In DC arc welding, magnetic bias blowing is the phenomenon of the electromagnetic force affecting the welding arc.
It has a significant negative impact on the welding process and quality, and must be addressed to ensure proper welding quality.
Related reading: The Ultimate Guide to Welding
There are many factors that cause magnetic bias blow, specifically:
1. Arc striking and arc stopping are welded at the edge of the workpiece
The magnetic flux density becomes compressed and distorted, causing a difference in magnetic flux density in front of and behind the arc.
The magnetic flux density near the edge of the workpiece is stronger than the magnetic flux density farther from the edge.
Based on the physical law of force exerted by the current in a magnetic field, the arc will move forward when starting, and magnetic bias blowing occurs when the arc deviates backwards during arc extinguishing.
Elimination measures:
- Add run on plate and run-off plate;
- Altering the travel angle of the electrode (or welding wire) by reversing it towards the side of the arc blow.
2. The position of ground wire is wrong with the welding direction
Due to the higher magnetic flux density behind the arc compared to the front of the arc, the arc tends to move forward.
Elimination measures:
- The ground wire is connected to the arc extinguishing end;
- Change the traveling angle of welding rod (or welding wire);
- Use non-magnetic ground clamps.
3. Multiple arcs close
When welding T-shaped or corner joints, simultaneous welding on both sides of the vertical plate is often used to reduce welding deformation and increase efficiency.
However, if this process is not handled properly, it can result in magnetic bias blowing.
Elimination measures:
- Use AC and DC power supply for simultaneous welding;
- Change the traveling angle of welding rod (or welding wire).
4. Unequal thickness of workpieces
When welding workpieces with varying thickness, magnetic bias blow can occur, as the arc is biased towards the thicker side of the workpieces. This is due to the strong magnetic field attraction of thicker workpieces, which greatly attracts charged arc particles.
Elimination measures:
- Adopt short arc welding;
- The angle between the electrode and the plate is larger;
- The ground wire is clamped on one side of the thick plate (change the position of the ground wire).
5. Weld arrangement
The arrangement of the welding seam greatly affects magnetic deflection blowing.
Magnetic deflection blow is more likely to occur in the following two scenarios:
- A large groove depth in butt welds
- Internal fillet welds.
Elimination measures:
- Adopt short arc welding;
- Increase the number of tack welds;
- Use AC power supply for welding.
6. The welding direction and sequence are longer in the weld
If straight-through welding is used, it can result in both significant welding deformation and magnetic bias blowing. In this situation, back welding is the most effective method to prevent magnetic biasblow.
7. Clamp and base plate
The fixtures and base plates can also greatly impact magnetic bias blowing. To reduce magnetic bias blow, using non-magnetic materials for clamps and base plates and adding additional plates are effective measures.
