How to Choose an Induction Heating System
Sizing an induction system comes down to two linked decisions — frequency and power — then a coil-design choice layered on top. Here's how to work through it before you call a supplier.
Short answer: frequency determines how deep the heat penetrates (and therefore your case depth), power determines how fast a part heats (and therefore your cycle time), and whether you run static or scanning hardening depends on part geometry and volume. Get those three right and the coil design follows from them.
Step 1 — Frequency sets your case depth
Induction heating works by inducing eddy currents near the surface of a conductive part — the higher the frequency, the shallower and more concentrated that current stays, which means a shallower, more precisely controlled hardened case. Lower frequency lets the effect penetrate deeper, for a thicker case on larger parts.
| Target case depth | Typical frequency | Example parts |
|---|---|---|
| 0.25–1.25mm | ~70–600 kHz | Bearings, rocker arms, small pins |
| 0.8–1.2mm | ~200–400 kHz | Small-to-mid shafts |
| 1–2mm | ~60–200 kHz | Mid-size shafts and gears |
| 1–4mm | ~10–200 kHz | Crankshafts, camshafts |
| 2–4mm | ~15–30 kHz | Larger gears and shafts |
| 5–15mm+ | ~500 Hz–10 kHz | Axle shafts, large sprockets |
| Very deep / massive parts | As low as ~50 Hz | Mill rolls |
Quick Estimator: Case Depth → Frequency
Drag the slider to your target case depth for a rule-of-thumb frequency range and example parts. This is a starting point for a conversation with a supplier, not a substitute for an engineering spec.
Step 2 — Power sets your cycle time
Once frequency is fixed by the case depth you need, power determines how fast the part actually reaches temperature — more power means a faster cycle, which matters directly for throughput. This is also where static and scanning hardening diverge sharply in requirements.
Static (single-shot) hardening
- Heats the whole target zone at once — faster cycle time
- More uniform heat at shoulders and diameter changes, which usually means less distortion on larger parts
- Needs a significantly larger power supply, since the whole zone heats simultaneously
- Coil is built for one specific part — expensive to fabricate, not reusable across a part family
Progressive (scanning) hardening
- Coil and quench travel the length of the part — needs less power at any one moment
- A simpler, cheaper coil can often handle a family of similarly-sized parts
- Slower overall — lower production rate than single-shot
- Can produce non-uniform hardness or quench deflection issues at large shoulders or diameter changes
Neither is universally better — the decision is driven by part geometry (does the design have large diameter changes?) and volume (does the production rate justify a dedicated single-shot coil?), not by cost alone.
Get the frequency and power decisions right, and the coil design mostly falls out of them.
Questions worth asking a supplier
- What case depth and material (carbon content) am I actually specifying?
- Does one coil need to cover a family of parts, or is this a single dedicated geometry?
- What cycle time / throughput does the line actually need?
- Given the part's shoulders and diameter changes, is static or scanning the better fit?
- What's the expected coil life, and what does replacement cost and lead time look like?
- Is there power headroom built in if new part variants get added later?
Frequently asked questions
What frequency should I use for induction hardening?
It depends on the case depth you need: roughly 70–600 kHz for a shallow 0.25–1.25mm case on small parts like bearings and pins, down to 500 Hz–10 kHz for a deep 5–15mm case on large parts like axle shafts, with mid-range frequencies covering everything in between. Higher frequency gives a shallower, more precise case; lower frequency penetrates deeper.
Should I choose static (single-shot) or scanning hardening?
Static hardening is faster and more uniform at shoulders and diameter changes but needs a larger power supply and a part-specific coil. Scanning hardening needs less power and can often handle a family of similar parts with one coil, but runs slower and can be less uniform on parts with large diameter changes. The choice depends on part geometry and production volume, not a universal answer.
What should I ask an induction heating equipment supplier before buying?
At minimum: target case depth and material carbon content, whether one coil needs to handle a family of parts, required cycle time and throughput, whether static or scanning suits the geometry, expected coil life and replacement cost, and how much power headroom is built in for future parts.
Working through a spec right now?
Send us the part, material, and target case depth — we'll walk through frequency, power, and coil design with you.