Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1998-03-02
2001-06-12
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S313000, C156S173000, C425SDIG001
Reexamination Certificate
active
06245274
ABSTRACT:
BACKGROUND OF THE INVENTION
This application is related to a provisional patent application filed Jun. 27, 1997.
The present invention relates to composite parts, and, in particular, relates to a process of making advanced grid stiffened structures.
Although it is widely accepted that composite materials will be used extensively in the next generation of launch vehicles, the specific structural type has yet to be determined. One possible structural type is the Advanced Grid Stiffened (AGS) structure, a skin-stringer configuration evolved from early isogrid stiffening concepts. AGS structures have recently gained popularity as a possible solution to many of the problems associated with traditional composite construction methods involving lamination of plates and sandwich type structures. AGS structures are characterized by a lattice of rigid, interconnected ribs, which proves to be an inherently strong and resilient arrangement for composite materials and lacks the material mismatch associated with laminated structures. AGS structures possess inherent resistance to impact damage, delamination and crack propagation while showing a high potential for automation during fabrication.
All AGS structures suffer from the same manufacturing difficulty: for an AGS structure to have all fibers continuous through a rib crossing point, there must be twice as much material in each crossing point than in each rib, making out-of-plane compaction difficult or impossible. For most manufacturing methods, this difficulty leads to a buildup at the nodal points, which is undesirable for many reasons. Known manufacturing methods for AGS structures are: Node Compaction: Brute force compaction through out-of-plane pressure using hard tooling; Fiber Cutting: Allowing only 50% of the fibers to pass through each node; Low Rib Fiber Volume: Having resin-rich ribs with 50% the fiber volume of the nodes; Lateral Compaction: Consolidating ribs from the sides, effectively causing the extra material at the node to lead to double node width rather than double node height; and Nodal Spreading: Spreading of fibers as they enter the node allowing out-of-plane pressure to lead to double node width rather than double node height. Of these methods, Nodal Spreading and Lateral Compaction are the only methods to experience high quality results; of these two, Lateral Compaction is the most cost effective. Lateral Compaction is typically performed with a silicon rubber tool that expands during the cure cycle, laterally compacting the AGS ribs. Unfortunately, this approach suffers from several drawbacks, including poor part geometry control, poor part stability, inability to manufacture large parts, inability to manufacture complex shapes and labor intensive processing.
Thus, there exists a need for a new technique to make AGS.
SUMMARY OF THE INVENTION
The hybrid tooling process implementation uses a high CTE silicon rubber expansion tooling channel insert into a thermally stable base tooling material, which may be composed of tooling epoxy, tooling foam, wood or metallics. While the base tool defines the part dimensions, the silicon rubber expansion tooling expands during the thermal cure cycle to provide rib compaction. This expansion tooling takes the form of a ‘U’ shaped channel section, centered on a node, with arms in each of the rib directions. The channel's cross-section dimensions must be carefully sized using developed theories. During tool manufacture, the channels are cast flat and laid into grooves machined in the base tool for both flat and curved parts. For cylindrical or flat sections, one channel size is sufficient. For conical sections, the channels must be cut to size.
The hybrid tooling process solves many of the problems associated with Lateral Compaction while providing a number of additional advantages. Hybrid tooling process offers an AGS structure manufacturing solution that is low cost, is highly automated, provides for good part compaction and provides for good geometry control. Using the hybrid tooling process and standard filament winding technology, AGS tooling can be created, machined and wound in a series of seamless, automated steps. Also, the resulting tooling is, in most cases, reusable.
The ideal Lateral Compaction tool combines high coefficient of thermal expansion (CTE), good predictability of thermal behavior, high tool stability, a light weight design, machinability and good part release. The hybrid tooling process approach recognizes the inability of any existing tooling material to provide all these attributes.
Therefore, the hybrid tooling process uses two different tooling materials for the two devices: one is a base tool and one is an expansion tool. These tools combined provide the advantages and mitigate the disadvantages of each material.
Therefore, one object of the present invention is to provide a hybrid tooling process for making advanced grid stiffened structures.
Another object of the present invention is to provide a hybrid tooling process having high CTE;
Another object of the present invention is to provide a hybrid tooling process having good predictability of thermal behavior;
Another object of the present invention is to provide a hybrid tooling process having high tool stability;
Another object of the present invention is to provide a hybrid tooling process having a light weight design;
Another object of the present invention is to provide a hybrid tooling process having high machinability;
Another object of the present invention is to provide a hybrid tooling process having good part release; and
Another object of the present invention is to provide a hybrid tooling process for making panels, sandwich cores and/or expansive networks of composite materials.
These and many other objects and advantages of the present invention will be ready apparent to one skilled in the pertinent art from the following detailed description of a preferred embodiment of the invention and the related drawings.
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Huybrechts Steven M.
Meink Troy E.
Underwood, Jr. Richard L.
Silbaugh Jan H.
Staicovici Stefan
Stover Thomas C.
The United States of America as represented by the Secretary of
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