Induction Coil Design & Engineering

It has been said that it is easy to design an induction heating coil that doesn’t work at all, and very difficult to design an induction heating coil that works really well. Fluxtrol has a reputation for solving the most complex coil design challenges with overwhelming success.

Fluxtrol focuses on designing induction heating coils that come as close as possible to achieving your ideal process. The Fluxtrol induction heating coil design team has many years of combined experience in modeling induction processes, designing induction heating coils, manufacturing induction heating coils, and operating induction heating systems.

How Fluxtrol designs a coil

Design starts with a full application description: performance and functionality targets, the part, the production rate and the machine and power supply available. Fluxtrol then deploys computer simulation , which it uses to begin nearly every project, to predict heating and electrical parameters. After simulation the coil is fully drawn in 3D for manufacturing. The engineering stage completes the coil head, SMC design, water cooling path, mechanical components and insulation. The full flow, from pre-production to existing-production applications, is on the induction coils page .

What a good coil design balances

The ASM Handbook Volume 4C chapter on inductor design lists what a heat treating coil must do: meet specifications at the desired rate, tolerate manufacturing variations, mount in the machine, match the power supply, deliver quench, last, run efficiently and repeat from coil to coil. Design is also shaped by part material, geometry, production rate and heat treatment specification, which set energy, frequency range and whether single-shot or scanning suits the job. Frequency affects power required, heating time, coil losses, local power distribution and the structural support needed.

Heat pattern control

When some areas must be hardened and others not, or case depths differ, single-shot coils must build the variation into the design. Three tools are used:

Coupling gap. The closer the coil is to the part, the more intense the heating, because current in the part flows in a narrower band.
Coil copper profile. Changing the geometry of the heat face, for example a larger gap in the middle than at the ends, shortens transition zones and keeps the pattern out of undercuts or snap ring grooves.
Magnetic flux controllers. SMC controllers concentrate the field and let the pattern be contoured; see custom flux controllers .

Cooling, structure and leads

Most heat treating coils are water cooled, and passages must suit the power level with minimal restriction. Fluxtrol’s Enhancing Induction Coil Reliability paper quantifies how cooling variables affect thermal fatigue in a single-shot coil, and its temperature prediction paper addresses controller temperatures. Low-frequency and high-power coils need a support structure, usually fiber-reinforced plastic. Leads and busswork should be kept close together, separated by an insulating resin, and contacts range from flared fittings to keyed machined blocks depending on power density and frequency.

Results in practice

In a wheel hub case, a coil with silicon steel laminations lasted 8,000 to 13,000 cycles. Replacing the laminations with Fluxtrol A raised life to 15,000 to 20,000 cycles, and a simulation-optimized design using Fluxtrol 50 extended life beyond 150,000 cycles. See case studies .

Design your next coil

Share your part, process and equipment and we will propose a design path. Contact Fluxtrol .

Real-world results

Case Harden Wheel Hub with Single Bearing Race

Lamination replaced with Fluxtrol A, then coil design optimized by simulation with Fluxtrol 50.

Original life of 8,000 to 13,000 cycles
Coil life extended to more than 150,000 cycles

Read the full study →

Best Practice for Design and Manufacturing of Heat Treating Inductors

ASM paper on eliminating failure points, material selection, cooling and flux control, with a CVJ stem hardening coil case.

Simulation predicts heat patterns in the part and in the coil
Design practices used for over 20 years

Read the full study →

Frequently asked questions

What does an induction coil have to do?

According to the ASM Handbook chapter by Fluxtrol authors, a heat treating coil must meet the heat treatment specification at the desired production rate, tolerate manufacturing variations, mount in the machine, match the power supply electrically, deliver quench, last, run efficiently and be repeatable from inductor to inductor.

How do you control the heat pattern of a coil?

Three main tools adjust a single-shot coil design: the coupling gap, the copper profile of the heat face, and magnetic flux controllers. A closer gap raises heating intensity, shaping the copper changes power along the part, and SMC controllers concentrate the field to push current onto the heat face and contour the pattern.

Why do induction coils fail?

Copper overheating is the leading cause of failure in heavily loaded heat treating inductors, typically thermal fatigue cracking in short cycles. Remedies include more water flow, lower water temperature, better water pockets or extra circuits, reducing heat source density, or redesigning the coil. Simulation can predict coil copper temperatures.

Does the existing machine constrain coil design?

Yes. When new tooling must run on an existing machine, the ASM chapter notes the degrees of freedom shrink and a less-than-optimal frequency or coil style may be forced. Deciding early whether the part will run on an existing system or a new machine simplifies the design.

What do you receive from the design stage?

Fluxtrol’s workflow completes the coil in 3D for manufacturing, including the coil head, SMC design, water cooling path, mechanical components and insulation, after simulation has predicted heating and electrical parameters for power supply selection.