Gas Metal Arc Welding Metal Transfer Modes
Brief Summary:
Spray
- Spray transfer GMAW was the first metal transfer method used in GMAW, best suited for welding aluminum and stainless steel while employing an inert shielding gas and a relatively thick electrode.
- Molten metal droplets (with diameters smaller than the electrode diameter) are rapidly passed along the stable electric arc from the electrode to the workpiece, essentially eliminating spatter and resulting in a high-quality weld finish.
- High amounts of voltage and current are necessary, which means that the process involves high heat input and a large weld area and heat-affected zone.
Short-circuiting
- Further developments in welding steel with GMAW led to a variation known as short-circuiting or short-arc GMAW, in which carbon dioxide shields the weld, the electrode wire is smaller, and the current is lower than for the globular method.
- As a result of the lower current, the heat input for the short-arc variation is reduced, making it possible to weld thinner materials while decreasing the amount of distortion and residual stress in the weld area.
Pulsed-spray
- The pulse-spray metal transfer mode is based on the principles of spray transfer but uses a pulsing current to melt the filler wire and allow one small molten droplet to fall with each pulse.
- The pulses allow the average current to be lower, decreasing the overall heat input and thereby decreasing the size of the weld pool and heat-affected zone while making it possible to weld thin work pieces.
- The pulse provides a stable arc and no spatter, since no short-circuiting takes place. This also makes the process suitable for nearly all metals, and thicker electrode wire can be used as well.
- The smaller weld pool gives the variation greater versatility, making it possible to weld in all positions.
- It generates lower heat input and can be used to weld thin work pieces, as well as nonferrous materials.
Globular
- GMAW with globular metal transfer is often considered the most undesirable of the four major GMAW variations, because of its tendency to produce high heat, a poor weld surface, and spatter.
- The method was originally developed as a cost efficient way to weld steel using GMAW, because this variation uses carbon dioxide, a less expensive shielding gas than argon.
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