JP3003126B2 - Powder molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a helical gear with a boss, in which a first cylindrical portion and a second cylindrical portion having an outer diameter larger than the first cylindrical portion are coaxially arranged. With this second
The present invention relates to a powder molding method for a compact having a beveled portion on the outer peripheral surface of a cylindrical portion of the present invention.

[0002]

2. Description of the Related Art A helical gear 1 with a boss as shown in FIGS. 7 and 8 is a sintered body obtained by sintering a compact formed by compressing a raw material powder mainly composed of a metal. In the helical gear 1 with a boss, a cylindrical boss portion 2 as a first cylindrical portion and a gear portion 3 as a second cylindrical portion having a larger outer diameter are coaxially and integrally arranged. And
The inside of the boss portion 2 and the gear portion 3 is a cylindrical through hole 4. A bevel portion 5 is formed on the outer peripheral surface of the gear portion 3. Further, a fixing hole 6 is formed by penetrating the boss 2 along one diameter thereof. The axial length of the helical gear 1 with boss is about 20 mm.

In manufacturing a helical gear 1 with a boss made of such a sintered body, a mold for powder molding as shown in FIG. 9 has conventionally been used. This mold uses a stepped die 11
It has a core rod 12, a rotatable lower punch 13 and a rotatable upper punch 14, and forms a formed body 16 as shown in FIG. That is, after filling the raw material powder between the die 11 and the lower punch 13 fitted into the die 11 from below and the core rod 12 fitted into the lower punch 13 from below,
An upper punch 14 is fitted between the core 11 and the core rod 12 from above, and the raw material powder is compressed and formed between the die 11 and the core rod 12 by the punches 13 and 14. The molded body 16 has an outer diameter of an upper portion of a cylindrical shape equal to an outer diameter of the lower gear portion 3. After the sintering of the molded body 16, the boss portion 2 having a predetermined shape is formed by cutting a portion (a portion indicated by cross-hatching) 17 on the upper side thereof on the outer peripheral side of the two-dot chain line. The fixing holes 6 are also formed by cutting after sintering. The reason why the boss portion 2 having a predetermined shape is formed by cutting after sintering is to enable the molded body 16 to be extracted from the single die 11.

[0004] Similarly, for the sake of extraction, a first molded body 22 and a second molded body 23 which are separately molded and sintered to produce a two-stage gear 21 as shown in FIG. Pressing is also performed. However, the boss portion 2 having a predetermined shape is formed by cutting after sintering,
If two separately molded and sintered compacts 22 and 23 are joined together, the production cost increases.

On the other hand, in order to enable the integral molding of the helical gear 1 with a boss as shown in FIG.
As described in Japanese Patent No. 116677, a split die type mold is also used. In the split die type mold, the die is divided into an upper die and a lower die which can be opened and closed in the vertical direction. The upper die forms the outer peripheral surface of the gear portion, and the lower die forms the outer peripheral surface of the boss portion and the step between the outer peripheral surfaces of the gear portion and the boss portion. Then, at the time of molding, after the raw material powder is filled between the overlapped dies, the core rod, and the lower punch, the upper punch is lowered with respect to the die, and the lower punch is raised to compress the raw material powder. Also, at the time of extraction, first lower the core rod to pull out from the helical gear with boss, then lower the lower die, pull out this lower die from the boss, then lower the lower punch to separate it from the boss, Lower the upper punch and pull out the gear from the upper die. However, the conventional powder molding method described in Japanese Patent Application Laid-Open No. 49-116677 is a double pressing method, and there is a raw material powder that does not move along the die. Due to the one-sided molding, there is a disadvantage that the filling state of the raw material powder is unbalanced and bad near the beveled portion, and the density near the beveled portion is likely to be uneven and low.

As described in Japanese Patent Application Laid-Open No. 1-195202, a boss is formed by using a mold in which a lower punch fitted into a die is divided into a lower first punch and a lower second punch. It has also been practiced to integrally mold a helical gear with attachment. The lower first punch forms a step between the outer peripheral surfaces of the gear portion and the boss portion and the outer peripheral surface of the boss portion, and the lower second punch forms an end surface of the boss portion. Then, at the time of molding, after the raw material powder is filled between the die, the lower first punch, the lower second punch, and the core rod, the upper punch is lowered and fitted between the die and the core rod from above. Thereafter, the die and the lower first punch descend integrally with the upper punch, and the raw material powder is compressed. Then, the die continues to descend even after the lower first punch is stopped.
The gear is pushed up by the punch and the gear part comes out of the die.
Thereafter, the lower first punch again descends integrally with the die, and is pushed up by the lower second punch, so that the boss portion comes off from the lower first punch. As described above, the powder molding method described in Japanese Patent Application Laid-Open No. 1-195202 is a withdrawal method, and the entire raw material powder in the vicinity of the beveled portion also moves relatively upward with respect to the die and the core rod. And the density near the beveled portion is improved and uniform. However, as described above, the lower punch fitted into the die
Division into a punch and a lower second punch is not possible when the difference between the inner diameter of the helical gear with boss and the root diameter is small.

[0007]

As described above, when manufacturing, for example, a helical gear with a boss by powder metallurgy, if a boss portion having a predetermined shape is formed by cutting after sintering as in the prior art, the manufacturing cost is increased. There is a problem of bulging. In addition, a helical gear with a boss is integrally formed by adopting a split die method in a mold for powder molding.However, the powder molding method described in Japanese Patent Application Laid-Open No. This is a pressing method, and in particular, since the vicinity of the beveled portion of the gear portion is formed by one-sided pressing, there is a problem that the density near the beveled portion tends to be uneven and low. On the other hand, the powder molding method described in Japanese Patent Application Laid-Open No. 1-195202 is a withdrawal method, in which the density near the beveled portion is improved and uniform, but the lower punch fitted into the die is used. The first
Since it is divided into a punch and a lower second punch, there is a problem that is impossible when the difference between the inner diameter and the root diameter of the helical gear with boss is small.

The present invention is intended to solve such a problem, and a first cylindrical portion and a second cylindrical portion having a larger outer diameter than the first cylindrical portion, such as a helical gear with a boss. The cylindrical portion is coaxially arranged, and when the molded body having the helical portion on the outer peripheral surface of the second cylindrical portion is integrally powder-molded, the density including the vicinity of the helical portion can be increased and uniformly. It is another object of the present invention to provide a powder molding method which can be applied to a case where the difference between the inner diameter and the root diameter of the compact is small.

[0009]

According to a first aspect of the present invention, there is provided a first cylindrical portion and a second cylindrical portion having an outer diameter larger than the first cylindrical portion. And a die for forming an outer peripheral surface of the second cylindrical portion, wherein the die is formed coaxially and has a beveled portion on the outer peripheral surface of the second cylindrical portion. A core rod forming an inner peripheral surface of both cylindrical portions, a lower punch forming an end surface of the second cylindrical portion, and a step surface between the outer peripheral surfaces of the two cylindrical portions and a first cylindrical portion. Using a die having an upper first punch forming an outer peripheral surface and an upper second punch forming an end face of the first cylindrical portion, the die, the core rod located in the die, and the die And after filling the raw material powder with the lower punch fitted between the core rods from below, the upper first punch with respect to the die. And lowering the upper second punch and raising the core rod to bring the upper first punch into contact with the upper surface of the die, fitting the core rod into the upper second punch, and further moving the die and the upper first punch relative to the lower punch. And lowering the upper second punch with respect to the upper first punch to compress the raw material powder, then raising the upper first punch with respect to the upper second punch, and raising the upper first punch with respect to the lower punch. In addition, the upper second punch is raised, and the die and the core rod are lowered to extract the molded body.

Further, the powder molding method according to the second aspect of the present invention uses a mold in which the upper surface of the core rod is tapered.
When filling the raw material powder, the upper surface of the core rod is positioned lower than the upper surface of the die, and the core rod is moved up with respect to the die after the upper first punch contacts the upper surface of the die.

On the other hand, according to the powder molding method of the present invention, the lower punch is divided into a lower first punch facing the upper first punch and a lower second punch facing the upper second punch. Using a mold, the upper surface of the lower second punch is positioned lower than the upper surface of the lower first punch when filling the raw material powder, and after the upper first punch contacts the upper surface of the die, the lower second punch is By lowering one punch, the upper surfaces of the lower second punch and the lower first punch are positioned at the same height.

[0012]

According to the first aspect of the present invention, the raw material powder is first filled between the die, the core rod, and the lower punch.
Thereafter, the upper first punch and the upper second punch are lowered with respect to the die, the core rod is raised, and the upper first punch is brought into contact with the upper surface of the die, and the core rod is fitted into the upper second punch, Further, the die and the upper first punch are integrally lowered with respect to the lower punch, and the upper second punch is lowered with respect to the upper first punch to compress the raw material powder. In this way, the forming is performed by the withdrawal method, whereby the density of the formed body including the vicinity of the beveled portion is improved and becomes uniform. Further, since the upper first punch which forms the step surface between the outer peripheral surfaces of the two cylindrical portions and the outer peripheral surface of the first cylindrical portion is in contact with the upper surface of the die, for example, the inner diameter of the molded body and the tooth bottom The difference from the diameter can be reduced. In removing the molded body, the upper first punch is raised with respect to the upper second punch, the upper first punch and the upper second punch are raised with respect to the lower punch, and the die and the core rod are lowered.

Further, in the powder molding method according to the second aspect of the present invention, the upper surface of the core rod is positioned lower than the upper surface of the die when filling the raw material powder. Next, after the upper first punch contacts the upper surface of the die, the core rod is raised with respect to the die. At this time, the raw material powder located above the core rod is guided by the tapered upper surface of the core rod and falls to a position below the upper second punch. As a result, the actual filling amount of the raw material powder in the lower position of the upper second punch increases, and the density of the first cylindrical portion increases.

In the powder molding method according to the third aspect of the present invention, the upper surface of the lower second punch is positioned lower than the upper surface of the lower first punch when filling the raw material powder. Then, at the time of transfer, after the upper first punch contacts the upper surface of the die, the lower first punch is lowered with respect to the lower second punch, and the upper surfaces of the lower second punch and the lower first punch are leveled. Position. Thereby, the density of the first cylindrical portion increases.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. The helical gear 1 with the boss as shown in FIGS. 7 and 8 described above is molded. First, the configuration of the powder molding press and its mold will be described with reference to FIGS. In FIG. 3 showing the mold configuration, reference numeral 31 denotes a die forming the outer peripheral surface of the gear portion 3 of the helical gear 1 with the boss, 32 denotes the inner peripheral surface of the boss portion 2 and the gear portion 3, that is, a core rod forming the through hole 4; Is a lower punch forming an end face of the gear portion 3, 34 is an upper first punch forming a step surface between the boss portion 2 and the gear portion 3 and an outer peripheral surface of the boss portion 2, and 35 is an end face of the boss portion 2. Upper second punch. The lower punch 33 is attached to the die 31
The die 31 is vertically movable with respect to the fixed lower punch 33.
Also, on the inner peripheral surface of the die 31, there is formed a sloping groove 36 which forms the helical tooth portion 5 on the outer peripheral surface of the gear portion 3, while
On the inner peripheral surface of the lower punch 33, there is formed a beveled tooth portion 37 which is slidably engaged with the bevel groove 36 of the die 31. And
As the die 31 moves up and down with respect to the lower punch 33 due to the engagement between the oblique grooves 36 and the oblique tooth portions 37, the lower punch 33
Is designed to rotate. The core rod 32 penetrates through the inside of the lower punch 33 so as to be able to move up and down from below. The upper first punch 34 moves up and down to contact the upper surface of the die 31 and is also a die. That is, this mold is of a split die type. The above second
The punch 35 is fitted in the upper first punch 34 so as to be vertically movable.

In FIG. 2 showing a powder forming press, reference numeral 41 denotes a bed on which a base plate 43 is supported via a bolster 42. A guide rod 44 penetrates through the base plate 43 so as to be movable up and down.
Has been fixed. The yoke plate 45 is connected to a lower ram driven by a hydraulic cylinder device such as an air cylinder device (not shown). A fluid pressure cylinder device 46 such as an air cylinder device is provided on the yoke plate 45. The piston 47 that moves up and down in the fluid pressure cylinder device 46 is
It is slidably fitted in the base plate 43,
The core rod 32 is fixed to the upper surface by a core rod retainer 48. The fluid pressure cylinder device 46 is intended to prevent leakage of the raw material powder P. Also,
Housings 49 and 50 are fixed on the base plate 43, and a lower punch holder 51 is supported in the housings 49 and 50 via bearings 52 and 53 so as to be horizontally rotatable. The lower punch 33 is coaxially fixed on the lower punch holder 51 by a lower punch retainer 54.
On the other hand, a die plate 55 is provided at the upper end of the guide rod 44.
The die 31 is fixed to the die plate 55 by a die holder 56 and a die holder 57. Note that guide posts 58 are erected on the die plate 55. Further, reference numeral 60 denotes an upper punch plate, which is an upper ram driven by a hydraulic cylinder device such as an air cylinder device (not shown).
61 is to be linked. Under the upper punch plate 60, a receiving plate 64 also serving as a housing for the fluid pressure cylinder devices 62 and 63 such as an air cylinder device is fixed. Equipment housing 65
Has been fixed. A first piston 66 that moves up and down is supported between the receiving plate 64 and the cylinder device housing 65, and the upper first punch 34 is attached to the receiving plate 67 below the first piston 66. And is fixed via an upper first punch presser 68. A second piston 69 that moves up and down is supported between the receiving plate 64 and the first piston 66, and the upper second punch 35 Are fixed via the receiving plate 70 and the upper second punch presser 71. The fluid pressure cylinder device 6
2, 63 are for the purpose of adjusting the filling amount and extracting. The guide post 58 penetrates a bush 72 fixed to the upper punch plate 60 so as to be vertically movable. In FIG. 2, (a) on the left side of the entire center line shows a state at the time of compression, and (b) on the right side shows a state at the time of extraction.

Next, a powder molding method using such a powder molding press will be described. At the time of filling the raw material powder P, as shown in FIG. 1A, the die 31 is at the raised position, and the core rod 32 is at the lowered position.
Further, the upper first punch 34 and the upper second punch 35 are located above and separated from the die 31. In this state, the raw material powder P is filled in a space opened upward between the die 31, the core rod 32, and the lower punch 33 by a feeder (not shown) moving on the die plate 55. The filling amount is set for the die 31, the upper first punch 34, and the upper second punch 35. Then, as shown in FIG.
By driving the 61, the upper first punch 34 and the upper second punch 35 are lowered. When the upper first punch 34 and the upper second punch 35 start to descend, the core rod 32 is raised by driving the fluid pressure cylinder device 46, and the core rod 32 is
Fits within 35. Then, when the upper first punch 34 comes into contact with the upper surface of the die 31, that is, when the upper first punch 34 reaches the compression position, the die 31 starts to descend integrally with the upper first punch 34. Incidentally, as the die 31 descends, the inclined groove 36
And the lower punch 33 rotates along the bevel portion 37. In this manner, as shown in FIG. 1C, the raw material powder P is compressed between the die 31 and the upper first punch 34 and the core rod 32 by the upper first punch 34, the upper second punch 35, and the lower punch 33. You. After the upper first punch 34 comes into contact with the upper surface of the die 31, the second piston 69 is kept in the raised position with respect to the receiving plate 64 by the driving of the hydraulic cylinder devices 62 and 63.
Piston 66 rises against the receiving plate 64, and the upper first punch
By lowering the upper second punch 35 with respect to 34, the raw material powder P particularly in the boss portion 2 is compressed. Then, when the upper ram descends to the bottom dead center position, the compression is completed. Thereafter, while the second piston 69 is lowered with respect to the first piston 66, the upper first punch 34 is raised together with the upper ram so that the formed helical gear 1 with boss is protruded by the upper second punch 35. First, the upper first punch 34 comes off from the boss portion 2 of the helical gear 1 with boss. Then, after the lowering of the second piston 69 with respect to the first piston 66 is completed, the upper second punch 35 moves upward from the end face of the boss 2. On the other hand, when the die 31 descends together with the lower ram, the gear portion 3 of the helical gear 1 with bosses comes out of the die 31 while rotating. At the same time, the core rod 32 is lowered by the driving of the fluid pressure cylinder device 46, and the helical gear 1 with the boss is pulled out of the core rod 32. Thus, the formed helical gear 1 with boss is extracted.

Thereafter, the raw material powder P is supplied again, and the above-described powder molding step is repeated. The helical gear 1 with a boss, which is a green compact thus formed, is sintered in a sintering furnace to form a sintered body. The fixing holes 6 are formed by cutting after sintering.

As described above, according to the configuration of the above-described embodiment, the boss 2 is not formed into a predetermined shape by cutting, but the helical gear 1 with the boss is integrally formed in the powder molding process. Is formed into a predetermined shape from the beginning, so that manufacturing costs can be reduced. In addition, it is not a one-sided molding method or a two-sided molding method but a withdrawal method, and the entire raw material powder P including the vicinity of the bevel portion 5 is relatively positioned with respect to the die 31, the upper first punch 34 and the core rod 32. To move upward, it is easy to be hardened by friction,
The density can be increased including the vicinity, and the density can be made uniform.
Further, instead of dividing the lower punch fitted into the die into two, the upper punch is divided into an upper first punch 34 and an upper second punch 35, and the outer peripheral surfaces of the boss 2 and the gear 3 are formed. The upper first punch 34, which forms the step surface between the boss portion 2 and the outer peripheral surface of the boss portion 2, does not fit into the die 31 but abuts on the upper surface of the die 31. It can be implemented even when the difference between the inner diameter and the root diameter is small.

Next, a second embodiment of the present invention will be described with reference to FIG. The powder molding press used in the second embodiment is obtained by adding a die control mechanism 76 and a die stop mechanism 77 to the powder molding press of the first embodiment. Then, at the time of molding, as shown in FIG. 4A, the raw material powder P is first filled between the die 31, the core rod 32, and the lower punch 33. The filling amount is set for the die 31, the upper first punch 34, and the upper second punch 35. Then, as shown in FIG. 4B, when the upper first punch 34 and the upper second punch 35 start to descend, the core rod 32 is raised. Next, as shown in FIG.
The die control mechanism 76 operates at the time when the 34 comes into contact with the upper surface of the die 31 (at the start of the transfer), and thereafter, the upper first punch 34 and the upper second punch 35 are connected to the die 31 while maintaining the filling amount. It descends integrally. Accordingly, the raw material powder P moves between the upper first punch 34, the upper second punch 35, and the core rod 32 (transfer). During that time, the raw material powder P in the gear section 3 is compressed. Then, FIG.
As shown in the figure, after the die 31 is stopped by the die stop mechanism 77 acting on the die 31 (at the end of the transfer), only the upper second punch 35 descends to the bottom dead center together with the upper ram 61, and the boss portion is formed. The second raw material powder P is compressed, and the compression is completed. Then, in the same manner as in the first embodiment, the formed helical gear 1 with a boss is extracted. In addition,
At this time, the braking of the lowering of the die 31 by the die stop mechanism 77 is released.

In the first embodiment in which the die control mechanism 76 and the die stop mechanism 77 are not provided, the upper first punch 34, the upper second punch 35, and the core rod
Before the raw material powder P has risen up to 32,
Since the upper second punch 35 descends and returns to the compression position with respect to the punch 34, the density of the boss portion 2 is hard to increase as compared with the density of the gear portion 3. On the other hand, according to the configuration of the second embodiment, the die control mechanism 76 and the die stop mechanism 77
The upper first punch 34 and the upper second punch 35 are lowered integrally with the die 31 while maintaining the filling amount, so that the upper first punch 34, the upper second punch 35, and the core rod 32 The raw material powder P is surely moved between the upper second punch 35
Is lowered with respect to the upper first punch 34 and returned to the compression position, so that the density of the boss 2 can be increased.

When the fluid pressure cylinder device 62 for the upper first punch 34 is an air cylinder device, when the density of the gear portion 3 increases with the compression of the raw material powder P, the fluid pressure cylinder device 62 When the pressure is lost, the upper first punch 34
There is a possibility that a gap may be formed between the gear portion 3 and the die 31, causing leakage of the raw material powder P, and a film may be formed on a step surface between the boss portion 2 and the outer periphery of the gear portion 3. In order to prevent this, it is necessary to sufficiently increase the pressure of the hydraulic cylinder device 62. For this purpose, it is preferable to use a hydraulic cylinder device or the like as the hydraulic cylinder device 62.

Next, a third embodiment of the present invention will be described with reference to FIG.
It will be described based on. The powder molding press used in the third embodiment has a conical tapered surface 81 at the upper end surface of the core rod 32, and the other points are almost the same as the powder molding press in the second embodiment. Then, as shown in FIG. 5 (a), when filling the raw material powder P, the tapered surface 81 of the upper end surface of the core rod 32 is positioned lower than the upper surface of the die 31. Therefore, the raw material powder P is filled not only above the lower punch 33 but also above the core rod 32 in the die 31. Thus, the filling amount is set between the lower punch 33 and the core rod 32. Then, as shown in FIG. 5B, after the upper first punch 34 contacts the upper surface of the die 31, the core rod 32 is raised and fitted into the upper second punch 35. In the meantime, the raw material powder P located above the core rod 32 is guided by the conical tapered surface 81 and falls uniformly below the upper second punch 25 over its entire circumference. Thereby, the filling amount of the raw material powder P in the position below the upper second punch 25 increases, and the density of the boss portion 2 increases. The compression steps shown in FIGS. 5C to 5D are the same as in the second embodiment.

As described above, the density of the boss 2 tends to be lower than that of the gear 3. One method of increasing the density of the boss 2 is to use the raw material powder P in the die 31.
Is to increase the filling amount. The upper first punch 34
And, even if the filling amount of the raw material powder P on the upper second punch 35 side is increased, the density does not change. In order to increase the filling amount of the die 31, the descending amount of the die 31 may be increased. However, if the descending amount of the die 31 is increased, not only the lower position of the upper second punch 35 but also the upper first punch 35 is increased. Even at a position below 35, the filling amount is large, and the density of the gear portion 3 is too high. On the other hand, according to the configuration of the third embodiment, the upper second punch
Only at the position below 35, the filling amount of the raw material powder P can be increased, and the density of the boss portion 2 can be increased without excessively increasing the density of the gear portion 3.

Incidentally, in order to carry out the third embodiment,
A core rod 32 is used for the powder compacting press of the second embodiment.
In addition to making the stroke of the piston 47 of the hydraulic cylinder device 46 larger, an adjusting mechanism for adjusting the vertical position of the core rod 32 for adjusting the filling amount is required.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
It will be described based on. In the powder molding press used in the fourth embodiment, the lower punch fitted into the die 31 is divided into a lower first punch 86 and a lower second punch 87. The lower first
The punch 86 is fitted into the die 31 from below, but has an inner diameter equal to the inner diameter of the upper first punch 34,
In addition, it faces the first punch 86. The lower second punch 87 is fitted between the lower second punch 86 and the core rod 32 from below.
The inner and outer diameters of the punch 35 are equal to each other, and are opposed to the upper second punch 35. The lower second punch 87 is fixed, while the lower first punch 86 moves up and down.

At the time of filling the raw material powder P, FIG.
As shown in (a), the upper surface of the lower second punch 87 is positioned lower than the upper surface of the lower first punch 86. Thus,
The filling amount is set for the lower first punch 86 and the lower second punch 87. Then, after the upper first punch 34 comes into contact with the upper surface of the die 31, the lower first punch 86 is lowered, and finally, as shown in FIG. The upper surface of the lower first punch 86 is positioned at the same height. Meanwhile, the raw material powder P is transferred and filled between the upper first punch 34 and the upper second punch 35.

According to the configuration of the fourth embodiment, the gear 3
The density of the boss portion 2 can be increased without excessively increasing the density of the boss portion 2. Moreover, this is possible more reliably than in the third embodiment. On the other hand, the third embodiment is excellent in that it can be carried out even when the difference between the inner diameter of the helical gear 1 with boss and the root diameter is small.

It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made. For example,
The configuration of the powder molding press is not limited to that shown in FIG.

[0030]

According to the first aspect of the present invention, like the helical gear with boss, the first cylindrical portion and the second cylindrical portion having an outer diameter larger than the first cylindrical portion are coaxially arranged, and the second cylindrical portion has the second cylindrical portion. In powder-forming a compact having an oblique tooth portion on the outer peripheral surface of the second cylindrical portion, a die forming the outer peripheral surface of the second cylindrical portion, and a core rod forming the inner peripheral surface of both the cylindrical portions. A lower punch forming an end surface of the second cylindrical portion, an upper first punch forming a step surface between outer peripheral surfaces of the two cylindrical portions and an outer peripheral surface of the first cylindrical portion, and a first cylinder. Since the mold having the upper end and the second punch for forming the end face of the cylindrical portion is used, the molded body having both the cylindrical portions as described above can be integrally formed, and the first portion is cut by post-processing.
It is not necessary to form the cylindrical portion in a predetermined shape, and the manufacturing cost can be reduced. Further, since the withdrawal method of lowering the die with respect to the lower punch together with the upper first punch and the upper second punch is employed, the density of the molded body including the vicinity of the beveled portion can be increased and can be made uniform.
Further, the upper punch is divided into an upper first punch and an upper second punch.
Since the upper first punch abuts on the upper surface of the die, it can be applied to the case where the difference between the inner diameter and the root diameter of the compact is small.

Further, according to the second aspect of the present invention, a mold having a tapered upper surface of the core rod is used, and the upper surface of the core rod is positioned lower than the upper surface of the die when filling the raw material powder. Raises the core rod with respect to the die after contacting the upper surface of the die, so that the density of the upper portion of the first cylinder can be increased without excessively increasing the density of the second cylindrical portion. It can be applied even when the difference between the inner diameter and the root diameter is small.

According to the third aspect of the present invention, the lower punch is divided into a lower first punch facing the upper first punch and a lower second punch facing the upper second punch. When filling the powder, the upper surface of the lower second punch is positioned lower than the upper surface of the lower first punch, and after the upper first punch contacts the upper surface of the die, the lower first punch is lowered with respect to the lower second punch. Since the upper surfaces of the lower second punch and the lower first punch are positioned at the same height, the density of the upper portion of the first cylinder can be reliably increased without excessively increasing the density of the second cylindrical portion. .

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a first embodiment of a powder molding method according to the present invention.

FIG. 2 is a cross-sectional view of the same powder molding press.

FIG. 3 is a cross-sectional view of the mold.

FIG. 4 is an explanatory view showing a second embodiment of the powder molding method of the present invention.

FIG. 5 is an explanatory view showing a third embodiment of the powder molding method of the present invention.

FIG. 6 is an explanatory view showing a fourth embodiment of the powder molding method of the present invention.

FIG. 7 is a sectional view of a helical gear with a boss formed by sintering a molded body.

FIG. 8 is a perspective view of the helical gear with the boss.

FIG. 9 is a cross-sectional view illustrating an example of a mold of a conventional powder molding press.

FIG. 10 is a cross-sectional view of a compact formed by the powder compacting press.

FIG. 11 is a sectional view of a two-stage gear showing another example of a conventional sintered body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Helical gear with boss (molded body) 2 Boss part (first cylindrical part) 3 Gear part (second cylindrical part) 5 Beveled part 31 Die 32 Core rod 33 Lower punch 34 Upper first punch 35 Upper second Punch 81 Taper surface (upper surface) 86 Lower first punch 87 Lower second punch

Claims (3)

(57) [Claims] 1. A first cylindrical portion and a second cylindrical portion having an outer diameter larger than that of the first cylindrical portion are coaxially arranged, and an oblique surface is formed on an outer peripheral surface of the second cylindrical portion. A powder molding method of a compact having a tooth portion, wherein a die forming an outer peripheral surface of the second cylindrical portion, a core rod forming an inner peripheral surface of the both cylindrical portions, and a second cylinder A lower punch forming an end surface of the cylindrical portion, a stepped surface between the outer peripheral surfaces of the two cylindrical portions and an upper first punch forming an outer peripheral surface of the first cylindrical portion; Using a mold having an upper second punch forming an end face, a raw material powder is placed between the die, the core rod located in the die, and the lower punch fitted between the die and the core rod from below. After filling, the upper first punch and the upper second punch are lowered with respect to the die, and the core rod is raised. The upper first punch is brought into contact with the upper surface of the die, the core rod is fitted into the upper second punch, and the die and the upper first punch are lowered integrally with the lower punch. Lowering the upper second punch to compress the raw material powder, then raising the upper first punch relative to the upper second punch, raising the upper first punch and the upper second punch relative to the lower punch, and lowering the die and the core rod A powder molding method, characterized in that the molded body is drawn out. 2. A mold having a tapered upper surface of a core rod. When filling the raw material powder, the upper surface of the core rod is positioned lower than the upper surface of the die, and after the upper first punch contacts the upper surface of the die. 2. The powder molding method according to claim 1, wherein the core rod is raised with respect to the die. 3. A mold in which the lower punch is divided into a lower first punch facing the upper first punch and a lower second punch facing the upper second punch. The upper surface of the lower second punch is positioned lower than the upper surface, and after the upper first punch contacts the upper surface of the die, the lower first punch is lowered with respect to the lower second punch to lower the lower second punch and the lower second punch. 2. The powder molding method according to claim 1, wherein the upper surface of one punch is positioned at the same height.