A 360° tool for making a one-piece composite tubular structure, such as a skin of an acoustic liner, is adjustable between a molding position and a non-molding position. The tool includes a base, a fixed segment mounted to the base, first and second doors hingedly connected on either side of the fixed sector, and third door hingedly connected to the second door. The third door has a circumferential extent that is less than one-fourth that of either the first or second door. Sealing members are provided between the doors. Collectively, the fixed sector, and the first, second and third doors have a predetermined shaped surface that corresponds to a portion of the contour of the tubular structure to be formed. After composite material is applied on the outer surfaces of the fixed sector and the doors, a vacuum bag is formed to surround the composite material and also the joint areas on the inner surface of the tool. The entire tool may be placed in an autoclave for curing. The tool may also be used for the layup and bonding of an acoustic core sandwiched between pre-cured skins.