Induction hardening in 3D using surface impedance
Induction hardening requires a transient thermal solution coupled to a time-harmonic electromagnetic solution where the workpiece is heated for a certain period and then the power source is switched off. This case study examines a 3-dimensional simulation. As shown in the figure, the workpiece is off-axis with respect to the coil.
The workpiece is made of stainless steel and the material properties (electric conductivity, thermal conductivity and volumetric heat capacity) are nonlinear and vary with temperature.
Results
Coupled simulation: The 3D coupled electromagnetic-thermal simulation capability in ThermNet is used to solve for the temperature from the time the power is switched on until it reaches a certain temperature on the surface. In this case, the power is switched on long enough to make sure that the surface temperature is raised to a certain level and then the power is switched off.
The 2-way coupling used in ThermNet makes sure that the effect of temperature on the material properties, and consequently, the effect on the power loss are taken into account. The material properties of the stainless steel used in the workpiece are defined at several temperatures and the system interpolates between these.
Surface impedance: In the case of induction hardening, the intention is to heat just the surface. For this reason, the frequency that is used in the power supply is high and the skin depth very small. In a case like this, the user can increase the computation speed significantly by using the surface impedance feature in MagNet to represent the workpiece. In this simulation, the surfaces of the workpiece were assigned the surface impedance condition.
MagNet automatically calculates the surface impedance based on material properties. As the temperature rises, the surface impedance is continuously updated to account for the resulting change in skin depth.
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