1. Introduction to(GMAW) Gas Metal Arc Welding
GMAW Unit 1 Lesson 1
Objective: Demonstrate proper setup and maintenance of GMAW equipment.

2. GMAW Process
Gas Metal Arc Welding (GMAW) uses an electric arc to melt a consumable wire electrode and fuse it with the base metal. The arc generates an intense heat of 6,000 to 10,000 degrees Fahrenheit. The process normally operates with direct current electrode positive (DCEP).

3. GMAW Equipment
The wire electrode is fed by the wire feeder through the gun cable to the welding gun.
The electric current is transferred from the power source through the gun cable and to the contact tip.
The contact tip conducts the electric current to the wire electrode.
The gun cable also transports the shielding gas to through the gas diffuser and out the nozzle.
The welding arc is stabilized and the molten filler and base metal are protected from oxidation by the shielding gas.

4. 7E2DA225-EFBF-A940-81C4-A9BDFE28FAFF
What does the abbreviation
GMAW stand for?
iRespond Question
Multiple Choice F
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A.) Gas Machine Arc Welding
B.) Gas Metal Arc Welding
C.) Gas Material Arc Welding
D.) Gas Method Arc Welding
E.)

5. In a GMAW system, how is the electric current transferred to the electrode?
iRespond Question
Multiple Choice F
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A.) Through the gun cable and liner
B.) Through the contact tube
C.) Through the wire feed rolls
D.) Through the gas diffuser
E.)

6. Process Setup GMAW machines can come in 2 types.
The most common being the power source and wire feeder in one unit.
The second type is when the power source and wire feeder are separate machines connected to each other.
Regardless of the machine type. The GMAW process has two main controls.
Wire speed- controls the amperage or heat
Voltage- controls the arc gap

7. Power supplies
The basic power supply used for GMAW is designed for the process. It is called a Constant Potential (CP) or more commonly Constant Voltage (CV). The Arc gap is controlled by the machine voltage. CV machines maintain a constant voltage by varying the amperage to maintain a consistent arc gap.

8. GMAW Guns
Spool Gun
Standard Gun
Push Pull Gun

9. What type of Power source is used for GMAW?
iRespond Question
Multiple Choice F
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A.) Constant Current
B.) Alternating Current
C.) Variable Voltage
D.) Constant Voltage
E.)

10. GMAW Modes of Metal Transfer
There are 3 basic types of metal transfer associated with GMAW.
Short Circuit Transfer
Globular Transfer
Spray Transfer

11. Short Circuit Transfer
Commonly referred to as short arc, this is probably the most widely used method of metal transfer. As the wire electrode touches the base metal a short circuit is created causing the electrode to melt through and deposit molten metal into the weld joint.
There are advantages and disadvantages to the short arc transfer mode.
Advantages:
Low heat input
Welds in all positions
Welds thin gauge materials
Can be used to bridge gaps in some weld joints
Disadvantages:
Small diameter wire, expensive.
Spatter
Cold starts, can cause cold lap on restarts.
Limited to materials 1/8” thick or less.

12. Short Circuit Transfer

13. Which of the following is an advantage with Short Circuit mode of metal Transfer?
iRespond Question
Multiple Choice F
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A.) Small diameter wire, expensive.
B.) Spatter
C.) Cold starts, can cause cold lap on restarts.
D.) Welds in all positions
E.)

14. Globular Transfer
The globular mode of metal transfer happens when the electrode melts and burns off before touching the base metal. Forming a molten droplet falls and then melts to the base metal.
Advantages:
High deposition rate
High quality welds are possible
Good penetration at high speeds
Disadvantages:
Considerable amount of smoke and spatter
Rough weld appearance
Can only be used in the flat position

15. Globular Transfer

16. Which of the following is a disadvantage Globular mode of metal Transfer?
iRespond Question
Multiple Choice F
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A.) High deposition rate
B.) Can only be used in the flat position
C.) High quality welds are possible
D.) Good penetration at high speeds
E.)

17. Spray-Arc Transfer
Spray-Arc often called Spray Transfer is a metal transfer mode where the electrode is fed into the weld zone and melted off above the base metal. Electromotive force propels the molten electrode to the base metal.
Advantages:
Very little or no spatter
High quality welds
High metal deposition
Faster welding speeds
Deep penetration
Disadvantages:
Very large weld pool
Very fluid weld pool
Can only be used in the flat position when making groove welds
Can only be used in the flat and horizontal position when making fillet welds

18. Spray-Arc Transfer

19. Modes of Transfer
Transitions from Short Circuit - Globular arc - Spray arc

20. Which of the following is a disadvantage spray-Arc mode of Transfer?
iRespond Question
Multiple Choice F
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A.) High quality welds
B.) High metal deposition
C.) Faster welding speeds
D.) Can only be used in the flat and horizontal position when making fillet welds
E.)

21. Pulsed Spray Transfer
A variation to the spray transfer process, pulsed spray is a method of pulsing the current forcing a drop of filler material from the end of the electrode at controlled time in the welding cycle.
Advantages:
Greater metal deposition at lower amperage levels.
Decreased warpage is possible
Decreased need for jigs or weld tooling
All positions
Disadvantages:
Need for special power supplies
Requires special gas mixtures