JP2016093837A - Method for manufacturing green compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a green compact capable of suppressing abrasion or damage of a die and a punch constituting a mold when the green compact is taken out from the mold after compression molding.SOLUTION: There is provided a method for manufacturing a green compact having a flange part 2 formed in the outer periphery of a short cylindrical part 1 by using a mold. The mold includes a die 10 having a round hole in the center thereof, lower punches 11 and 12 arranged in the round hole of the die 10, an upper punch 13 arranged over the lower punched 11 and 12 in the round hole of the die 10, and a core rod 14 arranged in the inside of the lower punches 11 and 12. At least one of the lower punches 11 and 12 and the upper punch 13 is constituted of a first punch 11 and a second punch 12 arranged in order from the outside in the round hole of the die 10. After compression molding of the green compact is completed, the inner diameter side of the short cylindrical part 1 of the green compact is opened by pulling out the core rod 14, and the spring back pressure of the green compact is released to the inner diameter side.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for producing a green compact. More specifically, the present invention relates to a method for producing a green compact from a powder material using a mold.

  There is a powder metallurgy method as a technique for manufacturing a machine part having a relatively complicated shape. In this method, powder materials having various compositions including iron-based materials are pressed into desired shapes, and the obtained green compact is heated and sintered. A sintered body is manufactured through such molding and sintering steps.

  The green compact is usually manufactured using a press molding machine equipped with a die, upper and lower punches, and a mold such as a core. For example, the green compact W having the shape shown in FIG. 8 includes a die 30, a first lower punch 31, a second lower punch 32, a third lower punch 33, and a first upper punch 34 as shown in FIGS. The second upper punch 35 and the core rod 36 are manufactured using a press molding machine having a mold.

  The green compact W has a disk shape, and includes a short cylindrical portion 40, a flange portion 41, and an arm portion 42. A flange portion 41 is formed on the outer periphery of one end of the short cylindrical portion 40 in the axial direction, and an arm portion 42 is projected from the inner periphery of the other end in the axial direction. A round hole 43 is formed in the center of the green compact W, and a plurality of teeth 44 are formed on the outer periphery of the flange portion 41.

  The die 30 has a round hole 37 as an opening at the center. The first lower punch 31, the second lower punch 32, the third lower punch 33, the first upper punch 34, the second upper punch 35, and the core rod 36 are arranged so as to be positioned in the round hole 37 when seen in a plan view. It is installed. Specifically, a first lower punch 31, a second lower punch 32, and a third lower punch 33 are disposed in this order from the outside in the round hole 37 of the die 30. Further, above the first lower punch 31, the second lower punch 32, and the third lower punch 33, a first upper punch 34 and a second upper punch 35 are disposed in the round hole 37 of the die 30 in order from the outside. ing. A core rod 36 is disposed inside the third lower punch 33.

  Each punch has a cylindrical shape, and each punch and the core rod 36 can be operated independently of each other by hydraulic pressure or a motor. The first lower punch 31 is disposed at a position where its upper end surface 31a can contact the lower surface 41a of the flange portion 41 of the green compact W (the lower surface in FIG. 8B). 32 is disposed at a position where the upper end surface 32 a can come into contact with the lower end surface 40 a of the short cylindrical portion 40 of the green compact W. The upper end surface 33a of the third lower punch 33 is disposed at a position where it can come into contact with the lower surface 42a of the arm portion 42 of the green compact W.

  On the other hand, the lower end surface 34a of the first upper punch 34 is disposed at a position where it can contact the upper surface 41b (the upper surface in FIG. 8B) of the flange portion 41 of the green compact W. The upper punch 35 is disposed at a position where the lower end surface 35 a can come into contact with the upper end surface 40 b of the short cylindrical portion 40 of the green compact W and the upper surface 42 b of the arm portion 42.

  A plurality of concave portions having a shape corresponding to the teeth 44 of the green compact W are formed on the inner periphery of the die 30 along the circumferential direction. In addition, teeth on the outer periphery of the first lower punch 31 and the first upper punch 34 that slide on the inner periphery of the die 30 have the same shape as the teeth 44 of the green compact W corresponding to the recesses. Are formed along the circumferential direction.

The green compact W is manufactured through the steps shown in FIGS.
First, as shown in the left half of FIG. 9 (a), a powder feeder (in a space defined by the die 30, the first lower punch 31, the second lower punch 32, the third lower punch 33, and the core rod 36). (Not shown) is used to fill the powder material P having various compositions including the iron-based material. Next, as shown in the right half of FIG. 9A, the die 30 and the core rod 36 are raised so that the upper surface of the powder material P filled in the space is lower than the upper end surfaces of the die 30 and the core rod 36. (Underfill).

Next, as shown in FIG. 9B, in conjunction with the lowering of the first upper punch 34 and the second upper punch 35, the die 30, the first lower punch 31 and the core rod 36 are lowered, and the space is reduced. Then, it is transformed into a space having a cross-sectional shape having a vertical dimension that is a predetermined multiple of the cross-sectional shape of the green compact W obtained by compression molding (transfer).
Next, as shown in FIG. 9C, the first upper punch 34 and the second upper punch 35 are lowered, and the powder material P filled in the space is compression-molded to form the green compact W. Make it. At that time, in conjunction with the lowering of the first upper punch 34 and the second upper punch 35, the die 30, the third lower punch 33 and the core rod 36 are lowered by a predetermined distance.

The compression molding of the powder material P is completed by the steps (a) to (c) in FIG. The green compact W obtained by compression molding is taken out from the mold by the steps shown in FIG. 9 (d) and FIG. 10 (e) to (h).
First, as shown in FIG. 9D, the die 30 is lowered by a predetermined distance. The die 30 is lowered until its upper surface 30a is located slightly below the lower surface 41a of the flange portion 41 of the green compact W. FIG. 10E shows a state where the lowering of the die 30 is completed. While the compression molding of the green compact W is completed and the die 30 operates downward, a holddown pressure of a predetermined magnitude is applied to the green compact W by the first upper punch 34 and the second upper punch 35. ing. This hold down pressure varies depending on the shape and size of the green compact W, but is generally about 5 to 20 t. The hold-down pressure is applied to the green compact W until the ascending process of the first upper punch 34 and the second upper punch 35 described later.

Next, as shown in FIG. 10F, the core rod 36 is lowered.
Thereafter, as shown in FIG. 10G, the first upper punch 34 and the second upper punch 35 are raised. At that time, if the first upper punch 34 and the second upper punch 35 are raised at the same time, the green compact W may adhere to the first upper punch 34 and the second upper punch 35 and rise together. Until the lower end surface 34a of the first upper punch 34 rises to the position of the lower end surface 35a of the second upper punch 35, the pressing force applied to the upper surface 42b of the arm portion 42 of the second upper punch 35 is maintained. Only the punch 34 is raised. Then, after the lower end surface 34a of the first upper punch 34 rises to the position of the lower end surface 35a of the second upper punch 35, the first upper punch 34 and the second upper punch 35 are raised to a predetermined height.

  Next, as shown in FIG. 10H, the die 30, the first lower punch 3, the second lower punch 32, and the core rod 36 are raised, and the green compact W is taken out of the mold. At that time, the second lower punch 32 is raised so that the upper end surface 32 a is positioned slightly above the upper end surface 31 a of the first lower punch 31.

However, the conventional manufacturing method described above has the following problems.
That is, the die 30 is lowered in the step of taking out the green compact W after the compression molding. At this time, the first upper punch 34 swells outward by the hold-down pressure and the spring back pressure of the green compact W described above. It deform | transforms so that it may contact with the inner periphery of die | dye 30 with a strong force. As the die 30 descends, the contact area between the die 30 and the first upper punch 34 decreases, and as a result, the contact surface pressure between both increases. For this reason, there is a problem that abnormal wear occurs at the upper end portion (entrance portion) of the inner periphery of the die 30 or seizure or stuffiness occurs at the outer peripheral tip portion of the first upper punch 34. When such abnormal wear or the like occurs, molding becomes difficult, and it is necessary to replace with a new member.
Such a problem is not limited to the case where the green compact W having the shape shown in FIG. 8 is manufactured, but a portion where a large amount of powder exists in the green compact (in the example shown in FIG. This can happen when an upper punch or a lower punch is placed between the outer circumference of the applicable) and the inner circumference of the die.

  The present invention has been made in view of such circumstances, and when taking out the green compact after compression molding from the mold, it is possible to suppress wear and damage of the die and punch constituting the mold. It aims at providing the manufacturing method of a compact.

A method for producing a green compact according to one aspect of the present invention is a method for producing a green compact having a flange portion formed on the outer periphery of a short cylindrical portion using a mold,
The mold includes a die having a round hole in the center, a lower punch disposed in the round hole of the die, an upper punch disposed in the round hole of the die above the lower punch, A core rod disposed inside the lower punch,
At least one of the lower punch and the upper punch is composed of a first punch and a second punch disposed in order from the outside in the round hole of the die,
After the compression molding of the green compact is completed, the core rod is extracted to open the inner diameter side of the short cylindrical portion of the green compact, and the spring back pressure of the green compact is released to the inner diameter side.

A method for manufacturing a green compact according to another aspect of the present invention uses a mold for forming a green compact in which a flange portion is formed on the outer periphery of a short cylindrical portion and an arm portion is formed on the inner periphery of the short cylindrical portion. A manufacturing method,
The mold includes a die having a round hole in the center, a first lower punch and a second lower punch disposed in order from the outside in the round hole of the die, and the first lower punch and the second lower punch. A first upper punch and a second upper punch disposed in order from the outside in the round hole of the die on the upper side;
After the compression molding of the green compact is completed, the inner diameter side of the short cylindrical portion of the green compact is opened to release the spring back pressure of the green compact toward the inner diameter side.

  According to the said invention, when taking out the green compact after compression molding from a metal mold | die, the abrasion and damage of the die | dye and punch which comprise the said metal mold | die can be suppressed.

(A) is a plane explanatory view of an example of a green compact, and (b) is a cross-sectional explanatory view thereof. It is process explanatory drawing of one Embodiment of the manufacturing method of the green compact of this invention. It is process explanatory drawing of one Embodiment of the manufacturing method of the green compact of this invention. It is process explanatory drawing of other embodiment of the manufacturing method of the green compact of this invention. It is process explanatory drawing of other embodiment of the manufacturing method of the green compact of this invention. It is sectional explanatory drawing of the other example of a compact. It is sectional explanatory drawing of the other example of a compact. (A) is a plane explanatory view of still another example of the green compact, and (b) is a cross-sectional explanatory view thereof. It is process explanatory drawing of the conventional manufacturing method of a green compact. It is process explanatory drawing of the conventional manufacturing method of a green compact.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.
A method for producing a green compact according to one embodiment of the present invention (hereinafter, also simply referred to as “manufacturing method”)
(1) A method of manufacturing a green compact having a flange portion formed on the outer periphery of a short cylindrical portion using a mold,
The mold includes a die having a round hole in the center, a lower punch disposed in the round hole of the die, an upper punch disposed in the round hole of the die above the lower punch, A core rod disposed inside the lower punch,
At least one of the lower punch and the upper punch is composed of a first punch and a second punch disposed in order from the outside in the round hole of the die,
After the compression molding of the green compact is completed, the core rod is extracted to open the inner diameter side of the short cylindrical portion of the green compact, and the spring back pressure of the green compact is released to the inner diameter side.

  In the manufacturing method according to this aspect, unlike the conventional method, the core rod is extracted and the inner diameter side of the green compact is opened without lowering the die after completion of compression molding. Thereby, the spring back pressure of the green compact can be released to the inner diameter side. As a result, the contact surface pressure between the outer peripheral surface of the punch (upper punch or lower punch, or both) that contacts the outer peripheral surface of the short cylindrical portion of the green compact and the inner peripheral surface of the die can be reduced, Wear and damage to the die and punch can be suppressed. Thereby, the lifetime of a die | dye and a punch can be lengthened and the cost reduction of green compact manufacture can be aimed at.

(2) In the manufacturing method of the above (1), the lower punch is composed of a first lower punch and a second lower punch arranged in order from the outside in the round hole of the die,
A first extrusion step of extracting the core rod to a first predetermined position where an inner peripheral surface of the short cylindrical portion is exposed after the compression molding of the green compact is completed;
After the first extrusion step, the first lower punch, the second lower punch, and the upper punch are simultaneously raised to a second predetermined position where the outer peripheral surface of the flange portion is exposed, and after the second extrusion step, Until the upper end surface of the second lower punch that presses the lower surface of the short cylindrical portion is flush with the upper end surface of the first lower punch that presses the lower surface of the flange portion, the upper surface of the short cylindrical portion is moved with the upper punch. The upper punch and the second lower punch are raised while pressing, and after the upper end surface of the second lower punch is flush with the upper end surface of the first lower punch, the upper punch is moved to the third predetermined position. It may include a third extrusion step of raising.
In this case, the core rod is pulled out without lowering the die after the compression molding is completed, and the inner peripheral surface of the short cylindrical portion of the green compact is exposed, so that the spring back pressure in the short cylindrical portion is released to the inner diameter side. Can do. Moreover, after extracting the core rod, the green compact is extracted from the die by raising the first lower punch, the second lower punch, and the upper punch other than the core rod and the die. As a result, the contact surface pressure between the die and the first lower punch can be reduced, and wear and damage of the die and the first lower punch can be suppressed. Thereby, the lifetime of a die | dye and a 1st lower punch can be lengthened, and the cost reduction of green compact manufacture can be aimed at.

A manufacturing method according to another aspect of the present invention includes:
(3) A method of manufacturing a green compact in which a flange portion is formed on the outer periphery of the short cylindrical portion and an arm portion is formed on the inner periphery of the short cylindrical portion using a mold,
The mold includes a die having a round hole in the center, a first lower punch and a second lower punch disposed in order from the outside in the round hole of the die, and the first lower punch and the second lower punch. A first upper punch and a second upper punch disposed in order from the outside in the round hole of the die on the upper side;
After the compression molding of the green compact is completed, the inner diameter side of the short cylindrical portion of the green compact is opened to release the spring back pressure of the green compact toward the inner diameter side.

  Also in the manufacturing method according to another aspect of the present invention, unlike the conventional method, the lower punch or the core rod that contacts the inner peripheral surface of the short cylindrical portion of the green compact without lowering the die after completion of compression molding is provided. The inner diameter side of the short cylindrical portion of the extracted green compact is opened. Thereby, the spring back pressure of the green compact can be released to the inner diameter side. As a result, it is possible to reduce the contact surface pressure between the punch (the upper punch and / or the lower punch, or both) in contact with the outer peripheral surface of the short cylindrical portion of the green compact and the inner peripheral surface of the die. The wear and damage of the punch can be suppressed. Thereby, the lifetime of a die | dye and a punch can be lengthened and the cost reduction of green compact manufacture can be aimed at.

(4) In the manufacturing method of (3), the flange portion is formed at one axial end of the short cylindrical portion,
The arm part is formed at the other axial end of the short cylindrical part,
The mold includes a third lower punch inside the second lower punch, and a core rod disposed inside the third lower punch,
A first extrusion step of lowering the core rod to a first predetermined position at which an inner peripheral surface of the arm portion is exposed after compression molding of the green compact is completed;
After the first extrusion step, the die, the first lower punch, the second lower punch, the first upper punch, the second upper punch, and the core rod are simultaneously raised to a second predetermined position where the inner peripheral surface of the short cylindrical portion is exposed. A second extrusion step,
After the second extrusion step, the first lower punch, the second lower punch, the first upper punch, and the second upper punch are simultaneously raised to a third predetermined position, and after the third extrusion step, the flange portion While pressing the upper surface of the arm portion with the second upper punch until the lower end surface of the first upper punch pressing the upper surface is flush with the lower end surface of the second upper punch pressing the upper surface of the arm portion, After the first upper punch is raised and the lower end surface of the first upper punch is flush with the lower end surface of the second upper punch that presses the upper surface of the arm portion, the first upper punch and the second upper punch Can be simultaneously raised to a fourth predetermined position, and then a fourth extruding step of raising the second lower punch contacting the lower end surface of the short cylindrical portion by a predetermined distance can be included.
In this case, the core rod is lowered to expose the inner peripheral surface of the arm portion of the green compact without lowering the die after completion of compression molding, so that the spring back pressure in the arm portion can be released to the inner diameter side. it can. Further, after lowering the core rod, the die, the first lower punch, the second lower punch, the first upper punch, the first punch other than the third lower punch that is in contact with the inner peripheral surface of the short cylindrical portion of the green compact 2 By raising the upper punch and the core rod, the green compact is extracted from the third lower punch, and the inner peripheral surface of the short cylindrical portion is exposed. Thereby, the spring back pressure of the whole green compact can be released to the inner diameter side. As a result, the contact surface pressure between the die and the first upper punch can be reduced, and wear and damage of the die and the first upper punch can be suppressed. Thereby, the lifetime of a die | dye and a 1st upper punch can be lengthened, and the cost reduction of green compact manufacture can be aimed at.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of the manufacturing method of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

<First embodiment>
The green compact W1 manufactured by the manufacturing method according to the present embodiment has a disk shape as shown in FIG. The green compact W1 includes a short cylindrical portion 1 and a flange portion 2 formed on the outer periphery of one end of the short cylindrical portion 1 in the axial direction. A round hole 3 is formed in the center of the green compact W1.

  The green compact W1 is manufactured using a press molding machine having a die having a die 10, a first lower punch 11, a second lower punch 12, an upper punch 13 and a core rod 14 as shown in FIGS. Is done.

  The die 10 has a round hole 15 as an opening at the center. The first lower punch 11, the second lower punch 12, the upper punch 13, and the core rod 14 are disposed so as to be positioned in the round hole 15 when viewed in plan. Specifically, the first lower punch 11 and the second lower punch 12 are arranged in order from the outside in the round hole 15 of the die 10. Further, an upper punch 13 is disposed in the round hole 15 of the die 10 above the first lower punch 11 and the second lower punch 12. A core rod 14 is disposed inside the second lower punch 12.

  Each punch has a cylindrical shape, and each punch and the core rod 15 can be operated independently of each other by hydraulic pressure or a motor. The first lower punch 11 is disposed at a position where the upper end surface 11a can contact the lower surface 2a of the flange portion 2 of the green compact W1 (the lower surface in FIG. 2B). 12, the upper end surface 12a is disposed at a position where the upper end surface 12a can come into contact with the lower end surface 1a of the short cylindrical portion 1 of the green compact W1.

  On the other hand, the upper punch 13 has a lower end surface 13a arranged at a position where it can contact the upper surface 2b of the flange portion 2 of the green compact W1 (the upper surface in FIG. 2B) and the upper end surface 1b of the short cylindrical portion 1. It is installed.

The green compact W1 is manufactured through the steps shown in FIGS.
First, as shown in FIG. 2A, a powder material is used by using a powder feeder (not shown) in a space defined by the die 10, the first lower punch 11, the second lower punch 12, and the core rod 14. P is filled.

Next, as shown in FIG. 2B, the upper punch 13 is lowered, and the powder material P filled in the space is compression-molded. At that time, in conjunction with the lowering of the upper punch 13, the die 10, the first lower punch 11 and the core rod 14 are lowered by a predetermined distance.
The compression molding of the powder material is completed by the steps (a) to (b) in FIG. The green compact W1 obtained by the completion of the compression molding is taken out from the mold by the steps shown in FIGS. 3C to 3E.

  First, instead of lowering the die 10 as in the prior art, as shown in FIG. 3 (c), only the core rod 14 is exposed at the position where the inner peripheral surface 1c of the short cylindrical portion 1 of the green compact W1 is exposed. Pull out to (first predetermined position) (first extrusion step). By exposing the inner peripheral surface 1c of the short cylindrical portion 1 of the green compact W1, the spring back pressure in the short cylindrical portion 1 can be released to the inner diameter side. As a result, the contact surface pressure between the die 10 and the first lower punch 11 can be reduced.

  Next, as shown in FIG. 3D, the first lower punch 11 is moved to a position (second predetermined position) where the upper end surface 11 a of the first lower punch 11 is substantially the same height as the upper surface 10 a of the die 10. The second lower punch 12 and the upper punch 13 are simultaneously raised (second extrusion step). Thereby, the green compact W1 can be extracted from the die 10 in a state where the contact surface pressure between the inner peripheral surface of the die 10 and the outer peripheral surface of the first lower punch 11 is reduced.

  Next, until the upper end surface 12a of the second lower punch 12 that presses the lower end surface 1a of the short cylindrical portion 1 is flush with the upper end surface 11a of the first lower punch 11 that presses the lower surface 2a of the flange portion 2, The upper punch 13 and the second lower punch 12 are raised while pressing the upper end surface 1 b of the short cylindrical portion 1 with the upper punch 13. Then, after the upper end surface 12a of the second lower punch 12 is flush with the upper end surface 11a of the first lower punch 11, the upper punch 13 is moved to a third predetermined position (the green compact W1 is handled by the handling mechanism (FIG. It is raised to a position where it can be taken out (not shown)) (third extrusion step).

  The green compact W1 can be taken out from the press molding machine through the first to third extrusion steps.

<Second Embodiment>
The configuration of the green compact W manufactured by the manufacturing method according to the present embodiment is the same as that shown in FIG. Therefore, for the sake of simplicity, description of the green compact W is omitted. Moreover, the structure of the metal mold | die in the press molding machine which manufactures a green compact is also the same as what is shown by FIGS. That is, as shown in FIGS. 4 to 5, the mold according to the present embodiment also includes the die 30, the first lower punch 31, the second lower punch 32, the third lower punch 33, the first upper punch 34, and the second upper punch. A punch 35 and a core rod 36 are provided. Therefore, for the sake of simplicity, common constituent elements are given the same reference numerals, and descriptions thereof are omitted.

  4-5 is process explanatory drawing of the manufacturing method which concerns on this embodiment. In the manufacturing method according to the present embodiment, the steps from powder feeding until compression molding is completed ((a) to (c) in FIG. 4) are the conventional manufacturing shown in (a) to (c) in FIG. The method is the same as that of the conventional manufacturing method shown in FIGS. 9 (d) and 10 (d), except that the step of taking out the green compact W from the mold after completion of compression ((d) to (g) in FIG. 5). Is different.

  First, as shown in the left half of FIG. 4A, a powder feeder is provided in a space defined by the die 30, the first lower punch 31, the second lower punch 32, the third lower punch 33, and the core rod 36. (Not shown) is used to fill the powder material P. Next, as shown in the right half part of FIG. 4A, the die 30 and the core rod 36 are raised so that the upper surface of the powder material P filled in the space is higher than the upper end surfaces of the die 30 and the core rod 36. Position below (underfill).

  Next, as shown in FIG. 4B, in conjunction with the lowering of the first upper punch 34 and the second upper punch 35, the die 30, the first lower punch 31 and the core rod 36 are lowered, and the space is reduced. Then, it is transformed into a space having a cross-sectional shape having a vertical dimension that is a predetermined multiple of the cross-sectional shape of the green compact W after compression molding (transfer). This “predetermined magnification” varies depending on the material and application of the green compact W, but is usually about 2 to 2.5 times.

Next, as shown in FIG. 4C, the first upper punch 34 and the second upper punch 35 are lowered, and the powder material P filled in the space is compression-molded. At that time, in conjunction with the lowering of the first upper punch 34 and the second upper punch 35, the die 30, the third lower punch 33 and the core rod 36 are lowered by a predetermined distance.
The compression molding of the powder material is completed by the steps (a) to (c) in FIG. The green compact W obtained by the completion of the compression molding is taken out from the mold through the steps shown in FIGS.

  First, instead of lowering the die 30 as in the prior art, as shown in FIG. 5D, only the core rod 36 is exposed at the position where the inner peripheral surface 42c of the arm portion 42 of the green compact W is exposed ( Lower to the first predetermined position (first extrusion step). By exposing the inner peripheral surface 42c of the arm portion 42 of the green compact W, the spring back pressure in the arm portion 42 can be released inward.

  Next, as shown in FIG. 5 (e), the die 30, the first lower punch 31, and the third lower punch 33 other than the third lower punch 33 in contact with the inner peripheral surface 40c of the short cylindrical portion 40 of the green compact W. The second lower punch 32, the first upper punch 34, the second upper punch 35, and the core rod 36 are raised to a position (second predetermined position) at which the inner peripheral surface 40c of the short cylindrical portion 40 is exposed (second extrusion step). . Thereby, the green compact W is extracted from the third lower punch 33, and the inner peripheral surface 40c of the short cylindrical portion 40 of the green compact W is exposed. By exposing the inner peripheral surface of the green compact W, the spring back pressure of the entire green compact W can be released to the inside. As a result, the contact surface pressure between the die 30 and the first upper punch 34 can be reduced.

  Next, as shown in FIG. 5 (f), the upper end surfaces 31 a and 32 a of the first lower punch 31 and the second lower punch 32 are positioned at the same height as the upper surface 30 a of the die 30 (a third predetermined position). The first lower punch 31, the second lower punch 32, the first upper punch 34, and the second upper punch 35 are simultaneously raised to the position (third extrusion step). Thereby, the green compact W can be extracted from the die 30 in a state where the contact surface pressure between the die 30 and the first upper punch 34 is reduced.

  Next, the lower end surface 34a of the first upper punch 34 that presses the upper surface 41b of the flange portion 41 is flush with the lower end surface 35a of the second upper punch 35 that presses the upper surface 42b of the arm portion 42. 2. The first upper punch 34 is raised while pressing the upper surface 42b of the arm portion 42 with the upper punch 35. Then, after the lower end surface 34a of the first upper punch 34 is flush with the lower end surface 35a of the second upper punch 35 that presses the upper surface 42b of the arm portion 42, the first upper punch 34 and the second upper punch 34 The punch 35 is simultaneously raised to a predetermined position (a position where the green compact W can be taken out by a handling mechanism (not shown); a fourth predetermined position), and then, as shown in FIG. The second lower punch 32 in contact with the lower end surface 40a of the short cylindrical portion 40 is raised by a predetermined distance (about 0.1 cm) (fourth extrusion step).

  The green compact W can be taken out from the press molding machine through the first to fourth extrusion steps.

  According to the manufacturing method according to the present embodiment (first embodiment and second embodiment), wear and damage of the die and punch can be reduced, and the height of burrs generated in the green compact is reduced. be able to. In the green compact manufacturing process, the powder material is extruded into the gap between the die and the punch and remains as burrs at the end of the green compact (for example, the end indicated by x in FIG. 8). In such a manufacturing method, since the contact surface pressure between the die and the green compact is reduced during the extrusion process, the height of the burr can be made smaller than that when the green compact is manufactured by the conventional method.

[Other variations]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims.
For example, in the above-described embodiment, the flange portion is formed on the outer periphery of one end in the axial direction of the short cylindrical portion of the green compact W, and the arm portion is formed on the inner periphery of the other end in the axial direction. The position of the arm portion in the axial direction can be appropriately changed as shown in FIGS. For example, in the green compact shown in FIG. 6A, a flange portion and an arm portion are formed at one end in the axial direction of the short cylindrical portion. Further, in the green compact shown in FIG. 6B, the flange portion and the arm portion are formed not at the axial end portion of the short cylindrical portion but at a position slightly closer to the center from the end portion.
Similarly, for the green compact W1, the position of the flange portion in the axial direction can be appropriately changed as shown in FIGS. 7 (a) to 7 (b).

Moreover, in embodiment mentioned above, although the tooth | gear is formed in the outer periphery of the flange part of the green compact W, this invention is applicable also to the green compact which does not form this tooth | gear.
Moreover, although the green compact W in embodiment mentioned above has the round hole formed in the center, it can also be set as the shape which abbreviate | omitted this round hole. In this case, the press molding machine does not require a core rod, and the arm portion can be formed by the upper punch and the lower punch. As shown in FIGS. 6A to 6B, the “arm portion” in the present specification is only one that protrudes inward from the outer peripheral surface of the short cylindrical portion by a predetermined distance to provide a round hole in the center. Instead, as shown in (c) of FIG. 6, it is a concept that includes a lid-like shape in which a round hole is not formed at the center.

  In the above-described embodiment, the second lower punch 32 that contacts the lower end surface 40a of the short cylindrical portion 40 of the green compact W is raised by a predetermined distance in the last stage of the fourth extrusion step. This is to make it easy to take out the green compact W. If the green compact W can be taken out even if this rise is omitted, the second lower punch 32 is moved a predetermined distance at the final stage of the fourth extrusion process. Only the step of raising can be omitted.

DESCRIPTION OF SYMBOLS 1: Short cylindrical part 1a: Lower end surface 1b: Upper end surface 1c: Inner peripheral surface 2: Flange part 2a: Lower surface 3: Round hole 10: Die 10a: Upper end surface 11: First lower punch 11a: Upper end surface 12: Second Lower punch 12a: Upper end surface 13: Upper punch 13a: Lower end surface 14: Core rod 15: Round hole 30: Die 30a: Upper surface 31: First lower punch 31a: Upper end surface 32: Second lower punch 32a: Upper end surface 33: First 3 Lower punch 33a: Upper end surface 34: First upper punch 34a: Lower end surface 35: Second upper punch 35a: Lower end surface 36: Core rod 37: Round hole 40: Short cylindrical portion 40a: Lower end surface 40b: Upper end surface 40c: Inside Peripheral surface 41: flange portion 41a: lower surface 41b: upper surface 42: arm portion 42a: lower surface 42b: upper surface 42c: inner peripheral surface 43: round hole 44: tooth P: powder material W: green compact W1: green compact

Claims (4)

A method for producing a green compact having a flange portion formed on the outer periphery of a short cylindrical portion using a mold,
The mold includes a die having a round hole in the center, a lower punch disposed in the round hole of the die, an upper punch disposed in the round hole of the die above the lower punch, A core rod disposed inside the lower punch,
At least one of the lower punch and the upper punch is composed of a first punch and a second punch disposed in order from the outside in the round hole of the die,
After the compression molding of the green compact is completed, the core rod is extracted to open the inner diameter side of the short cylindrical portion of the green compact, and the spring back pressure of the green compact is released to the inner diameter side.
, A method for producing green compacts. The lower punch is composed of a first lower punch and a second lower punch arranged in order from the outside in the round hole of the die,
A first extrusion step of extracting the core rod to a first predetermined position where an inner peripheral surface of the short cylindrical portion is exposed after the compression molding of the green compact is completed;
After the first extrusion step, the first lower punch, the second lower punch, and the upper punch are simultaneously raised to a second predetermined position where the outer peripheral surface of the flange portion is exposed, and after the second extrusion step, The upper punch presses the upper surface of the short cylindrical portion until the upper end surface of the second lower punch that presses the lower surface of the short cylindrical portion is flush with the upper end surface of the first lower punch that presses the lower surface of the flange portion. However, the upper punch and the second lower punch are raised, and after the upper end surface of the second lower punch is flush with the upper end surface of the first lower punch, the upper punch is raised to the third predetermined position. The manufacturing method of the green compact of Claim 1 including the 3rd extrusion process to make. A method of manufacturing a green compact in which a flange portion is formed on the outer periphery of a short cylindrical portion and an arm portion is formed on the inner periphery of the short cylindrical portion using a mold,
The mold includes a die having a round hole in the center, a first lower punch and a second lower punch disposed in order from the outside in the round hole of the die, and the first lower punch and the second lower punch. A first upper punch and a second upper punch disposed in order from the outside in the round hole of the die on the upper side;
A method for producing a green compact, wherein after the compression molding of the green compact is completed, the inner diameter side of the short cylindrical portion of the green compact is opened to release the spring back pressure of the green compact toward the inner diameter side. The flange portion is formed at one axial end of the short cylindrical portion,
The arm part is formed at the other axial end of the short cylindrical part,
The mold includes a third lower punch inside the second lower punch, and a core rod disposed inside the third lower punch,
A first extrusion step of lowering the core rod to a first predetermined position at which an inner peripheral surface of the arm portion is exposed after compression molding of the green compact is completed;
After the first extrusion step, the die, the first lower punch, the second lower punch, the first upper punch, the second upper punch, and the core rod are simultaneously raised to a second predetermined position where the inner peripheral surface of the short cylindrical portion is exposed. A second extrusion step,
After the second extrusion step, the first lower punch, the second lower punch, the first upper punch, and the second upper punch are simultaneously raised to a third predetermined position, and after the third extrusion step, the flange portion While pressing the upper surface of the arm portion with the second upper punch until the lower end surface of the first upper punch pressing the upper surface is flush with the lower end surface of the second upper punch pressing the upper surface of the arm portion, After the first upper punch is raised and the lower end surface of the first upper punch is flush with the lower end surface of the second upper punch that presses the upper surface of the arm portion, the first upper punch and the second upper punch 4. A method for producing a green compact according to claim 3, further comprising: a fourth extruding step of simultaneously raising the second punch to a fourth predetermined position and then raising the second lower punch contacting the lower end surface of the short cylindrical portion by a predetermined distance. .

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