Induction Heating for Weld Stress Relief
Seasoned welders know that induction heating is a fast, efficient method for preheating and stress relieving a weld area.Induction heating for weld stress relief also allows you to heat a very precise area, reducing cycle time and energy requirements and providing a more uniform, consistent temperature throughout the weld zone.
Why post weld heat treatment?
However, induction is an even more effective solution when used for post-weld stress relief. Welding creates stresses that, if not relieved, can lead to unwanted dimension changes, distortion or premature failure of the finished part. Using induction for stress relieving can slash two hours off of your overall welding cycle time.
For stress relieving, an induction system is ideally suited to provide the rapid heating required to bring metal up to its Curie temperature. The Curie temperature is the point at which the magnetic permeability of a ferromagnetic material reduces to one.
The alternating current passed through an induction coil generates lines of magnetic flux that extend through the susceptor assembly, heating it up to its Curie temperature. The magnetic flux lines are captured by a ferritic plate that is cut and formed to fit around the perimeter of the susceptor assembly. The plate acts as a concentrator and insulator, preventing the lines of magnetic flux from heating up any area outside of the susceptor assembly and restricting the heat output to the weld stress relief area.
The alternating electromagnetic field that the induction coil generates causes an oscillation of the magnetic dipoles inside of the ferromagnetic material. This push-pull between the electromagnetic fields produces a secondary flow of current, called an eddy current, that excites the molecules within the material, generating heat. This is the primary source of heating in induction. In addition, the hysteresis losses associated with the oscillation of the magnetic dipoles generate a small amount of additional heat.