Aggregate-based mandrels for composite part production and composite part production methods

Abstract

A method for forming a composite structure, using a mandrel that is later removed from the composite structure, involves production of a mandrel by depositing a particulate mixture, including an aggregate and a binder, into a mold and removing the mandrel from the mold. The mandrel may be treated while still in the mold by heating, curing with an agent, microwave energy, or by some combination thereof. Once finished, the mandrel can be used in manufacturing polymer and / or composite components. The mandrel can also be include materials that can be easily removed from the finished composite structure by water, shakeout, chemically dissolving, or by some combination thereof.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority to U.S. Provisional Patent Application No. 60 / 949,765, filed on Jul. 13, 2007, the contents of which are incorporated herein by reference and made part hereof.FIELD OF THE INVENTION[0002]The present invention relates to a process and method for producing composite parts. In particular, this invention relates to mandrels for the mass production of polymer or composite structures, and to processes and methods for forming such mandrels at sufficient rates for mass production.BACKGROUND OF THE INVENTION[0003]Composite materials, such as fiber-reinforced composites, can be used to produce corrosion resistant and lightweight structures. “Composite material,” as used herein, refers to a material comprised of two or more separate materials, which may include a fiber or polymer binder or a combination of the two. The most common composites are normally comprised of a fiber (Glass, Kevlar, Carbon, etc) impregnated wi...

AI Technical Summary

Benefits of technology

[0017]In one broad aspect, the invention relates to the production of complexly shaped mandrels with high precision without a pourable material that contains excess water. According to this aspect, the invention further eliminates the difficulties associated with mandrels produced by compression of materials such as by means of mechanical compaction that can result in uneven form filling. The above problems can be mitigated by transforming the aggregate / binder mixture into a fluidized state by application of kinetic energy to the mixture. In one embodiment, kinetic energy is imparted into a non liquid mandrel material, such as a binder / aggregate mixture, through a carrier fluid (most commonly a gaseous fluid such as air or nitrogen), by which the solids are able to be displaced as a semi fluid. Once in the semi fluid state, the mixture can then be directed / injected / blown into a mold in a similar fashion as a pourable material. As the material enters the mold, the carrier fluid is removed through properly placed vents while the material is remains contained in the mold. This technique affords the fast production of aggregate based mandrels that can readily be dried / cured using a host of processes, such as gas cure or heat drying.

[0018]In general, aspects of the present invention relate to methods of manufacturing composite structures wherein high quality mandrels can be produced in a relatively short period of time. Various arrangements for forming and curing mandrels are disclosed that may be used in an industrial or automated process whereby a large number of high quality mandrels may be made quickly and inexpensively.

[0020]Additional aspects of the invention relate to mandrel material compositions that can be cured quickly, thereby facilitating a mechanized or automated process for mandrel mass production. Further aspects of the invention relate to mandrel material compositions that may provide mandrels having sufficient strength with little or no curing such that the mandrel may be handled, stored, or shipped, wherein curing may be completed at a later time or even over time during the course of storage or shipment. Further, the invention may make use of other currently available water soluble binders for producing composite mandrels depending on the necessary properties.

[0021]Still further aspects of the invention relate to methods of manufacturing composite structures wherein the mandrel materials may be environmentally benign and water-soluble. Moreover, aspects of the invention allow for the reclamation of mandrel materials for reuse to further reduce costs and minimize the impact on the environment.

Problems solved by technology

In the aircraft industry, composite components were initially limited to secondary structures such as floorboards and engine cowlings due to limited experience with designing composite structures.

Composite materials also are used in automotive, recreational, 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, particularly when a seamless, hollow structure is desired.

For many applications, the mandrel is a single use mold / tool that is destructively removed from the finished part either by a chemical process or by mechanical agitation.

Plaster easily pours into a mold and forms a solid structure but requires a significant curing time.

Moreover, plaster is generally removed by mechanical agitation which can result in damage to the composite structure, after which the material is discarded as waste.

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.

Moreover, despite being soluble in water, eutectic salts produce corrosive, environmentally unfriendly waste streams when washed from the cured composite part.

The bladder process, however, is not useful for complex shapes and does not produce a composite structure with the same accuracy as a more conventional molded mandrel, particularly where the internal dimensions of the part are critical.

Each of these processes can be very labor and time intensive.

Eutectic salts mandrels require the salt to be melted at temperatures in excess of 350° F. and, once molten, must be manipulated into a mold where it must cool and set for extended periods of time, often causing burns unless special protective clothing is worn.

Further depending on the complexity of the mold and exposed cross section, significant amounts of water and time are needed to remove the eutectic salt from the mold, which also creates a highly corrosive waste stream.

This agitation leads to the formation of air bubbles within the material that can form significant defects in the resultant mandrel.

Once set, the mandrel can be removed from the mold, but is not ready for composite layup, since it still contains significant amounts of water.

Plaster is extremely time and energy intensive to dry since it forms a dense egg shell like skin, which acts as a heat and water barrier.

Mechanical methods are then used to remove the mandrel often damaging the composite due to delamination.

Prior works have attempted to produce a water soluble plaster material that aids in the removal of the core from the finished composite part, but has come at the cost of reduced strength in the core.

Further since these water soluble plasters still incorporate large amounts of water to pour the material there is a significant amount of time and energy needed to cure and dry the core.

These materials can be labor intensive or require expensive tooling since the materials must normally be packed at high pressure to ensure uniformity in the mandrel.

Further, complex shapes are very difficult to form since the materials are not very flowable and, as such, don't tend to fill molds with reverse cavities.

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