JP2000087104A - Method for forming green compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable compacting of a powder contg. a lubricant for warm compacting at the high compacting temp. of the powder and to obtain both the advantages of warm compacting and the lubricant for the warm compacting. SOLUTION: A powder P contg. a lubricant for warm compacting is primarily compacted at ordinary temp. and a resultant primary compact P1 is heated to the compacting temp. of the powder P and secondarily compacted in a secondary compacting mold to obtain the objective green compact P2. The compacting of the lubricant-contg. powder P at the high compacting temp. is enabled and the density of the green compact P2 is considerably increased. In the primary compacting step, the primary compact P1 is preferably formed in such dimensions that it can loosely be fitted in the secondary compacting mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of compacting a metal powder to form a green compact as a material for a sintered product in the field of powder metallurgy.

[0002]

2. Description of the Related Art When a metal powder is compression-molded to obtain a green compact, usually, the raw material is reduced in order to suppress mold wall friction during compression, mold abrasion during die-cutting, or friction between powders during compression. Lubricant is mixed into the powder, or lubricant is applied to the mold wall. As the lubricant, a stearic acid powder based on Al, Zn, Li, Mg or Ca is generally used, but besides this, wax or cellulose may be used. By the way, there has been conventionally proposed a technique in which a method of using a powder containing a lubricant or a lubricant itself is provided with characteristics and an effect based on the characteristics is obtained.

[0003] For example, Japanese Patent Application Laid-Open No. 61-19702 ...
In (1), the amount of lubricant used is reduced by distributing the lubricant-containing powder thinly on the mold wall, filling the remaining cavity with powder containing no lubricant, and compressing the powder. And that the adverse effect of the lubricant in the sintering process is suppressed. Also, Japanese Patent Application Laid-Open No. 9-272901 ...
In (2), a mold coated with a lubricant is used in a range of 150 to 400.
A method is disclosed in which it is believed that high density can be achieved by heating to a temperature of 0 ° C., filling the mold with a powder containing no lubricant heated to the same temperature, and compressing.
Further, Japanese Patent No. 2593632 (3) is a powder to which a high-temperature (warm) molding lubricant composed of specified components is added, and in this case, the powder is compressed at 370 ° C. or lower to obtain a high powder. We are trying to increase the density.

[0004]

According to the method disclosed in the above-mentioned publication (1), in order to fill the mold wall with the powder containing a lubricant and the inside with the powder containing no lubricant, Although there is a description that a partition is provided between the two, it is assumed that the work is actually complicated. Also,
When this green compact is sintered, the porosity of the surface layer portion containing the lubricant becomes lower than that of the inner layer portion, and it is not suitable as a method of manufacturing a member requiring high strength particularly in the surface layer portion. It is well known that the compaction of the green compact is achieved by compressing the powder at a high temperature. However, as described in the above-mentioned publication (2), the powder is heated in advance at a stage before filling in a molding die. To do so, it is necessary to use a technique that is more difficult than heating solids because the equipment is complicated or large, and it is difficult to uniformly heat the equipment. Further, when heating the powder to which the lubricant is added, if the heating temperature is approximately 150 ° C. or higher, the fluidity of the powder is significantly reduced due to the melting of the lubricant, and it becomes difficult to obtain a high-density compact, Strict temperature control is required. Therefore, as described in the above patent (3), the lubricant is 37
If it is for warm compaction that can be used at 0 ° C or lower, it will be possible to perform high-temperature compression while ensuring the fluidity of the powder. However, even with this lubricant, the fluidity of the powder decreases at 150 ° C or higher. It was confirmed that strict temperature control was required, and the practical advantage was low.

[0005] Accordingly, the present invention makes it possible to use powder containing a lubricant for warm compaction and to carry out compression molding of the powder at a high temperature depending on the molding temperature of the powder. It is an object of the present invention to provide a method for forming a green compact capable of enjoying both advantages of a lubricant.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for forming a green compact having a predetermined density by compressing a powder. Thus, the primary compression step of compressing to a density lower than the predetermined density and capable of handling, and the primary compact obtained in the primary compression step is heated to a molding temperature of the lubricant-containing powder. And a secondary compression step of obtaining a green compact by compressing to a predetermined density by a secondary molding die.

According to this method, the powder to be used is a lubricant-containing metal powder for warm compaction, and this powder is compressed at room temperature in the first primary compression step. The pressure at this time is lower than a predetermined density of the green compact finally obtained, and
The pressure is such that the molded body (primary molded body) can be handled. The density that can be handled here refers to a density that can be handled and held in a hand and does not damage at that time. In this primary compression step, the lubricant-containing powder for warm compaction is compressed at room temperature without heating to the molding temperature of this powder, so when filling the powder into the primary molding die, or during compression, heat is applied. A decrease in the fluidity of the powder does not occur, and a primary molded body having the desired density described above can be obtained. In addition, the normal temperature here means
It refers to a temperature from about ambient temperature to about 90 ° C., which is a temperature at which the primary molded body and the primary mold are heated by frictional heat due to continuous molding.

Next, in a secondary compression step, the primary compact is compressed at a molding temperature of the lubricant-containing powder used to obtain a green compact having a predetermined density and a desired shape. Specifically, for example, the primary compact and the secondary compact are each heated to a molding temperature of the lubricant-containing powder by a suitable heating means, and then the primary compact is set in the secondary compact. Then, the primary compact is compressed. At the time of the secondary compression, the primary compact is temporarily collapsed, and is finally formed into a green compact.

Since the primary molded body can be handled, it can be easily and quickly set in the secondary molding die. Also, since the primary compact is set in the secondary mold instead of the powder, the temperature at the time of compression, which was conventionally difficult to set to 150 ° C. or higher, to avoid a decrease in the fluidity of the powder, is set to the lubricant-containing powder. Can be raised to the upper limit of the molding temperature or a temperature close to the upper limit, and the temperature control is not required to be strict. In other words, the powder (in this case, the primary compact) can be compressed at a higher temperature than before,
The density of the green compact is greatly improved, and the quality is stabilized. The heating temperature of the primary compact is preferably within the range of the molding temperature of the powder and lower than the temperature at which the material based on the powder causes blue embrittlement.

According to the present invention, since the compression ratio is divided into primary compression and secondary compression, the degree of wear of each mold is reduced to enable long-term use, and the mold depth is short. As a result, the manufacturing cost of the mold is reduced. Furthermore, if a large amount of the primary compact is prepared and stocked in advance, and the secondary compact is obtained as necessary to obtain a compact, the powder is adjusted and filled every time the compact is molded. This saves time and improves productivity.

[0011] In the present invention, the primary molded body is formed so that the primary molded body can be easily set in the secondary mold.
In a preferred embodiment, the mold is formed to have a size that can be loosely fitted in the secondary mold, that is, a dimension that allows an appropriate gap between the mold wall of the secondary mold. For example, when the final compact is a spur gear and the compression direction is the axial direction, the primary compact is formed into a simple disk or polygonal shape, and in the secondary compaction process, the teeth are uniformly pitched around the same. Is formed.
If the primary molded body has a simple shape in this way, it can be more easily and quickly set in the secondary molding die, and the primary molding speed can be increased.

Further, the present invention includes not forming the primary molded body as a single body, but combining the primary molded body into a divided body that becomes a primary molded body having a desired shape. That is, the primary compact is divided into a plurality of pieces and compression-molded, and in the secondary compression step, the plurality of primary compacts are set in a combined state in a secondary mold, and the secondary compression is performed by the secondary compression. The bodies are joined together to obtain the final green compact.

Here, the density of each divided body as a primary molded body is based on the premise that handling can be performed as described above. In addition to this, at the time of compression, adjacent divided bodies are joined together. The required density is required. The lower the density, the better the joint between the divided bodies is made. However, if the density is too low, the handling becomes impossible this time. It is generally known that bonding is possible when the density ratio (the ratio of the density obtained by the compact to the true density of a metal having the same composition) is less than 76%. In addition, the probability that cracks occur at the bonding interface is increased, which is not preferable. Therefore, the density of the divided body is selected within a range where the density ratio is less than 76% and the handling is possible, and the range is 6%.
A density that achieves a density ratio of 0 to 75% is preferred. For example, when the powder is Fe-based, 4.7 to 5.9 g / c
For m ^3, Al in the case of 1.6~2g / ^cm 3, Cu system are suitable 5.3~6.6g / cm ^3.

In the present invention, the green compact to be molded is
It has a plurality of parts having different required properties, and the plurality of primary compacts are characterized in that each of them is primarily compressed with a powder, shape or density corresponding to the part. For example, when the green compact is the above-described spur gear, the primary compact is formed on the outer peripheral portion where high wear resistance is required, and on the inner side where less wear resistance is required and the function of the vibration damping material is required. Two of the meat parts. Then, the density of the primary molded body of the outer peripheral portion is made high, while the density of the primary molded body of the inner wall portion is made relatively low. If a plurality of primary compacts are formed in accordance with a part and then combined and secondarily compressed, characteristics of each part can be automatically obtained.

In the present invention, the green compact has a step on one end side in the compression direction, and the step is formed in a downward state in the primary compression step, and is formed in a downward state in the secondary compression step. It is characterized by being molded in an upward state. Specifically, the step portion is formed by the lower punch during the primary compression, and is formed by the upper punch during the secondary compression. For this reason, the structure of the lower punch is simple in both the primary and secondary molds, and the secondary mold only needs to have a punch for boss molding only on the upper side, so that the overall structure of each mold is simplified. .

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (1) First Embodiment FIGS. 1A to 1D sequentially show steps of a method for molding a green compact according to a first embodiment, and FIG. The resulting compact P2 of the spur gear is shown. Hereinafter, the molding process will be described together with the molding die used.

A. Primary Compression Step As shown in FIG. 1A, a primary molding die 1 used in the primary compression step includes a die 2 and upper and lower punches 3 and 4 inserted into the die 2. The die 2 has a cylindrical shape whose axial direction extends vertically, and upper and lower punches 3 and 4 are slidably inserted into the die.

In the primary compression, first, an appropriate amount of a lubricant-containing metal powder P for warm forming is filled into a cavity 2a formed by the die 2 and the lower punch 4. In the primary compression step, the primary mold 1 and the powder P are used at room temperature without performing heat treatment such as heating or cooling. Powder P
For example, it is said that compression molding can be performed while heating at a temperature of 370 ° C. or lower, and a high-density green compact can be obtained by high-temperature compression.

Next, as shown in FIG. 1 (a), the upper punch 3 is lowered and inserted into the cavity 2a, and the powder P is compressed in the vertical direction by the upper and lower punches 3 and 4 to form the primary compact P.
Mold 1. The pressure at that time is the primary molded body P after molding.
1 is controlled so that the density ratio is 60 to 75% and the density can be handled. The primary molded body P1 to be molded has a simple columnar shape corresponding to the inside of the die 2, the height is set higher than that of the green compact P2 to be molded, and the diameter is set smaller. Further, when the stand is set up in a mold of a secondary molding die to be described later, it is set to a state in which a gap is formed between the mold and the inner surface of the mold wall, that is, the dimension is set so as to be loosely fitted.
When the primary compact P1 has been formed, the upper punch 3 is raised, and the lower punch 4 is further raised, and the primary compact P1 is pulled out of the die 2.

B. Secondary Compression Step As shown in FIG. 1B, the primary compact P1 obtained in the primary compression step is heated by a heating means 5 such as an electric heater or electromagnetic induction heating. The heating temperature is selected within a range of the predetermined molding temperature of the powder P and lower than a temperature at which blue brittleness occurs in a material based on the powder P.
A temperature at or near the upper limit within such a range is preferable because significant densification is achieved. The temperature of the primary compact P1 obtained in the primary compression step is raised to about 50 to 90 ° C. due to frictional heat in continuous molding, although it varies depending on the size and the molding density of the primary compact P1. However, it is preferable to perform the heating shown in FIG.

As shown in FIGS. 1 (c) and 1 (d), a secondary molding die 11 used in the secondary compression step includes a die 12 and upper and lower dies slidably inserted into the die 12. Punch 13,
14 and a heating means 15 for heating the die 12 such as an electric heater or electromagnetic induction heating. On the mold wall of the die 12, there are formed internal teeth 12b corresponding to the teeth of the spur gear which is the green compact P2 to be formed.
14 has external teeth 1 fitted to the internal teeth 12b of the mold wall.
3b and 14b are formed respectively. The die 12 is heated by the heating means 15 to a temperature equivalent to the heating temperature of the primary compact P1, and the upper and lower punches 13, 14 are also heated from the die 12.

In the secondary compression molding, first, the secondary molding die 11 is formed by the die 12 and the lower punch 13 as shown in FIG. The heated primary compact P1 is set upright in the cavity 12a. Next, as shown in FIG. 1 (d), the upper punch 13 is lowered and inserted into the cavity 12a, and the upper and lower punches 13 and 14 compress the primary compact P1 in the vertical direction at a predetermined molding pressure. Primary molded body P1
Is collapsed and molded according to the shape of the cavity 12a to form a green compact P2. After this, the upper punch 13
And the lower punch 14 is further raised to make the green compact P
2 is extracted from the die 12 to obtain a green compact P2 shown in FIG.

(2) Second Embodiment FIGS. 2A to 2D sequentially show steps of a method for molding a green compact according to a second embodiment, and FIG. 3 shows a green compact P2 of a gear obtained by such a method. This gear P2 has a shaft hole 51 with a single boss 50. Hereinafter, the molding process will be described together with the molding die used.

A. Primary Compression Step As shown in FIG. 2A, a primary molding die 21 used in the primary compression step includes a die 22 and a die 2 which is a cylindrical void.
Upper and lower punches 23, 2 slidably inserted into the mold of No. 2
4 and a core rod 25. In this case, the lower punch is constituted by a combination of a cylindrical outer punch 24A slidably inserted into the die 22 and an inner punch 24B slidably inserted into the outer punch 24A. . The core rod 25 is for forming the shaft hole 51 of the green compact P2.
It is slidably inserted into the shaft core of 4B.

In the primary compression step, first, an appropriate amount of a lubricant-containing metal powder P for warm forming is filled into a cavity 22a formed by the die 22 and the lower punch 24. In this case, in the cavity 22a, a step for forming the boss 50 is defined downward by the outer punch 24A and the inner punch 24B of the lower punch 24. Next, as shown in FIG. 2 (a), the upper punch 23 is lowered and inserted into the cavity 22a, and the upper and lower punches 23 and 24 compress the powder P at room temperature at a pressure that allows handling. And
The primary compact P1 is formed. Next, the upper punch 23 is raised, and the lower punch 24 is further raised, so that the primary compact P1 is extracted from the die 22. Obtained primary molded body P
2 is a simple cylindrical shape having a single boss 50 and a shaft hole 51 as shown in FIG. 2 (b), the height of which is higher than that of the green compact P2 to be molded. The diameter of the shaft hole 51 is set so that the core rod of the secondary molding die can be loosely fitted therein, and the diameter of the shaft hole 51 is set so that the core rod of the secondary molding die can be loosely fitted therein.

B. Secondary compaction step The primary compact P1 obtained in the primary compaction step is heated by a heating means (not shown) to a temperature within the range of the molding temperature of the powder P and lower than the temperature at which blue brittleness occurs in the material based on the powder P. Heat with.

As shown in FIG. 2D, a secondary molding die 31 used in the secondary compression step includes a die 32, upper and lower punches 33 and 34, a core rod 35, and an electric heater for heating the die 32. And heating means 36 such as electromagnetic induction heating. On the mold wall of the die 32, there are formed internal teeth 32b corresponding to the teeth of the gear which is the green compact P2 to be molded, while on the outer peripheral surface of the lower punch 34, there are formed internal teeth 32b of the mold wall. External teeth 34b to be fitted are formed. The upper punch 33
An external punch 33A that can contact the upper surface of the die 32 to form the boss 50, and is slidably inserted into the external punch 33A, and the core rod 36 is slidably inserted to form the end surface of the boss 50. And an internal punch 33B. The inner punch 33B is directly operated by the upper ram 37, and the outer punch 33A is operated by a pusher 38 attached to the upper ram 37 so as to be vertically movable relative to the inner punch 33B. The die 32 is heated by the heating means 36 to a temperature equivalent to the heating temperature of the primary compact P1, and the upper and lower punches 33 and 34 and the core rod 35 are heated.
Is also heated from the die 32.

In the secondary compression molding, from the state where the secondary molding die 31 is heated to the above-mentioned temperature by the heating means 36, first, as shown in FIG. The heated primary compact P1 is passed through the core rod 35 with the boss 50 facing upward and set in the cavity 32a. Before setting the primary compact P1, a lubricant may be applied to at least one of the mold wall of the die 32 or the outer surface of the primary compact P1. Then, FIG.
As shown in (d), the upper punch 33 is lowered, and the upper and lower punches 33 and 34 are used to form the primary compact P at a predetermined molding pressure.
1 is compressed vertically. The primary compact P1 is molded following the shape of the cavity 32a after being once collapsed, and becomes a green compact P2. Thereafter, the upper punch 33 is raised, and the lower punch 34 is further raised to extract the green compact P2 from the inside of the die 32, thereby obtaining the green compact P2 shown in FIG.

According to each of the embodiments of the present invention, although the lubricant-containing powder for warm compaction is used, instead of heating the powder from the beginning to fill the cavity, the powder is first used. Primary compression is performed at room temperature, and the resulting primary compact is secondarily compressed at a warm temperature to obtain a green compact. According to such a molding method, since the primary molded body can be handled, it can be easily and quickly set in the secondary molding die. In addition, in order to avoid a decrease in the fluidity of the powder in the past, the temperature at the time of compression, which was difficult to set to 150 ° C. or more, is increased to a predetermined upper limit of the molding temperature of the lubricant-containing lubricant powder, or a temperature close to the upper limit. The temperature control or the properties of the lubricant do not require strictness. That is, the powder (in this case, the primary compact) can be compressed at a higher temperature than in the past, so that the density of the green compact is greatly improved, and the quality is stabilized.

Further, since the compression ratio is divided into primary compression and secondary compression, the degree of wear of the primary and secondary molds is reduced to enable long-term use, and the mold depth is short. As a result, the manufacturing cost of the mold is reduced. Furthermore, if a large amount of the primary compact is prepared and stocked in advance, and the secondary compact is obtained as necessary to obtain a compact, the powder is adjusted and filled every time the compact is molded. This saves time and improves productivity.

When a green compact having a boss (step) on one side in the compression direction is formed as in the second embodiment, the boss is formed by a lower punch at the time of primary compression, and is formed by secondary compression. In some cases, if the upper and lower molds are used for molding, the structure of the lower punch is simplified for both the primary and secondary molds, and the secondary mold only needs to have a boss molding punch on the upper side. The overall structure is simplified. In addition, it is possible to adopt a press machine having a simple structure.

The first and second embodiments are examples embodying the present invention, and the green compact formed by the present invention is not limited to these embodiments, but may be of any form. It is also applicable to green compacts. The present invention is not limited to the form of the green compact and includes the following molding method.

The primary molded body is not made into a single body, but is combined into a divided body that becomes a primary molded body having a desired shape.
That is, the primary compact is divided into a plurality of pieces and compression-molded, and in the secondary compression step, the plurality of primary compacts are set in a combined state in a secondary mold, and the secondary compression is performed by the secondary compression. The bodies are joined together to obtain the final green compact. In the above, the green compact to be molded has a plurality of portions having different required characteristics, and correspondingly, a plurality of primary compacts are formed for each of the portions, in accordance with the powder and shape corresponding to the portion. Alternatively, they are each subjected to primary compression with density and molded. If a plurality of primary compacts are formed in accordance with a part and then combined and subjected to secondary compression, a green compact having characteristics corresponding to each part can be obtained automatically.

[0034]

As described above, according to the present invention,
Conventionally, it is difficult to obtain a green compact by heating the lubricating powder for warm compaction at room temperature to obtain a green compact by primary compression at room temperature and heating to the molding temperature of the lubricating powder. Thus, the compression molding of the lubricant-containing powder at a high temperature is made possible, and as a result, an effect is obtained in that the density of the green compact can be significantly increased.

[Brief description of the drawings]

FIGS. 1A to 1D are cross-sectional views sequentially showing steps of a method for molding a green compact according to a first embodiment of the present invention, and FIG.
FIG. 3 is a perspective view of a green compact obtained by the same method.

2 (a), 2 (c) and 2 (d) are cross-sectional views sequentially showing steps of a method for molding a green compact according to a second embodiment of the present invention, and FIG. 2 (b) is a perspective view of a primary compact. (E) is a perspective view of the green compact obtained by the same method.

[Explanation of symbols]

1,21 ... primary molding die, 11, 31 ... secondary molding die, 50
... Boss (step), P ... Powder, P1 ... Primary molded body, P2 ...
Green compact.

Claims (5)

[Claims] 1. A method of compacting a powder to form a green compact having a predetermined density, comprising: forming a lubricant-containing powder for warm compacting at a room temperature at a temperature lower than the predetermined density by a primary molding die. And, a primary compression step of compressing to a density that can be handled, and the primary compact obtained in the primary compression step is heated to the molding temperature of the lubricant-containing powder, by a secondary molding die, A secondary compression step of obtaining a green compact by compressing the green compact to a predetermined density. 2. The method of molding a green compact according to claim 1, wherein, in the primary compression step, the primary compact is molded to a size that can be loosely fitted in the secondary molding die. 3. In the primary compression step, the primary molded body is divided into a plurality of parts and each is compressed, and in the secondary compression step, the plurality of primary molded bodies are combined in the secondary molding die. 3. The method of molding a green compact according to claim 1, wherein the green compact is set and joined to each other by secondary compression. 4. The green compact to be molded has a plurality of parts having different required properties, and the plurality of primary compacts are each provided with a powder, shape or density corresponding to the part. The method of molding a green compact according to claim 3, wherein the green compact is subjected to primary compression. 5. The green compact has a step on one end side in a compression direction, and the step is formed in a downward state in the primary compression step and in an upward state in the secondary compression step. The method of molding a green compact according to claim 1, wherein the green compact is molded.