Essentials of Induction Heating: What You Need To Know

How Does Induction Heating Work?  

An induction heating system comprises a power supply that converts line power into high-frequency alternating current. This energy flows to a workhead, generating an electromagnetic field in the attached coil. When a workpiece is placed in the coil, the field induces a current, heating the workpiece.  

Induction heating is widely used in processes like brazing, soldering, and shrink fitting, applicable to items ranging from hypodermic needles to large military tank wheels. Industries such as automotive, medical devices, and aeronautics efficiently utilize induction heating in their operations.

What's In An Induction Heating System?  

Induction heaters transform AC line power into high-frequency alternating current, transmitting it through a specialized cable to a workhead with capacitors and a custom work coil. This setup uses resonance to generate an electromagnetic field within the coil, efficiently transferring energy to the workpiece.  

The workpiece, placed in the electromagnetic field, experiences eddy currents that produce friction, resulting in precise, clean, non-contact heating. A water cooling system is typically needed to cool the work coil and the induction heating system.

What Is Operating Frequency?  

The operating or resonant frequency of an induction system is the frequency at which energy is transferred most efficiently.  

It is determined in the workhead by the capacitance of the tank circuit, the inductance of the induction coil, and the material properties of the workpiece.  

Typically, the larger the workpiece, the lower the frequency, and the smaller the workpiece, the higher the frequency.

Does Induction Heat Magnetic Materials?

If your work piece material is magnetic, such as carbon steel, it will be heated easily by induction's two heating methods, eddy current and hysteretic heating. Hysteretic heating is very efficient up to the Curie temperature (for steel 600°C (1100°F)) when the magnetic permeability reduces to 1 and the eddy current is left to do the heating.

What Is The Heating Depth Of Penetration?  

This refers to how deeply induction heats the workpiece.  

Induced current flows at the surface of the workpiece, with 80% of the heat generated in the outer layer (skin effect). Higher operating frequencies result in a shallow skin depth, while lower frequencies lead to a thicker skin depth and greater depth of penetration.

How Important Is Coupling Efficiency?  

The current flow in the workpiece and the distance between the workpiece and the induction coil are crucial; the closer the coil, the more current flows in the workpiece.  

However, the distance must be optimized for the required heating and practical workpiece handling. Various factors in the induction heating system can be adjusted to match the coil and improve coupling efficiency.

Is Coil Design Important In An Induction Heating System?  

The efficiency of an induction heater is optimized when the workpiece is placed inside the induction coil. If this isn't possible, the coil can be placed inside the workpiece.  

The size and shape of the water-cooled copper induction coil are tailored to the workpiece, ensuring heat is applied to the correct area.

Power Requirements  

The power needed to heat your workpiece depends on:  

- The mass of the workpiece  

- The material properties of the workpiece  

- The required temperature increase  

- The heating time needed for the process  

- The effectiveness of the field due to the coil design  

- Any heat losses during the heating process  

Once the power requirements are determined, we can select the appropriate induction heating equipment, considering coil coupling efficiency.

Is Induction Heating Cost-Effective & Energy Efficient?  

Heat losses and inconsistent heat application lead to increased scrap, reduced product quality, higher per-unit costs, and lower profits. The best manufacturing economies are achieved when energy application is controlled.  

Bringing a batch oven up to temperature and maintaining the required temperature for the process consumes much more energy than processing the parts. Flame-driven processes are inefficient, losing heat to the surroundings, while electrical resistance heating can waste energy on surrounding materials. Induction heating, on the other hand, applies energy only where it's needed.  

Induction focuses energy directly on the area of the part to be heated, ensuring consistent, efficient energy application. With no intervening media like flame or air, the process is precise.  

The precision and repeatability of induction heating reduce scrap rates, improve throughput, and allow for tight control over the heating process, cutting heating time and energy consumption.

Is Induction Heating More Production Efficient?  

Achieving the highest quality parts at the lowest cost and in the least time requires an efficient process, where materials and energy are tightly controlled. Induction heating's focused application of heat to the part or specific areas, combined with its repeatability, ensures uniform results at a lower cost. Repeatability and throughput are significantly improved with induction compared to resistance or flame heating.

Induction heating reduces process scrap rates, improves throughput, and optimizes energy usage. There's no need for process ramp-up, as heat is applied and stopped instantly. In contrast, batch heating in an oven consumes both time and energy, serving only the process, not the product. Induction heating enhances throughput and efficiency by applying just the amount of energy (heat) required for the product.

Is Induction Heating Considered To Be A Safe Process?  

Any heating process carries a risk of operator contact with heated materials. Induction heating reduces this risk by limiting operator contact to a smaller surface area. By focusing heat on the part and even within specific zones of the part, safety is further enhanced.

Unlike flame or hand-held heating, each induction heating cycle is identical, requiring no ongoing adjustments. Once established and proven, an induction heating process can be operated without the need for highly trained personnel.