JPH0227065B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a die casting method for reducing internal defects, particularly bubble entrainment defects. (Prior art) In die casting, in order to inject the molten metal injected into the injection sleeve into the cavity of the mold at high speed and high pressure using a plunger, the gas present in the cavity of the mold is completely removed through air removal etc. It is well known that some of the metal cannot be discharged properly and gets caught up in the molten metal, causing internal defects in the form of bubbles. Such bubbles may expand during subsequent heat treatment and may cause surface defects on the product. As methods for reducing the occurrence of such internal defects, two methods have been proposed and put into practical use. One method is called a vacuum die casting method, in which the molten metal is injected after creating a vacuum inside the cavity of the mold. Another method is to replace the gas (mainly air) already present in the cavity of the mold with a gas that reacts with the molten metal and then perform injection. However, in the vacuum die casting method, the injected molten metal easily enters the vacuum passage leading to the mold cavity and solidifies, so the lever must be unclogged before the next die casting process. There are drawbacks such as poor workability and operational efficiency, and in addition, there are many other troublesome problems that need to be solved, such as the problem of outside air entering through gaps such as between molds and the sealing mechanism to prevent this. In addition, in the die-casting method using reactive gas displacement, the above-mentioned problems in vacuum die-casting are avoided because the reactive gas is supplied at a pressure higher than atmospheric pressure.
There is a problem that a small amount of unreacted gas is drawn into the molten metal and forms bubbles in the same way as conventional air, which has not been solved. Under these circumstances, a casting method that combines a vacuum die-casting method and a die-casting method using reactive gas displacement has been proposed. For example, special public service in Showa 57
As described in Publication No. 140, the inside of the mold cavity and the injection sleeve are evacuated, and a reactive gas is injected into the mold cavity and the injection sleeve,
This is a method in which the molten metal supplied into the injection sleeve is press-fitted into the cavity of the mold in a reactive gas atmosphere under reduced pressure. This casting method achieves the effects of the reactive gas replacement die-casting method by injecting reactive gas in a vacuum state, achieving a high substitution rate with a small amount of reactive gas. It is intended to obtain the effects of vacuum die casting under a reduced pressure state with a not-so-high degree of vacuum. However, since this method performs casting under reduced pressure, the degree of vacuum may be low because a reactive gas is supplied, but there is a problem of intrusion of outside air through gaps such as between casting gaps. This type of intruding air mixes with reactive gases, and when caught in the molten metal, it does not react and remains as bubbles, so in practice, bubble generation cannot be sufficiently prevented when the vacuum is low. It was hot. In other words, if the degree of vacuum is brought close to atmospheric pressure, the intended effect of vacuum die casting will be reduced.
In addition, in order to realize die casting in a reduced pressure state with a low degree of vacuum, a sealing mechanism is adopted as described in column 6, lines 6 to 10 of the publication and shown in Figure 2. In addition, it is preferable to supply the reactive gas from the sealed portion, which has the disadvantage that the construction of the casting apparatus itself becomes complicated and expensive. For this reason, the conventional method of combining vacuum die-casting and die-casting using reactive gas displacement cannot be said to be a complete technology in practice, and the cost and effectiveness may vary depending on the shape of the product to be cast, etc. There were fundamental problems that affected its applicability. (Objective of the Invention) An object of the present invention is to further improve the conventional technology and provide a die casting method that can relatively easily and reliably reduce the occurrence of internal defects due to air bubble entrainment. (Summary of the invention) The present invention basically focuses on improving the die-casting method by replacing reactive gases, and in particular, improves the formation of bubbles due to the entrainment of unreacted gases in the reactive gas-replacing die-casting method. In order to reduce the generation of
This is carried out at a pressure of 0.1 Kg/cm2 or ^less , and under this pressure, scavenging (air and reactive gases are forced into the mold cavity) to forcefully form a flow of air through the mold cavity to the outside. The main feature is to extract information from More specifically, in the die-casting method according to the present invention, reactive gas is supplied into the die-casting apparatus through the injection sleeve, while continuously scavenging air is carried out from the mold cavity. This creates a flow of air that flows to the outside of the die-casting device through the flow, and this flow converts some or all of the air that originally exists in the mold cavity and the spaces inside the die-casting device such as the injection sleeve into reactive gas. At the same time, the internal pressure of the cavity of the mold is made slightly higher than atmospheric pressure, and under this condition, the plunger starts operating to inject the molten metal, and the movement of the plunger causes die casting. After the reactive gas supply port to the inside of the device is shut off, the reactive gas already filled in the injection sleeve is supplied into the mold cavity by the movement of the plunger. It is characterized by preventing the occurrence of an extreme depressurization state. The reason why we set the pressure inside the mold cavity slightly higher than atmospheric pressure and continuously scavenge air from the mold cavity was to first set the air pressure in the flow path to a positive pressure (above atmospheric pressure). By keeping the mold (mold)
The purpose is to prevent air from entering through gaps in the reactor, or in other words, to realize a reactive gas flow system that is completely sealed from the outside. In addition, by continuing to scavenge air during the process of filling the mold cavity with molten metal,
Since a sudden increase in the internal pressure of the cavity due to unreacted gas is suppressed, not only the flowability of the product is improved, but also the amount of gas trapped within the product is reduced, so internal defects due to air bubbles are reduced. According to the present invention, after the reactive gas supply port is shut off by driving the plunger, the reactive gas supplied to the mold cavity by moving the plunger replaces the previous reactive gas supply. It has also been found that forming a stream of air using a method is also advantageous in obtaining excellent results. For this reason, it has also been found that after the reactive gas supply port is shut off, it is preferable to set the amount of reactive gas fed by the plunger to be approximately equal to the scavenging amount. Here, the pressure state slightly higher than atmospheric pressure means the pressure state within the mold cavity before the plunger starts driving. Of course, the range of pressure fluctuation within the mold cavity after the plunger is driven is not constant due to factors such as the die-casting device itself, the space volume of the cavity, and the plunger drive speed. Furthermore, as a practical matter, it is very difficult to detect such pressure fluctuations after injection of molten metal into the cavity of the mold has started. Therefore, as a rough guide, the pressure state in the mold cavity before the plunger starts driving is used as a reference. However, in the present invention, it has been recognized that by using such a pressure as a guideline, it is possible to sufficiently reduce the generation of air bubbles in a cast product in a normal die casting method. (Description of the present invention with reference to the drawings) Fig. 1 shows a reactive gas displacement die-casting apparatus provided with a scavenging air scavenging port for explanation of carrying out the casting method of the present invention. Since the overall structure and operation of such die casting equipment is well known, a brief explanation will be given with reference numeral 1.
2 indicates a fixed platen, 2 indicates a fixed type, 3 indicates a movable type, and 4 indicates a fixed type and a movable type 3.
Cavity surfaces 2a and 3 formed on opposing surfaces of
A indicates the cavity that regulates the product shape. Further, reference numeral 5 indicates an injection sleeve, and reference numeral 6 indicates a plunger. The molten metal 8 injected into the injection sleeve from the pouring port 7 is injected into the cavity 4 through the runner 9 and the sprue 10 by the movement of the plunger 6. It's becoming like that. code 20
is a supply port for supplying a reactive gas (for example, oxygen gas) into the injection sleeve 5, which is connected to a suitable reactive gas supply source (not shown) and is connected to the supply port before injection of molten metal. 20 into the injection sleeve 5, and guide this reactive gas into the cavity 4 through the runner 9 and the sprue 10, thereby completely replacing the inside of the mold cavity with the reactive gas. be done. Reference numeral 11 indicates a gas vent passage leading from the cavity 4 to the outside, and reference numeral 12 indicates a pool of water formed in the middle of this gas vent passage 11. The sump 12 is for preventing the injected molten metal from being discharged to the outside through the gas vent passage 11, and is designed to quickly solidify the molten metal that reaches the sump 12.
Here, the entire space including the cavity 4, runner 9, sprue 10, degassing passage 11, tundish 12, etc. is referred to as a mold cavity. In order to carry out the casting method of the present invention, a scavenging means 30 is connected to the gas venting passage 11 for forcibly drawing out the gas (air and reactive gas) in the mold cavity (hereinafter referred to as scavenging). ing. The scavenging means 30 may be any evacuation device proposed for conventional vacuum die-casting equipment, and is not particularly limited. For example, a bench lily type suction means may be provided in the mold. An example of a preferred operation of the casting step, which is a feature of the present invention, performed using such a die-casting apparatus will be described below. First, after injecting the molten metal 8 into the injection sleeve 5 through the pouring port 7, the pouring port 7 is closed with a lid (not shown) or the pouring port 7 is blocked with the plunger 6 to isolate it from the outside air. Reactive gas is supplied into the injection sleeve 5 from the supply port 20 . In this case, before the molten metal 8 is injected into the injection sleeve 5, the air in the cavity of the mold can be replaced with a reactive gas in advance. As described above, at the same time as the reactive gas is injected into the injection sleeve 5 from the supply port 20, the scavenging means 30 starts scavenging air from the mold cavity. By supplying and scavenging the reactive gas, the reactive gas flows within the space of the casting apparatus, forming a stream. This replaces the reactive gas in the mold cavity. In the present invention, the interaction of reactive gas supply and scavenging is selected such that the pressure within the mold cavity is slightly above atmospheric pressure. This selection completely prevents air from entering from the outside through gaps such as the mold, gaps, and knockout pins (not shown). After the reactive gas has completely replaced the mold cavity, the molten metal 8 in the injection sleeve 5 is injected by operating the plunger 6. During this injection, when the plunger 6 moves to the left in the figure beyond the position of the supply port 20, the supply of reactive gas is cut off. On the other hand, the scavenging means 30 continues to scavenge air from the mold cavity. However, due to the movement of the plunger 6, the injection sleeve 5
The reactive gas already filled inside is forced and forced into the mold cavity. Therefore, there is no significant pressure drop in the cavity of the mold due to scavenging, and the inconveniences caused by so-called reduced pressure (vacuum) die casting do not occur (it is possible that the pressure is temporarily reduced). On the other hand, if the amount of air sent into the mold cavity by the plunger 6 is too large, the pressure inside the mold cavity will be inappropriately increased, which will result in an increase in back pressure that causes air bubbles to be trapped. Therefore, it is preferable that the amount of scavenged air is approximately equal to the amount of air supplied. Casting tests were conducted based on the casting method according to the invention. The casting test will be explained below. (Description of casting test) ADC12 aluminum alloy was used as the casting material in the test, and this molten metal was die-cast into a casting test piece using a die-casting machine with a capacity of 250 tons. In all casting tests, the plunger's slow drive speed was 15 cm/s, and the fast plunger's drive speed was 1 m/s, especially when moving the plunger to deliver the reactive gas in the injection sleeve. Metal pressure is 160
Kg/cm ² , and the metal pressure upon completion of filling was 250 Kg/cm ² . The casting test was conducted under 7 different conditions, and 15 test pieces (150 x 280 x 6 mm) were used for each casting test.
was cast. The casting conditions in each casting test are
As shown in the table. (Determination of the degree of bubble generation in the test piece) A. Visual inspection All test pieces cast in this way were heated at 500°C.
The material was heated for 30 minutes to induce swelling, and the appearance was inspected. The judgments made in this visual inspection are shown in Table 2.

【table】

【table】

[Table] As a result, in the casting tests (1) to (6), which are the casting conditions that satisfy the present invention, the oxygen replacement rate was 100% and the mold cavity was set at a positive pressure close to atmospheric pressure. Visual inspection of blisters in (1), (3), and (5) revealed that most of them satisfied criteria A in Table 2. On the other hand, in casting tests (2), (4), and (6) in which the oxygen exchange rate is not 100% and the mold cavity is under negative pressure, or the pressure is considerably higher than atmospheric pressure, the above-mentioned casting test A slight deterioration in quality was observed compared to that in . In addition, in a comparative casting test (7) in which the pressure inside the mold cavity was close to atmospheric pressure without scavenging air as in the conventional method, the results were considerably worse than in the case of the casting method of the present invention. It was showing. The results of the above visual inspection are shown in Figure 2. (b) Internal inspection In order to inspect the air bubbles formed inside the casting test piece, we conduct a casting test with a particularly good external inspection.
(1), (3), (5), and the comparative casting test (7), internal inspections were conducted using X-ray transmission. In this inspection, the same judgment as in the external appearance inspection in (a) was made on the image obtained by X-ray transmission. However, the evaluation criteria were further subdivided into good, moderate, and poor for each of the criteria A to E. The results of this determination are shown in FIG. Furthermore, the distribution curve obtained based on this determination result is shown in FIG. As a result, it was confirmed that the die casting method according to the present invention provides superior results compared to conventional casting methods. (Effects of the Invention) The die casting method of the present invention can reduce the generation of bubbles. The present invention can be easily applied to existing die casting equipment. In order to carry out the present invention, it is only necessary to provide a scavenging means, and the equipment cost does not increase significantly.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a die-casting apparatus as an example for carrying out the die-casting method of the present invention. Figure 2 shows a comparison of the quality of products obtained by the die-casting method of the present invention and products obtained by a conventional method based on appearance inspection, with the judgment criteria on the vertical axis and the casting test on the horizontal axis. Distribution map showing numbers. FIG. 3 is a distribution chart similar to FIG. 2, with judgment criteria on the vertical axis and casting test numbers on the horizontal axis, in order to compare and show the internal quality of the product. FIG. 4 is a diagram showing a quality distribution curve obtained from the determination results of FIG. 3. 1... Fixed platen, 2... Fixed type, 3... Movable type, 4... Cavity, 5... Injection sleeve,
6... Plunger, 7... Pouring spout, 8... Molten metal, 9... Runway, 10... Sprue, 11... Gas vent passage, 12... Reservoir, 20... Reactive gas supply port , 30...Scavenging means.

Claims (1)

[Claims] 1. While supplying reactive gas to the inside of the die-casting device via the injection sleeve, internal air or reactive gas is continuously scavenged from the mold cavity by suction, thereby eliminating the mold cavity and the reactive gas. In a casting method in which molten metal is injected by operating a plunger after replacing the air initially existing in a space inside a die-casting device such as an injection sleeve with a reactive gas, the reactive gas is injected into the injection sleeve 5. The reactive gas is supplied into the mold cavity through the provided reactive gas supply port 20, and the scavenging means 30 communicating with the mold cavity scavenges air from within the mold cavity, and the injection sleeve passes through the mold cavity to the die-casting apparatus. By creating a flow state of the reactive gas to the outside of the mold and adjusting the amount of reactive gas supplied and the amount of scavenged air from the mold cavity, the pressure in the mold cavity can be raised to a pressure slightly higher than atmospheric pressure. The die casting method is characterized by the fact that it has been made into a state. 2. After the reactive gas supply port to the inside of the die-casting device is blocked by the movement of the plunger, the previous supply of reactive gas is stopped by the reactive gas supplied into the mold cavity by the movement of the plunger. 2. The die casting method according to claim 1, wherein the air flow is maintained and the pressure inside the mold cavity is prevented from being greatly reduced. 3. The die casting method of claim 2, wherein the amount of reactive gas supplied into the mold cavity by the movement of the plunger is approximately equal to the amount scavenged from the mold cavity.