A study of the micro-hole geometry evolution on glass by abrasive air-jet micromachining

Abrasive air-jet (AAJ) micromachining has become an attractive technology for the fabrication of micro-structures on a wide range of engineering materials. However, problems specific to effective mould construction still remain challenging. This paper presents a study on the evolution of micro and blind holes on glass during abrasive air-jet machining. Experiments were conducted under different practical settings of air pressure, particle mass flow rate and drilling time. A 3D laser measurement microscope was used to characterize the machined hole profiles. It was found that there was a clear evolution of the profiles of the hole bottom surfaces. Three types of hole surface contours, i.e., convex, flat, and concave (reverse bell-shaped), were obtained within the operating range used, in which the first two types have rarely been reported in literature. The profile variation took place along with the setting parameters of particle flow rate and air pressure, which indicated that the particles distribution density across the cross section of a cylindrical nozzle also varied with the setting parameters. At a low flow rate, the hole bottom was formed with a convex shape, which might be attributed to the fact that the distribution of particles at the nozzle centre was less than that around the brim. As the particle flow rate increased, the bottom surface evolved from convex to flat or even concave. With a proper setting, AAJ can therefore be used to fabricate a micro hole with a desired bottom surface profile. The variation of abrasive particle distribution in the jet in the AAJ micromachining might be attributed to the flow bounce back and stagnation effects when the jet impacts on a target workpiece.