Forney 125 FC Operating Manual page 21

SPECIAL WELDING METHODS
Spot Welding
The purpose of a spot weld is to join pieces of metal together with a spot of weld instead of a
continuous weld bead. There are three methods of spot welding: Burn-Through, Punch and Fill,
and Lap.
Each has advantages and disadvantages depending on the specific application as well as personal
preference.
PUNCH AND Fill
1. The BURN-THROUGH METHOD welds two overlapped pieces of metal together by burning
through the top piece and into the bottom piece.
With the burn-through method, larger wire diameters tend to work better than smaller
diameters because they have greater current carrying capabilities allowing the arc to burn
through very quickly while leaving a minimal amount of filler metal build up.
Do not use 0.030 Inch self-shielding flux-core wires when using the burn-through method
unless the metal is very thin or excessive filler metal build-up and minimal penetration is
acceptable.
Always select the high heat setting with the burn-through method and tune-in the wire speed
prior to making a spot weld.
2. The PUNCH AND FILL METHOD produces a weld with the most finished appearance of the
three spot weld methods. In this method, a hole is punched or drilled into the top piece of
metal and the arc is directed through this hole to penetrate into the bottom piece. The puddle
is allowed to fill up the hole leaving a spot weld that is smooth and flush with the surface of the
top piece.
3. The LAP SPOT METHOD directs the welding arc to penetrate the bottom and top pieces at the
same time, right along each side of the lap joint seam.
Select the wire diameter, heat setting, and tune-in the wire speed as if you were welding the
same thickness material with a continuous bead.
Spot welding instructions
Select the wire diameter and heat setting recommended above for the method of spot welding you
intend to use.
1. Tune in the wire speed as if you were going to make a continuous weld.
2. Hold the nozzle piece completely perpendicular to and about 1/4 inch off the work piece.
3. Pull the trigger on the gun and release it when it appears that the desired penetration has been
achieved.
4. Make practice spot welds on scrap metal, varying the length of time you hold the trigger, until
a desired spot weld is made.
5. Make spot welds on the actual work piece at desired locations.
LAP SPOT
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