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CTU in Prague
Faculty of Mechanical Engineering
Ing. Petr Vondrouš, PhD., IWE
Arc welding
GMAW
1st semester 2015/2016
GMAW
Gas Metal Arc Welding
3
GMAW Definition
• GMAW stands for Gas Metal Arc Welding
• GMAW is commonly referred to as MIG or Metal Inert Gas welding
• During the GMAW process, a solid metal wire is fed through a welding gun and becomes the filler material
• Instead of a flux, a shielding gas is used to protect the molten puddle from the atmosphere which results in a weld without slag
GMAW is the most widely used arc welding process in the
United States
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
GMAW welding
GMAW is defined as arc welding using
a continuously fed consumable electrode
and a shielding gas.
Method no. acc. ČSN EN ISO 4063
13 – Gas shielded metal arc welding131
132
133
135
136
138
used names
GMAW – Gas Shielded Metal Arc Welding – USA
MIG – Metal inert gas
MAG - Metal active gas
5
1 - Electrode
• A GMAW electrode is:
– A metal wire
– Fed through the gun by
the wire feeder
– Measured by its
diameter
GMAW electrodes are commonly
packaged on spools, reels and
coils ranging from 1lb to 1000lbs
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Filler materials – solid and cored wires
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Basic parameters
Positions : all
Base material : MAG – structural steels
MIG- alloyed steels, Al, Cu, Ni alloys
Welded thickness : 2 - 100 mm
Current, voltage short circuit : I = 40 -190 A
U = 16 - 21 V
Spray : I = 120 - 500 A
U = 20 - 36 V
Diameter : 0,8 – 1,6 mm
Welding source : flat, solid wire mostly
DCEP, DC+
WIRE CONTROL
&
WIRE FEED MOTOR
POWER SOURCE
TRIGGER
INSTALLED
COMPONENTS
NOZZLE
CONTACT TIP
GAS DIFFUSER
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Types of wire feed rolls
Steel Solid wire
Non ferrous alloys
Cored wire
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Feeding far away
Removable wire feeder
PUSH-PULL gun
SPOOL-GUN
Wire feeders
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Welding technigue
Left, forward Right, backward welding
14
GMAW Components
• Let’s look a little closer at the GMAW process
Travel direction
Electrode
1Arc2
Weld Puddle
3
Shielding Gas4
5Solidified Weld Metal
Generally, drag on thin sheet
metal and push on thicker
materials
15
2 - Arc
• An electric arc
occurs in the gas
filled space between
the electrode wire
and the work piece
Electric arcs can generate
temperatures up to 6,000°C
16
4 - Shielding Gas
• GMAW welding
requires a shielding
gas to protect the
weld puddle
• Shielding gas is
usually CO2, argon
Ar, helium He or a
mixture
The gauges on the regulator show
gas flow rate and bottle pressure
Shielding in GMAW
Shielding gas can affect
– WM mechanical properties
– Chemical reactions
– Weld bead shape
– Arc heat, stability, and starting
– Surface tension
– Drop size
– Puddle flow
– Spatter
Important gas characteristics:
ionization potential – arc start, stability, arc heat – heat input
heat transfer ratio – heat trasfered to WM, heat input
influence on surface tenstion – drop size, puddle flow, spatter
Ar Ar-He He CO2
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Metallurgy reactions
Inert gas – Ar, He – no reaction at all
Active gas – „active“ = reactive
Gas dissociation in arc:
CO2 CO + O
Melt puddle reaction
Fe+O FeO + Q (heat)
C+FeO Fe+CO (porositzy)
Desoxidation elements - Mn, Si
FeO + Mn = MnO + Fe
2FeO + Si = SiO2 + 2Fe
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Desoxidation by filler alloying
100%CO2 wire G3Si1
82% Ar+18% CO2 wire G3Si1
Structural steel
20
GMAW Process Variables
• Welding variables
– Wire Feed Speed (WFS)
– Voltage
• Operator controlled variables
– Travel speed
– Gun angles
– Contact tip to work distance
(CTWD)
– Gas flow rate
What is the relationship
between WFS and amperage?
21
Modes of Metal Transfer
• GMAW is a process that
features several distinctive,
individual methods and types
of metal transfer
• The mode of metal transfer is
determined by a number of
welding variables
– Voltage
– Amperage
– Shielding Gas
• By changing one or more
variables, you can go from
one metal transfer mode to
another
22
Modes of Metal Transfer
• Two common conventional
modes of metal transfer are:
– Short arc
– Axial spray arc
• The application, joint design,
base material thickness, and
properties determine the
appropriate mode to use
Typical short arc
application
Typical axial spray
arc application
GMAW – MIG/MAG – Metal transfer modes
According to setting of the welding parameters,
there are SEVERAL modes of molten wire
transfer to the molten pool:
•1. short circuiting – small welding parameters,
till 150 A, 20-200 Hz, typical for MMA
•2 globular – 180 A , Ar–2% O2 shielding
Typical for CO2 Large spatter – not very suitable
• 3 spray transfer - Above a critical current- high el.-mag.
force (Lawrence force), small discrete metal drops,
e.g. 320A
4 Rotationg arc – at highest current levels
•Special Pulsed spray transfer - for special invertor sources
Pulsing of current can be done
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Short circuit – dip transfer
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Used gas mixtures - Ar + CO2 ( up to 25% )
- Ar + O2 (up to 12% )
IS = 40 - 190 A
UEO = 14 - 22 V
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Spray transfer
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
IS = 500 A
UEO = 20 - 36 V
No short circuits, used gasses - Ar + CO2 ( do 20% ),
- long arc - Ar + O2 ( do 10% )
- can not be done in pure CO2
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
Pulse transfer – Impuls transfer
FSW – Friction stir welding
ČVUT, Fakulta strojní, Ústav strojírenské technologie, skupina svařování
change between short and spray tranfer
- Ar + CO2 ( do 15% )
- Ar + O2 ( do 8% )
U = 20 – 50 V
I = 80 – 310 A