# Experimental Study of Tool Wear in Electrochemical Discharge Machining
## 1 Introduction  
Electrochemical discharge machining (ECDM) is an emerging special processing technology, which has the advantages of high efficiency, good flexibility and low cost [1; 2; 3; 4]. It can be used to handle non-conductive hard and brittle materials with fine structure [5; 6]. With the development of micro-electromechanical system (MEMS) and microfluidics technologies, higher technical requirements are raised for the microfabrication of non-conductive materials, such as glass, ceramics, and carbon fiber-reinforced polymer (CFRP) material. ECDM has rapidly developed and been studied as an important processing method [7; 8; 9]. Especially for the micro-machining of hard and brittle material with complicated 3D structures, many studies have been conducted to improve the machining precision, such as changing the motion control approach [10], parameter optimization using the response surface method [11] and building the tool wear simulation model [12]. In the ECDM drilling test for CFRP, the factors which affect the machining precision are from various aspects, including tool wear, the stability of gas film, the electrolyte components and the CFRP machining process. The machining process of ECDM is as shown in Figure 1. The tool electrode (cathode) and the auxiliary anode are immersed in the electrolyte, respectively, and then respectively connected to the negative and positive anodes of the pulse power supply. When a voltage is applied, the electrochemical reaction occurs, and hydrogen and oxygen are generated on the surface of cathode and auxiliary anode. The electrochemical reaction intensifies with the increase in voltage. Part of the hydrogen escapes fromthe surface of the cathode, and part is fused between bubbles. When the critical voltage is reached, the generation rate of hydrogen bubble equals to its escape rate, and an insulating gas film is formed on the cathode surface via fusion. As a result, the cathode is completely separated from the electrolyte, and a potential difference is generated. Under the effect of potential difference, electric discharge occurs, and sparks are generated. The workpiece is eroded by high-temperature melting. But this process is often accompanied with the tool wear, On the one hand, the tool wear has causes the change of tool length, and the immersed depth of the cathode also changes accordingly, which results in the insufficient feed of the cathode, and the machining precision cannot be guaranteed. On the other hand, the tool wear has also led to the deterioration in the stability of the gas film, and as a result, the gas film formation time and average spark discharge current present significant fluctuations, while the fluctuation in the spark output energy affects the machining stability, which greatly affects the stability and machining accuracy [13]. Therefore, it is especially necessary to study the tool wear of ECDM. In 1968, [PERSON] and [PERSON] [14] applied the spark discharge generated in the electrolysis process in the hole machining of non-conductive glass material for the first time. Since then, many studies on the ECDM process have been conducted. [PERSON] et al. [15] observed the loss and machining over-cutting of tungsten carbide, tungsten and 304 stainless steel cylindrical cathode materials with the diameter of 200 \(\upmu\)m in the 5 mol/L KOH electrolyte and under the speed of 500 rpm and a voltage of 28-46 V. They pointed out that the corner of the tool electrode has the highest current density, which increases in wear near the corner. The degree of wear is related to the melting point and thermal conductivity of the cathode material. By comparing the performances of three materials, it is found that when the tungsten carbide material is used as the cathode, it results in smaller overcutting and lower tool wear. [PERSON] and [PERSON] [16] studied the loss of brass, steel and tungsten carbide cathodes with different melting points at a high voltage, and used the tungsten carbide cathode for the micro-machining of ceramics.