Metal working – Method of mechanical manufacture – Utilizing transitory attached element or associated separate...
Reexamination Certificate
1999-10-07
2002-01-15
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Utilizing transitory attached element or associated separate...
C029S446000, C072S353400
Reexamination Certificate
active
06338189
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to methods and apparatuses for expansion forming and, more specifically, to a method and apparatus for expansion forming a workpiece using an external deformable supporting fixture.
BACKGROUND OF THE INVENTION
Oxide-dispersion-strengthened (ODS) high temperature alloys offer combinations of high-temperature strength, oxidation resistance, and hot corrosion resistance that can not be obtained from other alloys. For example, INCONEL alloy MA 754 has been considered as one of the ODS alloys with greater potential in the next generation advanced gas-turbine hot section components such as turbine vanes and combustor liners. In such applications, the ODS alloys are typically used to fabricate LAMILLOY sheets. As is known in the art, LAMILLOY is a multilayered porous material designed for cooled airframe and propulsion system components. It features a labyrinth of holes and passages in a laminated assembly. LAMILLOY is produced by photochemical machining an array of pedestals and holes in two or more layers of sheet material and subsequently diffusion bonding the layers into the laminated sheet configuration.
One particular use of MA 754 LAMILLOY material is in the construction of a combustor outer liner
10
for a gas turbine engine, as illustrated in FIG.
1
. The combustor liner
10
is formed by roll forming two LAMILLOY sheets into half cylinders (or conic sections)
12
and
14
, brazing the half cylinders
12
and
14
together at two lap joints
16
and
18
, and then expansion forming the brazed detail
10
into the required design dimension, as indicated by the dashed line
20
in FIG.
2
.
The MA754 LAMILLOY material
12
and
14
is preferably joined by brazing lap joints
16
and
18
rather than welding the two half cylinders
12
and
14
together at butt joints, because welding processes result in melting of the base material. Welding is unacceptable in MA754 LAMILLOY material due to agglomeration of the oxide dispersoids in the melted region resulting in drastic reductions in high temperature strength and environmental resistance.
The joining of two MA754 LAMILLOY sheets is accomplished by brazing, which is performed at a temperature below the melting point of the base material. The brazing process requires a lap joint (overlapping ends of the material to be brazed) instead of the butt joint normally used in welding. Therefore, the two half-cylinders
12
,
14
are configured with the two lap joints
16
,
18
which are brazed to form a permanent joint.
As shown in
FIG. 2
, the combustor liner
10
initially has a flat-sided configuration; however, the design requirements call for the sides to exhibit the curved configuration indicated by the dashed lines
20
. In order to achieve the configuration
20
, the workpiece
10
is placed onto a radial expander
22
(see FIG.
3
), which will exert radial forces upon the workpiece
10
until it assumes the configuration
20
. As is known in the art, the expander
22
includes a plurality of jaws
24
which may be moved in a radial direction under, hydraulic pressure.
Referring to
FIG. 4A
, a top plan view of the lap joint
16
,
18
is shown. When the expander
22
is operated, a biaxial tension state of stresses is produced in the directions shown by the arrows in FIG.
4
C. Because the half cylinders
12
,
14
lie in different planes in the area of the lap joint
16
,
18
, the braze joint plane
26
rotates through an angle
28
(see FIG.
4
B), which can be as much as 30 degrees relative to the stress axis.
This joint rotation results in loading the braze joints
16
,
18
in combination of shear, bending and direct tensile stresses. Stress analysis confirms that high stress concentrations exist in the LAMILLOY near the lap joints
16
,
18
during expansion forming. As an illustrative example, a combustor liner
10
was formed from two halves
12
,
14
of rolled MA 754 LAMILLOY. Two brazed lap joints
16
,
18
in the liner
10
, featured overlap dimensions of 0.250 inch wide and 6.750 inches in length. During expansion forming of this combustor liner
10
, the LAMILLOY material failed in a ductile manner due to strain localization near one of the brazed lap joints
16
,
18
with less than 2% bulk diametral expansion. The design deformation objective for this application was 4.5% diametral expansion.
A need exists for a method and apparatus that will allow expansion forming of a workpiece by minimizing the concentration of stresses in the workpiece, particularly stresses related to joint rotation out of the plane of the stress axis. The present invention is directed toward meeting this need.
SUMMARY OF THE INVENTION
The present invention generally relates to an external cylindrical or conic section shaped fixture which is tightly fit around the same shaped workpiece prior to expansion forming to a final dimension. During expansion forming, the external fixture is also deformed and is therefore designed for one-time use. The external cylindrical or conic section shaped fixture of the present invention is particularly useful for expansion forming of workpieces which contain brazed lap joints. The external fixture restrains out-of-plane joint rotation and, reduces the stress concentrations existing near the lap-joints. Additionally, the external fixture provides additional load carrying capability to allow better load distribution during expansion forming. No change is required to the expansion forming machinery or the inner expander dies (jaws) with use of the present invention. Because the external fixture fits tightly over the workpiece, applying a compressive force when the inner expander jaws expand during the forming process, the bending moment on the brazed lap joints is significantly reduced.
In one form of the invention, a method for expansion forming a workpiece is disclosed, comprising the steps of a) providing an expansion forming device; b) providing an external fixture; c) fitting the external fixture around the workpiece; d) fitting the workpiece and external fixture assembly around the expansion forming device, such that the workpiece is positioned between the expansion forming device and the external fixture; e) expanding the expansion forming device such that the workpiece and the external fixture are deformed; and f) removing the external fixture from the workpiece after step (e).
in another form of the invention, a method for expansion forming a workpiece is disclosed, comprising the steps of a) providing an expansion forming device; b) providing a fixture; c) coupling the workpiece to the expansion forming device; d) coupling the fixture to the workpiece; e) expanding the expansion forming device such that both the workpiece and the fixture are deformed; f) removing the fixture from the workpiece after step (e).
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Hammond Stephen N.
Helmink Randolph C.
Kennedy Jacque B.
Testin Robert A.
Xu Raymond Ruiwen
Allison Engine Company, Inc.
Blount Steven A
Hughes S. Thomas
Woodard Emhardt Naughton Moriarty & McNett
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