Erosion modeling in abrasive slurry jet micro-machining of brittle materials

Abrasive slurry jet micro-machining (ASJM) uses a relatively low pressure jet of abrasive slurry to machine features such as holes and channels. This study investigated the effect of alumina particle kinetic energy and jet impact angle on the roughness and erosion rate of channels machined in borosilicate glass using ASJM. A computational fluid dynamics model was used to calculate the local particle impact velocities and angles, and thus the kinetic energies of particles striking the surface. Consistent with earlier work on air-driven abrasive jets, the roughness and erosion rate of the channels machined at perpendicular incidence depended only on the kinetic energy of particles above the apparent cracking threshold of the glass target. Slurry jets of higher kinetic energy produced rougher channels and higher erosion rates since the impacting particles caused larger lateral cracks to form, and thus removed larger chips. The measured erosion rate at various impact angles, and the observed damage due to individual alumina particle impacts, indicated that the dominant mode of material removal was brittle erosion. Two similar analytical brittle-erosion models derived for air-driven abrasive jet micromachining (AJM), were found to predict reasonably well the roughness and the erosion rate of ASJM channels, despite the large differences in the fluid media, flow patterns, and particle trajectories in AJM and ASJM. A key requirement was that the average particle kinetic energy was calculated using the CFD model. With only minor modifications, the models predicted the channel erosion rate and centreline roughness with average errors of 12% and 17%, respectively. In addition, a numerical simulation, previously developed to predict the erosion in AJM of brittle materials, was used to predict the centreline average roughness, shape parameters and depth of ASJM channels for various machining conditions.