Arc welding GMAW CTU in Prague Faculty of Mechanical...

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



Filler materials – solid and cored wires



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



Types of wire feed rolls

Steel Solid wire

Non ferrous alloys

Cored wire



Feeding far away

Removable wire feeder

PUSH-PULL gun

SPOOL-GUN

Wire feeders



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



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



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



Short circuit – dip transfer



Used gas mixtures - Ar + CO2 ( up to 25% )

- Ar + O2 (up to 12% )

IS = 40 - 190 A

UEO = 14 - 22 V



Spray transfer



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



Pulse transfer – Impuls transfer



change between short and spray tranfer

- Ar + CO2 ( do 15% )

- Ar + O2 ( do 8% )

U = 20 – 50 V

I = 80 – 310 A

Arc welding GMAW CTU in Prague Faculty of Mechanical...

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