Abrasive waterjet cutting of a titanium alloy: The influence of abrasive morphology and mechanical properties on workpiece grit embedment and cut quality

Abrasive waterjet cutting of material involves the impingement of a high velocity jet of water with entrained abrasive particles (commonly 80 mesh garnet) onto the material to be cut. Embedment of abrasive is known to occur both on the cut-face and on the surface perpendicular to the cut-face where (due to jet divergence) the jet has impinged but not cut through; this grit embedment is a known disadvantage of the process. In this paper, the cut quality and abrasive embedment following waterjet cutting of a commonly used titanium alloy, Ti6Al4V with 80 mesh garnet from five different sources (differing significantly in their hardness, crushing strength and morphology) were examined and evaluated. The cut-face itself was examined to establish the presence or absence of sub-surface embedded abrasive; in addition, the top surface of the plate close to the cut where particles outside the main core of the jet may have impinged was also examined. Embedment levels, surface waviness and roughness and the mechanisms of abrasive–surface interactions were evaluated through a combination of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and profilometry. It was found that despite the differences in abrasive characteristics, no significant differences in cut quality or abrasive embedment was seen. It was shown that the forces on individual particles during impact can be estimated to be orders of magnitude greater than their crushing load. As such, it is proposed that the majority of abrasive particles will fracture in abrasive waterjetting, and thus any differences in the original abrasive particle morphologies do not dominate behaviour since it is the morphology of the fragments of these fractured particles which control embedment and cut quality.