JP4753290B2 - Manufacturing method of machine parts - Google Patents

Description

The present invention relates to a manufacturing method by cold forging of machine parts, and particularly uses a sintered material as a material for cold closed forging, and a finished product according to the thickness difference of each part of the sintered material. The present invention relates to a method of manufacturing a machine part that enables even higher density while correcting the density difference and making the density uniform even if there is a difference in the density of each part.

A typical manufacturing method for machine parts is a manufacturing method by cold forging. Cold forging can be manufactured with high efficiency and has good dimensional accuracy, and thus is widely used for manufacturing machine parts. However, cold forging using a molten material as a material can obtain a processed product in a state close to the final shape, but after cold forging, it has been necessary to perform machining such as cutting to adjust the shape. Therefore, there is a problem that the material yield is poor, the manufacturing cost is increased, and the environment is deteriorated. Moreover, if it is closed forging in which the mold is closed and cold forging is performed, the shape close to the end product can be obtained as much as possible, but since the melted material has a high density, the shape that can be manufactured is limited. In addition, there is a problem that the mold may be damaged due to an error in material dimensions.

On the other hand, there is sintering as a manufacturing method with good material yield and excellent productivity. When manufactured by sintering, the yield is very good and a shape close to the end product can be obtained as much as possible, but the shape of the part that can be manufactured because the density is low compared to the melted material and sufficient strength cannot be obtained. There was a problem that was limited.

In order to solve these problems, a manufacturing method by cold closed forging using a sintered material as a raw material is known. However, the density is low as compared with the smelted material even by a known method, and its method of use is limited.
JP 2004-18958 A

As described above, the conventional cold forging manufacturing method has problems such as poor material yield and increased manufacturing costs and adverse environmental effects. On the other hand, the manufacturing method by sintering has a problem that the finished product has a lower density than the melted material and the strength is not sufficient, so that the method of use is limited. The manufacturing method of the present invention manufactures mechanical parts with sufficient density and strength by cold forging using a sintered material as a material to reduce costs and reduce adverse effects on the environment by reducing processes such as cutting. It is intended.

In order to solve the above-mentioned problems, the present invention provides a machine part manufacturing method by cold forging according to the first aspect of the present invention, wherein the first pre-forming is performed by lowering the first die from above the material to a specified position. Subsequently, the second mold is raised from the lower side of the material to the specified position to perform the second preliminary molding, and then the third mold is lowered from the upper side of the material to the specified position to perform the main molding.

The invention described in claim 2 is characterized in that, in the invention described in claim 1, the cold forging is a closed forging or a closed forging.

The invention according to claim 3 is the invention according to claim 1 or claim 2, wherein the material is a sintered material preformed by sintering.

According to a fourth aspect of the present invention, there is provided a die structure for use in cold forging, comprising a first die and a third die that are independently slid downward by a specified amount, respectively, and wherein A first die and a third die disposed opposite to each other and a second die that slides upward by a prescribed amount, and the first to third die of the previous period slide upward or downward by a prescribed amount, A cavity is formed.

The invention described in claim 5 is the invention described in claim 4, characterized in that the cavity is closed or sealed.

According to the manufacturing method of the present invention, even if a mechanical part is manufactured by cold forging using a sintered material as a raw material, it is possible to manufacture a mechanical part having a density and strength close to those of a molten material. Therefore, machining processes such as cutting that cause an increase in cost can be reduced, which greatly reduces the cost. In addition, it is very effective in terms of environment, and can be used for manufacturing various machine parts.

Embodiments of the present invention will be described below with reference to the drawings. 1-5 is a figure showing preferable embodiment of the manufacturing method of the machine component concerning this invention.

In producing a helical gear used in various applications as a machine part, that is, a gear 20 having a shape as shown in FIG. 3, first, a raw material powder containing iron powder as a main component is preliminarily molded by a known method, Create a preform. Then, the preform is further subjected to a sintering process by a known method to produce a sintered material 10. The gear 20 has a substantially cylindrical shape and is provided with a through hole 21 at the center. A serration 22 and a tooth-shaped portion 23 are formed on the outer periphery in two stages.

When creating the sintered material 10, further lateral extrusion is performed so that the shape of the sintered material 10 approaches the finished product shape, that is, the gear 20 as much as possible, and the density of the sintered material 10 after forging is expected to increase. Therefore, it is necessary to design the preform and the sintered material so that the dimensional accuracy can be improved, and to prepare the mold properly.

Next, the sintered material 10 thus prepared is reworked in a cold forging process. This cold forging is a closed forging process.

In the case of manufacturing a complicated shaped metal processed product, that is, a shape like the gear 20 of this embodiment by closed forging, the tooth shape portion 23 which is a complicated shape portion is formed by side extrusion. However, the conventional techniques have problems such as lack of thickness, defective dimensions, and a decrease in the life of the mold, and have not been put into practical use.

In general, when cold forging of a sintered material is performed, the true density of a forged product produced by cold forging is only about 90% of the true density of the steel material. On the other hand, in the case of a shaped part such as the gear 20 of the present embodiment, the required strength of the tooth-shaped portion needs to be equal to the true density of the steel material, and the material intermediate portion is somewhat low density. It is necessary to perform special molding.

FIG. 1 shows a mold apparatus 1 for performing cold forging according to the present embodiment, and its configuration is as follows. A center pin 11 protrudes from below and is fixed, and a helical molding punch 12 slidable in the vertical direction is disposed to protrude from below so as to surround the periphery of the center pin 11. Further, a helical molding die 13 for molding the tooth-shaped portion 23 of the helical gear 20 is fixedly disposed around the helical molding punch 12. In addition, a serration molding punch 15 protrudes from the upper side symmetrically with the center pin 11, and similarly, a serration molding die 14 protrudes from the upper side so as to surround the periphery thereof. The serration molding die 14 and the serration molding punch 15 are set so as to be independently slidable in the vertical direction. The helical molding punch 12 and the serration molding die 14 preferably incorporate a thrust bearing at the base so that the sintered material 10 can be processed while turning.

The helical forming punch 12 protrudes to the vicinity of the center as shown in FIG. 1 before the operation, but is arranged below when the forming starts, and is raised by a servo press machine equipped with this die set at the time of forming. . And after shaping | molding is complete | finished, it protrudes further upwards and discharges | emits a molded article. On the other hand, the serration molding punch 15 is arranged upward as shown in FIG. 1 before operation, and is projected downward by a servo press machine equipped with this die set during molding. Similarly, the serration forming die 14 is disposed upward as shown in FIG. 1 before operation, and is pressed by a hydraulic device in the die set mechanism and protrudes downward during molding. After the molding is completed, the serration molding punch 15 and the serration molding die 14 slide upward to return to the original position in order to discharge the molded product.

Using the mold apparatus 1 of the present embodiment having the above configuration, the sintered material 10 is cold forged. The mold apparatus 1 is stationary in the state shown in FIG. 1 before operation. In this state, the sintered material 10 is first placed at a fixed position. At this time, the hole 21 of the sintered material 10 is inserted into the center pin 11. In the conventional helical gear manufacturing method using melted material, the tooth-shaped portion 23 is not formed on the processed material and there is no phase (directionality), so that the material is inserted into the mold for positioning. However, in the present embodiment, the tooth-shaped portion 23 is already formed at the stage of the sintered material 10, and there is a problem that it cannot be inserted into the mold unless the phases match. Therefore, it is desirable to provide a slight slit in advance at the lower end portion of the sintered material and to provide a corresponding convex portion on the mold 1 to determine the phase.

After the sintered material 10 is arranged, the serration molding die 14 and the serration molding punch 15 are lowered. Then, the sintered material 10 descends while rotating along the helical shape of the helical forming die 13 and is pushed in until the lower end of the serration forming die 14 contacts the upper end of the helical forming die 13. In addition, the serration die 14 is pressed by oil pressure to withstand closed forging after contacting the helical die 13, and the mold closing is completed.

When the mold closing is completed, recompression is performed to further increase the density of the sintered material 10 and to determine the size of the gear shape. The helical molding punch 12 is raised by the die cushion pressure, and the sintered material 10 is recompressed along the helical shape. At the same time, while maintaining the pressure on the die cushion side, the serration molding punch 15 and the serration molding die 14 are held under pressure and are more reliably recompressed. By doing so, the dimensional accuracy of the gear shape can be improved and the density of the upper part of the product can be improved.

In the conventional sintering forging, there are problems that the density variation in the upper and lower parts of the product and the density of the thin part such as the gear tooth shape part 23 are incomplete. However, when the manufacturing method of the present invention is used, a density close to that of the smelting material can be ensured by the product partial density.

In order to secure the deformability of the sintered material 10, it is preferable that the powder component is a mixture of a powder of graphite, molybdenum, zinc stearate, etc. with pure iron powder as a main component. The sintering conditions are 800 ° C to 1300 ° C. The sintered material 10 created under these conditions has ductility substantially equivalent to that of the rolled material. As a result, even if this sintered material 10 is used as a material and backward extrusion cold forging with a cross-sectional reduction rate of about 65% is performed, it can be formed without cracking even though it is an iron-based sintered body. In addition, the density of the forged product is much higher than that of the conventional powder metallurgy method, reaching 98% of the true density (7.9 grams / cubic centimeter) of the steel material.

In the case of manufacturing a machine part by cold forging using a conventional method, that is, using a drawn material as a raw material, many times of forging, annealing, and lubrication are required. Therefore, many processes are required and the manufacturing cost is very high. However, when the manufacturing method of the present invention is used, the process can be greatly shortened, and the manufacturing cost can be greatly reduced.

As a typical lubrication treatment performed by a conventional method, there is a bonderite process. Bonderite processing has a problem that a large amount of waste liquid is discharged and the environmental load is large. However, the use of the manufacturing method of the present invention eliminates the need for lubrication treatment, which is advantageous in terms of environment. is there.

Further, as shown in FIG. 5, the conventional sintering forging method requires the main sintering step again after cold forging. In the manufacturing method of the present invention, the main sintering step after the cold forging is unnecessary, thereby realizing energy saving and cost reduction.

The parts formed by cold forging are finally subjected to a carburizing heat treatment to raise the surface hardness to the level of the melted material. The normal carburizing depth is about 0.3 mm, but in this case, it is desirable to perform deep carburizing heat treatment that greatly exceeds that to compensate for the carbon deficiency in the powder metallurgy material.

According to the manufacturing method of the present invention, in addition to the gear of the present embodiment, it can be provided to manufacture various machine parts, and a manufacturing method that is extremely advantageous in terms of cost and environment can be provided.

It is sectional drawing showing the metal mold | die apparatus used for the manufacturing method of this invention, and represents the state before operation | movement. It is sectional drawing showing the metal mold | die apparatus used for the manufacturing method of this invention, and represents the state which cold forging process was complete | finished. It is a perspective view showing the gear 20 shape | molded in the Example of this invention. In the Example of this invention, it is a graph which shows the operation | movement stroke and operation | movement timing of an upper mold | type and a lower mold | type. It is the figure which compared the process of the manufacturing method of this invention, and the conventional manufacturing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold apparatus 10 Sintering material 11 Center pin 12 Helical molding punch 13 Helical molding die 14 Serration molding die 15 Serration molding punch 20 Gear 21 Hole 22 Serration 23 Tooth shape part

Claims (2)

A manufacturing method of machine parts by cold forging which is closed forging or closed forging ,
Sintered mixed powder containing iron powder as a main component to form a cylindrical molding material having a through-hole in the axial direction. The first mold descends from above the molding material while rotating to a specified position. First preforming is performed, and then the second mold is raised from the lower side of the molding material subjected to the first preforming while rotating to a specified position to perform second preforming, and then the second preforming is performed. A method of manufacturing a machine part, wherein the third mold is lowered to a specified position from above the molding material that has been molded to perform a main molding. A mold structure used for cold forging, which is closed forging or closed forging, and includes a first mold and a third mold that are independently slid downward by a specified amount, and the first mold is rotating while A second mold that is set to be slidable downward and is disposed opposite to the first mold and the third mold, and that slides while rotating upward by a specified amount. A mold structure for use in cold forging, wherein a cavity including an inner diameter portion of a first mold is formed by sliding three molds upward or downward by a specified amount.

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