KR20230033284A - Transmission gear manufacturing method and transmission gear - Google Patents

Abstract

Disclosed is a transmission gear manufacturing method comprising a step of preparing alloy steel; a step of forging the alloy steel; a step of heat-treating the forged alloy steel; a step of forming teeth in the heat-treated alloy steel; a step of heating to carburize the alloy steel in which the teeth are formed, followed by quenching and then tempering; and a step of high-frequency induction heating the contour of the tempered alloy steel using a dual frequency, followed by quenching and tempering. With the transmission gear manufacturing method, a transmission gear having improved wear resistance (durability) and increased power transmission efficiency can be provided.

Description

Transmission gear manufacturing method and transmission gear {TRANSMISSION GEAR MANUFACTURING METHOD AND TRANSMISSION GEAR}

The present invention relates to a transmission gear manufacturing method and a transmission gear manufactured thereby, and relates to a transmission gear manufacturing method for providing a transmission gear with improved durability and the like.

A transmission is a gear shifting device that converts power generated from an engine of a vehicle into rotational force required according to speed and transmits the same. Performance requirements in vehicles are generally increased power and torque and increased fuel economy. Therefore, high torque and light weight of the transmission are inevitable, transmission efficiency is emphasized, the driving environment of the gear becomes harsh, and required characteristics are also increasing.

In order for the transmission to have the required performance as above, it is necessary to change the design of the gear, which is a key part of the transmission. In order to satisfy the required performance of transmissions, gears require high durability and the ability to improve transmission efficiency. However, it is difficult to satisfy both characteristics simultaneously in reality.

It is necessary to improve the surface roughness of the gear to increase the transmission efficiency of the gear, but if a part of the surface of the gear is processed to improve the surface roughness, the durability of the gear may deteriorate.

There are two main ways to satisfy the above required performance. One is the development of alloy materials constituting gears, and the other is the development of a process for manufacturing gears.

The improvement of wear resistance through the development of alloy materials is disadvantageous in that the cost invested in research is high and the development time is long. Therefore, in the industry, process development, which partially changes the manufacturing process of gears or adds post-processes, is mainly adopted.

In the conventional transmission gear, ⓐ forging of alloy steel, ⓑ ISO (Isothermal annealing, after forging, heat treatment to remove residual stress inside the alloy steel and to make the non-uniform microstructure uniform, improve the workability of alloy steel and improve mechanical properties. can be improved), ⓒ gear cutting (forming teeth on alloy steel), ⓓ quenching and tempering after carburizing (as one of the surface heat treatments, carbon on the surface of gear teeth penetrates into the inside of the gear and is quenched to It is manufactured through ⓔCSP (Conventional shot peening, which physically collides shot balls on the gear surface to form compressive residual stress and improve durability by having an increased surface hardness value) lost.

However, the transmission gear manufactured through this process has a surface hardness of about HV780 to HV820, but a situation in which the gear surface may be damaged may occur in a harsh transmission driving environment.

In the present art, there is a need for a manufacturing process of a transmission gear with improved durability.

The matters described as the background art above are only for improving understanding of the background of the present invention, and should not be taken as an admission that they correspond to prior art already known to those skilled in the art.

Republic of Korea Patent Publication No. 10-2015-0019212 B1 (2015.02.25)

The present invention relates to a transmission gear manufacturing method for providing a transmission gear capable of improving wear resistance (durability) and increasing power transmission efficiency.

Transmission gear manufacturing method according to the present invention, preparing an alloy steel; forging alloy steel; Heat treating the forged alloy steel; forming teeth in the heat-treated alloy steel; Heating to carburize the tooth-formed alloy steel, followed by quenching and then tempering; and high-frequency induction heating, quenching, and then tempering the contour of the tempered alloy steel using a dual frequency.

In the step of heating the contour of the tempered alloy steel by using a dual frequency and tempering after quenching, frequencies of 5 to 15 kHz and 200 to 250 kHz may be used.

A frequency of 5 to 15 kHz is used for 40 to 70 ms, and a frequency of 200 to 250 kHz may be used for 100 to 150 ms.

In the step of induction heating the contour of the tempered alloy steel using a dual frequency and tempering after quenching, the high frequency induction heating can be performed within 1 second.

In the step of heating the contour of the tempered alloy steel using a dual frequency and tempering after quenching, the voltage of the current flowing during the high frequency induction heating may be 300 to 400V.

During quenching, it is possible to quench alloy steel through gaseous substances.

The transmission gear manufactured according to the transmission gear manufacturing method may have the following characteristics.

The surface hardness of the transmission gear may be HV850 to HV890.

The 10-point average roughness of the gear tooth surface of the transmission gear may be 1.0 μm or less.

The transmission gear manufactured through the transmission gear manufacturing method according to the present invention has improved durability due to improved surface hardness than the transmission gear manufactured according to the conventional manufacturing method, and has excellent surface roughness, so that the transmission efficiency of power is also excellent. .

1 is a flowchart of a method for manufacturing a transmission gear according to an embodiment of the present invention
Figure 2 is a photograph of a transmission gear.
3 and 4 are tables showing physical properties of a transmission gear manufactured according to an embodiment of the present invention;

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart of a method for manufacturing a transmission gear according to an embodiment of the present invention.

Transmission gear manufacturing method, preparing an alloy steel (S100); Forging alloy steel (S200); Heat-treating the forged alloy steel (S300); forming teeth on the heat-treated alloy steel (S400); Heating and quenching (quenching) and then tempering (tempering) to carburize the tooth-shaped alloy steel (S500); and high-frequency induction heating, quenching, and then tempering the contour of the tempered alloy steel using a dual frequency (S600).

In the present invention, in the conventional transmission gear manufacturing method described above, ⓓ quenching and tempering after carburization (one of surface heat treatment, infiltrating carbon on the surface of the gear teeth into the inside of the gear and rapidly cooling the durability of the gear teeth through the process After ⓔCSP (Conventional shot peening, physically colliding a shot ball on the gear surface to form a compressive residual stress and having an increased surface hardness value to improve durability) step is omitted, and tempering It is characterized by performing a step (S600) of high-frequency induction heating and quenching and then tempering the outline of the completed alloy steel using a dual frequency.

That is, steps S100 to S500 are similar to the conventional transmission gear manufacturing method, but characterized by including a step (S600) of hardening the outline of the alloy steel through high frequency induction heating using a dual frequency.

High-frequency induction heating can rapidly heat alloy steel in a short time. This is to increase the wear resistance of alloy steel. The principle of high-frequency induction heating is to heat alloy steel through a basic electromagnetic induction phenomenon.

That is, when a magnetic field is generated by applying a current to the coil, a magnetic field is also generated in the alloy steel, and as the current flows in the direction of canceling the magnetic field inside the alloy steel, heat is generated by the current and the electrical resistance of the alloy steel.

In the present invention, it is characterized in that a dual frequency is used in step S600. This is because the area to be heated varies according to the range of frequencies. Referring to FIG. 2, when using a medium frequency (5 to 30 kHz), the tooth bottom 20 is mainly heated, and when using a high frequency (100 to 400 kHz), the tooth 10 is mainly heated.

Therefore, when the dual frequency is used, the surface of the alloy steel can be hardened through heating of both the tooth bottom 20 and the tooth 10, which is helpful in improving durability compared to the case of using a single frequency.

That is, when only medium frequency is used, it is difficult to secure durability because the rest of the area except for the tooth bottom 20 is not heated, and when only high frequency is used, if the generation time of the induced current is increased to heat up to the tooth bottom 20, 10) There is a disadvantage in that it is difficult to secure durability because the part is excessively heated and accompanied by deformation due to heat.

In addition, when using the dual frequency, there is an effect of excellent energy efficiency. In the case of using a single frequency, since the time to generate the induced current must be longer than in the case of using a dual frequency (since heat treatment must be performed for a long time at low power to supply the same energy to alloy steel, heat is supplied only to the necessary part) difficult to do), using dual frequencies is better in terms of energy efficiency. That is, it can be said that generating a current of 198 kW by a medium frequency and a current of 40 kW by a high frequency for 0.5 seconds, respectively, is superior in energy efficiency to the case of generating a current of 110 kW by a single medium frequency for 4.5 seconds.

In addition, in the case of using the dual frequency, there is an advantage in that deformation due to heat can be minimized because heat moves only along the surface of the gear tooth.

Hereinafter, steps S100 to S500 will be described.

Preparing the alloy steel (S100) is a step of preparing the alloy steel required for manufacturing the transmission gear. Although SCM620HSi alloy steel was used for the test in this specification, the effect according to the present invention is not a result expressed by the characteristics of this steel type, so any alloy steel may be used.

The forging of the alloy steel (S200) corresponds to a step of putting the prepared alloy steel in a mold and applying heat and pressure to form the alloy steel before tooth processing in order to implement the overall gear shape. Forging conditions do not affect the generation of the effect of the present invention, and therefore can be arbitrarily selected.

Heat treatment of the forged alloy steel (S300) corresponds to the same step as ISO (Isothermal annealing) described above. After forging alloy steel, this is a heat treatment step performed to remove residual stress inside the alloy steel and to make the non-uniform microstructure uniform. Since the effect according to the present invention is not expressed by the ISO conditions, the ISO conditions may be arbitrarily selected.

The step of forming teeth in the heat-treated alloy steel (S400) corresponds to a step of forming the alloy steel to have gear teeth. This can be referred to as the cutting stage.

After forming the teeth, a step (S500) of heating, quenching, and then tempering to carburize the alloy steel in which the teeth are formed is performed. This is a step for improving the durability of the surface of the gear tooth formed on the alloy steel by heating the alloy steel at a temperature of 850 to 950 ° C. to infiltrate the carbon present on the surface of the alloy steel into the alloy steel, and then quenching the alloy steel. Like this step, since it is irrelevant to the effect generation according to the present invention, the condition can be arbitrarily selected.

More specifically for step S600, the dual frequencies used may range from 5 to 15 kHz and from 200 to 250 kHz. Also, a frequency of 5 to 15 kHz may be used for 40 to 70 ms, and a frequency of 200 to 250 kHz may be used for 100 to 150 ms. In addition, in the step of induction heating the contour of the tempered alloy steel using a dual frequency and tempering after quenching, the high frequency induction heating may be performed within 1 second.

Specifically, high-frequency induction heating may be performed by alternately using dual frequencies in the form of sine waves in the coil as follows.

On the other hand, in the transmission gear manufacturing method according to the present invention, quenching is performed twice, and during quenching, the alloy steel can be quenched through gaseous substances. Quenching is usually carried out by immersing alloy steel in oil or water, but when oil is used, there is a risk of fire, and when water is used, the part in direct contact with water, There is a disadvantage in that a transmission gear having non-uniform physical properties may be manufactured because the physical properties of the secondly contacted part and the roughness of the tooth surface are different.

Therefore, a uniform transmission gear can be obtained by providing a chamber in which the gaseous material is stored so that the rapidly heated alloy steel can be rapidly cooled through the gaseous material, and spraying the chamber.

It is preferable to use nitrogen gas or an inert gas with low reactivity as the gas used for cooling.

Hereinafter, the results of experiments on physical properties of transmission gears manufactured according to the prior art and the present invention will be described.

In all experiments, SCM620HSi alloy steel was used.

<Experimental Example 1> - One embodiment of the present invention

After forging the alloy steel at 1000 to 1250 ° C, heat treatment at 900 ° C for 60 minutes, cooling for 5 minutes, and heat treatment at 600 ° C for 60 minutes (ISO step). Thereafter, a tooth was formed in the alloy steel, and after carburizing, quenching and tempering were performed. Carburization was carried out at 900 ° C for 3 hours, and after quenching with nitrogen gas at -196 ° C, tempering was performed at 150 ° C for 1 hour in air.

Thereafter, after induction heating using frequencies of 5 to 15 kHz and 200 to 250 kHz, quenching and tempering were performed under the same conditions as above to manufacture a transmission gear according to Experimental Example 1.

<Experiment 2> - Prior art

After forging the alloy steel at 1000 to 1250 ° C, heat treatment at 900 ° C for 60 minutes, cooling for 5 minutes, and heat treatment at 600 ° C for 60 minutes (ISO step). Thereafter, a tooth was formed in the alloy steel, and after carburizing, quenching and tempering were performed. Carburization was carried out at 900 ° C for 3 hours, and after quenching with oil at 100 ° C, tempering was performed by air cooling at 150 ° C for 1 hour.

Thereafter, a transmission gear according to Experimental Example 2 was manufactured by performing CSP (Conventional shot peening, physically colliding a shot ball with an alloy steel surface).

<Experimental Example 3> - Modification of an embodiment of the present invention (using a single frequency)

Under the same conditions as Experimental Example 1, but after induction heating using a single frequency (30 kHz), quenching was performed using water instead of nitrogen gas.

<Experimental Example 4> - Modification of an embodiment of the present invention (quenching using water in step S600)

Quenching was carried out under the same conditions as Experimental Example 1, but using water instead of nitrogen gas.

Table 1 below is a table of physical properties of transmission gears manufactured according to Experimental Examples 1 to 4.

division ??Ching CSP surface hardness Tooth bottom effective hardening depth heat strain Roughness (Rz) gear endurance Tooth surface damage area after gear durability test Experiment 1 nitrogen gas X HV850~890 0.6mm cow 1.0㎛ over 10 million 5㎟ Experiment 2 oil O HV780~820 0.6mm minuscule 1.2㎛ over 10 million 113㎟ Experiment 3 water X HV850~890 0.6mm big 1.0㎛ over 10 million 161㎟ Experiment 4 water X HV850~890 0.6mm middle 1.5㎛ over 10 million 159㎟

According to Experimental Examples 1 to 4, the tooth bottom effective hardening depth (the depth of the point where the hardness is 550HV) was all the same at 0.6mm, and the gear durability test results were all able to withstand more than 10 million cycles.

However, the transmission gear manufactured by Experimental Example 1 had excellent surface hardness, little deformation of teeth due to heat, and excellent surface roughness (Rz). That is, the transmission gear of Experimental Example 1 has increased durability compared to the transmission gear of Experimental Example 2, and is expected to have excellent power transmission efficiency due to excellent roughness.

The transmission gear manufactured by Experimental Example 3 had excellent roughness, but deformation due to heat was large due to the use of a single frequency.

In the transmission gear manufactured by Experimental Example 4, water was used during quenching, and water cooling proceeded unevenly, resulting in insufficient roughness.

Table 2 below is a photograph of the surface of the transmission gear manufactured according to each experimental example.

Experiment 1 Experiment 2

Experiment 3 Experiment 4

Referring to Table 2, in the case of Experimental Example 1, when compared with Experimental Example 2, after an oxide film is formed in the carburizing process, it can be seen that almost no oxide film is formed and the surface shape is homogeneous.

In the case of Experimental Example 2, the oxide film formed during the carburizing process is uniformly distributed, and as the CSP process proceeds, the surface of the part in contact with the short ball is crushed and the surface shape is uneven.

In the case of Experimental Example 3, in addition to the formation of an oxide film by carburization, a plurality of oxide films are formed due to quenching by the water cooling method, but it can be seen that the surface shows a relatively uniform shape.

In the case of Experimental Example 4, in addition to the formation of an oxide film by carburization, it can be seen that quenching proceeds non-uniformly after induction heating using a dual frequency, and the surface shape is non-uniform.

Table 3 below is a surface photograph for measuring the pitting resistance (fatigue life) of the transmission gear manufactured according to each experimental example.

Experiment 1 Experiment 2

Experiment 3 Experiment 4

The pitting resistance test was conducted using the gear endurance tester for powertrains from Space Creation as shown below, 3200rpm, 150Nm of torque, flow rate = 1L/min, oil temp = 80℃, and was conducted for 16.67 hours.

As a result, the fitting area of the gear of Experiment 1 is 14 mm2, the fitting area of the gear of Experiment 2 is 84 mm2, the fitting area of the gear of Experiment 3 is 161 mm2, and the fitting area of the gear of Experiment 4 is 159 mm2. .

When comparing Experimental Example 1 and Experimental Example 2 corresponding to the prior art, it was confirmed that the fitting area was reduced by about 83%.

In Figures 3 to 4, manufacturing conditions (output voltage, frequency range, frequency use time) and physical properties of the transmission gear manufactured according to an embodiment of the present invention are shown (Examples 1 to 18).

The surface hardness required by the transmission gear is 780HV or more based on the point 50㎛ directly below the surface of the PCD part of the gear, the core hardness is 400 to 480HV, the depth of the effective hardened layer is located at 0.4 to 0.7mm, and the tooth shape/dimension is should be normal

In the case of Examples 1 to 4, all transmission gear requirements are met. At this time, the condition of the high-frequency induction heating using the double frequency is that the double frequency used has a range of 5 to 15 kHz and 200 to 250 kHz, and the frequency of 5 to 15 kHz is used for 40 to 70 ms, and the frequency of 200 to 250 kHz is used for 40 to 70 ms. It is used for 100 to 150ms, and the output voltage is 300 to 400V. Therefore, it is preferable to perform high-frequency induction heating to satisfy the above conditions.

In the case of other embodiments (5 to 18), when the above conditions are out of range, the surface hardness is less than 780HV, the effective tooth bottom hardening depth is less than 0.4 mm, or the tooth shape / dimension is abnormal, so the required physical properties are not met. confirmed to be

Looking at some examples, in the case of Examples 5 to 7, the output voltage was less than 300V, so the surface hardness was not sufficient, and in some examples, it was confirmed that the effective tooth bottom hardening depth was less than 0.4 mm.

In the case of Examples 8 to 10, the output voltage exceeded 400V, and in some examples, the PCD portion curing depth exceeded 0.7 mm, and in some examples, it was confirmed that the surface hardness was not sufficient. In addition, in Examples 8 to 10, all of the teeth/dimensions are abnormal, which is presumed to be an effect due to excessive output voltage.

As described above, the surface hardness of the transmission gear manufactured according to the transmission gear manufacturing method according to an embodiment of the present invention may be HV850 to HV890, and the 10-point average roughness of the gear tooth surface of the transmission gear may be 1.0 μm or less. Accordingly, A transmission gear with improved wear resistance and improved power transmission efficiency can be manufactured.

Although shown and described in relation to specific embodiments of the present invention, it is known in the art that the present invention can be variously improved and changed without departing from the technical spirit of the present invention provided by the claims below. It will be self-evident to those skilled in the art.

10: hit
20: toother

Claims (9)

preparing alloy steel;
forging alloy steel;
Heat treating the forged alloy steel;
forming teeth in the heat-treated alloy steel;
Heating to carburize the tooth-formed alloy steel, followed by quenching and then tempering; and
A method for manufacturing a transmission gear comprising the steps of high-frequency induction heating and tempering after quenching the contour of the tempered alloy steel using a dual frequency.
The method of claim 1,
In the step of high-frequency induction heating the contour of the tempered alloy steel using a dual frequency and tempering after quenching,
Transmission gear manufacturing method characterized in that using a frequency of 5 to 15 kHz and 200 to 250 kHz.
The method of claim 2,
A method for manufacturing a transmission gear, characterized in that a frequency of 5 to 15 kHz is used for 40 to 70 ms, and a frequency of 200 to 250 kHz is used for 100 to 150 ms.
The method of claim 1,
In the step of high-frequency induction heating the contour of the tempered alloy steel using a dual frequency and tempering after quenching,
High-frequency induction heating is a transmission gear manufacturing method, characterized in that carried out within 1 second.
The method of claim 1,
In the step of high-frequency induction heating the contour of the tempered alloy steel using a dual frequency and tempering after quenching,
Transmission gear manufacturing method, characterized in that the voltage of the current flowing during high-frequency induction heating is 300 to 400V.
The method of claim 1,
A method for manufacturing a transmission gear, characterized in that the alloy steel is quenched through gaseous substances during quenching.
Transmission gear manufactured according to the transmission gear manufacturing method according to claim 1.
The method of claim 7,
Transmission gear, characterized in that the surface hardness of the transmission gear is HV850 to 890.
The method of claim 7,
A transmission gear, characterized in that the ten-point average roughness of the gear tooth surface of the transmission gear is 1.0 μm or less.

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