JPH04319099A - Molding method for green compact having stepped shape and molding device therefor - Google Patents

Abstract

PURPOSE:To prevent the generation of cracks in a green compact by simultane ously parting an upper punch and a lower punch from the green compact after ending of the compression of powder. CONSTITUTION:The upper punch is retreated and simultaneously, the lower punch is retreated as well after the compression stage for compressing the powder packed into the hole in a die by the upper and lower punches and molding the green compact varying in thickness in the compression direction. A stress releasing stage for releasing the pressurizing force of the lower punch acting on the end face of the green compact is executed. A green compact extracting stage for extracting the green compact from the hole in the die by advancing the lower punch relatively with the die is thereafter executed. The application of bending stresses and shearing stresses on the green compact is obviated in this way and the generation of the cracks in the green compact is prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention aims to prevent cracks from occurring in the green compact during powder compaction and to make the density uniform in the compression direction when manufacturing stepped-shaped sintered parts with different thicknesses in the compression direction. The present invention relates to a method for molding a stepped powder compact and a molding apparatus therefor.

0002

[Prior Art] Conventionally, there have been various shaped sintered parts W1 to Wn as shown in FIG. 8 as stepped-shaped sintered parts having different thicknesses in the compression direction. The pressing mold used is generally a so-called with-low-al type pressing mold.

In this case, the press die is set in the form of a die set or in a press device having a fixed plate and a plurality of support plates that can be moved up and down, and the press die is placed above the fixed plate fixed to the press device. It is composed of a die connected to a vertical drive means, and a lower punch and an upper punch that are divided to correspond to the stepped shape.

However, if the molded part has an inner hole as shown in FIG. 3(a), it is configured to further include a core.

Generally speaking, the plurality of divided punches are formed such that the inner punch is formed long and supported by a movable plate or fixed plate located below the press device, and the outer punch is formed relatively short and is supported by a die. It is supported by a nearby movable or fixed plate.

[0006] When molding a stepped powder compact having different thicknesses in the compression direction using such a molding apparatus, the process is as follows.

That is, a plurality of lower punches are inserted into the die inner hole at different levels corresponding to the thickness of the green compact to be formed,
If necessary, the cavity in the mold is filled with powder with varying thickness by cutting off the top surface of the die depending on the filling depth of the powder, and then the die and upper and lower punches are moved relatively to each other. Press the filling powder evenly.

At this time, the lower punch hits a fixed block that restricts the lower punch from descending, thereby determining the size and shape of the molded article.

[0009] Next, the molded body is extracted from the inner hole of the die by lowering the die after retracting the upper punch from the pressing direction, or by further advancing at least one lower punch in the pressing direction.

[0010] Furthermore, as shown in FIGS. 8(b) to 8(f),
When the molded part is a cylindrical or columnar body that has a stepped shape but has a thinner part near the middle part or lower part in the height direction, a molding apparatus similar to the above is used, for example, As described in Publication No. 11701, instead of compressing the powder filled in the die inner hole as it is, the powder is first sandwiched between upper and lower punches, and then only the upper and lower punches for forming thin-walled parts are moved. After making the filled powder into a shape similar to the compact to be molded, the upper and lower punches are moved forward in the pressing direction to compact the powder and form the compact, which is then extracted from the die and released from the mold. .

By the way, when powder is compressed, a reaction force is generated in the green compact, and the die, upper and lower punches, etc. are elastically deformed and stress is generated.

[0012] Therefore, when the upper punch is moved back away from the powder compact after compressing the powder, the powder compact springs back toward the upper punch, and the lower punch and lower punch receiving plate return to their original shapes. As a result, the compact is pushed up.

[0013] At this time, the return distance of the lower punch, that is, the difference ΔA between the punch length when no pressure is applied and when it is compressed, is the stress Σ,
When the punch length is L and the Young's modulus of the punch material is E, it can be determined as follows: ΔA=ΣL÷E.

For example, if the length of the punch is 300 mm and its Young's modulus is 21000 kgf/mm2, and the stress when compressed is 70 kgf/mm2, then ΔA is 1 mm.
When the punch length is 200 mm, the deformation amount is 0.66 mm, and the longer the punch, the larger the amount of deformation.

As a result, bending stress is applied to the stepped powder compact, resulting in the problem of cracks occurring at the stepped portions.

In addition, the deflection amount ω of the lower punch backing plate is calculated by setting 1/2 of the outside diameter of the backing plate to a, when the backing plate is donut-shaped, the outer periphery is fixed, and a ring load is applied to the inner periphery. 1/2 of the diameter
When is b, the thickness of the backing plate is h, the deflection coefficient is α, the total load on the inner circumference is P, and the Young's modulus of the backing plate material is E, then ω=
It is determined by αPa2 ÷Eh3.

For example, a=200mm, h=30mm,
P=71000kgf, E=21000kgf/mm2
If this is the case, the maximum amount of deflection will be 1 mm, which will be added to the deflection of the lower punch, although this will vary depending on the dimensions and load of the receiving plate.

[0018] Conventionally, when forming a stepped powder compact, when the upper punch is moved back away from the powder compact after compressing the powder, the powder compact springs back toward the upper punch side and , the lower punch and the lower punch receiving plate push up the green compact in an attempt to return to its original shape, which has the disadvantage of causing cracks in the green compact.

[0019] Therefore, as one of the countermeasures, a method has been proposed in which when the lower punch pushes up the powder compact, the die follows this and rises, that is, the die is configured in a floating state.

In addition, a short lower punch is supported by a specially provided vertical drive means, and after the lower punch hits a fixed block that restricts its descent and the compression is completed,
A method has also been proposed in which a short lower punch is raised to follow the timing of the upper punch's rise, so that the pressure of the long lower punch is equal to the pressure with which the powder compact is pushed up.

[0021]

[Problem to be Solved by the Invention] However, in the former method, the die does not necessarily rise following the rise of the upper punch, but due to the thrusting force of the lower punch group and the upward bias that makes the die floating. It is just a matter of expecting it to rise, and there are problems such as the timing does not match the rise of the upper punch, or the amount of rise is less than desired due to the weight of the die and the resistance of the die floating mechanism. However, there is a problem in that it is difficult to prevent cracks from occurring in the green compact, especially for stepped parts with complex shapes.

Furthermore, although the latter method is preferable in principle, it is difficult to manufacture a press device for equalizing the pressure applied to each punch and controlling it in accordance with the timing of the rise of the upper punch. However, the problem is that the molding cost becomes relatively high.

[0023] On the other hand, in addition to the above-mentioned problem of the generation of cracks, the conventional molding method of stepped shaped powder compacts also has the problem that it is difficult to equalize the density in the compression direction. .

For example, as shown in FIG. 8(b), a step-shaped molded part having a thin wall portion below its upper end surface in the height direction is formed after filling the die inner hole with a predetermined amount of powder. The filling powder is sandwiched between the upper and lower punches, and then the upper and lower punches for forming thin-walled parts are moved downward to make the filling powder into a shape that is approximately similar to the green compact to be formed, and then the green compact is compacted. The density of the upper punch side main body part is lower than that of the lower punch side main body part, and when sintered, the upper and lower main body parts have different dimensions or mechanical strength, resulting in a non-uniform part.

The reason for this is that when moving the filling powder that will become the thin wall part to a predetermined position, there is powder resistance due to powder shear between the filling powder that will become the thin wall part and the filling powder that will become the body part, and when the thin wall part is formed. This is because the filling powder below the main body is compressed due to sliding friction resistance between the lower punch and the filling powder that becomes the main body, which causes a difference in density between the upper and lower parts of the main body.

The present invention has been made in view of the above-mentioned circumstances, and the first object is to simplify the control of the molding device and to prevent the occurrence of cracks caused by the return of bending of the pressing mold, etc. The second object is to provide a method for molding a stepped powder compact that can make the density in the compression direction uniform. It is in.

[0027]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a method for forming a stepped-shaped green compact having different thicknesses in the compression direction, as set forth in claim 1. , the powder filled into the inner hole of the die that regulates the outer surface of the powder compact is compressed by a lower punch with different lengths and multiple divisions, and a single or upper punch with different lengths and multiple divisions. In a molding method in which the green compact is extracted from the inner hole of the die, the powder filled in the inner hole of the die is compressed by upper and lower punches to form a green compact with different thicknesses in the compression direction. After the compression process, a stress release process is performed in which the upper punch is moved back, and the lower punch is also moved back at the same time to release the pressing force of the lower punch on the end face of the compact, and then the lower punch is moved forward relative to the die. The method is characterized in that a powder compact extraction step is performed in which the powder compact is extracted from the inner hole of the die.

Further, as claimed in claim 2, there is provided a method for forming a stepped powder compact having a thin wall portion below the upper end of a cylindrical or columnar body, the method comprising regulating the outer surface of the compact. The powder to be filled into the inner hole of the die is sandwiched between the upper and lower punches, which are divided into a punch for forming the body part of the green compact and a punch for forming the thin-walled part, and the upper and lower punches for forming the thin-walled part are moved to fill the powder. In a molding method in which powder is made into a shape substantially similar to the green compact to be molded, this is compressed to form a green compact, and then the green compact is extracted from the inner hole of the die, the powder is filled into the inner hole of the die. After the process, a pre-compression process is performed in which at least the upper punch enters the inner hole of the die to increase the apparent density of the filling powder, and then the upper and lower punches for forming thin-walled parts are moved to form the compacted powder into which the filling powder is to be formed. It is characterized by performing a compression process to form a green compact into a green compact after making it into a shape substantially similar to the body.

Further, as claimed in claim 3, the step is performed after the step of filling the powder into the die inner hole, and includes a step of increasing the apparent density of the filling powder by advancing at least the upper punch into the die inner hole. This is a process performed after the compression process and the compression process in which the upper and lower punches for forming thin-walled parts are moved to form a compact that is approximately similar to the powder compact to form the filled powder, and then the compact is made into a compact. It is characterized by comprising a stress release step of retracting the punch and retracting the lower punch at the same time to release the pressing force of the lower punch applied to the end surface of the compact.

Further, as described in claim 4, the pre-compressed packed powder has an apparent density equal to or higher than the tap density, and has a density ratio of 75.
% or less.

Further, as described in claim 5, a series of steps including the step of filling the powder into the die inner hole, the step of compressing the filled powder, and the step of extracting the green compact are sequentially controlled by the control means, and at least the direction of compression is controlled by the control means. a die having an inner hole for regulating the outer surface of the stepped powder compact having different thickness;
It is equipped with a lower punch that has different lengths and is divided into multiple parts, and an upper punch and a platen that are single or have different lengths and are divided into multiple parts, and the upper and lower punches are moved back and forth in the pressurizing direction to fill the inner hole of the die. In a molding device that compresses powder to form a green compact, (1) when the powder is filled into the die inner hole, a punch is introduced into the die inner hole to increase the apparent density of the filled powder; (2) A pre-compression command section which instructs the control means to start a pre-compression operation; (2) moves the upper and lower punches for forming thin-walled parts to make the filled powder approximately similar to the compact to be compacted; When a compression operation is performed, a command is started to the control means to cause the upper punch to retreat at the same time as the lower punch to release the pressing force of the lower punch applied to the end face of the compact. The present invention is characterized by having one or both of the following command parts: a stress release command part;

Powder filling and compaction may be accomplished in conventional manner. In addition, the method for extracting the green compact from the die is the same as the conventional method. For example, as described in Japanese Patent Publication No. 63-36880, the step of each lower punch is made to match the profile of the lower surface of the green compact, and each The support pressure of the platen is controlled so that the amount of relative positional displacement of the lower punch is always zero. In addition, when the die and the outer surface of the green compact are slid during extraction, the compressive stress generated in the lower punch adjacent to the die is made higher than the stress generated in the other punches.

That is, in extreme cases, a method may be adopted in which the material is extracted using only the lower punch adjacent to the die.

Similarly, when the powder compact has an inner hole and the core and the inner surface of the powder compact are slid, the compressive stress generated in the lower punch adjacent to the core becomes higher than the stress generated in the other punches. It can be controlled as follows.

Conventional phenomena occur unless the apparent density of the precompacted filler powder is higher than the tap density. However, if the apparent density is increased too much, cracks will remain at the boundary between the thin wall part and the main body when the thin wall part is moved to a predetermined position and then compressed, so the amount of compression for pre-compression should be 75% of the density ratio.
It is necessary to do the following. For example, if the filling powder is iron powder, it is 6g/cm3, and if it is aluminum powder, it is 2g.
/cm3, and in the case of copper powder, it corresponds to 6.6g/cm3.

[0036]

[Operation] According to the invention as claimed in claim 1, since the upper punch and the lower punch are moved away from the powder compact at the same time after powder compression is completed, the deflection of each punch and its receiving plate is reduced both above and below the powder compact. It is released at the same time, so that no bending stress or shear stress is applied to the powder compact, thereby preventing cracks from occurring in the powder compact.

According to the second and fourth aspects of the invention, by pre-compressing the filling powder, movement of the filling powder becomes difficult to occur, and the density in the compression direction can be made uniform.

According to the third aspect of the invention, it is possible to prevent the occurrence of cracks in the green compact and to make the density uniform in the compression direction.

According to the invention set forth in claim 5, a pre-compression command section and a stress release command section for simply retracting the drive mechanism of the upper and lower punches from the pressing direction after completion of compression are attached, so that the powder compact is The above effects are achieved with a simple molding device, which eliminates the complexity of conventional methods that require means for detecting and controlling multiple pressures and positions. do.

[0040]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sequence block diagram illustrating the steps of the molding method according to the present invention, and FIGS. 2 and 3 are block diagrams showing a schematic configuration diagram of the molding apparatus according to the present invention and its control system. .

The stepped shaped molded parts used in the explanation are those shown in FIGS. 8(a) and 8(b), and
For convenience of explanation, we will start by explaining the molding device.

As shown in FIG. 2, the forming apparatus P has a general structure in which a main body 11 housing upper and lower actuators 10 is connected to a support 1.
1a, and is provided with a stationary platen 16 in the middle of the support column 11, and on the upper and lower sides of this stationary platen 16, respectively, three platens, namely, a first platen 13, a second platen 14, a third platen 15, and A fourth platen 17, a fifth platen 18, and a sixth platen 19 are mounted so as to be movable up and down by rams 12.

[0044] Each of the above platens 13 to 19 and fixed platen 1
A stopper 9 whose height can be adjusted with a screw is provided on the top of the ram 6 to restrain the forward movement of each ram 12.

The die 1 is held on a fixed platen 16, and the upper punch 2 is placed on a fourth platen 17 above the fixed platen 16.
The core 7 is fixed to the first platen 13 at the lowest stage, the lower inner punch 5a is fixed to the second platen 14, and the lower outer punch 5b is fixed to the third platen 15.

The die 1 has an inner hole 1a that is filled with the powder F and regulates the outer surface of the green compact F' to be molded.

The lower punch 5 has different lengths and is divided into a lower inner punch 5a and a lower outer punch 5b, and the upper punch 2 is formed as a single punch.

However, depending on the shape of the green compact F' to be molded, the upper punch 2 may have different lengths and may be divided into a plurality of upper inner punches 2a and upper outer punches 2.
It is configured as b.

In this embodiment, the fifth platen 18 and the sixth platen 19 do not need to be raised or lowered. The press device used in this molding device P has a structure in which a plurality of platens (mounting bases) can be raised and lowered and stopped, such as the device described in Japanese Patent Publication No. 53-25976, Japanese Patent Publication No. 63-36880. A device such as that described in the publication is used, and the upper punch 2 side is
As described in Japanese Patent No.-85304, etc., a configuration in which an actuator 10 is attached to the upper ram 12 to move up and down can be applied. Further, 8 is a receiving plate.

Next, the control system of this molding apparatus P will be explained with reference to FIG.

[0051] Instructs the movable platen to move up and down, stop, and move up and down as necessary, and also controls the sequence of a series of processes from the preparation process 1 through the powder filling process 2 to the green compact release process 7. It includes a control means (CPU) 100 connected to an input terminal P1.

The control means 100 also has a relative position detecting section (not shown), and can control the stop position, stop time, operating timing, operating speed, etc. using a sequence circuit.

[0053] 101 is a precompression command section, and the die inner hole 1
When powder is filled into the die hole 1a, the powder filling detection means 102 detects this based on information from the control means 100, and by inputting this detection signal, at least the upper punch 2 is inserted into the die inner hole 1a. The control means 10 issues a command to start a pre-compression operation to increase the apparent density of the filled powder F.
Do it to 0.

103 is a stress release command unit, which moves the upper and lower punches 2 and 5 for forming thin-walled parts to make the filled powder F into a shape approximately similar to that of the green compact F' to be formed, and then moves it to the green compact F'. When a compression operation is performed, the compression end detection section 104 detects this based on information from the control means 100, and upon input of this detection signal, the upper punch 2 is retracted and at the same time the lower punch 5 is also retracted. The control means 100 is configured to move backward.
A stress release start command is issued to release the pressing force of the lower punch 5 applied to the end face of the powder compact F'.

Note that when the above command is input to the control means 100, the control means 100 drives the necessary mechanisms of the molding apparatus P via the drive command section 105.

[0056] Also, with this device, 7t/cm2 in the compression direction
When a pressure of There is a situation in which cracks occur at the stepped corners of the powder compact F'.

Next, a molding method that can prevent the occurrence of cracks will be explained.

-Example 1- Figs. 4(a) to 4(e) are explanatory cross-sectional views showing the steps from powder filling to mold release of the green compact in the stepped-shaped sintered part shown in Fig. 8(a). be.

Figure (a) shows the powder filling process (process 2 in Figure 2).
The lower inner punch 5a is inserted into the die inner hole 1a at the b1 position and the lower outer punch 5b is inserted into the c1 position to form a cavity for the press mold, and the powder F is filled into this cavity.

Figure (b) shows the compression process (step 4 in Figure 2), in which the upper punch 2 is lowered to the d1 position, the lower inner punch 5a is moved from the b1 position to the b2 position, and the lower outer punch 5b is moved to the c1 position. to c2 position, and compresses the powder F to form a green compact F'.

Figure (c) shows the stress release process (Step 5 in Figure 2).
The upper punch 2 is raised to the d2 position and released from the powder compact F', and at the same time, the lower inner punch 5a is lowered to the b3 position and the lower outer punch 5b is lowered to the c3 position to release the powder compact F'.
´ Release.

Each punch 2, 5 and the green compact F' in the figure
Although the gap between them is exaggerated in the illustration, the lower inner punch 5a and the lower outer punch 5b are stopped at a distance that is the sum of the deflection amount of the punch and the receiving plate and the displacement amount of the platen, respectively.

Further, the lower punches 5a and 5b may be lowered by approximately 1 mm more than the lower punches 5a and 5b.

It is preferable to set the lower inner punch 5a faster than the lower outer punch 5b when lowering the lower punch 5, since this eliminates the slightest chance of pushing up the powder compact F' due to the difference in the amount of deflection.

Figure (d) shows the extraction process (Step 6 in Figure 2), in which the upper punch 2 is extracted from the die 1 and raised to the top dead center, and the core 7, lower inner punch 5a and lower outer punch 5b are removed. are rising at the same rate.

In the powder compact as in this embodiment, a gap is provided between the lower inner punch 5a and the powder compact F', and each of the lower punches 5a, 5
Good results can be obtained by raising b and core 7 at the same speed.

Figure (e) shows the green compact release process (process 7 in Figure 2).
), which shows the state in which the green compact F' is extracted from the die 1.

[0068] In this state, the powder compact F' springs back and expands in dimension in the outer diameter direction, and is in a state where it is easy to release it from the core 7 and the lower inner punch 5a.

Next, although not shown, each lower punch 5a, 5
B and the core 7 are lowered to the powder F filling position shown in Figure (a), and one cycle is completed.

Next, a molding method capable of making the density in the compression direction uniform will be explained.

-Example 2- Figs. 5(a) to 5(c) show the main parts of the forming method when the stepped-shaped sintered part shown in Fig. 8(b) is used and the density in the compression direction is made uniform. It shows.

First, after the powder filling step (step 2 in FIG. 1) as shown in Figure (a), the upper inner punch 2a and upper outer punch 2b are deeply inserted into the die inner hole 1a as shown in Figure (b). At the same time, the lower outer punch 5b is raised to pre-compress the filling powder F (
Precompression step 3) in Figure 1.

At this time, the amount of descent of each upper punch 2a, 2b and the lower punch are adjusted so that the density ratio in the thin part is 75% or less and the powder density near the lower outer punch 5b is equal to or higher than the tap density. The amount of movement of 5a and 5b is determined.

[0074] In the case of a compact powder body F' having a short length, it may be possible to pre-compress the powder body without raising the lower punch 5 side.

Next, as shown in figure (c), the upper and lower inner punches 2
The thin-walled powder sandwiched between a and 5b is moved to make it approximately similar to the green compact to be molded, and then the compression step 4 is carried out in the same manner as in the previous example.
~Perform green compact mold release step 7.

That is, in contrast to the conventional forming method, this forming method moves each upper punch 2 downward from the surface of the die 1 by a distance α.
It has a pre-compression step of moving the lower outer punch 5b upward to a position a distance β.

In precompression, which is the gist of this example,
Apparent density when filled is 3g/cm3 (density ratio 3
8%) and tap density is 3.5g/cm3 (density ratio 44
In the case of iron powder of 76%).

FIG. 7 shows the relationship between the compacted density and density ratio of iron powder and the shearing force of the compact, and the shearing force is expressed as the shearing load per unit contact area between the thin wall portion and the main body.

[0079] When the density exceeds 6 g/cm3, the shearing force increases, indicating that the strength of the green compact F' is improved.

In Figure (c), the so-called green compact F' is sheared, but as shown in Figure 7, the shearing force at each density is small, so if it is higher than the tap density, it is due to the movement of the thin wall part. It can be seen that the increase in density is very small.

On the other hand, after moving the thin part of the pre-compressed packed powder F as shown in FIG. 5(c), the density was 6.8 g/cm3.
After compaction and mold release, and sintering, we observed the cross section of the root of the thin wall part and looked at the occurrence of cracks. When the pre-compression density was less than 6 g/cm3, no cracks were observed, and the shear force in Figure 7 very similar to the trend.

A similar tendency was observed for aluminum powder with a packed apparent density of 1.2 g/cm 3 .

The same applies to copper-based materials, but in industry, parts such as sintered bronze bearings have a density of 6 to 6.5 g/c.
m3 (density ratio of around 70%) in many cases, and in such cases, the precompression is naturally set to a state close to the tap density.

Next, based on FIGS. 6(a) to 6(f), the third
An example will be explained.

-Example 3- This example will be explained using a stepped-shaped sintered part shown in FIG. The upper punch 2 and the lower punch 5 are both divided into inner and outer parts, that is, an upper inner punch 2a, an upper outer punch 2b, and a lower inner punch 5.
a, a lower outer punch 5b is used, and the difference from the first embodiment is that the upper inner punch 2a is fixed to the fifth platen 18, the upper outer punch 5b is fixed to the fourth platen 17, and the core 7 is fixed to the fifth platen 18. Not prepared.

[0086] Figure (a) shows the powder filling step 2 shown in Figure 1.

Figure (b) shows the pre-compression step 3, in which the upper inner punch 2a and the upper outer punch 2b are slightly inserted into the die inner hole 1a to sandwich the powder F, and the lower inner punch 5a and the upper inner punch 2a are The filling powder F is moved downward at the same interval as shown by the arrow in the figure to make the filling powder F into a shape substantially similar to the green compact F' to be molded.

[0088] Thereafter, as shown in Figure (e), pressure is applied to complete the compression step 4.

Next, as shown in Figure (d), both upper punches 2a,
At the same time as the punch 2b is raised, both lower punches 5a and 5b are lowered to perform the stress release step 5.

At this time, the retreat timing of the inner punches 2a, 5a of both the upper punch 2 and the lower punch 5 is set earlier than that of the outer punches 2b, 5b, and the lower inner punch 5a is pulled out from the recess of the powder compact F'. lower to.

It is more preferable that the lower inner punch 5a is lowered so as to be in contact with the powder compact F' as in the first embodiment.

The powder compact F' is extracted by pushing up only the lower outer punch 5b and raising the lower inner punch 5a slowly, as shown in FIG. 3(e).

[0093] Figure (f) shows the state in which the green compact F' has been released from the die 1.

Thereafter, the lower outer punch 5b is lowered and the lower inner punch 5a is stopped and reaches the filling position, completing one cycle.

In this embodiment as well, good results can be obtained by lowering the lower inner punch 5a after completion of compression as shown in FIGS. 4(a) to 4(d).

As described above, according to the molding method according to the present invention, after the filling powder F is pressurized, all the upper and lower punches 2,
5 is simply retreated from the compact F', the load on the compact F' is released, and then the compact F' is extracted from the die 1, so the molding equipment is complicated and delicate. No control is required, and there is no risk of cracking caused by the return of the molding device from deflection.

[0097] Furthermore, when the stepped shaped part has a thin wall part near the middle part in the height direction or below, the thin wall part is transferred after precompressing the filling powder F before compressing it into the final shape. The upper and lower densities of the green compact F' become uniform, and the quality of the sintered product can be improved.

[0098]

As explained above, according to the invention as set forth in claim 1, the stress release step is provided after the compression step, and the upper punch and the lower punch are simultaneously moved away from the green compact after the compression of the powder is completed. The deflection of each punch and its backing plate is simultaneously released on both the top and bottom of the powder compact, so no bending stress or shear stress is applied to the powder compact, and cracks can be prevented from occurring in the powder compact. can.

Further, according to the invention as claimed in claims 2 and 4, since the pre-compression step is provided after powder filling and the filled powder is pre-compressed, movement of the filled powder becomes less likely to occur and the density in the compression direction is made uniform. can be achieved.

Furthermore, according to the invention according to claims 3 and 4, since the stress release step and the pre-compression step are included,
It is possible to prevent cracks from occurring in the green compact, and it is also possible to equalize the density in the compression direction.

Further, according to the invention as set forth in claim 5, a pre-compression command section and a stress release command section for simply retracting the drive mechanism of the upper and lower punches from the pressurizing direction after completion of compression are provided. This is a simple molding device that can prevent the occurrence of cracks in powder and make the density uniform in the compression direction, and eliminates the complexity of conventional methods that require means for detecting and controlling multiple pressures and positions. The above effect can be achieved as follows.

[Brief explanation of the drawing]

FIG. 1 is a sequence block diagram showing steps of a molding method according to the present invention.

FIG. 2 is a schematic configuration diagram of a molding apparatus according to the present invention.

FIG. 3 is a block diagram showing a control system of the molding apparatus according to the present invention.

FIG. 4 is an explanatory sectional view showing a first embodiment of the molding method according to the present invention.

FIG. 5 is an explanatory sectional view showing a second embodiment of the molding method according to the present invention.

FIG. 6 is an explanatory sectional view showing a third embodiment of the molding method according to the present invention.

FIG. 7 is a graph showing the relationship between iron-based compact density and density ratio and compact shear force.

FIG. 8 is an explanatory cross-sectional view of various stepped-shaped sintered parts having different thicknesses in the compression direction.

[Explanation of symbols]

1 Die 2 Upper punch 2a Upper inside punch 2b Upper and outer punch 5 Lower punch 5a　Downward punch 5b Lower outside punch 7 Core F Powder F´　　Powder compact

Claims (5)

[Claims] 1. A method for forming a stepped powder compact having different thicknesses in the compression direction, the powder being filled into an inner hole of a die regulating the outer surface of the compact, with different lengths and In the molding method, the powder compact is compressed by a lower punch divided into a plurality of parts and an upper punch divided into a single punch or a plurality of parts having different lengths, and then the green compact is extracted from the inner hole of the die. After the compression process in which the powder filling the inner hole is compressed by upper and lower punches to form a green compact with different thicknesses in the compression direction, the upper punch is moved back, and at the same time the lower punch is also moved back to form a green compact that hangs over the end surface of the green compact. A step characterized by performing a stress release step of releasing the pressing force of the punch, and then performing a powder compact extraction step of moving the lower punch forward relative to the die to extract the powder compact from the die inner hole. A method of forming a green compact with a shape. 2. A method for forming a stepped powder compact having a thin wall portion below the upper end of a cylindrical or columnar body, wherein the powder compact is filled into a die inner hole regulating the outer surface of the compact. The powder to be filled is sandwiched between the upper and lower punches, which are divided into a punch for forming the body part of the compact and a punch for forming the thin-walled part, and the upper and lower punches for forming the thin-walled part are moved to form the filled powder. In a molding method in which the compact is compressed into a shape substantially similar to the body, the green compact is then extracted from the inner hole of the die, and after the step of filling the powder into the inner hole of the die, at least was introduced into the inner hole of the die to perform a pre-compression step to increase the apparent density of the filler powder, and then the upper and lower punches for forming thin-walled parts were moved to make the filler powder approximately similar in shape to the green compact to be formed. A method for forming a stepped powder compact, which is characterized in that the compact is subsequently subjected to a compression process to form a compact. 3. A pre-compression step performed after the step of filling the powder into the die inner hole, in which at least the upper punch enters the die inner hole to increase the apparent density of the filled powder, and thin-walled portion forming. This is a process performed after the compression process in which the upper and lower punches for the filling powder are moved to form a compact that is approximately similar to the compact that is to be formed, and the compact is made into a compact. A method for forming a stepped powder compact, comprising a stress release step of also retracting the punch to release the pressing force of the lower punch applied to the end face of the compact. 4. The method for forming a stepped powder compact according to claim 2 or 3, wherein the pre-compressed packed powder has an apparent density of not less than a tap density and a density ratio of not more than 75%. 5. A series of steps including the step of filling the powder into the die inner hole, the step of compressing the filled powder, and the step of extracting the green compact are sequentially controlled by a control means, and at least a step with a different thickness in the direction of compression is performed. A die with an inner hole for regulating the outer surface of the powder compact, a lower punch of different lengths and divided into multiple parts, an upper punch and a platen of single or different lengths and divided into multiple parts. Prepare,
In a molding device that moves the upper and lower punches back and forth in the pressing direction to compress the powder filled in the inner hole of the die to form a green compact,
(1) When the powder is filled into the die inner hole, a precompression command is given to the control means to start a precompression operation that causes the punch to enter the die inner hole and increase the apparent density of the filled powder. (2) If a compression operation is performed to make the powder compact after moving the upper and lower punches for forming the thin-walled part and making the filled powder into a shape that is approximately similar to the powder compact to be compacted, the compaction a stress release command section that starts instructing the control means to retract the upper punch and simultaneously retract the lower punch in order to release the pressing force of the lower punch applied to the body end surface; A molding device for a stepped powder compact, characterized by having a command section.