Metal Fabrication

Introduction to common welding and cutting processes

2015

Choosing the best weld process gas

Why do we need a weld process gas?- Protects the weld pool- Assists in stabilising the arc- Assists in metal (droplet) transfer

(MIG/MAG)- Helps maintain metallurgical

properties of the material

Also…- Influences productivity - Influences weld quality- Influences the working

environmental

MIG/MAG

TIG

02_EN_M_Mar_2015

MIG/MAG Welding

Metal Inert Gas (MIG)

• Inert the process gas DOES NOT react with the weld material

Metal Active Gas (MAG)

• Active the process gas DOES react with the weld material

Ar

Ar

CO2

O2

H2

N2

Can be 100% CO2

Mixture of one or more of these gases in an inert base gas

He

He

MIG/MAG Welding Equipment

MIG/MAG Welding

Welding wire(electrode)

Contact tip

Weld

Parent Material

Weld process gas

Gas shroud

MIG/MAG Welding

Example of welding

TIG Welding

Tungsten Inert Gas

• Inert the process gas DOES NOT react with the weld material

Ar

• Active the process gas DOES NOT react with the weld material

H2

Mixture (up to 5%) in an inert base gasTAG terminology not used

Ar

He

He

TIG Welding Equipment

TIG Welding

Filler material

Weld

Parent material

Weld process gas

Tungsten electrode

Gas shroud

TIG Welding

Summary MIG/MAG & TIG

• Independent input of filler wire ...

• Requires a skilled operator

• Non-consumable electrode process

• Lower productivity / higher quality than MIG/MAG

• Semi-mechanized / robotic welding possible but not as common as in MIG/MAG

• Automatic feeding of filler wire

• Easy to use & highly productive

• Consumable electrode i.e. filler wire is the electrode

• Semi-mechanized / robotic welding (common)

• Can generate spatter - may require post-weld cleaning (time = cost)

TIGMIG/MAG

• Definition:Light Amplification by the Stimulated Emission of Radiation: LASER

• Laser Cutting is fast and precise

Laser Cutting

Laser Cutting

• Laser Gases (resonator gases – CO2 lasers

only)- Typically used for the laser beam either as a

premixed cylinder or as individual cylinders

- Low flow rates – small volumes

• Process assist gases (all laser types)- To assist in the removal of metal from the cut

area

- High pressures, high flow rates

CO2

N2

O2

N2

Carbon steel

Stainless steel

He

O2

N2

Ferrous materials: carbon steel

Ar

Non Ferrous: stainless steel (and aluminium)

Reactive materials such as titanium

Air Low cost – low-quality alternative

Laser Cutting – process assist gases

• Similar to TIG Welding

• Non-consumable Tungsten electrode

• Used a constricted plasma-arc created by an additional water cooled

plasma nozzle

• Electrode protected inside the torch

TIGPLASMA

Plasma Arc Welding

Plasma Arc Welding

Two distinct gas streams

• Plasma gas is inert the gas DOES NOT react with the weld or the tungsten electrode

Ar

• Weld process gas similar to TIG can be inert or active the process gas DOES react with the weld material

H2

Mixture (up to 15%) in an inert base gas

Ar

He

He

Plasma Arc Welding

Tungsten electrode

Gas shroud

Plasma gas

Nozzle

Weld

Weld process gas

Plasma Arc Welding

• Electric arc is the heat source

• Specialised welding process

• Independent input of filler wire but protected electrode and easy arc starting ... more suitable than TIG for automation

• Uses a plasma and a weld process gas (inert / active-reducing)

• Non-consumable electrode process

• Mechanized / robotic welding common

• Common problem – no problems but relatively expensive and complex torches vs. TIG

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