JPH057987A - Method for manufacturing plastic molding die - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent the occurrence of casting defects such as pinholes and shrinkage cavities, and to manufacture plastic molding dies in a short delivery time. [Composition] Aluminum 8 to 20% by weight, copper 5
After blowing a noble gas having a purity of 99.99% by volume or more into a molten zinc-based alloy containing ˜15% and 0.01-0.5% magnesium, the shape of the mold is close to that of the final mold. A method for producing a plastic molding die, which comprises casting and finishing the cast into a final shape in a post-processing step.

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 plastic molding die which has few casting defects such as pinholes and shrinkage cavities and is excellent in mechanical properties such as strength and hardness.

[0002]

2. Description of the Related Art As a material for conventional plastic molding dies, particularly injection molding dies, S55C-based carbon steel for machine structure has been widely used. This carbon steel for machine structure is not only good in strength, weldability, graining workability, polishing workability, etc., but also excellent in machinability and is relatively inexpensive among die materials. This is because it has the characteristic of being present. On the other hand, pre-hardened steel or the like has been used especially in a mold that requires mirror finishing.

In recent years, housings and components of various equipment such as office equipment, automobile components and the like have been plasticized, and frequent model changes have been made due to improvements in performance and changes in design. . Along with this, the life cycle of molded products has become shorter, resulting in high-mix low-volume production. Therefore, with respect to a mold for molding such a plastic molded product, there is an increasing demand for cost reduction and quick delivery.

By the way, when a die is manufactured using a steel material produced by forging such as carbon steel for machine structure, the machining process occupies a great number of man-hours, and this machining cost is the cost of die manufacturing. Since it occupies the majority, there was a problem that the price of the mold could not be reduced and the delivery time could not be shortened.

On the other hand, when precision and durability are not required as in the case of a trial mold, first, a wooden mold is manufactured, and then a sand mold is manufactured by using it as a model mold. A method has been used in which a good zinc-based alloy or the like is cast and shaped into a shape in which machining such as cutting is reduced as much as possible, and by performing copying or finish polishing, a die is produced. As the zinc-based alloy, there was, for example, Mitsui Mining & Smelting Co., Ltd., trade name: ZAS.

[0006] According to this method, as compared with a die produced by cutting a block of a material such as carbon steel for machine structure as a mass-produced die, the processing speed is faster and the cost is lower, and the delivery time is longer. It has the advantage of shortening.

However, the above-mentioned zinc-based alloy has mechanical properties such as strength and hardness which are far inferior to those of carbon steel for machine structural use. Therefore, the zinc-based alloy must be designed with a considerable margin,
Moreover, since a mirror surface cannot be obtained, the products and parts that can be used were limited. Furthermore, it is difficult to prevent casting defects such as pinholes and shrinkage cavities, and repairs such as welding are indispensable, but the cooling conditions change significantly near the welded part, causing unevenness in the structure, which is It also had the problem of being transferred to.

Aluminum alloys and copper alloys are also used for the same purpose. However, the former aluminum alloys have poor specularity because of their low hardness, and they are apt to form casting defects and pinholes, resulting in weldability. Since it is remarkably bad, it is extremely difficult to repair a casting defect that has occurred once, or to repair a mold due to a processing error or the like.

Further, the latter copper alloy also has drawbacks such as poor casting surface due to high casting temperature and poor electrical discharge machinability.

[0010]

Among these materials for molds, zinc-based alloys which have a low melting point, are easy to cast, and have excellent weldability have been reviewed. Attempts are being made. For example, Japanese Patent Publication Sho 51-534
As disclosed in JP-A No. 2 and JP-A No. 62-287030, the structure is made finer by increasing the composition ratio of aluminum or copper or adding a specific element, and mechanically The strength has been improved to some extent.

However, in this method, especially when the content of aluminum is increased, the specific gravity of aluminum is light, so that phase separation is likely to occur, and it is difficult to cause directional solidification, and shrinkage cavities are likely to occur. Since the amount of hydrogen gas in the molten metal increases rapidly, pinholes are likely to occur.

Further, Japanese Patent Application Laid-Open No. 2-187308 discloses a method of manufacturing a die by machining a block material made of a zinc-based alloy having improved mechanical properties. According to this method, the processing speed is higher than that of carbon steel for machine structure and the like, which is advantageous for producing a mold for forming a thin-walled molded product, but a thick-walled molded product is molded. When manufacturing a mold for, the number of man-hours for machining increases, and the cost becomes higher compared to the method of shaping the shape close to the final mold shape by casting,
We were not able to sufficiently shorten the delivery period.

On the other hand, in order to prevent casting defects such as pinholes, it is effective to remove hydrogen gas from the molten metal.
Conventionally, a method of introducing chlorine gas or a chlorine compound such as hexachloroethane or a fluorine compound into a molten metal has been used. However, according to this method, since chlorine gas, hydrogen chloride gas, hydrogen fluoride gas, etc. are released, there are problems such as environmental pollution, deterioration of working environment, and corrosion of mechanical equipment. Further, a large amount of capital investment is required to treat chlorine gas, hydrogen chloride gas, and hydrogen fluoride gas, which has led to an increase in cost.

The present invention solves the above-mentioned problems and can prevent casting defects such as pinholes even in a casting having a complicated shape such as a mold, and further improve mechanical strength by an inexpensive casting method. The present invention provides an excellent method for producing a plastic molding die.

[0015]

The method of manufacturing a plastic molding die of the present invention 1 is made of aluminum 8 by weight percentage.
-20%, copper 5-15%, magnesium 0.01-0.
After blowing 99.99% by volume or more of a rare gas into a molten zinc-based alloy containing 5%, it is cast into a mold and cast into a shape close to the final mold shape, and the cast product is subjected to a post-processing step. It is characterized by finishing to a final shape.

In the zinc-based alloy used in the present invention 1, if the aluminum content is too low, sufficient mechanical strength and hardness cannot be obtained, and if it is too high, segregation of the aluminum component occurs during solidification, which causes cavities. Therefore, its content is limited to 8 to 20% by weight.

If the copper content is too low, sufficient mechanical strength and hardness cannot be obtained, and if it is too high, brittleness increases and elongation, impact strength, etc. decrease, so the content is 8 to 1.
Limited to 5% by weight.

If the magnesium content is too low, intergranular corrosion occurs, and if it is too high, brittleness increases and elongation
Since the impact strength and the like decrease, its content is 0.01-
Limited to 0.5% by weight.

In the zinc-based alloy used in the present invention 1, tin, lead, cadmium,
Although iron, silicon, etc. are mixed in, it is preferable to keep the total amount to less than 0.5% by weight. Especially, tin, lead, and cadmium cause intergranular corrosion, so the total amount should be 0.05% or less. It is preferable to suppress

The melting method of the zinc-based alloy is not particularly limited, and any conventionally known melting method can be adopted. For example, a melting furnace such as a gas furnace, a heavy oil furnace, a high-frequency furnace, or the like can be used at 450 ° C. to 500 ° C. It is melted at ℃.

The rare gas used in the present invention 1 is the 0th gas.
It refers to a gas contained in the group, and for example, helium, argon, neon, krypton or the like can be used. When the purity of the rare gas is low, the molten metal is oxidized and the melt is generated, which causes casting defects. Therefore, the purity of the rare gas is limited to 99.99% by volume or more. The rare gas is generated by stopping the heating of the melting furnace. As a method for blowing a rare gas, any conventionally known method can be adopted. For example, a hollow carbon rod having a large number of holes with a diameter of about 0.3 to 3 mm at the tip of the bottom of the molten metal is arranged. A method such as inflowing a noble gas is used. The flow rate of the rare gas varies depending on the amount of alloy melted, but is, for example, 5
3 to 15 liters / in case of melting 00 kg of alloy
It is preferable to flow the gas at a flow rate of min for about 2 to 10 minutes. If the flow rate is too low, the hydrogen gas contained in the melt cannot be sufficiently removed, and if the flow rate is too high, the melt will scatter, which is dangerous and the melt temperature will drop, causing a large amount of crucible or ladle to be poured. A residue will form. Even if the inflow time is too short, the hydrogen gas contained in the melt cannot be sufficiently removed, and if the inflow time is too long, the temperature of the melt will drop, and a large amount of residue will be generated in the crucible and ladle during pouring. The molten metal is cast into a mold, cast into a shape close to the shape of the final mold, and the cast product is
The final shape is finished in the post-processing step.

The mold used in the manufacturing method of the present invention 1 is
Any conventionally known material can be used, for example, green sand mold,
A CO ₂ type, a ceramic type, a gypsum type, a die or the like is used. The above alloy is cast in a mold, cast into a shape close to the shape of the final mold, the casting is cooled, the mold is disassembled, and the final shape is finished in a post-processing step. As a post-processing method, if necessary, after performing milling processing such as NC processing or copying processing, after opening bolt holes and cooling holes, polishing processing is performed.

The method for producing a plastic molding die of the present invention 2 is the same as the zinc-based alloy used in the method for producing a plastic molding die of the present invention 1, but further includes yttrium, beryllium, titanium, zirconium, nickel, It is characterized by adding at least one metal selected from the group consisting of cobalt, manganese, a lanthanum element and silver. Addition of these metals contributes to improvement of mechanical strength, hardness, suppression of casting defects, and delay of dimensional change due to aging, and the content thereof is less than 0.01% by weight. If the content exceeds 2%, not only the effect obtained by adding more than 2% cannot be expected, but also the brittleness increases.
It is limited to 01 to 2%.

Also in the zinc-based alloy used in the present invention 2, as in the case of the present invention 1, inevitable impurities other than the above metals include tin, lead, cadmium, iron, silicon, etc., but the total amount thereof is It is preferable to control the content to less than 0.5% by weight, and particularly tin, lead and cadmium cause intergranular corrosion. Therefore, it is preferable to control the total amount to 0.05% or less.

[0025]

【Example】

Examples 1-15, Comparative Examples 1-17 The details of the present invention will be described with reference to examples.

500 kg of a zinc-based alloy ingot having the composition shown in Tables 1 and 2 was placed in a graphite crucible and heated in a crucible furnace for 3 hours to melt at 470 ° C. After the melting, argon gas having a purity of 99.99% was blown into the molten metal at a rate of 7 l / min for 3 minutes by using a bubbler made of clay carbon. After removing the melt from the melt, a width of 300 mm and a length of 300 m
m with a radius of 100 in the center of a rectangular mold with a depth of 200 mm
mm, and a height of 75 mm was cast in a CO ₂ mold provided with a cylindrical feeder to obtain a block-shaped casting. After casting, the mold was disassembled, the feeder was cut, and the six sides were milled to obtain a smooth block material, which was subjected to the following evaluations. The argon gas was blown into Examples 1 to 15 and Comparative Examples 16 and 17, and the argon gas was not blown into Comparative Examples 1 to 15. The above results are also shown in Tables 1 and 2.

[0027]

[Table 1]

[0028]

[Table 2]

Evaluation of Physical Properties Tensile strength A tensile test piece of JIS H 5301 Reference Figure 1 was prepared from the obtained block and the tensile strength was measured by an autograph. Hardness A hardness test piece of JIS H 5301 Reference Figure 2 was prepared from the obtained block, and the hardness was measured by a Brinell hardness meter. Judgment of casting defect 1 in 100 mm x 100 mm center part of the surface facing the feeder
After paper polishing was sequentially performed from No. 50 to No. 800, the polished surface was observed with a microscope, and the number of microscopic nests of 30 microns or more was visually counted.

[0030]

According to the method for producing a plastic molding die of the present invention, the weight percentage of aluminum is 8 to 20%,
Hydrogen gas in the molten metal is easily removed by blowing a rare gas having a purity of 99.99% by volume or more into a molten zinc-based alloy containing 5 to 15% of copper and 0.01 to 0.5% of magnesium. As a result, it is possible to easily cast a casting without pinholes. Further, due to the stirring effect by blowing a rare gas, even in a zinc-based alloy containing a large amount of aluminum such as the alloy used in the present invention, a casting without shrinkage cavities due to phase separation of aluminum can be easily formed. Not only is casting possible, but the composition of the final casting is excellent in dispersibility, so tensile strength is 40 kg / mm ² or more, Brinell hardness is 15
Since 0 or more materials for a plastic molding die were obtained, a plastic molding die having high wear resistance and excellent durability was obtained.

Furthermore, yttrium, beryllium, titanium, zirconium, nickel, cobalt,
Since 0.01 to 2% of at least one metal selected from the group consisting of manganese, lanthanum-based elements and silver can be easily and effectively dispersed in the molten metal, casting of hard spots, pinholes, etc. These metals can be added without causing defects.

Therefore, the method for producing a plastic molding die of the present invention can be applied to a complicated shape such as a die, and at the time of producing a die, the trouble required for correcting a defective portion can be saved and the cost can be reduced. It is possible to manufacture plastic molding dies with a short delivery time.

Claims (2)

[Claims] 1. Aluminum 8 to 20% by weight,
After blowing a noble gas having a purity of 99.99% by volume or more into a molten zinc-based alloy containing 5 to 15% of copper and 0.01 to 0.5% of magnesium, the shape of the mold was close to that of the final mold. A method for manufacturing a plastic molding die, which comprises casting into a shape and finishing the cast into a final shape in a post-processing step. 2. A zinc-based alloy comprising, by weight percentage, 8 to 20% aluminum, 5 to 15% copper, and 0.01 to magnesium.
0.5%, 0.01 to 2% of at least one metal selected from the group consisting of yttrium, beryllium, titanium, zirconium, nickel, cobalt, manganese, lanthanum-based elements and silver. The method for manufacturing a plastic molding die according to claim 1.