JP7578508B2 - Manufacturing method of molded body - Google Patents

Description

The present invention relates to a method for forming a compact from powder using a molding die.

In recent years, there has been an increasing need for products with excellent functionality, such as ceramics and carbide. For example, powder press molding, which allows for mass production, is often used to manufacture chip products for cutting tools. In powder press molding, a molding die consisting of a die and a punch is used, and the punch is inserted into a die filled with raw material powder to pressurize the raw material powder to produce a cylindrical, cylindrical, rectangular, or other shaped body. The shaped body is then sintered to produce a blank, and the blank's outer shape is then processed into the final product shape to manufacture the product. In products manufactured by powder press molding, if there are parts with uneven density inside the shaped body, there is a risk of increased dimensional variation in the blank's outer shape and damage occurring during processing of the blank. Dimensional variation in the blank's outer shape leads to an increase in the amount of processing in the subsequent processing steps and an increase in internal defects in the blank.

In powder press molding, in order to obtain high-precision blanks, molding is sometimes performed using a CNC powder molding machine that can precisely control the punch with a servo motor. However, even when molding is performed using this method, the powder around the punch inserted into the die tends to have a higher density than other areas due to friction with the die wall, resulting in differences in density distribution inside the compact. In particular, cylindrical and rectangular compacts are prone to uneven density distribution during molding, as powder movement within the die is less likely to occur during molding.

In order to eliminate such differences in density distribution inside the compact, various methods have been devised, such as a two-sided molding method in which a load is applied to the powder from above and below using an upper punch and a lower punch, and a withdrawal process method in which the punch is driven and the die is moved in the same direction as the punch to form the compact.
Patent Document 1 proposes a two-stage pressing method in which a first punch is moved first and then a second punch is moved during powder press molding, and discloses an example in which molding is performed by setting the movement amount of the first punch (upper punch) to 1 to 5 times the movement amount of the second punch (lower punch). Patent Document 2 also proposes a molding method in which a die is tapered.

JP 2003-272942 A JP 2001-3104 A

For example, in the molding method described in Patent Document 1, the movement amount of the first punch and the second punch are made different, so the movement amount of the raw material powder in the process of moving each punch is different, and the punch with the larger movement amount causes a large density variation, and it is not possible to fully eliminate the quality degradation due to dimensional variation and density unevenness in the blank sintered into the molded body. Also, even with the molding method described in Patent Document 2, although it is expected that the unevenness of the density distribution inside the molded body can be reduced by reducing the pressure applied to the molded body, it cannot be said to be sufficient. In consideration of the above problems, the present invention provides a manufacturing method for a molded body for manufacturing a molded body with a small difference in density distribution inside the molded body.

A method for manufacturing a molded body, comprising the steps of: filling a space formed by a through hole provided in a die and a first punch inserted into the through hole with raw material powder; inserting a second punch into the through hole so as to face the first punch; and relatively moving the first punch and the second punch to compress and mold the raw material powder, the method comprising the steps of: a first pressurizing step of moving the second punch a first predetermined amount toward the first punch from a position where the second punch contacts the raw material powder;
a second pressing step of moving the first punch toward the second punch by a second predetermined amount;
and a third pressurizing step of moving the second punch toward the first punch by a third predetermined amount, wherein the first pressurizing step, the second pressurizing step, and the third pressurizing step are carried out in sequence.
Furthermore, the second predetermined amount is equal to the sum of the first predetermined amount and the third predetermined amount in the method for producing a molded body.
Furthermore, the third predetermined amount is smaller than the second predetermined amount in the method for producing a molded article.

According to the present invention, it is possible to reduce the density distribution inside the molded body, and obtain a high-quality product with little dimensional variation and internal defects after sintering the molded body.

1A to 1C are diagrams for explaining an embodiment of the method for producing a molded body of the present invention. FIG. 2 is a diagram for explaining a method for manufacturing a molded body of Comparative Example 1. FIG. 13 is a diagram for explaining a method for producing a molded body of Comparative Example 3. FIG. 1 is a photograph of a pinhole formation state in a cross section of a blank in Example 1. FIG. 13 is a photograph of a pinhole formation state in a cross section of a blank in Comparative Example 2. FIG. 13 is a photograph of a pinhole formation state in a cross section of a blank in Comparative Example 3.

The method for manufacturing a molded body of the present invention is a method for manufacturing a molded body in which raw material powder is filled into a space formed by a through hole provided in a die and a first punch inserted into the through hole, a second punch is inserted into the through hole so as to face the first punch, and the first punch and the second punch are moved relatively to compress the raw material powder, in which the second punch is moved to compress the raw material powder, the first punch is then moved to compress the raw material powder, and then the second punch is moved to compress the raw material powder to produce a molded body.

Figure 1 is a diagram for explaining an embodiment of a method for manufacturing a molded body of the present invention. In this embodiment, the present invention will be explained using an example of a method for manufacturing a cylindrical molded body. The molded body is manufactured by a powder molding press equipped with a cylindrical die 3 with a through hole 3a, and a die having a cylindrical lower punch 1 and upper punch 2 inserted into the through hole 3a of the die 3. The lower punch 1 and upper punch 2 are inserted into the through hole 3a of the die 3, and each can move independently on the axis of the through hole 3a.

[Raw material powder filling process: Figure 1 (a)]
First, the lower punch 1 is inserted into one open end of the through hole 3a, and raw material powder 4 of the compact is supplied into the recess of the die 3 formed by the bottom surface of the lower punch 1 and the inner wall surface of the through hole 3a of the die 3.

[First pressurizing step: FIG. 1(b)]
Next, the upper punch 2 is inserted from the other open end of the through hole 3a, and the upper punch 2 is moved toward the lower punch 1 to pressurize and compress the raw material powder 4. At this time, the positions of the die 3 and the lower punch 1 are fixed, and the upper punch 2 moves a preset distance A from the position where it contacts the raw material powder 4 toward the lower punch 1. This process mainly moves the raw material powder 4 on the upper punch 2 side, and the raw material powder 4 is partially compressed due to friction with the inner wall surface of the through hole 3a, causing an increase in density in the vicinity of the upper punch 2. Note that there is no significant movement of the raw material powder 4 around the lower punch 1, so no significant increase in density occurs, and the density of the entire raw material powder 4 is in a non-uniform state.

[Second pressurizing step: FIG. 1(c)]
Next, with the die 3 and upper punch 2 held in fixed positions, the lower punch 1 is moved toward the upper punch 2 by a preset distance a to pressurize and compress the raw material powder 4. This process mainly moves the raw material powder 4 on the lower punch 1 side, causing an increase in density near the lower punch 1. At this time, the raw material powder 4 is in a state compressed to some extent by the first pressurizing process, and a larger increase in density occurs around the lower punch 1 than the increase in density around the upper punch 2 in the first pressurizing process. The amount of movement of the lower punch 1 in this process (predetermined distance a) is set to be larger than the amount of movement of the upper punch 2 in the first pressurizing process (predetermined distance A).

[Third pressurizing step: FIG. 1(d)]
Next, with the die 3 and the lower punch 1 held in fixed positions, the upper punch 2 is moved a preset distance α toward the lower punch 1 to pressurize and compress the raw material powder. After the second pressurizing step is completed, the density around the lower punch 1 is greater than that around the upper punch 2, but by carrying out this step, the density around the upper punch 2 increases.

In this way, by sequentially applying pressure from the upper punch 2 (first pressure application process), pressure from the lower punch 1 (second pressure application process), and pressure from the upper punch 2 (third pressure application process), movement (rearrangement) of the raw material powder 4 in the center of the recess of the die 3 is more likely to occur compared to when pressure from the upper punch 2 and pressure from below are applied simultaneously or separately once, and the compression of the raw material powder 4 can be promoted evenly, making it possible to reduce the difference in density distribution inside the compact 10.

The amount of movement of the upper punch 2 in the third pressurizing step (predetermined distance α) is preferably set to be smaller than the amount of movement of the upper punch 2 in the first pressurizing step (predetermined distance A) and the amount of movement in the second pressurizing step (predetermined distance a), and the sum of the amount of movement of the upper punch 2 in the first pressurizing step and the third pressurizing step (predetermined distance A + predetermined distance α) is set to be equal to the amount of movement of the lower punch 1 in the second processing step (predetermined distance a). In other words, by making the amount of movement of the upper punch 2 and the amount of movement of the lower punch 1 throughout each step equal, it is possible to manufacture a molded body 10 with a more uniform density.

[Discharge step: FIG. 1(e)]
Finally, the upper punch 2 and the lower punch 1 are moved to the other open end of the through hole 3a of the die 3, and the green compact 10 made of the raw material powder 4 compressed and molded in the through hole 3a is discharged from the die 3. In this manner, the green compact 10 made of the raw material powder 4 is completed. The green compact 10 is then sintered to form a blank, and the outer shape of the blank is polished to form a product with the desired outer diameter.

Next, the results of verifying the state of each of the molded bodies will be described using a blank (Example) sintered from a molded body manufactured by the molded body manufacturing method of the present invention and a blank (Comparative Example) sintered from a molded body manufactured by another manufacturing method not adopting the present invention. Here, the examples and comparative examples will be described using the symbols described in the above embodiment. In both the examples and comparative examples, a carbide die 3 with a through hole 3a of 1.2 mm in diameter, a carbide lower punch 1, and a carbide upper punch 2 were used as a molding die for manufacturing the molded body 10, and alumina powder to which a molding binder was added as the raw material powder 4 was powder press molded to manufacture the molded body 10. The molded body 10 was created with an outer shape of 1.2 mm in diameter and 1.2 mm in height. In both the examples and comparative examples, the molding conditions, sintering conditions, etc. not described in the steps described below were all the same,
The condition of the molded body 10 was evaluated by observing the difference in diameter between the upper surface (upper punch 2 side) and the lower surface (lower punch 1 side) of each blank in the examples and comparative examples, and the state of pinhole formation in the cross section of each blank.

[Example 1]
In Example 1, a molded body 10 was produced according to the embodiment of the present invention described above, and the total movement amount of each of the upper punch 2 and the lower punch 1 was set to 2.7 mm, the movement amount of the upper punch 2 in the first pressurizing step was 1.2 mm, the movement amount of the lower punch 1 in the second pressurizing step was 1.35 mm, and the movement amount of the upper punch 2 in the third pressurizing step was 0.15 mm, and the raw material powder 4 was compressed to produce the molded body 10.

[Example 2]
In Example 2, a molded body 10 was also manufactured according to the embodiment of the present invention described above, and the total movement amount of each of the upper punch 2 and the lower punch 1 was set to 2.7 mm, the movement amount of the upper punch 2 in the first pressurizing step was 1.15 mm, the movement amount of the lower punch 1 in the second pressurizing step was 1.35 mm, and the movement amount of the upper punch 2 in the third pressurizing step was 0.20 mm, and the raw material powder 4 was compressed to manufacture the molded body 10. The difference from Example 1 is that the movement amount of the upper punch 2 in the first pressurizing step was reduced by 0.05 mm, and the movement amount of the upper punch 2 in the third step was increased by 0.05 mm.

[Comparative Example 1]
Comparative Example 1 is an example in which the upper punch 2 and the lower punch 1 are moved once each in sequence, and the raw material powder 4 is pressed to produce a molded body 10. FIG. 2 is a diagram for explaining the method for producing a molded body of Comparative Example 1. In Comparative Example 1, the lower punch 1 is first inserted from one open end of the through hole 3a, and the raw material powder 4 of the molded body is supplied to the recess of the die 3, which is formed by the bottom surface of the lower punch 1 and the inner wall surface of the through hole 3a of the die 3 (FIG. 2(a): raw material powder filling step). Next, the upper punch 2 is inserted from the other open end of the through hole 3a, and the raw material powder 4 is pressed and compressed by moving the upper punch 2 toward the lower punch 1 (FIG. 2(b): first pressing step). At this time, the positions of the die 3 and the lower punch 1 are fixed, and the upper punch 2 is moved 2.25 mm from the position where it contacted the raw material powder 4 toward the lower punch 1, and the raw material powder 4 is pressed and compressed. Next, while the die 3 and the upper punch 2 were kept in fixed positions, the lower punch 1 was moved 0.45 mm toward the upper punch 2 to pressurize and compress the raw material powder 4 ( FIG. 2( c ): second pressurizing step). Finally, the upper punch 2 and the lower punch 1 were moved toward the other open end of the through hole 3 a of the die 3, and the molded body 10 made of the raw material powder 4 compressed within the through hole 3 a was ejected from the die 3 ( FIG. 2( d ): ejection step).

[Comparative Example 2]
In Comparative Example 2, a molded body 10 was produced by the same process as in Comparative Example 1. The difference from Comparative Example 1 is that the movement amount of the upper punch 2 in the first pressurizing step in Comparative Example 1 was 2.55 mm, and the movement amount of the lower punch 1 in the second pressurizing step was 0.15 mm.

[Comparative Example 3]
Comparative Example 3 is an example in which the upper punch 2 and the lower punch 1 are moved simultaneously to pressurize the raw material powder 4 to produce a molded body 10. FIG. 3 is a diagram for explaining the method for producing a molded body of Comparative Example 3. In Comparative Example 3, the lower punch 1 is first inserted from one open end of the through hole 3a, and the raw material powder 4 of the molded body is supplied to the recess of the die 3 in which a recess is formed by the bottom surface of the lower punch 1 and the inner wall surface of the through hole 3a of the die 3 (FIG. 3(a): raw material powder filling step). Next, the upper punch 2 is inserted from the other open end of the through hole 3a, and while the position of the die 3 is fixed, the upper punch 2 and the lower punch 1 are moved toward the opposing punches to pressurize and compress the raw material powder 4 (FIG. 3(b): first pressurizing step). At this time, the upper punch 2 and the lower punch 1 are simultaneously moved 1.35 mm from the position where the upper punch 2 contacts the raw material powder 4, and the raw material powder 4 is pressed and compressed. Finally, the upper punch 2 and the lower punch 1 were moved to the other open end of the through hole 3a of the die 3, and the compact 10 made of the raw material powder 4 compressed and molded within the through hole 3a was ejected from the die 3 (Figure 3(c): ejection process).

Table 1 shows the manufacturing conditions of the molded bodies of the examples and comparative examples, and the dimensional difference in diameter between the upper surface side (upper punch side) and the lower surface side (lower punch side) of each blank obtained by sintering the molded body 10 manufactured by each example and comparative example. The dimensional difference of each blank was calculated by measuring the dimensions of the upper surface side and the lower surface side with a micrometer. Also, Figure 4-1 is a diagram of the pinhole formation state in the blank cross section of Example 1, Figure 4-2 is a diagram of the pinhole formation state in Comparative Example 2, and Figure 4-3 is a diagram of the pinhole formation state in the blank cross section of Comparative Example 3. The blank cross section is a cross section cut horizontally in the pressure direction of the upper and lower punches during molding (the axial direction of the through hole of the die), and the state of the pinhole was observed and photographed using a stereo microscope at a magnification of 100 times. The black dots in the figure indicate pinholes.

From Table 1, Figures 4-1, 4-2 and 4-3, Example 1 has the smallest dimensional difference between the top and bottom surfaces of the blank, and although pinholes are present in the cross section of the blank, the amount is the smallest and they are uniformly distributed throughout the inside of the blank. From these results, it can be said that the inside of the blank (molded body 10) has a uniform density overall, there is little difference in density distribution and a good molded body 10 was obtained.

In Example 2, the dimensional difference between the upper and lower surfaces of the blank is moderate compared to the other examples, and the dimensional difference is large compared to Example 1. In Examples 1 and 2, the total movement amount of the upper punch 2 is the same, but in Example 2, the movement amount of the upper punch 2 in the first pressurizing step is reduced and the movement amount of the upper punch 2 in the third pressurizing step is increased compared to Example 1. The upper diameter of the blank in Example 2 is larger than the lower diameter, which is thought to be due to the fact that in the first pressurizing step, the raw material powder 4 in a state where the raw material powder is filled in the recess formed by the die 3 and the lower punch 1 is pressed, whereas in the third pressurizing step, the raw material powder 4 in a state compressed to a certain extent through the first and second pressurizing steps is pressed. The state of the pinholes is not shown, but the number and distribution were the same as in Example 1. In Example 2, the dimensional difference between the top and bottom surfaces of the blank is larger than in Example 1, so the density difference inside the blank is thought to be large; however, the dimensional difference is moderate and the pinhole condition is the same as in Example 1, so the density distribution difference within the molded body 10 is not that large, and it can be said that a good molded body 10 was obtained.

In Comparative Example 1, the compact broke into two in the center between the top and bottom sides during the compact ejection process, making it impossible to mold. This is thought to be because there was little powder movement in the center of the compact, which resulted in a low density in the center, and a large difference in density between the center and the bottom or top side. In Comparative Example 3, the bottom side was larger than the top side, which is thought to be why the density on the bottom side was so high in this comparative example.

Comparative Example 2 is the manufacturing method of Comparative Example 1, in which the movement amount of the lower punch was adjusted. In contrast to Comparative Example 1, a green body could be produced in Comparative Example 2, but the dimensional difference between the upper and lower surfaces of the blank into which the green body was sintered was 9 μm, with the lower surface being larger. Furthermore, more pinholes were observed than in Example 1. This shows that the difference in density distribution inside the blank is very large.

In Comparative Example 3, the dimensional difference between the top and bottom surfaces of the blank was smaller than in the other examples. However, the number of pinholes observed was greater than in Example 1, as in Comparative Example 2. From this, it is presumed that, in the manufacturing method of Comparative Example 3, although the external shape of the blank (molded body 10) can be formed with high precision, the density distribution inside the blank is non-uniform.

Specific examples of the method for producing a molded body of the present invention have been described in detail above, but these are merely examples and can be modified as appropriate without departing from the spirit of the method. For example, in the embodiment, the molded body is produced by sequentially performing the first pressurizing step, the second pressurizing step, and the third pressurizing step, but a step of further compressing the raw material powder after the third step may be included. Even in this case, by compressing the raw material powder by moving the upper punch and the lower punch alternately multiple times, it is possible to promote the movement of the raw material powder located in the center of the molded body, where movement is difficult, and to reduce the density distribution difference inside the molded body.

Reference Signs List 1 Lower punch 2 Upper punch 3 Die 3a Through hole 4 Raw material powder 10 Compact

Claims (1)

A method for manufacturing a molded body, comprising the steps of: filling a raw material powder into a space formed by a through hole provided in a die and a first punch inserted into the through hole; inserting a second punch into the through hole so as to face the first punch; and relatively moving the first punch and the second punch to compress and mold the raw material powder,
a first pressurizing step of moving the second punch by a first predetermined distance from a position where the second punch contacts the raw material powder toward the first punch;
a second pressing step of moving the first punch toward the second punch by a second predetermined amount;
a third pressurizing step of moving the second punch toward the first punch by a third predetermined amount;
and a discharge step of discharging the molded body from the die,
The first pressurizing step, the second pressurizing step, the third pressurizing step, and the discharging step are sequentially performed;
the first predetermined amount, the second predetermined amount, and the third predetermined amount satisfy a magnitude relationship of the third predetermined amount < the first predetermined amount < the second predetermined amount,
the third predetermined amount is 0.1 to 0.15 times the second predetermined amount;
The ejection step ejects the compact from an open end of a through hole provided in the die on a side of the second punch.
The method for producing a molded body comprising the steps of:

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