Inductive heating

Induction furnace, current density distribution  39,7kB

The numerical field calculation is a powerful tool to compute, for example, the induced power or the movement of the metal in the furnace?s melt. The calculations can be used to optimise the furnace?s geometry or the frequency of the currents in the coils. The picture shows the computed current densities in the coils and in the melt. The department developed several software packages that can optimise the efficiency and compute different coil arrangements, multi-frequency power supply, and the temperature while the furnace is being charged.

Induction furnace		Structural deformation

A 3D Finite Element analysis of the stray field of the induction furnace yields important information on the magnitude of the electromagnetic fields, which surround the furnace and which the service personnel is exposed to. As the 3D-FEM analysis can be carried out when the furnace is being designed, constructive measures for shielding can be planned in an early stage. Measurements have shown the accuracy of the stray field calculations.

Furnace sectional drawing 37,3kB

Animation of sectional drawing 1,13MB or of a model 1,82MB

The melting temperature can be estimated during furnace operation accurately by means of identification methods. Thus, the temperature can be used as an input value for the alloy process and the alloy process can be performed in its optimum even at different load levels. Another Finite Element software package of the department deals with the three-dimensional numerical calculation of the mechanical oscillations of the furnace and the acoustic noise they produce. The oscillations are caused by electromagnetic forces which are produced during the operation of the furnace. The results of this software package could also be verified by measurements. Therefore, this software package gives valuable insight into the mechanisms of electromagnetic, acoustic and structural properties of an induction furnace. It can be used to investigate the effects that constructive changes have on noise emissions without having to build expensive prototypes and do elaborate measurements.

Induction furnace, acoustic noise  37kB

Heating metal sheets is another possible application for inductive heating devices. They are an interesting alternative to the hot air processes, which are used currently. In inductive heating devices the metal sheet passes continuously through an inductor. One problem of these devices is the inhomogeneous temperature distribution in the metal sheet.

Inductor for metal sheet heating		Model of metal sheet heating 73,6kB and animation 1,07MB

The department developed a transient Finite Element software package that calculates the spatial distribution of the eddy currents, which are induced by the alternating magnetic field of the inductor in the metal sheet. The software package can also compute the spatial temperature distribution along the moving material. Therefore, with this software inductors can be properly designed for both different sheet materials and sheet widths.

Temperature distribution in the metal sheet  18,1kB

To achieve a uniform temperature distribution across the sheet width the inductor coils are pulsed. In addition, the software package was extended to ferro-magnetic materials. Because ferro-magnetic materials permeability depends on both the induction and the temperature, especially at the Curie-point, sophisticated solvers had to be developed.

 

Inductive heating of a billet for Thixoforming  20,6kB

Complex components are usually made by a forging or casting process while the material is either in its solid or liquid state. Thixoforming is the synthesis of both these processes. For Thixoforming the material must be heated up to a specific small temperature range, between solidus and liquidus temperature. In this temperature range the material is in a semi-solid, semi-liquid state and therefore can be handled by a robot and formed with minimal forces and energy into a complex shape.

Induced power, temperature distribution 23,9kB

To achieve optimal conditions during the moulding process the whole billet must have a homogeneous temperature in the specific temperature range. To analyze and optimize this transient heating process the department has calculated the eddy currents and the resulting temperature distribution within the billet taking all non-linearities into account. A new optimized geometry for the coil has been designed.
The research on the Thixoforming process is being done by an interdisciplinary group at the RWTH-Aachen.