EFFECT OF FLUSHING PRESSURE ON ELECTRO-DISCHARGE MACHINING AND RESULTANT SURFACE CHARACTERISTICS

Abstract

Electro-Discharge Machining (EDM) has become commonly used both in tool and die and aerospace industries. The purpose of this project is to investigate the effects of flushing on the machining performance, recast layer morphology and cracking propensity. AISI 01 tool steel and a high-energy machining condition were used in the present work. The flushing pressure was varied from 10 to 110 kPa in steps of 10kPa. The results show the flushing pressure effort can be divided into three ranges as follows: At low flushing pressures of 10 to 50 kPa, the material removal rate (MRR) increases while the hump density and the crack density of the recast layer decrease with flushing pressure. It was also found that the percentage of multi-layer recast decreases with flushing pressure. At intermediate flushing pressures of 50 to 75 kPa, the HRR decreases while the hump density and crack density increase with flushing pressure. Over this flushing pressure range, the percentage of multi-layer recast increases with flushing pressure. At high flushing pressures of 75 to 110 kPa, the MRR is low while the hump density and crack density are high. In this range, all these three parameters are insensitive to the flushing pressure. In addition to the above, it was found that the profile reproducibility degrades while the surface finish improves continuously with flushing pressure. The average ' thickness of recast and discharge gap width were found to decrease monotonically with increasing flushing pressure. The results were interpreted in terms of the effects of the flushing pressure on debris removal efficiency, frequency of shorting and machining stability. The mechanisms of crack formation and the effect of flushing on crack density were also discussed. The present work shows that there exists an optimum flushing condition where the MRR is maximum while the crack density of the recast is minimum. This corresponds to the flushing condition when an appropriate concentration of debris is maintained in the dielectric in the gap. Flushing that is too efficient will result in a very narrow discharge gap which in tum will lead to a higher frequency of shorting and the degradation of machining stability, causing the MRR to drop and the crack density to increase. For AISI 01 tool steel under the present test conditions, the optimum flushing pressure is about 50 kPa.