Metal founding – Process – With measuring – testing – inspecting – or condition determination
Reexamination Certificate
2002-02-12
2003-07-01
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
With measuring, testing, inspecting, or condition determination
C164S113000, C164S133000, C425S145000, C264S040100
Reexamination Certificate
active
06585031
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a method of injection molding a low-melting-point alloy, and more particularly to a method of injection molding a low-melting-point alloy in which a low-melting-point alloy, which is a molding material, is melted in a cylinder of a screw-type low-melting-point alloy injection molding machine and is injected into a mold by a screw to effect molding, and control is provided such that an appropriate quantity of material is fed from a material feeder in correspondence with a shot and the quantity of material detained in the cylinder is maintained appropriately.
2. Related Art
Conventionally, methods of injection molding a low-melting-point alloy include a pressure die casting process and a metal injection molding process. The low melting point referred to herein means a temperature up to 700° C. or thereabouts, and as specific materials which can be used, Al, Mg, Zn, Bi, Sn, and Pb alloys correspond to them. As shown in
FIG. 1
a
, a low-melting-point alloy injection molding machine using an in-line type screw as in the metal injection molding process is comprised of a screw-type, belt-type, or a vibration-type material feeder
16
for feeding material chips of a low-melting-point alloy, a screw
11
, a cylinder
12
, and a heater
13
for transporting and melting the fed material, a nozzle
14
and a high-speed injecting apparatus
17
for injecting and ejecting the molten material into a mold
19
, and so on.
With the above-described low-melting-point alloy injection molding machine, a metal in chip form which is obtained by cutting ingots, as shown in
FIG. 1
b,
is used as a raw material. In the low-melting-point alloy injection molding machine, the material stored in the hopper of the material feeder
16
is fed into the cylinder
12
by the material feeder
16
. The material thus fed is transferred forwardly inside the cylinder
12
by the rotation of the screw
11
disposed in the cylinder
12
so as to be rotatable and reciprocatable. The material, while being transferred, is set in a predetermined molten state on heating by the heater
13
(an electric heater, a induction heater, or the like) attached to an outer peripheral portion of the cylinder
12
.
At the time of the above-described heating, the screw
11
, while rotating in the cylinder
12
, retains the material in the molten state (a molten light metal) in a retaining section
15
at a distal end of the screw
11
, and retracts to the material feeder side at a fixed speed. The material in the molten state retained in the retaining section
15
is metered by the amount of this retraction. Namely, at the point of time when the screw
11
reaches a predetermined retraction stroke as the screw
11
rotates, the rotating and reciprocating motion of the screw
11
are finished, thereby completing the metering of a predetermined quantity of a molten light metal corresponding to the retraction stroke. In the injection process after completion of the metering, the screw
11
is advanced at high speed by the high-speed injecting apparatus
17
, and the molten light metal metered in the retaining section
15
is injected into the mold
19
through the nozzle
14
at the distal end of the cylinder
12
.
With such a low-melting-point alloy injection molding machine, there are cases where, during the metering operation, the rotational load pressure of the screw rises, and the number of revolution of the screw varies. If such a situation occurs, variations occur in the quantity of molten metal injected in an ensuing shot. It is experientially known that the rise of the rotational load pressure is related to the quantity of material detained in the cylinder and occurs when the quantity of material detained exceeds an upper limit. That is, the quantity of material detained is determined by the relationship between, on the one hand, the quantity of material chips (quantity of material chips=Q
in
) fed from the material feeder and, on the other hand, the quantity of molten metal discharged (shot weight=Q
out
) discharged into the mold in the injection process for each shot. The following situation occurs depending on the relationship between their relative magnitudes:
(A) In the case of Q
in
>Q
out
:
Since the quantity of material fed is large relative to the shot weight, the quantity of material detained, Q, inside the cylinder increases by
&Dgr;
Q
(=
Q
in
−Q
out
)
for each shot. Consequently, increments &Dgr;Q of the detained quantity are accumulated with the advance of molding, and there are cases where an abnormality occurs to the rotation of the screw when the quantity of material detained, Q, has exceeded an upper limit Q
max
.
(B) In the case of Q
in
<Q
out
:
Since the quantity of material fed is small relative to the quantity of molten metal discharged, the quantity of material detained, Q, decreases by
&Dgr;
Q
(=
Q
out
−Q
in
)
for each shot. Consequently, decrements &Dgr;Q of the detained quantity are accumulated with the advance of molding, and a short shot occurs when the quantity of material detained, Q, has fallen below a lower limit Q
min
.
As described above, the quantity of material detained in the cylinder exerts a large influence on the stability of the metering of the low-melting-point alloy injection molding machine, so that, in practice, a balance is established between them, and adjustment of molding conditions is carried out so as to effect molding in a state in which a fixed quantity of material is detained. As a specific countermeasure, while observing the change in the rotational load pressure or the state of filling of molded articles, and the like, settings of the quantity of material fed, q, per unit time or the feeding time t
s
of the material feeder, and the like are adjusted on the basis of experience so as to feed the material in a quantity commensurate with the shot weight. However, it has been difficult to stably and continuously maintain the quantity of material detained due to the variation of the shot weight and the variation of the quantity of material fed by the material feeder, or due to a change in the molten state of the material in the cylinder in consequence of the temporary stopping of the machine.
SUMMARY OF INVENTION
The invention has been devised to overcome the above-described problems, and its object is to provide a method of injection molding a low-melting-point alloy in which an upper limit and a lower limit of the quantity of material detained in the cylinder are set to eliminate an excess or a shortage of the quantity of material detained in the cylinder in the process of injection molding a low-melting-point alloy, and which is capable of automatically maintaining the quantity of material detained in the cylinder within the range between the set upper and lower limits.
To overcome the above-described problems, in accordance with the invention there is provided a control method of an injection molding in which a low-melting-point alloy, which is a molding material, melted in a cylinder of a screw-type low-melting-point alloy injection molding machine and injected into a mold by a screw to effect molding, and control is provided such that an appropriate quantity of material is fed from a material feeder in correspondence with a shot and the quantity of material detained in the cylinder is maintained appropriately, comprising the steps of:
setting a unit increment (&Dgr;Q
+
) and a unit decrement (&Dgr;Q
−
) as well as an upper limit (Q
max
) and a control lower limit (CQ
min
) of a quantity of material detained; and
automatically repeating the operation in which an injection process is executed by feeding the material in a quantity
(
Q
in
=Q
out
+&Dgr;Q
+
)
which is the unit increment (&Dgr;Q
+
) greater than each shot weight (Q
out
), and when the quantity of material detained (Q) in the cylinder has reached the upper limit (Q
max
) due to the accumulation of the unit increments (&Dgr;Q
+
) the quantity of mate
Elve M. Alexandra
Sughrue & Mion, PLLC
The Japan Steel Works Ltd.
Tran Len
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