Electric heating – Metal heating – By arc
Reexamination Certificate
1999-09-14
2001-08-07
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
C219S121630, C219S121650, C219S121660
Reexamination Certificate
active
06271499
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method for welding first and second metallic materials one of which having a surface with an optical pattern disposed thereon and, more particularly, to a method for welding first and second electroformed materials each having the optical pattern on at least one surface thereof while minimizing distortion and damage to the optical patterns as a result of the weld.
2. Prior Art
It is well known that many nickel-based alloys can be joined by a host of welding techniques including arc, solid state, electron-beam and laser beam. When it is required to maintain certain properties after the welding process, the proper choice of welding processes are limited. The following properties and geometric considerations are important when addressing the functionality of certain optical and structural components. In addition to minimizing overall component thermal distortions, an important structural consideration is the retention of the materials original metallurgical and mechanical properties such as those which correlate with fine grain structure, formability and low cycle fatigue. Fine grains will grow when subjected to extended levels of high temperature as might be experienced in a furnace, improperly cooled machining procedures, and high heat input welding processes.
To assure a trouble free final assembly process of complex hardware, it is good design practice to maintain geometric dimensions and tolerances of multiple components and subassemblies. This may be a potential problem when components and/or subassemblies require one or more welding procedures. Welding procedures can readily cause distortions in the components and/or subassemblies, such as warping of the components. Such distortions can result in dimensions and tolerances that do not meet specifications. This problem can be amplified if the component parts have residual stresses present resulting from a forming process or from unfavorable concentration of alloy constituents.
In addition to structural and geometric considerations, the surfaces of these component parts may be optically finished and may ultimately be coated. The welding process and any warping associated therewith cannot be tolerated because it disturbs the optical finish of the welded components and thus compromises the integrity of the optical finish or effects the material in ways which may preclude any subsequent coating process. The optical finish of the surfaces is the critical quality attribute when considering end use functionality.
SUMMARY OF THE INVENTION
Therefore it is an object of the present invention to provide a low heat input welding procedure which would minimize warping and other thermal distortion effects, limit grain growth to the weld, and minimize the size of a heat affected zone (HAZ) caused by the weld.
An additional objective of this invention is to effect a seam weld of optical components without compromising the integrity of any existing or to be applied optical coating. To optimize the functionality of the final hardware, it is important to maintain the desired optical quality of surfaces and any coatings as close to the resulting weld seams as possible.
Accordingly, a method is provided for welding a first metallic material to a second metallic material wherein at least one of the first and second metallic materials have at least one surface with an optical pattern thereon. The method comprising the steps of: arranging the first and second metallic materials into a final position in which they will be welded along a joint; directing focused energy at the joint from a neodymium: yttrium-aluminum-garnet (Nd-YAG) pulsed laser having an energy output in a range from about 10 Joules to about 30 Joules and a pulse length in a range from about 5 ms to about 9 ms; and traversing the joint at a predetermined welding speed while directing the focused energy such that a weld spot overlap in a range from about 50% to about 90% is maintained, resulting in a welded joint wherein a heat effect zone about the welded joint is minimized further resulting in minimal distortion and damage to an area of the optical pattern proximate to the welded joint.
In a preferred implementation of the method of the present invention at least one of the first and second materials comprises a composite having a substrate sandwiched by first and second metallic layers, at least one, and preferably both of the first and second metallic layers having the surface with the optical pattern thereon.
In an alternative version of the method of the present invention, the method further comprises the step of repairing a weld defect in the welded joint, wherein the repairing step comprises the sub-steps of: filling the weld defect with a filler material; directing focused energy at the weld defect from a second laser; and traversing the weld defect while directing the focused energy. Preferably, the second laser is the Nd-YAG pulsed laser.
REFERENCES:
patent: 4782209 (1988-11-01), Caers et al.
patent: 5055652 (1991-10-01), Jones et al.
patent: 5123074 (1992-06-01), Yokota et al.
patent: 6108144 (2000-08-01), Holderer et al.
Erikson Carl Edward
Jones Marshall Gordon
Sheldon Robert Gerard
Elve M. Alexandra
Lockheed Martin Corp.
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