Metal deforming – With cutting – By shearing tool-couple
Reexamination Certificate
1999-12-28
2001-11-06
Crane, Daniel C. (Department: 3725)
Metal deforming
With cutting
By shearing tool-couple
C072S327000
Reexamination Certificate
active
06311535
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a system for automatically embossing and creating a hole in a workpiece. More specifically, the present invention relates to making a hole with an embossed base for accommodating high voltage bushings in transformer tank enclosures.
BACKGROUND OF THE INVENTION
Due to the very nature of their operation, power system transformers must manage high voltage levels. For example, distribution transformers commonly reduce transmission voltages from distribution levels of 2.3 kV to 69 kV down to final utilization levels of 120V to 480V. In so doing, power system transformers use high voltage bushings to input the distribution level voltages. The high voltage bushings are attached to the primary windings of the transformer. Because the transformer windings reside in oil-filled tanks, the high voltage bushings commonly are affixed to the outside of oil-filled transformer tanks. The high voltage bushings are then connected to the primary windings through holes in the transformer tank. In the case of pad-mounted transformers, the oil-filled tanks and high voltage bushings are further surrounded by an outside enclosure for safety reasons.
In order to protect the transformer and protect the public from electrical hazards, the high voltage bushings are sized in accordance with strict industry standards. Accordingly, the corresponding holes made in the transformer tanks must be within strict tolerances. If the holes are out of tolerance, the standard sized high voltage bushings may be too large for the holes, rendering the tank unusable. Alternatively, the holes may be too large for the high voltage bushings, permitting water damage to the transformer and safety concerns for the public.
Manufacturing a pad-mounted transformer tank begins by making holes for the high voltage bushings in flat sheets of metal. The flat metal sheets eventually are formed into rectangular enclosures. The process of making holes for the high voltage bushings in pad-mounted distribution transformers is further complicated by an industry-accepted standard that requires each hole to have a circular raised base, formed at a twelve degree angle with the enclosure. In other words, before punching a hole in the metal sheet, the sheet must have a circular deformation that forms a twelve-degree angle with the rest of the metal sheet. Offsetting the high voltage bushing at twelve degrees permits easier installation and allows the high voltage bushing to use less space in the entire pad-mounted transformer enclosure.
A process called embossing is used to make the circular, raised deformation. Embossing is a process by which metal is lifted and deformed. Either before or after the metal sheet is embossed, a hole is punched such that the embossed portion forms a circular base around the punched hole.
FIGS. 1A and 1B
show one example of a prior art embossing and hole punching process
100
. In
FIG. 1A
, an embossing machine
101
embosses a metal sheet
104
by deforming
105
one side of metal sheet
104
with an embossing punch
103
, without causing, a hole. In order to meet the requirements for a high voltage bushing (not shown), embossing punch
103
has an angled punch head
107
at an angle &agr;. Angled punch head
107
creates an angle &bgr; in metal sheet
104
. In accordance with industry standards for high voltage bushings, angles &agr; and &bgr; commonly are set at twelve degrees.
An operator then removes embossed metal sheet
104
from embossing machine
101
and places it in a hole-punching machine
110
. As shown in
FIG. 1B
, hole-punching machine
110
has a hole punch
102
with a flat punch head
108
. Hole punch
102
also has a radius r
2
that is less than a radius r
1
of embossing punch
103
. The smaller radius r
2
forms a hole
106
with an embossed base raised at an angle of twelve degrees, as required in the transformer industry.
In order to punch a sufficiently round hole, the operator must rotate metal sheet
104
twelve degrees in a counterclockwise direction. The twelve-degree rotation permits hole-punching machine
110
to make a sufficiently circular hole to meet the strict industry standards. In addition, in order to ensure that a precision hole is formed, embossed portion
105
must be placed directly under hole punch
102
. Thus, in order to keep the radius of punched hole
106
within the specified tolerance, the machine operator must carefully align hole punch
102
over deformation
105
made by the embossing punch
103
. The further hole punch
102
is out of alignment with the deformation
105
, the more out of tolerance hole
106
will be. However, visually aligning deformation
105
with hole punch
102
is a difficult and imprecise process. Moreover, once the operator aligns hole punch
102
, metal sheet
104
may move while the operator is securing it to hole punch machine
110
. Accordingly, it often takes many attempts and many unusable metal sheets to create a hole within the strict tolerance required for transformer enclosures. Although there are laser-cutting devices that can create holes within the required tolerance, these devices are far more complex and more costly.
Therefore, it would be advantageous to provide a system and method that would remove the need for human intervention and eliminate the error inherent in aligning an embossed metal sheet with a hole punch. In addition, by removing human intervention, the embossing and punching process may be automated using robots. However, current robotic technology is incapable of rotating metal sheet
104
twelve degrees in a counterclockwise direction as required in prior art process
100
. Automating this process may also contribute to the robotic automation of an entire manufacturing or assembly line process.
SUMMARY OF THE INVENTION
The present invention provides a method and system that creates a hole with an embossed base in a planar sheet. The system comprises an embossing punch that forms a raised area in the planar sheet, a hole punch coupled to the embossing punch that forms a hole in the planar sheet, and a surface for holding the planar sheet. The surface has an aperture that permits the hole punch and the embossing punch to pass through the surface and contact the planar sheet.
In one embodiment, the embossing punch and the hole punch have angled heads whose angles are approximately equal, so that a hole formed in the raised area is circular. Other aspects of the present invention are disclosed below.
REFERENCES:
patent: 1642166 (1927-09-01), McCaffrey
patent: 2432804 (1947-12-01), Rieske
patent: 3442110 (1969-05-01), Walton
patent: 4356717 (1982-11-01), Okunishi
patent: 6101859 (2000-08-01), Shieh
patent: 28087 (1977-03-01), None
patent: 311800 (1989-12-01), None
ABB T&D Technology Ltd.
Crane Daniel C.
Woodcock Washburn Kurtz Mackiewicz & Norris
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