JPH01136906A - Manufacture of infiltration-joining sintered machining parts - Google Patents

Abstract

PURPOSE:To stably obtain the title machining part, which is a compositely combined part having air-tightness to the diametral direction and the end face direction by joining a hole member and a shaft member whose relative change in size is mutually differed between the heating process and cooling process, in the temperature range up to the melting point of the infiltrated material. CONSTITUTION:The compressed powder body having ferrous shaft part and the compressed powder body having stepped hole part are separately formed and the shaft member is fitted into the stepped hole member. Both member are combined so that the hole member is relatively expanded at larger than the shaft member by >=0.04% to develop the gap in the size changes at joining diameters during heating at less than the melting point of the infiltrating material in the process of sintering and copper infiltration for both members while adding the infiltrating material and the hole member is relatively shrunk at larger than the shaft member by >=0.05% after infiltration or during cooling. In order to obtain this purpose, it is considered that carbon content in the hole member molded form is more than it in the shaft member by 0.02wt.% or both members are combined by Fe-C series and Fe-C-P series, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the so-called sinter-infiltration joining method, in which a single sintered part is made by joining a plurality of green compacts by combination sintering and copper infiltration. It is particularly suitable for hydraulic and pneumatic parts that require pressure resistance.

Iron-based sintered parts with complex shapes that cannot be molded with pressing dies are
It is made by molding the parts into simple-shaped parts, combining the molded bodies or their sintered bodies, applying the difference in sintered dimension change of each part, or joining them by brazing or copper infiltration. There is.

Among these, joining by copper infiltration creates airtightness through the pores of the joining member, and has the characteristics of good material strength and wear resistance, and is particularly applied to hydraulic parts that require pressure resistance.

Further, the infiltrant is made of copper as a main component, and a material containing Co, Fe, Mn, etc. is used so as not to erode the iron-based base material during infiltration.

By the way, when joining two divided members by fitting them in the radial direction, it is preferable to use the infiltrated material so that the gap between the members at the joint after infiltration is as small as possible and the infiltrated material fills the gap. If the spacing between the subsequent members is set to 0.02 mm or less, the infiltrated steel will fill the joint, resulting in good airtightness. Furthermore, if the distance between the members is large, the suction of the infiltrated steel will be poor, and airtightness may not be ensured.

Furthermore, although the hole dimensions and shaft dimensions of the member are set based on experience, mass production is easy because they can be formed by pressing.

Furthermore, when joining two divided members at their end faces, the surface of the molded body is rough and the flatness is not very good, so the distance between the parts tends to be large. can.

In these infiltration bonding methods, a method in which the member is a compacted powder body and sintering and infiltration are performed in series is economically advantageous and has become mainstream.

However, when joining both the radial direction and the end face direction at the same time, such as a combination of a powder compact with a shaft bearing and a powder compact with a stepped hole, it is more difficult than joining only one side. . If an attempt is made to reduce the radial spacing, the shaft and hole surfaces will come into contact with each other during heating and metallurgical diffusion bonding will occur, resulting in restraint before the gap between the end surfaces becomes sufficiently small. As a result, the airtightness of the end surface joint is not 8-6. Therefore, if the amount of infiltrated steel is increased in an attempt to fill this end gap with infiltrated steel, the infiltrated steel will not necessarily remain in the gap, but will overflow to the surface of the member, resulting in a defective product.

On the other hand, if an attempt is made to avoid the above-described restriction by making the shaft member narrower, the end faces will be joined, but the radial joining will be insufficient. In addition, after the two members are assembled, the shaft member moves during the time between transportation and melting of the infiltrant material, so that it cannot be applied to parts that require precision in assembly position.

This invention was made with the aim of stably mass producing composite parts that are airtight in both the radial direction and the end face direction. Considering separately the difference in thermal expansion coefficient between the member and the hole member and the difference in thermal expansion during the infiltration or cooling process, a gap is created in the radial direction during heating and the gap becomes smaller during the cooling process between the shaft member and the hole member. I was able to solve the problem by combining them.

In other words, this manufacturing method involves molding a green compact with an iron-based shaft and a green compact with a stepped hole, and when fitting the shaft into the stepped hole, an infiltrant is applied. In the process of sintering and copper infiltration, the dimensional change in the joint diameter during heating below the melting point of the infiltrant material will cause the hole member to expand by 0.04% or more and create a gap at the joint; In addition, during the infiltration process or the cooling process, the hole member expands or contracts relative to the shaft member by 0.05%, and the combination is characterized by a combination in which the two members have different compositions.

In addition, as an actual M aspect of the present invention, the carbon content of the hole member molded body is increased by 0.02% or more by weight ratio than that of the shaft member, or Fe-C type, Fe-C-P type, Fe-C type and Fe-c
-x r system combinations, etc. are possible.

FIG. 1 is a conceptual diagram schematically showing the coefficient of thermal expansion of a member during the heating and cooling process to explain the basic operation of the present invention. This figure compares the expansion coefficients of both parts during the process of heating them in a sintering furnace with a quantity of infiltrated steel 3, sintering and infiltrating them with copper, and cooling them to room temperature.

When assembling the powder compacts as shown in (■) in the figure, the two members 1 and 2 are fitted in an interference fit or in an intermediate bottom position by matching the assembly phase. The shaft dimension is set to be plus 0.02 mm to minus 0.01 mm from the hole dimension.

If it is thicker than this, the member with the hole will necessarily be displaced by υ1 when fitting, and if it is thinner, it will be too loose and there is a risk that the combination phase will shift during movement. When the combined green compact is heated with infiltrated steel 3, the shaft member 2 has smaller thermal expansion and a gap is created in the radial direction as shown in ■. contact the area.

Next, when the infiltrated steel is melted as shown in (3), normal infiltration is performed and at least the end surface joints are filled with copper. Then, when the infiltration is finished and during the cooling process, the dimensions tend to be smaller than those during the infiltration, and the relative expansion coefficient of the two members 1 and 2 becomes larger for the shaft member 2. As a result, the radial gap becomes smaller as shown in (2), and depending on the combination conditions of the two members 1 and 2, the perforated member is pushed wider, and the contact surfaces are diffusion bonded.

In this way, both members 1 and 2 are combined depending on their composition. For example, if the holed member is made of an iron-based material containing carbon, the shaft member should have a carbon content less than that by 0.2% or more.

Example Examples of the present invention will be described in detail below.

Example 1 Table 1 shows the results of measuring the coefficient of thermal expansion during the process of sintering and copper infiltration of iron-based green compacts adjusted to various compositions. The mixed powder of each composition was molded to a density of 6.8 g/Cm3, and the infiltrated copper was heated in a reducing atmosphere with a molded body of copper alloy powder containing 2.5% CO. C, and the coefficient of linear expansion based on the molded body dimensions when held at 1130°C and at 800°C during cooling were measured.

For example, when comparing Sample No. 1 and Sample No. 3, the latter has a large expansion coefficient when the temperature rises, and a small expansion coefficient after infiltration and during cooling. It is presumed that if number 1 is adopted, the desired result will be obtained.

Example 2 The mixed powders of various compositions used in Example 1 were applied to parts having the shape shown in FIG. The shaft member 2 has a cylindrical shape with an outer diameter of 40 mm and has a notch in the A-A direction. The stepped hole member 1 has a cylindrical shape as a whole and is provided with a slit in the B-8 direction. In the A-A direction, only the end faces are joined, in the B-8 direction, only the radial direction is joined, and in the other directions, both are joined. The molding density of both members was 6.8 g/Cm3, and the outer diameter of the shaft member and the inner diameter of the hole member were set to be the same.

Two-member molded bodies of each composition were prepared, and all 324 combinations of each composition were carefully fitted together using a hand press.

The infiltrated copper is the same CU-Co material as in Example 1, and the infiltration rate is 9.
The weight was adjusted to 0%. Here, the infiltration rate is [calculated density after infiltration - density of compact] ÷ [calculated porosity of compact Xi
/100X infiltrated copper specific gravity]X100.

The combined sample was placed with the shaft member 2 on top, infiltrated copper was placed thereon, and sintered and infiltrated in 1130'C1 decomposed ammonia gas.

Then, an airtightness test was conducted on each infiltrated sample.

The results are shown in Table 2. The Q mark indicates that there was no leakage, and the * mark indicates that there was a leakage.

As shown in the cross-sectional view of FIG. 2, the test method involved closing the lower end face and the upper inner hole, introducing compressed air at a pressure cuff of kg/cm2 into the inner hole space, and submerging the sample in water.

In Table 2, when comparing the samples with leakage to the coefficient of thermal expansion in Table 1, the shaft member 2 expands more than the hole member 1 during temperature rise, or the amount of expansion of the shaft member after infiltration is too small. It can be seen that this is a combination of materials.

Among the combinations without omissions, an example with a clear trend is composition number 1.
-6 combinations. The carbon content of the hole member is 0.0 compared to the shaft member.
There are more than 2% more relationships. The same tendency is observed in composition numbers 7 to 10.11 to 14.15 to 18.

This is completely opposite to the idea of increasing the amount of carbon in the shaft member, which is carried out in the conventional sinter joining method.

There is no clear trend in the amount of phosphorus in combinations of materials containing phosphorus, but when the combinations have the same carbon content,
Good results are shown when the amount of phosphorus in the shaft member is large.

In combinations of materials containing nickel, the effect of carbon is apparent, and the orientation of nickel is not clear.

Furthermore, it can be seen that good bonding can be obtained even if the combination of different components satisfies predetermined requirements.

From Tables 1 and 2 above, the conditions under which good bonding was obtained are as follows.

First, the coefficient of thermal expansion during temperature rise is 0.0 for the hole member 1 than for the shaft member 2.
This combination is 0.04 to 0.66% larger.

Since the larger the gap, the better the contact between the ends tends to be, the combination should be 0.04% or more larger.

Next, the coefficient of thermal expansion in the cooling process after infiltration is 0.05% larger for hole member 1 than shaft member 2, and for shaft member 1
．． Within the range of 36% larger combinations. The hole member is 0
．． 05% larger means that the member spacing is 0 in the case of this sample.
．． There will be 02mm. Also, the fact that the shaft member is larger means that a good joint can be obtained with almost no gaps, but on the other hand, it means that the hole member is being pushed outward, and in the case of a shape that requires the use of thin-walled members, the expansion rate may be reduced. It is better to choose a composition combination with a small difference.

It goes without saying that even if the component system is other than that shown in this example, the same effect can be obtained as long as the combination of components meets the requirements of the present invention.

In addition, although FIGS. 3(a), (b), (c), and (d) are sectional views showing application examples of various mechanical parts obtained by the manufacturing method of the present invention, various other forms are also available. Conceivable.

As described above, according to the method of the present invention, during the heating process until the melting point of the infiltration material is reached, the hole member expands by 0.04% or more relative to the shaft member, creating a gap at the joint, and Since both members are joined so that the hole member expands or contracts relative to the shaft member by 0.05% during the cooling process, according to the present invention, the bonded sintered material has excellent airtightness. Parts can be mass-produced stably.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram for explaining the coefficient of thermal expansion of a molded body, Fig. 2 is an explanatory diagram for explaining the shape of the sample used in the present invention and the airtightness test method, and Fig. 3 is a conceptual diagram for explaining the coefficient of thermal expansion of a molded body. FIG. 3 is a cross-sectional view showing a combination of members. 1... Hole member 2... Shaft member 3... Infiltration material patent applicant Hitachi Powder Metallurgy Co., Ltd.

Claims (1)

[Claims] 1. Compressing iron-based metal powder to form a compact having a shaft portion and a compact having a stepped hole, respectively, and fitting the shaft member into the stepped hole member. In the method of obtaining complex-shaped mechanical parts by heating together with the infiltrant material, sintering, and copper infiltration, the dimensional change in the joint diameter of both parts during the heating process until the melting point of the infiltrant material is reached is as follows: The hole member expands by 0.04% or more relative to the shaft member, creating a gap at the joint, and the hole member expands or contracts relatively by 0.05% than the shaft member after infiltration or during the cooling process. A method for manufacturing an infiltration-bonded sintered mechanical part, which is characterized by a combination of two members having different compositions and having a relationship between them. 2. The carbon content of the hole member molded body is 0.0% by weight compared to the shaft member.
2. The method of manufacturing an infiltration bonded sintered machine part according to claim 1, wherein the increase is 0.2% or more.