Welding C

Obj 5 - identify welding equipment

• Amperage: used as the heat setting. Causes parent metal to melt.

  • increases metal deposition rate

  • Increases penetration

• Arc: voltage overcomes air gap resistance to conduct electricity

• Arc Blow:

  • condition encountered during DC welding. Not encountered during AC. Magnetic fields develop around the work/

  • Uncontrolled arc from side to side

  • Due to electric current in same direction for prolonged period.

  • Prevent by: change ground clamp location, adjust electrode angle, weld towards a heavy existing weld, lower current setting.

• Core - magnetic link between primary and secondary coils in welding transformer. Known as a moveable shunt can be moved to control amperage. It alters the link between transformer’s primary and secondary by coil.

• Constant Current- welding machine used for shielded metal arc welding. (SMAW). And gas tungsten arc welding (GMAW). Relatively high open cct voltage to establish weld arc. Steep voltage curve.

• Constant Voltage- aka constant potential- used for wire process welding. Stable voltage but amperage changes. Almost flat volt-amp curve.

• Cycle- complete rotation of sine wave. A 60 cycle AC changes direction at 120 times per second.

• Duty Cycle- NEMA (National Electric Manufacturer’s Association) rates welding machines. Based on max output of machine over a 10 minute period. Expressed as % of the 10 minutes that you can run at max output before needing to allow it to cool down.

  • ex: 300A, 60% duty cycle means you can run at 300A for 6 minutes out of 10. Or you can run at 60% of 300A for the full 10 minutes!

• Electron- negative charge, attracted to positive charge. Moves from negative to positive (current travels in the opposite direction of electron)

  • GTAW uses high frequency

• Inductance: conductor ability to transfer current into neighboring body without physical contact.

• Inverter : AC to DC, converter or Rectifier: DC to AC

• Magnetic field: created when current is forced to flow through a coil that is wrapped around iron core.

• Open circuit voltage: when welding machine is turned on for the first time, and no current flowing, you have open circuit voltage.

• Resistance: property of electrical conductor to oppose current flow- causes energy to turn into heat. The electrode work gap offers resistance to current flow which creates the heat needed for welding.

• Reverse polarity: DC welding circuit only.

  • electrode cable connected to positive terminal on welder.

  • deeper penetration

  • Slower rod melting

  • Narrower metal flow

  • 2/3 of arc associates with base metal (negative terminal)

  • You can test polarity by using any rod that has a 0 as its last digit, the arc is quiet sounds like bacon sizzling, minimal spatter, deep penetration.

• Straight Polarity: DC welding circuit only.

  • Electrode cable connected to negative terminal of welding machine.

  • electrode melts faster

  • 2/3 arc energy associates with electrode

  • Shallow penetration

  • Wider metal flow

  • Test polarity using any rod ending in 0 as its last digit, arc is loud hissing sound, produced more spatter, emits smoke fumes from arc.

• Voltage often called EMF (electromagnetic force).

  • responsible for:

    • Creating the arc: Arc starts at higher open circuit voltage around 50-100V. Once established, the voltage drops to arc voltage.

    • Maintaining the arc: During SMAW it drops to 17-40V.

    • Puddle fluidity/Flow: arc voltage directly affects width of weld bead and wetness of the puddle. More arc voltage is more puddle width and fluidity.

• Volt/amp curve (output slope):

  • Graphical illustration indicating output of welding machine

  • steep/drooping volt/amp (constant current): SMAW or GTAW

  • Flat volt/amp (constant voltage): wire feeding processes.

  • Open circuit voltage usually plotted where graph meets vertical axis.

• Welder Types:

  • AC Transformer

    • converts high voltage low current into low voltage high current for welding. Using more wraps on primary and fewer wraps on secondary coil. Via laminated steel core (induction)

    • Adv:

      • low cost, maintenance, operating

      • Quiet

      • No arc blow

    • Disadv:

      • not portable

      • AC output only

      • Limited selection of electrodes

      • SMAW only

  • AC-DC Transformer Rectifier:

    • AC machine with added diode rectifier to convert to DC.

    • Silicon diodes mounted on heat sinks (made of copper or aluminum plates)

    • Adv:

      • AC and DC output

      • Full electrode selection

      • Choice of polarity

      • Few moving parts

      • CC or CV machines (can use CC with voltage sensing feeder for GMAW)

    • Disadv:

      • more costly

      • Arc blow if using DC

      • Not portable

      • Need clean, cool environment

  • AC Alternator:

    • useful for remote locations, essentially a small engine driven device that is fuel powered (generator)

    • Adv:

      • Portable

      • High Duty Cycle compared to transformer

      • No arc blow

      • Can also run power tools

    • Disadv:

      • high cost, operating, maintenance

      • Noise

      • Limited electrode selection

  • DC Generator

    • Generator vs Alternator: Generators convert mechanical energy into electrical energy, while alternators produce alternating current and are typically more efficient at higher speeds.

      • Both use the principle where a current is produced when moved through a magnetic field. One component is stationary and one is rotating. Doesn’t matter which is stationary and which is rotating. (Conductor and Magnet).

  • DC Output Alternator

    • Many engine driven welding power sources use the alternator design.

    • AC output is rectified to DC.

    • Adv:

      • Major - capability of producing AC and DC output at high duty cycle rating

      • Choice of polarity

      • Smoother arc than AC

      • Portable

      • Full choice of electrodes

      • Can also run power tools

    • Disadv:

      • High cost, maintenance, operating

      • Noisier

      • Arc blow if using DC

  • Inverter

    • electronic circuit that can convert DC into AC. Output voltage and frequency can be adjusted sometimes.

    • Adv:

      • Excellent arc starting characteristics

      • Excellent output current control

      • Pulse current capability

      • May be CC or CV

      • small and lightweight

    • Disadv:

      • AC is noisy

      • needs clean environment

      • high cost

      • Arc blow with DC

      • electronics (fragile)

      • expensive repairs

• Welding Cables:

  • 8 sizes standardized.

    • #4, #3, #2, #1, 1/0, 2/0, 3/0, 4/0.

    • #4 is smallest, 4/0 is largest.

    • Cable size needed is determined by amperage and the length of distance from the welding machine. Longer distances and higher amperages require a bigger cable to be used.

    • You should connect a whip (small cable) at the electrode section, it is meant to make welding more comfortable as a very thick cable can be awkward to weld with. If overheating, upsize the whip.

• Cable Connectors:

  • Sized by amperage ratings.

  • Quick connect type using male and female ends twist together and lock. Usually brass or copper

  • Lugs attach to machines, work clamps, tables. They are not insulated in order to make good electrical contact.

  • Ensure connector or lug sizing is correct for application or else it will overheat!

• Electrode Holders (stingers):

  • 2 Types:

    • Alligator Jaw: clamps bare end of electrode in spring loaded jaw

    • Twist Head: bare end of electrode inserted into head, mechanical pressure tightens it into place as the head is twisted.

  • Electrode current capacity must match the amps used and welding cable amp capacity.

  • Holder is insulated to prevent stray arcs and for safety.

• Work Lead Clamps (ground clamp)

  • Must have clean connection.

  • Types:

    • C Clamp: allows for secure connection on thick or bulky workpieces.

    • Spring Loaded Clamp: Easy change of location if needed, most common on general SMAW.

    • Magnetic Clamp: quick, secure attachment. Cannot use on non magnetic material like aluminum.

  • Poor connections can cause accidental arcing, (hard and brittle spots forming on workpiece)

  • Never place ground where it may pass through a part not designed for current flow.

  • A poor work lead connection creates resistance to current flow which generates heat, you may see unstable arcs or overheating of welding cables.

• Electrode Types

  • 2 Categories:

    • Non Consumable:

      • Not to be consumed into weld puddle.

      • Ex: in GTAW (Gas Tungsten Arc Weld), the tungsten electrode only does the arc. If you are using a filler metal, it must be fed externally.

    • Consumable:

      • electrode is melted into weld puddle. Therefore, the electrode is also the filler metal.

      • Ex: in SMAW (shielded metal arc welding), you use these.

    • AWS (American Welding Society) and CSA (Canadian Standards Association) developed specs for carbon steel filler metals when using SMAW. This module is focused on carbon steel electrodes (aka mild steel).

  • Coated Electrodes:

    • diameter of electrode is determined via the core wire diameter. thickness and composition of outer flux coating varies.

    • Electrode also called a rod, it is a metal wire covered with materials called “flux coating”.

      • Flux ingredients are what differentiate operating characteristics for the weld deposit. This allows the weld to equal or exceed the parent material properties.

    • SMAW Process: electrode consumed during the welding operation contributes to the weld pool, providing both filler material and a protective atmosphere to minimize oxidation and contamination.

  • AWS Classification System for mild steel:

    • E6027 as an example.

      • E stands for Electrode.

      • First 2 digits (60) are minimum welded tensile strength of the weld material in PSI x 1000. This would be 60,000 psi. This may be 3 digits sometimes if the tensile strength needed is very high!

      • Third digit (2) indicates the satisfactory welding position applicable. This would be only Flat and Horizontal positions. This is the same as CSA standard.

        • 1- All positions

        • 2- Flat and Horizontal Fillets

        • 3- Flat only

        • 4- Flat, Overhead, Horizontal, Vertical Down

      • Fourth Digit (7) indicates the the type of flux coating and recommended type of current. This would be Iron Oxide, with AC or DC in either polarity. This is the same as CSA standard.

      • Recommended to read digits from back to front as the tensile strength rating may be in 3 digits sometimes!

  • CSA Classification system for mild steel:

    • Standardized with AWS, meaning their code system is the exact same. The only difference is the units of the tensile strength rating.

    • AWS uses PSI, but the CSA system denotes in MPa (Mega Pascals).

    • The first 2 digits for the tensile strength rating would be Megapascals / 10.

  • The last digit in both classification systems gives additional info about the electrode. Most common ones are

    • #0 =

      • Iron powder 0 - 10%

      • Deep Penetration

      • Easy to remove, thin slag

      • Bead appears flat with coarse ripples

      • Dynamic loads, fast freeze

    • #8 =

      • Iron powder 30 - 50%

      • Medium Penetration

      • Easy to remove, heavy slag

      • Bead appears smooth, concave, fine ripples.

      • Dynamic loads, low hydrogen weld desposits

• Core Wire

  • Mostly carbon steel, but can be alloyed with other elements in order to change core wire’s properties.

  • Common electrodes 43XX (60XX if AWS), and 49XX(70XX if AWS) series, core wire is from same wire stock - SAE 1010 carbon steel with carbon content of 0.05% to 0.15%.

• Electrode Coating

  • Oxides are low in tensile strength and ductility and reduce the base metal’s property. They are undesireable.

    • To prevent these from forming, the electrode provides and “automatic cleansing and deoxidizing” action. As the coating burns, it forms a gaseous atmosphere that surrounds and protects the molten end of the electrode and weld pool. Other ingredients from the coating form a slag to cover the deposited weld metal.

    • Other important functions:

      • improves weld appearance

      • easier arc striking

      • helps maintain stable arc and penetration depth

      • insulator for core wire

      • affects arc length and amperage

      • influences puddle fluidity and controls welding position that can be used.

    • Materials:

      • Cellulose:

        • wood pulp product

        • forms CO2 and H2, protective gas over weld puddle

      • Rutile:

        • titanium dioxide and traces of iron

        • arc stabilizing and slag forming

      • Iron Oxide:

        • found in iron ore such as magnetite and hematite

        • slag forming

      • Iron Powder:

        • increase deposition rate to help increase weld speed by 50%.

      • Calcium Carbonate:

        • limestone

        • low hydrogen type - produces CO2 and protects metal, lowest hydrogen atmosphere in arc.

      • Potassium Silicate:

        • arc stabilizer and enhances binding of flux coating to core wire.

• Slag Functions

  • Flux coating melts and forms a slag that covers the deposited weld material.

    • isolates oxygen and nitrogen from the weld until it has cooled to the point that they do not contribute to the weld making it hard and brittle.

    • dissolves impurities in weld and floats them to surface

    • controls shape and smoothness of bead

    • slows down the rate of cooling - improves weld quality.

  • Avoid trapping slag by removing slag from each weld bead before depositing another pass. Use chipping hammer or wire brush.

  • Heavy coated electrodes produce a heavier slag.

• Electrode Packaging, Storage, Handling

  • Cracked coating of electrode can result in substandard weld deposit.

  • Hydrogen can dissolve into molten pool that enters the arc, this can crack the weld when the weld cools and solidifies.

  • Porosity -

    • small pit holes.

    • Indicates that gases are trapped in the weld.

    • Start Porosity - porosity is more prevalent at the start of a weld.

    • Can be caused by too fast welding speed or too large of welding arc - coating did not heat enough to drive off moisture and gas shield not fully effective.

  • Electrodes with low hydrogen deposits

    • Lime Coated

    • designed for welding medium carbon and high carbon steels that crack from hydrogen absorption.

    • use this to weld steel with unknown weld properties. Reduces hydrogen induced cracking.

    • Packaged airtight (hermetic seal), and needs to be in electrode holding oven (rod oven) immediately after opening. This ensures minimum moisture content is maintained.

    • Oven should be 30-140C (50-250F) above ambient.

    • Can be re-baked for 1-2hr at 260-427C(500-800F).

  • Cellulose coated electrodes such as E4310 does not need to be in an oven. - moisture should be around 3-7%.

• Arc Length on amperage and voltage

  • Arc Length - distance between core wire and surface of material. Should be equal to 1 diameter of the core wire.

    • Too short : short circuit to plate, voltage drops to 0 and electrode sticks to the material. Need minimum 17 volts to maintain a stable arc.

    • Too Long: Amperage drops since voltage is high, not enough penetration in weld. Flux coating not as effective since it’s not melting properly. Arc stops if way too long length since there won’t be enough voltage.

    • Controlling Arc Length:

      • Using shorter arc length is beneficial for root beads and fill passes for better penetration with narrower bead. Higher amperage and less voltage.

      • Using longer arc length is beneficial for multi pass welds as you will get a wider bead with less penetration. Higher voltage and less amperage.