Method of forming honeycomb panels into compound curved shapes

Details Method of forming honeycomb panels into compound curved shapes Method of forming honeycomb panels into compound curved shapes

2000-02-25

2001-08-14

Crane, Daniel C. (Department: 3725)

Metal deforming

By use of non-deforming work-gripping clamp and relatively...

By individually non-deforming clamps

C072S302000, C072S379200

Reexamination Certificate

active

06272897

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to methods of metal forming and particularly to methods of forming difficult to form metal panels such as generally planar honeycomb metal panels which are comprised of a spaced apart pair of metal sheets commonly joined to an internal corrugated core into complex compound curved shapes.
BACKGROUND OF THE INVENTION
In many industries such as aviation fabrication, the need arises to provide materials and structures which are light-weight and strong. While many light-weight and strong structures may be provided through the use of exotic metals and alloys, a great number of structures are required which can not support the expense generally encountered through the use of exotic, light-weight, high-strength metals. One of the most useful fabrication materials for providing structures which maintain high-strength while simultaneously being light in weight is found in so-called “honeycomb” metal panels. Such panels are usually formed of a pair of generally planar metal sheets often referred to as face sheets together with a matrix or core material. In most honeycomb panels, the matrix or core is formed of a generally corrugated structure fabricated of long thin metal strips which are multiply curved or faceted and periodically joined together to form a high-strength matrix or core. One of the most common core structures utilizes elongated thin metal strips which form a core structure generally resembling a section of a common beehive. The face sheets are joined to the edges of the core strips by attachments such as welding or adhesive attachment. Other forms of attachments such as braising, crimping or other means may be used with the overall objective being secure attachment between the matrix or core edges and the face sheets to provide a strong, light-weight and substantially rigid panel.
FIG. 1
sets forth a partially sectioned perspective view of a typical honeycomb constructed in accordance with conventional fabrication techniques and generally referenced by numeral
10
. Panel
10
is shown to include a pair of generally planar metal sheets
11
and
12
formed of a material such as steel or other suitable metal. Panel
10
further includes a core
13
typically formed of a plurality of thin metal strips such as steel or the like multiply faceted and joined together to form a honeycomb-like structure. While not seen in
FIG. 1
, it will be understood in accordance with conventional fabrication techniques metal sheets
11
and
12
are commonly joined to their respective edges of core
13
by conventional fabrication such as welding, braising, adhesives or other attachment. For purposes of illustration, panel
10
is shown in a generally rectangular shape having opposed edges
14
and
15
. It will be understood however that honeycomb panels of different shapes are often used in particular fabrications.
While honeycomb panels of the type shown in
FIG. 1
provide an extremely cost effective and light-weight, high-strength fabrication material which is in many respects desirable for manufacturing processes, a substantial limitation has thus far arisen in the difficulty found in shaping such honeycomb panels to suit manufacturing needs. In many instances fabrications are provided in which the honeycomb panels are cut and welded together in sections to provide shapes which are generally angular or faceted in character. Unfortunately a substantial number of manufacturing needs such as those in aviation fabrication require that materials be formable into curved elements rather than faceted. The honeycomb core and face sheet combination of honeycomb panels does not allow the panels to be formed using conventional rolling or stamping processes due to the tendency of such processes to crush or deform the core material or overly stress the attachment of the core edges to the face sheets.
One of the most successful processes thus far developed for forming honeycomb panels into curved shapes for use in industries such as aviation fabrication is generally known as the “stretch wrap” or “stretch forming” process.
While stretch wrap or stretch forming processes have been developed in some variety, the basic stretch forming process utilizes an apparatus often referred to as “stretch wrap machine” in which the to-be-formed panel is positioned within a work station having a stationary support upon which a form block is secured. The form block defines a curved surface corresponding to the desired curvature which is to be imparted to the honeycomb panel. The remainder of the work station often referred to as a main frame supports a plurality of power driven articulated devices often referred to as articulated arms. Each supports a plurality of gripping jaws or other apparatus utilized in grasping the opposed edges of the honeycomb panel.
In some stretch wrap machines the jaw structures of the articulated arms may grip the panel edges directly. However, more often pluralities of elongated metal pull tabs are welded to each side of the honeycomb panel along opposed edges thereof. For the most part such pull tabs are usually arranged in pairs on each of the face sheets along the panel edges. The jaw structures of the articulated arms then grip the pluralities of pull tabs rather than the panel edges themselves. Once the panel is secured in the jaw structures within the stretch wrap machine, forces are applied to the articulated arms to draw the panel edges outwardly and thereby place the honeycomb panel in a predetermined tension. This tension is generally transverse to the major axes of the curved face of the form block. Once sufficient tension has been imposed upon the honeycomb panel, the articulated arms are then driven toward and beyond the form block to literally wrap it partially about the curved face of the form block. The wrapping process is carried forward while maintaining the panel in tension. It has been found that the maintenance of substantial tension upon the honeycomb panel during the wrapping process allows the panel to be formed into a curved shape without damaging the panel. The limitation on this process being care to ensure that the compressive strength of the core is not met or exceeded.
Once the wrapping process is complete, the tension applied to the panel is released and the panel curvature remains. Usually as the tension is relaxed a small amount of recovery or “spring back” occurs in the panel. However, for the most part, the panel retains its curvature.
For purposes of illustration, a perspective view of a simplified stretch wrap apparatus and honeycomb panel in FIG.
2
. Thus,
FIG. 2
shows a conventional stretch wrap machine generally referenced by numeral
20
having a stationary spine
16
supporting a form block
17
. Form block
17
defines a curved surface
18
which in the illustration of
FIG. 2
is a cylindrical segment. Stretch wrap machine
20
further includes pluralities of gripping jaws
23
and
24
supported by a pair of articulated arms
25
and
26
respectively. Arms
25
and
26
as well as pluralities of jaws
23
and
24
are fabricated in accordance with conventional fabrication techniques which are known in the art. While not seen in
FIG. 2
, it will be understood that conventional apparatus are utilized in stretch wrap machine
20
for supporting spine
16
and for articulating arms
25
and
26
. Further, gripping jaw pluralities
23
and
24
are conventional and include conventional means for gripping (not shown). In accordance with conventional stretch wrap machine forming processes a honeycomb panel
10
having edges
14
and
15
is positioned within stretch wrap machine
20
and is supported by a pair of pull tabs
22
along edge
14
and a pair of pull tabs
21
along edge
15
. As described above, pull tab pairs
21
and
22
are typically arranged on each side of one edge of panel
10
and are typically joined to the panel edge portions by welding attachment or the like. As is also mentioned above, jaw pluralities
23
and
24
grip the outwardly extending ends of pull tab pai

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