GE SpotChecker, Operating Manual

Page: 51 / 98

Good spot weld (OK)
Too small nugget
Stick weld
Loose joint
To determine a too small weld nugget diameter, the
nugget diameter is compared with the diameter of the
sound beam: if the nugget diameter is too small, in-
termediate echoes are produced. This is on the one
hand on the condition that the inspector positions the
probe at the spot weld center. If the probe is not ex-
actly at the center, intermediate echoes will likewise
be produced. This means that an adequately large
weld nugget may be evaluated as being “too small”.
Conversely, however, it is not possible that a too small
nugget be evaluated as being “OK”. The inspection
result is consequently always on the safe side with
regard to the nugget diameter, provided the inspector
does not make any fundamental mistakes, e.g. use a
wrong gain setting or a wrong probe.
On the other hand, the comparison of the nugget di-
ameter with the sound beam diameter requires a high
quality of the probes. Probe certi
fi cates are issued to
prove the sound beam properties.
Comparison of ultrasonic inspection with other
inspection methods
The shop methods include the button test, the de-
structive chipping test and the nondestructive chip-
ping test using hammer and chisel. In the case of the
button test and the destructive chipping test, the spot
welds are subjected to stress load until breakage oc-
curs using simple test equipment, without recording
any reading. Used as evaluation criteria are the type
of breakage and the size of the torn spot weld. The
volume of test scrap causes considerable amount of
cost.
The advantage of the chipping test using chisel is that
it can also be applied to a
fi nished component, e.g.
a body shell. In these cases it is nevertheless mainly
Ultrasonic inspection of spot welds within automotive industry
Individual inspection reports
SpotChecker Issue 02, 03/2009
51