Patent Application
20050023721
The present invention relates generally to the field of fabrication tooling and, more particularly, to fabrication of high performance tooling for bonding processes.
Composite products, spanning in production for the last fifty years, are utilized in industries such as automotive, commercial aircraft, boating, sports equipment and any other production industries utilizing thermosetting fiber/resin material systems. The structural integrity of composite laminates is severely compromised when such laminates are drilled or cut such as for the purpose of attachment. A hole or aperture in the laminate tends to compromise the integrity of the laminate and provides a site for structural failure.
In high-performance applications, such as aerospace structures, a typical composite may comprise a mat of interwoven high modulus filaments impregnated with a polymer. The drilling of such a laminate to provide a means of attachment destroys the continuity of the structural filaments contained within the composite.
Composite structures can also be attached by co-curing the structures with a similar joint material. However, this process is very time consuming, expensive, and often results in a composite joint with a structural integrity of much less than that of the joining structures.
The present invention provides a pressure intensifier to enable structurally sound bonding of composite structures avoiding the aforementioned attachment problems.
The present invention achieves technical advantages as a method for fabricating mandrels which are used as pressure intensifiers for cobonding or consolidation fabrication of composite assemblies. Mandrel molds are created using rapid prototyping, such as stereolithography, generated directly from a virtual model which is created with a processor aided design type program requiring little or no engineering drawings. The mandrel can be applied in a specific process for cobonding cured detailed parts using an uncured element enabling intensified pressure to the joint or fillet area during the bonding process.
For a more complete understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings, wherein like numerals refer to like elements, wherein:
The numerous innovative teachings of the present application will be described with particular reference to the presently preferred exemplary embodiments. However, it should be understood that this class of embodiments provides only a few examples of the many advantageous uses and innovative teachings herein. In general, statements made in the specification of the present application do not necessarily delimit any of the various claimed inventions. Moreover, some statements may apply to some inventive features, but not to others.
Referring now to
Referring now to
The ratio of radii 232 and 234 in the mandrel 230 can be selected to improve the part definitions in the fillet area. Preferably, the mandrel 230 is designed with a specific ratio of radii, as to design a large, outside radius 232 to act as a pressure multiplier (ratio of areas) to the smaller radius 234 and therefore consolidate the composite preform well. An exemplary ratio of radii 232 and 234 is R0.75 and R-0.03 respectively.
Rubber type parts can be fabricated by pouring or injecting rubber, as a fluid, into a metal or wood tool, for example, which is configured to simulate a rib and a skin, for example, intersecting at an arbitrary angle. The tool works essentially as a mold, allowing the rubber to cure into such a configuration, however, metal or wood molds typically require a machining processes to define the required shape. Conventional machine tool subtractive methods typically involve a large initial expense for engineering drawing and setting up the proper machining protocol and tools. As such, the set-up time is not only expensive, but relies a great deal on human judgment and expertise. Another difficulty associated with such conventional machine tool subtractive processes is the difficulty or impossibility of making many part configurations. Where a desired part is unusual in shape, the machining becomes more difficult. In many cases, a particular part configuration is not possible because of the limitations imposed upon the cutting tool placement on the part. These problems are exacerbated where only a small number of parts are desired. For example, an aircraft has many joint and corner areas which define the intersection of component parts which make-up the aircraft. Analyzing the cost and time attributed to every corner or edge being adhered to, it is appreciable to consider that a special tool or pressure intensifier must be designed, developed and manufactured for every unique joint and corner for that adhesion to take place. Rarely are two comers or joints exactly the same dimensions, thereby making production of a single composite structure, such as an aircraft fuselage, dependent upon a great deal of additional engineering. Such complexities substantially increase the cost of complex articles or entities, such as contoured aircraft, for example. Casting and extrusion techniques are also inefficient for many of the same reasons.
The replica mold is formed via a rapid-prototyping process such as stereolithography (SLA) 20. SLA is known in the art to produce a physical, three dimensional object using data from a data file. The replica mold is generated directly from the data file and therefore requires no engineering drawings. A stereolithography machine can use, for example, a computer controlled laser to cure a photo-sensitive resin, layer-by-layer, to create the prototype. SLA is “rapid-modeling” since the objects typically generated from existing photo-sensitive resins or photopolymers do not have the physical, mechanical, or thermal properties typically required of end-use production materials. However, stereolithography is capable of producing extremely complex parts with reduced design effort (i.e., no drawings are required). Parts are made directly from the CATIA solids in a relatively short time and for minimal expense compared to current mill tooled or sandcast methods.
The mandrel or pressure intensifier is formed 30 by pouring a suitable fluid material into the mold and curing. Such suitable materials include, but are not limited to, rubbers such as room temperature vulcanizing (RTV) rubbers, silicones, non-hardening polymers or materials exhibiting similar characteristics, for example. The use of RTV rubbers provides for a device which is inexpensive to reproduce and which conforms under autoclave pressure to the parts to which they are located. For multiple part molds, mating edges are first sealed to prevent the fluid material from escaping prior to curing or hardening. Subsequent to curing of the fluid material, the mold is removed from the new mandrel.
Since stereolithography machines can have limitation to the size of parts that can be produced, the pressure intensifier design can be separated into smaller multiple component parts. Following fabrication of the mold and curing of the fluid material, the smaller corresponding cured mandrels can be joined prior to application in the consolidation fabrication process.
Referring now to
Although preferred embodiments of the method and system of the present invention has been illustrated in the accompanied drawings and described in the foregoing detailed description, it is understood that obvious variations, numerous rearrangements, modifications and substitutions can be made without departing from the spirit and the scope of the invention as defined by the appended claims.
The present application is a continuation application of, and claims the benefit of U.S. patent application Ser. No. 09/801,461 filed Mar. 8, 2001, and entitled “MANDREL FABRICATION FOR COBOND ASSEMBLY,” the teachings of which are incorporated by reference herein.
This invention was made with Government support under Contract Number F33615-94-C-3210 awarded by The Department of the Air Force. The Government has certain rights in this invention.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09801461 | Mar 2001 | US |
| Child | 10926700 | Aug 2004 | US |
