Resistance spot welder process monitor
AssigneeGeneral Electric Company
InventorsHerman A. Nied, Stanley J. Godwin, Robert K. Cohen, Robert V. Klint, Hsin-Pang Wang
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Abstract
A multivariable process monitor and method of monitoring a resistance spot welding process to yield instantaneous information on weld quality during the weld cycle. Sensors on the machine measure welding input variables and workpiece response variables and provide signals to a microcomputer system. A simplified analytical model of the spot welding process is incorporated in the microcomputer and is the reference for the weld quality logic that accepts or rejects the weld. Faulty welds are diagnosed and the reason displayed.
Claims12
A method of monitoring a resistance spot welding process to provide information on weld quality during the weld cycle of a welding machine which applies an electrode mechanical load and has a secondary circuit that supplies power for a known welding time to the electrodes comprising:
- measuring a plurality of welding input variables such as electrode load and tip voltage, and secondary circuit current;
- during the weld measuring a plurality of welding response variables such as electrode displacement due to workpiece thermal expansion and electrode temperatures;
- providing said measured input variables, welding time, and known machine and workpiece parameters and material properties to a simplified analytical model comprising mathematical equations which simulates the spot welding process and predicts the formation and growth of a weld nugget and computes response functions of acceptable welds;
- deriving process response functions and rates per welding cycle from said measured response variables;
- and
- comparing and evaluating said process response functions and computed response functions using the latter as a reference and relative to criteria for good quality welds, and accepting or rejecting the weld.
A multivariable process monitor used with a resistance spot welding machine having electrodes between which a workpiece is held and welded by passage of current for a given time, comprising:
- first sensors to measure welding input variables and second sensors to measure welding response variables;
- means for inputting and storing known machine and workpiece parameters and material properties;
- means, to which signals from said first sensors, welding time, and parameters and properties are presented, for analytically modeling and simulating the spot welding process by a number of mathematical equations and producing computed response functions, welding cycle by welding cycle, under the actual welding conditions;
- means to which signals from said second sensors are presented for computing process response functions and rates, cycle by cycle;
- and
- means for comparing and evaluating said process response and computed response functions with reference to the latter and criteria in the form of logic statements to be met for good quality welds, and accepting or rejecting the weld.
A method of monitoring a resistance spot welding process performed on a welding machine which applies an electrode mechanical load to the workpiece and has an electrical energizing circuit that supplies power for a known welding time to the electrodes, comprising:
- measuring a plurality of welding input variables and workpiece response variables;
- deriving computed response functions during the welding operation from a simplified analytical model comprising a number of mathematical equations that simulates the spot welding process and predicts the formation and growth of a weld nugget, inputs to said model being the measured input variables and welding time, and known machine and workpiece parameters and material parameters;
- processing said measured response variables to produce process response functions and rates,
- comparing and evaluating said process response functions and computed response functions using said analytical model as a reference and weld criteria that are met in order to have a quality weld, and accepting or rejecting the weld;
- and diagnosing a faulty weld and displaying the reason for the unacceptable weld.
Dependencies are inferred from the claim text.