Patent Publication Number: US-2012040042-A1

Title: Composite Mold with Expandable Boot

Description:
This is a utility patent application based on U.S. Provisional patent application (Application No. 61/299,320) filed on Jan. 28, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains to closed molds used for manufacturing molded composite structures using heat and pressure or heat only. 
     2. Description of the Related Art 
     In some industries, parts and structures with different surfaces, flanges, connecting joints, and different wall thickness that were once made of metal are now made of lightweight composite material. Like metal parts or structures, composite parts or structures must be precisely manufactured. Unfortunately, designing molds and molding methods that reliably produce complex composite parts or structures is difficult. It can be especially difficult when different types of composite materials may be used, and when the curing step may use variable amounts of heat and pressure. 
     C-shaped or channel-shaped composite structures are commonly manufactured in a closed mold that includes an outside mold section and an inside mold section. When the two mold sections are joined together, an internal mold cavity is created which is then filled with uncured composite material. As the composite material cures inside the mold cavity, different areas on the composite structure cure and expand at different rates and amounts, thereby creating composite structures that may deviate from their desired specifications. 
     There are several types of closed molds used today to manufacture composite structures using heat and pressure. One type of closed mold is made up of two or more mold sections which are used to form the straight and curved surfaces of the composite structure. Each mold section includes a partially enclosing expansion cavity. Located inside the expansion cavity are two L or V-shaped side plates. The side plates are aligned inside the expansion cavity so that one leg on each side plate faces inward. A beveled edge is formed on the inward directed leg thereby forming an V-shaped void. Disposed over the inside surface of the horizontal legs on the two side plates is a flat compression plate. The compression plate includes a V-shaped projection that fits into and presses against the V-shaped void formed by the two mold sections. When downward pressure is exerted on compression plate, the V-shaped projection is forced into the V-shaped void causing the two side plates to separate and move laterally inside the expansion cavity. 
     Disposed over the compression plate and over the upper ends of the two side plates is a protruding tool member. The protruding tool member extends into the mold cavity and presses downward against the compression plate and between the two mold sections. A cap plate is then positioned over the exposed surface on the protruding tool member. 
     After assembly, uncured composite material is dispensed into a mold cavity created in the expansion cavity between the inside surfaces of the two mold sections and the outside surfaces of the two side plates. After the mold as been assembled and heat and external pressure is applied to the two mold sections and to the cap plate, the protruding tool member is forced against the compression plate and the composite material begins to expand. During the curing step, the composite material may expand causing the side plates to move at different rates and at different amounts. The only force resisting movement of the side plates is the pressure exerted by the compression plate. 
     What is needed is an improved closed mold for manufacturing composite structures that uses a compression plate and projecting tool core that the external pressure and expansion pressures to be more evenly distributed thereby producing cured composite structures with fewer defects. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is a mold and method of molding composite structures inside the closed cavity of the mold that uses a heat expandable boot that can be manufactured in different shapes and thickness using heat and external pressure or heat only. 
     In the first embodiment, the mold includes a base made up of two mold sections that when jointed form a partially enclosed mold cavity. Located inside the mold cavity are two L-shaped side parts. Each side part includes a horizontal leg and a vertical or diagonal le with an inward directed beveled edge. The two side parts are aligned inside the mold cavity so that the two beveled edges are adjacent a form a large V-shape void. Located above the two horizontal legs is a compression plate with a downward extending V-shaped projection designed to slidingly engage the V-shaped void. 
     A U or C-shaped expansion boot is then placed inside the expansion cavity with its horizontal section extending over the compression plate. The outer legs of the boot extend upward and parallel to the vertical or diagonal legs of the side plates. Formed inside the expansion boot is a intermediate cavity. A tool core is inserted into the intermediate cavity with its perimeter surfaces positioned against the inside surface of the boot. A cap plate is then placed over the top ends of the base and over the tool core and the ends of the boot. 
     During use, heat and external pressure is applied to the cap plate and mold sections. During the curing step, the composite material expands causing the side plates to move at different rates and at different amounts. The protruding tool core presses against the inside surfaces of the boot compression thereby resisting movement in every direction. 
     In a second embodiment, a second mold is used to manufacture a C-shaped composite structure that uses a tool core positioned against the composite material with the expandable boot positioned between the composite material and inside surface of the base. 
     In both embodiments, when the boot is placed inside the mold cavity, the boot applies evenly distributed pressure against the composite part as the mold is heated or when heated and pressurized. In the first embodiment, the boot may be positioned between the tool core and the composite plate. In the second embodiment, the boot is positioned between the composite part and the inside surface of the mold parts. In both embodiments, the boot is able to partially absorb and transfer forces to form composite structures with uniform shape and thickness. 
     An optional grid layer may be placed between the boot and the composite cavity that during the curing process, imparts a desirable smoothness or textured pattern on the composite part after curing. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is sectional side elevational view of a mold with an internal mold cavity used to manufacture a C-shaped composite structure made of composite material that is cured with heat and external pressure that uses an expandable boot to located between a tool core and three internal movable tool parts that are designed to evenly apply and distribute pressures against the composite structure, the tool core, the tool parts so that the composite part structure has the desired shape. 
         FIG. 2  is a sectional side elevational view of a second mold also used to manufacture a C-shaped composite structure made of composite material that cured with heat only that uses a tool core positioned against the composite material with the expandable boot positioned between he composite material and inside surface of the mold base with an optional grid layer located between the composite layer and the boot. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Disclosed herein is a mold  10 ,  60  used to manufacture a C or channel shaped composite structure  50 ,  100 , respectively, that has uniform thickness and less defects. The mold  10 ,  60  includes an expansion cavity which an expandable boot is placed and used to evenly distributed external pressures and expansion pressure when the mold is heated or when heated and pressurized. 
       FIG. 1  is sectional side elevational view of a first mold embodiment, indicated by the reference number  10 , with an internal mold cavity  12  formed in an expansion cavity formed in a base  20  that is used to manufacture a C-shaped composite structure  50 . The base  20  is made of at least two mold parts  21 A,  21 B held together with a suitable connector  22 . Formed in the base  20  is an expansion cavity  11 . The mold  10  includes a cap plate  15  that extends across the expansion cavity  11  and supported by the bases upper flat surfaces. Located under the cap plate  15  is a tool core  17  designed to downward extend into the expansion cavity  11   
     Located inside the expansion mold cavity  11  are two side parts  22 ,  22 ′. The side parts  22 ,  22 ′ are L or C shaped form a L or C shaped mold cavity  12  located between them and the insides surfaces of the two mold parts  21 A,  21 B. After assembly, the side plates  22 ,  22 ′ are able to move inward and outward along the inside surfaces of the mold parts  21 A,  21 B according to the balanced forces exerted on them by an external pressure source (indicated by the reference letter fx) applying pressure to the cap plate  15  and by the inward expansion pressure exerted by the composite material located in the mold cavity  12  when curing. 
     Each side part  22 ,  22 ′ includes a vertical leg  23 ,  23 ′ and a horizontal leg  24 ,  24 ′, respectively. Formed on the distal end of each horizontal leg  23 ,  23 ′ is a beveled edge  25 ,  25 ′, respectively. The length of the vertical legs  23 ,  23 ′ is less than the height of the mold part  21 A,  21 B, respectively. During assembly, the two side parts  22 ,  22 ′ are positioned inside the expansion cavity  11  so that the vertical legs  23 ,  23 ′ are aligned parallel to the two inside walls of the adjacent mold parts  21 A,  21 B and the horizontal legs  24 ,  24 ′ are aligned parallel to the inside bottom surface of the two mold parts  21 A,  21 B. The relative shaped and size of the side parts  22 ,  22 ′ depend on the shape and size of the composite structure and the structure&#39;s side wall thickness. When assembled, the horizontal legs  23 ,  23 ′ extend inward and the two beveled edges  25 ,  25 ′ together form a central, V-shaped void  30 . 
     Disposed over the inside surfaces of the two side parts  22 ,  22 ′ is a flat compression plate  32 . The compression plate  32  includes a downward extending, V-shaped projection  34  that fits into and presses against the V-shaped void  30  formed by the two side parts  22 ,  22 ′. By raising and lowering the compression plate  32  over the two side plates  22 ,  22 ′, the V-shaped projection  34  disengages and engages the V-shaped void  30  and thereby enables or forces the two side parts  22 ,  22 ′ to move inward and outward in the expansion cavity  11 . 
     Disposed over the top surface of the compression plate  32  and over the inside surfaces of the vertical legs  23 ,  23 ′of the two side parts  22 ,  22 ′, respectively, is an expandable boot  40 . The boot  40 , which is made of silicone, is a C-shaped in cross-section and similar to the shape to the mold cavity  12  formed between the base  20  and the two side parts  22 ,  22 ′. Formed on the boot  40  are two outward extending legs  42 ,  43  that bend and extend over the upper ends of the two side plates  22 ,  22 ′. The ends of the boot  40  bend upward and are positioned adjacent to the upper sections of the mold parts  21 A,  21 B. The distal ends  44 ,  45  of the boot  40  terminate at the cap plate  15 . 
     During assembly, the cap plate  15  is placed over the base  20 . Located below the cap plate  15  is a tool core  17 . The lower surface of the tool core  17  is complimentary in shaped to the boot  40  when formed and placed over the side parts  22 ,  22 ′ so that it presses tightly against the boot  40 . The tool core  17  includes two outer extending lips  18 ,  19  that press against the two extending legs  42 ,  43 , respectively, on the boot  40  forcing them outward. 
     In the embodiment shown in  FIG. 1 , optional plugs  55 ,  57 ′ are positioned on the top of the mold cavity  12  that act to limit the expansion of the composite structure  50  and to restrict outward expansion of the two side plates  22 ,  22 ′. The plugs  55 ,  57  are made of low expansion material, such as metal or glass and have a suitable thickness or diameter equal to the desired thickness of the composite structure  50 . 
       FIG. 2  shows a second embodiment of the mold  60  that is also used to manufacture a a C-shaped composite structure  100  made of composite material cured with heat only. With this embodiment, the tool core  67  positioned against the composite structure  100  and the expandable boot  90  is positioned between he composite structurre  100  and inside surface of the base  70 . Because pressure is not used, the amount of expansion of the composite structure  100  is less than the composite structure  50  formed using the first mold  10  and method. Also, an optional grid or laminate layer  110  may be located between the composite structure  100  and the boot  90  to produce an desired smoothness or textured pattern on the surfaces of the composite structure  100 . 
     The boot  40 ,  90  is made of silicone or polyurethane approximately 2 to 8.0 mm thick and expands 10 to 30%. The actual material selected for the boot  40 ,  90  and the thickness of the boot used depends on the type of composite material used and the general shape of the composite structure  100 . 
     In compliance with the statute, the invention described herein has been described in language more or less specific as to structural features. It should be understood, however, that the invention is not limited to the specific features shown, since the means and construction shown is comprised only of the preferred embodiments for putting the invention into effect. The invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the amended claims, appropriately interpreted in accordance with the doctrine of equivalents.