JP2521778B2 - Method for manufacturing infiltration-bonded sintered machine parts - Google Patents

Description

The present invention relates to an improvement of a so-called sinter infiltration joining method in which a plurality of green compacts are combined and joined by sintering and copper infiltration to make one sintered part. In particular, it is suitable for hydraulic and pneumatic components that require pressure resistance.

For iron-based sintered parts that have complicated shapes that cannot be formed by pressing, divide them into simple-shaped members and combine them, and combine each green compact or its sintered body to determine the difference in sintering dimensional change for each member. It is applied and made by brazing or copper infiltration.

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

Further, the infiltrant is mainly composed of copper, and a material containing Co, Fe, Mn or the like is used so as not to corrode the iron-based base material during the infiltration.

By the way, when two split members are fitted and joined in the radial direction, the member spacing of the joint after infiltration is as small as possible, and the infiltrant is preferably infiltrated so as to fill the gap. If the distance between the members is 0.02 mm or less, the infiltrated copper fills the joint and the airtightness is improved. In addition, if the distance between the members is large, the infiltration of the infiltrated copper becomes poor, and the airtightness may not be secured.

Further, the hole size and the shaft size of the member are set based on experience, but since they can be formed by a pressing die, mass production is easy.

Furthermore, when joining two split members at the end faces, the surface of the green compact is not good and the flatness is not so good, so the member spacing tends to be large, but by mounting the weight by the upper member's own weight or separately. Can be joined.

For these infiltration joining methods, a method of performing sintering and infiltration in series using a member as a green compact is economically advantageous and has become the mainstream.

However, in the case of simultaneously joining the radial direction and the end face direction, such as a combination of the green compact that bears the shaft portion and the green compact having the stepped hole portion, it is more difficult than joining only one.
If an attempt is made to reduce the radial distance, the shaft and the hole surface will come into contact with each other during heating to cause metallurgical diffusion bonding, and the gap will be restricted before the gap between the end faces becomes sufficiently small. As a result, the airtightness of the end face joint cannot be obtained. Therefore, if the amount of infiltrated copper is increased in an attempt to fill this end face gap with infiltrated copper, it will not necessarily stay within the gap but will overflow to the surface of the member, resulting in a defective product.

On the other hand, if the shaft member is thinly set and the above-mentioned constraint is avoided, the end faces are joined, but the joining in the radial direction becomes insufficient. In addition, after the two members are combined, the shaft member moves during transportation and before the infiltrant is melted, which cannot be applied to a part that requires a combination position accuracy.

The present invention was made for the purpose of stably mass-producing composite combination parts that are airtight in both the radial direction and the end face direction. Considering the difference in the coefficient of thermal expansion between the member and the hole member and the difference in the coefficient of thermal expansion during the infiltration or cooling process separately, a gap is created in the radial direction during the temperature rise, and becomes smaller during the cooling process. It could be solved by combination.

That is, in this manufacturing method, a powder compact having an iron-based shaft portion and a powder compact having a stepped hole portion are respectively molded, and when the shaft member is fitted into the stepped hole member, an infiltration material is added. In the process of sintering and copper infiltration, the dimensional change of the joint diameter during heating below the melting point of the infiltrant causes the pore member to expand by 0.04% or more to form a gap in the joint, and The hole member is 0.05% more than the shaft member in the cooling process after infiltration
It is characterized by a combination in which the compositions of both members have a relationship of contracting relative to the expanded state of.

Further, as an embodiment of the present invention, the carbon content of the hole member green compact is increased by 0.02% or more in weight ratio than the shaft member,
A combination of Fe-C system and Fe-C-P system, Fe-C system and Fe-C-Ni system, and the like are considered.

FIG. 1 is a conceptual diagram schematically showing the coefficient of thermal expansion of a member in a heating and cooling process for explaining the basic operation of the present invention. This figure shows a combination of a shaft member 2 and a hole member 1.
This is a comparison of the expansion coefficients of both members in the process of heating in a sintering furnace together with a required amount of infiltrated copper 3, sintering and infiltrating copper, and then cooling to room temperature.

When the green compacts are combined as shown in the figure, the phases of the combination of both members 1 and 2 are matched with each other, and they are fitted by interference fitting or intermediate fitting. The shaft dimension is plus 0.02 mm to minus 0 than the hole dimension.
Set to 01 mm. If it is thicker than this, the holed member may break during fitting, and if it is thin, it may be too loose and the combination phase may shift during movement. When the infiltrated copper 3 is added to the combination green compact and heated, the shaft member 2 has a smaller thermal expansion, and a gap is formed in the radial direction like the shaft member 2, and the shaft member 2 falls by its own weight and falls in the step portion of the hole member 1. To contact.

When the infiltrated copper is melted as described below, normal infiltration is performed, and at least the end face joint portion is filled with copper. At the end of infiltration and in the cooling process, the dimension tends to be smaller than the dimension during infiltration, and the relative expansion coefficient of both members 1 and 2 becomes larger in the shaft member 2. As a result, the radial gap becomes small as described above, and depending on the combination condition of both members 1 and 2, the member with holes is expanded, and the contact surfaces are diffusion-bonded.

In this way, the combination of both members 1 and 2 is performed depending on the composition. For example, when the perforated member is an iron-based material containing carbon, the shaft member has a carbon content lower than that of 0.2% or more.

Examples 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 in the process of sintering and copper infiltration of iron-based green compacts adjusted to various compositions. Molded mixed powder of each composition to a density of 6.8 g / cm ³ ,
Place a compact of copper alloy powder containing 2.5% Co on it and heat it in a reducing atmosphere. Hold the molded body size at 1000 ° C and 1130 ° C during heating, and at 800 ° C during cooling, measure the compact size. The coefficient of linear expansion based on the standard was measured.

For example, comparing sample No. 1 and sample No. 3, the latter shows a large expansion coefficient at the time of temperature rise, and a small expansion coefficient after infiltration and during cooling. It is estimated that the desired result can be obtained by adopting the number 1.

Example 2 The mixed powders of various compositions used in Example 1 were used and 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 AA direction. The stepped hole member 1 is entirely cylindrical and has a slit in the BB direction. In the AA direction, only the end faces are joined, in the BB direction, only the radial direction is joined, and in the other, both are joined. The molding density of both members was 6.8 g / cm ³ , and the outer diameter dimension of the shaft member and the inner diameter dimension of the hole member were set to be the same.

Both member green compacts of each composition were prepared, and 324 kinds of all combinations of each composition were carefully fitted with a hand press.

The infiltrated copper is the same Cu-Co material as in Example 1, and the infiltration rate is 90%.
The weight was adjusted so that Here, the infiltration rate is [calculated density after infiltration-compacted powder density] / [compacted powder calculated porosity x 1/100]
X Specific gravity of infiltrated copper] x 100.

The combined sample was placed with the shaft member 2 on the upper side, infiltrated copper placed thereon, and sintered and infiltrated in a decomposed ammonia gas at a temperature of 1130 ° C.

An airtight test was performed on each infiltrated sample. Table 2 shows the results. ○ indicates no leakage,
* Indicates that there was a leak.

In the test method, as shown in the sectional view of FIG. 2, the lower end surface and the inner hole at the upper portion were closed, compressed air having a pressure of 7 kg / cm ² was introduced into the inner hole space, and the sample was immersed in water.

In Table 2, the leaked sample is compared with the coefficient of thermal expansion in Table 1 so that the shaft member 2 expands more than the hole member 1 during the temperature rise, or the expansion amount of the shaft member is too small after infiltration. It can be seen that this is a material combination.

Among the leak-free combinations, the examples in which the tendency is clear are the compositions having composition numbers 1 to 6. The carbon content of the hole member is less than that of the shaft member.
There is a relationship of more than 2%. Such a relationship of carbon amount also shows the same tendency in the composition numbers 7 to 10, 11 to 14, and 15 to 18.

This is completely opposite to the concept of increasing the carbon content of the shaft member, which is used in the conventional sintering joining method.

In the combination of materials containing phosphorus, the tendency of the amount of phosphorus is not clearly shown, but when the combination of carbon contents is the same, good results are shown when the amount of phosphorus in the shaft member is large.

In the combination of materials containing nickel, the action of carbon is exerted, and the tendency of nickel is not clear.

Further, it is found that good bonding can be obtained even if the combination of different components satisfies the predetermined requirements.

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

First, the coefficient of thermal expansion during the temperature rise was 0.
It is a combination that is 04 to 0.66% larger. If the gap is large, the contact of the ends tends to be good, so a combination of 0.04% or more is sufficient.

Next, regarding the coefficient of thermal expansion in the cooling process after infiltration, the combination in which the hole member 1 is 0.05% larger than the shaft member 2 or the shaft member is 1.36.
% Within the range of large combinations. 0.05% for hole members
A large value means that the member interval is 0.02 mm in the case of this sample. In addition, the fact that the shaft member is larger means that there is almost no gap and good joining can be obtained, but on the other hand, the hole member is pushed outward, and in the case where a thin member must be used, the expansion coefficient It is better to use a composition combination with a small difference.

Needless to say, the same effect can be obtained even if the component system is other than the component system shown in this example as long as it is a member combination that meets the requirements of the present invention.

Further, FIGS. 3 (a), (b), (c), and (d) are cross-sectional views showing application examples of various mechanical parts obtained by the manufacturing method of the present application. Conceivable.

As described above, according to the method of the present invention, the hole member is preliminarily heated in the heating process before the hole member is relatively contracted more than the shaft member in the cooling process after the infiltration and the radial joining is performed. And a gap is formed between the shaft member and the shaft member. Therefore, when the gap is formed, the shaft member falls by its own weight, and the end face of the shaft member and the step of the hole member are surely contacted with each other, so that not only the radial direction but also the end face direction is sufficiently joined. Further, after the infiltrant is melted and the gap is filled, the joining is performed by the cooling process, so that the infiltration can be sufficiently performed and the airtightness between the members is improved. effective.

[Brief description of drawings]

FIG. 1 is a conceptual diagram for explaining the coefficient of thermal expansion of a green compact, FIG. 2 is an explanatory diagram for explaining the shape and airtightness test method of a sample used in the present invention, and FIG. 3 is obtained by the present invention. It is sectional drawing which shows the combination form of the member to be made. 1 ... Hole member 2 ... Shaft member 3 ... Infiltration material

Claims (2)

(57) [Claims] 1. An iron-based metal powder is compressed to form a green compact having a shaft portion and a green compact having a stepped hole portion, respectively.
In the method of obtaining a mechanical part with a complicated shape by heating with an infiltrant in a state in which a shaft member is fitted in a stepped hole member, sintering and copper infiltration, heating until reaching the melting point of the infiltrant The dimensional change of the joint diameter of both members in the process is 0.04
% And expands to form a gap in the joint, and in the cooling process after infiltration, the hole member has a relative contraction from the expanded state of 0.05% from the shaft member, a combination of both members with different compositions A method for manufacturing an infiltration-bonded sintered machine part, characterized by: 2. The method for producing an infiltration-bonded sintered machine component according to claim 1, wherein the carbon content of the green compact of the hole member is increased by 0.02% or more by weight ratio than that of the shaft member. .