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Hardening of sphere by induction heating
Induction heating explained
Induction heating is an accurate, fast, repeatable, efficient, non-contact technique for heating metals or any other electrically-conductive materials. By applying a high-frequency alternating current to an induction coil, a time-varying magnetic field is generated. The material to be heated is placed inside the magnetic field, without any contact to the coil. The alternating electromagnetic field induces eddy currents in the workpiece (material to be heated), resulting in resistive losses, which will be converted to heat inside the workpiece. Ferrous metals are heated by induction more easily than other materials due to the generated heat by hysterisis loss. Figure 1 shows a typical induction heating setup.
In this example, we show you how to simulate hardening of a sphere inside a coil using EMS coupled to thermal analysis.
Figure 1 - Induction heating setup
Electromagnetic-Thermal coupling capability of EMS
EMS ensures a Multi-physics simulation by the capability of coupling between electro-magnetic- structural- thermal field. In our case, an electro-magnetic- thermal simulation was carried on. To solve an induction heating problem in time varying domain, a transient magnetic study coupled to thermal analysis in EMS is needed.
Problem description
In this example, a sphere inside a coil will be heated by induction heating phenomenon. Figure 3 shows a 3D CAD of simulated model. The excitation waveform is sinusoidal and the frequency is 60 Hz.
Figure 3 - The simulated model
Simulation setup
After creating an Transient Magnetic study coupled to thermal analysis in EMS, four important steps shall always be followed:
- apply the proper material for all solid bodies
- apply the necessary electromagnetic inputs
- apply the necessary thermal inputs
- mesh the entire model and run the solver
Materials
Both coil and sphere are made of copper.
Table1 - Material properties
| Components / Bodies | Relative Permeability | Electrical Conductivity | Thermal Conductivity (W/m*K) | Specific Heat (J/Kg*K) | Masse Density (Kg/m^3) |
| Sphere/ Coil | 1 | 5.840e+7 | 401 | 384 | 8960 |
Electromagnetic inputs
In this study, only a wound coil is assigned as electromagnetic input.
| Number of turns | RMS total current | |
| Wound coil | 1000 | 6.468 A |
Meshing
Meshing is a very crucial step in any FEA simulation. EMS estimates a global element size for the model taking into consideration its volume, surface area, and other geometric details. The size of the generated mesh (number of nodes and elements) depends on the geometry and dimensions of the model, element size, mesh tolerance, and mesh control. In the early stages of design analysis where approximate results may suffice, you can specify a larger element size for a faster solution. For a more accurate solution, a smaller element size may be required.
Electromagnetic-thermal results
After finishing the setup, a successful run of Transient Magnetic simulation coupled to thermal analysis generates both magnetic and thermal transient results.
In the figure below is a 3D plot of magnetic flux density in the sphere at 50 ms.
In the figure 6,7, 3D plot of current density distribution shows the circulation of eddy current in the surface of sphere and figure 8 shows the temperature distribution in the sphere after 1.6 hour.
Conclusion
The electro-thermal simulation capability in EMS enables users to effectively test their coil designs for induction heating application. Engineers can now simulate multiple designs of their coils and choose the most effective coil based on the component to be heated. By studying the temperature distribution inside the heated component, one can complete understand the heating profile.