A sand core for casting, a method for forming the sand core, and a casting method are provided. The sand core includes a sand core shell that features a designed variability in wall thickness thereof, and has one or more venting paths that open to an external space formed therein. The sand core further includes molding sand partially filled in the sand core shell. The molding sand comprises coated, non-catalyzed sand. The sand core is formed by 3-Dimensionally (3D) printing the sand core shell. During casting, the sand core is placed a sand core into a cavity in a mold and a molten metal is poured into the cavity. The molten metal solidifies around the sand core to form a solidified metal structure. The solidified metal structure is then removed from the mold and the sand core is separated from the solidified metal structure.