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Sectioning and etching will disclose the presence of mis-shaped welds in a plane normal to that of the sheet.
To eliminate mis-shaped nuggets, use only electrodes that have been machine cut. Do not dress electrodes
with a file. Be sure the electrodes are properly aligned, and be sure that too small a radius is not used.
LOW STRENGTH IN A SPOT WELD CAN BE CAUSED BY:
1. Too small a weld for the sheet thickness.
2. No fusion, but only a “stick”.
3. Defects such as expulsion, cracking, or major indentation.
TESTS FOR WELDS
The above discussion of defects in welds has mentioned several tests of spot welds that are used to discover
defects and to evaluate the welds. The following tests are used on the welding floor and in the laboratory:
1. Visual inspection.
2. Peel test.
3. Twist test.
4. Macro test
Visual inspection will disclose defects on the surface such as surface burning, indentation and expulsion
near an edge, but it is never sufficient to evaluate the quality of a weld.
The peel test is a common test used in many shops where spot welding is done. This test consists of prying
the sheets apart and peeling one sheet back over the other, in “can opener” fashion. If failure occurs by
shearing through the nugget, the weld is considered unsatisfactory. If failure occurs by tearing a button
from the sheet, the weld is considered satisfactory.
The twist test consists of twisting the two sheets apart about an axis perpendicular to the sheet and at the
center of the weld. The torque required and the angle of twist attained before final separation are
approximate measures of the strength results can be expected in the tensile shear test.
The macro test is very simple and extremely useful in evaluating the quality of weld. The procedure is to:
1. Scribe a line through the center of the weld to be examined.
2. Cut to one side of the line, with a hack saw, power saw, cut off wheel of other means.
3. File to the tie, then polish with fine emery cloth.
The degree of smoothness required will depend on the amount of magnification used in examining the
section. For visual or low magnification, a good fine file finish is usually satisfactory. For higher
magnification a greater degree of polish is desirable.
Etch the surface with a suitable etchant, which will disclose the structure of the weld with sufficient contact
for satisfactory visual examination. Sometimes too drastic an etch will produce “defects” which are not
there. The degree of etch is somewhat dependent on the power of magnification to be used in inspecting
the weld.