In DC arc welding, the phenomenon of magnetic bias blowing caused by electromagnetic force on the welding arc is called magnetic bias blowing.
It has an important adverse effect on the welding process and quality.
Only by overcoming it can the welding quality be guaranteed.
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 is squeezed and deformed, resulting in the situation that the magnetic flux density in front of and behind the arc is different.
The magnetic flux density near the edge of the workpiece is higher than that far away from the edge of the workpiece.
According to the physical law of the force exerted by the current in the magnetic field, the arc tends to the front when starting the arc;
Magnetic bias blowing phenomenon when the arc is deflected to the rear during arc extinguishing.
- Add run on plate and run-off plate;
- Change the travel angle of the electrode (or welding wire) (reverse to the side of the arc blowing).
2. The position of ground wire is wrong with the welding direction
As the magnetic flux density behind the arc is greater than that in front of the arc, the arc is inclined to the front.
- 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 joints or corner joints, in order to reduce welding deformation and improve welding efficiency, the method of simultaneous welding on both sides of the vertical plate is usually adopted.
However, if this process measure is not properly considered, magnetic bias blowing will occur.
- 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 different thickness, magnetic bias blow will occur (the arc is biased to the thicker side of the workpieces), because the magnetic field attraction of thick workpieces is large, which has a great attraction to charged arc particles.
- 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 welding seam has great influence on magnetic deflection blowing.
Magnetic deflection blow is easy to occur in the following two cases: first, the groove depth of butt weld is large, and second, the internal fillet weld.
- 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 adopted, not only large welding deformation is easy to occur, but also magnetic bias blowing will occur.
In this case, back welding is the best way to avoid magnetic bias blowing.
7. Clamp and base plate
Fixture and base plate also have great influence on magnetic bias blowing.
Using non-magnetic materials as clamps and base plates and adding additional plates are effective measures to reduce magnetic bias blow.