Electric Arc Welding

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Electric Arc Welding
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Definition

• Electric arc welding A group of fusion welding
  processes that use an electric arc to produce the
  heat required for melting the metal and filler
  material.

Advantages of electric arc compared to gas
welding?
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Common Electric Arc Welding Processes

• SMAW
• GMAW
• FCAW
• GTAW

What do these acronyms stand for?
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Additional Arc Welding Processes

• SAW
• ESW
• EGW
• PAW
• ASW

Submerged Arc Welding
Electroslag Welding
Electrogas Welding
Plasma Arc Welding
Arc Stud Welding
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Arc Welding Requirements
How do these arc welding processes meet the three
requirements of arc welding?
Filler Material
Shielding
Heat
SMAW
GMAW
FCAW
GTAW
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Heat
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Arc Welding Electrical Terms
To understand how an electric arc welder produces
the correct heat for arc welding, you must
understand the following fourteen (14) electrical
terms.

• Electrical Circuit
• Direct current (DC)
• Alternating current (AC)
• Ampere
• Volt
• Resistance
• Ohms Law

• Constant potential
• Constant current
• Voltage drop
• Open circuit voltage
• Arc voltage
• Polarity
• Watt

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Terms 1 - Electrical Circuit

• An electrical circuit is a complete path for
  electricity.
• Establishing an arc completes an electric circuit
  .

Why is this important for arc welding?
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Terms2 - Direct Current

• Direct current A type of current where the flow
  of electrons is in one direction.

• In arc welding the direction of flow is called
  the polarity.

• Recommended for out of position welding and low
  hydrogen electrodes.

• How does changing the polarity change the
  application of the heat?

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Terms3 - 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.

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Terms4 - Ampere

• Amperes the unit of measure for current flow.
• One ampere is equal to 6.241509481018 electrons
  passing by a point per second.
• Electricity passing through a resistance causes
  heat.
• An air gap is a high resistance

Knowing these facts, how do you change the amount
of heat at the weld?
What are the characteristics of an electrode that
was used with excessive current density?
What is the effect when the electrode was used
with insufficient current?
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Terms5 - Voltage

• Voltage is the measure of electromotive force
  (Emf).
• Emf is measured in units of volts
• The voltage at the electrode for SMAW determines
  the ease of starting and the harshness of the arc.

• Voltage is adjustable on dual control machines.

If an arc welder has dual controls, what will the
two controls adjust.?
Why does the electricity jump across the air gap?
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Terms6 - Resistance

• Resistance is the characteristic of a material
  that impedes the flow of an electrical current.
• Measured in units of Ohms ( ? )
• When an electrical current passes through a
  resistance heat (BTU) is produced.

What determines the amount of heat that an
electric current will produce?
Is the resistance adjustable in the SMAW process?
Is the resistance adjustable in the GMAW process?
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Terms7 - Ohms Law

• Commonly expressed as
• Voltage is equal to amps x resistance
• For arc welding rearranged as
• Amperage is the voltage divided by the resistance.

How does Ohms law apply to arc welding?
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Terms7 - Ohms Lawcont.

• Ohms law also be used to teach a principle of
  electrical safety.
• Amperage is the harmful portion of electrical
  current.
• Rearranging Ohms Law for amperage shows that
  amperage (current flow) is determined by the
  voltage divided by the resistance.
• Voltage is fixed by the circuit design.
• The higher the resistance, the less current that
  will flow for a given voltage.

What should you do to keep you resistance high
when arc welding?
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.
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TermsConstant Potential Constant Current

• 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 limit this effect.

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Terms8 - Constant Potential

• A constant potential power supply is designed to
  produce a relatively constant voltage over a
  range of amperage changes.
• Primarily used for
• GMAW
• FCAW

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Terms8 - Constant Potentialcont.

• The voltage has only a small change for a large
  change in amperage.

What does this mean for GMAW and FCAW?
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Terms9 - Constant Current

• In a constant current power supply, the current
  (amperage) stays relatively constant over a
  narrow range of voltages.
• Primarily used for
• SMAW
• TIG

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Terms9 - Constant Current-cont.

• 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 supply?
Yes
How?
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Terms10 - 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.

• Are there any circumstances where excessive
  voltage drop can be a problem when stick welding?

Yes
Explain!
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Terms11 - Open Circuit Voltage

• 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?
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Terms12 - 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?
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Terms13 - 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?
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Terms14 - Watt

• Watts are a measure of the amount of electrical
  energy being consumed.
• 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?
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Arc Welding Power Supplies--cont.

• The type of current and the polarity of the
  welding current are one of the differences
  between arc welding processes.
• SMAW Constant current (CC), AC, DC or DC-
• GMAW Constant voltage (CV) DC
• FCAW Constant voltage (CV) DC-
• GTAW Constant Current (CC) ), AC, DC or DC-

What should be changed when switch a MIG welder
between the GMAW and the FCAW process?
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Safe Practices

• Arc welders need protection from
• Arcs rays
• Welding fumes
• Sparks
• Contact with hot metal

What BMP are used for each hazard?
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Twelve (12) Considerations When Selecting An Arc
Welding Power Supply

• Maximum Amperage
• Duty cycle
• Amperage range
• Amperage adjustment mechanism
• Input power requirements
• Initial cost and operating cost
• Size and portability

• Future needs for a power supply
• Available skills
• Safety
• Manufacturer's support
• Open circuit voltage

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1 Amperage Output

• 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.

What determines the best amperage for a weld?
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2 Duty cycle

• 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 cycle.
• 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?
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Joints, Welds Positions
Electric arc welding uses the same five (5) types
of joints and five (5) types of welds and five
(5) positions discussed in fusion welding.
Name the five (5) types of joints.
Name the five (5) types of welds.
Name the five (5) welding positions.
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Weld Defects

• A weld defect is any physical characteristic in
  the completed weld that reduces the strength
  and/or affects the appearance of the weld.
• 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 nondestructive testing.
• 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.

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Common Defects and Causes
Description
Cause(s)

• The depth of the weld is less than specifications.

Excessive heat Excessive speed.
The weld metal is not completely fused to base
metal or passes are not completely fused.
Incorrect angle Incorrect manipulation Insufficie
nt heat
Weld material flows over, but is not fused with
the base metal.
Slow speed
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Common Defects and Causes--cont.
Description
Cause(s)

• Weld bead does not extend to the desired depth.

Low heat Long arc Incorrect joint design
Small indentions in the surface of the weld
Excessive gas in the weld zone. Moisture Rust Dirt
Accelerated cooling
Small voids throughout the weld material.
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Common Defects and Causes--cont.
Description
Cause(s)

• Usually visible cracks on the surface or through
  the weld

Accelerated cooling Constrained joint Small weld
volume
Cracks in the transition zone between the weld
and base metal
Induced hydrogen Incompatible electrode or
wire Accelerated cooling
Misshapen and/or uneven ripples
Inconstant speed Incorrect manipulation Incorrect
welder settings
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Q u e s t i o n s