Effect of thermal-hydrodynamic coupling energy on the processing of Inconel 718 superalloy

Electrical discharge machining (EDM) is a nontraditional processing approach for subtractive manufacturing that is hardly affected by the material properties and widely used in the processing of nickel-based superalloys. However, its low machining efficiency and environmental problems have always been bottlenecks restricting its development and application. This paper presents an eco-friendly approach named moving arc milling for efficient machining of Inconel 718 superalloy by using thermal-hydrodynamic coupling energy. Firstly, the arc behaviors during machining processes and morphological characteristics of discharge craters are observed in the air and tap water. Secondly, the moving arc milling machining method using thermal-hydrodynamic coupling energy to achieve effective metal removal is proposed and proved practicable. Then, the flow velocity of flushing liquid in the discharge gap is analyzed using the fluid dynamics analysis, which helps to study the fluid momentum in the discharge gap under high-pressure flushing conditions, and contributes to explain the removal principle of molten metal and debris. Moreover, a new mechanism model for the molten metal removal in moving arc milling processes is established based on above analysis and experimental results. Finally, moving arc milling experiments on Inconel 718 are carried out with different flushing pressures. It is found that high velocity of working fluid is the key factor for removing molten metal in arc milling. The moving arc milling with a higher flushing pressure of 0.6 MPa could not only increase a much higher material removal rate but also decrease the tool electrode loss, as well as improve the quality of the machined surface.