Wire EDM makes no contact with the work piece and disregards hardness.
I am using EDM to cut different materials, and I notice a clear distinction between the rate each material gets cut. For example, copper is extremely slow, while aluminum is much faster -- almost three times faster than copper. Lead also gets cut by EDM very easily.
My question is what determines the distinction in cutting speed for different material? Is it the melting point, or the energy of fusion, or something else?