Aluminum alloy sintering apparatus and aluminum alloy sintering method

Abstract

To provide a method and apparatus for electric-current sintering that allow for reducing the cost of production.SOLUTION: A method for electric-current sintering according to one embodiment comprises: a pressure molding step of forming a compact 15 by pressurizing a powder 10 filled in a metal mold 11; a de-molding step of de-molding the compact 15 from the metal mold 11; and an electric-current sintering step of forming a sintered body 17 by supplying an electric current to the compact 15 de-molded from the metal mold 11. In the pressure molding step, a cylindrical metal mold 11 consisting of a material containing metal and opened at one and the other ends may be used to pressurize the powder 10 with a first punch inserted in one opening and a second punch inserted in the other opening.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method and apparatus for electric sintering.

Background Art

[0002] Patent Document 1 describes an electric sintering method in which a sintered body is formed by applying pressure to powder filled in a cylindrical mold with an upper punch and a lower punch while applying an electric current. The electric sintering method is also called a spark plasma sintering method (hereinafter referred to as the SPS method) or a pulse electric current sintering method. In the electric sintering method of Patent Document 1, a sintered body is formed through a powder filling step and a pressure-applied electric sintering step.

[0003] Non-Patent Document 1 describes a powder metallurgy method in which a compact is formed by applying pressure to powder filled in a mold with an upper punch and a lower punch, and the formed compact is heated at a high temperature to form a sintered body. In the powder metallurgy method of Non-Patent Document 1, a sintered body is formed through a powder filling step, a pressure molding step, and a heat sintering step.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the electric current sintering method of Patent Document 1, the punch displacement amount in the pressure electric current sintering step is large, and problems such as the powder that has bitten into the gap between the mold and the punch being sintered easily occur. Further, since the mold and the punch rub against each other in a high-temperature environment, the life of the mold is short due to the mold and the punch sticking together. Furthermore, since the mold is used in a high-temperature and wear environment, it is necessary to select a heat-resistant alloy having wear resistance for the material of the mold and the punch, and the manufacturing cost of the mold is high. Therefore, the electric current sintering method of Patent Document 1 cannot reduce the production cost. In Non-Patent Document 1, since the heating sintering step takes time, the productivity cannot be improved.

[0007] Other problems and novel features will become apparent from the description of this specification and the accompanying drawings.

Means for Solving the Problems

[0008] An electric current sintering method according to an embodiment includes a pressure molding step of molding a compacted body by pressing the powder filled in a mold, a mold release step of releasing the compacted body from the mold, and an electric current sintering step of forming a sintered body by applying an electric current to the compacted body released from the mold.

[0009] An electric current sintering apparatus according to an embodiment includes pressure molding means for molding a compacted body by pressing the powder filled in a mold, mold release means for releasing the compacted body from the mold, and electric current sintering means for forming a sintered body by applying an electric current to the compacted body released from the mold.

[0010] The electric sintering apparatus according to one embodiment includes a pressure molding means for forming a green compact by pressing powder filled in a mold, a demolding means for demolding the green compact from the mold, an electric sintering means for forming a sintered body by applying an electric current to the green compact demolded from the mold, a pressure molding section including the pressure molding means and the demolding means, an electric sintering section arranged side by side with the pressure molding section and including the electric sintering means, and a conveying means for conveying the green compact from the pressure molding section to the electric sintering section.

Effect of the Invention

[0011] According to the above-described embodiment, it is possible to provide an electric sintering method and an electric sintering apparatus capable of reducing production costs.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 10

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Figure 14

Mode for Carrying Out the Invention

[0013] For the sake of clarity of explanation, the following description and drawings are appropriately omitted and simplified. Also, in each drawing, the same reference numerals are assigned to the same elements, and duplicate explanations are omitted as necessary.

[0014] (Embodiment 1) Before explaining the electric current sintering method and the electric current sintering apparatus according to Embodiment 1, first, the sintering methods according to Comparative Example 1 and Comparative Example 2 will be explained. Then, the electric current sintering method of the present embodiment will be explained in comparison with the sintering methods of Comparative Example 1 and Comparative Example 2. Thereby, the features of the electric current sintering method of the present embodiment will be made clearer. Thereafter, the electric current sintering apparatus of the present embodiment will be explained.

[0015] <Comparative Example 1: Powder Metallurgy Method> As a sintering method according to Comparative Example 1, the powder metallurgy method will be described. The powder metallurgy method is a method of manufacturing high-strength materials and components by sintering a green compact formed by pressing powder with a press machine by heating it at a high temperature. FIG. 1 is a process diagram illustrating the powder metallurgy method according to Comparative Example 1. As shown in FIG. 1, the powder metallurgy method includes a powder filling step, a pressure molding step, a mold release step, a heat sintering step, and a discharge step. When the powder 10 to be used contains a plurality of types, a powder mixing step may be provided before the powder filling step.

[0016] In the powder mixing step, the powder 10 is mixed. The powder 10 contains materials necessary for forming a desired sintered body. The powder 10 may contain a plurality of types of materials. The powder 10 may contain, for example, powders of metals such as iron, copper, aluminum, nickel, chromium, tungsten, and molybdenum, alloy steels in which iron such as stainless steel contains chromium and nickel, or powders in which aluminum such as aluminum alloy contains at least any one of copper, manganese, silicon, magnesium, zinc, and nickel. Further, the powder 10 is not limited to metals, and may contain oxides such as alumina and zirconia, nitrides such as silicon nitride, carbides such as silicon carbide, titanium carbide, and tungsten carbide, bioceramics such as hydroxyapatite, layered compounds such as mica, and ceramics having ion conductivity such as garnet.

[0017] Further, the formed sintered body may be used, for example, in nano materials, gradient functional materials, amorphous materials, porous materials, intermetallic compounds, metallic glasses, biomaterials, hard materials, thermoelectric conversion materials, superconducting materials, magnetic materials, fine ceramics, die tools, cemented carbides, titanium alloys, super heat dissipation materials, sputtering target materials, dielectric and electronic device materials, carbon nanotube (CNT) composites, carbon nanofiber (CNF) composites, fiber reinforced concrete (FRC), fiber reinforced metal (FRM), aerospace components, etc. The plurality of types of powder 10 are previously mixed by a mixer with a plurality of types of raw material materials.

[0018] As shown in Fig. 1, in the powder filling step, powder 10 is filled into mold 111. The mold 111 is, for example, cylindrical with openings at both the upper and lower ends. A lower punch 112 is inserted into the lower opening of the mold 111. Thereby, a cavity is formed on the lower punch 112 inside the mold 111. The lower punch 112 may include a plurality of punch members. For example, the lower punch 112 may be composed of two punch members. Then, the powder 10 is filled into the cavity surrounded by the mold 111. An upper punch 113 is inserted into the upper opening of the mold 111 filled with the powder 10. The upper punch 113 may include a plurality of punch members. For example, the upper punch 113 may be composed of three punch members. In the powder filling step, the filling density of the powder 10 filled in the mold 111 is, for example, about 50 [%].

[0019] In the pressure molding step, the compact 115 is formed by pressing the powder 10 filled in the mold 111. Specifically, the powder 10 filled in the mold 111 is pressed by the upper punch 113 and the lower punch 112. The pressure is, for example, 100 - 700 [MPa] or 700 [MPa] or more. In the pressure molding step, it is not necessary to intentionally apply heat. The temperature is, for example, 300 [°C], specifically, room temperature to 400 [°C]. Thereby, a compact 115 in which the powder 10 is compressed is formed. In the pressure molding step, the powder filling density is changed, for example, from less than 60 [%] to 60 [%] or more. For example, the powder filling density is changed up to 80 [%]. Thereby, the particles of the powder 10 are compacted.

[0020] In powder metallurgy, a mold 111 made of a material containing metal is used. Therefore, a high pressure of 100 - 700 [MPa] or 700 [MPa] or more can be applied. Thus, using a mold 111 having a cavity surface with a complex shape, a complex-shaped compact 115 that accurately reflects the shape of the cavity surface of the mold 111 can be formed. Furthermore, with a single mold 111, compacts 115 of the same shape can be repeatedly produced. Thereby, a large number of compacts 115 of the same shape can be mass-produced.

[0021] The release step releases the compacted powder body 115 from the mold 111. For example, the compacted powder body 115 formed in the pressure molding step is pushed out of the mold 111 by the lower punch 112, thereby releasing the compacted powder body 115 from the mold 111.

[0022] The heat sintering step sinters the compacted powder body 115. In the heat sintering step, the compacted powder body 115 is heated at a high temperature inside the sintering furnace 116. The temperature is lower than the melting point of any component contained in the powder 10 in solid phase sintering, and in liquid phase sintering, a part of the components contained in the powder 10 is at a temperature higher than the melting point. The temperature is, for example, preferably 2 / 3 to 3 / 4 of the melting point or higher. For example, in the case of an iron material, the temperature is about 1000 [°C]. Thus, in the heat sintering step, the compacted powder body 115 is hardened over time at a temperature such that it does not melt and deform. Thereby, a sintered body 117 is formed. As a result, the particles of the powder 10 are sintered, for example.

[0023] In the heat sintering step, the powder filling density becomes slightly higher. The sintering furnace 116 continuously heats a large number of compacted powder bodies 115 by means of a moving means such as a belt conveyor.

[0024] The discharging step discharges the formed sintered body 117. In a general powder metallurgy method, a series of operations including pressure molding, release, conveyance of the compacted powder body 115 by the pressure molding step, and heat sintering by the continuous sintering furnace 116 are automated. Therefore, the powder metallurgy method can mass-produce parts of the sintered body 117 having a complex shape.

[0025] The following Table 1 is a table showing the advantages and disadvantages of the sintering methods of Comparative Example 1, Comparative Example 2, and Embodiment 1. As shown in Table 1, the powder metallurgy method of Comparative Example 1 can pressure mold a compacted powder body 115 having a complex shape, and thereby, a sintered body 117 having a complex shape can be formed. However, sintering in the sintering furnace 116 takes more time than pressure molding. For example, it takes several hours. Therefore, even if it is mass-produced by automation, the productivity remains at a certain level.

[0026]

Table 1

[0027] <Comparative Example 2: SPS method> As a sintering method according to Comparative Example 2, the SPS method will be described. In the SPS method, the powder 10 is filled into a carbon mold, and sintering is performed in a short time by applying an electric current while applying pressure. FIG. 2 is a process diagram illustrating the SPS method according to Comparative Example 2. As shown in FIG. 2, the SPS method includes a powder filling step, a pressure application and electric current sintering step, and a mold release and discharge step. Note that, similar to the powder metallurgy method of Comparative Example 1, when the powder 10 used includes a plurality of types of materials, a powder mixing step may be provided before the powder filling step.

[0028] In the powder filling step in the SPS method, the powder 10 is filled into the carbon mold 214. The powder 10 may be the same as that in Comparative Example 1. The carbon mold 214 may be, for example, a cylindrical shape with openings at the upper and lower sides. The lower punch 212 is inserted into the lower opening of the carbon mold 214. Thereby, a cavity is formed on the lower punch 212 inside the carbon mold 214. Then, the powder 10 is filled into the cavity surrounded by the carbon mold 214. The upper punch 213 is inserted into the upper opening of the carbon mold 214 filled with the powder 10. In the powder filling step, the filling density of the powder 10 filled into the carbon mold 214 is, for example, about 50 [%].

[0029] In the pressure-assisted electric sintering step, while applying pressure with the upper punch 213 and the lower punch 212, electric current is passed through the powder 10 filled in the carbon mold 214. Thereby, the sintered body 217 can be formed in a short time. In the SPS method, in order to pass an electric current through the powder 10, a carbon mold 214 containing carbon is used. Since a mold 111 with high strength such as in the powder metallurgy method cannot be used, it is difficult to apply a high pressure to the powder 10. The pressure is, for example, about 20 [MPa]. In the pressure-assisted electric sintering step, the powder filling density is changed, for example, from 50 [%] or less to 90 [%] or more. For example, the powder filling density is changed to 97 [%].

[0030] Also, electric current is passed through the powder 10 via the upper punch 213 and the lower punch 212. Due to the electric current, sintering or diffusion bonding occurs due to the heat generated between the particles of the powder 10, the heat generated inside each particle, and the heat transmitted by heat transfer from the outside of the particles. Since the gaps between the particles of the powder 10 have a large electrical resistance, Joule heat is generated due to the passage of electric current. Thereby, compared with the powder metallurgy method, the sintered body 217 can be formed in a short time. In the SPS method, since the sintering temperature can be made lower than that of general powder metallurgy as shown in FIG. 1, for iron materials, the temperature is, for example, 800 [°C] or higher.

[0031] Thus, in the pressure-assisted electric sintering step, by passing an electric current while applying pressure, the sintered body 217 can be formed from the powder 10 in the carbon mold 214. At this time, the powder 10 in the carbon mold 214 rapidly changes in volume while accompanying shrinkage.

[0032] The mold release and ejection step releases the sintered body 217 from the carbon mold 214. Specifically, for example, the sintered body 217 formed by the pressure-assisted electric sintering step is pushed out of the carbon mold 214 with the lower punch 212 to release the sintered body 217 from the carbon mold 214. Then, the released sintered body 217 is ejected.

[0033] As shown in Table 1, the SPS method of Comparative Example 2 can shorten the sintering time. For example, in the pressure-assisted electric sintering step, the time at the sintering temperature is several seconds to several minutes, for example, 1 [min]. However, in the SPS method, since high pressure cannot be applied to the carbon mold 214, a sintered body 217 with a complex shape cannot be formed.

[0034] In addition, the powder 10 in the carbon mold 214 shrinks rapidly during sintering. Therefore, the punch displacement amount in the pressure-assisted electric sintering step becomes large, and problems such as the powder that has bitten into the gap between the carbon mold and the punch being sintered easily occur.

[0035] Also, since the mold and the punch rub against each other in a high-temperature environment, the mold and the punch may stick together, etc., so the life of the mold is short. Furthermore, since the mold is used in a high-temperature and wear environment, it is necessary to select a heat-resistant alloy having wear resistance for the material of the mold and the punch, and the manufacturing cost of the mold is high. For these reasons, it is difficult to reduce the production cost.

[0036] <Embodiment: Electric Sintering Method> Next, the electric sintering method according to this embodiment will be described. The electric sintering method of this embodiment forms a high-density green compact by applying pressure at a low temperature and high pressure after filling the powder into the mold. Then, the formed green compact is demolded and energized to form a sintered body. FIG. 3 is a process diagram illustrating the electric sintering method according to Embodiment 1. FIG. 4 is a flowchart diagram illustrating the electric sintering method according to Embodiment 1. As shown in steps S11 of FIGS. 3 and 4, the powder filling step in this embodiment fills the powder 10 into the mold 11. The powder 10 may be the same as that in Comparative Example 1, but conductive powder 10 is preferred.

[0037] As shown in step S11 of FIGS. 3 and 4, the powder filling step in this embodiment fills the powder 10 into the mold 11. The powder 10 may be the same as that in Comparative Example 1, but conductive powder 10 is preferred.

[0038] The mold 11 is, for example, cylindrical with openings at the upper and lower ends. When pressurizing the powder 10 filled in the mold 11 from the vertical direction, the mold 11 is preferably cylindrical with openings at the upper and lower ends. When pressurizing the powder 10 filled in the mold 11 from a direction other than the vertical direction, it may be cylindrical with openings on one side and the other side in the pressurizing direction. For example, when pressurizing the powder 10 from the horizontal direction, the mold 11 may be, for example, cylindrical with openings in the left and right directions.

[0039] The lower punch 12 is inserted into the lower opening of the mold 11. Thereby, a cavity is formed on the lower punch 12 inside the mold 11. Then, the powder 10 is filled into the cavity surrounded by the mold 11. The upper punch 13 is inserted into the upper opening of the mold 11 filled with the powder 10. In the powder filling step, the filling density of the powder 10 filled in the mold 11 is, for example, about 50 [%], similar to Comparative Example 1 and Comparative Example 2. It should be noted that, similar to Comparative Example 1, the lower punch 12 and the upper punch 13 may be composed of a plurality of punch members.

[0040] Next, as shown in step S12 of FIGS. 3 and 4, in the pressure molding step, the compact 15 is formed by pressurizing the powder 10. Specifically, the powder 10 filled in the mold 11 is pressurized by the lower punch 12 inserted into one opening of the mold 11 and the upper punch 13 inserted into the other opening. Thereby, the compact 15 is formed. The pressure by the gauge pressure for pressurizing the powder 10 is, for example, 100 to 700 [MPa] or 700 [MPa] or more.

[0041] In the pressure forming step, the temperature of the powder is less than 500 [°C]. Preferably, it is not necessary to intentionally apply heat, for example, it is 300 [°C], specifically, room temperature to 400 [°C]. In this way, the compacted powder body 15 obtained by compressing the powder 10 is formed. In the pressure forming step, the packing density of the powder 10 is changed, for example, from less than 60 [%] to 60 [%] or more. In the case of a porous body used for an oil bearing or the like, it is changed, for example, up to 75 [%]. When forming a dense sintered body, it is changed, for example, from less than 90 [%] to 90 [%] or more. Specifically, when forming a dense sintered body, the packing density of the powder 10 is improved from about 50 [%] to, for example, 95 [%]. As a result, the particles of the powder 10 are compacted. In the pressure forming step, the powder 10 filled in the mold 11 may be processed in an air atmosphere, but processing in a reduced pressure atmosphere such as a vacuum or an inert gas atmosphere is preferred. The pressure applied to the powder 10 by the vertical movement of the upper punch 13 and the lower punch 12 is indicated by the gauge pressure.

[0042] In the electric sintering method of the present embodiment, a mold 11 other than a carbon mold may be used. For example, a mold 11 made of a material containing a metal may be used. Therefore, a high pressure of about 700 [MPa] can be applied. Thus, using a mold 11 having a cavity surface with a complex shape, a complex-shaped compacted powder body 15 that accurately reflects the shape of the cavity surface of the mold 11 can be formed. Further, with one mold 11, the same-shaped compacted powder bodies 15 can be repeatedly produced. As a result, a large number of the same-shaped compacted powder bodies 15 can be mass-produced.

[0043] Next, as shown in step S13 of FIGS. 3 and 4, in the mold release step, the compacted powder body 15 is released from the mold 11. For example, the compacted powder body 15 is released from the mold 11 by pushing out the compacted powder body 15 from the mold 11 with the lower punch 12.

[0044] Next, as shown in steps S14 of FIGS. 3 and 4, the electric current sintering step forms the sintered body 17 by applying an electric current to the green compact 15 released from the mold 11. For example, an electric current is applied to the green compact 15 via the upper punch 13 and the lower punch 12. In the electric current sintering step, due to the application of an electric current to the green compact 15, each particle of the powder 10 in the green compact 15 is sintered or diffusion-bonded by heat generated between the particles, heat generated inside each particle (the particle itself), heat transmitted by heat conduction from outside the particle, etc. For example, a dense body is formed by sintering, and a porous body is formed by diffusion bonding.

[0045] In the electric current sintering step, an electric current is applied to the green compact 15 without applying pressure by the upper punch 13 and the lower punch 12. That is, in the electric current sintering step, the green compact 15 is not subjected to pressure other than the inevitable pressure due to the contact of the upper punch 13 and the lower punch 12 for applying an electric current or the contact of an electrode or the like. That is, the minimum pressure (lower limit of the load limiter) necessary for the operation of the apparatus and inevitable pressure act, but no pressure other than the inevitable pressure is applied. In the electric current sintering step, the pressure for pressing the green compact 15 is 0 [MPa] except for such inevitable pressure, and the green compact 15 is not intentionally pressed. Note that the minimum pressure (lower limit of the load limiter) necessary for the operation of the apparatus may not substantially exist, but for example, the lower limit of the load limiter may be set to act with 100 [kgf]. The temperature of the green compact 15 due to the application of an electric current is set to a temperature lower than the melting point of the material of the powder 10. For example, in the electric current sintering step, the temperature of the green compact 15 is 500 [° C] or higher. In the case of sintering an aluminum alloy, for example, it is 600 [° C] or higher. In the case of an alloy mainly composed of iron, the temperature of the green compact 15 is preferably 800 [° C] or higher. It is extremely difficult to form a sintered body of an aluminum alloy by the powder metallurgy method of Comparative Example 1, and it can be formed by the SPS method of Comparative Example 2 or the present embodiment. Further, the electric current sintering method of the present embodiment is different from the SPS method of Comparative Example 2 in that the temperature during pressure molding and the temperature during electric current sintering are different.

[0046] In the electric current sintering step of this embodiment, by applying an electric current to the compacted powder 15, the compacted powder 15 is heated, for example, but the mold 11 does not have to be heated. Therefore, it is different from the SPS of Comparative Example 2 in that the carbon mold 214 is also heated together with the powder 10. In this way, the sintered body 17 is formed. In the electric current sintering step, keep the packing density of the powder 10 at, for example, 60[%] or more. In the case of a porous body, keep it at, for example, 60[%] or more. When forming a dense sintered body, keep it at, for example, 90[%] or more. For example, the powder packing density of the sintered body 17 after the electric current sintering step is 97[%. Also, in the electric current sintering step, the compacted powder 15 may be energized in a reduced pressure atmosphere such as vacuum or an inert gas atmosphere.

[0047] Next, as shown in step S15 of FIGS. 3 and 4, in the discharging step, the formed sintered body 17 is discharged. In this way, the sintered body 17 can be formed.

[0048] As shown in Table 1, the electric current sintering method of this embodiment can mold a compacted powder 15 with a complex shape, and thereby a sintered body 17 with a complex shape can be formed. Also, since it is electric current sintering, the sintered body 17 can be formed in a short time. For example, in the electric current sintering step, the time required for holding at the sintering temperature is several seconds to several minutes, for example, 1[min].

[0049] Furthermore, in the pressure molding step, since the compacted powder 15 is formed by compression, in the electric current sintering step, the compacted powder 15 does not shrink rapidly during sintering. Therefore, in the electric current sintering step, except for the displacement due to the thermal expansion of the punch material, etc., there is almost no punch displacement amount, and it is possible to suppress the deviation from the target dimensions and target shape and the generation of burrs in the sintered body 17. Thereby, the defective rate can be reduced and the dimensional accuracy and geometric accuracy can be improved.

[0050] In addition, since it is possible to prevent the powder 10 from sticking to the mold 11, the life of the mold 11 can be extended. For this reason, it is possible to mass-produce parts of the sintered body 17 having a complex shape by electric sintering, and the production cost can be reduced.

[0051] <Electrical sintering apparatus> Next, the electrical sintering apparatus of the present embodiment will be described. FIG. 5 is a configuration diagram illustrating the electrical sintering apparatus according to Embodiment 1. FIG. 6 is a configuration diagram illustrating the electrical sintering apparatus according to another example of Embodiment 1. As shown in FIGS. 5 and 6, the electrical sintering apparatuses 1 and 1a include a mold 11, an upper punch 13, a lower punch 12, a pressure molding means 18, a mold release means 19, and an electrical sintering means 20. Further, the electrical sintering apparatus 1 may include a chamber 21 and a powder filling means 22, or may have a pressure gauge, a thermometer, and an ammeter (not shown). Furthermore, as shown in FIG. 6, the electrical sintering apparatus 1a may include a control means 23 for forming the sintered body 17 by automation.

[0052] The mold 11 is, for example, cylindrical with openings on one side and the other side. The openings on one side and the other side are, for example, the lower and upper openings. The lower punch 12 is inserted into one opening. The upper punch 13 is inserted into the other opening. The mold 11 is made of a material containing metal. When the electrical sintering apparatus 1 includes the chamber 21, the mold 11 is disposed inside the chamber 21.

[0053] The chamber 21 can have a reduced-pressure atmosphere such as a vacuum or an inert gas atmosphere inside. Therefore, the powder 10 filled in the mold 11 may be pressure-molded in a reduced-pressure atmosphere or an inert gas atmosphere. Further, the released green compact 15 may be electrically sintered in a reduced-pressure atmosphere or an inert gas atmosphere. The reduced-pressure atmosphere or inert gas atmosphere inside the chamber 21 is controlled by an exhaust valve, an exhaust pump, an inert gas supply valve, etc. provided in the chamber 21.

[0054] The chamber 21 may have an upper outer wall including the upper punch 13 and a lower outer wall including the lower punch 12, for example, as in Patent Document 1. Thereby, the limited sealed space including the mold 11 may be made into a reduced-pressure atmosphere or an inert gas atmosphere.

[0055] The powder filling means 22 fills the mold 11 with the powder 10. The powder filling means 22 is, for example, a powder feeder.

[0056] The pressure molding means 18 forms the compact 15 by pressing the powder 10 filled in the mold 11. The pressure molding means 18 is, for example, a motor that performs a mechanical press. Note that the pressure molding means 18 is not limited to a motor as long as it can form the compact 15 by pressing the powder 10 filled in the mold 11. For example, a pump that performs a hydraulic press may also be used. The pressure molding means 18 presses the powder 10 with the lower punch 12 inserted into one opening of the mold and the upper punch 13 inserted into the other opening. The pressure molding means 18 sets the pressure for pressing the powder 10 to 100 to 700 [MPa] or 700 [MPa] or more in a state where the temperature of the powder is less than 500 [°C]. Thereby, the pressure molding means 18 changes the filling density of the powder 10 from, for example, less than 60 [%] to 60 [%] or more.

[0057] The mold release means 19 releases the compact 15 from the mold 11. The mold release means 19 is, for example, a motor of the lower punch 12. The mold release means 19 releases the compact 15 from the mold 11 by pushing out the compact 15 from the mold 11 with the lower punch 12. In this case, the mold 11 may be fixed. Note that the mold release means 19 is not limited to the motor of the lower punch 12 as long as it can release the compact 15 from the mold 11. For example, a pump of the lower punch 12 or the like may also be used, or a motor or pump or the like provided on the mold 11 and moving the mold 11 may also be used.

[0058] FIG. 7 is a configuration diagram illustrating an electric current sintering apparatus according to still another example of Embodiment 1. As shown in FIG. 7, in the electric current sintering apparatus 1b, the mold release means 19 may release the compacted powder body 15 from the mold 11 by removing the compacted powder body 15 from the mold 11, the lower punch 12, and the upper punch 13. Although not shown, the electric current sintering apparatus 1b may also include control means 23 for forming the sintered body 17 by automation.

[0059] As shown in FIGS. 5 to 7, the electric current sintering means 20 forms the sintered body 17 by passing an electric current through the compacted powder body 15 released from the mold 11. The electric current sintering means 20 is, for example, a power source. Note that the electric current sintering means 20 is not limited to a power source and may be a battery or a cell as long as it can form the sintered body 17 by passing an electric current through the compacted powder body 15 released from the mold 11.

[0060] As shown in FIGS. 5 and 6, the electric current sintering means 20 may pass an electric current through the compacted powder body 15 via the upper punch 13 and the lower punch 12. Specifically, the current-carrying path through which the current flows returns to the electric current sintering means 20 via the electric current sintering means 20, the electrode 24, the upper punch 13, the compacted powder body 15, the lower punch 12, and the electrode 25. The electrode 24 is disposed above the upper punch 13 and is connected to the electric current sintering means 20. The electrode 25 is disposed below the lower punch 12 and is connected to the electric current sintering means 20. The upper punch 13 and the lower punch 12 have the function of terminals for passing an electric current through the compacted powder body 15.

[0061] Also, as shown in FIG. 7, when the compacted powder body 15 is removed from the mold 11, the lower punch 12, and the upper punch 13, the electric current sintering means 20 may pass an electric current through the compacted powder body 15 via the terminal 26 and the terminal 27 without passing through the upper punch 13 and the lower punch 12. The terminal 26 is disposed between the electrode 24 and the compacted powder body 15. The terminal 27 is disposed between the electrode 25 and the compacted powder body 15. The current-carrying path through which the current flows returns to the electric current sintering means 20 via the electric current sintering means 20, the electrode 24, the terminal 26, the compacted powder body 15, the terminal 27, and the electrode 25. Note that the current-carrying path may return to the electric current sintering means 20 from the electric current sintering means 20 via the terminal 26, the compacted powder body 15, and the terminal 27 without passing through the electrode 24 and the electrode 25.

[0062] The electric sintering means 20 may raise the temperature of the powder to 500 [°C] or higher with the pressure applied to the powder being 0 [MPa] in a state other than the inevitable pressure. The electric sintering means 20 maintains the packing density of the powder 10, for example, at 60 [%] or higher. In the case of a porous body, it is maintained, for example, at 60 [%] or higher. When forming a dense sintered body, it is maintained, for example, at 90 [%] or higher. The electric sintering means 20 sinters or diffusion-bonds each particle of the powder 10 in the compacted powder 15 by heat generated between the particles, heat generated inside each particle, and heat transmitted by heat conduction from outside the particles, etc.

[0063] As shown in FIG. 5, the operations of the pressure forming means 18, the mold release means 19, the electric sintering means 20, the chamber 21, and the powder filling means 22 in the electric sintering apparatus 1 may be controlled manually. On the other hand, as shown in FIG. 6, the electric sintering apparatus 1a may include a control means 23 for controlling the operations of the pressure forming means 18, the mold release means 19, the electric sintering means 20, the chamber 21, and the powder filling means 22 for forming the sintered body 17 by automation.

[0064] The control means 23 is connected to the pressure forming means 18, the mold release means 19, the electric sintering means 20, the chamber 21, and the powder filling means 22 by a wired or wireless signal line or the like. The control means 23 may be connected to a pressure gauge, a thermometer, and an ammeter by a signal line or the like. The control means 23 is, for example, an information processing device such as a personal computer or a server.

[0065] The control means 23 controls to fill the mold 11 with the powder 10 in a preset supply amount by transmitting a signal to the powder filling means 22. Further, the control means 23 controls to press the powder 10 filled in the mold 11 at a preset pressure by transmitting a signal to the pressure forming means 18. Then, the control means 23 controls to release the compact 15 from the mold 11 by transmitting a signal to the mold release means 19. Also, the control means 23 controls to form the sintered body 17 by energizing the compact 15 released from the mold 11 by transmitting a signal to the electric sintering means 20.

[0066] The control means 23 may control the inside of the chamber 21 to be in a predetermined reduced-pressure atmosphere or an inert gas atmosphere by transmitting a signal to the chamber 21. The control means 23 may also control to discharge the formed sintered body 17.

[0067] The control means 23 may have a storage device such as a memory and store in the storage device a program for controlling the operations of the pressure forming means 18, the mold release means 19, the electric sintering means 20, the chamber 21, and the powder filling means 22. Then, the control means 23 may control the operations of the pressure forming means 18, the mold release means 19, the electric sintering means 20, the chamber 21, and the powder filling means 22 based on the program.

[0068] Next, as an example, an example of forming the sintered body 17 using the electric current sintering apparatus 1b shown in FIG. 7 will be described. FIG. 8 is a graph illustrating the relationship between the punch surface pressure in the pressure molding step and the packing density of the sintered body in the electric current sintering method using the electric current sintering apparatus 1b according to Embodiment 1. The horizontal axis represents the surface pressure [MPa], and the vertical axis represents the packing density [%]. In FIG. 8, black circles (●) indicate after powder pressing (after pressure molding), and white circles (○) indicate after sintering. FIG. 9 is a graph illustrating the relationship between the punch surface pressure in the pressure molding step and the shrinkage rate of the sintered body in the electric current sintering method using the electric current sintering apparatus 1b according to Embodiment 1. The horizontal axis represents the surface pressure [MPa], and the vertical axis represents the shrinkage rate [%]. In FIG. 9, the hatched bar graph indicates the shrinkage rate in the XY plane orthogonal to the pressing direction, and the white bar graph indicates the shrinkage rate in the Z-axis direction of pressing. FIG. 10 is a cross-sectional view illustrating the sintered body in the electric current sintering method using the electric current sintering apparatus 1b according to Embodiment 1. FIG. 11 is a cross-sectional view illustrating the microstructure of the sintered body in the electric current sintering method using the electric current sintering apparatus 1b according to Embodiment 1.

[0069] As shown in FIG. 8, in the pressure molding step, the packing densities of the green compacts 15 molded by pressing at surface pressures of 250, 500, and 750 [MPa] are 62.0, 78.4, and 82.2 [%], respectively. The packing densities of the sintered bodies 17 formed by sintering the green compacts 15 thus molded are 63.3, 79.6, and 84.8 [%], respectively. Thus, in the electric current sintering method of the present embodiment, in the pressure molding step, the packing density of the powder 10 is changed from less than 60 [%] to 60 [%] or more, and in the electric current sintering step, the packing density of the powder 10 is maintained at 60 [%] or more.

[0070] As shown in Fig. 9, in the pressure molding step, the shrinkage rates of the XY plane and the Z axis of the green compact 15 formed by pressing at a surface pressure of 250 [MPa] are 0.40 and 1.18 [%], respectively. In the pressure molding step, the shrinkage rates of the XY plane and the Z axis of the green compact 15 formed by pressing at a surface pressure of 500 [MPa] are 0.49 and 0.50 [%], respectively. In the pressure molding step, the shrinkage rates of the XY plane and the Z axis of the green compact 15 formed by pressing at a surface pressure of 750 [MPa] are 0.69 and 1.74 [%], respectively. Thus, in the electric current sintering method of the present embodiment, although it is slight in the case of 500 [MPa], generally, the shrinkage rate of the Z axis is larger than the shrinkage rate of the XY plane. In this way, as shown in Figs. 10 and 11, a high-quality sintered body 17 can be formed.

[0071] Next, the effects of the electric current sintering apparatus 1 of the present embodiment will be described. The electric current sintering apparatuses 1 to 1b are electric current sintering methods having the effects shown in Table 1 and can form the sintered body 17. Therefore, the electric current sintering apparatuses 1 to 1b can reduce the production cost of the sintered body 17.

[0072] Further, the electric current sintering means 20 can apply an electric current to the green compact 15 via the upper punch 13 and the lower punch 12. Thereby, the time taken to shift from pressure molding to electric current sintering can be shortened. On the other hand, the electric current sintering means 20 can apply an electric current to the green compact 15 via the terminal 26 and the terminal 27. Thereby, the loss of the electric current due to the flow of the electric current through the upper punch 13 and the lower punch 12 can be reduced, and the life of the upper punch 13 and the lower punch 12 can be improved.

[0073] The energized sintering means 20 of the present embodiment sinters each particle of the powder 10 by energized sintering using heat generated between the particles, heat generated inside each particle (the particle itself), heat transmitted by heat transfer from outside the particle, etc. Therefore, while maintaining the packing density of the powder 10 at 60% or more, the sintered body 17 can be densified. Also, since diffusion bonding is performed, a porous body can be formed while maintaining the packing density of the powder at 60% or more. Further, unlike the SPS method of Comparative Example 2, the pressure for pressing the green compact 15 is 0 MPa except for unavoidable pressure, so the punch displacement amount can be suppressed and the generation of burrs in the sintered body 17 can be suppressed. Also, the service life of the mold 11, the upper punch 13, and the lower punch 12 can be improved.

[0074] By controlling the pressure molding means 18, the mold release means 19, the energized sintering means 20, etc. by the control means 23, the formation of the sintered body 17 by energized sintering can be automated. Therefore, the production cost can be reduced.

[0075] (Embodiment 2) Next, the energized sintering apparatus 2 according to Embodiment 2 will be described. The energized sintering apparatus of the present embodiment separates the part for performing pressure molding and the part for performing energized sintering. Thereby, pressure molding and energized sintering can be performed in parallel.

[0076] FIG. 12 is a configuration diagram illustrating an energized sintering apparatus according to Embodiment 2. As shown in FIG. 12, the energized sintering apparatus 2 includes a powder filling section 31, a pressure molding section 32, an energized sintering section 33, a discharge section 34, and a conveying means 35. The energized sintering section 33 is arranged side by side with the pressure molding section 32. The powder filling section 31 may be arranged side by side with the pressure molding section 32 or may be integrated with the pressure molding section 32. The discharge section 34 may be arranged side by side with the energized sintering section 33 or may be integrated with the energized sintering section 33.

[0077] Also, the energized sintering apparatus 2 may include a chamber 21. The mold 11, the lower punch 12, and the upper punch 13 may be arranged inside the chamber 21.

[0078] The powder filling section 31 has powder filling means 22. In the powder filling section 31, the powder filling means 22 fills the mold 11 with the powder 10.

[0079] The pressure molding section 32 includes pressure molding means 18 and mold release means 19. In the pressure molding section 32, the pressure molding means 18 forms a compacted powder body 15 by pressing the powder 10 filled in the mold 11 using the upper punch 13 and the lower punch 12. Also, in the pressure molding section 32, the mold release means 19 releases the compacted powder body 15 from the mold 11.

[0080] The conveying means 35 conveys the compacted powder body 15 from the pressure molding section 32 to the electric current sintering section 33. The conveying means 35 may be, for example, a conveying stage for conveying the compacted powder body 15 or an arm for conveying the compacted powder body 15. The conveying means 35 may also convey the sintered body 17 from the electric current sintering section 33 to the discharge section 34.

[0081] The electric current sintering section 33 includes electric current sintering means 20. In the electric current sintering section 33, the electric current sintering means 20 forms the sintered body 17 by applying an electric current to the compacted powder body 15 released from the mold 11. The discharge section 34 discharges the formed sintered body 17 from the electric current sintering apparatus 2. The electric current sintering apparatus 2 may further include control means 23 for controlling the pressure molding means 18, the mold release means 19, the electric current sintering means 20, and the conveying means 35. Thereby, the formation of the sintered body 17 can be automated.

[0082] Next, the operation of the electric current sintering apparatus 2 of the present embodiment will be described. FIG. 13 is a flowchart illustrating the operation of the electric current sintering apparatus according to Embodiment 2. As shown in FIG. 13, the electric current sintering apparatus 2 can perform a compacted powder body forming step S20 and a sintered body forming step S30 in parallel. The compacted powder body forming step S20 includes a powder filling step S21, a pressure molding step S22, a mold release step S23, and a conveying step S24. The sintered body forming step S30 includes an electric current sintering step S31 and a discharge step S32.

[0083] The compact powder forming step S20 will be described. In the powder filling step S21 of FIG. 13, the powder filling means 22 fills the mold 11 with the powder 10. The mold 11 is made of a material containing metal and is cylindrical with openings on both sides.

[0084] Next, in the pressure forming step S22, the pressure forming means 18 forms the compact powder 15 by pressing the powder 10 filled in the mold 11. For example, the pressure forming means 18 presses the powder 10 with the upper punch 13 and the lower punch 12.

[0085] Next, in the mold release step S23, the mold release means 19 releases the compact powder 15 from the mold 11. For example, the mold release means 19 releases the compact powder 15 from the mold 11 by removing the compact powder 15 from the mold 11, the upper punch 13, and the lower punch 12.

[0086] Next, in the conveying step S24, the conveying means 35 conveys the compact powder 15 from the pressure forming section 32 to the electric sintering section 33.

[0087] Next, in step S25, it is determined whether to end the process of the compact powder forming step S20. If the compact powder forming step S20 is to be continued, return to step S21 and continue the powder filling step S21 to the conveying step S24. On the other hand, if the process of the compact powder forming step S20 is to be ended in step S25, end the process.

[0088] Next, the sintered body forming step S30 will be described. In the electric sintering step S31 of FIG. 13, the electric sintering means 20 forms the sintered body 17 by applying an electric current to the compact powder 15 conveyed from the pressure forming section 32. For example, the electric sintering means 20 applies an electric current to the conveyed compact powder 15 via the terminals 26 and 27.

[0089] Next, in the discharging step S32, the formed sintered body 17 is discharged. Next, in step S33, it is determined whether to end the process of the sintered body forming step S30. If the sintered body forming step S30 is to be continued further, the process returns to step S31 to continue the electric current sintering step S31 to the discharging step S32. On the other hand, if in step S33 the process of the sintered body forming step S30 is to be ended, the process is ended. In this way, the sintered body 17 can be formed. In the electric current sintering method of the present embodiment, in the pressure molding step S22, when molding the green compact 15a, in parallel, in the electric current sintering step S31, by applying an electric current to a green compact 15b different from the green compact 15a, the sintered body 17 can be formed. Specifically, when the pressure molding means 18 molds the green compact 15a, in parallel, the electric current sintering means 20 can form the sintered body 17 by applying an electric current to the green compact 15b.

[0090] Next, the effects of the present embodiment will be described. The electric current sintering apparatus 2 of the present embodiment separates a pressure molding unit 32 that performs pressure molding and an electric current sintering unit 33 that performs electric current sintering. Thereby, the molding of the green compact 15 by pressure molding and the formation of the sintered body 17 by electric current sintering can be performed in parallel. Therefore, the production time can be shortened.

[0091] Also, since the mold 11, the upper punch 13, and the lower punch 12 used for pressure molding and the terminals 26 and 27 used for electric current sintering can be separated, the service life of each member can be improved.

[0092] FIG. 14 is a configuration diagram illustrating the SPS apparatus according to Comparative Example 3. As shown in FIG. 14, the SPS apparatus 103 includes a powder filling section 331, a preheating section 332, a current sintering section 333, and a cooling section 334. The SPS apparatus 103 also includes a plurality of mold sets 310 and powder filling means 322. Each mold set 310 includes a carbon mold 314, an upper punch 313, and a lower punch 312. The plurality of mold sets 310 are continuously conveyed from the powder filling section 331 to the cooling section 334, and powder filling processing, preheating processing, current sintering processing, and cooling processing are performed in each of the powder filling section 331, the preheating section 332, the current sintering section 333, and the cooling section 334. In each section from the powder filling section 331 to the cooling section 334, one or more mold sets 310 are constantly being processed.

[0093] The SPS apparatus 103 of Comparative Example 3 can continuously perform powder filling processing, preheating processing, current sintering processing, and cooling processing, and can shorten the production time of the sintered body 317 to a certain extent. However, since the SPS apparatus 103 of Comparative Example 3 requires a large number of expensive carbon molds 314, the production cost increases.

[0094] On the other hand, the current sintering apparatus 2 of the present embodiment does not require an expensive carbon mold 314. Also, a plurality of green compacts 15 can be molded with one mold 11. Therefore, the production cost can be suppressed. Further, during current sintering, the green compact 15 is released from the mold 11, so the life of the mold 11 can be improved and the production cost can be further reduced. Other effects are included in the description of Embodiment 1.

[0095] As described above, the invention made by the present inventor has been specifically described based on the embodiments. However, it goes without saying that the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist thereof.

Description of Reference Numerals

[0096] 1, 1a, 1b, 2 Current sintering apparatus 10 Powder 11 Mold 12 Lower punch 13 Upper punch 15, 15a, 15b Compressed powder 17 Sintered body 18 Pressing means 19 Demolding means 20 Electric sintering means 21 Chamber 22 Powder filling means 23 Control means 24, 25 Electrodes 26, 27 Terminals 31 Powder filling section 32 Pressing section 33 Electric sintering section 34 Discharge section 35 Conveying means 103 SPS device 111 Mold 112 Lower punch 113 Upper punch 115 Compressed powder 116 Sintering furnace 117 Sintered body 212 Lower punch 213 Upper punch 214 Carbon mold 217 Sintered body 310 Mold set 322 Powder filling means 331 Powder filling section 332 Preheating section 333 Electric sintering section 334 Cooling section

Claims

1. A chamber including at least one of an exhaust valve and an inert gas supply valve for isolating the inside from the atmosphere and creating a predetermined atmosphere; a powder filling means for supplying a powder containing at least aluminum as a component to a mold provided inside the chamber; a pressurizing means for pressurizing the powder supplied to the die in the interior of the chamber; a demolding means for demolding the powder compact from the die within the chamber; a conveying means for conveying the powder compact released from the die within the chamber; a current sintering means for forming an aluminum alloy sintered body by passing a current through the powder compact in the chamber; Equipped with when forming the aluminum alloy sintered body by passing an electric current through the powder compact, the pressure for pressing the powder compact is zero except for unavoidable pressure caused by contact of an upper punch and a lower punch arranged above and below the powder compact for passing an electric current through the powder compact, or contact of electrodes for passing an electric current through the powder compact. Aluminum alloy sintering equipment.

2. The powder is an alloy powder containing aluminum and at least one of copper, manganese, silicon, magnesium, zinc, and nickel.

2. The aluminum alloy sintering apparatus according to claim 1.

3. an atmosphere control step of isolating the inside of the chamber from the atmosphere and creating a predetermined atmosphere; a powder filling step of supplying a powder containing at least aluminum as a component to a mold provided inside the chamber; a pressing step of pressing the powder supplied to the die in the interior of the chamber; a demolding step of demolding the powder compact from the die in the interior of the chamber; a conveying step of conveying the powder compact released from the die in the interior of the chamber; a current sintering step of forming an aluminum alloy sintered body by passing a current through the powder compact in the chamber; Equipped with In the electric current sintering step, the pressure applied to the powder compact is zero except for unavoidable pressure caused by contact of an upper punch and a lower punch arranged above and below the powder compact for passing current through the powder compact, or contact of electrodes for passing current through the powder compact. Aluminum alloy sintering method.

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