Study of spacing surface roughness parameters and proposal of a wear behaviour criterion in die-sinking EDM of cobalt-bonded tungsten carbide

Surface roughness analysis is crucial for assessing machining quality, with most studies emphasizing amplitude parameters due to their industrial relevance. However, spacing roughness parameters, such as Sm (mean spacing of profile irregularities) and Pc (peak count), provide complementary insights into the horizontal distribution of surface features, which are often overlooked. This study investigates the effect of current intensity (I) and pulse time (ti) on Sm and Pc during the die-sinking EDM of cobalt-bonded tungsten carbide (94WC-6Co), a material widely used in wear-intensive applications due to its exceptional hardness. A multilevel design of experiments (DOE) was performed, varying I from 2 to 6 A and ti from 10 to 100 µs. Results demonstrated a strong relationship between machining conditions and both parameters, with higher current intensities increasing feature spacing (Sm) and reducing peak number (Pc). The optimal surface quality, defined by Sm = 30 µm and Pc = 337 cm⁻1, was achieved at I = 2 A and ti = 10 µs. Polynomial regression models provided predictive insights for process optimization. Scanning Electron Microscopy (SEM) analysis validated these results, revealing distinct surface morphology variations associated with the machining parameters. Finally, an attempt to define a criterion for predicting wear behaviour under the experimental conditions considered in this study will be made, where this will be based on Pc and two additional surface roughness parameters such as Rsk (skewness) and Rku (kurtosis).