Patent ID: 11904402
Assignee: CAR-O-LINER GROUP AB
Field: Machine tools (Mechanical engineering)
Classification: CPC B | IPC B

Claim 12:
13. A method of controlling a resistance at a workpiece prior to performing a spot welding process to the workpiece using a welding machine, the welding machine comprising:
a welding gun including a pair of opposed electrodes for receiving the workpiece, the pair of electrodes comprising at least one movable welding tip portion;
a transformer having a primary input side and secondary output side, the secondary output side connected to the pair of electrodes;
a distance detector arranged to detect the distance moved by the movable welding tip portion; and
a control unit adapted to control the spot welding process,
wherein the method comprises the steps of:
controlling, using the control unit, the transformer for applying, prior to performing the spot welding process, a first welding pulse portion to the workpiece using the welding gun,
receiving, at the control unit from measurement means arranged at the secondary output side of the transformer, an indication of a first voltage and a first current applied in relation to the first welding pulse portion,
determining, at the control unit, a first resistance value based on the indication of the first voltage and the first current,
comparing, at the control unit, the first resistance value with a predetermined resistance threshold, wherein the predetermined resistance threshold is based on a thickness of the workpiece determined using information received from the distance detector,
controlling, using the control unit, the transformer for applying, prior to performing the spot welding process, a further second welding pulse portion to the workpiece using the welding gun if the first resistance value is above the predetermined resistance threshold, and
initiating, using the control unit, the spot welding process if the first resistance value is below the predetermined resistance threshold.