Comparative study of the influence of tool diameter on axial tool wear, cavity formation, and surface integrity in electro discharge drilling of Ti–6Al–4V

Electro discharge drilling (EDD) is widely used for producing deep, high-aspect-ratio holes in difficult-to-machine materials such as Ti-6Al-4V. However, excessive tool wear, limited cavity depth, and poor surface integrity remain major challenges, particularly with small-diameter electrodes. This study investigates the influence of tool diameter on EDD performance using tubular copper electrodes of 0.3, 0.5, and 0.7 mm diameter. The effects of discharge current, pulse-on time, pulse-off time, and capacitance were evaluated using the single-factor-at-a-time method. Material removal rate (MRR), tool wear rate, axial tool wear, cavity depth, and surface roughness were used to assess machining performance. Increasing discharge energy improved MRR but also increased tool wear and surface roughness. The effect of tool diameter on MRR depended on the discharge parameter: the 0.3 mm electrode produced the highest MRR under current and pulse-off time variations, whereas the 0.5 mm electrode achieved higher MRR under several pulse-on time and capacitance conditions. In contrast, the 0.7 mm electrode produced the deepest cavities (8.5−9.0 mm), lower axial tool wear, and superior surface integrity under moderate discharge conditions. Optical profilometry and scanning electron microscopy revealed debris adhesion and micro-crack formation under high-energy machining conditions. The results demonstrate that optimum EDD performance requires an appropriate combination of discharge parameters and tool diameter rather than maximizing discharge energy alone.