A mechanized lay up assembly line for composite structures has a tool delivery station having a plurality of rollers on its surface for moving tools across the surface. Adjacent to the tool delivery station is a work station. The work station includes a work surface. The work surface has a plurality of rollers that move from a position wherein the rollers extend above the work surface to support a tool above the work surface to a retracted position where the rollers descend below the work surface such that the tool is supported on the work surface. The mechanized lay up assembly line further includes a debulking diaphragm that moves toward and away from the work surface and a vacuum system for evacuating the space between the diaphragm and the work surface. Tools are moved from the delivery station to the work station with the work station rollers extended. When a tool is positioned on the work station its rollers are retracted to position the tool firmly on the working surface. A composite structure is laid up on the tool supported on the work surface. Debulking and compacting of the composite material is accomplished by vacuum sealing the diaphragm against the composite material on the tool and the working surface.