Influence of kinematic operating parameters on kerf geometry in abrasive waterjet machining of silicon carbide ceramics

Silicon carbide (SiC) is extensively used for manufacturing of highly engineered parts due to its high hardness, low coefficient of friction, wear resistance and high decomposition temperature. However, generating 3D surfaces (e.g. pockets) in such structural ceramics by conventional machining is a difficult task. In this context, abrasive waterjet (AWJ) machining, with its capability to cut any material with low specific cutting forces, seems to be the "ideal" processing technique for such materials; nevertheless machining 3D shapes by AWJ milling is still in its infancy. 3D shapes can be generated by "enveloping" them with successions of jet footprints (kerf geometries) generated by varying the process operating parameters. To enable this, the present work investigates the influence of key kinematic operating parameters (i.e. α-jet impingement angle and v-jet feed rate) on the kerf geometry and its dimensional characteristics. Furthermore, the kerf generation mechanism under multi-pass jet erosion was analysed to get control over erosion depth in multi-pass machining. It was found that by varying α (90°-40°), the symmetric/asymmetric kerf geometry is intimately dependent on the variation of standoff distance (SOD), abrasive particle velocity distributions and their local impact angles accounted across the jet footprint. Variation in v influences the exposure time of material to jet and enhances the erosion capability of abrasives impacting at shallow angle that results in different erosion rates along the kerf profile; this combined effect leads to departure of kerf geometry from simple cosine profile approximation to more elliptical type with the decrease of feed speed. Further, at lower jet feed rates, the depth of erosion increased and the low energy abrasive particles along trailing edge of jet plume get enough time to erode the material that results in variation of slope of kerf walls and hence, overall geometry. Based on these observations, the multi-pass trials showed that the successive passes have to account for both the local impact angles of abrasive particles as well as the actual SOD (SOD+initial kerf depth). In this way, by understanding the influence of key kinematic operating parameters (α and v) on the kerf geometry and its dimensional characteristics, the paper establishes a good basis for developing strategies for controlled 3D AWJ machining of complex shapes.