Control of welding energy flux density

• US 4,343,980 A
• Filed: 04/02/1980
• Issued: 08/10/1982
• Est. Priority Date: 04/02/1980
• Status: Expired due to Term

• Current Assignee: LTV Steel Company, Inc. (LTV Corp.)
• Original Assignee: Republic Steel Corp. (LTV Corp.)
• Inventors: Franklin, Joseph E., Dickinson, David W., Stanya, Andrew
• Primary Examiner(s): Shaw, C. C.
• Application Number:
  US06/136,518
• Time in Patent Office: 860 Days
• Field of Search: 219/108, 219/109, 219/110
• US Class Current: 219/110
• CPC Class Codes: B23K 11/25 Monitoring devices

Abstract

An electrical resistance spot welding system and method is disclosed. The system has adjustable output power circuitry for applying electrical heating energy to a weld site by way of weld tips, in accordance with a welding operation. An energy monitor senses instantaneous accumulated energy applied during the welding operation, and terminates the operation when an adjustable predetermined total energy has been applied. Other circuitry monitors applied welding voltage, and derives therefrom a signal which is a function of the energy density per unit area applied at the weld site. Circuitry responds to the energy density sensing to control the energy monitor and the power circuitry to govern the total energy applied in the welding operation. As weld energy flux density decreases, such as happens when weld tips spread or "mushroom", total applied energy is increased, compensating for weld tip changes, thereby holding the amount of applied energy per unit of weld site area relatively constant from one welding operation to another.

Claims

1. A welding system comprising:

(a) apparatus including electrodes and power circuitry for applying heating energy to a welding site to effect a weld between two workpieces in accordance with a cyclically repeatable welding process;

(b) means for monitoring the amount of heating energy applied in the welding process;

(c) circuitry for producing an electrical signal which is a function of the energy density applied per unit weld site area, said signal being a function of substantially only the voltage between the electrodes and

(d) circuitry responsive to said electrical signal for controlling the amount of energy per unit weld site area applied by the power circuitry during a weld process cycle.

2. An electrical resistance spot welding system comprising:

(a) means including power circuitry coupled to weld tips for applying heating energy to a weld site for welding workpieces together in accordance with a welding cycle;

(b) means for monitoring the instantaneous accumulated value of heating energy applied to the weld site during the welding cycle and for terminating the weld cycle when a predetermined amount of energy is applied;

(c) circuitry for monitoring the instantaneous value of electrical potential between the weld tips, and

(d) circuitry coupled to one of the terminating means and power circuitry and responsive to the monitored potential and independent of welding current for controlling the application of heating energy to the weld site during a welding cycle as a function of the monitored potential, said function defining a relationship between applied energy and monitored potential wherein, over a range, the energy applied becomes greater as the monitored potential becomes lesser.

3. The system of claim 2, wherein:

said control circuitry includes means for increasing the amount of energy applied in the welding cycle by increasing the power applied to the weld site.

4. The system of claim 3, wherein:

the control circuitry further includes means for increasing the amount of energy applied during the weld cycle by increasing the duration of the weld process.

5. An electrical resistance spot welding system including power circuitry adaptable for delivering electrical welding energy for spot welding workpieces together in weld cycles by way of welding tips having a susceptibility to deterioration with use, said spot welding system comprising:

(a) a total energy monitor coupled to the power circuitry and including circuitry for sensing the instantaneous accumulated value of energy applied to the weld site during each said welding cycle and energy select and comparator circuitry for controlling energy application as a function of the monitored total accumulated energy;

(b) an energy density monitor responsive to the electrical potential across the weld tips, and actuator circuitry responsive to the energy density monitor for controlling the power circuitry for compensating for deterioration of said weld tips by increasing the power applied in a weld cycle in response to a decrease in electrical potential across the weld, for maintaining a relatively constant total energy flux density delivered to the weld site during each of a succession of weld cycles during which the weld tips suffer change.

6. The system of claim 5, wherein said power circuitry includes means for adjusting the amount of power supplied to the weld site, and said control means comprises:

(a) means for comparing the sensed electrical potential across the weld tips to a predetermined standard, and

(b) apparatus and circuitry for increasing power applied to the weld site in stepwise fashion, each step increase being responsive to the detection of the weld tip potential difference having a value during a weld cycle lower than the predetermined value.

7. The system of claim 6, further comprising:

means for providing a tangible indication of the execution of a predetermined number of said stepwise adjustments in welding power.

8. A cyclically operable system comprising:

(a) power circuitry for applying welding energy to weld sites on workpieces;

(b) circuitry for controlling welding energy via the power circuitry;

(c) circuitry for detecting energy applied per unit of weld site area, and

(d) compensation circuitry responsive to the energy per unit area detection for influencing the energy control circuitry to maintain energy per unit area at a substantially constant level for each of a succession of weld cycles.

9. A welding system comprising:

(a) power circuitry for applying welding energy in cycles to weld sites on workpieces;

(b) circuitry for controlling welding energy via the power circuitry;

(c) circuitry for detecting weld energy flux density during, a first weld cycle and

(d) compensation circuitry responsive to the weld energy flux density detection for influencing the energy control circuitry to maintain energy flux density during each of a subsequent succession of weld cycles at substantially the same level as that of the first cycle.

10. A welding system comprising:

(a) power circuitry for applying welding energy to workpieces to execute weld cycles;

(b) circuitry for controlling welding energy via the power circuitry;

(c) circuitry for producing an energy density signal which is a function of the integral of the squared voltage across the weld, and

(d) compensation circuitry responsive to the energy density signal for controlling energy flux density during a succession of weld cycles.

11. A welding system comprising:

(a) apparatus for applying electrical heating energy to a succession of weld sites to effect welding between workpieces according to a weld process;

(b) a monitor for measuring a parameter of each weld;

(c) apparatus and circuitry responsive to the monitor for adjusting a weld parameter in steps after each weld in which said monitored parameter is outside a predetermined range, and

(d) means for indicating when a predetermined number of said step adjustments has occurred.

12. A welding control method comprising the steps of:

(a) applying heating energy to a succession of welding sites by way of weld tips in order to weld workpieces together in accordance with a succession of welding operations;

(b) monitoring a parameter of each said welding operation indicating the degree of mushrooming of the weld tips;

(c) adjusting in steps a welding parameter in response to said monitoring step for each weld in which the monitored parameter is outside a predetermined range, and

(d) producing an indication of the occurrence of a predetermined number of said step adjustments indicating the total amount of mushrooming of the weld tips.

13. A welding system comprising:

(a) means for applying heating energy to effect welds between workpieces in accordance with a series of welding operations;

(b) means for monitoring a parameter of each welding operation;

(c) means responsive to the monitoring means for adjusting a parameter of the welding operation in stepwise fashion, after each weld operation in which the monitored parameter is outside a predetermined range, and

(d) a device for providing an indication of the occurrence of a predetermined number of said stepwise adjustments.