Title: Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW) Objective: To expose and pract ically hand on in welding / joining processes. Introduction: Welding is one of joining pro cesses method which is widely used. During welding processes the interface of two parts to be joined are brought to a temperature above the melting point and then allowed to solidify s o t hat a permanent joining rakes place. Because of the permanent nature of the joint and strength being equal to o r sometimes greater than that of the parent metal makes welding one of the most extensively used fabrication method. Welding is not only used for making structures but also repair work such as the joining of bro ken casting. Shielded Metal Arc Welding (SMAW) / Stick Welding /Arc Welding Theory SMAW Shielded Metal Arc Welding (SMAW) is frequently referred to as stick welding orcovered electrode we ldin g. St ick welding is among the most widely used welding processes. It is also a manual arc we lding process that uses a consumable electrode co ated in flux to lay the weld. An electric current, in the form of either alternating current or direct current from a welding power supply, is used to form an electric arc between the electrode and the metals to be joined. As the weld is laid, t he flux coating of the electrode disintegrates, giving o ff vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.
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Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW)
Objective:
To expose and practically hand on in welding / joining processes.
Introduction:
Welding is one of joining processes method which is widely used. During welding
processes the interface of two parts to be joined are brought to a temperature above the melting point and then allowed to solidify so that a permanent joining rakes place. Because of the
permanent nature of the joint and strength being equal to or sometimes greater than that of the
parent metal makes welding one of the most extensively used fabrication method. Welding is not
only used for making structures but also repair work such as the joining of broken casting.
Shielded Metal Arc Welding (SMAW) / Stick Welding /Arc Welding
Theory SMAW
Shielded Metal Arc Welding (SMAW) is frequently referred to as stick welding or
covered electrode welding. Stick welding is among the most widely used welding processes. It is
also a manual arc welding process that uses a consumable electrode coated in flux to lay the
weld. An electric current, in the form of either alternating current or direct current from a
welding power supply, is used to form an electric arc between the electrode and the metals to be
joined. As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that
serve as a shielding gas and providing a layer of slag, both of which protect the weld area from
To strike the electric arc, the electrode is brought into contact with the work piece in a
short sweeping motion and then pulled away slightly. This initiates the arc and thus the melting
of the work piece and the consumable electrode, and causes droplets of the electrode to be passed
from the electrode to the weld pool. As the electrode melts, the flux covering disintegrates,
giving off vapors that protect the weld area from oxygen and other atmospheric gases. In
addition, the flux provides molten slag which covers the filler metal as it travels from the
electrode to the weld pool. Once part of the weld pool, the slag floats to the surface and protectsthe weld from contamination as it solidifies. Once hardened, it must be chipped away to reveal
the finished weld. As welding progresses and the electrode melts, the welder must periodically
stop welding to remove the remaining electrode stub and insert a new electrode into the electrode
holder. This activity, combined with chipping away the slag, reduce the amount of time that the
welder can spend laying the weld, making SMAW one of the least efficient welding processes.
In general, the operator factor, or the percentage of operator's time spent laying weld, is
approximately 25%.
The actual welding technique utilized depends on the electrode, the composition of the
work piece, and the position of the joint being welded. The choice of electrode and welding
position also determine the welding speed. Flat welds require the least operator skill, and can be
done with electrodes that melt quickly but solidify slowly. This permits higher welding speeds.
Sloped, vertical or upside-down welding requires more operator skill, and often necessitates the
use of an electrode that solidifies quickly to prevent the molten metal from flowing out of the
weld pool. However, this generally means that the electrode melts less quickly, thus increasing
the time required to lay the weld.
Safety
SMA welding, like other welding methods, can be a dangerous and unhealthy practice if
proper precautions are not taken. The process uses an open electric arc, presenting a risk of burns
which is prevented by personal protective equipment in the form of heavy leather gloves and
long sleeve jackets. Additionally, the brightness of the weld area can lead to a condition called
arc eye, in which ultraviolet light causes the inflammation of the cornea and can burn the retinas
of the eyes. Welding helmets with dark face plates are worn to prevent this exposure, and in
recent years, new helmet models have been produced that feature a face plate that self-darkens
upon exposure to high amounts of UV light. To protect bystanders, especially in industrial
environments, transparent welding curtains often surround the welding area. These curtains,
made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light
from the electric arc, but should not be used to replace the filter glass used in helmets.
In addition, the vaporizing metal and flux materials expose welders to dangerous gasesand particulate matter. The smoke produced contains particles of various types of oxides. The
size of the particles in question tends to influence the toxicity of the fumes, with smaller particles
presenting a greater danger. Additionally, gases like carbon dioxide and ozone can form, which
can prove dangerous if ventilation is inadequate. Some of the latest welding masks are fitted with
an electric powered fan to help disperse harmful fumes.
Gas Metal Arc Welding (GMAW) is frequently referred to as MIG welding. MIGwelding is commonly used high deposition rate welding process. Wire is continuously fed from a
spool. MIG welding is therefore referred to as a semiautomatic welding process.
Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas
(MIG) welding or metal active gas (MAG) welding, is a semi-automatic or automatic arc
welding process in which a continuous and consumable wire electrode and a shielding gas are
fed through a welding gun. A constant voltage, direct current power source is most commonly
used with GMAW, but constant current systems, as well as alternating current, can be used.
There are four primary methods of metal transfer in GMAW, called globular, short-circuiting,
spray, and pulsed-spray, each of which has distinct properties and corresponding advantages and
limitations.
Originally developed for welding aluminum and other non-ferrous materials in the 1940s,
GMAW was soon applied to steels because it allowed for lower welding time compared to other
welding processes. The cost of inert gas limited its use in steels until several years later, when
the use of semi-inert gases such as carbon dioxide became common. Further developments
during the 1950s and 1960s gave the process more versatility and as a result, it became a highly
used industrial process. Today, GMAW is the most common industrial welding process,
preferred for its versatility, speed and the relative ease of adapting the process to robotic
automation. The automobile industry in particular uses GMAW welding almost exclusively.
Unlike welding processes that do not employ a shielding gas, such as shielded metal arc welding,
it is rarely used outdoors or in other areas of air volatility. A related process, flux cored arc
welding, often does not utilize a shielding gas, instead employing a hollow electrode wire that is
The basic technique for GMAW is quite simple, since the electrode is fed
automatically through the torch. By contrast, in gas tungsten arc welding, the welder must handle
a welding torch in one hand and a separate filler wire in the other, and in shielded metal arc
welding, the operator must frequently chip off slag and change welding electrodes. GMAW
requires only that the operator guide the welding gun with proper position and orientation along
the area being welded. Keeping a consistent contact tip-to-work distance (the stickout distance) is
important, because a long stickout distance can cause the electrode to overheat and will also
waste shielding gas. Stickout distance varies for different GMAW weld processes and
applications. For short-circuit transfer, the stickout is generally 1/4 inch to 1/2 inch, for spray
transfer the stickout is generally 1/2 inch. The position of the end of the contact tip to the gasnozzle is related to the stickout distance and also varies with transfer type and application. The
orientation of the gun is also important it should be held so as to bisect the angle between the
work pieces; that is, at 45 degrees for a fillet weld and 90 degrees for welding a flat surface. The
travel angle or lead angle is the angle of the torch with respect to the direction of travel, and it
should generally remain approximately vertical. However, the desirable angle changes somewhat
depending on the type of shielding gas used with pure inert gases, the bottom of the torch is out
often slightly in front of the upper section, while the opposite is true when the welding
atmosphere is carbon dioxide.
Safety
Gas metal arc welding can be dangerous if proper precautions are not taken. Since
GMAW employs an electric arc, welders wear protective clothing, including heavy leather
gloves and protective long sleeve jackets, to avoid exposure to extreme heat and flames. Inaddition, the brightness of the electric arc can cause arc eye, in which ultraviolet light causes the
inflammation of the cornea and can burn the retinas of the eyes. Helmets with dark face plates
are worn to prevent this exposure, and in recent years, new helmet models have been produced
that feature a liquid crystal-type face plate that self-darkens upon exposure to high amounts of
UV light. Transparent welding curtains, made of a polyvinyl chloride plastic film, are often used
to shield nearby workers and bystanders from exposure to the UV light from the electric arc.
Welders are also often exposed to dangerous gases and particulate matter. GMAW
produces smoke containing particles of various types of oxides, and the size of the particles in
question tends to influence the toxicity of the fumes, with smaller particles presenting a greater
danger. Additionally, carbon dioxide and ozone gases can prove dangerous if ventilation is
inadequate. Furthermore, because the use of compressed gases in GMAW pose an explosion and
fire risk, some common precautions include limiting the amount of oxygen in the air and keeping
combustible materials away from the workplace. While porosity usually results from
atmospheric contamination, too much shielding gas has a similar effect; if the flow rate is too
high it may create a vortex that draws in the surrounding air, thereby contaminating the weld pool as it cools. The gas output should be felt (as a cool breeze) on a dry hand but not enough to
create any noticeable pressure, this equates to between 20±25 psi (mild and stainless steel).
Above 26 volts the gas debit should be augmented slightly since the weld pool takes longer to
cool. As a factor that is often ignored, many flow meters are never adjusted and typically run
between 35±45 psi. A healthy reduction of gas will not affect the quality of the weld, will save
money on shielding gas and reduce the rate at which the tank must be replaced.
Shielded Metal Gas Art Welding (SMAW) is performed with the heat of an electric arc
that is maintained between the end of a coated metal electrode and the work piece. The heat
generated melts a portion of the electrode tip, its coating, and the base metal in the immediate arc
area. The molten metal consists of mixture of the base metal, the electrode metal, and substances
from the coating on the electrode; this mixture forms the weld when it solidifies. The electrode
coating deoxidizes the weld area and provides a shielding gas to protect it from oxygen in the
environment. The SMAW process has the advantages of being relatively simple versatile and requiring a
smaller variety of electrode. The most common quality problems associated with SMAW include weld
spatter, porosity, poor fusion, shallow penetration, and cracking. Weld spatter, while not affecting theintegrity of the weld, damages its appearance and increases cleaning costs.
Gas Metal Arc Welding (GMAW) shields the weld zone with an external gas such as argon,
helium, carbon dioxide, or gas mixtures. Deoxidizers present in the electrode can completely prevent
oxidation in the weld puddle, making multiple weld layers possible at the joint. Benefit of Gas Metal Arc
Welding is the technique is easy then no need for slag cleaning and it is the extremely high productivity
that GMAW possible, high rate of filler metal deposition, narrow weld bead, minimum distortion of work piece, very easy to learn and lastly clean, precise welds. However the main disadvantages is expensive
and complex equipment and setting up equipment can be time consuming and tricky. Besides that,
GMAW also used on all thicknesses of steels, aluminums, nickel, stainless steel etc. in addition it also
suitable both for steel and unalloyed, low alloy and high alloy based materials.