KR20000011674A - Die-casting method and die-cast products - Google Patents

Abstract

PURPOSE: A die casting method is provided to reduce the gas amount by having both merits of a vacuum die casting and an oxygen die casting. CONSTITUTION: The method for die-casting aluminium or aluminium alloy comprises the steps of:emptying a cavity(2) of a die casting metal mold(1) for discharging gas from the cavity to a vacuous degree that is smaller than 100mb; blowing oxygen gas inside the cavity until exceeding the inner pressure of the cavity in atmosphere pressure; and injecting aluminium alloy(5) or dissolved aluminium inside the cavity by force. The die casting product made by injecting dissolved metal inside the cavity in the state of removing harmful gas, doesn't have defect such as a blow hole or a porousness generated by gas such as remained air or steam.

Description

Die casting method and die casting product {DIE-CASTING METHOD AND DIE-CAST PRODUCTS}

The present invention relates to a die casting method for a die cast product that can be used as a structural member as well as a functional member and relates to a die casting product produced by the method. In the conventional die casting method, molten aluminum or aluminum alloy (hereinafter referred to as molten metal) introduced into the sleeve is forcibly injected into the cavity of the die casting by the plunger. Most gases such as air and water vapor are removed from the cavity in response to the injection of molten metal, but some gas remains in the cavity after injection. Die casting molds, especially designed for thin-walled or multi-shape products, have bottle necks that interfere with gas flow, making it difficult to remove gas from the cavity completely.

Gas trapped in the cavity is contained in the diecast product when the injected molten metal cools and solidifies in the cavity. Therefore, die-cast articles obtained in this way are considered to be inadequate for functional use because of insufficient mechanical properties, which are for example scrolls, pistons, cylinder blocks, connecting rods or suspension parts. When casting defects arising from the gas content are solved, a die casting method excellent in productability can be applied to various technical fields.

Vacuum diecasting methods have been proposed to eliminate adverse effects from gas content. According to the vacuum die casting method, the cavity of the die casting mold is emptied before the molten metal is injected to remove gas from the cavity. The cavity is maintained at a vacuum in the range of 200 to 500 millibars by emptying. However, the internal pressure of the cavity cannot be reduced below this value due to the ingress of air through the narrow gap of the die. Air intrusion also occurs during the introduction of molten metal into the sleeve. As a result, casting defects such as porosity caused by the gas content are also detected in the product obtained by the vacuum die casting method even if the gas content is slightly reduced in comparison with the product obtained by the conventional die casting method. In this regard, the product is not good enough for use as a functional member.

Oxygen die casting methods have been developed to eliminate the drawbacks of vacuum die casting methods. According to the oxygen die casting method, as disclosed in JP B 50-21143, the cavity of the die casting mold is filled with oxygen at a pressure higher than the atmospheric pressure to replace the gas with oxygen before injecting the molten metal. Since the oxygen gas transferred into the cavity flows out through the narrow gap of the die as well as the injection hole, intrusion of the atmosphere gas through the narrow gap or the injection hole is prevented. In addition, the oxygen gas transferred into the cavity reacts with the dissolved metal and the reaction product Al ₂ O ₃ is dispersed as fine particles in the cast product without adversely affecting the obtained diecast product.

However, the replacement of the gas from the die casting mold cavity by oxygen injection is practically impossible even when oxygen is transferred into the cavity at a pressure higher than the atmospheric pressure. The gas remains in the cavity where it is difficult to replace. Die-casting molds designed to produce products with complex geometries have parts that are difficult for oxygen to reach, so gas such as air and steam cannot be replaced by the transported oxygen and so remain. Residual gas and water vapor from the separating agent are contained in the product causing defects.

Residual air is efficiently removed from the cavity by oxygen blowing during emptying as disclosed in JP B 57-140. But at the same time emptying and oxygen blowing are not effective for the removal of water vapor. In fact, casting defects caused by gas content are detected in cast products obtained by this method. Another die casting method is disclosed in JP B 1-46224 and oxygen blowing is performed after emptying. The cavity of the die casting mold is kept at reduced pressure during oxygen blowing. The confinement of the trapped gas causes the diecast product to be heat treated, such as T6 treatment (ie co-curing, quenching and then aging) to improve mechanical properties. To avoid these blisters, most diecast products are not heat treated.

The present invention aims to eliminate this problem as described above. It is an object of the present invention to significantly reduce the content of gases by combining the advantages of both vacuum die casting and oxygen die casting for die cast products usable as functional members.

The die casting method according to the present invention comprises the steps of emptying the cavity of the die casting with a vacuum not higher than 100 millibars to remove gas as well as water vapor from the cavity, blowing oxygen gas into the cavity, and the internal pressure of the cavity exceeds the atmospheric pressure. And forcibly injecting the molten metal.

First, the die casting cavity is emptied with a vacuum no less than 100 millibars. In particular, the gas is effectively released at a suction rate of 500 millibars per second or more. The cavity is filled with oxygen at a pressure slightly less than the atmospheric pressure. When the internal pressure of the cavity exceeds the atmospheric pressure, the injection of molten metal into the cavity begins.

Since molten metal is injected into the cavity maintained in this way, the gas trapped in the cast product is significantly reduced to levels below 1cc / 100g-Al. As a result, the obtained die cast product has excellent mechanical properties required for the functional member. Diecast products are also heat treated with T6 without blisters generated by trapped gases.

The gas contained in the die cast product is generated from the air remaining in the cavity of the die casting mold in the conventional die casting method. This residual air can be substantially reduced by vacuum or oxygen die casting. However, casting defects caused by trapped gases are unavoidable in die cast products obtained even when the remaining air is substantially reduced. The inventors studied and investigated the effects of casting defects and causes from various properties on diecast products in which adverse effects resulting from residual air are eliminated by vacuum or oxygen die casting methods. As a result, the inventors found that water diluting the separator adhering on the inner surface of the die casting is the main cause of the occurrence of casting defects and that the water in the casting defects clearly affects the residual air in the cavity. . When the cavity is emptied, the water containing the separator is evaporated and released as vapor from the cavity. However, a separator which is commonly used as a main component of water takes some time to dry even under vacuum. When the cavity is only emptied, the evaporation of water can be limited to the surface of the separator without evaporating from the interior of the separator so that the separator does not dry sufficiently. The generated water vapor is also partly in the cavity and therefore contained in the molten metal that is injected into the cavity.

1 is a schematic view showing a die casting machine to which the present invention is applied;

2 illustrates blowing oxygen into the cavity of the die casting mold through the sleeve, and

3 illustrates the introduction of molten metal into the sleeve.

According to the present invention, the water containing the separator is mostly released as a vapor from the cavity of the die casting by vaccum evacuation and the separator is sufficiently dried. Water vapor still remaining in the cavity diffuses into the oxygen gas and is discharged with oxygen gas from the cavity in a subsequent oxygen blowing step. The water containing the separating agent is completely released by the combination of oxygen blowing and vacuum emptying, so that the gas content in the die cast product obtained is greatly reduced. Evaporation of water from the separator is effectively enhanced when the cavity is emptied with a vacuum of less than 100 millibars to dry the separator. The suction speed is preferably set at 500 millibars / sec or more. This high-speed emptying results in bumping of the water and thus rapid drying.

Before the molten metal is injected into the cavity of the die casting mold, the cavity is in a state where the air and water vapor are significantly reduced. As a result, the gas content in the diecast is greatly suppressed and the casting defects generated from the gas content of the product are eliminated.

In the die casting method, the sleeve 3 attached to the cavity 2 is connected to the die casting mold 1 as shown in FIG. 1. The sleeve 3 has an inflow hole 4 through which the molten metal 5 flows into the sleeve 3. The molten metal 5 in the sleeve 3 is pressurized by the tip 7 attached to the plunger 6 and forcedly injected into the cavity 2. After the cavity 2 is filled with the molten metal 5, the molten metal 5 is cooled and solidified into a profile formed by the inner surface of the die casting mold 1. The die cast product obtained in this manner is taken out from the die casting mold 1 by pressing the ejector pin 8 and the like in the cavity 2 after the die cast product is cooled.

According to the invention, the suction nozzle 11 is attached to the die casting mold 1 at a suitable position such as its separating part to connect the cavity 2 to the vacuum pump 12 through the suction nozzle 11. When the cavity 2 is emptied through the suction nozzle 11, the ambient air enters through the part into which the ejector pin 8 is inserted while being emptied. This intrusion is prevented by sealing the gap between the ejector pin 8 and the die portion with a sealant 13. On the other hand, the injection hole 4 is closed by the plunger tip 7 so that ambient air cannot enter the inside of the sleeve 3 through the inlet hole 4.

After emptying, the oxygen nozzle 14 is opened into the sleeve 3 to blow oxygen into the cavity. The oxygen nozzle 14 is connected to an oxygen supply source through an adjustment valve 15.

When the cavity 2 is emptied through the suction nozzle 11, gases such as air and water vapor are removed from the cavity 2 as well as inside the sleeve 3 connected with the cavity 2. Even if the cavity 2 has a complex shape, the gas is removed from all nooks and corners of the cavity 2 by adjusting the suction speed preferably in the range of 500 millibar / sec or more. This high-speed emptying, together with the separating agent attached to the inner surface of the die casting mold 1, causes bumping of the water, resulting in a significant reduction in the water vapor from the cavity 2.

Emptying preferably continues for about 1 to 2 seconds under the condition that the inlet 4 is closed with the plunger tip 7. The emptying period is set relatively long in comparison with the conventional die casting method, whereby the cavity 2 is emptied for a time period shorter than one second without closing the inlet hole 4. The cavity 2 is emptied with a vacuum of less than 100 millibars due to the longer emptying period. Water vapor generated from the separator attached to the inner surface of the die casting mold 1 is separated from the inner surface of the die casting mold and discharged outward.

The removal of water vapor is effected more effectively by emptying as compared to blowing oxygen gas into the cavity because the gas stream flows faster in the cavity 2. However, if the cavity 2 is emptied with insufficient vacuum of 100 millibars or more, a relatively large amount of gas remains in the cavity 2. A large amount of gas remaining in the cavity 2 is not replaced by oxygen in the next oxygen blowing step, but is often not included in the cast product. On the other hand, if the cavity is emptied with a vacuum of less than 100 millibars, the water containing the separator is rapidly evaporated and released as vapor outside the cavity 2. The decrease in water is greatly reduced by high speed emptying of 500 millibars / sec or more, which results in water bumping. Bumping can evaporate water from the interior of the separator as well as the surface, greatly reducing the remaining water. The upper limit of the suction speed is about 800 millibars / sec considering the effective capacity of the vacuum apparatus.

After being emptied, the oxygen gas is blown into the cavity 2 through the nozzle 14. The oxygen supply flows out of the gas and oxygen through the separate portion of the die casting mold (1). Since oxygen is blown into the cavity 2 in a reduced pressure in the previous step, the oxygen gas flows to all the nuts and corners of the cavity 2 as a high speed stream. Water vapor generated from the water containing the dispersant and remaining in the cavity 2 is diffused in the oxygen gas and released together with the oxygen gas to the outside of the cavity 2. The effect of oxygen blowing for the removal of water vapor was unexpected in any of the methods disclosed in JP B 57-140 and JP B 1-46224 in which oxygen gas is blown into a cavity maintained under reduced pressure.

The plunger tip 7 returns to open the inlet hole 4 during continuous blowing of oxygen. When the inlet hole 4 is released, oxygen gas flows out through the inlet hole 4 as shown in FIG. The outflow of oxygen gas effectively suppresses the ingress of ambient air into the sleeve 3 through the inlet hole 4.

After the inlet hole 4 is opened, the molten metal 5 flows into the sleeve 3 from the ladle 16. Since the oxygen gas is effectively discharged during the inflow operation, the outflow of the oxygen gas effectively prevents the inflow of the ambient air accompanying the molten metal (5).

The die casting mold 1 is preferably preheated to 150 ° C. to 200 ° C. before the inflow step to reduce the heat shock generated by the inflowing molten metal 5 and improve the productability. The plunger rod 6 advances after the mass of molten metal 5 required for one cycle of die casting has entered the sleeve 3. The inlet hole 4 is closed by the forward movement of the plunger rod 6. Since the closed state does not introduce ambient air into the sleeve 3 through the inlet hole 4, the supply of oxygen gas can be stopped.

After gases such as air and water vapor have been completely removed from the interior of the cavity 2 and sleeve 3 as described above, the plunger rod 6 is advanced to forcibly inject the molten metal 5 into the cavity 2. Let's do it. The injected molten metal 5 is formed into a volume BULK having a profile that mimics the inner surface of the die casting mold 1. This volume is cooled and solidified into a die cast product having a predetermined shape. Then, blowholes or porosity generated by the gas content are not generated in the die cast product because gases such as air and water vapor are completely excluded from the cavity 2. Oxygen gas remaining in the cavity 2 reacts with the injected molten metal and the reaction product Al ₂ O ₃ disperses into fine particles in the diecast product without causing any adverse effects. Therefore, the die cast product obtained in this way has excellent characteristics.

Example

The die casting mold 1 used in this example has a cavity 2 of 150 mm in diameter and 120 mm in length. Suitable water cooling means are provided in the die casting mold 1 to partially cool the die casting mold 1.

After the cavity 2 has been cleaned by an air blow, the separating agent diluted with water is sprayed on the inner surface of the die casting mold 1 for 5 seconds. The die casting mold 1 is then preheated to 180 ° C. and placed in a suitable position in the die casting machine. The periphery surrounding the ejector pins 8 is sealed with a sealant 13 and the suction nozzle 11 is attached to the separating portion of the die casting mold 1.

The inlet hole 4 is closed by the plunger tip 7 and the gas is sucked through the suction nozzle 11 from the inside of the cavity 2 and the sleeve 3 by emptying the cavity 2 at a suction speed of 700 millibars / sec. . The vacuum gauge (not shown) provided to the vacuum system 12 represents 75 millibars.

After being emptied, the regulating valve 15 is opened to blow oxygen gas into the cavity 2 through the oxygen nozzle 14. In the oxygen blowing, oxygen flows out through the separating portion of the die casting mold 1.

If the oxygen blowing continues for 3.5 seconds, the plunger tip 7 returns to open the inlet hole 4. Thereafter, the molten metal alloy ADC 12 prepared by conventional molten metal treatment is introduced into the sleeve 3 through the inlet hole 4. Oxygen gas is continuously blown into the sleeve 3 through the oxygen nozzle 14 while the molten metal 5 is introduced into the sleeve 3 for 5 seconds.

After the inflow is completed, the supply of oxygen gas is stopped and the plunger rod 6 is advanced to forcibly inject the molten metal 5 into the cavity 2. Injection of the molten metal 5 is completed in a short time of approximately 0.1 seconds.

It takes about 5 seconds to solidify the injected molten metal 5 in the die casting mold 1. After the die cast product is cooled, it is taken out from the die casting mold 1. The diecast product N0.1 obtained in this manner is subjected to a lansley test and a mechanical test to determine the gas content in the diecast product.

For comparison, the die cast product N0.3 obtained by the conventional oxygen die casting method from the same aluminum alloy as the die cast product N0.2 obtained by the conventional vacuum die casting method is subjected to the same Lansley and mechanical test. In the die casting method, the cavity 2 is emptied for 1.5 seconds before the injection of the molten metal 5. In the oxygen die casting method, oxygen gas is blown into the cavity 2 for 2 seconds and then molten metal 5 is injected into the cavity 2 for 5 seconds while blowing oxygen gas.

The test results are shown in Table 1. This shows in Table 1 that according to the present invention, the amount of gas such as N ₂ and H ₂ in die cast N0.1 is extremely reduced compared to the values of die cast N0.2 and N0.3. The ductility and tensile strength of die cast product N0.1 is higher than the ductility and tensile strength values of die cast products N0.2 and N0.3. In addition, die cast N0.1 is characterized by extremely reduced gas impurity and mechanical properties by T6 treatment (heated at 480 ° C for 3 hours, quenched with water and then aged at 160 ° C for 5 cycles) without blister generation. Improve.

Effect of Die Casting Method on the Properties of Die Cast Products Sample No. Die casting method Gas impurity content (cc / 100g-Al) As casting After T6 treatment T.S. El. T.S. El. One The present invention 0.6 32 2.0 40 5.0 2 Vacuum die casting 6 23 0.8 Blister with 1-2 mm diameter 3 Oxygen Die Casting 2 27 1.5 Blister with 0.2-0.5mm diameter Note: T.S. stands for tensile strength (kg / mm 2) El. Stands for elongation (%).

Moreover, die casting was carried out under the same conditions except that the suction rate was varied within the range of 100 to 800 millibars / sec. Each diecast product is subjected to a lancel test to determine the amount of residual gas. Significant residual gas reduction is seen at suction rates above 500 millibars / sec. This resulted in high speed emptying of the separator attached on the inner surface of the die casting mold with the bumping of the water and accelerating the removal of the water from the cavity 2.

As described above, according to the present invention, gases such as water and air generated from the separator attached on the inner surface of the die casting mold are subjected to oxygen blowing in continuous emptying until the internal pressure of the cavity exceeds the atmospheric pressure. Is completely removed from the cavity of the die casting mold. Since the molten metal is injected into the cavity in which the harmful gas is completely removed, the obtained die-cast product does not contain defects such as blowholes or porosity generated by gas such as residual air or water vapor. Thus, this new diecasting method is applicable to the production of functional as well as structural members using the advantages of high productivity.

Claims (3)

In the method of die casting aluminum or aluminum alloy, Emptying the cavity of the die casting mold with a vacuum less than 100 millibars to release gas from the cavity, Blowing oxygen gas into the cavity until the internal pressure of the cavity exceeds the atmospheric pressure, and Forcing a molten aluminum or aluminum alloy into the cavity. The method of claim 1 wherein the cavity of the die casting mold is emptied at a suction rate of at least 500 millibars per second. A die cast product produced by the die casting method as defined in claim 1, wherein the die cast product contains gas impurities at a concentration of less than 1 cc / 100 g-Al.