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MIG Welding 101

What Can it Do?

Join two pieces of steel together!


Safety Considerations

  • Keep a fire extinguisher beside you

  • The biggest dangers come from our complacency and not being totally aware of what we are doing. Don't take shortcuts that compromise safety.

  • Point out the following safety equipment:

    • Fire extinguisher

      • At each doorway

    • Fire exits

    • First aid kits located at front desk

  • Metal Shop Safety Guidelines

    • Wear appropriate clothing:

      • Clothes should be made out of natural fibers such as cotton or wool. Do not wear synthetics as they melt to the skin

      • Full length pants which fit over your boots – to stop hot metal/sparks from getting into your footwear

      • Wear a long sleeved shirt and pants without cuffs and have your pant legs cover your shoes so sparks can't drop into your footwear

      • Wear leather boots, CSA approved boots are best, no sandals or open footwear (green shield)

      • Wear leather gloves (demonstrate different types of gloves)

      • Long hair, drawstrings and shirt tails/sleeves tucked in/ tied back,

      • Safety glasses at all times in shop, hearing protection recommended

      • Avoid wearing jewelry

    • Main causes of injury are:

      • Sharp metal edges

      • Sparks

      • Heat and flame

      • Arc Flash

      • Electric Shock

      • Welding Gases

      • Fumes

    • Metal safety:

      • Hold it like it's glass (sharp edges)

      • May be very hot, always check before you grab or wear gloves

    • Electricity:

      • Electric shock can occur when arc welding. This usually happens when the current passes from the electrode through the welder to the piece being welded and through contact with poorly maintained electrical cables

      • Don't set handle on table - hang from cart

      • Primary electric shock is much more hazardous because the voltage is much higher than the secondary or welding voltage.

      • AC is 2 to 3 times more dangerous than DC welding.

      • Inspect your equipment to make sure it has been properly maintained.

      • Wear proper PPE (personal protective equipment) to insulate yourself from electrical hazards, dry gloves and rubber soled boots.

      • NEVER touch ground & tip at the same time (ground is kept up at the front desk)

      • MIG (Metal Inert Gases) = cable is hooked up to (+) port on box

      • DCEP (Direct Current Electrode Positive) (electrode = welding gun)

      • Don't weld in damp conditions

    • Gas:

      • Never move without cap!

    • Fire Hazards:

      • No flammable items/substances in a welding area, e.g. no wood dust or stains, etc. (wood welding jigs are ok)

    • UV light:

      • Don't wear white (reflects under mask = neck burn)

      • Cover all skin (to prevent sunburns)

      • Always use red UV shield to protect others

      • Warn others before you start, e.g. "Arc up!"

      • Masks:

      • Auto-tint = when it sparks, vision darkens

      • Blocks UV light

      • "DIN" = can adjust auto-tint setting

      • 9 = brightest

      • 6 = plasma cutting

      • How to adjust knobs to head

    • Air extraction:

      • Can wear a mask, but welding mask may not fit over it

      • Open door, turn on overhead extraction

      • Aluminum is worst, steel not as bad

      • Rust & paint on metal pose dangers as fumes

      • Wear a mask if you grind off (dust)

    • Welding Fumes

      • When welding the melting metal oxidizes and produce gases such as carbon monoxide, carbon dioxide, oxides of nitrogen and ozone. We also use gases such as argon and carbon dioxide in the welding process to shield the weld and prevent oxidization.

      • Metals contain many alloys that can release contaminants into the atmosphere during the welding process.

      • A coating on metal which could emit harmful contaminants (such as lead, chromium, organic materials, or toxic combustion products) must be removed from the base metal, whenever practicable, before welding or cutting begins

    • Confined Spaces

      • Always test for oxygen levels before entering a confined space. Any reading lower than 19.5% (at sea level is said to be deficient). Use fans to ventilate the space or use a welding helmet with an air line bringing in an outside source of fresh air.

      • NOTE: Inert gases like argon are heavy and will displace oxygen in a confined space. If you see someone unconscious in a confined space DO NOT ENTER the space unless you a wearing a self contained breathing apparatus. In January 2003 four workers at Westminster Marine Services died. Three of them were would be rescuers.



Machine Setup


  • MIG (Metal Inert Gas) vs TIG (Tungsten Inert Gas)

    • (define, what they're used for, etc)

    • TIG stands for Tungsten Inert Gas and is technically called Gas Tungsten Arc Welding or GTAW. The process uses a non-consumable tungsten electrode that delivers the current to the welding arc. The tungsten and weld puddle are protected and cooled with an inert gas, typically argon.

    • Metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to melt and join.

  • Tank:

    • Don't open too fast

    • Watch gauges: flow (cfm) & pressure (psi)

      • 35 CFM

  • Machine:

    • Switch on back

    • Select settings:

      • Dial @ top

      • Guide inside box door - shows settings for different types of materials

    • Then use +/- to select material thickness

    • Spool inside machine (for steel/MIG)

    • We have a handheld spool gun for aluminum

    • Black knob = pressure; too much friction, wire won't push through

    • Pinch with fingers, guide roller under black knob should spin and spool still moves

  • Gun itself:

    • Nozzle comes off, spatter can be inside (which affects shielding gas) - can clean with MIG pliers

    • Contact tip (inside) - specific to wire size: 030 & 035 = standard wire sizes

  • Cable:

    • Both gun & gas run through

    • If it loops, do not pull on them - will kink wire

    • Expensive to replace

    • Treat carefully - don't step on it

  • Table setup:

    • Use magnetic squares to get 90-deg welds, etc.


Types of Welds


Welding Technique


    • Cleaner metal = better weld

      • Grinding taught in Metalshop 101

      • No sheet metal on bench grinder

      • Wire wheel/flap disc/grinding discs - clamp down!

    • MIG = adding material, needs somewhere to go

      • Grind 45-deg corner on each piece to make a valley

    • Start with wire out about 1/2"

    • Hold gun at 45-deg to the weld

    • Do a "tack weld” first

      • on both sides

      • so weld doesn't pull over

      • add one bead where you plan to end actual weld as well - cleaner ending

    • Then "stitch" back and forth between surfaces as you push/pull the puddle

    • Keep puddle the same size and moving

      • too slow = puddle may melt thru

      • too fast = only sits on top, like hot glue

      • want a consistent sizzling bacon sound - no popping or sputtering

    • Wire speed

      • this machine keeps it ok

      • assumes 2 metals are the same

      • whereas if two different gauge metals, wire could need adjusting

    • Close tank

    • Press trigger so gauges go back to zero

    • Turn flow handle so it's loose again (spins)

    • Turn off machine (switch at back of box)

Subpages (1): Welding Manuals
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