Effects of hybrid electrical discharge machining processes on surface integrity and residual stresses of Ti-6Al-4V titanium alloy

The performance of the produced parts in the electrical discharge machining (EDM) is strongly influenced by the final quality of surface. High thermal gradients in EDM process develop considerable changes in surface integrity of machined samples such as changing the chemical composition of the surface, micro cracks appearance, recast layer, residual stresses, and reduction in fatigue life and corrosion resistance. Ultrasonic-assisted EDM (USEDM) and powder-mixed dielectric EDM (PMEDM) are two techniques in improving EDM efficiency. This paper was an attempt to investigate the effects of USEDM, PMEDM, and powder-mixed dielectric USEDM (PM-USEDM) processes on main characteristics of the surface integrity such as surface roughness, micro cracks, heat-altered metal zone, and residual stress. Scanning electron microscopy (SEM) micrographs were used to analysis micro cracks and heat-altered metal zone, and nanoindentation method was utilized to measure the amount of residual stress of discharged surface. The results indicated that PMEDM process improved surface roughness as well, induced micro cracks in PM-USEDM were very low, and heat-altered metal layer was very thick in traditional EDM comparing to PM-USEDM process which was thinner. The results of the present study also confirmed that the amount of residual stress of ultrasonic-assisted process was partially in lower level and had different profile compared with traditional EDM and PMEDM process.