WO2024038949A1 - Method for manufacturing gear part by using liquid phase sintering, and gear part manufactured thereby - Google Patents

Abstract

The present invention relates to a method for manufacturing a gear part, and a gear part manufactured thereby. The method for manufacturing a gear part according to an embodiment of the present invention comprises the steps of: preparing iron-based powder for powder metallurgy; forming a molded body including a hollow part and teeth disposed on the outer peripheral surface thereof by molding the powder for powder metallurgy; preparing a core body made of bulk metal and assembling the core body such that the core body is disposed in the hollow part of the molded body; and sintering the assembled molded body and core body.

Description

Manufacturing method of gear parts using liquid sintering and gear parts manufactured by the manufacturing method

The present invention relates to a manufacturing method of gear parts and gear parts manufactured by the manufacturing method. In one embodiment, it can be manufactured by performing heterogeneous bonding using liquid phase sintering.

In general, the method of manufacturing gears involves manufacturing metal rods through several processes such as mechanical processing and heat treatment, which requires a lot of manpower and time, resulting in increased manufacturing costs and high unit costs.

To solve this problem, a gear manufacturing method using powder metallurgy is being developed, which has a simple manufacturing process, can be automated, and has a low manufacturing cost. However, compared to the existing method, the physical properties, i.e., sintering density and hardness, are lower, so it is applied to gear products. There is difficulty in

In addition, the raw material cost of the gear manufacturing method by powder metallurgy is approximately 1.5 times more expensive than that of metal powder, and the more alloying of the metal powder, the higher the raw material cost. This difference makes it difficult to secure price competitiveness in manufacturing costs compared to existing methods, even if manufacturing costs are reduced due to simplification of the manufacturing process.

Korean Patent Publication No. 10-1522513, a prior art, discloses a manufacturing method for manufacturing helical gears by sintering metal powder.

The purpose of the present invention is to provide a manufacturing method of gear parts that can reduce raw material and processing costs, and gear parts manufactured by the manufacturing method.

Additionally, the process is simple and manufacturing costs can be saved.

In addition, even if large-sized gear parts are manufactured, only a small number of parts are sintered, so deformation such as distortion can be prevented.

Additionally, carbon emissions can be reduced because additional heat treatment processes to secure physical properties are not required.

In addition, by securing a high shrinkage rate of the molded body, a strong bond between the heterojunction of the molded body and the core body is possible.

In addition, it has excellent physical properties such as sintered density and hardness.

A method for manufacturing gear parts according to an embodiment of the present invention includes preparing iron-based powder metallurgy powder; Forming a molded body including a hollow body and teeth disposed on the outer peripheral surface by molding the powder metallurgy powder; Preparing a core body made of bulk metal and assembling the core body so that the core body is disposed in the hollow of the molded body; and sintering the assembled molded body and core body.

The powder metallurgy powder may contain 0.5 to 10.0% chromium (Cr) and 0.5 to 3.0% carbon (C) based on the total weight of the powder metallurgy powder.

In the step of forming the molded body, the molding pressure may be 5.5 to 7.5 ton/cm ² .

In the step of forming the molded body, the molding density of the molded body may be 5.5 to 6.5 g/cm ³ , and in the sintering step, the sintered density of the sintered body produced by sintering the molded body may be 7.0 to 8.0 g/cm ³ .

In the sintering step, the powder metallurgy powder of the molded body may be liquid-phase sintered.

Gear parts according to embodiments of the present invention are manufactured by the manufacturing method described above.

The manufacturing method of gear parts according to an embodiment of the present invention can reduce raw material and processing costs in manufacturing gear parts.

Additionally, the process is simple and manufacturing costs can be saved.

In addition, even if large-sized gear parts are manufactured, only a small number of parts are sintered, so deformation such as distortion can be prevented.

Additionally, carbon emissions can be reduced because additional heat treatment processes to secure physical properties are not required.

In addition, by securing a high shrinkage rate of the molded body, a strong bond between the heterojunction of the molded body and the core body is possible.

In addition, gear parts manufactured by the above manufacturing method have excellent physical properties such as sintered density and hardness.

1(a) to (c) are photographs of the molded body, the core body, and the gear parts in which the sintered body and the core body are combined, respectively, manufactured in Example 6.

Figures 2(a) to (d) are photographs of the boundaries of the sintered body and the core body among the gear parts manufactured in Examples 1 to 4, respectively.

Figures 3(a) to (e) are photographs of the boundaries of the sintered body and the core body among the gear parts manufactured in Examples 5 to 9, respectively.

Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Additionally, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field. Throughout the specification, “including” an element means that other elements may be further included rather than excluding other elements, unless specifically stated otherwise.

A method for manufacturing gear parts according to an embodiment of the present invention includes preparing iron-based powder metallurgy powder; Forming a molded body including a hollow body and teeth disposed on the outer peripheral surface by molding the powder metallurgy powder; Preparing a core body made of bulk metal and assembling the core body so that the core body is disposed in the hollow of the molded body; and sintering the assembled molded body and core body.

The step of preparing the iron-based powder metallurgy powder can be prepared by purchasing or manufacturing the powder metallurgy powder. In this case, it can be prepared by mixing various types of powder.

The powder metallurgy powder may be a powder containing iron (Fe) as a main component, and may further include components such as chromium (Cr), nickel (Ni), molybdenum (Mo), and carbon (C). , it may further contain unavoidably added impurities.

The powder metallurgy powder may be one in which all elements such as chromium (Cr), nickel (Ni), molybdenum (Mo), carbon (C), and the balance iron (Fe) are included in one particle. In another embodiment, it may be a mixture of iron-based powder and powder containing other ingredients. In a preferred embodiment, the powder metallurgy powder may be any one of MetaMixs-1CR, MetaMixs-3CR, MetaMixs-4CR, and MetaMixs-8CR manufactured by Metacomposites.

The chromium (Cr) is used to provide hardness above a certain level to gear parts.

The content of chromium (Cr) may be 0.5 to 10.0%, preferably 0.8 to 8.5%, and more preferably 3.5 to 8.5%, based on the total weight of the powder metallurgy powder. If the content of chromium (Cr) is too low, there is a problem that the hardness of the sintered body formed by sintering the molded body is lowered. In particular, when the chromium (Cr) content is less than 0.8%, it is difficult to satisfy Rockwell C scale of 40 or higher. Conversely, if the chromium (Cr) content is too high, the molding pressure to form the molded body increases excessively, raw material costs increase, and there may be problems of defects and accidents.

The carbon (C) is used to improve the sintering characteristics of the molded body. More specifically, the carbon (C) can perform the function of causing liquid phase sintering when the molded body is sintered at 1000 to 1250°C. Liquid phase sintering means liquefying powder metallurgy powder to accelerate sintering between particles and densification. In one embodiment, by further including carbon (C) in the powder metallurgy powder, higher hardness can be obtained compared to the case of performing conventional solid-state sintering by sintering the iron-based powder metallurgy powder at 1000 to 1250 ° C. The bonding strength with the core body can be improved. In addition, by including more carbon (C), liquid sintering is possible at a low temperature, thereby solving problems such as occurrence of defects and increased process costs.

The content of carbon (C) may be 0.5 to 3.0%, preferably 1.5 to 2.5%, and more preferably 2.14 to 2.5% based on the total weight of the powder metallurgy powder. If the carbon (C) content is too low, liquid phase sintering does not occur, resulting in a decrease in sintered density and hardness. Conversely, if the carbon (C) content is too high, carbon (C) is not evenly dispersed in the powder metallurgy powder, so sintering does not occur evenly, and there is a problem that physical properties vary depending on the area.

The molybdenum (Mo) and nickel (Ni) function to increase the hardness of the sintered body.

The content of each component may be 0.1 to 5.0% for molybdenum (Mo) and 0.1 to 5.0% for nickel (Ni), based on the total weight of the powder metallurgy powder. If the content of molybdenum (Mo) and nickel (Ni) is higher than the corresponding content, the hardness of the powder particles increases, causing a problem of increasing the molding pressure, and the friction between powders increases, leading to a problem of having to further increase the content of lubricant. there is. If the content of molybdenum (Mo) and nickel (Ni) is lower than the corresponding content, there is a problem that the hardness of the sintered body is lowered.

The step of molding the powder metallurgy powder to form a molded body including a hollow body and teeth disposed on the outer peripheral surface is a step of manufacturing a molded body that maintains a constant shape by applying a certain pressure to the powder metallurgy powder.

This step can be performed by filling a mold with a certain shape with the powder metallurgy powder and then pressing the mold with molding pressure. The molding pressure is a value that allows the molding density of the molded body to reach a specific range described below, and may be 5.5 to 7.5 ton/cm ² , preferably 5.8 to 6.2 ton/cm ² . If the molding pressure is too low, the bonding force between the powders decreases, making it difficult to maintain the shape, and there is a problem that the molding density varies depending on the molding area. If the molding pressure is too high, the shrinkage rate decreases during sintering, which reduces the bonding force with the core body, and excessive force is applied to the mold, which can cause mold damage and increase manufacturing costs.

In this step, the process temperature and time may vary depending on the components of the powder metallurgy powder or the size of the part being manufactured. In one embodiment, this step can be performed at room temperature, preferably between 15 and 30°C.

The molded body manufactured in this step has a lower molding density compared to the sintered density of the sintered body obtained by sintering the molded body. In this way, by setting the molding density lower than the sintering density, the molded body can shrink by 3 to 10% (volume fraction) during the sintering process and be strongly bonded to the core body. In this step, the molding density may be 0.68 to 0.93, preferably 0.75 to 0.85, relative to the sintered density, and the molding density may be 5.5 to 6.5 g/cm ³ , preferably 5.7 to 6.0 g/cm ³ . If the molding density is low, it is easy to break when ejected and it is difficult to maintain the shape of the product. If the molding density is high, the shrinkage rate may decrease, which may result in poor bonding between the molded body and the core body, and high pressure must be applied during molding, which increases process costs and increases the incidence of defects.

The shape or size of the molded body is not particularly limited. However, the thickness suitable for manufacturing a more precise shape may be 15 to 25 mm. Additionally, the inner diameter may be 25 to 40 mm, and the outer diameter based on the outermost angle of the teeth may be 35 to 50 mm.

The step of assembling the core body so that it is placed in the hollow of the molded body is a step of arranging the core body and the molded body at a position for joining.

The core body may be made of various metals or alloys, and may preferably be made of steel or carbon steel. The core body may have already been manufactured through a sintering process, or may be manufactured through a forging or rolling process, and the subsequent sintering process causes shrinkage within 1% by volume, preferably within 0.5%. You can.

The core body may have a donut shape with a hollow interior, but its shape or size is not particularly limited. However, in order to ensure excellent adhesion to the molded body and minimize deformation of the molded body, the outer diameter of the core body may be 99 to 99.7% of the inner diameter of the core body. In this case, the outer diameter of the core body may be 24.7 to 39.6 mm. Additionally, the thickness of the molded body may be 15 to 30 mm and the inner diameter may be 15 to 20 mm. In this way, by setting the length ratio of the outer diameter of the core body and the inner diameter of the molded body, the bonding force between the core body and the molded body can be improved.

The step of sintering the assembled molded body and the core body is a step of converting the molded body into a sintered body and shrinking its volume to control the size of the molded body and contacting the molded body and the core body.

This step can be performed at a temperature of 1000 to 1250°C, preferably 1135 to 1200°C. If the sintering temperature is too high, there is a problem that the shape of the molded body is deformed and the process cost increases, and if the sintering temperature is too low, there is a problem that sintering density and hardness are lowered due to solid-phase sintering instead of liquid-phase sintering. In one embodiment, this step may be performed in a reducing atmosphere with a hydrogen:nitrogen volume ratio of 1:9. Although not particularly limited, this step can be performed for 20 minutes to 1 hour.

In this step, the molded body can be formed into a sintered body by liquid phase sintering. As described above, in the embodiment of the present invention, a high shrinkage rate of the molded body can be secured during sintering by liquid-phase sintering of the powder metallurgy powder, and the sintered body can be made to have high sintered density and hardness after sintering is completed.

As previously explained, the sintering density of the sintered body produced by sintering the molded body is higher than the molding density of the molded body. Specifically, sintering may be performed so that the molding density is 0.68 to 0.93 times the sintered density, preferably 0.75 to 0.85 times. In this step, the sintering density of the sintered body may be 7.0 to 8.0 g/cm ³ , preferably 7.4 g/cm ³ or more. Additionally, the hardness may be 40 or higher on the Rockwell C scale.

Manufacturing of gear parts

Example 1: MetaMixs-FE, an iron-based powder from Metacomposite (Korea) as a powder metallurgy powder (2.4% carbon and the balance iron based on the total weight of the powder), was placed in a mold and pressed in a 200 Ton press from Jeonghwa Press Co., Ltd. (Korea). The molding pressure was set to 6.0 Ton/cm2 per unit area, and a molded product was manufactured with an outer diameter of 40.7 mm, an inner diameter of 32.1 mm, and a height of 18.5 mm. The molding density of the molded product was measured using MD-300S from AlfaMirage (Japan), and the appearance of the molded product was observed with the naked eye. Next, a donut-shaped core body (outer diameter 32.0 mm, inner diameter 21.0 mm, and height 28 mm) manufactured by machining carbon steel S45C was prepared, placed in the hollow of the molded product, and sintered at a temperature of 1,140 in a belt sintering furnace of Fluidtherm (India). It was sintered at ℃ (sintering atmosphere hydrogen:nitrogen = 1:9) for 30 minutes. The sintered density of the sintered body was measured using MD-300S from AlfaMirage (Japan), and the hardness was measured using a Rockwell hardness tester HR-521 from Mitutoyo (Japan).

Example 2: Same as Example 1, except that MetaMixs-0.85Mo, an iron-based powder from Metacomposites (Korea) (0.88% molybdenum, 2.4% carbon, and the balance iron based on the total weight of the powder) was used as the powder metallurgy powder. It was prepared and measured properly.

Example 3: The same as Example 1, except that MetaMixs-1CR, an iron-based powder from Metacomposites (Korea) (0.9% chromium, 2.4% carbon, and the balance iron based on the total weight of the powder) was used as the powder metallurgy powder. Prepared and measured.

Example 4: The same as Example 1, except that MetaMixs-3CR, an iron-based powder from Metacomposites (Korea) (3.0% chromium, 2.4% carbon, and the balance iron based on the total weight of the powder) was used as the powder metallurgy powder. Prepared and measured.

Example 5: The same as Example 1, except that MetaMixs-4CR, an iron-based powder from Metacomposites (Korea) (4.2% chromium, 2.4% carbon, and the balance iron based on the total weight of the powder) was used as the powder metallurgy powder. Prepared and measured.

Example 6: The same as Example 1, except that MetaMixs-8CR, an iron-based powder from Metacomposites (Korea) (8.1% chromium, 2.4% carbon, and the balance iron based on the total weight of the powder) was used as the powder metallurgy powder. Prepared and measured.

Example 7: The same as Example 1, except that MetaMixs-12CR, an iron-based powder from Metacomposites (Korea) (12.4% chromium, 2.4% carbon, and the balance iron based on the total weight of the powder) was used as the powder metallurgy powder. Prepared and measured.

Example 8: The same as Example 1, except that MetaMixs-16CR, an iron-based powder from Metacomposites (Korea) (16.4% chromium, 2.4% carbon, and the balance iron based on the total weight of the powder) was used as the powder metallurgy powder. Prepared and measured.

Example 9: The same as Example 1, except that MetaMixs-17CR, an iron-based powder from Metacomposites (Korea) (16.9% chromium, 2.4% carbon, and the balance iron based on the total weight of the powder) was used as the powder metallurgy powder. Prepared and measured.

Example 10: Example 1, except that MetaMixs-8CR-LC, an iron-based powder from Metacomposites (Korea) (8.1% chromium, 1.5% carbon, and the balance iron based on the total weight of the powder) was used as the powder metallurgy powder. It was prepared and measured in the same way.

Comparative Example 1: MetaMixs-8CR, an iron-based powder from Metacomposites (Korea) (8.0% chromium, 2.4% carbon, and the balance iron based on the total weight of the powder), was used as a powder metallurgy powder, with an outer diameter of 40.7 mm, an inner diameter of 21 mm, and a height of 18.5 mm. It was molded in mm and manufactured and measured in the same manner as in Example 1, except that the core body was not used.

Comparative Example 2: Example 1 and Example 1, except that MetaMixs-8CR-REF (8.1% chromium, 0.03% carbon and the balance iron based on the total weight of the powder), an iron-based powder from Metacomposites (Korea), was used as the powder metallurgy powder. It was prepared and measured in the same way.

Comparative Example 3: Manufactured in the same manner as in Example 1, except that 89.34.03 Intralube HD (carbon 0.42%, molybdenum 0.83% and the balance iron based on the total weight of the powder) from Hoganas (Sweden) was used as the powder metallurgy powder. Measured.

Comparative Example 4: Powder metallurgy powder 89.34.03 Intralube HD from Hoganas (Sweden) (0.42% carbon, 0.83% molybdenum, and the balance iron based on the total weight of the powder) and F-10 from Imery, an artificial graphite, were mixed to the total weight of the powder. It was prepared and measured in the same manner as in Example 1, except that it was added to 2.80% of .

Comparative Example 5: Manufactured and measured in the same manner as Example 1, except that the molding pressure was set to 5.0 ton/cm ² .

Comparative Example 6: Manufactured and measured in the same manner as Example 1, except that the molding pressure was set to 8.0 ton/cm ² .

1(a) to (c) are photographs of the molded body, the core body, and the gear parts in which the sintered body and the core body are combined, respectively, manufactured in Example 6.

Figures 2(a) to (d) are photographs of the boundaries of the sintered body and the core body among the gear parts manufactured in Examples 1 to 4, respectively, and Figures 3(a) to (e) are photographs of the boundaries of the gear parts manufactured in Examples 5 to 9, respectively. This is a photo of the boundary between the sintered body and the core body among the gear parts manufactured in . Photographed at a magnification of 500 using MA-100 from Nikon (Japan). Based on the boundary shown in each photo, the upper part is the sintered body and the lower part is the core body.

In addition, the molding density, sintering density, and hardness measured in Examples and Comparative Examples, as well as the external observation results, are listed in Table 1.

division	carbon content (weight%)	molding pressure (ton/ cm2 )	structure	Visual observation results	Molding density (g/ cm3 )	Sintered Density (g/ cm3 )	Hardness (HRC)
Example 1	2.4	6.0	Core body + sintered body combined structure	Good	6.62	7.710	36.3
Example 2	2.4	6.0	Core body + sintered body combined structure	Good	6.47	7.687	38.9
Example 3	2.4	6.0	Core body + sintered body combined structure	Good	6.073	7.643	40.9
Example 4	2.4	6.0	Core body + sintered body combined structure	Good	6.013	7.737	44.3
Example 5	2.4	6.0	Core body + sintered body combined structure	Good	5.983	7.656	50.3
Example 6	2.4	6.0	Core body + sintered body combined structure	Good	5.983	7.656	59.7
Example 7	2.4	6.0	Core body + sintered body combined structure	Good	6.01	7.56	40.8
Example 8	2.4	6.0	Core body + sintered body combined structure	Good	5.955	7.563	43
Example 9	2.4	6.0	Core body + sintered body combined structure	Good	5.883	7.513	39.8
Example 10	1.5	6.0	Core body + sintered body combined structure	Good	6.178	7.186	34.5
Comparison example 1	2.4	6.0	Sintered body single structure	Good	6.253	7.598	57.9
Comparison example 2	0.03	6.0	Core body + sintered body combined structure	Good	6.330	7.065	4.1
Comparison example 3	0.42	6.0	Core body + sintered body combined structure	Good	7.130	7.154	17.2
Comparison example 4	3.22	6.0	Core body + sintered body combined structure	Observation of sintered body surface pores	5.526	7.610	61.5
Comparison example 5	2.4	5.0	Core body + sintered body combined structure	Some teeth of the molded product are broken	5.673	7.646	59.6
Comparison example 6	2.4	8.0	Core body + sintered body combined structure	Observation of multiple scratches on the tooth side of the molded product and pores on the surface of the sintered body	6.432	7.684	59.7

Comparative Example 1 is a case in which no core body was used inside, and distortion occurred because the sintered area was too large. Additionally, excessive shrinkage occurred, resulting in poor dimensional accuracy after sintering. Comparative Examples 2 and 3 contained less than 0.5% of carbon and did not contain chromium, so the molding density was high and the shrinkage rate was low, resulting in low sintered density and hardness.

Comparative Example 4 contained a carbon content of 3.22%, and although the hardness was high, some bubbles were observed due to the high carbon content making uniform mixing difficult.

In Comparative Example 5, when the molding pressure was low, the powder metallurgy powder of the molded product was weakly bonded, and the teeth were broken during the demolding operation to remove the molded product from the mold. Comparative Example 6 is a case where the molding pressure was too high, and excessive pressure was applied to the surface of the molded product, and small scratches were observed on the surface. Pores were also observed in the sintered body.

Among the examples, the molding density of Examples 5 and 6 was measured to be 6.0 g/cm ³ or less, which shows that the sintered density and hardness are excellent. In Examples 7 to 9, as the chromium content exceeded 10%, the sintered density and hardness tended to decrease.

Through the comparison of the above examples and comparative examples, it can be seen that the carbon content is suitable to be 0.5 to 3.0% based on the total weight of the powder metallurgy powder, and that the process of heterogeneous bonding by placing a core body inside is preferable. In addition, it can be seen that the content of chromium is preferably 0.5 to 10.0%, and most preferably 3.5 to 8.5%, based on the total weight of the powder metallurgy powder.

The present invention is not limited by the above-described embodiments and attached drawings, but is intended to be limited by the attached claims. Accordingly, various forms of substitution, modification, and change may be made by those skilled in the art without departing from the technical spirit of the present invention as set forth in the claims, and this also falls within the scope of the present invention. something to do.

Claims (6)

1. Preparing iron-based powder metallurgy powder;

   Forming a molded body including a hollow body and teeth disposed on the outer peripheral surface by molding the powder metallurgy powder;

   Preparing a core body made of bulk metal and assembling the core body so that the core body is disposed in the hollow of the molded body; and

   Comprising the step of sintering the assembled molded body and core body,

   Manufacturing method of gear parts.
2. According to paragraph 1,

   The powder metallurgy powder contains 0.5 to 10.0% chromium (Cr) and 0.5 to 3.0% carbon (C) based on the total weight of the powder metallurgy powder,

   Manufacturing method of gear parts.
3. According to paragraph 1,

   In the step of forming the molded body, the molding pressure is 5.5 to 7.5 ton/cm ²

   Manufacturing method of gear parts.
4. According to paragraph 1,

   In the step of forming the molded body, the molding density of the molded body is 5.5 to 6.5 g/cm ³ ,

   In the sintering step, the sintered body produced by sintering the molded body has a sintered density of 7.0 to 8.0 g/cm ³ ,

   Manufacturing method of gear parts.
5. According to paragraph 1,

   In the sintering step, the powder metallurgy powder of the molded body is liquid-phase sintered,

   Manufacturing method of gear parts.
6. Gear parts manufactured by the manufacturing method of claim 1.

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