Method and system for fabrication of composite parts

Details Method and system for fabrication of composite parts Method and system for fabrication of composite parts

1998-06-19

2001-05-29

Sheikh, Ayaz (Department: 2781)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C700S300000, C700S222000, C205S918000

Reexamination Certificate

active

06240333

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates in general to the field of fabrication of composite parts, and more particularly to an improved method and system for processing composite parts in an autoclave.
BACKGROUND OF THE INVENTION
Composite materials have a wide variety of commercial and industrial uses, ranging from aircraft and automobile to computer parts. Composite materials have many advantages which make them attractive to different industries. For instance, composite materials can reduce heat transfer, resist conduction of electricity, limit reflection of radar waves, are flexible but strong, and can be fairly easily formed into complex shapes during manufacturing. Some examples of commercial applications include the complex shapes of certain automobiles, airplanes, and boats which would be difficult to form with metal materials. Another important use of composite materials is the creation of stealth aircraft which minimize their radar cross section through the use of radar absorbing composite materials that form the majority of the aircraft's structure.
One example of an aircraft made largely from composite materials is the F-22 Raptor, the world's premier tactical aircraft, designed and manufactured by Lockheed Martin Tactical Aircraft Systems. The Raptor's composite parts are formed with flexible graphite fibers, called a ply, that are impregnated with epoxy or BMI resins which harden when subjected to the application of heat. The uncured plies are placed on tools, each tool corresponding to a composite part of the Raptor. Thus, when the graphite resin mixture hardens over the tool, the composite part is formed with the proper shape.
A number of production techniques are available for forming composite parts. Again, using the Raptor as an example, once the plies are placed over the tool, a vacuum bag is used to hold the plies securely to the tool during curing of the resin. The vacuum bag forces the material to the tool and prevents the formation of bubbles and other material deformities. The tools are then placed in an autoclave for heating. An autoclave is essentially a large oven with the ability to precisely control the thermal energy applied to tools during curing of composite parts. An autoclave operator can monitor and control the amount of thermal energy applied to the tools to maintain a predetermined heating rate of the composite parts. For instance, one typical resin will cure into the strongest possible material if the resin is heated from room temperature to just over 350° F. at a heating rate of between 1° F. per minute and 5° F. per minute. Variations from this heating schedule could result in defective parts.
The autoclaves used for curing of aircraft composite parts are necessarily large in order to accept large parts, and in order to mass produce a large number of parts. For instance, a typical autoclave is 50 feet long and has a heating container large enough to accept a forklift driven into it. The autoclave distributes thermal energy through the heating container by blowing heated air with a large fan located at one end of the heating container.
An autoclave operator must carefully distribute tools in the autoclave heating container in order to ensure that heating rate specifications are met, especially when larger autoclaves are used to produce parts of varied sizes and materials. The operator must ensure that only compatible materials are processed in each autoclave production run. Once the tools are placed in the autoclave, the autoclave operator generally must monitor the temperature and heating rate of the tools to compensate for variances in the thermal energy introduced by the autoclave, interference between tools caused by uneven airflow, and other difficulties. Operator intervention can ensure that the tools are heated within the proper specifications; however, all of this can be time consuming tasks for an autoclave operator. Further, when an autoclave operator attempts to compensate for uneven heating relating to variations in the distribution of thermal energy throughout the autoclave heating container, inefficiencies can be introduced to the production process. For instance, if an autoclave operator adjusts heating rates to a lower level in order to avoid over-heating of a part, the autoclave will require a greater amount of time to cure other parts, increasing the time required for the entire production run. Finally, if the parts are distributed improperly, the autoclave operator may have to violate the heating rate specifications for some of the tools, thus wasting the parts on those tools, in order to obtain useful parts from other tools.
SUMMARY OF THE INVENTION
Therefore, a need has arisen for a method and system for fabrication of composite parts which increases the efficiency of production equipment to allow greater throughput of high quality parts with minimal wasted materials.
In accordance with the present invention, a method and system for fabricating composite parts is provided that substantially eliminates or reduces disadvantages and problems associated with previously used methods for producing composite parts.
The method includes the steps of selecting plural tools, each tool associated with one of plural parts selected for fabrication, and each tool having a thermal performance. A layout pattern for the tools in an autoclave heating container is determined so as to provide a minimum autoclave processing time for fabrication of the plural parts, with the minimum processing time determined by using the thermal performances of the tools. The layout pattern can then be displayed for use by an autoclave operator.
More specifically, the method and system of the present invention allow an autoclave operator to achieve efficient and user-friendly production of predetermined composite parts. The autoclave operator may receive an order or schedule for production of specific predetermined parts in an autoclave run, or may select predetermined parts as a subset of an order. The autoclave operator can select a tool for each predetermined part as needed. Once the autoclave operator has selected tools for the desired parts, he can input these tool selections into a computer system to obtain a layout pattern for maximizing the efficiency of the production process by minimizing the time needed for processing in the autoclave.
The computer system provides an easy-to-use graphical user interface for accepting inputs from the autoclave operator and displaying the tool layout pattern. One window on the graphical user interface displays a tool library which can include all of the tools available for selection by the autoclave operator. The tool library window interacts with a tool library which stores data relevant to each tool, such as the thermal performance of the tool. The computer system also includes an autoclave library for storing thermal characteristics of the autoclave available to the autoclave operator. The graphical user interface accepts tool selections from the autoclave user, such as the tool selections corresponding to the predetermined composite parts for fabrication, and provides the tool selections to a layout engine. The layout engine determines a layout pattern by using the tool selections, the thermal performances associated with each tool selected and the thermal performance of the selected autoclave to determine a layout pattern for the selected tools. The layout engine provides the layout pattern to the graphical user interface for display to the autoclave operator, who can then load the autoclave and process the desired composite parts.
The layout pattern provided by the layout engine can optimize production for a given autoclave and a given set of tools based on a number of production goals. One important production goal is to minimize autoclave processing time for a given set of tools. Another important production goal is to reduce waste of production space and materials by insuring that the parts included in a particular autoclave production run will cure within the desired spec

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