Expulsion detection method in electric resistance welding and apparatus therefor

An expulsion detection apparatus in electric resistance welding for welding plural metal plates by energizing a workpiece, which is formed by superimposing the plural metal plates, by a pair of electrodes while pressurizing, the expulsion detection apparatus in the electric resistance welding comprising:

• data accumulation means that detects an energization resistance reduction amount between the pair of electrodes at a specified time interval during each welding process under a specified welding condition and accumulates data on said energization resistance reduction amount;
• frequency distribution calculation means that calculates frequency distribution of the energization resistance reduction amount under said welding condition on the basis of the data in the data accumulation means;
• and
• determination means that fits frequency distribution, which is calculated by the frequency distribution calculation means, with a Gaussian function and determines occurrence of expulsion under said welding condition based on said fitting.