# US 5,707,576 A · Process for the fabrication of composite hollow crown-stiffened skins and panels

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- Number: US 5,707,576 A
- Document ID: US5707576A
- Status: Granted
- Kind: A
- Application number: 08/475,696
- Filed: 1995-06-07
- Granted: 1998-01-13
- Earliest claimed: 1994-10-04
- Assignees: Boeing North American, Inc.
- Inventors: Don L. Asher
- Web page: https://patentgrep.com/patent/US5707576A

## CPC

- B29D 99/001: {Producing wall or panel-like structures, e.g. for hulls, fuselages, or buildings (articles with hollow walls B29D24/00)}
- B29C 70/446: {Moulding structures having an axis of symmetry or at least one channel, e.g. tubular structures, frames}
- B29D 99/0014: {provided with ridges or ribs, e.g. joined ribs}
- Y10S 428/902: High modulus filament or fiber
- B29D: PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE (making granules B29B9/00; making preforms B29B11/00)
- B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00)
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

A process for forming composite hollow crown stiffened skins and panels in which a first layer or skin is placed on a forming surface of a female mold and, after forming a plurality of U-shaped stiffener elements in the first skin, a second skin is placed over the first skin, whereupon the resulting assembly is prepared for autoclave curing. The stiffener elements are formed by pressing the first skin into U-shaped depressions in the female mold surface and inserting a hollow, expandable rubber mandrel into each of the depressions on top of the first skin. Valve stems in the mandrels enable maintaining the pressure inside at atmospheric pressure. The mandrels are maintained in their "pressurized" state during subsequent formation and autoclave curing steps.

## Claims

### Claim 1

A method for forming a unitary panel structure from fiber-reinforced composite material, comprising the steps of:
(a) forming a first subassembly on a tool, said first subassembly including a first skin and a plurality of channel-shaped elements, the channel-shaped elements being disposed atop the skin and being aligned with one another, said channel-shaped elements having inflatable mandrels disposed therein and secured to a surface of said tool, the channel-shaped elements and the first skin comprising said composite material,
(b) forming a second assembly comprising the first subassembly and a second skin of composite material, the first and second skins being disposed on opposite sides of said channel-shaped elements, and
(c) inflating said mandrels while curing said second subassembly in an autoclave at a temperature not greater than 350.degree. F. to form a unitary, one-piece panel structure.

### Claim 2 (depends on 1)

The method of claim 1, wherein said step of forming a first subassembly further comprises providing said tool which has channel-shaped depressions on said molding surface, and pressing said first skin into said channel-shaped depressions before securing said mandrels in said depressions.

### Claim 3 (depends on 2)

The method of claim 2, wherein said step of forming said first subassembly further includes disposing said expandable mandrels over the deformed first skin in alignment with said depressions.