Experimental Research On Vacuum Boiling Electroforming In Microchannels

A large number of experiments about electrolyte vacuum boiling electrodeposition did before proved that:in macro conditions, this process can obtain high-quality electrodeposition coating and part under conditions of high deposition speed and no additive. So if this process can achieve a good result in the micro conditions? To this end we studied the vacuum boiling process in micro hole conditions. The results showed that:the process has obvious influence on the bubble dynamics and flow characteristics. Meanwhile, in the micro electroforming, holes and channels are two electroforming environment that the most frequently encountered, then we have to ask, in the micro channel, what kind of influence the vacuum boiling electroforming process will have on the bubble dynamics? And if this influence can obtain a good effect as it have in the macro condition? In order to answer this question, and also for the experiments’ continuous and integrality, this dissertation which was supported by National Natural Science Foundation (51175152) and Henan Province University Science and Technology Innovation Talent Support Plan (2012HASTIT012), taken the vacuum boiling electroforming in micro groove experimental research as the theme, bubble dynamics characteristics in micro groove under different process condition were visualization researched, the change of electric field characteristics and the surface quality and micro hardness of electroforming layer caused by vacuum boiling bubbles were studied. Details are as follows:(1) bubble dynamics characteristics in micro groove under different process condition were visualization researched based on the experimental platform of electrolyte vacuum boiling electroforming in micro groove, the results show that:The vacuum boiling bubbles in micro groove basically followed the typical evolutionary process of "nucleationâ†'grow in micro grooveâ†'the bubble out of notchâ†'notch bubbles continue to growâ†'the gas ring in micro groove atrophyâ†'the bubble detachmentâ†'the bubble continues to shrinkâ†'the bubble burst; but under certain conditions, the bubble will show repeated expansion and contraction, polymerization, boundary contact but not polymerization, blocking groove, splitting during growing and other acts; the evolutionary process of vacuum boiling bubbles in micro groove is basically the same in the presence or absence of deposition; the change of process conditions does not change the evolution process of the boiling bubbles, only influence the bubble dynamic characteristics, such as growth rate, departure diameter or departure frequency; compared with the vacuum boiling electroforming in micro hole, in addition to the depth to width ratio, the bubble dynamics is basic similarity when the process conditions change.(2) in the micro groove environment, vacuum boiling bubble growth curve is linear relationship when the dimensionless growth time is less than 0.24, and it’s exponential relationship when the dimensionless growth time is greater than 0.24, the value of kl kp and n is basically not influenced by the change of technological conditions; compared with the vacuum boiling electroforming in macro conditions, in this study, the vacuum boiling bubble two dimensionless growth curve model is: R+=2.486t+t+<0.24 R+=t+0.332 t+>0.24 Compare the experimental data with the model results, it shows that the prediction error is less than±15%.(3) The Inter electrode resistance characteristics during vacuum boiling electroforming in micro groove were researched. The results show that:reduce the vacuum or increase the cathode temperature will lead to the interelectrode resistance increases, increase the current density, the interelectrode resistance is reduced; while increase the groove depth width ratio, the interelectrode resistance first increased and then decreased, but the volatility is significantly enhanced; compared with the macro environment, the mass transfer enhancement effect caused by boiling bubbles is weaker in the micro groove.(4) The performance analysis of vacuum boiling electroforming work-pieces. The surface quality and micro hardness under different conditions was analyzed. The results show that, the vacuum boiling electroforming process can greatly reduce the pinhole defect; and the pinhole are more concentrated in the upper of the work-pieces; meanwhile, this process also show great potential in high aspect ratio, or even ultra high aspect ratio electroforming.