In a method of manufacturing, before making the first layer: the working tray is covered with a support sheet able to be biased against it, forming a rigid and fixed surface for receiving the successive layers, which is able to hold thereon the successive layers as formed; and the support sheet is biased against the working tray; the green piece is formed by the technique of additive manufacturing; and when the green piece is thus formed, the biasing is suppressed in order to detach, from the tray, the support sheet on which the green piece is located with the portion of the photocurable composition which has not been cured; the non-cured photocurable composition portion is removed; and the green piece is unhooked from the support sheet.