System and method of forming composite structures

A method of making a composite structure in a mold having opposing mold surfaces for receiving the composite structure therebetween, wherein the composite structure has at least two outer polymeric layers spaced apart from each other and defining a cavity therebetween, a foam core located between the two polymeric layers and made of a core material capable of exhibiting a foamed character and a resinous character, at least one fibrous layer located between a respective one of the polymeric layers and the foam core, and at least one resinous layer made of the core material and located between an outer polymeric layer and respective fibrous layer, wherein the cavity between the outer polymeric layers is defined by at least one first region extending between the at least one fibrous layer and a respective outer polymeric layer, and at least one second region located on an opposite side of the at least one fibrous layer and respective outer polymeric layer, the method comprising the steps of:

• providing the at least two outer polymeric layers between the opposing mold surfaces with the outer polymeric layers spaced apart from each other and defining the cavity therebetween, forming in at least one of the outer polymeric sheets a gate connectable in fluid communication with the cavity and means for sealing the gate extending about a periphery thereof, introducing the core material in the resinous character through the gate and into the cavity, and transitioning the core material from a turbulent flow;
• providing the at least one fibrous layer between the at least two outer polymeric layers and creating the first and second regions of the cavity;
• evacuating the cavity and creating a predetermined vacuum therein;
• introducing the core material in a resinous character into the second region of the evacuated cavity;
• activating a blowing agent of the core material by subjecting the core material to the vacuum within the cavity and, in turn, converting the core material in the second region of the cavity from a resinous character to a foamed character;
• substantially filling the second region of the evacuated cavity with the foamed core material;
• converting the foamed core material that contacts the at least one fibrous layer from a foamed character to a substantially resinous character, and creating a relatively dense resinous interface between the at least one fibrous layer and foamed core material;
• initiating a catalytic reaction within the foamed core material to cure the foamed core material;
• creating a negative pressure gradient in the direction from the foamed core material toward the at least one fibrous layer;
• using the negative pressure gradient to cause the resinous core material at the interface of the at least one fibrous layer and foamed core to penetrate the at least one fibrous layer and, in turn, substantially fill the at least one first region with the resinous core material;
• and
• curing the resinous core material in the at least one first region to thereby fixedly attach the resinous core material and at least one fibrous layer to the outer polymeric layers.