The Theory Of Small Hole EDM Drilling And Experimental Study Of Cu Electrode Coated By Chromium

During the processing of Electrical discharge machining,the metal is melted by the instantaneous heat generated when the discharge point discharging.Both tool electrode and workpiece are subject to the high temperature and hitted by ions and electronic,they are both lossed.There are many disadvantages during the machining processing of Small hole EDM drilling,such as the serious electrode loss and the slow material remove rate. The speed of processing declined sharply and the machining even stop with the machining depth increasing, therefore the machining depth has limits. Because of the loss of electrode, the corner wear resulting taper shape.as result,the choice of the tool electrode materials is very important.The copper electrode is used commonly in the machining processing of small hole EDM drilling.The copper electrode with good electrical conductivity,but because of its low melting point,in the processing its loss is serious.because of the edge of electrod repeated loss, the Sharp edge rounded. Not only the processing efficiency is reduces,also the machining accuracy is lower. Compared with the copper material, chromium has a relatively high melting point, while the chromium has a high specific heat capacity, chromium increases the same temperature requires more heat. In the same heat conditions, the loss of chromium electrode is less than the loss of the copper electrode. Considering thermal performance of the chromium, chromium is very suitable used as tool electrode materials. However, due to its conductivity is not enough good, as a coating, coated on the surface of copper is a good choice.This composite electrode not only has the strength and electrical conductivity of copper, but also has excellent thermal properties of chromium.After the brush electroplating processed, the chromium is coated on the outer wall of copper tube electrode. The hole processing is tested on the D703F spark high-speed small hole machine tool of the Finishing Processing Laboratory of Taiyuan University of Technology. By changing the peak current and pulse width, to get the change of processing speede and electrode wear rate with the change of peak current and pulse width during the machining processing of small hole EDM drilling.Experimental results indicated that comparing the Cu electrode, adopting Cu-Cr composite electrode for small hole EDM drilling can remarkably improve the processing speed,reducing the taper and electrode loss.The main research contents:(1) Explore the mechanism of spark erosion,analysis the impact of composite electrode on the discharge gap, discharge channel, electrical corrosion pits, processing speed and electrode wear.(2) Modeling and simulation of the electric field of the discharge gap, obtain the distribution of electric field between the electrode and workpiece, analysis the impact of electric field of the discharge gap on excluding of electric erosion products.(3) Modeling and Simulation of the Flow Field of EDM, analysis the impact of processing depth on excluding speed of electric erosion products.(4) Based on the above conclusions, the experiment was carried adopting the Cu-Cr composite electrode. Experimental results verify the impact of the electrical parameters and the coating on processing speed, electrode wear and machining accuracy on the EDM small hole processing.