Cathodic discharge plasma in electrochemical jet machining: Phenomena, mechanism and characteristics. (April 2023)

• Record Type: Journal Article
• Authors: Zhan, Shunda; Lyu, Zhaozhi; Dong, Bangyan; Liu, Weidong; Zhao, Yonghua
• Is Part Of: International journal of machine tools & manufacture. Volume 187(2023)
• Publication Date: 2023-04
• Subjects: Electrochemical jet machining -- Extreme current density -- Hydrogen gas evolution -- Cathodic discharge plasma -- Machining characteristics; Machine-tools -- Periodicals; Manufacturing processes -- Periodicals; Machines-outils -- Périodiques; Fabrication -- Périodiques; Electronic journals; 621.902
• DOI: 10.1016/j.ijmachtools.2023.104015
• Languages: English
• ISSNs: 0890-6955

Abstract

Abstract: An ultrahigh voltage is frequently required in electrochemical jet machining (EJM) to produce extreme current densities (>900 A/cm 2 for this study) to achieve maximum dissolution rates. However, such a high electric field easily induces a cathodic discharge at the nozzle, and the generation mechanism and characteristics remain unexplored. For the first time, this study shows a direct visualisation of the hydrogen evolution and cathodic discharge in EJM using high-speed photography. An in-depth analysis of the discharge behaviour was carried out based on electrical monitoring, temperature measurement, and characterisation of the resulting changes in the electrode surface. It was revealed that the current density threshold determines the discharge ignition. Discharge occurs preferentially at the inner edge of the nozzle end face, which can cause nozzle wear and reduce localisation of anode workpiece dissolution. The discharge intensity can be controlled by varying the applied voltage and pulse frequency. The electrolyte flow velocity and gap distance influence the discharge behaviour. With appropriate process control, cathodic plasma can enhance the EJM performance while minimising its negative impact. Furthermore, cathodic discharge can be significantly suppressed by designing the geometry of the nozzle tip to avoid local electric field concentration. Graphical abstract: Image 1 Highlights: Revealing cathodic phenomena when performing ultra-high current density EJM. Visualisation of hydrogen evolution, droplet formation and cathodic discharge in EJM. Demonstration of formation and regulation mechanisms of cathodic plasma. A mechanistic model describing cathodic discharge and its role in EJM is developed. The impact of cathodic discharge plasma on EJM performance is presented.