JPH10272548A - Method for casting semi-solidified die casting product and casting method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the enclosure of gas into molten metal and to obtain a casting excellent in mechanical property without developing blister and oxide, etc., by measuring the temp. of the molten metal in a casting sleeve and executing the injection- control into a die. SOLUTION: The inner parts of a mouthpiece 7, the casting sleeve 2 and the cavity of the die 1 are held to inert gas atmosphere. A movable die 1b of the die 1 is horizontally shifted to open a part of the upper surface of the casting sleeve 2, and an air cylinder 12 is advanced and also, a base table is shifted and a sheath thermocouple 11 is inserted to that the tip part thereof coincides with the molten metal surface level to be supplied (differ according to a product to be cast) into the casting sleeve 2. Successively, the molten metal 20 is flowed into the casting sleeve 2 from the mouthpiece 7 through a molten metal supplying hole 4 so as to become laminar flow. When the molten metal 20 reaches the prescribed level, the detected temp. of the thermocouple 11 is raised, and then, it is detected that the molten metal level reaches the prescribed level, and a command is given to a molten metal supplying device with a signal from a temp. detector 15 so as to held the molten metal level as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semi-solid die casting method and apparatus for producing a high quality casting having excellent mechanical properties.

[0002]

2. Description of the Related Art A die casting method is a casting method in which a molten metal (hereinafter, abbreviated as "molten metal") in a casting sleeve is pressure-filled into a mold cavity and solidified to produce a casting.
This die casting method has the advantages that the obtained casting has high dimensional accuracy, can be mass-produced at high speed, and can be completely automated, and is frequently used for casting low-melting metal castings such as aluminum alloys. On the other hand, in the die casting method, there is a problem that the molten metal injected into the casting sleeve is quenched on the inner wall of the casting sleeve and solidified pieces are generated, and the solidified pieces are cast to lower the mechanical strength of the product. . Further, if air in the casting sleeve is caught in the molten metal and mixed into the casting at the time of injection, blisters called blisters are generated when heat treatment is performed, which also causes a reduction in mechanical strength. Therefore, it is difficult to apply a casting obtained by the die casting method to a strength member requiring high strength as it is.

As a means for solving the above problem, there is a special die casting method. The special die casting method includes a hot sleeve method in which the casting sleeve is heated in order to prevent the formation of solidified pieces on the inner wall of the casting sleeve, and a vertical injection method in order to reduce air entrainment in the casting sleeve. There is a die casting method. However, even in these special die-casting methods, when the injection speed increases, the molten metal in the casting sleeve is disturbed, air is entrained and taken into the product, and causes a decrease in mechanical properties.

[0004] Apart from the above various die casting methods, Japanese Patent Application Laid-Open No. Hei 8-257722 discloses that a primary crystal of a molten metal is granulated in a casting sleeve to form a semi-molten state, which is then pressure-filled into a mold cavity and solidified. A semi-solid die casting method characterized by the following is disclosed. According to the die casting method disclosed in Japanese Patent Application Laid-Open No. Hei 8-257722, hot water is supplied to the casting sleeve from a temperature near the liquidus line, and the temperature of the molten metal is lower than the liquidus line and lower than the liquidus line. By lowering at a predetermined cooling rate to a predetermined temperature higher than the eutectic line and substantially granulating the primary crystal of the molten metal to be in a semi-molten state, thixotropic by the granular primary crystal and the liquid having a temperature higher than the eutectic temperature is reduced. It is stated that by using a thixotropic property of the semi-molten molten metal to fill the mold from the sleeve into a laminar flow, gas entrainment during filling the mold cavity can be reduced. That is, by setting the solid phase ratio in the semi-molten state to 30% or more, it is possible to impart thixotropic property to the molten metal. It is said that the movement of the liquid phase and the movement of the liquid phase occur at the same time, causing a phenomenon in which the solid and liquid move together, thereby reducing defects in the cast product, reducing the gas content, and preventing blisters from being generated even by heat treatment. The thixotropy is a property of a mixture of a granular solid and a liquid in a certain ratio, and is a phenomenon in which the solid is liquefied by vibration or shear force and solidified when left.

[0005]

However, in the die casting method disclosed in Japanese Patent Application Laid-Open No. Hei 8-257722, as a means for substantially granulating the primary crystals, the molten metal is heated at a temperature near the liquidus line. Hot water is supplied to the casting sleeve, and the temperature of the molten metal is lowered at a predetermined cooling rate from a temperature near the liquidus to a predetermined temperature lower than the liquidus and higher than the solidus or eutectic,
It is necessary to substantially granulate the primary crystals of the molten metal, but no means for detecting the temperature is disclosed.

A thermocouple is generally used for measuring the temperature of molten aluminum in a melting furnace or a holding furnace. In order to prevent the molten aluminum from being melted, a protective tube made of ceramic such as silicon nitride or alumina is used. Insert and use a thermocouple inside. However, the temperature measurement method in which the thermocouple is incorporated in the ceramic protection tube requires a response time of several tens of seconds to about 1 minute, and is applicable to the temperature measurement in the above-mentioned application requiring a fast response. Can not. In temperature measurement that requires a fast response speed, a sheath thermocouple in which a thermocouple wire and an insulating material such as magnesium oxide are put in a thin metal protective tube such as stainless steel or Inconel is used. However, when trying to measure the temperature of the molten aluminum in the sleeve with the sheath thermocouple continuously immersed, the metal of the sheath thermocouple from the vicinity of the contact surface with the molten metal surface of the metal protective tube surface in a short period of time The surface wears out and eventually breaks and becomes unusable. In addition, when intermittently immersed in molten aluminum and used for temperature measurement, the molten aluminum gradually adheres to and grows on the surface of the metal protection tube, resulting in a problem that the response time of the measured temperature becomes longer.

In the die casting method disclosed in Japanese Patent Application Laid-Open No. Hei 8-257722, primary crystals of a molten metal are substantially granulated in a casting sleeve to form a semi-molten state and pressure-filled into a mold cavity. Although it is said that the solidification can prevent entrapment of gas into the molten metal, if the molten metal is dropped from the upper part of the casting sleeve using a ladle or the like, the molten metal falls and flows inside the casting sleeve, causing air to flow. Not only causes blisters, but also causes the problem that oxidation of the molten metal proceeds, and a defect caused by oxides finally occurs in the solidified product, resulting in a decrease in mechanical strength. The present invention measures the temperature of the molten metal in the casting sleeve, confirms that the molten metal has reached a semi-molten state, and then injects the molten metal into the mold cavity, and prevents gas from getting into the molten metal to prevent blisters and oxides. An object of the present invention is to obtain a casting having excellent mechanical properties without occurrence of cracks.

[0008]

SUMMARY OF THE INVENTION A semi-solid die casting method of the present invention is characterized in that a primary crystal of a molten metal is substantially granulated in a casting sleeve to form a semi-molten state and pressure-filled into a mold cavity. It is characterized in that the temperature of the molten metal in the sleeve is measured to control the injection into the mold. In order to substantially granulate the primary crystal of the molten metal, the temperature of the molten metal in the casting sleeve is increased at a predetermined speed from a temperature near the liquidus to a predetermined temperature lower than the liquidus and higher than the solidus or eutectic. There is a method of fluidizing the molten metal by mechanical stirring, electromagnetic stirring, or the like in this process while lowering the temperature. The temperature near the liquidus line is, for example, about 10 ° C. below the liquidus line to about 40 ° C. above the liquidus line for A357 alloy. If it is higher than that, dendrite tends to grow, and if it is lower than that, dendrite is generated before hot water is supplied. To achieve a given cooling rate,
The casting can be performed by providing a cold crucible structure, applying a heat quantity while electromagnetically stirring the molten metal at a high frequency, and cooling the sleeve. Preferably, the cooling rate is less than about 10 ° C./sec. It is desirable to control the above by actually measuring the temperature in the casting sleeve.

The molten metal is supplied into the casting sleeve by laminating the molten metal at a temperature near the liquidus from the bottom of the casting sleeve. Thereby, the oxidation of the molten metal can be prevented by minimizing the entrapment of air into the molten metal during hot water supply. Furthermore, when the molten metal is supplied to the casting sleeve, the interior of the casting sleeve is set to an inert gas atmosphere so that the surface of the molten metal is covered with an inert gas. Can be prevented.

The temperature of the molten metal in the casting sleeve is measured by coating the metal protective tube of the sheath thermocouple with a ceramic coating, inserting the sheath thermocouple into the molten metal and swinging the molten metal while preventing the metal protective tube from being melted. Prevents adhesion. The oscillation is performed at a frequency of 1 Hz or more.
It is desirable to carry out at 5 Hz or more. In addition, the semi-solid die casting method of the present invention detects the molten metal level in the casting sleeve at the time of hot water supply by supplying the molten metal into the casting sleeve by increasing the temperature of the sheath thermocouple in which the metal protective tube is coated with ceramics. Thereafter, the temperature of the molten metal is detected by being immersed in the molten metal and oscillating, and the injection into a mold is controlled. That is, by arranging the tip of the sheath thermocouple at a predetermined position corresponding to the amount of molten metal supplied into the casting sleeve, the temperature rise of the thermocouple at the time of hot water supply is detected, and the level of molten metal in the casting sleeve is detected. can do. As a result, it is possible to control the amount of molten metal supplied into the casting sleeve to be constant each time.

Further, the semi-solid die casting apparatus according to the present invention provides a semi-solid die casting in which primary crystals of a molten metal are substantially granulated in a casting sleeve to form a semi-molten state under pressure into a mold cavity and solidify. In the casting apparatus, a sheath thermocouple having a ceramic coating applied to a metal protective tube, a moving means for moving a tip of the sheath thermocouple to be inserted into a casting sleeve, and a rocking means for rocking the sheath thermocouple, The gas supply hole has a perforated molten metal channel, and a mouthpiece for supplying the molten metal from the hot water supply device to the casting sleeve is provided.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the semi-solid die casting apparatus of the present invention. In FIG. 1, reference numeral 1 denotes a die of a vertical die casting apparatus, which is composed of a fixed die 1a and a movable die 1b, and has a structure divided into right and left. Reference numeral 2 denotes a casting sleeve using a non-magnetic metal material. The casting sleeve has a vertical arrangement structure in which an upper end is fitted to a sprue provided below the mold 1, and an inner cylinder 3 made of ceramic is provided on the inner surface in contact with the molten aluminum. It is configured by fitting. The casting sleeve 2 has a lower side surface and an injection tip 5.
A hot water supply port 4 for the molten aluminum is provided at a position where it is opened when the metal is retracted, and a high-frequency coil 6 is installed around the casting sleeve 2 from above the hot water supply port to above the casting sleeve 2.
The casting sleeve 2 corresponding to the high-frequency coil 6 is perforated with a cooling passage 10 so as to have a so-called cold crucible structure in which a medium such as water or air can be circulated and cooled.

A mouthpiece 7 having a flow path of molten metal having the same diameter as the hot water supply port is connected to the hot water supply port 4, and a hot water supply pipe 9 of molten aluminum is connected to the other end connection port of the mouthpiece 7. A vertical pipe section is provided in the middle of the flow path of the mouthpiece 7, and a gas supply port 8 is pierced at the top of the vertical pipe section to connect a pipe so that an inert gas such as argon gas or nitrogen can be supplied. . The mouthpiece 7 can be made of a refractory material such as silicon carbide or carbon ceramic. The hot water supply pipe 9 is configured to communicate with an aluminum hot water supply device or an aluminum holding furnace (not shown) so as to supply the molten aluminum 20.
The liquid surface of the molten aluminum 20 is normally held at an arbitrary position in the vertical portion of the mouthpiece 7. As the aluminum hot water supply apparatus, an electromagnetic pump method or a gas pressurization method can be used, but a method capable of controlling the start and stop of the supply of molten metal and the supply amount is desirable. The mouthpiece 7 and the hot water supply pipe 9 are provided with a sheath heater or a cartridge heater outside thereof in order to prevent the molten aluminum from solidifying in the pipe, and are further kept warm by a heat insulating material to prevent heat radiation from the surface (not shown). ). The heater is controlled so that the temperature of the mouthpiece 7 can maintain the temperature of the molten metal therein near the liquidus temperature.

The thermocouple 11 for measuring the temperature of the molten metal includes a base 30.
2, the air cylinder 12 is moved forward while the mold 1 is open as shown in FIG. 2, and the base 30 is moved (the moving device is not shown). The structure is such that the pair 11 is inserted into the casting sleeve 2.
A sheath thermocouple is used as the thermocouple, and a ceramic powder such as, for example, boron nitride is applied to the surface of the metal protection tube of the sheath thermocouple, and ceramic coating is performed. The air cylinder 12 is provided with a forward end sensor 14 and an intermediate sensor 13, and repeatedly swings forward and backward between the forward end sensor 14 and the intermediate sensor 6 while the thermocouple 11 is immersed in the molten aluminum. This operation requires another cylinder with a short stroke.
It is also possible to substitute by attaching a table. Thermocouple 11
Is connected to the temperature detector 15, and by setting the temperature at which the molten aluminum is in a semi-molten state in advance to the temperature detector 15, the timing of raising the injection tip 5 can be set.

The casting process of the semi-solid die casting method of the present invention will be described with reference to FIG. 1 and FIG. An inert gas is supplied from a gas supply port 8 at an upper portion of the mouthpiece 7, and the mouthpiece 7, the casting sleeve 2, and the cavity of the mold 1 are kept in an inert gas atmosphere. The movable mold 1b of the mold 1 is horizontally moved to open a part of the upper surface of the casting sleeve, the air cylinder 12 is advanced, and the base 30 is moved. Insert it so that it is at a predetermined position. The position of the distal end of the sheath thermocouple 11 matches the level of the molten metal to be supplied into the casting sleeve 2. The level of the molten metal in the casting sleeve varies depending on the product to be cast, and the position of the distal end of the sheath thermocouple can be adjusted according to the level (not shown). Subsequently, the supply of the molten metal 20 to the casting sleeve 2 is started by the hot water supply device. The molten metal flows from the mouthpiece 7 through the hot water supply port 4 into the casting sleeve 2 so as to have a laminar flow. When the molten metal reaches a predetermined level, the detected temperature of the thermocouple 11 rises to detect that the molten metal is at the molten metal level, and a signal from the temperature detector 15 instructs the hot water supply apparatus to keep the molten metal level as it is. At this time, the molten metal is supplied with the surface thereof covered with an inert gas. By providing a check valve in the pipe between the gas supply port 8 and the gas cylinder, it is possible to prevent the inflow of the molten aluminum even if the pressure on the mouthpiece rises.

Next, the injection tip 5 rises inside the casting sleeve 2 and stops at a position where the tip end passes through the hot water supply port 4 and is closed as shown in FIG. 2, and the molten metal is supplied to the hot water supply device by the vertical pipe of the mouthpiece. Order to return to the part. The stop position of the tip of the injection tip 5 can be controlled by constantly monitoring the movement distance with a sensor. At this time, the molten metal surface in the casting sleeve 2 rises by the moving amount of the injection tip 5, and the tip of the thermocouple 11 is immersed in the molten metal. In addition, hot water supply 4
Is closed by the injection tip 5, and argon gas or nitrogen gas is supplied from the gas supply port 8 provided in the upper part of the mouthpiece 7, so that the lowering of the molten metal in the mouthpiece is promoted, and Oxidation can be prevented.

The molten metal in the casting sleeve 2 is cooled by a cooling medium in a cooling passage 10 perforated in the casting sleeve 2 to form primary crystals, and the molten metal is also subjected to electromagnetic stirring by the high-frequency coil 6. To make the tissue spherical.
At this time, the temperature of the molten metal is continuously measured while oscillating the thermocouple 11 for measuring the temperature of the molten metal up and down in the molten metal, and the solid phase ratio of 10 is measured.
Detecting that a predetermined solid phase ratio within a range of 〜60% has been reached, a signal from the temperature detector 15 causes the air cylinder 12 to retract, and the base 30
After returning to the original position, the movable mold 1b is tightened, the injection tip 5 is raised, and the molten metal in a semi-solid state is injected into the mold cavity.

FIG. 3 shows a sheath thermocouple obtained by coating a 1 mm diameter ceramic coating on molten aluminum for 30 seconds.
The measurement result of the response time in the temperature measurement when immersing while rocking up and down is shown. Here, the response time is the time required for the thermocouple to reach the maximum temperature after being immersed in the molten aluminum. The first measurement was performed with no aluminum adhered, and the second and subsequent measurements were performed continuously with aluminum adhered. At this time, the swing amplitude of the thermocouple was 30 mm, and the immersion depth was 55 mm at the maximum. As a result, when the rocking frequency is 1.9 Hz or 2.9 Hz, the amount of aluminum deposited does not change and the response time becomes almost constant even when immersion is repeated, but the rocking frequency becomes 0.9 Hz. Accordingly, the response time increases. Thus, the oscillation frequency is preferably 1 Hz or more, and more preferably 1.5 Hz or more.

[0019]

As described above, according to the present invention, the temperature of the molten metal in the casting sleeve is measured to control the injection into the mold. As a result, the entrainment of air can be minimized by using the hot water flow as a laminar flow. Also, by supplying the molten metal from the lower part of the casting sleeve in an inert gas atmosphere, the generation of oxides at the time of hot water supply is suppressed, and as a result, the mechanical properties of the resulting product are improved, and high strength is required. Enables casting of components.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a semi-solid die casting apparatus of the present invention.

FIG. 2 is a view for explaining a molten metal temperature measurement in the semi-solid die casting method of the present invention.

FIG. 3 shows the relationship between the number of times of immersion and the response time depending on the oscillation frequency of the sheath thermocouple.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Mold 2 Casting sleeve 3 Inner cylinder 5
Injection tip 6 High frequency coil 7 Mouthpiece 9 Hot water supply pipe 11 Sheath thermocouple 12 Air cylinder 15 Temperature detector 20 Molten metal

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Ryoichi Shibata 11 Kinuigaoka, Moka City, Tochigi Prefecture Hitachi Metals Co., Ltd.Materials Research Laboratory (72) Inventor Yoshio Kanai 11 Kinugaoka, Moka City, Tochigi Prefecture Hitachi Metals Inside Materials Research Laboratory, Inc.

Claims (7)

[Claims] In a semi-solid die casting method, a primary crystal of a molten metal is substantially granulated in a casting sleeve to form a semi-molten state under pressure and filled in a mold cavity and solidified. A semi-solid die casting method characterized by performing a control of injection into a mold by measuring a temperature. 2. The semi-solid die casting method according to claim 1, wherein molten metal having a temperature near the liquidus is supplied into the casting sleeve by laminar flow from the bottom of the casting sleeve. . 3. The semi-solid die casting method according to claim 1, wherein the temperature measurement of the molten metal is performed by inserting a sheath thermocouple coated with a ceramic coating on the metal protective tube into the molten metal and swinging the sheath thermocouple. . 4. The semi-solid die casting method according to claim 3, wherein the temperature is oscillated at a frequency of 1 Hz or more. 5. A hot-water supply amount according to claim 3, wherein the level of molten metal at the time of hot-water supply into the casting sleeve is detected by a sheath thermocouple in which a metal coating tube is coated with a ceramic. Control the
A semi-solid die casting method characterized by immersing in a molten metal and oscillating to measure the temperature of the molten metal. 6. The semi-solid die-casting method according to claim 1, wherein the molten metal surface is injection-molded into a mold while the surface of the molten metal is covered with an inert gas. Casting method. 7. A semi-solid die casting apparatus in which a primary crystal of a molten metal is substantially granulated in a casting sleeve to form a semi-molten state under pressure and solidified by pressure into a mold cavity. Sheath thermocouple subjected to the following, moving means for moving the distal end of the sheath thermocouple into the casting sleeve, oscillating means for oscillating the sheath thermocouple, and molten metal having a gas supply hole perforated A mouthpiece having a flow path and supplying molten metal from a hot water supply device to a casting sleeve.