Resistance welding controller and method including thermal conduction simulation of weld nugget condition

An apparatus for controlling resistance welding, comprising:

• a current detection means for detecting a welding current;
• a voltage detection means for detecting a voltage between welding electrodes;
• a first operating means for outputting an estimated condition value, which represents a state of a nugget being formed, obtained by inputting said voltage and current detected, and applying a thermal conduction simulation on a welding part;
• a second operating means for outputting a modification to a welding condition, based on the result of a comparison between said estimated condition value and a change rate of the temperature at a point of a simulation calculation model for forming a desired nugget;
• and
• an output means which changes said welding condition of a welding unit in accordance with the modification to said welding condition.