Water soluble tooling materials for composite structures

Abstract

The present invention relates to a low density, water-soluble coring and tooling material used for the fabrication of composite parts. One aspect of the present invention relates to a lightweight, strong composite coring material that can be easily shaped and removed from cured composite parts. Another aspect of the present invention relates to a lightweight, strong composite tooling material that is easily tailored to provide a specific coefficient of thermal expansion and thermal conductivity, thus providing a tooling material that can be matched to the composite structure and material being fabricated.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of U.S. patent application Ser. No. 10 / 092,843, filed Mar. 6, 2002, entitled “Water Soluble Tooling Material For Composite Structures, which is based on, and claims the benefit of, U.S. Provisional Application No. 60 / 274074, filed on Mar. 7, 2001, entitled “Water Soluble Tooling Material For Composite Structures.”[0002] The present invention was made with U.S. Government support under grant Number N68335-01-C-0053 awarded by the Naval Air Warfare Center. Accordingly, the Government may have certain rights in the invention described herein.FIELD OF THE INVENTION [0003] The present invention relates to a novel coring and tooling material for polymer composites. Particularly, the present invention relates to a low-density, water-soluble composite blend used to form a core material for the fabrication of composite parts. In addition, the present invention relates to a low density, water-soluble composite ble...

AI Technical Summary

Benefits of technology

[0014] The present invention offers alternative coring and tooling system and materials. The present invention offers novel low-cost coring and tooling materials for composite parts. Unlike conventional coring and tooling materials, the materials of the present invention are readily soluble in water and can easily be washed away from the finished part. Furthermore, the coring and tooling materials can be used in the manufacture of a wide range of composite parts that can be cured at higher temperatures than heretofore possible.

[0016] Another object of the present invention is to provide coring and tooling materials that can be easily shaped and subsequently removed from cured composite parts.

[0018] Furthermore, an object of the present invention is to provide tooling materials that can be tailored to provide a specific coefficient of thermal expansion and thermal conductivity, thus providing tooling materials that can be matched to the composite structure being fabricated.

Problems solved by technology

Initially, composite components were limited to secondary structures such as floorboards and engine cowlings due to limited experience with designing composite structures.

Composite materials also are used in military and defense applications, where the performance requirements may be even more demanding.

A significant drawback to the use of composite structures in aerospace applications, whether commercial or military, is the complicated and expensive tooling that is required for their fabrication.

The difference in the coefficient of thermal expansion of the composite and of the tool can create geometrical inaccuracies as well as residual stresses.

If the tool material has a low thermal conductivity, significant time can be spent simply getting sufficient heat to the composite part.

Thus, curing irregularities can develop between areas of thick and thin tooling.

These irregularities also translate into geometric inaccuracies and residual stresses.

Also, metal mold materials generally require complex and time-consuming machining operations in order to create the tool surface, which further contributes to design complexities.

For larger components, the time required to generate the surface of the tool can become unacceptable.

Additionally, it can be very difficult to make any modifications to metal tooling once made, if changes to a part are subsequently identified.

Although composite-tooling materials may seem ideal due to the matched coefficient of thermal expansion, such tooling requires another complex composite component fabrication cycle for the tool itself.

Generally, this results in the use of thermoplastic tooling systems that are difficult and expensive to work with.

Additionally, the functional properties of PEOx, such as its glass transition temperature, may not be compatible with certain composite formulations for the parts made using the mandrels.

These materials pose certain processing problems associated with removal of the materials from the cured parts, as well as with the disposal of the materials.

Furthermore, salt mandrels are brittle and must be cast into the desired shape while molten to avoid machining them with diamond tooling.

Despite being soluble in water, eutectic salt mandrels produce corrosive, environmentally unfriendly waste streams when washed from the cured composite part.

Sodium silicate-bonded sand mandrels are readily washed from the cured composite and do not produce corrosive waste streams.

Unfortunately, silicate-bonded mandrels are heavy and brittle, making them difficult to machine without resorting to diamond tooling.

Mandrels made from ceramic microspheres bonded together by poly(vinyl alcohol) have low densities and form relatively easily but have a limited range of temperatures between which they can be used, because poly(vinyl alcohol) polymer binder becomes crosslinked above 200° C., making it difficult to wash the mandrel from the cured part.

Images