METHOD AND APPARATUS FOR MONITORING WELD QUALITY

• US 3,609,285 A
• Filed: 09/04/1968
• Issued: 09/28/1971
• Est. Priority Date: 09/04/1968
• Status: Expired due to Term

• Current Assignee: August F. Scarpelli, Frederick J. Trulson
• Original Assignee: August F. Scarpelli, Frederick J. Trulson
• Inventors: Scarpelli, August F., Trulson, Frederick J.
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Smith, J. G.
• Application Number:
  US04/757,320
• Time in Patent Office: 1,119 Days
• Field of Search: 219/108,109,110,114,86 324/34P,34TK
• US Class Current: 219/109
• CPC Class Codes: B23K 11/25 Monitoring devices

Abstract

A circuit for monitoring spot welding is responsive to electrode separation and welding current and voltage to monitor the weld soft point and upset, the cold length of the parts, the number of cycles of welding current, and the energy consumed in producing the weld nugget. A reject signal is provided if any of the five parameters fall outside of predetermined limits. A special feature is the upset circuitry which uses a memory circuit and a comparison circuit to compare the initial electrode separation with the final separation.

Claims

1. Weld quality-monitoring means for welding equipment having a plurality of spaced electrodes and means to apply clamping pressure and welding power to opposite sides of parts to be welded together, said quality-monitoring means having weld upsetmonitoring means including sensor means for producing a signal as a function of separation of the electrodes, said sensor means being connected with one of the electrodes to vary its output signal as a function of the separation of the electrodes, first switching means connected to the sensor means, a memory circuit connected to the first switching means to store the signal at the initiation of the welding operation, a comparison circuit connected to the sensor means and to the memory circuit to provide a signal indicative of the displacement of the said one electrode at the conclusion of the weld after the electrodes have pressed into the surfaces of the parts to be welded relative to its initial position, and circuit means for determining whether the signal is within acceptable limits, whereby weld upset and its acceptability is determined.

2. Weld quality-monitoring means for welding equipment having a plurality of spaced electrodes and means to apply clamping pressure and welding power to opposite sides of parts to be welded together, said quality-monitoring means having weld upset-monitoring means including inductance means for producing a signal as a function of separation of the electrodes, said inductance means having a movable core connected to one of the electrodes to move therewith and change the inductance value of the inductance means, demodulator means connected to the inductance means, first switching means connected to the demodulator means, a memory circuit connected to the first switching means to store the signal, a comparison circuit connected to the demodulator means and to the memory circuit to provide A signal indicative of the displacement of the said one electrode relative to its initial position, limit circuit means connected in series with the comparison circuit for determining whether the signal is within acceptable limits, further switching means in series with the comparison circuit for effecting an output indicative of the weld acceptability, and means for actuating the first switching means at the initiation of welding and for actuating the further switching means at the termination of welding.

3. Weld quality-monitoring means for welding equipment having a plurality of spaced electrodes and means to apply clamping pressure and welding power to opposite sides of parts to be welded together, said quality-monitoring means including inductance means for producing a signal having a movable core connected to one of the electrodes to move therewith and change the inductance value of the inductance means, demodulator means connected to the inductance means, first switching means connected to the demodulator means, a memory circuit connected to the first switching means to store the signal, a comparison circuit connected to the demodulator means and to the memory circuit to provide a signal indicative of the displacement of the said one electrode relative to its initial position, limit circuit means in series with the comparison circuit for determining whether the signal is within acceptable limits, further switching means in series with the comparison circuit for effecting an output indicative of the weld acceptability, and means for actuating the first switching means at the initiation of welding and for actuating the further switching means at the termination of welding, wherein the switching-actuating means includes a cycle counter having an output energized at the initiation of welding and connected to the first switching means, and a weld end detector having an output energized at the termination of welding and connected to the further switching means.

4. Weld quality-monitoring means for welding equipment having a plurality of spaced electrodes and means for applying clamping pressure and welding power to opposite sides of parts to be welded together, said monitoring means including inductance means having a movable core connected to one of the electrodes to move therewith and change the inductance value of the inductance means, demodulator means connected to the inductance means, a plurality of quality-monitoring circuits connected to the demodulator means including a soft point-monitoring circuit having a differentiating means for producing a soft point signal when a soft point is reached during the welding operation, the differentiating means being connected to the demodulator means, a count-controlled gate connected to the differentiating means, means for energizing the gate to accept the soft point signal during a predetermined period and to produce a reject signal when the soft point signal occurs outside the predetermined period, an upset-monitoring circuit having memory means connected to the demodulator means for registering the initial position of the said one electrode, comparing means connected to the memory means and to the demodulator means for detecting electrode displacement and upset limit circuit connected to the comparing means for determining the acceptability of the amount of upset, a cold length-monitoring means comprising a cold length limit circuit connected to the memory means for determining acceptability of the initial separation of the electrodes, a cycle-monitoring means comprising cycle-counting means connected to the means for applying clamping pressure and welding power for counting the number of cycles of welding current and a cycle limit means connected thereto for determining acceptability of the number of cycles, and a reject gate means for simultaneously sampling the outputs of the count-controlled gate, the cold length limit circuit, the upset limit circuit and the cycle limit means for producing a reject signal when any of the outputs indicates that a parameter falls without its prescribed limit.

5. Weld quality-monitoring means for welding equipment as described in claim 4 wherein the cycle-counting means has outputs for controlling the count-controlled gate, and the memory means.

6. Weld quality-monitoring means for welding equipment as described in claim 4 and further including weld energy-monitoring means comprising means associated with the welding electrodes for sensing welding voltage and current, an energy-monitoring circuit responsive to such voltage and current for measuring the amount of energy consumed in making a weld nugget, an energy limit circuit connected to the energy-monitoring means for determining acceptability of the energy value measured, and for producing an output signal when the energy value is too high or too low to produce a good weld, the energy limit circuit being connected to the reject gate, whereby the reject gate produces a reject signal in response to the output signal.

7. Weld quality-monitoring means for welding equipment having a plurality of spaced electrodes and means for applying clamping pressure and welding power to opposite sides of parts to be welded together, said quality-monitoring means including sensor means connected to one of the electrodes for producing an output signal as a function of electrode separation, energy-monitoring means associated with the welding electrodes for measuring the energy consumed in forming a weld nugget, an energy limit circuit connected to the energy-monitoring means for determining whether the value of energy consumed is between predetermined limits, upset-monitoring means comprising switching means connected to the sensor means, means for opening the switching means at the initiation of welding, a memory circuit connected to the switching means for registering a signal indicative of the initial position of the one electrode, a comparison circuit connected to the sensor means and the memory circuit for determining the difference between the initial electrode position and its final position thereby providing a measure of upset, an upset limit circuit connected to the comparison circuit for determining whether the amount of upset is within predetermined limits, and gate means connected to the energy limit circuit and upset limit circuit for producing a reject output signal when the energy level or upset is without predetermined limits, and utilization means responsive to the reject output signal.

8. A method of monitoring the quality of a weld during formation of the same by the application of electrical power comprising the steps of clamping the parts to be welded between the welding electrodes and maintaining pressure thereon, obtaining an electrical signal value that is representative of the distance between the adjacent ends of the electrodes, storing the same for reference, applying welding power and completing the weld to soften the material permitting the electrodes to press into the surface, obtaining a second signal representative of final electrode spacing at the conclusion of the weld, determining the difference between the signals to obtain a difference signal and utilizing said difference signal to indicate the quality of the weld obtained.

9. A method of monitoring the quality of a weld during formation of the same by the application of electrical power comprising the steps of clamping the parts to be welded between welding electrodes and maintaining pressure thereon, producing a first electrical signal that is proportional to the separation of the adjacent ends of the electrodes, storing the value of the first electrical signal, applying welding power and completing the weld to permit the electrode separation to decrease, producing a second signal proportional to final electrode separation at the conclusion of the weld, determining the difference between the second signal and the stored value of the first signal to obtain a difference signaL, producing a reject signal when the difference signal is outside an acceptable range, and operating a control means in response to the reject signal.