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A novel high-pressure (water pump pressure up to 250 MPa) abrasive slurry micro-machining (HASJM) system was introduced. By feeding a premixed slurry into the mixing chamber of a water jet machine with a micro-nozzle (mixing tube diameter of 254 μm), premature erosion of system components was avoided. An optimum erosion rate of 2.7 mg/g was reached when machining Al6061-T6 with a slurry of 25 μm aluminum oxide particles under conditions (slurry flow rate=200 g/min and water pump pressure=235 MPa) near to those which theoretically maximized momentum transfer between the inlet slurry and the water jet entering the mixing chamber from the orifice. It was found that when the standoff distance increased tenfold, the erosion rate almost doubled in glass, but decreased by 50 % in Al6061-T6, due to differences in the erosion at the jet periphery for the two materials. For aspect ratios greater than 0.9, high-quality symmetric channels with a centerline waviness below 6.9 μm and a centerline roughness below 1.1 μm could be produced using a single pass at a low traverse velocity of 40 mm/min. The use of multiple machining passes at a relatively high traverse speed (~1000 mm/min) was found to produce asymmetric channels when the aspect ratio was greater than 0.9, owing to jet deflection from steps formed on the cutting front. Channels produced by micro-milling Al6061-T6 and glass had a 50 % lower centerline waviness and 16 % lower centerline roughness than those made with the conventional abrasive water jet in which air and abrasive entered the mixing chamber.

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