Hub shaft induction heat treatment process part 2: hub shaft induction heat treatment process development
1. Induction heating mode
Based on regional analysis: wheel shaft quenching wheel axle shaft for variable cross-section steps, at the same time request the rounded induction hardening and the range of 110 ~ 120 mm continuous hardening layer, therefore the technology development of induction heating mode choice heating quenching heating quenching in a short period of time at the same time, the heating method is to quenching workpiece need to quench hardening area and at the same time put in sensor heating, after reaching the heating temperature and cooling; Due to the constant relative position of the inductors in the workpiece hardening region, the hardening layer is more uniform, the operation is simple, and the production efficiency is high. However, the power requirement must be large enough to meet the quenching demand.
2. Design and manufacture of sensors
According to the requirements of the wheel shaft hardening area and heating mode, the sensor, on the whole, is half a circle type rectangular sensor, due to different diameter of axial and give attention to two or more things rounded heating, so the effective axial heating circle should be as far as possible make copying structure, circumferential effective heating circle to rotate Angle (typically for 45 °), in order to meet the varying section plane and the heating of the rounded at the same time in the circle of effective conductor mount “Π” form magnetizer, made the current largest cluster in the conductor surface, in order to improve the heating efficiency. There are two rounded corners with the technology development of wheel shaft R1, R2, at the same time, heating and quenching temperature, which requires the rounded corners R1, R2, heating the effective length of a circle and “Π” form magnetizer reasonable allocation, ensure consistency of quenching temperature, which requires multiple process test to determine the final allocation proportion.
The design of effective ring inner diameter can be referred to as D = D + 2A (where D is the diameter of part and A is the clearance between part and an effective ring of the inductor). In the design of the inductor, in order to prevent the top temperature of the hub shaft spline from being too high, the distance between the workpiece and effective ring inner diameter of the inductor is set at a minimum value of 6mm. The height of the effective ring is designed according to H = (1.05-1.2) L (L is the length of the hardened area).In the design of this inductor, L shall be the minimum value required for quenching zone, and the coefficient shall be 1.1; Effective circle in the process of real design sensor height H than quenching area long, this is because when the induction hardening workpiece hardening area the edge effect, lead to in the actual process of hardening workpiece hardening of shallow and deep, the middle of the hardening layer on both ends so in sensor design sensor ring height is longer than quenching area effectively, to ensure that the hardening area and quench hardening layer depth meet technical requirements;4 water spray boxes are used to fix the cooling device on the inductor, which are evenly distributed around the hub and axis. The inductor and heating mode are shown in Figure 3.
FIG. 3 Sensor structure and heating mode
3. Determination of process parameters of induction heat treatment
After the design of the inductor is completed, the most important process is the debugging of the induction hardening process, and in the debugging process, frequency, power, and other power-related heating parameters are very important. The equipment used in this process development is an IGBT transistor frequency conversion power supply. Zvrc-2 double-station quenching machine is adopted, with the output maximum power of 350kW, and the working frequency is 4 ~ 20kHz and 20 ~ 80kHz.
(1) Frequency selection
The choice of frequency is not to choose a correct frequency value, but to choose the most appropriate frequency order of magnitude, that is, a reasonable frequency range. Reasonable frequency segment has obvious advantages in energy utilization, workpiece quality, etc. Reasonable frequency selection can realize penetration-type heating, otherwise, it is conduction heating. Penetration-type heating is better than conduction heating in the induction heating process. According to the theoretical analysis, the selection range of frequency is 15625/x2 < F < 250,000 /x2, in general, the optimal frequency value is F = 60,000 /x2, (x is the depth of the hardening layer, mm); After calculation, the process test frequency F is set at 12kHz.
(2) Selection of specific power and power supply
When medium frequency power supply is used, specific power P0 = 0.5 ~ 2kW/cm2; In general, the lower the current frequency, the smaller the workpiece size (diameter), the required depth of the hardening layer is shallower, the greater the power of the selection; On the contrary, the smaller the power is chosen.
According to the heating area of the parts, the recommended specific power is calculated and the power supply is selected. The power supply can be calculated by the following formula:
P = AP0 / eta eta 1 2
Here P — power supply power (kW);
A — Surface area of workpiece heated simultaneously (cm2);
P0 — specific power (kW/cm2);
1 — Quenching transformer efficiency, usually 80%;
Eat a better pie 2 – Sensor efficiency, usually 80%.
The calculated power of the selected power supply is about 160kW.
(3) Selection of quenching cooling medium and cooling time
The cooling method is jet cooling which is the most common in induction heating quenching.PAG water-based quenching cooling medium was selected and its concentration was 3% ~ 5%. As a one-shot quenching is adopted, the cooling injection pressure is relatively large at 0.25mpa. The cooling time is calculated according to TC = (1 ~ 2) tH, and the TC can be finally determined after trial or correction. Whether the cooling time is appropriate mainly depends on the surface hardness of the parts, the depth of the hardened layer, and the metallographic structure of the hardened layer.
The hub shaft after induction heating and heat treatment is shown in Figure 4.
FIG. 4 Hub shaft after induction heating and heat treatment