JP2007021565A - Apparatus for reduced pressure die casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for reduced pressure die casting having little erosion and low developing ratio of casting defect, even in the reduced pressure die casting machine having a charging type for molten light alloy for casting in a holding furnace from the lower part onto a horizontal type injection sleeve through a molten metal supplying tube by reducing the pressure in a cavity in the die. <P>SOLUTION: In the reduced pressure die casting apparatus provided with the structure filling up molten metal into the cavity under reduced pressure state, with a plunger tip sliding in the injection sleeve after charging the molten light alloy for casting in the holding furnace into the horizontal type injection sleeve from the lower part by reducing pressure in the cavity in the die; the above sleeve is characterized in that the inner wall surface in contact with the molten metal is formed of a metal-based composite material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vacuum die casting apparatus in which the inside of a cavity is constantly depressurized from filling of a molten metal into a sleeve to completion of injection into a mold, and a vacuum die casting product excellent in mechanical strength is stably manufactured. It relates to a possible vacuum die casting apparatus.

  The die casting method is a technique for filling a molten metal into a mold at a high speed and a high pressure, and has advantages such as higher dimensional accuracy, beautiful casting surface, and higher productivity than other molten metal forming methods. However, if the speed at which the molten metal is filled is lowered, the molten metal temperature decreases, the flowability of the molten metal in the mold deteriorates, and a thin and light product cannot be obtained. Therefore, although it is necessary to fill at high speed, gas, such as the air | atmosphere which exists around, will be caught in molten metal. For this reason, it is known that inclusions such as oxides formed by reacting a large amount of gas and gas and metal exist inside the casting, and the use as a structural member has been limited.

As a method of avoiding gas entrainment while maintaining the filling speed, conventionally, a reduced pressure die casting method for reducing the pressure inside the mold cavity, or a reactive gas such as oxygen that reacts the atmosphere inside the mold cavity with the molten metal. A PF (pore-free) die casting method is known in which a gas defect in a product is reduced by replacing and reacting with a reactive gas in a mold cavity while filling a molten metal. By filling the molten metal in a jet state and cavity filling within a predetermined filling time, the reactive gas (oxygen) reacts with the light alloy molten metal having a large surface area in the jet to be temporarily filled in a high vacuum state. It is. Since the produced oxidation product is finely pulverized by a jet, the mechanical properties of the cast product are not affected.
However, in the PF method, it is necessary to pour molten metal from a pouring port provided in the sleeve, and after the plunger tip closes the pouring port, it is necessary to fill the molten gas with a reactive gas. As a result, there is a problem that the casting cycle becomes longer and the productivity deteriorates. In addition, even if reactive gas is blown into the molten metal passage, it is difficult to completely replace it, and gas such as air remains. The molten metal generates gas from the lubricant in the sleeve and the release agent in the mold cavity by the heat. While it is necessary to react the reactive gas in the mold cavity with the molten metal while filling the molten metal, the gas itself will react with the reactive gas before that, so there is not much gas in the atmosphere. It becomes a state that does not change and a gas defect occurs in the product.

Therefore, improvements such as a decompression method and a sealed structure are mainly studied rather than a technique for replacing the atmosphere in the cavity. As these pressure-reducing die-casting methods, as disclosed in Patent Document 1, there is disclosed a method having a press-fitting chamber (sleeve) that can be filled with molten metal from a heat retaining device through a suction pipe by a vacuum connection part attached to a mold. Yes. In a vacuum die casting machine having this structure, the inside of the communicating sleeve is decompressed simultaneously by decompressing the cavity, and the decompression is continuously performed until the molten metal is pulled up from the heat retaining device to the sleeve through the suction pipe. Depressurization can be continued for a substantially longer time than a vacuum die casting machine. For this reason, most of the gas generated from the lubricant in the sleeve and the release agent in the mold cavity due to the heat of the molten metal is sucked out of the cavity until the molten metal is filled into the sleeve. For this reason, since the molten metal is press-fitted into the cavity without mixing these gases, a sound casting with few casting defects can be obtained.
JP-A-6-126415 ((0011), FIG. 1)

However, in the structure of the casting machine of Patent Document 1, the molten metal supplied from the holding furnace moves through the narrow suction pipe at a speed of about 0.4 to 5.0 m / s and blows up into the sleeve. There is a problem that the melt damage of the peripheral portion where the molten metal flows becomes severe. This is because the molten metal supply port connected to the sleeve is designed to be small in order to slide with the plunger, and it is an unavoidable phenomenon considering the pressure reduction speed for operating in a predetermined pressure and cycle. there were.
As shown in FIG. 3, the sleeve of the conventional vacuum die casting machine is mainly composed of a steel material such as hot tool steel SKD61 material or S45C material. However, in the vacuum die casting machine having the above structure, since the surface of the molten metal to be poured is not oxidized, the activity is large, and since the molten metal holding furnace is directly under the sleeve, the molten metal temperature is high. The inner wall surface is easily melted. As the erosion progresses, the sliding friction between the sleeve and the plunger tip increases, making it difficult to press the molten metal into the cavity at the set timing and amount of pouring, resulting in problems such as hot water wrinkles, hot water boundaries, and internal defects. there were.

  Accordingly, an object of the present invention is to provide a low-pressure die casting machine having the above-described configuration that has a low melting loss and a low incidence of casting defects.

  The present invention relates to a plunger that slides in the injection leaf after charging the molten light alloy for casting in the holding furnace into the horizontal injection leaf from below through the hot water supply pipe by reducing the pressure in the cavity of the mold. A vacuum die casting apparatus having a structure in which the molten metal is filled into the cavity in a reduced pressure state by a chip, wherein the sleeve has an inner peripheral surface in contact with the molten metal formed of a metal matrix composite material. To do. It is preferable that the entire inner peripheral surface is formed of a metal matrix composite material. However, if 80% or more of the inner peripheral surface is a metal matrix composite material, it is within the scope of the claims of the present application.

As the metal matrix composite material, one having a thermal conductivity at 300 ° C. of 25 W / (m · K) or less (not including 0 W / (m · K)) is used. For example, a normal cermet alloy, Si ₃ N ₄ group A sialon of a dense sintered body composed of the above composite structure, a metal ceramic composite material that is a composite material of a titanium alloy and ceramic particles such as an MC material manufactured by HIP manufactured by Kubota Corporation can be used.
Moreover, it is preferable to use steel materials, such as carbon steel S45C material for machine structures, and SKD61 material, for the outer peripheral side of a metal matrix composite material from a cost, sleeve crack countermeasure, etc. The metal matrix composite and the steel are fixed together by thermal spraying or shrink fitting.

  For casting light alloys, general casting aluminum alloys such as Al-Si-Cu, Al-Si-Mg, and Al-Mg, such as ADC3, ADC5, ADC10, and ADC12 are used as appropriate. do it. The same applies to the Mg material and the zinc material. The use of wrought alloys such as A2000 series, A6000 series, and A7000 series is also possible.

  The casting machine of the present invention is preferably used for supplying 0.3 to 0.6 kg of molten metal per second from the start of vacuum generation to the start of casting through a hot water supply pipe in the sleeve. The average flow rate of the molten metal at the upper end of the hot water supply pipe is about 0.4 to 6.0 m / sec. If the supply amount of molten metal and the average flow rate are equal to or less than the above values, the conventional sleeve as shown in FIG. 3 can sufficiently prevent melting damage, and the casting machine of the present invention has excessive performance. On the contrary, when the supply amount of molten metal and the average flow rate are equal to or higher than the above values, sufficient time for depressurizing the inside of the cavity cannot be obtained, and the high vacuum performance that the die casting machine of the present invention is good at is sufficiently obtained. Absent.

The lubricant supplied to the inner peripheral surface of the injection leaf is preferably a non-water-soluble lubricant solidified with wax and granulated to about 0.3 to 1.5 mm. In the case of a water-soluble material, a gas containing various components is generated by heat with the molten metal, and is combined with a reactive gas such as oxygen supplied to finally react with the molten metal. A powdery mold release agent such as graphite can also be applied, but it is expensive, and it becomes difficult to control the amount adhered to the injection leaf.
It is preferable to apply a synthetic oil-based release agent to the mold cavity. Since the amount of gas generated is much smaller than that of water-soluble, and the amount of unnecessary gas entrained in the die-cast product can be reduced, it exerts a remarkable effect in suppressing the occurrence of gas defects.

  As described above, by using the vacuum die casting apparatus of the present invention, it is possible to suppress the occurrence of melting damage in the sleeve and reduce casting defects. In addition, by using an injection sleeve whose inner peripheral surface is formed of a metal matrix composite material, it is possible to continuously use an injection sleeve that has been exchanged for about 10,000 shots up to about 50,000 shots. The operation efficiency can be improved because the exchange work inside is reduced.

Example 1
FIG. 1 is a cross-sectional view of a vacuum die casting apparatus 10 according to the first embodiment. A vacuum die casting apparatus 10 of FIG. 1 includes a cavity 16 formed by a fixed die 16c and a movable die 16d, a leaf 11 communicating with the cavity 16, and a plunger tip 12 that can be fitted and moved forward and backward in the leaf 11. A holding furnace 13 under the sleeve 11 for containing the molten metal M, a hot water supply pipe 14 having one end communicating with the hot water supply port 11a formed in the sleeve 11 and the other end immersed in the molten metal M in the holding furnace 13, a cavity Depressurization means such as a cut-off valve 18a and a vacuum pump 18 are provided for depressurizing the inside 16 to a vacuum state and loading the molten metal M in the holding furnace 13 into the sleeving 11 via the hot water supply pipe 14.

The fixed die 16c is attached to the fixed platen 16a, and the movable die 16d is attached to the movable platen 16b. The holding furnace 13 is placed on the lifting platform 15, and the molten metal M surface is made constant by moving the lifting platform 15 up and down. The hot water supply pipe 14 is made of a ceramic whose inner surface is coated with BN to prevent reaction with the molten metal M, and an orifice 14a is formed at the lower end. The outer periphery of the hot water supply pipe 14 is surrounded by a heater (not shown) to keep the hot water supply pipe 14 near the temperature of the molten metal M. The sleeve 11 is a super sialon (density 3.2 g / cm ³ , bending strength 1050 MPa, hardness 300 Hv, thermal expansion coefficient), which is a Si ₃ N ₄ metal matrix composite manufactured by Hitachi Metals whose inner peripheral surface is ^{3 to} 20 mm thick. 3.0ppm / K, thermal conductivity of 25W / (m · K) or less) and the outer peripheral side is made of SKD61 tool steel (JIS-G4404, thermal expansion coefficient about 12ppm / K), and both are shrink-fitted It is one.

  A supply device (not shown) for supplying a water-insoluble lubricant to the injection leaf 11 and a coating device (not shown) for applying a synthetic oil release agent into the mold cavity 16 are separately provided. Is provided. This supply means sprays from the mold side opening of the injection leaf to supply the lubricant, and the coating device applies the mold release agent to the mold cavity surface after the mold is opened and the product is taken out. is there. In particular, the amount of the synthetic oil release agent used is about 0.1 to 10 g, and the coating apparatus is provided with a spraying function in order to apply this amount to the entire cavity surface.

A two-wheel subframe (weight 1.5 kg, projected area approximately 420 mm × 400 mm) was continuously cast using the die casting apparatus of the present invention. During casting, the degree of vacuum in the cavity was 50 hPa or less, and about 1.21 kg of molten metal per second was supplied into the sleeve through the hot water supply pipe from the start of vacuum generation to the start of casting. The average flow rate of the molten metal at the upper end, which is the minimum cross section of the hot water supply pipe, was 0.8 m / sec.
When the number of castings and the occurrence rate of defective products such as hot water wrinkles, hot water boundaries, internal defects, etc., generated due to melting of the injection sleeve were investigated, defective products were produced even when the number of castings exceeded 10,000. The rate of occurrence was almost the same as the rate at which casting was started (2.8%), and it was confirmed that sufficient measures were taken against melting damage.
Moreover, the same measurement was performed using the injection sleeve formed with the steel material shown in FIG. The sleeve of FIG. 3 is made of SKD61 tool steel (JIS-G4404, coefficient of thermal expansion of about 12 ppm / K). As a result of the measurement, the occurrence rate of defective products at the beginning of casting was almost the same as that of the vacuum die casting machine of the present invention. However, when 10,000 shots were cast, the occurrence rate of defective products was 30% or more, and the injection sleeve was replaced. Was necessary.

1 is an example of a vacuum die casting machine according to the present invention. It is a figure which shows the structure of an injection leaf. It is a figure which shows the structure of the injection leaf of the conventional pressure reduction die-casting machine.

Explanation of symbols

1: Metal matrix composite,
2: Steel,
10: Vacuum die casting device,
11: Slief,
11a: hot water outlet,
12: Plunger tip,
13: Holding furnace,
14: Hot water pipe
14a: orifice,
15: Lift platform,
16: mold cavity,
16a: fixed platen,
16b: movable platen,
16c: fixed type,
16d: movable type,
18: vacuum pump,
18a: vacuum valve,
M: molten metal
V: Depressurization

Claims (3)

The molten metal for casting in the holding furnace is charged into the horizontal injection leaf from below through the hot water supply pipe by depressurizing the inside of the mold cavity, and then the molten metal is moved by the plunger tip that slides in the injection leaf. A vacuum die casting apparatus having a structure for filling the cavity in a reduced pressure state,
2. The vacuum die casting apparatus according to claim 1, wherein the sleeve has an inner wall surface in contact with the molten metal formed of a metal matrix composite material. 2. The vacuum die casting apparatus according to claim 1, wherein the injection sleeve has an inner wall surface in contact with the molten metal formed of a metal matrix composite material and an outer peripheral portion formed of a steel material. The decompression die casting apparatus supplies 0.3 to 6 kg of molten metal per second from the start of vacuum generation to the start of casting through the hot water pipe in the injection sleeve, and has a minimum cross section of the hot water pipe. 3. The vacuum die casting apparatus according to claim 1, wherein an average flow rate of the molten metal in the portion is 0.4 to 5.0 m / sec.

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