# Induction Heating and Hardening

#### Induction Heating

Temperature profile through a nickel plate which has been induction heated by a coil.

Induction heating occurs when eddy currents are excited in conductive media. This phenomenon can be modelled using Opera’s multi-physics capabilities.

Heating arising from simple AC or from complex transient excitations can be simulated to provide accurate thermal results. Additionally, electromagnetic forces, thermal expansion and mechanical stress can also be included in the simulation if required.

One of the features available in Opera is a surface boundary condition. This can be used to model eddy current flows and resultant heating without having to capture surface currents using a fine numerical mesh and it is therefore computationally efficient. To illustrate this, the method has been used to calculate the temperature distribution in a nickel plate that has eddy currents induced by an AC coil placed close to the plate.

Velocity joint casing. The inner surface is to be induction hardened using the exciter coils shown in red.

#### Induction Hardening

An interesting use of induction heating is so called induction hardening. This is used when selective surfaces of a steel fixture are induction heated and then quenched to cause a martensitic surface transformation. This increases the hardness of the surface and thereby its wear resistance.

The example (right) shows a constant velocity joint casing used in an automotive application. In this case it is the inner surface that was to be hardened. Induction heating was provided by a series of coils (coloured red).

Section through the velocity casing showing the temperate profile resulting from induction heating.

The coils were operated at a relatively high frequency of 10 kHz to ensure eddy currents, and thereby heating, were constrained to the surface of the casing.

This simulation included temperature dependent electrical conductivity and permeability. The latter is important because the surface to be hardened is raised above its Curie temperature before the martensitic transformation occurs.