Induction heating internal splines

• Campeze
In summary, when using induction heating to surface heat internal splines, it is important to arrange the coil(s) to only induce currents in the internal surface and to quench the surface immediately after heating. For a long workpiece, the processes should be coordinated in one movement. When calculating the required power and current, it is necessary to consider the mass of the volume of metal being heated, which may be the whole workpiece or only a limited part. It is also important to minimize the heated mass to avoid distortion and maintain tolerance. The heated mass can be calculated by multiplying the material density by the heated volume, which is determined by the area being heated and the depth of heating.
Campeze
TL;DR Summary
Using induction heating to surface harden the hollow internal part of a metal cylinder workpiece that has splines on the inside.
I want to surface heat internal splines with induction heating with an internal diameter coil. It is a cylinder, uniform shape, and the teeth are 1mm wide and 2mm deep. The inside diameter of the hollow section is 19mm and the length is 55cm.
I was wondering when calculating power/resistance, do I take into consideration the whole workpiece or just the area of workpiece I want to heat?

Campeze said:
I was wondering when calculating power/resistance, do I take into consideration the whole workpiece or just the area of workpiece I want to heat?
Welcome to PF.

It is easy to generate a current that runs around the outside of a workpiece. It is more difficult to induce a current inside a sleeve. To heat the inside you need to arrange the coil(s) to induce currents in the internal surface only. You must also quench that surface immediately after heating because an induction heated surface is shallow and will be chilled quickly. You may need to spin the workpiece as it is heated because of the induction loop polarisation.

For a long workpiece you will need to arrange the two processes to occur in one movement, say as the workpiece is removed vertically downwards from the induction coils past the quenching jets.

Thanks for your reply. I am just struggling with calculating the power and current required in the coil.

It weighs 0.7 kgs and the ideal penetration depth is 1mm. With the formula Pworkpiece = mc(Tf-Tin/sec), would m be the mass of the whole object or just the zone I want the eddy currents to penetrate?

That equation is a generalisation. It applies only to the mass of the volume of metal heated. That may be over the whole workpiece, or only a limited part.

In this case it is only the internal part of the workpiece that is being heat treated. Any unwanted or stray heating that occurs must be included in the total, and will increase distortion. If you heated the entire workpiece to full depth, distortion would take the workpiece out of tolerance.

With well designed coils you can minimise the heated mass to the area needing heat treatment. Thermal energy change = mass * thermal capacity * temperature change. Think of it as an energy budget. Minimise the heated mass.

The heated mass will be the material density multiplied by the heated volume. The heated volume will be the area being heated multiplied by the depth of the heating. The depth of heating will be a function of skin effect and the heating time.

1. What is induction heating?

Induction heating is a method of heating an electrically conductive material by using an alternating magnetic field. This is achieved by placing the material inside an induction coil and passing a high-frequency alternating current through it. The induced current creates resistance and generates heat in the material.

2. How does induction heating work for internal splines?

Induction heating for internal splines involves using an induction coil that is specially designed to fit around the spline. The alternating magnetic field created by the coil induces eddy currents in the spline, which causes it to heat up. The heat is then transferred throughout the entire spline, providing uniform heating.

3. What are the advantages of using induction heating for internal splines?

There are several advantages of using induction heating for internal splines. It is a fast and efficient method of heating, as the heat is generated directly in the material without the need for a heating element. It also allows for precise control of the heating process, resulting in consistent and repeatable results. Additionally, induction heating is a clean and environmentally friendly process, as it does not produce any emissions.

4. What materials can be heated using induction heating for internal splines?

Induction heating can be used to heat a wide range of materials, including steel, aluminum, copper, and other electrically conductive materials. The material must have a certain level of electrical conductivity for the process to be effective.

5. Is induction heating for internal splines safe?

Yes, induction heating for internal splines is a safe process when performed correctly. The heating process is localized, so there is minimal risk of burns or other injuries. However, it is important to follow proper safety precautions and use appropriate protective equipment when working with high temperatures.

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