Research On Electrochemical Micromachining Of Mico-dimples

Micro-dimples have played an important role in reducing friction or increasing friction,anti-wear,decreasing vibration,anti-adhesion and creeping etc.Therefore,the fabrication of micro-dimples with high machining efficiency and high machining accuracy has become a research focus in manufacturing field.A number of methods have been widely developed for generating micro-dimples,including conventional machining,laser beam machining(LBM),electrical discharge machining(EDM)and electrochemical machining(ECM).Many researchers have paid more attention for the ECM technology because of its advantages such as no residual stresses,no tool wear and high machining efficiency.Photoetching electrochemical micromachining is an effective ECM method for generating micro-dimples.Firstly,the insulated patterned mask is prepared on anodic workpiece surface with photolithography process,and then micro-dimples are fabricated by electrochemical reaction.Photoetching electrochemical micromachining could machine micro-dimples with large area at one time.However,there are still some shortcomings: the photolithography process for preparing patterned mask is complicated and time-consuming;there would be an ?island? phenomenon in the center of micro-dimples and the dimensional uniformity is poor for micro-dimples.In this paper,the ECM method with independent micro-electrolytic cell is proposed for enhancing the profile and machining accuracy of micro-dimples.The main contents of the dissertation are as follows:(1)An ECM method with independent micro-electrolytic cell is developed for generating micro-dimples.Both the numerical simulations and experimental results show that the current density distribution is improved,therefore,the ?island? of micro-dimples could be removed and machining accuracy of micro-dimples could be improved.(2)The influence of process parameters on the dimensions of micro-dimples has been investigated in the ECM with independent micro-electrolytic cell.The dimensions of micro-dimples change little with the increase of thickness of mask,applied voltage and machining time.There is about 4 ?m in depth of micro-dimples could be prepared.The CCD online observations indicate that there are a large number of insoluble electrolytic products and bubbles accumulating on the enclosed electrochemical reaction cell at the initial 10 s machining time.The current signal monitoring shows that the current signal decreases sharply from 0.7 A to 0.04 A within 10 s,and then stabilizes around 0.04 A.(3)The multiple cycles ECM method with independent micro-electrolytic cell is proposed,in which the depth of micro-dimples could be significantly enhanced.With 15 V applied voltage and 10 s machining time for one cycle experiment,micro-dimples of 18 ?m in mean depth and 1.09 ?m in depth standard deviation,120 ?m in mean diameter and 1.15 ?m in diameter standard deviation could be generated with the 12 th cycle experiment.(4)The porous metal cathode is employed to obtain micro-dimples.There is more than ten micrometer in depth of micro-dimples could be machined at one time,because the irregular distribution of micro-holes in porous metal cathode is beneficial to the removing of electrolytic products.The experimental results exhibit that both the porous metal cathode immersed in the electrolyte and lateral flow mode of electrolyte,the current power supply could improve the dimensional uniformity and machining accuracy of micro-dimples,compared with direct power supply.With lateral flow mode of electrolyte,10 samples of anodic workpiece are machined under the 40 % pulse duty ratio,4 KHz pulse frequency,15 V applied voltage and 6 s effective machining time.The mean dimensions of all the micro-dimples are 110.28 ?m in diameter and 14.89 ?m in depth,and the standard deviations are 1.28 ?m in diameter and 1.13 ?m in depth.(5)The micro-dimples are successfully machined on the cylindrical surface with porous metal cathode.Micro-dimples of 116.2 ?m in mean diameter and 1.18 ?m in diameter standard deviation,17.3 ?m in mean depth and 1.16 ?m in depth standard deviation could be generated on the cylindrical surface on ductile iron.