What is MIG welding? Working process Process Parameters Advantages Limitations Applications MIG welding is an arc welding process in which a continuous solid wire electrode is fed through a welding gun and into the weld pool, joining the two base materials together. A shielding gas is also sent through the welding gun and protects the weld pool from contamination. In fact, MIG stands for “Metal Inert Gas”. The technical name for it is "Gas Metal Arc Welding" (or GMAW).

1. GAS METAL ARC WELDING
(MIG)
Presented by
N.SANKAR/AP /MECH

2.  Basics
 What is MIG welding?
 Working process
 Process Parameters
 Advantages
 Limitations
 Applications

3.  Welding is a process of joining two metal pieces
by the application of heat.
 Welding is the least expensive process and widely
used now a days in fabrication.
 Welding joints different metals with the help of a
number of processes in which heat is supplied
either electrically or by mean of a gas torch.
 Different welding processes are used in the
manufacturing of Auto mobiles bodies,
structural work, tanks, and general machine
repair work.

4. Welding
Processes
Beam
Processes
LBW, EBW
Arc Welding:
SMAW, GMAW,
GTAW, PAW
Solid state
Welding
USW, FRW,
EXW
Resistance
Welding
Spot, Seam,
Projection

5.  MIG welding is an arc welding process in which a
continuous solid wire electrode is fed through a
welding gun and into the weld pool, joining the two
base materials together.
 A shielding gas is also sent through the welding
gun and protects the weld pool from
contamination.
 In fact, MIG stands for “Metal Inert Gas”. The
technical name for it is "Gas Metal Arc Welding" (or
GMAW).

6.  Along with the wire electrode, a shielding gas feeds
through the welding gun, which shields the
process from contaminants in the air.
 The process can be semi-automatic or automatic.
 A constant voltage, direct current(dc) power source
is most commonly used with GMAW, but
constant current systems, as well as alternating
current, can be used.

8.  Power Supply
 Gas Supply
 Wire feeder
 Gun and
Whip
 Process

9.  A. Most welders used for MIG welding are direct
current machines of the constant voltage type.
 B. MIG welding machines must be designed to
produce a constant voltage.
◦ With a constant voltage MIG machine, the output
voltage will change very little with large changes in
current.
 C. Welding voltage has an effect on bead width,
spatter, undercutting, and penetration.
 D. The constant voltage welding machines are
designed so that when the arc voltage changes, the arc
current is automatically adjusted or self-corrected.

11.  E. Most MIG welding units have three
adjustments which must be in balance to
achieve a quality weld.
 These are voltage control, wire feed speed,
and shielding gas flow rate.

12.  To move the electrode wire from the spool to the
MIG welding gun, run the wire through a
channel and system of drive wheels.

13.  The constant rate of wire feed is necessary to
assure a smooth even arc.
 Wire speed varies with the metal thickness being
welded, type of joint, and position of the weld.
 These drive wheels, depending upon their location
in the wire feed unit, are either the push type or the
pull type.
 The pull-type drive wheels are located relatively
close to the MIG gun and exert a pulling action on
the wire.
 Pull-type drive wheels are used on most spool
guns.

14.  The electrode holder is commonly referred to
as the MIG gun.
 The MIG gun has a trigger switch for
activating the welding operation, a gas nozzle
for directing the flow of the shielding gas, and
a contact tip.

15.  The nozzle is made of copper alloy to help
remove the heat from the welding zone.

16.  The contact tip helps to guide the wire electrode
into the puddle as well as transmit the weld
current to the electrode wire.
◦ The electrode wire actually touches the contact tip as
it is fed through the MIG gun.
◦ During this contact, the weld current is transmitted to
the electrode.

17.  A Shielding gases are necessary for gas metal arc
welding to protect the welding area from
atmospheric gases such as nitrogen and oxygen,
which can cause fusion defects, porosity and
spatter.
 In the metal fabrication industry, argon is used to
create an inert gas shield during welding.
 Argon is frequently blended with carbon dioxide
(CO2), hydrogen (H2), helium (He) or oxygen (O2) to
enhance the arc characteristics or facilitate metal
transfer in Gas Metal Arc Welding (GMAW or MIG).

19.  Has a low ionization potential and therefore
creates a very stable arc when used as a
shielding gas.
 The arc is quiet and smooth sounding and has
very little spatter.
 Argon is a good shielding gas for welding sheet
metal and thin metal sections.
 Pure argon is also used for welding aluminum,
copper, magnesium, and nickel.
 Pure argon is not recommended for use on
carbon steels.

20.  The most often used gas in MIG welding because
it gives good bead penetration, wide beads, no
undercutting and good bead contour and it costs
much less than argon or helium.
 The main application of carbon dioxide shielding
gas is welding low and medium carbon steels.
 When using pure carbon dioxide shielding gas,
the arc is unstable, which causes a lot of
spatter.

21.  When used in a mixture with argon, oxygen helps to
stabilize the arc, reduce spatter, eliminate
undercutting, and improve weld contour.
 The mixture is primarily used for welding stainless
steel, carbon steels, and low alloy steels.
 An argon-helium mixture is used for welding thick
non-ferrous metals.
 This mixture gives the same arc stability as pure
argon with very little spatter, and produces a deep
penetrating bead.

22.  The tank supplying the shielding gas will
have a gauge and a gas flow meter.
 The volume of gas directed over the weld zone
is regulated by the flow meter.

23.  There are factors to consider when selecting
the correct electrode.
1. Consider the type of metal to be welded
and choose a filler wire to match the base
metal in analysis and mechanical properties.

24. 2. Consider the joint design.
 Thicker metals and complicated joint designs usually
require filler wires that provide high ductility.
 Ductility is the ability to be formed into a new form
without breaking.
3. Examine the surface condition of the metal to be
welded.
 If it is rusty or scaly, it will have an effect on the type
of wire selected.
4. Consider the service requirements that the welded
product will meet.

25.  MIG electrode wire is classified by the
American Welding Society (AWS).
 An example is ER70S6.
 For carbon-steel wire, the “E” identifies it as
an electrode
 “R” notes that it is a rod

26.  The basic technique for GMAW is very simple, since
the electrode is fed automatically through the torch
(head of tip).
 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.

27.  Keeping a consistent contact tip-to-work distance
(the stick out distance) is important, because a long
stick out distance can cause the electrode to
overheat and also wastes shielding gas.
 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.

28.  The welding process variables mainly affect the
geometry of the weld bead such as the
penetration, bead reinforcement, bead width and
the deposition rate, which is the weight of the
metal deposited per unit of time.
 These variables are as follows:
Welding Current
Welding Voltage
Travel Speed
Wire Electrode Size
Type of Shielding Gas
Electrode Extension
Electrode Angle
Weld Joint Position
Process parameters

29. As the welding current and voltage are increased
above the maximum recommended for short arc
welding, metal transfer will begin to take on a
different appearance.
This welding technique is commonly known as
globular transfer, with metal transferring through the
arc.
Usually, the drops of molten metal have a greater
diameter than the wire itself.
This mode of metal transfer can be erratic, with
spatter and occasional short circuiting being
common.

31.  The angle at which the MIG gun leans toward
or away from the direction of movement.
◦ A travel angle of 10 degrees to 20 degrees is
used for most welding.
◦ Travel angle is sometimes referred to as drag
angle.

33.  Is perpendicular to the line of travel and
varies considerably, depending upon the type
of weld being made and the welding position.
 The work angle for a flat position surfacing
weld should be 15 degrees to 25 degrees.

35.  Perpendicular to the
base metal.

36.  Leaning in the
direction of travel,
also known as the
backhand or pull
position.

37.  Leaning opposite the
direction of travel, also
known as the forehand
or push position.

38.  Welding jobs can be performed faster with
the MIG process.
 The continuous wire feed eliminates the need
to change electrodes.
 Weld cleaning and preparation time is less
for MIG welding than for stick electrode
welds.
 Since the gaseous shield protects the molten
metal from the atmospheric gases, there is no
flux or slag, and spatter is minimal.

39.  Little time is required to teach individuals
how to MIG weld.
 Because of the fast travel speed at which MIG
welding can be done, there is a smaller heat-
affected zone than with the shielded metal
arc welding process.
 The weld visibility is generally good.
 There is less smoke and fumes so operator
environment is improved.

40.  Both thick and thin metals can be welded successfully
and economically with the MIG process.
 Less time is needed to prepare weld joints since the
MIG welds are deep penetrating.
◦ Narrow weld joints can be used with MIG welding
and still secure sound weldments.
 The MIG welding process can be used to join both
ferrous and nonferrous metals.
◦ The development of electrode wire and the use of
spool guns has made the MIG process widely used
for aluminum, stainless steel, high-carbon-steel, and
alloy-steel fabrication.

41.  Sensitive to contaminants – the process
can only handle low to moderate levels of
surface contaminants such as rust, mill
scale, dirt, oil and paint. All these have
potential to create problems such as porosity,
incomplete fusion, bad bead appearance and
even cracking.
 Portability – moving the welding equipment
may not be that tough, but you also have to
handle the high pressure cylinders that
contain the shielding gas. Proper care must
be taken.

42.  Sensitive to wind – the shielding gas used
for MIG welding can easily be blown away
when welding outdoors. Even inside, a fan or
a wind draft of as low as 5mph can be
enough to cause porosity
 Lack of fusion – due to the ability to weld at
low currents this process has the potential
for lack of fusion when running in short
circuit mode.
 Open arc process – as with most welding
process, GMAW exhibits an open arc. Proper
care must be taking to shield the welder and
bystanders from the harmful UV rays.

43. Why MIG welding is used in Manufacturing?
 High productivity can lead to higher profits.
 In manufacturing, productivity is the central focus.
 The primary advantage of MIG welding is welding
speed.
 It is much quicker than traditional welding.
 High productivity can be achieved in many
manufacturing operations with the use of MIG
welding for its clean welds.
 It welds metals quickly and highly economic.

44.  Repairs can be carried out on a number of
different vehicles whether they be large,
small, light, or heavy.
 Capable of proving a strong weld even down
to 0.5mm.

45. Rebuilding:-
To repair, especially to dismantle and reassemble with
new parts.
Example to rebuild an old car.
When it comes to fixing broken parts in the field, there
are three steps to master:
*Cutting and removal of the failed component.
*Preparation of the new joint/part.
*Welding and cleanup.
worn parts can be repaired by using MIG welding in a
variety of coatings (stainless steel, bronze, nickel,
aluminum or hard surfacing) and in a range of hardness,
for a fraction of the cost of purchasing a new part.

47. • It is more economical to use a track based roboticwelding
system than it is to actually man the assembly line.
Four Reasons to Choose Automated Pipe Welding with
Robots:
1. New Technologies
2. Flexibility
3. Weld Quality
4. Productivity

48. It can even be used to reinforce the surface of a
worn out railroad track.
It can be difficult to join metals of different
types, but by choosing the right filler wire you
can actually achieve it over time.

49.  Other type of welding needs highly skilled workers to
produce high quality weld.
 Maximum weld quality is assured by maintaining
cleanliness—all equipment and materials used must be
free from oil, moisture, dirt and other impurities, as these
cause weld porosity and consequently a decrease in weld
strength and quality.
 MIG welding is a huge improvement over some of the
previous techniques.
 MIG welding will help contribute to the creation of
automobiles, the building of bridges, and even more
importantly, a more efficient way to weld.