Electric heating – Inductive heating – With heat exchange
Reexamination Certificate
1999-09-02
2002-04-02
Hoang, Tu Ba (Department: 3742)
Electric heating
Inductive heating
With heat exchange
C219S603000, C219S633000, C219S673000, C219S675000
Reexamination Certificate
active
06365883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, generally, to apparatus for joining two structural sheets by heating a bonding material disposed between the juxtaposed edges of two metal sheets and, more specifically, to electrical heating apparatus for heating a bonding material to join two sheets together.
2. Description of the Art
The use of a heat curable, adhesive bonding material to join two juxtaposed structural elements or metal sheets is widely used in the automotive industry. Such a bonding technique is employed for doors, deck lids, hoods and like assemblies in which two metal sheets or panels are arranged in an edge overlapping manner with a suitable bonding material placed between the two sheets before the edge of one sheet is hemmed over the adjacent edge of the other sheet. Heat is then applied to the bonding material to cure the material and form a high-strength joint between the two structural elements or sheets.
It is well-known that the assembly of automotive vehicles involves high production rates. As such, electric induction coils have been employed to provide the necessary heat to quickly cure the bonding material. Such induction coils carry a high frequency electrical current which generates a magnetic field and causes heating of the metal sheets, which heat is conducted to and cures the bonding material disposed between the two sheets. Since the hemmed perimeter areas of doors, deck lids, hoods and the like can be quite large, it is common to employ such induction coils at only selected locations along the length of any hem so as to spot cure the bonding material only at the locations of the induction coils. The remainder of the bonding material is cured at a later time during the assembly process, such as when the automotive vehicle passes through a paint oven. It is also known to use induction coils around the entire perimeter edge or edges of an assembly to cure all of the bonding material at one time.
A typical prior art induction coil for bonding applications is shown in FIG.
1
. In this typical arrangement, an induction coil
10
is positioned below an insulating material support
12
. The support
12
receives and supports a hemmed edge
13
of an outer sheet or panel
14
and an inner sheet or panel
16
. A strip of adhesive bonding material
18
is disposed between the outer and inner sheets
14
and
16
prior to the hemming operation. The passage of a high frequency electrical current through the induction coil
10
generates a magnetic field which induces heat in the metal sheets
14
and
16
, which heat is conducted to and cures the bonding material
18
in the area of the induction coil
10
.
FIG. 2
depicts another typical induction coil which is described in greater detail in U.S. Pat. No. 4,950,348. The induction coil
20
includes a generally rectangular-shaped coil assembly having a pair of outwardly extending legs
22
, only one being shown in
FIG. 2
, which are connected to a source of electrical power, such as a transformer, not shown. A riser
24
and mounting base
26
are connected to the coil
20
to provide a suitable mount for the coil
20
. Cores
28
are disposed about selected portions of the coil
20
for concentrating the magnetic field generated by the coil
20
. In use, the prior art coil
20
, shown in
FIG. 2
, is disposed on only one side of a hem joint between two overlapping sheets, such as the sheets
14
and
16
shown in FIG.
1
.
The use of a single induction coil, as shown in the prior art arrangements of
FIGS. 1 and 2
, requires long heating times to cure the bonding material to a sufficient strength. Further, since the single induction coil is located on only one side of the hemmed joint of two sheets, more heat is generated at one sheet than on the other sheet resulting in an uneven heating of the bonding material.
FIG. 3
depicts yet another prior art induction coil used in bonding applications. In this arrangement, which is described in greater detail in U.S. Pat. No. 4,602,139, a lower fixture
30
attached to any suitable tool or support, not shown, carries a first or lower induction coil
32
which is mounted in a block of electrically insulating material
34
. The lower fixture
30
also supports the hemmed joint formed between a lower outer sheet
36
and an inner disposed upper sheet
38
, with a strip of adhesive bonding material
40
disposed therebetween. An upper fixture
42
supports a second or upper induction coil
44
which is also mounted in a block of electrical insulating material
46
in the upper fixture
42
. The upper fixture
42
and the lower fixture
30
are movable with respect to each other so as to be separated from each other to permit the mounting or removal of the hemmed sheets
36
and
38
between the two fixtures.
In one mode of operation, the upper fixture
42
is lowered over the hemmed sheets
36
and
38
to place the second induction coil
44
above one surface of the hemmed edge of the sheets
36
and
38
. The first or lower induction coil
32
is positioned substantially in line with the second coil
44
, but is located below the hemmed edges of the sheets
36
and
38
. The use of two induction coils
32
and
44
on opposite sides of the hemmed joint of the sheets
36
and
38
creates a more even heating of the bonding material
40
since heat is applied to the sheets
36
and
38
from both sides at the same time. However, the design of the tooling in this arrangement is more complicated since at least one of the fixtures, such as the upper fixture
42
, must be movable with respect to the other fixture to permit the mounting and removal of the hemmed sheets
36
and
38
therebetween.
U.S. Pat. Nos. 5,365,041 and 5,442,159, assigned to the Assignee of the present invention, disclose an apparatus and method for heating adhesively bonded metal sheets utilizing an L-shaped coil. The L-shaped coil has a first leg which is disposed underneath the hemmed metal sheet joint and a perpendicular second leg located adjacent to the side edge of the hemmed joint in close proximity to the outer surface of the upper metal sheet.
This L-shaped coil, as compared to single side heating, causes the temperature of the upper sheet to more closely approximate that of the lower sheet. The temperature of the lower sheet is slightly hotter than the upper sheet due to the first coil leg being disposed in near proximity to the lower sheet; while the upper sheet is primarily influenced by the second leg of the coil which is not in as near proximity to the upper sheet as the first coil leg is to the lower sheet. Although the upper surface temperature is cooler than that of the lower sheet, the temperature difference between the two sheets is less than that obtained with single side heating thereby providing a better adhesive bond.
However, if the joined sheets have a lower surface which is convex, as it typical in an automotive body panel, the inclusive angle between the first and second legs of the coil must be greater than the preferred 90° to facilitate loading of the panel onto the fixed coils. This inclusive angle adversely increases the temperature difference between the lower and upper sheets.
Thus, it would be desirable to provide a novel induction bonding apparatus and method which cures a bonding material to a higher strength than in prior art bonding apparatus. It would also be desirable to provide an induction bonding apparatus and method which creates a high strength, cured bond between two sheets or panels in less time than with previously devised heating apparatus for bonding applications. It would also be desirable to provide an induction bonding apparatus and method which uniformly heats both of the upper and lower surfaces of a hemmed adhesive joint.
SUMMARY OF THE INVENTION
The present invention is an induction heating coil for curing a bonding material disposed between overlapped or hemmed portions of two structural members or metal sheets by heating the bonding material to a cured state.
In one aspect of the invention, the in
Hoang Tu Ba
Robotron Corporation
Young & Basile P.C.
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