Grahame Collins
18th January 2006, 09:34 AM
Gas Metal Arc Welding (MIG) This process consists of feeding a bare metal filler wire made of the same material being welded--in conjunction with a shielding gas through a hand held torch unit. The welding wire picks up electric current supplied by a standard power source. On contact, it creates an arc that does the welding.
As wire is fed from the unit to the work, it functions as a continuous, consumable electrode, therefore requiring fewer starts and stops.
For routine joining applications, a MIG welder probably offers more advantages than any other welding process. Here's some advantages of MIG welding:
It's the easiest welding process to learn. With a little practice, even a first-time MIG user can achieve a good-looking weld.
Welds light gauge material or thick plate (with multiple passes).
Welds all common metals_carbon steel, stainless steel and aluminum.
Welding can be done in all positions, including overhead.
There is no need to remove flux, as the shielding is provided by a gas.
High welding speeds can be obtained_up to four times faster than stick welding_reducing repair or fabrication time.
A power supply that gives direct current reverse polarity (DCRP) is recommended for use with the MIG welding process. Generally, (stick ) welders use straight polarity current, which means the flow of electricity moves from the torch to the workpiece. In reverse polarity welding, current travels from the workpiece to the welding torch. For MIG welding, a DCRP current produces the best arc transfer and a smoother weld surface than other types of currents.
Special consideration is required when welding outdoors or in drafty areas with a MIG welder because air or drafts can blow the shielding gas from the weld puddle and cause porosity. The MIG welding process also requires more complex equipment, which is initially more costly. The following equipment and supplies are necessary for MIG welding:
A power supply and welding cables,
An electrode wire feeder/MIG welding gun system, and
A gas cylinder with 75 percent argon and 25 percent CO2, plus hoses and regulators.
The same constant voltage equipment used for MIG welding also performs flux cored welding. The difference is the wire that is used as an electrode. Rather than running a solid wire coupled with a shielding gas, flux cored welding uses self shielded wire with flux inside (some flux cored wires require a shielding gas).
Cored wires are generally used on thicker material (4 mm and up) than the solid wires used with the MIG process. Advantages of flux cored welding are:
Less affected by drafts, so better suited for outdoor work.
Works as well as stick welding on rusty or dirty material.
Continuous wire feed, which minimizes starts and stops.
Deep penetration for welding thick sections.
Increased metal deposition (two or three times that of stick welding
Porosity is a problem for welders. It often occurs in drafty areas when welding with a shielding gas. This difficulty can be overcome by using self shielded, flux cored wire. It performs similarly to a stick welder in such conditions so windy conditions are less detrimental on the weld. (Note this requires a machine where the polarity can be switched if you intend to do this buy a model that can perform both functions are some are fixed on one process)
Importantly, the material used to fill flux cored wires can be custom formulated to match the base metal, which helps produce a better weld. This can also make flux cored welding less sensitive to rust and scale on the welded piece than other processes.
Between its MIG and flux cored capabilities, a wire welder can perform most tasks a stick welder can do, and often more efficiently. While a good quality wire welder costs $1000 to $4,000 (depending on its size), the costs for consumables (wire and gas) are less than that for stick welding rods. Coupled with the ability to weld aluminum and sheet metal, a wire welder can pay for itself very quickly. (note I said sheet metal -not aluminium sheet. Take a MIG to most tinnies ( small aluminium boats of 3mm metal thickness and less) and you are liable to end up with more holes than boat.
Other considerations for welding alumininium is that pure argon shielding gas is required and the torch gun assembly supplied for welding steel is poorly suited to running aluminium wire as the wire is soft and pushed up the gun/torch assembly made for steel wire. There are dedicated aluminiummig welding torches,but they are specialised beasts and accordingly they are priced at a level making them inaccessible to most handyman welders.
- still more to come on setting up and welding
cheers
Grahame
As wire is fed from the unit to the work, it functions as a continuous, consumable electrode, therefore requiring fewer starts and stops.
For routine joining applications, a MIG welder probably offers more advantages than any other welding process. Here's some advantages of MIG welding:
It's the easiest welding process to learn. With a little practice, even a first-time MIG user can achieve a good-looking weld.
Welds light gauge material or thick plate (with multiple passes).
Welds all common metals_carbon steel, stainless steel and aluminum.
Welding can be done in all positions, including overhead.
There is no need to remove flux, as the shielding is provided by a gas.
High welding speeds can be obtained_up to four times faster than stick welding_reducing repair or fabrication time.
A power supply that gives direct current reverse polarity (DCRP) is recommended for use with the MIG welding process. Generally, (stick ) welders use straight polarity current, which means the flow of electricity moves from the torch to the workpiece. In reverse polarity welding, current travels from the workpiece to the welding torch. For MIG welding, a DCRP current produces the best arc transfer and a smoother weld surface than other types of currents.
Special consideration is required when welding outdoors or in drafty areas with a MIG welder because air or drafts can blow the shielding gas from the weld puddle and cause porosity. The MIG welding process also requires more complex equipment, which is initially more costly. The following equipment and supplies are necessary for MIG welding:
A power supply and welding cables,
An electrode wire feeder/MIG welding gun system, and
A gas cylinder with 75 percent argon and 25 percent CO2, plus hoses and regulators.
The same constant voltage equipment used for MIG welding also performs flux cored welding. The difference is the wire that is used as an electrode. Rather than running a solid wire coupled with a shielding gas, flux cored welding uses self shielded wire with flux inside (some flux cored wires require a shielding gas).
Cored wires are generally used on thicker material (4 mm and up) than the solid wires used with the MIG process. Advantages of flux cored welding are:
Less affected by drafts, so better suited for outdoor work.
Works as well as stick welding on rusty or dirty material.
Continuous wire feed, which minimizes starts and stops.
Deep penetration for welding thick sections.
Increased metal deposition (two or three times that of stick welding
Porosity is a problem for welders. It often occurs in drafty areas when welding with a shielding gas. This difficulty can be overcome by using self shielded, flux cored wire. It performs similarly to a stick welder in such conditions so windy conditions are less detrimental on the weld. (Note this requires a machine where the polarity can be switched if you intend to do this buy a model that can perform both functions are some are fixed on one process)
Importantly, the material used to fill flux cored wires can be custom formulated to match the base metal, which helps produce a better weld. This can also make flux cored welding less sensitive to rust and scale on the welded piece than other processes.
Between its MIG and flux cored capabilities, a wire welder can perform most tasks a stick welder can do, and often more efficiently. While a good quality wire welder costs $1000 to $4,000 (depending on its size), the costs for consumables (wire and gas) are less than that for stick welding rods. Coupled with the ability to weld aluminum and sheet metal, a wire welder can pay for itself very quickly. (note I said sheet metal -not aluminium sheet. Take a MIG to most tinnies ( small aluminium boats of 3mm metal thickness and less) and you are liable to end up with more holes than boat.
Other considerations for welding alumininium is that pure argon shielding gas is required and the torch gun assembly supplied for welding steel is poorly suited to running aluminium wire as the wire is soft and pushed up the gun/torch assembly made for steel wire. There are dedicated aluminiummig welding torches,but they are specialised beasts and accordingly they are priced at a level making them inaccessible to most handyman welders.
- still more to come on setting up and welding
cheers
Grahame