Microstructures on metal surfaces with diameters of tens to hundreds of micrometers and depths of several micrometers to tens of micrometers can improve the performance of engineering parts. Air-shielding electrochemical micromachining (AS-EMM) is a promising method for fabricating these microstructures, owing to its advantage of high efficient and better localization. However, the machining performance is often influenced by the machining or nonmachining parameters in AS-EMM. In order to get a better machining result in AS-EMM, the optimization of AS-EMM, including nozzle inclination and process parameters, was studied in this paper. Firstly, nozzle inclination was optimized by the different selected air incidence angles (θ) in simulation, and θ = π/4 was advised. Then, the grey relational analysis based on the orthogonal test method was used to analyze the grey relational grade for parameters and obtain the optimal parameter combination, i.e., at electrolyte velocity 5.5 m/s, gas velocity 160 m/s, and voltage 8 V. Finally, the optimization result was verified experimentally.

Radial ultrasonic rolling electrochemical micromachining (RUR-EMM) is a new method of electrochemical machining (ECM). By feeding small and rotating electrodes aided by ultrasonic rolling, an array of pits can be manufactured, which is called microstructures. However, there still exists the problem of choosing the optimal machining parameters to realize the workpiece machining with high quality and high efficiency. In the present study, response surface methodology (RSM) was proposed to optimize the machining parameters. Firstly, the performance criteria of the RUR-EMM are measured through investigating the effect of working parameters, such as applied voltage, electrode rotation speed, pulse frequency and interelectrode gap (IEG), on material removal amount (MRA) and surface roughness (Ra). Then, the experimental results are statistically analyzed and modeled through RSM. The regression model adequacies are checked using the analysis of variance. Furthermore, the optimal combination of these parameters has been evaluated and verified by experiment to maximize MRA and minimize Ra. The results show that each parameter has a similar and non-linear influence on the MRA and Ra. Specifically, with the increase of each parameter, MRA increases first and decreases when the parameters reach a certain value. On the contrary, Ra decreases first and then increases. Under the combined effect of these parameters, the productivity is improved. The experimental value of MRA and Ra is 0.06006 mm2 and 51.1 nm, which were 0.8% and 2.4% different from the predicted values.

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Micro-structure on metal surface can be created with high precision and good surface quality by ultrasonic-assisted electrochemical micromachining (USEMM). One of the prevalent material removal mechanisms in ultrasonic machining (UM) is cavitation erosion. However, the mechanism of material erosion is not clear and worth investigating. This study of the mechanical and chemical effects of the ultrasonic vibration in 6061 aluminium alloy is targeted to reveal the material processing mechanism in USEMM. Based on the built model, the velocity of micro-jet produced near the workpiece surface by ultrasonic cavitation reaches up to 350 m/s when bubble collapses computed by software MATLAB. The impact of micro jet produces plastic micro-pits on the metal surface and the convex peak around the edge of the pits, which is verified in ABAQUS software. The metallographic microscope and curves of the electrochemical polarization behaviour results indicate a significant grain refinement and a marked increase of anodic dissolution current, as well as a weaker resistance than the original workpiece in NaNO3 electrolyte during UM. The current-time curve during machining demonstrates the passive layer forms on the metal surface and then breaks down at the time of less than 0.0066s in USEMM. Micrographs of scanning electron microscope (SEM) of the machined surface in different stages show that many uniform and flat pits are formed in USEMM, compared with the local uneven pits in EMM.