Wear Mechanism of The Si_3N_4 Ceramic Tools in Cutting Cast Iron

The silicon nitride ceramic Si_3N_4 is superior to the conventional oxide ceramic Al_2O_3 in several characteristics. It has greater shock resistance, the low rate of expansion at high temperature, and somewhat superior thermal conductivity. The Si_3N_4 ceramic tools used for this experiment were made by sintering method. Tool wear mechanism of Si_3N_4 ceramic tools in cutting has been studied with regard to ceramic grades and cutting edge failures. Ceramic tool's properties were varied by changing the chemical compositions and the sintering methods. Machining tests were conducted on a turning machine and a milling machine by cutting FC25 cast iron. Cutting speed was varied from 100m/min to about 1000m/min and feed rate was used at 0.2 or 0.3mm/tooth whereas depth of cut was used constantly on these tests. After test runs, the following conclusions were obtained : (1) There is a great deal of influence in tool toughness, when the tools are intertwined with the rod type of the silicon nitride particles. (2) It is found that the cutting ability of the tool relate with hradness and fracture toughness. This type of tools minimizes the fall off of the silicon nitride particles on the cutting edge and reduces wears on the flank face.