Research On Fabrication Of Microstructure Arrays By Foamed Cathode Through-mask Electrochemical Machining

Surface texturing with microstructures has been proved to be an effective approach in many fields to improve the functionalities and performances of some metallic components,such as lower friction and improved tribological performance,enhanced heat and mass transfer efficiency,and obtaining superhydrophobic surface property.Various techniques have been exploited to make surface textures.Among these,through-mask electrochemical micromachining?TMEMM?technique has a variety of advantages over other techniques including no additional residual stress,no recast layer,and few limits in workpiece materials regardless of their mechanical performances.Therefore,this technique has attracted many attentions of industries and academics.A novel TMEMM using the foamed metal as the cathode was proposed to cost-effectively generate high-quality microdimple arrays on the metallic workpiece.This work was financially supported by the National Natural Science Foundation of China?No.51475149?,Technology Innovation Talent Support Program of Henan Province?No.154100510008?,Program for Science&Technology Innovation Team in Universities of Henan Province?No.15IRTSTHN013?and Program for Science&Technology Innovation Team in Henan Polytechnic University?No.T2014-1?.In this TMEMM process,a foamed metal film offers enough convenience and capacity for the necessary mass transfer and the mask fixture because of its good pliancy performance and a huge number of interconnected micropores.In the meanwhile,it is also introduced to serve as the cathode,which is further integrated with the reusable through-mask and workpiece to form a sandwich-like assembly.This proposed TMEMM deserves more attentions and explorations because of the multifunctional foamed cathode and the sandwich-like configuration with the interelectrode gap being reduced to an extremely small value equivalent to the mask thickness.The machining principles,executive methods,parameters and results were investigated experimentally.Some main research contents and conclusions of this thesis are made as follows.?1?The machining principle of the foamed cathode TMEMM was interpreted,and the physical model used for the foamed cathode TMEMM process was established for simulating current distribution within the microcavities.The simulation results showed,in comparison with the conventional TMEMM,the change of the current density keeps synchronous and the current density distribution within each microcavity is constantly same regardless of the position of the microcavity and the machining time.?2?After the feasibility of this technique was proved by the pre-experiment,the influences of main machining parameters?such as voltages,mask thicknesses and perforation diameters?on the fabricated microdimples'profiles and dimensions were systematically investigated,and the fabrication of microdimple arrays on the planar and cylindrical surface was implemented.The results showed the microdimples fabricated by the foamed cathode TMEMM had a fairly smooth surface and a favorable consistency in the shape ranging from 53.38?m to 61.33?m in depth and from 349.6?m to 377.3?m in diameter,respectively,with the coefficient of variation for the microdimples'depth and diameter(CV_depth and CV_diameter)being about 5.6%and 2.4%.What's more,the uniform micro-dimple arrays on the entire 360°cylindrical surface were accomplished in only one operation.To some degree,it may be not convenient to press the mask by the mechanical force,and may be more sophisticated when machining the cylindrical workpiece.?3?A new method using the magnetic force to press the mask was proposed to accomplish the uniform fixture for the mask on the workpiece and no effect on the mass transfer in the gap.Based on the foamed cathode TMEMM with the magnetic field,a self-circulated executive method for the electrolyte flow without the pump was created.In this method,the sandwich-like machining assembly runs duplex motions including slightly swinging and moving in a circumferentially translational way to stir and circulate the electrolyte.The machining principle was interpreted,and the experiment was made with the designed apparatus.The study showed this self-circulated method for the mass transfer improves the convenience and practicability of the foamed cathode TMEMM.The microdimple array fabricated by this method exhibited the CV_depth and CV_diameteriameter as 6.8%and 3.5%respectively when utilizing optimized parameters.Nevertheless,the flow speed and machining efficiency caused by this self-circulated method are a little low,and this method may not be suitable to manufacture deeper microdimples.?4?With the magnetically pressed mask,a new self-circulated method in which the machining assembly moves in a linearly reciprocating way to circulate the electrolyte was proposed to further promote the machining efficiency and applicability of the foamed cathode TMEMM.The machining principle was interpreted and the experimental system used for this method was built.The experimental results showed this mass transfer method can offer more convenience and applicability for the foamed cathode TMEMM,and is able to efficiently fabricate uniform microdimple arrays with the minimum CV_depth and CV_diameteriameter as 5.4%and 1.9%respectively,when utilizing the optimized condition that the power source is available only when the machining assembly moves downward.The foamed cathode TMEMM has a dominant superiority in efficiently fabricating uniform microdimple arrays.The novel self-circulated mass transfer methods including the machining assembly running duplex motions or moving in a linearly reciprocating way facilitate the better applicability and convenience of the foamed cathode TMEMM.