Mig Welding

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Mig Welding

Text of Mig Welding

  • *

    GMAW Principles

  • *GMAW Definition GMAW stands for Gas Metal Arc Welding GMAW is commonly referred to as MIG or Metal Inert Gas weldingDuring the GMAW process, a solid metal wire is fed through a welding gun and becomes the filler materialInstead of a flux, a shielding gas is used to protect the molten puddle from the atmosphere which results in a weld without slagGMAW is the most widely used arc welding process in the United States

  • *GMAW CircuitThree things happen when the GMAW gun trigger is pulled:The wire electrode begins to feedThe 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

  • *GMAW Components Lets look a little closer at the GMAW processTravel directionElectrode1Arc2Weld Puddle3Shielding Gas45Solidified Weld MetalGenerally, drag on thin sheet metal and push on thicker materials

  • *1 - ElectrodeA 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

  • *2 - ArcAn electric arc occurs in the gas filled space between the electrode wire and the work pieceElectric arcs can generate temperatures up to 10,000F

  • *3 - Weld PuddleAs the wire electrode and work piece heat up and melt, they form a pool of molten material called a weld puddleThis 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

  • *4 - Shielding GasGMAW 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

  • *5 - Solidified Weld MetalThe welder lays a bead of molten metal that quickly solidifies into a weldThe resulting weld is slag freeAn aluminum weld done with the GMAW process

  • *Troubleshooting Welds

  • *Troubleshooting WeldsGOAL - Make Good Welds

    Eliminate Porosity

    Eliminate Ropey Convex bead

    Eliminate Excessive Spatter

  • *AWS Classification of GMAW Electrodes

  • *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 GAWS Classification of GMAW Electrodes

    *SECTION OVERVIEW:These slides are meant to lead into the discussion on the components involved with GMAW welding.

    TEACHER NOTES:Slides 8-16: When using these slides, discussion could include:With semi-automatic MIG welding, the electrode wire is fed through a welding gun controlled by the operator. The operator starts the arc and controls the puddle. In automatic MIG welding, a robot or automated machine makes the weld. An arc digs into the base metal much like water from a nozzle on a garden hose digs into the earth. (The flow of the water is like welding current and water pressure is similar to voltage)Molten metal forms a molten pool or crater and tends to flow away from the arc while cooling and solidifying. A continuous even flow of shielding gas is needed to protect the molten weld metal from atmospheric contaminants such as oxygen and nitrogen. The shielding gas comes from a gas cylinder and flows through the gun and cable assembly, through the gas nozzle, and into the welding zone.

    *********SECTION OVERVIEW:The next slide explains about troubleshooting welds.TEACHER NOTES:Slide 32-33: Corrective actions for common GMAW problems:Porosity Check for proper gas flow/ block any winds or draftsClean joints from moisture, paint, etc.Check for proper WFS and Voltage settingsDecrease CTWD, drag angle, and travel speedRopey and Convex Check or reset WFS & Volts (increase voltage first)Decrease CTWD, travel speed, and drag angle (push angle)Excessive Spatter Check and reset WFS and VoltsIncrease drag angleDecrease CTWD and travel speedEliminate Stubbing Check or rest WFS & Volts (increase voltage first)Decrease CTWDIncrease drag angle**SECTION OVERVIEW:This section is meant to lead into a discussion about the AWS Classification of GMAW Electrodes

    TEACHER NOTES: Slides 37-38

    For more information on the AWS classification of GMAW electrodes see Lincoln Electrics free GMAW Welding Guide - http://content.lincolnelectric.com/pdfs/products/literature/c4200.pdf*