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What is induction heating. How does it work?

Induction heating - an introduction

Putting the smarter heat to smarter use.

What is induction heating?

Induction heating is a flame-free, fast, clean, energy-efficient and non-polluting method  of heating metals and conductive materials.

Induction heating is:

Fast. The produced heat in induction heating is instant. It takes less than one second to achieve a uniform surface temperature of 1,000°C on small metal components.

Accurate. Precisely the right temperature is delivered, only where it’s needed to individual workpieces, and because of the range of frequencies available, to just the right depth. We can customize induction coils to suit practically any shape or size of workpiece. Customized coils ensure optimal heat patterns with minimal energy consumption.

Controllable. Transistorized converters and process control software deliver complete control over the entire heating process. Equipment can also feature in-built telemetry devices for remote diagnostics and off-site monitoring.

Repeatable. Induction heating lets you accurately repeat your desired heating cycle. (In fact, the produced heat from a frequency converter normally varies as little as 1-2%.) You can duplicate all the key parameters: temperature, penetration depth, heat pattern, speed-of-temperature increase. Ramp-up and dwell times can be pre-set and repeated.

Clean, safe and compact. No gas, no open flames, no noticeable increase in ambient temperature, and no excessive floor space occupied by furnaces, makes induction heating both sustainable and superior to other methods of heating.

Faster. Better. Cheaper - The technical features of induction heating deliver three key benefits: improved throughput, better and consistent quality, reduced costs
The values used in this table are approximations only, designed as a general guide. The performance rating of the three heating methods can vary from case to case, depending on the application involved, workpiece characteristics, operator skills, etc

Applications – when and where to use it

Induction heating is a technology that touches virtually all aspects of modern life, and EFD induction's solutions are used to make everything from faucets to spaceships, from solar cells to bulldozers. 

EFD Induction equipment can be used for practically any industrial application involving heat treatment of metals. 

Since many of our solutions are compact enough to be mobile, you will find EFD Induction equipment on offshore platforms, wind farms and power stations. 

Click on the application to read more:

Hardening and tempering with induction heating


Optimizes mechanical properties in workpieces that have been hardened.

Brazing with induction heating


Joins a wide range of metals, even ferrous to non-ferrous.

Induction heating for tube and pipe welding


Induction welding is used for longitudinal welding in the tube and pipe industry.

Induction heating for bonding


Bonds steel and aluminium sheet metal, new lightweight composite and carbon fibre materials.

Preheating with induction heating


Induction preheating is a process where materials or workpieces are heated by induction prior to further processing. 

Postheating with induction heating


Heat workpieces or materials that have already undergone significant processing.

Shrink-fitting with induction heating

Shrink fitting

Shrink fit gears and rings, repair planes, trains and trucks, and remove the giant nuts and bolts in the turbines of power stations.

Induction heating for forging


Heat metal parts before they are shaped or ‘deformed’ by presses or hammers.

Melting with induction heating


Our solutions melt everything from ferrous and non-ferrous metals to nuclear material and medical/dental alloys.

Induction heating of wire and cable

Wire and cable heating

Our solutions are ideal for key phases in the manufacturing and processing of wire and cable products.

How does induction heating work?

Induction can turn a precisely defined section of a metal bar cherry red in seconds. How is this possible?

Let us show you!

The fundamentals

The induction heating process is based on a combination of electromagnetic induction and Joule heating.

Induction heating is the process of heating an electrically conductive object (usually a metal) by electromagnetic induction, where currents are generated within the metal and the resistance of the material leads to Joule heating of the metal.

Large amounts of alternating current (AC) are passed through an induction coil (or electromagnet), which is water-cooled to keep it from overheating. As a result, the coil's high current generates powerful magnetic pulses.

These magnetic pulses then cause electrons to flow internally within the piece of metal. This internal flow of electrons is referred to as an eddy current (like swirling eddies in a stream).

Different converters come with different power outputs and frequencies. Output power, the shape of the induction coil and the characteristics of the workpiece determine the heat pattern. The depth of heat penetration into the workpiece depends on the frequency: the lower the frequency, the deeper the penetration.

This means that induction heating can be used for different applications like hardening, tempering, welding, brazing, and bonding.

(For a more detailed explanation of the physics part of it, please skip to the last chapter in this article).

Induction coil
It doesn’t get hot. It doesn’t touch the component. So how can a coil heat metal cherry red in a few seconds?

Quality is everything

The induction coil, also known as an ‘inductor’, is essential to the induction heating process.

A correctly designed, manufactured and maintained induction coil is therefore critical to the overall efficiency of induction heating solutions. That’s why we at EFD Induction invest so much in highly qualified coil technicians and advanced coil design equipment.

EFD Induction has perhaps the world’s most advanced coil making and coil care programs. We not only design and make customized coils for all materials and applications, but we also have the solutions for preventive maintenance and coil logistics.

These initiatives ensure you always use the right coils, and that their working life is maximized.

If you would like to know more—about us, or the technical and commercial benefits of induction heating—please contact us.

Induction coils
EFD Induction has years of experience designing and supplying customized, long-life coils for the full spectrum of applications and materials.

Faster. Better. Cheaper.

The technical features of induction heating deliver three key benefits:

- Improved throughput.

- Better and consistent quality.

- Reduced costs.


Integrating induction heating into the production line improves production efficiency. You cut lead times and speed up throughput. The heating process itself is faster than with open-flame and oven alternatives.

Accurate repeatability means you get to be faster because you get it right the first time.


Quality improves because you can apply pre-set temperatures to pre-set parts of individual workpieces. And because induction coils are tailor-made for specific workpieces, you know, in advance, the delivered heat pattern.

Also, precise heat delivery means any adjoining components and/or materials remain unharmed during the heating process.


Costs go down because of shorter lead times and increased throughput.

Integrated in-line induction heating means lower administration and logistics costs.

Production yields go up. Swift heat cycles, precise delivery and accurate repeatability minimize waste and scrap.

Energy costs go down because you heat only what you need to heat—there are no costly heat losses as with conventional ovens.

(EFD Induction frequency converters are particularly effective at lowering energy costs, as they have a proven higher efficiency and power factor than competing converters.)

Additionally, since induction heating lets you abandon hazardous gas and open flames, you can negotiate lower insurance premiums.


How can induction heating benefit my business?

A can of peaches, a cruise liner’s hull, a tub of yogurt, power station turbines, cables under the ground, pipelines under the waves, and countless trains, planes, and automobiles.

What unites these different products is that induction heating is used to make them, maintain them, repair them, and recycle them. (In case the yogurt tub intrigues you, induction heating attaches the foil lid to the plastic container. As for canned peaches, induction heating helps coat the tin on the can’s inside so that conserved foods remain untainted.)

Simply put, our induction heating solutions can be profitably used in virtually any industrial application that requires heat.

EFD Induction has been developing induction technology for more than 70 years. Our unique experience and knowhow make us the ideal partner to advice and guide you, no matter what your heating needs may be.

Our hardening machines, for example, are widely used in the automotive and automotive supply industries for surface hardening and tempering of mechanical parts such as shafts, gears, axles and valves. You’ll also find our converters curing the adhesives that join body panels in doors, hoods and deck lids.

Beyond the automotive and automotive supply segments, EFD Induction equipment is commonly found in the electrotechnical, metal and foundry, tube and pipe, wire and cable, aviation, shipbuilding, white goods, glass, plasma, and optical fibre industries.

EFD Induction has been developing induction heating solutions since 1950. Today we are one of the world's largest manufacturers of industrial induction equipment.

Click on the industry below to read more about the benefits:

Induction heating automotive parts


Automotive components must be heated to the very highest standards with solutions that meet the automotive industry’s tough cost-control demands.

Induction heating tube and pipe

Tube and pipe

The excellent reliability, efficiency and robustness of our high frequency, solid-state Weldac tube welders confirm our leading position as a provider of cost-effective, high-uptime systems. 

Amazing facts about induction heating


- An EFD Induction frequency converter with an output power of 100 kW can harden a 60 mm diameter shaft to a depth of 2 mm (800°C at 2 mm) with a feeding speed of 1 m per minute.

- Using one of our mobile converters, you can heat 1 kg of steel from 20°C to 800°C in five seconds flat. That’s a speed-of-temperature increase of 160°C per second.

- Induction heating is ten times more efficient than conventional ovens at curing the adhesives in automobile hoods. To cure one hood normally requires 220 kWs. As induction heating uses     340 kWs from the mains net, efficiency is 65%. Conventional ovens use something in the range of 4,000 kWs per hood, resulting in an efficiency of only 5.5%.


Time for a brief physics class

The phenomena of induction heating begin with generating a magnetic field by feeding an alternating current through a coil.

The strength of the field is proportional to the current that passes through the coil. The field is concentrated in the coil's contained area, and its magnitude is determined by the current's strength and the number of turns in the coil. (See Figure 1).

An alternating current flow through a coil
Fig. 1: An alternating current flow through a coil, creating magnetic field (the blue lines).

Eddy currents are induced in any electrically conductive object, a metal bar for example, placed inside the coil. (Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction.)

In the area where the eddy currents are flowing, the phenomenon of resistance then generates heat. Increasing the strength of the magnetic field increases the heating effect.

The total heating effect, however, is also influenced by the object's magnetic properties and the distance between it and the coil. (Figure 2)

Eddy currents are induced (hence the term ‘induction’) on the surface of the workpiece within the coil
Fig. 2: Eddy currents are induced (hence the term ‘induction’) on the surface of the workpiece within the coil. Note that induction is a no-contact heating method, at no time does the coil actually touch the workpiece.

The eddy currents create their own magnetic field that opposes the original field produced by the coil. This opposition prevents the original field from immediately penetrating to the center of the object enclosed by the coil.

The eddy currents are most active close to the surface of the object being heated but weaken considerably in strength towards the center. (Fig. 3)

 The distance from the surface of the heated object to the depth where current density drops to 37% is the penetration depth. This depth increases in correlation to decreases in frequency. It is therefore essential to select the correct frequency to achieve the desired penetration depth.

Penetration depth is closely linked with frequency
Fig. 3: Penetration depth is closely linked with frequency, heating times, power input and workpiece characteristics.
Preventive Maintenance Keeps Induction Heating Systems In Peak

How can we help you?

If you have any questions, don't hesitate to reach out.


Annealing is a heat treatment that alters the microstructure of a material, causing changes in its properties such as strength and hardness. It is a process that produces equilibrium conditions by heating a material and maintaining it at a suitable temperature, and then cooling it very slowly.

The process is used to induce softness, relieve internal stresses, refine the structure and improve cold working properties.

Bonding is structurally joining parts by adhesive cured under elevated temperature.

Brazing or "hard soldering" is a joining process whereby a non-ferrous filler metal or alloy is heated to melting temperature above 450°C (800°F) and distributed between two or more close-fitting parts by capillary action.

Curie point (also called Curie temperature) is the temperature at which certain magnetic materials undergo a sharp change in their magnetic properties.

Specification: the temperature at which there is a transition between the ferromagnetic and paramagnetic phases. Above the Curie point, the ferromagnetic material is purely paramagnetic.

Eddy current (also known as Foucault current) is caused by a time-varying magnetic field intersecting a conductor or vice versa.

Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux.

Flux is used in brazing to remove oxides, prevent oxidation, and wet the joining areas. Excess flux should be removed when the joint is completed. Flux left in the joint can lead to corrosion.

Frequency converter is the power source supplying the highfrequency alternating current. Modern frequency converters for induction are based on semi-conductor technology.

An induction coil is a coil carrying high- or medium- frequency alternating current and intended to induce eddy currents to heat objects placed in the interior of the coil.

The induced current also generates its own magnetic field, in opposition to the field generated by the coil, thus preventing the latter field from penetrating to the center of the heated object.

Induction heating is a process of heating electrically conductive material by electromagnetic induction, where eddy currents are generated within the material and its resistance leads to the heating.

Induction surface hardening is the process of hardening the surface of steel or cast-iron objects by heating only the surface to produce martensitic microstructure in the heated zone after quenching.

Magnetic flux is the integral of the magnetic field times the perpendicular area that it penetrates.

Normalizing means to heat ferrous alloy to a suitable temperature above the transformation range and then cool it in air to a temperature substantially below the transformation range. Steel is normalized to refine grain size, make its structure more uniform, or to improve machinability.

Penetration depth is the distance from the surface to the depth where current density has dropped to 37%. The depth of penetration increases as the frequency decreases.

It is essential that the frequency is chosen with respect to the dimensions and electrical properties of the object to be heated.

Post heating of weldments occurs immediately after welding, for tempering, for stress relieving, or for providing a controlled rate of cooling to prevent formation of a hard or brittle structure.

Preheating occurs before a heating or mechanical process is applied to the material.

Quenching generally means rapid cooling of metals and alloys to below the critical temperature range to harden them.

Soft soldering is a process of low temperature soldering using a solder with a melting point below 450 °C (800 °F).

Stainless steel is a common name for steel alloys that are resistive to corrosion and oxidation (rust). These normally include:

- Austenitic steel—the largest category of stainless steel, ac - count ing for about 70% of all production. The austenitic class offers the most resistance to corrosion in the stainless group, due to its substantial nickel (Ni) content and higher levels of chromium (Cr). The steel is nonmagnetic and has no Curie point.

- Ferritic steel—the second-largest class of stainless steel, constituting approximately 25% of stainless production. Ferritic stainless steels are plain chromium (Cr) steels with no significant nickel (Ni) content; the lack of nickel results in lower corrosion resistance than the austenitic (chromium-nickel stainless steels). The steel is magnetic and has a Curie point.

- Martensitic steel—a small category of stainless steel characterized using heat treatment for hardening and strengthening. Martensitic stainless steels are plain chromium (Cr) steels with no significant nickel (Ni) content. The steel is magnetic and has a Curie point.

Tempering is a reheating process that increases the ductility and impact strength of a hardened structure (martensite). The microstructure of quenched and tempered steel is referred to as tempered martensite.

Tube welding is in this connection a method of longitudinally welding steel and aluminum tubes, pipes, and profiles by using induction coils or electrical contacts.

The raw material is coiled and sheared in strips in a width and thickness that correspond to the dimensions of the final product. The strip is fed into a forming and welding line and formed by rollers before the edges are welded together. The welding process is done without using filler metal or alloy as the edges are heated up to the forging temperature and pressed together.