mig welding arc welding as used in this unit refers to shielded metal arc welding(smaw) an electric...

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MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature of the electric arc is about 9, 000 degrees F

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Page 1: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

MIG WELDINGArc welding as used in this unit refers to shielded metal arc welding(SMAW)

An electric welder and flux covered electrodes are used

Temperature of the electric arc is about 9, 000 degrees F

Page 2: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Welding area should be equipped with metal benches

These serve both for fire protection and to electrically ground the work

Fire extinguishers suitable for class A, B and C fires should be available

Safety equipment and a first-aid kit should be within easy reach at all times

Wool fire blanket in another piece of fire control equipment

Page 3: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Water spilled on the floor of the work area must be removed seeing that it will create an electric shock hazard

All grease, oil, paper, rags and other flammable materials must be removed from areas where welding is completed

The number 10 shade lens must always be worn when welding, however is too dark to see through except when the arc is burning

Page 4: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Wear safety glasses under helmetAll skin areas must be covered“Sun-burning” will occur from the rays of

the arcThe method described is called the

“scratch method” of striking an arcA bead is called a “stringer bead” if it is

made without weavingWeaving means moving the electrode

back and forth sideways to create a bead that is wider than normal

Page 5: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Beginners should lean the electrode slightly in the direction of travel

A 75 to 80 degree angle should be usedThe arc length should sound like bacon

fryingThe best method to control movement is

to watch the welded metal solidify behind the puddle

When the speed is correct, evenly spaced semicircles form

Page 6: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

The first pass is called a “root pass”The “root pass” is the most important

weld in the processWelds made by moving horizontally

across a vertical piece of metal is called “horizontal welding”

Low amperage results in narrow, stringy beads

Other symptoms are:-electrode covering turns brown-the bead does not have clear marks

Page 7: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

-the puddle burns through the plate-the arc is noisy

Welding Joints:When welding one bead or a layer of

beads this process is called a “pass”Welds made by moving downward

across a vertical piece of metal are called “vertical down” welds

Welds made by moving upward across metal are called “vertical up”

Page 8: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Metal Inert Gas (MIG) welding became popular when manufacturers began using thin-gauge, high strength, low alloy steels

In addition, it is possible to weld aluminum castings with MIG

The MIG welding method uses a welding wire that is fed automatically at a constant speed as an electrode

Page 9: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Since the wire is fed automatically at a constant rate, this method is also called semi-automatic arc welding

When the heat is sufficient to cause the metal to melt, the process is called “spot welding”

The device used to spot weld is called a “spot welder”

During the welding process, either inert or active gas shields the weld from the atmosphere and prevents oxidation of the base metal

Page 10: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

For most steel welds, carbon dioxide (CO2) is used

With aluminum, either pure argon or a mixture of argon and helium is used

It is also possible to weld stainless steelMIG welding is sometimes called carbon

dioxide arc weldingThe term MIG is used to describe all gas

metal arc welding processes

Page 11: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

In fact, many welders in the industry can use CO2 (active gas) or argon (inert gas) by simply changing the gas cylinder and the regulator

MIG welding uses the short circuit arc method which is a unique method of depositing molten drops of metal onto the base metal

The short circuit arc method used very thin welding rods, low current and low voltage

Page 12: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Heating and cooling occurs on a average of 100 times a second

The nozzle works as a constricting force in the direction of the center of the cylinder

This action is known as the “pinch effect” and the size of the force is called the “pinch force”

Before starting to weld, the operator sets:

- wire speed

Page 13: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

- arc voltage- gas flow rate- then presses the power button

The wire is positive and the workplace is negative

Weld penetration is greatest using this connection

Weld penetration is also greatest using CO2 gas, however CO2 provides a harsher more unstable arc

Page 14: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

In MIG welding, the polarity of the power source is important in determining the penetration to the work piece

Direct Current (DC) power sources used for MIG welding typically use DC reverse polarity which leads to increased spatter

It is preferable to use argon/CO2

PLASMA ARC CUTTING

Page 15: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Plasma- fluid portion of blood found in region of electrical charge-discharge (arc)

Ionized Gas- plasma created by an arcBoth electrons and positive ions whose charges are nearly equal

to each otherPlasma results when a gas is heated to a

high enough temperature to convert into positive and negative ions-11, 000 to 23,000 degrees F

Page 16: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Arc Plasma- defined as a gas that has been heated to at least a partially ionized condition

Plasma arc- used to refer to the arc plasma used in welding

and cutting processes

* Produces both high temperature and intense light

* Arc welding like cutting

Page 17: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Plasma torch- creation & control of the plasma for welding or

cuttingTorch body- special plastic-resistant to

high temperatures-ultraviolet light and impact

*available in variety of lengths and sizes

Generally the longer, larger torches are used for the higher capacity machines

Page 18: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Body is called a “barrel”Torch Head- angles 75-90-180

cooling for low power torches may either be by air or water

Power Switch- variety of optionsElectrode Setback- spacing between

electrode tip and nozzle tip critical for proper operation

Nozzle tip- small, cone shaped, constricting orifice in the center

Page 19: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Space between the electrode tip and nozzle tip is where the electric current forms the plasma

Nozzle- referred to as the “cup”* made of ceramic* high temperature resistant substance

Common Torch Parts:-electric tip -nozzle insulator-nozzle tip -nozzle guide-nozzle

Page 20: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

The torch parts are made of copperElectrode tip- made of copper with

tungsten tip-keeping tip cools, lengthens the life of the tip and allows better quality cuts for longer period of time

Nozzle insulator- between electrode tip and nozzle tip

Gas Hose- 2 types of hoses-1 hose carries gas used to produce plasma and one produces a shielding gas coverage

Page 21: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Central wire- 2 conductors-low voltage stranded copper wire connects power switch to power supply

Water tubing- medium/high amperage torches may use water-failure to use de-ionized water will result in the torch arching out internally

Water Shroud- water surrounding the tip is used to control the hazards of light, fumes and noise

Page 22: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Power and Gas cables- power cable-high voltage rated insulation made of finely stranded copper wire to allow for maximum flexibilityPower Conductors- positive & negative-size and current carrying capacity of this cable is a controlling factor to the power range of the torch

Voltage- production of plasma requires a drooping arc voltage or constant current

Page 23: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

direct current high voltage power supply-this allows for a rapid start of the plasma arc at the high open voltage

Amperage- flow is much lower than with most welding processes-PAC torches operate on 10 amps-the higher the amperage capacity the faster & thicker they will cut

Stack Cutting- sheets of steel

Page 24: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Dross- metal compound that re-solidifies & attaches itself to the bottom of a cut-made up of un-oxidized metal

Water table- used to reduce the noise level, control the light, trap sparks and eliminate fumes

Plasma arc gouging- similar to air carbon arc gouging

Safety Hazards: light-fumes-sparks-electrical shock-moisture-noise

Page 25: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Heat Input- Jouls-per inch of heat the cut will receive-work per linear foot

Distortion- metal is heated and moves (bends) up towards the heat, while the metal is cooled moves

( bends) away from the heated areaHeat Affected Zone- area heated for

workPAC- Plasma Arc CuttingCutting Speed- high-25 feet per

minute-1/4 mile per hour

Page 26: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Standoff distance- distance from the nozzle tip to the work-distance is crucial for quality cuts

Starting Methods- most common type is high frequency, alternating current

Pilot air- arc between the electrode tip & the nozzle tip within the torch head

Kerf- space left in the metal as the metal is removed during a cut

Page 27: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

Factors for Success:-standoff distance -gas used-orifice diameter -travel speed-power setting -water injection-swirling of gas -electrode tip

Factors that affect the cut by changing the gas:

-force -heat content-central concentration

Page 28: MIG WELDING Arc welding as used in this unit refers to shielded metal arc welding(SMAW) An electric welder and flux covered electrodes are used Temperature

-kerf width -dross formation-top edge rounding -metal type

HAPPY WELDING & CUTTING