JP5418942B2 - Mold for molding, sizing mold and method for manufacturing sintered part using the same - Google Patents

Description

  The present invention relates to a method for manufacturing a sintered part. More specifically, the present invention relates to a method for manufacturing a sintered part in which metal powder is molded and sintered and then sized, and more particularly to a method for increasing the dimensional accuracy of a sizing product.

  In the method of manufacturing a sintered part, first, iron powder is introduced into a molding hole formed in a molding die, and the powder is pressed and solidified by the molding die to produce a molded product. Thereafter, the molded product is introduced into a sintering furnace and sintered to produce a sintered product. Recently, since the required dimensional accuracy has been increased, dimensional correction is often performed by repressurizing the sintered product with a sizing die.

  A die, an upper punch, and a lower punch are used for the molding die. If the product has an inner diameter, a core is also used. When the product has a ridge, a convex or a concave, the upper punch or the lower punch is increased, and the ridge, convex or concave is formed by the second and third punches. However, when the tip area of the flange, convex or concave portion is very small, or when the side surface and the corner of the end surface of the flange, convex or concave portion are sides, the outer diameter of the core of the molding die or the die A stepped core or stepped die having a step in the inner diameter may be used (see, for example, Patent Document 1). Patent Document 1 describes a method of forming a cylindrical green compact having a convex portion on its inner diameter using a stepped core.

JP 2008-272895 A

  In the case where a molded product having a convex portion having a side surface that protrudes in the outer diameter direction and the axial direction at a corner portion where the component outer periphery and the component end surface intersect with each other is formed by the stepped core or the stepped die.

  In general, when molding is performed using a stepped core or a stepped die, an axially downward tensile stress is generated in a portion formed by the stepped portion when the molded product is extracted from the mold above the die after molding. If the tensile stress is equal to or higher than the fracture strength of the molded product, there is a possibility of causing cracks.

  In order to prevent this crack, measures are taken to prevent the generation of tensile stress by tapering the side surface of the stepped portion. However, when the taper shape is not allowed as the shape of the product, it is necessary to remove the taper by processing after sintering.

  In the case of a molded product having a convex part having a side surface that protrudes in the outer diameter direction and the axial direction at the corner part where the part outer periphery and the part end surface intersect, when the convex part is formed with a stepped die, the molded product outer periphery or convex part side surface Thus, the taper shape is formed, and it is necessary to remove the taper by processing after sintering.

  In a molded body having a convex portion having a side surface that protrudes in the outer diameter direction and the axial direction at the corner portion where the component outer periphery and the component end surface intersect, when the convex portion is not formed by a stepped die, the outer diameter direction and the axial direction On the protruding side surface, a portion corresponding to the outer diameter from the outer periphery of the component is formed by a die, and a portion corresponding to the inner diameter side from the outer periphery of the component is formed by a core or a lower punch. The fitting portion of the die and core or die and punch is called a mold dividing position. Since the respective molds move relative to each other, a certain amount of clearance is provided in the fitting portion. There is also a clearance between the molds at the mold dividing position. There is a possibility that powder enters the clearance, and mold split bars are formed in the molded product as burrs during molding. In this case as well, when the mold dividing bar is not allowed as the shape of the product, it is necessary to remove the mold dividing bar by processing after sintering.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a product having a convex portion having a side surface that protrudes in an outer diameter direction and an axial direction at a corner portion where a component outer periphery and a component end surface intersect. Another object of the present invention is to provide a manufacturing method that does not remove the taper shape by the processing after sintering or remove the mold dividing streaks.

In order to solve the above problems, in the present invention,
A method for manufacturing a sintered part in which a convex part having a side surface protruding in the outer diameter direction and the axial direction is formed at a corner part where the outer periphery and end face of the part intersect,
The manufacturing method includes a molding process, a sintering process, and a sizing process,
For the molding die in the molding step, a molding die set so that a molding die dividing position between the molding die and the molding core or the molding punch is provided on the side surface of the convex portion is used.
The molding die division position is a straight line extending in the molding axis direction from the corner on the side surface of the convex part,
In the sizing die in the sizing step, a sintered part manufacturing method using a sizing die set so that a sizing die dividing position is provided on a side surface of a convex portion different from the molding die dividing position is used. .

  In the sizing step, the sizing margin at the molding die dividing position is preferably -0.05 to 0. By setting the sizing margin at the mold division position to −0.05 to 0, the mold division stripes can be effectively removed.

  Since the molding die of the present invention uses a molding die provided with a molding die dividing position of a molding die and a molding core or molding die and a molding punch on the side surface of the convex portion, A part of the outer periphery of the molded product and a part of the convex portion in the outer diameter direction is formed by the molding die. Since no taper is imparted to the outer periphery, it is not necessary to remove the tapered shape after molding.

  In the sizing step, a sizing mold is used in which a sizing mold dividing position is provided on a side surface of a convex portion different from the molding mold dividing position. Therefore, the sizing mold comes into contact with the mold dividing line formed at the molding mold dividing position, and the shape of the mold dividing line is corrected by the sizing mold, or the mold dividing line is removed. . Therefore, it is not necessary to remove the mold dividing stripe after sizing.

Sectional drawing which shows the outline | summary of an example of the metal mold | die for shaping | molding of this invention (A) A perspective view from the upper surface of the molded product molded with the molding die of the present invention, (b) a perspective view from the lower surface of the molded product molded with the molding die of the present invention. The perspective view which cut | disconnected the molding die of this invention in the XX cross section of Fig.3 (a). Sectional drawing which shows the outline | summary of an example of the metal mold | die for sizing of this invention (A) The perspective view from the upper surface of the sizing product processed with the sizing mold of the present invention, (b) The perspective view from the lower surface of the sizing product processed with the sizing mold of the present invention The perspective view which cut | disconnected the molding die of this invention in the YY cross section of Fig.5 (a).

Embodiments of the present invention will be described below with reference to the drawings.
The method for manufacturing a sintered part according to the present invention is to manufacture a sintered product by molding a molded product with a molding die and then sintering with a sintering furnace, and then sizing the sintered product with a sizing die. Is. The target sintered part is a sensor ring for automobile parts. Hereinafter, the molding process, the sintering process, and the sizing process will be described.

[Molding process]
The molding die shown in FIG. 1 is configured by combining a molding die 1, a molding upper punch 2, a molding lower punch 3 facing the molding upper punch 2, and a molding core 4. Yes. The molding die 1 is supported by a die plate (not shown) of a molding press. The molding upper punch 2 is supported by an upper punch plate (not shown) driven by the upper ram of the molding press, and the molding lower punch 3 is supported by a base plate (not shown). The molding core 4 is connected to a yoke plate (not shown) driven by the lower ram of the molding press.

As the raw material powder for the sintered part, iron powder having a composition of 2.0 Cu-0.8 C-residual Fe is used. The raw material powder is introduced into a cavity formed in a molding die, and pressed by a molding die 1, a molding upper punch 2, a molding lower punch 3 and a molding core 4 to have a density of about 6.8 g / cm. ³ molded product 5 is formed. The molded product outer peripheral surface 6, the convex outer peripheral surface 7, and the convex side surface 14 on the outer diameter side of the mold dividing position 12 are molded by the molding die 1 as shown in FIG. The end surface 9, the inner peripheral surface 10, the convex inner peripheral surface 11, and the convex side surface 13 on the inner diameter side of the mold dividing position 12 are molded by the molding core 4 having a step. The convex end face 8 of the molded product is molded by the lower punch 3 for molding.

  When the molded product is extracted from the mold above the die after molding, a downward tensile stress is generated on the molded product 5 due to friction between the molded product 5 and the molding die 1. However, since the end surface 9 and the convex end surface 8 of the molded product 5 are supported by the molding core 4 and the lower punch 3 for molding, the molded product 5 is not cracked. Therefore, in the present invention, it is not necessary to form a taper for extracting the molded product in the molding die, and it is not necessary to remove the tapered shape formed in the molded product 5 after the molding when the taper is formed.

  When the radial distance between the convex inner circumferential surface 11 formed on the molded product 5 and the molded product inner circumferential surface 10 is large, the second molding lower surface is different from the lower punch 3 for molding the end surface 9 of the molded product 5. It is also possible to mold using a punch. When the convex inner peripheral surface 12 and the molded product inner peripheral surface 11 formed on the molded product 5 coincide with each other, the step of the molded core 4 is not necessary, and the end surface 9 of the molded product 5 is the second lower punch. It is formed by.

[Sintering process]
The molded product 5 is introduced into a sintering furnace and sintered at 1100 to 1200 degrees.

[Sizing process]
The sizing mold shown in FIG. 4 is a combination of a sizing stepped die 101, a sizing upper punch 102, a sizing lower punch 103 opposed to the sizing upper punch 102, and a sizing stepped core 104. It is configured. Each die is connected to a sizing press machine in the same manner as the molding die.

  The sintered product is introduced into a sizing hole formed in a sizing mold, and is sized by being pressed by a sizing die 101, a sizing upper punch 102, a sizing lower punch 103, and a sizing core. The sizing product outer peripheral surface 106, the convex portion outer peripheral surface 107, the convex portion side surface 112, and the sizing product end surface 109 of the sizing product 105 shown in FIG. 5B are processed by a sizing die 101 having a step. The sizing product end surface 109 is an end surface of the sizing product 105 corresponding to the outer peripheral surface 106, and is an end surface of the sizing product between the convex portions. The inner peripheral surface 110 of the sizing product, the inner peripheral surface 111 of the convex portion, and the end surface 113 of the sizing product are processed by the sizing core 104 having a step. The sizing product end surface 113 is an end surface of a sizing product on the inner diameter side of the convex portion. The convex end surface 113 is formed by the lower punch 103 for sizing.

  The sizing mold is provided with a signing allowance for correcting the size of the sintered product. The sizing die is smaller than the sintered product by the size of the sizing die 101 and the sizing core 104 by the amount of the sizing allowance. If so, it is made large. The sizing allowance is positive when the sintered product is compressed, that is, when the sizing die is smaller than the sintered body and the core is larger than the sintered body. When there is a clearance between the sizing die or core and the sintered product, the value of the sizing allowance was negative. Generally, a sizing allowance is not provided or a clearance is provided at a site that does not require dimensional correction.

Since there is a gap between the molds at the mold dividing position 12 of the molding die, iron powder enters the gap, and a small protrusion is formed on the molded body 5 as a mold dividing line. After the sintering, the mold parting bars remain without being removed, so that a mold parting bar having a height of about 0.1 mm is formed in the sintered product. In the sizing according to the present invention, the sizing die 105 slides on the mold dividing position 12 to size the mold dividing bars, whereby the mold dividing bars can be processed and removed. By setting the sizing allowance at the mold dividing position 12 to -0.05 mm to 0 mm, the height of the mold dividing stripe after sizing became 0.03 mm or less.
When the sizing allowance is −0.05 mm or more, the mold dividing line is about 0.1 mm, and therefore the mold dividing line is effectively removed. When the sizing allowance is 0 mm or less, the mold dividing bars can be removed without applying unnecessary stress to the sintered product.

  Sizing the entire sizing product end surface 112 with a sizing die is preferable because the entire sizing product end surface 112 is sized uniformly and no streaks are formed. In addition, there is an advantage that it is easy to assemble sizing dies.

  When the radial distance between the convex inner peripheral surface 111 and the sizing product inner peripheral surface 110 formed in the sizing product 105 is large, or when the convex inner peripheral surface 111 and the sizing product inner peripheral surface 110 coincide, It is also possible to size the end surface 109 of the sizing product 105 using a second lower sizing punch different from the sizing lower punch 103 without providing a step to the core.

DESCRIPTION OF SYMBOLS 1 Molding die 2 Molding upper punch 3 Molding lower punch 4 Molding stepped core 5 Molded product 6 Molded product outer peripheral surface 7 Molded product convex part outer peripheral surface 8 Molded product convex part end surface 9 Molded product end surface 10 Molded product inner circumference Surface 11 Convex inner peripheral surface 12 Mold division position 13 Convex side surface 14 on the inner diameter side from the mold division position 8 Convex side surface 101 on the outer diameter side from the mold division position 8 Sizing die 102 Top for sizing Punch 103 Sizing lower punch 104 Sizing core 105 Sizing product 106 Sizing product outer peripheral surface 107 Sizing product convex outer peripheral surface 108 Sizing product convex side surface 109 Sizing product end surface 110 corresponding to the sizing product outer peripheral surface 106 Sizing product inner peripheral surface 111 Sizing product convex inner surface 112 Sizing product convex end surface 113 Sizing product convex inner surface corresponding to the sizing convex convex inner surface 111

Claims (3)

A method for manufacturing a sintered part in which a convex part having a side surface protruding in the outer diameter direction and the axial direction is formed at a corner part where the outer periphery and end face of the part intersect,
The manufacturing method includes a molding process, a sintering process, and a sizing process,
For the molding die in the molding step, a molding die set so that a molding die dividing position between the molding die and the molding core or the molding punch is provided on the side surface of the convex portion is used.
The molding die division position is a straight line extending in the molding axis direction from the corner on the side surface of the convex part,
A method of manufacturing a sintered part using a sizing die set so that a sizing die dividing position is provided on a side surface of a convex portion different from the molding die dividing position for the sizing die in the sizing step.   2. The method for manufacturing a sintered part according to claim 1, wherein, in the sizing step, a sizing allowance at the molding die dividing position is −0.05 to 0. 3.   The method for manufacturing a sintered part according to claim 2, wherein the molding die dividing position is a straight line extending in an axial direction from the corner portion on the side surface of the convex portion.

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