JPH049403A - Manufacture of precise metal parts with powder compacting - Google Patents

Abstract

PURPOSE:To stabilize fluidity at the time of compacting and dimension of a sintered body and to easily obtain the sintered body having density near the true density by using metal powder composed of one or more kinds of metals controlled with oxygen content and having single and uniform spherical shape and uniform particle size distribution. CONSTITUTION:The metal powder having single and uniform spherical shape and uniform particle size distribution and about 0.5 - 60wt% oxygen content (the total oxygen content in the metal powder in terms of element analysis value) and about 1 - 7% reduction reducing ratio (wt. reducing ratio in the case of heating under hydrogen reduction atmosphere), and produced by controlling reduction ratio in producing process for the metal powder is used. One or more kinds of this metal powder and organic binder are mixed and the organic binder is sufficiently removed from a green compact formed of this mixed material to the desired shape, and after reducing the above metal powder, the main sintering is executed to obtain a precise metal parts.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing precision metal parts by powder compaction, and more particularly to a method for manufacturing precision metal parts as a sintered particle structure. After mixing metal powder and an organic binder and molding this mixture into a desired shape, the organic binder is removed from the molded body, the metal powder constituting the molded body is reduced, and it is sintered as a pure metal. The present invention relates to a method for manufacturing precision metal parts, which is characterized by obtaining a sintered body with close to true density by sintering.

[Conventional technology]

Recently, various sintered parts using metal powder or ceramic powder have become widely used in fields such as general industrial materials, precision mechanical parts, electronic parts, electrical parts, and automobile parts. Accordingly, quite strict requirements have been made regarding the exact dimensions, physical properties, shape, etc. of these parts.

The production of powder for molding using a spray dryer and the subsequent production of molded products for sintering using a rubber press, which is currently widely practiced, not only has the problems of extremely complicated processes and extremely low yields. However, it has the disadvantage that a molded product with a complicated shape cannot be obtained.

In order to deal with these demands and problems, a suitable resin is added to metal powder or ceramic powder to give it thermoplasticity, which is then molded by injection molding, and then the resin contained in this molded body is Several methods have been proposed and implemented to obtain desired metal or ceramic powder injection molded parts by carrying out main firing after thermal decomposition and removal (for example, Japanese Patent Publication No. 51-29170, Japanese Patent Application Laid-Open No. 55-113).
510, Japanese Patent Application Laid-Open No. 55-113511) 0 These methods not only prevent cracks from forming in the molded product during injection molding, but also prevent cracks, bulges, and The problem is to remove the organic binder, which is a resin, in a short time without causing deformation.

However, even if these problems are solved, it is difficult to manufacture precision metal parts characterized by obtaining a sintered body with close to true density using powder compaction, which is the object of the present invention.

Additionally, in metal powders, in general, when the average particle size is reduced, the amount of oxygen increases, and when reduction treatment is applied to reduce this amount of oxygen, the average particle size tends to increase, resulting in agglomeration of constituent unit particles. agglomeration occurs. In the conventional method, emphasis is placed on the purity of the metal powder, and the shape is not substantially spherical, but the average -
In terms of shape, metal powder with a low oxygen content was used.

[Problem to be solved by the invention]

Conventionally, metal powders produced by a mechanical pulverization method, a reduction method, an electrolytic method, a carbonyl method, a gas atomization method, a water atomization method, etc. have been used for powder compaction. It is desired that the metal powder used for powder compaction has a single and uniform spherical shape and a uniform particle size distribution. In particular, this powder property is strongly desired for powder injection molding, which is one of the powder molding methods. The reason for this is the flowability of the mixture of metal powder and organic binder during molding, and the stabilization of the dimensions of the sintered body depending on this.

However, in the metal powder currently used for powder compacting, each constituent unit particle coagulates or aggregates with each other, and is not substantially spherical. For example, JP-A-57-16103
The Inco type 123 nickel powder shown in Example 1 of the publication is not substantially spherical but has a spike-like agglomerated spherical shape, and the oxygen content is 0.15 wt% or less, so the surface of the metal powder is not active. However, the constituent unit particles coagulate with each other and do not have a substantially spherical shape. Even if such metal powder is used, it is difficult to stabilize the flowability and the dimensions of the sintered body, and the purpose of the present invention is to obtain a sintered body with close to true density using powder compaction. Manufacturing precision metal parts is difficult.

Furthermore, when a metal compound consisting of a metal and oxygen as disclosed in JP-A-58-153702 is used, the amount of oxygen is very large and oxygen is present inside the metal compound powder.
The reduction treatment before sintering takes time and is not necessarily an industrially satisfactory method, so it is difficult to obtain a sintered body with close to true density using powder compaction, which is the purpose of the present invention. It is difficult to manufacture precision metal parts characterized by this.

In other words, it is possible to obtain a sintered body with close to true density by using powder that has a uniform particle size distribution and a single, uniformly spherical shape that allows for stable flowability and sintered body dimensions. There was a strong desire to provide a method for manufacturing precision metal parts.

[Means to solve the problem]

In view of this, the present inventor uses a powder having a single, uniformly spherical shape and a uniform particle size distribution as the metal powder to stabilize the flowability during molding and the dimensions of the sintered body,
With the aim of finding a manufacturing method for precision metal parts that can easily produce a sintered body with a density close to true density, we have conducted intensive research and studies to find a metal made of one or more types with a controlled amount of oxygen. Using a powder, the metal powder with a controlled amount of oxygen and an organic binder are mixed, this mixture is molded into a desired shape, and then the organic binder is sufficiently removed from this molded body to form a molded body. It has been found that the above object can be achieved by reducing the metal powder with a controlled amount of oxygen before main sintering and performing main sintering.

The metal powder used in the present invention has a single, uniformly spherical shape, and has a uniform particle size distribution, and the amount of reduction is controlled in the manufacturing process of the metal powder, and the amount of oxygen is 0.65 wt% to 6.0 wt%.
and preferably from 1.0 wt% to 3.0 wt%,
The reduction reduction rate is 1% to 7%, preferably 2% to 3%.
It is a metal powder made of one or more kinds controlled at %, and may be an alloy powder.

The oxygen content here is an elemental analysis value of the metal powder, and indicates the total oxygen content in the metal powder. Further, the reduction amount is the weight reduction amount when the metal powder is heated in a hydrogen reducing atmosphere, and includes nitrogen other than oxygen, adsorbed water, and the like. The average particle size of the metal powder is 10 μm or less, preferably 5 μm or less.

The organic binder used in the present invention is a known organic binder. Specifically, each organic binder component is removed at least 90% below the sintering temperature of the metal powder used, preferably below the calcination temperature, such as ethylene-vinyl acetate copolymer, polyethylene, atactic polypropylene, These include polystyrene, polybutyl methacrylate, paraffin wax, carnauba wax, etc.

In the present invention, the metal powder and the organic binder are mixed by a known method. Specifically, by melting and kneading metal powder and organic binder in a pressure kneader, it is possible to efficiently form a homogeneous mixture that has a certain flowability and a certain weight and density. It is possible to obtain a mixture of

The homogeneous mixture in the present invention is molded by a known method using an injection molding machine or the like to obtain a molded product in a desired shape.

At this time, by using a homogeneous mixture of a metal powder and an organic binder that has a single, uniformly spherical shape and a uniform particle size distribution, stable molding can be performed.

The organic binder in the present invention is removed by a known method. At this time, the removal rate of the organic binder is preferably 90% or more, more preferably 95% or more. Furthermore, the atmosphere during removal of the organic binder is preferably an inert atmosphere, but may also be a hydrogen atmosphere, or both atmospheres may be used.

In the present invention, the amount of reduction is controlled in the manufacturing process of metal powder, and the amount of oxygen is 0.5 wt% to 6.0 wt%,
Reduction treatment of metal powder consisting of one or more metal powders, preferably controlled to 1.0 wt% to 3.0 wt%, with a reduction reduction rate of 1% to 7%, preferably 2% to 3%. is carried out in a reducing atmosphere furnace at a temperature below the main sintering temperature of the metal powder, preferably below the calcination temperature of the metal powder. At this time, more than 90% of the organic binder covering the metal powder surface is removed, the porosity in the structure increases, and the structure surface and internal metal surface are substantially exposed to a reducing atmosphere. This makes it possible to carry out aggressive reduction processing.

Therefore, it is preferable that 100% of the organic binder be removed before the metal powder reduction treatment step. Through this reduction treatment process of the metal powder, the metal powder becomes substantially pure metal powder. This metal reduction treatment step can also be performed in the organic binder removal step.

Sintering in the present invention is performed at a predetermined sintering temperature under a predetermined atmosphere depending on the metal powder. In this sintering process, 1
If less than 0% organic binder is present as a residual, the organic binder is removed in a reducing atmosphere at a temperature below the calcination temperature or below the main sintering temperature, and at the same time, the metal powder is subjected to a reduction treatment. , sintering is performed at a predetermined sintering temperature.

By performing each process using the metal powder shown above, the flowability during molding and the dimensions of the sintered body are stabilized,
This has made it possible to manufacture precision metal parts that can produce sintered bodies with close to true density.

〔Example〕

The effects of the present invention will be shown below with reference to Examples, but the present invention is not limited thereto.

(Example 1) As a metal powder, the powder density was 7604 g/cI11 when the oxygen amount was controlled to 0.7 wt% and the reduction reduction amount was controlled to 2.62 wt% (1000 ° C. - 30 minutes), and the average particle size was 134 μ
An iron powder having a single, uniformly spherical shape and a uniform particle size distribution was used as an organic binder, and a mixed organic binder of ethylene-vinyl acetate copolymer, polybutyl methacrylate, polystyrene, wax, and dibutyl phthalate was used as an organic binder. Parts were mixed.

The iron powder and the mixed organic binder are thoroughly melted and mixed at 130° C. and 4 Kg f /cnl using a pressure kneader, and then this mixture is mixed. Made into a beret.

This pellet is molded using an injection molding machine at a nozzle temperature of 150°C.
, injection pressure 1t/c self, mold temperature 30'C, diameter 10
A cylindrical molded body with a thickness of 2 cm was molded. The organic binder was removed from the molded body by heating it from room temperature to 450'C for 8 hours in a nitrogen atmosphere according to a predetermined heating program. At this time, the removal rate of the organic binder was 95%. Furthermore, when the surface of the molded article after the organic binder removal treatment was observed, no cracks, blisters, or deformations were observed. Next, this molded body was heated in a hydrogen reducing atmosphere from room temperature to 600'C in 1 hour to completely remove 5% of the remaining organic binder, and at the same time, the iron powder was reduced. .

Thereafter, the iron powder was heated from 600° C. to 1300° C. in 1 hour, and the iron powder was further reduced at a temperature below the sintering temperature during this heating process to obtain substantially pure iron. Then 3 at 1400℃
A sintered body was obtained by holding for a certain period of time.

The relative density of this sintered body was 99.5%, which was a much higher value than conventional products. Furthermore, the reproducibility of the flowability of the mixture of metal powder and organic binder was examined using a flow tester, and the flow value was stable without large fluctuations.

(Comparative Example 1) Oxygen content, which is commonly used as metal powder, is 0.
04wt%, reduction reduction amount 0.17wt% (1000℃
-30 minutes) powder density was 7.824 g/cr
a, and non-uniformly shaped iron powder containing coagulated and agglomerated powder with an average particle size of 4.40 μm was used. Organic binder melt mixing, molding, organic binder removal, reduction treatment, and baking were performed in the same manner as in Example 1. The relative density of the sintered body obtained in this way was as low as 90.3%.In addition, the reproducibility of the flowability of the mixture of metal powder and organic binder was tested using a flow tester. When we looked into it, we found a large swing.

Ta.

(Example 2) The relationship between the relative density of the sintered body and the sintering temperature was investigated using two types of iron powder with different amounts of oxygen and reduction reduction amounts in the metal powder. Amount of oxygen '40.7w
t%, reduction reduction amount 2.62wt% (1000℃-30
Iron powder with a powder density controlled at 7.604 glC and an average particle size of 134 μm, uniformly spherical in shape, and with a uniform particle size distribution, and a commonly used iron powder as shown in Example 2. The powder density was 7.824 g/cot when the oxygen content was controlled to 0.04 wt% and the reduction reduction amount was controlled to 0.17 wt% (1000°C-30 minutes), and the average particle size was 4.
．． Sintered bodies with different relative densities were obtained in the same manner as in Example 1 except that only the sintering temperature was varied, using iron powder of non-uniform shape including coagulated and agglomerated powder of 40 μm. These results are shown in FIG. When the commonly used iron powder shown in Comparative Example 1 is used, the melting point of pure iron is 1.
Since the temperature is 535°C, in order to obtain a stable sintered body of F with a relative density of 99% or more, a sintering temperature of 450°C or higher is required, and the actual sintering temperature range is about 70°C. Only ℃・. Furthermore, even if a stable sintered body with a relative density of 99% or higher is obtained at a sintering temperature of 1450°C or higher, the surface will be severely roughened due to coarsening of grain boundaries, making it impossible to use it as precision metal parts. (・.On the other hand, when the iron powder shown in Example 1 according to the present invention is used, the relative density is 9
A sintered body in a stable state of 9% or more can be obtained even at a sintering temperature of 1100°C, which is much lower than the commonly used sintering temperature of 1300°C. Therefore, when using the iron powder shown in Example 1 according to the present invention, it is possible to obtain a stable sintered body with a relative density of 99% or more at a lower temperature than before and over a wide sintering temperature range. It is. In other words, the present invention is very effective for manufacturing precision metal parts with high density, good reproducibility, and good dimensional accuracy.

Also, from an industrial perspective, lowering the sintering temperature is
This leads to a reduction in parts manufacturing costs and is extremely effective.

(Example 3) The powder density shown in Example 1 was controlled to 0.7 wt% and the reduction reduction amount to 2.62 wt% (1000°C - 30 minutes), and the average powder density was 7.604 g/ct. Particle size 134
1000 fired bodies were obtained in the same manner as in Example 1 using iron powder having a single and uniform spherical shape of μm and a uniform particle size distribution. FIG. 2 shows the results of dimension measurements of 1000 sintered bodies as the degree of variation in outer diameter with respect to the target value.

It is possible to obtain a sintered body with small dimensional fluctuations, good reproducibility, and excellent dimensional accuracy.

(Comparative Example 2) The powder density shown in Comparative Example 1 was controlled to 0.04 wt% and the reduction reduction amount to 0.17 wt% (10,00°C-30 minutes), and the powder density was 7.824 g/ca. , average particle size 4
1000 fired bodies were obtained in the same manner as in Example 1 using non-uniformly shaped iron powder containing coagulated and agglomerated powder of 40 μm. FIG. 3 shows the results of dimension measurements of 1000 sintered bodies as the degree of variation in outer diameter with respect to the target value. Compared to FIG. 2, the dimensional variation of the sintered body is large, making it impossible to obtain a sintered body with good reproducibility and excellent dimensional accuracy.

(Example 4) As a metal powder, the powder density was 7.603 g 1 ctA with the oxygen content controlled to 1.96 wt% and the reduction reduction value controlled to 3.90 wt% (5009C-3 hours), and the average particle size was 12. Fe-50wt%Co alloy powder having a single and uniform spherical shape of 4 μm and a uniform particle size distribution was used, and the organic binder, melt mixing, molding, organic binder removal, and reduction treatment were performed in the same manner as in Example 1. The sintering was performed from room temperature to 600°C for 1 hour at 600°C in a hydrogen reducing atmosphere.
℃ to 700℃ for 1 hour, 700℃ to 1400℃
After raising the temperature to 1,400℃ for 3 hours,
The mixture was cooled down to room temperature in a furnace for 2 hours. The relative density of the sintered body thus obtained was 95.5%.

(Comparative Example 3) As a metal powder, the powder density was 8.15 g / cl with the oxygen amount controlled to 0.26 wt% and the reduction reduction amount to 0.16 wt% (500 ° C. for 3 hours), and the average particle size 11.3
Fe-50wt%Co alloy powder with a single and uniform spherical shape of 7 μm and a uniform particle size distribution was used, and the organic binder, melt mixing, molding, organic binder removal, reduction treatment, and firing were the same as in Example 4. I went there. The relative density of the sintered body thus obtained was 875%, a value lower than that of Example 4.

〔Effect of the invention〕

From the results of the Examples and Comparative Examples above, it is clear that the metal powder of the present invention, which is composed of one or more types with controlled oxygen content, has a single and uniform spherical shape, and has a uniform particle size distribution, Metal powder with a controlled amount of oxygen and an organic binder are mixed, this mixture is molded into the desired shape, and then the organic binder is removed from the molded object in small pieces to control the amount of oxygen that makes up the molded object. By reducing the metal powder and lowering the temperature before main sintering, it is also possible to reduce the cost of manufacturing parts. In other words, we have found a method for stably manufacturing precision metal parts with higher sintered body density and higher dimensional accuracy than conventional methods.

[Brief explanation of drawings]

Figure 1 shows the relationship between the sintering temperature and the relative density of the sintered body, so the * mark is the iron powder of the present invention, and the ○ mark is the conventionally used iron powder. . FIG. 2 shows the degree of variation in the outer diameter with respect to the target value in relation to the dimensional accuracy and the number of sintered bodies when 1000 sintered bodies were manufactured using the iron powder of the present invention. Figure 3 shows that 100
The degree of variation in the outer diameter with respect to the target value when 0 sintered bodies are manufactured is shown in terms of the relationship between dimensional accuracy and the number of sintered bodies. Aida 1 Miyado (0/.)

Claims (6)

[Claims] (1) A method for manufacturing precision metal parts by powder compaction, which is characterized by using metal powder made of one or more types with a controlled amount of oxygen in order to manufacture precision metal parts as a sintered particle structure. (2) Consists of one or more types in which the amount of reduction is controlled in the manufacturing process of metal powder, the amount of oxygen is 0.5 wt% to 6.0 wt%, and the reduction reduction rate is controlled to 1% to 7%. A method for manufacturing precision metal parts by powder molding, characterized by using metal powder. (3) In order to manufacture precision metal parts as a sintered particle structure, a process of mixing metal powder consisting of one or more types with a controlled amount of oxygen and an organic binder to form a homogeneous mixture. [1], a step of molding this mixture into a molded object of a desired shape [2], a step of removing the organic binder from the molded object obtained in the step [3], and the step [
Step [4] of reducing the metal powder composed of one or more kinds with a controlled amount of oxygen, which constitutes the compact obtained in step [3].
and a step [5] of sintering the molded body obtained in the step [4].
A method for manufacturing precision metal parts by powder compaction, characterized by obtaining a sintered body with close to true density. (4) In the step [3] of removing the organic binder from the molded body as set forth in claim (3), at least one metal powder comprising one or more metal powders with a controlled amount of oxygen is used to form the molded body. A method for manufacturing precision metal parts by powder molding, characterized in that 90% or more of the organic binder is removed before the reducing step [4]. (5) The step [4] of reducing the metal powder consisting of one or more kinds with a controlled amount of oxygen constituting the compact as set forth in claim (3) is performed before the main sintering. A method for manufacturing precision metal parts by powder molding, characterized by: (6) In order to manufacture precision metal parts as a sintered particle structure, the sintering shrinkage rate is controlled by the reduction reduction amount of the metal powder to accurately control the part dimensions and obtain a sintered body with close to true density. A method for manufacturing precision metal parts by powder molding, characterized by: