Apparatus and method for monitoring and controlling resistance spot welding
First Claim
1. In resistance spot-welding apparatus that includes a pair of electrodes positioned to receive workpieces between them, means for moving one electrode toward the other to apply a squeezing force to the workpieces, means for causing an electrical current to flow from one electrode to the other through the workpieces to form a weld, and means for controlling the duration of the flow of current through the workpieces, the improvement wherein the means for moving one electrode to apply a squeezing force to the workpieces includes a member that is movable under a force in a direction to apply the squeezing force, means for applying a force to the member substantially greater than a desired squeezing force, stop means engageable by the member for limiting the movement of the member in said direction, and a mechanical spring interposed between the member and the movable electrode for applying to the movable electrode a force that varies as a function of the indentation of the electrodes into the workpieces when the current melts them, and further comprising transducer means for detecting the force exerted by the mechanical spring and generating a welding signal indicative thereof, and signal processing means responsive to the transducer means for producing a signal indicative of a change in the squeezing force on the workpieces.
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Accused Products
Abstract
The quality of an electrical resistance spot weld is determined by monitoring the squeezing force applied through the electrodes to the workpieces by a force-transmitting device that exerts a squeezing force that varies when indentation of the workpieces occurs.
46 Citations
13 Claims
- 1. In resistance spot-welding apparatus that includes a pair of electrodes positioned to receive workpieces between them, means for moving one electrode toward the other to apply a squeezing force to the workpieces, means for causing an electrical current to flow from one electrode to the other through the workpieces to form a weld, and means for controlling the duration of the flow of current through the workpieces, the improvement wherein the means for moving one electrode to apply a squeezing force to the workpieces includes a member that is movable under a force in a direction to apply the squeezing force, means for applying a force to the member substantially greater than a desired squeezing force, stop means engageable by the member for limiting the movement of the member in said direction, and a mechanical spring interposed between the member and the movable electrode for applying to the movable electrode a force that varies as a function of the indentation of the electrodes into the workpieces when the current melts them, and further comprising transducer means for detecting the force exerted by the mechanical spring and generating a welding signal indicative thereof, and signal processing means responsive to the transducer means for producing a signal indicative of a change in the squeezing force on the workpieces.
- 8. In a resistance spot welding method in which workpieces are squeezed between a pair of electrodes and an electrical current is conducted between the electrodes through the workpieces to form a weld, the improvement comprising the steps of applying to a movable member a force substantially greater than a desired squeezing force, stopping the movement of said member at a predetermined location while maintaining said force, transmitting a force from said member to a movable electrode through a mechanical spring to provide a squeezing force through the electrodes on the workpieces that varies as a function of the indentation of workpieces by the electrodes when the current melts them, detecting the squeezing force during welding and generating a welding signal indicative thereof, and processing the welding signal to produce a signal indicative of a change in the squeezing force applied to the workpieces.
Specification