U.S. patent application number 15/094449 was filed with the patent office on 2017-06-08 for die-casting apparatus for fabricating vehicle part casing and method of fabricating vehicle part casing using the same.
The applicant listed for this patent is Hyundai Motor Company, KODACO CO., LTD.. Invention is credited to Kwi Seung IN, Dong Ha KANG, Jung Ho LEE, Tae Seong LIM.
Application Number | 20170157668 15/094449 |
Document ID | / |
Family ID | 58798146 |
Filed Date | 2017-06-08 |
United States Patent
Application |
20170157668 |
Kind Code |
A1 |
KANG; Dong Ha ; et
al. |
June 8, 2017 |
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.
Inventors: |
KANG; Dong Ha; (Seoul,
KR) ; LIM; Tae Seong; (Hwaseong-si, KR) ; IN;
Kwi Seung; (Yongin-si, KR) ; LEE; Jung Ho;
(Pyeongtaek-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hyundai Motor Company
KODACO CO., LTD. |
Seoul
Cheonan-si |
|
KR
KR |
|
|
Family ID: |
58798146 |
Appl. No.: |
15/094449 |
Filed: |
April 8, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22D 21/007 20130101;
C22C 21/02 20130101; B22D 17/2218 20130101; B22D 25/02 20130101;
B22D 17/002 20130101; B22D 17/2023 20130101; B22D 17/145 20130101;
B22D 17/02 20130101 |
International
Class: |
B22D 25/02 20060101
B22D025/02; B22D 17/02 20060101 B22D017/02; C22C 21/02 20060101
C22C021/02; B22D 17/20 20060101 B22D017/20; B22D 17/22 20060101
B22D017/22; B22D 21/00 20060101 B22D021/00; B22D 17/00 20060101
B22D017/00; B22D 17/14 20060101 B22D017/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 4, 2015 |
KR |
10-2015-0171950 |
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.degree. C. to 665.degree. 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.degree. C. to 250.degree. 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.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] 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
[0002] 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
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] The step of preparing the molten Al alloy may include
heating the Al alloy at a temperature ranging from 645.degree. C.
to 665.degree. C.
[0016] The step of preheating the die-casting mold may include
preheating the die-casting mold at a temperature ranging from
220.degree. C. to 250.degree. C.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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
[0030] 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.
[0031] 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.
[0032] FIG. 2 is a view illustrating a fixed mold according to an
embodiment in the present disclosure.
[0033] FIG. 3 is a view illustrating a movable mold according to an
embodiment in the present disclosure.
[0034] FIG. 4 is a view illustrating a die-casting apparatus for
fabricating a vehicle part casing according to an embodiment in the
present disclosure.
[0035] FIG. 5 is a view illustrating a sleeve part according to an
embodiment in the present disclosure.
[0036] 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.
[0037] 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.degree. C.
[0038] FIG. 8 is an image illustrating defects formed when a
vehicle part casing was fabricated using molten Al having a
temperature above 665.degree. C.
[0039] 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.
[0040] 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.degree. C. according to an
example in the present disclosure.
[0041] FIG. 11 is an image illustrating hit checks formed in a
die-casting mold preheated to a temperature above 250.degree. C.
according to an example in the present disclosure.
[0042] 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.degree. C. according to an
example in the present disclosure.
DETAILED DESCRIPTION
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] FIG. 5 is a view illustrating a sleeve part according to an
embodiment in the present disclosure.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.degree. C. to 665.degree.
C.
[0066] 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.
[0067] 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.degree. 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.degree.
C.
[0068] As illustrated in FIGS. 7 and 8, when a temperature of a
molten Al alloy was less than 645.degree. 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.degree. 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.degree. C. to 665.degree. C.
[0069] 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.
[0070] As illustrated in FIG. 9, in the present example, an Al
alloy was heated to 660.degree. 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.degree. C., a vehicle part
casing having fine microstructures and uniform fractured surfaces
was fabricated.
[0071] 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.degree. C. to 250.degree. C.
[0072] 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.degree. 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.degree. 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.degree. C. according to an
example in the present disclosure.
[0073] As illustrated in FIGS. 10 to 12, when the die-casting mold
was preheated to a temperature below 220.degree. C., a temperature
difference of 400.degree. 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.degree. 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.degree. C. to
250.degree. C.
[0074] In the present example, the temperature of the die-casting
mold was preheated at a temperature of 250.degree. C.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] The vehicle part casing from which burs are removed is then
subjected to visual inspection before being shipped.
[0087] 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
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
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