Experimental study of subsurface damage and material removal mechanisms in abrasive waterjet milling process of aluminum oxide ceramic

Machining of hard and brittle materials such as aluminum oxide ceramic by conventional machining processes is very difficult due to the high hardness and wear resistance of this material, subsurface damages, poor surface quality and severe wear of the cutting tool. In this regard, abrasive water jet machining is widely used for machining of hard and brittle materials due to its excellent properties such as lack of thermal stresses, low machining forces, lack of mechanical contact between the specimen and cutting tool and compatibility with environment. Hence, in this research, abrasive water jet milling of aluminum oxide ceramic was experimentally investigated. In this respect, the influence of input parameters such as water jet pressure, feed rate, abrasive particles weight fraction and nozzle gap was evaluated on subsurface damages and material removal mechanisms (i.e. micro-cutting and micro-fracture). The obtained results indicate that the dominant material removal mechanism for aluminum oxide is micro-fracture, in which, material removal takes place by formation of micro-cracks and micro-craters beneath the abrasives indentation depth. Also, the results demonstrate that the probability of subsurface damages formation increases by increasing the jet pressure, decreasing feed rate, decreasing the nozzle gap and increasing the abrasives weight fraction. The statistical analysis of variance (ANOVA) revealed that the most significant parameters affecting subsurface damage depth are water jet pressure, weight fraction of abrasive particles, feed rate and nozzle gap, respectively. The contribution percentage of these parameters is 54.37%, 31.15%, 12.91% and 1.57%, respectively.