JPH09324204A - Method for molding double layer green compact molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of the crack of a double layer green com pact molding or sintered compact by preventing the generation of a shearing stress in molding. SOLUTION: First powder is packed into the first cavity of a die and is previously compressed under prescribed load to form a precursor 201. Second powder 202 is packed into a second cavity adjacent to this precursor 201 in its thickness direction. The molding is formed by simultaneously compressing the precursor 201 and the second powder 202 at the same stroke length. Since the precursor 201 and the second powder 202 are compressed simultaneously at the same stroke length, the shearing stress does not act between the layers of both.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a powder compact formed of metal powder or ceramic powder, and more specifically, a multilayer having a multilayer structure composed of a plurality of material layers different in the thickness direction. The present invention relates to a method for molding a powder compact. According to the molding method of the present invention, defects such as cracks due to stress concentration between layers can be eliminated.

[0002]

2. Description of the Related Art For example, in a cylindrical bearing member having an inner peripheral surface as a sliding surface, the outer peripheral portion is formed of a general inexpensive steel material in order to suppress the raw material cost, and only the inner peripheral portion has mechanical characteristics. It is formed from high-strength brass such as excellent MBA (Cu-Zn-Al-Mn-Si).

Such a bearing member is obtained by forming a multi-layer powder compact having a multi-layer structure by the method disclosed in, for example, Japanese Patent Laid-Open No. 60-258401 and sintering it. Being manufactured. JP-A-60-258401
A method of manufacturing a cylindrical bearing member having a two-layer structure using the molding method disclosed in Japanese Patent Publication No. 1994-242242 will be described below.

12 to 16 are sectional views of a mold for forming a multi-layer powder compact. This die comprises a cylindrical die 100 that defines the outer diameter of the multi-layer powder compact and a cylindrical lower outer punch 101 that is in sliding contact with the inner peripheral surface of the die 100.
A cylindrical lower inner punch 102 that slidably contacts the inner peripheral surface of the lower outer punch 101, a core rod 103 that slidably contacts the inner peripheral surface of the lower inner punch 102 and defines the inner diameter of the multilayer compact, and the die 100. And a cylindrical upper punch 104 that is in sliding contact with the inner peripheral surface of the core rod 103 and the outer peripheral surface of the core rod 103, and they are arranged so as to have the same axial center.

The lower outer punch 101 has a lower end fixed to a first movable plate 105, and the first movable plate 105 is vertically driven by a first cylinder 106. The lower inner punch 102 has a second lower end portion.
It is fixed to the movable plate 107, and the second movable plate 107 is configured to be vertically driven by the second cylinder 108. A stopper 109 is provided below the first movable plate 105.
Is fixed, and the first movable plate 105 comes into contact with the stopper 109 to restrict the downward movement. Further, the second movable plate 107 comes into contact with the base 110 to restrict the downward movement thereof.

<First Step> First, as shown in FIG. 12, the lower outer punch 101 is lowered so that it is between the inner peripheral surface of the die 100, the outer peripheral surface of the lower inner punch 102 and the tip surface of the lower outer punch 101. The formed cavity is filled with the first powder 200 made of a raw material such as atomized Fe powder by free fall and abrasion.

<Second Step> Next, as shown in FIG. 13, a part of the powder box 111 is arranged above the die 100, and the first cylinder 106 is driven to drive the first movable plate 105 and the lower outer punch 101. With a predetermined stroke,
The first powder 200 is compressed to form the precursor 201. This precursor 201 is made longer than the intended length, and its density is lower than the intended density of the multilayer powder compact.

<Third Step> After that, as shown in FIG.
The lower inner punch 1 is driven by driving the second cylinder 108.
02 is lowered until the second movable plate 107 comes into contact with the base 110, and the inner peripheral surface of the precursor 201, a part of the inner peripheral surface of the lower outer punch 101, the outer peripheral surface of the core rod 103, and the tip surface of the lower inner punch 102. The second powder 202 made of a raw material such as MBA high-strength brass is filled in the cavity formed in between by free fall and abrasion.

At this time, the second powder 202 is filled so as to have a length longer than that of the precursor 201. When the second powder 202 has the same density as the precursor 201 by compression, it has the same length as the precursor 201. ing. Therefore, the tip surface of the lower inner punch 102 in this state is located below the tip surface of the lower outer punch 101.

<Fourth step> Then, as shown in FIG.
The precursor 201 and the second powder 2 are formed by the upper punch 104.
Compress 02. At this time, the driving force of the first cylinder 106 is released, and the lower outer punch 101 moves to the precursor 20.
Since it descends with 1, the precursor 201 is hardly compressed, and the second powder 202 is mainly compressed.

When the first movable plate 105 comes into contact with the stopper 109 and its lowering is restricted, the lower outer punch 101.
Of the second powder 202 compressed with the precursor 201 and the front surface of the lower inner punch 102 are flush with the front surface of the lower inner punch 102.
Have almost the same density. And the upper punch 104
The pressing force is received by the stopper 109 and the base 110, and the upper punch 104 simultaneously compresses the precursor 201 and the second powder 202 in a predetermined stroke.

<Fifth step> Hold in that state for a while,
As shown in FIG. 16, finally, the upper punch 104 is separated from the die 100, and the die 100 and the core rod 1 are removed.
03 is lowered to take out the multilayer powder compact. This multi-layer compacted body is integrally sintered by being heated, for example, at 1120 ° C. for 0.5 hours in a nitrogen atmosphere to manufacture a multi-layered bearing member.

[0013]

However, in the conventional molding method described above, the compression stroke length of the second powder 202 is longer than the compression stroke length of the precursor 201 in the fourth step. Therefore, the second powder 202 and the precursor 201
Shear stress acts between the inner and outer layers of the formed multi-layer compact and the internal stress of the multi-layer compact does not change even if there is no visible abnormality. The residual may cause cracks at the interface during sintering.

Further, in the above-mentioned two-layer structure bearing member, it is desirable to reduce the cost by making the inner layer made of an expensive material as thin as possible. For that purpose, it is necessary to reduce the thickness of the lower inner punch 102. However, it is difficult to reduce the thickness of the punch to less than the thickness thereof, because the minimum thickness of the punch is restricted by the pressure applied during molding and the strength of the punch material. Therefore, the lower inner punch 102 cannot be made thinner than a predetermined thickness, and the inner layer of the bearing member becomes unnecessarily thick, resulting in waste of using an expensive material more than necessary.

In the fourth step, the pressing force of the upper punch 104 is first applied to the lower inner punch 102, and at that time, the lower outer punch 101 is moved downward by the pressing force of the upper punch 104. During the movement of the lower outer punch 101, a frictional force is generated between the lower outer punch 101 and the second powder 202, and the frictional force prevents the lower outer punch 101 from descending. Therefore, the pressing force of the upper punch 104 acts on the lower outer punch 101, a large load is applied to the lower outer punch 101, and the life thereof is shortened.

Furthermore, since the stroke length for compressing the second powder 202 is long, the second movable plate 107 must be positioned below the first movable plate 105. Therefore, it is necessary to increase the length of the lower inner punch 102, and there is also a problem that the strength must be increased more than necessary in order to prevent buckling. The present invention has been made in view of such circumstances, and its main purpose is to prevent the occurrence of shear stress at the time of molding, thereby preventing the occurrence of cracks in the multilayer powder compact or the sintered body. To do.

[0017]

The features of the method for forming a multi-layer green compact according to the present invention for solving the above-mentioned problems are that a multi-layer green compact composed of a plurality of material layers different in the thickness direction is formed. A first step of filling a first cavity of a mold with a first powder and pre-compressing with a predetermined load to form a precursor;
A second step of filling a second cavity adjacent to the precursor in the thickness direction with the second powder and simultaneously compressing the precursor and the second powder with the same stroke length to form a compact.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In the molding method of the present invention, first of all,
In the step, the first powder is filled in the first cavity of the mold and pre-compressed with a predetermined load to form a precursor. This first step can be performed in the same manner as the conventional method,
The precursor is formed so as to have a density lower than that of the intended multilayer compacted body.

In the next second step, the second powder is filled in the second cavity adjacent to the precursor in the thickness direction, and the precursor and the second powder are simultaneously compressed under the same stroke length. That is, since the precursor and the second powder are simultaneously compressed with the same stroke length, shear stress does not act between the layers. Therefore, it is possible to prevent cracks from being generated between the layers of the multi-layer green compact, and since there is almost no residual stress, it is also possible to prevent cracks from being generated between the layers during sintering.

In the initial stage of the second step, the density of the second powder is lower than that of the precursor because the second powder is not compressed. Since the precursor is compressed with the same stroke length, as the compression progresses, the precursor having higher density presses the second powder in the thickness direction, and finally, the compressed precursor and the compressed second powder are generated. And have the same density. That is, since the second powder is pressed in the thickness direction as well, if the amount of the second powder filled in the second cavity is made smaller than in the conventional case, the portion formed from the second powder will be irrespective of the thickness of the punch. Can be made thinner than before. Therefore, when the material of the second powder is expensive, it is possible to reduce the cost of the obtained multilayer powder compact. Further, since it is not necessary to reduce the thickness of the punch, there is no problem that the strength is reduced.

Since the precursor and the second powder are simultaneously compressed with the same stroke length, the friction force from the second powder does not act on the specific punch to cause resistance. Further, the length of the punch corresponding to the lower inner punch described in the related art does not have to be unnecessarily long. Therefore, a means for improving the buckling strength of the punch becomes unnecessary.

[0022]

The present invention will be described below in detail with reference to examples. (Embodiment 1) FIG. 6 shows a multi-layer powder compact formed by the molding method of this embodiment. This multilayer compacted body is composed of a cylindrical outer layer 300 and an inner layer 301 integrally bonded to the inner peripheral surface of the outer layer 300.

1 to 5 show a method of molding the multilayer powder compact of the present embodiment. Since the used mold and molded body have an axially symmetrical shape, FIGS. 2 to 5 are shown as a half sectional view of only one side with respect to the axis. The mold used is a cylindrical die 1 that defines the outer diameter of the multi-layer powder compact, a cylindrical lower outer punch 2 that is in sliding contact with the inner peripheral surface of the die 1, and an inner peripheral surface of the lower outer punch 2. A cylindrical lower inner punch 3 that is in sliding contact with the surface, and a core 40 that is in sliding contact with the inner peripheral surface of the lower inner punch 3 and that defines the inner diameter of the multi-layer powder compact.
With a core rod 4, and an upper punch 5 that makes sliding contact with the inner peripheral surface of the die 1 and the outer peripheral surface of the head of the core rod 4.
And, and are arranged so as to have the same axis.

The lower outer punch 2 has a lower end fixed to the first movable plate 20, and the first movable plate 20 includes the first cylinder 2
It is configured to be driven up and down by 1. The lower inner punch 3 has a lower end fixed to the second movable plate 30, and the second movable plate 30 is vertically driven by the second cylinder 31. The stopper 6 is fixed below the first movable plate 20, and
By contacting the stopper 6, the downward movement is restricted. Further, the second movable plate 30 comes into contact with the first movable plate 20 to restrict the downward movement thereof.

<First Step> First, as shown in FIG. 1, with the lower outer punch 2 lowered, the inner peripheral surface of the die 1 and the lower inner punch 3 with the first movable plate 20 in contact with the stopper 6. The Fe sprayed in the cavity formed between the outer peripheral surface of the and the tip surface of the lower outer punch 2.
The first powder 200 made of powder is filled by free fall and abrasion.

Next, as shown in FIG. 2, a part of the powder box 111 is placed above the die 1, and the first cylinder 21 is driven to drive the first movable plate 20 upward. As a result, the lower outer punch 2 is lifted with a predetermined stroke, and the first powder 200 is compressed to form the precursor 201. This precursor 201 is made longer than the intended length, and its density is
The density is about 60%, which is lower than the density of the intended multi-layer green compact.

<Second Step> After that, the powder box 111 is retracted to open the upper part of the cavity. Then, as shown in FIG. 3, the second cylinder 31 is driven to move the second movable plate 30 to the first position.
It is lowered until it comes into contact with the movable plate 20. At this time, the tip surface of the lower outer punch 2 and the lower inner punch 3
Is arranged so as to be located on the same plane as the tip surface of the.

Then, the second powder 202 made of a Cu--Ni alloy is freely dropped into the cavity formed between the inner peripheral surface of the precursor 201, the outer peripheral surface of the core rod 4, and the tip surface of the lower inner punch 3. Fill by scraping. Then, as shown in FIG. 4, the upper punch 5 is lowered to simultaneously pressurize the precursor 201 and the second powder 202. Then, the pressing force presses the lower outer punch 2 and the lower inner punch 3 through the precursor 201 and the second powder 202, so that the second movable plate 30 becomes the first movable plate 2.
The first movable plate 20 descends in a state of abutting 0, and the lower outer punch 2 and the lower inner punch 3 are regulated in a position where the first movable plate 20 abuts the stopper 6.

At this time, since the driving force of the first cylinder 21 and the second cylinder 31 is extremely smaller than the pressing force of the upper punch 5, the densities of the precursor 201 and the second powder 202 are determined by the first movable plate 20. There is almost no change until they come into contact with the stopper 6, which are about 60% and about 30%, respectively. The pressurization by the upper punch 5 is further continued, and the precursor 201 and the second powder 202 are strongly compressed. At this time, since the precursor 201 and the second powder 202 are compressed with the same stroke length, no shear stress is generated at the interface between the precursor 201 and the second powder 202. Further, since the density of the precursor 201 is higher than the density of the second powder 202, a force that the precursor 201 presses the second powder 202 in the radial direction is also generated.

In this way, the precursor 201 and the second powder 2
02 is compressed in the axial direction, and the second powder 202 becomes the precursor 20.
When the precursor 201 and the second powder 202 are both compressed in the radial direction by 1 and the densities of both the precursor 201 and the second powder 202 become about 85%, the pressing by the upper punch 5 is stopped. After holding in that state for a while, as shown in FIG. 5, the upper punch 5 is driven to rise and the die 1 and the core rod 4 are lowered to take out the multi-layer powder compact including the outer layer 300 and the inner layer 301.

The multi-layer powder compact molded in this manner was of good quality, with no cracks occurring between the outer layer 300 and the inner layer 301. Also lower inner punch 3
Although the thickness of the inner layer 301 was 1 mm, the inner layer 301 was formed as thin as 0.6 mm. The multi-layer green compact was heated in a nitrogen atmosphere at 1120 ° C. for 0.5 hours to be integrally sintered, and a multi-layer bearing member was manufactured. Also in the bearing member after sintering, defects such as cracks did not occur between the outer layer and the inner layer, and the quality was good.

That is, as shown in FIG. 7, in the conventional molding method, the compression stroke length of the second powder 202 is longer than that of the precursor 201. Therefore, the precursor 201 and the second powder 2
In some cases, a shear stress was applied to the interface of No. 02 to cause cracking in A between the inner layer and the outer layer of the molded body. Second powder 2
The thickness of 02 is the same in the initial stage and the latter stage of compression. On the other hand, in this embodiment, as shown in FIG. 8, in the second step, the precursor 201 and the second powder 202 are simultaneously compressed with the same stroke length to have the same density. Therefore, no shear stress acts on the interface between the precursor 201 and the second powder 202, no shear stress acts on the interface between the outer layer 300 and the inner layer 301, and cracking is prevented.

Further, since the second powder 202 is compressed in the radial direction, as shown in FIG.
The layer thickness of 2 is reduced from t1 to t2. Therefore, it is possible to mold a molded body in which the layer thickness of the inner layer 301 is thinner than conventional ones. (Example 2) Fig. 11 shows a cross-sectional view of a multilayer powder compact obtained by the molding method of this example. In this multilayer powder compact, the axial length of the inner layer 301 is shorter than that of the outer layer 300,
The same as Example 1 except that it has a concave cross section.

9 and 10 show the mold used in this embodiment. This mold has the same configuration as that of the first embodiment except that the lower inner punch 3 has a short length. In this embodiment, first, the precursor 201 is formed as in the first embodiment. Next, the powder box 201 is retracted to open the upper part of the cavity.
Then, as shown in FIG. 9, the second cylinder 31 is driven,
The second movable plate 30 is lowered until it contacts the first movable plate 20. At this time, the front end surface of the lower inner punch 3 is located above the front end surface of the lower outer punch 2, and the difference in the length thereof is the inner layer 301 and the outer layer 300 of the target molded body.
Is configured to be the same as the difference in length.

Then, the second powder 202 made of Cu-Ni alloy is freely dropped into the cavity formed between the inner peripheral surface of the precursor 201, the outer peripheral surface of the core rod 4, and the tip surface of the lower inner punch 3. And fill by grinding. Then, as shown in FIG. 10, the upper punch 5 is lowered to simultaneously compress the precursor 201 and the second powder 202. Then, the pressing force presses the lower outer punch 2 and the lower inner punch 3 through the precursor 201 and the second powder 202, and the second movable plate 30 is moved first while the second movable plate 30 is in contact with the first movable plate 20. When the plate 20 descends and the first movable plate 20 contacts the stopper 6, the lower outer punch 2 and the lower inner punch 3 are restricted from descending.

The compression by the upper punch 5 is further continued, and the precursor 201 and the second powder 202 are strongly compressed. At this time, since the precursor 201 and the second powder 202 are compressed with the same stroke length, the precursor 201 and the second powder 2
No shear stress is generated at the interface of 02. Then Example 1
When the multi-layer powder compact was taken out in the same manner as above, no cracks and the like occurred between the outer layer 300 and the inner layer 301, and the quality was good. Then, it was sintered in the same manner as in Example 1,
No cracking occurred and a good quality sintered product was obtained.

[0037]

[Effects of the Invention] That is, according to the method for molding a multi-layer powder compact of the present invention, a compact having no defects such as cracks between layers can be easily and surely molded. Further, it is possible to form a molded body having a thin layer thickness, which has been difficult in the past, and it is possible to reduce the use ratio of an expensive raw material, so that the raw material cost can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a mold in which a first powder is filled in a cavity according to an embodiment of the present invention.

FIG. 2 is a half sectional view of a mold showing a precursor formed in one example of the present invention.

FIG. 3 is a half-sectional view of a mold showing a state in which a second powder is filled in a cavity according to an embodiment of the present invention.

FIG. 4 is a half cross-sectional view of the mold shown in a state immediately before the end of the second step in the embodiment of the present invention.

FIG. 5 is a half cross-sectional view of a mold shown in a state immediately before taking out a multilayer powder compact in one embodiment of the present invention.

FIG. 6 is a perspective view of a multilayer powder compact molded according to an embodiment of the present invention.

FIG. 7 is an explanatory diagram showing the operation of a conventional molding method.

FIG. 8 is an explanatory diagram showing the operation of the molding method according to the embodiment of the present invention.

FIG. 9 is a half sectional view of a mold showing a state in which a second powder is filled in a cavity in the second embodiment of the present invention.

FIG. 10 is a half cross-sectional view of a mold shown in a state immediately before the end of the second step in the second embodiment of the present invention.

FIG. 11 is a cross-sectional view of a multilayer powder compact molded according to the second embodiment of the present invention.

FIG. 12 is a cross-sectional view of a mold in which a cavity is filled with the first powder in a conventional example.

FIG. 13 is a half sectional view of a mold showing a state in which a precursor is formed in a conventional example.

FIG. 14 is a half-sectional view of a mold showing a state in which a second powder is filled in a cavity in a conventional example.

FIG. 15 is a half cross-sectional view of a mold shown in a state immediately before the end of compression with an upper punch in a conventional example.

FIG. 16 is a half cross-sectional view of a mold shown in a state immediately before taking out a multilayer powder compact in a conventional example.

[Explanation of symbols]

1: Dice 2: Lower outer punch 3: Lower inner punch 4: Core rod 5: Upper punch 6:
Stopper 20: First movable plate 30: Second movable plate 20
1: precursor

Claims (1)

[Claims] 1. A method for molding a multi-layer powder compact comprising a plurality of material layers different in the thickness direction, wherein the first cavity is filled with the first powder and pre-compressed with a predetermined load. To form a precursor, and a second cavity is formed in a second cavity adjacent to the precursor in the thickness direction.
A second step of forming a compact by filling powder and compressing the precursor and the second powder at the same stroke length at the same time.