KR101856387B1 - High density molding method mixed powder - Google Patents

Abstract

According to an embodiment of the present invention, a high density mixed powder molding method molds a sintering component for a vehicle with metal powder, and comprises: a preparation step of preparing metal powder and a single component system lubricant; a mixed powder manufacturing step of mixing the metal powder and the single component system lubricant to prepare mixed powder; and a molding step of filling the mixed powder in a mold to be pressurized at 80-100°C for a molding body to be manufactured.

Description

TECHNICAL FIELD [0001] The present invention relates to a high-

More particularly, the present invention relates to a high-density powder mixture molding method capable of securing a molding density of 7.15 g / cm 3 or more at a temperature of 100 ° C or lower .

Generally, the powder metallurgy method is a method of producing a sintered part by pressing a metal powder in a metal mold and then sintering to produce a mechanical part having a complicated shape with high precision, And is used mainly in the manufacture of automobile parts.

In order to manufacture automobile sintered parts in the above-described manner, metallic powder having high strength, high toughness and light weight is required, and such metal powders are not used alone as iron (Fe) Alloys such as carbon (C), nickel (Ni), copper (Cu), and molybdenum (Mo) are added according to various purposes.

In particular, sintered parts for automobiles such as planetary carriers and sprockets require a high density molding density in addition to the above characteristics. Such sintered parts conventionally require a molding density of at least 7.15 g / cm 3 after molding.

In order to mold at a high density as described above, it is difficult to use a general molding method. Therefore, a warm molding method in which a metal powder and a metal mold are heated to a temperature of about 110 to 130 캜 and then molded is used.

In this case, a complex lubricant such as EBS and a stearate lubricant mixed with at least one material is used as the high temperature lubricant. Such a composite lubricant usually has a low melting point lubricant having a melting point of less than 100 DEG C and a lubricant having a melting point higher than 100 DEG C A melting point lubricant is mixed and used.

However, in order to achieve a molding density of 7.15 g / cm 3 or more, the lubricant should exhibit a lubricating property of a certain level or higher. The temperature of the lubricant should be about 120 캜. Low melting point lubricants having a melting point of 100 캜 or lower in the complex lubricant, Local rolling phenomenon occurs and the filling property in the mold is lowered, so that local pores are formed in the molded body to cause defects or cause crack defects in the sintered parts.

In addition, since the compound lubricant has a multi-component system by mixing lubricants having various melting points, there is a problem that the cohesion phenomenon in which the metal powder coagulates due to the difference in melting point of the lubricants causes the molding property to be deteriorated.

On the other hand, since the warming is mainly performed at a temperature of 120 to 130 ° C, the manufacturing cost is increased due to the cost for heating the mixed metal powder and the mold, and a separate cooling step is required after the manufacturing, The productivity is lowered.

It should be understood that the foregoing description of the background art is merely for the purpose of promoting an understanding of the background of the present invention and is not to be construed as adhering to the prior art already known to those skilled in the art.

(2012. 09. 19. 2012)

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems, and provides a high-density powder mixture molding method capable of securing a molding density of at least 7.15 g / cm 3 at a temperature of 100 ° C or lower.

The present invention also provides a high-density mixed powder molding method capable of preventing the coagulation phenomenon due to the difference in melting point of the lubricant by using a single component lubricant, thereby improving the molding quality.

According to an embodiment of the present invention, a method for forming a high-density mixed powder is a method of forming a sintered part for an automobile using a metal powder, comprising: preparing a metal powder and a single component lubricant; Mixing the metal powder and the single component lubricant to prepare a mixed powder; And a molding step of filling the mold with the mixed powder and pressing the mixture at a temperature of 80 to 100 ° C to produce a molded body.

Wherein the mixing step comprises mixing 0.2 to 0.3 parts by weight of the single component lubricant with 100 parts by weight of the metal powder to prepare a first mixture; Stirring the mixture at a temperature of 155 to 180 ° C at a speed of 250 to 400 rpm for 20 to 30 minutes to attach a single component lubricant to the surface of the metal powder to prepare a second mixture, ; And 0.3 to 0.4 parts by weight of the single component lubricant are added to 100 parts by weight of the second mixture, followed by stirring at room temperature for 5 to 20 minutes to prepare the mixed powder.

It is preferable that the forming step is performed by pressing at a pressure of 600 to 700 MPa to form the molded body, and the molded body may have a molding density of 7.1 g / cm 3 or more.

The mixed powder has an apparent density of 3.4 g / cm 3 or more and a fluidity of 30 sec / 50 g or less.

The single component lubricant may be lithium 12 hydroxy stearate in which a 12th carbon (C) ring is bonded with a hydroxy group (-OH).

At this time, it is preferable that the single-component lubricant is formed into a needle-like shape.

The single component lubricant may be any one of zinc hydroxystearate and calcium hydroxystearate having a hydroxy group (-OH) bonded to the 12th carbon (C) ring, and is preferably formed in the form of a needle.

According to the embodiment of the present invention, a molding density of 7.15 g / cm < 3 > or more can be secured while lowering the molding temperature to 100 DEG C or less, thereby reducing manufacturing cost and manufacturing time, and reducing manufacturing cost.

Further, by using a single-component lubricant, it is possible to prevent coagulation due to a difference in melting point, thereby minimizing defects in the produced molded article and improving the quality thereof.

In addition, it is possible to omit the surface treatment step such as application of a surface treatment agent for attaching a lubricant to the surface of the metal powder, thereby reducing manufacturing cost and improving productivity.

1 is a flow chart illustrating a method of forming a high-density mixed powder according to an embodiment of the present invention,
2 is a photograph showing a mixed powder prepared according to an embodiment of the present invention,
FIG. 3 is a graph showing the apparent density of the mixed metal powder using a single component lubricant according to an embodiment of the present invention,
FIG. 4 is a graph showing a flow rate of a mixed metal powder using a single component lubricant according to an embodiment of the present invention,
FIG. 5 is a graph comparing the apparent density and the fluidity of the embodiments of the present invention and the comparative examples,
FIG. 6 is a graph showing density changes according to molding pressures according to embodiments of the present invention and comparative examples.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know. Wherein like reference numerals refer to like elements throughout.

The present invention relates to a process for producing an automobile sintered component by press molding of a metal powder, which comprises the steps of forming a needle 12 from a single component lubricant, lithium hydroxystearate (lithium 12) having a hydroxy group (-OH) hydroxy stearate is used to improve the adsorption degree of the lubricant by using the electrostatic attraction and to improve the fluidity of the metal powder so that the molding density of 7.15 g / do.

1 is a flowchart showing a method of forming a high-density mixed powder according to an embodiment of the present invention.

As shown in FIG. 1, the method for forming a high-density mixed powder according to an embodiment of the present invention includes a step of preparing a metal powder and a lubricant, a step of preparing a mixed powder by mixing metal powder and a single component lubricant, And a molding step of producing a molded body by press molding the mixed powder.

(C), nickel (Ni), copper (Cu), and molybdenum (Mo) are added to the iron (Fe) powder so as to satisfy the properties required according to the use and environment of the sintered parts of the automobile to be manufactured. A single component lubricant consisting of a single component is provided to minimize defects due to the agglomeration of the metal powder and the metal powder in the form of a mixture of an alloy element such as a mixture of the elements.

The single component lubricant used in the present invention is preferably lithium hydroxystearate. More specifically, lithium 12 hydroxy stearate in which a hydroxy group (-OH) is bonded to the 12th carbon (C) ring is used. Is preferably used.

More specifically, in the present invention, as a single-component lubricant, lithium 12 hydroxy stearate in a powder state having a melting point range of 211 to 213 ° C. and a particle size of 99% to 100 mesh (99% finer than 100 mesh) Is preferably used.

FIG. 2A is a photograph showing mixed powders prepared using acicular hydroxystearic acid lithium according to an embodiment of the present invention, and FIG. 2B is a photograph showing mixed powders prepared using conventional lithium hydroxystearate.

As shown in FIG. 2, lithium hydroxystearate which is conventionally used as a lubricant is formed in a plate-like shape. On the other hand, as described above, lithium hydroxystearate according to an embodiment of the present invention is formed into a needle- The fluidity of the powder is further improved and the molding density can be improved even if the powder is molded under the same pressure.

Also, the lithium 12 hydroxy stearate is formed in a needle-like shape to improve the fluidity of the metal powder, and the hydroxyl group (-) bonded to the 12th carbon (C) OH), it is possible to improve the lubrication performance by improving the adsorption degree on the metal powder.

Therefore, even if only about half of the lubricant conventionally used in the preparation of the mixed powder is added, a similar level of lubrication performance can be exhibited. By attaching the lubricant to the surface of the metal powder using the electrostatic attraction difference, It is possible to reduce the manufacturing cost and improve the productivity.

In addition, since it is formed as a single component system having a melting point of 200 ° C or higher, it is possible to prevent agglomeration of the metal powder due to the difference in melting point, minimize the occurrence of defects such as formation of pores due to melting during molding, It is possible to prevent defects such as cracks in the manufactured sintered parts for automobiles.

The single component lubricant may be zinc stearate hydroxystearate having a hydroxy group (-OH) bonded to the 12th carbon (C) ring according to the conditions such as molding conditions and metal powder composition, lithium hydroxystearate, lithium hydroxystearate, Calcium stearate, and the like can be optionally used.

When the metal powder 100 and the single component lubricant 200 are provided, the metal powder 100 and the single component lubricant 200 are mixed in the step of manufacturing the mixed powder 10 to form a single component lubricant 200) is attached to the mixed powder (10).

The step of preparing the mixed powder according to an embodiment of the present invention includes a mixing step of mixing 0.2 to 0.3 parts by weight of the single component lubricant 200 with respect to 100 parts by weight of the metal powder 100 to prepare a first mixture, The first mixture is stirred to prepare a second mixture having a single component lubricant 200 adhered to the surface of the metal powder 100 and a first mixture of 0.3 part of the single component lubricant 200 To 0.4 part by weight of the mixture, followed by stirring to produce a mixed powder (10).

At this time, in the mixing step according to an embodiment of the present invention, 0.5 to 0.9 parts by weight of the single component lubricant 200 is mixed with 100 parts by weight of the metal powder 100, The lubricant 200 is uniformly adhered to the surface of the composite powder 10, thereby improving the moldability of the mixed powder 10 and uniformly maintaining the quality of the produced powder.

In this case, when the single component lubricant 200 is mixed at less than 0.5 part by weight, it is difficult to manufacture a high-density molded body due to insufficient lubricity during press molding. When the lubricant is added in an amount exceeding 0.9 parts by weight, And the moldability due to the spring back is lowered. Therefore, it is preferable to limit the above range.

The first stirring process according to an embodiment of the present invention will be described in more detail. It is preferable that the first mixture is added to a stirrer and stirred at a temperature of 155 to 180 ° C for 20 to 30 minutes at a speed of 250 to 400 rpm .

This is because the single-component lubricant 200 can not adhere smoothly to the surface of the metal powder 100 at a temperature lower than 155 ° C., and when the temperature exceeds 180 ° C., the single-component lubricant 200 undergoes a phase change, Therefore, it is limited to the above range.

On the other hand, it is preferable that the second stirring process is carried out at a temperature of 250 to 400 rpm for 5 to 20 minutes at room temperature because, when stirring is performed for less than 5 minutes, the second mixture prepared in the first stirring process, If the lubricant 200 is not evenly mixed and it is more than 20 minutes, the single component lubricant 200 adhering to the metal powder 100 is detached rather lowering the flowability of the prepared mixed powder 10, It is possible to induce a phenomenon and cause defects, so that the above range is limited.

FIG. 3 is a graph showing the apparent density of the mixed metal powder using a single component lubricant according to an embodiment of the present invention, and FIG. 4 is a graph showing the apparent density of the mixed metal powder using a single component lubricant according to an embodiment of the present invention. Of the present invention.

As shown in FIG. 3 and FIG. 4, the first stirring step of warm stirring at a temperature of 155 to 180 ° C. has the lowest apparent density (AD) at 25 minutes because the metal powder (100 ), The apparent density is increased, and then the single-component lubricant 200, which is initially charged, is attached to the surface of the metal powder 100, and the apparent density is decreased. After that, the apparent density is increased again. The sphericalization of the second mixture is excessively advanced and defects due to springback may be generated. Therefore, it is limited to 30 minutes or less, and when stirring is performed for less than 20 minutes, Since the component-based lubricant 200 is not sufficiently adhered, it is limited to the above range.

On the other hand, the second mixture prepared in the first stirring process is prepared as the mixed powder 10 through the second stirring process in which the single-component lubricant 200 is added and stirred at room temperature. In this case, Component lubricant 200 adhering to the surface of the metal powder 100 begins to fall off, and the lubricity gradually decreases, so that it is preferable to limit the range to the above range.

FIG. 5 is a graph comparing the apparent density and the fluidity of the embodiments of the present invention and the comparative examples.

In Comparative Example 1, lithium stearate having a single component system was mixed with a lubricant and a metal powder. Comparative Example 2 was a mixed powder in which a multicomponent lubricant and a metal powder were mixed, And Examples 1 and 2 are mixed powders prepared according to one embodiment of the present invention.

As can be seen from FIG. 5, the single-component lithium stearate was used as a lubricant and the apparent density was good, but the flowability was poor at 38 sec / 50 g, and thus the moldability was deteriorated. In Comparative Example 1, lithium stearate was in a plate- And thus the flowability of the metal powder is lowered.

On the other hand, Examples 1 and 2, which are the mixed powders 10 prepared according to the embodiment of the present invention, are similar to those of Comparative Example 2 using a multicomponent lubricant used in warm forming of conventional metal powders, It can be seen that the apparent density and the fluidity can be secured.

FIG. 6 is a graph showing changes in density after molding at a temperature of 100.degree. C. at different molding pressures in Comparative Examples 1 and 2 and Examples 1 and 2. FIG.

As shown in FIG. 6, it can be seen that even in the case of Comparative Examples 1 and 2, even at a temperature of 100 ° C and a molding pressure of 700 MPa, the formed compact has a molding density of less than 7.15 g / cm 3 and does not satisfy the reference value.

In particular, although Comparative Example 2 shows excellent flowability and bulk density in the mixed powder state as compared with Examples 1 and 2, it can be understood that the molding density after molding does not satisfy the reference value, This is because lubrication performance can be exhibited at a temperature of 120 캜 or higher.

On the other hand, the molding densities of the molded articles produced by pressure molding at a pressure of 600 MPa in Examples 1 and 2 are 7.157 g / cm3 and 7.188 g / cm3, respectively, all of which meet the reference molding density of 7.15 g / cm3.

 It is possible to secure a molding density of 7.15 g / cm < 3 > or more even at a temperature of 100 DEG C or less in the production of a molded body by press molding the metal powder, thereby reducing manufacturing costs and improving productivity.

Although the present invention has been described with reference to the accompanying drawings and the preferred embodiments described above, the present invention is not limited thereto but is limited by the following claims. Accordingly, those skilled in the art will appreciate that various modifications and changes may be made thereto without departing from the spirit of the following claims.

10: mixed powder 100: metal powder
200: Single component lubricant

Claims (8)

A method of forming a sintered part for automobiles using metal powder,
Preparing a metal powder and a single component lubricant;
Mixing the metal powder and the single component lubricant to prepare a mixed powder; And
Filling the mold with the mixed powder and pressurizing the mixed powder at a temperature of 80 to 100 ° C to form a molded body,
Wherein the mixing powder is prepared by mixing 0.2 to 0.3 parts by weight of the single component lubricant with 100 parts by weight of the metal powder to prepare a first mixture; Stirring the mixture at a temperature of 155 to 180 ° C at a speed of 250 to 400 rpm for 20 to 30 minutes to attach a single component lubricant to the surface of the metal powder to prepare a second mixture, ; And a second agitating step of adding 0.3 to 0.4 parts by weight of the single component lubricant to 100 parts by weight of the second mixture and stirring the mixture at room temperature for 5 to 20 minutes to prepare the mixed powder.
delete The method according to claim 1,
The forming step comprises:
Wherein the compact is pressurized at a pressure of 600 to 700 MPa to form the compact.
The method of claim 3,
The molded article may further comprise:
And a molding density of 7.1 g / cm < 3 > or more.
The method according to claim 1,
The mixed powder,
Wherein an apparent density is 3.4 g / cm 3 or more and a fluidity is 30 sec / 50 g or less.
The method according to claim 1,
The single-component lubricant may include,
, And lithium 12 hydroxy stearate in which a hydroxy group (-OH) is bonded to the 12th carbon (C) ring.
The method of claim 6,
The single-component lubricant may include,
Wherein the powder is formed in a needle-like shape.
The method according to claim 1,
The single-component lubricant may include,
Wherein the hydroxystearic acid is any one of zinc hydroxystearate and calcium hydroxystearate in which a hydroxy group (-OH) is bonded to the 12th carbon (C) ring, and is formed in an acicular shape.

Images