The three-dimensional transient temperature distribution and crater formation of the wire during a single discharge period in the electrical discharge machining process are determined by an explicit finite-difference model. The heat load on the wire is simulated by a variable heat flux boundary condition that part of the circumference where the discharge channel interacts with the wire. The heat-flux value is calculated from the radius of the time-dependent discharge channel and the input power. The melting point isotherms, obtained at the end of the discharge duration, are considered congruent with the crater shape. They are compared qualitatively with cross-sectional micrographs taken from wire samples from the experiments. © 1997 Elsevier Science S.A.