High frequency quenching of automobile brake camshaft

High frequency quenching of automobile brake camshaft

  Abstract: This article briefly introduces the induction hardening process of automobile brake camshafts. The brake camshaft is an important component of automobile brake parts. The surface of the brake camshaft is required to have high hardness and wear resistance, and the heart must have a certain Toughness to meet high fatigue strength requirements. In order to meet these requirements, a comprehensive design has been carried out in terms of the structure of the inductor, power supply parameters, heating methods and cooling methods. The results show that this quenching process fully meets the requirements of the camshaft quenching process.
Keywords: camshaft, surface hardening, 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 technology requires a surface hardness of 52~63HRC, a shaft hardened layer depth of 2~3.5mm, and a peach tip hardened layer depth of <10mm.

As shown in Figure 1, the automobile brake camshaft is mainly composed of a core part, a shaft part and a spline. The core part and the spline are profiled quenching, which has 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 main parameters need to be determined: heating frequency and power.The depth of the hardened layer is mainly affected by the heating frequency, power density and cooling rate, among which the heating frequency is the main factor affecting the layer depth. According to the requirements of camshaft layer depth, the heating frequency can be selected from 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 high. Therefore, when meeting the layer depth requirements, the frequency should be as high as possible, so the heating frequency is 25KHZ.

  The power of the equipment can be calculated based on the size of the workpiece and the power density. After calculation, 80KW intermediate frequency heating power supply should be selected, and the heating frequency should be 25KHZ. The heating equipment used in the test is Polaris-etek medium frequency induction heating power supply Doubhe 80/100, which has stable heating effect and good test results.The quenching machine is a shaft-type vertical quenching machine with a stroke of 600mm.

3. Sensor structure design

  The shaft part adopts a single-turn ring sensor with auxiliary water spray ring; the peach core part adopts a profiling single-turn sensor with auxiliary water sprayer, as shown in Figure 2. The quenching method adopts continuous heating scanning quenching method. The shaft and the core part 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.
When quenching the core of the peach, attention should be paid to the heating of the peach tip. The sharp corner part is easy to overheat when heated. In order to avoid overburning of the peach tip or serious decarburization on the surface of the peach tip, the coupling distance of the peach tip should be increased when making the sensor; The concave surface of the peach core is not easy to be heated, so it is necessary to add silicon steel sheet to the concave surface of the sensor to avoid the temperature of the concave surface is too low, resulting in insufficient hardness and layer depth.

Figure 2 Camshaft quenching inductor

4. Induction heating quenching process
 
  The cooling method of camshaft quenching is spray cooling method. The heated part of the workpiece is cooled by the auxiliary water spray ring to complete the transformation of martensite structure. There are often large internal stresses in the quenched workpiece, which is not conducive to the performance of the workpiece. After quenching, the workpiece needs to be tempered to eliminate the internal stress; there is another tempering method. , When cooling the workpiece, after the cooling, the workpiece still has a certain residual temperature, 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 quenching medium flow rate or cooling medium concentration. The quenching medium uses PAG-based aqueous solution, sencro-p75 quenching medium, with a concentration of 11%, a working temperature of 10-50℃, and a PH value of 9-11. The cooling capacity decreases with the increase of concentration.

Table 1 Process parameters used in quenching

5. Analysis of experimental results
 
Test the hardness of the quenched sample and the depth of the hardened layer. The experimental data are shown in Table 2:

Table 2 Data Sheet of Brake Camshaft Quenching Experiment

  It can be seen from Table 2 that the surface hardness distribution after quenching is uniform, the depth of the base circle hardened layer meets the process requirements, and the depth of the hardened layer at the peach tip meets the process requirements.

  The depth of the hardened layer of the shaft is shown in Figure 3. It can be seen from the figure that the depth of the hardened layer is distributed very uniformly; Figure 4 is a picture of the surface of the peach core after quenching.

  The surface heat treatment of the camshaft can be achieved through induction heating quenching. Compared with other surface heat treatment methods, such as: surface carburizing, surface nitriding, carbonitriding, etc., induction heating quenching is more environmentally friendly, efficient and economical. And suitable for continuous mass production.

Table 3 Comparison of energy consumption of single heat treatment

  It can be seen from Table 3 that among the 11 individual heat treatment processes, high (medium) frequency induction quenching has the lowest energy consumption, and energy consumption accounts for 60%-80% of the heat treatment cost.

6. Summary

  It has been nearly a hundred years since the invention of induction heat treatment. With the continuous innovation of industrial technology, compared with traditional heat treatment processes, the increasingly mature induction heat treatment processes continue to show their advantages and serve modern industries.