2
Snap-on Tools Corporation Kenosha, WI 53141-1410
POWER SOURCE
WIRE SPOOL
FEED
ROLLS
WORK
MIG
TORCH
+
REVERSE
POLARITY
(STD.)
_
SHIELDING GAS
SHORT ARC OR DIP TRANSFER
Short arc transfer occurs at 12 to
22 arc volts (voltage while weld-
ing), depending on wire size. Weld-
ing commences as the arc is struck
and a weld pool is formed. The tip
of the electrode wire dips into the
pool and causes a short circuit.
The short circuit current flow
causes a rapid temperature rise in
the electrode wire and the end of
the wire is melted off. An arc is
immediately formed between the tip
of the wire and the weld pool,
maintaining the electrical circuit
and producing sufficient heat to
keep the weld pool fluid. The
electrode continues to feed and
again dips into the pool.
ELEC-
TRODE
WORK
INTRODUCTION
The Snap-on Tools MM140SL is a
combination welding power source,
remote feed unit, MIG torch and
accessory package. It operates on
115 volts AC input current and is
designed to meet the requirements
of autobody repair shops. The
MM140SL produces fusion welds by
the Gas Metal Arc Welding process
(GMAW or MIG), on steel and aluminum
up to "1/4" thick, using .023"
through .045" steel wire and .025"
through 3/64" aluminum wire with
the optional MHG5-B spool gun.
(optional liners must be purchased
to cover given wire sizes). Heavier
sections can be easily welded using
slightly different techniques.
The number of controls on the unit
have been reduced to assist inexpe-
rienced operators to learn MIG
welding. This facilitates rapid
set up for welding various thick-
nesses of material requiring vari-
ous heat inputs. The VOLTAGE
control adjusts the welding voltage
and the WIRE FEED control adjusts
the speed of the wire feed motor.
This sequence of events is re-
peated up to 200 times per second.
Short arc transfer is suitable for
positional welding. The heat input
to the workpiece is kept to a
minimum which limits distortion and
makes possible the welding of thin
sheet material.
THE MIG PROCESS
AS APPLIED TO THE MM140SL
The MIG process uses a bare,
consumable electrode in the form of
spooled wire, which is fed by a
controllable speed feed unit
through the cable and torch to the
weld. The emerging wire and the
weld are shielded by a stream of
CO2, Argon, or a mixture of the two,
which prevents oxidation of the
molten weld puddle. The gas shield
enables high quality welds to be
made without the use of flux,
eliminating the need for slag or
flux removal after the weld is
completed.
The consumable electrode wire is
melted and transferred to the weld
puddle by "short arc" or "dip"
transfer mode.
FIG. 1. SCHEMATIC OF M.I.G. PROCESS
FIG. 2. SHORT ARC TRANSFER
