JPH02270932A - Manufacture of iron-copper series powder metallurgical product - Google Patents

Abstract

PURPOSE:To reduce the surface roughness and shrinkage in a sintered body, at the time of packing iron series powder into a compacting die under no pressure, heating the powder together with the compacting die and executing sintering to obtain a large sized member, by mixing the iron-series powder with Al powder. CONSTITUTION:Iron-series powder is packed into a compacting die under no pressure, is heated together with the compacting die and is sintered, to which copper-series infiltrating material is infiltrated into a powder metallurgical manufactured article. At this time, the iron-series powder is mixed with Al powder and the mixed powder is packed into the compacting die under no pressure. For firmly Sintering the green compact packed under no pressure, fine powder is required to be incorporated into the iron-series powder. The amt. of the Al powder to be mixed is not defined, but 1 to 15wt.% is suitable, and simultaneously with the increase of the amt. to be mixed, the amt. of the sintered body to be shrunken at the time of sintering and infiltrating is linearly reduced. Furthermore, the average grain size of the Al powder is preferably regulated to 1 to 500mu. By this method, the shrinkage of the sintered body in the sintering and infiltrating stage is suppressed without deteriorating the surface roughness, so that the improvement of the dimensional accuracy and the prevention of constrained cracks can be attained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing large sintered members such as molds.

[Prior Art] Large sintered members such as molds are manufactured by applying powder metallurgy. The inventors of the present invention have demonstrated that this method can produce members with complex shapes in a short period of time.
No. 322,869 and No. 62-322,870.

These are made by filling iron-based powder into a mold without pressure.

In order to improve the mechanical properties of the sintered body by sintering it together with a mold to obtain a large member, it is also effective to infiltrate the sintered body with a copper-based infiltrant material to fill the voids.

In order to firmly sinter a molded body filled without pressure, it is necessary to include fine powder with a particle size of 10 μm or less in the iron-based powder, but sintering and infiltration are performed in a state where it is restricted by the mold. This is because the filling body shrinks due to excess fine powder during sintering and infiltration.

The sintered body may be deformed or damaged, making it impossible to obtain a satisfactory member. Therefore, the particle size structure of the iron-based powder must be selected so that such shrinkage does not occur, and a coarser powder than the above-mentioned fine powder is required. However, if too coarse powder is used, the surface roughness of the produced sintered body will be large (when used as a mold material, etc., it will be necessary to significantly grind one surface, resulting in high cost, and it will also be complicated). There are limits to creating shaped members.

Therefore, in Japanese Patent Application No. 62-322869, it was revealed that the surface roughness could be reduced by optimizing the particle size structure of the powder. However, the smaller the surface roughness required for plastic injection molded parts, the better, and further improvement in surface quality and suppression of shrinkage during sintering and infiltration are desired.

[Problems to be Solved by the Invention] The present invention has been made to solve the above problems, and even when iron-based powder containing fine particles is used to reduce the surface roughness of a sintered body, The purpose is to suppress the shrinkage of the sintered body during sintering and infiltration, and to make it possible to obtain a sintered member that is free from deformation and damage.

[Means for Solving the Problems 1] As a result of intensive study by the present inventors to solve the above problems, the inventors found that by mixing aluminum powder with iron-based powder, sintering and
It was discovered that shrinkage during infiltration can be suppressed and a sintered member with small surface roughness can be obtained, leading to the present invention.1 The present invention involves filling a mold with iron-based powder without pressure, When producing a powder metallurgy product by heating and sintering the product and then infiltrating it with a copper-based infiltrant, the iron-based powder is mixed with aluminum powder, and then the mixed powder is filled into a mold without pressure. The present invention provides a method for producing an iron-copper powder metallurgy product characterized by the following.

[Effect]

In the present invention, a mixed powder in which iron-based powder and aluminum powder are mixed is used as the raw material powder.

If necessary, elements such as graphite powder or other metal powder that are alloyed during sintering and are useful for improving the mechanical properties of the sintered body may be further mixed.

Mixing of aluminum powder is necessary to suppress shrinkage of the sintered body during sintering and infiltration, and to obtain a sintered body with small surface roughness. The mechanism of action of the aluminum powder is not clear, but it is thought that the molded body expands as it melts as the temperature rises and reacts with the iron-based powder, thereby compensating for the shrinkage of the molded body due to sintering. .

The amount of aluminum powder mixed is not limited, but it is 1-1% of the total weight of iron-based powder and aluminum powder.
15% by weight is suitable.

According to experiments conducted by the present inventors, the amount of shrinkage of the sintered body during sintering and infiltration decreases linearly as the amount of aluminum powder mixed increases, and the shrinkage amount is approximately
The reduction in shrinkage is about 1%. Since the shrinkage rate when aluminum powder is not mixed is about 10% at most, shrinkage can be sufficiently suppressed by mixing 15% by weight, while 1% by weight has little effect.

The particle size of aluminum powder is related to the filling properties of the mixed powder after being mixed with iron-based powder and the surface roughness of the sintered body.If the average particle size is less than lum, the filling properties of the mixed powder will deteriorate, and the average If the particle size exceeds 500 μm, the surface roughness of the sintered body will increase, so the average particle size is preferably in the range of 1 to 500 μm.

The purity of the aluminum powder is not limited as long as it does not deteriorate the properties of the sintered body, but if the total amount of impurities is 20
% or less.

On the other hand, iron-based powder makes up the majority of the raw material powder, and depending on the characteristics requirements of the sintered body, pure iron powder or alloy steel powder is used.
In order to improve the packing density and surface smoothness, for example, a material having a maximum particle size of 500 μm and containing fine powder with a particle size of 1 μm or less is preferably used.

A normal V-type mixer, double cone mixer, or the like is used to mix the iron-based powder and the aluminum powder.

The above mixed powder is filled into a mold prepared in advance. The mold should have sufficient strength up to the temperature at which the powder improves its strength through sintering and correctly transfers the shape of the mold, and does not impair the transfer of the mold due to a significant reaction with the powder.Normally, high temperature We use a ceramic mold that can maintain strength up to

The shape of the mold is such that the sintered body can function as a mold or the like after the sintering process, either as it is or without significant processing. The manufacturing method may be by machining or by the manufacturing method of ceramic molds used in precision casting, but in short, any manufacturing method can be used as long as the roughness of the transfer surface is small and the strength is excellent. Also good.

Filling is done in a dry manner, and the packing density can be improved by adding vibration. The vibration method may be any method such as electromagnetic vibration or mechanical vibration.

In addition, by applying extremely lower pressure during vibration than in conventional pressure molding methods, filling properties can be further improved. This pressure may normally be 1 kg/crn' or less, and there is an advantage that not only the filling property is improved by applying the pressure, but also the transfer property of the edge portion of the mold is improved. By using such a filling method, large-sized products can be formed easily and inexpensively without using the expensive presses used in normal powder metallurgy, making it possible to mold injection molds as large as 1 m x 1 m. Very suitable for manufacturing etc.

Next, the mold filled with powder is placed in a furnace and sintered. Sintering is done in a reducing atmosphere, an inert atmosphere.

Alternatively, perform it in a vacuum and break the mold after sintering.

Since the obtained sintered body alone does not have sufficient strength as a mold or the like, the pores remaining in the sintered body are infiltrated with a copper-based infiltrant to increase its strength.

Copper, brass, etc. are used as the copper-based infiltrant, and infiltration can be performed in a reducing atmosphere, an inert atmosphere, or a vacuum.

Note that even if the sintering and infiltration steps are performed in one step, that is, in one heat cycle, there is no change in the effect obtained, but there is an advantage that the manufacturing process can be shortened by combining them into one step.

As described above, according to the present invention, an iron-copper yarn powder metallurgy product with a small surface roughness can be manufactured while suppressing shrinkage during the sintering and infiltration steps.

[Example] Example 1 Iron-based powder with an average particle size of 139 um (particle size range of 100 um)
25 parts by weight of atomized pure iron powder with an average particle size of 29 μm (particle size range 15 to 63 μm), 25 parts by weight of atomized pure iron powder with an average particle size of 4.2 μm (particle size range 10 μm)
Iron powder was used in which the particle size structure was adjusted by mixing 25 parts by weight of carbonyl iron powder with a particle diameter of less than m. 94.3 parts by weight of this mixed iron powder has a purity of 98% and an average particle size of 61 um (particle size range 45~
(2) 5.7 parts by weight of aluminum powder (00 μm) was mixed to prepare a mixed powder.

A ceramic mold with a surface roughness (Ra value) of 0.3 μm was used as a mold, and the mixed powder was filled by vibration. A copper-based infiltrant material formed by press-molding brass powder was placed on the surface of the filling body, and the ceramic mold, powder filling body, and infiltration material were placed in a furnace, and heated to 1010 °C in a nitrogen gas atmosphere.
After sintering the filler by heating at .degree. C. for 70 minutes, the temperature was raised to 1130.degree. C. over 2 hours to melt the infiltrant and advance infiltration. The holding time at 1130°C was 100 minutes.
After that, the furnace was cooled.

After cooling, the l@-immersed sintered body was taken out from the ceramic mold, its dimensions were measured, and the shrinkage rate during sintering and infiltration was determined to be 1.4%.

In addition, the surface roughness of the side surface that was in contact with the ceramic mold was measured, and Ra = 1.6 μm was obtained. This value is 1, which can be used for example in molds for plastic injection molding.

[Comparative Example 1] Example 1 except that the aluminum powder was not mixed.
The test was conducted assuming that the

As a result, the shrinkage rate during sintering and infiltration was 5.6%.

If the shrinkage is large (more than 2%) like this, it is best to restrain it in a mold with a complicated shape and sinter it.

Sintering is impossible because restraint cracks occur in the sintered body.

Note that the surface roughness was Ra = 1.7 μm, which was the same as in Example 1.

[Example 2] Atomized alloy copper powder (1.5%Ni, 0.5%Cu, 0.5%Ni, 0.5%Cu, 0.5%Ni, 0.5%Cu, 0.5%Ni, 0.5%Cu, 0.5%Ni, 0.5%Cu, 0.5%Ni, 0.5%Cu, 0.5%Ni, 0.5%Cu, 0.5%Ni, 0.5%Cu, 0.5%Ni, 0.5%Cu, 0.5%Ni, 0.5%Cu, 0.5%Ni).
5% MO)91. ．． The test was conducted in the same manner as in Example 1 except that 8.1 parts by weight of aluminum powder having a purity of 99% and an average particle size of 36 μm (particle size range 15 to 63 μm) was mixed with 9 parts by weight. As a result, the shrinkage rate during sintering and infiltration was 0.7%, and the surface roughness of the sintered body was Ra = 1.2.
It was a satisfactory value of μm.

[Comparative Example 21 The test was carried out in the same manner as in Example 2 except that no aluminum powder was mixed.

Although the shrinkage rate during sintering and infiltration was large at 6.8% and the surface roughness was good at Ra = 1.6 μm, sintering was impossible due to the occurrence of restraint cracks as in Comparative Example 1. .

[Effects of the Invention] According to the present invention, in the manufacturing method of iron-copper powder metallurgy products, shrinkage of the sintered body in the sintering-infiltration process is suppressed without impairing surface roughness, and dimensional accuracy is improved. This also made it possible to prevent restraint cracking.

Claims (1)

[Claims] 1 Iron-based powder is filled into a mold without pressure, heated and sintered together with the mold, and then infiltrated with a copper-based infiltrant to create a powder metallurgy product. Aluminum powder is mixed with iron-based powder. After that, the mixed powder is filled into a mold without pressure.