Gas metal arc welding is a versatile and fast welding process that produces a significantly strong joint finish. It is an ideal welding process for a variety of metal types, including aluminium, carbon steel, stainless steel and copper. Consequently, the process is very popular in many manufacturing operations.
The gas metal arc welding process uses three major modes to transfer metal from the electrode to the work piece – which are short circuit transfer, spray transfer and globular transfer. Several variables will dictate which type of transfer mode you should use, such as the welding current, electrode surface, shielding gas and the contact tip-to-work distance.
Short circuit transfer
The short circuit transfer mode uses a low heat input where the transfer of metal from the electrode to weld puddle occurs through a series of electrical shorts. It produces a small, fast-freezing weld suited for joining thin sections and for bridging large root openings. Metal is transferred from the electrode to the work piece by direct contact at a rate of 20 to 200 times per second. It is the most common transfer mode used for gas metal arc welding.
Advantages of short circuit transfer include:
- Good for thinner applications (1/8” & under)
- Low heat prevents blowing through the base material
- All-position welding
- Low cost – can be powered through low-end sources
- Great application for gaps
Limitations of short circuit transfer include:
- Limited to sheet metal
- The spike in amperage generates spatter, which increases clean up time and reduces electrode efficiency
- Poor welding procedure can result in incomplete fusion
Spray transfer mode is ideal to use on thicker metals for butt or fillet joints due to its high amperage and voltage levels. The spray transfer process works by a spray of molten metal that is transferred over the arc – similar to water coming out of a garden hose with a restricted open. These droplets are deposited at a higher-energy level and propelled axially across the arc.
Advantages of spray transfer include:
- Very little spatter generation
- Good metal fusion and penetration
- High metal deposition rates
- Capable of using larger diameter electrode wires
Limitations of spray transfer include:
- Limited to flat and horizontal weld positions
- Only suitable for thicker materials
- Welding fume generation is higher
The globular transfer mode utilises a continuously fed solid or metal-cored wire electrode that is deposited in a combination of short circuits and gravity-assisted large drops. The difference between globular transfer and short circuit transfer is in the amount of current and voltage levels – globular transfer uses a higher current and voltage level. The globular transfer mode is typically difficult to control and the spatter is severe.
Advantages of globular transfer:
- Welding equipment is inexpensive
- Welds at very high travel speeds
- CO2 shielding gas is inexpensive
Limitations of globular transfer:
- High spatter can result in costly clean-up
- Reduced operator appeal
- Prone to incomplete fusion defects
- Weld bead shape is convex
The team at Rapid Fab are experts in the welding and fabrication industry and are happy to give advice on gas metal arc welding. Contact the team at 07 5529 2622 to discuss anything and everything to do with welding and welding materials.