Surface textures, especially micro-dimple arrays, can significantly improve the friction performance of engineering parts. Through-mask electrochemical micromachining is an effective method for generating micro-dimple arrays. In this article, a new method is introduced to fabricate a large-area polydimethylsiloxane mask containing micro through-holes. Using this technique, a stainless steel mould with micro-pillar arrays is generated by wire electrical discharge machining. A combination of pressure and weight of electrolyte is then proposed to keep the polydimethylsiloxane mask closely attached to the workpiece, which helps to achieve high machining accuracy. The effects of applied voltage, effective machining time and pulse duty cycle on the micro-dimples are investigated. The profiles of the micro-dimples are not sensitive to applied voltage, but pulse duty cycle is a significant factor influencing the depth of the micro-dimples. Micro-dimples of width 95 µm, depth 19 µm and a machining area of diameter 40 mm are successfully generated using a polydimethylsiloxane mask, and the standard deviations of the micro-dimple width and depth are only 0.84 and 0.23 µm, respectively. The present experiments verify that it is feasible to obtain large-area micro-dimple arrays with high machining accuracy using this technique.
Titanium alloys are widely used in the aerospace and biomedical industries. Micro-dimple arrays, as a kind of surface texture, have been applied on titanium alloy surfaces to enhance tribological behaviour as well as to affect the biological performance of titanium implants. Through-mask electrochemical micromachining (TMEMM) is a promising approach to generate micro-dimple arrays on metal surfaces. In general, sodium bromide and methanol-sulfuric acid, which could dissolve the passive oxide layer on titanium alloy surfaces, are used as electrolytes to generate micro-dimple arrays. However, these electrolytes are caustic, which can damage the equipment, and are unfavourable for industrial applications. In this paper, an environmentally friendly NaNO 3 electrolyte was employed to generate micro-dimple arrays on titanium alloy surfaces in TMEMM with a reusable mask; this made the process more efficient and safer. Experiments showed that there was serious stray corrosion on the titanium alloy surfaces when the micro-dimple arrays were generated using direct current. To obtain high-quality micro-dimple arrays, a pulsed current was employed in TMEMM. The results showed that machining parameters of applied voltage of 24 V, pulse duty cycle of 10 % and frequency of 100 Hz were appropriate to improve the machining quality. Micro-dimple arrays with no stray corrosion were thus generated. Moreover, the electrolyte temperature also influenced the machining accuracy, and a low electrolyte temperature of 20°C was useful to reduce the undercutting of micro-dimples and improve machining localization. With the optimized parameters, micro-dimples with a diameter of 110 μm and depth of 20 μm were generated.
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