JPS6318004A - Production of sintered parts - Google Patents

Abstract

PURPOSE:To uniformize the sintering density over the entire part and to prevent the generation of strength defects by a difference in density by using powder materials which are different in sinterability to form the part where the volumetric amt. of green compact is large and the part where said amt. is small and sintering the materials at a specific temp. at the time of molding and sintering parts having the shape in which the volumetric amt. of the green compact varies partially. CONSTITUTION:Steel powder 10 is packed into a mold 11 and is precompacted by an upper punch 12 and a lower punch 13 in order to form a flange part D where the volumetric amt. of the green compact is small at the time of producing a connecting rod, etc., of an automobile by a powder metallurgical method. The upper punch 12 is than raised and spacers 15 are mounted. Powder 16 having the sinterability at the temp. lower than for the iron powder 10 is packed between the spacers 15 in order to compact a web part C where the volumetric amt. of the green compact is large. The lower punch 13 is lowered and the steel powder 10 is packed into the mold and is compacted by the upper punch 12 in order to form the other flange part E. The spacers 15 are removed and the powder C is sintered in the gaseous N2 atmosphere at the temp. above the sintering temp. of the powder DE parts sintered in the liquid phase. The connecting rod which has the uniform sintering part in the web C and the flanges D, E and is free from the strength defects is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial advantages of the invention The present invention relates to a method for manufacturing sintered parts. The present invention relates to a method for manufacturing sintered parts having different shapes in volume (hereinafter referred to as powder volume).

Prior art powder metallurgy methods have various advantages over other manufacturing methods, such as higher material yields and better dimensional accuracy. Therefore, in recent years, the applications of sintered parts manufactured by powder metallurgy have been expanding more and more, and they have come to be widely used in machine parts and the like. However, on the other hand, the shapes required for sintered parts have become increasingly diverse, and sintered parts with shapes that cannot be accommodated by conventional mold pressing methods are often required. Products with so-called undercuts, such as automobile stoves, are one example.

Japanese Patent Application Laid-Open No. 59-219401 discloses that when manufacturing a sintered part having such an undercut part on the side surface, the sintered part is divided into upper and lower parts with the undercut part as a boundary, and after powder compression molding, the sintered part is sintered. We are proposing a method for manufacturing. That is, when manufacturing gears, for example, as shown in FIG. 1, a mold consisting of a die 1, a lower punch 2, and a core rod 3 is first filled with raw metal powder 4, and then, as shown in FIG. As shown, the upper bunch 5 is lowered and primary powder compression molding (hereinafter referred to as powder molding) is performed to obtain a lower half primary molded product 6. After that, the upper punch 5 is raised once, and as shown in FIG. 3, a spacer 7 made of ceramic or the like is attached to the part corresponding to the undercut part.
The raw metal powder 4 is filled and the upper punch 5 is lowered again to carry out main powder compaction, and then the spacer 7 is removed or infiltrated into the sintered body during sintering. , a sintered part 8 having an undercut portion on the side surface as shown in FIG. 4 is obtained.

Problems to be Solved by the Invention - According to the method disclosed in JP-A No. 59-219401, it is certainly possible to manufacture a sintered part having an undercut portion. It was found that the sintered parts had a problem in that the density of the B part in FIG. 4 was lower than the density of the A part, and the product did not have sufficient strength. It is recognized that this density difference increases as the difference between the thickness 2T of the thickest portion and the thickness 2t of the portion excluding the undercut portion increases. This is because during the second compaction and the main compaction, the compression of the thinner parts, that is, the parts with less powder volume, reaches saturation first and cannot be compressed any further. Therefore, in contrast, thicker areas, that is, areas with a large volume of compacted powder, cannot be further compressed even though they have not yet been compressed to the desired degree. This is thought to be due to the fact that it cannot be compressed to the desired density and the compression ratio between the two parts inevitably differs. Moreover, the density of this thicker part, that is, the part with a large powder volume, is usually lower than the density when compacting a part with the same powder volume in the absence of an undercut part. Therefore, its lack of strength was a serious defect. In order to prevent compaction in areas with a large volume of compacted powder, if the compaction is forced, the air existing between the powder particles will have nowhere to escape, resulting in excessive compression. Cracks were often observed during compaction. This phenomenon is particularly noticeable in areas with a small volume of compacted powder, or when using powder with a small particle size, and has become a fatal defect.

Such problems during powder compaction are not limited to parts with undercuts, but are common to parts with shapes where there are local differences in powder volume, such as parts with a T-shaped cross section. This was a problem that was strongly desired to be solved.

Purpose of the Invention The present invention provides a method for manufacturing a sintered part having a shape in which the powder volume during compaction differs depending on the part.
Provides a method for manufacturing sintered parts that makes it possible to equalize the density between parts with different powder volumes, thereby freeing strength defects caused by differences in density due to compression molding in each part of the part. The purpose is to

Composition of the Invention The object of the present invention is to form a part with a large volume of compacted powder, compared to a powder used for forming a part with a small volume of compacted powder.
Compacting using low-temperature sinterable powder, and using the low-temperature sintering powder at a temperature equal to or higher than liquid phase sintering or semi-liquid phase sintering and for forming a portion with a small volume of the compacted powder. This is achieved by sintering the entire powder at a temperature higher than the sintering temperature of the powder.

In the present invention, the powder that can be used for compacting the portion with a large powder volume is a powder whose sintering temperature is lower than that used when compacting other portions. It requires that.

Here, the degree of sintering temperature difference required varies depending on the type of powder used for molding each part, and is difficult to determine generally, but it is usually about 50 to 200°C.
It is desirable that there is a sintering temperature difference of . If the sintering temperature difference becomes too large, parts with a large volume of green powder may melt, or
Alternatively, dimensional shrinkage may become excessive, resulting in a problem that desired dimensional accuracy cannot be obtained.

In the present invention, when a part with a large volume of green powder is compacted using low-temperature sinterable powder and sintered at the sintering temperature of a part with a small volume of green powder, the volume of green powder in each part is The reason why the densities of each part after sintering are the same despite the difference in volume is because the low-temperature sinterable powder in the parts with a large volume of compacted powder generates a liquid phase during sintering. This is thought to be because the density of the portion with a large volume of green powder increases by promoting sintering.

In the present invention, the temperature at which the entire compact is sintered after compaction is determined by the temperature at which the low-temperature sintering powder used in the area with a large volume of compacted powder undergoes liquid-phase sintering or semi-sintering, which generates a eutectic melt. The temperature must be higher than that for liquid phase sintering. If it is less than this, the density of the portion with a large volume of compacted powder after sintering will not increase sufficiently. The temperature at which the entire compact is sintered after powder compacting must also be higher than the sintering temperature of the powder used for powder compacting other parts. Below this temperature, the entire compact cannot be sintered.

EXAMPLES Hereinafter, examples of the present invention will be described in detail based on the accompanying drawings.

Example 1 An automobile connecting rod, whose top view is shown in FIG. 5 and a sectional view taken along the line A-A in FIG. 6, was manufactured according to the present invention. As is clear from FIG. 6, when manufacturing connecting rods by powder metallurgy,
When using the method disclosed in No. 19401, the density of the web part (0 parts) with a large powder volume is lower than that of the flange parts (parts D and E) with a smaller powder volume, Inevitably, it becomes smaller, and sufficient strength cannot be obtained.

On the other hand, in a preferred embodiment of the present invention, Fe containing 1% by weight of carbon is first used as the powder for compacting the flange portion (D section) of the connecting rod with a small powder volume. Powder 10, which is a mixture of powder and 1% by weight of zinc stearate as a lubricant, was put into mold 11 made of 5KDII.
After filling, as shown in FIG. 7, a pressure of 500 kg/cd was applied using the upper punch 12 and the lower punch 13 to perform preliminary compaction. After that, the preliminary compacted compact 1
4 in the mold 11, raise the upper bunch 12 and lower the lower punch 13, as shown in FIG.
A spacer 15 made of DII is installed in the mold 11, and as shown in FIG. The powder 16 is a mixture of low-temperature sinterable Fe powder containing 0.6% by weight of P, 3% by weight of Mo, and 1% by weight of carbon with 1% by weight of zinc stearate as a lubricant. Type 11
filled inside. Next, as shown in FIG. 10, the lower punch 13 is further lowered, and the powder 10 for compacting the other flange part (E part) is filled to a rate of 5000 kg/cd.
It was compacted at a pressure of

After compaction, the spacer 15 was removed, and the product was sintered at 1150° C. for 1 hour in a nitrogen atmosphere.

The densities of the flange parts (parts D and E) and the web part (part 0) before sintering are 6. 9g/c+4.6.
The density after sintering was 6.4g/c+1 for the flange part (part D and part E). 9g/cJ, web part (0
) was 7.0 g/ci, which was found to be almost the same.

Example 2 In addition, the amount of P added in the powder 16 was varied from 0.2 to 1.0.
When we conducted a similar experiment by varying the weight percentage, we found that
Results similar to those described above were obtained.

Example 3 Furthermore, in the powder 16, instead of P, 0.2 to 1
．． When a similar experiment was conducted with the addition of 0% by weight of B, the same results as described above were obtained.

Example 4 In addition, in the powder 16, instead of P, C: 3.4% by weight, Si: 1.97% by weight, S:O, S7% by weight, M
n: 0.69% by weight, Mo: 0.01% by weight, Cr: 0
．． The same result was obtained when using alloyed cast iron powder containing 0.093% by weight and the balance being Fe.

However, when using B or alloyed cast iron powder instead of P in the powder 16, the temperature at which the eutectic melt is generated is higher than that of P (around 1150°C), so the sintering temperature is set to Powder 10 has a slightly higher temperature than that of 1200°C, which gives more favorable results.
It was found that sintering at a temperature of

The present invention is not limited to the above embodiments (it goes without saying that various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention). .

For example, in the embodiment described above, the spacer 15 is removed after the main powder compaction and before sintering, but it may be made of a material that is infiltrated during sintering (or may not be removed). Alternatively, the spacer 15 may be a metal or other rigid body with a plated layer made of a material that can be infiltrated by sintering, such as Cu, or a foil made of such a material. It can also be preferably used.

Further, each powder to be compacted is mixed with a solvent or the like to form a slurry, and the slurry is filled into a mold 11 having solvent discharge holes in the upper and lower parts of the spacer 15, and compacted. It's okay.

Furthermore, in the above embodiment, an example was shown in which a connecting rod having a so-called undercut portion was manufactured. Of course, this is not limited to a sintered part having a wide shape (such as a sintered part having a T cross section), and where the volume of the powder to be compacted is partially different. It can be suitably used for manufacturing joint parts.

Effects of the Invention According to the present invention, a low-temperature sinterable powder is used for forming a portion with a large volume of compacted powder, and the low-temperature sinterable powder is subjected to liquid phase sintering or semi-liquid phase sintering. Since sintering is carried out at a temperature higher than that at which a eutectic melt is generated, sintering is promoted in areas with a large volume of compacted powder, and despite the unavoidable lack of physical compaction, it is possible to achieve the desired density. This makes it possible to obtain sintered parts without any strength defects, even if the shapes have different volumes of compacted powder in each part.

Further, during powder compacting, it is possible to compress and sinter a portion with a large powder volume to a desired degree without causing cracks in the compact.

[Brief explanation of drawings]

1 to 4 are schematic diagrams illustrating the manufacturing steps of a sintered part in the prior art. FIG. 5 is a road view of a connecting rod for an automobile, which is a sintered part to be manufactured in an embodiment of the present invention, and FIG. 6 is a schematic cross-sectional view taken along line A-A. 7 to 10 are schematic cross-sectional views showing the manufacturing steps of a sintered part in an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Die, 2...Lower punch, 4...Raw metal powder, 5...Upper punch, 6...-Next molded product,
7... Spacer, 8... Sintered part, 10.16.
...Powder, 11...Mold, 12...Upper punch, 1
3...Lower punch, 14...Preliminary compacted compact, 15...Spacer Fig. 1 and Fig. 3 Fig. 5 Fig. 2 Fig. 4 Fig. 8 Fig. 6 Fig. 7 Fig. 9 Ward 10

Claims (1)

[Claims] In a method of manufacturing a sintered part having a shape in which the volume of the powder to be powder compression molded differs partially, the powder used for other parts is In contrast, powder compression molding is performed using low-temperature sinterable powder,
A sintered part characterized in that the low-temperature sinterable powder is sintered at a temperature higher than the temperature at which liquid phase sintering or semi-liquid phase sintering occurs and higher than the sintering temperature of the powder used for the other parts. manufacturing method.