JP3100954B2 - Method of manufacturing thin aluminum die-cast molded product - Google Patents

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 thin aluminum die-cast product. More specifically, the present invention provides a thin-walled aluminum die-cast molded product having a good appearance with a thickness of 0.4 to 1.2 mm using a mold having a thin gate, and a gate portion having a good molten metal flowability. And a method for efficiently producing the same.

[0002]

2. Description of the Related Art Aluminum has excellent properties as a metal, such as excellent light weight, plastic workability, corrosion resistance, and good electrical and thermal conductivity. If copper, magnesium, zinc, silicon, lithium, nickel, chromium, manganese, iron, zirconium, etc. are added to this aluminum and alloyed, the mechanical properties at room temperature and high temperature due to solid solution hardening, work hardening, age hardening, etc. Is remarkably improved, and characteristics such as corrosion resistance, abrasion resistance, and a low coefficient of thermal expansion are also added. Therefore, aluminum or aluminum alloys with such properties can be used in household goods and beverage cans, furniture, interiors, aerospace, automobiles, electrical and electronic products,
It is widely used in many fields such as vehicles, ships, civil engineering and construction. Die casting is known as one of the processing methods of aluminum-based materials such as aluminum and aluminum alloys, and is currently widely used for producing various molded products. In this die casting method, a molten metal is injected into a metal mold at a high speed (about 20 to 60 m / sec) by a press plunger and at a high pressure (about 30 to 200 MPa).
Injection, filling, and rapid solidification in the casting method, it is possible to manufacture thin castings with a minimum wall thickness of about 1mm, has good dimensional accuracy and casting surface, and has the advantages of high productivity. Have. However, in this die casting method, since the injection speed of the molten metal is high and the filling time is as short as about 0.3 seconds, the air and the reaction gas in the mold space (cavity) are easily entrained. (Porocity)
Is likely to occur. Therefore, in order to improve the quality, (1) a low-speed filling die-casting method in which the injection speed is reduced to 1 m / sec or less, (2) an Accurad method in which two-stage pressurization is performed with a time difference to eliminate shrinkage in a thick portion, and (3) a thickness. A local squib method in which the meat portion is locally pressurized to eliminate shrinkage, (4) a vacuum die casting method in which the inside of the mold is reduced by reducing the pressure in the mold, and (5) an oxygen atmosphere in the mold, A PF die-casting method has been developed in which all are dispersed as fine oxides to prevent entrapment as a gas. However, these conventional techniques are all aimed at improving the quality of a die-cast molded product, and are not intended to reduce the wall thickness. For an aluminum-based die-cast molded product, the thickness is limited to about 1 mm. In fact, a thinner molded product could not be obtained. By the way, in recent years,
ICs provided with a microelectronic circuit in which elements including a large number of semiconductors and internal wirings are combined as one solid by a special method are increasing. In such an IC, a large amount of heat is generated during the operation of the semiconductor,
If the temperature rises, the operation of the semiconductor itself becomes unstable,
There is a possibility that an undesirable situation such as the destruction of the semiconductor may be caused. For this reason, the heat sink for cooling the semiconductor is
And heat exchange between the radiator plate and air to release the heat of the semiconductor into the air, thereby preventing the semiconductor from becoming hot, becoming unstable in operation, and being destroyed. As such a heat radiating plate, one having a large number of elongated heat radiating pins arranged on a substrate is used, and for this, an aluminum-based die-cast molded product is frequently used. With the recent heat-dissipating ICs becoming more compact, it is desired to reduce the weight of the heat-dissipating plate. In addition, aluminum-based die-cast products are frequently used in case covers of portable electronic devices, and similarly to the above, miniaturization of electronic devices (for example, notebook computers).
Accordingly, the weight reduction is required. As a lightweight material, a magnesium-based material such as magnesium (specific gravity of aluminum: 2.70) having a specific gravity of 1.74 or a magnesium alloy is known. However, a molded article made of this magnesium-based material has disadvantages that it is more expensive than an aluminum-based molded article and has a high defect rate.
Therefore, there is a demand for an inexpensive aluminum-based die-cast product which is as lightweight as a magnesium-based product. In order to make an aluminum-based die-cast molded product comparable to a magnesium product having a small specific gravity, it is necessary to reduce the wall thickness. However, as described above, in the prior art, an aluminum-based die-cast molded product having a thickness of less than 1 mm is manufactured. Is difficult and therefore 1mm thick
There has been a demand for the development of a technique for efficiently producing an aluminum-based die-cast molded product having a size of less than. Therefore, the present inventor
We have conducted intensive research on a method of manufacturing a thin aluminum die-cast molded product having a wall thickness of less than 1 mm. First, a part of the member surrounding the cavity does not allow the molten aluminum-based material to pass therethrough, but does allow gas to pass therethrough. By providing at least one porous member made of iron in contact with the gas passage opened to the outside, press-filling the cavity with a molten metal of an aluminum-based material, and discharging the gas and air to the outside through the porous member, It has been found that a thin aluminum die-cast molded product having a thickness of less than 1 mm can be obtained. By the way, when the molten metal of the aluminum-based material is press-fitted into the cavity of the mold, the molten metal is charged from the gate. The aluminum-based material in the gate portion is separated from the obtained die-cast product. Therefore, as the thickness of the gate is smaller, the molded article is less likely to be damaged, and a molded article having a good appearance can be obtained. However, if the thickness of the gate is too thin, the flowability of the molten metal deteriorates. Therefore, in the production of a conventional aluminum die-cast molded product (thickness of 1 mm or more), generally, the thickness is about 0.6 to 1 times the thickness of the molded product. The thickness of the gate is used. That is, the thickness of the gate is limited to about 0.6 mm. If the thickness is less than this, the flowability of the molten metal is poor, and a high quality aluminum die-cast product cannot be obtained.
Therefore, in the production of a thin-walled aluminum die-cast product having a thickness of less than 1 mm, a gate with good melt flowability has been desired even if the thickness is about の of the thickness of the product. By using such a gate having a small thickness and good flowability of the molten metal, it is expected that a thin aluminum-based die-cast molded product having a good appearance and a good quality can be obtained.

[0003]

SUMMARY OF THE INVENTION Under such circumstances, the present invention uses a mold having a thin gate thickness, and has a good appearance and a good thickness of 0.4 to 1.2 mm. The purpose of the present invention is to provide a method for efficiently producing a thin aluminum-based die-cast molded product having a good melt flowability.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, as a mold, the thickness of the gate is not less than 0.2 mm and not more than the thickness of the molded product. The present inventors have found that the object can be achieved by using a member constituting the gate that has been subjected to a nitriding treatment, and have completed the present invention based on this finding. That is, the present invention relates to (1) a method of manufacturing an aluminum die-cast product having a thin portion having a thickness of 0.4 to 1.2 mm by press-filling a molten metal of an aluminum material into a cavity of a mold. A mold having a gate thickness of 0.2 mm or more and a thickness of a part to be cut off from the gate portion of the molded product and having a surface of a member constituting the gate subjected to nitriding treatment. (2) As a mold, a part of a member surrounding a cavity does not allow a molten metal of an aluminum material to pass therethrough, but allows gas to pass through and opens to the outside. 2. The method for producing a thin aluminum die-cast product according to claim 1, wherein one or more iron porous members in contact with the gas passage are provided, and (3) a cavity is formed as a mold. 3. A method for producing a thin aluminum die-cast product according to the above item 1 or 2, wherein the surface of the member is subjected to a nitriding treatment.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The aluminum-based material used in the method for producing a thin aluminum-based die-cast product of the present invention is not particularly limited as long as it is a metal material containing aluminum as a main component. It is preferable to appropriately select from aluminum alloys for casting according to the use of the die-cast molded article.
As an aluminum alloy for casting, for example, Al-Cu
System, Al-Si system, Al-Mg system, Al-Si-Cu
System, Al-Si-Mg system, Al-Co-Cu system, Al-
Mn-Mg-based, Al-Mn-Fe-based, Al-Mn-Zn
-Fe-Mg type and the like. In the method of the present invention, the molten aluminum-based material is press-filled into a cavity of a mold to produce a thin aluminum-based die-cast product having a thickness of 0.4 to 1.2 mm. This thickness 0.4
~ 1.2mm thin aluminum die cast products
It is not necessary that the entire molded article has a thickness of 0.4 to 1.2 mm, and a part of the molded article may have a thickness of 0.4 to 1.2 mm. In the present invention, a mold having a gate thickness of not less than 0.2 mm and not more than the thickness of a molded product and having a surface of a member constituting the gate subjected to nitriding treatment is used. If the thickness of the gate is less than 0.2 mm, the flowability of the molten metal is poor, and a molded product of good quality cannot be obtained. If the thickness of the molded product exceeds the thickness, the molded product is easily damaged when the gate is cut off. Good molded products cannot be obtained. As a material of a member constituting the gate, a material capable of nitriding, for example, a steel material such as cast iron, carbon steel, alloy steel, steel for nitriding including Al, Cr, V, and the like is used.

There is no particular limitation on the method of nitriding treatment.
Conventionally, it can be appropriately selected and used from methods commonly used as a nitriding treatment method for imparting wear resistance and the like. Various methods have been developed as the nitriding method, but (1) salt bath nitriding, (2) gas nitriding, (3) gas soft nitriding, and (4) ion nitriding are particularly preferable. In the salt bath nitriding method of the above (1), the member to be treated is immersed in a salt bath of a mixed salt containing an alkali cyanate such as sodium cyanate or potassium cyanate, and is subjected to 500 to 700
This is a method of performing a nitriding treatment by performing a heat treatment at a temperature of about ° C. and using nitrogen generated by the decomposition of alkali cyanate. Among these salt bath nitriding methods, the tuftride method is particularly preferred. In this tuftride method, a mixed salt bath of alkali cyanate, alkali cyanide, and alkali carbonate is used. The member to be treated is immersed in the mixed salt bath, and heated while blowing an oxygen-containing gas such as air. And
A nitriding process is performed. The member thus nitrided is usually immersed in an oxidation bath at 350 to 450 ° C., and is subjected to quenching simultaneously with neutralization. The gas nitriding method (2) is a method in which a member to be processed is heated at a temperature of about 500 to 550 ° C. in an ammonia gas stream at a gas pressure of about 8,000 to 10,000 Pa. In this method, the nitriding treatment is performed by atomic nitrogen generated by decomposition of ammonia on the surface of the member to be treated. In the gas nitrocarburizing method (3), ammonia gas and N ₂ 40
The member to be processed is heated at a temperature of about 550 to 600 ° C. in a gas stream containing a mixed gas consisting of 40% by volume of H _2, 40% by volume of H ₂ and 20% by volume of CO ₂ at a volume ratio of about 50:50. It is a method of processing. In this method, carburizing and nitriding occur at the same time, the nitriding is promoted by the carburizing action, and the processing time is shorter than in the gas nitriding method (2). On the other hand, in the ion nitriding method of (4), a member to be treated is used as a cathode and a container wall is used as an anode in a closed vessel under a mixed gas atmosphere of nitrogen and hydrogen at a gas pressure of about 0.1 to 2.5 MPa. This is a method of applying a DC voltage of about 1,500 V. In this method, a glow discharge occurs near the surface of the member to be processed, and as a result, the N ₂ gas is ionized near the cathode, and the ionized N ⁺ ions are accelerated at a high speed and collide with the member to be processed. Its surface is nitrided. By nitriding the surface of the member forming the gate by these methods, when filling the cavity with the molten metal of the aluminum material from the gate into the cavity, the molten metal is about 1.5 to 2 times as large as the case without nitriding. Flowability is improved. Further, the wear resistance of the members constituting the gate is improved, and the durability is also improved.

The mold used in the method of the present invention is a mold having a surface of a gate constituting a nitride as described above, and having a gate thickness of 0.2 mm or more and a molded product thickness or less. Any mold can be used as long as it can produce a thin aluminum die-cast molded product having a thickness of 0.4 to 1.2 mm. There is no particular limitation, but the cavity formed by the contact between the fixed mold and the movable mold can be formed. A part of a member surrounding the cavity, provided with at least one iron porous member which does not allow the molten metal of the aluminum-based material to pass therethrough but allows the gas to pass therethrough and which is in contact with the gas passage opened to the outside. Is preferred. When the porous member is press-filled with a molten metal of an aluminum-based material into the cavity, the flowability of the molten metal is degraded by gas or reaction gas and air in the cavity caused by a lubricant or the like present in the molten metal. This is provided to discharge the gas or air from the cavity to the outside for the purpose of preventing the above. Therefore, it is necessary that the porous member be capable of passing gas without passing through the molten aluminum-based material, and has a resistance to the temperature of the molten aluminum-based material. Iron is used because it has appropriate mechanical strength and can be welded to a mold member. As such a porous member, for example, “Porcelax” [trade name,
Shinto Kogyo Co., Ltd.].
The porous member is provided in a part of the member surrounding the cavity, but there is no particular limitation on the installation location, and it is appropriately selected according to the type of the die-cast molded product. For example, when the die-casting product is a heat radiating plate having a plurality of heat radiating pins provided on a substrate, it is advantageous to provide the heat radiating pin portion in the cavity at the tip end side. Further, when the die-cast molded product is a case cover of a portable electronic device, it is preferably provided on a part of a mold member along a molten metal flow in a cavity. This iron porous member may be provided singly, or may be provided in plurality as required. The cavity is formed by abutment between a fixed mold and a movable mold.To form the cavity, the cavity may be directly carved in the fixed mold or the movable mold, or both, or may be nested. It may be carved into the main mold.

Next, a preferred embodiment of the present invention will be described with reference to the accompanying drawings, taking production of a heat sink as an example. FIG. 1 is a cross-sectional view of one example of a die casting mold (for manufacturing a heat sink) used for carrying out the present invention. The die casting mold 1 includes a fixed mold 2, a movable mold 3, The movable mold 3 is composed of a main mold 3a, a nesting mold 3b, and a presser mold 3c. Main mold 3a
A cavity 5 for a heat sink is engraved, and a nesting mold 3b provided with a slit for connecting to each heat radiating pin portion 5 'of the cavity 5 and a porous member 6 in contact with the slit. Fitted and secured with bolts.
Each porous member 6 is made of iron, has a property of allowing gas in the cavity to pass therethrough without passing through a molten metal of an aluminum-based material, and has a gas passage opened to the outside provided in the presser die 3c. It touches 4. A gate 9 which is nitrided and has a thickness in the above-mentioned range communicates with the cavity 5, and the gate 9 communicates with the inside of the sleeve 7 via a flow path 10. The sleeve 7 is filled with the internal molten metal 8
A plunger tip 11 for press-fitting at a pressure of 1,000 kg / cm ² is mounted. When forming an aluminum-based die-casting product, first, the main mold 3a into which the nesting mold 3b is fitted is heated (not shown).
After the mold is heated to a temperature at which molding can be performed, a mold release agent for easily taking out a die-cast molded product is applied to a member forming the cavity 5, and the fixed mold 2 and the movable mold 3 are closed. Next, a molten metal (a temperature of about 680 to 800 ° C.) 8 of an aluminum-based material accommodated in the sleeve 7 is poured into the cavity 5 from the gate 9 through the flow path 10 by the plunger tip 11 into the cavity 5. Press-fill with a pressure of 000 kg / cm ² . The gas generated by the injection of the molten metal and the air in the cavity pass through the porous member 6 and are smoothly discharged from the gas passage 4 to the outside. Therefore, the molten aluminum-based material can be easily filled,
It easily flows into the tip of each heat radiation pin 5 '. When the filling of the molten aluminum-based material is completed in this manner, the die casting mold 1 is cooled by a cooling device (not shown) for about 5 to 8 seconds, and then the fixed mold 2 and the movable mold 3 are cooled. Is opened, and a die-cast molded product is extruded from the main mold 3a with an ejector pin (not shown), and the gate portion is cut off. The aluminum-based die-casting heat radiator thus obtained is free from burrs and void defects, and has good quality. According to this method, the thickness is less than 1 mm, preferably 0.4 to 0.8 mm.
It is possible to easily manufacture a heat radiating plate having heat radiating pins of the order. Thus, by providing the porous member,
The flowability of the molten metal in the cavity is improved, and a thin aluminum die-cast molded product of good quality can be obtained.However, in order to further improve the flowability of the molten metal, if necessary, on the surface of a member constituting the cavity, The nitriding treatment can be performed as in the case of the gate.

[0009]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Example 1 As a mold, a gate having a thickness of 0.3 mm shown in FIG. 1 was used, and a plurality of heat radiation pins having a thickness of 0.5 mm, a height of 7 mm, and a width of 100 mm were provided on a substrate. An aluminum die-cast heat sink was manufactured. First, steel SKD-61
Bath nitriding treatment by the tuftride method was performed on the surface of the member constituting the gate made of as follows. The member to be treated is immersed in a mixed salt bath containing sodium cyanate, potassium cyanide and sodium carbonate, heated at 600 ° C. for 60 minutes while blowing air, and then the member to be treated is placed in an oxidizing bath at 450 ° C. After immersion in for 30 minutes, a nitriding treatment was performed by water cooling. When an Al—Mn—Fe alloy (DM2) was used as an aluminum-based material and a heat sink was manufactured according to the method described in the description of the present specification, no burrs or void defects were generated, and a high-quality heat sink pin was used. A heat sink having a thickness of 0.5 mm was obtained. The temperature of the molten metal is 740 ° C, and the filling pressure of the molten metal is 650 kgf / c.
m ² , the injection time was 0.2 ^second , and the molten metal flowability at the gate was good. A radiator plate having a gate thickness of 0.4 mm was used and a radiator plate was manufactured in the same manner. Comparative Example 1 A plurality of heat dissipating pins having a thickness of 0.5 mm, a height of 7 mm, and a width of 100 mm were prepared in the same manner as in the example, except that the surface of the member constituting the gate was not subjected to nitriding. Manufactured an aluminum die-cast heat sink provided on a substrate. As a result, the temperature of the molten metal was 740 ° C., the filling pressure of the molten metal was 900 kgf / cm ² , and the injection time was 0.3 seconds. The height is 7-
(0.5-3.5) mm, which was not uniform.

[0010]

According to the present invention, a mold having a thin gate and a good thickness of 0.4 to 1.2 mm with good appearance is used.
The thin aluminum-based die-cast molded product of the above can be manufactured efficiently with good flowability of the molten metal at the gate portion. The method of the present invention is particularly preferably used for manufacturing a heat sink or a case cover of a portable electronic device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one example of a die casting mold used for carrying out the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die-casting mold 2 Fixed mold 3 Movable mold 3a Main mold 3b Nesting mold 3c Holding mold 4 Gas passage 5 Heat sink cavity 5 'Heat sink pin part 6 Porous member 7 Sleeve 8 Aluminum-based molten metal 9 Gate 10 Flow path 11 Plunger tip

Claims (3)

(57) [Claims] 1. A thin portion having a thickness of 0.4 to 1.2 mm is filled by press-fitting a molten metal of an aluminum material into a cavity of a mold.
When manufacturing an aluminum die-cast molded product having a thickness of 0.2 mm or more as a mold,
A method for producing a thin aluminum die-cast product, which is not more than the thickness of a part to be cut off from a gate portion of the product, and which has been subjected to nitriding on the surface of a member constituting the gate. 2. An iron-made porous member, which does not allow a molten metal of an aluminum-based material to pass through but partially passes through a gas passage and which is in contact with a gas passage opened to the outside, as a mold. The method for producing a thin-walled aluminum-based die-cast product according to claim 1, wherein the product provided as described above is used. 3. The method for producing a thin aluminum die-cast product according to claim 1, wherein the mold is formed by nitriding the surface of a member constituting a cavity.