The invention relates to a half-mold comprising a joint face; an opposing assembly face), where the longitudinal cross-section of the assembly face is in the form of an arc of a circle centered on a reference axis. The reference axis is offset longitudinally towards the front relative to the joint face. The invention also concerns a molding assembly, a molding unit and a forming facility comprising such half-molds. The invention also concerns a method for producing such half-molds and a method for producing a surface for receiving such half-molds.