Method for fabricating composite grid-stiffened structures with integrated fluid channels

• US 8,657,984 B1
• Filed: 07/26/2010
• Issued: 02/25/2014
• Est. Priority Date: 07/26/2010
• Status: Active Grant

• Current Assignee: US Department of The Air Force (U.S. Department Of Defense)
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Williams, Andrew D., Underwood, Richard Lee Jr., Busch, Greg Thomas
• Primary Examiner(s): Tucker, Philip
• Assistant Examiner(s): WU, VICKI H
• Application Number:
  US12/843,160
• Time in Patent Office: 1,310 Days
• Field of Search: 156/245
• US Class Current: 156/245
• CPC Class Codes: B29D 99/0014 provided with ridges or ribs, e.g. joined ribs
• CPC Class Codes: F28F 21/084 from aluminium or aluminium alloys
• CPC Class Codes: F28F 2210/02 with particular branching, e.g. fractal conduit arrangements
• CPC Class Codes: F28F 3/12 Elements constructed in the shape of a hollow panel, e.g. with channels F28D1/02, F28D1/03 take precedence

Abstract

A method for fabricating a grid-stiffened panel which incorporates a network of fluid channels and passageways into the ribs and face sheet is described. The method is comprised of a base tooling assembly, an expansion tooling assembly, a composite prepreg, plugs, a face sheet and a network of valves and pumps, wherein the prepreg is draped over said expansion tooling and assembled with the base tooling assembly to form a rib structure. Channel plugs are placed therein such that gaps between adjacent expansion tooling blocks are filled, and the entire rib structure assembly is autoclaved. The face sheet may be comprised of a plurality of layers, whereby channels are machined into the lower layer(s). The upper layer(s) are bonded to the lower layer(s) to seal the channels, and said face sheet is bonded to the rib structure.

Claims

1. A method for fabricating a grid-stiffened composite structure for supporting and cooling electronic components comprised of a rib structure with integrated fluid channels and a face sheet, comprising:

a. milling an aluminum block to form a base tooling assembly;

b. fabricating a set of expansion tooling blocks having a geometry to fit within said base tooling assembly;

c. covering the expansion tooling blocks with composite prepreg material;

d. pre-compressing said prepreg using de-bulking blocks;

e. placing said expansion tooling blocks covered with said prepreg in the base tooling assembly;

f. filling any voids between adjacent expansion tooling blocks with plugs;

g. enclosing the assembly thus formed from said base tooling assembly, the covered expansion tooling blocks, and the plugs with a cover plate or bag;

h. autoclaving said assembly thus formed to compact and cure said prepreg to form the rib structure of said grid-stiffened composite structure with integrated fluid supply channels;

i. forming a composite face sheet having a lower layer with machined channels cut into said lower layer to form a looped fluid distribution pattern of a smaller size and spacing than said integrated fluid supply channels of said rib structure to create a surface area through which heat transfer can occur, and having an upper layer comprised of one or more layers configured to accept electronic components requiring support and cooling;

j. bonding said upper layer to said lower layer to seal said machined channels;

k. applying said lower layer of said face sheet to said cured rib structure; and

l. autoclaving said assembly including said face sheet applied to said cured rib structure to cure the bond between said face sheet and said rib structure and to thereby seal the channels integrated into said rib structure in fluid communication with the loop fluid distribution pattern formed in the face sheet to provide for variable fluid flow throughout the assembly and face sheet.

2. The method of claim 1 wherein said base tooling assembly is comprised of graphite, ceramic, wood, tooling foam, tooling epoxy, steel, or aluminum.

3. The method of claim 1 wherein said expansion tooling blocks are comprised of silicon rubber.

4. The method of claim 1 wherein a mold release is applied such that neither said base tooling assembly nor said expansion tooling blocks adhere to said cured rib structure.

5. The method of claim 1 wherein thermal stresses on said cured rib structure are mitigated by selecting a base tooling material with a coefficient of thermal expansion approximating a coefficient of expansion for said cured rib structure.

6. The method of claim 1 wherein thermal stresses on said cured rib structure are mitigated by creating a buffer zone between the expansion tooling blocks and the base tooling assembly.

7. The method of claim 1 wherein the junction between said face sheet and said rib structure is filleted.

8. The method of claim 1 wherein a network of pumps and/or valves is installed between the adjacent expansion tooling blocks in place of the plugs.

9. A method for fabricating a grid-stiffened composite structure for supporting and cooling electronic components comprised of a rib structure with integrated fluid channels and a face sheet, comprising:

a) milling an aluminum block to form a base tooling assembly;

b) fabricating a set of expansion tooling blocks having a geometry to fit within said base tooling assembly;

c) covering the expansion tooling blocks with composite prepreg material;

d) pre-compressing said prepreg using de-bulking blocks;

e) placing said expansion tooling blocks covered with said prepreg in the base tooling assembly;

f) incorporating a network of pumps and/or valves between said adjacent expansion tooling blocks;

g) enclosing the assembly thus formed from said base tooling assembly and the covered expansion tooling blocks with a cover plate or bag;

h) autoclaving said assembly thus formed to compact and cure said prepreg to form the rib structure of said grid-stiffened composite structure with integrated fluid supply channels;

i) forming a composite face sheet having a lower layer with machined channels cut into said lower layer to form a looped fluid distribution pattern of a smaller size and spacing than said integrated fluid supply channels of said rib structure to create a surface area through which heat transfer can occur, and having an upper layer comprised of one or more layers configured to accept electronic components requiring support and cooling;

j) bonding said upper layer to said lower layer to seal said machined channels;

k) applying said lower layer of said face sheet to said cured rib structure; and

l) autoclaving said assembly including said face sheet applied to said cured rib structure to cure the bond between said face sheet and said rib structure and to thereby seal the channels integrated into said rib structure in fluid communication with the loop fluid distribution pattern formed in the face sheet to provide for variable fluid flow throughout the assembly and face sheet.

10. The method of claim 9, wherein said base tooling assembly is comprised of graphite, ceramic, wood, tooling foam, tooling epoxy, steel, or aluminum.

11. The method of claim 9, wherein said expansion tooling blocks are comprised of silicon rubber.

12. The method of claim 9, wherein a mold release is applied such that neither said base tooling assembly nor said expansion tooling blocks adhere to said cured rib structure.

13. The method of claim 9, wherein thermal stresses on said cured rib structure are mitigated by selecting a base tooling material with as coefficient of thermal expansion approximating a coefficient of expansion for said cured rib structure.

14. The method of claim 9, wherein thermal stresses on said cured rib structure are mitigated by creating a buffer zone between the expansion tooling blocks and the base tooling assembly.

15. The method of claim 9, wherein the junction between said face sheet and said rib structure is filleted.