Sustainable and green sinking electrical discharge machining utilizing foam water as working medium

Sinking electrical discharge machining (EDM) is a vital machining technology used in modern mechanical manufacturing. However, the conventional sinking EDM, which utilizes an oil-based working medium, presents disadvantages such as low machining efficiency, harmful gas emissions, and fire hazards. Although researchers have attempted to use pure water as the working medium, pure water cannot replace oil and has not yet been industrially applied as a working medium because of its low machining efficiency and thick surface recast layer. Herein, we propose sustainable and green sinking EDM utilizing foam water (SEDM-FW) as the working medium, a method that uses pressurized foam water, ultrastrong energy discharge, and upward electrode feeding. The proposed method is cost effective, and its machining efficiency is more than three times higher than that of the conventional sinking EDM at the same peak current. The use of foam water instead of oil as the working medium solves environmental pollution problems associated with the conventional sinking EDM. In terms of environmental performance, the SEDM-FW produces gas byproducts that do not contain any harmful components, including 1,3-butadiene and benzene, which are present in the conventional sinking EDM. Compared with using pure water, using foam water as the working medium in conjunction with an appropriate gas-to-liquid ratio can double the machining efficiency, reduce the thickness of the recast layer by more than half, and reduce the size of surface microcracks. Using gas-dominated foam water, surface microcracks can be eliminated, and a zero-thickness recast layer can be achieved.