Welding Principles

Module 2: Terms of Welding

 Primary Power: Power supplied by the power company by a generator

o Common voltages: 120 (standard), 240 (industrial), 480 (Heavy Industrial),
575(Canadian, Heavy Industrial)
 VAC: Volts of alternating current
 Single Phase: Two fuses to complete a circuit
o 1 SIN Wave of AC Power
o Two electrically “hot” power lines connect to your welding power source and one green
ground wire connects to the earth.
 Three Phase: 3 fuses
o Supplies 3 electrically “hot” power lines to the welding power source and one ground
wire to the earth
o 3 SIN Wave of AC Power
o More electrically efficient
o More power over smaller wires; provides constant load voltage and current
o Delta or WYE Configuration
o Requires three measuring devices, one for each phase; Higher voltage is Primary Voltage
 Grounded Connection: electrical conductor connected directly to the earth; protects from shock
 Work Clamp: Completes the secondary welding circuit
 Primary Frequency
o Hertz: sin waves/second
o US Standard: 60 Hz; EU Standard: 50Hz
 Ways to link the Power Source and Primary Voltage
o Fixed Voltage: Manufactured to accept only ONE Primary Input Voltage
 Exception, not the rule
o Manual Linking: Place small brass jumpers into the appropriate configuration
 Manually configuring the machine
o Auto-Link: Circuits that automatically link the power source for the primary voltage
coming in from the wall.
 For customers who need to frequently move their welding power source but
don’t want to remove the cover and link it for different primary voltages
 Accepts 208, 230, 460V primary input voltage
 Single or Three Phase
 Change the plug to accommodate the new input voltage
o Auto-Line: Auto sets the welding power source to operate on any voltage within a range
 On any voltage between 120 and 460VAC
 Single or 3 Phase
 50 or 60Hz
o Fuses and Circuit Breakers: Over-current protection device. Limits amount of current
that can flow in a circuit
Welding Power Sources

 Arc Welding Power Sources: Classified in terms of their voltage and amperage output
characteristics.
o Can produce a constant current, a constant voltage, or both
 Welding Amp or Load Current is adjusted or set on Constant Current (CC) type of welding power
sources
o Constant Current is also referred as Drooper (due to its downward slope of the volt/amp
curve) or Variable Voltage
o CC machines are normally used for SMAW, GTAW, Air Carbon Cutting & Gouging, WAS,
FCAW, GMAW (Spray Transfer Mode)
o Avoid Using for FCAW & MIG processes in seismic applications
 Ohm’s Law
o Amperage is prest on the power supply
o Resistance is established by the cables and their connections, and by the arc length. Arc
Length gap can vary the resistance by being larger or smaller.
o Resistance levels are very low and do not vary much
 Constant Voltage Power Sources: Used for continuous electrode wire processes
o GMAW, FCAW, SAW, SMAW
o Provide a relatively flat volt-amp weld output characteristic. Load voltage at a set load
voltage is responsive to how quickly you feed the consumable electrode wire into the
arc.
o Current at the arc is approx. proportional to the wire feed speed for all wire diameters.
o Voltage is directionally proportional to arc length; voltage setting establishes the arc
length. Allows for wire feed speed to remain constant
o CV: Adjust Voltage, 14.0-38.0 V, visible decimal places
o CC: Adjust Amperage, 0-100 A, no decimal places
 Used only with a voltage sensing wire feeder to adjust the current
 CC GMAW arc can only deliver a spray or globular transfer
 Voltage and wire feed speed change constantly
 Using for GMAW may violate welding codes, NOT recommended
 Transformer-Rectifier (Conventional Welding Power Source): Welding Power Source converts
high-voltage, low-amperage primary input power to low-voltage, high amperage secondary
welding power.
o Primary Power > Step Down Transformer > Control Circuit > Rectifier (From AC to DC) >
Filter (smoother DC Current needed to weld) > Filtered DC Welding Output
o Single Phase
 Light Welding
 Under 200 amps needed
 115V AC or 230 V AC
o Three Phase
 Over 200 Amps needed
 Inverter: Converts high-voltage, low-amperage primary input power to low-voltage secondary
power
 o Use less energy, more efficient
o Less heat loss b/c it operates at a higher internal operating frequency
o Generates less heat in the physical components of a welding power source
o Allows high current levels to pass through smaller components
o Smaller, lighter
o Can quickly vary its output for processes
o Amperage adjustments in milliseconds, fine control
 Secondary Switching Power Source: Half Conventional, Half Inverter
o Primary AC Input Power is converted like a conventional power supply
 Passes through step down transformer > rectifier > filter
o Secondary Power is converted using the same types of components as in an inverter
 Power is sent through a switching device called an IGBT, this turns the DC power
ON and OFF at frequencies like an inverter.
 Controls output by varying the percentage of ON-time versus OFF-time
o Combination of conventional and inverter gives multi-process capabilities that are
better than conventional and more like inverter machines
o Still not as efficient as an inverter
 Engine-Driven Power Source: Produces AC Power like that from the power company
o Could be like an inverter or conventional
o Requires:
 Magnetic lines of force
 A good electrical conductor
 Relative motion
o Similar output as Step Down Transformer
o Power either supplies an internally mounted inverter or produces low-V, high-A power
o Portable, easy to use
 Duty Cycle: Percentage of Time during a specified test period that a power source or its
accessories can be operated at a rated output before it exceeds the temp limits of the insulation
in the comp parts
o The actual amount of time that a welding power source can operate before it overheats
o Rated Output = Rated Amperage at the Rated Load Voltage
o Ex: 50% Duty Cycle would mean that source needs to rest 5 out of every 10 minutes
o 100% duty cycle can be operated continuously at or below its rated output
o Welding Amp (Power Demand) Decreases, Duty Cycle Increases
o Operating Factor vs Duty Cycle
 Operating Factor: Operator’s ability to keep the arc ON
 Duty Cycle: Machine’s ability to keep the arc ON before it needs to cool down
 Selecting the Right Welding Power Source
o Welding Power Required
o Duty Cycle
o Process Capabilities
o Remote Control Capabilities
o Portability needs
o Primary Power Available
o Allow room for growth as your efficiency improves
o Expected replacement time
o What processes will the machine need to perform
o Machine Placement
History and Overview

 GMAW (MIG): Gas Metal Arc Welding; arc welding process that uses an arc between a
continuous filler metal electrode and the weld pool
 Use External gas a shielding
 Created in 1940’s as an alternative to GTAW
 MIG: Metal Inert Gas; name is outdated because more reactive gases are now more commonly
used
 Consumable wire functions as the electrode in the weld circuit and the source of filler metal
 GMAW uses four modes of transfer: short circuit, globular, spray, and pulsed spray
 Microprocessors control welding power sources
o Improve response time
o Provides precise control of welding output
 Power Source > Electrode lead > wire feeder > gun > Wire > arc > workpiece > work clamp >
work cable > Power Source
 Ferrous metals, aluminum, stainless steel
 Travel speeds and deposition rates may be higher than TIG or Stick Welding
 Little to no slag
 Arc and weld pool are clearly visible during welding and minimal amount of post-weld cleanup is
required.
 Advantages
o Faster than GTAW and SMAW
o Reduces deposit time of metal
o Provides higher deposition rates while minimizing starting and stopping; uses a
continuous spool/supply of electrode wire
o Reduces post weld clean up by eliminating slag removal
 Applications
o Maintenance, manufacturing, hobbyist, repairs, metal fabrication
o Apps that require work on a wide range of metals
 Semi-automatically: Welder controls the gun angles and travel speeds, but not the welding
power source or torch. Manual welding with equipment that automatically controls one or more
welding conditions.
 Automatically: Doesn’t require a welder to control the gun or adjust the travel speed. Operator
loads part to fixture, presses a start button, everything else is automatic.
o Fixed automation: Utilizes a dedicated machine specifically designed for arc welding the
same specific parts on a continuous production basis.
 Arc spot weld
 Plug/slot weld
 Linear weld
 Circumferential weld
o Flexible automation: A robot arc welding system where parts can be changed and the
robot can be programmed to change and even adapt to part variations.
o Programmable automation

Equipment
 GMAW Power Sources
o Conventional Transformer-Rectifier
 Converts high-voltage, low amp, primary > low-voltage, high amp, secondary
 Step down transformer>Control Circuit>Rectifier>Filter
 Single
 Light welding
 Under 200 amps needed
 115Vac or 230Vac
 3 Phase
 Over 200 amps needed
o Inverter
 Converts high-voltage, low amp, primary > low-voltage, high amp, secondary
 Use less energy
 Less heat loss
 Generates less heat in the physical components
 Allows high current levels to pass through smaller components
 Smaller and lighter
 Can quickly vary its output for processes
 Amperage adjustment in milliseconds
o Engine-Driven
 Can be like an inverter or a conventional power source
 Produces AC power like the power company or DC power to be altered for
welding
 Portable
o Secondary-Switching
 Half conventional, half inverter
 Primary AC input power is converted like a conventional power supply
 Step down transformer > rectifier>filter>power switches>filter/stabilizer
 Multi-processing capabilities and arc characteristics similar to the inverter
machine
 More efficient than a conventional machine
 Not quite as efficient as an inverter
 Significantly larger
 Duty Cycle
o Actual amount of time that a welding power source can operate before it needs to rest
 Operating Factor
o Operator’s ability to keep the arc on
 Selecting the right welding power source
o Welding power required
o Duty cycle
o Process capabilities
o Remote control capabilities
o Portability means
o Primary power available
Wire Feeders

 Supply the filler metal, electrical current, and shielding gas to the gun and arc during welding
 GMAW uses continuous electrode referred to as a welding wire.
 Constant Speed
o Gets the power to turn the drive motor from the control cable
o Control Cable : “Brain”, 14 pin cable, supports up to 14 wires
o Basic control that only regulates gas flow, wire feed speed, and the output contactor OR
they can control a complete, timed, weld sequence
 Voltage Sensing
o Gets power from welding power source
o Portable
o Long distance welding
o Can be setup with a CC power source but shouldn’t be used; consistent arc voltage
 Wire Feeder
o Spool Supports
o Drive Motor
o Control System
o Drive Housing: connects the welding power, shield gas, and welding wire to the gun
o Drive Rolls: Pull wire from the spool and feed into the gun
o GMAW Gun
 Control System
o Trigger: Start weld by pulling gun trigger
o Purge: Manually turn on the shielding gas
o Jog: Feed wire into gun without activating shielding gas or welding power
o Remote Voltage Control
o Digital Meters
o Wire Feeder
 Welding Sequence
o Preflow>Run-in>Start>Weld>Crater>Burnback>Post flow
o Run-in: Controls how fast the wire initially feeds until the arc is established
o Start: Establishes the welding parameters used to begin the weld
o Weld: Parameters are typically adjusted on the power source
o Crater: Reduces chance of crater crack and fills in the end of the weld
o Burnback: Timed event stops the wire from feeding
o Post flow: Keep the shielding gas on after the welding has stopped
 Drive Rolls
o V-Grooved
 Most common
 Excellent grip for easy feeding
 Some slip if wire is stuck
 Will deform around wire if overtightened
o V-knurled
 Extra bite for softer wires
 o U-grooved
 Used for soft wires
 Grip for feeding and don’t deform wire
 Overtighten will cause slight deformation
o U-Cogged
 Least used.
 Used mostly for feeding large diameter wires
o Drive Housing
 Gear box: Converts mech energy to turn drive rolls
 Tension Adjustment controls the amount of force that the drive roll places on
the wrie
 Inlet Guides: direct wire from the spool to drive roll
 Intermediate Guides: Conduct wire between two sets of drive tolls on a four
drive roll system
 GMAW Gun
 Gas Connection
 Welding Power Connection

Welding Gun

 Specific amperage rating from 150 to 750A

 Parts can wear out: trigger, liner, contact tips, nozzles
 GMAW Gun is specifically designed for GMAW process
o More expensive and complex
 Connection
o Welding Power: Carries welding power to contact tip
o Shielding Gas: Ensures adequate shielding gas to protect the molten weld pool
o Electrode/filler metal: Joins the filler rod to feed to the end of the gun
o Trigger: Allows the low voltage signal to tell the wire feeder when the trigger has been
pulled
 Curved head gun used for all metals (including aluminum)
o 45, 60, 80 degrees are common angles
 Flexible necks increase operator’s comfort
 Gun Selection
o Amp requirements
o Duty Cycle (100% is unlikely)
o Gun weight/comfort
o Work site location
o Cost
 Lower amperage gun
o Lighter
o More flexible
o More cost effective
 Consumables
o Diffueser
 o Nozzle
o Contact Tips
o HI quality
 Better shielding gas coverage
 Less porosity
 More stable arc
 Longer contact tip and nozzle life
 Reduced burn backs
 Fewer weld defects
 Labor = 85% of welding expenses
 Contact Tips
o What’s important
 Quality
 Maintenance
 How it’s used
o Hardness contributes to lifespan. Harder it starts, longer it will last
o Keyhole can lead to irregularities in the arc
o Bore size of contact tip 0.004 to 0.007 inches larger than wire diameter
o Threaded tips: popular through 1990s but difficult to remove and poor
electrical/thermal conductivity
o Non-threaded: seated surface, take less time to change, nozzle holds the tip on
 Gun Liners
o Rigid
o Resistant to buckling
o Long life
o Change liner when switch electrodes out
 Nozzle: Primarily provide shielding gas
 Large nozzle = more gas coverage
 Contact tip position
o Flush
o Extended
o Recessed
 Copper Nozzle: used in heavy industrial apps
o Can withstand higher temps
o Popular choice for spray, pulse, and flux-cored welding
 Brass Nozzle: resistant to spatter
o NOT as heat tolerant
o Popular choice for short circuit transfer and RMD transfer with shorter electrode
extension
 Spot Nozzles: Make spot welds
o Slotted design allow gases to exhaust away from spot weld
o Styles: Flat, inside corner, outside corner