DIE-CASTING APPARATUS FOR FABRICATING VEHICLE PART CASING AND METHOD OF FABRICATING VEHICLE PART CASING USING THE SAME

Abstract

A method of fabricating a vehicle part casing using a die-casting apparatus includes preparing a molten aluminum (AL) alloy by heating an Al alloy. A die-casting mold is preheated, and then, the vehicle part casing is molded by pouring the molten Al alloy into the die-casting mold. The vehicle part casing is removed from the die-casting mold and a surface of the vehicle part casing is trimmed. Burs on the vehicle part casing are removed.

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority to Korean Patent Application No. 10-2015-0171950 filed on Dec. 4, 2015, the entire content of which is incorporated herein for all purposes by this reference.

TECHNICAL FIELD

The present disclosure relates to a die-casting apparatus for fabricating a casing and a method of fabricating the casing using the same. More particularly, the present disclosure relates to a die-casting apparatus for fabricating a vehicle part casing and a method of fabricating a vehicle part casing using the same, in which a casing for a vehicle part or a machine part is fabricated from aluminum using a die-casting process.

BACKGROUND

In general, casting refers to a process of solidifying metal into a certain shape by pouring metal into a mold, and a product formed through this process is referred to as a cast-iron product. Casting technology is one of the most basic metal machining technologies and important in the development of the metal industry.

Casting technology is closely related to and has been used in the vehicle industry to the extent that about 50% of cast-iron products fabricated by the casting technology are used in vehicles.

Recently, light weight vehicle bodies are desirable in order to reduce exhaust due to environmental regulations and improve fuel efficiency. In this regard, research into aluminum (Al) alloy materials, in which environmental friendliness, high functionality, light weight, high sensitivity, and the like are considered, have been actively undertaken.

In particular, there exists a need to develop technologies for fabricating a vehicle part casing using an Al material. Vehicle part casings, a major component of a vehicle, are typically heavy parts. In addition, it is required to develop a vehicle part casing for maintaining the structural strength of existing products while being light-weighted.

Recently, active researches and development have been undertaken in order to fabricate vehicle part casings using Al alloy die-casting technology, which fabricates Al alloy products by pouring a molten Al alloy, in which Cu, Si, Mg, Ni, and the like are added to the major component of Al, at a high pressure into a metal mold.

However, Al die-casting molds of the related art have a limited ability to exhaust gas contained in a molten Al alloy in the process of die-casting a vehicle part casing having a complicated shape. In addition, voids are formed in a product, which reduces structural strength of the product, thus, deteriorating productivity.

The information disclosed in the Background of the Invention section is only for the enhancement of understanding of the background of the invention, and should not be taken as an acknowledgment or as any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.

SUMMARY

The present disclosure has been made keeping in mind the above problems occurring in the related art. An aspect of the present disclosure provides a die-casting apparatus for fabricating a vehicle part casing capable of improving the ability to pour a molten metal into a mold and reducing a period of time for cooling products, thereby improving workability of products, and a method of fabricating a vehicle part casing using the same.

Another aspect of the present disclosure provides a die-casting apparatus for fabricating a vehicle part casing capable of maintaining die-casting conditions due to flowing characteristics of an Al alloy, thereby improving denseness of products and reducing a defective rate of products, and a method of fabricating a vehicle part casing using the same.

Another aspect of the present disclosure provides a die-casting apparatus for fabricating a vehicle part casing capable of reducing the weight of an Al alloy and improving supporting strength thereof, and a method of fabricating a vehicle part casing using the same.

Another aspect of the present disclosure provides a die-casting apparatus for fabricating a vehicle part casing capable of improving ability to exhaust gas contained in a molten Al alloy and reducing the amount of gas residing in a cavity in order to reduce voids formed in die-cast products, thereby improving fabrication efficiency, and a method of fabricating a vehicle part casing using the same.

According to an exemplary embodiment in the present disclosure, a method of fabricating the vehicle part casing using a die-casting apparatus includes: preparing a molten aluminum (Al) alloy by heating an Al alloy; preheating a die-casting mold; molding a vehicle part casing by pouring the molten Al alloy into the die-casting mold; removing the vehicle part casing from the die-casting mold and trimming a surface of the vehicle part casing; and removing burs on the vehicle part casing.

The step of preparing the molten Al alloy may include heating the Al alloy at a temperature ranging from 645° C. to 665° C.

The step of preheating the die-casting mold may include preheating the die-casting mold at a temperature ranging from 220° C. to 250° C.

The step of pouring the molten Al alloy into the die-casting mold may include pouring the molten Al alloy to a lower part of the die-casting mold.

The step of pouring the molten Al alloy into the die-casting mold may include pouring the molten Al alloy at a pressure ranging from 90 MPa to 110 MPa while maintaining an internal vacuum pressure of a cavity in the die-casting mold in a range from 140 mbar to 160 mbar.

The composition of the Al alloy may include 88.2% to 80.3% Al, 9.6% to 12.0% Si, 1.5% to 3.5% Cu, 0.1% to 0.5% Mn, 0.1% to 0.3% Mg, 0.1% to 0.5% Ni, 0.1% to 0.9% Fe, 0.1% to 0.5% Ti, 0.1% to 1.0% Zn, 0.1% to 0.3% Sn, 0.0% to 0.1% Pb, 0.0% to 0.1% Cr, and inevitable impurities, based on 100% by weight of the alloy composition.

The step of pouring the molten Al alloy into the die-casting mold may include molding the vehicle part casing while exhausting gas from the molten Al alloy using vacuum.

According to another exemplary embodiment in the present disclosure, a die-casting apparatus for fabricating a vehicle part casing includes: a fixed mold having a negative shape so that one side of the vehicle part casing is carved thereinto; and a movable mold disposed movable in a direction towards the fixed mold, and having a positive shape so that another side of the vehicle part casing is carved in relief. The movable mold is engaged with the fixed mold between which a cavity having a shape of the vehicle part casing is formed. An exhausting part is connected to the cavity and decreases an internal pressure of the cavity. The exhausting part exhausts gas contained in the molten Al alloy that is inserted into the cavity.

The movable mold may include a molten metal path connected to a lower part of the cavity, in which a molten metal enters the cavity through the molten metal path. A plurality of first gas outlets are formed in an upper part of the cavity, in which the gas is contained in the plurality of first gas outlets. A plurality of second gas outlets are connected to the exhausting part to form a vacuum in an interior of the cavity.

The movable mold may have: first gas paths; and second gas paths connecting the plurality of first gas outlets and the plurality of second gas outlets to the cavity. A diameter of each of the second gas paths is smaller than that of the first gas paths.

The die-casting apparatus may further include a pressure sensor connected to one first gas outlet among the plurality of first gas outlets to measure an internal pressure of the cavity.

The die-casting apparatus may further include a sleeve part connected to the molten metal path through which the molten metal is poured. The sleeve part has a gas outlet in an upper part to exhaust the gas therefrom.

As set forth above, the present disclosure is directed to preheating the die-casting mold after melting an Al alloy. It is thereby possible to improve the ability to pour molten metal into a mold and to reduce a period of time for cooling products, thereby improving workability of products.

In addition, each of the temperature of the molten Al alloy and the preheating temperature of the die-casting mold is limited to a predetermined temperature range before the molten Al alloy is poured into the cavity. Thus, it is possible to maintain die-casting conditions due to flowing characteristics of the Al alloy, thereby improving denseness of fabricated vehicle part casings and reducing a defective rate thereof.

Furthermore, in the Al alloy, the content of Al is reduced, the content of Si is increased, and a small amount of Ni, Ti, Sn, or Cr is added. It is therefore possible to reduce the weight of the Al alloy and improve supporting strength thereof.

In addition, the die-casting mold is implemented as a vacuum die-casting mold. It is therefore possible to exhaust gas contained in the molten Al alloy and reduce the amount of gas residing in the cavity in order to reduce voids formed in die-cast products, thereby improving fabrication efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a side-elevation view illustrating a die-casting apparatus for fabricating a vehicle part casing according to an embodiment in the present disclosure.

FIG. 2 is a view illustrating a fixed mold according to an embodiment in the present disclosure.

FIG. 3 is a view illustrating a movable mold according to an embodiment in the present disclosure.

FIG. 4 is a view illustrating a die-casting apparatus for fabricating a vehicle part casing according to an embodiment in the present disclosure.

FIG. 5 is a view illustrating a sleeve part according to an embodiment in the present disclosure.

FIG. 6 is a flowchart illustrating a method of fabricating a vehicle part casing using a die-casting apparatus according to an embodiment of the present disclosure.

FIGS. 7A-7F are a series of images illustrating defects formed when a vehicle part casing was fabricated using molten Al having a temperature below 645° C.

FIG. 8 is an image illustrating defects formed when a vehicle part casing was fabricated using molten Al having a temperature above 665° C.

FIGS. 9A and 9B are a series of images illustrating a fractured surface of a vehicle part casing fabricated according to an example in the present disclosure.

FIG. 10 is an image illustrating surface voids formed when a vehicle part casing was fabricated using a die-casting mold preheated to a temperature below 220° C. according to an example in the present disclosure.

FIG. 11 is an image illustrating hit checks formed in a die-casting mold preheated to a temperature above 250° C. according to an example in the present disclosure.

FIG. 12 is an image illustrating shrinkage defects when a vehicle part casing was fabricated using a die-casting mold preheated to a temperature above 250° C. according to an example in the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in greater detail to exemplary embodiments in the present disclosure, examples of which are illustrated in the accompanying drawings. However, it should be understood that the present disclosure is by no means limited to or restricted by the embodiments. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. In this manner, the components illustrated in different figures and descriptions thereof may be referred to. Descriptions of some features well-known to a person skilled in the art or repeated descriptions of some features may be omitted.

FIG. 1 is a side-elevation view illustrating a die-casting apparatus for fabricating a vehicle part casing according to an embodiment in the present disclosure, FIG. 2 is a view illustrating a fixed mold according to an embodiment in the present disclosure, FIG. 3 is a view illustrating a movable mold according to an embodiment in the present disclosure, and FIG. 4 is a view illustrating a die-casting apparatus for fabricating a vehicle part casing according to an embodiment in the present disclosure.

As illustrated in FIGS. 1 to 4, a die-casting apparatus for fabricating a vehicle part casing according to an embodiment of the present disclosure fabricates the vehicle part casing, such as a differential gear casing, using a molten aluminum (Al) alloy. The die-casting apparatus includes a fixed mold 100, a movable mold 200 movable in a direction of the fixed mold 100 to define a cavity C, and an exhausting part 300 lowering the internal pressure of the cavity C by evacuating an interior of the cavity C.

The fixed mold 100 has a negative shape of one side of a vehicle part casing carved thereinto, and is engaged with a fixed end to be constantly fixed during a die-casting operation. In a certain embodiment, a gradient angle may be applied to a surface of the fixed mold 100 that performs sliding engagement with the movable mold 200 such that a completed die-cast vehicle part casing can be removed.

The movable mold 200 is movably disposed while being detachably attached to the fixed mold 100, and has a positive shape of another side of the vehicle part casing carved in relief. The movable mold 200 is engaged with a movable end, such that the movable mold 200 moves in the direction of the fixed mold 100 during the die-casting operation. The movable mold 200 is brought into close contact with the fixed mold 100, thereby defining the cavity C having a vehicle part casing shape between the fixed mold 100 and the movable mold 200.

In addition, when the die-casting operation is completed, the movable mold 200 is detached from the fixed mold 100, and the vehicle part casing molded within the cavity C is separated and discharged from the cavity C using a push pin.

The movable mold 200 has a plurality of first gas outlets 220 and a plurality of second gas outlets 230, through which gas contained in the molten Al alloy is exhausted. The plurality of second gas outlets 230 communicate with the exhausting part 300.

In addition, the movable mold 200 has a first gas path 221 and a second gas path 231 connecting the plurality of first and second gas outlets 220 and 230 to the cavity C. In a certain embodiment, a diameter of the plurality of second gas outlets 230 is greater than that of the plurality of first gas outlets 220.

Thus, the amount of gas exhausted through the plurality of second gas outlets 230 may be greater than the amount of gas exhausted through the plurality of first gas outlets 220.

In a certain embodiment, a distance between adjacent second gas outlets 230 of the plurality of second gas outlets 230 increases in a direction away from the cavity C. Therefore, a molten alloy path expands in a direction towards a downstream portion in which gas is exhausted, thereby improving gas exhausting ability.

A pressure sensor 240 may be connected to one of the plurality of first gas outlets 220 in order to detect the degree of vacuum within the cavity C.

Here, the movable mold 200 has a detection block which communicates with the corresponding first gas outlet 220 and on which the pressure sensor 240 being disposed. The pressure sensor 240 is detachably attached to the detection block, and the detection block may be opened and closed.

The exhausting part 300 is disposed at a downstream of the plurality of second gas outlets 230 in a direction in which gas flows, such that the exhausting part 300 communicates with the plurality of second gas outlets 230. The exhausting part 300 may evacuate gas contained in the molten Al alloy by forming a vacuum by lowering the internal pressure of the cavity C. For example, the exhausting part 300 may include a vacuum pump, a vacuum block, a vacuum valve, a vacuum hose, and the like that are commonly used in, for example, a high-vacuum die-casting method.

In particular, the exhausting part 300 is implemented as an exhaust passageway including a plurality of bent exhaust paths formed in a vacuum block. Due to the bent exhaust paths of the vacuum valve, the exhausting part 300 functions as a cooling block through which the molten alloy is cooled. The exhausting part 300 can reduce casting pressure while reducing the amount of residual gas during the die-casting process, thereby increasing life of the die-casting apparatus including the molds.

Here, the movable mold 200 has exhaust channels connecting the plurality of second gas outlets 230 to the exhausting part 300. The exhaust channels extend in bent shapes, through which gas is exhausted from the plurality of second gas outlets 230 by the exhausting part 300.

FIG. 5 is a view illustrating a sleeve part according to an embodiment in the present disclosure.

As illustrated in FIG. 5, the die-casting apparatus for fabricating a vehicle part casing according to the present disclosure further includes a sleeve part 400 connected to a molten metal path 210 to supply a molten Al alloy to the cavity C.

Here, the sleeve part 400 has a gas outlet 410 at an upstream portion in a direction in which the molten Al alloy flows, such that gas within the sleeve part 400 can be naturally exhausted in a low-speed pouring section. The gas outlet 410 may be configured to be opened and closed.

According to the present disclosure, the gas, which occurs during the process of pouring the molten Al alloy inside the sleeve part 400, can be exhausted into the cavity C, thereby improving quality of a vehicle part casing fabricated thereby. Here, the molten Al alloy may be poured into a lower part of the cavity C.

In addition, one side of the molten metal path 210 is connected to the sleeve part 400 and another side of the molten metal path 210 is connected to the cavity C. The other side of the molten metal path 210 connected to the cavity C may be divided into a plurality of paths connected to the cavity C. The other side of the molten metal path 210 may be connected to lower part of the cavity C.

FIG. 6 is a flowchart illustrating a method of fabricating a vehicle part casing using a die-casting apparatus according to an embodiment in the present disclosure.

As illustrated in FIG. 6, a method of fabricating a vehicle part casing using a die-casting apparatus includes a preparation step S1, a mold preheating step S2, a molding step S3, a surface treatment step S4, and a finishing step S5.

In the preparation step S1, a molten Al alloy is prepared by heating and melting an Al alloy, and a temperature of the molten Al alloy is maintained in the range from 645° C. to 665° C.

In a certain embodiment, the composition of the Al alloy includes 88.2% to 80.3% Al, 9.6% to 12.0% Si, 1.5% to 3.5% Cu, 0.1% to 0.5% Mn, 0.1% to 0.3% Mg, 0.1% to 0.5% Ni, 0.1% to 0.9% Fe, 0.1% to 0.5% Ti, 0.1% to 1.0% Zn, 0.1% to 0.3% Sn, 0.0% to 0.1% Pb, 0.0% to 0.1% Cr, and the inevitable impurities, based on 100% by weight of the alloy composition. According to the Al alloy having the above-defined composition, the content of Al is reduced, the content of Si is increased, and small amounts of Ni, Ti, Sn, Cr, and the like are added, whereby the weight of a fabricated vehicle part casing can be reduced and supporting strength of the vehicle part casing can be improved.

FIGS. 7A-7F are a series of images illustrating defects formed when a vehicle part casing was fabricated using molten Al having a temperature below 645° C., and FIG. 8 is an image illustrating defects formed when a vehicle part casing was fabricated using molten Al having a temperature above 665° C.

As illustrated in FIGS. 7 and 8, when a temperature of a molten Al alloy was less than 645° C., flowability of the molten Al alloy was decreased. In the process of pouring the molten Al alloy into the cavity C, premature solidification and an inaccurately-molded surface occurred, thereby deteriorating quality of a fabricated vehicle part casing. When the temperature of a molten Al alloy was above 665° C., the amount of fuel consumed was increased, thereby increasing fabrication costs. Localized heating occurred on a die-casting mold, thereby decreasing the life of the die-casting mold. In a certain embodiment, the temperature is limited to the range from 645° C. to 665° C.

FIGS. 9A and 9B are a series of images illustrating a fractured surface of a vehicle part casing fabricated according to an example in the present disclosure.

As illustrated in FIG. 9, in the present example, an Al alloy was heated to 660° C. to melt, and the molten Al alloy was maintained at this temperature. When the molten Al alloy was maintained at the temperature of 660° C., a vehicle part casing having fine microstructures and uniform fractured surfaces was fabricated.

In the mold preheating step S2, a die-casting mold including a fixed mold 100 and a movable mold 200 is preheated prior to pouring a molten Al alloy into the die-casting mold. The die-casting mold is preheated to a temperature ranging from 220° C. to 250° C.

FIG. 10 is an image illustrating surface voids formed when a vehicle part casing was fabricated using a die-casting mold preheated to a temperature below 220° C. according to an example in the present disclosure, FIG. 11 is an image illustrating hit checks formed in a die-casting mold preheated to a temperature above 250° C. according to an example in the present disclosure, and FIG. 12 is an image illustrating shrinkage defects when a vehicle part casing was fabricated using a die-casting mold preheated to a temperature above 250° C. according to an example in the present disclosure.

As illustrated in FIGS. 10 to 12, when the die-casting mold was preheated to a temperature below 220° C., a temperature difference of 400° C. or higher occurred between the die-casting mold and the poured molten Al alloy. Thus, the poured molten Al alloy was caused to be prematurely solidified, thereby deteriorating formability and causing shrinkage cracks defects in a product and due to a release agent. When the die-casting mold was preheated to a temperature above 250° C., a prolonged period of time was required to cool the molten Al alloy after pouring the molten Al alloy into the die-casting mold. This may consequently increase a working time, thereby degrading productivity. During solidification of the molten Al alloy, shrinkage defects occurred, and the degree of dimensional accuracy was decreased. In addition, deteriorations in the die-casting mold may rapidly occur, thereby reducing the longevity of the mold. Thus, in a certain embodiment, a temperature is limited to the range from 220° C. to 250° C.

In the present example, the temperature of the die-casting mold was preheated at a temperature of 250° C.

The molding step S3 according to the present disclosure is a process of pouring the molten Al alloy into the cavity C, and includes a mold-closing step, a molten Al alloy-pouring step, a mold-opening step, and a mold-cleaning step.

In the mold-closing step, the fixed mold 100 and the movable mold 200 of the die-casting apparatus for fabricating a vehicle part casing are engaged such that the fixed mold 100 and the movable mold 200 are in close contact with each other, thereby defining the cavity C between the fixed mold 100 and the movable mold 200. In the mold-closing step, an insert core and a slide core are fitted into the die-casting mold.

The molten Al alloy-pouring step is a step of pouring the molten Al alloy into the cavity C defined between the fixed mold 100 and the movable mold 200. The molten Al alloy fed into the sleeve part 400 is poured into the cavity C using, for example, a plunger, such as a piston. Here, the molten Al alloy may be poured into the lower part of the cavity C.

Here, a discharge tip positioned at a distal end of the sleeve part 400 moves forwards at a speed of 0.2 m/s. After the discharge tip passes by the inlet of the molten Al alloy, an interior of the sleeve part 400 turns into an airtight state. Thus, in order to prevent gas within the sleeve part 400 from entering the cavity C to cause defects in a product, the gas outlet 410 having a diameter of 30 mm is opened to enable natural ventilation. Here, the gas outlet 410 is formed on an upper part of the sleeve part 400, within the range of 300 mm from a starting point of the plunger.

In a certain embodiment, a pouring pressure, i.e. a casting pressure, of the molten Al alloy ranges from 90 MPa to 110 MPa. When the pouring pressure is less than 90 MPa, flowability of the molten Al alloy is degraded, which prolongs a period of time for pouring the molten Al alloy, thereby lowering productivity. When the pouring pressure is greater than 110 MPa, the flowability of the molten Al alloy may be improved. However, the molten Al alloy flows backwards due to characteristics of a dipper cup having an axially symmetrical and radial shape, thereby causing voids.

In a certain embodiment, the interior of the cavity C has a degree of vacuum ranging from 140 mbar to 160 mbar. This range may obtain dense internal structures from the Al alloy poured in the cavity C, thereby increasing the density thereof. In addition, this range satisfies mechanical characteristics required for the fabricated vehicle part casing.

In the present example, the degree of vacuum within the cavity was maintained at 150 mbar while the casting pressure was maintained at 100 MPa.

In the mold-opening step, a fabricated vehicle part casing is removed by separating the movable mold 200 from the fixed mold 100 after the vehicle part casing is molded by cooling the molten Al alloy which is filled in the cavity C. After the mold is cooled for a predetermined period of time and the insert core and the slide core are removed, the vehicle part casing is removed.

In the mold-cleaning step, the fixed mold 100 and the movable mold 200 are cleaned for the subsequent operation after the vehicle part casing is removed. Here, after first cleaning, a release agent is applied to inner surfaces of the mold, and second cleaning is performed.

The surface treatment step S4 is a step of trimming the removed vehicle part casing. Runners or overflows and vent holes attached to an exterior of the vehicle part casing are removed therefrom on a trimming die.

When the surface treatment on the vehicle part casing is completed, the finishing step S5 is performed. In the finishing step S5, a worker manually removes burs having a size less than 2 mm, residing on surface of the vehicle part casing, using a manual tool, such as a grinder.

The vehicle part casing from which burs are removed is then subjected to visual inspection before being shipped.

As set forth above, the present disclosure is directed to preheating the die-casting mold after melting an Al alloy. It is thereby possible to improve an operation of pouring a molten metal into a mold and to reduce a period of time for cooling products, thereby improving workability of products

In addition, each of the temperature of the molten Al alloy and the preheating temperature of the die-casting mold is limited to a predetermined temperature range before the molten Al alloy is poured into the cavity from below. Thus, it is possible to maintain die-casting conditions due to the flowing characteristics of an Al alloy, thereby improving denseness of fabricated vehicle part casings and reducing a defective rate thereof.

Furthermore, in an Al alloy, the content of Al is reduced, the content of Si is increased, and a small amount of Ni, Ti, Sn, or Cr is added. It is therefore possible to reduce the weight of the Al alloy and improve the supporting strength thereof.

In addition, the die-casting mold is implemented as a vacuum die-casting mold. It is therefore possible to exhaust gas contained in the molten Al alloy and reduce the amount of gas residing in the cavity in order to reduce voids formed in die-cast products, thereby improving fabrication efficiency.

Although the exemplary embodiments in the present disclosure have been described for illustrative purposes, a person skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the present invention as disclosed in the accompanying claims.

Claims

1. A method of fabricating a vehicle part casing using a die-casting apparatus, comprising:

preparing a molten aluminum (Al) alloy by heating an Al alloy;

preheating a die-casting mold;

molding the vehicle part casing by pouring the molten Al alloy into the die-casting mold;

removing the vehicle part casing from the die-casting mold and trimming a surface of the vehicle part casing; and

removing burs on the vehicle part casing.

2. The method according to claim 1, wherein the step of preparing the molten Al alloy comprises heating the Al alloy at a temperature ranging from 645° C. to 665° C.

3. The method according to claim 1, wherein the step of preheating the die-casting mold comprises preheating the die-casting mold at a temperature ranging from 220° C. to 250° C.

4. The method according to claim 1, wherein the step of molding the vehicle part casing comprises pouring the molten Al alloy to a lower part of the die-casting mold.

5. The method according to claim 4, wherein the step of pouring the molten Al alloy into the die-casting mold comprises pouring the molten Al alloy at a pressure ranging from 90 MPa to 110 MPa while maintaining an internal vacuum pressure of a cavity in the die-casting mold in a range from 140 mbar to 160 mbar.

6. The method according to claim 1, wherein a composition of the Al alloy comprises 88.2% to 80.3% Al, 9.6% to 12.0% Si, 1.5% to 3.5% Cu, 0.1% to 0.5% Mn, 0.1% to 0.3% Mg, 0.1% to 0.5% Ni, 0.1% to 0.9% Fe, 0.1% to 0.5% Ti, 0.1% to 1.0% Zn, 0.1% to 0.3% Sn, 0.0% to 0.1% Pb, 0.0% to 0.1% Cr, and inevitable impurities, based on 100% by weight of the alloy composition.

7. The method according to claim 1, wherein the step of molding the vehicle part casing comprises molding the vehicle part casing while exhausting gas from the molten Al alloy using vacuum.

8. The method according to claim 1, wherein the die-casting mold includes a fixed mold and a movable mold, in which the fixed mold has a negative shape so that one side of the vehicle part casing is carved thereinto and the movable mold has a positive shape so that another side of the vehicle part casing is carved thereinto.

9. A die-casting apparatus for fabricating a vehicle part casing comprising:

a fixed mold having a negative shape so that one side of the vehicle part casing is carved thereinto;

a movable mold disposed movable in a direction towards the fixed mold, the movable mold having a positive shape so that another side of the vehicle part casing is carved thereinto, in which the movable mold is engaged with the fixed mold between which a cavity having a shape of the vehicle part casing is formed; and

an exhausting part connected to the cavity and decreasing an internal pressure of the cavity, in which the exhausting part exhausts gas contained in a molten Al alloy which is inserted into the cavity.

10. The die-casting apparatus according to claim 9, wherein the movable mold comprises:

a molten metal path connected to a lower part of the cavity, so that a molten metal enters the cavity through the molten metal path;

a plurality of first gas outlets formed in an upper part of the cavity, in which the gas is contained in the plurality of first gas outlets; and

a plurality of second gas outlets connected to the exhausting part to form a vacuum in an interior of the cavity.

11. The die-casting apparatus according to claim 10, wherein the movable mold has: first gas paths; and second gas paths connecting the plurality of first gas outlets and the plurality of second gas outlets to the cavity, and

wherein a diameter of each of the second gas paths is smaller than that of each of the first gas paths.

12. The die-casting apparatus according to claim 10, further comprising a pressure sensor connected to one first gas outlet among the plurality of first gas outlets to measure the internal pressure of the cavity.

13. The die-casting apparatus according to claim 10, further comprising a sleeve part connected to the molten metal path through which the molten metal is poured, wherein the sleeve part has a gas outlet in an upper part to exhaust the gas therefrom.