ARC VOLTAGE SENSOR FOR MONITORING OF PENETRATION IN TIG WELDS

This paper describes the development of an are voltage sensor for the measurement of the degree of penetration in tungsten-inert gas (TIG) welds. It is shown that the rate of change of the are voltage is directly related to the rate of movement of the weld pool surface. Weld penetration occurs when the surface of the weld pool falls. The sensor also detects the frequency of induced weld pool oscillations, which occur in one;of two well defined modes according to the degree of penetration present. Spectral analysis of the voltage data, using the fast Fourier transform (FFT), provides a means of measuring weld bead size once full penetration has been detected. The sensor may be used to give closed loop computer control of bead size by varying the welding parameters.