Experimental Study On High Efficiency And Low Wear Edm Process For Seal Slots With High Aspect Ratio

In aerospace and mold industries,there are many seal slots with high aspect ratio which is difficult to process through traditional processing methods constrained by the limitation of material hardness and tool strength,while EDM become the most effective processing method due to the ability of machine any conductive material regardless of hardness.Graphite is becoming the first choice of electrode material for its advantages of high temperature resistance,low electrode wear and easy forming.However,the etching products cannot be effectively ejected in EDM seal slot machining and it is easy to cause short circuit,arc,concentrated carbon deposition and other adverse phenomenon,which not only leads to the reduction of processing efficiency,but also increases electrode loss and lower forming accuracy.This paper is mainly devoted to the study on the processing technology and low electrode wear in EDM seal slots machining with graphite electrode.Firstly,Single factor experiment was designed and performed to study the basic technology law and analyzed the reasons.Archimedes principle was adopted to measure the tiny change of electrodes volume in the experiment,thus avoiding the quality error caused by the oil absorbed by graphite.The influences of processing parameter including electrode material,processing polarity,pulse duration,peak current,duty cycle,reference voltage,discharge area and tool lifting on processing efficiency,electrode wear and surface roughness were studied.Then the reasonable and feasible parameter ranges of each factor were defined and the phenomenon of processing instability caused by carbon deposition concentrated at corners was analyzed and explained.According to the single factor experimental results,main influencing factors and representative horizontals were selected to design orthogonal experiments.Based on the analysis of the basic principle of support vector regression,a model with support vector machine regression about efficiency and electrode wear ratio in EDM seal slots machining with graphite electrode was established by taking orthogonal experiment results as training samples and the validation experiment proved the effectiveness of the model.Designing the non-dominated sorting genetic algorithm with elitist and taking the model as the fitness function,the multi-objective optimization solution was carried out by using the genetic algorithm obtaining the Perato optimal solution of EDM seal slots machining with graphite electrode.The negative electrode wear phenomenon appearing in the single experiments was further studied.Through the main effect analysis,the order of influence of each factor on electrode wear ratio and processing efficiency is determined and the interaction among the influential factors was further analyzed.A comprehensive experimental exploration about pulse duration and peak current was carried out to investigate the excessive process of electrode wear and the parameter ranges of different wear degrees were defined further.The character of carbon deposition layer on graphite electrode such as microstructure,tissue composition and hardness was analyzed and the formation of carbon layer is considered to be the main reason of low wear.The characteristics of processing speed of EDM seal slots machining with graphite electrode was analyzed and an exponential model of processing speed is established.According to the influence of duty ratio and tool lifting on processing speed,a variable parameter processing strategy was formulated to improve processing efficiency.