Buffalo Tools MMIG125, Assembly & Operating Instructions

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20
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 (see Figure 20).
Each has advantages and disadvantages
depending on the specific application as well
as personal preference.
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 small-
er 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. Wire diameters that tend to work
best, with the burn-through method are
0.035 inch self-shielding flux-core wire.
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 mini-
mal 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 pro-
duces a weld with the most finished
appearance of the three spot weld meth-
ods. In this method, a hole is punched or
drilled into the top piece of metal and the
arc is directed through the hole to pene-
trate 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.
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.
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
1. Select the wire diameter and heat setting
recommended above for the method of
spot welding you intend to use.
2. Tune in the wire speed as if you were
going to make a continuous weld.
3. Hold the nozzle piece completely perpen-
dicular to and about 1/4 inch off the work
piece.
4. Pull the trigger on the torch and release it
when it appears that the desired penetra-
tion has been achieved.
5. Make practice spot welds on scrap metal,
varying the length of time you hold the
trigger, until a desired spot weld is made.
6. Make spot welds on the actual work
piece at desired locations.
Figure 20. Spot Welding