Structural Panel Fabrication

Sandwich Structured Composite Conventional sandwich or structural panel construction:

• The wekipedia definition gives a very good description of the typical honeycomb panel construction. This is a very dependable lightweight solution that has been used for many years. For more demanding applications where large internal pockets are required consider some variation of the GridLock, IsoGrid or cellular metal truss core designs.
  


• General Design Guidelines

1. Specifications

• MIL-STD-1530................................ Aircraft Structural Intregrity Program (ASIP)
• MIL-A-83444 .................................. Airplane Damage Tolerance Requirements SUPERSEDED by MIL-A-87221

2. Publications

• Hnbk of Al Bonding Technology ...... Google books.

3. Vendor Data

• Hexcel Composites............................ Honeycomb Attributes and Properties.
• New Focus........................................ Offers honeycomb solutions for laser research, microscope workstations and optics platforms.
• Cellular metal truss core .................... CMI's solution to replace a honeycomb core.

• The patented BF Goodrich  GRID-LOCK® joints (US Patent no. 5,273,806), developed by Goodrich's Aerostructure - Division, allow for easy assembly by incorporating machined grooves into skin build ups, essentially eliminating the need for alignment tools. Here is an image of a panel used on the F15, which is a link from the Goodrich image library.

• Defect Identification: A dissertation submitted for partial fulfillment of the requirements for the degree of Doctor of Philosopy, Mechanical Engineering.

1. Other Vendors

• Elbit Systems.................................... Composite and Metal Processing Technologies.

2. US Patents

• 5273806............................................ Structural Element with Interlocking Ribbing.

• Wikipedia definition: This is conventionally a machining operation, however; new techniques are being investigated.


• Water Jet machining to specified depths:
  This article, although old, indicates that water jetting is a viable machining alternative for isogrids. It is projected that a 48-inch-diameter skirt 12 inches high could be milled with an isogrid pattern in 6.3 hours. Milled isogrid patterns can be controlled to 0.001 inch, and thin walls of less than 0.025 inch are achievable. See the Water Jet section.

1. Specifications

• AIAA 2008-2274...........................................Postbuckling of Composite Panels with Isogrid Stiffeners
  
• NASA-CR-124075.......................................IsoGrid Design Handbook

2. Companies using IsoGrid
   

• General Dynamics.......................................This article states that it is King of Lightweight Design.
• IsoGrid Structural Applications.........White paper.
  
• Report No. PD 73-0123....................Conical IsoGrid adapter structural test results
  
• PS Associates....................................IsoGrid-SST, Pictures of IsoGrid Structures.
  

3. US Patents

• 6007894........................................... Quasi-Isotropic Composite Isogrid structure.
• 6286289........................................... Multiple Face Sheet Isogrid Structures.
• 6054352........................................... Composite Isogrid structures for Parabolic surfaces.

• The wekipedia definition gives a little more insight into this attractive machining alternative for large panel fabrication.

• Design Guidelines These may change depending on the vendor selected.

1. Specifications

• AWS Welding Handbook................. Ninth Edition, Volume 3 Welding Processes, Part 2, mentions water jet cutting at the end.

2. Publications

• Engineers Handbook ........................ Manufacturing processes, water jet machining.

3. Vendors

• Ormond, LLC................................. They have machined a .75 thick aerospace part with .012 internal walls. Check out their brochure.
• Waterjets.org ................................. The most complete water jet resource on the web.
• Omax worldwide ............................ Some machines will take work pieces up to 6'8" x 13'4" (2 m x 4 m).