INTRODUCTION TO(GMAW)

GAS METAL ARC WELDING

GMAW Unit 1 Lesson 1Objective: Demonstrate proper setup and

maintenance of GMAW equipment.

GMAW PROCESSGas 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).

GMAW EQUIPMENTThe 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.

WHAT DOES THE ABBREVIATION GMAW STAND FOR?A.) Gas Machine Arc Welding

B.) Gas Metal Arc Welding

C.) Gas Material Arc Welding

D.) Gas Method Arc Welding

IN A GMAW SYSTEM, HOW IS THE ELECTRIC CURRENT TRANSFERRED TO THE ELECTRODE?A.) Through the gun cable and liner

B.) Through the contact tube

C.) Through the wire feed rolls

D.) Through the gas diffuser

PROCESS SETUPGMAW 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

POWER SUPPLIESThe 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.

GMAW GUNS

Push Pull Gun

Standard Gun

Spool Gun

WHAT TYPE OF POWER SOURCE IS USED FOR GMAW?A.) Constant Current

B.) Alternating Current

C.) Variable Voltage

D.) Constant Voltage

GMAW MODES OF METAL TRANSFERThere are 3 basic

types of metal transfer associated with GMAW.

Short Circuit Transfer

Globular Transfer Spray Transfer

SHORT CIRCUIT TRANSFERCommonly 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.

SHORT CIRCUIT TRANSFER

WHICH OF THE FOLLOWING IS AN ADVANTAGE WITH SHORT CIRCUIT MODE OF METAL TRANSFER?A.) Small diameter wire, expensive.

B.) Spatter

C.) Cold starts, can cause cold lap on restarts.

D.) Welds in all positions

GLOBULAR TRANSFERThe 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

GLOBULAR TRANSFER

WHICH OF THE FOLLOWING IS A DISADVANTAGE GLOBULAR MODE OF METAL TRANSFER?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

SPRAY-ARC TRANSFERSpray-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

SPRAY-ARC TRANSFER

MODES OF TRANSFER Transitions from Short Circuit -

Globular arc - Spray arc

WHICH OF THE FOLLOWING IS A DISADVANTAGE SPRAY-ARC MODE OF TRANSFER?A.) High quality welds

B.) High metal deposition

C.) Faster welding speedsD.) Can only be used in the flat and horizontal position when making fillet welds

PULSED SPRAY TRANSFERA 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