JP2001279302A - Method of manufacturing sintered machine part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and economically manufacture an iron sintered machine part with different material and mechanical properties part by part in one component. SOLUTION: The green compact comprises a portion 12 of a composition having a low appropriate sintering temperature and a portion 11 of a composition having a high appropriate sintering temperature, and a regular sintering is performed to the entire green compact at the low appropriate sintering temperature, and the partial sintering at a predetermined high temperature by the induction heating is performed only to a portion requiring the high temperature sintering. Compared with the high temperature regular sintering of the entire green compact, the time required for this manufacturing method is considerably short, and the machine part with each portion having a desired characteristic can be obtained inexpensively.

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 machine part, and more particularly to a sintering method suitable for manufacturing a sintered machine part partially having different materials or mechanical properties.

[0002]

2. Description of the Related Art Sintered machine parts are made by molding and sintering raw material powder into a required shape, so that pores exist in the member as a property inherent to a sintered metal material. There may be advantages or disadvantages depending on the application. Applications that actively utilize the presence of pores include sintered filters and sintered oil-impregnated bearings. For example, in the case of copper-based oil-impregnated bearings, the oil content (close to the effective porosity) is given priority over the strength of the member, It is required that the bearing life in lubrication be long.

[0003] On the other hand, the presence of pores reduces the strength and other mechanical properties of the member. Therefore, when powder metallurgy is used in the manufacture of ordinary mechanical parts, the molding pressure and sintering temperature must be increased, or the sintering must be repeated. The density is increased by means such as compression. Therefore, in this case, instead of using the properties inherent in the sintered material, mass production that can produce more economically a product with a quality comparable to that of a machined component manufactured by cutting or other plastic working on an ingot material. It is used as a means.

[0004] Sintered machine parts are generally made entirely of the same raw material powder and homogeneously. Recently, however, members of partially different materials are used depending on the use of the parts or for cost reasons. Parts (composite parts) integrating
Also, there is an increasing demand for mechanical parts in which the strength and other properties are partially changed even though the component composition of the alloy is the same. A part of this is shown by using a copper-based sintered alloy on the inner side including the sliding surface and a ferrous sintered alloy on the outer side of the sintered oil-impregnated bearing. An inexpensive and strong oil-impregnated bearing can be obtained. Incidentally, as a method for manufacturing such a multilayer bearing, two types of raw material powders are concentrically filled in a mold and molded, or a copper-based raw material powder is added to a cylindrical green compact of an iron-based raw material powder. A method is known in which a cylindrical green compact is fitted and sintered integrally.

[0005] In the case of a valve seat for an internal combustion engine, a member requiring high heat resistance and wear resistance includes Co,
High-grade materials to which expensive alloy elements such as Ni, Cr, and Mo are added are generally used. However, since the low alloy steel is sufficient for the parts other than the seat surface where wear due to sliding contact with the valve is a problem, a high-grade sintered material is used for the part including the seat surface and a relatively low-grade sintered material is used for the other parts. The cost can be reduced by forming a two-layer structure using a binding material.

In the case of the rocker arm that constitutes the valve operating mechanism, the pad portion that is in sliding contact with the cam of the camshaft requires a high-grade material that does not wear the cam of the mating member together with its own wear resistance. Is a relatively low-grade material having appropriate toughness. For forming such a multi-layer green compact, for example, an apparatus described in Japanese Utility Model Publication No. Sho 62-9293 and Japanese Patent Publication No. Sho 62-26879 can be used. The basic description of the two-layer filling of the powder is described in “Molding of Metal Powder” published by Nikkan Kogyo Shimbun, page 141-.

[0007]

As described above, it is easy to form a green compact having such a structure when manufacturing a composite part having a partially different material, but the problem is the firing of the green compact. It is in the final stage. That is, for example, when the inner cylinder is a copper-based sintered oil-impregnated bearing and the outer cylinder is an iron-based sintered oil-impregnated bearing, the appropriate sintering temperature on the inner cylinder side is about 790 ° C. in the case of a raw material powder in which tin powder is mixed with copper powder. Where powder is used, the temperature is around 810 ° C., whereas the appropriate sintering temperature on the outer cylinder side is 1050 ° C. or higher for a normal iron-copper system, depending on the alloy components. Even when the composite member is made of iron-based materials, if one of the members is a heat-resistant high-alloy steel, the appropriate sintering temperature is 1200 ° C. or more.

[0008] As described above, when a portion suitable for low-temperature sintering and a portion suitable for high-temperature sintering coexist in one green compact, sintering the green compact at a low temperature causes the high-temperature portion to be unsintered. On the other hand, when sintering at a high temperature, there is a possibility that a portion oriented at a low temperature is excessively sintered to cause a change in material or structure, or a bearing may cause a decrease in oil content. In addition, even if excessive sintering does not lead to deterioration of the quality, even if the furnace price and maintenance cost are high, a high-temperature sintering furnace (the higher the furnace temperature, the more easily the furnace materials and heating elements are eroded by atmospheric gases, High-temperature sintering uniformly to the parts suitable for low-temperature sintering using
It also wastes heat energy.

In the case of sintering in a continuous sintering furnace, the passage time (often referred to as sintering time) of the furnace in the soaking zone (a zone where a predetermined sintering temperature is maintained) is taken. For example, even around 20 minutes, the time required from the inlet to the outlet of the furnace reaches several hours, including the time required in the preheating / dewaxing zone before that and the cooling zone following the soaking zone. Under such circumstances, it has been desired to develop a sintering method capable of efficiently and economically treating both low-temperature portions and high-temperature portions at appropriate temperatures.

[0010]

Means for Solving the Problems Ordinary sintering of the entire green compact at a temperature suitable for a portion suitable for low-temperature sintering and partial heating by induction heating of the portion at a temperature suitable for a portion suitable for high-temperature sintering Use with sintering. This method is also useful in the case of a green compact made of one type of raw material powder, for example, by performing induction heating sintering on a required portion such as a tooth portion of a gear,
The mechanical properties of the portion can be improved as compared with a body that is usually sintered only. The order of performing the normal sintering and the induction heating sintering is as follows: the component composition of each raw material powder forming the green compact, the appropriate sintering temperature, the size and shape of the green compact,
It is appropriately set in consideration of the required characteristics of the sintered body. In general, the material of the mechanical component is generally iron-based, but the present invention is not limited to the iron-based material as long as it is a material capable of induction heating.

As a means for reducing friction during compression molding of the raw material powder, a so-called powder lubrication method in which zinc stearate or another powder lubricant is added to the raw material powder is usually used. However, when a powder lubricant is present between the powder particles, the electrical resistance of the green compact increases, so that the heating efficiency when performing induction heating decreases, and the time required to reach a certain temperature increases. Therefore, when induction heating sintering precedes ordinary sintering, it is preferable to use a stamping lubrication method (such as a method of applying and drying a solution of a powder lubricant to form a lubricating film on the stamping surface) rather than a powder lubrication method. When the powder lubrication method is used, or when it is used in combination with the press-type lubrication, the amount of the powder lubricant should be limited to 0.2% or less. In this specification, all percentages are indicated by mass unless otherwise specified.

Incidentally, when ordinary sintering is performed first, that is, when induction heating sintering is performed on a sintered body, such consideration is not required unlike the case of a green compact. Hereinafter, an example in which the present invention is applied to the cam shown in FIG. 1 will be described in detail. A cam is generally a kind of vehicle having a curved edge and performing a rotary motion. Many cams act as a main joint and give a periodic motion to a follower contacting the curved edge. In the case of the plate cam as shown in the figure, the distal end (11) farthest from the rotating shaft (the shaft hole is shown in the figure) receives the most load, and this portion is particularly strengthened more than the main body (12). There is a need to. It should be noted that hatching is applied to the tip portion 11 in the figure for the purpose of clarifying the main portion, and is not a cross-sectional display.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) In the case of the plate cam shown in FIG. 1, sintered materials capable of satisfying the required characteristics from the application are, for example, Ni 5-7%, Mo 0.4-0. 6%, Mn
... 0.05 to 0.25%, C ... 0.4 to 0.65%, C
u is a high alloy steel of 0.5 to 1.5% and the balance of Fe, but forming the entire cam with this expensive material is excessive quality and cost is not suitable. Therefore, the tip 11 is made of the above-mentioned high alloy sintered steel, and the main body 12 of the cam is Cu ... 1-2%, C ...
The use of low alloy steel of 0.7-1% and the balance of Fe makes use of both quality and cost. By the way, the appropriate sintering conditions for ordinary sintering of both alloys (indicating sintering in a continuous sintering furnace usually used for the production of sintered parts) are as follows. In the case of the former high-alloy steel, the temperature is originally 1250 ° C.
195 ° C. for 110 minutes is supplemented by extending the time.

First, a predetermined amount of graphite powder is added to an alloy powder having a composition obtained by removing carbon from the composition of the high alloy sintered steel described above, and zinc stearate is added as a powder lubricant by adding 0% zinc powder. A mixed powder to which 0.2% was added was prepared. Then, the mixed powder was filled in a mold which had been subjected to press-type lubrication in advance, and was temporarily formed at a low pressure into a compact having a contour of the shape of the tip portion 11 of the cam and a height slightly larger than the thickness of the product (cam). . Then, a predetermined amount of copper powder and graphite powder is mixed with iron powder to obtain a composition of the low alloy sintered steel, and a mixed powder containing 0.2% of zinc stearate is prepared. Similarly, the cam body 12 was provisionally molded at a low pressure. Next, the tip 11 and the main body 1
Combining both green compacts (pressed and pre-lubricated)
It was placed in a mold, compressed under an original molding pressure (490 MPa) and integrated to prepare a required cam-shaped green compact.

For the sintering of the green compact, first, induction heating was applied to the tip portion 11 of the cam using a high-frequency heating device. That is, at a frequency of 100 kHz in a vacuum of 10 ^-4 torr.
Heat at z, output 15kW, 95 for dewaxing etc.
After maintaining the temperature at 0 ° C. for 90 seconds, induction heating sintering was performed at 1250 ° C. for 60 seconds. Next, the sintering of the main body portion 12 of the cam (actually, the entire cam) was performed in a continuous sintering furnace, and ordinary sintering was performed at 1130 ° C. for 30 minutes in a purified exothermic gas atmosphere.

The sintered density of the product (cam) thus obtained was 6.85 g / cm ³ (body). And the metal structure at the tip is almost entirely martensitic,
Regarding the mechanical properties, the hardness HRA was 65 to 67 based on the data of impact test pieces obtained by compacting, induction heating sintering and ordinary sintering of the raw material powder at the tip under the same conditions, and the impact value was 2
0 to 24 J / cm ² , indicating that the abrasion resistance is excellent. Also, the time required for the sintering step (induction heating of the tip portion + normal sintering of the whole) is only about one third of the time required for normal sintering of the tip portion (described above). This result indicates that the present invention is useful not only in product quality but also in efficiency and economy.

(Embodiment 2) In this embodiment, the order of the sintering process in the embodiment 1 is changed, the ordinary sintering of the entire cam is performed first, and then the induction heating sintering is applied to the tip (of the sintered body). It has been subjected to. Therefore, the process is exactly the same as that of the first embodiment until the separately formed tip portion 11 and main body portion 12 are combined and recompressed to produce a green compact having a required cam shape. First, this cam-shaped green compact was heated at 1130 ° C. for 30 minutes using a continuous sintering furnace in a purified exothermic gas atmosphere.
Sintering for 1 minute, then the tip 1 of this sintered body
No. 1 was subjected to induction heating sintering by the high frequency heating apparatus used in Example 1. The procedure is sintering at 1250 ° C. for 30 seconds after holding at 950 ° C. for 60 seconds.

Both the sintered density of the cam, the metal structure of the tip thereof, and the data of the impact test piece produced under the same conditions as the tip, obtained the same results as those of Example 1. The reason that the quality of the product does not change even if the induction heating time is shortened in this way is probably because the influence of the powder lubricant has been eliminated by the precedence of sintering. In addition, although it is not a big factor in the use of the cam, in the case of the sintered alloy steel used for the main body, the strength (ring strength) is about 10% higher in the case of normal sintering in comparison. There is a tendency.

[0019]

As described in detail above, when a portion having a low sintering temperature and a portion having a high sintering temperature coexist in a green compact,
According to the present invention, only the latter part is sintered at a required high temperature in a short time, so that a mechanical part having each desired material and characteristics can be efficiently and economically manufactured. In addition, even in the case of a green compact having a uniform component composition,
The portion subjected to partial sintering by induction heating is improved in sintering density, mechanical properties, microstructure, and the like, and a functionally graded member is obtained as a whole.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

[Explanation of symbols]

 10 cam, 11 tip of cam, 12 body of cam

Claims (5)

[Claims] 1. In producing a sintered mechanical part having partially different materials or mechanical properties, a green compact having a part having a low composition and a part having a high composition having an appropriate sintering temperature is produced.
It is characterized by subjecting this green compact to normal sintering of the whole green compact at the lower appropriate sintering temperature and partial sintering at the required high temperature by induction heating only to the parts requiring high-temperature sintering. Method of manufacturing sintered machine parts. 2. First, a part of the green compact having a composition having a high proper sintering temperature is subjected to partial sintering at a required high temperature by induction heating, and then the sintered body is subjected to a lower proper sintering. The method for producing a sintered machine part according to claim 1, wherein ordinary sintering at a temperature is performed. 3. First, normal sintering of the entire green compact is performed at a lower appropriate sintering temperature, and then, the portion of the sintered body having a composition having a higher appropriate sintering temperature is subjected to the required heating by induction heating. The method for producing a sintered machine component according to claim 1, wherein partial sintering is performed at a high temperature. 4. The method for manufacturing a sintered machine part according to claim 2, wherein lubrication at the time of compression molding of the raw material powder is by press lubrication. 5. The method for producing a sintered machine part according to claim 2, wherein the amount of the powder lubricant added to the raw material powder is 0.2% or less by mass ratio.