Arc Blow — What It Is and Why It Matters
Arc blow is the deflection of the welding arc from its intended path by magnetic fields in the workpiece. The arc wanders, flickers, or pushes to one side, causing erratic bead placement, lack of fusion, porosity, and excessive spatter. Arc blow occurs almost exclusively with DC welding and is most severe near the ends of magnetic workpieces and around ground clamp connections.
The magnetic fields causing arc blow can originate from residual magnetism in the workpiece, the magnetic field created by the welding current itself, proximity to magnetized fixtures or equipment, and unbalanced current path geometry between the arc and the ground connection.
Mitigation strategies include switching to AC welding (the alternating polarity disrupts the magnetic interference), repositioning the ground clamp, wrapping the work lead around the workpiece to create an opposing magnetic field, demagnetizing the workpiece, welding toward heavy tack welds that anchor the arc, and using short arc lengths that are more resistant to deflection.
Frequently Asked Questions
What causes arc blow?
Arc blow is caused by unbalanced magnetic fields around the welding arc. Common causes include: welding near the end of a piece (the current path becomes asymmetric), poor ground clamp placement creating unequal current distribution, residual magnetism in the workpiece, and proximity to magnetized equipment or heavy steel masses.
How do I fix arc blow?
Try these in order: move the ground clamp to a different location (try both ends of the workpiece), reduce arc length, change welding direction, switch to AC polarity if your process and electrode allow it, or wrap the work cable around the workpiece several times near the weld to create a counteracting magnetic field.