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April 26, 2022
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Using Simulation to Evaluate Induction Coil Performance

Aug. 24, 2020
Can computer simulation be used to gauge billet-heating performance and increase induction coil service life?

The value of simulation in forging operations not limited to planning projecting and planning forming processes: there is an emerging understanding of simulation's role in the wider scope of plant operations, and indeed in system maintenance.

The CENOS Platform introduced in 2019 is a 3D simulation software focused specifically on induction heating that uses open-source components and algorithms, making it affordable for small and medium-sized operations. CENOS Platform is capable of simulating various types of induction heating for forging, including both static heating and progressive heating where the billet is moved through the coil with constant velocity.

Because induction heating systems are so critical to forging operations, it's a logical step to apply simulation to evaluate the performance of those systems. Induction coils, for example, are critical components of an induction heating system: without properly working coils, billet heating become unreliable, and that reduces productivity throughout the forging production sequence.

Let's consider, then, whether computer simulation can be used to evaluate induction coils' performance.

Many induction coils are low-maintenance elements of the furnace unit, particularly the coils that are used on lower power densities and those without magnetic flux concentrators. If any leaks develop, the coils should be removed from production, cleaned, and repaired. In the worst cases, they should be replaced.

Coil performance factors — Some of the most common issues affecting inductor performance are:

Mishandling. Usually, human error can be the reason inductors are physically damaged, due to improper care. Often they are dropped, knocked off workbenches, or not cleaned or stored properly. All this can be avoided with good housekeeping and safety rules for employee training.

Arcing. Arcing may occur due to the coil coming into contact with a workpiece, or it could be the result of foreign debris. Anytime arcing occurs, production should be stopped and the condition remedied. If the workpiece is hitting a coil, the condition could be due to vibration resulting from restriction of the coil to the cooling water; poor positioning of the workpiece relative to the coil; or eccentric rotation of the workpiece.

Arcing across the turns of a coil or bus support of the coil usually is due to scale or oil contamination in the quench system. Better cleaning of the coil or scale removal from the quench system should be done.

Arcing may occur across the flux concentrator as it degrades, and is another factor that should be monitored and addressed.

Fatigue. Coils with high current concentrations may exhibit flexure, particularly at soldered joints that have abrupt changes in direction of the cooling water. Ultimately this may cause coil fatigue and lead to it breaking.

Also, some coils may have localized current concentrations, which can cause the coils to overheat and fail. Coils usually fail at a stress point, where there is an abrupt change in direction of the coil, such as a right angle with a brazed joint.

Deterioration of electrical contact. The bolts holding the coil or bus to electrical contact may loosen, causing the current to flow through the bolt. This results in overheating and melting of both, with subsequent loss of current to the coil.

Degradation of the magnetic flux concentrator. All concentrators degrade over time in service. This is a natural phenomenon; the concentrator material degrades due to the intensity of the magnetic flux field and the heat from radiation.

Overheating. Overheating may result in coil failure. Water flow can be reduced by cooling system problems, or leaks can occur for any reason. Flux concentrators also can have insufficient cooling, resulting in overheating and premature failure. To fix this, one must either increase the water flow by removing sharp turns, adding in-line pumps or larger cooling passages, or by changing the coil design.

Better Coil Design Will Help — Inductor overheating can cause the coil to crack, crumble, "burn," or even melt. Overheating poses the biggest threat to induction coil service life, so an overheating coil needs either more cooling water or a better design.

Making a better design with multiple lab tests is the traditional and most common way to proceed, but is there a faster, cheaper way to increase a coil service? Enter simulation.

Using good design practices, one can improve coil longevity and improve production quality. By eliminating failure points in the initial design, proper material selection, improved cooling, and proper magnetic flux control, induction tooling life can be increased. Computer simulation has been proven to be an effective tool for predicting not only electromagnetic parameters of a designed system, but also heat patterns in a given part and in the induction coil itself.

For the first case, a simple, 2D wedge-shaped inductor profile with a flux concentrator was simulated at 10kHz.

The second case featured a radically different cooling channel as well as a filleted nose and slightly cut concentrator.

To simulate the cooling effect from the fluid flow in the channel, a convection boundary condition was applied to the inside of the inductor. The heat-transfer coefficient was decreased in the smaller parts of the profile to approximate boundary layer fluid effects.

The results highlight clearly the importance of cooling channel shape. In the first case, the nose of the inductor reaches over 600 °C.

Most experienced induction coil designers will understand how the changes demonstrated here affect the temperature distribution, however it is very hard to predict the magnitude of these effects.

CENOS allows the user to explore these effects at various frequencies, powers, and geometries — saving countless hours of physical experimenting. Using simulation thus makes it feasible, and effective, for evaluating induction coils and induction system.

Martins Vilums is the head of marketing for CENOS Platform, a desktop software for fully automated processing of CAD files for a workpiece, coil, and flux concentrators, and presenting the simulated heating results in 3D. The software is downloadable from