GMAW or MIG GAS METAL ARC WELDING or METAL INERT GAS GMAW

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GMAW or MIG

• GAS METAL ARC WELDING or METAL INERT GAS

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GMAW DEFINED

• GMAW (also referred to as Metallic Inert Gas
  MIG). A continuous consumable wire fed
  automatically which may or may not be covered by
  an inert shielding gas. Deep penetration is
  provided by the use of DCRP for most solid wires
  and the concentration of heat in a small weld
  zone.

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Types of Metal Transfer

• Short circuiting/ Short Arc/ Dip Transfer. The
  arc is short circuited 20 to 200 times per
  second. Average of 100 for light welding. The
  electrode (wire) touches the weld puddle creating
  a short circuit causing the wire to heat and melt
  off. This happens with solid wire only.

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Types of Metal Transfer (cont.)

• Spray Arc-Usually done on thicker metal using
  larger diameter wires and higher amperage (over
  200 amps). A shielding gas mixture of argon with
  1 to 5 oxygen is desireable. Out of position
  welding is not recommended. Used with solid wire
  welding.

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Types of Metal Transfer (cont.)

• Globular transfer- similar to the short arc
  process but higher amperages are required and out
  of position welding is not possible. Used on
  heavier metals where large deposits are required.

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Shielding Gases

• There are six true inert gasses. These are
  gasses that will not break down during the
  welding process nor will they chemically react
  with the molten metal.
• Test Question

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Six inert gasses

• Argon, Helium, Krypton, Neon, Xenon and Radon are
  the true inert gases. The last four are rarely
  used due to cost and availability. Carbon
  dioxide is inert at room temperature but changes
  during the welding process. It then goes back to
  its original state once it starts to leave the
  weld zone. It does an adaquate job on mild
  steel.
• Test Question

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Puposes of shielding gases

• To displace atmospheric gases such as oxygen,
  hydrogen and nitrogen.
• Oxygen produces undesirable oxides which leads
  to porosity.
• Nitrogen produces nitrides which cause low
  ductility and fractures.
• Hydrogen causes internal pressures and stress
  risers also known as under bead cracking.
• Test question

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Puposes of shielding gases

• To help form the weld allowing for out of
  position welding.
• This is much like the shielding process in arc
  welding. The gasses will help the weld to form
  correctly and to be free of slag.
• Test question

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Shielding gases and their uses.

• Argon Aluminum and magnesium
• Argon/Helium Heavy section of Aluminum
• Argon/ CO2 Mild and stainless steel
• Helium/Argon/CO2 Mild and stainless
• CO2 Mild steel
• Argon/Oxygen Mild steel, stainless and alloy
  steels

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Advantages of the GMAW process

• Shorter training time. Easier to learn than most
  welding processes.
• Saving of welding time. No stopping and starting
  as in SMAW.
• Narrower heat affected zone. Less warpage in
  light gage metal.
• No slag and a minimum of splatter.
• Test Question

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Advantages of the GMAW process (cont.)

• High deposition rate. 95 of the wire is used in
  the process.
• Fewer impurities in the weld.
• Weld a wide range of metal thicknesss with one
  diameter wire.
• Excellent for bridging gaps and misaligned fit
  ups.
• Test question

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Disadvantages of the GMAW process.

• Metal must be clean to weld on. Solid wire
  welding provides very little cleaning. Flux
  cored wire offers some but not a lot.
• Prone to wind drafts. Winds may blow the
  shielding gas out of the zone.
• Test question

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Problems /Concerns with GMAW

• Porosity An inadaquate gas coverage will cause
  holes in the weld.
• Cold lapping No fussion on edges (toe) of weld.
  Caused by wrong set up.
• Birdnesting When the tension for the feed
  roller is too tight and wire continues to feed
  internally when the contact tube is closed off.
• Bridging When splatter bridges between the
  contact tube and the nozzle.
• Test Question

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GMAW welding wires

• Solid wire comes 0.23 to5/32 in diameter.
  ER70S (1-6). The higher the last number the more
  silica in it.
• Flux cored can used with Dual Shield Welding or
  without gas. Wite is very expensive and the slag
  must be cleaned off before welding over it.
• The wire you use will depend on the metal
  thickness, position, joint design and
  specifications for the job.

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SAFETY

• Use fully protective clothing helmet, jacket and
  gloves.
• Weld in a shielded area to prevent Flashes to
  others.
• Always say cover before starting to weld.
• Provide for proper ventilation. Don not stand
  over the flume (exhaust).

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SAFETY (cont.)

• Use a 10-12 gold lense to protect your eyes.
• Do not get your gloves wet as you will not be
  insulted from shock.
• Do not walk on any welding leads, especially the
  GMAW lead.
• Do not weld on any metal that is coated
  (galvanized, zinc, paints, etc.

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Setting up the GMAW equipment.

• Visual check of all equipment. Look for damage
  to the regulator, leads, contact tube, nozzle,
  etc.
• Open the cylinders all the way SLOWLY as inert
  cylinders are high pressure just like the Oxygen
  cylinders.

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Set up cont.

• Set the regulator to 18 to 25 cfh. Argon
  requires less pressure because of its wieght.
  Make sure wire feed roller is disengaged as to
  not waste welding wire.
• Use the chart provided to set the WFS and the
  voltage. If one is not provided, you will have
  to set up the welder using the trial and error
  method.

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Set up cont.

• Make sure metal is clean from oils and mill scale
  and work area is free from combustibles.
• You should not exceed 19 volts for the work we do
  in the learning process. Spray arc uses 21 volts
  or more.
• Should sound smooth and consistent. No popping
  or snapping. Sound is a key factor in setting up
  the GMAW equipment.
• Keep the contact tube and nozzle clean and free
  from splatter. Use dip gel while the contact
  tube are hot.

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Steps to shut down

• Turn off the gas source.
• Release the wire feed roller.
• Pull the trigger and relieve the regulator.
• Undial the regulator.
• Clean up the area, roll up leads (in big loops)
  cool all metal

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Setting the WFS and voltage

• The wire feed speed also controls the amperage.
  When determining the WFS and voltage, only change
  one parameter at a time. Example
• Set the voltage low (14-15) and turn the WFS
  down. As you weld, you or someone else can
  adjust the WFS up until is sound smooth and
  consistent. Look at the weld, if it is too tall
  and lacks penetration then turn the voltage up
  one volt and turn the WFS down.

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Setting the WFS and voltage cont.

• Start welding and turn up the WFS until it sounds
  as it should. Repeat this process until you have
  the desired weld qualities ( slightly convex with
  excellent tie-in on the toe of the weld.
  Experience will help to determine setting and how
  to indentify quality welds.

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