Electric current sintering mold, electric current sintering apparatus, and method for manufacturing sintered compact

Abstract

To provide: an electric current sintering mold, improved in mold durability, capable of efficiently pressurizing a rectangular sintered compact as viewed from above, and capable of improving productivity in manufacturing the rectangular sintered compact as viewed from above; an electric current sintering apparatus using the electric current sintering mold; and a method for manufacturing a sintered compact using the electric current sintering apparatus.SOLUTION: An electric current sintering mold having a rectangular cavity part 1 as viewed from above, to be used in an electric current sintering apparatus, comprises an inner mold 10 made of tungsten or a hard metal surrounding the cavity part 1, and an outer mold 40 made of graphite surrounding the inner mold 10. It is preferable that corners of the cavity part 1 of the inner mold 10 are rounded. It is preferable that the mold includes upper and lower molds made of tungsten or hard metal surrounding the upper and lower parts of the cavity part 1.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an electric sintering mold used in an electric sintering apparatus for sintering powder materials while applying pressure and passing an electric current.

Background Art

[0002] Conventionally, as an electric sintering apparatus for sintering powder materials while applying pressure and passing an electric current, there are a uniaxial electric sintering apparatus that passes an electric current in the vertical direction with the same pressure axis and electric conduction axis, and a multi-axis electric sintering apparatus that separates the pressure axis and the electric conduction axis and passes an electric current in the horizontal direction. Since the uniaxial electric sintering apparatus uses the same axis for pressure application and electric conduction, the temperature distribution in the radial direction (horizontal direction) of the sintered portion tends to be non-uniform. To improve this drawback, a multi-axis electric sintering apparatus that separates the pressure axis and the electric conduction axis has been developed.

[0003] As a material for the molding die for containing powder materials, graphite is generally used, but other materials are also used and the shape is devised. For example, Patent Document 1 describes an invention related to an electric sintering die in which the outer peripheral portion is formed of graphite and the inner peripheral portion is formed of heat-resistant steel, thereby ensuring the strength of the die and effectively utilizing graphite.

[0004] Further, Patent Document 2 describes an invention related to a discharge plasma sintering die that prevents defects such as cracks from occurring in the die and the sintered body by combining the shape of the die.

[0005] Further, Patent Document 3 describes an invention related to an electric sintering die made of a metal material that enables efficient mass production of sintered bodies with high accuracy and high shape freedom.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] As an application of a sintered body manufactured by an electric current sintering apparatus, there is a heat dissipation plate disposed under a power device of an automobile part. The shape of such a heat dissipation plate is generally rectangular in plan view (hereinafter, “rectangle” includes “square”). In order to suppress the loss of the sintered body and manufacture the heat dissipation plate efficiently, the space (cavity portion) for putting the powder material for electric current sintering mold may be rectangular in plan view.

[0008] Here, when the cavity portion is rectangular in plan view, when pressurized from the vertical direction, the stress generated thereby concentrates on the four corners of the mold having a rectangular shape in plan view. Therefore, in the case of a general graphite mold, the mold itself is weak, especially the corners cannot withstand the pressure and frequently crack. When the mold cracks, it must be replaced with a new mold, so the productivity of the heat dissipation plate decreases. Even in the case of a graphite mold, if the cavity portion is formed in a cylindrical shape, stress concentration of the mold can be prevented and cracking can be prevented. However, since the obtained sintered body is cylindrical, when the sintered body is processed into a rectangular shape in plan view, the sintered body of the removed end material portion becomes wasted, and the productivity of the heat dissipation plate decreases.

[0009] On the other hand, in order to prevent cracking of the mold, it is conceivable to use a material having a higher strength than graphite as the material of the mold forming the cavity portion.

[0010] Examples of high-strength materials include heat-resistant steels such as austenitic heat-resistant steels and ferritic heat-resistant steels. However, austenitic heat-resistant steels have a high heat-resistant temperature but a large coefficient of thermal expansion. Therefore, the cavity portion deforms and cannot efficiently transmit the pressure from the vertical pressing axis to the sintered body having a rectangular shape in plan view. In the case of electric current sintering with a short cycle time, there is a concern about a decrease in the strength of the mold due to fatigue caused by a rapid temperature cycle. In addition, ferritic heat-resistant steels have a small coefficient of thermal expansion and excellent fatigue resistance against temperature cycles, but since their heat-resistant temperature is low, there are limitations on the powder materials that can be sintered. That is, simply having a high-strength material for the mold forming the cavity portion cannot improve the productivity of sintered body production.

[0011] The present invention solves the above-described conventional problems, and provides an electric current sintering mold that has improved durability, can efficiently press a sintered body having a rectangular shape in plan view, and can improve the productivity of manufacturing a sintered body having a rectangular shape in plan view, an electric current sintering apparatus using the electric current sintering mold, and a method for manufacturing a sintered body using the electric current sintering apparatus.

Means for Solving the Problems

[0012] In order to solve the above problems, the electric current sintering mold of the present invention is an electric current sintering mold having a cavity portion having a rectangular shape in plan view used in an electric current sintering apparatus, and is characterized by having an inner mold made of tungsten or cemented carbide surrounding the cavity portion and an outer mold made of graphite surrounding the inner mold.

[0013] Preferably, the inner mold is a split mold.

[0014] Preferably, the inner mold is an integral mold.

[0015] Preferably, a rounded portion is provided at a portion corresponding to a corner of the cavity portion of the inner mold.

[0016] Preferably, it has upper and lower molds made of tungsten or cemented carbide that surround the upper and lower parts of the cavity section.

[0017] Preferably, the cavity section is divided into multiple layers by the upper and lower molds.

[0018] Also, the electric sintering apparatus of the present invention uses the above-described electric sintering mold.

[0019] Also, the method for manufacturing a sintered body of the present invention uses the above-described electric sintering apparatus.

[0020] Note that the "rectangle" having a rectangular shape in plan view includes a "square", and also includes those with rounded corners.

Advantages of the Invention

[0021] According to the present invention, it is possible to provide an electric sintering mold with improved durability and improved productivity in manufacturing a sintered body having a rectangular shape in plan view.

[0022] Also, in the electric sintering mold of the present invention, the cavity section is difficult to expand due to the pressure in the vertical direction, and the pressure from the pressurization axis in the vertical direction can be efficiently transmitted to the sintered body having a rectangular shape in plan view.

[0023] Also, tungsten and cemented carbide have a small coefficient of thermal expansion and excellent shape stability. Also, its coefficient of thermal expansion is close to that of graphite. Therefore, even at high temperature and high pressure, the cavity section is difficult to deform, and it is possible to make the outer mold made of graphite that surrounds the inner mold made of tungsten or cemented carbide less likely to crack.

[0024] Also, when the inner mold is a split mold, the manufacture of the inner mold is easy.

[0025] Also, when the inner mold is an integral mold, the operability of the inner mold is good.

[0026] In addition, when a rounded portion is provided at a portion corresponding to a corner of the cavity portion of the inner mold, stress at the four corners can be dispersed, so that stress concentration at the four corners can be more effectively addressed.

[0027] In addition, when an upper and a lower mold made of tungsten or cemented carbide surrounding the upper and lower portions of the cavity portion are provided, by using the hard upper and lower molds, pressure from the vertical pressing axis can be efficiently transmitted to a sintered body having a rectangular shape in plan view.

[0028] In addition, when the cavity portion is divided into a plurality of layers by the upper and lower molds, pressure from the vertical pressing axis can be efficiently transmitted to a plurality of sintered bodies having a rectangular shape in plan view.

[0029] In addition, since the electric current sintering apparatus of the present invention uses the above-described electric current sintering mold, the durability of the mold is improved, a sintered body having a rectangular shape in plan view can be efficiently pressed, and the productivity of manufacturing a sintered body having a rectangular shape in plan view can be improved.

[0030] In addition, since the method for manufacturing a sintered body of the present invention uses the above-described electric current sintering apparatus, the durability of the mold is improved, a sintered body having a rectangular shape in plan view can be efficiently pressed, and the productivity of manufacturing a sintered body having a rectangular shape in plan view can be improved.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0032] First, the electric current sintering apparatus used in this embodiment will be described. The electric current sintering apparatus sinter the powder material placed in the mold in the vacuum container by applying current in the mold while pressing it with a vertical pressing shaft having an upper punch and a lower punch.

[0033] Depending on the difference in the current application method, the electric current sintering apparatus includes a uniaxial electric current sintering apparatus that applies current in the vertical direction with the same pressing shaft and current application shaft, and a multi-axis electric current sintering apparatus that separates the pressing shaft and the current application shaft and applies current in the horizontal direction. Since the uniaxial electric current sintering apparatus uses the same shaft for pressing and current application, the temperature distribution in the radial direction (horizontal direction) of the sintered part tends to be non-uniform. In order to improve this drawback, a multi-axis electric current sintering apparatus separates the pressing shaft and the current application shaft. In this embodiment, it is possible to use a uniaxial electric current sintering apparatus, but it is more preferable to use a multi-axis electric current sintering apparatus from the viewpoint of making the temperature distribution uniform.

[0034] Next, with reference to FIGS. 1-6, the mold for electric current sintering according to the embodiment of the present invention will be described. FIG. 1 is a front view showing a mold 100 for electric current sintering according to the embodiment of the present invention. FIG. 1 is a figure common to Embodiments 1-5 described later.

[0035] The mold 100 for electric current sintering has a cavity part for putting the powder material inside. In order to apply pressure to the main body material placed in the cavity part from above and below, the upper punch 2 and the lower punch 3 move along the vertical pressing shaft. And a horizontal current application shaft (not shown) is connected to the sintering mold 100 for current application to heat the powder material placed in the cavity part. In this embodiment, the “rectangle” having a rectangular shape in plan view includes a “square”, and those having rounded corners (rounds) are also included.

[0036] (Embodiment 1) FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1, showing the electric current sintering mold 101 according to Embodiment 1. In the center of the electric current sintering mold 101, a cavity portion 1 having a rectangular shape in plan view, which is a space for putting powder materials, is formed. The electric current sintering mold 101 is roughly composed of a cylindrical inner mold 10 and a cylindrical outer mold 40.

[0037] The inner mold 10 is a split mold composed of four corner members 11 and four connecting members 12. The corner member 11 is a member having a substantially arc-shaped cross section corresponding to the corner of the cavity portion 1, and has a recess for fitting to the end of the connecting member 12. The connecting member 12 is a member having a substantially U-shaped cross section, and both ends thereof are adapted to fit into the recesses of the corner members 11. Then, by connecting the adjacent corner members 11 with the connecting members 12, an inner mold 10 of a cylindrical body having four recesses on the outer periphery and a rectangular space (cavity portion 1) in plan view on the inner periphery is formed.

[0038] Rounding is provided at a portion corresponding to the corner of the cavity portion 1 of the inner mold 10. The size of the rounding is the length of the radius of curvature, and can be, for example, 0% or more and less than 50% according to the length of the short side of the rectangular shape in plan view. From the viewpoints of preventing cracking of the mold and improving the productivity of the sintered body, the ratio of the rounding is preferably more than 0%, more preferably 0.1% or more, and further preferably 0.5% or more. Also, the ratio of the rounding is preferably 40% or less, more preferably 25% or less, and further preferably 10% or less. Note that the ratio of the rounding means the ratio of the length of the radius of curvature to the length of the short side of the rectangular shape in plan view at one corner.

[0039] The outer mold 40 is composed of an outer portion 41 having a cross section with an octagonal outer periphery and a circular inner periphery, a cylindrical intermediate portion 42 having a ring-shaped cross section, and an inner portion 43 having a substantially rectangular cross section, from the outside to the inside. Then, the intermediate portion 42 is fitted to the inner periphery of the outer portion 41, and the inner portions 43 are arranged at four locations on the inner periphery of the intermediate portion 42 to form the outer mold 40 of a cylindrical body, which is adapted to fit on the outer periphery of the inner mold 10. The material of the outer mold 40 is graphite (artificial graphite).

[0040] The material of the inner mold 10 is tungsten or cemented carbide. It is preferable that the coefficient of thermal expansion of the inner mold 10 is close to that of the material (graphite) of the outer mold 40. Although the coefficient of thermal expansion of graphite varies depending on the product, it is about 4.0 to 6.0 (×10 -6 / K). When cemented carbide is used as the material of the inner mold 10, it is preferable to use one with a coefficient of thermal expansion of 4.0 to 6.0 (×10 -6 / K), and more preferably 4.0 to 5.0 (×10 -6 / K). The coefficient of thermal expansion of tungsten is 4.5 (×10 -6 / K). The same applies to the following embodiments.

[0041] The general composition of cemented carbide is WC (tungsten carbide) and Co (cobalt), but it can also be combined with Ni (nickel) or Cr (chromium) instead of Co (cobalt).

[0042] (Embodiment 2) FIG. 3 is a cross-sectional view taken along line A-A of FIG. 1, showing the electric current sintering mold 102 according to Embodiment 2. Note that the electric current sintering mold 102 has substantially the same configuration as the electric current sintering mold 101 according to the embodiment, and the same parts are denoted by the same reference numerals and the description thereof is omitted.

[0043] Unlike the inner mold 10 in Embodiment 1 shown in FIG. 2, the inner mold 20 of the electric current sintering mold 102 is an integral type. That is, it is formed by integrally molding the four corner members 11 and the four connecting members 12 of the inner mold 10. The material of the outer mold 40 is graphite (graphite). Since the inner mold 20 is an integral type, the operability is good.

[0044] (Embodiment 3) FIG. 4 is a cross-sectional view taken along line A-A of FIG. 1, showing the electric current sintering mold 103 according to Embodiment 3. In the center of the electric current sintering mold 103, a cavity portion 1 having a rectangular shape in plan view, which is a space for putting powder material, is formed. The electric current sintering mold 103 is roughly composed of a cylindrical inner mold 30 and a cylindrical outer mold 40.

[0045] The inner mold 30 is an integral type with a substantially rectangular outer circumference and inner circumference, in the shape of a square tube, and has four arrow-shaped protrusions 31. And it has a space (cavity part 1) that is rectangular in plan view on the inner circumference. The parts corresponding to the corners of the cavity part 1 of the inner mold 30 are rounded. The size of the rounding can be, for example, 0% or more and less than 50% according to the length of the short side of the rectangle in plan view. From the viewpoints of preventing cracking of the mold and improving the productivity of the sintered body, the ratio of the rounding is preferably more than 0%, more preferably 0.1% or more, and even more preferably 0.5% or more. Also, the ratio of the rounding is preferably 40% or less, more preferably 25% or less, and even more preferably 10% or less.

[0046] The outer mold 40 is composed of an outer side part 44 with a square tube shape having an octagonal outer circumference and a rectangular inner circumference, prism-shaped short side parts 45, 45 with a substantially convex cross-section, and prism-shaped long side parts 46, 46 with a substantially convex cross-section, from the outside to the inside. And the protrusions 31 of the inner mold 30 are fitted into the recesses formed by the short side parts 45, 45 and the long side parts 46, 46, so that the outer mold 40 of the cylindrical body is formed. The material of the outer mold 40 is graphite (artificial graphite).

[0047] (Embodiment 4) FIG. 5 is a cross-sectional view taken along line B-B of FIG. 1, showing the electric current sintering mold 104 according to Embodiment 4. The electric current sintering mold 104 is provided with upper and lower molds 50, 50 in addition to any of the electric current sintering molds 101 - 103 according to the aforementioned Embodiments 1 - 3.

[0048] The upper and lower molds 50, 50 are plate-like members arranged at positions surrounding the upper and lower parts of the cavity part 1. The material of the upper and lower molds 50 is tungsten or cemented carbide, similar to the inner molds 10, 20, 30.

[0049] The outer mold 40 is composed of an outer side part 47 and a spacer part 48. By providing the upper and lower molds 50, 50, the pressure from the vertical pressure axis can be efficiently transmitted to the sintered body that is rectangular in plan view by using the hard vertical molds.

[0050] (Embodiment 5) FIG. 6 is a cross-sectional view taken along line B-B of FIG. 1, and shows an electric current sintering mold 105 according to Embodiment 5. The electric current sintering mold 105 is obtained by further adding upper and lower molds 50 to the electric current sintering mold 104 according to Embodiment 4.

[0051] The electric current sintering mold 105 has three upper and lower molds 50, 50, 50 arranged at positions surrounding the upper and lower sides of the cavity portion 1, and the cavity portion 1 is divided into a plurality of layers (two layers). Note that four or more upper and lower molds 50 can also be used. By dividing the cavity portion 1 into a plurality of layers by the upper and lower molds 50, 50, 50, the pressure from the vertical pressing axis can be efficiently transmitted to a plurality of sintered compacts having a rectangular shape in plan view.

[0052] Hereinafter, description will be made based on examples.

Examples

[0053] Using a multi-axis electric current sintering apparatus having a vertical pressing axis and a horizontal electric current axis, a sintered compact made of a graphite-copper composite material was obtained with the sintering material being flaky natural graphite and copper powder. The volume ratio of each raw material blend was set to a predetermined ratio, and the theoretical density was calculated from the volume ratio. In the comparative example, in order to prevent cracking, the cavity portion was formed in a cylindrical shape to obtain a sintered compact and then cut into a rectangular shape in plan view.

[0054] (Example 1 and Comparative Example 1) As the electric current sintering mold for Example 1, the electric current sintering mold according to Embodiment 1 shown in FIG. 2 having a cavity portion with a rectangular shape in plan view was used. Also, as Comparative Example 1, an electric current sintering mold having a cavity portion with a rectangular shape in plan view formed at the center of the graphite mold was used. When the pressure during electric current sintering was set to the same condition of 50 MPa, in Example 1 with the inner mold made of tungsten, the number of durable cycles was 40 or more, whereas in Comparative Example 1 with the inner mold made of graphite, the inner mold cracked after one time and a desired sintered compact could not be obtained.

[0055] (Example 2) As the mold for electric sintering, the mold for electric sintering according to Embodiment 1 shown in FIG. 2 with a rectangular cavity portion in plan view was used. The material of the inner mold 10 was tungsten, and it was manufactured by wire-cutting a tungsten block. The size of the cavity portion 1 was 62 mm in length × 62 mm in width × 15 mm in height, and the radius of the rounded portion corresponding to the corner of the cavity portion was 1 mm (the ratio of the radius was 1.6%). Electric sintering was performed with a pressure of 50 MPa applied by a vertical pressure axis. A plurality of samples with dimensions of 30 mm in length × 30 mm in width × 3 mm in height were prepared from the obtained sintered body. The density of 10 of these samples was measured, the relative density with respect to the theoretical density was calculated, and the average value of the relative densities was calculated.

[0056] (Comparative Example 2) As the mold for electric sintering, a graphite mold with a cylindrical cavity portion was used. The size of the cavity portion was 32 mm in diameter × 15 mm in height. Electric sintering was performed with a pressure of 60 MPa applied by a vertical pressure axis. The obtained sintered body was cut to prepare a plurality of samples with dimensions of 22 mm in length × 22 mm in width × 3 mm in height. The density of 8 of these samples was measured, the relative density with respect to the theoretical density was calculated, and the average value of the relative densities was calculated.

[0057] Table 1 shows a comparison of the relative densities (average) of Example 2 and Comparative Example 2.

[0058]

Table 1

[0059] In Example 1, cracks do not occur even when stress concentrates at the corners of the cavity portion having a rectangular shape in plan view. Also, in Example 2, although the pressure from the vertical pressure axis was smaller than that in Comparative Example 2, a sintered body with a relative density equivalent to that of Comparative Example 2 could be obtained.

[0060] The mold for electric sintering according to this embodiment is a mold for electric sintering having a cavity portion 1 in a rectangular shape in plan view, which is used in an electric sintering apparatus, and includes inner molds 10, 20, 30 made of tungsten or cemented carbide surrounding the cavity portion 1, and an outer mold 40 made of graphite surrounding the inner molds 10, 20, 30. Therefore, even if stress concentrates at the four corners, it can be received by the hard inner molds 10, 20, 30, and cracking can be prevented. Further, if the inner molds 10, 20, 30 are made of tungsten or cemented carbide, the cavity portion 1 is not easily expanded by the pressure in the vertical direction, so that the pressure from the vertical pressure axis can be efficiently transmitted to the sintered body in a rectangular shape in plan view. Further, since the inner mold 10 is a split mold, the manufacture of the inner mold is easy.

[0061] Further, since a rounded portion is provided at a portion corresponding to the corner of the cavity portion 1 of the inner mold 10, the stress applied to the four corners can be dispersed, so that the stress concentration at the four corners can be more effectively dealt with.

[0062] Further, since the electric sintering apparatus according to this embodiment uses the above-described mold for electric sintering, a sintered body in a rectangular shape in plan view can be efficiently pressurized, and the productivity of manufacturing a sintered body in a rectangular shape in plan view can be improved.

[0063] Further, since the method for manufacturing a sintered body according to this embodiment uses the above-described electric sintering apparatus, the durability of the mold is improved, a sintered body in a rectangular shape in plan view can be efficiently pressurized, and the productivity of manufacturing a sintered body in a rectangular shape in plan view can be improved.

[0064] As described above, according to the mold for electric sintering, the electric sintering apparatus using the mold for electric sintering, and the method for manufacturing a sintered body using the electric sintering apparatus according to this embodiment, the durability of the mold is improved, a sintered body in a rectangular shape in plan view can be efficiently pressurized, and the productivity of manufacturing a sintered body in a rectangular shape in plan view can be improved.

[0065] As described above, the mold for electric sintering according to the embodiment of the present invention has been explained. However, the present invention is not limited to the above-described embodiments, and various other modifications are possible.

Explanation of Reference Numerals

[0066] 1 Cavity part 2 Upper punch 3 Lower punch 10 Inner mold 20 Inner mold 30 Inner mold 40 Outer mold 50 Upper and lower mold 100 Mold for electric sintering

Claims

1. An electric sintering mold having a cavity portion in a rectangular shape in plan view, which is used for an electric sintering apparatus, characterized in that it has an inner mold made of tungsten or cemented carbide surrounding the cavity portion and an outer mold made of graphite surrounding the inner mold.

2. The electric sintering mold according to claim 1, wherein the inner mold is a split mold.

3. The electric sintering mold according to claim 1, wherein the inner mold is an integral mold.

4. The electric sintering mold according to claim 1, wherein a rounded portion is provided at a portion corresponding to a corner of the cavity portion of the inner mold.

5. The electric sintering mold according to claim 1, characterized by having upper and lower molds made of tungsten or cemented carbide surrounding the upper and lower portions of the cavity portion.

6. The electric sintering mold according to claim 1, wherein the cavity portion is divided into a plurality of layers by the upper and lower molds.

7. An electric sintering apparatus using the electric sintering mold according to any one of claims 1 to 6.

8. A method for manufacturing a sintered body using the electric sintering apparatus according to claim 7.

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