Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2002-08-07
2003-09-16
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S086250, C219S091200, C219S086410, C219S119000
Reexamination Certificate
active
06621036
ABSTRACT:
TECHNICAL FIELD
This invention relates to spot welding apparatus, particularly to so-called pogo welding with a single electrode welding gun.
BACKGROUND OF THE INVENTION
It is known in the art relating to spot welding to connect the central portions of large sheet assemblies by so-called pogo welding. In this method, a welding gun having a single electrode is moved sequentially to a series of welding locations at each of which spot welding is performed by transmitting current from the welding gun electrode through the sheets to be joined to backup electrodes located below the specified welding locations.
FIG. 1
shows the concept of a prior pogo welding apparatus
10
, which includes a programmable robot
12
having a linearably movable base
13
supporting a movable jointed arm
14
carrying a welding gun
16
with a single pogo electrode
18
. The electrode is connected electrically with a transformer
20
, also connected with an electrically conductive stand
22
. The stand supports a plurality of copper backup electrodes
24
, each of which engages one of selected welding locations
25
on the lower side
26
of a temporary or loose assembly of two metal sheets, supported on the stand to be spot welded into a permanent assembly
28
.
In operation, the pogo electrode
18
is moved sequentially by the robot
12
to each of the selected locations
25
on the opposite upper side
30
of the assembly
28
. There, the electrode engages the upper side
30
opposite from each of the backup electrodes
24
in sequence. At each location
25
, the welding gun
16
is energized to conduct welding current through the assembly
28
to the opposite backup electrode
24
, spot welding the metal sheets together.
In this prior arrangement, a part of the welding current travels through the metal sheets to the neighboring backup electrodes
24
while the remainder passes through the assembly between the opposing electrodes to perform the spot welding process. Significant current shunting may lead to discrepant welds. The prior process requires a different table or tool tray specifically designed to engage the selected locations for each differing component design that is to be spot welded. Thus, a new or modified component requires provision of a modified welding fixture with the backup electrodes positioned in the changed locations.
SUMMARY OF THE INVENTION
The present invention replaces the conductive stand or tray with a suitable support, where needed, and a programmable positioner carrying a single backup electrode. The support holds the metal sheets in temporary assembly during the spot welding procedure. The positioner carries the single backup electrode on a movable head, which is universally movable within a desired envelope. The positioner is programmed to move the backup electrode sequentially to the various selected locations to be spot welded so that the backup electrode is positioned against one side of the sheet assembly at selected locations when the robot carried pogo electrode is moved against the opposite side of the assembly at the respective selected locations. Various types of positioners may be utilized which may be suitable for the particular components to be welded.
Unlike, the prior table or tray with multiple prepositioned backup electrodes arranged for use with a single component design, the positioner of the invention may be used with differing component designs as may be desired by merely reprogramming the controller for the positioner instead of requiring a new or modified electrode tray or table. The invention further eliminates shunting of welding currents away from the active welding location, since only two opposing electrodes are provided for conducting current through each of the selected welding locations. Thus, weld quality becomes more consistent and the fixture costs resulting from design changes are substantially reduced.
A modification of the invention includes a multi head back-up electrode usable in the inventive apparatus and method to facilitate contact with interior back-up locations that would otherwise be more difficult or less efficient to reach.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.
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Linn Douglas Martin
Sun Peter C.
Wampler, II Charles Weldon
Wang Pei-Chung
General Motors Corporation
Marra Kathryn A.
Stoner Kiley
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