Experimental Characterization of Vibration-Assisted Reverse Micro Electrical Discharge Machining (EDM) for Surface Texturing

Abstract

There are several examples in nature where the biological surfaces exhibit unique functional response, such as velcro, fish scale and lotus leaves. The texture on lotus leaf exhibits super-hydrophobicity and self cleaning properties. Lotus leaf has hemispherical protrusions of 20–30 μm in diameters which are randomly distributed over the surface. This work is focused on creating similar textured surfaces on Ti6Al4V rods via a vibration assisted reverse micro Electrical Discharge Machining (R-MEDM) process. Textured surfaces containing micropillars of 40–50 μm in diameter spaced at 35 μm have been created during the process. These textured surfaces are expected to exhibit hydrophobicity and hemocompatibility. To experimentally characterize the process, a full factorial design of experiments has been conducted to analyze the effects of voltage, capacitance, amplitude and frequency of the anode (plate electrode) vibrations on the erosion rate and process stability. The process stability is expressed in terms of the percentages of the normal, open circuit and the short circuit durations in the voltage-current (VI) signature obtained during the process. It has been observed that the normal discharge durations increase with an increase in the amplitude and the frequency of the vibrations. Fabricated texture exhibits hydrophobicity and the measured contact angles in a sessile drop test with water varied between 110 and 115°. Also, the textured surface was subjected to hemotoxicity tests which yielded positive results. Based on these results, it can be seen that the machined textured surface are hydrophobic and biocompatible in nature which could potentially find applications in cardiovascular biomedical implants. In addition, this process has been used to create hierarchical structures comprising of primary and a secondary structure over it to mimic the hierarchical structures found on lotus leaves.