JP3685442B2 - Molding method of green compact - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the field of powder metallurgy, the present invention relates to a method of forming a green compact that becomes a material of a sintered product by compressing metal powder.
[0002]
[Prior art]
When compacting metal powder to obtain a green compact, a lubricant is usually added to the raw material powder to suppress mold wall friction during compression, mold wear during die cutting, or friction between powders during compression. Or a lubricant is applied to the mold wall. As the lubricant, stearic acid powder based on Al, Zn, Li, Mg, or Ca is generally used, but in addition, wax, cellulose, or the like may be used. By the way, the technique of giving the characteristic based on the usage method of the powder containing a lubricant and the lubricant itself, and obtaining the effect based on it has been proposed.
[0003]
For example, in Japanese Patent Laid-Open No. 61-19702 (1), a powder containing a lubricant is thinly arranged on a mold wall, and the remaining cavity portion is filled with a powder not containing a lubricant. By compressing, the amount of lubricant used can be reduced and adverse effects of the lubricant in the sintering process can be suppressed. In JP-A-9-272901 (2), a mold coated with a lubricant is heated to 150 to 400 ° C., and a powder containing no lubricant heated to the same temperature is contained in the mold. A method is disclosed in which the density can be increased by filling and compressing. Furthermore, Japanese Patent No. 2593632 (3) is a powder to which a high temperature (warm) molding lubricant comprising the specified components is added. In this case, the powder is compressed at 370 ° C. or lower. We are trying to increase the density.
[0004]
[Problems to be solved by the invention]
In the method of the above publication (1), in order to fill the mold wall with the powder containing the lubricant and the powder without the lubricant inside the mold, a partition is provided between them. Although there is a statement to that effect, it is actually assumed that the work is complicated. In addition, when this green compact was sintered, the porosity of the surface layer portion containing the lubricant was lower than that of the inner portion, which was not suitable as a method for producing a member that requires particularly high strength in the surface layer portion.
[0005]
In addition, it is well known that if the powder is compressed at a high temperature, the density of the green compact is increased. However, as described in the above publication (2), the powder is heated in advance before filling into the mold. This requires a technique that is more difficult than heating a solid, for example, because the equipment becomes complicated or large, or is not easily heated uniformly. In addition, it is complicated to apply a lubricant to the mold wall of the mold every time the powder is filled, which reduces the work efficiency. Although these problems can be avoided by using powder mixed with a lubricant, on the other hand, the amount of lubricant used increases and the energy required for combustion or dewaxing of the lubricant during sintering increases. In addition, the working environment is deteriorated. In addition, when the lubricant-containing powder is warm-formed, 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, making it difficult to obtain a high-density green compact. Temperature control is required.
[0006]
Therefore, as in the above patent (3), if the lubricant is used for warm forming that can be used at 370 ° C. or less, high temperature compression will be possible while ensuring the fluidity of the powder. Even at 150 ° C. or higher, it was confirmed that the fluidity of the powder was lowered, and strict temperature control was still required, and the practical advantage was low.
[0007]
Therefore, the present invention can achieve equipment cost reduction and energy saving by compression molding at room temperature, and also reduce wear of the mold wall while reducing the amount of lubricant used, thereby suppressing high-density green compact. It is an object of the present invention to provide a method for forming a green compact that can be obtained.
[0008]
[Means for Solving the Problems]
The present invention is obtained by a primary compression step of compressing a powder to a density lower than a predetermined density of a green compact to be molded by a primary molding die at room temperature and a density that can be handled. In the green compact forming method, the primary compact is compressed to a predetermined density by a secondary mold at room temperature to obtain a green compact, and the powder used is substantially a lubricant. In the primary compression step, the primary molded body has a dimension that can be loosely fitted in the secondary mold, and the cross-sectional shape orthogonal to the compression direction is a circular or polygonal simple shape. In the secondary compression step, the surface of the primary molded body is coated with a lubricant as a lubricating means during compression, and the primary molded body is once collapsed and molded into a gear-shaped green compact during secondary compression. It is characterized by. The term “normal temperature” as used in the present invention refers to a range from atmospheric temperature to about 90 ° C., which is a temperature at which the molded body and the mold are heated by frictional heat generated by continuous molding.
[0009]
According to this method, powder containing substantially no lubricant (including about 0.1% by weight or less) is compressed at room temperature in the first primary compression step. The pressure at this time is set to a pressure that is lower than a predetermined density of the finally obtained green compact and that allows the molded body (primary molded body) to be handled. The density that can be handled here refers to a density that can be handled by hand and that does not break down. In this primary compression step, the powder containing substantially no lubricant is compressed at room temperature without heating, so there is no decrease in the fluidity of the powder due to heating when filling the powder into the primary mold or during compression. A primary molded body having the above desired density can be obtained.
[0010]
In addition, the primary molded body has a dimension that can be loosely fitted in the secondary mold, that is, a dimension in which an appropriate gap is left between the primary mold and the mold wall of the secondary mold, and the cross-sectional shape orthogonal to the compression direction is circular. Or it shape | molds so that it may become a polygonal simple shape. For this reason, coupled with the fact that handling is possible, the setting to the secondary mold can be performed easily and quickly, and the speed of the primary molding can be increased. For example, when the green compact to be finally obtained is a spur gear and the compression direction is the axial direction, the primary compact is made into a simple disk shape or polygonal shape, and teeth of equal pitch around it in the secondary compression process To be shaped.
[0011]
In the next secondary compression step, first, the surface of the primary molded body is coated with a lubricant as a lubricating means on the surface of the primary molded body. As means for coating with a lubricant, means such as applying a liquid lubricant such as wax or attaching a powdery lubricant by an electrostatic coating method is used. By adopting such a lubricating means, the working efficiency of introducing the lubricant is improved as compared with the case of applying to the mold wall surface. In addition, since the lubricant is attached only to the surface of the primary molded body, the amount of lubricant used is reduced, the energy required to remove the lubricant during sintering and the working environment are improved. Is planned. Furthermore, compared with the case where the lubricant is mixed into the powder, the porosity is reduced and the density is increased when the sintered product is obtained.
[0012]
In this way, the primary molded body whose surface is coated with the lubricant is compressed with a secondary mold at room temperature to obtain a green compact having a predetermined density and a desired shape. At the time of the secondary compression, the primary molded body is once collapsed, and then finally molded into a green compact.
[0013]
According to the present invention, in addition to the various functions and effects described above, both primary compression and secondary compression are performed at room temperature, so that facility cost reduction and energy saving can be achieved. In addition, since the compression ratio is divided into primary compression and secondary compression, the degree of wear of each mold is reduced, enabling long-term use, and the mold depth of each primary and secondary mold is short. This reduces the manufacturing cost of the mold. In particular, the strength of the primary molded body is higher than when a powder containing a lubricant is used, and the pressure during secondary compression for compressing the primary molded body may be relatively low. Therefore, it is easy to increase the density of the green compact, the density is greatly improved, and the quality is stabilized. In addition, if a large amount of primary compacts are made in advance and stocked, and compacted by secondary compression as necessary, the powder is adjusted and filled each time the compact is molded. This saves time and improves productivity.
[0014]
Moreover, in this invention, it does not make a primary molded object single-piece | unit, but makes it the division body which becomes a primary molded object of desired shape by combining. That is, the primary molded body is divided into a plurality of parts and compression molded, and in the secondary compression step, the plurality of primary molded bodies are set in a combined state in the secondary mold, and the adjacent compression is performed by secondary compression. The bodies are joined together to obtain the final green compact.
[0015]
Here, the density of each divided body which is a primary molded body is premised on handling as described above, but in addition to this, there is a density at which adjacent divided bodies can be joined together during compression. Desired. The lower the density, the better the joining between the divided bodies is. However, if the density is too low, handling becomes impossible this time. It is generally known that the density ratio (ratio of the density obtained by the molded body to the true density of the metal having the same composition) is less than 76% as a condition for joining. The probability of cracks occurring at the bonding interface increases, which is not preferable. Therefore, the density of the divided body is selected within a range in which the density ratio is less than 76% and can be handled, and a density at which a density ratio of 60 to 75% is realized is preferable. For example, if the powder is 3, Cu-based 1.6~2g / ^cm in the case when the Fe-based 4.7~5.9g / ^cm 3, Al preferably 5.3~6.6g / cm ³ It is said.
[0016]
Further, in the present invention, the green compact to be molded has a plurality of parts having different required characteristics, and the plurality of primary molded bodies are respectively primary with a powder, shape or density corresponding to the part. It is characterized by being compressed. For example, when the green compact is the above-described spur gear, the primary molded body has an outer peripheral portion that requires high wear resistance and an inner portion that does not require so much wear resistance and requires the function of a damping material. Two meat parts. And the primary molded object of an outer peripheral part is made into a high density, On the other hand, the density of the primary molded object of an inner side meat part is made comparatively low. In this way, if a plurality of primary molded bodies are molded according to a part, combined and subjected to secondary compression, the characteristics of each part can be automatically obtained.
[0017]
In the present invention, the green compact has a stepped portion on one end side in the compression direction, and the stepped portion is formed in a downward state in the primary compression step, and is in an upward state in the secondary compression step. It is characterized by being molded with. Specifically, the step portion is formed with the lower punch at the time of the primary compression, and is formed with the upper punch at the time of 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 the boss molding punch on the upper side, so the overall structure of each mold is simplified. .
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(1) First embodiment Figs. 1 (a) to 1 (d) sequentially show the steps of the green compact forming method according to the first embodiment, and Fig. 1 (e) shows the steps. The green compact P2 of the spur gear which has the shaft hole 41 obtained by such a method is shown. Hereinafter, the molding process will be described together with the mold used.
[0019]
A. Primary compression process As shown in FIG. 1A, a primary mold 1 used in the primary compression process includes a die 2, upper and lower punches 3 and 4 inserted into the die 2, and a core rod 5. Composed. The die 2 has a cylindrical shape whose axial direction extends in the vertical direction, and the upper and lower punches 3 and 4 are slidably inserted into the die. The core rod 5 is for forming the shaft hole 41 of the green compact P2, and is slidably inserted into the shaft cores of the upper and lower punches 3 and 4.
[0020]
In the primary compression, first, metal powder P containing substantially no lubricant (including about 0.1% by weight or less) is contained in the cavity 2a formed by the die 2, the lower punch 4 and the core rod 5 at room temperature. Fill the appropriate amount.
[0021]
Next, as shown in FIG. 1 (a), the upper punch 3 is inserted into the cavity 2a, and the powder P is compressed in the vertical direction by the upper and lower punches 3 and 4, thereby forming a primary compact P1. The pressure at that time is controlled so that the density ratio of the primary molded body P1 after molding is 60 to 75% and the density can be handled. The primary molded body P1 to be molded has a simple cylindrical shape having a shaft hole 41 as shown in FIG. The diameter of the shaft hole 41 is such that the height of the primary molded body P is higher than that of the green compact P2 to be molded, and the outer diameter can be loosely fitted in a die of a secondary mold described later. Each is set so that the core rod of the secondary mold can be loosely fitted. When the primary molded body P1 is formed, the upper punch 3 is raised, and the lower punch 4 is further raised to extract the primary molded body P1 from the die 2.
[0022]
B. Secondary compression step First, as shown in FIG. 1 (b), a liquid lubricant L such as wax is sprayed on the surface of the primary molded body P1 obtained in the primary compression step, or a powder is applied. A body-like lubricant is adhered by an electrostatic coating method.
[0023]
As shown in FIGS. 1C and 1D, the secondary forming die 11 used in the secondary compression process includes a die 12 and upper and lower punches 13 slidably inserted into the die 12 die. 14 and a core rod 15. On the mold wall of the die 12, internal teeth 12b corresponding to the teeth of the spur gear which is the green compact P2 to be molded are formed. On the other hand, on the outer peripheral surfaces of the upper and lower punches 13 and 14, External teeth 13b and 14b that are fitted to the internal teeth 12b are formed.
[0024]
In the secondary compression, first, the primary molded body P1 is set up in a cavity 12a formed by the die 12, the lower punch 13 and the core rod 5, as shown in FIG. Next, as shown in FIG. 1D, the upper punch 13 is inserted into the cavity 12a, and the upper and lower punches 13 and 14 compress the primary molded body P1 in the vertical direction with a predetermined molding pressure. The primary molded body P1 is once collapsed and then molded according to the shape of the cavity 12a to become a green compact P2. Thereafter, the upper punch 13 is raised, the lower punch 14 is further raised, and the green compact P2 is extracted from the die 12 to obtain the green compact P2 shown in FIG.
[0025]
(2) Second embodiment Figs. 2 (a) to 2 (d) sequentially show the steps of the green compact forming method according to the second embodiment, and Fig. 2 (e) shows the steps. The green compact P2 of the gear obtained by such a method is shown. This gear P2 has a shaft hole 51 with a single boss 50. Hereinafter, the molding process will be described together with the mold used.
[0026]
A. Primary compression process As shown in FIG. 2 (a), a primary mold 21 used in the primary compression process is a slidably inserted into a die 22 and a die 22 which is a cylindrical space. Punches 23 and 24 and a core rod 25. The lower punch in this case is configured by a combination of a cylindrical external punch 24A slidably inserted into the die 22 and an internal punch 24B slidably inserted into the external punch 24A. . The core rod 25 is for forming the shaft hole 51 of the green compact P2, and is slidably inserted into the shaft cores of the upper punch 23 and the inner punch 24B.
[0027]
In the primary compression, first, an appropriate amount of metal powder P substantially not containing a lubricant as in the first embodiment is filled in the cavity 22a formed by the die 22 and the lower punch 24 at room temperature. In this case, the cavity 22a has a stepped portion for forming the boss 50 downwardly defined by the outer punch 24A and the inner punch 24B of the lower punch 24. Next, as shown in FIG. 2A, 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 a pressure that allows handling, and perform primary molding. The body P1 is molded. Next, the upper punch 23 is raised, and the lower punch 24 is further raised, and the primary compact P1 is extracted from the die 22. As shown in FIG. 2B, the obtained primary molded body P1 has a simple cylindrical shape with a single boss 50 and a shaft hole 51, and the height thereof 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 mold can be loosely fitted, so that the outer diameter can be loosely fitted in a die of a secondary mold described later.
[0028]
B. Secondary compression process First, as shown in FIG. 2 (b), a liquid lubricant L such as wax is sprayed and applied to the surface of the primary molded body P1 obtained in the primary compression process, or a powder A body-like lubricant is adhered by an electrostatic coating method.
[0029]
As shown in FIG. 2 (d), the secondary forming die 31 used in the secondary compression step is composed of a die 32, upper and lower punches 33 and 34, and a core rod 35. On the mold wall of the die 32, internal teeth 32b corresponding to the teeth of the gear that is the green compact P2 to be molded are formed. On the other hand, the inner teeth 32b of the mold wall are formed on the outer peripheral surface of the lower punch 34. The external teeth 34b to be fitted are formed. The upper punch 33 can be brought into contact with the upper surface of the die 32, and an external punch 33A for forming the boss 50 is slidably inserted into the external punch 33A, and the core rod 36 is slidably inserted into the boss. It is comprised from the internal punch 33B which shape | molds 50 end surfaces. 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 movable up and down relative to the inner punch 33B.
[0030]
In the secondary compression, first, at a normal temperature, as shown in FIG. 2C, the primary molded body P1 is placed in the cavity 32a formed by the die 32, the lower punch 34, and the core rod 35 with the boss 50 side facing up. And set it through the core rod 35. Next, as shown in FIG. 2D, the upper punch 33 is lowered, and the upper and lower punches 33 and 34 compress the primary molded body P1 in the vertical direction with a predetermined molding pressure. The primary molded body P1 is once collapsed and then molded according to the shape of the cavity 32a to become a green compact P2. Thereafter, the upper punch 33 is raised, the lower punch 34 is further raised, and the green compact P2 is extracted from the die 32 to obtain the green compact P2 shown in FIG.
[0031]
According to each embodiment of the present invention, first, in the primary compression step, the powder containing substantially no lubricant is compressed at room temperature without being heated. The flowability of the powder does not decrease due to the above, and the primary molded body can be molded to a desired density that can be handled. In addition, the primary molded body is dimensioned to be loosely fitted in the secondary mold, and the cross-sectional shape orthogonal to the compression direction is molded into a simple circular shape, coupled with the fact that handling is possible. The secondary mold can be easily and quickly set, and the primary molding speed can be increased.
[0032]
In the next secondary compression step, since the surface of the primary molded body is coated with a lubricant, the working efficiency of introducing the lubricant is improved as compared with the case where the surface is applied to the mold wall surface. In addition to reducing the amount of lubricant used, the energy required for dewaxing the lubricant during sintering can be reduced, and the working environment can be improved. Furthermore, compared with the case where the lubricant is mixed into the powder, the porosity is reduced and the density is increased when the sintered product is obtained.
[0033]
Overall, since primary compression and secondary compression are both performed at room temperature, facility cost reduction and energy saving can be achieved. In addition, since the compression ratio is divided into primary compression and secondary compression, the degree of wear of the primary and secondary molds is reduced, enabling long-term use, and the mold depth of these molds is short. The manufacturing cost of the mold is reduced. In particular, the strength of the primary molded body is higher than when a powder containing a lubricant is used, and the pressure during secondary compression for compressing the primary molded body may be relatively low. Therefore, it is easy to increase the density of the green compact, the density is greatly improved, and the quality is stabilized. In addition, if a large amount of primary compacts are made and stocked in advance and then compressed as necessary to obtain a compact, the powder is adjusted and filled each time the compact is molded. This saves time and improves productivity.
[0034]
Further, as in the second embodiment, when forming a green compact having a boss (step part) on one side in the compression direction, the boss is formed with a lower punch during primary compression and an upper punch during secondary compression. In this case, the structure of the lower punch becomes simple in 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.
[0035]
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. It can also be applied to. Further, the present invention includes the following forming method without being limited to the form of the green compact.
[0036]
{Circle around (1)} The primary molded body is not a single body, but is combined to form a divided body that becomes a primary molded body of a desired shape. That is, the primary molded body is divided into a plurality of parts and compression molded, and in the secondary compression step, the plurality of primary molded bodies are set in a combined state in the secondary mold, and the adjacent compression is performed by secondary compression. The bodies are joined together to obtain the final green compact.
(2) In the above (1), the green compact to be molded has a plurality of parts having different required characteristics. Correspondingly, a plurality of primary molded bodies are provided for each part. Are first compressed and molded with powder, shape or density according to the above. Thus, if a some primary molded object is shape | molded according to a site | part and it combines and carries out secondary compression, the compact which has the characteristic according to each site | part automatically can be obtained.
[0037]
【The invention's effect】
As described above, in the present invention, when a green compact is obtained by subjecting powder substantially free of lubricant to primary compression and secondary compression at room temperature, the primary molded body is placed in the secondary molding die. Because the cross-sectional shape perpendicular to the compression direction is formed into a circular or polygonal simple shape that can be loosely fitted, and the surface of the primary molded body is covered with a lubricant during secondary compression. In addition to reducing the cost of equipment and saving energy, it is possible to obtain a high-density green compact by reducing wear of the mold wall while reducing the amount of lubricant used.
[Brief description of the drawings]
FIGS. 1A to 1D are cross-sectional views sequentially showing steps of a green compact forming method according to a first embodiment of the present invention, and FIG. 1E is a view of a green compact obtained by the same method. It is a perspective view.
FIGS. 2A to 2D are cross-sectional views sequentially showing steps of a green compact forming method according to a second embodiment of the present invention, and FIG. 2E is a view of a green compact obtained by the same method. It is a perspective view.
[Explanation of symbols]
1, 21 ... Primary mold, 11, 31 ... Secondary mold, 50 ... Boss (step part),
L: Lubricant, P: Powder, P1: Primary molded body, P2: Green compact.

Claims (4)

A primary compression step in which the powder is compressed to a density that is lower than a predetermined density of the green compact to be molded by a primary mold at room temperature and can be handled, and a primary molded body obtained in this primary compression step In a green compact molding method comprising a secondary compression step of obtaining a green compact by compressing to a predetermined density by a secondary molding die at room temperature,
The powder is substantially free of lubricant, and in the primary compression step, the primary molded body has a size that can be loosely fitted in the secondary mold and is orthogonal to the compression direction. In the secondary compression step, the surface of the primary molded body is coated with a lubricant as a lubricating means, and the primary molded body is temporarily collapsed during secondary compression. And forming into a gear-shaped green compact. In the primary compression step, the primary molded body is divided into a plurality of pieces and compressed, and in the secondary compression step, the plurality of primary molded bodies are set in a combined state in the secondary mold, The method for forming a green compact according to claim 1, wherein the green compact is bonded to each other by compression.   The green compact to be molded has a plurality of parts having different required characteristics, and the plurality of primary compacts are primarily compressed with powder, shape, or density corresponding to each part. A method for forming a green compact according to claim 1 or 2.   The green compact has a step portion on one end side in the compression direction, and the step portion is formed in a downward state in the primary compression step, and is formed in an upward state in the secondary compression step. The method for forming a green compact according to any one of claims 1 to 3.

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