How do these arc welding processes meet the three requirements
of arc welding?
Arc Welding Electrical
To understand how an electric arc welder produces the correct heat
for arc welding, you must understand the following fourteen (14)
1. Electrical Circuit
2. Direct current (DC)
3. Alternating current (AC)
Open circuit voltage
7. Ohms Law
1 - Electrical
An electrical circuit is a complete
path for electricity.
Establishing an arc completes an
electric circuit .
2 - Direct
• Direct current: A
type of current
where the flow of
electrons is in one
direction. the direction
In arc welding
of flow is called the polarity.
• Recommended for out of position welding and low hydrogen electrodes.
• Electricity flows from negative to positive. The positive terminal will
Alternating current: The
type of current where the
flow of electrons reverses
direction at regular
for SMAW general
purpose electrodes and
4 - Ampere
• Amperes: the unit of measure for
• One ampere is equal to
6.24150948×1018 electrons passing by a
point per second.
• Electricity passing through a resistance
Change the amperage or change the resistance.
• An air gap is a high resistance
Excessive amperage for the diameter of the electrode (current
density) over heats the electrode, excessive penetration.
Insufficient amperage for the diameter of electrode makes the
electrode hard to start, reduced penetration.
Voltage is the measure of
electromotive force (Emf).
Emf is measured in units of
Voltage is adjustable the electrode
The voltage at on dual control machines.
for SMAW determines the
ease of starting and the
harshness of the arc.
Terms 6 Resistance
Resistance is the characteristic of a material that
impedes the flow of an electrical current.
Measured in units of Ohm’s ( )
When an electrical current passes through a
resistance heat (BTU) is produced.
7 - Ohm’s
Commonly expressed as:
Voltage is equal to amps x
For arc welding
Amperage is the voltage
divided by the resistance.
7 - Ohm’s Law—cont.
• Ohm’s law also be used to teach a principle of
Amperage is the harmful portion of electrical
Rearranging Ohm’s Law for amperage shows
that amperage (current flow) is determined by
the voltage divided by the resistance.
Voltage is fixed by the circuit design.
What should you do
to keep you
resistance high when
The higher the resistance, the less current that
will flow for a given voltage.
If you accidently come in contact with electric current while arc
welding the severity of the shock is determined by the voltage in the
circuit and your resistance.
Constant Potential &
• In the normal operation of a transformer, the amperage and voltage change
in opposite direction.
• As amperage is increased, the voltage decreases, and vies versa.
• Electrical arc welding power supplies are designed to limit this effect.
8 - Constant
A constant potential power supply is designed to
produce a relatively constant voltage over a range of
Primarily used for
8 - Constant
In the short circuiting process, the voltage stays constant as the amperage
changes. Helps with restarting of the arc after it is broken.
9 - Constant
• In a constant current power supply, the current (amperage)
stays relatively constant over a narrow range of voltages.
• Primarily used for:
9 - Constant
Increasing the voltage from 20 to 25
volts (25 %) causes the amperage to
change from 123 to 132 Amp (4.8%).
The voltage is not adjustable for most
constant current power supplies.
Is it possible to change the voltage
while welding with a SMAW power
10 - Voltage Drop
Voltage drop is the reduction in voltage in an electrical circuit
between the source and the load.
Primary cause is resistance.
Excessive voltage drop reduces the heat of the arc.
11 - Open Circuit
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.
Is the OCV on a welding power supply adjustable?
12 - Arc Voltage
Arc voltage is the electrical potential between the
electrode and the metal after the arc has started.
Which will have the higher value, OCV or arc voltage?
Is the arc voltage constant once the arc has started?
13 - Polarity
Polarity (positive & negative) is present in all electrical circuits.
Electricity flows from negative to positive
Controlling the polarity allows the welder to influence the
location of the heat.
When the electrode is positive (+) it will be slightly hotter than
the base metal.
When the base metal is positive (+) the base metal will be slightly hotter
than the electrode.
What abbreviations are used to indicate the polarity of the electrode?
14 - Watt
Watts are a measure of the amount of electrical energy
Watts = Volts x Amps
The greater the Watts of energy flowing across an air
gap the greater the heat produced.
Is the wattage for a weld controlled by adjusting the Volts or the amps?
Both, depends upon the welding
Arc Welding Power
The type of current and the polarity of the welding current are
one of the differences between arc welding processes.
Constant current (CC), AC, DC+ or DC-
Constant voltage (CV) DC+
Constant voltage (CV) DC-
Constant Current (CC) ), AC, DC+ or DC-
What should be changed when switch a MIG welder between the GMAW
and the FCAW process?
Arc welders need protection from:
– Arc’s rays
– Welding fumes
– Contact with hot metal
An Arc Welding Power
1. Maximum Amperage
2. Duty cycle
3. Amperage range
4. Amperage adjustment
8. Future needs for a power
9. Available skills
5. Input power requirements
11. Manufacturer's support
6. Initial cost and operating cost
12. Open circuit voltage
7. Size and portability
The maximum output of the power
supply determines the thickness of
metal that can be welded before joint
beveling is required.
185 to 225 amps is a common size.
For an individual weld, the optimum output amperage is determined
► Thickness of the metal,
► The type of joint,
► Welding position and
► Type of electrode.
The amount of continuous welding time a
power supply can be used is determined by
the duty cycle of the power supply.
Duty cycle is based on a 10 minute interval.
Many power supplies have a sloping duty
Note in the picture there is a circle around the
75 amp setting. Why is it there?
What is the guaranteed outcome of exceeding
a power supply duty cycle?
Joints, Welds &
Electric arc welding uses the five (5) types of joints and five (5)
types of welds and five (5) positions.
The five (5) types of joints are;
1-butt 2-corner 3-edge 4-lap 5-T
The five (5) types of welds are:
1-Surface 2-groove 3-fillet 4-plug 5-slot
The five (5) welding positions.
1-Flat 2-horizontal 3-vertical up 4-vertical down 5-overhead
A weld defect is any physical characteristic in the completed weld
that reduces the strength and/or affects the appearance of the
The mark of a good welder is the ability to identify weld defects
and adjust the welding parameters to eliminate them.
Defects that are not visible must be detect by using destructive or
If the defects in a weld exceed the specifications, the weld must
be removed and redone.
Welds are removed by grinding, gouging and cutting.
Eliminating a weld defect is time consuming and expensive -- you
must be able to complete the weld correctly the first time.
Common Defects and
The depth of the weld is
less than specifications.
The weld metal is not
completely fused to base
metal or passes are not
Weld material flows over,
but is not fused with the
Common Defects and
Weld bead does
not extend to the
Incorrect joint design
Small indentions in
the surface of the
Excessive gas in the
throughout the weld
Common Defects and
Usually visible cracks
on the surface or
through the weld
Small weld volume
Cracks in the transition
zone between the weld
and base metal
Incorrect welder settings