U.S. patent application number 09/837220 was filed with the patent office on 2001-08-16 for injection control method and device of die-casting machine.
Invention is credited to Kodama, Shinobu, Tsuji, Makoto.
Application Number | 20010013403 09/837220 |
Document ID | / |
Family ID | 18023383 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013403 |
Kind Code |
A1 |
Kodama, Shinobu ; et
al. |
August 16, 2001 |
Injection control method and device of die-casting machine
Abstract
In a die-casting machine having an injection cylinder device
(10) for injecting molten material to a casting die and a boost
cylinder device (20) for boosting a hydraulic oil supplied to the
injection cylinder device (10), back-pressure of the injection
cylinder device (10) and back-pressure of the boost cylinder device
(20) are synchronously controlled by a flow-rate control valve (17)
capable of continuously adjusting flow-rate of the hydraulic oil
discharging channel (16). Accordingly, boosting characteristic can
be made in accordance with burr critical boost curve, thereby
avoiding burr occurrence in die-casting products in advance.
Therefore, high-quality die-casting products without burrs can be
manufactured even in a high-speed casting method or using
low-accuracy dies.
Inventors: |
Kodama, Shinobu; (Zama-shi,
JP) ; Tsuji, Makoto; (Yamato-shi, JP) |
Correspondence
Address: |
Pillsbury Winthrop LLP
Intellectual Property Group
East Tower, Ninth Floor
1100 New York Avenue, N.W.
Washington
DC
20005-3918
US
|
Family ID: |
18023383 |
Appl. No.: |
09/837220 |
Filed: |
April 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09837220 |
Apr 19, 2001 |
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09432256 |
Nov 2, 1999 |
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6241003 |
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Current U.S.
Class: |
164/457 ;
164/312 |
Current CPC
Class: |
B22D 17/32 20130101 |
Class at
Publication: |
164/457 ;
164/312 |
International
Class: |
B22D 046/00; B22D
017/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 2, 1998 |
JP |
10-311949 |
Claims
What is claimed is:
1. An injection control method of a boost-type die-casting machine
including an injection plunger for injecting molten material into a
casting die, an injection cylinder device having an injection
piston for driving the injection plunger, and a boost cylinder
device for boosting hydraulic oil supplied to the injection
cylinder device, comprising the steps of: providing a flow-rate
control valve capable of continuously regulating flow-rate of
hydraulic oil discharging channel of the injection cylinder device;
and during boosting process by the boost cylinder device,
synchronously controlling back-pressure of the injection cylinder
device and back-pressure of the boost cylinder device.
2. The injection control method of a die-casting machine according
to claim 1, wherein the flow-rate control valve is controlled so
that a relationship between casting pressure and boost time in the
casting die changes in accordance with a selective curve along a
predetermined critical boost curve for avoiding burr occurrence to
the casting die during the synchronous controlling process.
3. The injection control method of a die-casting machine according
to claim 2, wherein the flow-rate control valve is controlled by
comparing a detected pressure value detected by the injection
cylinder device and the boost cylinder device with a command
pressure value for every elapsed time given in accordance with a
predetermined program to eliminate difference between the pressure
values.
4. The injection control method of a die-casting machine according
to claim 3, wherein the flow-rate control valve is controlled by
comparing difference between the detected pressure value and the
command pressure value and open-degree of the flow-rate control
vale so that the open-degree corresponds to the difference.
5. An injection control device of a boost-type die-casting machine
comprising an injection plunger for injecting molten material to a
casting die, an injection cylinder device having an injection
piston for driving the injection plunger, and a boost cylinder
device having a boost cylinder for boosting hydraulic oil supplied
to the injection cylinder device, characterized in further having;
a flow-rate control valve capable of continuously controlling a
flow-rate in a hydraulic discharging channel of the injection
cylinder device; and a synchronous controller for synchronously
controlling a back-pressure of the injection cylinder device and a
back-pressure of the boost cylinder device during boosting process
by the boost cylinder device.
6. The injection control device of a die-casting machine according
to claim 5, wherein the synchronous controller controls the
flow-rate control valve so that a relationship between a casting
pressure and boost time of the casting die changes in accordance
with along a selective curve along a predetermined critical boost
curve for avoiding burr occurrences to the casting die during the
synchronous controlling process.
7. The injection control device of a die-casting machine according
to claim 6, the synchronous controller compares a detected pressure
value detected by the injection cylinder device and the boost
cylinder device and a command pressure value for every elapsed time
given in accordance with a predetermined program and controls the
flow-rate control valve to eliminate difference between the
pressure values.
8. The injection control device of a die-casting machine according
to claim 7, wherein the synchronous controller compares difference
between the detected pressure value and the command pressure value
and open-degree of the flow-rate control vale and controls the
flow-rate control valve so that the open-degree corresponds to the
difference.
9. The injection control device of a die-casting machine according
to claim 5, wherein the flow-rate control valve is a
high-responsive electrohydraulic servovalve.
10. The injection control device of a die-casting machine according
to claim 5, wherein the hydraulic discharging channel of the
injection cylinder device and a hydraulic discharging channel from
the boost cylinder device are connected.
11. The injection control device of a die-casting machine according
to claim 5, wherein the flow control valve has a main spool to be
opened and shut by a pilot servovalve.
12. The injection control device of a die-casting machine according
to claim 11, further comprising a position sensor for detecting
open-degree of the main spool.
13. The injection control device of a die-casting machine according
to claim 12, wherein a command signal outputted by the position
sensor and a difference between a command pressure value outputted
by a boost controller and a detected pressure value detected by the
injection cylinder device and the boost cylinder device are fed
back to an input of the pilot servovalve.
14. The injection control device of a die-casting machine according
to claim 5, the synchronous controller further comprising a
pressure detector for detecting a casting pressure of the injection
cylinder device, a pressure processor for processing an output from
the pressure detecting means, a boost controller for outputting a
command pressure value for every elapsed time according to a
predetermined program, and a comparator for calculating a
difference between a pressure outputted by the pressure processing
means and a command pressure value outputted by the boost
controller.
15. The injection control device of a die-casting machine according
to claim 14, the synchronous controller further comprising a servo
amplifier for controlling the flow-rate control valve so that a
relationship between a casting pressure and boost time of the
casting die changes in accordance with a selective curve along a
predetermined critical boost curve for avoiding burr occurrence in
die-casting products during the casting die during the boosting
process by the boost cylinder device based on a difference
outputted by the comparator.
16. The injection control device of a die-casting machine according
to claim 5, further comprising a boost control valve for
controlling boosting time on a hydraulic oil supply side of the
boost cylinder.
17. The injection control device of a die-casting machine according
to claim 16, the boost control valve further comprising a spool
movable by operating a switching valve and an adjusting stopper for
adjusting a moving amount of the spool, a distal end portion of the
hydraulic oil supply side of the spool being tapered for narrowing
the flow-rate of the hydraulic oil to regulate pressure and
flow-rate of pressurizing portion of the boost piston.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an injection control method
and injection control device of a die-casting machine, which can be
specifically used for injection control of a die-casting machine
for manufacturing high-quality die-casting products without burr
occurrence.
[0002] 1. Field of the Invention
[0003] 2. Description of Related Art
[0004] Conventionally, it is known that quality of die-casting
molding products is largely affected by an injection speed and
injection pressure in filling molten material into mold die.
Especially, sufficient pressurization is required before the molten
material solidifies and therefore a die-casting machine having
double-stage driving cylinder devices for injection and boost has
been used.
[0005] Generally, in the die-casting machine of this type, an
injection plunger advances at a low speed and the molten material
is started to be filled into the mold cavity while avoiding the
molten material from getting choppy. When an end of the molten
material reaches a gate portion of the die and pressure of filling
injection cylinder device increases, the injection plunger is
advanced at a high speed for avoiding the temperature of the molten
material from being lowered to fill the mold cavity with the molten
material rapidly.
[0006] In succession to the injection process, when the molten
material is filled into the mold die to further raise the pressure
of the injection cylinder device or when the injection plunger
reaches a predetermined position corresponding to completion of
filling, high pressure is applied to a boost cylinder device to
conduct boosting process for increasing pressurizing force of the
injection pressure in the mold die.
[0007] Specific arrangement of the conventional double-stage
cylinder type die-casting machine will be described below.
[0008] In FIG. 6, molten material 92 to be filled in the mold
cavity 91 is supplied to injection sleeve 93 of a die-casting
machine 90. An injection plunger 94 is driven by a filling
injection cylinder device 95 to inject the molten material 92.
After completing filling process, hydraulic oil at a backside of
the injection cylinder device 95 is pressurized by boost cylinder
device 96 with a large diameter to a high pressure to boost the
molten material 92 filled in the mold cavity 91 through the
injection cylinder device 95.
[0009] Injection speed level CV and injection pressure level CP
during injection process and boosting process in the die-casting
machine are shown in FIG. 7. In the figure, the injection cylinder
device 95 advances initially at a low speed VL and fills the molten
material rapidly at a high speed VH from time point t1 which is
braked by virtue of filling pressure of the molten material 92 in
accordance with completion of filling process. The boost cylinder
96 is actuated at time point t2 to pressurize the molten material
92 so that the molten material 92 in the mold cavity 91 reaches
pressure PH. The injection cylinder 95 is further advanced and is
stopped at time point t3 when solidification of the molten material
is completed.
[0010] For linking control of the injection cylinder device 95 and
the boost cylinder device 96 (switching process from the injection
process and the boosting process), sequence-valve method for
detecting injection pressure fluctuation to conduct switch and
limit-switch method for detecting the advancing position of the
injection plunger have been used.
[0011] Following hydraulic circuit is used in the above sequence
valve method.
[0012] In FIG. 8, an injection hydraulic circuit 114 from a check
valve 111 and injection speed control valve 112 to an accumulator
113 is connected to the injection cylinder device 95. On the other
hand, a boost hydraulic circuit 117 reaching the accumulator 113
through a pilot operation boost control valve 116 to be opened and
shut by a sequence valve 115.
[0013] The sequence valve 115 opens the boost control valve 116
when the pressure of the injection hydraulic circuit 114 exceeds a
predetermined boost initiation pressure. Accordingly, when
advancement of the injection cylinder device 95 is started by
operating the injection speed control valve 112 for 30 conducting
the injection process and filling pressure is increased in
accordance with completion of filling molten material into the mold
die to reach the predetermined boost initiation pressure, the
sequence valve 115 is actuated to open the boost control valve 116
to start advancement of the boost cylinder device 96, thereby
conducting boosting process.
[0014] As shown in FIG. 9, the injection cylinder device 95 has an
injection piston 95A, which is advanced by hydraulic pressure of
hydraulic oil supplied to a backside thereof by the injection
hydraulic circuit 114. Flow-rate of the hydraulic oil from the
injection hydraulic circuit 114 is controlled by the injection
speed control valve 112 to switch advancement and suspension of the
injection piston 95A and adjust advancing speed thereof.
[0015] The boost cylinder device 96 has a boost piston 96A
thereinside, which is advanced by hydraulic pressure of the
hydraulic oil supplied to a backside thereof from the boost
hydraulic circuit 117 to pressurize the injection piston 95A from
backside through an intermediate member 95B of the injection
cylinder device 95. The flow of the hydraulic oil from the boost
hydraulic circuit 117 is controlled by the boost control valve 116,
which switches advancement and suspension of the boost piston
96A.
[0016] On-off operation of the boost control valve 116 is conducted
by the sequence valve 115. An electrovalve or the like for
switching in response to filling pressure by an appropriate means
is suitably used for the sequence valve 115.
[0017] Incidentally, in the above-described double-stage
die-casting machine, the flow-rate of the hydraulic oil given to
the boost cylinder device stays constant without being variably
controlled in the boosting process for boosting the injection
cylinder device by the boost cylinder device. This is because
on-off operation of the hydraulic oil is conducted by the boost
control valve and an on-off two-position switching type constant
flow valve is conventionally used for the boost control valve.
[0018] Since the hydraulic oil is supplied at a constant flow-rate
to the boost cylinder device, boost characteristics of casting
pressure becomes the injection pressure level CP shown in FIG. 7,
in which increase curve is represented as a quadratic curve being
less gradient as approaching to maximum pressure PH. This is
because the injection plunger receives much resistance in
accordance with solidification of the molten material in the mold
die and the boost is blunted. More specifically, the casting
pressure P is in proportion to square root of product of elapsed
time t and parameter a.
[0019] On the other hand, burr critical boost curve is known in
boosting process. The burr is generated when an excessive pressure
is applied to the mold die in boosting process etc. to leak the
molten material from parting surface of the mold die. The burr
critical boost curve is given as a curve CX where the casting
pressure P is in proportion to a product of square of elapsed time
t and parameter a (see FIG. 7).
[0020] The burr critical boost curve CX becomes such quadratic
curve because the molten material in the mold die is not solidified
at the initial stage of boosting process and fluidity of the molten
material is high enough to leak the molten material from the
parting surface, which prevents high pressure from being applied.
On the other hand, when the molten material is solidified in
accordance with elapsed time, the leakage to the parting line is
hard to be caused, so the burr is not likely to be generated when
high pressure is applied.
[0021] However, in the conventional die-casting machine where the
hydraulic oil is supplied to the boost cylinder device at a
constant flow-rate, the boost characteristic of the casting
pressure is difficult to be approximated to the burr critical boost
curve, so that burrs are frequently generated in conducting
high-speed casting or using a mold die having low parting surface
accuracy, which makes it impossible to manufacture die-casting
products with high-quality.
SUMMARY OF THE INVENTION
[0022] An object of the present invention is to provide a injection
control method and device of a die-casting machine for
manufacturing high-quality die-casting products without burrs even
in high-speed casting and mold die of low accuracy.
[0023] To achieve the above object, after filling the molten
material into the cavity by advancing the injection piston, the
pressure is controlled in accordance with a predetermined selective
boost curve set along a burr critical boost curve for avoiding burr
occurrence in the casting die during boosting process by the boost
cylinder device in the present invention. More specifically, the
present invention is arranged as follows:
[0024] A method according to the present invention is an injection
control method of a boost-type die-casting machine including an
injection plunger for injecting molten material into a casting die,
an injection cylinder device having an injection piston for driving
the injection plunger, and a boost cylinder device for boosting
hydraulic oil supplied to the injection cylinder device. The method
is characterized in including the steps of: providing a flow-rate
control valve capable of continuously regulating flow-rate of
hydraulic oil discharging channel of the injection cylinder device;
and, during boosting process by the boost cylinder device,
synchronously controlling back-pressure of the injection cylinder
device and back-pressure of the boost cylinder device.
[0025] A device according to the present invention is an injection
control device of a boost-type die-casting machine having an
injection plunger for injecting molten material to a casting die,
an injection cylinder device having an injection piston for driving
the injection plunger, and a boost cylinder device having a boost
cylinder for boosting hydraulic oil supplied to the injection
cylinder device. The device is characterized in further having; a
flow-rate control valve capable of continuously controlling a
flow-rate in a hydraulic discharging channel of the injection
cylinder device; and a synchronous controller for synchronously
controlling a back-pressure of the injection cylinder device and a
back-pressure of the boost cylinder device during boosting process
by the boost cylinder device.
[0026] According to the above arrangement, since the flow-rate in
the hydraulic oil discharging channel is continuously controlled by
the flow-rate control valve to set the flow-rate variable, boost
characteristic can be adjusted to correspond to the burr critical
boost curve, thereby preventing generating burr in advance.
Accordingly, high-quality die-casting products without burr can be
manufactured even in high-speed casting or using low-accuracy mold
die. Further, since both of the back-pressures of the injection
cylinder and the boost cylinder, the size of the device can be
reduced.
[0027] Incidentally, either one of open-control and real-time
feedback control can be preferably used for the control method.
[0028] In the method of the present invention, the flow-rate
control valve is preferably controlled so that a relationship
between casting pressure and boost time in the casting die is
changed in accordance with a selective curve along a predetermined
critical boost curve for avoiding burr occurrence to the casting
die during the synchronous controlling process.
[0029] In the device of the present invention, the synchronous
controller preferably controls the flow-rate control valve so that
a relationship between a casting pressure and boost time of the
casting die changes in accordance with a selective curve along a
predetermined critical boost curve for avoiding burr occurrence to
the casting die during the synchronous controlling process.
[0030] In the above arrangement, since the boosting process is
conducted by a flow-rate control valve composed of a
high-responsive electrohydraulic servovalve using a controller
along a predetermined critical curve not causing the burr, the burr
can be prevented from generating, thus manufacturing high-quality
die-casting products without burr even in high-speed casting or
using low accuracy mold die. Further, since the high-responsive
electrohydraulic servovalve is used, responsivity and accuracy can
be improved.
[0031] In the method of the present invention, the flow-rate
control valve is preferably controlled by comparing a detected
pressure value detected by the injection cylinder device and the
boost cylinder device and a command pressure value for every
elapsed time given in accordance with a predetermined program to
eliminate difference between the pressure values.
[0032] In the device of the present invention, the synchronous
controller preferably compares a detected pressure value detected
by the injection cylinder device and the boost cylinder device and
a command pressure value for every elapsed time given in accordance
with a predetermined program and controls the flow-rate control
valve to eliminate difference between the pressure values.
[0033] According to the above arrangement, since the control is
conducted along the predetermined critical curve not causing the
burr, the burr generation can be prevented in advance, thereby
manufacturing high-quality die-casting products without burr even
in high-speed casting process or using low-accuracy mold die.
[0034] In the method according to the present invention, the
flow-rate control valve is preferably controlled by comparing
difference between the detected pressure value and the command
pressure value and open-degree of the flow-rate control valve so
that the open-degree corresponds to the difference.
[0035] In the device according to the present invention, the
synchronous controller preferably compares difference between the
detected pressure value and the command pressure value and
open-degree of the flow-rate control vale and controls the
flow-rate control valve so that the open-degree corresponds to the
difference.
[0036] According to the above arrangement, responsivity of
open-degree control and accuracy of the flow-rate control valve can
be improved.
[0037] In the device according to the present invention, the
flow-rate control valve may preferably be a high-responsive
electrohydraulic servovalve.
[0038] According to the above arrangement, the responsivity and
accuracy of the flow-rate control valve can be improved.
[0039] In the device of the present invention, the hydraulic
discharging channel of the injection cylinder device and a
hydraulic discharging channel from the boost cylinder device are
preferably connected.
[0040] According to the above arrangement, since back-pressure side
of the injection cylinder device and the boost cylinder device are
interconnected for synchronization and both of the back-pressures
of the injection cylinder and the boost cylinder can be controlled,
the size of the device can be reduced.
[0041] In the device according to the present invention, the flow
control valve preferably has a main spool to be opened and shut by
a pilot servovalve.
[0042] According to the above arrangement, the open-degree can be
more accurately and easily controlled by the main spool.
[0043] In the above, a position sensor for detecting open-degree of
the main spool may preferably be provided.
[0044] According to the above arrangement, the open-degree of the
main spool can be accurately and easily conducted.
[0045] A command signal outputted by the position sensor and a
difference between a command pressure value outputted by a boost
controller and a detected pressure value detected by the injection
cylinder device and the boost cylinder device are preferably fed
back to an input of the pilot servovalve.
[0046] According to the above arrangement, responsivity and
accuracy of the open-degree control of the main spool can be
improved.
[0047] In the device according to the present invention, the
synchronous controller may further have a pressure detector for
detecting a casting pressure of the injection cylinder device, a
pressure processor for processing an output from the pressure
detecting means, a boost controller for outputting a command
pressure value for every elapsed time according to a predetermined
program, and a comparator for calculating a difference between a
pressure outputted by the pressure processing means and a command
pressure value outputted by the boost controller.
[0048] And, the synchronous controller may further have a servo
amplifier for controlling the flow-rate control valve so that a
relationship between a casting pressure and boost time of the
casting die changes in accordance with a selective curve along a
predetermined critical boost curve for avoiding burr occurrence to
the casting die during the boosting process by the boost cylinder
device based on a difference outputted by the comparator.
[0049] According to the above arrangement, since the boosting
process is conducted along a predetermined critical curve without
generating burr, the burr generation can be prevented in advance,
thereby high-quality die-casting products without burr can be
produced even in high-speed casting process or by using a mold die
with low-accuracy.
[0050] In the device of the present invention, a boost control
valve for controlling boosting time may preferably provided on a
hydraulic oil supply side of the boost cylinder.
[0051] In the above arrangement, the boost control valve may have a
spool movable by operating a switching valve and an adjusting
stopper for adjusting a moving amount of the spool, a distal end
portion of the hydraulic oil supply side of the spool being tapered
for narrowing the flow-rate of the hydraulic oil to regulate
pressure and flow-rate of pressurizing portion of the boost
piston.
[0052] According to the above arrangement, since the spool of the
boost control valve is configured in a shape capable of narrowing
the flow-rate of the hydraulic oil, even when a trouble disabling
the function of the flow-rate control valve is occurred, the
open-degree of the spool can be adjusted to be small using the
adjusting stopper to set a spool open-degree position capable of
obtaining predetermined boost curve. Accordingly, normal boosting
process can be temporarily secured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0053] FIG. 1 is a schematic diagram showing an embodiment of the
present invention;
[0054] FIG. 2 is a cross section showing cylinder device of the
aforesaid embodiment;
[0055] FIG. 3 is a block diagram showing a control system of the
aforesaid embodiment;
[0056] FIG. 4 is a graph showing injection process and boosting
process of the aforesaid embodiment;
[0057] FIG. 5 is a block diagram showing a modification of the
aforesaid embodiment;
[0058] FIG. 6 is a cross section showing basic arrangement of
conventional die-casting machine;
[0059] FIG. 7 is a graph showing injection process and boosting
process of the conventional die-casting machine;
[0060] FIG. 8 is a schematic diagram showing a hydraulic circuit of
the conventional die-casting machine; and
[0061] FIG. 9 is a cross section showing a conventional cylinder
device.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)
[0062] An embodiment of the present invention will be described
below with reference to attached drawings.
[0063] Since the present embodiment is implemented by modifying a
control method of existing die-casting machine and primary
components of the existing die-casting machine (e.g.
above-described arrangement of the die-casting machine shown in
FIGS. 6 to 9) such as mold die and injection plunger can be
selectively used, description thereof is omitted. And description
of injection cylinder device, boost cylinder device and hydraulic
circuit for supplying hydraulic oil thereto will be mentioned
below.
[0064] In FIG. 1, an injection hydraulic circuit 14 extending
through a pilot check valve 11 to an injection accumulator 13 is
connected to an injection cylinder device 10. The check valve 11 is
controllably opened and shut by a open-shut electroswitching valve
12, which is manipulated to open the check valve 11 to feed the
hydraulic oil from the injection accumulator 13 to the injection
cylinder device 10 to advance the injection piston 15.
[0065] When the hydraulic flow from the injection accumulator 13 to
the injection cylinder device 10 is stopped to eliminate
differential pressure between inlet and outlet, the check valve 11
prevents backflow of the hydraulic oil during boosting process by
moving a valve body by a spring provided thereinside.
[0066] A hydraulic discharging channel 16 for discharging the
hydraulic oil of the rod of the injection piston 15 is connected to
the injection cylinder device 10 and an injection speed controlling
flow-rate control valve 17 is connected to the hydraulic
discharging channel 16.
[0067] The injection speed controlling flow-rate control valve 17
is composed of high-speed responsive large-flow servovalve, of
which spool open-degree is controlled to narrow the hydraulic
discharging channel 16 in advancing the injection cylinder device
10 to apply back-pressure to the injection piston 15 to adjust
advancing speed.
[0068] A boost hydraulic circuit 24 extending through a boost
control valve 21 controllably opened and shut by a switching valve
22 to a boost accumulator 23 is connected to a boost cylinder
device 20. The boost control valve 21 is opened by operating the
switching valve 22, so that the hydraulic oil from the boost
accumulator 23 is supplied to the boost cylinder device 20 to
advance the boost piston 25.
[0069] As shown in FIG. 2, the boost control valve 21 has a spool
211 of which maximum moving amount is externally controlled by a
screw member 213 as an adjusting stopper. Accordingly, supplied
hydraulic oil flow-rate can be changed according to a configuration
and moving amount of the spool.
[0070] The boost cylinder device 20 has a boost cylinder
discharging channel 16A, which is connected to the hydraulic
discharging channel 17 of injection piston through a branch channel
16B. The injection speed controlling flow-rate control valve 17 is
connected to the hydraulic oil discharging channel 16. In other
words, the injection cylinder device 10 and the boost cylinder
device 20 jointly owns the flow-rate control valve 17. The
injection cylinder device 10 and the boost cylinder device 20 are
synchronously controlled by the flow-rate control valve 17.
[0071] As mentioned above, the flow-rate control valve 17 is made
of high-speed responsive large-flow servovalve, of which spool
open-degree is adjusted to narrow the hydraulic oil discharging
channel 16 to apply back-pressure to the injection piston 15 and
the boost piston 25 to control advancing speed. The back-pressure
is detected by a pressure sensor 37.
[0072] The flow-rate control valve 17C has a pilot servovalve 17C
for opening and shutting the main spool, and output of a position
sensor for detecting the open-degree of the main spool is
double-stage servo mechanism for feedback to an input of the pilot
servovalve 17C.
[0073] The flow-rate control valve 17 controls the advancing speed
by adjusting the main spool open-degree when the injection cylinder
device 10 is advanced. When the injection cylinder is advanced, the
boost piston 25 is at a retraction limit. In other words, the boost
piston 25 is at a position remote from the position of the
injection piston 15 and the hydraulic oil is filled between the
pistons 15 and 25. The boost by the boost cylinder 20 is started
with both of the pistons 15 and 25 being separated.
[0074] As shown in FIG. 1, hydraulic oil feeding channel 31 from a
hydraulic source 30 is connected to the injection accumulator 13
and the boost accumulator 23, to which high-pressure hydraulic oil
is supplied. An electromagnetic accumulator fill switching valve 32
is disposed at a halfway of the hydraulic feeding channel 31 for
conducting on-off operation of hydraulic oil supply to the
respective accumulators 13 and 23. Generally speaking, since the
injection process is conducted based on oil amount in the
accumulator, the switching valve 32 is used in a shut condition.
However, when accumulator pressure is decreased, the switching
valve 32 is opened to fill respective accumulators with pressure
oil.
[0075] A branch channel 33 from the hydraulic oil feeding channel
31 is connected to a backside of the boost accumulator 23, and an
electromagnetic casting pressure control valve 34 is disposed at a
halfway thereof.
[0076] The back-pressure of the boost accumulator 23 is increased
by feeding the hydraulic oil from the hydraulic source 30 by the
casting pressure control valve 34, so that the maximum hydraulic
pressure of the boost hydraulic circuit 24 is increased to increase
the maximum casting pressure applied to the boost cylinder device
20.
[0077] On the contrary, when the hydraulic oil is discharged by the
casting pressure control valve 34 to decrease the back-pressure of
the boost accumulator 23, the maximum hydraulic pressure of the
boost hydraulic circuit 24 is reduced to lessen the maximum casting
pressure applied to the boost cylinder device 20.
[0078] A sensor 35 for detecting the pressure at the backside is
disposed to the boost accumulator 23, so that back-pressure value
of the boost accumulator 23 can be checked in the above-described
adjusting process of the casting pressure.
[0079] As shown in FIG. 1, a pressure sensor 36 for detecting boost
on a head side and a pressure sensor 37 for detecting back-pressure
on a rod side are disposed to detect the casting pressure of the
injection cylinder device 10, respectively directly checking
injection pressure value in adjusting the above-described casting
pressure. For example, the injection pressure value can be more
correctly detected by a pressure difference between head side B and
rod side A than an actual pressure value. Incidentally, in
accordance with ratio between a diameter D1 of the injection piston
15 and a plunger chip D2 of an injection plunger 151, the injection
pressure PR is given as a value of product of detected pressure PS
and square of (D1/D2).
[0080] An encoder 152 for detecting advance position of the
injection plunger 151 is disposed to the injection cylinder device
10, so that stroke position in injection process can be directly
detected.
[0081] A controller 40 is provided for receiving signals from
respective sensors 36, 37 etc. and for controlling operation of
respective valves.
[0082] The controller 40 is constructed mainly of existing computer
systems, programmable controllers etc., which operates respective
valves according to predetermined operation program in accordance
with predetermined steps to implement injection and boosting.
[0083] The controller 40 controls respective portion in accordance
with predetermined programs to perform injection process and
boosting process, which includes a controlling circuit for
controlling the speed controlling flow-rate control valve 17 and
for actuating the boost cylinder device 20 to conduct boosting
process. The controller 40 has a boost controller 41 as a boost
controlling means, a servo amplifier 42, a pressure detecting
amplifier 43 and a position feedback servo amplifier 44.
[0084] The boost controller 41 works according to a predetermined
program and outputs command pressure value based on the elapsed
time in boosting process in accordance with predetermined boost
control setting curve. The servo amplifier 42 manipulates the pilot
servovalve 17C of the speed controlling flow-rate control valve 17
according to output of the boost controller 41 to regulate the
open-degree of the main spool 17A.
[0085] The pressure detecting amplifier 43 deals with the output
from the respective pressure sensors 36 and 37 to output a boost
feedback signal 45 to the input side of the servo amplifier 42. At
this time, the pressure detecting amplifier 43 is capable of
selectively outputting either one of the outputs of the respective
pressure sensors 36 and 37 or combinedly operating respective
outputs to output.
[0086] The position feedback servo amplifier 44 deals with
open-degree position of the main spool detected by the position
sensor of the flow-rate control valve 17 to output a minor feedback
signal 46 to the output side of the servo amplifier 42.
[0087] When the boosting process is implemented by the controller
40, command pressure value according to the elapsed time is
outputted from the boost controller 41 and the servo amplifier 42
regulates the open-degree of the main spool 17A in accordance with
the command pressure value by the pilot servovalve 17C of the
flow-rate control valve 17. Then, flow of the hydraulic oil
corresponding to the open-degree of the main spool of the flow-rate
control valve 17 disposed in the hydraulic discharging circuit 16
to conduct boosting process thereby increasing the pressure inside
the injection cylinder device 10.
[0088] The pressure is detected by the respective pressure sensors
36 and 37 and is looped back to the input side of the servo
amplifier 42 as a pressure feedback signal 45. Boost control in
response to the command pressure value from the boost controller 41
in accordance with elapsed time is conducted by the pressure
feedback path, which improves responsivity and precision of
boosting process in accordance with a boost control setting
curve.
[0089] Incidentally, the respective pressure sensors 36, 37 and the
pressure detecting amplifier 43 are not necessarily provided, in
other words, the pressure feedback signal 45 is not inputted to the
servo amplifier 42 but boost control in accordance only with the
command pressure value of the boost controller 41 may be
conducted.
[0090] The open-degree of the main spool 17A is looped back to the
output of the servo amplifier 42 (input of the pilot servovalve) as
the minor feedback signal 46 through the position sensor 17B and
the position feedback servo amplifier 44. The minor feedback path
improves responsivity and precision of the open-degree control of
the main spool.
[0091] Further, as shown in FIG. 1, a retraction circuit 16C for
retracting the injection piston 15 of the injection cylinder device
10 and the boost piston 26 of the boost cylinder device 20 are
connected to the discharging circuit 16A of the boost cylinder 20.
A logic valve 18 and an open-shut switching valve 19 are provided
to the retraction circuit 16C. When the hydraulic oil is fed from
the hydraulic oil feeding circuit 31 in the condition shown in the
drawing, the hydraulic oil is fed to a back-pressure side of the
injection cylinder device 10 and the boost cylinder device 20,
thereby retracting respective pistons 15 and 25.
[0092] In the above arrangement, the controller 40 controls
respective portions in accordance with a predetermined program to
perform prearranged injection process and boosting process.
[0093] Specifically, the plunger 151, the piston 15 and the piston
20 of the boost cylinder 20 start at a retraction limit
position.
[0094] Initially, the molten material is fed to the injection
sleeve to be thus capable of being injected to the mold die, the
check valve 11 is opened to feed the hydraulic oil from the
injection accumulator 13 to the injection cylinder device 10 to
advance the injection plunger 151.
[0095] At this time, the injection speed controlling flow-rate
control valve 17 is narrowed to set the injection speed at low.
Subsequently, when the injection plunger 151 is advanced to a
position where the molten material reaches the die gate, the
injection speed controlling flow-rate control valve 17 is opened to
fill the molten material at a stroke into the mold die by switching
the injection speed high. When the injection plunger 151 comes to a
predetermined position (detected by a position sensor 152) or the
pressure sensors 36 and 37 show a predetermined value, the
switching valve 22 is operated to open the boost control valve 21
while conducting the control by the injection speed controlling
valve 17, so that the hydraulic oil from the boost accumulator 23
is supplied to the backside of the boost piston 25 of the boost
cylinder device 20 to pressurize the hydraulic oil at back-pressure
side of the boost piston 25 of the boost cylinder device 20. The
boost piston 25 pressurize the hydraulic oil at the back-pressure
side of the injection piston 15 to pressurize the injection plunger
151 from the backside of the injection piston 15 through the
pressurized hydraulic oil.
[0096] The speed controlling flow-rate control valve 17 is
controlled so that the pressure at the intermediary stage of
boosting and the time before reaching the maximum pressure is
controlled to draw a boost pressure curve approximated to the burr
critical boost curve defined in advance by measurement etc. by
narrowing the main spool open-degree of the control valve 17 and
changing the open-degree at the intermediary of the process while
checking the present boost feedback signal 45 in accordance with
the boost control setting curve.
[0097] In the boost controller, the boost control setting curve is
defined as follows.
[0098] In FIG. 4, the boost curve CPI is a boost curve of an
existing die-casting machine, which gradually comes less slanted.
On the other hand, when the main spool open-degree of the boost
flow-rate control valve 17 is narrowed, inclination of the pressure
increase becomes less slanted as the boost curve CP2 and the time
before reaching the maximum pressure PH become longer. When the
spool open-degree of the flow-rate control valve 17 is widened, the
pressure increase speeds up as time elapses to reach the maximum
pressure PH at time t4.
[0099] The boost time (t4-t2) shown in FIG. 4 is a short time
period of approximate 50 to 100 msec. Though the boost curve CP2 by
the conventional on-off two position switching is influenced by
impact pressure and surge pressure when the valve is switched for
boosting process, since the inclination is less slanted than the
conventional boosting, the influence is not applied.
[0100] In order to obtain desired lenient inclination
characteristics, as shown in FIG. 2 and as described above, the
configuration of the distal opening of the spool 211 of the boost
control valve 21 (flowing side of the hydraulic oil) is tapered, in
other words, a stepped configuration having smaller diameter of
distal end than a body so that the flow-rate can be regulated by
moving the spool 211 and the spool maximum moving amount at the
maximum spool open-degree can be adjusted by the screw member 213
as a stopper member. Accordingly, as shown in FIG. 4, the boost
curve CP3 can be modified to have a desired kick-off
characteristics, thereby obtaining a curve similar to the
above-described burr critical curve CX in FIG. 7.
[0101] The flow-rate narrowing configuration of the opening of the
spool 211 of the boost control valve 21 is defined considering
following case too.
[0102] If the boost control valve 21 has no above-described
flow-rate narrowing function, when the flow-rate control valve 17
does not work for some reason, die-casting boost function is
disabled because pressure control is impossible.
[0103] However, when the spool 211 of the boost control valve 21 is
configured in a shape capable of narrowing the flow-rate, when the
flow of molten material is fed from the boost accumulator 23 to the
boost cylinder device 20, the flow-rate passing the spool 211 can
be reduced, thereby regulating the pressure and flow-rate to the
pressurized portion of the boost piston 25.
[0104] According to the opening configuration of the spool 211, the
boost characteristic in open condition can be approximated to the
burr critical boost curve as possible. When the boost control by
regulating the flow control valve 17, the spool is further opened
to secure wide open-degree position by the screw member 213.
[0105] If a trouble disabling the function of the flow-rate control
valve 17 occurs, the screw member 213 is used to adjustably lessen
the open-degree of the spool 211 so that a spool open-degree
position capable of obtaining desired boost curve is set.
[0106] Accordingly, though only a temporary disposition, normal
boosting process can be secured.
[0107] Thus established boost control setting curve is summarized
into data as pressure increment .DELTA.P for each elapsed time
.DELTA.t of boosting process, which is set in the boost controller
41 to be outputted at the start of operation as a pressure value to
be taken at present in response to elapsed time from initiation of
the boosting process. In summarizing into the data, .DELTA.P is
defined as
.DELTA.P/.DELTA.T=Q/V*.beta.,
[0108] where V is volume of the hydraulic oil to be boosted (volume
etc. at the advancement limit position); .beta. is a
compressibility of the hydraulic oil; and Q is a flow-rate of the
hydraulic oil supplied to the boost cylinder device 20 in boosting
process.
[0109] .SIGMA..DELTA.P of the total sum of .DELTA.P corresponds to
difference between boost initiation pressure (fill completion
pressure) P0 and boost completion pressure PH.
[0110] The data is defined because of following reasons.
[0111] The hydraulic oil supplied to the injection cylinder device
10 and the boost cylinder device 20 has a slight compressibility.
Therefore, even when the hydraulic oil supply is the same for the
respective cylinder device 10 and 20, the advancing position of the
injection piston 15 is shifted according to pressure.
[0112] For example, assuming that the volume of the hydraulic oil
at the head side at the advancement limit position of the injection
cylinder device 10 is V and the compressibility of the hydraulic
oil is .beta., there occurs shift of;
.DELTA.V=V(1-.beta.).
[0113] When the casting die is exchanged, since the advancement
limit is changed to change the volume of the hydraulic oil in the
injection cylinder device 10 at the advancement limit position, the
shift is also changed. Accordingly, when the boost control is
conducted according only to the position in the injection cylinder
device 10 or the supplied hydraulic oil amount (e.g. control only
by commanding open-degree of the main spool), exchange of the
casting die can not be coped with, thereby requiring changing
control command for each casting die.
[0114] In contrast thereto, when compression command is defined by
relational expression considering the compressibility and the
volume, the compression shift of the hydraulic oil can be dealt
with only by imputing the volume at the advancement limit and the
like in exchanging the casting die, thereby facilitating to deal
with the exchange of casting die and securing high-precision
control.
[0115] Incidentally, actual injection pressure can be checked by
the pressure sensors 36 and 37 in the previous boosting process,
and the pressure target value is corrected by the learning function
of the controller 40 by taking deviation against desired injection
pressure. Such control target data processing and correction by the
learning function can be implemented by existing software
techniques.
[0116] According to the present embodiment, following effects can
be obtained.
[0117] 1) Since the hydraulic oil supply flow-rate to the boost
cylinder device 20 can be related not by on-off operation in
boosting process continuously by the controller 40 using the flow
control valve 17 of the hydraulic oil discharging channel 16, the
flow-rate can be set variable. Accordingly, the boosting process
can be controlled in accordance with burr critical boost curve CX,
thereby preventing generation of burrs, which enables producing
high-quality die-casting products.
[0118] 2) Since the feedback control by pressure is possible based
on the pressure target value in accordance with the boost control
setting curve set on the boost controller 41 while checking the
actual boost pressure by the pressure sensors 36, 37 and the
pressure detecting amplifier 43 for boost control, boosting process
in line with the predetermined boost control setting curve can be
securely performed even when the mold die is exchanged.
[0119] 3) High-speed control is possible since both of the control
command and the control object are based on pressure so that
operation process for feedback control etc. can be simplified.
[0120] 4) Since the flow-rate control valve 17 has therein a pilot
servovalve 17C for controlling the open-degree of the main spool
17A and two-stage servovalve mechanism in which the output of the
position sensor 17B is fed back to the input of the pilot
servovalve 17C (output of the servo amplifier 42) is used,
stability as the servo mechanism can be enhanced, thereby
effectively improving response speed and precision in boost control
by the variable flow-rate.
[0121] 5) Since the pressure sensors 36 and 37 respectively
provided to the head side B and rod side A of the injection
cylinder device 10 and the pressure detecting amplifier 43 for
selectively operating either one of respective output or both of
them are provided, the actual pressure value in the injection
cylinder can be more precisely detected, which is effective for
implementing boost control by the variable flow-rate.
[0122] 6) Since the advancement of the injection cylinder device 10
can be speed-controllably controlled by back-pressure during
injection process and the flow-rate control valve can be controlled
so that the pressure detected by the pressure sensor follows a
predetermined curve in proceeding to the boosting process by the
injection speed controlling flow-rate control valve 17, the single
flow-rate control valve 17 can be used for both of the injection
and boost, thereby reducing the size of the device.
[0123] 7) Since injection control according to open control and
real-time feedback control by the flow-rate control valve 17 using
one high-responsive electrohydraulic servovalve can be conducted
for controlling the speed and boost of the two cylinder devices 10
and 20, high-quality die-casting products can be manufactured.
[0124] 8) Since the controller 40 can easily, securely and
precisely control the hydraulic oil flow-rate for boosting process
for each elapsed time, effective boost control by variable
flow-rate is possible.
[0125] 9) Since the injection accumulator 13 and the boost
accumulator 23 are independently provided, the pressure for the
injection process and the boosting process can be independently
conducted. Further, since the back-pressure of the boost
accumulator 23 is controlled by the casting pressure control valve
34, the maximum pressure by the boosting process can be easily and
securely controlled at will.
[0126] 10) Since the spool 211 of the boost control valve 21 is
configured in the tapered shape capable of narrowing the flow-rate,
when the molten material is fed from the boost accumulator 23 to
the boost cylinder device 220, the flow-rate passing the spool 211
can be regulated. Accordingly, even when a trouble disabling the
function of the flow-rate control valve 17 is occurred, the
open-degree of the spool 211 can be adjusted small to set to an
open-degree position capable of obtaining predetermined boost
curve, so that the boosting process by the boost control valve 21
is possible, thereby securing normal boosting process, however
temporary it may be.
[0127] Incidentally, the scope of the present invention is not
limited to the aforesaid embodiment, but includes following
modification.
[0128] Though two accumulators of injection accumulator 13 and the
boost accumulator 23 are provided in the above-described
embodiment, a single accumulator may be provided to be used for
both purposes.
[0129] The accumulator fill switching valve 32, the respective
pressure sensors 35 and 36, the encoder 152 etc. can be selectively
substituted by the other arrangement, or may be omitted as
necessary.
[0130] The configuration and size, material and the like of the
boost control valve 21, the injection speed controlling flow
control valve 17 may be appropriately selected for
implementation.
[0131] Further, the flow-rate control valve 17 may be arranged to
be servo-driven in accordance with given command open-degree. For
instance, as shown in FIG. 5, alternating current or direct current
servo motor 2111 may be used as a driving source for adjusting the
open-degree of the main spool and a rotary encoder 2131 may be used
as a position sensor, thereby forming local position feedback.
* * * * *