Instrumentation For Quality Assurance In Arc Welding

TWI Industrial Member Report Summary 175/1982

By J A Street and J C Needham

Background

Two aspects of in-process quality assurance are considered. Firstly analog type instrumentation, designed for arc welding, voltage, current and wire feed speed, is described. These are based on LED arrays which show short and long-term deviations from preset desired values, with 1% discrimination and with an inherent response of less than 1/50sec. Secondly portable battery operated standards, for in situ check testing of instrumentation, are detailed.

The characteristics and performance are given for standards of steady-state d.c. voltage (10, 20, 30V), d.c. (200A), wire feed speed (up to 7m/min) and rotation (for tachometers). In addition the voltage source provides a standard square wave to represent a short-circuiting arc, and the stepping-motor controlled wire feed calibrator also serves as a precision wire feeder with instant start/stop suitable for pulsed operation.

The possibilities for extending these standards to a.c. are also briefly considered, as well as standards for controlled current waveforms and higher power operation.