Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2000-10-23
2002-10-08
Lin, Kuang Y. (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S113000, C164S267000, C164S312000
Reexamination Certificate
active
06460596
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a method of coating a powder lubricant in a metallic injection molding machine having a die composed of a stationary die and a movable die, a sprue hole, runner groove, gate hole and cavity being formed on parting faces of these dies, molten metal being injected into the cavity via the sprue hole and runner groove so as to fill the cavity with the molten metal. Also, the present invention relates to a die used for metallic injection molding.
2. Related Art
As one of the high pressure casting methods of producing a metallic product from a low melting point metallic material such as aluminum, magnesium and zinc alloy, there is proposed a thixotropic molding method, which is disclosed in Japanese Examined Patent Publication Nos. 1-33541 and 2-15620. According to this method, a part is obtained as follows. When a raw material of alloy is agitated in a state in which solid and liquid are coexisting, the formation of dendrite is suppressed. Therefore, it is possible to obtain a slurry in which fine solid particles and liquid are coexisting. This semi-solid slurry is injected into a die in a short period of time and soldified. In this way, a part of alloy, in the microstructure of which solid is substantially uniformly distributed, can be obtained. Concerning the thus obtained molding, a ratio of contraction caused by solditication is low, and micro-shrinkage is small, that is, the number of trap holes is small and also the number of cavity holes caused by the contamination of gas is small. Therefore, the dimensional accuracy of the thus obtained part is high, and the mechanical property are excellent. An injection molding machine is used for the above method of manufacturing a molding of alloy in which the property of slurry is used. Briefly speaking, the injection molding machine is composed of a heating cylinder and a screw arranged in the heating cylinder, wherein this screw is capable of rotating in the rotational direction and driven in the axial direction. In general, an open type injection nozzle is provided in the front of the heating cylinder. In the outer peripheral sections of the heating cylinder and the injection nozzle, there are provided a plurality of heaters, the heating temperatures of which are individually controlled.
When molten metal is measured by an injection molding machine having an open type injection nozzle, it is necessary to set a plug in order to prevent the molten metal to be measured from leaking out from a forward end portion of the injection nozzle. A cold plug, which is formed when the molten metal is cooled and solidified to some extent, is used for this plug. The cold plug is formed as follows. After the shot, the injection nozzle coming into contact with the die is quickly deprived of heat, that is, heat is quickly conducted to the die. As a result, the molten metal staying at a forward end portion of the injection nozzle is solidified and the cold plug is formed. This cold plug is formed into such hardness that the cold plug can stand the pressure of molten metal, which is being measured, and also the cold plug can be drawn out when the injection pressure is given to it. Accordingly, when the screw is rotated, metallic slurry is successively conveyed to the forward end portion of the barrel. At this time, slurry is melted by the heat given from the heater around the barrel and also by the heat generated by the shearing and the frictional action when the screw is rotated. The thus slurry is stored in the measurement chamber provided in the forward end portion of the heating barrel. At this time, the sprue hole, runner groove and cavity are coated with a powder lubricant, and the screw is driven at high speed in the axial direction. Then, the slurry stored in the measurement chamber is injected into the cavity via the sprue hole, runner groove and gate hole and filled. At this time, the cold plug is caught by the cold plug catcher provided in the movable die. After the slurry has been cooled and solidified, the die is opened. Then, the part can be easily taken out from the die because the powder lubricant is coated inside the die. AT the same time, the sprue and runner are also discharged from the die.
On the other hand, another method of manufacturing a metallic mold is known which is a cold chamber type die casting method. As disclosed in Japanese Unexamined Patent Publication Hei. 6-320246, the die casting machine
50
used for this die casting method is composed as follows. As shown in
FIG. 3
, the die casting machine
50
includes: a stationary die
52
attached to the stationary base
51
; a movable die
53
which composes a pair together with the stationary die
52
; a sleeve
54
penetrating the stationary base
51
; and a plunger
55
arranged in the sleeve
54
being capable of moving in the axial direction. In the sleeve
54
, there is provided a molten metal supply port
56
. This molten metal supply port
56
is closed by the shutter
57
′ when the powder lubricant is coated. The powder lubricant supply nozzle
57
is attached to this shutter
57
′. When molten metal is poured into the sleeve
54
, the powder lubricant supply nozzle
57
is retracted together with the shutter
57
′. On the parting line between the stationary die
52
and the movable die
53
, there is formed a cavity
60
for forming a part. The first exhaust passage
61
is open to an end portion of this cavity
60
. The first exhaust passage
61
is opened and closed by the shut-off pin
63
driven by the hydraulic piston cylinder unit
62
. The second exhaust passage
64
branches from the first exhaust passage
61
in such a manner that the second exhaust passage
64
makes a right angle with the first exhaust passage
61
. Although not shown in
FIG. 3
, the second exhaust passage
64
is connected with a valve, vacuum tank and exhaust pump via the flexible hose
65
. In this connection, the powder lubricant supply nozzle
57
is connected with a powder lubricant supply device, from which a predetermined quantity of powder lubricant is supplied by compressed air, via the flexible hose
58
. This powder lubricant supply device is not shown in
FIG. 3
, either. The ejector plate and ejector pin are not shown in
FIG. 3
, either.
It is possible to obtain a part as follows by the die casting machine
50
which is composed as described above. As shown in
FIG. 3
, the movable die
53
is fastened to the stationary die
52
, and the shut-off pin
63
is retracted as shown in FIG.
3
. Then, the exhaust pump is driven. Then, air is discharged from the cavity
60
, gate passage
66
, sprue
67
and sleeve
54
into the vacuum tank. Due to the foregoing, the inside of each component is decompressed. At this time, the shutter
57
′, to which the powder lubricant supply nozzle
57
is attached, closes the molten metal supply port
56
. Due to the foregoing, air is prevented from being sucked from a portion close to the molten metal supply port
56
. Powder lubricant is supplied from the powder lubricant supply device by compressed air for a predetermined period of time. Therefore, the powder lubricant adheres onto the inner surfaces of the cavity and others. The shut-off pin
63
is driven by the hydraulic piston cylinder unit
62
, so that the first exhaust passage
61
is closed. After that, a predetermined quantity of molten metal is supplied from a crucible into the sleeve
54
via the molten metal supply port
56
. The thus supplied molten metal is injected into the cavity
60
by the plunger
55
. When the movable die
53
is opened after the thus injected and charged molten metal has been cooled and solidified, the ejector protrudes and a part can be provided.
As described above, according to the metal injection molding machine, it is possible to obtain a part, the dimensional accuracy of which is high and the mechanical property of which is excellent. However, problems may be encountered in the method of coating a powder lubricant. Concerning these problems, th
Gohonjo Keiji
Sakamoto Ryuichi
Takayasu Hidenori
Tange Toshiyuki
Tukeda Tadayoshi
Lin Kuang Y.
The Japan Steel Works Ltd.
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