METHOD AND APPARATUS FOR CONTROL OF RESISTANCE WELDING

• US 3,553,420 A
• Filed: 07/11/1969
• Issued: 01/05/1971
• Est. Priority Date: 07/11/1969
• Status: Expired due to Term

• Current Assignee: Charles M. Peters, Jon D. Tincher, Thomas W. Shearer Jr
• Original Assignee: Charles M. Peters, Jon D. Tincher, Thomas W. Shearer Jr
• Inventors: Shearer, Thomas W. Jr., Peters, Charles M., Tincher, Jon D.
• Application Number:
  US04/840,929
• Time in Patent Office: 543 Days
• US Class Current: 219/110
• CPC Class Codes: B23K 11/253 the measured parameter being a displacement or a position

Abstract

In spot welding, weld nugget growth is monitored by an arrangement including an hydraulically operated electrode, and a check valve to trap fluid in the hydraulic cylinder. Thermal expansion of the workpiece produces a force on the electrodes and a pressure rise in the hydraulic fluid. An electrical transducer senses the pressure rise and produces an electrical signal proportional to work expansion which operates a circuit for terminating welding current when the pressure rise ceases. For pneumatically driven electrodes, an auxiliary hydraulic locking cylinder provides the pressure signal.

Claims

1. In a method of resistance welding including clamping the parts to be welded between electrical energy applying electrodes and applying electrical energy to the parts thereby causing thermal expansion of the parts which tends to cause electrode separation:

the method of controlling the applied electrical energy to achieve optimum nugget growth and to prevent the application of excessive electrical energy to the parts comprising;

generating a hydraulic pressure signal as a function of electrode separation due to said thermal expansion;

generating an electrical signal as a function of the hydraulic pressure signal and responsive thereto; and

controlling the applied electrical energy in response to the electrical signal.

2. In a method of controlling applied electrical energy in resistance welding including clamping the parts to be welded between electrical energy applying electrodes and applying electrical energy to the parts thereby causing thermal expansion of the parts which tends to cause displacement of one of the electrodes relative to the other:

the method of controlling the applied electrical energy to achieve optimum nugget growth and to prevent the application of excessive electrical energy to the parts comprising;

generating a hydraulic pressure signal as a function of electrode displacement due to said thermal expansion by pressurizing liquid in a confined volume by the displaced electrode;

generating an electrical signal as a function of the hydraulic prEssure signal by a transducer subject to the pressurized liquid; and

controlling the applied electrical energy according to a programmed function of the electrical signal.

3. A method of controlling applied electrical energy in resistance welding to achieve optimum weld nugget size and to prevent the application of excessive electrical energy to the work comprising:

positioning the work to be welded between a pair of electrical energy applying electrodes;

forcing one of the electrodes toward the other and against the work by a hydraulic motor operated by pressurized hydraulic fluid;

blocking flow of fluid from the hydraulic motor;

applying electrical energy to the work thereby causing thermal expansion of the work which tends to displace the said one electrode thereby producing in the hydraulic motor a pressure signal proportional to electrode displacement;

generating an electrical signal as a function of the pressure signal by a transducer subject to the pressurized liquid; and

controlling the applied electrical energy according to a programmed function of the electrical signal.

4. A method of controlling applied electrical energy in resistance welding to achieve optimum weld nugget size and to prevent the application of excessive electrical energy to the work comprising:

positioning the work to be welded between a pair of electrical energy applying electrodes;

forcing one of the electrodes toward the other and against the work by a hydraulic motor operated by pressurized hydraulic fluid;

blocking flow of fluid from the hydraulic motor;

applying electrical energy to the work thereby causing thermal expansion of the work which tends to displace the said one electrode thereby producing in the hydraulic motor a pressure signal proportional to electrode displacement;

generating an electrical signal as a function of the pressure signal by a transducer subject to the pressurized liquid whereby an increase in the electrical signal signifies weld nugget growth;

controlling the applied electrical energy by diminishing the welding current when the electrical signal ceases to increase; and

permitting fluid flow from the hydraulic motor to allow electrode movement from the work when the weld is completed.

5. In a method of controlling applied electrical energy in resistance welding including clamping the parts to be welded between welding electrodes, and applying electrical energy to the parts through the electrodes thereby causing thermal expansion of the parts and causing a force proportional to the expansion to be applied to the electrodes;

the method of controlling the applied electrical energy to achieve optimum nugget growth and to prevent the application of excessive electrical energy to the parts comprising;

transferring the force through an electrode to a confined body of liquid thereby producing a pressure signal in the body of liquid proportional to the expansion of the parts;

generating an electrical signal as a function of the pressure signal and responsive thereto; and

controlling the applied electrical energy in response to the electrical signal.

6. In a method of controlling applied electrical energy in resistance welding including clamping the parts to be welded between welding electrodes, and applying electrical energy to the parts through the electrodes thereby causing thermal expansion of the parts and causing a force proportional to the expansion to be applied to the electrodes:

the method of controlling the applied electrical energy to achieve optimum nugget growth and to prevent the application of excessive electrical energy to the parts comprising;

transferring the force through an electrode to a confined body of liquid thereby producing a pressure signal in the body of liquid proportional to the expansion of the parts;

generating an electrical signal as a function of the pressure signal and responsive thereto whereby an increase in the electricaL signal is a function of the weld nugget growth; and

controlling the applied electrical energy in response to the electrical signal by diminishing the electrical current applied to the parts when the electrical signal ceases to increase.

7. In a resistance welding apparatus having a pair of opposed electrodes for engaging the work to be welded the improvement comprising:

a hydraulic pressure source;

a hydraulic motor connected to the pressure source and actuated thereby;

Means connecting one of the electrodes to the hydraulic motor for exerting a clamping force on the work;

means for supplying electrical energy to the work through the electrodes whereby the work is caused to thermally expand and as a result exert an additional force on the electrodes proportional to the expansion of the work; and

means for monitoring growth of the weld nugget as reflected by the expansion of the work between the electrodes comprising;

valve means for preventing fluid flow from the hydraulic motor thereby confining a body of fluid, whereby the additional force on the electrode produces a pressure signal in the confined body of fluid; and

transducer means in communication with the body of fluid for producing an electrical signal as a function of the pressure signal and the growth of the weld nugget, utilization means responsive to said signal.

8. In a resistance welding apparatus having a pair of the opposed electrodes for engaging the work to be welded the improvement comprising:

a hydraulic pressure source;

a hydraulic motor connected to the pressure source and actuated thereby;

means connecting one of the electrodes to the hydraulic motor for exerting a clamping force on the work;

means for supplying electrical energy to the work through the electrodes whereby the work is caused to thermally expand and as a result exert an additional force on the electrodes proportional to the expansion of the work, the means for supplying electrical energy including a control circuit for controlling the amount of the supplied electrical energy; and

means for monitoring growth of the weld nugget as reflected by the expansion of the work between the electrodes and for controlling the application of electrical energy to the work so that optimum nugget growth is achieved and the application of excessive electrical energy to the work is prevented comprising;

valve means for preventing fluid flow from the hydraulic motor thereby confining a body of fluid, whereby the additional force on the electrode produces a pressure signal in the confined body of fluid;

transducer means in communication with the body of fluid for producing an electrical signal as a function of the pressure signal and the growth of the weld nugget; and

a circuit responsive to the electrical signal and having its output connected to the control circuit for diminishing the supplied electrical energy according to a programmed function of the electrical signal.

9. In a resistance welding apparatus having a pair of opposed electrodes for engaging the work to be welded the improvement comprising:

a hydraulic pressure source;

a hydraulic motor connected to the pressure source and actuated thereby;

means connecting one of the electrodes to the hydraulic motor for exerting a clamping force on the work;

means for supplying electrical energy to the work through the electrodes whereby the work is caused to thermally expand and as a result exert an additional force on the electrodes proportional to the expansion of the work, the means for supplying electrical energy including a control circuit for controlling the amount of the electrical energy;

means for monitoring growth of the weld nugget as reflected by the expansion of the work between the electrodes and for controlling the application of electrical energy to the work so that optimum nugget growth is achieved and the application of excessive electrical energy to the work is preVented comprising valve means for preventing fluid flow from the hydraulic motor thereby confining a body of fluid, whereby the additional force on the electrode produces a pressure signal in the confined body of fluid;

transducer means in communication with the body of fluid for producing an electrical signal as a function of the pressure signal and the growth of the weld nugget; and

a compensating circuit responsive to the electrical signal and having its output connected to the control circuit to affect the operation thereof, the compensating circuit including signal detecting means for detecting the rate of change of the electrical signal amplitude and for producing an output signal when the rate of change becomes zero, the output signal causing the supplied electrical energy to be diminished.

10. In a resistance welding apparatus having a pair of opposed electrodes for engaging the work to be welded:

a hydraulic pressure source;

a hydraulic motor connected to the pressure source and actuated thereby;

means connecting one of the electrodes to the hydraulic motor for exerting a clamping force on the work;

means for supplying electrical energy to the work through the electrodes whereby the work is caused to thermally expand and as a result exert an additional force on the electrodes proportional to the expansion of the work, the means for supplying electrical energy including a control circuit for controlling the amount of the electrical energy; and

means for monitoring growth of the weld nugget as reflected by the expansion of the work between the electrodes and for controlling the application of electrical energy to the work so that optimum nugget growth is achieved and the application of excessive electrical energy to the work is prevented, comprising;

valve means for preventing fluid flow from the hydraulic motor thereby confining a body of fluid, whereby the additional force on the electrodes produces a pressure signal in the confined body of fluid;

transducer means in communication with the body of fluid for producing an electrical signal as a function of the pressure signal and the growth of the weld nugget;

a compensating circuit responsive to the electrical signal and having its output connected to the control circuit to affect the operation thereof, the compensating circuit including signal detecting means for detecting the rate of change of the electrical signal amplitude and for producing an output signal when the rate of change becomes zero, the output signal causing the supplied electrical energy to be diminished; and

means in the compensating circuit for rendering the output signal ineffective comprising a timer means and a detector means for sensing a predetermined minimum value of the electrical signal, the timer means and the detector means being electrically connected with the signal detecting means to override the output signal until a predetermined time or predetermined value of the electrical signal is attained.