Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2002-05-13
2004-11-02
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S319000
Reexamination Certificate
active
06810940
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure casting process, especially relates to a drive control method for a squeeze pin used in the process.
2. Description of Related Art
Generally, in a pressure casting such as an operation in a die-casting machine, volume contraction arises in molten metal when it is injected into a mold cavity and solidifice therein. Then, shrinkage holes occur in mold article, which influence undesirable effects on strength and air-tight of the mold article.
Especially, in the die-casting machine, there is provided with a sharp slope of temperature, and shrinkage holes occur frequently. Therefore, various ways to avoid occurrence of such shrinkage holes have been proposed. A typical way is to use a pin which squeezes molten metal to homogenize matrix of a mold article by protruding into a cavity after the molten metal is injected and filled in the cavity.
FIGS. 4
to
FIG. 12
illustrate such way to use a squeeze pin.
FIG. 4
illustrates a main composition of a die-casting machine. In
FIG. 4
, numeral
1
designates a pair of mold dies. Molten metal
4
is teemed or injected into a cavity
2
formed by the mold dies
1
. The mold dies
1
are formed with a moving mold die
5
and a fixed mold die
6
. The moving mold die
5
is mounted on a moving die plate
51
, and the fixed mold die
6
is mounted on a fixed die plate
61
.
Operation for die clamping or die opening and closing is executed by moving the moving die plate
51
. An injection sleeve
3
is mounted on the fixed die plate
61
. An opening portion at the most right top of the sleeve
3
communicates through a gate
7
with the cavity
2
. The molten metal
4
in the sleeve
3
is injected to the cavity
2
by an injection plunger
8
which is slidably inserted in the injection sleeve
8
. The injection plunger
8
is driven by a injection cylinder
9
which is co-axially arranged with the injection sleeve
3
. Numeral
10
designates a detector mounted on the injection cylinder
9
for detecting an injection pressure.
Also, in the mold dies
1
, there are provided with a squeeze pin
11
and a squeeze cylinder
12
to drive the squeeze pin
11
between the moving mold die
5
and the moving die plate
51
.
The squeeze pin
11
is inserted in a hole
13
located on the moving die
5
with its top capable of protruding into the cavity
2
. The squeeze cylinder
12
and the squeeze pin
11
are arranged co-axially.
Also, there is provided with a stroke sensor
14
inside the squeeze cylinder
12
for detecting stroke quantities or length of the squeeze pin
11
. This stroke sensor
14
is an absolute type of position detector using a differential transformer, which output signal to an identical stroke position is always kept to be the same because of determining the position of origin by the sensor itself.
Namely, as shown in
FIG. 6
, there are provided with a sleeve like coil portion
16
screwed into a bore formed inside a piston
17
of the squeeze cylinder
12
, and a core
18
movably inserted therein, fixedly mounted on a cylinder head
15
of the squeeze cylinder
12
.
Accordingly, the sleeve like coil portion
16
generates a signal corresponding to relative displacement between the core
18
and the coil portion
16
when the piston
17
moves in the cylinder
12
.
The squeeze pin
11
is fixedly connected with the piston
17
(not shown in FIG.
6
).
Therefore, the stroke quantity of squeeze pin
11
can be detected by means of a position of the piston
17
. An increment type of stroke sensor may be used. However, such type of sensor needs a signal corresponding to the position of origin that brings about space or environment problems. Therefore, it is preferable to use the absolute type of stroke sensor.
In
FIG. 4
, each output signal of the stroke sensor
14
and the injection pressure sensor
10
is applied to an input unit
21
of a controller
20
which provides with a central processing unit (CPU)
22
, a memory
23
and an output unit
24
besides the input unit
21
. The output unit
24
is connected through an amplifier
25
to a solenoid valve
26
which directly controls the operation of the squeeze cylinder
12
.
Also, numeral
27
designates a control apparatus for controlling various operations of a die-casting machine, which is connected to the controller
20
to input various control information such as initial value S
0
of optimal stroke length and etc.
FIGS. 8
(
a
) and (
b
) show wave forms of the injection pressure P and the piston stroke S
0
in relation to a drive control operation of the squeeze pin
11
. As shown
FIG. 8
, an count timer
201
starts its time counting operation at the time when the injection pressure P reaches a set value P
0
(at the time of switching to boosting). When the time counting operation reaches time up state, that is, a time interval T
0
passes, the count timer
201
generates a signal so as to switch the solenoid valve
26
, which in turn causes the squeeze cylinder
12
to move the squeeze pin
11
, thereby squeeze operation being executed.
FIG. 7
shows a control block diagram of the controller
20
. In
FIG. 7
, actual stroke quantity Sa of the squeeze pin
11
is detected by the stroke detector
14
and then it is fed back to confirm whether or not the detected value Sa is within a target zone (allowance zone) S
0
±&agr;. Based on the confirmation, a correct means
200
supplies to the count timer
201
a corrected time interval T
0
±&Dgr;T where &Dgr;T is small time unit as a parameter stored in the memory
23
. Then, next step of injection molding is executed.
In the next step, the count timer
201
starts its time counting operation at the time when the injection pressure P reaches the set value P
0
stored in the memory
23
. When the corrected time interval T
0
+&Dgr;T elapses by the counting operation, the count timer
201
generates the signal so as to switch the solenoid valve
26
, which in turn causes the squeeze cylinder
12
to move the squeeze pin
11
, thereby squeeze operation being executed in accordance with the corrected time interval.
In a trial molding process, each molding step is repeated by modifying the time interval in such a way described above so that the stroke of actual squeeze pin
11
comes into the optimal target zone S
0
+&agr;.
FIG. 5
is a flow chart showing a process for drive control of the squeeze pin
11
. At the step
1
of
FIG. 5
, parameters such as injection pressure P
0
, optimal stroke S
0
, allowance zone ±&agr; for the optimal stroke S
0
, code N
0
of mold die
1
, time interval T
0
corresponding to time up of count timer
201
, small time unit &Dgr; T for modifying the time interval T
0
and shot repeat number n for modifying the time interval T
0
are preset. At the step
2
, injection operation starts. Then, at the step
3
, the injection pressure P detected by the pressure senor
10
is compared with the preset value P
0
. When detected injection pressure P reaches preset value P
0
, the count timer
201
starts to the counting operation. Then, at the step
4
it is judged that the count timer
201
becomes time up or not. In case of time up, at the step
5
, the timer
201
supplies a signal through the output unit
24
to the solenoid valve
26
which causes the squeeze cylinder
12
to move the squeeze pin
11
. As the squeeze pin
11
moves, molten metal
4
in the cavity
2
is squeezed.
The squeezed molten metal
4
is also on the way to solidification. When the solidification progresses to an extent, the squeeze pin
11
can not move further and stops. At the step
6
, the stroke sensor
14
detects a stroke Sa of the squeeze pin
11
when it stops. Then, at the step
7
, the detected stroke Sa is compared with the optimal stroke S
0
stored in the memory
23
at the CPU
22
, and judged whether or not the detected stroke Sa is within the target zone S
0
±&agr;. In case of the stroke Sa to be within the target zone, the initial preset value of time interval T
0
±
Nakano Toshiaki
Toyoshima Toshioki
Tsuji Makoto
Lin Kuang Y.
Pillsbury & Winthrop LLP
Toshiba Kikai Kabushiki Kaisha
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