Multi-objective optimization of surface morphology using fractal and multi-fractal analysis for dry milling of AISI 4340

•The surface defect types can be described using the novel fractal and multi-fractal features of the machined surface;•The multi-fractal features, together with the surface roughness, are able to assess the machined surface flatness;•Multi-objective optimization of the fractal, multi-fractal and roughness features obtains high-quality machining of 4340.