A forming tool and method for its use with flat pre-preg composite laminate assemblies which incorporates a mandrel segmented into multiple forming blocks, the forming blocks sized to receive a draped composite laminate assembly with all portions of the composite laminate assembly spaced from a shaping surface on each block. A spline plate engages the shaping surface of the forming blocks to provide a neutral axis for maintaining the entire composite laminate assembly in tension during forming. In the exemplary embodiments, the draped composite laminate assembly is formed to the forming blocks from the flat composite laminate assembly and maintained in contact with the forming blocks using a vacuum bag. The mandrel forming blocks arc then displaced to a desired curvature on the spline plate.