Research On Photoetching Electrochemical Micromachining Of Micro-dimple Arrays With A Flexible Mask

Micro-dimple arrays can significantly improve the tribological performance of contacted friction pair surfaces.They can decrease the friction coefficient and the friction wear,which improve the service life of the friction pair.The fabrication of large-area micro-dimple arrays with high machining accuracy becomes a research focus.Photoetching electrochemical micromachining is an effective method for generating micro-dimple arrays.In conventional photoetching electrochemical micromachining,a mask is prepared by complex photolithography using photoresist.The photoresist is a single-use mask that must be peeled off from the anode workpiece after machining,making it expensive for mass production,and giving it a long lead time.Moreover,challenges remain in the fabrication of large-area micro-dimple arrays with high machining accuracy because of the marginal effect of electrical field.To overcome the challenges above,in this paper,a polydimethylsiloxane(PDMS)mask is introduced to fabricate large-area micro-dimple arrays with high machining accuracy by photoetching electrochemical micromachining.The major research are as follows:(1)PDMS masks were fabricated by vacuum-aided process.A method for fabricating a stainless steel mould with micro-pillar arrays by wire electrical discharge machining was presented,and a PDMS mask with through-holes was fabricated.A modified method was employed to fabricate SU-8 mould,by using double-deck SU-8 photoresist.A PDMS mask with a diameter of 90 mm was fabricated using the SU-8 mould,meeting the demand of fabricating large-area micro-dimple arrays.(2)A modified electrolyte method with high pressure and low velocity was presented to generate micro-dimple arrays.A combination of pressure and weight of electrolyte was then proposed to keep the PDMS mask closely attached to the workpiece,which helped to achieve high machining accuracy.The effects of applied voltage,machining time and pulse duty cycle on the micro-dimples were investigated.The experimental results showed that the metal removed rate was not sensitive to the certain voltage.The accumulation of the electrolytic products in the micro-dimple arrays could weaken the effect of non-uniform distribution of electrical field on generating micro-dimple arrays and improve machining accuracy.Pulse duty cycle was a significant factor influencing the depth of the microdimples and current efficiency was low at a high pulse duty cycle.Micro-dimples of width 95 μm,depth 19 μm and a machining area of diameter 40 mm were successfully generated using a PDMS mask,and the standard deviations of the micro-dimple width and depth were only 0.84 and 0.23 μm,respectively.The present experiments verified that it was feasible to obtain large-area micro-dimple arrays with high machining accuracy using this technique.(3)High hydrostatic pressure was introduced into the TMEMM in order to improve machining accuracy.All points of the PDMS mask bear high hydrostatic pressure evenly,and the escape of the electrolytic product is suppressed,which is of value when seeking high machining accuracy.Moreover,high hydrostatic pressure can also help to keep the PDMS mask closely attached to the workpiece.The results indicated that high pressure was essential for improving the quality of micro-dimple arrays,and that 0.5 MPa was suitable for generating micro-dimple arrays with high machining accuracy.(4)The application of large-area micro-dimple arrays generated by photoetching electrochemical micromachining with PDMS mask was investigated.Micro-dimple arrays with high machining accuracy were successfully prepared on the surface of workpiece with through-holes.Micro-dimple arrays with high machining accuracy were successfully fabricated on the surface of a cylinder by high hydrostatic pressure.