JP7115274B2 - Cold forging method and cold forging equipment - Google Patents

Description

The present invention relates to a cold forging method and a cold forging apparatus.

Compared to hot forging, which requires a cutting process as a post-process, cold forging is a processing method that allows the product to have a higher shape accuracy and a final product shape or a shape close to it. However, in cold forging, if a large amount of deformation is given to the material in one step, there is a concern that the mold may be damaged or defective. For this reason, cold forging is often performed in multiple steps using a single press machine. In this specification, this forging is also called "multi-step cold forging".

The major issues in multi-step cold forging of high-strength materials are (a) reduction of working load and (b) suppression of material breakage. In multi-process cold forging, if the processing load exceeds the processing load limit of the forging machine, it becomes necessary to add a manufacturing device (press machine) or replace the mold before manufacturing.

Therefore, in multi-step cold forging processing, processing with the lowest possible processing load is effective for efficient manufacturing because it leads to downsizing and cost reduction of the forging machine and avoids an increase in manufacturing time. is.

So far, inventions have been disclosed that aim to reduce the processing load in cold forging of high-strength materials.

Patent Document 1 discloses a die that forms the outer peripheral surface of a cylindrical material, a first punch that presses the end surface of the material on one end side in the axial direction while the material is placed in the die, and a material that is placed in the die. A closed forging apparatus is disclosed that includes a second punch that presses the end surface of the raw material on the other axial end side in an arranged state.

In this closed forging apparatus, the die has a peripheral surface cam recess into which the metal material of the material flows when the first and second punches press the material to form a peripheral cam on the peripheral surface of the material. At least one of the first punch and the second punch has a protrusion recess into which the metallic material flows to form the end face protrusion. The protrusion recess has an extra space that is not filled with the metal material when the peripheral cam recess is filled with the metal material. This improves the fillability of the material by the closed forging mechanism and reduces the processing load.

In Patent Document 2, in order to reduce the processing load and ensure productivity, the punch-side die set and the die-side die set are shuttle-moved in opposite phases, and molding in multiple steps is performed by a single single-acting press machine. A press device is disclosed that repeats at the center of the press.

In this press machine, in the process of reciprocating the slide, the piston rods of the opposing gas springs of the die-side die set are pushed by the rod portions of the punch-side die set positioned at the center of the press. As a result, the reciprocating motion of the slide can be used to fix the die set to the press body, eliminating the need for a die clamper and suppressing a decrease in productivity caused by an increase in cycle time.

JP 2017-100152 A Patent No. 6137489

The closed forging apparatus disclosed by Patent Document 1 aims at reducing the processing load in a single process, and the operation of the die is complicated. For this reason, with this closed forging apparatus, it is not possible to reduce the processing load in the multi-step cold forging and to reduce the size and cost of the forging machine.

In order to achieve high-speed and high-precision processing using the press disclosed in Patent Document 2, a special mechanism is required to slide the die set at high speed and position it with high accuracy. Therefore, although it is possible to reduce the processing load in multi-step cold forging, it is not possible to reduce the cost of the forging process.

In view of the problems of the conventional technology, the present invention provides a cold forging method and a press that can reduce the processing load in multi-step cold forging and process high-strength materials even with a small and inexpensive press. intended to

FIG. 1 is a diagram showing a configuration example of a conventional multi-step cold forging apparatus.
As shown in FIG. 1, a conventional cold forging apparatus includes a mold pair (upper die 2a, lower die 2b) for carrying out a forward extrusion process as a first process, and a forward extrusion process as a second process. A mold pair (upper mold 3a, lower mold 3b) for carrying out, a mold pair (upper mold 4a, lower mold 4b) for carrying out the backward extrusion process as the third process, and a punching process as the fourth process A pair of molds (upper mold 2a, lower mold 2b) for carrying out is provided. Upper dies 2a, 3a, 4a, 5a of each mold pair are supported by slides 6, and lower dies 2b, 3b, 4b, 5b of each mold pair are supported by bolsters 7. As shown in FIG. Press 11 moves the relative positions of slide 6 and bolster 7 . As a result, cold forging in the first to fourth steps is performed in one press stroke.

FIG. 2 is a graph illustrating the relationship between the press stroke of a press machine and the working load in a conventional multi-step cold forging apparatus. Although the processing load history of each processing method differs slightly depending on the shape of the forged product or forged semi-finished product to be manufactured, it is generally as follows.

The processing load of forward extrusion processing rises sharply at the beginning of processing, reaches a maximum at a relatively early stage, then decreases slightly and stabilizes (see the first step in FIG. 2), or stabilizes at a maximum. (Refer to the second step in FIG. 2), and it drops sharply after the completion of processing. The processing load in backward extrusion gradually increases from the beginning of processing, reaches a maximum immediately before the completion of processing, and drops sharply after the completion of processing (see the third step in FIG. 2). The processing load in punching sharply rises at the beginning of the processing and drops sharply after the processing is completed (see the fourth step in FIG. 2).

As shown in FIG. 2, the working loads of the first to fourth processes are usually concentrated in the vicinity of the bottom dead center of the press stroke of the press. This is the reason why multi-step cold forging cannot be performed with a small and inexpensive press. Therefore, if the working load can be dispersed by shifting the timing of application of the working load in the first to fourth processes, the working load applied to the entire forging machine can be reduced. In order to shift the timing at which the processing load is applied, it is effective to perform the forming in several steps with a press stroke before the bottom dead center.

As a result of intensive studies from this point of view, the present inventors found that in order to complete molding in several steps before the bottom dead center, the upper die (punch etc.) or support the lower die (die etc.) via a buffer mechanism. That is, the cushioning mechanism is a mechanism that does not shrink during plastic working by the upper and lower dies, but shrinks after plastic working to reduce the load applied to the press machine. For example, the set load of the buffer mechanism is changed during the plastic working and after the plastic working is completed. In the case of using a hydraulic mechanism, the set pressure of the hydraulic mechanism is set high during plastic working and lowered after completion of plastic working. As a result, the hydraulic mechanism does not shrink under the load during plastic working by the upper and lower dies, but shrinks under the load when the upper and lower dies come into contact with each other. This makes it possible to adjust the timing at which the maximum load is applied to a specific pair of dies regardless of the operating conditions of the press. Therefore, it is possible to make the timing when the maximum load is generated on the mold pair having the buffer mechanism different from the timing when the maximum load is generated on the other mold pairs. As a result, the maximum load applied to the press can be reduced.

In addition, instead of the above configuration, the buffer mechanism does not shrink under the load during plastic working by the upper and lower dies, but has a predetermined load (for example, a predetermined load greater than the load when the upper and lower dies contact each other). It may be configured to contract when a load) is applied. In the case of using a hydraulic mechanism, the set pressure of the hydraulic mechanism is higher than the pressure corresponding to the load during plastic working and is a predetermined pressure (for example, a predetermined pressure equal to or higher than the pressure when the upper mold and the lower mold are in contact with each other. ) may be set to a lower value. As a result, although the load during plastic working by the upper and lower dies does not cause shrinkage, the load when the upper and lower dies contact each other causes shrinkage.

The present invention is based on such findings, and is as listed below.
(1) Equipped with a plurality of mold pairs composed of an upper mold and a lower mold,
a slide that supports one mold that constitutes each mold pair;
a bolster that supports the other mold paired with the one mold;
a pressing machine that moves the relative positions of the slide and the bolster to perform cold forging with the pair of dies;
A method of cold forging by a cold forging device comprising
In at least one of the pair of molds, either one of the upper mold and the lower mold is supported by the slide or the bolster via a buffer mechanism,
The cushioning mechanism does not shrink during the plastic working by the upper mold and the lower mold, but shrinks after the completion of the plastic working. Differentiate the time when the maximum load occurs on the mold pair,
Cold forging method.

(2) having a plurality of mold pairs each composed of an upper mold and a lower mold;
a slide that supports one mold that constitutes each mold pair;
a bolster that supports the other mold paired with the one mold;
a press machine that moves the relative positions of the slide and the bolster to perform cold forging with the mold pair,
In at least one of the pair of molds, either one of the upper mold and the lower mold is supported by the slide or the bolster via a buffer mechanism,
The cushioning mechanism does not shrink during the plastic working by the upper mold and the lower mold, but shrinks after the completion of the plastic working. Differentiate the time when the maximum load occurs on the mold pair,
Cold forging equipment.

According to the present invention, in multi-step cold forging, since the timing at which the maximum load occurs in each step can be adjusted, the processing load as a whole can be reduced, so multi-step cold forging can be performed with a small and inexpensive press. It can also be done on a machine.

FIG. 1 is a diagram showing a configuration example of a conventional multi-step cold forging apparatus. FIG. 2 is a graph illustrating the relationship between the press stroke of a press machine and the working load in a conventional multi-step cold forging apparatus. FIG. 3 is a diagram showing a configuration example of a multi-step cold forging apparatus according to this embodiment. FIG. 4 is a graph illustrating the relationship between the press stroke of the press machine and the working load in the multi-process cold forging apparatus according to this embodiment.

FIG. 3 is a diagram showing a configuration example of a multi-step cold forging apparatus according to this embodiment.
As shown in FIG. 3, the cold forging apparatus according to the present embodiment includes a pair of dies (upper die 2a, lower die 2b) for carrying out a forward extrusion process as a first process, and a forward extrusion process as a second process. A mold pair (upper mold 3a, lower mold 3b) for carrying out the extrusion step, a mold pair (upper mold 4a, lower mold 4b) for carrying out the backward extrusion step as the third step, and as the fourth step A pair of molds (upper mold 5a, lower mold 5b) is provided for performing the punching process. The upper dies 2a, 5a are supported by the slide 6 via the shock absorber 8, and the upper dies 3a, 4a are directly supported by the slide 6. Also, the lower dies 2b, 3b, 4b, 5b are supported by a bolster 7. As shown in FIG. Press 1 moves the relative positions of slide 6 and bolster 7 . As a result, cold forging in the first to fourth steps is performed in one press stroke.
In the example shown in FIG. 3, the upper dies 2a, 3a, 4a, 5a are punches and the lower dies 2b, 3b, 4b, 5b are dies, but the configuration is not limited to this. Also, the shock absorber 8 may be installed between the bolster 7 and the mold.

The press machine 1 of the multi-step cold forging apparatus according to this embodiment differs from the press machine 11 of the conventional multi-step cold forging apparatus in that the upper dies 2a, 5a in the first and fourth steps are hydraulically operated, for example. It is supported by the slide 6 via a buffer mechanism 8 such as a mechanism or a gas pressure mechanism. The buffer mechanism 8 can control the load applied to the upper dies 2a, 5a independently of the press stroke.

In other words, the buffer mechanism 8 does not shrink during the plastic working by the upper dies 2a, 5a and the lower dies 2b, 5b in the first and fourth steps, but shrinks after the plastic working, thereby reducing the load applied to the press. mechanism. For example, the set load of the buffer mechanism is changed during the plastic working and after the plastic working is completed. In the case of using a hydraulic mechanism, the pressure of the hydraulic mechanism is previously set higher than the pressure during plastic working, and plastic working is performed at that pressure. Then, when a predetermined press stroke corresponding to the plastic working completion point is reached, the pressure of the hydraulic mechanism is reduced. This allows the hydraulic mechanism to adjust the timing at which the maximum load is applied to a specific pair of dies, regardless of the operating conditions of the press. The maximum load applied to the press machine can be reduced by making the timing when the maximum load is generated on the mold pair having the buffer mechanism different from the timing when the maximum load is generated on the other mold pairs.
The upper dies 2a and 5a in the first and fourth steps may be connected to the same buffer mechanism 8 or may be connected to different buffer mechanisms. Moreover, the buffer mechanism 8 may be connected to the same pressure control device (not shown), or may be connected to a different pressure control device.

If the buffer mechanism 8 is a hydraulic mechanism, it is extremely difficult to precisely stop the machining of the process in which the hydraulic mechanism 8 is provided at a predetermined position only by hydraulic control of the hydraulic mechanism 8 . Therefore, the upper dies (punches) 2a, 5a for the first and fourth steps are provided with stoppers 2c, 5c for accurately stopping the machining of this step by generating a large reaction force at a predetermined position. is desirable.

As a result, the molding by the upper die 2a and the lower die 2b in the first step and the molding by the upper die 5a and the lower die 5b in the fourth step are completed in the stroke before the press bottom dead center of the press machine 1. can be made Therefore, as exemplified in the graph of FIG. 4 described above, it is possible to disperse the processing load in the first to fourth steps by shifting the timing at which the processing load is applied in the first to fourth steps. processing load can be reduced.

That is, as shown in FIG. 4, the processing load in the forward extrusion processing as the first step rises sharply in the initial stage of processing, reaches a maximum at a relatively early stage, and then decreases slightly and then stabilizes. It drops sharply after the completion of processing. This point is the same as the first step in the conventional multi-step cold forging apparatus. In addition, the processing load in the forward extrusion processing as the second step rises sharply in the initial stage of processing, reaches a maximum at a relatively early stage, then stabilizes at a maximum, and rapidly decreases after processing is completed. This point is the same as the second step in the conventional multi-step cold forging apparatus. The processing load in the backward extrusion processing as the third step gradually rises from the beginning of processing, reaches a maximum just before the processing is completed, and drops sharply after the processing is completed. This point is the same as the third step in the conventional multi-step cold forging apparatus. The processing load in the punching process as the fourth step rises sharply in the initial stage of the process and drops sharply after the process is completed. This point is the same as the fourth step in the conventional multi-step cold forging apparatus.

However, as shown in FIG. 2 above, in the press machine 11 in the conventional multi-process cold forging apparatus, all of the first to fourth processes are completed substantially simultaneously near the bottom dead center of the press machine 11 . For this reason, the processing loads of the first to fourth processes are concentrated near the bottom dead center. For example, assuming that the processing load near the bottom dead center of each process is 1st process: 500 kN, 2nd process: 800 kN, 3rd process: 1600 kN, and 4th process: 800 kN, all the 1st to 4th processes are combined. The total working load reaches up to about 3700 kN.

On the other hand, in the press machine 1 of the multi-process cold forging apparatus according to the present embodiment, as shown in FIG. Since the punches 2a and 5a are used, machining can be completed in a stroke before the bottom dead center by the stroke of the hydraulic mechanism 8 (for example, 30 mm).

FIG. 4 is a graph illustrating the relationship between the press stroke of the press machine and the working load in the multi-process cold forging apparatus according to this embodiment.

As shown in FIG. 4, by completing the forming in the first step and the fourth step with a stroke before the bottom dead center, the timing at which the processing load is applied in the first to fourth steps is shifted to shift the first step. It is possible to disperse the processing load of ~4 processes, and reduce the processing load applied to the entire press machine. Here, in the press machine 1 of FIG. 3, the relative positional relationship between the tips of the upper dies 2a and 5a in the first and fourth processes and the tips of the upper dies 3a and 4a in the second and third processes is as shown in FIG. The relative positional relationship between the tips of the upper dies 2a and 5a in the first and fourth processes and the tips of the upper dies 3a and 4a in the second and third processes in the press machine 11 is wider than the relative positional relationship. In other words, the mold pair having the buffer mechanism 8 is configured to start the plastic working earlier than the mold pair not having the buffer mechanism 8 . As a result, the processing load in the first to fourth steps can be more easily distributed, and the processing load applied to the entire press machine 1 can be further reduced.

By lowering the hydraulic pressure of the hydraulic mechanism 8 after finishing the machining in the first and fourth steps, the load in the first and fourth steps can be lowered to about 100 kN, and at the same time the hydraulic mechanism 8 contracts. Therefore, with the machining in the first and fourth processes completed, the machining in the second and third processes is continued until the bottom dead center as in the case of the press machine 11 .

As a result, in the press machine 1, as shown in the graph of FIG. 4, the processing load that becomes maximum near the bottom dead center of the press machine 11 can be reduced. The processing load near the bottom dead center of the 1st to 4th processes is 100kN for the 1st process, 800kN for the 2nd process, 1600kN for the 3rd process, and 100kN for the 4th process. The total working load is reduced to approximately 2600 kN.

Table 1 compares the total working load near the bottom dead center in the first to fourth steps of the press machines 1 and 11.

Therefore, the present invention can be carried out with a 3000 kN press machine, and the size and cost of the forging machine can be reduced.

Next, the effects of the present invention will be confirmed by taking as an example the case of performing multi-step cold forging in which a forward extrusion step as a first step and a backward extrusion step as a second step are performed.

In a conventional example using a multi-process cold forging apparatus without a hydraulic mechanism, the processing loads in the first and second processes near the bottom dead center of the press are 800 kN and 1500 kN, respectively. Therefore, the total processing load for the first and second steps is about 2300 kN at maximum.

On the other hand, in the example of the present invention in which the upper die in the first step is supported by sliding through the hydraulic mechanism, the pressure of the hydraulic mechanism can be lowered and contracted immediately after the plastic working in the first step is completed. This makes it possible to reduce the load in the first step after plastic working to about 100 kN. By reducing the load in the first step to about 100 kN and then performing the plastic working in the second step, concentration of the load near the bottom dead center of the press can be prevented.

In this way, according to the present invention, it is possible to disperse the processing load, which is maximum near the bottom dead center in the conventional example. According to the present invention, the working load near the bottom dead center in the first and second processes is 100 kN for the first process and 1500 kN for the second process.

Therefore, while the maximum load was about 2300 kN (=800+1500) in the conventional example, it is reduced to about 1600 kN (=100+1500) in the example of the present invention.

Table 2 compares the total processing load near the bottom dead center in the first and second steps of the conventional example and the example of the present invention.

Therefore, the present invention can be implemented with a 2000 kN press machine, and the size and cost of the forging machine can be reduced.

1 Multi-process cold forging device 2a according to the present embodiment Upper die (punch)
2b lower mold (die)
2c Stopper 3a Upper die (punch)
3b lower mold (die)
4a Upper die (punch)
4b lower mold (die)
5a Upper die (punch)
5b lower mold (die)
5c Stopper 6 Slide 7 Bolster 8 Buffer mechanism 11 Conventional multi-process cold forging device

Claims (2)

Equipped with multiple mold pairs consisting of an upper mold and a lower mold,
a slide that supports one mold that constitutes each mold pair;
a bolster that supports the other mold paired with the one mold;
a pressing machine that moves the relative positions of the slide and the bolster to perform cold forging with the pair of dies;
A method of cold forging by a cold forging device comprising
In at least one of the pair of molds, either one of the upper mold and the lower mold is supported by the slide or the bolster via a buffer mechanism,
The cushioning mechanism does not shrink during the plastic working by the upper mold and the lower mold, but shrinks after the completion of the plastic working. Differentiate the time when the maximum load occurs on the mold pair,
Cold forging method. Equipped with multiple mold pairs consisting of an upper mold and a lower mold,
a slide that supports one mold that constitutes each mold pair;
a bolster that supports the other mold paired with the one mold;
a press machine that moves the relative positions of the slide and the bolster to perform cold forging with the mold pair,
In at least one of the pair of molds, either one of the upper mold and the lower mold is supported by the slide or the bolster via a buffer mechanism,
The cushioning mechanism does not shrink during the plastic working by the upper mold and the lower mold, but shrinks after the completion of the plastic working. Differentiate the time when the maximum load occurs on the mold pair,
Cold forging equipment.

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