Metal fusion bonding – Process – Diffusion type
Reexamination Certificate
1999-07-14
2001-07-24
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Diffusion type
C228S184000, C228S194000, C228S262500
Reexamination Certificate
active
06264095
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods of bonding and sealing together metal parts. In particular, the present invention relates to processes of fabricating and repairing hollow beryllium structures, such as thermal control devices and other pressure vessels for space flight applications, through high temperature isostatic pressure bonding.
2. Background of the Invention
Typically beryllium vessels have been formed by welding or brazing using a filler metal, such as aluminum or silver. The problem with such vessels is that the coefficient of thermal expansion (CTE) of the filler metal is substantially different from that of the bulk beryllium. The use of a filler metal for joining results in low strength properties. Although these methods are adequate for systems that require lower strength properties and do not go through a large range of temperatures during thermal cycling, they reduce the reliability of the system.
U.S. Pat. No. 3,964,667 to Anderson teaches diffusion bonding of beryllium parts under pressure, using a coating of nickel between the beryllium parts. U.S. Pat. No. 5,615,826 to Dixon et al. teaches joining of beryllium parts by welding with an aluminum alloy (e.g., aluminum and silicon).
These bonding methods should not be used with pressure vessels having high internal pressures and that are subjected to large temperature variations, AT. One example of such a vessel is a space flight Thermal Storage Unit (TSU). TSUs translate across a large temperature swing (&Dgr;T~300° K), and require large factors of safety in the bond area to meet the aerospace requirements.
A need therefore exists for improved bonding methods that provide the necessary reliability.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a means for building or repairing fabricated structures, which meets aerospace requirements.
It is a further object of the present invention to provide a hot isostatic pressure (HIP) bond method of sealing outer shells.
It is proposed that the bonding method of the present invention can be used to seal thermal control devices and other pressure vessels for space flight applications. Typically these systems require weight optimization, high reliability and the ability to withstand large temperature cycling throughout their functional life. The HIP bond method of sealing a pair of outer shells is ideal for these applications, providing a seamless vessel with a homogeneous material composition.
Bonding of beryllium shells to form a beryllium vessel with an interior void (HIPV) is a process that requires four interrelated steps: (1) preparation of beryllium blanks; (2) tooling fabrication and assembly of tooling with beryllium blanks; (3) bonding at high temperature and pressure (i.e., the HIP process); and (4) machining of the vessel exterior. Each of these steps is further defined below.
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Bourke Patrick
Marder James M.
Ryczek Lawrence H.
Stouffer Charles J.
Dunn Tom
Pittman Zidia T.
Roberts Abokhair & Mardula LLC
Swales Aerospace
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