Emily Hartman
WDT 124 Final Exam Project
GMAW in welding stands for gas metal arc welding. It is the process of an electrode,
(typically a wire in this instance) being used to strike an arc with a piece of metal, thus melting
the wire into a puddle. The puddle then slightly penetrates the base metal, leaving it with a
strong bond that shouldn’t be able to be broken easily. However, in order for the puddle to
solidify properly, without reacting with any number of reactants in the atmosphere, a shielding
gas must be used. The gas is typically a mixture of argon and carbon dioxide, but sometimes is
completely argon. Whichever shielding gas ratio is used affects how the puddle will be
dispersed.
Another type of welding besides GMAW is FCAW. FCAW stands for flux core arc weld
and is quite different. FCAW is a hollow wire that is filled with flux, hints the name. FCAW also
has a higher deposit and penetration rate compared to GMAW. A disadvantage to flux core,
however, is that it produces slag over the weld which must be chipped off before being able to
continue welding. Also, flux cannot be used on thinner metals.
As far as GMAW goes, there are four different modes of metal transfer possible. Shortcircuit transfer is when the electrode touches the base metal and short circuits, which causes
the wire to melt and transfer to the base metal. Globular transfer is when the weld metal
transfers across the arc in droplets usually larger than the electrode’s diameter, which makes
the puddle like a glob. Spray transfer is when the weld metal disperses across the arc in tiny
droplets in a cone shape. Pulse-spray transfer is similar to spray transfer, except that the
current is continuously fluctuating.
In order to set up the welding machine to have a short circuit transfer mode a few
things must be done. First, the shielding gas mixture should be 25% CO2 75% Argon. Next, the
amperage, also known as the wire feed speed, needs to be on the lower side. The voltage needs
to be as well. If the welding current is too high, the amount of spatter will increase. The wire
size used should be of a relatively smaller diameter, not exceeding 0.045 inches. The metal
welded on should be thinner as well.
For spray transfer, the shielding gas mixture will usually be a minimum of 80% argon.
The amperage (wire feed speed) will be higher for spray transfer. The voltage will also be higher
for spray. Spray transfer can be used on thicker metals. It is also usually only done in the
horizontal or flat position based on the higher deposit rate.
As far as globular transfer goes, it is relatively similar to short circuit. Globular transfer
requires a medium amount of voltage. The wire feed speed is also on the slower side. Also, the
shielding gas ratio is about the same as short circuit. One must be cautious of the spatter that
globular typically causes on the nozzle, though.
The set-up process for pulse spray is similar to normal spray mode. The shielding gas
ratio must be at the very least 80% argon. The only difference with pulse is the fact that the
current is alternating. Pulse welding’s peak current needs to be above the transition point for
the specific wire diameter being used. Pulse can be used on both thick and thin metals.
As far as my favorite transfer type to use, I enjoy spray the best. I like the limited
amount of spatter produced. I also like how the weld is clean and smooth looking. It feels
smooth and the sound produced is quieter than some of the others. The arc also looks rather
nice and is easily visible.
The MIG gun has many parts and each has a unique purpose. The first part is the wire
feeder. The wire feeder feeds the wire from the wire spool through the gun liner, which has the
sole purpose of keeping the wire straight till it reaches the contact tip. The contact tip has the
important job of heating the wire and transferring current to it, giving it the ability to arc when
coming in contact with the grounded metal. Then, around the contact tip is the nozzle. The
nozzle’s main job is to direct the shielding gas to the weld puddle.