Critical wall thickness in electrical discharge machining

Abstract

Electrical discharge machining (EDM) is capable of fabricating thin wall structures due to the absence of physical contact between the tool and workpiece. However, the presence of impulsive force does exist during the sparking process, which could give rise to limitations in fabricating small features. The L9 Taguchi method together with the analysis of variance was used to determine the significance of various machining parameters on the specific impulsive force. Through the statistical analysis, it was observed that discharge energy was the most significant factor that influenced the specific impulsive force. Hence, it is important to understand the effects of specific impulsive force in EDM and to investigate its influence that limits the fabrication of thin wall structures. The limit in which the machined part is able to maintain its geometrical integrity is described as the critical wall thickness. The effects of specific impulsive force on thin wall structure were studied through determining the critical wall thickness for various discharge energies. The experimental work showed that both electrothermal erosion and brink erosion, which is attributed by the specific impulsive force was responsible for the loss of geometrical integrity of the wall structure. As the wall thickness falls below a critical value in a given discharge energy setting, the brink erosion was observed. The limit that established the critical wall thickness was elucidated by conflating the thermal erosion and brink erosion.