Induction welding

Induction welding is a form of welding that uses electromagnetic induction to heat the workpiece. The welding apparatus contains an induction coil that is energised with a radio-frequency electric current. This generates a high-frequency electromagnetic field that acts on either an electrically conductive or a ferromagnetic workpiece. In an electrically conductive workpiece, such as steel, the main heating effect is resistive heating, which is due to magnetically induced currents called eddy currents. In a ferromagnetic workpiece, such as plastic doped with ceramic particles, the heating is caused mainly by hysteresis as the magnetic component of the electromagnetic field repeatedly distorts the crystalline structure of the ferromagnetic material. In practice, most materials undergo a combination of these two effects.

As suggested above, nonmagnetic materials such as plastics can be induction-welded by implanting them with metallic or ferromagnetic compounds, called susceptors, that absorb the electromagnetic energy from the induction coil, become hot, and lose their heat energy to the surrounding material by thermal conduction.

Induction welding is used for long production runs and is a highly automated process, usually used for welding the seams of pipes. It can be a very fast process, as a lot of power can be transferred to a localised area, so the faying surfaces melt very quickly and can be pressed together to form a continuous rolling weld.

The depth that the current, and therefore heating, penetrates from the surface is proportional to the frequency of the current flowing in the coil. The temperature of the metals being welded and their composition will also effect the penetration depth. This process is very similar to resistance welding, except that in the case of resistance welding the current is delivered using contacts to the workpiece instead of using induction.

ee also

*Induction heating

References

AWS Welding Handbook, Volume 2, 8th Edition