Proceedings of the Seventeenth CIRP Conference on Electro Physical and Chemical Machining (ISEM) vol:6 pages:633-638
Seventeenth CIRP Conference on Electro Physical and Chemical Machining (ISEM) edition:17 location:Leuven, Belgium date:9-12 April 2013
In Electrolytic In-Process Dressing (ELID) grinding the metallic wheels are kept sharp through an electrolytic passivation process. The outer part of the iron bonding is dissolved to form a passivating layer of oxides and hydroxides. This lowers the holding force of abrasives which are dulled during grinding and fresh abrasives are constantly protruding fr m the wheel. This paper presents an electrical equivalent model of the electrolytic dressing process and explains how the total resistance of a grinding wheel changes during electrolytic dressing. At the beginning of the electrolytic dressing process, the interfaces between the fresh metallic wheel, the electrolyte and the external electrode are characterized by a high capacitance due to the presence of a double layer. Once the wheel is covered with a small passivating layer the capacitance is much lower because the charge cannot move freely in t he oxides and hydroxides. Subsequently, as dressing continues, the growth of the layer leads to an increase in electrical resistance of the system. The total resistance is the key parameter to monitor the layer growth. Experimental results show the influence of power supply settings on the passivation speed of the grinding wheel. During the initial dressing minutes the resistances are increasing in a random way, independently of the electric power. The growth of the initial oxide layer depends on several random factors, such as the local a mount of diamonds in the metal bonding and the actual gap width. Only after several minutes of dressing it becomes clear that the most powerful settings lead to the fastest growth in resistance, according to Faraday's law of electrolysis. The effects of the grinding speed and the abrasive grit size of the wheel are also shown in this paper. In general, lower wheel speeds lead to faster passivation and are therefore preferable during pre-dressing. Furthermore, the layer grows more rap idly in the case of big abrasives. Final experiments indicate that a commercially available electrolyte is not passivating the wheel at all. The substances of the used electrolyte are crucial to obtain a proper passivation.