Investigations on the Surface Integrity of Ti6Al4V under Modified Dielectric(s)-Based Electric Discharge Machining Using Cryogenically Treated Electrodes

Abstract

The surface integrity of machined components is considered to be an important part of the quality matrix for high-performance applications in the aviation industry. Therefore, close attention is given to the components made up of hard-to-cut materials such as Ti6Al4V, which face processability challenges. In this regard, among the non-conventional machining processes, electric discharge machining is widely preferred for cutting Ti6Al4V. In this study, the potentiality of cryogenic-treated tool electrodes (graphite and aluminum) with unmodified (kerosene) and modified (kerosene with Span 20, Span 60, and Span 80) dielectrics are comprehensively investigated. A three-phased experimentation framework is deployed based on the following process parameters, i.e., surfactant type, surfactant concentration, electrode material, and pulse ON:OFF time. Thorough statistical analyses are performed based on the full factorial design of experiments, and the results are characterized by process physics. It is found that the cutting mechanism is highly dependent on the surfactants, especially their hydrophilic–lipophilic balance in the dielectric. The desirability-based process optimization results show that the unmodified process (with kerosene) produced relatively higher roughness values of 7.5 µm and 5.8 µm for aluminum and graphite electrodes, respectively. However, the modified process (with surfactant) resulted in a lower degree of roughness on the workpiece. The graphite electrode using S-60 with a resulting Ra of 1.73 µm outperformed the aluminum electrode using S-20, yielding an Ra of 3.4 µm. The S-60 surfactant resulted in minimum roughness on the workpiece with the fewest surface defects at the 25 g/L concentration, 50:25 µSec pulse ON:OFF time, and with the cryogenically treated graphite electrode.