Modeling of two-scale array microstructure and prediction of apparent contact angle based on WEDM

The core issue in the theoretical design of superhydrophobic surfaces is to elucidate the relationship between surface microstructure and wettability. In this paper, four two-scale array microstructure models with different shapes are proposed to predict the apparent contact angles (CAs) of EN-GJL-250 (Grey Cast Iron) surface under different wire-cut electrical discharge machining (WEDM) discharge parameters. The primary microstructure is the artificially designed semicircle, rectangular, sawtooth and square column array microstructure, and the secondary microstructure is the micro-nanostructure of the surface machined by WEDM. Firstly, the mechanical analysis of water droplets placed on the primary array microstructure is carried out by the force balance method. According to Newton's third law, equations containing CA parameters are listed. Secondly, the finite element method (FEM) was used to analogue simulation the distribution of material surface temperature and flow field in the WEDM single-pulse discharge machining process. The surface equivalent geometric model of WEDM was established by a uniform arrangement of single pulse pits obtained by simulation, the surface roughness coefficients under different discharge parameters were calculated, and the influence of the surface roughness coefficients on the surface wettability was studied. The numerical results show that the CA is jointly determined by the surface roughness coefficient under different discharge parameters, and the shape and size parameters of the microstructure. Finally, semicircle, rectangular, sawtooth and square column array microstructures were fabricated on EN-GJL-250 surface by high-speed WEDM. Experimental results show: The CA of water droplets on the square column array microstructure is the largest, the predicted values of the CA were in good agreement with the experimental values, and the average relative error was 7.83%.