GMAW Welding

Short-Circuiting Metal Transfer Mode

A continously fed solid or metal-cored wire electrode is deposited during electrical short-circuits. It's low heat input mode of metal transfer, and uses the pinch effect

Globular Transfer Mode

A continously fed solid wire electrode is deposited in combination of short-circuits and gravity assisted large drops

The Welding Arc

A region of high complexity that's comprised physical forces and chemical reactions. Interaction of the components of the arc affects metal transfer and quality of the finished weld

Advantages of Pulsed Spray Transfer

Absent or low levels of spatter More resistant to lack of fusion defects Excellent weld bead appearance High operator appeal Reduces the tendency for arc blow Handles poor-fit up

Advantages of Short-Circuiting Metal Transfer

All position capability Poor-fit up really well Capable root pass Higher operator appeal and ease of use Low heat input reduces weldment disortion Higher electrode efficiencies, 93% or more

Filler Metals For Axial Spray Transfer

Carbon and Low Alloy Solid Steel, Carbon and Low Alloy Composite Steel, and Stainless Steel

Axial Spray Transfer Mode

Continously fed solid or metal-cored wire electrode is deposited a higher energy level, resulting in a stream of small molten droplets.

Limitations of Pulsed Spray Transfer

Equipment to support the process is expensive rather than traditional systems Blends of argon based shielding gas is more expensive than catbon dioxide Adds complexity to welding Requires windscreens

Surface Tension Forces

Forces that are normal to the surface of a molten droplet. Act both on interior and the exterior surface of the droplet. Together serve to support the form of a molten droplet. Inward pull of the of the forces applied to the surface.

Advantages of Axial Spray Transfer

High deposition rates High electrode efficiency of 98% or more Employs a wide range of filler metal types in an equally wide range of electrode diameters Excellent weld appearence

Jet Forces

Higher currents

Limitations of Globular Transfer Mode

Higher spatter levels result in costly cleanup Reduced operator appeal Prone to cold lap or shut incomplete fusion defects, costly repairs Weld bead shape is convex and weld exhibits poor wetting at the toes Electrodes efficiency to a range of 87-93%

Pulsed Spray Transfer Mode

Highly controlled variant of Axial Spray Transfer, the welding current is cycled between a high peak current level to a low background current level

Advantages of Globular Transfer Mode

Inexpensive CO2 shielding gas, but is frequently used w/ argon +CO2 blends Capable of making welds at high travel speeds Inexpensive solid or metal cored electrodes Welding equipment is inexpensive

Limitations of Axial Spray Transfer

Restricted to flat and horizontal Welding fume generation is higher Higher-radiated head, generation of a very bright arc, requires extra welder and bystander protection Shielding used to support AST costs more than 100% CO2

Limitations of Short-Circuiting Metal Transfer

Restricted to sheet metal thickness range Open roots of groove joints on heavier sections Poor welding procedure control results incomplete fusion Colp lap and shut additional terms that serve fusion defects Poor procedure control results in excessive spatter, increases weldment cleanup cost Prevent loss of shielding gas to the wind, windscreens

Modes of Metal Transfers

Short-circuiting metal transfer mode, Axial Spray Transfer, Pulsed-Spray Transfer, and Globular Transfer

Background Current

The descent to the lower current (provides arc stability and is largely responsible for the overall heat of the weld)

Peak Current

The highest point, one molten droplet is attached

History of GMAW

The industrial introduction was started in the late 1940's, the development of the GMAW process was the early 1950's and the power source technology improved was in the 1950's

Frequency

The number of times the period occurs a second or cycles per second

Period

The time, which includes the peak current and the background current (is known as a cycle)

The Behavior of The Arc are Influenced By:

Type of diameter of the filler metal Base metal conditions- clean or millscale Shielding gas Welding parameters - voltage and current Interaction of physical forces - gravity, surface tension, jet forces, and electromagnetic force

Electromagnetic Forces

When currents flows through a conductor, magnetic field builds and surrounds the conductor. Mathmatically proportional to the square of the applied current affect the metal transfer