KR20110054426A - Method of manufacturing sintered gear for transmission - Google Patents

Abstract

PURPOSE: A method of manufacturing sintered gear for transmission, which can reduce manufacturing costs by minimizing post processes is provided to increase the density of the sintered gear and to improve strength. CONSTITUTION: A method of manufacturing sintered gear for transmission comprises the next step. Carbon(C) 0.2 ~ 0.3 wt% is mixed in alloyed powder consisting of chrome(Cr) 1.3 ~ 1.7 wt%, molybdenum(Mo) 0.15 ~ 0.30 wt% and remainder iron(Fe). The pressure is added in the mixed powder and tooth form is given to the mixed powder. The molded materials are sintered in 1200 ~ 1300°C. The sintered materials(1) are rolled between two rolling dies(3,5) in room temperature. The rolled materials are heat-treated.

Description

Sintering gear manufacturing method for transmissions {METHOD OF MANUFACTURING SINTERED GEAR FOR TRANSMISSION}

The present invention relates to a method for manufacturing a sintering gear for a transmission, and more particularly, to a method for manufacturing a sintering gear for a transmission that can achieve a high density as well as reduce manufacturing costs by minimizing a post-process.

In general, the vehicle is provided with a power transmission device for reducing the power generated from the engine to transmit to the tire.

The manual transmission is equipped with a plurality of helical gears on the input shaft and the output shaft, and the automatic transmission is equipped with a planetary gear and a sun gear in the planetary carrier so as to mesh with the outer annulus gear to rotate. Consists of.

Many of the helical gears mounted in the transmission are manufactured by forging and machining. The material is mainly forged using SCM and SCr alloy steel and various processing methods such as hobbing, grinding, shaving, broaching, etc. are mobilized for cutting.

On the other hand, the sintered material is a material produced by the powder metallurgy method, and sintering is produced by forming various metal / ceramic powders and generating a necking phenomenon due to diffusion of the material between the powder and the powder at high temperature. I say that. Such a sintering method is used in various metal / ceramic mechanical structural materials, electronic materials and the like.

In particular, the metal-based sintering method has been used in a variety of automotive structural parts, because it gives a shape on the mold during molding because the post-processing process can be minimized to reduce the manufacturing cost.

Recently, various techniques for alloying or joining iron powders and elements such as Ni, Mo, and Cu have been attempted in order to minimize the post-processing process and increase the density / high strength of the sintered material. Recently, alloys of chromium (Cr) alloys, which have not been used as sintered gold elements due to their high oxidizing properties, have also been introduced to promote high strength of sintered materials.

Accordingly, an object of the present invention is to provide a method for manufacturing a sintered gearbox for a transmission that can minimize the post-process compared to forging and machining methods, thereby reducing manufacturing costs and improving the strength by implementing high density.

The object is 0.2 ~ 0.3 wt in the alloy powder consisting of 1.3 ~ 1.7 wt% chromium (Cr), 0.15 ~ 0.30 wt% molybdenum (Mo) and the balance of iron (Fe) according to the manufacturing method of the sinter gear for the transmission of the present invention Mixing% carbon (C); Applying pressure to the mixed powder and at the same time imparting teeth and shaping; Sintering the molded body under the condition of 1200 to 1300 ° C; Rolling the sintered sintered body at room temperature; It is achieved by the process of heat-treating the rolled precursor.

Here, in the rolling process, it is preferred that the sintered body is engaged with two rolling dies having opposite shapes of the finished teeth, and is rotated and pressed, thereby densifying the tooth surface and simultaneously completing the teeth.

At this time, the tooth surface density after the precursor process is 7.75g / cc or more, the core density is 7.5g / cc or more density level, the densification depth is preferably 200 ~ 400㎛.

The molding process is preferably performed to have a density of at least 7.5 g / cc.

The rolling process may be made of at least one of the tooth surface and the base portion.

As described above, according to the present invention, it is possible to minimize the post-process compared to the prior art, as well as reducing the manufacturing cost, there is provided a sinter gear manufacturing method for a transmission that can implement high density / high strength.

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

As shown in FIG. 1, a method of manufacturing a sintered gear for a transmission according to the present invention includes mixing a powder, molding a mixed powder into a gear, sintering a molded body, and It comprises the process of rolling a sintered compact, and the process of heat processing.

In the powder mixing process, an alloy powder composed of 1.3 to 1.7 wt% chromium (Cr), 0.15 to 0.30 wt% molybdenum (Mo) and a balance of iron (Fe), and 0.2 to 0.3 wt% carbon (C) are prepared and mixed with each other. do.

When the chromium (Cr) is less than 1.3 wt%, there is a concern that the mechanical properties of the material are lowered. If the chromium (Cr) is more than 1.7 wt%, the material ratio is increased. do.

If the molybdenum (Mo) is less than 0.15 wt%, the heat treatment hardenability is lowered, and if the molybdenum (Mo) is more than 0.30 wt%, an increase in material ratio and a deterioration of moldability are concerned.

When the carbon (C) is less than 0.2 wt%, there is a fear of lowering the core density during the heat treatment, and when the carbon (C) is more than 0.3 wt%, the impact resistance due to brittleness after the heat treatment is feared, so it is limited to the above range.

The powder thus mixed is pressurized and molded into a molded body having a gear tooth. If the Helix Angle is not 0 degrees, helical molding may be applied. At this time, the molded body can achieve the target value of the present invention by having a density of 7.5g / cc or more.

The molded article thus formed undergoes a process of sintering at a temperature of 1200 to 1300 ° C. If the sintering temperature is less than 1200 ° C material diffusion between the powder and necking (necking) is not smooth, if the mass exceeds 1300 ° C productivity is significantly lowered, it is preferable to sinter under the above temperature conditions.

Next, by rolling the sintered sintered body at room temperature, the tooth surface is densified and the effect of completing the tooth shape can be obtained. The precursor process is performed as shown in FIG. That is, two rolling dies 3 and 5 having opposite shapes are installed and the sintered bodies 1 are positioned between the two rolling dies 3 and 5 so that both rolling dies 3 and 5 are sintered bodies ( Engage with 1) to rotate / press to form the finished tooth. Through this rolling process, the tooth surface of the sintered body 1 is densified, and after rolling, the tooth surface density is 7.75 g / cc or more as shown in FIG. 3, and the core density has a density level of 7.5 g / cc or more. The depth is preferably 200 µm to 400 µm. In this case, the surface to be densified corresponds to both the tooth surface and the bottom of the gear, but may be any one of the tooth surface and the bottom. If the densification depth is less than 200㎛ can not satisfy the desired mechanical properties, if the precursor is to be exceeded 400㎛ is disadvantageous due to the increase in thermal strain during heat treatment due to excessive residual stress by the rolling.

Finally, the hardness of the tooth surface is increased by performing various heat treatments such as carburization and carburization and nitriding on the finished precursor. If necessary, the annealing treatment may be performed after the heat treatment.

Specifications of the sintered gear manufactured by the above process are shown in Table 1.

TABLE 1

Ref. Tooth Profile Normal Tooth Profile Full Depth Tooth Module 1.500 Pressure Angle 17.5 ° Number of Teeth 33 Helix Angle 0 Lead - Reference pitch circle diameter
(Standard Pitch Circle Dia) φ49.5 Base Circle Dia. φ47.21 Whole Depth 3.35 Amount of Addendum Modification 0 Measurement Over Balls φ55.317 Ball Dia. φ3.25 T.I.F Dia. φ47.606

Molding density of the manufactured sintered gear was 7.5g / cc, sintering temperature was carried out at 1250 ℃, and the tooth surface was densified to 250㎛ using the rolling method of FIG. Also, note that carburizing and annealing treatments have been performed to secure surface hardness.

In order to compare the bending fatigue load of the sintered gear of the present invention as described above and the gear made of a conventional alloy steel forging (SCr420H), a bending stress was applied to the tooth surface using a magnetic resonance fatigue tester. When the maximum load was called L _max , the minimum load was set to 0.1 L _max (Load Ratio = 0.1), and the form and period of the stress were set to 40 to 50 Hz in the form of sin wave. As a result, it was possible to obtain a graph as shown in FIG. 4, while the conventional forged gear exhibited a bending fatigue property of 19 kN, while the sintered gear of the present invention exhibited 20.5 kN and exhibited about 8% improved fatigue fatigue property. there was.

As such, the sintered gear manufactured by the manufacturing method according to the present invention can minimize post-processing compared to the conventional forging gear, thereby reducing the manufacturing cost and increasing the density / high strength.

1 is a process chart showing a method for manufacturing a sinter gear for a transmission according to the present invention.

2 is a view for explaining the principle that the tooth of the gear is formed through the rolling process of FIG.

3 is a view showing the density and densification depth of the tooth surface and the tooth base of the gear after rolling.

Figure 4 is a graph for comparing the bending fatigue load of the sintered gear of the present invention produced by the process of Figure 1 and the conventional forged gear.

Claims (5)

Mixing 0.2 to 0.3 wt% carbon (C) in an alloy powder composed of 1.3 to 1.7 wt% chromium (Cr), 0.15 to 0.30 wt% molybdenum (Mo), and a balance of iron (Fe); Applying pressure to the mixed powder and at the same time imparting teeth and shaping; Sintering the molded body under the condition of 1200 to 1300 ° C; Rolling the sintered sintered body at room temperature; A method for manufacturing a sinter gear for a transmission, comprising the step of heat-treating the rolled precursor. The method according to claim 1, In the rolling process, the sintered body is engaged with two rolling dies having opposite shapes of the finished tooth, and is rotated and pressed, thereby densifying the tooth surface and simultaneously completing the tooth. The method according to claim 2, The tooth surface density after the rolling process is 7.75g / cc or more, the core density has a density level of 7.5g / cc or more, the densification depth is 200 ~ 400㎛ manufacturing method for a sinter gear for a transmission. The method according to claim 1, The forming process is a sinter gear manufacturing method for a transmission, characterized in that the density is performed to have a density of 7.5g / cc or more. The method according to claim 1, The rolling process is a sintered gear manufacturing method for a transmission, characterized in that at least one of the tooth surface portion and the bottom portion.

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