8630196
120 Volt spot Welder
V 4.2
12
For technical questions call 1-800-665-8685
OPERATION
FUNDAMENTALS OF RESISTANCE SPOT WELDING
PRINCIPLE
Resistance welding is accomplished when current is
caused to flow through the electrode tips and the
separate pieces of metal to be joined. The resistance of
the base metal to the electrical current flow causes
localized heating in the joint, and the weld is made. The
resistance spot weld is unique because the actual weld
nugget is formed internally with relation to the surface
of the base metal. Figure 2 shows a resistance spot weld
nugget compared to a gas tungsten-arc (TIG) spot weld.
The gas tungsten-arc spot is made from one side only. The resistance spot weld is normally made
with electrodes on each side of the workpiece. Resistance spot welds may be made with the workpiece
in any position.
The resistance spot weld nugget is formed when the interface of the weld joint is heated due to the resistance
of the joint surfaces to electrical current flow. In all cases, of course, the current must flow or the weld cannot
be made. The pressure of the electrode tips on the workpiece holds the part in close and intimate contact
during the making of the weld. Remember, however, that resistance spot welding machines are NOT designed
as force clamps to pull the workpieces together for welding.
HEAT GENERATION
A modification of Ohm’s Law may be made when watts and heat are considered equal. When current is passed
through a conductor, the electrical resistance of the conductor to the current flow will cause heat to be
generated. The basic formula for heat generation may be stated as:
H = I
2
R
Values
H
Heat
I
2
Welding Current Squared
R
Resistance
The secondary portion of a resistance spot welding circuit, including the parts to be welded, is actually a series
of resistances. The total additive value of this electrical resistance affects the current output of the resistance
spot welding machine and the heat generation of the circuit.
The key fact is, although the current value is the same in all parts of the electrical circuit, the resistance values
may vary considerably at different points in the circuit. The heat generated is directly proportional to the
resistance at any point in the circuit.
