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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