PROCESS FOR CONTROLLING SPOT WELDING AND NON-DESTRUCTIVE TESTING OF SPOT-WELDED JOINTS

• US 3,746,829 A
• Filed: 02/22/1971
• Issued: 07/17/1973
• Est. Priority Date: 03/07/1970
• Status: Expired due to Term

• Current Assignee: Jurgen Petzold
• Original Assignee: Jurgen Petzold
• Inventors: Petzold, Jurgen
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Peterson, Gale R.
• Application Number:
  US05/117,309
• Time in Patent Office: 876 Days
• Field of Search: 219/110,109,108,114,112,111,131R
• US Class Current: 219/110
• CPC Class Codes: B23K 11/256 the measured parameter being the inter-electrode electrical resistance

Abstract

A process for controlling spot welding by adjusting the electric energy used for the welding in accordance with the gradient of the rising branch of the curve plotting the electric resistance as a function of time. This process permits the maintenance of the overall welding time constant. At the same time the process permits non-destructive testing of a spot-welded joint by utilizing the gradient of the rising branch of the curve representing the welding resistance as a function of time. This gradient then indicates the quality of the spot weld.

Claims

1. A process for controlling the spot welding of two work pieces between welding electrodes, comprising ascertaining a reference resistance gradient of the rising region of a reference time-response electricresistance curve during the time of welding which is necessary for producing an optimum weld between the two pieces, and during each subsequent welding, ascertaining the actual resistance gradient within the time limits of the rising region of said reference curve, applying the reference gradient and the actual gradient to comparing means thereby obtaining a differential therebetween, and varying the electric energy fed to the welding electrodes until said differential has substantially been reduced to zero value while maintaining the time of each welding substantially constant.

2. Process as defined in claim 1 wherein the determined by the change of the voltage between the welding electrodes.

3. Process as defined in claim 1 wherein the welding electrodes are fed with an impulse-like welding current and wherein said gradient deviation is determined by comparing the amplitudes of two predetermined resistance impulses within the range of the rising region of the time resistance curve, said resistance impulses being triggered by impulses derived from the welding current.

4. Process as defined in claim 3 wherein said gradient is determined by comparing the mean values of the amplitudes of two sets of predetermined resistance impulses which are triggered by impulses of the welding current at predetermined time intervals within the range of the rising region of the time resistance curve.

5. Process as defined in claim 1 where in the electric energy fed to the welding hugget is controlled by varying the relative phase of the welding current.

6. In a process for controlling the spot welding of two work pieces between welding electrodes, a non-destructive testing method for the spot-welded joints, comprising:

determining during the welding an actual gradient of the rising region of the time-response curve of the resistance between the welding electrodes by measuring the amplitudes of the voltage between said electrodes at two different time points within said rising region of said curve on a voltage measuring device and producing the difference between said amplitudes in a difference circuit;

comparing said difference with a predetermined reference value thereof and obtaining the deviation of said difference from said reference value;

said deviation determining the quality of the welding joint.