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

1. SAW
2. ESW
3. EGW
4. PAW
5. ASW
Additional Arc Welding Processes
Submerged Arc Welding
Electroslag Welding
Electrogas Welding
Plasma Arc Welding
Arc Stud Welding
4

Arc Welding Requirements
How do these arc welding processes meet the three requirements of arc welding?
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
2. Direct current (DC)
3. Alternating current (AC)
4. Ampere
5. Volt
6. Resistance
7. Ohms Law
8.
9.
10.
Constant potential
Constant current
Voltage drop
11.
Open circuit voltage
12.
Arc voltage
13.
Polarity
14.
Watt
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
× 10 18 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
• 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 Ohm’s law apply to arc welding?

E = I R
I =
E
R
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.
E
I =
R
 Rearranging Ohm’s Law for amperage shows that amperage (current flow) is determined by the voltage divided by the resistance.
What should you do to keep you
 Voltage is fixed by the circuit design.
resistance high when
 The higher the resistance, the less current that arc welding?
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.
15

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.
16

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
17

Terms
8 - Constant Potential —cont.
80
70
60
50
40
30
20
10
0
0 50 100
Anperes
150 200 250
The voltage has only a small change for a large change in amperage.
What does this mean for GMAW and FCAW?
18

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
19

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?
20

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?
22

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?
23

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?
24

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?
25

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
– GTAW
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?
26

Arc welders need protection from:
– Arc’s rays
– Welding fumes
– Sparks
– Contact with hot metal
What BMP are used for each hazard?
27

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
7. Size and portability
8.
Future needs for a power supply
9.
Available skills
10. Safety
11. Manufacturer's support
12. 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?
29

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?
30

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.
31

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 .
32

Common Defects and Causes
Description
The depth of the weld is less than specifications.
Cause(s)
Excessive heat
Excessive speed.
The weld metal is not completely fused to base metal or passes are not completely fused.
Incorrect angle
Incorrect manipulation
Insufficient heat
Weld material flows over, but is not fused with the base metal.
Slow speed
33

Common Defects and Causes--cont.
Weld bead does not extend to the desired depth.
Low heat
Long arc
Incorrect joint design
Small indentions in the surface of the weld
Small voids throughout the weld material.
Excessive gas in the weld zone.
Moisture
Rust
Dirt
Accelerated cooling
34

Common Defects and Causes--cont.
Description
Usually visible cracks on the surface or through the weld
Cause(s)
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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