Page 32 - Metallforming Magazine December 2020

Fabrication: Welding Well
To cure excess spatter:
1. Adjust the welding parameters. Excess amperage or insufficient voltage can make the arc too cold and result in spatter. Try reducing the wire-feed speed (when using GMAW ) or increasing the voltage.
2. Check the wire stickout. Excess stickout can cause spatter.
3. If shielding with straight CO2, try switching to a CO2- Ar mixture.
4. Ensure that surfaces are clean. Metal covered in paint, oil, rust or dirt can cause spatter.
5. Be sure to use the right polarity setting, as the wrong polarity can cause a lot of spatter.
Weld Cracking
Cracks that form in the weld bead will reduce the strength of the weld. Cracks can be hot or cold.
Hot cracks can occur when the weld metal is just below the solidus (solidifying) temperature—the highest temper- ature at which an alloy remains solid. A lack of ductility at this temperature can make the metal brittle. Hot cracking usually appears along the weld axis in the middle of the weld.
Cold cracks (or hydrogen cracking) usually occur in high- strength steels where hydrogen is present in the weld metal. Tensile stress on the weld joint also can contribute to cracking.
To help prevent cracking:
1. Reduce heat input. Lower heat helps the weld metal cool more quickly, so it spends less time near the solidus in a brittle state.
2. Be sure to use the correct, recommended filler metal. When welding austenitic stainless steels, particularly prone to cracking, use filler metal containing ferrite.
3. Ensure that there are no sources of hydrogen, such as paint, rust, water, oil, grease or coatings, that might con- taminate the weld.
Incomplete Penetration
...is when the weld metal does not penetrate the full thickness of the base material. The weld bead should fully penetrate the toe of a fillet weld; shallow fusion can lead to
joint failure. The most common causes of incomplete pen- etration are insufficient weld current and incorrect workpiece alignment.
To troubleshoot incomplete penetration:
1. Check the welding current. Increasing amperage will provide more power to melt the filler metal.
2. Ensure a properly fixtured weld joint, with the proper gap and alignment.
3. Reduce travel speed.
Burnthrough
The opposite of incomplete penetration, burnthrough occurs when the weld metal penetrates all the way through
the base material. This occurs most often when welding thin sheet metal (less than 0.25 in. thick).
To address burnthrough:
1. Reduce the voltage or the wire-feed speed to reduce heat input to the weld. Excess heat is the most common cause of burnthrough.
2. Increase travel speed. This works particularly well when welding thin aluminum where heat can build up quickly.
Cold Lap/Lack of Fusion
Cold lapping or lack of fusion occurs when the weld metal fails to properly fuse with the base metal. This usually
occurs when the weld pool grows too large and overlaps onto the toe of the weld, or if the arc is not properly directed into the weld joint. If the heat of the arc cannot sufficiently melt the base metal, lack of fusion can occur.
To troubleshoot:
1. Check the welding-gun angle; be sure to hold the gun at an angle between 0 and 15 deg.
2. Try increasing travel speed and keep the arc on the leading edge of the weld puddle.
3. Ensure that the amperage is high enough to properly fuse the metal. Increase the voltage and wire-feed speed where necessary.
4. If using the weave technique, try holding the arc on the weld-joint sidewalls for a little longer period of time, to help increase heat input and promote good fusion. MF
30 MetalForming/December 2020
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