Micro-machining with abrasive slurry-jets: effects of dissolved polymer concentration and nozzle design

The resolution of features machined with abrasive slurry jets is dependent on the diameter of the erosion footprint on the workpiece and on the stability of the jet. Previous work has shown that the footprint size decreases, but the jet oscillation increases, with increasing polymer concentration. The present study investigated the effect of nozzle design on jet stability in abrasive slurry-jet micro-machining of glass using slurries with dissolved polymers. A variety of transparent acrylic nozzles were made with different geometries and a 180-μm sapphire orifice to study the oscillation of jets of water mixed with high molecular-weight polyethylene oxide. Fluorescent streak photography of the flows within the nozzles confirmed the presence of unstable vortices that can lead to jet oscillation. However, the dependence of these vortices on nozzle geometry and PEO concentration was unclear. Jet oscillation was then measured photographically and found to increase nonlinearly with polymer concentration for all nozzle geometries. These results were used to design and manufacture a new steel nozzle with a 30° tapered entrance region which reduced jet oscillation. Micro-channels were then machined in glass plates using a range of polymer slurries containing aluminium oxide particles. The polymer concentration that produced the best combination of a relatively small footprint while simultaneously minimizing the jet oscillation amplitude resulted in channels that were 11% narrower than reference channels machined with a pure water slurry and a standard nozzle.