Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2000-07-21
2001-10-16
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S086240, C219S086410, C219S091100
Reexamination Certificate
active
06303893
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a resistance projection welder for welding together first and second work pieces, one of which has a series of projections contacting the other work piece to establish electrical conductivity between the work pieces and form the weld therebetween; and, more particularly, sensing the relative orientation between the first and second work pieces in determining if the orientation is proper.
2. Related Art
Resistance welding is a well-known technique for welding together two work pieces, especially sheet metal and similar materials. A typical resistance welder comprises spaced electrodes between which are positioned the two work pieces to be welded together. The electrodes are brought into contact with the two work pieces and clamp the work pieces together. An electric current is then passed from one electrode to the other through the work pieces. The resistance of the work pieces generates sufficient heat to render the metal semi-molten, forming a weld nugget between the two work pieces and thereby welding them together.
In a resistance projection welding process, one of the work pieces has a series of projections extending from a body of the one work piece. The work pieces are oriented such that the projections from the one work piece contact the other work piece to conductively couple together the work pieces. The electrodes clamp the first and second work pieces together. Electric current applied through the work piece travels through the projections, heating the projections and the material of the other work piece in contact with the projections. The projections form a weld nugget along with the corresponding contacting portions of the other work piece. In essence, the projections provide additional material to form a weld nugget between the first and second work pieces.
In a resistance projection welding process, it is very important for the work pieces to be properly oriented. That is, it is very important for the projections to extend from the one work piece body to the other work piece, instead of the body of the one work piece contacting the other work piece and the projections extending away from the other work piece. Since many resistance projection welding processes produce high volume output, it is possible for the work pieces to be improperly oriented. It is desirable to have a simple, reliable and reproducible method for determining the proper orientation of the work pieces prior to their welding together.
One previous attempt to determine the orientation of the work pieces in a resistance projection welding process relied on applying a source of pressurized air to the electrode contacting the work piece with the projections and measuring the back pressure in the air system. If the work pieces were properly aligned, the work piece with the projections would substantially block the flow of air exiting the air system and thereby increase the back pressure in the air system. Alternatively, if the work piece with the projections was improperly aligned, the projections would form an air gap relative to the electrode permitting the escape of air from the air system and reducing the back pressure within the air system. This solution proved inadequate as the system was not capable of discerning fine changes in back pressure indicative of proper or improper orientation of the work pieces, resulting in either two few or two many indications of improper orientation.
It is still desirable to have a resistance projection welding apparatus and method capable of identifying when the work pieces are properly oriented prior to their welding. However, the apparatus and method must be capable of repeatedly and accurately discerning the orientation of the work pieces.
SUMMARY OF THE INVENTION
The invention relates to a resistance projection welder for welding first and second work pieces to each other. The fist work piece has a body with opposing sides, with at least one projection extending from one of the opposing sides and contacting the second work piece to thereby space the body from the second work piece and define an air gap therebetween when the first and second work pieces are properly oriented. The resistance projection welder comprises first and second electrodes that are spaced relative to each other for receiving the first and second work pieces therebetween. The electrodes are movable relative to each other from the spaced position to an electrically coupled position where the first electrode is adjacent the first work piece and the second electrode is adjacent the second work piece. The electrodes are electrically coupled to a source of electrical current for applying an electrical current through the first and second work pieces. A source of pressurized air is provided for directing a stream of pressurized air toward an interface between the first work piece and one of the second work piece and the first electrode. An air flow sensor is provided for detecting the air flow rate of the air stream directed toward the interface to determine if the work pieces are properly oriented based on the detected air flow rate.
Preferably, the resistance projection welder comprises a controller coupled to the air flow sensor and the electrodes for applying an electrical current to the electrodes and through the work pieces when the air flow sensor indicates that the work pieces are properly oriented. The controller can include a status indicator, such as an indicator light, for informing an operator of the resistance projection welder of the proper or improper orientation of the work pieces.
An actuator can be provided to move the electrodes from the spaced position to the electrically coupled position. Preferably, the actuator is a manually controlled actuator operated by the welding operator.
The source of pressurized air is preferably mounted to the first electrode and positioned to direct the stream of pressurized air toward the interface between the first work piece and the first electrode. The first electrode can include an orifice extending through an end of the electrode that abuts the first work piece when the first electrode is in the electrically coupled positioned and the source of pressurized air is fluidly coupled to the orifice to direct the stream of pressurized at the interface between the first electrode and the first work piece. The second electrode can include an end from which extends a pin being received within openings in the first and second work pieces to align the work pieces relative to the electrodes and each other.
The resistance projection welder can further include a pressure regulator fluidly connected between the pressurized air source and the air flow sensor for controlling the air flow rate provided to the sensor. An air filter can also be fluidly connected between the pressurized air source and the pressure regulator to remove impurities from the air flow to prevent the degradation of the air flow sensor.
In another embodiment, the invention relates to a method for resistance projection welding a first work piece to a second work piece. The first work piece has a body with opposing sides with at least one projection extending from one of the opposing sides and contacting the second work piece to space the body from the second work piece and define an air gap therebetween when the first and second work pieces are properly oriented. The method comprises: moving first and second electrodes relative to the first and second work pieces and into an electrically coupled position relative to the first and second work pieces; directing a stream of air toward an interface between the first work piece and one of the second work piece and the first electrode; determining the flow rate of the air stream directed toward the interface; and applying an electric current to the first and second work pieces if the determined air flow rate is indicative of the first and second work pieces being properly oriented.
Other objects, features, and advantages of the invention will be apparent fro
Cooke Colleen P.
Dunn Tom
Perks MFG Engineering Company
Rader, Fishman, Grauer & McGarry
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