Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-03-06
2001-10-30
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S425000
Reexamination Certificate
active
06310131
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to reconfigurable tooling for the fabrication of composite structures from materials such as resins, fibers and fillers. More particularly the present invention relates to compositions/mixtures of materials suitable for the inexpensive fabrication of molds, mandrels etc. for the fabrication of such structures.
BACKGROUND OF THE INVENTION
In the fabrication of so-called composites for use in the aircraft and aerospace industry, tooling and assembly costs are major drivers. Conventional tooling for the fabrication of composites generally has a fixed geometry and is very costly to manufacture. Additionally, such current tooling may have short lifetimes and demonstrate inappropriate shrinking characteristics.
Aluminum is the most popular tooling material for low volume production, up to 100 parts, whereas steel is the first choice for volumes over about 100 parts. For the creation of master patterns, plaster is the most popular material followed by wood, modeling board and aluminum. Invar (iron-nickel) has been used to some extent in the aerospace industry because of a good match of thermal expansion coefficients with those of graphite/epoxy materials. This tooling material is, however, very expensive and requires significant lead times for machining. As a result, significant effort has been applied in developing CAD software to reduce the time needed for tooling design to shorten the overall prototype or product fabrication cycle. To the best of our knowledge, there have been no breakthroughs in tooling materials, techniques or approaches in the last decade.
The above problems are especially acute in the fabrication of mandrels. Commonly used techniques for the fabrication of this tooling include the use of: nylon bagged styrofoam cores; solid metal mandrels; soft inflatable bladders; hollow silicone mandrels; thermoplastic mandrels; machined foam flyaway; and water soluble substances such as eutectic salts. In the use of such systems, depending upon that used, demolding and materials costs are significant problems. As a consequence, most mandrels are machined from solid pieces of material such as aluminum or cast into a fixed shape and cannot be easily reconfigured.
Accordingly, the availability of relatively low cost tooling that is reconfigurable and readily and cheaply fabricated would be of significant value to the aircraft and aerospace industries in the fabrication of composite structures.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide compositions suitable for the relatively inexpensive manufacture of tooling for composite fabrication.
It is another object of the present invention to provide composite fabrication tooling, molds and mandrels, prepared from such compositions.
SUMMARY OF THE INVENTION
According to the present invention there are provided compositions and tooling useful in the fabrication of composite structures and prepared from compositions that are mixtures of elastomeric and ceramic materials that can be tailored to obtain desired mechanical properties or thermal expansion coefficients. The compositions and tooling prepared therefrom are inexpensive and easy to fabricate and reconfigure. Such compositions generally comprise blends of clays that harden at elevated temperatures, clays that soften at elevated temperatures and uncured silicone rubbers that exhibit high temperature stability. Compositions comprising from about 5% to about 60% by weight of uncured silicone rubber, from about 20% to about 80% by weight of a clay that hardens at elevated temperature and from about 5% to about 50% by weight of clays that soften at elevated temperatures are specifically preferred. Inert filers that do not adversely affect the thermal expansion coefficients of the inventive compositions such as mica, calcium carbonate etc. may also be included.
DETAILED DESCRIPTION OF THE INVENTION
Improving the cycle time and reducing the fabrication costs of composite structures have been long term goals in the aerospace industry for many years. Much of the cost associated with such manufacture relates to the time, processes and materials used to fabricate the tooling, molds, dies and mandrels, used to fabricate composite products. Most efforts to reduce such costs in recent years have been aimed at the development of improved software, CAD products, to improve and thereby shorten the design segment of the process. Little effort has been directed to the development of improved tooling materials that allow shortening of the tooling manufacturing cycle and reduction of the manufacturing cost that remain two of the major hurdles facing composites in mass production.
The present invention addresses the high cost of manufacture of composite structures by describing a class of compositions compounded from relatively low cost materials, which compositions are easily, and cheaply fabricated into tooling and are readily reconfigurable when changes must be made. The compositions, their method of manufacture and tooling made therefrom are all described herein.
The tooling compositions of the present invention comprise blends of 1) an elastomeric material; 2) clay that hardens at elevated temperatures; and 3) clay that softens at elevated temperatures. The compositions can be loaded with a variety of fillers that enhance their mechanical and thermal properties, i.e. thermal expansion coefficients.
Tooling for the fabrication of composite structures preferably exhibits coefficients of thermal expansion (CTE's) somewhat higher than those of the composite materials being cured or processed (above about 6.18 m/m/° C.) so as to be able to provide sufficient support for consolidation. Accordingly, the compositions of the present invention exhibit CTEs above this level. Materials such as silicone rubber, mica, calcium carbonate and quartz all exhibit these CTEs and accordingly can be used as fillers in the compositions of the present invention. Additionally, silicon oxide, ceramic powders and chopped ceramic fibers that exhibit these characteristics can also be used as fillers.
Preferred compositions include mixtures or blends of: 1) cured or uncured silicone rubber, filled or unfilled with, for example mica; 2) a clay that hardens at elevated temperatures such as a structural clay; and 3) a clay that softens at elevated temperatures such as a modeling or styling clay. In this mixture, the elevated temperature hardening clay provides the mechanical properties required in tooling used at elevated temperatures but too high a percentage thereof yields a mixture that does not soften and therefore cannot be or are very difficult to reconfigure. The modeling or high temperature softening clay remains soft and therefore workable or reconfigurable at high and low or ambient temperatures. The elastomeric uncured silicone rubber exhibits very good thermal stability, and serves as a binder for the other constituents of the composition. Alone silicone rubber does not provide the mechanical properties demanded of a good tooling material
Preparation of the blends or mixtures of the present invention is achieved by chopping the constituents into relatively fine particles such as a powder to enhance blending and blending using, for example, a roll mill or an extruder. With a roll mill, several passes may be necessary to achieve homogeneity, while with an appropriate extruder, blending can generally be obtained in a single pass.
Highly preferred compositions are those comprising from about 5% to about 60% uncured silicone rubber, from about 20% to about 80% structural clay and from about 5% to about 50% modeling or styling clay. Mica, calcium carbonate and other thermally stable materials may be added as fillers as long as the coefficients of thermal expansion remain within the prescribed limits.
It is important in that the product composition not contain more than about 5% by weight of water. Hot rolling or extruding at temperatures up to about 220° C. will remove excess moisture in the blending step. If blending is p
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