Arc Welding Power Source
Dr.P.Sathiya
Professor
Department of Production Engineering
National Institute of Technology
Tiruchirappalli-620 015
Email: psathiya@nitt.edu
Electrical Circuit
Establishing an arc completes an
electric circuit .
An electrical circuit is a complete path
for electricity.
Why is this important for
arc welding?
2
Direct Current
• Direct current: A
type of current
where the flow of
electrons is in one
• In arc welding the direction of
direction. flow is called the polarity.
• Recommended for out of position welding and low hydrogen electrodes.
3
Alternating Current
Alternating current: The
type of current where the
flow of electrons reverses
direction at regular
intervals.
Recommended current for
SMAW general purpose
electrodes and flat position.
4
Basic Electricity and the Science of
Welding
Voltage – The electrical potential or pressure that
causes current to flow
Measured in Volts
Current – The movement of charged particles in a
specific direction
Measured in Amps
Polarity
DC- (Direct Current
Electrode Negative) -Straight Polarity
DC+ (Direct Current
Electrode Positive) -Reverse Polarity
AC (Alternating Current)
11 - 9
Constant Current
Output Slope
Some jobs require steep volt-ampere curve
Other jobs use less steep
volt-ampere curve
• Open circuit voltage is the
potential voltage between
the electrode and the
work when the arc is not
present.
• The higher the OCV the
easier the arc is to start.
• The higher the OCV the
steeper the volt – amp
curve.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
POWER SOURCE-
CONSTANT CURRENT
Increasing the
voltage from 20 to
25 volts (25 %)
causes the amperage
to change from 120
to 113 Amp (4.8%).
CONSTANT VOLTAGE
Functions of slag
Forehand & Back hand welding technique
Shielding Gases
Argon is the most commonly used shield gas (for the OD
of the tube)and the purge gas (for the ID of the tube).
Helium is often used for welding on copper material.
Mixed gases such as 98% Argon/2% Hydrogen, 95%
Argon/5% Hydrogen, 90% Argon/10% Hydrogen or 75%
Helium/25% Argon my be used when the wall thickness
to be welded is heavy (.1" or above).
Using mixtures of 95% Argon/5% Hydrogen is
incompatible with carbon steels and some exotic alloys,
often causing hydrogen embrittlement in the resultant
weld.
As a general rule, for simplicity and reduction of shield
gas cost, use 100% argon gas.
TIG Shielding Gases
Argon Helium
►Good arc starting ►Faster travel speeds
►Good cleaning action ►Increased penetration
►Good arc stability ►Difficult arc starting
►Focused arc cone ►Less cleaning action
►Lower arc voltages ►Less low amp stability
►10-30 CFH flow rates ►Flared arc cone
►Higher arc voltages
►Higher flow rates (2x)
►Higher cost than argon
38
TIG Shielding Gases
Argon/Helium Mixtures
►Improved travel speeds over pure argon
►Improved penetration over pure argon
►Cleaning properties closer to pure argon
►Improved arc starting over pure helium
►Improved arc stability over pure helium
►Arc cone shape more focused than pure
helium
►Arc voltages between pure argon and pure
helium
►Higher flow rates than pure argon
►Costs higher than pure argon
39
Tungsten Electrode Selection
Guide to selecting a tungsten electrode based on amperage range
40
*Figure copied from “Guidelines to Gas Tungsten Arc Welding (GTAW)”
Tungsten Electrode
2% ceriated and 2% thoriated electrodes are the most
commonly recommended materials for orbital welding
equipment. Helium is often used for welding on copper
material.
Sharper Electrodes Blunter Electrodes
Usually harder to start
Easy arc starting
the arc
Handle less amperage Handle more amperage
Wider arc shape Narrower arc shape
Potential for more arc
Good arc stability
wander
Less weld penetration Better weld penetration
Shorter electrode life Longer electrode life
Smaller Tip Larger Tip
Usually harder to start
Easier arc starting
the arc
Potential for more arc wander Good arc stability
Less weld penetration More weld penetration
Shorter electrode life More electrode life
METAL TRANSFER IN GMAW
Short circuit transfer
Low voltage & current Applications
Thin sheet &
all position welding
capability
Globular transfer Spray transfer
Medium voltage & current High voltage & current
Applications
Down hand position welding
Sheet thickness > 2 mm
Conventional Dip Transfer Mode of Welding
Pulsed Arc Transfer (GMAW-P)
Submerged arc welding:
BASICITY INDEX
1
CaO + MgO + CaF2 + Na2O + K 2O + ( MnO + FeO )
Basicoxides 2
Acidicoxides SiO2 + 1 ( Al2O3 + TiO2 + ZrO2 )
2
Electrode Manufacturing
