U.S. patent application number 10/102081 was filed with the patent office on 2002-10-24 for die-casting method and die-casting apparatus.
Invention is credited to Fujita, Yoshio, Hiramatsu, Osamu, Ito, Masafumi, Kawaguchi, Masahiro, Ota, Masaki, Yoshida, Yoshiharu.
Application Number | 20020153120 10/102081 |
Document ID | / |
Family ID | 18938949 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020153120 |
Kind Code |
A1 |
Ito, Masafumi ; et
al. |
October 24, 2002 |
Die-casting method and die-casting apparatus
Abstract
A method of producing a die-cast article by die-casting, the
die-cast article having at least one of an inner and an outer
circumferential surface, the method comprising the steps of:
preparing a mold assembly including a hollow portion having a
molding surface for molding one of the inner and outer
circumferential surfaces of the die-cast article; closing the mold
assembly to define therein a mold cavity having a configuration
corresponding to that of the die-cast article; subjecting the
hollow portion to an elastic deformation in a direction toward the
one of the inner and outer circumferential surfaces of the die-cast
article to be produced; introducing a molten metal into the mold
cavity while the hollow portion is subjected to the elastic
deformation; opening the mold assembly and permitting the elastic
deformation to be removed from the hollow portion after the molten
metal has solidified; and removing the die-cast article from the
mold assembly. An apparatus for practicing the method is also
disclosed.
Inventors: |
Ito, Masafumi; (Kariya-shi,
JP) ; Kawaguchi, Masahiro; (Kariya-shi, JP) ;
Ota, Masaki; (Kariya-shi, JP) ; Fujita, Yoshio;
(Kariya-shi, JP) ; Hiramatsu, Osamu; (Kariya-shi,
JP) ; Yoshida, Yoshiharu; (Kariya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154
US
|
Family ID: |
18938949 |
Appl. No.: |
10/102081 |
Filed: |
March 19, 2002 |
Current U.S.
Class: |
164/113 ;
164/312 |
Current CPC
Class: |
B22D 17/24 20130101;
B22D 17/20 20130101; B22D 17/2236 20130101 |
Class at
Publication: |
164/113 ;
164/312 |
International
Class: |
B22D 017/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2001 |
JP |
2001-083085 |
Claims
What is claimed is:
1. A method of producing a die-cast article by die-casting, said
die-cast article having at least one of an inner circumferential
surface and an outer circumferential surface, the method comprising
the steps of: preparing a mold assembly including a hollow portion
which has a molding surface for molding one of said inner and outer
circumferential surfaces of said die-cast article; closing said
mold assembly so as to define therein a mold cavity having a
configuration which corresponds to that of said die-cast article;
subjecting said hollow portion to an elastic deformation in a
direction toward said one of said inner and outer circumferential
surfaces of said die-cast article to be produced; introducing a
molten metal into said mold cavity while said hollow portion is
subjected to said elastic deformation; opening said mold assembly
and permitting said elastic deformation to be removed from said
hollow portion after said molten metal has solidified in said mold
cavity; and removing said die-cast article formed in said mold
cavity from said mold assembly.
2. A method according to claim 1, wherein said hollow portion has a
non-molding surface which is opposite to said molding surface, said
non-molding surface being a tapered surface, a dimension of which
in a direction perpendicular to a direction parallel to a
centerline of said hollow portion gradually changes in said
direction, said step of subjecting a hollow portion to an elastic
deformation comprising steps of preparing a tapered member having a
tapered surface which corresponds to said tapered surface of said
hollow portion, and causing said elastic deformation of said hollow
portion by an interference fit between said tapered surface of said
hollow portion and said tapered surface of said tapered member.
3. A method according to claim 1, wherein said hollow portion is a
hollow cylindrical member having a circular shape in transverse
cross section.
4. A method according claim 1, wherein said die-cast article is a
cylinder block which is used for a swash plate type compressor and
which includes a plurality of cylinder bores, said at least one of
said inner and outer circumferential surfaces of said die-cast
article being an inner circumferential surface of each of said
cylinder bores.
5. A method according to claim 1, wherein said die-cast article is
a front housing which is used for a swash plate type compressor and
which includes a hollow cylindrical recess, said at least one of
said inner and outer circumferential surfaces of said die-cast
article being an inner circumferential surface of said hollow
cylindrical recess of said front housing.
6. A die-casting apparatus for producing a die-cast article having
at least one of an inner circumferential surface and an outer
circumferential surface, comprising: a mold assembly including a
hollow portion which has a molding surface for molding one of said
inner and outer circumferential surfaces of said die-cast article;
and deforming device for elastically deforming said hollow portion
such that said hollow portion is subjected to an elastic
deformation in a direction toward said one of inner and outer
circumferential surfaces of said die-cast article to be
produced.
7. An apparatus according to claim 6, wherein said mold assembly
includes a first mold and a second mold which are moved toward and
away from each other, so that said first mold and said second mold
are opened and closed, said hollow portion extending in a direction
parallel to a direction in which said first mold and said second
mold are opened and closed.
8. An apparatus according to claim 6, wherein said mold assembly
has a main body in which an engaging portion is formed, said hollow
portion being provided by a member separate from said main body,
and wherein at least a part of said hollow portion, which part is
adjacent to said molding surface, and said engaging portion are
positioned relative to each other such that there is a clearance in
a radial direction therebetween.
9. An apparatus according to claim 6, wherein said molding surface
of said hollow portion for molding said one of said inner and outer
circumferential surfaces of said die-cast article is an outer
circumferential surface of said hollow portion, and wherein said
deforming device for elastically deforming said hollow portion
includes: an expanding member which engages an inner
circumferential surface of said hollow portion; and a pushing
device which forces said expanding member onto said inner
circumferential surface of said hollow portion, so that said hollow
portion is expanded.
10. An apparatus according to claim 6, wherein said molding surface
of said hollow portion for molding said one of said inner and outer
circumferential surfaces of said die-cast article is an inner
circumferential surface of said hollow portion, and wherein said
deforming device for elastically deforming said hollow portion
includes: a contracting member which engages an outer
circumferential surface of said hollow portion; and a pushing
device which forces said contracting member onto said outer
circumferential surface of said hollow portion, so that said hollow
portion is contracted.
11. An apparatus according to claim 6, wherein said hollow portion
has a non-molding surface which is opposite to said molding
surface, said non-molding surface being a tapered surface, a
dimension of which in a direction perpendicular to a direction
parallel to a centerline of said hollow portion gradually changes
in said direction, said deforming device for elastically deforming
said hollow portion including: a tapered member having a tapered
surface which corresponds to said tapered surface of said hollow
portion; and a device for effecting an interference fit between
said tapered surface of said hollow portion and said tapered
surface of said tapered member.
12. An apparatus according to claim 11, wherein said tapered member
is held by said main body of said mold assembly such that said
tapered member and said hollow portion are axially movable relative
to each other, said device for effecting an interference fit
including an axial moving for moving said tapered member and said
hollow portion relative to each other in an axial direction of said
tapered member.
13. An apparatus according to claim 12, wherein said axial moving
device includes a hydraulic cylinder which is fixed to said mold
assembly.
14. An apparatus according to claim 11, wherein said mold assembly
includes a first mold and a second mold which are moved toward and
away from each other, said tapered member being fixed to one of
said first and second molds, which one mold is opposite to the
other of said first and second molds which is equipped with said
hollow portion, said first and second molds being opened and closed
by an opening and closing device which also functions as said
device for effecting an interference fit.
15. An apparatus according to claim 7, wherein the other of said
first and second molds which is equipped with said hollow portion
includes an ejecting device which pushes said die-cast article in a
direction away from the other mold to remove said die-cast article
from said hollow portion.
16. An apparatus according to claim 6, wherein said hollow portion
is a hollow cylindrical portion having an annular shape in
transverse cross section, and wherein said deforming device for
elastically deforming said hollow portion includes: a collet which
engages, at one of inner and outer circumferential surfaces
thereof, a non-molding surface of said hollow portion, which
non-molding surface is opposite to said molding surface for molding
said one of said inner and outer circumferential surfaces of said
die-cast article; and a collet-diameter changing device for
changing a diameter of said collet so as to force said collet onto
said non-molding surface.
17. An apparatus according to claim 16, wherein the other of said
inner and outer circumferential surfaces of said collet, which the
other circumferential surface is opposite to said one
circumferential surface which engages said non-molding surface of
said hollow cylindrical portion, is tapered to give a first tapered
surface whose diameter gradually changes in an axial direction of
said hollow cylindrical portion, and wherein said collet-diameter
changing device includes: a tapered member having a second tapered
surface which corresponds to said first tapered surface; a
multiplicity of balls interposed between said collet and said
tapered member such that said balls maintain a constant position
relative to each other, and such that said balls are rotatable
independently of each other, at least while said first and second
tapered surfaces engage each other; and an axial moving device
which moves said tapered member and said hollow cylindrical portion
relative to each other in an axial direction of said tapered member
and said hollow cylindrical portion, so that said first and second
tapered surfaces engage each other with an interference fit
therebetween via said balls.
Description
[0001] This application is based on Japanese Patent Application No.
2001-083085 filed Mar. 22, 2001, the contents of which are
incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates in general to a method of
producing a die-cast article having at least one of an inner and an
outer circumferential surface which does not have an inclination
corresponding to a draft provided on a casting mold, or which is
provided with a relatively small angle of inclination. The present
invention is also concerned with a die-casting apparatus suitable
for practicing the method.
[0004] 2. Discussion of the Related Art
[0005] One example of a method of producing a die-cast article
having at least one of an inner and an outer circumferential
surface comprises steps of: positioning a slide core within a mold
cavity formed in a casting mold, so that an outer circumferential
surface of the slide core functions as a part of a molding surface
partially defining the mold cavity; and introducing a molten metal
into the mold cavity, so that the inner circumferential surface of
the die-cast article is formed by the outer circumferential surface
of the slide core. The slide core is retracted from the mold cavity
after the molten metal has solidified to give the intended die-cast
article, so that the slide core is removed from the die-cast
article. Since the molten metal shrinks upon its solidification,
the slide core is subjected to a holding force caused by shrinkage
due to the solidification of the molten metal, so that the slide
core cannot be easily removed from the die-cast article. For easy
removal of the slide core from the die-cast article, the slide core
is generally provided with a draft, so that the die-cast article
produced by using the slide core has an inclined inner
circumferential surface corresponding to the draft of the slide
core. In general, the die-cast article which is produced by using
the slide core desirably has a straight inner circumferential
surface having a constant diameter. Accordingly, the inclined inner
circumferential surface of the die-cast article is subjected, after
the die-casting process, to a machining operation to provide the
straight inner circumferential surface. For minimizing the required
amount of the stock removal by the machining operation, it is
desirable to minimize the angle of the draft of the slide core. To
this end, EP 0642855 A (corresponding to JP-A-7-60399) discloses a
casting mold having a slide core which is formed of a material
whose thermal expansion coefficient is equal to or higher than that
of a molten metal to be introduced into the mold cavity. According
to this arrangement, the slide core has been heated to a
temperature substantially equal to that of the molten metal before
the metal molten solidifies into a die-cast article. Thereafter,
the temperature of the slide core is lowered with a decrease of the
temperature of the die-cast article. Since the thermal expansion
coefficient of the slide core is equal to or higher than that of
the molten metal, the slide core is subjected to shrinkage whose
amount is equal to or larger than that of shrinkage of the molten
metal. Therefore, the slide core is easily removed from the
die-cast article. In the proposed method, however, the material of
the slide core is inevitably limited to that which is suitable for
a casting mold and which has a thermal expansion coefficient equal
to or higher than the molten metal for forming the die-cast
article. In addition, the proposed method is not available for
eliminating or reducing an angle of inclination to be provided on
an outer circumferential surface of the die-cast article.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of the present invention to
provide a method of die-casting which permits reduction in the
angle of inclination provided on an inner or an outer
circumferential surface of a die-cast article, and a die-casting
apparatus suitably used for the method. This object may be achieved
according to any one of the following modes of the present
invention, each of which is numbered like the appended claims and
depends from the other mode or modes, where appropriate, to
indicate and clarify possible combinations of elements or technical
features of the present invention, for easier understanding of the
invention. It is to be understood that the present invention is not
limited to the technical features or any combinations thereof which
will be described for illustrative purpose only. It is to be
further understood that a plurality of elements or features
included in any one of the following modes of the invention are not
necessarily provided all together, and that the invention may be
embodied without some of the elements or features described with
respect to the same mode.
[0007] (1) A method of producing a die-cast article by die-casting,
the die-cast article having at least one of an inner
circumferential surface and an outer circumferential surface, the
method comprising the steps of: preparing a mold assembly including
a hollow portion which has a molding surface for molding one of the
inner and outer circumferential surfaces of the die-cast article;
closing the mold assembly so as to define therein a mold cavity
having a configuration which corresponds to that of the die-cast
article; subjecting the hollow portion to an elastic deformation in
a direction toward the one of the inner and outer circumferential
surfaces of the die-cast article to be produced; introducing a
molten metal into the mold cavity while the hollow portion is
subjected to the elastic deformation; opening the mold assembly and
permitting the elastic deformation to be removed from the hollow
portion after the molten metal has solidified in the mold cavity;
and removing the die-cast article formed in the mold cavity from
the mold assembly.
[0008] If the molten metal is introduced into the mold cavity and
solidified therein with the hollow portion of the mold assembly
being elastically deformed in the direction toward one of the inner
and outer circumferential surfaces of the die-cast article to be
produced, the die-cast article and the hollow portion engage each
other with an interference fit therebetween. Thereafter, the hollow
portion is freed or released from the elastic deformation and is
restored to its original state, that is, deformed in a direction
opposite to the above-indicated direction. Described in detail,
where the outer circumferential surface of the hollow portion of
the mold assembly serves as the molding surface, the hollow portion
which has been expanded by the elastic deformation contracts. Where
the inner circumferential surface of the hollow portion serves as
the molding surface, the hollow portion which has been contracted
by the elastic deformation expands. Accordingly, the die-cast
article and the hollow portion, which have been held in an
interference fit with each other, are positioned relative to each
other such that there is a clearance therebetween, so that the
hollow portion and the die-cast article can be easily removed away
from each other. According to the present method, it is possible to
minimize or eliminate a draft provided on the molding surface of
the hollow portion, so that the inner or outer circumferential
surface of the die-cast article has a minimum inclination
corresponding to the minimized draft of the molding surface, or no
inclination.
[0009] (2) A method according to the above mode (1), wherein the
hollow portion has a non-molding surface which is opposite to the
molding surface, the non-molding surface being a tapered surface, a
dimension of which in a direction perpendicular to a direction
parallel to a centerline of the hollow portion gradually changes in
the direction, the step of subjecting a hollow portion to an
elastic deformation comprising steps of preparing a tapered member
having a tapered surface which corresponds to the tapered surface
of the hollow portion, and causing the elastic deformation of the
hollow portion by an interference fit between the tapered surface
of the hollow portion and the tapered surface of the tapered
member.
[0010] According to the above mode (2), the hollow portion can be
easily elastically deformed when the hollow portion and the tapered
member engage each other with an interference fit between the
respective tapered surfaces of the hollow portion and the tapered
member.
[0011] (3) A method according to the above mode (1) or (2), wherein
the hollow portion is a hollow cylindrical member having a circular
shape in transverse cross section.
[0012] The transverse cross sectional shape of the hollow portion
is not particularly limited. While the principle of the present
invention is advantageously applicable to an arrangement wherein
the hollow portion has an axsymmetric shape in transverse cross
section such as a regular polygonal shape, the present invention
provides a particularly desirable effect where the hollow portion
has a circular shape in transverse cross section.
[0013] (4) A method according to any one of the above modes
(1)-(3), wherein the die-cast article is a cylinder block which is
used for a swash plate type compressor and which includes a
plurality of cylinder bores, the at least one of the inner and
outer circumferential surfaces of the die-cast article being an
inner circumferential surface of each of the cylinder bores.
[0014] The present method is suitably used for producing a cylinder
block for the swash plate type compressor. Where a plurality of
cylinder bores are formed in the cylinder block such that the
cylinder bores are adjacent to each other, the roundness of each
cylinder bore may be deteriorated when the hollow portion has a
complete circular shape in transverse cross section. In this case,
the hollow portion is preferably arranged to have a transverse
cross sectional shape which slightly deviates from a complete
circular shape at least while the hollow portion is subjected to
the elastic deformation, so that each cylinder bore to be formed in
the cylinder block as the die-cast article has a complete circular
shape in transverse cross section.
[0015] (5) A method according to any one of the above modes
(1)-(3), wherein the die-cast article is a front housing which is
used for a swash plate type compressor and which includes a hollow
cylindrical recess, the at least one of the inner and outer
circumferential surfaces of the die-cast article being an inner
circumferential surface of the hollow cylindrical recess of the
front housing.
[0016] The hollow cylindrical recess of the front housing for the
swash plate type compressor has an inner circumferential surface
which is slidable relative to a rotation preventing part of a
piston of the compressor, for preventing a rotary motion of the
piston about its centerline. Accordingly, it is required that the
inner circumferential surface of the hollow cylindrical recess of
the front housing has a high degree of dimensional accuracy.
According to the present method, it is possible to reduce the
required amount of stock removal from the inner circumferential
surface of the hollow cylindrical recess of the front housing in
the machining operation conducted thereon. Alternatively, the
machining operation can be eliminated.
[0017] (6) A die-casting apparatus for producing a die-cast article
having at least one of an inner circumferential surface and an
outer circumferential surface, comprising: a mold assembly
including a hollow portion which has a molding surface for molding
one of the inner and outer circumferential surfaces of the die-cast
article; and deforming device for elastically deforming the hollow
portion such that the hollow portion is subjected to an elastic
deformation in a direction toward the one of inner and outer
circumferential surfaces of the die-cast article to be
produced.
[0018] The method of producing a die-cast article according to the
above mode (1) can be practiced by using the die-casting apparatus
according to the above mode (6).
[0019] (7) An apparatus according to the above mode (6), wherein
the mold assembly includes a first mold and a second mold which are
moved toward and away from each other, so that the first mold and
the second mold are opened and closed, the hollow portion extending
in a direction parallel to a direction in which the first mold and
the second mold are opened and closed.
[0020] The hollow portion may extend in a direction which
intersects the direction in which the first mold and the second are
opened and closed. (The direction in which the first and second
molds are opened and closed is hereinafter referred to as a
"parting direction" of the two molds.) The present arrangement
wherein the hollow portion extends in the direction parallel to the
parting direction of the two molds permits the hollow portion to be
easily subjected to the elastic deformation, or permits the hollow
portion to be easily removed from the die-cast article after the
hollow portion has been freed from the elastic deformation.
[0021] (8) An apparatus according to the above mode (6) or (7),
wherein the mold assembly has a main body in which an engaging
portion is formed, the hollow portion being provided by a member
separate from the main body, and wherein at least a part of the
hollow portion, which part is adjacent to the molding surface, and
the engaging portion are positioned relative to each other such
that there is a clearance in a radial direction therebetween.
[0022] The engaging portion has an engaging hole and an engaging
protrusion. Where the molding surface is an outer circumferential
surface of the hollow portion, the engaging portion is provided by
the engaging hole. Where the molding surface is an inner
circumferential surface of the hollow portion, the engaging portion
is provided by the engaging protrusion. In either case, if at least
a part of the hollow portion, which part is adjacent to the molding
surface of the hollow portion, is positioned relative to the
engaging portion such that there is a clearance in a radial
direction therebetween, the above-indicated part can be easily
subjected to the elastic deformation, so that the hollow portion
including the molding surface can be subjected to substantially
uniform elastic deformation over an entire axial length
thereof.
[0023] (9) An apparatus according to any one of the above modes
(6)-(8), wherein the molding surface of the hollow portion for
molding the one of the inner and outer circumferential surfaces of
the die-cast article is an outer circumferential surface of the
hollow portion, and wherein the deforming device for elastically
deforming the hollow portion includes: an expanding member which
engages an inner circumferential surface of the hollow portion; and
a pushing device which forces the expanding member onto the inner
circumferential surface of the hollow portion, so that the hollow
portion is expanded.
[0024] The expanding member according to the above mode (9) may be
provided by a tapered member or a collet described below, for
instance. Where the expanding member is provided by the tapered
member, the pushing device is a device for effecting an
interference fit described below. Where the expanding member is
provided by the collet, the pushing device is a collet-diameter
changing device described below.
[0025] (10) An apparatus according to any one of the above modes
(6)-(8), wherein the molding surface of the hollow portion for
molding the one of the inner and outer circumferential surfaces of
the die-cast article is an inner circumferential surface of the
hollow portion, and wherein the deforming device for elastically
deforming the hollow portion includes: a contracting member which
engages an outer circumferential surface of the hollow portion; and
a pushing device which forces the contracting member onto the outer
circumferential surface of the hollow portion, so that the hollow
portion is contracted.
[0026] The contracting member according to the above mode (10) may
be provided by a tapered member or a collet described below, for
instance. Where the contracting member is provided by the tapered
member, the pushing device is a device for effecting an
interference fit described below. Where the contracting member is
provided by the collet, the pushing device is a collet-diameter
changing device described below.
[0027] (11) An apparatus according to any one of the above modes
(6)-(8), wherein the hollow portion has a non-molding surface which
is opposite to the molding surface, the non-molding surface being a
tapered surface, a dimension of which in a direction perpendicular
to a direction parallel to a centerline of the hollow portion
gradually changes in the direction, the deforming device for
elastically deforming the hollow portion including: a tapered
member having a tapered surface which corresponds to the tapered
surface of the hollow portion; and a device for effecting an
interference fit between the tapered surface of the hollow portion
and the tapered surface of the tapered member.
[0028] The die-casting apparatus according to the above mode (11)
is suitably used for practicing the method according to the above
mode (2).
[0029] (12) An apparatus according to the above mode (11), wherein
the tapered member is held by the main body of the mold assembly
such that the tapered member and the hollow portion are axially
movable relative to each other, the device for effecting an
interference fit including an axial moving device for moving the
tapered member and the hollow portion relative to each other in an
axial direction of the tapered member.
[0030] The present arrangement is particularly advantageous when
the hollow portion and the tapered member are located such that
they extend in a direction which intersects the above-indicated
parting direction of the two molds. The present arrangement is
applicable to an arrangement wherein the hollow portion and the
tapered member extend in a direction parallel to the parting
direction of the two molds.
[0031] (13) An apparatus according to the above mode (12), wherein
the axial moving device includes a hydraulic cylinder which is
fixed to the mold assembly.
[0032] (14) An apparatus according to the above mode (11), wherein
the tapered member is fixed to one of the first and second molds,
which one mold is opposite to the other of the first and second
molds which is equipped with the hollow portion, the first and
second molds being opened and closed by an opening and closing
device which also functions as the device for effecting an
interference fit.
[0033] (15) An apparatus according to any one of the above modes
(7)-(14), wherein the other of the first and second molds which is
equipped with the hollow portion includes an ejecting device which
pushes the die-cast article in a direction away from the other mold
to remove the die-cast article from the hollow portion.
[0034] The ejecting device permits the die-cast article to be
easily removed from the hollow potion. The die-cast article can be
easily removed from the hollow portion especially when the ejecting
device is actuated after the hollow portion has been freed from the
elastic deformation. It is particularly advantageous to employ the
feature of this mode (15) and the feature of the above mode (14) in
combination. In this case, at the same time when the first and
second molds are opened, the tapered member and the hollow portion
are separated away from each other, so that the hollow portion is
freed from the elastic deformation for permitting easy removal of
the die-cast article from the hollow portion. In this state, the
ejecting device is actuated, whereby the die-cast article can be
easily removed from the hollow portion.
[0035] (16) An apparatus according to the above mode (6), wherein
the hollow portion is a hollow cylindrical portion having an
annular shape in transverse cross section, and wherein the
deforming device for elastically deforming the hollow portion
includes: a collet which engages, at one of inner and outer
circumferential surfaces thereof, a non-molding surface of the
hollow portion, which non-molding surface is opposite to the
molding surface for molding the one of the inner and outer
circumferential surfaces of the die-cast article; and a
collet-diameter changing device for changing a diameter of the
collet so as to force the collet onto the non-molding surface.
[0036] In the above mode (16), the collet is a hollow cylindrical
member which consists of a plurality of segments that are arranged
in a spaced-apart relation with each other in the circumferential
direction. The thus constructed collet is easily expanded or
contracted in its radial direction. If the spacing between the
adjacent segments of the collet is relatively large, the amount of
the elastic deformation of the hollow portion is undesirably small
at portions thereof corresponding to the relatively large spacing
of the segments of the collet. In this case, the roundness of the
outer or inner circumferential surface of the hollow portion is
deteriorated, leading to deterioration of the roundness of the
inner or outer circumferential surface of the die-cast article
provided by the corresponding outer or inner circumferential
surface of the hollow portion. In view of this, the spacing between
the adjacent segments of the collet is preferably minimized. While
the segments of the collet may be completely separated from each
other, it is desirable that the segments of the collet are
partially connected to each other so as to constitute an integral
unitary member.
[0037] (17) An apparatus according to the above mode (16), wherein
the other of the inner and outer circumferential surfaces of the
collet, which the other circumferential surface is opposite to the
one circumferential surface which engages the non-molding surface
of the hollow cylindrical portion, is tapered to give a first
tapered surface whose diameter gradually changes in an axial
direction of the hollow cylindrical portion, and wherein the
collet-diameter changing device includes: a tapered member having a
second tapered surface which corresponds to the first tapered
surface; a multiplicity of balls interposed between the collet and
the tapered member such that the balls maintain a constant position
relative to each other, and such that the balls are rotatable
independently of each other, at least while the first and second
tapered surfaces engage each other; and an axial moving device
which moves the tapered member and the hollow cylindrical portion
relative to each other in an axial direction of the tapered member
and the hollow cylindrical portion, so that the first and second
tapered surfaces engage each other with an interference fit
therebetween via the balls.
[0038] The multiplicity of the balls are accommodated and held in a
recess formed in one of the first and second tapered surfaces, such
that each ball is rotatable and such that a part of each ball
projects outwardly from the recess. In this case, the ball is held
in contact with the other of the first and second tapered surfaces
at its projecting portion. Alternatively, the balls may be held by
a retainer which is a separate member from the tapered member and
the hollow cylindrical portion. The balls are held by the retainer
such that the balls are rotatable and such that the balls project
from the inner and outer surfaces of the retainer, respectively, so
that the balls are held in rolling contact with and between the
first and second tapered surfaces. Either of those arrangements are
effective to reduce the friction caused between the tapered member
and the hollow cylindrical portion when the tapered member and the
hollow cylindrical portion engage each other with an interference
fit therebetween. Accordingly, the present arrangement improves the
durability of the die-casting device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The above and optional objects, features, advantages and
technical and industrial significance of the present invention will
be better understood and appreciated by reading the following
detailed description of presently preferred embodiments of the
invention, when considered in connection with the accompanying
drawings, in which:
[0040] FIG. 1 is a front elevational view in cross section of a
swash plate type compressor produced according to one embodiment of
a die-casting method and apparatus of the present invention;
[0041] FIG. 2 is a perspective view showing a cylinder block of the
swash plate type compressor of FIG. 1;
[0042] FIG. 3 is a front elevational view partly in cross section
schematically showing a casting system including the die-casting
apparatus;
[0043] FIG. 4 is a front elevational view in cross section showing
a principal part of the die-casting apparatus;
[0044] FIG. 5 is a front elevational view in cross section showing
a die-casting apparatus constructed according to another embodiment
of the present invention;
[0045] FIG. 6 is a front elevational view in cross section showing
a die-casting apparatus constructed according to still another
embodiment of the present invention; and
[0046] FIG. 7 is a side elevational view showing a part of the
die-casting apparatus of FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] Referring to the accompanying drawings, there will be
described presently preferred embodiments of a die-casting method
and apparatus according to the present invention as applied to the
production of a swash plate type compressor.
[0048] Referring first to FIG. 1, there is shown a compressor of
swash plate type used for an air conditioning system of an
automotive vehicle. In FIGS. 1 and 2, reference numeral 10 denotes
a cylinder block having a plurality of cylinder bores 12 (seven
cylinder bores in this embodiment) formed so as to extend in its
axial direction such that the cylinder bores 12 are arranged along
a circle whose center lies on a centerline L of the cylinder block
10 and such that the cylinder bores 12 are equiangularly spaced
from each other in the circumferential direction of the cylinder
block 10. Single-headed pistons generally indicated at 14
(hereinafter simply referred to as "piston 14") are reciprocably
received in the respective cylinder bores 12. To one of the axially
opposite end faces of the cylinder block 10, (the left end face as
seen in FIG. 1, which will be referred to as "front end face"),
there is attached a front housing 16. To the other end face (the
right end face as seen in FIG. 1, which will be referred to as
"rear end face"), there is attached a rear housing 18 through a
valve plate 20. The front housing 16, rear housing 18 and cylinder
block 10 cooperate to constitute a housing assembly of the swash
plate type compressor. The rear housing 18 and the valve plate 20
cooperate to define a suction chamber 22 and a discharge chamber
24, which are connected to a refrigerating circuit (not shown)
through an inlet 26 and an outlet 28, respectively. The valve plate
20 has suction ports 32, suction valves 34, discharge ports 36 and
discharge valves 38.
[0049] A rotary drive shaft 50 is disposed in the cylinder block 10
and the front housing 16 such that the axis of rotation of the
drive shaft 50 is aligned with the centerline L of the cylinder
block 10. The drive shaft 50 is supported at its opposite end
portions by the front housing 16 and the cylinder block 10,
respectively, via respective bearings. The cylinder block 10 has a
central bearing hole 56 formed in a central portion thereof, and
the bearing is disposed in this central bearing hole 56, for
supporting the drive shaft 50 at its rear end portion. The front
end portion of the drive shaft 50 is connected, through a clutch
mechanism such as an electromagnetic clutch, to an external drive
source (not shown) in the form of an engine of an automotive
vehicle. In operation of the compressor, the drive shaft 50 is
connected through the clutch mechanism to the vehicle engine in
operation so that the drive shaft 50 is rotated about its axis.
[0050] The rotary drive shaft 50 carries a swash plate 60 such that
the swash plate 60 is axially movable and tiltable relative to the
drive shaft 50. The swash plate 60 has a central hole 61 through
which the drive shaft 50 extends. The diameter of the central hole
61 of the swash plate 60 gradually increases in the axially
opposite directions from its axially intermediate portion towards
the axially opposite ends. (In other words, the inner dimension of
the central hole 61 as measured in a vertical direction of FIG. 1
is larger at the axially opposite ends than the axially
intermediate portion.) To the drive shaft 50, there is fixed a
rotary member 62 as a torque transmitting member, which is held in
engagement with the front housing 16 through a thrust bearing 64.
The swash plate 60 is rotated with the drive shaft 50 by a hinge
mechanism 66 during rotation of the drive shaft 50. The hinge
mechanism 66 guides the swash plate 60 for its axial and tilting
motions. The hinge mechanism 66 includes a pair of support arms 67
fixed to the rotary member 62, guide pins 69 which are formed on
the swash plate 60 and which slidably engage guide holes 68 formed
in the support arms 67, the central hole 61 of the swash plate 60,
and the outer circumferential surface of the drive shaft 50.
[0051] The piston 14 indicated above includes an engaging portion
70 engaging the radially outer portion of the opposite surfaces of
the swash plate 60, and a head portion 72 formed integrally with
the engaging portion 70 and fitted in the corresponding cylinder
bore 12. The head portion 72, cylinder bore 12, and valve plate 20
cooperate with one another to define a pressurizing chamber 79. The
engaging portion 70 engages the radially outer portion of the
opposite surfaces of the swash plate 60 through a pair of
hemispherical shoes 76.
[0052] A rotary motion of the swash plate 60 is converted into a
reciprocating linear motion of the piston 14 through the shoes 76.
A refrigerant gas in the suction chamber 22 is sucked into the
pressurizing chamber 79 through the suction port 32 and the suction
valve 34, when the piston 14 is moved from its upper dead point to
its lower dead point, that is, when the piston 14 is in the suction
stroke. The refrigerant gas in the pressurizing chamber 79 is
pressurized by the piston 14 when the piston 14 is moved from its
lower dead point to its upper dead point, that is, when the piston
14 is in the compression stroke. The pressurized refrigerant gas is
discharged into the discharge chamber 24 through the discharge port
36 and the discharge valve 38. A reaction force acts on the piston
14 in the axial direction as a result of compression of the
refrigerant gas in the pressurizing chamber 79. This compression
reaction force is received by the front housing 16 through the
piston 14, swash plate 60, rotary member 62 and thrust bearing 64.
The engaging portion 70 of the piston 14 has an integrally formed
rotation preventive part (not shown), which is arranged to contact
the inner circumferential surface of the front housing 16, for
thereby preventing a rotary motion of the piston 14 about its
centerline to prevent an interference between the piston 14 and the
swash plate 60.
[0053] The cylinder block 10 has a supply passage 80 formed
therethrough for communication between the discharge chamber 24 and
a crank chamber 86 which is defined between the front housing 16
and the cylinder block 10. The supply passage 80 is connected to a
solenoid-operated valve 90 having a solenoid coil 92. The
solenoid-operated valve 90 is selectively energized and
de-energized by a control device (not shown) constituted
principally by a computer. During energization of the solenoid coil
92, the amount of electric current applied to the solenoid coil 92
is controlled depending upon the air conditioner load, so that the
amount of opening of the solenoid-operated valve 90 is controlled
according to the air conditioner load.
[0054] The rotary drive shaft 50 has a bleeding passage 100 formed
therethrough. The bleeding passage 100 is open at one of its
opposite ends to the central bearing hole 56, and is open to the
crank chamber 86 at the other end. The central bearing hole 56
communicates at its bottom with the suction chamber 22 through a
communication port 104.
[0055] The present swash plate type compressor is of variable
capacity type. By controlling the pressure in the crank chamber 86
by utilizing a difference between the pressure in the discharge
chamber 24 as a high-pressure source and the pressure in the
suction chamber 22 as a low pressure source, a difference between
the pressure in the crank chamber 86 and the pressure in the
pressurizing chamber 79 is regulated to change the angle of
inclination of the swash plate 60 with respect to a plane
perpendicular to the axis of rotation of the drive shaft 50, for
thereby changing the reciprocating stroke (suction and compression
strokes) of the piston 14, whereby the displacement capacity of the
compressor can be adjusted. Described in detail, the pressure in
the crank chamber 86 is controlled by controlling the
solenoid-operated valve 90 to selectively connect and disconnect
the crank chamber 86 to and from the discharge chamber 24. The
maximum angle of inclination of the swash plate 60 is limited by
abutting contact of a stop 106 formed on the swash plate 60, with
the rotary member 62, while the minimum angle of inclination of the
swash plate 60 is limited by abutting contact of the swash plate 60
with a stop 107 in the form of a ring fixedly fitted on the drive
shaft 50.
[0056] Between the rotary member 62 and one of the opposite major
surfaces of the swash plate 60 which is remote from the rear
housing 18, an elastic member in the form of a compression coil
spring 108 is disposed to function as biasing means for biasing the
swash plate 60 toward the stop 107 so that when the compressor is
in its off state, the swash plate 60 is positioned substantially at
right angles with respect to the centerline of the cylinder block
10, in abutting contact with the stop 107. When the compressor is
turned off, the swash plate 60 is moved to its minimum inclination
position by the biasing force of the compression coil spring 108
and is kept at the position until the compressor is re-started.
[0057] The cylinder block 10 and each piston 14 are formed of an
aluminum alloy. The piston 14 is coated at its outer
circumferential surface with a fluoro resin film which prevents a
direct contact of the aluminum alloy of the piston 14 with the
aluminum alloy of the cylinder block 10 so as to prevent seizure
therebetween, and makes it possible to minimize the amount of
clearance between the piston 14 and the cylinder bore 12. Other
materials may be used for the cylinder block 10, the piston 14, and
the coating film.
[0058] The cylindrical wall of each of the cylinder bores 12 of the
cylinder block 10 is formed with an extension 150 (FIG. 2) at a
first circumferential part thereof which corresponds to a radially
outer portion of the cylinder block 10 and which is more distant
from the centerline L of the cylinder block than a second
circumferential part which corresponds to a radially inner portion
of the cylinder block 10. The extension 150 extends from the
above-indicated first circumferential part of each cylinder bore 12
in the axial direction toward the crank chamber 86. Front end faces
152 of the extensions 150 are connected to each other in the
circumferential direction of the cylinder block 10 so as to be
flush with each other. The front housing 16 is attached to the
front end faces 152 of the extensions 150. The inner
circumferential surface of each cylinder bore 12 has a complete
cylindrical surface 154, and a part-cylindrical surface 156 on the
side of the front housing 16. Owing to provision of the extensions
150, the cylindrical wall of each cylinder bore 12 has a larger
axial length at the above-indicated first circumferential part of
the cylinder bore 12 which corresponds to the radially outer
portion of the cylinder block 10 and which is distant from the
centerline L of the cylinder block 10, than the second
circumferential part of the cylinder bore 12 which corresponds to
the radially inner portion of the cylinder block 10 and which is
near to the centerline L of the cylinder block 10. Accordingly, the
piston 14 placed at its end of the compression stroke engages the
inner circumferential surface of the cylinder bore 12 over a larger
axial distance corresponding to the axial dimension of the
extension 150, at the above-indicated first circumferential part of
the cylinder bore 12 corresponding to the radially outer portion of
the cylinder block 10. This arrangement is effective to prevent the
engaging portion 70 of the piston 14 from being inclined toward the
radially outer portion of the cylinder block 10. Therefore, the
piston 14 can be smoothly retracted into the cylinder bore 12
without being adversely influenced by an excessively large
resistance of friction which would be otherwise caused between the
inner circumferential surface of the cylinder bore 12 and the outer
circumferential surface of the piston 14. Accordingly, the swash
plate 60 can be moved to its minimum inclination position without
being adversely influenced by the piston 14. Since the extension
150 is not formed at the above-indicated second circumferential
part of each cylinder bore 12 which corresponds to the radially
inner portion of the cylinder block 10 and which is near to the
centerline L of the cylinder block 10, the swash plate 60 is not
inhibited from moving from its maximum inclination position to its
minimum inclination position.
[0059] There will be next described a method of producing, by
die-casting, the cylinder block 10 constructed as described above,
according to a first embodiment of the present invention. Referring
to FIG. 3, there is schematically shown a casting system 200 which
includes a die-casting apparatus for producing the cylinder block
10. The casting system 200 includes a pair of stationary platens
204, 206 which are located on a main frame 202 of the system 200 in
opposed relation to each other. Four guide rods 208 extend between
the two stationary platens 204, 206, such that each guide rod 208
connects one of four corners of the stationary platen 204 to the
corresponding one of four corners of the stationary platen 206. The
four guide rods 208 are parallel to one another. A movable platen
210 is slidably supported by the four guide rods 208. The
stationary platen 204 is provided with a hydraulic cylinder 214
which is adapted to open and close the mold assembly described
below. The hydraulic cylinder 214 is a kind of a hydropneumatic
cylinder, and includes a housing 216 which is fluid-tightly fixed
to one of the opposite major surfaces of the stationary platen 204
which is remote from the movable platen 210. The hydraulic cylinder
214 further includes a piston 218 which is carried by a piston rod
220 and which is slidably and fluid-tightly received in the housing
216. The piston rod 220 of the hydraulic cylinder 214 extends
through the stationary platen 204 toward the movable platen 210,
and is connected at its distal end to the movable platen 210. The
movable platen 210 is advanced toward and retracted from the
stationary platen 206 by the hydraulic cylinder 214 while being
guided by the guide rods 208. A maximum distance of retracting
movement of the movable platen 210 away from the stationary platen
206 is determined by suitable limiting means not shown.
[0060] A stationary mold 224 is removably attached to one of the
opposite major surfaces of the stationary platen 206 on the side of
the movable platen 210, while a movable mold 226 is removably
attached to the other major surface of the movable platen 210 on
the side opposite to the hydraulic cylinder 214. As described
above, the casting system 200 includes the mold assembly of the
stationary and movable molds 224, 226. The stationary mold 224
consists of a plurality of plate members which are superposed on
one another. The plate members comprise a mold plate, and a fixing
plate at which the stationary mold 224 is fixed to the stationary
platen 206. Similarly, the movable mold 226 consists of a plurality
of plate members which are superposed on one another. The plate
members comprise a mold plate, and a fixing plate at which the
movable mold 226 is fixed to the movable platen 210. The stationary
and movable molds 224, 226 are fixed, with a high degree of
positional accuracy, to the stationary platen 206 and the movable
platen 210, respectively, by engagement of engaging grooves formed
in the respective stationary and movable platens 206, 210 with
engaging protrusions provided on the respective stationary and
movable molds 224, 226, for instance. Alternatively, the stationary
and movable molds 224, 226 are fixed to the stationary and movable
platens 206, 210, respectively, while the two molds 224, 226 are
positioned relative to each other such that a positioning pin
provided on one of the two molds 224, 226 is fitted in a pin hole
formed in the other of the two molds 224, 226.
[0061] The two molds 224, 226 are butted together and are spaced
apart from each other at their contact surfaces 230, 232, as shown
in FIG. 4. The movable mold 226 is moved toward the stationary mold
224 by a drive force of the hydraulic cylinder 214, so that the two
molds 224, 226 are closed together with the contact surfaces 230,
232 being held in close contact with each other. The two molds 224,
226 have respective molding surfaces 240, 242 which cooperate with
each other to define therebetween a mold cavity 236 whose
configuration follows a profile of the cylinder block 10 to be
obtained. A molten metal (a molten aluminum alloy whose major
component is aluminum, in the present embodiment) is injected into
the mold cavity 236 for die-casting the cylinder block 10.
[0062] The lower end of the mold cavity 236 is held in
communication with a sleeve 250 (FIG. 3) via a runner (not shown)
which extends in a direction parallel to the contact surfaces 230,
232. The sleeve 250 is provided with a molten metal inlet. The
runner has a gate provided at one of its opposite open ends on the
side of the mold cavity 236. The gate has a cross sectional area
smaller than that of the other portion of the runner. The sleeve
250 is a cylindrical member which extends through the stationary
platen 206, so that one of opposite end portions of the sleeve 250
remote from the mold cavity 236 is located outside the two molds
224, 226. A plunger chip 254 formed at one end of a plunger 252 and
having a diameter larger than that of the plunger 252 is slidably
fitted in the above-indicated one end portion of the sleeve 250
located outside the two molds 224, 226. The plunger 252 is fixed to
a piston rod 258 of a plunger drive cylinder 256 as a plunger drive
device. The plunger drive cylinder 256 is a hydraulically operated
cylinder, and is fixedly supported by the main frame 202. The
sleeve 250, plunger 252, plunger chip 254, plunger drive cylinder
256, and piston rod 258 cooperate with one another to constitute an
injecting device for injecting the molten aluminum alloy into the
mold cavity 236 via the molten metal inlet of the sleeve 250.
[0063] Within the movable mold 226, there is provided an ejecting
device 260 which includes a pushing cylinder 262 (FIG. 3) and a
pushing member 266 (FIG. 4) having a plurality of eject pins 264.
The pushing cylinder 262 is a hydraulically operated cylinder, and
fixed to the movable mold 226 such that the pushing cylinder 262
does not interfere with other members. When the pushing cylinder
262 is actuated, the piston rod 268 of the pushing cylinder 262 is
advanced, for thereby pushing the pushing member 266 toward the
main body 283 of the movable mold 226. Accordingly, the distal end
of each eject pin 264 is moved from its retracted position in which
the distal end of the eject pin 264 cooperates with the molding
surface 242 to partially define the mold cavity 236, to its
advanced position in which the distal end of the eject pin 264
projects into the mold cavity 236 so as to eject the die-cast
article therefrom. When the piston rod 268 of the pushing cylinder
262 is retracted, the pushing member 266 is also retracted. A
maximum distance of advancing movement of the pushing member 266 is
determined by abutting contact of its front surface with one of two
stops provided on the movable mold 226 while a maximum distance of
retracting movement of the pushing member 266 is determined by
abutting contact of its rear surface opposite to the front surface,
with the other stop.
[0064] The hydraulic cylinder 214, plunger drive cylinder 256, and
pushing cylinder 262 are controlled by a control device not shown
principally constituted by a computer. More specifically described,
directional control valves provided in the fluid passages which are
connected to those cylinders are controlled by the control
device.
[0065] The movable mold 226 is provided with a hollow cylindrical
portion 280. Described in detail, a hollow cylindrical member 282,
which is provided by a separate member from a main body 283 of the
movable mold 226, is fixed to the main body 283 by suitable fixing
means, such that the axial direction of the hollow cylindrical
member 282 is parallel to the parting direction of the stationary
and movable molds 224, 226, and such that the hollow cylindrical
member 282 is not movable relative to the main body 283 of the
movable mold 226. The distal end portion of the hollow cylindrical
member 282 which projects from the molding surface 242 into the
mold cavity 236 by a predetermined axial length functions as the
hollow cylindrical portion 280 that is subjected to an elastic
deformation to change (to increase or decrease) its diameter. The
distal end face of the hollow cylindrical member 282 is flush with
the contacting surface 232 of the movable mold 226. The hollow
cylindrical member 282 is suitably formed of alloy tool steels
(e.g., SKD 61 of SKD tool steels specified according to the
Japanese Industrial Standard), which are usually used for forming
the casting mold. It is desirable that at least portions of the
stationary and movable molds 224, 226, which portions define the
mold cavity 236, are formed of the alloy tool steels.
[0066] The proximal end portion of the hollow cylindrical member
282, which is opposite to the hollow cylindrical portion 280, is
fitted in an engaging hole 284 formed in the main body 283 of the
movable mold 226. The engaging hole 284 extends in a direction
parallel to the parting direction of the two molds 224, 226. An
engaging pin 288 having a large-diameter engaging portion 290 at
its distal end is fitted in the proximal end portion of the hollow
cylindrical member 282, such that the large-diameter portion 290 is
held in engagement with a shoulder 286 formed in the inner
circumferential surface of the hollow cylindrical member 282. The
proximal end portion of the engaging pin 288, which is opposite to
the large-diameter engaging portion 290 and which extends through
the main body 283 of the movable mold 226 toward the pushing member
266, is externally threaded, and two nuts 292, 293 are engaged
therewith, whereby the hollow cylindrical member 282 is fixed to a
fixing member 294, and the fixing member 294 is in turn fixed to
the main body 283 of the movable mold 226.
[0067] The engaging hole 284 formed in the main body 283 of the
movable mold 226 has, at one of its axially opposite ends which is
nearer to the molding surface 242, a large-diameter portion 296
having a diameter slightly larger than the other portion of the
engaging hole 284. While the hollow cylindrical member 282 is not
elastically deformed, the outer circumferential surface of the
hollow cylindrical member 282 has a constant diameter over an
entire axial length thereof as indicated by a two-dot chain line in
FIG. 4. A portion of the outer circumferential surface of the
hollow cylindrical member 282, which portion is adjacent to a
molding surface 300 of the hollow cylindrical portion 280 (which
will be described), is fitted in the large-diameter portion 296 of
the engaging hole 294, such that there is a small clearance in a
radial direction therebetween. The outer circumferential surface of
the hollow cylindrical portion 280 functions as the molding surface
300 for forming the inner circumferential surface of the cylinder
bore 12 of the cylinder block 10 to be produced. Namely, the
molding surface 240 of the stationary mold 224, the molding surface
242 of the movable mold 226, and the molding surface 300 of the
hollow cylindrical portion 280 cooperate to define the mold cavity
236 having a configuration which follows that of the cylinder block
10. In FIG. 4, one of a plurality of the hollow cylindrical
portions 280 (seven in the present embodiment) is shown for forming
one of a plurality of the cylinder bores 12 (seven in the present
embodiment). The inner circumferential surface of the hollow
cylindrical portion 280 is a tapered surface 304 whose diameter
linearly decreases in the axial dimension of the hollow cylindrical
portion 280 from its open end on the side of the stationary mold
224 toward the movable mold 226.
[0068] The stationary mold 224 is provided with a tapered member
310 such that the tapered member 310 is coaxial with the hollow
cylindrical portion 280 of the movable mold 226. The tapered member
310 is fixedly attached to a main body 312 of the stationary mold
224 by suitable fixing means. The main body 312 of the stationary
mold 224 is formed with an engaging hole 314 which extends in the
axial direction of the stationary mold 224. At one of opposite
axial ends of the engaging hole 314 which is remote from the
movable mold 226, there is formed an internally threaded portion
316. The tapered member 310 is formed, at one of its opposite ends
which is remote from the movable mold 226, an externally threaded
portion 320. The externally threaded portion 320 of the tapered
member 310 is held in engagement with the internally threaded
portion 316, whereby the tapered member 310 is fixed to the
stationary mold 224. The tapered member 310 may be otherwise fixed
to the stationary mold 224. For instance, the tapered member 310
may be fixed to the stationary mold 224 such that the tapered
member 310 is press-fitted into an engaging hole formed in the
stationary mold 224. The tapered member 310 has a head potion 322
formed at its proximal end adjacent to the externally threaded
portion 320. The head portion 322 of the tapered member 310 has a
diameter larger than the other portion. With the externally
threaded portion 320 being engaged with the internally threaded
portion 316 such that one of the opposite end faces of the head
portion 322, which end face is adjacent to the externally threaded
portion 320, is held in abutting contact with the end face of the
stationary mold 224, as shown in FIG. 4, the distal end portion of
the tapered member 310 (which is opposite to the externally
threaded portion 320) projects a suitable axial distance from the
contact surface 230 and the molding surface 240 of the stationary
mold 224 in a direction toward the movable mold 226. The outer
circumferential surface of the distal end portion of the tapered
member 310 is a tapered surface 326 corresponding to the tapered
inner circumferential surface 304 of the hollow cylindrical portion
280.
[0069] The movable mold 226 is moved toward the stationary mold
224, so that the two molds 224, 226 are closed together with the
contact surfaces 230, 232 being held in close contact with each
other. In this state, the tapered inner circumferential surface 304
of the hollow cylindrical portion 280 and the tapered outer
circumferential surface 326 of the tapered member 310 engage each
other with an interference fit therebetween, so that the hollow
cylindrical portion 280 and an axial part of the hollow cylindrical
member 282, which part is adjacent to the hollow cylindrical
portion 280, are elastically deformed in a radially outward
direction, whereby the diameter of the hollow cylindrical portion
280 and the above-indicated axial part of the hollow cylindrical
member 282 is increased, as shown in FIG. 4. For easier
understanding, the amount of the elastic deformation is exaggerated
in FIG. 4. The above-indicated axial part adjacent to the hollow
cylindrical portion 280 is radially outwardly expanded by the
elastic deformation, so that the outer circumferential surface of
the axial part adjacent to the hollow cylindrical portion 280 is
held in sealing contact with the inner circumferential surface of
the large-diameter portion 296 of the engaging hole 284.
Accordingly, the engaging hole 284 is fluid-tightly closed at its
open end on the side of the molding surface 242, for inhibiting
fluid communication with the mold cavity 236. The axial dimensions
of the hollow cylindrical portion 280 and the tapered member 310
are determined such that there is left an axial clearance between
the front end faces of the tapered member 310 and the
large-diameter engaging portion 290 of the engaging pin 288 when
the tapered member 310 is entirely press-fitted into the hollow
cylindrical portion 280. When the movable mold 226 is moved away
from the stationary mold 224, the tapered member 310 is retracted
from the hollow cylindrical portion 280, so that the hollow
cylindrical portion 280 is freed from the elastic deformation and
restored to its original state.
[0070] There will be next explained a method of die-casting the
cylinder block 10 by using the die-casting apparatus constructed as
described above. Initially, the hydraulic cylinder 214 is actuated
so as to move the movable mold 226 toward the stationary mold 224,
so that the two molds 224, 226 are closed together with the contact
surfaces 230, 232 being held in close contact with each other. When
the two molds 224, 226 are closed together so as to define
therebetween the mold cavity 236, the tapered inner circumferential
surface 304 of the hollow cylindrical portion 280 and the tapered
outer circumferential surface 326 of the tapered member 310 engage
each other with an interference fit therebetween, so that the
hollow cylindrical portion 280 is elastically deformed in a
direction toward the inner circumferential surface of the cylinder
bore 12 of the cylinder block to be produced, namely in a radially
outward direction. Since the engaging hole 284 formed in the
movable mold 283 is fluid-tightly sealed as described above, the
engaging hole 284 is inhibited from communicating with the mold
cavity 236. While the two molds 224, 226 are closed together, the
sleeve 250 is held in fluid communication with the mold cavity 236
via the runner, and the plunger chip 254 is placed in its retracted
position at which the molten metal inlet of the sleeve 250 is held
in communication with the mold cavity 236. In this state, the
molten metal (e.g., the molten aluminum alloy) is introduced from
the molten metal inlet into the sleeve 250. Subsequently, the
plunger chip 254 is advanced toward the two molds 224, 226, so that
the level of the molten metal in the sleeve 250 is raised, whereby
the molten metal is introduced into the runner. Thereafter, the
advancing speed of the plunger chip 254 is increased, so that the
molten metal is jetted into the mold cavity 236 through the narrow
gate provided at the end of the runner. The plunger chip 254 is
kept actuated after the mold cavity 236 has been filled with the
molten metal, and the molten metal in the mold cavity 236
solidifies under a sufficiently high pressure.
[0071] The molten metal in the mold cavity 236 solidifies into the
cylinder block 10 a predetermined time after the mold cavity 236
has been filled with the molten metal. The inner circumferential
surface of the cylinder bore 12 is formed by the molding surface
300, i.e., the outer circumferential surface of the hollow
cylindrical portion 280 which is radially outwardly expanded by the
elastic deformation. Thereafter, the movable mold 226 is moved away
from the stationary mold 224. At the same time when the two molds
224, 226 are opened, the hollow cylindrical portion 280 is moved
away from the tapered member 310, so that the tapered inner
circumferential surface 304 of the hollow cylindrical portion 280
and the tapered outer circumferential surface 326 of the tapered
member 310 which have been held in an interference fit with each
other are disengaged from each other. Accordingly, the elastically
deformed hollow cylindrical portion 280 is restored to its original
state. That is, the hollow cylindrical portion 280 which has been
radially outwardly expanded by the elastic deformation is radially
inwardly contracted. Accordingly, the molding surface 300 of the
hollow cylindrical portion 280 and the inner circumferential
surface of the cylinder bore 12 of the cylinder block 10, which
have been held in an interference fit with each other, are
positioned relative to each other such that there is a radial
clearance therebetween. Thereafter, the pushing cylinder 262 is
actuated to advance the eject pins 264, whereby the die-cast
cylinder block 10 held by the movable mold 226 is pushed in a
direction away from the movable mold 226. Since there exists a
radial clearance between the molding surface 300 of the hollow
cylindrical portion 280 and the inner circumferential surface of
the cylinder bore 12 as described above, the cylinder lock 10 can
be easily removed from the movable mold 226.
[0072] In the present embodiment, the molding surface which forms
the inner circumferential surface of the cylinder bore 12 of the
cylinder block 10 is provided by the outer circumferential surface
of the hollow cylindrical portion 280. The hollow cylindrical
portion 280 corresponds to a hollow portion. The tapered inner
circumferential surface 304 of the hollow cylindrical portion 280
is a tapered surface, a dimension of which in a direction
perpendicular to a direction parallel to the centerline of the
hollow portion gradually changes in the direction. The tapered
outer circumferential surface 326 of the tapered member 310 is a
tapered surface which corresponds to the above-indicated tapered
surface of the hollow portion. The engaging hole 284 is an engaging
portion. The stationary mold 224 and the movable mold 226
correspond to a pair of molds of the die-casting apparatus, which
molds are moved toward and away from each other. The hydraulic
cylinder 214 constitutes an axial moving device for moving the
tapered member and the hollow portion relative to each other in the
axial direction of the tapered member. The axial moving device is
one example of a device for effecting an interference fit between
the tapered surface of the hollow portion and the tapered surface
of the tapered member. The hydraulic cylinder 214 corresponds to an
opening and closing device for opening and closing the stationary
and movable molds 224, 226. In the present embodiment, the
hydraulic cylinder 214 also functions as the device for effecting
an interference fit described above. The tapered member 310 is one
example of an expanding member which engages the inner
circumferential surface of the hollow cylindrical portion 280. The
hydraulic cylinder 214 functioning as the above-described device
for effecting an interference fit constitutes a pushing device
which forces the expanding member onto the inner circumferential
surface of the hollow cylindrical portion 280 for expanding the
hollow cylindrical portion 280.
[0073] According to the present embodiment, the cylinder block 10
formed in the mold cavity 236 can be easily removed from the
movable mold 226 without any problem even where the hollow
cylindrical portion 280 which forms the inner circumferential
surface of the cylinder bore 12 is provided with a relatively small
angle of draft or no draft. Therefore, the present arrangement
permits a reduction in the required amount of stock removal by the
machining operation to be conducted on the inner circumferential
surface of the cylinder bore 12, or eliminates the machining
operation, resulting in a reduction in the cost of manufacture of
the compressor. The outside diameter and the amount of the elastic
deformation of the hollow cylindrical portion 280 are suitably
determined depending upon the dimension of the intended inner
circumferential surface of the cylinder bore 12.
[0074] The hollow cylindrical portion 280 may be provided on the
stationary mold 224 while the tapered member 310 may be provided on
the movable mold 226. The tapered member 310 may be arranged to be
axially movable relative to the two molds 224, 226 by a suitable
drive device such as a hydraulically operated cylinder which is
provided independently of the hydraulic cylinder 214.
[0075] The present die-casting apparatus and the die-casting method
may be employed in producing a die-cast article other than the
cylinder block 10 described above. Referring next to FIG. 5, there
will be described a die-casting apparatus constructed according to
a second embodiment of the invention for producing the front
housing 16 of the swash plate type compressor. The front housing 16
has a hollow cylindrical recess, as shown in FIG. 1. Since the
structure of the casting system which includes the die-casting
apparatus of this second embodiment (FIG. 5) is similar to that of
the casting system 200 shown in FIG. 3, a detailed explanation of
which is dispensed with. Like the die-casting apparatus of FIG. 4
of the above-described first embodiment, the die-casting apparatus
of the second embodiment includes a stationary mold 400 and a
movable mold 402, which are moved toward and away form each other.
Each of the stationary and movable molds 400, 402 consists of a
plurality of plate members which are superposed on one another. The
movable mold 402 is moved toward and away from the stationary mold
400 by a suitable opening and closing device such as a hydraulic
cylinder, and the two molds 400, 402 are closed together at their
contacting surfaces 404, 406. The stationary mold 400 is provided
with a hollow cylindrical member 408 such that the hollow
cylindrical member 408 extends in a direction parallel to the axial
direction of the two molds 400, 402, in other words, in a direction
parallel to the parting direction of the two molds 400, 402. The
hollow cylindrical member 408 includes a hollow cylindrical portion
410 which projects from the contact surface 404 in the axial
direction of the hollow cylindrical member 408, and an engaging
portion 414. The engaging portion 414 is adjacent to the hollow
cylindrical portion 410 and fitted in an engaging hole 412 formed
in a main body 411 of the stationary mold 400, such that the
engaging portion 414 is axially unmovable with respect to the
stationary mold 400. At one of the opposite axial ends of the
engaging portion 414 which is remote from the hollow cylindrical
portion 410, there is formed a flange 416 having a diameter larger
than that of the hollow cylindrical portion 410 and the engaging
portion 414. The engaging hole 412 includes a large-diameter
section on the side which is remote from the contact surface 404,
and a small-diameter section on the side which is nearer to the
contact surface 404. The diameter of the inner circumferential
surface of the small-diameter section of the engaging hole 412 is
made smaller than that of the outer circumferential surface of the
flange 416 of the engaging portion 414 of the hollow cylindrical
member 408. The hollow cylindrical member 408 is inserted from its
distal end into the large-diameter section of the engaging hole
412, until the flange 416 of the hollow cylindrical member 408 is
brought into abutting contact with a shoulder surface formed
between the large- and small-diameter sections of the engaging hole
412. Thus, an amount of protrusion of the hollow cylindrical
portion 410 from the contact surface 404 is determined by the
abutting contact of the flange 416 with the shoulder surface of the
engaging hole 412. Further, a fixing member 417 is inserted into
the large-diameter section of the engaging hole 412 until the end
face of the fixing member 417 is brought into abutting contact with
the end face of the flange 416. The fixing member 417 is fixed to
the main body 411 of the stationary mold 400 by suitable fixing
means in the form of bolts, so that the hollow cylindrical member
408 is inhibited from moving in the axial direction away from the
main body 411 of the stationary mold 400. The thus fixed fixing
member 417 serves as a part of the main body 411 of the stationary
mold 400. While the hollow cylindrical member 408 is not subjected
to the elastic deformation, the engaging portion 414 of the hollow
cylindrical member 408 is fitted in the engaging hole 412 such that
there is a clearance therebetween in the radial direction, as
indicated by the two-dot chain line in FIG. 5. The outer
circumferential surface of the hollow cylindrical portion 410 has a
constant diameter over an entire axial length thereof, and function
as a molding surface 420 for forming the inner circumferential
surface of the front housing 16. The molding surface 420 cooperates
with a molding surface 422 of the stationary mold 400 and a molding
surface 424 of the movable mold 402 to define a mold cavity 426
whose configuration follows that of the front housing 16. The
molding surface 424 of the movable mold 402 which forms the outer
surface of the front housing is provided with a draft in its axial
direction. The inner circumferential surface of the hollow
cylindrical member 408 is a tapered surface 428 whose diameter
gradually decreases in a direction parallel to the centerline of
the hollow cylindrical member 408 from the stationary mold 400
toward the movable mold 402.
[0076] As shown in FIG. 5, the lower end of the mold cavity 426 is
held in communication with a sleeve (not shown) having a molten
metal inlet, via a runner 430. The runner 430 extends in a
direction parallel to the contact surfaces 404, 406, and is
provided, at one of its opposite open ends on the side of the mold
cavity 426, with a gate having a cross sectional area smaller than
the other portion of the runner 430. In this second embodiment,
too, the injecting device which includes the sleeve, plunger,
plunger chip, and plunger drive device is employed. The structure
of the injecting device is similar to that of the injecting device
used in the first embodiment described above, and a detailed
explanation of which is dispensed with. The movable mold 402 is
provided therein with an ejecting device (not shown) whose
structure is similar to that of the ejecting device 260 used in the
above-described first embodiment.
[0077] The stationary mold 400 is provided with a tapered member
440. The tapered member 440 is supported by the stationary mold 400
such that the tapered member 440 is axially movable within the
inner space of the hollow cylindrical member 408. The tapered
member 440 extends in the axial direction of the hollow cylindrical
member 408 such that the axes of the tapered member 440 and the
hollow cylindrical member 408 are aligned with each other. The
outer circumferential surface of the tapered member 440 at its
distal end which is on the side of the hollow cylindrical portion
410 is a tapered surface 444 corresponding to the tapered inner
circumferential surface 428 of the hollow cylindrical member 408.
The tapered member 440 is connected to a piston rod 446 of a
tapered-member-moving cylinder (not shown) which is fixed to the
stationary mold 400. The tapered-member-moving cylinder is a
hydraulically operated actuator.
[0078] The movable mold 402 is moved toward the stationary mold
400, so that the two molds 400, 402 are closed together at the
contact surfaces 404, 406. After the two molds 400, 402 have been
closed together, the tapered-member-moving cylinder is actuated so
as to move the tapered member 440 in the axial direction toward he
hollow cylindrical member 408, so that the tapered inner
circumferential surface 428 of the hollow cylindrical portion 410
and the tapered outer circumferential surface 444 of the tapered
member 440 engage each other with an interference fit therebetween.
Accordingly, the hollow cylindrical portion 410 and an axial part
of the hollow cylindrical member 408 adjacent to the hollow
cylindrical portion 410 (in other words, the entirety of the hollow
cylindrical member 408) are elastically deformed in a radially
outward direction, whereby the outside diameter of the hollow
cylindrical member 408 is increased. The above-indicated axial part
adjacent to the hollow cylindrical portion 410 is radially
outwardly expanded within the engaging hole 412, so that the outer
circumferential surface of the axial part is held in close contact
with the inner circumferential surface of the engaging hole 412.
Accordingly, the open end of the engaging hole 412 on the side of
the molding surface 422 is fluid-tightly sealed for inhibiting the
fluid communication with the mold cavity 426. At the same time, the
advancing movement of the tapered member 440 is stopped, and the
end faces of the tapered member 440 and the hollow cylindrical
portion 410 are flush with each other. With the hollow cylindrical
portion 410 being elastically deformed, the molten metal such as a
molten aluminum alloy is introduced into the mold cavity 426. After
the molten metal in the mold cavity 426 has solidified and before
the stationary mold 400 and the movable mold 402 are opened, the
tapered member 440 is retracted in the axial direction away from
the hollow cylindrical portion 410 toward the stationary mold 400.
Accordingly, the tapered outer circumferential surface 444 of the
tapered member 440 and the tapered inner circumferential surface
428 of the hollow cylindrical portion 410 are disengaged from each
other, whereby the elastically deformed hollow cylindrical member
408 including the hollow cylindrical portion 410 is restored to its
original shape. In this state, there is a radial clearance between
the molding surface 420 and the inner circumferential surface of
the hollow cylindrical recess of the front housing 16 to be
obtained. Thereafter, the movable mold 402 is moved away from the
stationary mold 400 with the front housing 16 being held by the
movable mold 402. After the two molds 400, 402 have been fully
opened, the front housing 16 is pushed by the ejecting device in a
direction away from the movable mold 402.
[0079] The front housing 16 produced as described above is formed
with a through-hole through which the rotary drive shaft 50
extends. This through-hole may be formed by a machining operation
after the die-casting process. Alternatively, the through-hole may
be formed in the die-casting process. In this case, the
through-hole may be formed by an axial member provided with a draft
having a suitable taper angle. The through-hole may be formed by
using a mold assembly which is equipped with a hollow cylindrical
portion and a device for elastically deforming the hollow
cylindrical portion, which are similar to those described in the
present embodiment. In this case, the hollow cylindrical portion is
provided with a relatively small angle of draft, or the hollow
cylindrical portion does not have a draft.
[0080] The hollow cylindrical portion 410 may be fixed to the main
body 411 of the stationary mold 400 by the fixing means similar to
that as described above with respect to the first embodiment of
FIGS. 1-4. On the contrary, in the above-described first
embodiment, the hollow cylindrical portion 280 may be fixed to the
movable mold 226 by the fixing means as described with respect to
the second embodiment of FIG. 5. The hollow cylindrical portion 410
and the tapered member 440 may be provided on the movable mold 402.
The ejecting device may be provided on either the stationary mold
400 or the movable mold 402.
[0081] The present die-casting method and the die-casting apparatus
permit formation of the inner circumferential surface of the axial
through-hole such as the inner circumferential surface of the
cylinder bore 12, as described with respect to the first embodiment
of FIGS. 1-4, and the inner circumferential surface of the recess
having a closed end such as the inner circumferential surface of
the front housing 16, as described with respect to the second
embodiment of FIG. 5.
[0082] Referring next to FIG. 6, there is explained a die-casting
apparatus constructed according to a third embodiment of the
present invention, which die-casting apparatus is arranged to form
an outer circumferential surface of a die-cast article by an inner
circumferential surface of a hollow cylindrical portion. Like the
die-casting apparatuses of the above-described first and second
embodiments, the die-casting apparatus of this third embodiment
includes a stationary mold 500 and a movable mold 502 which are
moved toward and away from each other, so that the two molds 500,
502 are opened and closed. The structure of the casting system
including the die-casting apparatus in this embodiment is similar
to that of the casting system 200 shown in FIG. 3, a detailed
description of which is dispensed with. Each of the stationary and
movable molds 500, 502 consists of a plurality of plate members
which are superposed on one another. The movable mold 502 is moved
toward and away from the stationary mold 500 by an opening and
closing device for opening and closing the two molds 500, 502 (not
shown) in the form of a hydraulically operated cylinder, for
instance. The two molds 500, 502 are closed together at their
contact surfaces 504, 506.
[0083] The movable mold 502 is provided with a hollow cylindrical
member 512 which extends in a direction parallel to the parting
direction of the two molds 500, 502, in other words, in the axial
direction of the two molds 500, 502. The hollow cylindrical member
512 is fixed at its flat fixing plate portion 514 to a main body
511 of the movable mold 502 by suitable fixing means such as bolts,
such that the hollow cylindrical member 512 is not movable relative
to the main body 511 of the movable mold 502. The hollow
cylindrical member 512 includes a hollow cylindrical portion 510
which axially extends from an inner peripheral portion of the
fixing plate portion 514 toward the stationary mold 500. The hollow
cylindrical portion 510 has an annular shape in transverse cross
section. An engaging member 520 is fitted in the hollow cylindrical
member 512. The engaging member 520 includes, at its proximal end
which is opposite to the hollow cylindrical portion 510, a fixing
portion 522 having a diameter larger than the other portion of the
engaging member 520. Like the hollow cylindrical member 512, the
engaging member 520 is fixed to the main body 511 of the movable
mold 502 at the fixing portion 522.
[0084] The engaging member 520 has a tapered outer circumferential
surface 524 at its distal end portion which is opposite to the
fixing portion 522. The hollow cylindrical potion 510 is subjected
to an elastic deformation such that the hollow cylindrical portion
510 is radially outwardly expanded or radially inwardly contracted.
While the hollow cylindrical portion 510 is not subjected to the
elastic deformation, there is a radial clearance between the inner
circumferential surface of the hollow cylindrical portion 510 and
the tapered outer circumferential surface 524 of the engaging
member 520. The inner circumferential surface of the hollow
cylindrical portion 510 serves as a molding surface 530 while the
front end face of the engaging member 520 serves as a molding
surface 532. The stationary mold 500 has a protrusion 536 which
protrudes in the axial direction of the stationary mold 500 from
the contact surface 504 toward the movable mold 502. The protrusion
536 is located within a space defined by the molding surfaces 530,
532 when the stationary and movable molds 500, 502 are closed
together at the contact surfaces 504, 506. The outer
circumferential surface, and the front end face of the protrusion
536 which is remote from the stationary mold 500, serve as molding
surfaces 538, 539, respectively. The molding surfaces 530, 532,
538, 539 cooperate to define a mold cavity 540 having a
configuration which follows that of an intended die-cast article.
The protrusion 536 is provided with a draft such that the diameter
of the protrusion 536 gradually decreases in the axial direction
from its proximal end toward its distal end.
[0085] A collet 550 is fitted on the outer circumferential surface
544 of the hollow cylindrical portion 510, which outer
circumferential surface 544 is opposite to the molding surface 530.
As shown in FIG. 7, the collet 550 consists of a plurality of
segments 551 (preferably, six or more segments) which are
equiangularly spaced from each other in the circumferential
direction of the collet 550. The diameter of the colet 550 is
mechanically changed (i.e., decreased) by a collet-diameter
changing device 552, so that the inner circumferential surface 554
of the collet 550 is forced onto the outer circumferential surface
544 of the hollow cylindrical portion 510, for thereby elastically
deforming or contracting the hollow cylindrical portion 510 in a
radially inward direction. The collet 550 has a tapered outer
circumferential surface 556 whose diameter gradually decreases in
the axial direction of the collet 550 from the stationary mold 500
toward the movable mold 502.
[0086] The collet-diameter changing device 552 includes as major
components a tapered member 560, and an axial moving device for
axially moving the tapered member 560. The tapered member 560 is a
generally cylindrical member, and has a tapered inner
circumferential surface 568 which corresponds to the tapered outer
circumferential surface 556 of the collet 550. A multiplicity of
balls 570 are interposed between those tapered inner and outer
circumferential surfaces 568, 556. The balls 570 are held by a
retainer 572, such that the balls 572 maintain a constant position
relative to each other, and such that the balls are rotatable
independently of each other. The retainer 572 is a member separate
from the collet 550 and the tapered member 560. Each of the balls
572 projects from the retainer 572 in both of the radially inward
and outward directions of the retainer 572, and cooperates with the
retainer 572 to constitute a rolling bearing. Namely, the rolling
movement of the balls 570 between the tapered outer circumferential
surface 556 of the collet 550 and the tapered inner circumferential
surface 568 of the tapered member 560 of the collet-diameter
changing device 552 effectively reduces friction caused when the
tapered member 560 and the collet 550 engage each other with an
interference fit therebetween by the axial moving device 564. The
rolling bearing constituted by the balls 570 and the retainer 572
is prevented from moving apart from the collet 550 and the tapered
member 560, by abutting contact with stops 576, 578 which are
formed at two axial portions of the tapered member 560. The axial
moving device 564 for axially moving the tapered member 560
includes a hydraulic actuator in the form of a hydraulically
operated cylinder (not shown) as a drive source, a piston rod 580
of the hydraulically operated cylinder, and a connecting member 582
for connecting the piston rod 580 and the tapered member 560.
[0087] An ejecting device 590 is provided within the movable mold
502 such that the ejecting device 590 does not interfere with other
components of the movable mold 502. Like the ejecting device 260 in
the above-indicated first embodiment, the ejecting device 590
includes a pushing cylinder 592 fixed to the movable mold 502 and a
pushing member 596 equipped with a plurality of eject pins 594.
When the pushing cylinder 592 is actuated, a piston rod of the
pushing cylinder 592 is advanced so as to move the pushing member
596 toward the stationary mold 500, so that the front end face of
each eject pin 594 is moved from its retracted position in which
the front end face of each eject pin 594 is flush with the molding
surface 532 so as to partially define the mold cavity 540, into its
advanced position in which the front end face of each eject pin 594
projects into the mold cavity 540 so as to push the die-cast
article in a direction away from the movable mold 502.
[0088] The mold cavity 540 is held in fluid communication with a
sleeve 602 having a molten metal inlet, via a runner 600. The
runner 600 is provided, at one of its opposite open ends on the
side of the mold cavity 540, with a gate having a cross sectional
area smaller than the other portion of the runner 600. In this
third embodiment, too, the injecting device which includes the
sleeve 602, a plunger 608, a plunger chip 610, and plunger drive
device is employed. The structure of the injecting device is
similar to that of the injecting device used in the first
embodiment described above, and a detailed explanation of which is
dispensed with. The movable mold 402 is provided therein with an
ejecting device (not shown) whose structure is similar to that of
the ejecting device 260 used in the above-described first
embodiment.
[0089] The movable mold 502 is moved toward the stationary mold
500, so that the two molds 500, 502 are closed together with their
contact surfaces 504, 506 being held in close contact with each
other. After the two molds 504, 506 have been closed together, the
axial moving device 564 is actuated to move the tapered member 560
toward the stationary mold 500, whereby the tapered inner
circumferential surface 568 of the tapered member 560 and the
tapered outer circumferential surface 556 of the collet 550 engage
each other with an interference fit therebetween. Accordingly, the
hollow cylindrical portion 510 and an axial part of the hollow
cylindrical member 512 adjacent to the hollow cylindrical portion
510 are elastically deformed in a radially inward direction, so
that the diameter of the inner circumferential surface of the
hollow cylindrical portion 510 (the molding surface 530) is
decreased, as shown in FIG. 6. The above-indicated axial part of
the hollow cylindrical member 512 adjacent to the hollow
cylindrical portion 510 is radially inwardly deformed such that its
inner circumferential surface is held in close contact with the
tapered outer circumferential surface 524 of the engaging member
520, for thereby inhibiting a fluid communication between the mold
cavity 540 and the inside of the movable mold 500 in which the
axial moving device 564 and other components are disposed. With the
hollow cylindrical portion 510 being elastically deformed, a molten
metal such as a molten aluminum alloy is introduced into the mold
cavity 540. After the molten metal has solidified in the mold
cavity 540, the stationary mold 500 and the movable mold 502 are
separated away from each other with the die-cast article being held
by the movable mold 502. Thereafter, the tapered member 560 is
retracted in a direction away from the stationary mold 500, and the
tapered inner circumferential surface 568 of the tapered member 560
is disengaged from the tapered outer circumferential surface 556 of
the collet 550, so that the elastically deformed hollow cylindrical
portion 510 is restored to its original state, namely, the diameter
of the hollow cylindrical portion 510 which has been reduced is
increased to the original value. In this state, there is a radial
clearance between the molding surface 530 of the hollow cylindrical
portion 510 and the outer circumferential surface of the die-cast
article. Accordingly, the die-cast article held by the movable mold
502 is easily pushed by the ejecting device 590 in a direction away
from the movable mold 502. The die-casting apparatus according to
this embodiment is suitably used in die-casting a blank for a head
portion of a compressor piston, for instance.
[0090] In the present embodiment wherein the tapered surfaces are
formed on the tapered member 560 and the collet 550, the thickness
of the hollow cylindrical portion 510 can be made constant over an
entire axial length thereof, so that the hollow cylindrical portion
510 can be uniformly subjected to the elastic deformation in the
radially inward direction. Since the tapered member 560 and the
collet 550 engage each other with an interference fit via the
rolling bearing constituted by the retainer 572 and the balls 570,
the tapered member 560 and the collet 550 have a relatively small
degree of mutually frictional resistance. Accordingly, the tapered
member 560 can be axially moved by the axial moving device 564 with
high efficiency for the interference fit with the collet 550,
resulting in a reduced size of the axial moving device 564.
Further, the present arrangement wherein the tapered member 560 and
the collet 550 engage each other via the rolling bearing assures a
reduction of the wear and an improved durability of the two
members.
[0091] For elastically deforming the hollow cylindrical portion 510
while keeping its roundness, the number of the segments 551 of the
collet 550 is desirably maximized. It is desirable that the
circumferential clearance between the adjacent ones of the
plurality of segments 551 is minimized while the collet 550 is
radially inwardly contracted for reduction of its diameter. On the
other hand, it is desirable that the circumferential clearance
between the adjacent ones of the plurality of segments 551 is
constant while the collet 550 is in its original state. To this
end, as in an ordinary collet, the segments of the collet 550 are
connected to each other by an elastically deformable connecting
member, rather than completely separated from each other. This
elastically deformable connecting member is provided at one of
opposite axial ends of the collet 550, e.g., at an axial end
portion of the collet 550 which is remote from the hollow
cylindrical portion 510 and which is nearer to the movable mold
511.
[0092] As is apparent from the foregoing description, in the
present embodiment, the molding surface which forms the outer
circumferential surface of the die-cast article is provided by the
inner circumferential surface of the hollow cylindrical portion
510. The hollow cylindrical portion 510 corresponds to the hollow
portion. The tapered outer circumferential surface 556 of the
collet 550 is a first tapered surface whose diameter gradually
changes in the axial direction of the hollow portion, while the
tapered inner circumferential surface 568 of the tapered member 560
is a second tapered surface which corresponds to the first tapered
surface. The collet 550 and the collet-diameter changing device 552
cooperate to constitute a deforming device for elastically
deforming the hollow portion. The collet 550 is a contracting
member which engages the outer circumferential surface of the
hollow cylindrical portion 510. The collet-diameter changing device
552 is a pushing device which forces the contracting member onto
the outer circumferential surface 544 of the hollow cylindrical
portion 510 for contracting the hollow cylindrical portion 510. The
collet and the collet-diameter changing device for mechanically
changing the diameter of the collet used in the present third
embodiment may be employed in the above-described first and second
embodiments of FIGS. 1-4 and FIG. 5, respectively, wherein the
molding surface which forms the inner circumferential surface of
the die-cast article is provided by the outer circumferential
surface of the hollow portion.
[0093] The present die-casting apparatus and the die-casting method
using the apparatus are suitably employed in producing articles
such as the cylinder block 10 having the cylinder bores 12 and the
front housing 16 having the hollow cylindrical recess, which
articles are formed of a material whose major component is
aluminum. The present die-casting apparatus and the die-cast method
can be employed in producing articles other than the described
above.
[0094] While the presently preferred embodiments of this invention
have been described above, for illustrative purpose only, it is to
be understood that the present invention may be embodied with
various changes and improvements such as those described in the
SUMMARY OF THE INVENTION, which may occur to those skilled in the
art.
* * * * *