WELDINGWELDING

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What is MIG?What is MIG?

Metal Inert Gas (MIG) Metal Inert Gas (MIG) MIG is an arc welding process that uses a MIG is an arc welding process that uses a

continuous solid wire electrode for the filler continuous solid wire electrode for the filler metal and a shielding gas to protect the weld metal and a shielding gas to protect the weld zone.zone.

The molten puddle is shielded by an external The molten puddle is shielded by an external shielding gasshielding gas– ARGON/CO2 MIXARGON/CO2 MIX– CO2CO2

Welding SafetyWelding Safety

- Leather glovesLeather gloves

- SleevesSleeves

- Full face helmetFull face helmet

- Welding shade 9-14Welding shade 9-14

- Arc weld can be 8 Arc weld can be 8 times brighter than the times brighter than the sun! “ welders flash”sun! “ welders flash”

MIG welder setup

-The cart- secures all the components

-The tank- filled with an inert gas 2k to 3k psi

-The regulator- controls tank pressure 15 to 20psi

-The welder - converts AC voltage to DC voltage - controls the wire speed and heat

Welder schematic

RegulatorRegulator

-The regulator reduces tank pressure

-The gauge closest to the tank reads tank pressure

-The gauge closest to the hose outlet reads working pressure

-Working pressure should be 15 to 20 psi

-The adjuster screw should backed off when not in use

Ground clamp

-Supplies the welded metal a ground

-The surface must be clean and rust free

-Should be as close to the weld as possible

Welding gun

1. Gun housing

2. Electrical insulator

3. Positive electrode and gas discharge

4. Contact tube

5. Fill wire “electrode”

MIG gun and weld area

Welding process

MIG PROCESS

GUN MOVEMENTS

Kalpakjian

Welding Flaws

www.ndt-ed.org/EducationResources

www.mig-welding.co.uk

-Welding Flaws at the

Underside of the weld

-Incomplete Penetration

(not enough heat input)

Kalpakjian

Distortion from Welding Processes

• Non-uniform shrinkage of weld bead

• Difficult to maintain alignments

• Solution: Rigid fixtures, pre-compensate for warping, loose tolerances

Kalpakjian

Types of Joints

Weld bead profile: Convex or Concave?

• Solidification of molten bead leads to shrinkage

• Shrinkage of a concave bead leads to tension on surface tends to crack

• Shrinkage of a convex bead leads to compression on surface does not crack

• Generally, slightly convex beads are preferred.

Lincoln Electric

WELDING WITHOUT GAS

Wire WelderWire WelderMAKE SURE TO TURN ON FLOW GAGES!!MAKE SURE TO TURN ON FLOW GAGES!!

Millermatic 35Millermatic 35– Set heat 1—6 (Turn & Set heat 1—6 (Turn &

Pull)Pull)– Set wire speedSet wire speed

Usually around 50Usually around 50

– Adjust heat and speed as Adjust heat and speed as needed.needed.

Blue HobartBlue Hobart– Determine type of metal Determine type of metal

and positionand position– Lift cover and determine Lift cover and determine

welder preset selection welder preset selection for heat and speed.for heat and speed.

– Adjust machineAdjust machine– Fine adjustment wire Fine adjustment wire

speed and heat to speed and heat to individual needs.individual needs.

Wire Welder ProblemsWire Welder Problems

1. Make sure your turn on the flow gages.1. Make sure your turn on the flow gages.– Setting to around 25—30 Setting to around 25—30

2. Make sure your hoses are straight2. Make sure your hoses are straight 3. Popping Noise—Adjust wire speed down.3. Popping Noise—Adjust wire speed down. 4. Check wire tips4. Check wire tips 5. Dip wire tips into nozzle lubricant 5. Dip wire tips into nozzle lubricant 6. Make sure you have good penetration.6. Make sure you have good penetration. Internet Site: Internet Site:

http://www.lincolnelectric.com/knowledge/articles/chttp://www.lincolnelectric.com/knowledge/articles/content/gmaw.asp ontent/gmaw.asp