Final answer:
In GMAW (MIG) welding, there are four primary modes of metal transfer: short-circuiting, globular, streaming, and spray transfer, each with its own characteristics and suitable applications based on metal thickness and other welding parameters.
Step-by-step explanation:
The Gas Metal Arc Welding (GMAW) process, commonly known as Metal Inert Gas (MIG) welding, involves several types of metal transfer. In GMAW, an electric arc is formed between a consumable wire electrode and the metal workpiece, melting both to form a weld pool. There are four primary modes of metal transfer in GMAW: short-circuiting, globular, streaming, and spray transfer.
Short-circuiting transfer is characterized by repeated short-circuits that occur when the wire electrode touches the weld pool, causing the metal to transfer in small droplets across the arc. Globular transfer occurs when the molten metal forms larger droplets, which detach and fall into the weld pool. This is often associated with higher heat input and may lead to increased spatter.
Streaming or projected transfer is a transition between globular and spray transfer, where the droplets are propelled across the arc in a steady stream. Spray transfer is used for welding thicker sections as the molten metal is transferred in small droplets in a spray pattern at a higher current and voltage. The chosen transfer method affects the quality and characteristics of the weld, such as penetration, heat input, and spatter amount.