Induction Hardening — Dominant Electrical Parameter In induction hardening of steel components, which electrical parameter is typically operated at a high level to induce shallow, controllable surface heating?

Introduction / Context:
Induction hardening relies on electromagnetic induction to rapidly heat a component’s surface before quenching to form a martensitic case. Process control hinges on electrical parameters that govern depth of heating and rate of temperature rise.

Given Data / Assumptions:

• AC power supplies ranging from medium to high frequency are used.
• Skin effect concentrates current near the surface.
• Aim is a controlled case depth with minimal core heating.

Concept / Approach:
The skin depth δ in induction heating is inversely proportional to the square root of frequency (δ ∝ 1/√f). Higher frequency confines heating to a thinner surface layer, enabling precise case depths for gears, shafts, and cams. While current and voltage contribute to total power, the distinguishing operating feature for case depth control is high frequency.

Step-by-Step Solution:
Relate skin depth to frequency: δ ≈ k / √f for given material and temperature.To obtain shallow heating, increase f → reduce δ → heat surface rapidly.Thus, “frequency is high” describes induction hardening.

Verification / Alternative check:
Industrial practice uses audio-frequency, medium-frequency, and radio-frequency generators depending on required case depth (e.g., a few millimetres at tens to hundreds of kHz).

Why Other Options Are Wrong:

• Current/voltage: matter for power, but do not alone define case depth.
• Temperature: is an outcome, not an electrical parameter.
• Power factor: an efficiency metric, not the key to case depth.

Common Pitfalls:
Confusing power level with penetration control; frequency is the primary knob for depth.

Final Answer:
frequency