9
SHEAR STRENGTH
The shear strength of a spot weld for
a given wire chemistry is directly proportional to the area of the weld
nugget at the interface of the two sheets
being welded. Figure 11-5 shows
two spot welds made on mild steel.
Both welds were made with the same shielding gas and electrode wire but with different
welding conditions.
Notice that one weld is less penetrated and contains less nugget cross-sectional
area at the interface.
This weld has a shear strength of 1100 lbs. (499.5kg) less than the fully penetrated
weld. For a full
penetrating spot weld on a given plate thickness, the area of the interface will
depend to a large extent
on the shielding gas and the arc voltage. Spot welds on mild steel, for example,
will exhibit maximum nugget
area at the interface if carbon dioxide shielding gas is used and the arc voltage
is increased to a level
that is just below the point where the weld puddle becomes excessively turbulent.
Table 11-3 lists typical
shear strength values for spot welding both mild steel and aluminum. Note that
variations in the surface
condition of the work-piece, fixturing and arc voltage may significantly change
the shear strength. Table
11-3 – Typical Shear Strength Levels Spot Welding MILD
STEEL – E70S-4 ELECTRODE CO2 SHIELDING
PLATE THICKNESSES AVG.
SHEAR STRENGTH IN.
mm LBS
kg
.031 0.8
900 408
. 047 1.2
1600 762
. 063 1.6
1800
817 .
074 1.9
2600 1180
.105 2.7
3300
1497 .
130 3.3
4300 1951
. 177 4.5
5000
2269 .250
6.4 6800
3085
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