# Research and Progress on Truing and Sharpening Process of Diamond Abrasive Grinding Tools
## 3 Dressing Method of Diamond Abrasive Grinding Tools
### Sharpening Technology of Diamond Abrasive Grinding Tools
#### 3.2.3 Electric Discharge Machining (EDM) Sharpening Method  
EDM sharpening methods mainly include the EDM dressing method and the electrolytic online dressing method. EDM grinding wheel dressing technology was first proposed by [PERSON] et al. [40]. Figure 11 shows a schematic diagram of the EDM dressing technology. The diamond abrasive grinding tool rotates clockwise and is connected to the positive pole of the power supply, while the tool electrode is connected to the negative pole of the power supply. The discharge medium, such as working fluid, is introduced between the diamond abrasive grinding wheel and the tool electrode to make the pulse voltage pass through, thereby generating a pulsed spark and forming a discharge channel. The phenomenon of electric corrosion eliminates the bond material and achieves the purpose of sharpening the diamond abrasive grinding wheel. [PERSON] et al. [41] conducted experimental research on EDM dressing of the bronze-bonded diamond abrasive grinding wheel using an internal impact arc copper tungsten electrode and found that the surface abrasive grains were prominent, large in number, and high in density.  
Electrolytic in-process dressing technology (ELID) was developed in Japan in the early 1990s for precision mirror grinding of dressing grinding wheels. Figure 12 shows a schematic diagram of the electrolytic in-process dressing technology. The working principle of ELID is to use tool electrodes and diamond abrasive grinding wheels as cathode and anode, while the nozzle sprays special electrolytic grinding fluid between the two poles. Under the action of the power supply, the diamond abrasive grinding wheel is dressed online through the anode dissolution effect. When the bond material is eroded, a layer of dense oxide film is formed on the surface of the grinding wheel, which can slow down the electrolysis speed, prevent excessive electrolysis and avoid excessive wear of the grinding wheel. However, as the oxide film becomes thinner and the conductivity increases, the electrolysis speed of the bond materials is accelerated to realize the cycle of online  
Figure 10: Comparison of grinding wheel surface morphology before and after grinding wheel dressing [34].  
electrolyte sharpening. During the sharpening process, the surface of the grinding wheel can maintain the most ideal morphology and achieve ultra-precision mirror grinding. [PERSON] et al. [42] proposed an ultrasonic-assisted electrolytic process sharpening method, which combined the high-frequency ultrasonic vibration method with the electrolytic method in parallel and carried out comparative experiments on this. It was found that the method could improve the removal rate and machining surface quality and overcome the difficulty of continuous dressing of the fine diamond abrasive grinding wheel in the machining process. [PERSON] et al. [43] found that electrochemical machining could remove the metal bond to make abrasive grains protrude and maintain their cutting ability.  
Figure 13 shows a comparison of the grinding wheel surface before and after EDM dressing [44]. It can be seen from the figure that the grinding wheel surface after the dressing is smooth and flat, the outer contour is clear and has a sharp cutting edge. The research showed that the dressing efficiency of the EDM sharpening method was high--approximately 50\(\sim\)60%. After dressing, the surface of the abrasive grinding tool had chip space, and the abrasive protruding bond height was ideal.  
Figure 11: Schematic diagram of electric spark dressing technology.  
Figure 12: Schematic diagram of electrolytic in-process dressing technology.  
Although the EDM dressing method, the electrolytic in-process dressing method, or other compound EDM dressing methods can better achieve the precision dressing of diamond abrasive grinding tools, their disadvantages, such as high cost, insufficient environmental protection, and easy to form thermal damage, restrict the development of their technology.