KR101782147B1 - Method for precsion casting - Google Patents

Abstract

The present invention relates to a precision casting method, which comprises a step of producing a wax model having the same shape as a casting, a step of forming a first coating layer by first coating the surface of the wax model with sand for molding, Forming a second coating layer of a conductive material, heating the mold to remove the wax pattern from the mold, injecting the molten metal into the mold with the wax removed, placing the coil-shaped solenoid portion surrounding the mold outside, Applying current, cooling the form, and removing the form. According to the present invention, the surface of the casting can be formed smoothly, durability of the casting and durability of the parts physically combined with the casting become high due to impurities, mechanical and physical mobility is increased, Since the unevenness does not occur and spreads evenly, the center of gravity is balanced and the completion of the casting becomes high.

Description

[0001] METHOD FOR PRECISION CASTING [0002]

The present invention relates to a precision casting method. More specifically, the present invention relates to a sand casting method using sand or the like.

A conventional conventional precision casting method is a method of manufacturing a wax model, such as a product design stage, a product wax model making step, a wax model forming step, a wax removing step A step of injecting molten metal into the mold, and a step of cooling the molten metal and removing the mold. Such a conventional precision casting method has a problem when an impurity such as a foreign substance is contained in a base material forming a form or a molten metal injected into a mold. Specifically, impurities are exposed to the surface in the inside, and the surface is not uniform. More specifically, when an impurity is exposed on a surface where mechanical or physical movement is performed, durability is deteriorated and the service life of the component is reduced and damaged. Also, mechanical or physical movement may be affected due to impurities exposed on the surface. Further, due to the gravity acting on the impurities in one direction, the gravity is concentrated only in one direction, the center of gravity is not balanced, and mechanical or physical movement problems may occur. In addition, various unintended problems may occur unlike product design.

Prior Art 1: Korean Patent Publication No. 1999-0037177 (published on November 19, 1996)

A technical object of the present invention is to provide a precision casting method for producing a casting having a smooth surface.

It is another object of the present invention to provide a precision casting method for preventing durability of a finished product due to impurities such as foreign substances in a molten metal or mold.

The technical object of the present invention is to prevent unbalanced center of gravity of a finished product due to impurities such as foreign matter in a molten metal or a mold.

It is still another object of the present invention to provide a precision casting method that prevents a mechanical or physical movement from occurring in a finished product due to impurities such as molten metal or foreign matters in the mold.

Furthermore, a technical object of the present invention is to provide a precision casting method in which time and cost are low in an additional process for controlling impurities such as molten metal in a mold or a mold.

It is another object of the present invention to provide a precision casting method capable of preventing surface breakage of a casting and minimizing post-processing by making it easy to remove a form when removing a form.

According to an aspect of the present invention, there is provided a method of manufacturing a wax mold, comprising the steps of: preparing a wax model having the same shape as the casting; forming a first coating layer by first coating the surface of the wax model with sand for molding; Forming a second coating layer of the mold, removing the wax pattern from the mold by heating the mold, injecting the molten metal into the mold with the wax removed, placing the coil-shaped solenoid portion surrounding the mold outside, A step of cooling the mold, and a step of removing the mold.

According to the present invention, the above-described problems can be solved, the surface of the casting can be smoothly formed, durability of the casting due to the impurities and durability of the parts physically coupled to the casting are improved and mechanical or physical mobility is increased, Since the casting does not occur in one direction of the casting but spreads evenly, the center of gravity is balanced and the completion of the casting becomes high.

1 is a flowchart showing a precision casting method according to an embodiment of the present invention.
2 is a flowchart showing a casting of the precision casting method according to an embodiment of the present invention.
3 is a flowchart showing a precision casting method according to an embodiment of the present invention.
4 is a view showing a step of applying a current to a solenoid portion of the precision casting method according to an embodiment of the present invention.
5 is a cross-sectional view showing a casting manufactured by the precision casting method according to an embodiment of the present invention.
6 and 7 are cross-sectional views of a precision casting method according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Also, in order to clearly illustrate the present invention in the drawings, portions not related to the present invention are omitted, and the same or similar reference numerals denote the same or similar components.

The objects and effects of the present invention can be understood or clarified naturally by the following description, and the objects and effects of the present invention are not limited only by the following description.

The objects, features and advantages of the present invention will become more apparent from the following detailed description. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The precision casting method according to an embodiment of the present invention is a sand casting method in which a mold 200 is manufactured using sand 201 for casting and the molten metal 300 is injected and cooled And the casting 10 is obtained by removing the mold 200. Fig.

1 and 3 are flowcharts schematically showing steps of a precision casting method according to an embodiment of the present invention. The precision casting method according to an embodiment of the present invention includes the steps of producing a wax model 100 having the same shape as the casting 10, A step S200 of forming a mold 200 to form a first coating layer 210 by a first coating process and a step S200 of forming a second coating layer 400 of a conductive material on an outer surface of the first coating layer 210, (S400) of removing the wax model (100) from the mold (200) by heating the wax mold (200), injecting the molten metal (300) into the mold A step S600 of placing the coil-shaped solenoid unit 500 surrounding the coil 200 and applying a current E to the solenoid unit 500, a step S700 of cooling the die 200, and a step of removing the die 200 Step S800 may be included. Here, when the current E is applied to the solenoid portion 500, the second coating layer 400 is changed into an electromagnet and is included in the molten metal 300 by the second coating layer 400 having the magnetic force M The impurity P existing in the second coating layer 400 can be moved in the direction of the second coating layer 400. In addition, it is preferable that the melting point of the molten metal 300 has a melting point lower than the melting point of the impurity (P) so that the impurity (P) remains in a solid state. The molding step 200 for forming the first coating layer 210 by first coating the surface of the wax model 100 with the casting sand 201 may further include the step of forming the mold 200 with a thermal expansion coefficient A cross member 600 contacting two different kinds of metals may be added to be included in the formwork 200. Specifically, the crucible member 600 contacts each of the planar portions of the second member 620 having the " ㅜ " shape having a different thermal expansion coefficient from the first member 610 and the second member 620 of the " And may be provided in a cross shape. In addition, the wax and mold 200 used in the precise casting method described can be used to produce castings 10 with one core, but it is also possible to use conventional cell division castings Can be planned and cast. Hereinafter, each step will be described in detail with reference to the drawings.

Referring to FIGS. 1 and 3, a step S100 of manufacturing a wax model 100 having the same shape as the casting 10 is a step of designing a casting 10 to be made to produce a model of a wax material. In detail, the wax model 100 may be a wax model 100 modeled through injection molding or the like and having the same shape as the casting 10. Here, although it may be different depending on the shape of the casting 10 to be made, it is generally preferable to design and manufacture the entire core by dividing the core into two parts. In addition, since the molten metal 300 can not reach all the corners due to the inclusion of bubbles, inclusions, the occurrence of cracks due to the reduction of the volume during solidification, and the lack of fluidity (fluidity) in the casting 10, It should be designed so that no defect or the like occurs. Although the wax model 100 is manufactured in the same shape as the casting 10, the wax model 100 may be designed so as to have a predetermined size smaller or larger than the product in consideration of the chemical properties of the wax or the shrinkage rate and the expansion rate according to the temperature change . In the present invention, the casting is formed into a cylindrical shape and has a columnar shape of a circular opening 11 along the longitudinal direction of the center shaft. In order to further explain the objects and effects of the present invention, the casting 10 is a casting 10 in which another part is assembled in a circular opening 11 in the inside of the casting 10 to mechanically or physically move the casting 10 A description will be made of a hypothetical example in which the inner surface of the opening 10 of the casting 10 is made uniform and smooth and the center of gravity of the casting 10 is uniform. Although the casting 10 is described as an example, it may be made of castings 10 of various shapes including the technical spirit of the present invention, and it is also natural that the present invention also belongs to the present invention. Therefore, the wax model 100 manufactured in the step S100 may be manufactured as a wax model 100 having the same columnar shape as the casting 10 as in the above-described example.

The step 200 of forming the mold 200 for forming the first coating layer 210 by first coating the surface of the wax model 100 with the sand 201 for casting is a step of forming the wax model 100 into a slurry In a process of first coating the surface of the casting sand 201 on the surface, the wax model 100 is immersed in the immersed sand, and then the coating is repeated a plurality of times to coat the wax model 100 first. In general, it is preferable to repeat the coating operation for about 8 times to perform the first coating, but it may be added or subtracted depending on the chemical property or purpose of the molten metal 300, the casting sand 201 or the casting 10 to be produced. The sand for casting 201 may be sand such as silica sand, alumina sand, olivine sand, chromite sand, zirconium sand, mullite sand, artificial sand, or artificial aggregate.

A step S300 of forming a second coating layer 400 made of an electrically conductive material on the outer surface of the first coating layer 210 is a second coating process on the outer surface of the first coating layer 210 with a conductive material. A variety of coating methods can be used in general. The material used for manufacturing the second coating layer 400 may have a conductive (conductive) property. In detail, the second coating layer 400 may be electromagnetically provided with a magnetic force M by a solenoid unit 500 described later. Accordingly, the second coating layer 400 should be made of a conductive (conductive) material. In detail, the second coating layer 400 may be formed of a ferromagnetic substance (Ferromagnetic Substance). In more detail, the second coating layer 400 may be formed of soft ferrite.

In step S400 of heating the mold 200 and removing the wax pattern 100 from the mold 200, a part of the mold 200 is burnt and the mold 200 is heated to liquefy the wax, Is removed. In detail, the step of removing the wax (S400) includes a step of removing the wax from the mold 200 by discharging the wax from the inside of the mold 200 to the outside by heating the heat at a temperature higher than the melting point of the wax as a dewaxing process to be. Therefore, it is preferable that the melting point at which the wax is liquefied is lower than the melting point of the molding sand 201 or the mold 200.

In step S500 of injecting the molten metal 300 into the mold 200 from which the wax has been removed, the molten metal 300 is injected into the mold 200 having the shape of the casting 10 by removing the wax, Is a pouring step in which the mold (200) is heated to the same shape as the casting (10). The molten metal 300 may be determined depending on the characteristics of the casting 10 to be manufactured by the user and may be injected into the mold 200 while maintaining an appropriate temperature in consideration of deterioration of the molten metal 300 due to excessive overheating . In detail, the aluminum or aluminum alloy is poured at a temperature of 600 to 700 degrees Celsius, the iron or iron alloy is poured at a temperature of 1300 to 1400 degrees, the bronze is poured at a temperature of 1100 to 1300 degrees, It is preferable to pour the solution at a temperature of 1100 deg. Here, in the case where another mixture is added to the base molten metal 300, the pouring temperature can be increased or decreased depending on the working environment.

1, 3, and 4, a step S600 of placing a coil-shaped solenoid unit 500 surrounding the mold 200 and applying a current E to the solenoid unit 500, A magnetic force M is applied to the second coating layer 400 made of a conductive material located inside the solenoid portion 500 by applying a current E to the first coating layer 500. In detail, the solenoid unit 500 may be provided with a helical coil. In more detail, the solenoid unit 500 may be a solenoid in which the helical coil is provided in a cylindrical shape. The diameter of the helical coil of the solenoid unit 500 may be larger than the mold 200 or the second coating layer 400 so as to surround the mold 200 or the second coating layer 400. The solenoid unit 500 has a cathode and an anode polarity at one end and the other end, and current E flows in one direction by applying current E. A magnetic field is formed in the conductor line of the solenoid unit 500 according to the electromagnetic induction law of Faraday (1791 to 1867) when a current (E) flows along the solenoid unit 500 by applying the current (E). In detail, a spiral type solenoid which is closely and tightly wound in a cylindrical shape with a helical shape is formed with a magnetic field of 0 outside the solenoid and a relatively uniform magnetic field inside the helical solenoid when current (E) flows. The current E flows through the second coating layer 400 located in the inward direction of the solenoid portion 500 through the induction current E so that the second coating layer 400 is electrically connected to the magnetic force M). Therefore, when the electric current E is applied to the solenoid portion 500, the second coating layer 400 is changed into an electromagnet, and the second coating layer 400 having the electric power changes the impurities contained in the molten metal 300 P may be moved in the direction of the second coating layer 400. More specifically, impurities P contained in the molten metal 300 in the mold 200 are removed by the second coating layer 400 having the electromagnetism property by the magnetic force M in the outward direction where the second coating layer 400 is located, And is uniformly distributed or distributed. More specifically, the impurity P contained in the molten metal 300 is usually dissolved due to the temperature of the molten metal 300. In the case of the impurity P having a higher melting point than the molten metal temperature, In some cases. If the pouring temperature is raised to remove the impurities P, the chemical property of the molten metal 300 is changed. Therefore, the impurities P are removed in the outer direction of the molten metal 300 in the direction of the second coating layer 400 without removing the impurities P. [ Is moved. Here, it is preferable that the melting point of the molten metal 300 has a melting point lower than the melting point of the impurity (P) so that the impurity (P) maintains a solid state. The impurities P are moved in the outer direction of the casting 10 and the impurities P are moved in the inner direction of the casting 10 to position the molten metal 300 with high purity. That is, the inside of the casting 10 has a relatively durable and smooth surface, and another part is fastened to the opened inside of the finished casting 10, so that even if mechanical or physical movement is performed, it is not easily broken. In addition, since the impurities P irregularly distributed in the molten metal 300 are evenly distributed through the magnetic force M in the outward direction in the direction of the second coating layer 400, the center of gravity does not shift in one direction. In detail, the impurities P irregularly distributed in the molten metal 300 can be solved by being gravity-balanced in the direction of the ground by gravity, or cooled while being uniformly tilted in the upward direction, so that the center of gravity is unbalanced. The second coating layer 400 may be formed entirely on the outer surface of the first coating layer 210 but may be formed on only a predetermined one surface of the outer surface of the first coating layer 210. [ In the present invention, the second coating layer 400 is formed only in the circumferential direction of the first coating layer 210 corresponding to the circumferential direction of the cylindrical casting 10. Another example will be described on the basis of the above description. The casting 10, which is mechanically or physically moving along the outer circumferential surface of the casting body 10 other than the open center of the casting body 10, The second coating layer 400 surrounding the circumferential outer layer of the first coating layer 210 may be formed on the inner peripheral surface of the casting 10 in the opened direction. When the magnetic force M is applied to the second coating layer 400 coated on the inner peripheral surface of the mold 200, impurities P contained in the molten metal 300 may flow toward the second coating layer 400 So that the outer circumferential surface can be relatively smooth and highly durable.

In the step S700 of cooling the mold 200, the molten metal 300 is poured into the mold 200, and then the mold 200 is cooled to solidify the molten metal 300. Here, since the rapid cooling of the cooling method may cause excessive cracking or expansion and shrinkage of the mold 200, it is preferable to naturally cool at room temperature as much as possible. It is also desirable to control the applied rectification so that the current E applied to the solenoid portion 500 is stopped immediately before, during, or after cooling. Or the amount of the electric current E applied to the solenoid portion 500 after the start of the cooling of the form 200 is calculated based on the fact that the magnetic force M changes according to the amount of the electric current E applied to the solenoid portion 500 The solenoid unit 500 can be stopped by gradually decreasing the magnetic force M gradually. This makes it possible to instantaneously prevent the solenoid unit 500 from being stopped and the impurities P which have been moved by the magnetic force M to instantly fall or move.

The step S800 of removing the mold 200 is a step of finally obtaining the casting 10 which is poured into the mold 200 by applying an impact or polishing to the outer surface of the mold 200 to be cooled. Here, if the pouring temperature is relatively low, such as aluminum, the casting 10 may be damaged if the casting mold 200 is impacted, so that the mold 200 must be removed by various suitable methods depending on the material of the casting 10 .

6 and 7, a step 200 (step S200) for forming the first coating layer 210 by first coating the surface of the wax model 100 with the sand 201 for casting, May be included in the first coating layer 210 or the mold 200 by adding a cross member 600 contacting two types of members having different thermal expansion coefficients to the sand 201 for casting. Specifically, the cross member 600 is formed by contacting each flat portion of the "" "shaped first member 610 and the" second "shaped second member 620 having a different thermal expansion coefficient from the first member 610, . The cross member 600 may be bent in one direction or the other as the temperature is changed. Specifically, the cross member 600 may be provided with a bimetal whose shape and volume change as the temperature changes. More specifically, the cross member 600 may be provided so that the first member 610 and the second member 620 having a thermal expansion coefficient different from that of the first member 610 are in contact with each other. More specifically, the crucible member 600 includes a first member 610 in the shape of "ㅗ", and a flat portion of the second member 620 in the shape of "ㅜ" having a different thermal expansion coefficient from the first member 610 And may be provided in a cross shape. More specifically, the cross member 600 may be made of a metal material. More specifically, the first member 610 and the second member 620 may be made of different metals, each having a different coefficient of thermal expansion. Therefore, the cruciform member 600 provided in a cross shape is provided so that the flat portions of the first member 610 and the second member 620 having different thermal expansion rates are in contact with each other. Therefore, when the temperature changes, It is possible to generate the crack 601 in the first coating layer 201 or the mold 200. That is, since the first member 610 and the second member 620 having a specific thermal expansion coefficient are provided, cracks 601 can be generated in the mold 200 when the mold 200 is at a predetermined temperature, A crack 601 is generated in the mold 200 due to the member 600, so that the mold 200 can be easily removed. Since the fine cracks 601 are uniformly dispersed in the mold 200 due to the cross member 600, the surface or inner surface of the casting 10 obtained after removing the mold 200 is uniform, The process is simplified.

The precision casting method according to another embodiment of the present invention includes the steps of manufacturing a wax model having the same shape as the casting, forming a mold by coating the surface of the wax model with the sand for molding, heating the mold, Placing a cylindrical portion of a conductive material in a shape that surrounds the outside of the mold, placing a coil-shaped solenoid portion surrounding the outside of the cylindrical portion, and supplying a current to the solenoid portion A step of cooling the mold, and a step of removing the mold. Here, a different step from the conventional method is to coat the surface of the wax model with sand for molding to form a mold, to place a cylindrical portion of a conductive material surrounding the outside of the mold, Since the step of positioning the solenoid portion of the shape and applying the electric current to the solenoid portion is different and the other steps are the same, only the different steps will be described except for the redundant description.

The step of coating the surface of the wax model with the sand for molding is a process of coating the sand for the casting mold with the wax model on the surface. The wax model is immersed in the immersed sand, And repeating the process a plurality of times to coat the wax pattern. In general, it is preferable to repeat the coating operation about 8 times, but it may be added or subtracted depending on the chemical properties or the purpose of the molten metal, the casting sand or the cast material to be produced. In addition, the sand for casting may be sand such as silica sand, alumina sand, olivine sand, chromite sand, zirconium sand, mullite sand, artificial sand or artificial aggregate.

The step of positioning the cylindrical portion of the conductive material that surrounds the outer side of the mold is a step of positioning the cylindrical portion that surrounds the outer side of the mold into which the molten metal is injected. Here, the cylindrical portion can be an electromagnet by being given a magnetic force by a solenoid portion described later. Therefore, the cylindrical portion must be made of a conductive (conductive) material. In detail, the cylindrical portion may be formed of a ferromagnetic substance (Ferromagnetic Substance). In more detail, the cylindrical portion may be provided with a soft ferrite (soft magnetic body). Also, the cylindrical portion may be provided in a columnar shape of the main body so as to surround the outer surface of the mold. In the present invention, since the casting of the cylinder is manufactured, the mold is also formed into a cylindrical shape. Therefore, it is preferable to be provided so as to be located on the same central axis as the central axis of the mold of the cylindrical portion.

The step of placing a coil-shaped solenoid portion surrounding the outside of the cylindrical portion and applying a current to the solenoid portion is a step of applying a magnetic force to a cylindrical portion of a conductive material located inside the solenoid portion by applying a current to the solenoid portion. In detail, the solenoid portion may be provided with a helical coil. More specifically, the solenoid portion may be a solenoid in which a helical coil is provided in a cylindrical shape. The diameter of the helical coil of the solenoid portion may be larger than the diameter of the cylindrical portion so as to surround the cylindrical portion. The solenoid portion has a negative polarity and a positive polarity at one end and the other end, and a current can flow in one direction by applying a current. When a current is applied and current flows along the solenoid portion, a magnetic field is formed in the lead line of the solenoid portion according to the electromagnetic induction law of Faraday (1791 ~ 1867). In detail, a spiral type solenoid which is formed by winding a wire into a spiral closely and uniformly in a cylindrical shape has a magnetic field outside the solenoid and a relatively uniform magnetic field inside the coil. Based on the above-described technique, a current flows through an induction current in a cylindrical portion located in an inner side of a solenoid portion, and the cylindrical portion has a magnetic force through the induced current. Therefore, when a current is applied to the solenoid portion, the cylindrical portion changes its nature to an electromagnet, and impurities contained in the molten metal can be moved toward the cylindrical portion by the cylindrical portion having a magnetic force. Specifically, the impurities contained in the molten metal in the mold are drawn and distributed by the magnetic force in the outward direction in which the cylindrical portion is positioned by the cylindrical portion having the electromagnetism property. More specifically, the impurities contained in the molten metal are usually melted and removed due to the temperature of the molten metal. In the case of the impurities having a higher melting point than the molten metal temperature, they may remain in the molten metal. However, when the pouring temperature is raised to remove the impurities, the chemical properties of the molten metal are changed, so that the impurities are moved toward the outside of the molten metal in the direction of the cylinder without removing the impurities. Here, it is preferable that the melting point of the molten metal has a melting point lower than the melting point of the impurities so that the impurities maintain a solid state. According to the above-described method, the impurities are moved toward the outer side of the casting and the impurities are moved in the inner direction of the casting, and the high-purity molten metal is located. That is, the inside of the casting has a relatively durable and smooth surface, and another part is fastened to the open inside of the finished casting, so that even if mechanical or physical movement is performed, it is not easily broken. In addition, since the irregularly distributed impurities in the molten metal are evenly distributed through the magnetic force in the outward direction in the direction of the cylinder, the center of gravity does not shift in one direction. In detail, the irregularly distributed impurities in the molten metal can be cooled by being gravity-balanced in the direction of the ground by the gravity force, or cooled down while being uniformly concentrated in the upward direction, so that the center of gravity is unbalanced. To describe another example on the basis of the above-described technique, if the casting that becomes the mechanical or physical movement along the outer circumferential surface other than the open center of the casting is changed to a virtual environment by changing the previously set virtual environment, An iron core having a ferromagnetic material or a soft magnetic material may be provided so as to pass through the open inside of the casting instead of the cylindrical portion surrounding the mold. In this case, when a magnetic force is applied to the iron core, the impurities contained in the molten iron are moved in the direction of the central axis in the iron core direction, so that the outer circumferential surface is relatively smooth and durable.

It will be apparent to those skilled in the art that various modifications, additions and substitutions are possible, without departing from the spirit and scope of the invention as defined by the appended claims. Should be regarded as belonging to the above-mentioned patent claims.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventive concept as defined by the appended claims. But is not limited thereto.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

10: casting 100: wax model
200: Die 201: Sand for molding
210: first coating layer 300: molten metal
400: Second coating layer 500: Solenoid part
600: cross member 610: first member
620: second member M: magnetic force
P: impurity E: current

Claims (3)

(S100) a wax model (100) having the same shape as the casting (10);
A step (S200) of forming a mold 200 for forming a first coating layer 210 by first coating the surface of the wax model 100 with the sand 201 for molding;
Forming a second coating layer (400) of a conductive material on the outer surface of the first coating layer (210);
(S400) heating the mold (200) to remove the wax model (100) from the mold (200);
(S500) injecting the molten metal (300) into the mold (200) from which the wax is removed;
(S600) of placing a coil-shaped solenoid unit (500) surrounding the mold (200) and applying a current (E) to the solenoid unit (500);
Cooling the mold 200 (S700); And
(S800) of removing the mold 200,
When the current E is applied to the solenoid portion 500, the second coating layer 400 is changed to an electromagnet and the second coating layer 400 having the magnetic force M is applied to the molten metal 300 And the impurity (P) contained therein is moved toward the second coating layer (400).
The method according to claim 1,
Wherein the melting point of the molten metal (300) has a melting point lower than a melting point of the impurity (P) so that the impurity (P) remains in a solid state.
The method according to claim 1,
The step 200 of fabricating the mold 200 for forming the first coating layer 210 by first coating the surface of the wax model 100 with the sand 201 for molding may include the step of forming the mold 200 with a thermal expansion coefficient A cross member 600 contacting two different kinds of metals is added to be included in the first coating layer 210,
The cross member 600 is formed by contacting each flat portion of the first member 610 having the "ㅗ" shape and the second member 620 having the """shape having the thermal expansion coefficient different from that of the first member 610, Wherein the first member (610) and the second member (620) are made of a metal material.

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