Electrochemical machining has continued to attract significant research attention as a promising technique for mass production and machining of difficult-to-machine materials. It removes material from the workpiece through an electrochemical process without the need for a cutting force. Owing to its economy, high production and good surface qualities advantages, numerous studies have been undertaken to improve its efficiency and applications. In particular, increasing the machining resolution has been an area of interest. Since the machining resolution largely depends on the actual electrochemical machining area and the end area of the electrode tool, limiting the electrochemical dissolution to a specified area has been widely speculated to enhance the machining resolution. This was proved by developing nanosecond pulse electrochemical machining techniques that showcased numerous potential strategies for improving the machining resolution, thus inspiring subsequent studies on the subject.
Nanosecond pulse electrochemical machining technology has been extensively investigated. By optimizing various machining parameters, complex microstructures, including three-dimensional microspheres, can be fabricated at relatively highly machining resolution. A combination of ultrashort pulse electrochemical micromachining and tool vibration has produced remarkable improvement in the surface quality and machining accuracy. Moreover, these methods, combined with computing techniques, have allowed for simulations and extensive investigations of different factors like pulse width, duty cycle and the temperature distribution that affect the machining processes and resolution. Nevertheless, despite good progress, a viable and cost-effective process for realizing high machining resolution is yet to be developed.
The duration of the pulse voltage is deemed the main control parameter affecting machining resolution in the electrochemical micromachining technique. Unfortunately, controlling this parameter requires expensive pulse power to achieve the desired accuracy. Moreover, incorporating other control parameters such as adjustable inductance, though effective for improving the machining accuracy, is rather complex as it requires the peak voltages to be adjusted for every inductance. Therefore, the development of simpler methods is highly desirable.
On this account, Professor Lizhong Xu, Jin Ning (Postgraduate student) and Dr. Chuanjun Zhao from the Mechanical Engineering School at Yanshan University developed a new method for improving the machining resolution by increasing the time constant of the circuit. Though sparsely explored in the literature, this method is promising to enhance the machining resolution in pulse electrochemical micromachining under the ordinary pulse duration. The work is currently published in the research journal, Mechanical Systems and Signal Processing.
Their approach entailed an electrochemical micromachining equivalent circuit with an additional positive feedback loop for tuning the time constant of the circuit. The authors also proposed a time constant control method using the feedback gain as an effective control parameter. The dependence of the machining resolution on the feedback gain was experimentally investigated and discussed. Additionally, various factors affecting the machining resolution, such as the current pulse width and feedback gain, were discussed in detail.
Results showed that increasing the time constant of the electrochemical micromachining process significantly improved the machining resolution. Instead of the expensive pulse power, the method utilized an ordinary pulse width to tune the gain of the feedback loop and improve the machining precision. The precision of the ECM was achieved by adjusting and controlling two key parameters: feedback gain coefficients and pulse width. Furthermore, the technique was successfully used to machine micro and nanostructures with high machining resolution.
In a nutshell, a time constant increase method for improving the machining accuracy and resolution of electrochemical machining was reported and verified. The proposed method was economically viable as it did not require the costly ultra-short pulse power. Moreover, it exhibited remarkable improvement in the machining accuracy and resolution when the time constant was increased. The theoretical simulation results agreed well with the experimental results, validating the feasibility of the proposed method. In a statement to Advances in Engineering, Professor Lizhong Xu explained that the newly proposed method is a promising solution for robust and cost-effective microstructure machining.
Xu, L., Ning, J., & Zhao, C. (2020). Electrochemical micromachining based on time constant control. Mechanical Systems and Signal Processing, 145, 106920.