In this paper, we present a new knowledge-based application dedicated to hot forging. Hot forging is a multiple stages plastic deformation of metal starting from an initial part -- named billet. The main difficulty of this process is to get each intermediate metal part -- named preform -- that is actually defined by blacksmiths thanks to forging rules and know-how. Our application supplies automatically the entire process: it reduces the 3D desired forged part into some appropriate slices thanks to morphological and geometrical criteria. For each slice, it extracts trade features and deforms the slice according to forging rules. Finally, it creates the preform by assembling the deformed slices. The application may iterate on this preform if necessary. In this study, we focus mainly on slices determination, trade features extraction and part reconstruction.