Mechanism of Improved Surface Roughness in Electroforming Assisted by Ultrasonic Vibration

doi:10.3901/JME.2019.07.243

Abstract

Abstract: A mechanism is proposed that can explain the improvement of surface roughness in electroforming assisted by ultrasonic vibration. Experiments have shown that ultrasonic vibration, in particular, ultrasonic vibration from a cathode plate can significantly improve surface roughness in electroforming. Building upon our experiments, the mechanism is summarized as the following three points. (1) Ultrasonic vibration from the cathode plate produces numerous eddies in the boundary layer on the top of the cathode plate, alternating the flow directions of eddies at an ultrasonic frequency, and as a consequence, the electrolyte in the boundary layer is well mixed leading to evener distributions of the concentration of nickel ions. In another words, the effective diffusion coefficient of nickel ions in the electrolyte is increased by ultrasonic vibration. (2) The evener distributions of the concentration of nickel ions suppress the growth of dendrites and bumps. (3) Ultrasonic microjet from the cathode plate can drive tiny nuclei of hydrogen gas at the initial stage of their formation inhibiting the continuing growth of tiny gas (needle) hole. In this way, the rate of hydrogen production is decreased with the efficiency of electric current improved. The mechanism is supported by the calculation of the natural vibration modes of the cathode plate, the numerical simulation of the flow field of electrolyte in the boundary layer, the numerical simulation of the effective coefficient of nickel ions in the electrolyte, and the measurement of surface roughness and the SEM images of the surfaces fabricated by the electroforming.

Key words: crystallization, diffusion, electroforming, mechanisms, surface roughness, ultrasonic vibration

CLC Number:

TQ153

YANG Guang, HU Zhichao, ZHANG Jun, PI Jun, LIU Zhongsheng. Mechanism of Improved Surface Roughness in Electroforming Assisted by Ultrasonic Vibration[J]. Journal of Mechanical Engineering, 2019, 55(7): 243-248.

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