WO2005065866A1

WO2005065866A1 - Method and apparatus for manufacturing forming material with spherical structure

Info

Publication number: WO2005065866A1
Application number: PCT/KR2004/002977
Authority: WO
Inventors: Han-Jung Lee
Original assignee: Han-Jung Lee
Priority date: 2004-01-07
Filing date: 2004-11-17
Publication date: 2005-07-21
Also published as: KR20050072582A

Abstract

The invention relates to a method and apparatus for manufacturing molded articles having a spherical structure, and more particularly a method and apparatus for manufacturing molded articles having a spherical structure process. In the method, an intensive flow is generated in molten metal by electromagnetic field agitation to suppress growth of dendrites generated in a solid and liquid phase upon solidification of the molten metal during a process of pouring the molten metal into a mould and then forming the molten metal into a preform, so that the molded preform has a fine spherical structure from molten metal through a low pressure die casting

Description

METHOD AND APPARATUS FOR MANUFACTURING FORMING MATERIAL WITH SPHERICAL STRUCTURE

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method and apparatus for manufacturing molded articles having a spherical structure, and more particularly to a method and apparatus for manufacturing molded articles having a spherical structure from molten metal through a low pressure die casting process.

Description of the Related Art In general, low pressure die casting is a method for pouring molten metal into a mould equipped at an upper portion of a low pressure die casting apparatus via a feeding tube by pushing the molten metal upward against gravity through application of a gas, such as low pressure air or an inert gas, into a space where the molten metal is poured. Referring to Fig. 7, a conventional low pressure die casting apparatus 1 comprises a gate 112 through which molten metal is poured, a molten metal holding furnace 110 having a gas introduction port 114 formed therein and through which a gas is introduced, a molding part 120 including upper and lower dies 122 and 124 equipped to the molten metal holding furnace 110, and a feeding tube 130 equipped between the molten metal holding furnace 110 and the upper and lower dies 122 and 124 for feeding the molten metal into the molding part 120. With such a construction, as a pressure of about 0.2 ~ 0.9 kg/cπf is gradually applied to the molten metal by injecting the gas onto the molten metal poured into the molten metal holding furnace, the molten metal is raised to the upper and lower dies 122 and 124 of the molding part 120 through the feeding tube 130, and fills a space between the upper and lower dies. As such, when the pressure is removed after application of the pressure for a predetermined period, the molten metal in the space between the upper and lower dies is solidified and molded into an article. However, since the molten metal below the lower die 124 and within the feeding tube 130 is in a molten state, the molten metal returns to the molten metal holding furnace 110. Then, after maintaining the upper and lower dies in this state to cool the upper and lower dies 122 and 124, a molding operation through a series of low pressure die casting processes is completed by removing the molded part from the upper and lower dies . As such, in comparison to a general casting method, the low pressure die casting method provides an excellent casting yield, and clean and precise castings having various shapes, while minimizing manufacturing costs and installation costs. However, as shown in Fig. 8, the part molded through the low pressure die casting method as described above has a fine and brittle dendritic structure, which reduces the toughness and durability of the products. In order to solve this problem, an agitating technology using an electromagnetic field has been developed. However, it is necessary to provide a technology, which can create primary crystal particles having a spherical shape close to an ideal shape instead of the dendritic structure, and microstructures surrounding the primary crystal particles, thereby minimizing macro- segregation of solute elements, and casting defects, while ensuring mechanical properties, formability at a subsequent process, environmentally friendly operation, and competitive manufacturing costs.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for manufacturing a molded product having a spherical structure through a low pressure die casting process. It is another object of the present invention to maintain molten metal at an optimal temperature for forming a spherical structure. It is still another object of the present invention to form a finer structure, thereby enhancing mechanical properties . In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a method for manufacturing a molded article having a spherical structure through a low pressure die casting process, wherein an intensive flow is generated in molten metal by electromagnetic field agitation to suppress growth of dendrites generated in a solid and liquid phase region upon solidification of the molten metal during a process of pouring the molten metal into a mould and then forming the molten metal into a preform, so that the molded preform has a fine spherical structure. Preheating of the molten metal may be performed in conjunction with the electromagnetic field agitation. The molded preform having the spherical structure may be subjected to multi-stage compression, so that the molded article has a microstructure having excellent mechanical properties . In accordance with another aspect of the present invention, a low pressure die casting apparatus is provided, wherein the apparatus comprises an electromagnetic agitator located between a molten metal holding furnace and upper and lower dies for generating an electromagnetic field in a feeding tube by application of electricity. The apparatus may further comprise a pre-heater located between the feeding tube and the electromagnetic agitator. The apparatus may further comprise a pressing member located above the upper die, the pressing member being provided with a closing member for closing a sprue of the lower die, and a pressing means for compressing the upper die .

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Figs. 1 to 3 are diagrams illustrating a forming process using a low pressure die casting apparatus equipped with an electromagnetic agitator according to the present invention; Fig. 4 is a diagram illustrating molten metal in a state of being agitated by an electromagnetic field generated by the electromagnetic agitator according to the present invention; Fig. 5 is a diagram illustrating the molten metal having a structure changed in shape through agitation of the present invention; Fig. 6 is a micrograph illustrating a microstructure of a molded article formed according to the present invention; Fig. 7 is a schematic diagram illustrating conventional low pressure die casting; and Fig. 8 is a micrograph illustrating a microstructure of a molded article formed using the conventional low pressure die casting of Fig. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments will now be described in detail with reference to the accompanying drawings. Figs. 1 to 3 are diagrams illustrating a forming process using a low pressure die casting apparatus equipped with an electromagnetic agitator according to the present invention. As shown in the drawings, as with a conventional low pressure die casting apparatus, a low pressure die casting apparatus 1 of the present invention also comprises a molten metal gate (not shown) through which molten metal is poured, a molten metal holding furnace 110 having a gas introduction port 114 formed therein and through which gas is introduced, a molding part 120 comprising upper and lower dies 122 and 124 equipped to the molten metal holding furnace 110, and a feeding tube 130 equipped between the molten metal holding furnace 110 and the upper and lower dies 122 and 124 for feeding the molten metal into the molding part 120. In addition to these components, the low pressure die casting apparatus 1 of the invention further comprises an electromagnetic agitator 10 located between the molten metal holding furnace 110 and upper and lower dies 122 and 124 for generating an electromagnetic field in the feeding tube 130 by application of electricity. Preferably, the low pressure die casting apparatus 10 further comprises a typical pre-heater 20, such as a heater generating heat by application of electricity, located between the feeding tube 130 and the electromagnetic agitator 10, so that the molten metal within the feeding tube can be maintained at a constant temperature together with the electromagnetic field agitation by the electromagnetic agitator 10, thereby allowing efficient electromagnetic field agitation. Furthermore, the apparatus 1 may comprise a well-known pressing member 140 located above the upper die 122, in which the pressing member 140 is provided with a closing member 30 for closing a sprue 124a of the lower die 124, and a well-known pressing means 40 for pressing and ejecting the upper die 122. With the construction as described above, molten metal poured into the molten metal holding furnace 110 is pressed by gas, and is fed into a space between the upper and lower dies 122 and 124 of the molding part 120 through the feeding tube 130, as shown in Fig. 1. At this time, immediately before the molten metal is fed into the space between the upper and lower dies 122 and 124, electromagnetic field agitation is performed for 1 to 3 minutes by means of the electromagnetic agitator 10 located between the molten metal holding furnace 110 and upper and lower dies 122 and 124. That is, as shown in Fig. 4, as the molten metal passes through the feeding tube 130 where the electromagnetic agitator 10 is equipped, an intensive flow of the molten metal is generated by an electromagnetic field to suppress growth of dendrites created in a solid and liquid phase region upon solidification of the molten metal, thereby providing a fine spherical structure. At this time, transformation from the dendrite particles into spherical particles is performed, as shown in Fig. 5, through steps of 1) destruction of growing dendrite particles by means of electromagnetic agitation, 2) movement of the broken particles into the solid and liquid phase region, 3) dissolving of some part of the broken particles while retaining the rest, 4) growth of the broken particles, and 5) transformation of the particles into isometric particles. Additionally, upon agitation of the molten metal by means of the electromagnetic agitator 10, the molten metal in the feeding tube is maintained at a temperature of the solid and liquid phase region or at a temperature (about 550 ~ 650 ^°C) of liquid phase region by use of the pre-heater 20 provided between the feeding tube 130 and the electromagnetic agitator 10, thereby maximizing agitation effect by means of the electromagnetic field. As such, the molten metal agitated by the electromagnetic field is compressed and filled in the space between the upper and lower dies 122 and 124, and is then primarily molded into a preform having a fine spherical structure. As the sprue 124a of the lower die 124 is closed, as shown in Fig. 2, by the closing member 30 of the pressing member 140 located above the upper die 122, the pressure is released from the molten metal holding furnace 110, thereby completing a primary molding. Then, after completing the primary molding as described above, the upper die 122 is subjected to multi- stage compression by the pressing means 40 provided to the pressing member 140, as shown in Fig. 3, so that the preform between the upper and lower dies 122 and 124 can be formed into a final molded article having a microstructure excellent in mechanical properties . Upon solidification of the article between the upper and lower dies 122 and 124, as described above, compressing and electromagnetic agitation at the feeding tube are performed at the same time, thereby allowing preparation of a continuous operation. As shown in Fig. 6, according to results of inspecting the molded article manufactured by the method and apparatus of the present invention by use of a well-known optical microscope, it can be appreciated that the molded article has a fine spherical structure. As apparent from the above description, according to the method and apparatus of the present invention, the molten metal is formed to have the fine spherical structure between the dies through the electromagnetic agitation, thereby allowing the molded article to have a light weight, excellent mechanical properties, and formability while remarkably reducing the manufacturing costs. Additionally, upon the electromagnetic agitation, the molten metal is maintained at a constant temperature, thereby promoting transformation into the spherical structure. Additionally, the preform between the upper and lower dies subjected to multi-stage compression by the pressing means, so that the finished article has the microstructure excellent in mechanical properties. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

What is claimed is;

1. A method for manufacturing a molded article having a spherical structure through a low pressure die casting process, wherein an intensive flow is generated in molten metal by electromagnetic field agitation to suppress growth of dendrites generated in a solid and liquid phase region upon solidification of the molten metal during a process of pouring the molten metal into a mould and then forming the molten metal into a preform, so that the molded preform has a fine spherical structure.

2. The method as set forth in claim 1, wherein preheating of the molten metal is performed in conjunction with the electromagnetic field agitation.

3. The method as set forth in claim 1 or 2, wherein the molded preform having the spherical structure subjected to multi-stage compression, so that the molded article has a microstructure having excellent mechanical properties.

4. A low pressure die casting apparatus, wherein the apparatus comprises an electromagnetic agitator located between a molten metal holding furnace and upper and lower dies for generating an electromagnetic field in a feeding tube by application of electricity.

5. The apparatus as set forth in claim 4, further comprising: a pre-heater located between the feeding tube and the electromagnetic agitator.

6. The apparatus as set forth in claim 4 or 5, further comprising: a pressing member located above the upper die, the pressing member being provided with a closing member for closing a sprue of the lower die, and a pressing means for compressing the upper die.