Influence of process parameters on the surface integrity of micro-holes of SS304 obtained by micro-EDM

The present research deals with the evaluation of surface integrity of micro-holes machined in stainless steel (SS304) sheet, using ultrasonic vibration-assisted micro-EDM process. Experimental results showed that pulse duration, gap voltage, and the application of ultrasonic vibration significantly affected the surface integrity in terms of the changes in recast layer thickness, micro-hardness, and the chemical composition of the machined surface. It is observed that the thickness of the recast layer is in the range of 6–23 µm, but the recast layer thickness was less with application of the ultrasonic vibration of the work piece. The heat-affected zone (HAZ) could not be observed both in FESEM and optical images. The micro-hardness in the HAZ was found in the range of 146–238 HV. The lower values of the micro-hardness were obtained with the application of vibration to the work piece. The changes in the chemical composition of the edge of the fabricated micro-holes were analyzed through EDS test, and it was found that lower amounts of carbon, oxygen, and tungsten were present in the machined surfaces.