In-Process Weld Quality Monitoring Techniques for Resistance-Spot Welds

Abstract

Dynamic resistance and thermal condition of the weld are the two
process parameters which are monitored and related to weld quality of
resistance-spot welds in mild steel.

The investigation reported in Part I is concerned with measurement
and application of dynamic or instantaneous resistance of spot welds.
Thus, an electronic instrumentation system has been designed which
computes dynamic resistance. The results of investigation show that
the pattern of variation exhibited by the instantaneous resistance of
a spot weld is indicative of the state of nugget growth and therefore
can be used in monitoring weld quality.

In Part II of the dissertation thermal condition of the weld is
related to the state of nugget growth. The thermal condition of the
weld, in this instance, is assessed from the monochromatic radiant
emission from the weld surface, thermal radiation from the weld being
collected through an aperture at the electrode tip.

In addition, a mathematical equation has been developed for initial
static resistance of the weldment; also, probable forms of equations
relating dynamic resistance and time are suggested. It is also
demonstrated that the classical w-6 theorem is a more reliable basis
for deriving any relationship connecting weld voltage and weld temperature.

Date of Award	1972
Original language	English