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Chapter 10 Gas Metal Arc Welding Equipment, Setup, and Operation

TRUE/FALSE

1. When first introduced, SMAW was immediately accepted because it was more productive than GTAW and produced higher quality welds than GMAW.

ANS: F PTS: 1 REF: 234

2. In the beginning, the GMAW process was used to weld aluminum using argon gas for shielding.

ANS: T PTS: 1 REF: 235

3. The short-circuiting process works better with a long electrode stickout.

ANS: F PTS: 1 REF: 238

4. The heat produced during axial spray welding using large diameter wire or high current may be intense enough to shatter the filter lens in a welding helmet.

ANS: T PTS: 1 REF: 239

5. Pulsed-arc welding systems were developed in the 1960s.

ANS: T PTS: 1 REF: 239

6. The thin copper coating on a steel wire electrode either burns off or is diluted into the weld pool with no significant effect to the weld bead.

ANS: T PTS: 1 REF: 244

7. It is possible to make acceptable welds with the wrong type of power supply.

ANS: F PTS: 1 REF: 245

8. As the slope increases, both the short-circuit current and pinch effect are increased.

ANS: F PTS: 1 REF: 246

9. Helium is not considered to be an inert gas.

ANS: F PTS: 1 REF: 249

10. GMA spot welding is an excellent process for auto body repair.

ANS: T PTS: 1 REF: 257

MULTIPLE CHOICE

1. MAG is short for ____.

a. metal arc gas welding

b. metal active gas welding

c. metal action gas welding

d. metal anion gas welding

ANS: B PTS: 1 REF: 235

2. Which of the following tasks is done by a machine?

a. Providing the joint travel in semiautomatic welding processes.

b. Providing the joint guidance in machine welding processes.

c. Providing the joint guidance in semiautomatic welding processes.

d. Maintaining the arc in semiautomatic welding processes.

ANS: D PTS: 1 REF: 235

3. Which of the following tasks are done by the welder?

a. Feeding the filler metal in semiautomatic welding processes.

b. Providing the joint travel in machine welding processes.

c. Providing the joint guidance in machine welding processes.

d. Maintaining the arc in automatic welding processes.

ANS: C PTS: 1 REF: 235

4. The shielding gas used on carbon steel is ____.

a. helium

b. carbon dioxide, or a mixture of carbon dioxide and argon

c. argon

d. argon, or a mixture of argon and helium

ANS: B PTS: 1 REF: 237

5. Which of the following is true of axial spray metal transfer?

a. It is rarely used by itself.

b. It transfers metal across the arc in larger droplets.

c. It involves a pulsing current.

d. There are hundreds of drops per second crossing from the wire to the base metal.

ANS: D PTS: 1 REF: 238

6. In axial spray metal transfer, the shielding gas is usually a mixture of ____.

a. 95% to 98% argon and 2% to 5% oxygen

b. 2% to 5% argon and 95% to 98% oxygen

c. 50% argon and 50% oxygen

d. 5% argon and 95% oxygen

ANS: A PTS: 1 REF: 238

7. Which of the following is true of axial spray transfers using high current settings?

a. Higher currents are needed with smaller diameter wires.

b. High current aids welding sheet metal because the high heat cuts through sheet metal.

c. High current settings may cause the weld to be difficult to control in out-of-position welds.

d. The need for higher current removes some restrictions on the process.

ANS: C PTS: 1 REF: 238

8. Which of the following is true of globular transfer?

a. It is used in combination with pulsed-spray transfer.

b. The arc’s real work occurs when the current pulses above the transition current.

c. There are hundreds of drops per second crossing from the wire to the base metal.

d. The process requires a current level above the transition current.

A PTS: 1

238

9. Globular transfer occurs at a rate of ____ drops per second.

a. a few

c. thousands of b. hundreds of

d. millions of

ANS: A PTS: 1 REF: 238-239

10. In the pulsed-arc metal transfer current cycle, ____ refers to how the electric current in a transformer takes a few milliseconds to build up the magnetic field to full strength once the coil is energized.

a. pulse width

b. ramp down

c. ramp up

d. overshoot

ANS: C PTS: 1 REF: 241

11. In the pulsed-arc metal transfer current cycle, ____ refers to the surging electrical current passing through the transformer like a wave on water.

a. overshoot

b. ramp up

c. high pulse current

d. pulse width

ANS: A PTS: 1 REF: 241

12. In the pulsed-arc metal transfer current cycle, ____ is the peak current that flows across the arc during the high current pulse.

a. ramp up

b. high pulse current

c. high current time

d. step-off current

ANS: B PTS: 1 REF: 241

13. In the pulsed-arc metal transfer current cycle, ____ is a function of the time it takes the magnetic field in the transformer to collapse once the coil is de-energized.

a. step-off current

b. high current time

c. ramp up

d. ramp down

ANS: D PTS: 1 REF: 242

14. With the addition of ____ to the argon gas, the transfer becomes progressively more ____.

a. oxygen, spatter-prone

b. argon, rapid

c. helium, globular

d. inert gas, reactive

ANS: C PTS: 1 REF: 243

15. As much as ____ can be added to the argon to increase the power in the arc without affecting the desirable qualities of the spray mode.

a. 10% oxygen

b. 20% nitrogen

c. 50% carbon dioxide

d. 80% helium

ANS: D PTS: 1 REF: 243

16. GMAW power supplies are ____ type machines.

a. constant-current, constant-voltage

b. constant-voltage constant-potential

c. drooping arc voltage, constant-current

d. constant-current, constant-potential

ANS: B PTS: 1 REF: 245

17. Which of the following is true of backhand welding?

a. It has good joint visibility and makes welds with less joint penetration.

b. It works well on vertical up and overhead welds.

c. It has good bead visibility and makes welds with deeper joint penetration.

d. It has a good balance between penetration and reinforcement and is used on automated welding.

ANS: C PTS: 1 REF: 251

18. Which of the following is true of perpendicular welding technique?

a. It has a good balance between penetration and reinforcement and is used on automated welding.

b. It has good bead visibility and makes welds with deeper joint penetration.

c. It has good joint visibility and makes welds with less joint penetration.

d. It works well on vertical up and overhead welds.

ANS: A PTS: 1 REF: 251

19. The purpose of the ____ is to provide a steady and reliable supply of wire to the weld.

a. power source

b. electrode feed unit

c. electrode conduit

d. welding gun

ANS: B PTS: 1 REF: 253

20. GMA welding machines have ____ duty cycle.

a. 20 percent

b. 60 percent

c. 80 percent

d. 100 percent

ANS: D PTS: 1 REF: 253

21. Which of the following is true of pull-type feed systems?

a. Feed motors are located at both ends of the electrode conduit.

b. The gun is heavier and more difficult to use.

c. Rethreading the wire takes little time.

d. The feed system uses a synchronized system.

ANS: B PTS: 1 REF: 254

22. An advantage of the ____ feed system is that the bulky system of gears is eliminated.

a. linear

b. pull-type

c. push-type

d. push-pull-type

ANS: A PTS: 1 REF: 254

23. ____ is a series of ridges cut into the groove.

a. Ridging

b. Smoothing

c. Knurling

d. V-grooving

ANS: C PTS: 1 REF: 254

24. In the ____ feed system, the electrode must have enough strength to be pushed through the conduit without kinking.

a. push-type

b. pull-type

c. push-pull-type

d. linear

ANS: A PTS: 1 REF: 254

25. Which of the following is true of GMA spot welding?

a. Welds can only be made in thin materials.

b. The weld cannot be made if only one side of the materials to be welded is accessible.

c. The weld cannot be made when there is paint on the interfacing surfaces.

d. The burning back of the thin material allows the thicker metal to be melted.

ANS: D PTS: 1 REF: 257

COMPLETION

1. MIG, MAG, and wire welding are other names for ____________________.

ANS: gas metal arc welding GMAW gas metal arc welding (GMAW)

PTS: 1 REF: 235

2. GMAW is relatively free from spatter because it uses a mode of metal transfer called ____________________ metal transfer.

ANS: axial spray

PTS: 1 REF: 238

3. The axial spray metal transfer process requires a current level above a critical amount, called the ____________________ current.

ANS: transition

PTS: 1 REF: 238

4. ____________________ transfer can be used on thin materials and at a very low current range.

ANS: Globular

PTS: 1 REF: 238

5. ____________________ systems interlock the power supply and wire feeder.

ANS: Synergic

PTS: 1 REF: 239-240

6. The ____________________ rate, measured in inches per minute or pounds per hour, is the rate at which the arc consumes the wire.

ANS: wire melting

PTS: 1 REF: 244

7. The ____________________ rate is the measure of the weld metal deposited.

ANS: deposition

PTS: 1 REF: 244

8. The relationships between current and voltage with different combinations of arc length or wire-feed speeds are called ____________________ characteristics.

ANS: volt-ampere volt ampere

PTS: 1 REF: 245

9. The rate of voltage decrease as the amperage increases within the working range is known as ____________________.

ANS: slope

PTS: 1 REF: 246

10. The ____________________ is the distance from the contact tube to the arc measured along the wire.

ANS: electrode extension stickout

PTS: 1 REF: 249

SHORT ANSWER

1. Explain the axial spray metal transfer process.

ANS:

This process is identified by the pointing of the wire tip from which very small drops are projected axially across the arc gap to the molten weld pool. There are hundreds of drops per second crossing from the wire to the base metal. These drops are propelled by arc forces at high velocity in the direction the wire is pointing. This projection of drops enables welding in the vertical and overhead positions without losing control of transfer. Some axial spray transfers using high current settings can produce a large molten weld pool that is very fluid, and the weld may be difficult to control in out-of-position welds. Because the drops are very small and directed at the molten weld pool, the process is spatter free.

This spray transfer process requires three conditions: argon shielding (or argon-rich shielding gas mixtures), DCEP polarity, and a current level above a critical amount called the transition current.

PTS: 1 REF: 238

2. Explain why the power supply is critical in the short-circuiting transfer process.

ANS:

The power supply is most critical. It must have a constant potential output and sufficient inductance to slow the time rate of current increase during the short-circuit interval. Too little inductance causes spatter due to high current surges. Too much inductance causes the system to become sluggish. The short-circuiting rate decreases enough to make the process difficult to use. Also, the power supply must sustain an arc long enough to premelt the electrode tip in anticipation of the transfer at recontact with the weld pool.

PTS: 1 REF: 238

3. Explain why the use of GMA welding can help reduce waste of filler metals.

ANS:

GMA welding’s 98% deposition rate of filler metal into the weld makes it one of the most efficient welding processes. Filler metal carries a high cost when it does not get deposited into the weld because of spatter or electrode stubs and becomes wasted material. Using GMA welding will reduce waste.

PTS: 1 REF: 244

4. Explain how to measure the wire-feed ipm.

ANS:

To accurately measure wire-feed ipm, snip off the wire at the contact tube. Squeeze the trigger for 6 seconds; release and snip off the wire electrode. Measure the number of inches of wire that was fed out in the 6 seconds. Now using basic shop math, multiply its total length in inches by 10. The result is how many inches of wire were fed per minute.

PTS: 1 REF: 246

5. Explain how the GMAW molten weld pool is affected by the travel speed.

ANS:

Because the location of the arc inside the molten weld pool is important, the welding travel speed cannot exceed the ability of the arc to melt the base metal. Too high a travel speed can result in overrunning of the weld pool and an uncontrollable arc. Fusion between the base metal and filler metal can completely stop if the travel rate is too fast. If the travel rate is too slow and the weld pool size increases excessively, it can also restrict fusion to the base plate.

PTS: 1 REF: 249

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