GMAW Welding Basic information Gas Metal Arc Welding

GMAW Welding Basic information

Gas Metal Arc Welding • Is a process where a continuously fed metal electrode (Wire) contacts the base metal and an electric arc produces heat. • The arc heat melts the base metal and electrode wire producing a weld puddle that solidifies into a weld bead. • The arc and weld puddle is shielded from atmospheric pollution by a shielding gas.

So What is GMAW ? Answer, Click the picture

Shielding Gas • Air in the welding zone is displaced by a shielding gas to “Shield” the molten weld pool contamination from Oxygen, Nitrogen and Hydrogen gasses that are present in our atmosphere. For more information click picture

GMAW Welds • Let’s look a little closer at the GMAW process 4 Shielding Gas Solidified Weld Metal 5 2 Arc 3 Weld Puddle Electrode 1

GAS Metal Arc Welding History and description. CLICK ON ICON TO SEE VIDEO CLIP

GMAW Advantages • The arc is more clearly visible by the operator with the absence of smoke from the burning flux. • GMAW has a higher welding speed; less time is spent stopping and removing slag and replacing welding rods. • Welds in all positions. • Produces high quality welds.

GMAW Disadvantages • Limited use outdoors, wind will blow the shielding gas away from the arc during the welding process. • SMAW welding cables can run up to fifty feet or longer while the MIG welder is limited to within about fifteen feet of the welder.

GMAW Components • • • Direct Current (DC) power supply Shielding gas source (cylinder) & regulator Manually held Gun Wire feeder controller Drive roller assembly Work clamp

• The GMAW process is performed using DCEP ( Direct Current Electrode Positive). • Some machines have the wire feeder attached but separate, see Picture A. • Some machines have the wire feeder inside see Picture B. A B

Gas Metal Arc Welding is GMAW • GMAW is commonly referred to as MIG welding. • During the GMAW process, a solid metal wire is fed through a welding gun and becomes the filler metal. • Instead of a flux, a shielding gas is used to protect the molten puddle from the atmosphere which results in a weld without slag.

GMAW electrode Wire • A metal wire Fed through the gun by the wire feeder. • It is measured by its diameter. • It is consumable (it becomes part of the weld bead). • Mild steel solid wires are usually plated with copper to prevent oxidation, aid in electrical conductivity and help increase the life of the welding contact tip.

AWS Classification of GMAW Electrodes (wires) ER 70 S-X Electrode Rod 70, 000 psi Min. Tensile Strength Solid Amount of Deoxidizers (cleaners)added to the wire to improve weld quality. X=2, 3, 4, 6, 7 or G

Shielding Gas • GMAW welding requires a shielding gas to protect the weld puddle. • Shielding gas is usually CO 2, argon, or a mixture of both. The gauges on the regulator show gas flow rate and bottle pressure

• Gas flow is set and measured in cubic feet per hour (CFH) NOT PSI. • The gauges on the regulators show gas flow rate (CFH) and cylinder pressure.

Possible causes for poor shielding gas coverage. Shielding gas cylinder empty or valve not open. The Shielding gas flow not set correct. Shielding gas flow blocked by spatter in Nozzle. Air movement disrupting the Shielding gas coverage. • Porosity is the result of poor shielding (holes in the weld bead). • • To see porosity click picture

Lets look at the wire gun and parts. Click on the picture

Manually held GMAW gun The Gas nozzle Contact tip Insulator Gas diffuser Gun trigger • Together, these components are responsible for guiding the welding wire through the GMAW gun and for establishing the electrical conductivity necessary to create the arc.

• Gas nozzle The device placed directly over the welding gun end. It encompasses the shielding gas, directing it to the weld pool for protection from atmospheric contamination. Click for more information

• Insulator A small non-conductive piece of material placed inside the welding gun to prevent the gas nozzle from becoming electrically charged. Part of the Nozzle A separate piece

• Contact tip This device is located on the end of the welding gun. It conducts the electrical current into the wire electrode as it passes through toward the puddle. • It is usually made of copper. Click for more information

• Shielding gas diffuser This device inside the welding gun spreads the gas flow through the gas nozzle for uniform shielding protection. Two Different styles

Wire gun trigger • A lever on the welding gun. When a welder pulls (squeezes) the trigger the welding process can begin. Click for more information

• Welding gun An instrument used in the Gas Metal Arc Welding processes that contains the components that conduct electricity, guides the wire electrode, directs the shielding gas, and houses the wire gun trigger.

3 things happen when the GMAW gun trigger is pulled: 1. The wire electrode begins to feed. 2. Shielding gas flows through the gun and out the nozzle. 3. The circuit becomes electrically “hot”. Current flows from the power source through the gun cable, gun, contact tip to the wire and across the arc. On the other side of the arc, current flows through the base metal to the work cable and back to the power source.

GMAW Wire drive roll feed Operation: • Wire is pinched between two rollers. • One roller is DC Motor driven when the operator pulls the gun trigger. • Other roller is gear driven by the first roller.

Drive roll assembly The drive roll, as the name implies, drives or feeds the wire through the gun by applying pressure on the wire. It is important to check the drive roll size and tension.

• The drive roll size should match the welding wire diameter. • Notice the. 035 V • This roll is for Steel wire. 035 diameter.

WIRE FEEDER The Main functions are to: ü Pull the wire from the spool and feed it to the arc. üControl wire feed speed (inches per minute) üRegulate the starting and stopping of wire Click for more feed. information

Work Clamp Connection • Make sure the clamp is in good working condition. • Grind off rust or paint, and ensure that the work clamp is connected as close to the work area as possible.

• During the welding process an electric arc is established from the electrode (Wire) to the workpiece, then back to the power source. • The workpiece clamp and lead becomes the path for the electricity from the welding process to return to the power source (the welding machine).

Poor WORK Connections • Poor work lead connections may arc and weld the connection to the workpiece. • Poor connections reduce the voltage at the welding arc. • This may cause poor arc starting, excessive spatter, poor bead shape, and reduced weld quality.

• Good work lead connections affect the welding arc and the quality of the finished weld. • Having good work lead connections are also important to minimize electrical shock hazards.

The Workpiece Connection is not a Ground Clamp. • Unfortunately, the workpiece connection and lead are often incorrectly called the ground by many welders. • The welding cable does not bring a ground connection to the workpiece. It provides a path for the electricity to return to the power source from the welding process.

Another reminder