MIG WeldingMIG Welding
Manufacturing and Materials ProcessesManufacturing and Materials Processes
(GMAW) MIG Welding(GMAW) MIG Welding
Gas Metal Arc Welding (GMAW) is frequentlyreferred to as MIG welding. Gas Metal Arc Welding (GMAW) is frequentlyreferred to as MIG welding.
MIG welding is a commonly used highdeposition rate welding process. MIG welding is a commonly used highdeposition rate welding process.
Wire is continuously fed from a spool. Wire is continuously fed from a spool.
MIG welding is therefore referred to as asemiautomatic welding process. MIG welding is therefore referred to as asemiautomatic welding process.
MIG Welding BenefitsMIG Welding Benefits
All position capability All position capability
Higher deposition rates than SMAW Higher deposition rates than SMAW
Less operator skill required Less operator skill required
Long welds can be made without starts andstops Long welds can be made without starts andstops
Minimal post weld cleaning is required Minimal post weld cleaning is required
MIG Welding Shielding GasMIG Welding Shielding Gas
The shielding gas, forms the arc plasma,stabilizes the arc on the metal being welded,shields the arc and molten weld pool, and allowssmooth transfer of metal from the weld wire tothe molten weld pool. The shielding gas, forms the arc plasma,stabilizes the arc on the metal being welded,shields the arc and molten weld pool, and allowssmooth transfer of metal from the weld wire tothe molten weld pool.
The primary shielding gasses usedare:The primary shielding gasses usedare:
Argon Argon
Argon – 95% to 5% Oxygen Argon – 95% to 5% Oxygen
Argon – 75% to 25% CO2 Argon – 75% to 25% CO2
Argon/Helium Argon/Helium
CO2 is also used in its pure form in some MIGwelding processes. However, in someapplications the presence of CO2 in theshielding gas may adversely affect themechanical properties of the weld. CO2 is also used in its pure form in some MIGwelding processes. However, in someapplications the presence of CO2 in theshielding gas may adversely affect themechanical properties of the weld.
Welding Parameters and TechniquesWelding Parameters and Techniques
Welding currentWelding current
Wire electrode extensionWire electrode extension
Welding voltageWelding voltage
Arc travel speedArc travel speed
WELDING CURRENTWELDING CURRENT
The welding current is the electrical amperage inthe power system as the weld is being made.The welding current is the electrical amperage inthe power system as the weld is being made.
welding current is directly related to wire- feedspeed (if the wire extension beyond the guide tipis constant). As the wire-feed speed is varied, thewelding current will vary in the same direction.In other words, an increase (or decrease) in thewire-feed speed will cause an increase (ordecrease) of the current.welding current is directly related to wire- feedspeed (if the wire extension beyond the guide tipis constant). As the wire-feed speed is varied, thewelding current will vary in the same direction.In other words, an increase (or decrease) in thewire-feed speed will cause an increase (ordecrease) of the current.
WIRE ELECTRODE EXTENSIONWIRE ELECTRODE EXTENSION
Wire extension or ”stick-out” is the distancebetween the last point of electrical contact,usually the end of the contact tip, and the end ofthe wire electrode.Wire extension or ”stick-out” is the distancebetween the last point of electrical contact,usually the end of the contact tip, and the end ofthe wire electrode.
WIRE ELECTRODE EXTENSIONWIRE ELECTRODE EXTENSION
Controlling tip-to-work distance is important.Long extensions result in excess weld metalbeing deposited with low arc heat. This cancause poor bead shape and low penetration. Inaddition, as the tip-to-work distance increases,the arc becomes less stable.Controlling tip-to-work distance is important.Long extensions result in excess weld metalbeing deposited with low arc heat. This cancause poor bead shape and low penetration. Inaddition, as the tip-to-work distance increases,the arc becomes less stable.
WELDING VOLTAGEWELDING VOLTAGE
voltage setting directly controls the arc length.voltage setting directly controls the arc length.
In addition, a certain range is required tomaintain arc stability at any given weldingcurrent level.In addition, a certain range is required tomaintain arc stability at any given weldingcurrent level.
ARC TRAVEL SPEEDARC TRAVEL SPEED
As the material thickness increases, the travelspeed must be lowered.As the material thickness increases, the travelspeed must be lowered.
For a given material thickness and joint design,as the welding current is increased, so is the arctravel speed. The converse is also true.For a given material thickness and joint design,as the welding current is increased, so is the arctravel speed. The converse is also true.
Higher welding speeds are attainable by usingthe forehand welding technique.Higher welding speeds are attainable by usingthe forehand welding technique.
WELDING TECHNIQUESWELDING TECHNIQUES
Torch PositionTorch Position
Split the angle (90 degrees = 45 degree split)Split the angle (90 degrees = 45 degree split)
5 degree rake5 degree rake
GoodWeld
Voltage toHigh
Voltage toLow
Too Fast
Too Slow
Less StickOut