GE SpotChecker Operating Manual page 52

Individual inspection reports
applied as a nondestructive inspection, i.e. the joint is
not subjected to load until breakage occurs. The costs
for this inspection are comparatively low, but so is also
the value of its inspection results. This especially ap-
plies to the nondestructive chipping test using chisel.
It can only be used for detecting defective spot welds
whose strength already lies way below the permissible
minimum value, e.g. so-called "stick welds". Added to
this is the fact that the inspection results vary within
wide limits due to the relatively indefi nite inspection
conditions that cannot be kept constant.
The inspection methods using testing machines in-
clude the shearing test, the peeling tensile test, the
top tensile test and the torsional test as standard-
ized inspection methods. Their advantage is that the
strength tested under defi ned conditions in each case,
e.g. shearing load at the breakage of the welded joint,
is reliably determined. This statement should be quali-
fi ed by saying that only information on the strength
under the selected load can be obtained, e.g. the pure
top tension, and not the mixed loads generally occur-
ring. A disadvantage of these methods is the fact that
an inspection on the fi nished component is not pos-
sible.
52
Ultrasonic inspection of spot welds within automotive industry
The micrographic examination enables information to
be obtained on the nugget geometry, on the internal
fl aws, and assessments to be made about the struc-
ture. The good correlation between the nugget geom-
etry and the results of destructive tests using stan-
dardized inspection methods makes the results of the
micrographic examination an important and reliable, if
only indirect, assessment scale for the strength of the
spot weld.
Three disadvantages limit the application of this in-
spection method:
a) The spot has to be destroyed.
b) The inspection cannot be carried out on the fi n-
ished car body to be further used.
c) The inspection costs are relatively high in compari-
son with all other inspection methods.
With the exception of the nondestructive inspection
methods mentioned above, all other inspection meth-
ods are used in the production. A 100 % volume in-
spection is nevertheless not possible for economic
reasons and, in the case of destructive inspection
methods, also for technical reasons. As a result of
Issue 02, 03/2009 SpotChecker