JPH06330108A - Production of sintered composite mechanical parts - Google Patents

Abstract

PURPOSE:To obtain high strength of joining by solid-phase diffusion in joining of an outer of a sintered member and an inner of a smelted steel product. CONSTITUTION:This process for production of sintered composite mechanical parts consists in heating and sintering the green compact outer having a hole part formed by compression molding of a powder mixture contg. iron metallic powder and the inner of the smelted steel product having a shaft part in a fitted state, thereby joining both members. The inner having the carbon content in at least the front layer part larger by >=0.3wt.% than the carbon content of the outer is used and the hole part size of the outer is made smaller by 0 to 60mum than the shaft part size of the inner. The inner and the outer are fitted by shrinkage fit and are sintered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintering joining method in which a shaft hole of a ferrous green compact having a cam or gear shape and a shaft of a molten steel material are combined and heat-sintered to integrate both members. The present invention relates to a method of manufacturing a mechanical component.

[0002]

2. Description of the Related Art In the case of making a complex sintered machine part, a green compact is prepared in advance by dividing it into a plurality of members.
It is made by combining them and heating and sintering, and is used to manufacture double gears and hydraulic equipment parts. For this joining, a method of adding a metal that produces a liquid phase to the joining surface portion or a material combination that changes the sintering dimension such that the outer member holds the inner member during sintering is adopted. There is.

On the other hand, manufacture of a part in which a shaft of molten steel and a member of a sintered alloy are joined is not as easy as in the case of combining the above-mentioned green compacts, and it is difficult to obtain a sufficient joining strength, so that it is generally impossible. Methods such as pressing the sintered outer into the shaft and fixing with a key, welding or brazing are used.

[0004] In the case of joining a member of a sintered alloy to the shaft of a molten steel material, as a proposal of a technique similar to the powder compact joining method, for example, there is a technique described in Japanese Patent Publication No. 1-43803.

This method is a method for manufacturing a camshaft,
When joining a cam made of a sintered alloy to the shaft of a steel material, a cam lobe is a sintered alloy with a high carbon content that produces a liquid phase, and combines both members with the liquid phase produced by heating in combination. . In the case of this method, carbon diffuses from the cam lobe side to the shaft side during heating, and the material of the cam lobe changes, so the surface of the shaft of the molten steel is carburized in advance and the carbon amount of the cam lobe is changed. The difference is small and it is processed at low temperature.

[0006]

This method is intended to reduce the cost of the joining process. However, when a large amount of liquid phase is generated to increase the joining force during the joining process, the size of the sintered body is increased. The accuracy is worse than that of ordinary sintered parts. Also,
Since the cam lobe that is the outer is pre-sintered before it is fitted to the shaft, there is a problem that the shaft hole is distorted and the dimensional variation among the sintered bodies occurs, and the fit with the shaft can vary. was there.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a mechanical component in which a sintered alloy is joined to a steel shaft having good dimensional accuracy and high joining strength. .

[0008]

In order to achieve this object, the present invention provides a powder compact outer having a hole formed by compression molding a mixed powder containing an iron-based metal powder, and a molten steel material having a shaft. When joining the two members by heat-sintering in a state where they are fitted with the inner of the above, the gist is to increase the carbon content of at least the surface layer part of the shaft part by 0.3 wt% or more than the carbon content of the outer part. The outer hole size is made smaller than the inner shaft size by 0 to 60 μm, and the inner and outer parts are fitted together by an interference fit and sintered.

The outer green compact has a gear, a cam, an arm shape or the like, and the inner may be a normal central shaft, a pin, a nut or the like.

The cross-sectional shape of the fitting portion can be variously applied, such as a circle, a polygon, and a keyway.

When the carbon content of the outer member is relatively low, a commercially available steel material in which the carbon content of the outer member is higher by 0.3% or more can be applied as the inner member, but when the carbon content of the outer member is high. Is subjected to normal gas carburization or ion carburization on the surface of the shaft. Ion carburization is suitable for carburizing.

As an auxiliary means for increasing the joining force between the members, the surface roughness of the joining surface of the shaft can be finished into a mirror surface to increase the contact area with the outer member. Also,
Sintering can be activated by heating in the atmosphere to oxidize the surface before press-fitting the powder compact outer or the steel inner having a predetermined carbon amount.

After press-fitting, both members are heat-sintered by using an ordinary sintering furnace, but when the material softens, a sintering furnace having a high cooling rate is used. Further, the sintering and the quenching can be continuously carried out by processing in a furnace integrally provided with a quenching device on the outlet side of the sintering furnace.

If necessary, the sintered members may be subjected to heat treatment such as sizing, cutting, and induction hardening after joining.

[0015]

In the outer green compact, the hole is formed by the die with high dimensional accuracy, and the fitting with the shaft is more stable than in the case of the sintered body.

When the amount of carbon in the inner surface layer portion is larger than that in the outer portion, a part of the carbon in the inner surface layer portion diffuses into the outer portion during sintering, and diffusion bonding is performed without generating a liquid phase. The bonding strength is extremely low when the difference in the amount of carbon is 0.1%, but increases gradually until the difference gradually increases up to about 0.3%, and gradually increases when the difference is 0.4% or more.

If the steel inner and the green compact outer are tightly fitted together, the members will not move or will not shift during sintering, and the joint surfaces will be in firm contact and metallurgical diffusion will easily occur. The outer diameter of the inner is larger than the inner diameter of the outer by 10 μm, and the fitting and sintering is extremely low, but the joint outer diameter is the same as the outer inner diameter, or the outer inner diameter is smaller by 10 μm. A tight fit significantly increases the joint strength. As the dimensional difference further increases, the bonding strength gradually increases. However, if the dimensional difference is 65 μm or more, the outer green compact may be broken during press-fitting combination, which is not practical.

[0018]

EXAMPLES The present invention will be described below with reference to examples.

Example 1 Chrome molybdenum steel (SCM420) was used as the inner material of the ingot. The composition is C0.
2%, Si0.25%, Mn0.7%, Cr1.0%,
Mo 0.2% and Fe residue. The outer diameter of the inner is processed by grinding to a diameter of 10 mm and carburized to have a carbon content of 0.8% in the surface layer and 1.2%.
Was manufactured.

On the other hand, a mixed powder prepared by adding 1.5% electrolytic copper powder, a predetermined amount of graphite powder and 1% zinc stearate powder to reduced iron powder was prepared, and the outer diameter dimension was 18 mm, the length was 5 mm, and the inner diameter was 5 mm. The size is 10 μm smaller than the inner diameter,
Compression molding was performed using a mold so that the density was 6.8 g / cm ³ . Graphite powder is added in three types, that is, not added and 0.4% and 0.7% added.

Next, each green compact outer was press-fitted into the inner, and each sample was heated and sintered at 1130 ° C. in a butane metamorphic gas.

The strength of each obtained composite sintered body was measured.
The measuring method is to support the end face of the outer by a jig, apply an axial load to the inner, measure the maximum load until breaking, and divide the load by the joint area of both members to obtain the strength. did.

FIG. 1 (a) shows the relationship between the difference in carbon content of the outer green compact with respect to the carbon content of the inner surface layer and the joint strength of the sintered body.

When the difference in carbon content is 0.1%, the bonding strength is low. It can be seen that the strength is remarkably increased when the difference in carbon content is up to 0.2%, but it is unstable. Carbon content difference is 0.3%
With the above, the bonding strength is gradually increased. Further, the sample having a large amount of carbon in the inner surface layer has a high bonding strength.

(Example 2) The method of preparing the sample is almost the same as the previous example, but a steel inner having a carbon content of 0.8% in the surface layer and a mixed powder containing 0.4% of a graphite powder are used. To produce a powder-molded outer. In producing the outer, the dimensions of the core rod of the mold were changed to prepare various samples having different inner hole dimensions. Each outer was press-fitted into the inner and sintered in the same manner as in the previous example, and then the joint strength was measured. The result is shown in FIG.

Outer inner hole is 9μ compared to inner outer diameter
Those having a larger m have extremely low bonding strength. A joint having the same outer diameter and inner bore has significantly higher bonding strength. Furthermore, it can be seen that the joint strength increases as the amount of interference fit increases.

When microscopically observing the cross-sections of these samples with a microscope, in the samples with low bonding strength, many gaps were observed on the mating surface, and carbon migration on the inner surface was not noticeable, whereas the bonding was low. In the case of the sample having high strength, the fitting surface has few gaps, the inner carbon is carburized in the outer, and the carbon amount in the vicinity of the joint surface of both members is almost uniform.

On the other hand, if the dimensional difference exceeds 60 μm,
May crack when pressed into the inner.

(Embodiment 3) Next, the inner has a length of 3
A 5 mm SCM420 material was polished to have an outer diameter of 12 mm, and the amount of carbon in the surface layer portion was 1.2% by ion carburization.

The outer is 1.5% copper powder in reduced iron powder,
Using a mixed powder containing 0.8% graphite powder and 1% zinc stearate, a density of 6.8 g / cm ³ and a thickness of 5 m
m, and a gear-shaped green compact having a dimensional difference of 30 μm between the inner hole and the inner hole was produced. The gear has 14 teeth and a tip diameter of 24.
5 mm, module 1.5.

The outer green compact was pressed into a predetermined position of the inner and sintered as in the previous example.

With respect to the sintered sample, both end faces of the outer member were pressed using a mold and the tooth portion was sized, and then the outer end face and the tooth tip were cut.

Two of the obtained samples were mounted in the aluminum alloy housing of the oil pump. The operating condition was as good as the conventional product.

[0034] (Example 4) using a powder mixed with 1.5% of zinc powder 1% stearic acid copper powder to iron powder, green density 6.6 g / cm ³ in a disc shape having a hole at four An outer body and an inner member made of a carbon steel material for general structure having a carbon content of 0.4% and having a pipe-shaped inner diameter provided with a screw were prepared.
The outer diameter of the inner member was set to be 50 μm larger than the hole diameter of the outer member. The inner member was press-fitted into the four holes of the outer member and sintered as in the previous example.

The resulting composite part having an internal thread was used as a screw fastening part mounting plate.

Example 5 The inner member has an outer diameter of 10
A carbon steel pipe for general structure (STK) having a length of 100 mm, a length of 100 mm and a carbon content of 0.2% is subjected to an ion carburizing treatment to have a surface carbon content of 1.0%.

The outer member has a composition of 4% Ni, 0.5
% Alloy, 1.5% Cu, and the remaining iron alloy powder consisting of Fe,
Using a mixed powder containing 0.3% of graphite powder and 1% of zinc stearate powder, a green compact having an inner hole and an outer surface having a cam shape was molded to have a density of 7.0 g / cm ³ .

The dimensional difference between the fitting portions of both members is 50 μm, which is an interference fit.

After press-fitting two outer members into the inner member, the temperature is changed to 1130 in butane shift gas as in the previous example.
It was sintered by heating at ℃.

This composite part was used for a camshaft for opening and closing a valve of an internal combustion engine by polishing the cam surface.

[0041]

As described above, in the sintering joining method of the present invention, the carbon content of at least the surface of the steel inner member is made larger than the carbon content of the green compact outer member so that the inner member of Carbon is diffused to the outer green compact side to achieve diffusion bonding at the joint surface. Since there is little deformation of the outer member and material change and high joint strength can be obtained, it is applied to the manufacture of gear parts and camshafts. In addition, it is possible to expand the application to machine parts that require a joining combination of a molten metal shaft that requires mechanical strength and a powder metallurgy product characterized by material selection such as formability and wear resistance.

[Brief description of drawings]

FIG. 1 (a) is a graph showing the relationship between the carbon content difference between the outer member and the inner member surface layer and the bonding strength, and FIG. 1 (b) shows the relationship between the fitting size difference of the outer and the inner member and the bonding strength. Graph.

Claims (2)

[Claims] Claims: 1. Both members are heat-sintered in a state in which a green compact outer body having a hole formed by compression-molding a mixed powder containing iron-based metal powder and an inner member of a molten steel material having a shaft portion are fitted together and sintered. In the method of joining, the carbon content of at least the surface layer portion of the inner member is 0.3% by weight more than the carbon content of the outer compact.
A method for manufacturing a sintered composite machine component, characterized in that the number is greater. 2. The sintered composite according to claim 1, wherein the outer hole size is smaller than the inner shaft size by 0 to 60 μm, and the inner and outer parts are fitted with an interference fit to sinter. Machine parts manufacturing method.