基础问题的答案：（1）加工屑和气泡在狭长且形位多变的极间流场中的运动规律如何？（2）能否以更好的机床运动方式，充分利用重力形成顺其自然的排屑方式？研究工作将聚焦以下方面：（1）对深窄槽加工的加工屑和气泡在不同加工姿态下的运动规律进行观测与分析；（2）对不同加工姿态下加工屑和气泡在极间的分布和运动进行建模和仿真，探究形成顺应式排屑条件的加工姿态调整方式；（3）提出同步调整工具电极和工件姿态的“共轭运动”，实现加工屑和气泡的交替顺应式排出，从而提高深窄槽加工深度和加工效率。研究成果将有助于提升轮胎模具、压铸模、飞机发动机等高端零部件的制造水平。

本项目针对深窄槽电火花加工中气泡和加工屑难以排出、正常放电率随加工过程逐渐降低导致加工效率低的问题，提出并验证了有利于提升深窄槽电火花加工效率的变化姿态辅助运动模式。主要工作包括：（1）搭建可变姿态电火花加工机电系统，实现无需暂停即可调整进给方向的电火花加工；（2）使用激光粒度分析仪和光学显微镜观察并分析了深窄槽电火花加工产生的加工屑颗粒，使用高速摄像机观察了加工屑和气泡在间隙中的运动，总结固定姿态深窄槽电火花加工产生的加工屑和气泡的尺寸和运动规律；（3）进行不同固定姿态下的深窄槽电火花加工实验，建立固定姿态下的深窄槽电火花加工效率模型；（4）对固定和变化姿态下的深窄槽电火花加工的极间流场进行建模和仿真，初步探索了改变加工姿态的旋转角速度对气泡和加工屑排出时间的影响规律；（5）通过变化姿态下的深窄槽电火花加工实验，研究旋转角度范围、旋转起始深度和旋转角速度对深窄槽加工效率和放电状态的影响，总结了提升加工效率的加工姿态调节策略。本项目获得的重要结果包括：（1）放电加工过程中气泡对加工屑的排出起主要作用；大部分加工屑聚集在气泡边缘，随气泡运动排出工件侧面间隙；部分加工屑在跟随气泡运动过程中，在重力的作用下向下沉降；（2）在固定姿态下从0至5 mm深度的加工过程中，加工效率曲线会出现1~2个明显的转折点，其主要原因是气泡在狭长的侧面间隙中合并导致气泡运动速度降低，使得加工屑排出困难甚至无法排出、逐渐在底部放电间隙中聚积，进而导致正常放电率下降；（3）在-180°~0°内以尽可能高的速度从加工一开始就旋转，可以获得较好的放电状态和加工效率；（4）旋转角速度为40°/s时的平均加工用时可比固定姿态横向进给的平均加工用时缩短13.02%、比传统的竖直向下进给的平均加工用时缩短19.04%。本项目的研究结果可为轮胎模具和飞机发动机零部件中所包含的深窄槽类难加工结构提供新的电火花加工方案设计思路。