mig welding

13
1 GMAW Principles

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Mig Welding

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Page 1: Mig Welding

1

GMAW Principles

Page 2: Mig Welding

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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

Page 3: Mig Welding

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GMAW Circuit

• Three things happen when the GMAW gun trigger is pulled:– The wire electrode

begins to feed– The circuit becomes

electrically ‘hot’

• Current flows from the power source through the gun cable, gun, contact tip to the wire and across the arc. On the other side of the arc, current flows through the base metal to the work cable and back to the power source

– Shielding gas flows through the gun and out the nozzle

Page 4: Mig Welding

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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

Page 5: Mig Welding

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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

Page 6: Mig Welding

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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 10,000°F

Page 7: Mig Welding

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3 - Weld Puddle

• As the wire electrode and work piece heat up and melt, they form a pool of molten material called a weld puddle

• This is what the welder watches and manipulates while welding .045” ER70S-6 at 400 ipm wire feed

speed and 28.5 Volts with a 90% Argon/ 10% CO2 shielding gas

Page 8: Mig Welding

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4 - Shielding Gas

• GMAW welding requires a shielding gas to protect the weld puddle

• Shielding gas is usually CO2, argon, or a mixture of both

The gauges on the regulator show gas flow rate and bottle pressure

Page 9: Mig Welding

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5 - Solidified Weld Metal

• The welder “lays a bead” of molten metal that quickly solidifies into a weld

• The resulting weld is slag free

An aluminum weld done with the GMAW process

Page 10: Mig Welding

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Troubleshooting Welds

Page 11: Mig Welding

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Troubleshooting Welds

• GOAL - Make Good Welds

• Eliminate Porosity

• Eliminate Ropey Convex bead

• Eliminate Excessive Spatter

Page 12: Mig Welding

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AWS Classification of

GMAW Electrodes

Page 13: Mig Welding

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ER70S-XElectrodeRod70,000 psi Min. Tensile StrengthSolidChemistry, Amount of Deoxidizers (Silicon, Manganese and/or Aluminum, Zirconium and Titanium) X=2,3,4,6,7 or G

AWS Classification of GMAW Electrodes