Many automotive and industrial metal parts require induction hardening to increase the surface hardness of the workpiece. After induction heating, the surface hardness of the workpiece increases, and the service life will be longer.

The induction hardening method is very important for the hardening effect, we will introduce two main methods below.

Two induction hardening methods

Due to different shapes of the heated parts and different sizes of the hardened areas, different adaptive processes must be adopted for operation. These processes can be classified into two categories in principle.

1. Simultaneous Heating and Hardening

The entire hardened area is heated simultaneously, and then cooled simultaneously after the heating is stopped. The position of the heated part relative to the inductor remains unchanged during the heating. Simultaneous heating can be further classified into two types in the applications: one with rotating parts and the other with non-rotating parts. Cooling can be classified into two types: falling into a water sprayer and inductor spraying.

From the perspective of improving the utilization efficiency of the generator (except that one generator supplies multiple hardening machines), both the productivity and the utilization efficiency of the generator by the method of parts falling into a water sprayer after simultaneous heating are higher than those by the inductor spraying method.

2. Scanning Hardening

Scanning hardening is also known as continuous hardening. In this method, a part of the area to be hardened is subjected to simultaneous heating. The heating area is gradually moved through the relative movement between the inductor and the heated part, thereby realizing the heating of all hardened areas.
Scanning hardening can be classified into two types: one with rotating parts and the other with non-rotating parts. In addition, scanning hardening can also be classified into scanning circumferential hardening (such as outer contour hardening of large cam) and scanning plane hardening (such as surface hardening of flat round filing board).

Scanning hardening is suitable for situations where the surface area to be heated is large and the power supply equipment has insufficient power. Extensive production experience shows that under the condition of the same power supply, the production efficiency of parts by the simultaneous heating method is higher than that by the scanning hardening method, and the hardening equipment occupies less floor space. For shaft parts with steps, during scanning hardening, there is often a transition zone with insufficient heating from the large-diameter step to the small-diameter step due to offset of the electromagnetic field of the inductor, resulting that the hardening layer is discontinuous over the whole length of the shaft. At present, simultaneous heating method with longitudinal current has been widely used to keep the hardening layer of the stepped shaft continuous over the whole length, thus improving the torsional strength of the shaft.

Generally, high-power induction heating machines are usually used for simultaneous heating and hardening, and induction hardening machine tools are used for scanning quenching, including vertical induction hardening machine and horizontal induction hardening machine.