A controlled shear vacuum forming method that includes forming a three-dimensional (3D) structure from a preform material on a molding tool using restraints during vacuuming to prevent wrinkling. The restraints are withdrawn during vacuuming to allowing the preform material to come into contact with the sidewalls of the molding tool in a gradual manner. Such forming method is particularly suitable for forming wing spars with bent sections and/or curved contours.