JPH05279704A - Production of sintered and forged parts - Google Patents

Abstract

PURPOSE:To provide the process for production of the sintered and forged parts which can minimize plastic deformation and can easily separate these parts to two. CONSTITUTION:The mechanical characteristics (density, C, Cu contents, etc.) near the breaking part of a molding W1 (W2) in the process for production of the sintered and forged parts including respective stages for powder mixing, premolding, sintering, forging, cooling and separating are varied from the characteristics in the other parts and the molding W1 is broken and separated at the temp. lower than a brittle fracture initiation temp. The impact value of metallic materials in general increases in proportion to their density and inverse proportion to their C and Cu contents. Then, the impact value near the breaking part of the molding W1 (W2) before the sepn. by breaking decreases locally if the density near the above-mentioned breaking part is previously made smaller than the density of the other parts or if the C and Cu contents are previously enriched and, therefore, the molding W2 is easily plastically broken in the breaking part simply by applying small energy thereto. The molding is separated to the two parts (connecting rod body 15A and bearing cover 15B). The plastic deformation of the molding W2 at the time of the is thus minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sintered forged part including a separation step due to brittle fracture.

[0002]

2. Description of the Related Art Sintered forged parts obtained by a so-called powder metallurgy method are widely used as automobile parts and the like because they are expected to have high material yield and high precision.

By the way, in the production of connecting rods for internal combustion engines, for example, these are integrally molded as sintered forged parts, and then the large end is mechanically cut to separate the connecting rod body and the bearing cover, and the mating surface between them is formed. After smooth machining, the bearing cover was assembled to the connecting rod body and, in this state, a crank pin hole at the large end was bored, which required an increase in the number of machining steps and an increase in cost.

Therefore, a notch such as a scribe groove is formed in advance at the large end of the connecting rod which is a sintered forged component, and a shock is applied to the large end to cause brittle fracture of the large end at the notch. A method of separating the bearing cover from the end has been proposed (for example, see Japanese Patent Laid-Open No. 1-272705).

[0005]

However, according to the above conventional method, a large amount of energy is required for brittle fracture, and a large plastic deformation occurs at the large end during fracture,
When the bearing cover is reassembled, there has been a problem that the mating surface between the bearing cover and the connecting rod body is displaced.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for manufacturing a sintered forged component which can be easily separated into two parts while minimizing plastic deformation. To do.

[0007]

In order to achieve the above object, the present invention provides a method for producing a sintered forged part including powder mixing, preforming, sintering, forging, cooling, and separating steps. It is characterized in that the mechanical properties in the vicinity of the fractured part of are different from those of other parts.

Further, in the present invention, in the manufacturing method, the mechanical properties in the vicinity of the fractured portion of the molded body are made different from those of other portions, and the molded body is fractured at a temperature lower than the brittle fracture start temperature. The feature is that they are separated.

[0009]

[Function] Generally, the impact value of a metal material is proportional to the density,
It increases in inverse proportion to the C and Cu contents. Therefore, the density in the vicinity of the fractured part of the molded body before the fracture separation (the intermediate molded body that has undergone the preforming, sintering or forging process) is made smaller than that of the other portions, or the C and Cu contents are changed to other contents. If it is made larger than that of the part, the impact value in the vicinity of the rupture part will locally decrease, so the molded body will be easily plastically ruptured at the rupture part and separated into two parts only by applying a small amount of energy. In this case, the plastic deformation of the formed body is minimized, and a high quality sintered forged part can be obtained.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

1 (a) to 1 (h) are explanatory views showing the method of the present invention in the order of steps thereof, and in this embodiment, a method for manufacturing a connecting rod for an internal combustion engine will be particularly described.

First, as shown in FIG. 1A, raw material powders Fe, C and Cu powders are put in a container 1 and agitated by a stirrer 2 to uniformly mix them. At this time,
As the content of C and Cu powder, a value (for example, 0.7 ± 0.1% C, 2% Cu) that gives a shock value as small as possible without impairing the function as a connecting rod is set. Is set.

Next, the uniformly mixed raw material powder is shown in FIG.
As shown in (b), it is placed in a mold 3 and pressed by a press 4 to be preformed, and a preformed body (forging material) W1.
To get At this time, as shown in FIG. 2A, a notch 7 for propagating cracks is formed in the fractured portion (the inner peripheral portion of the crankpin hole 6) of the connecting rod large end portion 5 of the preform W1. .. The notch 7 is, as shown in FIG.
You may form in the site | part except the outer side surface of a fracture part.

The preform W1 obtained as described above is put into a sintering furnace 10 as shown in FIG. 1 (c) and heated to a predetermined temperature by a heater 11.
The metal powder (Fe, C, Cu that constitutes the preformed body W1
Particles of (powder) are firmly bonded by sintering. At this time, in the vicinity of the fractured portion of the connecting rod large end portion 5 of the preform W1 (the area surrounded by the chain line in FIGS. 2A and 2B) S
The C and Cu contents of are locally increased by the solid phase diffusion method. As a specific method of locally increasing the Cu content, a method of sintering the copper wire around the cut portion S while the copper wire is wound can be considered. On the surface of the notch 7 formed in the preform W1, a Fe ₃ O ₄ coating having a thickness of 5 to 10 μm is formed by steam treatment.

Next, the preformed body W1 which has been subjected to the above-mentioned sintering treatment is taken out from the sintering furnace 10, put in a forging die 12 as shown in FIG. 1 (d), and hot forged by a forging machine 13. ,
A final molded body W2 having a shape close to the final product as shown in FIG. 1 (e) is obtained. At this time, in the vicinity of the fractured part where the notch 7 of the final molded body W2 is formed (in FIGS. 2 (a) and 2 (b)). The density of a region S surrounded by a chain line is set to be smaller than that of other portions. As a specific method for locally lowering the density in the vicinity S of the fracture portion, for example, as shown in FIG.
There are methods shown in (b) and (c). That is, this method
Using the upper and lower molds 8 and 9 as shown in FIG.
A method for obtaining a molded product W2 ′ having a thick portion S (shaded portion) S near the fractured part as shown in (b), and according to the method, the mold pressure applied to the vicinity S of the cut portion of the molded product W2 ′ is small. Therefore, the volume in the vicinity S of the cut portion becomes larger than that in the other portions, so that the density becomes small. And FIG.
By cutting the build-up portion (the portion outside the broken line) in the vicinity S of the cut portion of the formed body W2 ′ shown in FIG.
It is possible to obtain a compact W2 having a small density only in the vicinity S of the cut portion as shown in (c).

As a result of the forging, the notch 7 is formed as shown in FIG.
As shown in (a) and (b), the notch 7 has a slit shape when closed, but since the Fe ₃ O ₄ coating is formed on the surface of the notch 7 as described above, the slit surfaces of the notch 7 are There is no sticking. If the notch 7 is not formed during the preforming, the notch 7 may be formed in this forging step.

The final compact W2 obtained by the above forging is, as shown in FIG. 1 (e), a coolant (liquid nitrogen, alcohol / dry ice mixed liquid, etc.) in the constant temperature bath 14.
It is immersed in L for a predetermined time and cooled to a temperature lower than the brittle fracture start temperature (the temperature at which the impact value starts to decrease). Note that it is not necessary to uniformly cool the entire final formed body W2 as in the present embodiment, but only the vicinity S of the cut portion may be cooled.

When the final molded body W2 is cooled to the above temperature, a bolt hole 5a is formed in the connecting rod large end portion 5 of the final molded body W as shown in FIG. 1 (f), and the connecting rod large end portion 5 is formed. Is applied with a force in the direction of the arrow shown. Then, brittle fracture occurs at the notch 7 in the connecting rod large end portion 5, and the final molded body W2 is separated into the connecting rod body 15A and the bearing cover 15B.

By the way, the characteristics of the impact value depending on the density, C, Cu content and temperature of the metal material are shown in FIGS. 5, 6, 7 and 8.
As is clear from these figures, the impact value (toughness) increases in proportion to the density and decreases with an increase in C, as shown in FIG. Further, there is a region where the impact value becomes the lowest for a specific Cu content. Further, as shown in FIG. 8, in the region R where the temperature is lower than the brittle fracture initiation temperature T ₀ ,
The impact value becomes extremely small (that is, the energy required for breaking is small).

Therefore, as in this embodiment, the molded body W1
(W2) The density of the vicinity S of the fractured part is set to be small, and
If the u content is enriched and further the fracture occurs in the temperature range R lower than the brittle fracture initiation temperature T ₀ , the connecting rod large end portion 5 of the final compact W2 can be formed by adding a small amount of energy.
Easily plastically ruptures from the notch portion 7, and the final molded body W2
Is separated into the connecting rod body 15A and the bearing cover 15B, and the plastic deformation of the final molded body W2 at the time of breakage is suppressed to the minimum.

Next, the separated bearing cover 15B is shown in FIG.
As shown in (g), it is fitted to the connecting rod body 15A, and a tightening bolt 16 is screwed into the bolt hole 5a formed in the large end portion 5 of the connecting rod to fasten the bearing cover 15B to the connecting rod body 15A to integrally connect the two. Turn into. At this time, the fracture surface of the connecting rod body 15A and the bearing cover 15B is not a smooth surface, but a large number of minute irregularities are formed, and as described above, the plastic deformation of the final molded body W2 at the time of fracture is minimized. The connecting rod body 1
5A and the bearing cover 15B are joined and integrated in a state where their fracture surfaces are closely fitted to each other, and there is no deviation between the mating surfaces of the two. The bolt holes may be processed after the forging process.

After that, if the bearing cover 15B is fastened to the connecting rod body 15A by the fastening bolts 16 as described above and the two are connected and integrated, the final finishing process is performed as shown in FIG. 1 (h). The final product, connecting rod 1
5 is obtained.

By the way, in the above-mentioned embodiments, the manufacturing method using the raw material powder mainly composed of Fe has been described.
When the raw material powder mainly containing i is used, it is not always necessary to cool the final molded body to a temperature lower than the brittle fracture start temperature.

Although the above-mentioned present embodiment refers to an example in which the method of the present invention is applied particularly to the production of a connecting rod for an internal combustion engine, the method of the present invention is applicable to the production of any other sintered forged parts. Of course.

[0025]

As is apparent from the above description, according to the present invention, in a method for producing a sintered forged part including the steps of powder mixing, preforming, sintering, forging, cooling and separating, a compact is obtained. The mechanical properties in the vicinity of the fractured part were made different from those in other parts, or in addition to this, the molded body was fractured and separated at a temperature lower than the brittle fracture initiation temperature, so that the impact value near the fractured part By locally applying a small amount of energy, the compact is easily plastically ruptured at the rupture part and separated into two parts, and the plastic deformation of the compact at the time of rupture is minimized and high quality sintering is performed. A forged part is obtained.

[Brief description of drawings]

1A to 1H are explanatory views showing the method of the present invention in the order of steps thereof.

2A and 2B are perspective views of a large end portion of a connecting rod showing a notch formed in a preformed body after preforming.

3 (a), (b) and (c) are explanatory views showing a method of locally reducing the density.

4 (a) and 4 (b) are perspective views of a connecting rod large end showing a state of a notch after forging.

FIG. 5 is a diagram showing changes in impact value with respect to density of a metal material.

FIG. 6 is a diagram showing changes in impact value with respect to C content of a metal material.

FIG. 7 is a diagram showing changes in impact value with respect to Cu content of a metal material.

FIG. 8 is a diagram showing a change in impact value with respect to temperature of a metal material.

[Explanation of symbols]

 7 Notches 15 Connecting Rod (Sintered Forging Parts) 15A Connecting Rod Body 15B Bearing Cover S Near Breakage W1 Preform (Form) W2 Final Form (Form)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Tanada Sanshin Kogyo Co., Ltd. 1400 Shimbashicho, Hamamatsu City, Shizuoka Prefecture

Claims (2)

[Claims] 1. In a method for producing a sintered forged part, which includes powder mixing, preforming, sintering, forging, cooling, and separating steps, the mechanical characteristics in the vicinity of the fractured part of the formed body are different from those of other parts. A method for manufacturing a sintered forged part, which is characterized by differentiating. 2. In a method for manufacturing a sintered forged part, which includes steps of powder mixing, preforming, sintering, forging, cooling, and separating, the mechanical characteristics in the vicinity of the fractured part of the molded body are different from those of other parts. A method for manufacturing a sintered forged part, characterized in that the molded body is broken and separated at a temperature lower than a brittle fracture start temperature while being made different.