GTAW Flashcards
Gas Tungsten Arc Welding (GTAW)
Arc welding process in which shielding gas protects the arc between a non-consumable tungsten electrode and the base metal
Non-consumable Electrode
An electrode that does not melt and become part of the weld
What kind of power source does tig use?
A constant current (CC) machine that is capable of AC, DC and high frequency (HF)
High Frequency (HF)
High-voltage, low-current pulses over 16,000 cycles per second (16 kHz)
What is HF used for?
To start an arc without touching an electrode to the workpiece. In DC, for arc starting only. In AC, for maintaining the arc.
Where is most of the heat concentrated on in DCEN polarity?
About 70% of the heat is directed towards the base metal. DCEN has the lowest heat concentration in the electrode tip.
What metals use DCEN?
Carbon steel, stainless steel, other ferrous metals, copper, brass
Which polarity has more narrower, deeper-penetrating action?
DCEN
What kind of weld results from using DCEP?
A wide, shallow-penetrating weld, must use a large diameter electrode
What kind of metals must use AC in order to weld them?
Nonferrous metals such as aluminum and magnesium that have tough oxide coatings that melt at much higher temperatures than the base metal. Coating must be removed before welding
What is cathodic bombardment?
The removal of the oxide coating on the base metal by bombarding it with gas ions during the positive half-cycle of AC, also called Cleaning Action
What are the three power sources that produce different AC waveforms?
Conventional sine wave transformer-rectifiers, conventional square wave transformer-rectifiers, inverters
Conventional Sine Wave Transformer-Rectifier
A power source that produces a sinusoidal waveform
Sinusoidal Waveform
60 cycle per second (60 Hz) sine wave with equal amounts of electrode positive current and electrode negative current
How many times does a sinusoidal waveform pass through zero in a second?
120 times
What happens to the arc when the current passes through zero in a sinusoidal waveform?
The arc extinguishes
Conventional Square Wave Transformer-Rectifier
A power source that produces a relatively square 60 Hz waveform
What are the advantages of a Square Wave Transformer-Rectifier relative to a Sine Wave Transformer-Rectifier?
- The change from positive to negative is immediate, therefore resulting in a smoother arc
- More efficient than a sine wave because the arc spends more time at peak
- An adjustable balance between positive and negative
Inverter
A power source that produces a true square AC waveform
What is the advantage of using an inverter?
Allows for more precise control of the AC waveform (balance, frequency, amplitude)
Electrode Extension
The distance from the end of the collet to the tip of the electrode
Stickout
The distance from the end of the nozzle to the tip of the electrode
Inert Gas
Gas that does not readily combine with other elements
Postflow
The flow of shielding gas after the arc is extinguished
What is the general rule when applying postflow?
1 sec of postflow for every 10 amps
What is the benefit of postflow?
Ensures that the weld zone has cooled enough to prevent oxidation from exposure to the atmosphere
What is the benefit of preflow?
Ensures that the shielding gas is present during arc starting.
Use sparingly, if timer is too high, results in wasted gas and arc will not start until timer runs out
Where can remote current controls be located?
They can be foot operated with a pedal or located on the torch and operated by finger or hand
What is the function of a remote current control?
Starts the flow of electricity and shielding gas and controls the amount of amperage sent to the torch
Rheostat
A variable resistor used to control the flow of electric current by adjusting resistance
What type of shielding gas is most commonly used?
Straight argon
What happens when no shielding gas is used?
Porosity in the weld
Autogenous Weld
A weld made without the addition of filler metal
What advantages are there to using filler metal?
Reinforce the joint (especially butt and T-joints) and reduce weld cracking
