Fractal approach to EDM surface quality assessment of robot workpieces

Electrical discharge machining (EDM) is intended for machining products from difficult-to-machine materials for robotics, as well as shipbuilding, aviation, where increased requirements are set on materials. The surface texture of products after EDM differs from traditional cutting methods. Therefore, surface quality analysis requires additional evaluation parameters. This paper proposes an assessment with a fractal analysis, which well describes tribological and adhesion properties that are the most important for robot workpieces. Heat-resistant steel specimens were machined using a full factorial experiment of modes. The specimen profiles were measured in the longitudinal and transverse machining directions. Spectral analysis of roughness was carried out using the accumulated spectral power. It was found that the roughness is mainly formed by spatial frequencies within 0.05 µm ^-1 . It is confirmed that the arithmetic mean height Ra increases with increasing discharge current. The calculation of fractal dimensionality by area-scale method was performed. The fractal-like properties of profiles were found in the scale range of 20–500 µm, and the pulse current affects both Ra and fractal dimension. The pulse duration affects the height roughness parameters, but does not affect the fractal dimension of the surface. The results provide useful information on the improvement of surface quality during EDM.