JPH0820807A - Method for compacting green compact - Google Patents

Abstract

PURPOSE:To produce parts having complicated shape by a powder compaction die without causing material loss by using an ordinary die. CONSTITUTION:Lower punches 51, 52, fitted to a die 3, are raised to fill a part of powder into a die cavity. A core 1 made of fusible alloy is inserted and the lower punches 51, 52 are lowered by the prescribed distance and prescribed amount of powder is filled into the cavity again, and the powder is compacted by upper punches 61, 62 and the lower punches 51, 52. By regulating the compaction distances of the upper and the lower punches 61, 62, 51, 52, the density in respective parts of the resulting green compact can be uniformized. The green compact is drawn out from the die 3 and the core 1 is removed by heating and melting. Then, the green compact 2 is fed into a sintering furnace and the fusible alloy is used repeatedly as a material for the core 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a green compact, and more particularly to a method for molding a sintered part having an annular groove on its outer circumference.

[0002]

2. Description of the Related Art When powder is compacted by using a metal mold or the like, the shape of the powder compact has a hole in the direction perpendicular to the pressurizing direction, and the outer shape is small because of the convenience of compressing and extracting the powder with the upper and lower punches. If the shape of the drum is convex or the inner diameter is convex, for example, Japanese Patent Publication No.
A movable die is used as described in Japanese Patent No. 2-8551, Powder Metallurgical Technology Association, Powder Metallurgical Technology Course “Molding of Metal Powder” and the like. In the method using this movable die, the molding die is divided into two members which can slide vertically with respect to each other, and a concave or convex shape having a shape corresponding to the convex or concave side surface of the green compact to be molded is provided. The molded green compact is extruded from the die body together with the die member and released.

A molded product such as a V-pulley or a double sprocket that has an annular recess in the outer diameter is divided into two parts which can be molded using a normal mold, and the two parts are fitted together. Manufactured by sintering and metallurgically combining them into a desired shape, or by manufacturing a sintered body having a shape without an annular recess and then cutting the recess. .

On the other hand, a technique for producing a part having an undercut and a molded body having a groove on the entire outer periphery by using a normal die is described in JP-A-2-236203. As described above, a core made of a burnable material having a shape corresponding to the recess is put in a predetermined position in the powder molding die, the molding powder is filled and compressed, and the core buried at the time of sintering is burned off to form the recess. There is a method of modeling. In this case, a method has also been proposed in which the material of the core is a substance that dissolves in a liquid, the material is heated at about 800 ° C., and then the core is dissolved and removed in the liquid.

[0005]

The molding method using the movable die has a problem that the mold structure is complicated and an operation failure is likely to occur during use. According to the cutting process, problems remain in the loss of material and the disposal of chips. On the other hand, in the method of using the core made of the burnable material, the core is burned, so that the core material is consumed and the air may be polluted. In addition, the method of dissolving and removing the core in a liquid requires a large amount of solvent, and there is a problem that processing and recovery of the dissolved solution requires a lot of trouble.

It is an object of the present invention to provide a technique for solving such a problem, and a part having a groove portion on the outer peripheral surface or the inner peripheral surface of a shape which cannot be molded by a normal powder molding die. It was created for the purpose of producing a material using a normal die without material loss.

[0007]

According to the present invention, a die cavity of a powder molding die is filled with a molding powder and a shaped core made of easy fusion metal, and the filling is pressed to obtain a green compact. And a core are formed, and the core of the molded body extracted from the molding die is heated to melt the fusible metal and separate the green compact and the core. A method for molding powder is provided.

[0008] Further, the molten easy-melting alloy is atomized into a powder, which is then compacted into a core shape, or the molten easy-melting alloy is cast to form a core. It is characterized by being recycled and used. As the fusible alloy, a Bi-based, Sn-based, or Pb-based alloy having a melting point of about 250 ° C. or less, as described in “Metal Handbook” edited by the Japan Institute of Metals, may be applied. it can.

Bi-based alloys are Pb 20-31%, Sn8-
34%, Cd 12% or less, In 19% or less, Hg4
%, Or Sb 9% or less, and the most preferable alloy is a wood alloy having a melting point of about 70 ° C. and almost no volume change due to solidification from the molten metal. The composition of the wood alloy is, for example, Pb24% -Sn14% -Cd12% -B.
i is the rest.

Sn-based alloys include, for example, Pb 38% or T
Examples of the alloy containing 144% Pb-based alloy include a solder containing Sn and an alloy containing about 10% Sb. The fusible alloy preferably has a low melting point and appropriate hardness and rigidity. The molded core made of easy fusion metal is placed at a predetermined position where a part of it is in contact with the molding die surface and is exposed on the surface of the molded body, so when heated and the core melts, it flows out from the green compact. Then, a molded body in which the portion becomes a shell is obtained.

The fusible alloy melted and flowed out is collected in a container equipped with a heater and stored in a molten state. This molten metal is poured into a predetermined core-shaped mold to remove burrs and the like, and then supplied to powder molding. For casting, die casting is preferable because of its high finishing accuracy. In addition, the easy fusion gold melt is
It can be used by supplying it to a gas atomizer with nitrogen or the like to form a powder, and compacting into a core shape in the same manner as usual powder compacting.

[0012]

Since the core is a low melting point alloy, it can be melted and removed with a small amount of heat energy, and the core material can be reused repeatedly with little loss. Resource saving and less pollution. In the molding method of the present invention, since the core of the easy fusion metal is embedded or fitted in the green compact and pressure molding is performed, and the core is heated, melted and separated, there is no restriction on the core and the shape of the molded body. The degree of freedom is improved.

By using a rigid alloy for the core, it is possible to obtain a near-net-shape green compact, which is less deformed during compression of the compacted powder. On the other hand, it is possible to obtain a near net shape green compact by utilizing the plastic deformation of the core during compression using an alloy having low rigidity. Further, when the present invention is applied to a long pipe-shaped molded product and powder is pressed from a direction perpendicular to the axis, a molded product having a uniform partial density can be obtained.

The core may be melted by heating at least the core, and depending on the shape, the entire compact may be heated.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings of the embodiments. Each drawing is shown in a vertical cross section when the compression is completed. FIG. 1 relates to a method for obtaining a molded product having a shape like a double sprocket. Lower punches 51 and 52 on the die 3,
The upper punches 61 and 62 and the core 4 are mounted as in the conventional case. First, the lower punches 51, 52 are raised to fill a part of the powder into the die cavity, and then the core 1 made of easy fusion metal shaped into a predetermined shape is inserted, and the lower punches 51, 52 are lowered by a predetermined distance. Then, a predetermined amount of powder is filled again. Then, the powder is compressed by the upper and lower punches. At this time, the density of each part of the green compact can be made uniform by adjusting the compression distance of the pair of upper and lower punches. FIG.
As described above, the inner diameter of the core 1 can be eccentric. Further, the end surface of the core 1 can be a ratchet. After the molded body is extracted from the die, it is heated at a temperature at which the easy fusion metal (core 1) melts. The entire compact may be heated, but when the mass of the green compact 2 is large, the amount of heat may be small by blowing hot air or a burner flame onto the core 1 to melt it. The green compact 2 from which the core 1 has melted has an annular groove formed on the outer periphery thereof and is sent into the sintering furnace. The melted fusion gold is
It is collected in a heat retaining container with a heater provided below the heating section.

FIG. 8 is a process chart for explaining the molding cycle. After compacting, the melt of the fusible alloy taken out by melting and removing the core is pulverized by gas atomization etc. as shown by the solid line, and then the core is produced by core compaction using a powder molding die. Alternatively, as shown by a dotted line, there is a method in which the molten metal is directly pumped into a mold to produce a core by casting core molding. Synchronizing core molding and powder compacting can minimize the amount of fusible alloy.

FIG. 2 relates to a method for obtaining a powder compact 2 having an hourglass-shaped outer shape by utilizing the plastic deformation of the core 1. The mold structure is the same as the conventional one. The cylindrical core 1 is mounted in the cavity of the die 3 and the inner hole of the core 1 is filled with powder. When the upper and lower punches 51 and 61 compress the whole of the core 1 including the ends thereof, the inner hole of the core 1 is deformed and the powder is compressed, so that the green compact 2 is formed into a drum shape. The shape in which the core 1 is plastically deformed can be adjusted by the hardness of the core 1 and the pressing speed. The melting and removal of the core 1 is the same as that described with reference to FIG.

FIG. 3 relates to a method for obtaining a molded body in which the end face of the green compact 2 has arcuate irregularities inclined with respect to the pressing direction.
After filling the cavity of the die 3 similar to that in FIG. 2 with a predetermined amount of powder, the core 1 having irregularities is covered on the powder and compressed by the upper and lower punches 51 and 61. The powder is pressure-fed to the concave portion of the core 1 to form irregularities. In this case, the core 1 serves as a removable upper punch 61. The melting removal of the core 1 is the same.

FIG. 4 relates to a method for obtaining a bottle-shaped green compact 2. The upper and lower punches 5 to obtain a green compact with a uniform density.
1, 52, 53, 61, 62 are divided into concentric circles so that the compression ratio of the powder can be changed. The lower punch 53 is slightly lowered, the small diameter portion of the core 1 is inserted into the inner hole of the lower punch 52, and the powder is filled in the cavity of the die 3. Then, the punches 51, 52, 53, 61 and 62 are compressed by a predetermined amount so that the powder is uniformly compressed around the core 1. The melting removal of the core 1 is the same as described above.

FIG. 5 shows an example of compaction molding of a lightweight gear, which relates to a method of forming a cavity in the compacted powder 2 as in the example of FIG. The lower punches 51 and 52 are divided into two in order to increase the external tooth density. After raising the lower punches 51 and 52 to fill a part of the powder, the core 1 is placed on the powder,
After lowering the lower punch 61, powder is filled and compressed so as to cover the core 1. The thin portion of the inner diameter of the core 1 is the molten metal outlet, which may be continuous in the circumferential direction or about three protrusions.

FIG. 6 relates to a method of shaping the outer shape of the green compact 2 by using the inner diameter of the core 1 instead of the die 3. The lower punch 51 is a punch for supporting and withdrawing the core 1.
The dusting is performed by the lower punch 52 and the upper punch 61 that fit with the inner diameter of the core 1. First, the core 1 is fitted and fitted to the die 3 and the lower punch 51, a predetermined amount of powder is filled in the inner hole of the core 1, and only the powder is compressed by the upper and lower punches. The core 1 and the green compact 2 are extracted from the die 3 together by the pair of lower punches 51 and 52. If the plastic deformation of the core 1 is utilized, the crowning gear can be compacted.

FIG. 7 shows an example of molding the long pipe-shaped green compact 2. First, the lower punch 51 is raised to fill half the required amount of powder, and then the core 1 is placed on the powder, and the core 1 is slightly pushed into the powder so that the core 1 comes to the center of the powder compact,
Next, the lower punch 51 is lowered by a predetermined amount to fill the remaining half of the powder and press the powder. In ordinary compression molding, since the upper and lower punches compress from both ends of the pipe shape, the density of the middle part of the pipe-shaped green compact becomes low, and when the pipe is curved in the conventional molding method, I can not mold,
According to the method shown in FIG. 7, since the interval between the upper and lower punches is narrow and the pressure is well propagated to the powder, it is possible to uniformly form the powder with a high density.

[0023]

As described above, according to the powder compacting method of the present invention, the core of the easy fusion metal is buried or fitted in the powder compact and is melted by heating, so that the shape of the compact can be freely set. The degree is improved, and a green compact of near net shape can be obtained. Since the core is a low melting point fusible alloy, it can be melted and removed with a small amount of heat energy, and since the core material can be repeatedly used with little loss, it is possible to obtain the effects of resource saving and less air pollution.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating molding of a green compact having an annular groove on its outer diameter.

FIG. 2 is a cross-sectional view for explaining molding of a green compact having an hourglass-shaped outer diameter.

FIG. 3 is a cross-sectional view for explaining the molding of a green compact having an inclined top and bottom ridge.

FIG. 4 is a cross-sectional view illustrating molding of a bottle-shaped green compact.

FIG. 5 is a cross-sectional view illustrating molding of a green compact of a hollow gear.

FIG. 6 is a cross-sectional view illustrating molding of a green compact having a die formed of a core.

FIG. 7 is a cross-sectional view illustrating molding of a long pipe-shaped green compact.

FIG. 8 is a diagram showing a dusting process cycle of the invention.

[Explanation of symbols]

 1 core 2 powder compact 3 die 4 core 51, 52, 53 lower punch 61, 62 upper punch

Claims (3)

[Claims] 1. A die cavity of a powder molding die is filled with a molding powder and a molded core made of easy fusion metal,
The filling is pressed to form a molded body composed of a green compact and a core, and the core of the molded body extracted from the molding die is heated to melt the fusible metal, and the green compact and the core. A method for molding a green compact, characterized in that 2. The method for molding a green compact according to claim 1, wherein the melt of the fusible alloy separated from the green compact is atomized into a powder, and then the powder is compacted to form a core. . 3. The method for molding a green compact according to claim 1, wherein the core is formed by casting a melt of the fusible alloy separated from the green compact into a mold.