JPH0313281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a method and apparatus for press-molding cemented carbide powder or ceramic powder for structural materials into a cylindrical shape with (length)/(diameter) larger than 3.

(b) Prior art and its problems In the powder metallurgy method, many improvements have been made in the past regarding the molding of materials with a large ratio of length to equivalent diameter.

There is a method of standing it up in the length direction and molding it. This involves putting powder into a die with a circular hole and compressing it with circular lower and upper punches. This is called the vertical molding method. It is called a vertical type because pressure is applied in the longitudinal direction of the member.

If the ratio of length to equivalent diameter is about 1, a uniform cylindrical molded body can be obtained. However, when the ratio of length to equivalent diameter becomes large, sufficient density cannot be obtained at the center of the length.

Although it depends on the powder material, powders of cemented carbide and ceramics for structural materials have poor fluidity and cannot be made with a length/diameter ratio of 3 or more.

Another method uses hydrostatic pressure. This can be molded into long cylindrical shapes. However, it is inferior to mass production. It is not an economical manufacturing method.

Therefore, in order to make a cylinder with a large length/diameter ratio, horizontal molding as shown in FIG. 1 is performed, followed by grinding to give it a cylindrical shape.

In the horizontal molding method, a lower punch with an elongated pressure surface is inserted into a die with an elongated hole, powder is put into the hole, and then the powder is pressure-molded with an upper punch with an elongated pressure surface. Pressure is applied in a direction transverse to the longitudinal direction of the molded body. That's why it's called horizontal.

What is obtained by the horizontal molding method is typically a bar with a square cross section. If it has a square cross section, it can be molded to a uniform density.

In order to make this into a cylindrical shape, it was necessary to finish the molded body with a square cross section into a cylindrical shape by means of lathes, setterless, etc.

Processing a molded object requires a long time when the amount of processing increases. Also, a large amount of processed waste powder is generated. This was an uneconomical method that was wasteful both in terms of time and materials.

A typical shape obtained by horizontal molding is a bar with a square cross section. This allows for uniform density. However, grinding a square piece into a cylinder is time consuming and results in a lot of material loss. However, until now, cylindrical members have been made by molding a square bar, grinding it into a cylinder, and sintering it.

Therefore, in order to reduce processing time and material loss, attempts were made to create a shape as close to a cylinder as possible by molding.

What is shown in FIG. 2 is an example of a molded body obtained by the horizontal molding method through such an attempt.

4 in FIG. 2 has a shape close to a prism. It is a square column with chamfered corners. This poses no problem in terms of molding technology. Can be molded to uniform density. However, it takes time to grind this into a cylindrical shape.
Expenses increase. The loss of powder material is also large.

5 in FIG. 2 is an improved version of 4. However, this requires a lot of time and cost to process into a cylinder.

6 in FIG. 2 has a further improved shape and has an elliptical shape. However, horizontal molding compresses the material in the vertical direction, resulting in an elliptical shape that is thinner in the vertical direction.
To make this into a cylinder, the outer circumferential surface must be ground over a wide area.

The one shown in FIG. 2 thus had to be ground into a cylindrical shape after molding in any case.

It is desirable to make it into a cylindrical shape all at once by molding a model. But I couldn't do this. I will explain the reason.

In order to form it into a cylindrical shape, we thought that the radius of curvature of the pressing surfaces of the lower and upper punches should be made even smaller than 6 in Figure 2, and the position of the lower punch should be lowered further than in Figure 1. Let's be.

A powder supply device supplies powder of the material to the hole of the die. Conventional powder feeding devices have an opening at the bottom, but no holes on the sides. Therefore, when the powder is fed into the hole of the die, the upper surface of the powder becomes horizontal as shown in FIG. The process of leveling the powder is sometimes called “Masukiri”.

Cemented carbide and ceramics for structural materials must have high density, so powder materials with fine particle sizes of around 1 μm are used.

These materials, compared to ferrite powder etc.
Poor liquidity.

When powder is pressure-molded using a lower punch with an upwardly concave surface and an upper punch with a downwardly concave surface, the powder does not move sufficiently into the center during pressing. This results in a low density in the center.

This should not be. It must be of uniform density throughout. If you try to make the density uniform, the second
It had no choice but to become a flat elliptical cylinder like 6 in the figure.

In other words, as shown in Figure 1, when feeding powder,
Since the upper surface of the powder is a horizontal plane, the amount of powder in the center is insufficient, and it is not possible to form a cylinder even when pressurized with a semicircular punch.

The present invention has been made to further improve FIGS. 4, 5, and 6.

(C) Disclosure of the Invention The present invention was achieved by dramatically changing the way of thinking in order to solve the above-mentioned problems.

In the conventional method, due to the structure of the powder feeding device, the upper surface of the packed powder had to be a horizontal plane, as shown in FIG.

The present invention improves the powder feeding case and the powder feeding case guide rod so that the powder can be fed so as to be raised in a convex shape above the hole of the die.

Since it is raised in a convex shape, when this is pressed down with an upper punch to form a round bar, the density in the central part does not become low.

The main improvements are in the powder feeding case and the powder feeding case guide rod, but since cylindrical objects are molded all at once,
The shapes of the upper and lower punches have also been carefully designed.

The holding surface of the upper punch is a downwardly concave semi-cylindrical surface.

The holding surface of the lower punch is an upwardly concave semi-cylindrical surface.

In other words, the punch has a cylindrical surface when the pressing surfaces of the upper punch and the lower punch are combined.

Further, the value obtained by dividing the lateral length by the diameter of this cylindrical surface is set to be 3 or more.

Furthermore, when the powder is compressed and molded using the upper punch and the lower punch, the value obtained by dividing the vertical diameter by the horizontal diameter of the resulting molded product excluding the ears should exceed 0.7.

The present invention will be explained with reference to FIG.

1 is the upper punch and 2 is the die.

The lower end of the upper punch 1 serves as a pressing surface for pressing the powder material. This is a downwardly concave semi-cylindrical surface. It is not a square cross section, nor a semi-ellipsoid, but a semi-cylindrical surface. In other words, it is a semi-cylindrical surface with a radius of curvature that allows a desired cylinder to be formed only by molding.

Furthermore, the pressing surface of the upper punch 1 is long in the lateral direction.
The value obtained by dividing the length in the lateral direction by the diameter of the semi-cylindrical surface of the holding surface is 3 or more.

The reason why it is 3 or more is as follows.

The vertical molding method explained first can mold a complete cylinder, but it can also mold a cylinder with a ratio of length divided by diameter of about 1. It's difficult to make something like 2.
3 or more is not possible with vertical molding methods.

However, in the horizontal molding method, (length)/(diameter)
Even if the ratio is 3 or more, it can be easily molded. Rather, a larger ratio is more convenient. For this reason, in the present invention, the ratio of the lateral length divided by the diameter is 3 or more.

The die 2 has a hole 11 in the center.

This hole 11 is a space for molding. The length of this hole 11 defines the length of the molded body.

A lower punch 3 and an upper punch 1 are inserted into the hole 11. The inner dimensions of the hole and the outer dimensions of the punches 1 and 3 are approximately equal. Of course, appropriate clearance is required.

7 is a powder supply case for supplying powder to the hole 11 of the die 2.

A powder supply pipe 8 is provided to feed powder into the powder case 7 from a powder storage chamber (not shown) in the upper part.

The amount of powder supplied is controlled within a certain range.

The powder supply case 7 is partitioned at the top and sides by walls,
The bottom is open. There is a powder material inside.

Unlike conventional powder feeding cases, there are
There are semicircular notches 9 and 9' in the powder supply case.

On the die 2 and the table, upwardly convex semi-cylindrical powder feeding case guide rods 10 and 10' are fixed.

The powder feeding case guide rod 10, 10' is divided into two parts having the same cross section. These are provided on the longitudinal extension of the hole 11 of the die.
However, the powder feeding case guide rods 10, 10' are not present directly above the hole 11 of the die. They are on both sides of hole 11.

The radius of curvature of the semicircle of the powder feeding case guide rods 10, 10' is approximately the same as or slightly larger than the radius of curvature of the semicircular cylinder of the holding surface of the upper punch.

The powder feeding case notches 9, 9' fit into the powder feeding case guide rods 10, 10'. Therefore, the radius of curvature of the semicircle of the powder feeding case notches 9, 9' is:
It is slightly larger than the radius of curvature of the semi-cylindrical cylinder of the powder feeding case guide rods 10, 10'.

The powder feeding case 7 has powder feeding case guide rods 10, 10'.
The die 2 reciprocates in the longitudinal direction on the table.

In the above configuration, the operation will be explained.

Insert the lower punch 3 into the hole 11 of the die 2.

The powder feeding case 7 is moved to pass over the hole 11 of the die 2.

The holes 11 are filled with powder. It also rises above the hole 11 in a semicircular shape. This has almost the same shape as the powder feeding case guide rod 10.

FIG. 3 shows this state.

The dotted area is the bulge of powder.

Lower the upper punch 1. The pressing surface at the lower end of this comes into contact with the raised powder. Push the powder up further. In the hole 11 of the die, the powder is strongly compressed by the lower punch 3 and the upper punch 1. In this way, a cylindrical molded body with small ears is produced.

FIG. 4 shows a molded body obtained by the present invention.

After this, the ears are ground and removed. In this way, a perfect cylinder is obtained.

After this, it is further sintered. When molded into a cylinder, the value obtained by dividing the vertical diameter by the horizontal diameter excluding ears was less than 0.7 using the conventional horizontal molding method.

In the present invention, this value can be set to 0.95. Therefore, in the present invention, the value obtained by dividing the lateral diameter by the vertical diameter is set to exceed 0.7.

Examples of the present invention will be described.

The radius of curvature of the semi-cylindrical surfaces of the upper punch 1 and lower punch 3 was set to 4 mm. The length is 50mm. (length)/
(diameter) ratio is 6.25.

The upper end surface of the lower punch 3 was set 4 mm below the upper surface of the hole 11 of the die.

The powder feeding case guide rods 10, 10' have a radius of curvature.
It has a semi-cylindrical shape of 4.15 mm. This is die hole 1
It is installed on the longitudinal extension line of 1.

The powder feeding case notches 9, 9' have a radius of curvature.
It is a 4.2mm semicircle.

Cemented carbide powder was supplied to the powder supply case 7 through the powder supply pipe 8 .

By moving the powder feeding case 7, powder was supplied to the hole 11 of the die 2 so as to rise in a convex shape.

The upper punch 1 was pushed up, and the powder was pressed by the upper and lower presses. The pressure was 4 tons.

The obtained molded body had a shape as shown in FIG.

The cross section is almost a perfect circle, but there are ears at the edges of the punch.

The value of (vertical diameter)/(lateral diameter) of the portion excluding the ears was 0.95.

In conventional horizontal molding, the upper limit of this value is 0.7.

The ears on both sides of the molded body thus formed are removed by grinding. Then, it was sintered using a known method.

Although shrinkage occurs due to sintering, it was confirmed that the above-mentioned diameter ratio did not change within the range of error.

This means that the powder packing density was ideally uniform in the center and periphery of the cross section of the molded body.

Describe the effects.

Cemented carbide powder and ceramic powder for structural materials, which have a particle size of 1 μm or less and have poor flowability, can be formed into a cylindrical shape by horizontal molding.

After molding, it is only necessary to remove the slightly protruding ears. This process does not take much time and can be done in an instant. There is also less generation of powder waste.

This is because the shape after molding is close to a perfect circle. (Vertical diameter) / (lateral diameter) from 0.95 to
This is because it is possible to set it to 1.

In vertical molding, it is almost impossible to produce a material with a (length)/(diameter) ratio of 2 or more, but with the present invention, a material with a ratio of (length)/(diameter) of 3 or more can be easily produced.

The present invention can be used for manufacturing micro drill materials using cemented carbide powder, molding round bar materials, ceramics, etc.

That is, conventionally, it was impossible to mold a long and slender cylinder all at once using these powder materials, but the present invention has made this possible. This is an excellent and useful invention.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the manufacturing process of a round bar by conventional horizontal molding. FIG. 2 is a perspective view showing an example of a rod-shaped molded body made by improved conventional horizontal molding. FIG. 3 is a schematic perspective view of the powder molding apparatus of the present invention. FIG. 4 is a perspective view of a cylindrical molded body made by the apparatus of the present invention. 1... Upper punch, 2... Die, 3... Lower punch, 4, 5, 6... Molded body obtained by conventional method, 7
...Powder feeding case, 8...Powder supply pipe, 9,
9'...Powder feeding case notch, 10,10'...
Powder feeding case guide rod, 11... hole.

Claims (1)

[Claims] 1. A lower punch 3 having an upwardly concave semi-cylindrical surface, an upper punch 1 having a semi-cylindrical surface having approximately the same radius of curvature as the downwardly concave lower punch, and a lower punch. a die 2 having a hole 11 into which the powder material and the lower end of the upper punch 1 are to be inserted; powder feeding case guide rods 10, 10' provided in a straight line on both sides of the hole 11;
The powder feeding case guide rod 10, 1 is concave toward the bottom.
The powder feeding case guide rods 10, 1 have powder feeding case notches 9, 9' with a semicircular cross section slightly larger than 0'.
This is a powder molding device for molding cemented carbide powder or ceramic powder for structural materials into a cylindrical shape. The ratio divided by the diameter of the cylindrical surface of the upper punch and the lower punch is 3 or more, and the diameter in the vertical direction of the cylindrical molded body of powder formed by the upper punch and the lower punch in the hole 11 of the die in the horizontal direction A powder molding device characterized by a value divided by the diameter exceeding 0.7. 2. A lower punch 3 having an upwardly concave semi-cylindrical surface, an upper punch 1 having a semi-cylindrical surface having approximately the same radius of curvature as the downwardly concave lower punch, the upper end of the lower punch 3, and the powder material. and the lower end of the upper punch 1, the die 2 having a hole 11 into which the upper punch 1 and the lower end are inserted, and a die 2 having a convex semicircular cross-section facing on approximately the same radius of curvature as the upper punch, and a die 2 having a convex semicircular cross section on both sides of the hole 11 on the upper surface of the die. powder feeding case guide rods 10, 10' provided in a straight line;
The powder feeding case guide rod 10, 1 is concave toward the bottom.
The powder feeding case guide rods 10, 1 have powder feeding case notches 9, 9' with a semicircular cross section slightly larger than 0'.
By moving the powder feeding case 7 containing cemented carbide powder or ceramic powder for structural materials, the powder feeding case 7 is reciprocated along the axis 0' and has an open bottom surface. This is a powder molding method in which the powder is fed so that it swells into a cylindrical shape, and the powder is pressed down and pressurized by an upper punch to form the powder into a cylindrical shape. The ratio divided by the diameter of the surface is 3 or more, and the value obtained by dividing the vertical diameter by the lateral diameter of the cylindrical powder body formed by the upper and lower punches in the die hole is 0.7. A powder molding method that is characterized by exceeding