Transcript Electric Arc Welding

Electric Arc Welding
1
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?
2
Common Electric Arc Welding Processes
1. SMAW
2. GMAW
3. FCAW
4. GTAW
What do these acronyms stand for?
3
Additional Arc Welding Processes
1. SAW
Submerged Arc Welding
2. ESW
Electroslag Welding
3. EGW
Electrogas Welding
4. PAW
Plasma Arc Welding
5. ASW
Arc Stud Welding
4
Arc Welding Requirements
How do these arc welding processes meet the three requirements
of arc welding?
Heat
Shielding
Filler
Material
SMAW
GMAW
FCAW
GTAW
5
Heat
6
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.
1. Electrical Circuit
8.
Constant potential
2. Direct current (DC)
9.
Constant current
3. Alternating current (AC)
10.
Voltage drop
11.
Open circuit voltage
12.
Arc voltage
13.
Polarity
14.
Watt
4. Ampere
5. Volt
6. Resistance
7. Ohms Law
7
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?
8
Terms
2 - 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?
9
Terms
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.
10
Terms
4 - Ampere
•
•
•
•
Amperes: the unit of measure for current flow.
One ampere is equal to 6.24150948×1018 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?
11
Terms
5 - 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?
12
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.
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?
13
Terms
7 - Ohm’s Law
•
E= I R
Commonly expressed as:
– Voltage is equal to amps x resistance
•
For arc welding rearranged as:
– Amperage is the voltage divided by
the resistance.

E
I=
R
How does Ohm’s law apply to arc welding?

14
Terms
7 - Ohm’s Law—cont.
• Ohm’s law also be used to teach a principle of
electrical safety.
 Amperage is the harmful portion of electrical
current.
 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.
 The higher the resistance, the less current that
will flow for a given voltage.
E
I=
R
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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Terms
Constant 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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Terms
8 - 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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Terms
8 - Constant Potential—cont.
80
70
60
Volts
50
40
30
20
10
0
0
50
100
150
200
250
Anperes
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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Terms
9 - 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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Terms
9 - 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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Terms
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.
•
Are there any circumstances where excessive voltage drop can be a
problem when stick welding?
Yes
Explain!
21
Terms
11 - 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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Terms
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?
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Terms
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?
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Terms
14 - 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:
– Arc’s 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
1. Maximum Amperage
2. Duty cycle
3. Amperage range
4. Amperage adjustment
mechanism
5. Input power requirements
6. Initial cost and operating cost
8. Future needs for a power
supply
9. Available skills
10. Safety
11. Manufacturer's support
12. Open circuit voltage
7. Size and portability
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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
The depth of the weld is
less than specifications.
The weld metal is not
completely fused to base
metal or passes are not
completely fused.
Weld material flows over,
but is not fused with the
base metal.
Cause(s)
Excessive heat
Excessive speed.
Incorrect angle
Incorrect manipulation
Insufficient heat
Slow speed
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Common Defects and Causes--cont.
Description
Weld bead does not
extend to the
desired depth.
Small indentions in
the surface of the
weld
Small voids
throughout the weld
material.
Cause(s)
Low heat
Long arc
Incorrect joint design
Excessive gas in the
weld zone.
Moisture
Rust
Dirt
Accelerated cooling
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Common Defects and Causes--cont.
Description
Usually visible cracks on
the surface or through the
weld
Cracks in the transition
zone between the weld
and base metal
Misshapen
and/or uneven
ripples
Cause(s)
Accelerated cooling
Constrained joint
Small weld volume
Induced hydrogen
Incompatible electrode
or wire
Accelerated cooling
Inconstant speed
Incorrect manipulation
Incorrect welder settings
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