JPH0257609A - Injection-molding metal powder, its compound, and production of sintered injection-molded part using said compound - Google Patents

Abstract

PURPOSE:To obtain the title injection-molding metal powder capable of stably providing a high-density metal powder sintered body having excellent dimensional precision by specifying the diameter range and shape factor of the particles. CONSTITUTION:The mean particle diameter of the injection-molding metal powder is controlled to 5-15mum. The particle shape factor is defined by the equation SF=L<2>/A.pi/4 (SF is the shape factor of the powder particle cross section, L is the maximum length of the particle cross section, and A is the particle cross-sectional area), and the shape factor of >=50% of the powder is controlled to 1.0-1.5. The powder can be formed by the water atomization process for the molten metal. The injection-molding compd. having good fluidity and orientational property is obtained from 95-85wt.% of the metal powder and 5-15wt.% org. binder. The org. binder contains 40-80% thermoplastic resin, 6-13% plasticizer, and 20-50% paraffin wax or beeswax. The compound is injection-molded at 400-2,000kgf/cm<2> pressure and at 120-170 deg.C. The molded body is heated to 450-600 deg.C at the temp. increasing rate of <=200 deg.C/hr to remove the binder, and then sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a metal powder and compound for injection molding, and a method for manufacturing metal sintered parts using the compound.

<Prior Art> Generally, sintered mechanical parts are produced by press-forming a mixture of iron-based powder as a main ingredient, adding alloy powder and a lubricant, and then sintering it in a non-oxidizing atmosphere.

However, this method cannot produce complex three-dimensional parts because the mold is formed using upper and lower punches in a mold.

On the other hand, ceramic products are manufactured by mixing ceramic raw material powder and a binder, extrusion molding or injection molding, and then firing to remove the binder, resulting in products with complex shapes, thin walls, and small parts.

In recent years, injection molding technology using metal powder has attracted attention as a technology that surpasses conventional powder metallurgy because it can mass-produce products with complex shapes, and has been partially industrialized.

The metal powder injection molding method consists of a kneading process in which metal powder is kneaded with an organic binder to obtain a raw material, an injection molding process in which the raw material is injection-molded to obtain a molded body in the same way as in the case of plastic molding, and a heat treatment is applied to the molded body. This is a method in which a degreasing step of removing the binder from the molded body and a sintering step of sintering the degreased molded body are carried out in sequence, and is known from JP-A-57-16103 and JP-A-59-229403.

<Problems to be Solved by the Invention> However, the above method uses a rather fine metal powder used in ordinary mold molding, and the fluidity of the compound peculiar to injection molding and the metal powder mold The density ratio of the metal powder sintered body (
It is well known that it is better to stably maintain the sintered density (ratio of sintered density to theoretical density) at 93% or higher, but it is not only impossible to maintain it at 93% or higher, but also the dimensional accuracy of parts, which is the most important part of the product, is No consideration was given.

Therefore, the present invention solves the problems of the prior art described above, and
An object of the present invention is to obtain a metal powder for injection molding, a compound, and a method for manufacturing injection sintered parts using the compound, which can stably obtain a metal powder sintered body having a density ratio of 1.9% or more and excellent dimensional accuracy. purpose.

Means for Solving the Problems> Therefore, in order to achieve the above-mentioned object, the present inventors have created a metal powder for injection molding that has an average particle size of 5 to 15 μm and a particle shape coefficient defined below. Provided is a metal powder for injection molding, characterized in that 50% or more of the powder is in the range of 1.0 to 1.5.

SF: Shape factor of powder particle cross section L: Maximum length of particle cross section A: Particle cross sectional area Further, an injection molding compound comprising 95 to 855 to 85 of the metal powder and 5 to 15% by weight of a mechanical binder, The composition of the organic binder is a thermoplastic resin 40
~80m'￥8:%, 6 to 13% by weight of plasticizer and 20% of one or two of paraffin wax and beeswax.
An injection molding compound having a weight of ~500 to 50% is provided.

Then, when injection molding is performed using the injection molding compound, the injection molding is performed under conditions of an injection pressure of 400 to 2000 kgf/am2 and a molding temperature of 120 to 170°C, and then this injection molded product is heated in a non-oxidizing atmosphere. Temperature speed 2
Provided is a method for manufacturing an injection sintered part, characterized in that depinder is performed by heating at a heating temperature of 450 to 600°C at a temperature of 00°C/hr or less, and then sintering.

The present invention will be explained in detail below.

In the metal powder for injection molding used in the present invention, the type of metal may be any common metal, including iron and SUS.

In the present invention, the appropriate particle size of the metal powder for injection molding is an average particle size of 5 to 15 μm.

Common powder manufacturing methods include water atomization, pulverization, and the like. However, with the water atomization method etc., the average particle size is 5 μm.
It is difficult to obtain metal powder with a particle size of less than m, and although it is possible to provide it by classification after pulverization, the yield decreases and costs increase. Furthermore, the expected effect of increasing the density of the sintered part cannot be obtained.

Further, if the diameter exceeds 15 μm, the fluidity during injection molding will be poor unless the amount of binder is increased, and the density of the sintered part will be low, so it is not suitable for the present invention.

Further, in the present invention, it is preferable that the particle shape factor (SF) defined by the following formula [1] is in the range of 1.0 to 1.5, and that 50% or more of powder in this range is contained.

SF: Shape factor of powder particle cross section L: Maximum length of particle cross section A: Particle cross-sectional area This is because it affects the dimensional accuracy of the sintered body.

In other words, powder with a particle shape coefficient in the range of 1.0 to 15,
If it contains less than 50%, the particles will be irregular,
It is unsuitable because the fluidity of the compound is poor, and the irregular metal powder particles come into contact with each other, resulting in poor orientation, resulting in uneven shrinkage during sintering and poor dimensional accuracy.

Next, in the components/composition of the organic binder, 40 to 80% by weight of thermoplastic resin, 6 to 13% by weight of plasticizer,
It is preferable that the wax agent is contained in an amount of 20 to 50% by weight.

The thermoplastic resin is not particularly limited, and may include ethylene vinyl acetate copolymer (hereinafter referred to as EVA), polystyrene (
(hereinafter referred to as PS), polypropylene (hereinafter referred to as PP)
1 of polymethacrylic acid esters (P M E ), etc.
f! ! Alternatively, it is preferable to select from a mixture of two or more types.

In particular, it is more preferable to include EVA because it has excellent fluidity and degreasing properties.

If the amount of thermoplastic resin constituting the binder is less than 40%, the strength of the molded product will be weak, making it difficult to handle in the production of parts. Moreover, if it exceeds 80%, it becomes difficult to remove the binder.
This is not preferable because the amount of C in the sintered body becomes high and the properties of the sintered body are impaired.

As the plasticizer, it is preferable to use one or more of dibutyl phthalate (hereinafter referred to as DBP) and diethyl phthalate (DEP). These plasticizers improve the compatibility of the components constituting the binder, homogenize the binder, and improve the fluidity of the compound during injection molding.

Further, if the amount is less than 6%, the above-mentioned effect cannot be obtained, and if the amount is more than 13%, the molded product becomes brittle, which is not preferable.

As the wax, it is preferable to use one or more of paraffin wax, beeswax, etc.

These have the effect of improving the fluidity of the mixture during injection molding and improving the wettability between the raw material powder and the binder to homogenize the compound. The amount added to achieve these effects is 20% or more, and if it exceeds 50%, the strength of the molded product will decrease, which is not preferable.

Next, the amount of the organic binder added to the metal powder is preferably 5 to 15 wt% relative to 95 to 85 wt% of the metal powder.

If the amount of organic binder added is less than 5%, there is only enough binder to fill the gaps between the powder fillers, and the amount necessary to provide fluidity is insufficient, resulting in decreased fluidity during molding and injection molding. become unable.

On the other hand, if the amount exceeds 15%, the amount of binder is too large and the density of the sintered body decreases, which is not preferable.

The metal powder and organic binder are kneaded to form a compound using a conventional method.

Then it is injection molded. In the present invention, the pressure during injection molding is preferably 400 to 2000 kgf/cm2.

If the injection pressure is less than 400 kgf/cm', a satisfactory injection molded article cannot be obtained. Also, the injection pressure is 2,
If the pressure is 000 kgf/cm2, it is possible to injection mold parts with sufficiently complex shapes, and there is no advantage in applying a pressure exceeding 2000 kgf/cm2 in terms of cost and equipment.

Further, the molding temperature is preferably 120 to 170°C. If the molding temperature is less than 120°C, a satisfactory injection molded product cannot be obtained, and if it exceeds 170°C, gas generation from the binder becomes significant, resulting in poor appearance of the molded product.

After the desired molding is performed, degreasing is performed.

The degreasing process in the present invention is performed in an inert gas atmosphere, at a heating rate of 200°C/hr or less, and at a heating temperature of 450 to 600°C.
It is best to remove the binder by heating it.

If the heating rate exceeds 200° C./hr, cracks or blisters may occur in the molded product, making it difficult to obtain a satisfactory molded product, which is not suitable.

Furthermore, if the heating temperature for binder removal is less than 450° C., complete binder removal will not be performed and carbon will remain in the sintered body, causing poor dimensional accuracy. Also, 60
Removal of the binder at a temperature exceeding 0°C is undesirable because the molded product may warp.

After this, sintering can be carried out using conventional methods to obtain injection sintered parts.

<Example> Hereinafter, the present invention will be specifically explained based on Examples.

(Example) Water atomized iron powder or 5US316 stainless steel powder and a binder were kneaded using a pressure kneader according to the components and compositions shown in Table 1 to produce raw materials for inventive examples and comparative examples.

In order to obtain the desired particle size, the iron powder and stainless steel powder of the present invention are water atomized by adjusting the water solubility ratio in the range of 25 to 30 kg/min at a water pressure of 800 to 1000 kgf/cm2 to determine the average particle size and particle size. Powders of different shapes were prepared.

Comparative examples of iron powder and stainless steel powder had a water pressure of 400 kg.
It was obtained by water atomization at a temperature of less than f/cm'' and then classification.

The average particle diameter was determined by the microtrack method, and the particle shape was determined by the following formula by embedding a representative sample of the powder used in resin, enlarging the cross section of the powder 200 times, and processing images of 1200 to 1400 powders. , defined.

SF: Shape factor L of powder particle cross section Maximum length of 1 particle cross section A: Particle cross sectional area When the shape factor is 1, it indicates a perfect round sphere, and as the value becomes larger than 1, it means an irregularly shaped powder. .

Each molding raw material was molded into a plate-shaped test piece with a thickness of 4 mm, a width of 15 mm, and a length of 30 mm under the injection molding conditions shown in Table 2. After arranging this on a stainless steel mesh and depineurizing it in Ar scum W 121El air under the conditions shown in Table 2, the iron powder compact was further molded into stainless steel using decomposed ammonia gas at 1150°C for 30 minutes. The body was sintered in vacuum at 1350°C for 60 minutes.

The sintered density of the obtained test pieces was measured, and the density ratio was calculated as a percentage of the theoretical density.The dimensional change was calculated by measuring the dimensional change before and after sintering in the width direction of each 10 test pieces, and the standard deviation was calculated. I asked for it.

Note that FIG. 1 shows an SEM image of the iron powder used in Inventive Example 2, and FIG. 2 shows an SEM image of the iron powder used in Comparative Example 1. The particle shape of most of the metal powders used in the present invention is close to spherical, and the shape factor is 1.
The powder in the range of ~1.5 is 50% or more, has excellent fluidity during injection molding, and has good orientation of the metal powder, so the density ratio of the sintered body is as high as 93% or more, and , dimensional accuracy is also excellent.

<Effects of the Invention> When producing a sintered part using the metal powder injection molding method, the metal powder and compound of the present invention and the injection sintered part manufactured using the compound have a density of 93% or more. It is possible to obtain sintered parts with high ratio and dimensional accuracy, and it is possible to improve the product holding capacity.

[Brief explanation of the drawing]

FIGS. 1 and 2 are photographs substituted for drawings showing the structure of particles. FIG. 1 is a SEM photograph at a magnification of 500 of the iron powder used in Invention Example 1. FIG. 2 is a SEM photograph of the iron powder used in Comparative Example 2 at a magnification of 500.

Claims (3)

[Claims] (1) The average particle size of the metal powder for injection molding is 5 to 15 μm, and the particle shape factor defined below is 1.0 to 1.
A metal powder for injection molding, characterized in that 50% or more of the powder falls within the range of 5. SF=L^2/A・π/4 [I] SF: Shape factor of powder particle cross section L: Maximum length of particle cross section A: Particle cross sectional area (2) An injection molding compound comprising 95 to 85% by weight of the metal powder and 5 to 15% by weight of the organic binder, wherein the organic binder has a composition of 40% by weight of a thermoplastic resin.
-80% by weight, 6-13% by weight of plasticizer and 20-50% of one or two of paraffin wax and beeswax.
An injection molding compound characterized by containing % by weight. (3) When injection molding is performed using the injection molding compound, the injection pressure is 400 to 2000 kgf/cm^2 and the molding temperature is 120 to 170°C, and the injection molded product is then placed in a non-oxidizing atmosphere. , heating rate 2
A method for manufacturing an injection sintered part, characterized in that the binder is removed by heating at a heating temperature of 450 to 600°C at a temperature of 00°C/hr or less, and then sintering.