JPH0530558B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for making compression molded articles from granular materials;
Regarding equipment and compression molded products.

The production of shaped articles using metal or ceramic powders or compacted metal powder lumps has been carried out by sintering or compaction methods, including hot pressing or hot isostatic pressing. This sintering method has the disadvantage of requiring high temperatures to improve the sintering effect. As a result, the resulting product typically exhibits a large grain size structure that inhibits the development of maximum strength in the product. As an alternative to hot compression or hot isostatic compression, the batch method has been proposed for certain limited products.
The cost will be high. The hot compression method requires that each mold be individually compressed by mechanical means under a vacuum or an inert gas atmosphere. The mechanical compression method provides only uniaxial force due to the directionality of the mechanical press. In the latter case, ie, hot isopressing, some cost savings are possible. The reason is that atmospheric pressure is used. There is also a multi-axial compression method, which uses the accumulation of gas pressure at high temperatures before the pressurization operation.
Requires extra expense to encapsulate the powder compact in a degassed metal can. Also, the molded parts must be removed mechanically or by acid etching, which are expensive and time consuming methods.

The present invention relates to a method and apparatus for making compression molded articles from granular materials, as well as to the molded articles themselves. This invention relates to a method, device, and compression molded product that utilizes the generated compression force. The temperature can be varied over a range sufficient to obtain the desired powder compact.

Ductile metallic materials with high thermal expansion are used to compact particulate materials or compression molded bodies (hereinafter sometimes referred to as compacts). The mold itself surrounds this ductile metal material, and by restraining the volumetric expansion of the ductile metal material in directions other than the direction of compaction, the volumetric expansion of the ductile metal material is converted into a compressive force three times as much. It is configured so that it can be added to a compact space.

The mold consists of a metal object structure made of a material with relatively low thermal expansion, in which a cavity is formed, a part of which has a female mold part for the molded part, and in which part of the cavity is formed a cavity. The compact is loaded. A ductile material is disposed on at least one side of the powder, the ductile metal material having a thermal expansion significantly greater than that of the mold material, and having a volume at a temperature below the sintering temperature of the compact. The compact is of sufficient volume so that, by its volumetric expansion, a compression force is applied onto the compact to produce the desired compression molded article. The degree of compression is controlled by the volume ratio of the ductile metal material to the compact, and this ratio can be extremely large.

According to the method of molding metal powder using the volumetric expansion effect according to the method of the present invention, it is possible to produce a high-density molded product, for example, at a low temperature of 100 to 200°C or less, which is the temperature required for sintering the powder. It has the advantage of being able to produce products with a density close to 100% of the theoretical value at lower temperatures. Since sintering methods typically use high temperatures that promote grain size growth, the availability of such low temperatures avoids the risk of grain size growth caused by sinter compression methods.

Furthermore, the molding method of the present invention eliminates the need for electrical-mechanical external contacts required for pressing and the need for environmental control required in hot compression or hot isostatic compression methods, thereby reducing operating costs. It's going to be cheap.

Since the mold equipment can be reused, there is no need to invest in mold equipment for each molded product, which is required in the isobaric compression method, resulting in cost savings.

Finally, in thermal expansion molding, the compressive force applied can be easily controlled along the axis by appropriately aligning the molds and adjusting the position of the high-expandable metal material surrounding the powder compact. There are advantages.

Hereinafter, each example of the present invention will be described in detail according to the accompanying drawings to further clarify the above-mentioned features of the present invention.

The present invention takes advantage of differences in volumetric expansion between materials with different thermal expansion properties. These materials form an integral part of a mold for making compression molded articles from powder compacts. This body expansion effect amplifies the compressive force by up to three times the linear expansion effect.

An overview of the invention is illustrated in FIG. 1, in which a mold 10 includes a cavity 12 partially filled with a compressed powder compact 14 into which the final product is to be formed by compression molding. There is. The remainder of cavity 12 is filled with a metal material 16 having relatively high thermal expansion. Plug 17 then seals the opposite end of the cavity and the entire cavity is filled with either compact 14 or thermally expandable metal material 16. Mold 10 is made from a low thermal expansion material with high yield strength, while thermally expandable metal material 16 is made from a material with high thermal expansion and relatively low yield strength (particularly at the compression temperatures employed). .

A combination of metal materials that satisfies this condition is when the mold 10 is made of molybdenum and the expandable material 16 is made of copper.

As shown in the process flow chart of FIG.
In the initial charging step 30, one batch of powder compact 14 is charged into the cavity 12.
A thermally expandable metal material 16 is additionally charged into the mold 10, and the mold 10 is sealed in step 32. After the charging is completed, the tightened mold 10 is subjected to a thermal action such as high-temperature heating in step 34, so that the thermally expandable metal material (element 16) becomes relative to other elements of the mold. As a result, a compressive force is generated within the cavity space 12 to form the desired compression molded article. This high temperature is maintained for a predetermined period of time until the thermal cycle is completed, as shown in step 36, and then step 3
At step 8, the molded product is cooled and taken out.

In the method of the present invention, the compression effect can be increased three times by using a thermally expandable metal material 16 that expands in all directions, ie, in three orthogonal axes. In FIG. 1, for example, the difference in thermal expansion between the mold 10 and the element 16 is expressed as "a" per unit length.
shall be. In this case, element 16 is line 18
It should expand linearly by al. In FIG. 1, l is the horizontal distance. Also, the element 16 has a thickness
It should expand by aw. However, w is the thickness of the element 16 assuming that the cross section is square. Expansion in the thickness direction is here prevented by the structure of the mold, so that the element 16 is elastically and /or deform plastically.

Looking at this expansion from the perspective of volume effect, expansion in the l direction results in a volumetric expansion equal to al times the end area W ² .
The volume will increase by alw ² . As the thickness in each direction expands, a volume corresponding to aw times the lateral area wl is added, resulting in expansion by awlw, that is, alw ² . Therefore, the total expanded volume is 3alw ² ,
That is, it is three times the linear expansion, and this amount of expansion is entirely used to compress the compact 14 due to the plastic flow of the element 16.

Thermally expandable metal material 16 is sized relative to compact 14 in volume such that compact 14 can be compressed as desired at elevated temperatures. Therefore, to achieve the desired compression,
There is a trade-off between the volume of expandable metal material 16 and the degree of temperature rise. So step 34
The actual temperature at which the metal powder is heated and maintained in steps 36 and 36 can be determined by the user depending on the desired physical properties of the compression molded article. For example, when using samarium-cobalt powder, which represents a useful compact characterized by rare earth/transition metal combinations, the compacting temperature can be maintained well below the temperature at which sintering effects occur. Therefore, the particle size is small and the strength of the final product is improved. Ceramics can also be compression molded under such temperature control. For example, if the particulate material is samarium-cobalt, a temperature selected from the range of about 750-1050°C, which is below the sintering temperature of samarium-cobalt, is typically used. The fifth part will be discussed later.
In the case of Figures 1 to 8, the actual heating temperature was approximately 950°C.

If the particulate material is a low melting point material such as lead or plastic, the sintering can be carried out at a temperature below their sintering temperature, and moreover at a low temperature of about 100 to 200°C.

Therefore, although the heating temperature varies depending on the particulate material,
A temperature below the sintering temperature of the particulate material is used. By using a temperature below the sintering temperature of the granular material, a high-density compression molded product can be obtained economically with a simple device.

In the above example, the low expansion elements making up the mold 10 are made from molybdenum and the high expansion elements 16 are made from copper. High thermal expansion elements, such as copper element 16, exhibit fluidity at relatively low temperatures, whereas mold 10 has a much lower relative thermal expansion and little or much less flow at molding temperatures. The use of many other materials is also possible within the scope of the rule.

Molds designed for powder compaction according to the present invention can be utilized for uniaxial or multiaxial compression methods.
Figures 3 to 5 and Figure 8 are for a single axis, Figures 6 and 7.
The figure illustrates a mold for multiaxial compression. Third
The mold is shown disposed inside a low thermal expansion cylinder 50 which holds the powdered material to be molded and has a space 54 suitable for producing the desired molded article.
is restrained. Top plate 56 and bottom plate 58 are secured to projections 6 on plates 56 and 58 by bolts 60 and 62.
4 and 66 can be fixed at positions facing the powder material space 54. bolts 60 and 62
and cylinder 50 is typically made of a low thermal expansion material such as molybdenum, while end plates 56 and 58, particularly projections 64 and 66, are
It is made from a material with high thermal expansion, such as copper. The compact facing portions of cylinder 50 and projections 64 and 66 can be shaped to match the desired surface shape of the final molded article.

In this and other molds, molybdenum foil or the like may be inserted between the compact and the copper to avoid chemical reactions between the materials, if desired. When the mold and molded product are cooled after compression, they mutually contract and can be easily separated.

FIG. 4 shows a variant of the mold, which includes a mold block 70 having a cavity 72;
The lower portion of the cavity 72 is bounded by a space 74 which contains the final molded powder compact. After inserting the plunger 78 into the cavity 72 and positioning it between the screw cap 76 and the space 74, the block 70 at the top connects the screw cap 76.
It is sealed with.

Typically, mold block 70 and threaded cap 76 are both made from a low thermal expansion material such as molybdenum, while thermally expansive plunger 78 is made from a high coefficient of thermal expansion metallic material.

Since the block 70 forms a lateral support for the plunger 78, the plastic deformation of the copper plunger 78 further converts the lateral expansion into additional linear expansion, creating a uniaxial force on the space 74. Amplify.

FIG. 5 shows a modification of FIG. 4, in which the mold block 80 includes an elongated cavity 82, and the compacting space 84 within the cavity is separated by a compacting space 84 on the sides of the block 80 and on both the top and bottom slugs ( It is comprised between 86 and 88 (generic term for small metal materials). Above the top slug 86 is an extension plunger 9.
0 is placed and the plunger has another slug 92
and a mold screw cap 94. Typically, mold block 80,
Slugs 86, 88 and cap 91 are made of a low thermal expansion material such as molybdenum, and thermal expansion plunger 90 is made of copper. However, these slugs may also be made from high thermal expansion materials. The slug 8 is inserted between the space 84 and the plunger 90.
By partitioning with 6, 88, and 92, chemical reaction between the compact and the copper plunger can be avoided. Opening 94 is used to vent the contents during heating of the mold.

FIGS. 6 and 7 are examples of the present invention for applying multiaxial compression on a compact using the volumetric expansion effect. As shown in FIG. 6, the mold block 100
are made from low thermal expansion, high strength materials such as molybdenum. The mold base is provided with a molybdenum slug 102 which provides a strong removable base for the compact 104 surrounded by a copper annular collar 106. A further molybdenum slug 108 is placed over the compact 104 and collar 106 to define the top surface for the compact 104.
will be placed. A copper plunger 110 is placed on top of the slug 108, and the plunger is connected to the mold 1.
00 by suitable means as described above.

During compression, when the mold and contents are heated to the desired temperature, plunger 110 not only expands downward compressing both compact 104 and collar 106 with a three-fold volume effect, but also causes collar 106 itself to become tertiary. Although it originally expands, the slag 102, 108
and the constraint between the mold 100 forces its expansion radially inward and toward the compact 104. In this way, vertical and radial compressive forces will be applied to the compact 104. The flow characteristics of the copper collar 106 are utilized to convert the downward pressure of the plunger 110 into both downward and radial compressive forces applied to the compact 104. The additional thermal expansion provided by copper collar 106 will exert additional compressive force on compact 104. FIG. 7 shows a variation of the mold of FIG. 6 in which the two copper blocks 112 and 114 are shaped to fit within the cavity of the mold 100 and have opposing faces for receiving the compact 104. An opening is provided at the top. The upper copper block 114 is further molded with molybdenum or other material as needed.
held vertically within. Blocks 112 and 114
Thermal expansion is concentrated in the compact 104 in this example as well. Since the volume ratio of copper blocks 112 and 114 and compact 104 is extremely large, compact 1
The compressive force on 04 is amplified. compact 10
Copper blocks 112 and 11 exert a compression force that exceeds the desired/or achievable compression force on copper blocks 112 and
It may also be desirable in practice to generate an expansion of 4 and perform compression onto the compact 104. In this case, the degree of compression can be adjusted by utilizing the flow characteristics of the copper blocks 112 and 114 to cause the copper to flow through the openings 94 for inserting each element into the mold 100. This self-regulating effect also uses a slug made from a special material with a known flow point in terms of temperature and/or pressure, thereby creating well-defined compression limits for the compact to be compacted. You can achieve it even if you let it.

FIG. 8 shows another example in which the present invention is used for compression by volumetric expansion. In this case, the mold 120 has a compact 12 in its cavity.
2 is surrounded by a collar 124 made of the same low-expansion, high-strength material as the mold 120. Immediately above the compact 122 and the collar 124 is a high thermal expansion laminar disk 126 on which is placed a suppressor 128 of a low expansion material.
Although this high-expansion disk 126 is quite thin, its total volume increases with lateral expansion, so that the volume ratio between the disk 126 and the compact 122 remains sufficiently high. Because the disk 126 has flow characteristics at operating temperatures and operating pressures, its volumetric expansion can cause it to be directed downwardly relative to the compact 122 within the central opening of the collar 124.

As mentioned above, some type of foil is used to separate the elements of the mold cavity from each other to avoid chemical reactions with each other, and also to facilitate separation of the mold elements after the hot compression process. You can also use It is also possible to use different metal materials other than those exemplified as high-expansion and low-expansion materials. In this regard, even low-expansion materials may be able to be used as mold materials to some extent, as long as they are sufficiently thick and do not crack or become misaligned. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the apparatus according to the present invention, FIG. 2 is a flowchart of the compression molded product forming process according to the present invention, and FIG.
8 are cross-sectional views of various typical molds for utilizing the effective volumetric expansion effect in the method of forming a compression molded article according to the present invention. 10,100,120...Mold, 12,72,
82... Cavity, 14, 54, 104, 12
2...compact, 16...thermally expandable material, 50
...Cylinder, 56...Top plate, 58...
...lower plate, 60, 62...bolt, 64,
66... Protrusion, 70, 80, 100, 120...
... Mold block, 76, 94 ... Screw-in cap, 78, 90, 110 ... Plunger, 8
6,88,102,108...slag, 94...
Opening, 106... annular collar, 124... collar, 126... disc, 128... suppressor.

Claims (1)

[Claims] 1. A method of compression molding a volume of granular material to form a high-density compression molded article, comprising: at least one thermally expandable non-hollow metal element made of a material having high thermal expansion properties; When a particulate material is enclosed in a mold cavity having a thermal expansion characteristic lower than that of the metal element and heated to a temperature below the sintering temperature of the particulate material, thermal expansion of the metal element other than toward the particulate material occurs. 1. A method for producing a compression-molded article, comprising compressing the granular material by restraining the granular material so that an amplified compressive force acts on the granular material. 2. The method according to claim 1, wherein the granular material includes a mixture of rare earth metal powder and transition metal powder. 3. Claim 2, wherein the granular material includes samarium powder and cobalt powder.
The method described in section. 4. A high thermal expansion solid non-hollow material having a coefficient of thermal expansion and ductility greater than those of the mold material, the step of applying a compressive force to the granular material includes the step of heating the metal element and the granular material; 2. The method of claim 1, including the step of employing a metal element. 5. The method according to claim 1, wherein the granular material is compression-molded to form a high-density compression-molded product by the following steps: (a) encapsulating the granular material in the mold cavity; (b) the metal element. (c) When heated to a temperature below the sintering temperature of the granular material, the thermal expansion of the metal element other than toward the granular material is restrained, so that the amplified (d) maintaining the temperature for a predetermined period of time to produce a compression molded article. 6. The method according to claim 5, wherein the particulate material is a metal powder. 7. The method according to claim 5, wherein the particulate material is ceramic powder. 8. The method according to claim 5, wherein the temperature of 200° C. or less is below the sintering temperature of the particulate material. 9 Claim 5 in which the compression is uniaxial compression
The method described in section. 10. The method of claim 5, wherein the metal element includes a high thermal expansion collar surrounding the cavity as a means for creating a multiaxial compressive force on the cavity. 11 The process for limiting the compressive force on the particulate material includes the step of compressing the particulate material using a material that plastically flows under preset compression conditions. The method described in Section 5. 12. An apparatus for compression molding a volume of particulate material to form a high-density compression molded article, the particulate material being combined with at least one thermally expandable non-hollow metal element made of a material having high thermal expansion properties. a mold having a thermal expansion characteristic lower than that of the metal element having a cavity for enclosing the particulate material; means for heating the particulate material to a temperature below the sintering temperature of the particulate material; An apparatus for producing a compression molded article, comprising means for restricting thermal expansion of the metal element other than toward the granular material so that an amplified compressive force acts on the granular material. 13 The ductility of the metal element is greater than that of the mold at the temperature
Apparatus described in section. 14. The apparatus of claim 12, wherein the metal element includes copper and the mold includes a molybdenum body surrounding the cavity and the metal element. 15 A patent claim in which either a disc or a foil is inserted between the metal element in the mold and other materials in the cavity as a means of preventing the risk of chemical reactions with other materials in the cavity. The device according to item 12. 16. The apparatus of claim 12, wherein the mold is made of molybdenum and the metal element is made of copper. 17. A patent claim comprising a low thermal expansion collar surrounding the cavity as a means for facilitating plastic flow of the metal element into the cavity to generate a uniaxial compressive force on the granular material. The device according to scope item 12. 18. The device according to claim 17, further comprising a disk or foil inserted between the metal element and the cavity. 19. The apparatus of claim 12, wherein said metal element includes a high thermal expansion collar surrounding said cavity as a means for creating a multiaxial compressive force on said cavity.