JP2000052016A - Method of manufacturing die-cast products with less casting defects - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain die-cast products superior in resistance to scab and having a good appearance by restraining casting defects such as cavity or blowholes attributable to gas entrainment. SOLUTION: When a molten aluminum alloy is injected into the die cavity filled with oxygen gas through a runner and a product gate from a sleeve, the amount of the molten alloy flowing into the die cavity at low flow rate of 30 m/second or more at the product gate is controlled to 1.5% or less of the capacity of the die cavity. The timing for switching the plunger moving speed from low to high is preferably set before the main tip portion of the molten alloy reaches the product gate and during the period when the aluminum alloy occupies 85-97% of the runner capacity. By using the dies with the product gate provided in the direction not in agreement with the speed vector of the molten alloy flowing through the runner, it is possible to reduce the amount of the molten alloy flowing into the die cavity at a low speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a die-cast product having few casting defects such as nests and blowholes.

[0002]

2. Description of the Related Art In a usual die casting method, molten aluminum poured into a sleeve is pressed into a cavity of a mold by a plunger. Most of the gas such as air and water vapor filling the cavity is purged from the cavity by press-fitting the molten aluminum, but some gas remains in the cavity after press-fitting. Particularly, in a mold designed for a thin product or a product having a complicated shape, a portion that becomes a bottleneck of a fluid is likely to occur, and it is difficult to completely remove a gas component from a cavity. The gas remaining in the cavity is cooled when the molten aluminum solidifies in the mold.
It gets caught in the aluminum material and is brought into die-cast products as casting defects such as nests and blowholes.
As a result, the obtained die-cast product was inferior in mechanical properties such as strength and elongation, and was unsuitable for use as a functional material. In addition, when heat treatment is performed to improve the strength or the like, blisters are generated in the die-cast product due to expansion of the gas. As a method for preventing entrapment of gas which causes casting defects such as cavities and blowholes, an oxygen die casting method (see Japanese Patent Application Laid-Open No. 50-21143) is known. In the oxygen die casting method, oxygen is filled in the cavity at a pressure higher than the atmospheric pressure in order to replace the gas in the cavity with oxygen. The sent oxygen reacts with the molten aluminum to form fine Al ₂ O ₃ and is dispersed in the product, and does not adversely affect the die cast product.

[0003]

In the oxygen die casting method, it is important how the molten metal injected into the mold and the oxygen gas react with each other. In order to efficiently react the molten metal and oxygen gas, the product gate dimensions should be reduced,
It is necessary to increase the ejection speed of the molten metal injected into the mold cavity. Therefore, until the molten metal poured into the sleeve reaches the product gate, the plunger is moved at a low speed so that the molten metal in the sleeve and the runner does not entrain the gas, and the molten metal is relatively slowly fed into the mold. Has been adopted. The moving speed of the plunger at this stage is specifically about 0.3 m / sec. Next, after the molten metal reaches the product gate, the plunger is moved at a high speed of about 2.05 m / sec, and the molten metal is ejected from the product gate into the mold cavity at a high speed. However, it is sometimes observed that even if the speed of jetting the molten metal is increased, a die-cast product of poor quality may be obtained. Above all, when performing die casting using a single-piece mold or a multiple-piece mold having a plurality of product gates, a poor quality die-cast product tends to occur.

[0004]

SUMMARY OF THE INVENTION The present invention considers that the initial state of the molten metal injected into the mold cavity has a cause of quality deterioration, suppresses the occurrence of casting defects such as nests, blowholes, etc. An object is to obtain a die-cast product having a casting structure. In order to achieve the object, the manufacturing method of the present invention, when injecting the molten aluminum alloy from the sleeve into the mold cavity filled with oxygen gas through the runner and the product gate, the flow velocity of the molten metal at the product gate. 3
The amount of molten metal flowing into the mold cavity at a low speed of 0 m / sec or less is regulated to 1.5% or less of the volume of the mold cavity. The timing of switching the moving speed of the plunger from low speed to high speed is before the main tip of the molten metal reaches the product gate, and furthermore, 85 to 97% of the runner volume.
Is preferably set to a period occupied by the aluminum alloy. Further, when a mold provided with a product gate in a direction that does not match the velocity vector of the molten metal flowing in the runner is used, the amount of molten metal flowing into the mold cavity at a low speed can be reduced.

[0005]

The present inventor has investigated and studied the effect of the flow state of the molten metal injected into the mold on the quality of the die-cast product. As a result, it has been found that the molten metal slightly flows into the mold cavity even when the plunger is moving at a low speed, and that the slightly flowing molten metal greatly affects the quality. That is, in the initial stage of casting, the plunger is moved at a low speed so that the molten metal does not get caught in the sleeve and the runner. Flows into the cavity. According to investigations and studies by the present inventors, it has been found that when the amount of molten metal flowing into the mold cavity at a low speed is large, the quality of a die-cast product tends to deteriorate. This is presumed to be because the molten metal flowing into the mold cavity at a low speed does not sufficiently react with the oxygen gas, and the oxygen gas is caught in the molten metal as a gas without becoming an oxide.

Further, when the quantitative relationship between the amount of molten metal and the quality deterioration was investigated, it was found that when the amount of molten metal flowing into the mold cavity at a low speed was set to 1.5% by volume or less of the volume of the mold cavity.
Clarified that casting defects such as nests and blowholes were greatly suppressed. The molten metal amount of 1.5 vol% is a critical value obtained from the result of the investigation by the present inventors, and when the molten metal amount exceeds 1.5 vol%, the blister rate starts to increase. In order to reduce the amount of molten metal flowing into the mold cavity at low speed, a method is adopted in which the timing of switching the moving speed of the plunger from low to high is set before the main tip of the molten metal reaches the product gate. . That is, in the stage before the main tip of the molten metal reaches the product gate, the speed of the molten metal in the runner calculated by the equation (1) is set to 5 m / sec or less (preferably,
(2 m / sec or less). Melt speed in runner = (S ₁ / S ₃ ) × V (1) S ₁ : Cross-sectional area of sleeve S ₃ : Cross-sectional area of runner V: Plunger speed

Next, just before the main tip of the molten metal reaches the product gate, the molten metal speed at the product gate is reduced to 30.
The moving speed of the plunger is switched from a low speed to a high speed so that the speed is at least m / sec. Since the melt speed at the product gate cannot be measured, the value calculated according to the equation (2) is used as the melt speed. Melt speed at product gate = (S ₁ / S ₂ ) × V (2) S ₁ : Sleeve cross-sectional area S ₂ : Product gate cross-sectional area V: Plunger speed Melt speed at product gate is 30 m / sec or more As a result, the molten metal sufficiently reacts with oxygen in the mold, and the entrapment of gas, which is a cause of cavities, blowholes, etc., is greatly reduced. For a sufficient reaction between the molten metal and the oxygen gas, if the sectional area of the product gate is extremely reduced, the molten metal and the oxygen gas can be sufficiently reacted even if the molten metal speed is 30 m / sec or less. However, in this case, the cycle time becomes too long, the productivity decreases, and local solidification of the molten metal proceeds, and defects such as a molten metal boundary easily occur.

[0008] Even if the runner and the product gate are designed such that the velocity vector at the tip of the molten metal flowing in the runner does not coincide with the direction of the product gate, the amount of molten metal flowing into the mold cavity at a low speed can be reduced. . Specifically, as shown in FIG. 1, the molten metal poured into the sleeve 1 is supplied from the first runner 2 to the second runner 3 and the product gate 4.
The product gate 4 is set at a position shifted from the extension of the first runner 2 at this time. As a result, the tip of the molten metal deflected from the first runner 2 and flows into the second runner 3 has a velocity vector in the left-right direction on the paper surface, and the flow energy of the molten metal is directly transmitted to the inside of the mold cavity. Disappears. On the other hand, in a mold in which the velocity vector at the tip of the molten metal flowing through the second runner 3 matches the direction of the product gate 4, the molten metal flows into the mold cavity 5 with the same velocity vector, and the amount of molten metal flowing at a low speed. Is more than 1.5% by volume.

When the extension 6 is provided in the second runner 3 as shown in FIG. 2, the velocity vector at the tip of the molten metal is directed to the extension 6, so that the energy for pushing the molten metal into the mold cavity 5 is reduced. . Further, in order to keep the flow speed of the molten metal in the product gate 4 of each mold cavity 5 constant, the sectional area of the second runner 3 is changed intermittently or continuously according to the distance from the first runner 2. Can also. Although FIG. 1 and FIG. 2 show a four-cavity mold, one mold cavity 5 is connected to the second runner 3 through a plurality of product gates 4, 4,. Even when a mold is used, the amount of molten metal flowing into the mold cavity at a low speed can be reduced by a similar design. Also,
No. An overflow portion 7 is provided in each of the mold cavities 5.

The timing for switching the moving speed of the plunger from low speed to high speed is set before the main tip of the molten metal flowing in the runner 3 reaches the final product gate 4. If the moving speed of the plunger is switched at a timing later than this, the amount of molten metal that can flow into the mold cavity 5 at a low speed becomes a large amount exceeding 1.5% by volume, and oxygen gas remaining in the mold cavity 5 is caught in the molten metal. Will be able to Switching the moving speed at this timing is particularly effective in a mold having many product gates 4. However, if the timing of switching the moving speed is too early, there is a high possibility that gas is caught in the molten metal by the sleeve 1 and the runners 2 and 3.
In this regard, the switching of the moving speed is preferably performed after the molten metal poured into the sleeve 1 occupies 60% by volume or more of the volume of the runners 2 and 3. The optimum timing of the switching depends on the design of the runners 2 and 3 and the product gate 4, but it is preferable that the melt fills 85 to 97% of the runner volume.

After switching the moving speed, the molten metal speed at the product gate 4 is 30 m / sec or more (preferably 60 m / sec).
(m / sec or more). The molten metal is instantaneously filled into the runners 2 and 3 by the high-speed movement of the plunger, and is ejected from the product gate 4 into the mold cavity 5. Since the ejection becomes a droplet or a mist, the reaction between the oxygen in the mold cavity 5 and the molten metal is promoted, and substantially all of the oxygen gas is consumed as oxide. For this reason, the amount of oxygen gas taken into the die cast product that is involved in the molten metal is reduced, and the quality of the die cast product is improved.

[0012]

EXAMPLE Example 1 Mold cavity 5 of size 15 mm × 18 mm × 6 mm
Aluminum alloy JIS A maintained at 660 ° C. using a single-piece die connected to the second runner 3 via a product gate having an inner diameter of 4 mm and a gate length of 5 mm.
DC3 was die cast. Prior to casting, the inside of the mold was replaced with oxygen gas of 0.1 to 0.2 MPa, and the mold was preheated to 150 ° C. After pouring the molten aluminum alloy into the sleeve, the plunger was moved at a low speed of 0.3 m / sec, and the molten aluminum alloy was fed from the sleeve 1 to the first runner 2 and the second runner 3. At this time, the flow velocity of the molten metal flowing through the second runner 3 via the first runner 2 was 3 to 4 m / sec. It is known in advance that the time t _{1 at} which the molten metal reaches the product gate 4 is 1.013 seconds as a result of calculation by the three-dimensional flow simulation. Therefore, at the timing t ₂ the molten metal amount flowing at low speed into the mold cavity 5 is equal to or less than 1.5% by volume of the volume of the mold cavity 5, the moving speed of the plunger 2.05
m / sec. The moving speed of the molten metal passing through the product gate 4 during the high-speed movement of the plunger was calculated to be 80 m / sec.

The die-cast product thus obtained was subjected to solution treatment at 510 ° C. × 120 minutes, and the product volume before and after the solution treatment was compared to calculate the blister rate according to the formula (3). Table 1 shows the obtained swelling ratio together with the casting conditions. When the blistering rate exceeds 1%, it is said that there is a failure in appearance or a decrease in strength after the solution treatment, and the solution is rejected. Also, the time required for the molten metal to reach the product gate 4 and the amount of the molten metal flowing into the mold cavity 5 at a low speed in Table 1 are as follows:
Although obtained by the three-dimensional flow simulation, it can also be calculated by an experimental method such as a partial shot, a molten metal reaching sensor, and a water model. Swelling rate (%) = (V ₂ −V ₁ ) / V ₁ × 100 (3) V ₁ : Volume of product before solution treatment V ₂ : Volume of product after solution treatment

For comparison, the moving speed of the plunger is low.
To switch to high speed t _Two The molten metal is the product game
Time t when the vehicle reaches point 4₁ Similar items except for the settings below
Under the same conditions, and the obtained die-cast product
The blister rate was determined. As can be seen from the survey results in Table 1,
Switching timing t_Two Is the time t₁Set faster
In the example of the present invention, the die-cast product was subjected to solution treatment.
The swelling rate is lower than 1%. This
On the other hand, the switching timing t_Two Is the time t₁ of
In the comparative example set later, a large blister rate exceeding 1%
showed that. Switching timing t_Two Difference in blister rate
Appears at the switching timing t_Two Slow down and low
The amount of molten metal flowing into the mold cavity 5 at high speed increases,
The cause is that the product is caught in the product. this thing
Is the switching timing t intentionally_Two Comparative Example H
Very large blister rate exceeding 2% at ~ J
It is clear from this.

[0015]

Example 2 Four-piece molds each having a mold cavity 5 having a size of 15 mm × 20 mm × 40 mm and connected to a second runner 3 via a product gate 4 having a width of 3 mm × 4 mm and a length of 4 mm. A mold (FIGS. 1 and 2) was used. Prior to casting, the inside of the mold was replaced with oxygen gas of 0.1 to 0.2 MPa,
The mold was preheated. Then, the aluminum alloy JIS ADC12 held at 650 ° C. was die-cast. In the die casting using the mold shown in FIG. 1, the timing t _{2 at} which the moving speed of the plunger is switched from the low speed of 0.3 m / sec to the high speed of 2.05 m / sec is changed to the time t ₁ (0. 088 seconds). In the die casting using the mold of FIG. 2, the moving speed of the plunger was switched from a low speed to a high speed after the molten metal reached the product gate 4. In any case, when the plunger is moving at high speed, the moving speed of the molten metal passing through the product gate 4 is 1
It was calculated as 00-110 m / sec. In the same manner as in Example 1, the amount of molten metal flowing into the mold cavity 5 at a low speed was calculated, and the blister rate of each of the obtained die-cast products was determined. Further, the appearance defect was detected by visual observation, and the defect rate was calculated.

As can be seen from the investigation results in Table 2, in the example of the present invention using the mold (FIG. 1) in which the velocity vector of the molten metal does not coincide with the direction of the product gate 4, the moving speed of the plunger is increased from a low speed to a high speed. also the timing t ₂ to switch in the case of slower than the molten metal reaching time t _1, No. 1-4
The amount of molten metal flowing into any one of the mold cavities 5 at a low speed was as small as 1.5% by volume or less. The obtained die-cast product exhibited a low blistering rate of 1% by volume or less, and a low appearance defect rate. Further, the timing t ₂ to switch the moving velocity of the plunger using the same mold (FIG. 1) from a low speed to a high speed when set earlier than the molten metal reaching time t ₁ flows at a low speed into the mold cavity 5 melt The amount was greatly reduced, and both the blistering rate and the appearance defect rate were greatly improved. In contrast, in the comparative example was slow timing t ₂ switch than the molten metal reaches the time t ₁ with mold velocity vector of the melt coincides with the direction of the product gate 4 (FIG. 2), the mold cavity 5 at a low speed The amount of molten metal flowing into the furnace increased, and the blister rate exceeded 1% by volume, and the appearance defect rate also increased.

[0018]

[0019]

As described above, in the present invention, when the molten metal in the sleeve is injected into the mold cavity and die-casting is performed, the amount of molten metal flowing into the mold cavity at a low speed when the plunger is moved at a low speed is determined by the metal. The timing for switching the moving speed of the plunger from low speed to high speed is set so as to be 1.5% by volume or less of the volume of the mold cavity, or the speed vector of the molten metal does not match the direction of the product gate. Since the amount of molten metal flowing into the mold cavity at low speed is small, the oxygen gas filled in the mold cavity reacts sufficiently with the molten metal to form oxides, and the amount of oxygen gas remaining in the molten metal is greatly increased. Less. As a result, casting defects such as cavities and blow holes caused by gas entrapment are suppressed, and a die-cast product having excellent blister resistance and a good appearance can be obtained.

[Brief description of the drawings]

FIG. 1 A mold in which the velocity vector of the molten metal does not match the direction of the product gate

FIG. 2 A mold in which the velocity vector of the molten metal matches the direction of the product gate

[Explanation of symbols]

1: Sleeve 2: First runner
3: Second runner 4: Product gate 5: Mold cavity
6: overflow part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takaaki Inogari 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Within the Nippon Light Metal Co., Ltd. Group Technology Center 1-34-1, Nippon Light Metal Co., Ltd. Group Technology Center

Claims (3)

[Claims] When a molten aluminum alloy is injected into a mold cavity filled with oxygen gas from a sleeve through a runner and a product gate, the flow speed of the molten metal at the product gate is as low as 30 m / sec or less. A method for producing a die-cast product having few casting defects, wherein the amount of molten metal flowing into the cavity is regulated to 1.5% or less of the volume of the mold cavity. 2. The timing for switching the movement speed of the plunger from low speed to high speed is set to 85 to 97% of the runner volume.
2. The method for producing a die-cast product having few casting defects according to claim 1, wherein the temperature is set to a period occupied by the aluminum alloy. 3. The method for producing a die-cast product having few casting defects according to claim 1, wherein a mold provided with a product gate is used in a direction that does not coincide with a velocity vector of the molten metal flowing in the runner.