Title: Apparatus and method for manufacturing die-cast product
Abstract: Fluid pressure of a first fluid chamber of a driving means, which acts as a back pressure, is monitored by a monitoring means when a core pin is driven by the driving means in an inserting direction before injection of a molten material into a cavity of a die arrangement. When the monitored fluid pressure of the first fluid chamber exhibits abnormal behavior that is different from normal behavior observed during a normal period, the monitoring means controls the driving means to stop the driving of the core pin in the inserting direction.
Patent Number: 6,871,688 Issued on 03/29/2005 to Yamazaki, et al.
| Inventors:
|
Yamazaki; Kenji (Nishio, JP);
Terui; Masanari (Gamagori, JP);
Nishikawa; Koji (Okazaki, JP)
|
| Assignee:
|
Denso Corporation (Kariya, JP)
|
| Appl. No.:
|
654467 |
| Filed:
|
September 4, 2003 |
Foreign Application Priority Data
| Sep 30, 2002[JP] | 2002-286327 |
| Current U.S. Class: |
164/132; 164/137; 164/452; 249/64; 249/151 |
| Intern'l Class: |
B22D 029//00 |
| Field of Search: |
164/452,113,132,137
249/151,64
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Stoner; Kiley S.
Assistant Examiner: Tran; Len
Attorney, Agent or Firm: Nixon & Vanderhye P.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is based on and incorporates herein by reference Japanese
Patent Application No. 2002-286327 filed on Sep. 30, 2002.
Claims
What is claimed is:
1. A method for manufacturing a die-cast product, which includes a cast
hole, the method comprising:
driving a core pin in an inserting direction until the core pin reaches an
insertable limit position to insert the core pin into a cavity of a die
arrangement by supplying working fluid into a second fluid chamber of a
driving means while draining working fluid from a first fluid chamber of
the driving means, wherein the driving of the core pin in the inserting
direction includes monitoring a fluid pressure of the first fluid chamber,
which acts as a back pressure, during the driving of the core pin in the
inserting direction, and the monitoring of the fluid pressure of the first
fluid chamber includes stopping of the core pin when the monitored fluid
pressure of the first fluid chamber exhibits abnormal behavior that is
different from normal behavior exhibited in a normal operation;
injecting a molten material from an injecting means into the cavity;
solidifying the molten material received in the cavity to form the die-cast
product;
driving the core pin in a retracting direction until the core pin reaches a
retractable limit position to remove the core pin from the cavity; and
removing the die-cast product from the cavity.
2. The method according to claim 1, wherein the driving of the core pin in
the inserting direction further includes maintaining the fluid pressure of
the first fluid chamber at a predetermined value by forcing working fluid
out of the first fluid chamber through use of the core pin during the
driving of the core pin in the inserting direction.
3. The method according to claim 1, wherein the monitoring of the fluid
pressure of the first fluid chamber further includes driving the core pin
in the retracting direction when the monitored fluid pressure of the first
fluid chamber is dropped to a fixed threshold value set for the first
fluid chamber.
4. The method according to claim 1, wherein the driving of the core pin in
the retracting direction includes monitoring a fluid pressure of the
second fluid chamber, which acts as a back pressure, during the driving of
the core pin in the retracting direction.
5. The method according to claim 4, wherein the driving of the core pin in
the retracting direction further includes maintaining the fluid pressure
of the second fluid chamber at a predetermined value by forcing working
fluid out of the second fluid chamber through use of the core pin during
the driving of the core pin in the retracting direction.
6. The method according to claim 5, wherein the monitoring of the fluid
pressure of the second fluid chamber includes outputting a notification
and keeping the driving of the core pin in the retracting direction when
the monitored fluid pressure of the second fluid chamber is dropped to a
fixed threshold value set for the second fluid chamber.
7. The method according to claim 1, wherein a draft angle of the core pin
is in a range of 0 to 30 degrees.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for
manufacturing a die-cast product.
2. Description of Related Art
Various die-cast products, which have a cast hole and are manufactured by
die-casting, are previously known. For example, such a die-cast product
can be produced as follows. First, a hydraulic cylinder is driven to
insert a core pin in a die arrangement and thereby to place the core pin
in a cavity of the die arrangement. Thereafter, a molten material is
filled into the cavity to produce the die-cast product. Then, the
hydraulic cylinder is driven to retract the core pin away from the cavity,
and the die-cast product is removed from the die arrangement.
In the above case, when the core pin is inserted into the cavity, the core
pin could collide with the die arrangement due to, for example, occurrence
of a deviation of a central axis of the core pin. When the drive force is
kept applied to the core pin to drive the core pin in the inserting
direction upon the collision of the core pin with the die arrangement, the
die arrangement can be damaged. Particularly, in a case where a plurality
of cavity inserts, through which the core pin is inserted, is placed in
the die arrangement along the central axis of the core pin, the core pin
can be easily collide with the cavity inserts, causing a high incidence of
damage of the cavity inserts which have a relatively low strength. Such
damage of the die arrangement reduces the productivity of the die-cast
product.
SUMMARY OF THE INVENTION
Thus, it is an objective of the present invention to provide an apparatus
and a method for manufacturing a die-cast product in a manner that
restrains a damage of a die arrangement in advance.
To achieve the objective of the present invention, there is provided an
apparatus for manufacturing a die-cast product, which includes a cast
hole. The apparatus includes a die arrangement, an injecting means, a core
pin, a driving means and a monitoring means. The die arrangement defines a
cavity therein. The injecting means is for injecting a molten material
into the cavity. The core pin is reciprocable into and out of the cavity.
The driving means is for reciprocably driving the core pin. The driving
means includes a first fluid chamber and a second fluid chamber. The first
fluid chamber applies fluid pressure to the core pin in a retracting
direction of the core pin to move the core pin away from the cavity. The
second fluid chamber applies fluid pressure to the core pin in an
inserting direction of the core pin to move the core pin into the cavity.
The driving means reciprocably drives the core pin by adjusting the fluid
pressure of each of the first fluid chamber and the second fluid chamber.
The monitoring means is for monitoring the fluid pressure of the first
fluid chamber, which acts as a back pressure, when the core pin is driven
by the driving means in the inserting direction before injection of the
molten material from the injecting means into the cavity. When the
monitored fluid pressure of the first fluid chamber exhibits abnormal
behavior that is different from normal behavior observed during a normal
period, the monitoring means controls the driving means to stop the
driving of the core pin in the inserting direction.
Alternative to the above monitoring means, there may be provided a
monitoring means for monitoring information that relates to at least one
fluid pressure, which is applied to the core pin to drive the core pin. In
such a case, when the information indicates occurrence of abnormal
behavior of at least one of the at least one fluid pressure, which is
different from normal behavior of the at least one of the at least one
fluid pressure observed during a normal period, upon driving of the core
pin by the driving means in the inserting direction, the monitoring means
controls the driving means to stop the driving of the core pin in the
inserting direction.
To achieve the objective of the present invention, there is also provided a
method for manufacturing a die-cast product, which includes a cast hole.
According to the method, a core pin is driven in an inserting direction
until the core pin reaches an insertable limit position to insert the core
pin into a cavity of a die arrangement by supplying working fluid into a
second fluid chamber of a driving means while draining working fluid from
a first fluid chamber of the driving means. A fluid pressure of the first
fluid chamber, which acts as a back pressure, is monitored during the
driving of the core pin in the inserting direction. Furthermore, the core
pin is stopped when the monitored fluid pressure of the first fluid
chamber exhibits abnormal behavior that is different from normal behavior
exhibited in a normal operation. Then, a molten material is injected from
an injecting means into the cavity. Thereafter, the molten material
received in the cavity is solidified to form the die-cast product. Next,
the core pin is driven in a retracting direction until the core pin
reaches a retractable limit position to remove the core pin from the
cavity. Then, the die-cast product is removed from the cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention, together with additional objects, features and advantages
thereof, will be best understood from the following description, the
appended claims and the accompanying drawings, where like numerals
represent like components, in which:
FIG. 1 is a schematic view showing a structure of a manufacturing apparatus
according to an embodiment of the present invention;
FIG. 2 is a longitudinal cross sectional view of a sleeve manufactured
according to the embodiment of the present invention;
FIG. 3A is a schematic view showing one operational state of the
manufacturing apparatus shown in FIG. 1;
FIG. 3B is a schematic view showing another operational state of the
manufacturing apparatus shown in FIG. 1;
FIG. 4 is a schematic view showing a core pin of FIG. 1 in an enlarged
scale;
FIG. 5 is a flow chart for describing sleeve molding operation of the
manufacturing apparatus shown in FIG. 1;
FIG. 6A is a characteristic diagram for describing abnormality monitoring
operation of the manufacturing apparatus shown in FIG. 1 during a normal
period;
FIG. 6B is a characteristic diagram for describing abnormality operation of
the manufacturing apparatus shown in FIG. 1 during an abnormal period;
FIG. 7A is another characteristic diagram for describing abnormality
monitoring operation of the manufacturing apparatus shown in FIG. 1 during
a normal period; and
FIG. 7B is another characteristic diagram for describing abnormality
monitoring operation of the manufacturing apparatus shown in FIG. 1 during
an abnormal period.
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to
the accompanying drawings.
FIG. 1 shows a manufacturing apparatus for a die-cast product according to
the embodiment of the present invention. The manufacturing apparatus 10
produces a sleeve 1 of a solenoid valve, such as one shown in FIG. 2,
through die-casting. The sleeve 1, which serves as a die-cast product, is
made, for example of aluminum alloy and is shaped into a generally
cylindrical form that has a cast hole 2. A plurality of grooves 4a-4e,
which are aligned in an axial direction, is provided in an inner
peripheral wall surface 3 of the sleeve 1, which defines the cast hole 2.
Furthermore, a plurality of through holes 5a-5e, which penetrate from a
base of each corresponding one of the grooves 4a-4e to an outer peripheral
wall surface 6 of the sleeve 1, is provided in the sleeve 1. In FIG. 2,
dot-dot-dash lines indicate location of an inner peripheral wall surface
3', which is produced by the cutting operation performed after the
die-casting operation in the manufacturing apparatus 10.
As shown in FIG. 1, the manufacturing apparatus 10 includes a die
arrangement 11, a die closure arrangement 15, an injecting arrangement 22,
a core pin 26, connecting pipe lines 34-37, a cylinder block 46, a
hydraulic pump 52, a solenoid valve 54, pressure sensors 55, 56 and a
control unit 58.
The die arrangement 11 includes a stationary die 12, a movable die 13 and a
plurality of cavity inserts 14a-14e. The die closure arrangement 15, which
opens and closes the die arrangement 11, has a die closure mechanism
normally used in a general die-casting machine and includes a stationary
platen 16, a movable platen 17 and an ejector pin 18.
The stationary die 12 and the movable die 13 are installed to the
stationary platen 16 and the movable platen 17, respectively. When the
movable platen 17 is driven by a drive device (not shown) of the die
closure arrangement 15, the movable die 13 can be reciprocated to move
toward and away from the stationary die 12. When the stationary die 12 and
the movable die 13 are engaged with each other, a cavity 19 is defined
between the stationary die 12 and the movable die 13. The cavity 19 has a
circular lateral cross section and extends along a contact surface between
the dies 12, 13 to correspond with an outer contour of the sleeve 1. A
through hole 20, which extends along both the stationary die 12 and
movable die 13, is communicated with one of two ends of the cavity 19,
which are opposed along a central axis 0 of the cavity 19. The through
hole 20 is coaxial with the cavity 19 and extends along the contact
surface between the dies 12, 13 such that the through hole 20 has a
circular cross section, which has a diameter larger than a minimum
diameter of the cavity 19. A gate 21, which extends through the stationary
die 12, is communicated with the other one of the ends of the cavity 19,
which are opposed along the central axis 0 of the cavity 19. The ejector
pin 18, which extends in the movable die 13 in a manner that allows
movements of the ejector pin 18 into and out of the cavity 19, is used to
eject the sleeve 1 after the die-casting.
Each of the cavity inserts 14a-14e is shaped into an identical annular
plate form and has a plate thickness, which corresponds to a width of a
corresponding groove 4a-4e of the sleeve 1. One cavity insert 14b is held
by the movable die 13, and the rest of the cavity inserts 14a, 14c-14e are
held by the stationary die 12. When the stationary die 12 and the movable
die 13 are engaged with each other, each cavity insert 14a-14e is aligned
within the cavity 19 along the central axis 0.
The injecting arrangement 22 has an injecting mechanism that is normally
used in a die-casting machine of a cold chamber type. The injecting
arrangement 22 includes a sleeve 23 and a plunger 24. The sleeve 23 is
connected to the gate 21 and receives the plunger 24. The injecting
arrangement 22 introduces a molten material, such as molten aluminum
alloy, into the sleeve 23 and pressurizes the molten material by the
plunger 24 to inject the molten material into the cavity 19. The injecting
arrangement 22 serves as an injecting means.
The core pin 26 includes a rod 27 and a piston 28. The rod 27 is arranged
in a manner that allows reciprocable movements of the rod 27 into and out
of the cavity 19. The piston 28 receives hydraulic pressure.
The rod 27 is shaped into an elongated stepped cylindrical form and has a
small diameter portion 29 and a large diameter portion 30 separated by a
step. The rod 27 is arranged coaxially with the cavity 19 of the die
arrangement 11 defined upon engagement of the dies 11, 12. The rod 27 is
inserted into the cavity 19 through the through hole 20 of the die
arrangement 11. In FIGS. 1, 3 and 4, "X" indicates an inserting direction
of the rod 27 into the cavity 19. At an insertable limit position of the
rod 27 in the cavity 19 shown in FIG. 3A, the small diameter portion 29 of
the rod 27 extends through all of the cavity inserts 14a-14e of the die
arrangement 11, and the large diameter portion 30 of the rod 27 closes the
through hole 20 in an air-tight manner. Furthermore, when the rod 27 is
moved from the insertable limit position in a retracting direction, which
is away from the cavity 19 and is indicated by "Y" in FIGS. 1 and 3, the
rod 27 is removed from the cavity inserts 14a-14e and the through hole 20.
As shown in FIG. 4 in an enlarged scale, the small diameter portion 29 of
the rod 27 is tapered toward an inserting end side thereof and has a draft
angle .theta.. Although the draft angle .theta. can be set to any
appropriate value, the draft angle .theta. is set to be within a range of
0-30 degrees in the present embodiment. By adapting such a small draft
angle .theta., it is possible to reduce an amount "d" of cut (FIG. 2) at
the time of finishing the original inner peripheral wall surface 3 after
the die-casting of the sleeve 1. In this way, the finished inner
peripheral wall surface 3' produced after the cutting is located in close
proximity to the original inner peripheral wall surface 3 where less
blowholes are present. Thus, it is possible to reduce the amount of
blowholes exposed in the finished inner wall surface 3'.
The piston 28 is formed as an annular flange located in the large diameter
portion side end of the rod 27. A surface of the piston 28, which is
perpendicular to a central axis P of the rod 27 and faces in the inserting
direction X, constitutes a first pressure receiving portion 31, and
another surface of the piston 28, which is perpendicular to the central
axis P of the rod 27 and faces in the retracting direction Y, constitutes
a second pressure receiving portion 32.
The connecting pipe lines 34, 35 are connected to the cylinder block 46 and
the solenoid valve 54 and form a first flow passage 38 and a second flow
passage 39, respectively. A portion of each connecting pipe line 34, 35 is
branched into two branched pipes, which receive a flow rate control valve
40 and a check valve 41, respectively. The flow rate control valve 40
adjusts a flow rate of working fluid, which flows in the corresponding
flow passage 38, 39, to a predetermined value. The check valve 41 prevents
flow of working fluid in the corresponding flow passage 38, 39 from the
cylinder block 46 side to the solenoid valve 54 side.
The connecting pipe lines 36, 37 are connected to the solenoid valve 54 and
the hydraulic pump 52 and form a third flow passage 42 and a fourth flow
passage 43, respectively.
The cylinder block 46 cooperates with the piston 28 to form a reciprocable
hydraulic cylinder, which reciprocates the core pin 26. The cylinder block
46 is shaped into a cylindrical form having closed ends, and a piston side
portion of the core pin 26 is coaxially received in the cylinder block 46.
With this arrangement, the piston 28 can axially reciprocate in the
cylinder block 46 while an outer peripheral edge of the piston 28 is
slidably engaged with an inner peripheral wall of the cylinder block 46.
As shown in FIG. 3A, when the core pin 26 reaches the insertable limit
position, the first pressure receiving portion 31 is engaged with a first
engaging wall 47 located at one end of the cylinder block 46. On the other
hand, as shown in FIG. 3B, when the core pin 26 reaches the retractable
limit position, the second pressure receiving portion 32 is engaged with a
second engaging wall 48 located at the other end of the cylinder block 46.
As shown in FIG. 1, when the core pin 26 is placed between the insertable
limit position and the retractable limit position, the inner space of the
cylinder block 46 is partitioned into two spaces by the piston 28. In this
way, the cylinder block 46 forms a first fluid chamber 49 in one of the
partitioned spaces, which faces the first pressure receiving portion 31,
and a second fluid chamber 50 in the other one of the partitioned spaces,
which faces the second pressure receiving portion 32. The first flow
passage 38 is communicated with the first fluid chamber 49. The working
fluid, which is supplied from the first flow passage 38 to the first fluid
chamber 49, applies hydraulic pressure to the first pressure receiving
portion 31 in the retracting direction Y. The second flow passage 39 is
communicated with the second fluid chamber 50. The working fluid, which is
supplied from the second flow passage 39 to the second fluid chamber 50,
applies hydraulic pressure to the second pressure receiving portion 32 in
the inserting direction X.
The hydraulic pump 52 takes working fluid from an oil pan 53 and discharges
the working fluid into the third flow passage 42. The oil pan 53 also
serves as a drain for draining working fluid from the fourth flow passage
43.
The solenoid valve 54 is a four port valve and is electrically connected to
the control unit 58. When the solenoid valve 54 drives a spool (not shown)
received therein from a neutral position toward one side based on a
corresponding command signal received from the control unit 58, the first
flow passage 38 is communicated with the fourth flow passage 43, and the
second flow passage 39 is communicated with the third flow passage 42. On
the other hand, when the solenoid valve 54 drives the spool from the
neutral position toward the other side based on a corresponding command
signal received from the control unit 58, the first flow passage 38 is
communicated with the third flow passage 42, and the second flow passage
39 is communicated with the fourth flow passage 43.
The first pressure sensor 55 is arranged between the cylinder block 46 and
the branched pipes in the connecting pipe line 34 and measures hydraulic
pressure of the first fluid chamber 49 conducted to the first flow passage
38. The second pressure sensor 56 is arranged between the cylinder block
46 and the branched pipes in the connecting pipe line 35 and measures
hydraulic pressure of the second fluid chamber 50 conducted to the second
flow passage 39. Each pressure sensor 55, 56 is electrically connected to
the control unit 58 and transmits a signal indicating the measured
hydraulic pressure to the control unit 58.
The control unit 58 includes an electronic circuit and computes hydraulic
pressure of each fluid chamber 49, 50 based on the measurement signal
received from each pressure sensor 55, 56. The control unit 58 generates a
command signal of the solenoid valve 54 based on the computed hydraulic
pressure of each fluid chamber 49, 50 and transmits the generated command
signal to the solenoid valve 54. The solenoid valve 54 is operated based
on the received command signal, so that "the transmission of the command
signal from the control unit 58 to the solenoid valve 54" will be
hereinafter referred to as "control of the solenoid valve 54 by the
control unit 58" for the sake of convenience.
The control unit 58 further includes a monitor 59 and controls a display of
the monitor 59 based on the computed hydraulic pressure of each fluid
chamber 49, 50.
The structure of the manufacturing apparatus 10 have been described.
Die-casting operation of the sleeve 1 with use of the manufacturing
apparatus 10, i.e., a manufacturing method of the sleeve 1 with use of the
manufacturing apparatus 10 according to the embodiment will be described
with reference to steps S1-S6 of FIG. 5.
At step S1, the die closure arrangement 15 is operated to drive the movable
die 13 toward the stationary die 12 and thereby to close the die
arrangement 11.
At step S2, the core pin 26 is driven in the inserting direction X to
insert the rod 27 into the cavity 19 of the die arrangement 11 through the
cavity inserts 14a-14e.
Specifically, the solenoid valve 54 is controlled by the control unit 58,
so that the first flow passage 38 is communicated with the fourth flow
passage 43, and the second flow passage 39 is communicated with the third
flow passage 42. Thus, the hydraulic pressure (hereinafter, referred to as
a first hydraulic pressure) of the first fluid chamber 49 is shifted to a
drain pressure, which is lower than the discharge pressure of the
hydraulic pump 52, and the hydraulic pressure (hereinafter, referred to as
a second hydraulic pressure) of the second fluid chamber 50 coincides with
the discharge pressure of the hydraulic pump 52. Therefore, a resultant
force F.sub.1, which is a sum of the force generated by the first
hydraulic pressure received by the first receiving portion 31 and the
force generated by the second hydraulic pressure received by the second
pressure receiving portion 32, acts as a force exerted in the inserting
direction X, so that the core pin 26 initiates movement in the inserting
direction X. At this time, the core pin 26 pushes working fluid through
the first pressure receiving portion 31 to drive the working fluid out of
the first fluid chamber 49 into the first flow passage 38, so that the
first hydraulic pressure of the first fluid chamber 49 is increased as the
back pressure, as shown in FIG. 6A. In the present embodiment, the flow
rate of working fluid in the first flow passage 38 is adjusted through the
flow rate control valve 40, so that the first hydraulic pressure is
increased to a predetermined pressure P.sub.10 and is thereafter
maintained at that pressure, as shown in FIG. 6A. The maintaining pressure
P.sub.10 is set such that the maintaining pressure P.sub.10 does not
prevent the movement of the core pin 26 in the inserting direction X of
the core pin 26.
The core pin 26, which is driven in the inserting direction X, is stopped
at the insertable limit position through the engagement between the first
pressure receiving portion 31 and the first engaging wall 47 of the
cylinder block 46. When the core pin 26 is stopped at the insertable limit
position, the first hydraulic pressure is returned to the drain pressure,
and the second hydraulic pressure is maintained at the discharge pressure
of the hydraulic pump 52, as shown in FIG. 6A. In this way, retraction of
the core pin 26 from the cavity 19 is prevented when the core pin 26
receives the injecting pressure of the molten material at the following
step S3.
At step S3, while the clamping pressure is applied to the stationary die 12
and the movable die 13 from the die closure arrangement 15, the molten
material is injected from the injecting arrangement 22 into the cavity 19
of the die arrangement 11. At this time, the injecting pressure is set to
a relatively low pressure to restrain inclusion of air bubbles into the
molten material, and then the injecting pressure is increased to a
relatively high pressure to fill the molten material throughout the cavity
19. Here, it should be noted that although next step S4 can be initiated
after completion of solidification of the entire molten material filled in
the cavity 19, next step S4 is actually initiated upon solidification of
only a contacting surface layer of the molten material, which contacts the
core pin 26, in this embodiment. In this way, tight engagement of the
sleeve 1 to the core pin 26, which is caused by solidification and
shrinkage of the molten material, can be alleviated. Thus, in the present
embodiment, the solidification of the molten material means solidification
of at least part of the molten material.
At step S4, the core pin 26 is driven in the retracting direction Y to
retract the rod 27 from the cavity inserts 14a-14e of the die arrangement
11 and the through hole 20.
Specifically, the solenoid valve 54 is controlled by the control unit 58,
so that the first flow passage 38 is communicated with the third flow
passage 42, and the second flow passage 39 is communicated with the fourth
flow passage 43. Thus, the first hydraulic pressure of the first fluid
chamber 49 coincides with the discharge pressure of the hydraulic pump 52,
and the second hydraulic pressure of the second fluid chamber 50 is
shifted to the drain pressure, which is lower than the discharge pressure
of the hydraulic pump 52. Therefore, a resultant force F.sub.2, which is a
sum of the force generated by the first hydraulic pressure received by the
first receiving portion 31 and the force generated by the second hydraulic
pressure received by the second pressure receiving portion 32, acts as a
force exerted in the retracting direction Y, so that the core pin 26
initiates movement in the retracting direction Y. At this time, the core
pin 26 pushes working fluid through the second pressure receiving portion
32 to drive the working fluid out of the second fluid chamber 50 into the
second flow passage 39, so that the second hydraulic pressure of the
second fluid chamber 50 is increased as the back pressure, as shown in
FIG. 7A. In the present embodiment, the flow rate of working fluid in the
second flow passage 39 is adjusted through the flow rate control valve 40,
so that the second hydraulic pressure is increased to a predetermined
pressure P.sub.20 and is thereafter maintained at that pressure, as shown
in FIG. 7A. The maintaining pressure P.sub.20 is set such that the
maintaining pressure P.sub.20 does not prevent the movement of the core
pin 26 in the retracting direction Y of the core pin 26.
The core pin 26, which is driven in the retracting direction Y, is stopped
at the retractable limit position through the engagement between the
second pressure receiving portion 32 and the second engaging wall 48 of
the cylinder block 46.
At step S5, the clamping force applied from the die closure arrangement 15
is released, and the movable die 13 is driven in a direction away from the
stationary die 12 to open the die arrangement 11.
At step S6, the die-cast sleeve 1 is pushed by the ejector pin 18 to
release the sleeve 1 from the movable die 13. The thus manufactured sleeve
1 includes the cast hole 2 formed by the core pin 26, the grooves 4a-4e
formed by the cavity inserts 14a-14e, and the through holes 5a-5e formed
by the stationary die 12 or the movable die 13.
The die-casting operation of the sleeve with use of the manufacturing
apparatus 10 has been described. Abnormality monitoring operation of the
manufacturing apparatus 10, i.e., a monitoring method for monitoring
abnormality during manufacturing of the sleeve 1 according to the
embodiment of the present invention will be described.
In the manufacturing apparatus 10, at step S2, while the core pin 26 is
driven in the inserting direction X, the first hydraulic pressure, which
now acts as the back pressure, of the first fluid chamber 49 is measured
and is monitored through the first pressure sensor 55. When the core pin
26 does not collide with the cavity inserts 14a-14e during the movement of
the core pin 26 in the inserting direction X, the first pressure is
increased and is maintained at the maintaining pressure P.sub.10. On the
other hand, when the core pin 26 collides with any of the cavity inserts
14a-14e, the core pin 26 receives resistive force from the cavity insert
14a-14e in a counter direction, which causes limitation of the movement of
the core pin 26 in the inserting direction X, so that the core pin 26 is
stopped. Thus, the first hydraulic pressure is reduced below the
maintaining pressure P.sub.10, as shown in FIG. 6B. At this time, the
second hydraulic pressure coincides with the discharge pressure of the
hydraulic pump 52, so that the resultant force F.sub.1, which is a sum of
the force generated by the first hydraulic pressure and the force
generated by the second hydraulic pressure, is increased due to the
reduction in the first hydraulic pressure. Therefore, when no
countermeasure is taken against this, the first hydraulic pressure is
reduced to a destructive critical pressure P.sub.12, as indicated by a
dot-dot-dash line in FIG. 6B, so that damage of the cavity inserts 14a-14e
will occur. However, in the manufacturing apparatus 10, when the first
hydraulic pressure reaches a threshold pressure P.sub.11, which is set to
be higher than the destructive critical pressure P.sub.12, the solenoid
valve 54 is controlled by the control unit 58, so that the first flow
passage 38 and the second flow passage 39 are communicated with the third
flow passage 42 and the fourth flow passage 43, respectively. As a result,
as shown in FIG. 6B, the first hydraulic pressure is increased, and the
second hydraulic pressure is reduced. Therefore, the movement of the core
pin 26 in the inserting direction X is stopped, and the core pin 26 is
then driven in the retracting direction Y. In this way, damage of the
cavity inserts 14a-14e is effectively prevented.
Furthermore, in the manufacturing apparatus 10, at step S4, while the core
pin 26 is driven in the retracting direction Y, the second hydraulic
pressure, which now acts as a back pressure, of the second fluid chamber
50 is measured and is monitored through the second pressure sensor 56.
When the die-cast sleeve 1 is not tightly engaged with the core pin 26,
the second hydraulic pressure is increased and is held at the maintaining
pressure P.sub.20, as described above. On the other hand, when the sleeve
1 is tightly engaged with the core pin 26 due to, for example, the
solidification and shrinkage of the molten material or galling of the
material, the core pin 26 receives resistive force from the sleeve 1 in a
counter direction, which causes limitation of the movement of the core pin
26 in the retracting direction Y, so that second hydraulic pressure is
reduced below the maintaining pressure P.sub.20, as shown in FIG. 7B. In
the manufacturing apparatus 10, when the second hydraulic pressure is
reduced and is reached to a threshold pressure P.sub.21, as shown in FIG.
7B, the controlled state of the solenoid valve 54 is maintained by the
control unit 58 to continuously drive the core pin 26 in the retracting
direction, and a warning message (notification) is indicated on the
monitor 59 to notify the occurrence of the tight engagement between the
sleeve 1 and the core pin 26. Because of the notification, an operator of
the apparatus 10 can notice the occurrence of the tight engagement between
the core pin 26 and the sleeve 1 in advance to the release of the sleeve 1
from the die arrangement performed at step S6. The sleeve 1, which is
tightly engaged with the core pin 26, may have a defect, such as, galling,
of the sleeve 1 when the core pin 26 is forcefully pulled out of the
sleeve 1. However, the operator, who can notice the occurrence of the
tight engagement of the sleeve 1 and the defect caused by the tight
engagement in advance, can dispose or discard such a defective sleeve 1
without inspecting it after release of the sleeve 1 from the die
arrangement 11.
As described above, according to the present embodiment, the first
hydraulic pressure and the second hydraulic pressure correspond to the
first hydraulic pressure and the second fluid pressure, respectively, and
the threshold pressure P.sub.11 and the threshold pressure P.sub.21
correspond to a fixed threshold value of the first fluid pressure and a
fixed threshold value of the second fluid pressure, respectively. In the
present embodiment, the cylinder block 46, the solenoid valve 54, the
hydraulic pump 52 and the connecting pipe lines 34-37 cooperate together
to form a driving means for reciprocably driving the core pin 26 through
adjustment of the hydraulic pressure of each fluid chambers 49, 50. In the
present embodiment, the first pressure sensor 55, the second pressure
sensor 56 and the control unit 58 cooperate together to form a monitoring
means for monitoring the hydraulic pressure of each fluid chamber 49, 50
or information that relates to the hydraulic pressure of each fluid
chamber 49, 50 and for controlling the driving means.
With use of the manufacturing apparatus 10 described above, damage of the
cavity inserts 14a-14e can be effectively prevented at the time of driving
the core pin 26 in the inserting direction X, and the sleeve 1, which has
the defect generated at the time of driving the core pin 26 in the
retracting direction Y, can be disposed without inspecting it. Thus, the
productivity of the die-cast product can be improved.
Furthermore, in the manufacturing apparatus 10, the first hydraulic
pressure, which becomes the back pressure at the time of driving the core
pin 26 in the inserting direction X, shows a reduction from the constant
pressure P.sub.10 as abnormal behavior (or abnormal change), which is
different from normal behavior (or normal change) observed during the
normal operation, at the time of collision of the core pin 26 with the
cavity insert 14a-14e. In addition, in the manufacturing apparatus 10, the
second hydraulic pressure, which becomes the back pressure at the time of
driving the core pin 26 in the retracting direction Y, shows a reduction
from the constant pressure P.sub.20 as abnormal behavior (or abnormal
change), which is different from normal behavior (or normal change)
observed during the normal operation, at the time of occurrence of the
tight engagement between the core pin 26 and the sleeve 1. Such a
reduction of the hydraulic pressure from the corresponding constant
pressure P.sub.10, P.sub.20 can be easily detected through the pressure
sensors 55, 56. Thus, the monitoring accuracy of the first hydraulic
pressure and the second hydraulic pressure can be improved.
Also, in the manufacturing apparatus 10, the draft angle .theta. of the
core pin 26 is set to the small value of 0-30 degrees to reduce the amount
of cut required in the cutting operation performed after the die-casting
operation. In such a setting of the draft angle, there is an increased
possibility of collision of the core pin 26 with the cavity inserts
14a-14e. However, with use of the manufacturing apparatus 10, the
collision of the core pin 26 with the cavity inserts 14a-14e can be
notified based on the monitored hydraulic pressure of the first fluid
chamber 49. Thus, damage of the cavity inserts 14a-14e caused by the
collision can be prevented regardless of the excessively small draft angle
.theta. of the core pin 26.
In the above embodiment, the first fluid chamber 49 and the second fluid
chamber 50 are formed in the single cylinder block 46. Alternatively, for
example, two pistons can be provided in the core pin 26. In such a case,
the first fluid chamber can be formed by one cylinder block, which
receives one of the pistons, and the second fluid chamber can be formed by
another cylinder block, which receives the other one of the pistons.
Furthermore, in the above embodiment, the first hydraulic pressure, which
serves as the first fluid pressure, is monitored at the time of driving
the core pin 26 in the inserting direction, and the second hydraulic
pressure, which serves as the second fluid pressure, is monitored at the
time of driving the core pin 26 in the retracting direction.
Alternatively, the monitoring of one of the first hydraulic pressure and
the second hydraulic pressure can be omitted.
Furthermore, in the above embodiment, when the second hydraulic pressure is
dropped to the threshold pressure P.sub.21, which serves as the fixed
threshold value, the occurrence of such a pressure drop is notified to the
operator. Alternatively, when the occurrence of drop of the second
hydraulic pressure to the threshold pressure P.sub.21 is detected, the
sleeve 1, which is the die-cast product released from the die arrangement,
can be automatically disposed by, for example, a robot machine. In this
way, the productivity of the sleeve 1 can be further improved.
Furthermore, in the above embodiment, the present invention is embodied in
the manufacturing apparatus 10 and the manufacturing method for
manufacturing the sleeve 1 of the solenoid valve, which serves as the
die-cast product. Alternatively, the present invention can be applied to
manufacturing of various die-cast products manufactured through
die-casting.
Additional advantages and modifications will readily occur to those skilled
in the art. The invention in its broader terms is therefore, not limited
to the specific details, representative apparatus, and illustrative
examples shown and described.
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