Abrasive jet micromachining of acrylic and polycarbonate polymers at oblique angles of attack

Masked and unmasked micro-channels were machined in polymethylmethacrylate (PMMA) using an abrasive jet of 25 μm Al2O3 particles at a variety of impact angles. The erosion rate was found to depend on the jet scanning direction when the nozzle was inclined with respect to the target surface at 55°. This effect was explained in terms of the relative number of particles embedded in the target surface when scanning in the forwards, as opposed to backwards, directions. A simple, fast and relatively accurate analytical technique was introduced to predict the profiles of masked and unmasked micro-channels machined at oblique impact angles, and masked micro-holes machined at normal impact. Comparison of the predicted and measured profiles of micro-channels and micro-holes machined in PMMA showed good agreement in both shape and depth. Masked holes at normal incidence were also micromachined in LUCITE™ (an acrylic) and LEXAN™ (a polycarbonate), and revealed a similar shape to that found for PMMA (flat bottom and very steep side walls), implying that the present analytical technique may also be used for the prediction of the profile of abrasive jet micromachined features in a variety of polymers.