Stock material or miscellaneous articles – All metal or with adjacent metals – Embodying fibers interengaged or between layers
Reexamination Certificate
1999-04-06
2001-04-24
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Embodying fibers interengaged or between layers
C428S614000, C428S652000, C428S653000, C228S160000, C228S174000, C228S190000, C228S252000
Reexamination Certificate
active
06221507
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is concerned with composite panels of all metal construction. All metal honeycomb panels are shown in U.S. Pat. No. 4,013,210. Applicant's U.S. Pat. No. 5,192,623 describes a process for producing laminated structural panels having considerable strength and resistance to bending. Such panels include alternate layers of flat sheets and perforated sheets with the flat sheets either clad with a brazing layer or with a separate brazing layer between the flat and perforated sheets. The sheets are stacked with the perforations aligned, if desired, then vacuum brazed to form a solid panel. Such panels are capable of further processing such as bending, stamping, drilling, or sawing without danger of delamination.
There are current requirements in processing machinery, particularly for the electronic chip and panel display industry, for structural panels which can be subjected to comparatively high temperatures (400-450° C.) and to significant loading without significant bending. For such applications, it is also necessary that the structural panels which support production of electronic panel displays operate at high temperature in a corrosive atmosphere without degassing or emitting particles which can contaminate the product.
SUMMARY OF THE INVENTION
The metal most commonly used for the above applications is aluminum. The major reason is that aluminum does not contaminate the product, such as electronic chips, with particles released under high vacuum, high temperature and chemically corrosive and/or plasma environment and it can be anodized. The problem with aluminum is that it loses its strength at elevated temperatures (above 250° C.). The machines that produce computer display panels require temperatures in the range of 400-450° C. and the productivity of these machines increases with higher temperatures.
The following description of the method for producing this type of new hybrid materials for the requirements described above will be concentrated mainly on aluminum and its alloys but similar methods and manufacturing procedures can be applied to other metals.
The basic concept of this invention is the insertion of high strength, high temperature layer material between layers of aluminum plates and brazing them to a single part. In order to have a continuous joint through the width of the part the high strength layer is perforated in order to enable braze alloy to penetrate through the perforations and create a uniform integrated structure. A second purpose for the perforations is to increase the elasticity of the high strength, high temperature perforated layer in order to match the difference in the thermal expansion coefficient of the two or more alloys. The thickness of the layers and the type of materials used should be carefully chosen with regard to the thickness, thermal expansion coefficient, type of perforations, the pattern, percent of the open area of the perforated layer and its placement in the stack in order to minimize distortion in the final assembly as a function of temperature.
Panels made as described herein using perforated high strength high temperature magnetic materials can be used in space station or space vehicle applications where magnetic properties are needed to walk in an essentially zero gravity or very low gravity environment using magnetic shoes. Such panels will add strength and magnetic properties to aluminum structures with minimum weight penalty. Such magnetic panels can also be used for packaging electronic equipment which is sensitive to electromagnetic interference (EMI) or electromagnetic pulse (EMP).
The high temperature, high strength perforated layers can be manufactured by several methods. For low and medium volume chemical etching, metal cutting laser or water jet is recommended. For high volume production, stamping or precision fine blanking are the preferred methods. When wire cloth is used, laser or a stamping die can be used.
The inner layer(s) which are machined or stamped from an aluminum plate are basically a center core material and are usually in the neutral region during bending and/or under compressive loads only. In some cases, an additional inner layer will be made from clad material in order to have sufficient thickness and/or braze material to fill all the perforated area/volume of the high strength layers.
Exterior layers can be produced from the same or a more expensive alloy than the inner core. In most cases this layer will be a clad layer with braze alloy rolled into it.
Once the individual plates are fabricated, the plates are chemically cleaned and stacked on top of each other as required. The type of brazing used will differ according to the type of metals utilized. Vacuum brazing is preferred in aluminum because it provides a cleaner and stronger joint. Brazing should be uniform and continuous across all the layers of the assembly. Multiple cycle brazing is also an option. In some cases, a portion of the layers are brazed first then reprocessed and additional secondary braze operations are performed, usually with lower temperatures and different braze alloys.
Following the brazing step, any quenching, straightening, stress relieving and/or aging steps may be required. Final matching of the exterior surfaces is done to establish final thickness parallelism and surface finish required.
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Lockhart Industries
Smith Robert C.
Wagner John E.
Zimmerman John J.
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