JPH0551604A - Device for press-forming powder compact to be sintered - Google Patents

Abstract

PURPOSE:To prevent the inner periphery of a die from getting by a first lower punch on the outer peripheral side deformed by the internal pressure at the time of press-forming the powder compact to be sintered having a large-diameter part and a small-diameter part such as a two-stage sprocket. CONSTITUTION:A first lower punch 13 is vertically movably engaged with the through-hole of a die from the lower part to press the end face of the large- diameter part. A second lower punch is engaged with the inner periphery of the first lower punch 13 to press the end face of the small-diameter part. An upper punch is engaged from the upper part, and the powder material is compressed by the punches. A tapered surface 26 is formed on the tip surface of the first lower punch 13 to produce an inward component force in pressing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the production of a sintered part such as a two-stage idle sprocket in which a large diameter sprocket and a small diameter sprocket are integrated.
The present invention relates to improvement of a pressure molding device for pressure molding a powder molded product before sintering.

[0002]

2. Description of the Related Art Sintering is widely used as a method for manufacturing a relatively small machine part. In this sintering, a long and slender part having a large axial length is formed because of the pressure molding of a powder material. Manufacturing is generally difficult.

By the way, FIG. 8 shows a two-stage idle sprocket used in a valve train of an internal combustion engine.
This is one in which a large-diameter sprocket portion 1 that meshes with the first timing chain on the crankshaft side and a pair of small-diameter sprocket portions 2 that mesh with the second timing chain on the camshaft side are integrated. In the case of manufacturing by sintering, sintering is performed in the shape shown by the imaginary line in FIG. That is, the large-diameter sprocket part 1 having teeth on the outer periphery and the small-diameter part 3 having a constant cross-section having teeth corresponding to the small-diameter sprocket part 2 continuous in a substantially cylindrical shape are once sintered into a shape, afterwards,
Grooves 4 and 5 (see the drawing) are machined in the small diameter portion 3 to form the small diameter sprocket portion 2 separately.

Therefore, the pressure forming prior to the sintering is performed for the shape as shown by the imaginary line in FIG. 8, and the pressure forming apparatus as shown in FIG. 9 is used for this pressure forming. .. In the figure, 11 is a die having a through hole filled with powder material 12, 13 is a substantially cylindrical first lower punch fitted in the inner periphery of the die 11 so as to be vertically movable from below, and 14 is a first A second lower punch 15 fitted to the inner periphery of the lower punch 13 so as to be vertically movable, and 15 is the lower punch 1
An upper punch which is opposed to 3, 14 and is fitted into the die 11 from above, and 16 is a core rod for forming a central hole of the sprocket, and each punch 13 to 15 is moved up and down by hydraulic pressure, for example. ing. Then, as shown in the drawing, after filling the die material 11 with a predetermined amount of the powder material 12, the upper punch 15 is lowered and the first and second lower punches 13 and 14 are raised, so that the powder material 1 is obtained.
2 is strongly compressed from both upper and lower sides to obtain a pressure molded product as shown in FIG. At this time, the upper punch 15
The flat surface side of the large diameter sprocket portion 1 is pressed, and the second lower punch 14 presses the end surface of the small diameter portion 3. Further, the first lower punch 13 presses the end surface of the large diameter sprocket portion 1 which projects outward from the small diameter portion 3. The molded product thus pressure-molded is then heated and sintered at around 1100 ° C.,
And after performing an appropriate post-treatment, as described above, the groove portion 4,
Processing of 5 is performed. (For example, see "Automotive Engineering Complete Book 19", page 55, etc., published by Sankaido Co., Ltd. in April 1980)

[0005]

However, when an attempt is made to press-form a two-step shaped product having a large axial length of the small diameter portion 3 as shown in FIG. 8, the first lower punch 13 will inevitably result in The shape is such that it largely projects from the tip of the second lower punch 14. Therefore, as shown in the explanatory view of FIG. 10, the tip end of the first lower punch 13 is strongly pushed toward the outer peripheral side by the internal pressure of the pressurized powder material 12, and the clearance with the inner periphery of the die 11 is excessively small. As a result, galling tends to occur between the two. Therefore, there is a problem in that the durability of the molding die such as the die 11 is likely to be impaired, and the pressing force required for molding increases, resulting in a significant decrease in production efficiency.

[0006]

The present invention comprises a disc-shaped large diameter portion and a small diameter portion having a relatively large axial length,
A pressure molding device for pressure molding a powder molding product for sintering having teeth formed on the outer periphery thereof, which is vertically movably fitted in a die and protrudes outward from a small diameter portion. And a substantially cylindrical first lower punch that presses the end surface of the large diameter portion, and vertically movably fitted to the inner peripheral side of the first lower punch,
And a second lower punch that presses the end surface of the small diameter portion, and a lower die that is fitted into the die so as to face the lower punch,
In a pressure forming apparatus including an upper punch that presses the other end surface of the large diameter portion, a taper surface in a direction in which a component force to the inner peripheral side is generated at the time of pressing, at the tip surface of the first lower punch. It is characterized by the provision of.

[0007]

When the powder material is vertically compressed between the first lower punch and the upper punch, the reaction force generates a component force toward the inner peripheral side along the taper surface of the tip surface of the first lower punch. To do. That is, the tip portion of the first lower punch is pushed toward the inner peripheral side, and the clearance with the die is appropriately maintained against the internal pressure of the powder material corresponding to the small diameter portion.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to the sintering of the above-described two-stage idle sprocket will be described in detail with reference to the drawings.

FIG. 3 is a sectional view showing the overall construction of the pressure molding apparatus according to the present invention. A die 11 supported by a frame (not shown) has a through hole for filling the powder material 12. 21 is formed along the up-down direction, and the core rod 16 for forming the center hole of the sprocket is arranged along the center portion thereof. The core rod 16 is fixed relatively to the die 11.
Further, spline-shaped teeth corresponding to the tooth shape of the large diameter sprocket portion 1 are formed on the inner peripheral surface of the through hole 21 of the die 11.

A substantially cylindrical first lower punch 13 is fitted into the through hole 21 from below. This first lower punch 1
3 presses the end surface of the large-diameter sprocket portion 1 that protrudes outward from the small-diameter portion 3, and as shown in FIG. 2, the spline-shaped teeth are approximately the same as the tooth shape of the large-diameter sprocket portion 1 on the outer peripheral surface. 22 and is fitted to the teeth on the side of the through hole 21 described above so as to be vertically movable. Then, the first lower punch 13
The holder 23 is linked to a hydraulic lift mechanism (not shown). Further, on the inner peripheral surface of the first lower punch 13, spline-shaped teeth 24 corresponding to the tooth shape of the small diameter sprocket portion 2 are formed.
Are formed (see FIG. 2). In addition, the teeth 2 on the inner peripheral side
4 is provided only on the tip end portion corresponding to the molded product, and the tooth 24 is provided at the tip end corresponding to the connection portion with the large diameter sprocket portion 1 which is finally finished by machining the groove portion 5. Not formed (see FIG. 1).

A substantially cylindrical second lower punch 14 is arranged between the inner periphery of the first lower punch 13 and the core rod 16. The second lower punch 14 presses the end surface of the small diameter portion 3, and has spline-shaped teeth on the outer peripheral surface of the tip end portion that are substantially the same as the tooth shape of the small diameter sprocket portion 2.
This is fitted to the teeth 24 on the inner circumferential side of the first lower punch 13 described above so as to be vertically movable, and the core rod 16 is slidably fitted to the inner circumferential surface having a circular cross section. The second lower punch 14 is linked to a hydraulic lift mechanism (not shown) via a holder 25.

Above the through hole 21 of the die 11, the upper punch 15 is arranged so as to face the lower punches 13 and 14.
Are arranged. The upper punch 15 has spline-shaped teeth on the outer peripheral surface that are substantially the same as the tooth shape of the large-diameter sprocket part 1, and these are fitted in the teeth on the inner periphery of the through hole 21 so as to be vertically movable. Further, the tip end surface thereof is a substantially flat surface so as to press the end surface of the large diameter sprocket part 1 on the flat surface side. The upper punch 15 is also linked to a hydraulic lift mechanism (not shown) so that it can be moved up and down by hydraulic pressure.

On the other hand, the tip surface of the first lower punch 13 is
As shown in detail in FIG. 4, a part of the inner peripheral portion is tapered surface 26.
Has become. The tapered surface 26 has an angle of about 10 °, for example, and the inner peripheral portion is inclined so as to project toward the distal end side so that a component force is generated toward the inner peripheral side by the pressing force. In other words, the inner peripheral side portion of the flat surface 27 near the outer periphery projects in a substantially triangular cross section. Further, the inner peripheral edge 28 and the connection portion 29 with the flat surface 27 are each an appropriate R surface so that an edge-shaped concave portion that causes stress concentration does not occur on the surface of the molded product. It should be noted that the outer peripheral edge of the tip surface of the first lower punch 13 is provided with a loose R projection 30 corresponding to the tooth portion of the large diameter sprocket part 1.

In order to mold the above-mentioned powder molded product for a sprocket using the pressure molding device constructed as described above, first, the die 11 and the first and second lower punches 13 and 14 are used.
A predetermined amount of the powder material 12 is filled in the concave portion formed by
The upper punch 15 is lowered from above and the first and second lower punches 13 and 14 are raised so that the powder material 12 is strongly compressed from both upper and lower sides. And after compressing enough,
The upper punch 15 is released, and the molded product is pushed up by the first lower punch 13 or the second lower punch 14 to raise the die 11.
Take out from. As a result, a two-step powder molded product in which the large diameter sprocket portion 1 and the small diameter portion 3 are integrated as shown in FIG. 6 is obtained.

Here, in the pressure forming apparatus, the taper surface 26 provided on the tip surface of the first lower punch 13 causes the component force to the radially inner peripheral side at the time of pressing, as shown in FIG. F1 is generated and the powder material 12 opposes the internal pressure F2 which tends to expand toward the outer peripheral side. Therefore, the first lower punch 13
Despite being largely projected from the second lower punch 14, the deformation of the first lower punch 13 toward the outer peripheral side, and by extension, the die 1
1 The galling with the inner circumference is prevented. Therefore, the durability of the molding die such as the die 11 is improved, and the pressing force required for the pressure molding is relatively small. Also, the first
The pressurization and compression by the lower punch 13 can be performed more reliably, and the tooth surface at the connecting portion between the small diameter portion 3 and the large diameter sprocket portion 1 and the inner peripheral portion of the large diameter sprocket portion 1 are firmly and accurately. It can be molded well. Incidentally, in the pressed powder molded product, a slight recess 31 is formed corresponding to the tapered surface 26 as shown in FIG. 6, but this is not a problem.

The above-mentioned powder molded product is then heated and sintered at a temperature of 1100 ° C. Then, after appropriate post-treatment, the groove portions 4 and 5 are machined to finally obtain a two-stage idle sprocket including the large diameter sprocket portion 1 and the small diameter sprocket 2 as shown in FIG. Of.

In the above embodiment, only the inner peripheral side portion of the tip surface of the first lower punch 13 is the tapered surface 26, but the entire tip surface may be a gentle taper surface.

Further, the pressure molding apparatus of the present invention can be applied to sintering of a gear in which a large-diameter gear and a small-diameter gear are integrated, in addition to the sprocket as described above.
When it is used for molding such a gear, the connection between the large-diameter gear and the small-diameter gear can be finished neatly, so that excess thickness and machining can be minimized.

[0019]

As is apparent from the above description, according to the pressure molding apparatus for a powder molded product for sintering according to the present invention, the disk-shaped large diameter portion has the small diameter portion having a large axial length. The integrated powder molded product can be easily pressure-molded. In particular, galling of the first lower punch surrounding the small diameter portion and the die can be prevented, the durability of the forming die can be improved, and the forming can be performed with high precision with a relatively small pressing force.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a first lower punch of a pressure molding device according to the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a sectional view showing the entire pressure molding apparatus.

FIG. 4 is an enlarged cross-sectional view of an essential part showing a tip surface of a first lower punch.

FIG. 5 is an explanatory view at the time of pressure molding in this example.

FIG. 6 is a half cross-sectional view of a powder molded product obtained by the pressure molding device of this example.

FIG. 7 is a half cross-sectional view of a two-stage idle sprocket formed based on the powder molded product.

FIG. 8 is a cross-sectional view of a two-stage idle sprocket formed by using a conventional device.

FIG. 9 is a cross-sectional view of a main part of a conventional pressure molding device.

FIG. 10 is an explanatory view of this conventional example at the time of pressure molding.

[Explanation of symbols]

 11 ... Die 13 ... First lower punch 14 ... Second lower punch 15 ... Upper punch 26 ... Tapered surface

Claims (1)

[Claims] 1. A pressure molding for pressure-molding a powder molding product for sintering, comprising a disk-shaped large-diameter portion and a small-diameter portion having a relatively large axial length, and teeth formed on the outer periphery of each. A first lower punch having a substantially cylindrical shape, which is fitted in a die so as to be vertically movable from below and presses an end face of a large-diameter portion projecting outward from a small-diameter portion, and the first lower punch. A second lower punch that fits vertically inward on the inner peripheral side and presses the end surface of the small diameter portion, and a second lower punch that is fitted into the die from above so as to face these lower punches, and In a pressure forming apparatus including an upper punch that presses the other end surface, a taper surface is provided on the tip end surface of the first lower punch in a direction in which a component force is generated toward the inner peripheral side during pressurization. Pressure molding equipment for powder molding products for sintering.