manufacturing processes lab 1 (met 1321) prof s. nasseri manufacturing processes lab i met 1321...

Manufacturing Processes Lab 1 (MET 1321)Prof S. Nasseri

Manufacturing Processes Lab I

MET 1321Metal Inert Gas Welding (MIG)

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Welding Processes

ARC Welding(AW)

1. Shielded Metal Arc Welding (Stick welding)2. Gas Metal Arc Welding (MIG)3. Gas Tungsten Arc Welding (TIG)4. Flux Cored Arc Welding5. Submerged Arc Welding6. Plasma Arc Welding

Oxyfuel WeldingOFW Oxyacetylene Welding (OAW)

Resistance WeldingRW



MIG is an arc welding process that uses an arc between a continuous wire electrode and the weld pool. Wire is continuously fed from a spool.

MIG welding is a commonly used high deposition rate welding process. MIG welding is therefore referred to as a semi-automatic welding process.

Gas Metal Arc Welding (GMAW) orMetal Inert Gas (MIG) Welding

Metal Active Gas (MAG) Welding



Shielding gases

The shielding gas completely covers and protects the weld pool.

Argon (or mixture of Argon and Oxygen) is used as a shielding gas for nonferrous metals such as aluminum, and

Carbon dioxide (or carbon dioxide mixtures with argon) are used as a shielding gas for steels.



AdvantagesThe MIG welding process provides many advantages in manual

and automatic metal joining for both low and high production applications. Its combined advantages when compared to covered (stick) electrode, submerged arc, and TIG are:

1) Welding can be done in all positions. 2) No slag removal required. 3) High weld metal deposition rate. 4) Overall times for weld completion about 1/2 that of covered

electrode. 5) High welding speeds. Less distortion of the workpiece. 6) High weld quality. 7) Large gaps filled or bridged easily, making certain kinds of

repair welding more efficient. 8) No stub loss as with covered electrode.



GMAW or MIG equipmentsMIG equipment consists of a welding gun, wire

feeder, and shielding gas.

A constant voltage, direct current (DC) power source is most commonly used with GMAW.



MIG torch nozzle GMAW torch nozzle cutaway image. (1) Torch handle, (2) Molded dielectric (shown in white) and threaded

metal nut insert (yellow), (3) Shielding gas nozzle, (4) Contact tip, (5) Nozzle output face



MIG wireWires are made of mild steel, Aluminum, Stainless Steel, Copper

and Copper-based Alloy. The size is between 0.02 to 0.125 inches.

Welding wire designations are based on AWS classifications:

For Mild steel:

ER – 60 S -1

Stainless steel wire

Electrode

RodTensile strength in psi/1000

Solid bare wire

Chemical composition of the wire



MIG welding• Direct Current (DC) is only used.

• AC should not be used, since the burn-offs are unequal on each half-cycle.

• The consumable wire electrode diameter is between .02 to .125 inches.

• Amperage between 60 to 250 A.

– This is determined by trial and error.

– Set the wire feed speed according to the current chosen.

• Voltage is between 16-40 V (the voltage controls the arc length).

• Gas flow rate is approximately 20 cfh (cubic feet per hour) to 35 cfh.

• Wattage is between 1 to 20 kW.



DCEP or DCEN?!Direct Current Electrode Positive (DCEP) provides

deep penetration and excellent cleaning action.

Direct Current Electrode Negative (DCEN) should not be used, because

• Weld penetration is shallow and wide,• Metal transfer is erratic,• There is excessive spatter, and• No surface cleaning occurs.

More heat in electrode

More heat in the workpiece



Metal transfer modes

Metal transfer modes in GMAW are – short circuiting transfer, spray transfer, pulsed

spray transfer, and globular transfer.

The type of metal transfer that occurs depends on welding wire size, shielding gas, arc voltage and welding current.

As current increases, the transfer mode changes from short circuiting to globular and then (with 80% argon) to spray.



Stickout

Stickout is the distance the welding wire projects from the end of the nozzle of the welding gun.

The proper nozzle-to-work distance must be maintained to ensure adequate shielding gas coverage.



Stickout

short circuiting transfer

Or Dip (short arc) transferArc voltage: 15 - 22VCurrent: below 200AMetals: steel and steel alloysConnection: DC electrode positiveContact tube: 5 mm in front of nozzle tip

Spray transferArc voltage: 27 - 54VCurrent: higher than 200AMetals: aluminum (other metals in flat position)Connection: DC electrode positiveContact tube: 5 mm inside nozzle tip



Stickout

Stickout can be adjusted to alter the current and voltage conducted to the arc.

A shorter stickout creates a hotter arc, A longer stickout reduces penetration on thin metal

(suitable for thin metals).



How to weld

Welding parameters are set based on the thickness of the metal used.

Steel backing bars are required for welding copper 1/8 inches thick or less.

Preheating copper at 400F (204 C) is advisable on sections 3/8 inches thick or more.



How to weldEnsure that the contact tube and gas nozzle

orifices are clean to prevent clogging, which restricts wire feed and shielding gas flow.

Set the voltage, wire feed and shielding gas flow to the standard conditions for the required type of welding.

Adjust the welding wire to the proper stickout.



How to weldStart the arc and move the welding gun at a uniform speed,

maintaining the proper work angle ( 25˚ travel angle and 90˚ working angle).

Move the welding gun along the joint using the pushing or pulling techniques.

25

90



How to weldA slight weaving motion is helpful to ensure penetration.

Do not remove the welding gun from the weld area until the weld pool has solidified. The shielding gas prevents cracks from developing in the molten weld pool.

Cold lap occurs if the arc does not melt the base metal sufficiently.

Check the weld for surface porosity, which is usually caused by improper gas shielding.



How to weld

Shut down the machine when welding is completed– turn off wire speed control,– Shut off shielding gas flow at cylinders,– Squeeze welding gun trigger to bleed the lines,– Shut off welding machine,– Hang up welding gas.



Flux cored arc weldingA related process, flux cored arc welding, often does not

utilize a shielding gas, instead employing a hollow electrode wire that is filled with flux on the inside.



Both DCEN and DCEP in MIG welding, provide good quality weld. TrueFalse

Test yourself!

Argon is used as a shielding gas for Aluminum and carbon monoxide is used for steels.

TrueFalse

Carbon dioxide



Test yourself!Which one is spray transfer and which is short circuiting transfer?

spray transfer short circuiting transfer



Test yourselfCracks in MIG welding happen, because:

1- the welding wire is not adjusted to the proper stickout.

2- the welding gun is removed from the weld area before the weld pool has solidified.

3- the arc does not melt the base metal sufficiently.

Cold lap


manufacturing processes lab 1 (met 1321) prof s. nasseri manufacturing processes lab i met 1321...

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