U.S. patent application number 12/447000 was filed with the patent office on 2010-01-07 for die casting machine and die casting method.
This patent application is currently assigned to Ube Machinery Corporation, Ltd.. Invention is credited to Kazuki Hiraizumi, Yoshinori Okazaki, Masashi Uchida.
Application Number | 20100000699 12/447000 |
Document ID | / |
Family ID | 39324458 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000699 |
Kind Code |
A1 |
Uchida; Masashi ; et
al. |
January 7, 2010 |
DIE CASTING MACHINE AND DIE CASTING METHOD
Abstract
A die casting machine that suppresses the occurrence of surge
pressure, prevents the occurrence of burrs and spouting of molten
metal, and further minimizes variations in the quality of a molded
product on site. The die casting machine comprises a mold (101)
that cast-molds a product, an injection cylinder (102) for
injecting molten metal (15) to the mold, and a hydraulic device
(103) for pressing under high pressure the injection cylinder. The
hydraulic device comprises a piston ACC (20) that supplies
hydraulic oil to press under pressure a piston (13) of the
injection cylinder (102) and an injection cylinder inlet valve
(31). The piston ACC comprises a high pressure fast
pressure-raising piston accumulator (22, 322) and a low-pressure
injection piston accumulator (21, 321).
Inventors: |
Uchida; Masashi; (Yamaguchi,
JP) ; Hiraizumi; Kazuki; (Yamaguchi, JP) ;
Okazaki; Yoshinori; (Yamaguchi, JP) |
Correspondence
Address: |
IP GROUP OF DLA PIPER LLP (US)
ONE LIBERTY PLACE, 1650 MARKET ST, SUITE 4900
PHILADELPHIA
PA
19103
US
|
Assignee: |
Ube Machinery Corporation,
Ltd.
Ube-shi, Yamaguchi
JP
|
Family ID: |
39324458 |
Appl. No.: |
12/447000 |
Filed: |
October 11, 2007 |
PCT Filed: |
October 11, 2007 |
PCT NO: |
PCT/JP2007/070296 |
371 Date: |
April 24, 2009 |
Current U.S.
Class: |
164/113 ;
164/155.1; 164/314 |
Current CPC
Class: |
B22D 17/203 20130101;
B22D 17/32 20130101 |
Class at
Publication: |
164/113 ;
164/314; 164/155.1 |
International
Class: |
B22D 17/00 20060101
B22D017/00; B22D 17/20 20060101 B22D017/20; B22D 17/32 20060101
B22D017/32 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2006 |
JP |
2006-290165 |
Sep 4, 2007 |
JP |
2007-229335 |
Claims
1. A die casting machine, comprising: a mold that cast-molds a
product; an injection cylinder for injecting molten metal to the
mold; and a hydraulic device for pressing under high pressure the
injection cylinder, wherein the hydraulic device comprises: a
piston accumulator (ACC) that supplies hydraulic oil, which presses
under pressure a piston of the injection cylinder, to the injection
cylinder; and an injection cylinder inlet valve for
releasing/closing a flow of the hydraulic oil from the piston
accumulator (ACC) to the injection cylinder, and wherein the piston
accumulator (ACC) comprises a high pressure fast pressure-raising
piston accumulator (ACC-B) and a low-pressure injection piston
accumulator (ACC-A).
2. The die casting machine according to claim 1, wherein the piston
of the injection cylinder is first pressed under pressure by a high
hydraulic oil pressure supplied by the fast pressure-raising piston
accumulator (ACC-B) and operates at a fast injection speed, and
then is pressed under pressure by a low hydraulic oil pressure
supplied by the injection piston accumulator (ACC-A) and operates
when the hydraulic oil pressure supplied by the fast
pressure-raising piston accumulator (ACC-B) is shut off.
3. The die casting machine according to claim 1, wherein the fast
pressure-raising piston accumulator (ACC-B) comprises an ACC-B
piston that separates/forms a gas chamber and a hydraulic oil
chamber within the fast pressure-raising piston accumulator (ACC-B)
and reciprocates therein, and a projection part fixed on the ACC-B
piston and extending up to a side of the hydraulic oil chamber, and
penetrating and extending through an end wall on a side of the
hydraulic oil chamber of the fast pressure-raising piston
accumulator (ACC-B), wherein the injection piston accumulator
(ACC-A) comprises an ACC-A piston that separates/forms a gas
chamber and a hydraulic oil chamber within the injection piston
accumulator (ACC-A) and reciprocates therein, and wherein the
projection part is capable of penetrating through an end wall on a
side of the gas chamber of the injection piston accumulator
(ACC-A), invading the gas chamber of the injection piston
accumulator (ACC-A), and detachably coming into contact with and
pressing under pressure the ACC-A piston.
4. The die casting machine according to claim 3, wherein the fast
pressure-raising piston accumulator (ACC-B) and the injection
piston accumulator (ACC-A) are formed integrally into one unit.
5. The die casting machine according to claim 1, further comprising
a pressure-increasing accumulator for holding under pressure molten
metal in the mold at a predetermined pressure for a predetermined
period of time after the injection molding of the molten metal.
6. The die casting machine according to claim 1, wherein the
injection cylinder inlet valve is capable of adjusting the flow
rate of the hydraulic oil from the piston accumulator (ACC) to the
injection cylinder.
7. The die casting machine according to claim 1, further comprising
a stroke sensor for detecting a stroke of the piston of the
injection cylinder.
8. The die casting machine according to claim 7, wherein the
injection of the molten metal is controlled by the stroke
sensor.
9. The die casting machine according to claim 1, wherein the
hydraulic device further comprises a pump, and wherein the pump is
capable of supplying hydraulic oil to the injection cylinder and
the piston accumulator (ACC).
10. The die casting machine according to claim 1, wherein pressure
of the fast pressure-raising piston accumulator (ACC-B) in its
initial state is set to 14 to 21 MPa and pressure of the injection
piston accumulator (ACC-A) in its initial state is set to 5 to 12
MPa.
11. A die casting method using a die casting machine, the machine
comprising: a mold that cast-molds a product; an injection cylinder
for injecting molten metal to the mold; and a hydraulic device for
pressing under high pressure the injection cylinder, wherein the
hydraulic device comprises a piston accumulator (ACC) that supplies
hydraulic oil, which presses under pressure a piston of the
injection cylinder, to the injection cylinder and an injection
cylinder inlet valve for releasing/closing a flow of the hydraulic
oil from the piston accumulator (ACC) to the injection cylinder,
and wherein the piston accumulator (ACC) comprises a high pressure
fast pressure-raising piston accumulator (ACC-B) and a low-pressure
injection piston accumulator (ACC-A), the die casting method
comprising: a high-pressure injection step for supplying
high-pressure hydraulic oil from the fast pressure-raising piston
accumulator to the injection cylinder and pressing under pressure
the piston of the injection cylinder to inject molten metal; and a
low-pressure injection step for supplying low-pressure hydraulic
oil from the injection piston accumulator to the injection cylinder
when shutting off hydraulic oil from the fast pressure-raising
piston accumulator to the injection cylinder, and pressing under
pressure the piston of the injection cylinder to continue injection
of molten metal.
12. The die casting method according to claim 11, wherein the
hydraulic device of the die casting machine further comprises a
pressure-increasing accumulator for holding under pressure molten
metal in the mold at a predetermined pressure for a predetermined
period of time, and wherein the method further comprises a step for
further continuing to apply pressure to the molten metal using the
pressure-increasing accumulator after the injection of molten metal
by the fast pressure-raising piston accumulator and the injection
piston accumulator is completed.
13. The die casting method according to claim 11, wherein the
hydraulic device of the die casting machine further comprises a
pump, and wherein the method further comprises a step, before the
high-pressure injection step and the low-pressure injection step,
for supplying hydraulic oil from the pump to the injection cylinder
to move forward the piston of the injection cylinder.
14. The die casting method according to claim 11, wherein the
hydraulic device of the die casting machine further comprises a
stroke sensor for detecting a stroke of the piston of the injection
cylinder, and wherein the high-pressure injection step and the
low-pressure injection step are commenced, respectively, based on
the stroke of the piston detected by the stroke sensor.
15-16. (canceled)
17. A die casting machine comprising: a mold that cast-molds a
product; an injection cylinder for injecting molten metal to the
mold by moving a piston comprised by the injection cylinder, the
injection cylinder comprising a head chamber that moves forward the
piston toward the mold when hydraulic oil is supplied to the head
chamber and a rod chamber that moves back the piston so that it
moves away from the mold when hydraulic oil is supplied to the rod
chamber; and a hydraulic device for supplying hydraulic oil to the
injection cylinder, wherein the hydraulic device comprises: an
injection piston accumulator that supplies hydraulic oil, which
presses under pressure the piston of the injection cylinder, to the
injection cylinder, the injection piston accumulator comprising a
hydraulic oil chamber that stores hydraulic oil and a gas chamber
that stores gas, the hydraulic oil chamber and the gas chamber
being partitioned in a fluidically tight manner; a fast speed
adjusting valve for controlling/closing a flow of hydraulic oil
from the injection piston accumulator to the head chamber of the
injection cylinder; and at least one gas bottle installed so as to
communicate fluidically with the gas chamber of the injection
piston accumulator via a filling force pattern adjusting valve, and
wherein the filling force pattern adjusting valve is capable of
variably setting its valve opening degree and adjusting the filling
force of hydraulic oil to the injection cylinder by adjusting the
opening degree of the filling force pattern adjusting valve.
18. The die casting machine according to claim 17, further
comprising an automatic control device, wherein the automatic
control device comprises an operation circuit for selecting a
filling force pattern using a fast injection stroke and a fast
injection speed of the injection cylinder as parameters, and
wherein the opening degree of the filling force pattern adjusting
valve is adjusted so as to match with a filling force pattern
selected by the operation circuit.
19. The die casting machine according to claim 17, wherein the
hydraulic device further comprises: a pressure-increasing
accumulator that communicates fluidically with the head chamber of
the injection cylinder and increases pressure of molten metal in
the mold for holding the molten metal at a predetermined pressure
for a predetermined period of time after an injection filling of
molten metal; a pressure-increasing opening/closing valve installed
between the pressure-increasing accumulator and the injection
cylinder and releasing/shutting off a flow of hydraulic oil from
the pressure-increasing accumulator to the injection cylinder; and
a pressure-increasing time adjusting valve installed in series to
the pressure-increasing opening/closing valve between the
pressure-increasing accumulator and the injection cylinder and
adjusting pressure-increasing time of injected molten metal by
changing its opening degree.
20. The die casting machine according to claim 17, wherein the
hydraulic device further comprises: a hydraulic pump that
communicate fluidically with the head chamber and the rod chamber
of the injection cylinder; and an injection switching valve
installed between the hydraulic pump and the injection cylinder and
switching between guiding a flow of hydraulic oil from the
hydraulic pump to the head chamber of the injection cylinder and
guiding it to the rod chamber.
21-22. (canceled)
23. A die casting method using the die casting machine according to
claim 17, the die casting method comprising: a low-speed injection
step for pressing under pressure molten metal in the injection
cylinder at a low speed; and a fast injection step for pressing
under pressure and injecting the molten metal in the injection
cylinder at a high speed into the mold, wherein the fast injection
step comprises an opening setting procedure for setting the opening
degree of the filling force pattern adjusting valve in accordance
with a fast injection speed and an injection filling force.
24. The die casting method according to claim 23, wherein the die
casting machine further comprises an automatic control device
comprising an operation circuit for determining an opening degree
of the filling force pattern adjusting valve using a fast injection
stroke, a fast injection speed, and a final filling force of the
injection cylinder as parameters; and wherein the opening setting
procedure comprises a stage for determining an opening degree of
the filling force pattern adjusting valve by the operation
circuit.
25. The die casting method according to claim 23, wherein the
hydraulic device further comprises: a pressure-increasing
accumulator that communicates fluidically with the head chamber of
the injection cylinder and increases a pressure of molten metal in
the mold for holding the molten metal at a predetermined pressure
for a predetermined period of time after an injection filling of
molten metal; a pressure-increasing opening/closing valve installed
between the pressure-increasing accumulator and the injection
cylinder and releasing/shutting off a flow of hydraulic oil from
the pressure-increasing accumulator to the injection cylinder; a
pressure-increasing time adjusting valve installed in series to the
pressure-increasing opening/closing valve between the
pressure-increasing accumulator and the injection cylinder and
adjusting a pressure-increasing time of injected molten metal by
changing its opening degree; a hydraulic pump that communicate
fluidically with the head chamber and the rod chamber of the
injection cylinder; and the injection switching valve installed
between the hydraulic pump and the injection cylinder and switching
between guiding a flow of hydraulic oil from the hydraulic pump to
the head chamber of the injection cylinder and guiding it to the
rod chamber, wherein in the low-speed injection step, the hydraulic
oil is supplied by the hydraulic pump to the head chamber of the
injection cylinder to move forward the piston of the injection
cylinder toward the mold, wherein the fast injection step further
comprises a procedure for controlling an opening degree of the fast
speed adjusting valve, wherein after the fast injection step, a
pressure-increasing step is performed, and wherein the
pressure-increasing step comprises: a procedure for closing the
fast speed adjusting valve; a procedure for opening the
pressure-increasing opening/closing valve; and a procedure for
holding an open state of the pressure-increasing opening/closing
valve until a predetermined pressure is reached.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present invention claims patent based on the priority of
Japanese Patent Application No. 2006-290165 filed on Oct. 25, 2006
and Japanese Patent Application No. 2007-229335 filed on Sep. 4,
2007 and these contents are incorporated herein as reference and
continued in the subject application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a die casting machine and a
die casting method and, more particularly, to a fast (high-speed)
injection metal die casting machine and a die casting method.
[0004] 2. Description of the Related Art
[0005] A die casting method and a die casting machine using a light
metal material, such as aluminum, for molding are widely used in
various fields, such as the automobile industry and die casting
manufacturing. In the die casting method, a product having a
predetermined shape is molded by pumping under pressure molten
metal supplied into a plunger sleeve through a molten metal supply
inlet by a plunger tip to fill a mold cavity (hollow) therewith. A
light metal, such as aluminum alloy, has a shorter solidification
time compared to that of a synthesis resin, and therefore, an
increase in injection speed becomes important. Further, from the
standpoint of productivity, an increase in injection speed has been
in demand.
[0006] FIG. 1 shows an illustrative diagram of a general die
casting machine 100 for light metal, such as aluminum. In the
explanation of the present invention to be given later, the
configuration of the die casting machine 100 is explained in
detail, and therefore, only important items are explained here. The
die casting machine 100 for light metal is generally a hydraulic
type, in which hydraulic oil is supplied to the head side of an
injection cylinder 102 to drive a piston rod 4 and press molten
aluminum (AL) 15 stored in a plunger sleeve 7 via a plunger rod 2
with a plunger tip 1, and thereby, a cavity 12 within a mold 8, 9
is filled therewith by injection molding.
[0007] In recent die casting, it is reported that gas enclosing
blowholes are eliminated by removing gas in a mold at a high vacuum
(about 5 kPa) and thus the injection speed is increased, and by
shortening the filling time to reduce the number of blowholes
(cavities) that occur internally, the mechanical property of a
molded product by die casting is improved remarkably. For the
latest die casting machine, there is an increasing demand to
improve the quality of a molded product by shortening the filling
time to minimize the reduction in temperature of molten metal. In
this case, the injection speed is 5 to 7 m/sec, about 2.5 times the
normal speed, which is 2 to 3 m/sec (the numerical values of the
above speeds are those in the state where molten metal is pushed
into a mold at a speed at actual molding (actual injection speed)),
however, in the actual molding site, if the speed is increased to
this level, surge pressure occurs in molten aluminum (AL) because
of the impact when injection filling is completed, and therefore,
the mold clamping device breaks down and the mold opens slightly
and thus a burr occurs (molten metal erupted from the slit of the
mold solidifies into a burr). Even more so, spouting of molten
metal occurs, and either way, there arises a problem that
"continuation of production is no longer possible".
[0008] Because of this, various methods for reducing surge pressure
have been proposed. However, each proposal has a problem. Surge
pressure occurs as a combination of that which occurs due to the
inertial force of the plunger tip 1, the plunger rod 2, an
injection coupling 3, the piston rod 4, and a piston head 5 that
are traveling at a high speed shown in FIG. 1 and that which occurs
due to the inertia of hydraulic oil that flows into a cylinder 6 at
a high speed. A graph of the change of the injection speed and
surge pressure with time (or injection stroke) is shown in FIG. 12.
In FIG. 12, a first surge pressure that appears first results from
the plunger tip 1, the plunger rod 2, the piston rod 4, and the
piston 5 and this surge pressure affects most the occurrence of
burr.
[0009] As a method for reducing the first surge pressure, it is
conceived basically (1) to reduce the weight of a moving body and
(2) to reduce speed before filling is completed. This method is
already put to practical use currently and as the method (2) to
reduce speed before filling is completed, the following two methods
are adopted. A method frequently used is (2-1) to hydraulically
apply breaks to the plunger tip 1 (that is, the piston rod 4) when
a scheduled position is reached by detecting the injection stroke,
however, in this method, because of the variations in the amount of
molten aluminum (AL) to be supplied into the plunger sleeve 7 (in
general, there are variations of certain level in the amount of
molten metal to be supplied to and stored in the plunger sleeve 7
resulting from the reason relating to the precision of a supply
mechanism), there are variations in the position at which the
injection speed of molten metal into the mold is reduced and this
causes the defect in quality, such as the occurrence of cold
shut/molten metal wrinkle of a molded product, and this is a big
problem for a product that strictly prevents such defects. That is,
when applying breaks by detecting the injection stroke (i.e., the
position of the plunger tip 1), if the amount of molten metal in
the sleeve 7 is large, the increasing rate of the pressure of
molten metal is high and surge pressure occurs earlier before
breaking is activated (the braking timing is delayed relatively),
and therefore, the leak of molten metal occurs and a burr occurs.
On the other hand, if the amount of molten metal within the sleeve
7 is small, breaking is activated before molten metal is
sufficiently distributed in the mold cavity (the breaking timing is
advanced relatively), and therefore, a defect that molten metal is
insufficient may occur.
[0010] The other method is to (2-2) reduce the power of the
injection cylinder at a fast (high-speed) filling step and reduce
the speed spontaneously according to the increase in resistance of
the flow of molten metal in the mold that occurs during filling. In
this case, the influence of the variations in the amount of molten
metal is removed and the defect of quality, such as the occurrence
of cold shut/molten metal wrinkle, in the molded product in the
above-described method (2-1) no longer occurs. However, the
following problem occurs. If power at a fast filling step is
reduced, the fast pressure-raising time is lengthened, and
therefore, there arises a problem that a fast peed cannot be
obtained. An example is shown by the dotted line in FIG. 14. FIG.
15 shows the outline of a device used in a test to obtain the graph
in FIG. 14. This device comprises a mold 101 and the injection
cylinder 102 similar to those shown in FIG. 1 and further
comprising a piston ACC (accumulator), a gas bottle, a valve 31
similar to a seventh valve, etc., similar to those in FIG. 2. In
the example in FIG. 14, the pressure of the accumulator (ACC) is
reduced from 14 MPa (normal pressure) to 9 MPa. Due to this, the
fast pressure-raising time from 0.2 to 3.2 m/sec is 15 msec at 14
MPa (solid line), however, at 9 MPa (dotted line), it is 22 msec,
that is 7 msec longer. Further, in the molding test under this
condition (9 MPa), a significant burr still occurs. However, if the
pressure is further reduced, the pressure-raising time is
lengthened and the fast speed is reduced and the defect in the run
of molten metal (misrun: molten metal does not reach any part in
the cavity) occurs, and therefore, this condition is a compromise
one in the actual molding test. As for the condition of 9 MPa, if
the fast pressure-raising and the fast (high) speed operation are
not affected, it is necessary to reduce the fast injection output
to remove the burr and with this method to reduce pressure (i.e.,
power), no satisfactory molding result could be obtained in the
molding test.
[0011] In order to exhibit the fast actual injection speed
performance, a performance of 10 m/sec or more is required for
no-load injection (no molten metal is put into the sleeve and there
is no flow resistance of molten metal). What is severe is the need
to reach this speed within a slight distance of 50 mm, and
therefore, the injection cylinder and the hydraulic circuit are
configured so that a high pressure is generated at the fast
speed-raising step. Then, if filling is completed without any
action taken, the pressure of molten metal in the cavity sharply
increases (surge pressure occurs) when the filling is completed and
the mold opens, spouting of molten metal occurs, and a very
dangerous state where a molding operation is no longer possible is
brought about.
[0012] In order to prevent this, a method for forcedly reduce the
speed of the injection piston immediately before the completion of
filling is adopted (FIG. 25) (in contrast to this, a machine with a
fast injection speed of 2 to 3 m/sec as specifications has a speed
not so high and a low pressure at a fast filling step, and
therefore, the speed is reduced spontaneously while balancing with
the increasing fluid resistance of molten metal in the mold, the
impact value when filling is completed is reduced, and burr and
spouting of molten metal are unlikely to occur). A machine having a
fast speed of 10 m/sec or more as specifications at a no-load
injection step is referred to as an ultrafast machine, and molding
by an ultrafast machine has a difficult problem. The problem is
that a high precision is required for the amount of molten metal to
be supplied by a molten metal supplier and if the amount of molten
metal is excessive, filling is completed before the speed is
reduced sufficiently and a surge pressure occurs, and if the amount
of molten metal is insufficient, scattering (or splash) of tip of
molten metal occurs, discontinuous filling results, and the defect
of cold shut occurs, and what is worse, gas inclusion defect
occurs. The mechanism of the occurrence of the defect when the
amount of molten metal is insufficient and the reduction in speed
is put into effect too early is illustrated in FIG. 26. However, it
is very difficult to improve the precision of molten metal supply
of a supplier and a method for solving the problem is hard to
find.
[0013] The graph in FIG. 25 shows how the position of the plunger
tip when filling is completed changes depending on the amount of
molten metal. The position at the time of completion when the
amount of molten metal is proper (as planned) is shown as the
"ideal position at the time of completion" (broken line). When the
amount of molten metal is excessive, the position at the time of
completion becomes more distant from the gate 6, and therefore, is
the position shown by the alternate long and short dash line. When
the amount of molten metal is insufficient, the position at the
time of completion comes nearer to the gate 6, and therefore, is
the position shown by the alternate long and two dashes line. As
described above, the position at the time of completion varies
depending on the amount of molten metal, and therefore, there
arises a problem that surge pressure occurs or scattering of tip of
molten metal occurs. On the other hand, it is difficult to improve
the precision of molten metal supply of a supplier and also to
grasp the amount of molten metal, and therefore, it is also
difficult to adjust the position at which reduction in speed is
commenced by grasping the amount of molten metal.
[0014] For a die casting machine, there has been made a proposal
that the weight of a moving body is reduced (for example, refer to
patent document 2), however, the proposal has not disclosed the
proposal of the present invention. There has been made another
proposal (refer to patent document 1), however, with this proposal,
it is not possible to suppress the occurrence of surge pressure and
defect of product quality because an error is produced at the
position of the commencement of reduction in speed of the injection
rod when there are variations in the amount of molten metal stored
in the plunger sleeve as described above. [0015] [Patent document
1] Japanese Unexamined Patent Publication (Kokai) No. 2001-300714
[0016] [Patent document 2] Japanese Unexamined Patent Publication
(Kokai) No. 2004-216432
SUMMARY OF THE INVENTION
[0017] The present invention has been developed the above-described
circumstances being taken into account and an object thereof is to
suppress the occurrence of surge pressure, prevent the occurrence
of burr and spouting of molten metal or scattering (or splash) of
tip of molten metal, and further minimize the variations in the
quality of molded product on site in a die casting method or a die
casting machine capable of fast (high-speed) injection molding.
[0018] In order to achieve the above-described object, a die
casting machine according to a first aspect of the present
invention comprises a mold (101) that cast-molds a product, an
injection cylinder (102) for injecting molten metal (15) to the
mold (101), and a hydraulic device (103, 203) for pressing under
high pressure the injection cylinder (102). The hydraulic device
(103, 203) comprises a piston accumulator (ACC) (20) that supplies
hydraulic oil, which presses under pressure an piston (13) of the
injection cylinder (102), to the injection cylinder (102) and an
injection cylinder inlet valve (31) for releasing/closing the flow
of hydraulic oil from the piston accumulator (ACC) (20) to the
injection cylinder (102). The piston accumulator (ACC) (20)
comprises a high pressure fast pressure-raising piston accumulator
(ACC-B) (22, 322) and a low-pressure injection piston accumulator
(ACC-A) (21, 321).
[0019] With such a configuration, it is possible to suppress the
occurrence of surge pressure of molten metal in the cavity of a
mold, prevent the occurrence of burr and spouting of molten metal,
and further minimize the variations in the quality of molded
product on site in a die casting machine capable of fast injection
molding by activating the piston of the injection cylinder under
high pressure and switching the drive to a low-pressure drive at a
predetermined stroke of the piston, even if there are variations in
the amount of molten metal in a plunger sleeve of the mold.
[0020] In a second aspect of the present invention, according to
the above-mentioned first aspect, the piston (13) of the injection
cylinder (102) is first pressed under pressure by a high hydraulic
oil pressure supplied by the fast pressure-raising piston
accumulator (ACC-B) (22, 322) and operates at a fast injection
speed, and then is pressed under pressure by a low hydraulic oil
pressure supplied by the injection piston accumulator (ACC-A) (21,
321) and operates when the hydraulic oil pressure supplied by the
fast pressure-raising piston accumulator (ACC-B) (22, 322) is shut
off.
[0021] According to the present aspect, it is possible to suppress
the occurrence of surge pressure by switching the pressing force to
the low-pressure pressing force with a proper timing rather than
continuing to press under high pressure the piston of the injection
cylinder.
[0022] In a third aspect of the present invention, according to
either the above-mentioned first or second aspect, the fast
pressure-raising piston accumulator (ACC-B) (22) comprises an ACC-B
piston (221) that separates/forms a gas chamber (217) and a
hydraulic oil chamber (228) within the fast pressure-raising piston
accumulator (ACC-B) and reciprocates therein and a projection part
(222) fixed on the ACC-B piston (221) and extending up to the side
of the hydraulic oil chamber, and penetrating and extending through
an end wall (226) on the side of the hydraulic oil chamber of the
fast pressure-raising piston accumulator (ACC-B). The injection
piston accumulator (ACC-A) (21) comprises an ACC-A piston (211)
that separates/forms a gas chamber (217) and a hydraulic oil
chamber (218) within the injection piston accumulator (ACC-A) and
reciprocates therein. The projection part (222) is capable of
penetrating through an end wall (216) on the side of the gas
chamber of the injection piston accumulator (ACC-A) (21), invading
the gas chamber (217) of the injection piston accumulator (ACC-A)
(21), and detachably coming into contact with and pressing under
pressure the ACC-A piston (211).
[0023] According to the present aspect, by using the piston
accumulator (ACC) having the special structure as described above,
it is possible to avoid the discontinuity of speed at a fast
raising step, which is produced when a large-sized valve and check
valve are opened/closed etc., and ensure the continuity, and
therefore, a molded product of high quality can be manufactured.
Further, the piston accumulator (ACC) having the special structure
makes the installation space compact, and therefore, its
superiority can be exhibited in terms of cost.
[0024] In a fourth aspect of the present invention, according to
the above-mentioned third aspect, the fast pressure-raising piston
accumulator (ACC-B) (22) and the injection piston accumulator
(ACC-A) (21) are formed integrally into one unit.
[0025] According to the present aspect, a configuration is
provided, in which switching from the fast pressure-raising piston
accumulator (ACC-B) to the injection piston accumulator (ACC-A) can
be done smoothly and at the same time, a piston accumulator (ACC)
consisting of the fast pressure-raising piston accumulator and the
injection piston accumulator can be formed compact.
[0026] A fifth aspect of the present invention, according to any
one of the first to fourth aspects, further comprises a
pressure-increasing accumulator (23) for holding under pressure the
molten metal (15) in the mold at a predetermined pressure for a
predetermined period of time after the injection molding of the
molten metal.
[0027] According to the present aspect, the configuration of the
hydraulic device capable of ensuring the excellent quality of a
product is further clarified.
[0028] In a sixth aspect of the present invention, according to any
one of the first to fifth aspects, the injection cylinder inlet
valve (31) is capable of adjusting the flow rate of the hydraulic
oil from the piston accumulator (ACC) (20) to the injection
cylinder (102).
[0029] According to the present aspect, the configuration capable
of controlling the injection speed more excellently is further
clarified.
[0030] A seventh aspect of the present invention, according to any
one of the first to sixth aspects, further comprises a stroke
sensor (46) for detecting a stroke of the piston (13) of the
injection cylinder (102).
[0031] According to the present aspect, the configuration in which
the stroke of the piston of the injection cylinder is detected with
the stroke sensor in order to control the injection of the
injection cylinder is further clarified.
[0032] In an eighth aspect of the present invention, according to
the seventh aspect, the injection of the molten metal (15) is
controlled by the stroke sensor (46).
[0033] According to the present aspect, by detecting the stroke of
the piston of the injection cylinder with the stroke sensor, it is
possible to perform control, such as switching between high
pressure/low pressure of the drive (pressing) pressure for the
cylinder.
[0034] In a ninth aspect of the present invention, according to any
one of the first to eighth aspects, the hydraulic device further
comprises a pump. The pump is capable of supplying hydraulic oil to
the injection cylinder (102) and the piston accumulator (ACC)
(20).
[0035] According to the present aspect, the configuration of the
hydraulic device of the die casting machine of the present
invention is further clarified.
[0036] In a tenth aspect of the present invention, according to any
one of the first to ninth aspects, the pressure of the fast
pressure-raising piston accumulator (ACC-B) (22, 322) in its
initial state is set to 14 to 21 MPa and the pressure of the
injection piston accumulator (ACC-A) (21, 321) in its initial state
is set to 5 to 12 MPa.
[0037] According to the present aspect, the initially set pressure
of the fast pressure-raising piston accumulator and the injection
piston accumulator is clarified, and therefore, the configuration
of the drive (pressing under pressure) control of the injection
cylinder is further clarified.
[0038] A die casting machine (100) used in a die casting method in
an eleventh aspect of the present invention comprises a mold (101)
that cast-molds a product, an injection cylinder (102) for
injecting the molten metal (15) to the mold (101), and the
hydraulic device (103, 203) for pressing under high pressure the
injection cylinder (102). The hydraulic device (103, 203) comprises
a piston accumulator (ACC) (20) that supplies hydraulic oil, which
presses under pressure a piston (13) of the injection cylinder
(102), to the injection cylinder (102) and an injection cylinder
inlet valve (31) for releasing/closing the flow of the hydraulic
oil from the piston accumulator (ACC) (20) to the injection
cylinder (102). The piston accumulator (ACC) comprises a high
pressure fast pressure-raising piston accumulator (ACC-B) (22, 322)
and the low-pressure injection piston accumulator (ACC-A) (21,
321). The die casting method that uses such a die casting machine
is characterized by comprising a high-pressure injection step for
supplying high-pressure hydraulic oil from the fast
pressure-raising piston accumulator (22, 322) to the injection
cylinder (102) and pressing under pressure the piston (13) of the
injection cylinder (102) to inject molten metal and a low-pressure
injection step for supplying low-pressure hydraulic oil from the
injection piston accumulator (21, 321) to the injection cylinder
(102) when shutting off the hydraulic oil from the fast
pressure-raising piston accumulator (22, 322) to the injection
cylinder (102), and pressing under pressure the piston (13) of the
injection cylinder (102) to continue injection of molten metal.
[0039] With such a configuration, it is possible to suppress the
occurrence of surge pressure of molten metal in the cavity of a
mold, prevent the occurrence of burr and spouting of molten metal,
and further minimize the variations in the quality of molded
product on site in a die casting method capable of fast injection
molding by activating the piston of the injection cylinder under
high pressure and switching the drive to a low-pressure drive at a
predetermined stroke of the piston, even if there are variations in
the amount of molten metal in the plunger sleeve of the mold.
[0040] In a twelfth aspect of the present invention, according to
the eleventh aspect, the hydraulic device (103, 203) further
comprises a pressure-increasing accumulator (23) for holding under
pressure molten metal in the mold (101) at a predetermined pressure
for a predetermined period of time. The method further comprises a
step for further continuing to apply pressure to the molten metal
using the pressure-increasing accumulator (23) after the injection
of molten metal by the fast pressure-raising piston accumulator
(22, 322) and the injection piston accumulator (21, 321) is
completed.
[0041] According to the present aspect, the configuration of the
method is further clarified, which is capable of ensuring the
excellent quality of a product by applying pressure continuously to
molten metal using the pressure-increasing accumulator after the
completion of injection of molten metal.
[0042] In a thirteenth aspect of the present invention, according
to either the eleventh or the twelfth aspect, the hydraulic device
(103, 203) further comprises a pump, and the method further
comprises a step, before the high-pressure injection step and the
low-pressure injection step, for supplying hydraulic oil from the
pump to the injection cylinder (102) to move forward the piston
(13) of the injection cylinder (102).
[0043] According to the present aspect, the step for moving forward
the piston of the injection cylinder up to a predetermined position
in the previous stage of the commencement of injection molding is
further clarified.
[0044] In a fourteenth aspect of the present invention, according
to any one of the eleventh to thirteenth aspects, the hydraulic
device (103, 203) further comprises a stroke sensor (46) for
detecting a stroke of the piston (13) of the injection cylinder
(102). The high-pressure injection step and the low-pressure
injection step are commenced, respectively, based on the stroke of
the piston (13) detected by the stroke sensor (46).
[0045] According to the present aspect, the configuration of
control under which the high-pressure injection (drive of the
piston at a fast speed) is commenced and ended (i.e., the
commencement of the low-pressure injection) based on the stroke of
the piston (13) of the injection cylinder (102) is further
clarified.
[0046] A die casting machine according to a sixteenth aspect of the
present invention comprises a mold (101) that cast-molds a product,
an injection cylinder (102) for injecting molten metal (15) to the
mold (101) by moving a piston (13) comprised by itself (injection
cylinder), the injection cylinder (102) comprising a head chamber
(16H) that moves forward the piston (13) toward the mold (101) when
hydraulic oil is supplied thereto and a rod chamber (16R) that
moves back the piston (13) so that it moves away from the mold
(101) when hydraulic oil is supplied thereto, and a hydraulic
device (303) for supplying hydraulic oil to the injection cylinder
(102). In the die casting machine (100), the hydraulic device (303)
is characterized by comprising the injection piston accumulator
(20) that supplies hydraulic oil, which presses under pressure the
piston (13) of the injection cylinder (102), to the injection
cylinder (102), the injection piston accumulator (20) comprising a
hydraulic oil chamber (218) that stores hydraulic oil and a gas
chamber (217) that stores gas, the hydraulic oil chamber (218) and
the gas chamber (217) being partitioned in a fluidically tight
manner, a fast speed adjusting valve (31) for controlling/closing
the flow of hydraulic oil from the injection piston accumulator
(20) to the head chamber (16H) of the injection cylinder (102), and
a plurality of gas bottles (71, 72, 73) arranged in parallel so as
to communicate fluidically with the gas chamber (217) of the
injection piston accumulator (20) via respective switching valves
(75, 76, 77).
[0047] Preferably, in the die casting machine, the number of the
plurality of gas bottles is three and the ratio of internal volumes
between the three gas bottles is 1:2:4.
[0048] A die casting machine according to a sixteenth aspect of the
present invention comprises a mold (101) that cast-molds a product,
an injection cylinder (102) for injecting molten metal (15) to the
mold (101) by moving a piston (13) comprised by itself (injection
cylinder), the injection cylinder (102) comprising a head chamber
(16H) that moves forward the piston (13) toward the mold (101) when
hydraulic oil is supplied thereto (to the head chamber) and a rod
chamber (16R) that moves back the piston (13) so that it moves away
from the mold (101) when hydraulic oil is supplied thereto (to the
rod chamber), and a hydraulic device (403) for supplying hydraulic
oil to the injection cylinder (102). The hydraulic device (403)
comprises an injection piston accumulator (20) that supplies
hydraulic oil, which presses under pressure the piston (13) of the
injection cylinder (102), to the injection cylinder (102), the
injection piston accumulator (20) comprising a hydraulic oil
chamber (218) that stores hydraulic oil and a gas chamber (217)
that stores gas, the hydraulic oil chamber (218) and the gas
chamber (217) being partitioned in a fluidically tight manner, a
fast speed adjusting valve (31) for controlling/closing the flow of
hydraulic oil from the injection piston accumulator (20) to the
head chamber (16H) of the injection cylinder (102), and at least
one gas bottle (80) installed so as to communicate fluidically with
the gas chamber (217) of the injection piston accumulator (20) via
a filling force pattern adjusting valve (82). The filling force
pattern adjusting valve (82) is characterized by being capable of
variably setting its valve opening degree and adjusting the filling
force of hydraulic oil to the injection cylinder (102) by adjusting
the opening degree of the filling force pattern adjusting valve
(82).
[0049] Preferably, the die casting machine further comprises an
automatic control device. The automatic control device comprises an
operation circuit for selecting a filling force pattern using the
fast injection stroke and the fast injection speed of the injection
cylinder (102) as parameters, and is characterized in that the
opening degree of the filling force pattern adjusting valve (82) is
adjusted so as to match with the filling force pattern selected by
the operation circuit.
[0050] It is preferable for the hydraulic device (303, 403) to
further comprise a pressure-increasing accumulator (23) that
communicates fluidically with the head chamber (16H) of the
injection cylinder (102) and increases the pressure of molten metal
in the mold for holding the molten metal at a predetermined
pressure for a predetermined period of time after the injection
filling of molten metal, a pressure-increasing opening/closing
valve (35) installed between the pressure-increasing accumulator
(23) and the injection cylinder (102) and releasing/shutting off
the flow of hydraulic oil from the pressure-increasing accumulator
(23) to the injection cylinder (102), a pressure-increasing time
adjusting valve (78) installed in series to the pressure-increasing
opening/closing valve (35) between the pressure-increasing
accumulator (23) and the injection cylinder (102) and adjusting the
pressure-increasing time of the injected molten metal by changing
its opening degree, a hydraulic pump that communicate fluidically
with the head chamber (16H) and the rod chamber (16R) of the
injection cylinder (102), and an injection switching valve (26)
installed between the hydraulic pump and the injection cylinder
(102) and switching between guiding the flow of hydraulic oil from
the hydraulic pump to the head chamber (16H) of the injection
cylinder (102) and guiding it to the rod chamber (16R).
[0051] A die casting method using the die casting machine according
to the sixteenth aspect comprises a low-speed injection step for
pressing under pressure the molten metal (15) in the injection
cylinder (102) at a low speed and a fast injection step for
pressing under pressure and injecting the molten metal (15) in the
injection cylinder (102) at a high speed. The fast injection step
is characterized by comprising an opening setting procedure for
setting the opening degree of the filling force pattern adjusting
valve (82) in accordance with the fast injection speed and the
injection filling force.
EFFECT OF THE INVENTION
[0052] In particular, in the die casting method or die casting
machine capable of fast injection molding, by properly selecting a
combination of a plurality of gas bottles, a fast speed raising is
achieved in a brief time under high pressure at start time by
utilizing pressure drop of hydraulic oil in the accumulator due to
the expansion of gas without performing complicated control, the
fast speed value is reduced by spontaneous reduction in speed due
to the fluid resistance of the molten metal in the mold, the
pressure is reduced to an optimum value before the completion of
filling, and thus the impact value at the time of completion of
filling is relaxed and the fast injection molding is enabled, and
at the same time, the occurrence of surge pressure of molten
aluminum in the cavity of the mold is suppressed and the occurrence
of burr and spouting of molten metal, or scattering of tip of
molten metal, etc., are prevented.
[0053] Further, even if there are variations in the amount of
supply of molten metal, the plunger is reduced in speed
spontaneously before the position of the completion of filling due
to the fluid resistance of the molten metal that has flowed into
the mold, and therefore, the position of reduction in speed in the
mold is the same and thus the occurrence of surge pressure is
suppressed and the occurrence of burr and spouting of molten metal,
or scattering of tip of molten metal etc., are prevented.
[0054] The symbols in the parenthesis attached to each means
indicate the relationship of correspondence with specific means in
embodiments, which will be described later.
[0055] The present invention may be more fully understood from the
description of the preferred embodiments of the invention set forth
below, together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] FIG. 1 is a schematically explanatory diagram of a die
casting machine according to a first embodiment of the present
invention, showing a configuration in the vicinity of a mold 101
and an injection cylinder 102 of the die casting machine.
[0057] FIG. 2 is a system diagram of a hydraulic device 103 of a
die casting machine 100 according to the first embodiment of the
present invention.
[0058] FIG. 3 is a system diagram for explaining various operating
states (outline) of the die casting machine 100 in FIG. 1, showing
the flow of hydraulic oil at the time of a low-speed operation of a
piston of an injection cylinder etc.
[0059] FIG. 4 is a system diagram for explaining various operating
states (outline) of the die casting machine 100 in FIG. 1, showing
the flow of hydraulic oil at the time of a fast pressure-raising
operation of a piston of an injection cylinder etc.
[0060] FIG. 5 is a system diagram for explaining various operating
states (outline) of the die casting machine 100 in FIG. 1, showing
the flow of hydraulic oil at the time of an injection operation
etc.
[0061] FIG. 6 is a system diagram for explaining various operating
states (outline) of the die casting machine 100 in FIG. 1, showing
the flow of hydraulic oil at the time of a pressure-intensifying
operation etc.
[0062] FIG. 7 is a system diagram for explaining various operating
states (outline) of the die casting machine 100 in FIG. 1, showing
the flow of hydraulic oil at the time of a charging operation of an
injection piston ACC-A etc.
[0063] FIG. 8 is a system diagram for explaining various operating
states (outline) of the die casting machine 100 in FIG. 1, showing
the flow of hydraulic oil at the time of a charging operation of a
fast pressure-raising piston ACC-B etc.
[0064] FIG. 9 is a system diagram for explaining various operating
states (outline) of the die casting machine 100 in FIG. 1, showing
the flow of hydraulic oil at the time of a moving back operation of
an injection cylinder etc.
[0065] FIG. 10 is a system diagram of a hydraulic device 203 of a
die casting machine according to a second diagram of the present
invention, corresponding to FIG. 2.
[0066] FIG. 11 is a schematically explanatory section view of a
special piston accumulator (ACC) used in the die casting machine in
the first embodiment of the present invention.
[0067] FIG. 12 is a chart of the injection speed and metal pressure
in a conventional fast die casting method, wherein the horizontal
axis represents the stroke and time axis.
[0068] FIG. 13 is a chart of the injection speed and metal pressure
in a fast die casting method according to the present invention,
wherein the horizontal axis represents the stroke and time
axis.
[0069] FIG. 14 is a chart of a delay in pressure raising when a
fast output (pressure of a fast accumulator) with respect to
injection, showing a comparison by the pressure of accumulator.
[0070] FIG. 15 is an explanatory diagram of a device used in a test
to obtain the graph in FIG. 14.
[0071] FIG. 16 is a system diagram of a hydraulic machine of a die
casting machine according to a third embodiment of the present
invention.
[0072] FIG. 17 is a table showing the total amount of gas by
combinations when three kinds of gas bottle are used.
[0073] FIG. 18 is a graph showing the reduction in pressure of a
head chamber at the time of fast no-load injection (injection in a
state where there is no molten material) for eight kinds of total
gas capacity in an example of a die casting machine of 800-ton
class (the reduction in pressure with respect to the fast injection
stroke is shown).
[0074] FIG. 19 is a system diagram of a hydraulic device of a die
casting machine according to a fourth embodiment of the present
invention.
[0075] FIG. 20 shows an explanatory diagram of the change of a
filling force pattern by the change of the opening degree of a
filling force pattern adjusting valve, showing the change of the
pressure (PH) (MPa) in a head chamber with respect to the time
progress when the fast injection speed is 2 (m/sec) (this graph is
referred to as a filling force pattern).
[0076] FIG. 21 shows an explanatory diagram of the change of a
filling force pattern by the change of the opening degree of a
filling force pattern adjusting valve, showing the change of the
pressure (PH) (MPa) in a head chamber with respect to the time
progress when the fast injection speed is 5 (m/sec).
[0077] FIG. 22 shows an explanatory diagram of the change of a
filling force pattern by the change of the opening degree of a
filling force pattern adjusting valve, showing the change of the
pressure (PH) (MPa) in a head chamber with respect to the time
progress when the fast injection speed is 8 (m/sec).
[0078] FIG. 23A is a chart showing the change of the injection
speed, the injection pressure (pressure in a head chamber 16H of
the injection cylinder 102), etc. with respect to the time
progress, and the state of a piston rod, each valve, etc., at that
time in the third embodiment, showing the upper part of the
chart.
[0079] FIG. 23B is a chart showing the change of the injection
speed, the injection pressure (pressure in the head chamber 16H of
the injection cylinder 102), etc. with respect to the time
progress, and the state of a piston rod, each valve, etc., at that
time in the third embodiment, showing the lower part of the
chart.
[0080] FIG. 24A is a chart showing the change of the injection
speed, the injection pressure (pressure in the head chamber 16H of
the injection cylinder 102), etc. with respect to the time
progress, and the state of a piston rod, each valve, etc., at that
time in the fourth embodiment, showing the upper part of the chart,
a diagram similar to that in FIG. 23A.
[0081] FIG. 24B is a chart showing the change of the injection
speed, the injection pressure (pressure in the head chamber 16H of
the injection cylinder 102), etc. with respect to the time
progress, and the state of a piston rod, each valve, etc., at that
time in the fourth embodiment, showing the lower part of the chart,
a diagram similar to that in FIG. 23B.
[0082] FIG. 25 is an explanatory diagram of the injection speed of
ultrafast injection speed molding etc., showing a positional
relationship when injection is completed for the amount of molten
metal etc.
[0083] FIG. 26 is an explanatory diagram for illustrating a
mechanism of the occurrence of defect when the amount of molten
material runs short and the reduction in speed finishes before
filling is completed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0084] A die casting machine (device) in embodiments of the present
invention is explained below in detail based on the drawings. FIG.
1 is a schematically explanatory diagram of a part in the vicinity
of a mold 101 and an injection cylinder 102 of a common die casting
machine 100 for light metal, such as aluminum, as already
explained, and the die casting machine 100 of the present invention
also comprises the same mold 101 and the injection cylinder 102.
FIG. 2 is a system diagram of a first embodiment of the die casting
machine 100 according to the present invention and FIGS. 3 to 9 are
system diagrams for explaining various operating states (outline)
of the die casting machine 100 in FIG. 1. FIG. 11 is a
schematically explanatory section view of a special piston
accumulator (ACC) 20 used in the die casting machine 100 in the
first embodiment of the present invention.
[0085] First, referring to FIG. 1, the mold 101 and the injection
cylinder 102 of the die casting machine 100 of the present
invention are shown schematically. Although FIG. 1 is already
explained in the explanation of the prior art, it is explained in
more detail here. Normally, the die casting machine 100 in FIG. 1
casts a product of light metal, such as aluminum. The die casting
machine 100 comprises the mold 101 and the injection cylinder 102
and in the mold 101, a fixed mold 8 and a movable mold 9 are
provided between a pair of fixed platen 10 and movable platen 11
opposing each other and as shown in FIG. 1, by the engagement of
the fixed mold 8 and the movable mold 9, a cavity (hollow) 12 is
formed therebetween and molten aluminum (AL) 15 is injected/filled
in the cavity 12 and thus a molded product is produced. The
injection cylinder 102 is provided in order to inject the molten
aluminum 15 and the fixed platen 10 is provided with a plunger
sleeve 7 that can store the molten aluminum 15 and the plunger
sleeve 7 penetrates through the fixed platen 10 and the fixed mold
8 and communicates fluidically with the cavity 12.
[0086] In the present embodiment, the injection cylinder 102 is a
hydraulic-driven reciprocating piston/cylinder for injecting molten
aluminum. The injection cylinder 102 comprises a cylinder 6 and a
piston 13. The piston 13 engages with the plunger sleeve 7 as shown
in FIG. 1. The piston 13 comprises a piston head 5 at its left end
in FIG. 1 and a plunger rod 2 is linked to a piston rod 4
integrated with the piston head 5 by an injection coupling 3 and at
the front end of the plunger rod 2, a plunger tip 1 is attached.
The plunger tip 1 is inserted into the plunger sleeve 7,
reciprocates within the plunger sleeve 7, and pumps under pressure
the molten aluminum 15 in the plunger sleeve 7, and thereby, the
molten aluminum 15 is injected and filled. In the present
embodiment, the injection cylinder 102 is of hydraulic type, and
therefore, it supplies hydraulic oil to the head side of the
cylinder 6 to drive the piston head 5 and the piston rod 4 and
presses the molten aluminum (AL) 15 stored in the plunger sleeve 7
to inject and fill it into the cavity (hollow) 12 within the fixed
mold 8, 9, and thus a molded product is molded.
[0087] FIG. 2 illustratively shows the hydraulic circuit of a
hydraulic device 103 in the first embodiment of the present
invention, which drives the injection cylinder 102. On the line on
the inlet side of a head chamber 16H of the cylinder 6, a seventh
valve 31 that controls the injection speed and the piston ACC
(accumulator) 20 capable of discharging oil at a high flow rate for
fast (high-speed) injection are provided, and in the present
embodiment, that the piston ACC (accumulator) 20 has a preferred
configuration is one of the characteristics. The piston ACC 20 is
divided into two parts, that is, an upper part and a lower part,
and a piston 221 in a fast pressure-raising piston ACC
(accumulator)-B 22 at the upper part has a projection part 222 of a
rod part and the projection part 222 presses the upper surface of a
piston 211 of an injection piston ACC (accumulator)-A 21 at the
lower part. In the fast pressure-raising piston ACC-B 22 at the
upper part, a high-pressure gas (for example, 14 MPa) is
accumulated under pressure, which is detected/managed by a pressure
sensor-Pb 44 and in the injection piston ACC-A 21 at the lower
part, a low-pressure gas (for example, 6 MPa) is accumulated under
pressure, which is detected/managed by a pressure sensor-Pa 43.
Although depending on the capacity of the accumulator, it is
preferable to set the accumulation pressure (in particular, initial
pressure) of the high-pressure gas in the fast pressure-raising
piston ACC-B 22 in a range between 14 and 21 MPa and the
accumulation pressure (in particular, initial pressure) of the
low-pressure gas in the injection piston ACC-A 21 in a range
between 5 and 12 MPa.
[0088] Next, the function of each valve comprised by the hydraulic
device 103 in the present embodiment is explained. A first valve 24
is installed between a pump pressure supply inlet and the injection
cylinder 102 and provided for the purpose of introducing
pressurized hydraulic oil from a pump (not shown) to the head
chamber 16H of the cylinder 6 for low-speed injection forward
movement. A second valve 25 is installed between a tank 40 and the
injection cylinder 102 and provided for the purpose of returning
the hydraulic oil in the head chamber 16H of the cylinder 6 for
injection back movement. A third valve 26 is installed between the
pump pressure supply inlet and the injection cylinder 102 and
provided for the purpose of introducing hydraulic oil from a pump
(not shown) to a rod chamber 16R of the cylinder 6 for injection
back movement. A fourth valve 27 is installed between the tank 40
and the injection cylinder 102 and provided for the purpose of
returning hydraulic oil in the head chamber 16H of the cylinder 6
for injection forward movement. A fifth valve 28 is installed on
the side of the hydraulic oil exit of the fast pressure-raising
piston ACC-B 22 and provided for the purpose of causing the fast
pressure-raising piston ACC-B 22 at the upper part to start
descending at a high speed and stop in the middle of injection. A
sixth valve 29 is installed between the piston ACC 20 and the
injection cylinder 102 and provided for the purpose of introducing
hydraulic oil at a high speed to the ACC (accumulators)-(A and B)
21, 22. The seventh valve 31 is installed between the sixth valve
29 and the injection cylinder 102 and provided for the purpose of
controlling the injection speed.
[0089] An eighth valve 32 is provided for the purpose of supplying
hydraulic oil to the piston ACC 20 from the pump. A ninth valve 33
is provided for the purpose of compressing the gas in a gas
bottle-a 41 to a target pressure. A tenth valve 34 is provided for
the purpose of compressing the gas in a gas bottle-b 42 to a target
pressure. The eighth to tenth valves 32, 33, 34 are installed
between the pump pressure supply inlet and the piston ACC 20,
between the pump pressure supply inlet and the gas bottle-a 41, and
between the pump pressure supply inlet and the gas bottle-b 42,
respectively. An eleventh valve 35 is provided between a
pressure-increasing ACC (accumulator) 23 and the injection cylinder
102 for the purpose of supplying hydraulic oil at a preset pressure
into the cylinder head chamber 16H of the cylinder 6 by the
hydraulic pressure from the pressure-increasing ACC (accumulator)
23. On the exit side (the injection cylinder side) of the eleventh
valve 35, a variable speed controller 36 is provided and preferably
capable of pressurizing (pressure-intensifying) a molded product at
a fixed pressure and at the same time, of adjusting the flow rate
(pressurizing rate) of hydraulic oil. Preferably, the seventh valve
31 is driven by a motor, however, it may be another type that is
driven by hydraulic pressure, pneumatic pressure, etc. Preferably,
the first to eleventh valves except for the seventh valve 31 are an
electromagnetic valve, however, they may be one of another type.
FIG. 2 shows a preferred hydraulic circuit.
[0090] Next, the operation of the hydraulic device 103 (therefore,
the operation of the injection cylinder 102) is explained.
[0091] First, before use, the eighth valve 32 is turned ON
(conduction (open) state, that is, pump pressure is supplied),
pistons of ACC 21, 22 at the upper and lower parts are pushed up to
the upper limit, and the gas in the gas bottle-a 41 is pressurized
to a target pressure (for example, 6 MPa) by turning ON the ninth
valve 33 (conduction (open) state, that is, pump pressure is
supplied). Similarly, the gas in the gas bottle-b 42 is pressurized
to a target pressure (for example, 14 MPa) by turning ON the tenth
valve 34 (conduction state, that is, pump pressure is supplied). It
is preferable to pressurize so that the target pressure in the gas
bottle-a 41 is 5 to 12 MPa and the target pressure in the gas
bottle-b 42 is 14 to 21 MPa.
[0092] In FIG. 3, the operation of the device at the time of
low-speed traveling of the piston 13 is explained by explaining the
flow of hydraulic oil. The first valve 24 and the fourth valve 27
are turned ON. Next, the seventh valve 31 for controlling speed is
opened gradually until a target piston speed is reached. The
hydraulic oil from a pump (not shown) is introduced into the
cylinder head chamber 16H of the cylinder 6 from the first valve 24
at a flow rate limited by the seventh valve 31 for controlling
speed, and the hydraulic oil in the cylinder rod chamber 16R is
returned from the fourth valve 27 to the tank 40 and the piston rod
4, the plunger rod 2, and the plunger tip 1 (piston 13) move
forward at a low speed (state between T0 and T1 in FIG. 13).
[0093] When the piston 13 moves forward and a stroke sensor-Sa 46
detects that a high-speed switching position is reached (T1 point
in FIG. 13), the hydraulic circuit switches from the state in FIG.
3 to the state in FIG. 4. In FIG. 4, the fifth valve 28 and the
sixth valve 29 are turned ON and the seventh valve 31 for
controlling speed opens wide. At this time, the fast
pressure-raising piston ACC-B 22 at the upper part presses down
under high pressure the piston 211 of the injection piston ACC-A 21
at the lower part (here, for example, it starts at 14 MPa) and high
pressure oil is supplied into the head chamber 16H of the cylinder
6 and it moves forward with high output, and therefore, the speed
of the piston 13 is increased to a high speed value in a very short
stroke. The stroke of the piston 13 is detected by the stroke
sensor-Sa 46 and the piston 13 is moved forward about 50 to 100 mm
and then the fifth valve 28 is turned OFF at the position included
in the normal injection region. The timing with which the fifth
valve 28 is turned OFF is obtained from a test and set so that a
good casting can be obtained.
[0094] The state of the hydraulic circuit at this time is shown in
FIG. 5. The discharge exit of the fast pressure-raising piston
ACC-B 22 at the upper part is closed, and therefore, it stops
descending and the injection operation is continued by only the
injection piston ACC-A 21 at the lower part. However, the gas
pressure to move the piston is low (low pressure of the gas
bottle-a 41, here, about 6 MPa, for example) and therefore the
molten aluminum (AL) 15 is cooled down while it flows into the
cavity 12 within the mold and its viscosity increases. And the
piston 13 reduces its speed while balancing with the resistance of
the molten aluminum and thus the filling of the molten aluminum 15
is completed in a state with less shock.
[0095] The difference between the present invention and the
conventional example is explained with reference to FIG. 12 and
FIG. 13, particularly as to the injection speed and the metal
pressure. FIG. 12 and FIG. 13 are charts of the injection speed and
the metal pressure Pm (pressure of molten aluminum in the cavity
within the mold) in the fast (high speed) casting method, wherein
the horizontal axis denotes the stroke (mm) and time (msec) and the
vertical axis denotes the injection speed (m/sec) represented by a
dotted line and the metal pressure (MPa) represented by a solid
line, corresponding to the conventional example and the present
invention, respectively. In the conventional example in FIG. 12,
when the high pressure raising of the piston of the injection
cylinder commences at time T11, the injection speed (V) increases
instantaneously and the metal pressure increases temporarily at
this time. Further, the piston is kept on being pressed under high
pressure continuously, however, this conventional example is a case
where the amount of molten metal in the sleeve 7 is large and where
the timing (point T12) with which the pressing pressure of the
piston is reduced is delayed relatively. If the timing is delayed,
a surge pressure occurs, i.e., the metal pressure increases rapidly
near T12. This surge pressure causes the occurrence of burr and
spouting of molten metal.
[0096] On the other hand, in the case of the present invention
shown in FIG. 13, the state of high pressure raising and after that
(from T0 to T2) is the same as that in the conventional example,
however, at the point T2, the pressure to press the piston 13 is
switched to a lower one. At this point T2, the metal pressure does
not increase yet and the piston is kept on being pressed under low
pressure and moves forward by the inertial force of the piston
itself, however, due to the resistance of the metal pressure Pm,
the speed of the piston 13, that is, the injection speed V reduces
gradually. Although the piston speed reduces, the piston 13 is kept
on being pressed under low pressure, and therefore, the piston 13
further moves forward, the metal pressure begins to increase near
point T3 and finally it reaches a predetermined metal pressure. As
described above, in the case of the present invention, no surge
pressure occurs, and therefore, it is unlikely that the occurrence
of burr and spouting of molten metal are caused.
[0097] In the state of the hydraulic circuit shown in FIG. 6, after
the filling of the molten metal 15 into the cavity is completed,
the first valve 24 is turned OFF, the eleventh valve 35 is turned
ON, the piston head 5 of the injection cylinder 102 is pressed by
the pressure-increasing ACC (accumulator) 23, and the molded
product is pressurized at the preset metal pressure Pm.
[0098] FIG. 7 shows a state where hydraulic oil is charged to the
piston ACC (accumulator) 20 while the solidification of molten
aluminum of the molded product is awaited with continuous
application of pressure. The eighth valve 32 is turned ON (and the
fifth valve 28 is kept in the OFF state) and hydraulic oil is
introduced from a pump (not shown) into hydraulic oil chambers 218,
228 of the piston ACC 20. Because the injection piston ACC 21 at
the lower part is under lower pressure, the piston 211 at the lower
part ascends first. When the piston 211 at the lower part of the
piston ACC 20 ascends and hits the projection part 222 of the
piston 221 at the upper part, the charge of the fast
pressure-raising piston ACC-B 22 at the upper part begins. The
state of the hydraulic circuit at that time is shown in FIG. 8.
[0099] Next, the state at the time of back movement of injection in
FIG. 9 is explained. The second valve 25 and the third valve 26 are
turned ON. The hydraulic oil from a pump is introduced into the rod
chamber 16R of the cylinder 6 through the third valve 26 and the
hydraulic oil in the rod chamber 16H passes through a branch line
between the seventh valve 31 and the injection cylinder 102 and is
returned through the second valve 25 to the tank 40 via a check
valve installed on the line, and the piston 13, that is, the piston
rod 4, the plunger rod 2, and the plunger tip 1 move back (move
back so that the volume of the cylinder head chamber 16H
decreases).
[0100] Next, with reference to FIG. 11, the piston ACC
(accumulator) 20 in the first embodiment of the present invention
is explained. FIG. 11 is a schematic transverse section view of the
piston ACC (accumulator) 20. As already explained, the piston ACC
(accumulator) 20 comprises the fast pressure-raising piston ACC-B
22 at the upper part and the injection piston ACC-A 21 at the lower
part, and the fast pressure-raising piston ACC-B 22 at the upper
part and the injection piston ACC-A 21 at the lower part are
linked. At the linking portion, the two accumulators (ACC) are
linked so that a lower wall 226 of the fast pressure-raising piston
ACC-B 22 at the upper part and an upper wall 216 of the injection
piston ACC-A 21 at the lower part are closely arranged and in the
center of the walls 226, 216, a through hole 202 is provided and at
the same time, a sealing mechanism 201 is also provided.
[0101] The fast pressure-raising piston ACC-B 22 comprises the
piston 221 and the projection part 222 attached to the center of
the piston 221 in the downward direction and preferably in the form
of a cylindrical rod. The projection part 222 slidably penetrates
through the through hole 202 and the sealing mechanism 201 and the
sealing mechanism 201 seals the projection part 222 in the form of
a cylindrical rod and separates hermetically the hydraulic oil
chamber 228 of the fast pressure-raising piston ACC-B 22 at the
upper part from a gas chamber 217 of the injection piston ACC-A 21
at the lower part.
[0102] The fast pressure-raising piston ACC-B 22 comprises a gas
chamber 227 at the upper part and the hydraulic oil chamber 228 at
the lower part and the gas chamber 227 and the hydraulic oil
chamber 228 are sealed hermetically by the piston 221. The
injection piston ACC-A 21 also comprises the gas chamber 217 at the
upper part and the hydraulic oil chamber 218 at the lower part and
the gas chamber 217 and the hydraulic oil chamber 218 are sealed
hermetically by the piston 211. An upper wall in opposition to the
piston 221 of the fast pressure-raising piston ACC-B 22 is provided
with a high-pressure gas inlet 224, which connects a gas
supply/discharge line from the gas bottle-b 42 to the gas chamber
227. A sidewall near the lower wall 226 of the fast
pressure-raising piston ACC-B 22 is provided with a hydraulic oil
discharge exit 225, to which a hydraulic oil supply/discharge line
from the hydraulic oil chamber 228 is connected. A lower wall in
opposition to the piston 211 of the injection piston ACC-A 21 is
provided with a hydraulic oil discharge exit 215, to which a
hydraulic oil supply/discharge line to the hydraulic oil chamber
218 is connected. A sidewall near the upper wall 216 of the
injection piston ACC-A 21 is provided with a low-pressure gas inlet
214, to which a gas supply/discharge line from the gas bottle-a 41
to the gas chamber 217 is connected. With the configuration of the
piston ACC 20 described above, the above-mentioned operations of
the hydraulic circuit of the hydraulic device 103 in the present
embodiment are enabled.
[0103] A second embodiment of the present invention is shown in
FIG. 10. Referring to FIG. 10, the constituent parts in FIG. 10 the
same as or similar to those in the first embodiment shown in FIGS.
2 to 9 are specified by the same reference symbols. A die casting
machine in the second embodiment is configured for the same purpose
as that of the die casting machine in the first embodiment
described above, and by comparison with the first embodiment, only
a hydraulic device 203 is different. That is, the mold 101 and the
injection cylinder 102 are completely the same as those in the
first embodiment. In a hydraulic circuit shown in FIG. 10, the
injection piston ACC (accumulator)-A 21 and the fast
pressure-raising piston ACC (accumulator)-B 22 of the piston ACC 20
in the first embodiment are replaced with an injection piston ACC
(accumulator)-A 321 and a fast pressure-raising piston ACC
(accumulator)-B 322, as separate units, respectively, in the second
embodiment, and this point is a difference between the first
embodiment and the second embodiment. The injection piston ACC-A
321 and the fast pressure-raising piston ACC-B 322 are not an
accumulator having a special structure, as the piston ACC 20 in the
first embodiment, but both have a structure of an already known
general accumulator.
[0104] As described above, by dividing the single piston
accumulator (ACC) into two separate accumulators, in the second
embodiment in FIG. 10, a hydraulic system around the injection
piston ACC-A 321 and the fast pressure-raising piston ACC-B 322
also differs from that in the first embodiment. That a fifth valve
228 is provided between the hydraulic pressure connection inlet of
the fast pressure-raising piston ACC-B 322 and the sixth valve 29
is the same as that in the first embodiment, however, a hydraulic
oil filling line (line from the eighth valve 32) 51 to the two
accumulators 321, 322 is connected to a line (pipe) between the
fifth valve 228 and the high-pressure-raising piston ACC-B 322 (M
point). The line 51 also connects to, as in the first embodiment, a
line 52 from the hydraulic oil exit of the injection piston ACC-A
321 (N point), and therefore, on the line 51, a check valve 37 is
provided between the M point and the N point. The check valve 37
prevents hydraulic oil from flowing from the fast pressure-raising
piston ACC-B 322 under high pressure into the injection piston
ACC-A 321 under low pressure.
[0105] A line 53 that connects to the inlet side of the sixth valve
29 from the fast pressure-raising piston ACC-B 322 under high
pressure via the fifth valve 228 joins the line 52 from the
hydraulic oil exit of the injection piston ACC-A 321 under low
pressure at P point as shown in FIG. 10. Consequently, because
there is a possibility that high-pressure hydraulic oil may flow
into the injection piston ACC-A 321 under low pressure via the line
53, the injection piston ACC-A 321 under low pressure is provided
with a check valve 38 between the N point and the P point on the
line 52 to prevent this, and thus, the high-pressure hydraulic oil
is prevented from flowing into the injection piston ACC-A 321.
Because of such a configuration as described above, the fifth valve
228 in the second embodiment has a structure different from that of
the fifth valve 28 in the first embodiment as can been seen from
comparison between FIG. 2 and FIG. 10, that is, a structure in
which the line is closed at the OFF time, not a structure in which
a system that communicates with the tank 40 is formed at the OFF
time.
[0106] Next, the operation of the device is explained, which
relates to the difference between the first embodiment and the
second embodiment. In the second embodiment also, the piston 13 of
the injection cylinder 102 is activated under high pressure by the
fast pressure-raising piston ACC-B 322 and the speed of the piston
is increased to a high speed in a short stroke. At this time, the
fifth valve 228 and the sixth valve 29 are set to the ON state.
Then, the piston 13 is moved forward about 50 to 100 mm by
similarly detecting that the piston stroke reaches a predetermined
value with the stroke sensor-Sa 46 and the fifth valve 228 is
turned OFF at the position where the normal injection region is
entered.
[0107] Although the exit side of the fast pressure-raising piston
ACC-B 322 is closed, the sixth valve 29 is in the ON state, and
therefore, the injection operation is continued by only the
injection piston ACC-A 321. The gas pressure to move the piston is
low (low pressure of the gas bottle-a 41, here, about 6 MPa, for
example) and therefore the molten aluminum (AL) is cooled down
while it flows into the cavity 12 within the mold and its viscosity
increases, and the piston 13 reduces its speed while balancing with
the resistance of the molten AL and thus the filling is completed
in a state with less shock (the same as that in the first
embodiment). As described above, the operation of the hydraulic
circuit is substantially the same as that in the first embodiment.
Other operations of the hydraulic circuit, i.e., the operation up
to the activation of the fast pressure-raising piston ACC-B 322,
the operation of the pressure-increasing ACC 23, the operation to
return the piston 13 of the injection cylinder 102 after injection
molding, the operation to fill the hydraulic oil chamber of the
fast pressure-raising piston ACC-B 322 and the injection piston
ACC-A 321, etc., are the same as those in the first embodiment. The
configuration of the second embodiment other than the above is
basically the same as that in the first embodiment, and therefore,
an explanation is omitted to avoid duplication.
[0108] FIG. 16 illustratively shows a hydraulic circuit of a
hydraulic device 303 in a third embodiment of the present
invention, which drives the injection cylinder 102. On a connection
inlet line to the head chamber 16H of the cylinder 6, the injection
piston accumulator (ACC) 20 is provided so as to communicate
fluidly therewith, which is capable of discharging at a high flow
rate for fast injection via the fast speed adjusting valve (the
seventh valve) 31 that controls the injection speed. In general,
the cylindrical injection piston accumulator 20 is partitioned into
two chambers by the piston 211 that slides and reciprocates in the
piston accumulator 20, one of them is the hydraulic chamber 218 in
which hydraulic oil is stored and the other is the gas chamber 217
in which gas is stored. The gas chamber 217 is provided with
high-pressure gas from a gas bottle to press under pressure the
piston 211 to supply the hydraulic oil in the hydraulic oil chamber
to the hydraulic circuit of the hydraulic device 303, that is, the
head chamber 16H of the injection cylinder 102. In the present
embodiment, the gas chamber 217 communicates fluidly with first,
second, and third gas bottles 71, 72, 73 in parallel via three
switching valves, that is, first, second, and third switching
valves 75, 76, 77 as shown in FIG. 16. In the hydraulic device 303
in the present embodiment, as shown in FIG. 16, the head chamber
16H of the injection cylinder 102 further communicates fluidly with
the pressure-increasing piston accumulator (ACC) 23 via a
pressure-increasing time adjusting valve 78 and the
pressure-increasing opening/closing valve (eleventh valve) 35.
[0109] The connection inlet line of the rod chamber 16R of the
injection cylinder 102 communicates fluidly with the tank 40 via
the tank switching valve (fourth valve) 27 and also communicates
fluidly with a pump pressure supply inlet 55 via the injection
switching valve (third valve) 26. The connection inlet of the head
chamber 16H connects to another connection inlet of the injection
switching valve (third valve) 26. It is preferable for the
injection switching valve (third valve) 26 to be an electromagnetic
switching valve having three switching positions and as shown in
FIG. 16, the two connection inlets on one side connect to the
connection inlet of the head chamber 16H of the injection cylinder
102 and to the connection inlet of the rod chamber 16R,
respectively, and the two connection inlets on the other side
connect to the tank 40 and the pump pressure supply inlet
(discharge exit of the hydraulic pump) 55, respectively.
[0110] Each valve of the hydraulic device 303 shown in FIG. 16 is
explained. It is preferable for the fast speed adjusting valve
(seventh valve) 31 to be a motor-driven valve capable of changing
the valve opening degree continuously from the fully-open position
to the fully-closed position. It is preferable for the
pressure-increasing time adjusting valve 78 to be a motor-driven
throttle valve capable of changing the valve opening degree
continuously and eventually adjusting the pressure-increasing time
by changing the resistance of the flow passage. The injection
switching valve (third valve) 26 is already explained. The three
positions are a flow passage closing position, a forward flow
passage opening position, and an intersecting flow passage opening
position, as shown schematically in FIG. 16. It is preferable for
the first, second, and third switching valves 75, 76, 77 of the gas
bottle, the pressure-increasing opening/closing valve (eleventh
valve) 35, and the tank switching valve (fourth valve) 27 to be an
electromagnetic switching valve that switches between open and
close.
[0111] Next, the operation of the die casting machine 100 and the
hydraulic device 303 in the present embodiment is explained. The
overall operation of the die casting machine 100 is the same as
that of a normal die casting machine, and therefore, explanation is
given roughly. First, the molten AL 15 is supplied to the plunger
sleeve 7 and the injection operation is performed without delay
before the temperature of the molten metal reduces. First, the
molten metal 15 is pressed by the piston 13 at a low speed toward
the cavity 12 of the mold 101 (low-speed injection stage). At this
time, the drive of the piston 13 may be performed by operating the
injection switching valve 26 so that the hydraulic pump (or pump
pressure supply inlet, i.e. variable pump, or combination of
constant discharge pump and flow rate control valve) 55 supplies
hydraulic oil to the head chamber 16H in the present embodiment, or
may be performed by driving a booster (not shown) with a servo
motor (not shown) to supply hydraulic oil to the head chamber 16H
of the injection cylinder 102 in a hybrid die casting machine. In
other die casting machines, the drive is performed similarly by
supplying hydraulic oil to the head chamber 16H of the injection
cylinder 102. When the piston 13 has moved a predetermined stroke
or the piston 13 has reached a predetermined position, the
low-speed injection stage is switched to the fast injection stage.
Next, the fast speed adjusting valve (seventh valve) 31 is
activated to drive the piston 13 at a high speed (fast injection
stage). In this fast injection stage, the novel configuration of
the present invention effectively functions. In this fast injection
stage, the cavity 12 is filled with the molten metal 15. Next, the
fast speed adjusting valve (seventh valve) 31 is closed and at the
same time, the pressure-increasing opening/closing valve (eleventh
valve) 35 is opened, the hydraulic oil in the pressure-increasing
piston accumulator 23 is introduced to the head chamber 16H, and
the pressure in the cavity is increased to a predetermined pressure
in a predetermined period of time (pressure-increasing stage).
Next, the predetermined pressure is held for a predetermined period
of time (pressure-holding stage). After that, the product is
extracted (mold-opening stage). The above is the outline of the
injection molding process.
[0112] Next, the operation of the hydraulic device 303 in the
present embodiment is explained. In the example shown in FIG. 16,
it is preferable to comprise three gas bottles different in
capacity from one another. However, the number of gas bottles may
be less (two) or more (four or more). In the present embodiment, in
order to give more specific explanation, it is assumed that the die
casting machine is of 800-ton class. In this case, it is preferable
for the gas chamber capacity of the injection piston accumulator 20
to be 10 L (liters). In this case, it is preferable for the
diameter of the piston head 5 of the injection cylinder 102 to be
150 mm, for the stroke (fast stroke) of the piston 13 of the
injection cylinder 102 at the fast injection step to be 200 mm or
more, and for the charge pressure (pressure in the gas chamber 217
before the injection operation) of the injection piston accumulator
20 to be 18.6 MPa. In this case, according to the gas chamber
capacity (10 L) of the injection piston accumulator 20, it is
preferable for the capacity of the first gas bottle 71 to be 10 L,
for that of the second gas bottle 72 to be 20 L, and for that of
the third gas bottle 73 to be 40 L, respectively, for the
capacities of the three gas bottles. In this manner, it is
preferable for the ratio between the capacities of the three gas
bottles to be 1:2:4.
[0113] In the present embodiment, the three gas bottles 71, 72, 73
having three kinds of capacity are provided, and therefore, there
can be conceived eight combinations as a total capacity of the gas
bottles that press under pressure the injection piston accumulator
(refer to Table in FIG. 17). That is, it can be seen from this
Table in FIG. 17 that these eight combinations can be realized by
operating the first, second, and third switching valves 75, 76, 77
attached to each gas bottle. That is, when all of the three
switching valves 75, 76, 77 are closed, the gas bottle capacity is
0 L and the effective total gas capacity is the capacity 10 L of
the gas chamber 217. Similarly, when only the first switching valve
75 is opened, the total gas capacity is 20 L, when all of the three
switching valves 75, 76, 77 are opened, the total gas capacity is
gas bottle total capacity 70 L+gas chamber capacity 10 L, that is,
80 L. A graph is shown in FIG. 18, which shows the pressure drop in
the head chamber 16H in a specific mold at the fast injection step
for the eight kinds of total gas capacity of the gas bottles in the
example of the die casting machine of 800-ton class (pressure drop
in the fast injection stroke is shown). FIG. 18 may be obtained by
actually operating the injection system (no-load injection), or may
be obtained by calculation (adiabatic expansion change of gas). The
larger the total gas capacity of the gas bottle, the less is the
pressure drop and the higher is the average pressure to press the
piston 4, and therefore, the injection speed is increased.
[0114] According to the present embodiment, the method is one for
realizing a fast injection speed by selecting an optimum
combination of gas bottles (operating the opening/closing of
switching valves) in accordance with the characteristics (capacity
of the cavity and projection area) of a mold for molding and at the
same time, for preventing the occurrence of surge pressure etc. by
utilizing pressure drop that occurs in the expansion of a gas
caused at the fast injection step to spontaneously reduce the
speed.
[0115] In an actual operation, it is preferable to perform a trial
injection as follows, as a method for determining an injection
speed, a final filling force (hydraulic pressure on the side of the
injection cylinder head: PH), and a holding pressure with which a
high-quality molded product can be molded. In this method, first,
in order to avoid damage to the mold, injection is started at a low
speed (about 2 m/sec), a low pressure (about 10 MPa), and a holding
pressure of about 5 MPa. If the injection speed is low, molten
metal solidifies in the middle of filling and the misrun of molten
metal occurs, and therefore, the injection speed is increased if
the run of molten metal is not sufficient by checking a molded
product. At this time, if the set value of the final filling force
is small (the total gas capacity is small), the injection speed
drops below the set value during the injection operation because
the fluid resistance reduces the filling force too much, and
therefore, the measured data of the speed is checked and when the
drop is remarkable, the final filling force is also increased (the
total gas capacity is increased) and adjustment is made so that the
fast injection speed spontaneously reduces and the process transits
smoothly to the pressure-increasing process and the
pressure-holding process. When burr occurs as a result of an
increase in the final filling pressure, the final filling pressure
is reduced. Then, when there is no problem about the run of molten
metal or burr, the holding pressure is increased and the occurrence
of casting blow hole, shrinkage, and cold shut defect are avoided.
In addition, the opening degree of the pressure-increasing time
adjusting valve 78 is changed and thereby the pressure-increasing
time is also adjusted. In order to further improve the quality, the
injection speed is increased again and the quality is checked.
[0116] FIG. 23 shows a chart representing the change of the
injection speed, the injection pressure (pressure in the head
chamber 16H of the injection cylinder 102), etc. with respect to
the time progress, and the state of the piston rod, each valve,
etc., at that time in the present embodiment. In FIG. 23, PH
denotes the pressure in the head chamber 16H and Pm denotes the
holding pressure of the pressure-increasing piston accumulator. In
FIG. 23, the low-speed injection stage corresponds to time between
t0 and t1, the fast injection stage corresponds to time between t1
and t2, the pressure-increasing stage corresponds to time between
t2 and t3, and the pressure-holding stage corresponds to time
between t3 and t4. At t2, switching from the fast injection stage
to the pressure-increasing stage (that is, switching of the fast
speed adjusting valve (seventh valve) 31 (from a desired valve
opening degree to a closed state) and switching of the
pressure-increasing opening/closing valve (eleventh valve) 35 (from
open to close) is performed by detecting the pressure (PH) in the
head chamber 16H, or detecting the position of the injection piston
4, or using both the detected values of the pressure PH and the
position of the piston. The operation of the piston 4, the
operation of each valve, etc., can be understood sufficiently by
viewing FIG. 23, and therefore, their detailed explanation is
omitted.
[0117] FIG. 19 is a system diagram of a fourth embodiment of a
hydraulic device of the die casting machine 100 according to the
present invention. A hydraulic device 403 in the fourth embodiment
differs from the hydraulic device 303 in the third embodiment only
in the configuration near the gas bottle. That is, in a hydraulic
circuit of the hydraulic device 403 in FIG. 19, the first, second,
and third gas bottles 71, 72, 73 and the first, second, and third
switching valves 75, 76, 77 in the hydraulic circuit of the
hydraulic device 303 in FIG. 16 are replaced with a gas bottle 80
and a filling force pattern adjusting valve 82. In the hydraulic
device 403, other configurations are basically the same as those in
the hydraulic device 303 in the third embodiment shown in FIG.
16.
[0118] The operation of the die casting machine and the hydraulic
device 403 in the present embodiment differs from that in the third
embodiment only in the operation in the fast injection stage, and
therefore, only the operation in the fast injection step (stage),
which is the only difference between the present embodiment and the
third embodiment, is explained. In the present embodiment, the
capacity of the gas bottle 800 has only one kind, and therefore,
the final filling force (the filling force when the fast injection
stage is completed) of hydraulic oil to the head chamber 16H of the
injection cylinder 102 is adjusted and thereby the occurrence of
surge pressure is suppressed by changing the opening degree of the
filling force pattern adjusting valve 82 to change the flow
resistance of the pipe conduit from the gas bottle 80 to the
injection piston accumulator 20 and thereby change and adjust the
pressing force of the gas against the piston 211. It is preferable
for the filling force pattern adjusting valve 82 to be a
motor-driven throttle valve.
[0119] FIGS. 20 to 22 show explanatory diagrams of the change of
the filling force pattern by the throttle valve (filling force
pattern adjusting valve 82) on a gas supply line. FIGS. 20 to 22
each show the change of the pressure (PH) (MPa) in the head chamber
with respect to the time progress at the time of no-load injection
when the fast injection speed is 2, 5, and 8 (m/sec), respectively
(this graph is referred to as a filling force pattern). As
parameters, those when the valve opening degree is 0.02 m (solid
line), 0.003 m (broken line), 0.001 m (alternate long and short
dash line), and 0.0002 m (alternate long and two short dashes line)
are shown, respectively. FIGS. 20 to 22 may be obtained by
theoretical calculations or may be obtained by the actual no-load
injection. In FIGS. 20 to 22, differences in the drop pattern of
the pressure (PH) in the head chamber with respect to the time
progress according to the valve opening degree at each injection
speed are shown. The pressure at the lowest point of the pressure
(PH) in the head chamber is the final filling force. The larger the
pressure drop, the larger is the drop in drive force of the piston
of the injection cylinder 102, that is, the larger is the reduction
in speed of the piston (drop in the filling force), and thus the
occurrence of surge pressure is suppressed. It is seen from FIGS.
20 to 22 that the pressure of the injection cylinder head once
dropped begins to increase again, however, before the pressure
increases again, the hydraulic valves are switched (the
pressure-increasing opening/closing valve 35 is opened and the fast
speed adjusting valve 31 is closed) and thus the fast injection
stage transits to the pressure-increasing stage. It can be seen
from FIGS. 20 to 22 that there is an enough time for the transition
to be done.
[0120] In the present embodiment, as shown in FIGS. 20 to 22, the
filling force pattern can be calculated as a function of the fast
injection stroke (injection stroke in the fast injection stage),
the fast injection speed, and the opening degree of the filling
force pattern adjusting valve, and therefore, it is preferable for
the die casting machine in the present embodiment to comprise an
automatic control device having an operation circuit for
calculating the filling force pattern. Actually, a configuration is
preferable, in which the opening degree of the filling force
pattern adjusting valve 82 is finally determined by an automatic
operation circuit of the automatic control device when the
injection stroke, the fast injection speed, and the final filling
force in the fast injection stage are input.
[0121] It is preferable to perform a method for determining an
optimum valve opening degree by a trial injection also in the
present embodiment, as already described in the third embodiment
(refer to page 35 lines 1 to 18 in Japanese text (i.e. page 41 line
30 to page 42 line 26 in the English text)). In the present
embodiment, a trial injection is performed in such a manner that
the opening degree of the filling force pattern adjusting valve 82
is increased sequentially from smaller one. In each trial
injection, the quality of a molded product is checked and an
optimum condition is selected.
[0122] FIG. 24 is a chart representing the change of the injection
speed, the injection pressure (pressure in the head chamber 16H of
the injection cylinder 102), etc. with respect to the time
progress, and the state of the piston rod, each valve, etc., at
that time in the fourth embodiment. FIG. 14 is basically the same
as FIG. 23 and the symbols etc. are the same as those in FIG. 23.
The first, second, and third switching valves 75, 76, 77 in FIG. 23
do not exist in FIG. 24, and instead, the time chart of the filling
force pattern adjusting valve 82 is shown. It is known from FIG. 24
that the filling force pattern adjusting valve 82 is maintained at
a fixed valve opening degree after molding is started.
[0123] Next, the effects and working of the above-mentioned
embodiments are explained. According to the die casting machine in
the first embodiment of the present invention, the following
effects can be expected.
[0124] In particular, in the die casting method or the die casting
machine capable of fast injection molding, it is possible to
suppress the occurrence of surge pressure of molten aluminum in the
mold cavity and prevent the occurrence of burr and spouting of
molten metal by activating the piston under high pressure without
reducing the pressure to drive (press under pressure) the piston of
the injection cylinder and switching to the low-pressure drive at a
predetermined stroke of the piston.
[0125] Further, even if there are variations in the amount of
supply of molten metal, the variations in the quality of a molded
product on site can be minimized.
[0126] By using the piston accumulator (ACC) having the special
structure of the present invention, the discontinuity in the speed
at the fast pressure-raising step caused by the opening/closing
etc. of the large-sized valve and the check valve can be avoided
and the continuity can be ensured, and therefore, it is possible to
manufacture a high-quality molded product.
[0127] Further, due to the piston accumulator (ACC) having the
special structure, the installation space can be made compact, and
therefore, it is possible to exhibit the superiority in terms of
cost.
[0128] According to the die casting machine in the second
embodiment of the present invention, the following effects can be
expected.
[0129] As in the first embodiment, it is possible to suppress the
occurrence of surge pressure of molten metal in the mold cavity,
prevent the occurrence of burr and spouting of molten metal, and
further reduce the variations in the quality of a molded product on
site.
[0130] According to the die casting machine in the third embodiment
of the present invention, the following effects can be
expected.
[0131] In particular, in the die casting method or the die casting
machine capable of fast injection molding, by properly selecting a
combination of the plurality of gas bottles, a fast speed is
achieved in a brief time under high pressure at start time by
utilizing pressure drop of hydraulic oil due to the expansion of
gas without performing complicated control, the pressure is reduced
to the optimum value by the completion of filling, the fast speed
value of the injection is reduced before spontaneous reduction in
speed due to the fluid resistance of the molten metal in the mold,
and thus the impact at the time of completion of filling is relaxed
and the fast injection molding is enabled, and at the same time,
the occurrence of surge pressure of molten aluminum in the mold
cavity is suppressed and the occurrence of burr and spouting of
molten metal, or scattering of tip of molten metal are
prevented.
[0132] Further, even if there are variations in the amount of
supply of molten metal, the occurrence of surge pressure is
suppressed, and the occurrence of burr and spouting of molten
metal, or scattering of tip of molten metal are prevented.
[0133] According to the die casting machine in the fourth
embodiment of the present invention, the following effects can be
expected.
[0134] By providing the throttle valve capable of changing its
opening degree on the gas supply line from the gas bottle to the
injection piston accumulator to limit the flow rate of supply of
gas from the gas bottle during fast injection and cause the
pressure drop to occur, (that is, by the adjustment of the opening
degree of the filling force pattern adjusting valve in the
above-mentioned embodiment), it is possible to suppress the
occurrence of surge pressure of molten metal in the mold cavity,
prevent the occurrence of burr and spouting of molten metal, or
scattering of tip of molten metal, and further reduce variations in
the quality of a molded product on site as similarly to the first
embodiment.
[0135] Because the number of gas bottles can be reduced to one, it
is possible to reduce the cost of the hydraulic device, and
therefore, the cost of the die casting machine.
[0136] In the hydraulic circuit in the embodiments described above
or shown in the accompanied drawings, only the minimum components
are described basically in order to make explanation
easier-to-understand, however, it may also be possible to add
components, such as a valve, a filter, and a sensor, which are
necessary in accordance with the function, control, arrangement,
etc., of the device.
[0137] In the above-described embodiments, the material of molten
metal is described as aluminum, however, other material may be
used.
[0138] The numerical values described in the present specification
and, for example, in FIGS. 17, 18, etc., are used for convenience
of explanation, and the present invention is not limited by these
numerical values in particular, and the numerical values may vary
when, for example, the type of the die casting machine changes.
[0139] The above-described embodiments are only examples of the
present invention and the present invention is not limited to the
embodiments but defined only by the description in claims and other
embodiments can also be embodied.
[0140] While the invention has been described by reference to
specific embodiments chosen for the purposes of illustration, it
should be apparent that numerous modifications could be made
thereto, by those skilled in the art, without departing from the
basic concept and scope of the invention.
* * * * *