High frequency quenching of automobile brake camshaft - Beichen Yike, the first choice enterprise

High frequency quenching of automobile brake camshaft
Abstract: This paper briefly introduces the induction hardening process of the automobile brake camshaft
The brake camshaft is an important component of the automobile brake components
Its surface is required to have high hardness and wear resistance, and its center must have a certain toughness to meet the requirements of high fatigue strength
In order to meet these requirements, the sensor structure, power parameters, heating mode and cooling mode are designed in an all-round way
The results show that the quenching process can fully meet the requirements of camshaft quenching process

Keywords: camshaft   Surface quenching   induction heating
1 overview of quenching process requirements
The brake camshaft used in the experiment is made of 45 steel with a shaft diameter of 40mm
The quenching technical requirements are that the surface hardness is 52~63hrc, the depth of the shaft hardening layer is 2~3
5mm, and the depth of the peach tip hardening layer is less than 10mm

As shown in Figure 1, the automobile brake camshaft is mainly composed of a peach core, a shaft and splines, of which the peach core and splines are profile quenched and have special requirements for the quenching process

Figure 1 camshaft
2 quenching induction heating power supply and machine tool selection
For the selection of induction heating power supply, two parameters should be determined: heating frequency and power

The depth of hardened layer is mainly affected by heating frequency, power density and cooling rate, and the heating frequency is the main factor affecting the depth of hardened layer
According to the requirements of camshaft layer depth, the heating frequency can be 15~25khz through formula calculation
When the heating frequency is high, the penetration depth is shallow, the energy is more concentrated, and the heating efficiency is also high
Therefore, when meeting the requirements of layer depth, the frequency should be as high as possible, so the heating frequency should be 25kHz

The equipment power can be calculated according to the workpiece size and power density
After calculation, 80kW medium frequency heating power supply with heating frequency of 25kHz shall be selected
The heating equipment used in the test is Beichen Yike medium frequency induction heating power supply double80/100, with stable heating effect and good test results

The shaft type vertical quenching machine with a stroke of 600mm is selected as the quenching machine tool

3 sensor structure design
The shaft adopts a single ring sensor with an auxiliary spray ring; The peach heart adopts profiling single loop sensor with auxiliary sprinkler, as shown in Figure 2
The quenching method adopts the continuous heating scanning quenching method
The shaft and peach core parts are quenched
When the shaft is quenched, the camshaft moves up and down and rotates at the same time, which can make the heating and cooling more uniform

For the quenching of peach heart, attention should be paid to the heating of peach tip
When heating the sharp corner, it is easy to overheat
In order to avoid overheating of peach tip or serious decarburization on the surface of peach tip, the coupling distance of peach tip should be increased when making sensors; Secondly, the concave part of the peach heart is not easy to be heated
It is necessary to add silicon steel sheet at the concave part of the sensor to avoid low temperature at the concave part, resulting in insufficient hardness and layer depth

(a) peach core quenching sensor
(b) shaft quenching inductor
Fig
2 camshaft quenching sensor
4 induction heating quenching process
The quenching and cooling method of camshaft is spray cooling method
The heated part of the workpiece is cooled by auxiliary water spray ring to complete the transformation of martensite structure
There is usually a large internal stress in the quenched workpiece, which is not conducive to the service performance of the workpiece
After quenching, the workpiece needs to be tempered to eliminate the internal stress; In addition, there is another tempering method
When cooling the workpiece, the workpiece will still have a certain residual temperature after cooling, and the temperature is controlled at 200-300 ℃, so that the workpiece can use its own residual temperature for self tempering to eliminate stress
The temperature after cooling can be adjusted by changing the flow rate of quenching medium or the concentration of cooling medium
PAG based aqueous solution and sencro- p75 quenching medium are selected as the quenching medium
The concentration is 11%, the service temperature is 10-50 ℃, and the pH value is 9-11
The cooling capacity decreases with the increase of concentration

　　
5 Analysis of experimental results
The hardness of the quenched sample and the depth of the quenched layer show that the surface hardness is evenly distributed after quenching, the depth of the base circle quenched layer meets the process requirements, and the depth of the peach tip quenched layer meets the process requirements

The depth of the shaft hardening layer is shown in Figure 3
It can be seen from the figure that the depth distribution of the hardening layer is very uniform

Fig
3 shaft hardening layer
 
Induction heating quenching can well realize the surface heat treatment of camshaft
Compared with other surface heat treatment methods, such as surface carburization, surface nitriding, carbonitriding, etc
, induction heating quenching is more environmentally friendly, efficient and economical, and is suitable for continuous mass production

Among the 11 single heat treatment processes, the energy consumption of high (medium) frequency induction quenching is the lowest, accounting for 60%-80% of the heat treatment cost

6 Summary
It has been nearly a century since the invention of induction heat treatment
With the continuous innovation of industrial technology, compared with the traditional heat treatment process, the increasingly mature induction heat treatment process continues to show its own advantages and serve the modern industry