Gear quenching 1

Gear quenching 1

Overview:
 

  For transmission parts such as gears, the surface must have high hardness and wear resistance, and at the same time, it must have sufficient fatigue strength under alternating loads and impact loads. But for workpieces with uneven surface structures such as gears, conventional single-frequency induction hardening technology cannot achieve satisfactory treatment results. The pinion gears after conventional single-frequency induction hardening treatment often have all the teeth hardened, which leads to a decrease in the fatigue strength of the gear, and fatigue fracture is prone to affect the performance.

Figure 1 Gear single frequency quenching diagram
 

Aiming at workpieces with uneven surfaces like gears, how to obtain a uniform hardened layer so that the surface of the teeth is hardened while the core still maintains a certain degree of toughness, dual-frequency induction heating technology has emerged as the times require. The early dual-frequency induction heating technology is asynchronous dual-frequency, that is, the high frequency and intermediate frequency output by the equipment are not synchronized, and the intermediate frequency is used to preheat first, and then the high frequency is used to heat the teeth to the quenching temperature. After continuous development and improvement, more advanced synchronous dual-frequency induction hardening technology has been produced.

Figure 2 Gear double frequency quenching diagram

Introduction of dual-frequency induction heating technology

  Due to the skin effect, it is difficult to uniformly heat workpieces with uneven surfaces such as gears through a single frequency in the heat treatment of workpieces. If the intermediate frequency is used for heating, the penetration depth of the induced current will be very large. The induced current generated on the gear only passes through the tooth bottom and does not pass through the tooth top. The tooth bottom heats up faster than the tooth top, resulting in good tooth bottom hardening but insufficient tooth top hardening ; If high-frequency heating is used, since the penetration depth of the induced current is small, only the top of the gear can be heated, and the bottom of the tooth heats up slower than the top of the tooth, resulting in good hardening of the top of the tooth but insufficient hardening of the bottom of the tooth.

  The single-frequency heating gear is not uniformly heated, which is prone to large deformation or cracks, and the qualified rate is low.

  Figure 3 Gear single frequency heating effect left (medium frequency) right (high frequency)
 

  Therefore, it is difficult to obtain the ideal heating effect for single frequency heating, no matter whether high frequency or intermediate frequency is used. If the high frequency and intermediate frequency can be combined to heat the gear, this problem can be solved well. In this case, dual-frequency induction heating has a unique advantage. Dual-frequency induction heating uses high-frequency heating of the tooth tip and medium-frequency heating of the tooth root to achieve the purpose of uniform heating of the surface of gear workpieces. When using dual-frequency heating, the gear heating effect is shown in Figure 4. At this time, both the tooth tip and the tooth root can be effectively hardened, and a better profiling hardened layer can be obtained.

  Figure 4 Gear dual-frequency heating effect
 

  Synchronous dual-frequency induction heating technology refers to the simultaneous output of two different frequencies of high frequency and intermediate frequency on an induction coil to quickly heat a workpiece. Synchronous dual-frequency induction heating technology can realize the separate adjustment of the two frequency intensities, thereby adjusting the output ratio of the two frequency components, so that the hardening depth of the tooth surface and the tooth root can meet the process requirements, thereby improving the performance index of the workpiece.

  Figure 5 Schematic diagram of dual-inverter synchronous dual-frequency induction heating
 

As shown in Figure 6, the intermediate frequency wave F1 and the high frequency wave F2 are superimposed and simultaneously applied to the induction coil.

  Figure 6 Synchronous dual-frequency induction heating technology
 

  The synchronous dual-frequency induction generator includes a high-frequency and intermediate-frequency converter with normal power output, and superimposes high-frequency oscillation on the basis of intermediate-frequency oscillation through IGBT technology. The synchronous dual-frequency induction heating speed is fast, the heating time is generally less than 0.5s, and it can obtain very small austenite grains, which greatly improves the quality of heat treatment, obtains a uniform profiling hardened layer, and improves the productivity of the workpiece And reduce the deformation of the workpiece quenching.

  When heating gears with different modulus, it is found that the modulus of the gear has a great influence on the selection of current frequency. When heating a certain modular gear, there is an optimal frequency. When the frequency is higher than the optimal value, the tooth tip temperature is higher than the tooth root; conversely, when the frequency is lower than the optimal value, the tooth root temperature is higher than the tooth tip .

  Therefore, some scholars have put forward the formula for selecting the best current frequency of the gear. After several corrections, the following formula is formed: f≈250/m2

  Where f-current frequency, KHZ;m-the modulus of the gear.

Table 1 The best frequency of heating for different modulus gears

  The heating time is also closely related to the gear modulus, and the heating time should be as close as possible to the following formula. T≈m2/4

  In the formula, T——heating time, s;m-the modulus of the tooth.

  It can be seen that single-frequency induction heating cannot meet the change of gear modulus, and it is extremely inconvenient to process gears with different moduli. The dual-frequency induction heating can adjust the heating frequency and power for different modulus gears, making it more flexible and convenient to use.

  The dual-frequency induction heating equipment developed by Polaris-etek has an intermediate frequency output frequency of 10KHZ and a high frequency output frequency of 120~150KHZ. When heating different modulus gears, adjust the proportion of the intermediate frequency output power and the high frequency output power. Match the size of the gear modulus, the high-frequency output power decreases with the increase of the gear modulus. Basically meet the surface heat treatment processing of small module gears.

  At the same time, the use of ANSYS software for thermal simulation can accurately match the output power and frequency.

Comparison of different heat treatment processes

  Compare the three common heat treatment processes of carburizing and quenching, single-frequency induction hardening and synchronous dual-frequency induction hardening.

  The gas carburizing method is to put the workpiece in a closed carburizing furnace, carburize the workpiece in a high temperature carburizing atmosphere of 920 ℃, and then perform quenching treatment. The carburizing and quenching heat treatment time is relatively long, so its deformation is relatively large, the cost is high, and it is not suitable for partial quenching, and its flexibility is poor.

  Figure 7 Carburizing furnace

  Single-frequency induction hardening is ordinary induction hardening, with small deformation and high heating efficiency, which is suitable for local quenching, but for contoured workpieces with uneven surfaces, the heating is uneven and a uniform hardened layer cannot be obtained.

Figure 8 Gear single frequency quenching	Figure 9 Gear dual-frequency heating

  Synchronous dual-frequency induction hardening is to simultaneously induce dual-frequency eddy currents on the surface of the workpiece, heat it to the quenching temperature, and then rapidly cool it to obtain the required performance. Synchronous dual frequency has a wider application range than single frequency quenching, with less deformation, extremely short heating time, high production efficiency, suitable for partial quenching and profiling quenching, and suitable for batch and streamlined operations.

Test parameters of foreign companies
 

The test gear is a cylindrical gear m=2, Z=36, full tooth height 4.7mm, and tooth width 20mm.

Table 2 Three different test process parameters of gears

In order to have a profiling concept for quenching along the tooth profile, the term profiling rate is introduced.

Profiling rate=(100-(Ds/h)*100)*%
 

Where Ds——the depth of the hardened layer at the tooth top (measured to HV450); h-tooth height.

Table 3 Parameter measurement results of three heat treatment processes

  It can be seen from the above table that after dual-frequency quenching, the residual compressive stress of the gear is the highest, which is close to 800MPa. The company believes that dual-frequency induction hardening of gears can obtain higher strength than single-frequency hardening and carburizing hardened gears, and the smaller deformation is its outstanding advantage.

in conclusion

· Gear synchronous dual-frequency induction hardening can replace the carburizing and hardening process of some gears. The most obvious advantages are small deformation, high production efficiency, low cost, energy saving, and low environmental pollution;

· Gear synchronous dual-frequency induction hardening equipment is simple and convenient to operate, suitable for mass, streamlined production;

· Combined with advanced simulation technology, frequency and power can be accurately matched;

· With the corresponding mechanical structure, fully automated or semi-automated production can be realized, saving labor costs.

Company Profile

  POLARIS ETek was founded in 2009 by Dr. Chang Hong from Xi’an Jiaotong University, majoring in control theory and control engineering. Committed to developing the integrated application capabilities of embedded systems, automation and numerical control technology, to provide customers with fully automated integrated control engineering solutions.

  The company now has 15 R&D personnel, including 2 doctors and 5 masters. The core technology is "full digital induction heating control system", and it has the design and manufacturing capabilities of special equipment, automation systems, and industrial robots. It provides customers with a complete set of solutions based on digital induction heating technology, including induction heating power supply design and inductor simulation Design, fully automatic special machine and production line, remote monitoring and induction heating industrial robots, etc. The application industry involves various industries and fields such as aerospace, machinery manufacturing, medical equipment, hardware and electrical machinery, refrigeration and heating and ventilation.

  "Science and technology innovation" is the soul of our enterprise, and "frank passion" is the driving force for our progress. I hope that the services and products of "Polaris-etek" can contribute to the development of your business.