Abstract: The process comprises the modelling of the piece and its negative in three dimensions, determination of a main joint plane of the two mold parts, searching for the unstrippable zones by simulating a relative translational movement between the model of the piece and the two parts of the model of its negative defined by the reference plane and by determining the contact zones between the piece and the negative, a determination of the offset joint plane in successive sections of the model of the negative including the zones, modelling of the mobile and fixed impressions as a function of the previously determined joint planes, and manufacture of the mold whose fixed and mobile parts comprise joint planes and impressions in accordance with those previously determined.