In this study, oil and water are successfully separated using a copper filter that is fabricated using only laser beam machining. Even though copper is hydrophilic and recast copper material, which inevitably results during laser beam machining, is super-hydrophilic, the filter can prevent the water from penetrating and allow oil to flow based on surface tension of the liquids at the hole exit. For practical uses of the filter, both the pressure differences at which the filter is able to retain its ability to separate and the oil penetration rate of the filter are revealed. The fabrication process is simple and time-saving, and the filter has high durability because of lack of surface coating or surface chemical modification.

A novel laser beam machining (LBM) method is proposed to achieve higher precision and better quality beyond the limits of a commercialized nanosecond pulsed laser system. The use of a cover plate is found to be effective for the precision machining of a thin metal foil at micro scale. For verifying the capability of cover plate laser beam machining (c-LBM) technology, a 30 by 30 array of micro-holes was fabricated on 8 µm-thick stainless steel 304 (STS) foil. As a result, thermal deformation and cracks were significantly reduced in comparison with the results using LBM without a cover plate. The standard deviation of the inscribed and circumscribed circle of the holes with a diameter of 12 µm was reduced to 33% and 81%, respectively and the average roundness improved by 77%. Moreover, the smallest diameter obtainable by c-LBM in the given equipment was found to be 6.9 µm, which was 60% less than the minimum size hole by LBM without a cover plate.

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