Transcript MIG Welding - KSU Web Home

Manufacturing Processes Lab I
MET 1321
Metal Inert Gas Welding (MIG)
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Welding Processes
ARC Welding
(AW)
Oxyfuel Welding
OFW
Resistance Welding
RW
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
1.
2.
3.
4.
5.
6.
Shielded Metal Arc Welding (Stick welding)
Gas Metal Arc Welding (MIG)
Gas Tungsten Arc Welding (TIG)
Flux Cored Arc Welding
Submerged Arc Welding
Plasma Arc Welding
Oxyacetylene Welding (OAW)
Gas Metal Arc Welding (GMAW) or
Metal Inert Gas (MIG) Welding
Metal Active Gas (MAG) Welding
MIG is an arc welding process that
uses an arc between a continuous
wire electrode and the weld pool.
Wire is continuously fed from a
spool.
MIG welding is a commonly used
high deposition rate welding
process. MIG welding is therefore
referred to as a semi-automatic
welding process.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Shielding gases
The shielding gas completely covers and protects the
weld pool.
Argon (or mixture of Argon and Oxygen) is used as a
shielding gas for nonferrous metals such as aluminum,
and
Carbon dioxide (or carbon dioxide mixtures with argon)
are used as a shielding gas for steels.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Advantages
The MIG welding process provides many advantages in manual and
automatic metal joining for both low and high production
applications. Its combined advantages when compared to covered
(stick) electrode, submerged arc, and TIG are:
1)
2)
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4)
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7)
8)
Welding can be done in all positions.
No slag removal required.
High weld metal deposition rate.
Overall times for weld completion about 1/2 that of covered
electrode.
High welding speeds. Less distortion of the workpiece.
High weld quality.
Large gaps filled or bridged easily, making certain kinds of repair
welding more efficient.
No stub loss as with covered electrode.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
GMAW or MIG equipments
MIG equipment consists of a welding gun, wire feeder,
and shielding gas.
A constant voltage, direct
current (DC) power source
is most commonly used with
GMAW.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
MIG torch nozzle
GMAW torch nozzle cutaway image.
(1) Torch handle,
(2) Molded dielectric (shown in white) and threaded
metal nut insert (yellow),
(3) Shielding gas nozzle,
(4) Contact tip,
(5) Nozzle output face
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
MIG wire
Wires are made of mild steel, Aluminum, Stainless Steel, Copper and
Copper-based Alloy. The size is between 0.02 to 0.125 inches.
Welding wire designations are based on
AWS classifications:
For Mild steel:
ER – 60 S -1
Stainless steel wire
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
MIG welding
• Direct Current (DC) is only used.
• AC should not be used, since the burn-offs are unequal on each
half-cycle.
• The consumable wire electrode diameter is between .02 to .125
inches.
• Amperage between 60 to 250 A.
– This is determined by trial and error.
– Set the wire feed speed according to the current chosen.
• Voltage is between 16-40 V (the voltage controls the arc length).
• Gas flow rate is approximately 20 cfh (cubic feet per hour) to 35 cfh.
• Wattage is between 1 to 20 kW.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
DCEP or DCEN?!
More heat
in electrode
Direct Current Electrode Positive (DCEP) provides
deep penetration and excellent cleaning action.
Direct Current Electrode Negative (DCEN) should not
be used, because
More heat
• Weld penetration is shallow and wide,
in the
• Metal transfer is erratic,
workpiece
• There is excessive spatter, and
• No surface cleaning occurs.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Metal transfer modes
Metal transfer modes in GMAW are
– short circuiting transfer, spray transfer, pulsed
spray transfer, and globular transfer.
The type of metal transfer that occurs depends on
welding wire size, shielding gas, arc voltage and
welding current.
As current increases, the transfer mode changes from
short circuiting to globular and then (with 80% argon)
to spray.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Stickout
Stickout is the
distance the welding
wire projects from the
end of the nozzle of
the welding gun.
The proper nozzle-towork distance must be
maintained to ensure
adequate shielding gas
coverage.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Stickout
short circuiting transfer
Or Dip (short arc) transfer
Arc voltage: 15 - 22V
Current: below 200A
Metals: steel and steel alloys
Connection: DC electrode positive
Contact tube: 5 mm in front of nozzle tip
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Spray transfer
Arc voltage: 27 - 54V
Current: higher than 200A
Metals: aluminum (other metals in flat
position)
Connection: DC electrode positive
Contact tube: 5 mm inside nozzle tip
Stickout
Stickout can be adjusted to alter the current and
voltage conducted to the arc.
A shorter stickout creates a hotter arc,
A longer stickout reduces penetration on thin metal
(suitable for thin metals).
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
How to weld
Welding parameters are set based on the
thickness of the metal used.
Steel backing bars are required for welding
copper 1/8 inches thick or less.
Preheating copper at 400F (204 C) is
advisable on sections 3/8 inches thick or
more.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
How to weld
Ensure that the contact tube and gas nozzle orifices
are clean to prevent clogging, which restricts wire
feed and shielding gas flow.
Set the voltage, wire feed and shielding gas flow to
the standard conditions for the required type of
welding.
Adjust the welding wire to the proper stickout.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
How to weld
Start the arc and move the welding gun at a uniform speed,
maintaining the proper work angle ( 25˚ travel angle and 90˚
working angle).
25
Move the welding gun
along the joint using
the pushing or pulling
techniques.
90
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
How to weld
A slight weaving motion is helpful to ensure penetration.
Do not remove the welding gun from
the weld area until the weld pool
has solidified. The shielding gas
prevents cracks from developing in
the molten weld pool.
Cold lap occurs if the arc does not
melt the base metal sufficiently.
Check the weld for surface
porosity, which is usually caused by
improper gas shielding.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
How to weld
Shut down the machine when welding is completed
– turn off wire speed control,
– Shut off shielding gas flow at cylinders,
– Squeeze welding gun trigger to bleed the lines,
– Shut off welding machine,
– Hang up welding gas.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Flux cored arc welding
A related process, flux cored arc welding, often does not utilize a
shielding gas, instead employing a hollow electrode wire that is
filled with flux on the inside.
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Test yourself!
Argon is used as a shielding gas for Aluminum and
carbon monoxide is used for steels.
Carbon dioxide
True
False
Both DCEN and DCEP in MIG welding, provide
good quality weld.
True
False
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
Test yourself!
Which one is spray transfer and which is short circuiting transfer?
spray transfer
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri
short circuiting transfer
Test yourself
Cracks in MIG welding happen, because:
1- the welding wire is not adjusted to the proper
stickout.
2- the welding gun is removed from the weld area
before the weld pool has solidified.
3- the arc does not melt the base metal
sufficiently.
Cold lap
Manufacturing Processes Lab 1 (MET 1321)
Prof S. Nasseri