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

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

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

Wear safety glasses under helmet All skin areas must be covered “Sun-burning” will occur from the rays of the arc The method described is called the “scratch method” of striking an arc A bead is called a “stringer bead” if it is made without weaving Weaving means moving the electrode back and forth sideways to create a bead that is wider than normal

Beginners should lean the electrode slightly in the direction of travel A 75 to 80 degree angle should be used The arc length should sound like bacon frying The best method to control movement is to watch the welded metal solidify behind the puddle When the speed is correct, evenly spaced semicircles form

The first pass is called a “root pass” The “root pass” is the most important weld in the process Welds 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

-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”

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

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

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 steel MIG welding is sometimes called carbon dioxide arc welding The term MIG is used to describe all gas metal arc welding processes

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

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

- 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

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

Plasma- fluid portion of blood found in region of electrical charge- discharge (arc) Ionized Gas- plasma created by an arc Both electrons and positive ions whose charges are nearly equal to each other Plasma 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

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

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

Body is called a “barrel” Torch Head- angles cooling for low power torches may either be by air or water Power Switch- variety of options Electrode Setback- spacing between electrode tip and nozzle tip critical for proper operation Nozzle tip- small, cone shaped, constricting orifice in the center

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

The torch parts are made of copper Electrode 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

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

Power and Gas cables- power cable- high voltage rated insulation made of finely stranded copper wire to allow for maximum flexibility Power 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

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

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

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 area Heat Affected Zone- area heated for work PAC- Plasma Arc Cutting Cutting Speed- high-25 feet per minute-1/4 mile per hour

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

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

-kerf width-dross formation -top edge rounding-metal type HAPPY WELDING & CUTTING