JPS642469B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-stage vacuum die casting process and apparatus.

Generally, during injection molding using a die casting machine, the presence of gas within the mold cavity poses a problem. That is, if gas is present in the mold cavity, the supplied molten metal will entrain the gas, creating cavities in the molded die-cast product, making it impossible to obtain a good die-cast product.

Therefore, in the past, just before injection,
A low-pressure die-casting method is used, in which the gas in the mold cavity is removed and the injection operation is performed under a vacuum condition.

By the way, generally speaking, in the injection operation, as shown in the diagram of FIG. 1, the injection speed is initially set low and injection is started from point A, and high-speed injection is started from point D after a predetermined time has elapsed. Then, braking is rapidly applied at point E, which is the injection completion point, and filling of the molten metal is completed.

On the other hand, if we take as an example the case where various die-casting methods are adopted, the changes in the gas pressure within the cavity in response to the injection operation performed with the above-mentioned changes in injection speed are shown in Figure 2. A curve showing the pressure state inside the cavity is obtained as shown in .

In other words, curve 1 in Fig. 2 shows the case where a general conventional die-casting method is used without using a pressure reduction method, and the gas pressure in the mold cavity increases from point A, which is the injection start point, to the injection sleeve. The pressure does not rise until point B, when the sprue is blocked by the chip, but after point B, as low-speed injection progresses,
The pressure gradually increases, increases even more rapidly during high-speed injection, and reaches the maximum pressure at the end of injection.

This means that a large amount of gas exists in the cavity, which is the worst molding condition.

The curve indicated by numeral 2 in Fig. 2 shows the pressure change when a die casting method equipped with an auto air vent valve is used, although pressure reduction is not performed. However, from point D, which is the start of high-pressure injection, the pressure inside the cavity begins to rise, indicating that gas remains, which is still a bad condition for molding conditions. The auto air vent valve is initially open during injection operation, allowing gas inside the cavity to escape to the outside, but as molten metal advances, the valve automatically closes due to the action of the molten metal. This is a valve for venting gas inside the mold.

The curve indicated by numeral 3 in Fig. 2 shows the pressure change when the conventionally known reduced pressure die casting method is adopted. The pressure begins to rise, and this method is also unfavorable as a molding condition.

Further, the curve indicated by reference numeral 4 in FIG. 2 shows the change in gas pressure when an auto air vent valve is employed and a one-stage pressure reduction method is employed. In this method, pressure reduction is started at point _C1 immediately before point D, which is the start point of high-speed injection.

When this method is adopted, pressure reduction starts immediately before high-speed injection, so if the high-speed injection speed is selected appropriately,
Although molding is carried out in relatively good conditions, the gas mixed into the molten metal in the sleeve during the low-speed injection process cannot be sufficiently removed because the pressure is not reduced.

On the other hand, the curve indicated by reference numeral 5 uses an auto air vent valve and adopts the pressure reduction method, but the pressure reduction starts at a high degree of vacuum from the time the chip closes the pouring port of the sleeve. but,
When this method is used, there is a gap between the injection sleeve and the chip, and if the pressure is reduced at a high degree from the beginning, air will be sucked in at high speed through that gap, resulting in ripples inside the sleeve. There is a risk that some of the molten metal may become splashed and enter the cavity, solidifying before other molten metal and impairing the quality of the product.

Additionally, there is a risk that molten metal droplets may be sucked into the auto air vent valve or pressure reducing pipe, clogging the drain pipe.

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and provides a two-stage vacuum die casting method and apparatus that make it possible to obtain high quality die cast products.

Incidentally, the curve indicated by reference numeral 6 in FIG. 2 shows the pressure change due to the two-stage vacuum die-casting method of the present invention.

In the following, the method and apparatus of the invention will be explained in conjunction with the embodiments shown in the drawings.

FIG. 3 is an illustration of an embodiment of a die-casting apparatus employing the method of the present invention. In the figure, the reference numeral 1 indicates a fixed die, the reference numeral 2 indicates a movable die, and there is a gap between the two. A cavity 3 is formed. The cavity 3 communicates with the injection sleeve 4 via a runner 4a, and the injection sleeve 4 is formed with a pouring port 5 for pouring molten metal.

Reference numeral 6 indicates an injection cylinder, and an injection plunger 7 is connected to the tip of the piston rod.A plunger tip 8 is fixed to the tip of the injection plunger 7.
is slidably fitted into the injection sleeve 4.

A striker 9 is provided on the rod of the injection cylinder 6, and at a position where the tip of the striker 9 can come into contact, a limit switch LS-1 for starting the primary decompression of low vacuum and a limit switch LS-1 for starting the secondary decompression of high vacuum are activated. 2, and a high-speed injection limit switch LS-3.

On the other hand, a gas venting groove 10 is formed in a part of the abutting surface between the fixed mold 1 and the movable mold 2, and the tip of this gas venting groove 10 is connected to a bypass 10.
The tips of the bypasses 10a and 10a are opened on both sides of the valve 12 of the auto air vent valve 11, which is fixed to the fixed mold 1 side and provided on the mating surface with the movable mold 2. ing. Third
In the figure, for clarity, bypass 10
Although the bypass 10a is drawn in the molds 1 and 2, the bypass 10a is actually formed into a groove shape on the separation surface of the movable mold 2. 11a is a compression spring, and 11b is a cylinder.

That is, the auto air vent valve 11 is
As shown in FIG. 3, on the separation surface of the molds 1 and 2,
A gas venting groove 10 led from the cavity 3, a valve 12 that slides in the axial direction of the gas venting groove 10 at the end of the gas venting groove 10 by the direct action of the injected melt advancing from the cavity 3, and A detoured bypass 10a is provided from the middle of the drainage groove 10 to the side surface of the valve 12 portion, and a passage that can directly regulate communication and isolation between the bypass 10a and the outside by moving the valve 12 in the axial direction is provided as a valve. This is a degassing device for molds installed in the section. Auto air vent valve 1
1 utilizes the difference in specific gravity between gas and molten metal, for example, the difference in specific gravity between air and molten aluminum, which is about 1:2000, and the difference in inertia based on this difference in specific gravity. The valve 12 does not close due to the action of the gas with a low specific gravity that first advances, but closes automatically when the molten metal with a high specific gravity that advances following the gas directly hits the lower surface of the valve 12. will be closed to. As a result, the gas in the cavity 3 is sufficiently exhausted, but the molten metal is not discharged to the outside beyond the valve 12 section or the bypass section 10a.

A pipe 13 is led out from the middle of the auto air vent valve 11, and the tip of this pipe 13 further branches into first and second pipes 14, 15, and the first pipe 14 is a non-return valve. Vacuum tank 1 for low vacuum via valve 16 and electromagnetic switching valve 17
8 is connected. Vacuum tank 18 is motor M
It is connected to a vacuum pump 19 for low vacuum driven by. The electromagnetic switching valve 17 is switched by a signal from a limit switch LS-1 for starting primary pressure reduction.

On the other hand, the second pipe 15 is connected to a high vacuum vacuum tank 22 via a check valve 20 and an electromagnetic switching valve 21, and the vacuum tank 22 is a high vacuum vacuum pump driven by a motor M. It is connected to 23. Reference numeral 24 indicates a pressure gauge.

Next, the operation of this embodiment configured as above will be explained.

First, with the mold clamped and the valve 12 open,
Supplying a predetermined amount of molten metal from the molten metal pouring port 5 of the injection sleeve 4 and operating the injection cylinder 6;
The injection plunger 7 starts moving forward. Then, when the plunger tip 8 closes the pouring port 5, the striker 9 simultaneously activates the limit switch to start the primary decompression.
LS-1 is activated, the electromagnetic switching valve 17 is switched in response to the signal, and the low vacuum vacuum pump 19 is activated to drain the gas in the cavity 3 to the gas vent groove 10, the bypass 10a, and the open valve 12. suction through. However, in this case, since the vacuum is low, air is not sucked in at high speed from the gap between the injection sleeve 4 and the plunger tip 8, and the molten metal droplets rippling inside the injection sleeve 4 are removed. is not guided into cavity 3.

Eventually, as the injection plunger 7 advances, the striker 9 activates the limit switch for starting secondary decompression.
When the LS-2 is activated, the electromagnetic switching valve 21 is switched in response to the signal, and the high vacuum pump 22 is activated to release the gas in the cavity 3 to the gas vent groove 10, the bypass 10a, and the open valve. 12 parts to create a high vacuum inside cavity 3.

Immediately after that, limit switch LS for high-speed injection
-3 is struck by the striker 9, and high-speed injection is performed. Therefore, a cavity-free injection product without gas entrainment is obtained. After the cavity 3 is filled with molten metal, the molten metal rising in the gas vent groove 10 acts directly on the lower surface of the valve 12, pushing the valve 12 up and closing it. Molten metal bypass 10
a, but since the valve 12 closes automatically,
It never leaves the bypass 10a.

Curve 6 shown in Figure 2 shows the pressure change inside the cavity that occurs during the above operation, and point B corresponds to the point at which limit switch LS-1 is struck.
Point C ₂ corresponds to the time when limit switch LS-2 is struck. Point D indicates the start of high-speed injection, and point E indicates the completion of injection. As is clear from Figure 2, a two-stage depressurization method is used, in which the pressure is initially reduced to a low vacuum during low-speed injection, and then reduced to a high vacuum just before high-speed injection, thereby preventing molten metal from splashing. There is no suction into the cavity 3 and no clogging of the auto air vent valve 11.
Good vacuum die casting is performed.

FIG. 4 explains another embodiment of the present invention. In this embodiment, two electromagnetic switching valves 17 and 21 are connected in parallel following the piping 13 after the auto air vent valve 11. The electromagnetic switching valve 17 is connected to one vacuum tank 22 for high vacuum, and a throttle 25 is provided on the side of the electromagnetic switching valve 17 for low vacuum.
The structure is such that when the switching occurs, the inside of the cavity 3 becomes a low vacuum. Of course, the limit switch LS-1 and the electromagnetic switching valve 17 are linked, and the LS-
2 and the electromagnetic switching valve 21 are in an interlocking relationship. Even if such a device is adopted, effects exactly similar to those of the embodiment shown in FIG. 3 can be expected.

FIG. 5 explains still another embodiment of the present invention. In this embodiment, a pressure reduction cylinder 26 is connected to the pipe 13 after the auto air vent valve 11, and this pressure reduction cylinder 26 is operated. A low vacuum electromagnetic switching valve 17 is connected to the cylinder 27,
An electromagnetic switching valve 21 for high vacuum is connected in series with this electromagnetic switching valve 17, and a bypass passage 28 is provided by bypassing the electromagnetic switching valve 21 for high vacuum. A cylinder drive source 30 such as a power source or a compressed air pressure source is connected to an electromagnetic switching valve 17. Due to the presence of the throttle 29, the electromagnetic switching valve 17
is in communication and the solenoid switching valve 21 is closed, the inside of the cavity 3 becomes a low vacuum, and the solenoid switching valve 1 is closed.
When both 7 and 21 are connected, cavity 3
There will be a high vacuum inside. Of course, even in this embodiment, the limit switch LS-1 and the electromagnetic switching valve 17 are
Furthermore, the LS-2 and the electromagnetic switching valve 21 are in an interlocking relationship. Even if such a structure is adopted, the same effects as in each of the above embodiments can be obtained. In the above embodiment, the electromagnetic switching valves 17 and 21 were switched by the operation of the limit switches LS-1 and LS-2, but this could be done by other position detection sensors such as non-contact switches or phototubes, or by This may be done using a signal from a timer that starts counting from the start of injection.

As is clear from the above description, according to the present invention, during low-speed injection, the cavity is heated to low vacuum via an auto air vent valve attached to the mold, and immediately before high-speed injection, the cavity is heated to high vacuum via the auto air vent valve. Die casting is performed by reducing the pressure inside the chamber and automatically closing the auto air vent valve by the action of the molten metal before the injected molten metal reaches the gas discharge port of the auto air vent valve. There is no inconvenience caused by air being sucked into the cavity as droplets or sucked into the auto air vent valve and causing it to clog, and good vacuum die casting can be performed with the cavity inside being sufficiently depressurized. , you can be sure to easily obtain high quality injection products without cavities.

[Brief explanation of drawings]

Figure 1 is a diagram explaining the relationship between the time after the start of injection and the injection speed, Figure 2 is a diagram showing the time after the start of injection and the pressure change in the cavity, Figures 3 to 5
The figures are schematic configuration diagrams showing different embodiments of the present invention. 1... Fixed mold, 2... Movable mold, 3... Cavity, 6... Injection cylinder, 8... Plunger tip, 11... Auto air vent valve, 1
2... Valve, 17, 21... Solenoid switching valve, 18, 2
2... Vacuum tank, 19, 23... Vacuum pump,
26...Reduction cylinder, 27...Cylinder.

Claims (1)

[Claims] 1. During the low-speed injection stroke of a cold chamber die-casting machine, the injection sleeve is initially filled with a low vacuum from the vicinity where the plunger tip closes the pouring port of the mold via an auto air vent valve attached to the mold. The pressure is reduced to a high degree through the auto air vent valve near the beginning of the high-speed injection process, and the auto air vent valve is closed before the molten metal reaches the gas discharge port of the auto air vent valve. A two-stage vacuum die-casting method that is characterized by producing high-quality die-cast products with extremely little residual gas in a closed manner. 2 Two decompression lines, low vacuum and high vacuum, are connected to the mold via an auto air vent valve installed in the mold, and are connected to the mold by a position detection sensor or timer signal that operates near the start of low-speed injection of the die-casting machine. A valve that opens to start low vacuum depressurization is attached to the low vacuum decompression line, and a valve that opens and starts high vacuum depressurization in response to a signal from a position detection sensor or timer that operates near the start of high-speed injection is installed on the other side. The auto air vent valve is installed in the high vacuum decompression line of the auto air vent valve, and is equipped with a valve device that closes the gas outlet before molten metal reaches the auto air vent valve's gas outlet. A two-stage vacuum die-casting device that enables the production of extremely small quantities of high-quality die-cast products.