Mathematical modelling of part voltage and weld current in resistance welders.

摘要

A mathematical model is presented to describe the part voltage and weld current that occur in a single-phase resistance welder. Developing an accurate model of part voltage and current is the first step toward understanding instrumentation, testing, calibration, and measurement requirements. Measurement requirements for dynamic part resistance, calculated from these basic process variables, can ultimately be determined using this analysis. This model utilizes electrical characteristics of the welder, power system, and parts, as well as geometric parameters of voltage-sensing wires to describe the resultant time functions. The complete equivalent circuit involves many resistive and inductive components in the welder primary and secondary circuits. These components are reduced to a simple equivalent circuit to obtain a closed-form solution for part voltage and weld current time functions. Actual measurements were acquired from a welder using a constant resistance load to verify accuracy of the model. Accuracy of the model is estimated to be within the measurement uncertainty and is, in general, approximately (plus minus)3% for current and (plus minus)5% for part voltage. Pertinent limitations of the model's accuracy and range of applications are also discussed briefly. 28 refs., 10 figs.