How to Do Induction Hardening of Groove Parts?

At present, there are many kinds of groove quenching parts, such as camshaft open grooves and differential cases.

However, the quenching quality of groove parts has not been guaranteed, and quenching is also very difficult.

In this article, the groove quenching inductor in the form of “one come and two go” is improved and adjusted in the process debugging, so that the quenching effect is ideal and meets the requirements of various groove parts.

1. Discussion on quenching inductor of groove parts

(1) Current situation of groove type quenching inductor

The inner side of the part slot is heated, especially when the width of the inner side is small, it is difficult to design the inductor.

The inductor in Fig. 1 uses the principle of proximity effect to heat the inner side, with high efficiency.

The effective part of the inductor is the middle two conductive tubes.

Since the current directions of the two tubes are in the same direction at any time, the current on the conductive tube is squeezed to the outside.

Although the two conductive tubes are not provided with conductive magnets, they have a relatively high heating efficiency.

Fig. 1 two wire heating sensor inside the notch

(2) Design of quenching inductor with small opening groove

As the groove width is 9mm, the inductor is made of two conductive tubes, the copper tube used is very small, the manufacturing is difficult, and the life of the inductor is very short.

Therefore, it is improved to use a single copper tube for heating and use the proximity effect of induction heating (see Fig. 2).

Fig. 2 improved inductor structure

2. Application of groove type quenching inductor

The camshaft groove and differential case opening groove are used for the quenching test respectively.

(1) Quenching process test of camshaft opening groove

Our company has received the entrustment of a camshaft manufacturer to quench the camshaft opening groove.

The opening groove is 9.3mm wide and 9mm deep, and the groove width deformation is ≤ 0.1mm (see Fig. 3).

Fig. 3 technical requirements for camshaft opening groove

The heating part of the inductor is first heated by rectangular cross-section copper tube (see Fig. 4), the gap between the heating surface and the bottom surface of the open groove is adjusted, and the quenching is carried out with the frequency of 50KW and 30kHz.

The quenching area is only about 4mm, which is far from meeting the technical requirements.

Therefore, the inductor structure needs to be improved.

Fig. 4 copper tube quenching sample block (30kHz) with effective heating surface of rectangular section

The heating part of the inductor is made of trapezoidal cross-section copper pipe (see Fig. 5).

The gap between the heating surface and the bottom surface of the open groove is adjusted, and the quenching is conducted at the frequency of 30kHz and 50KW.

The quenching area is only 8mm, which still does not meet the requirements of 9mm, but it is very close to the technical requirements.

At this time, the process parameters need to be adjusted.

Fig. 5 copper tube quenching sample block with trapezoidal section effective heating surface (30kHz)

Try to use trapezoidal section copper tube for the heating part of the inductor, adjust the gap between the heating surface and the bottom surface of the open groove, and heat it with 5.8kHz frequency and 90kw for quenching.

The depth and hardness of the hardened layer on both sides of the entire open groove meet the technical requirements.

There are also hardened layers on the bottom surface and right angles of the open groove (see Fig. 6), and the deformation is small (see the attached table).

The customer is very satisfied.

Fig. 6 copper tube quenching sample block with trapezoidal section effective heating surface (5.8kHz)

Inspection table for quenching deformation of camshaft opening groove

(2) Process test of the open groove of differential case

Entrusted by an automobile manufacturer, our company quenched the connecting groove (see Fig. 7) of the differential case.

The groove is 18.5mm wide and 9mm deep.

Eight grooves are evenly distributed in the Φ 120 and Φ 75.

The technical requirements are quenching and tempering treatment after forging 90-230HBW, induction hardening of the dotted line part, surface hardness 53-59HRC, Ds = 2-3mm.

Fig. 7 technical requirements for opening groove of differential case

Because the quenching effect of the trapezoidal section inductor used in the front is ideal, the structure of this inductor is also used in the rear for testing.

5.8kHz and 98kW are used for heating and quenching.

The gap between the inductor and the bottom surface of the groove is 0.5-1mm, and the heating time is 5.2s (Note: auxiliary cooling system is added to prevent tempering in the quenching area near the open groove).

Check that there is no hardened layer at R2mm fillet (see Fig. 8).

The position and process parameters of the inductor need to be corrected.

Fig. 8 first quenching sample of differential case

According to the above tests, the following corrections are made: increase the bottom gap to 1-1.5mm, use 5.8kHz and 98kw for heating and quenching, and extend the heating time to 6.5s for heating and quenching (Note: add auxiliary cooling system to prevent tempering in the quenching area near the open groove).

Test results:

The surface hardness of both sides of the groove is 55 ～ 56HRC, DS = 2mm;

Surface hardness at r2mm is 55HRC, DS = 1.5mm;

The surface hardness of the groove bottom is 56hrc, Ds = 3mm (see Fig. 9).

The test results meet the technical requirements.

Fig. 9 second quenching sample of differential case

3. Conclusion

The key points for quenching of groove parts are as follows: inductor structure and effective heating surface structure, gap between inductor and quenching part, matching of quenching process parameters (frequency, power, heating time, etc.), and anti-tempering cooling system near quenching area.

In addition, the gap has a very obvious effect on the depth of the hardened layer of such parts.

It is difficult to ensure that the gaps between the two sides of the inductor and the side of the open groove are exactly the same, which makes the depth and shape of the hardened layer on the two sides asymmetric.

Therefore, the accuracy of the positioning fixture is very important.