The invention relates to a mold for manufacturing plastics parts, including a first element and a second element, the two elements defining a volume of a molding chamber in the closed position of the mold. At least one of the elements is provided with a system for adjusting the volume of the molding chamber. The system includes a movable block and a mechanical movement system capable of moving the movable block in a given direction, in a direction that reduces a volume of the molding chamber and/or in an opposite direction for increasing a volume of the molding chamber. The invention also relates to a method of compression molding, to a method of expansion molding and to a method of compression and expansion molding.