JP3598238B2 - Casting mold, casting method and molded product thereof - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a casting mold for molding a metal material.
[0002]
[Prior art]
When performing casting, a mold as shown in FIG. 2 is generally used. In FIG. 2, the mold is mainly constituted by a fixed mold part 4 and a movable mold part 5, and a cavity 3 is provided between the two molds 4. Reference numeral 1 denotes a gate to the mold, 6 denotes a runner, and 2 denotes a gate to the cavity 3.
[0003]
In the case of molding using this mold, when a molten metal in which a molding material is brought into a molten state is poured from a molding machine into the gate 1, the molten metal flows into the cavity 3 through the runner 6 and the gate 2. The molten metal is cooled in the cavity, solidifies while maintaining a shape corresponding to a predetermined three-dimensional shape provided in the cavity, and a mold having a desired shape is obtained by opening a mold.
[0004]
When the molding material is, for example, a metal-based material, the molten metal is generally maintained at a temperature of 500 ° C. or higher in a molding machine in order to maintain a molten state. On the other hand, since the temperature of the mold is set to 300 ° C. or less, when the molten metal is injected into the cavity, heat radiation to the mold is started, and the temperature of the molten metal itself drops.
[0005]
Further, when the molten metal is, for example, a magnesium alloy, the solid fraction increases as the temperature decreases, but if the cavity is not filled within a relatively short time during which the molten metal is solidified, poor filling occurs. .
The inventors have already completed the invention of delaying the solidification time of the molten metal by providing a layer of a material having low thermal conductivity on the inner surface of the mold, and have filed a patent application for the invention (see, for example, No. 11-77240).
[0006]
[Problems to be solved by the invention]
A casting mold part base material is generally formed of an iron-based material, and its thermal expansion coefficient is generally about 10 to 12 μm / m / ° C. On the other hand, as the surface layer material having a low thermal conductivity that forms a layer facing the inner surface of the mold, a material such as ceramics is often used, and its thermal expansion coefficient is about 5 μm / m / ° C. or less. For example, in such a mold having a layer of a material having a low thermal conductivity on the inner surface of the mold, when a temperature change of about 200 ° C. occurs, the difference in the amount of thermal expansion between the mold part base material and the surface layer material is increased. Is 0.1 mm per 10 cm of mold. 1 mm.
[0007]
In addition, when injection molding is repeatedly performed using such a mold, the temperature of the mold surface rises approximately 200 to 250 ° C. almost instantaneously when the molten metal flows into the mold, and within a few seconds thereafter. Upon cooling, the mold surface and the temperature of the melt fall to the initial mold temperature. Thus, the casting mold is subjected to heat shock with such rapid heating and cooling, and if the mold is used for mass production, this process is repeated as many cycles.
[0008]
Accordingly, at the interface between the mold part base material and the surface material layer, which are two materials having different coefficients of thermal expansion, the amounts of thermal expansion of the two due to such a heat shock cycle are different. Peeling may occur, and as a result, the life of the mold may be shortened.
[0009]
For example, under severe conditions in which the temperature changes in a short time and / or the injection pressure (injection pressure in the case of injection molding) is large, such as when molding is performed using a molten alloy, one to several times Peeling and cracks are generated by shots, and there is a problem in industrial production for mass production that it is not sufficiently practical.
[0010]
Therefore, as a means for solving such a problem, in addition to providing a layer of a material having a low thermal conductivity on the inner surface of the mold, the coefficient of thermal expansion of the material of such a layer is reduced by the mold parts. It is conceivable to select a material that does not cause a very large difference with the coefficient of thermal expansion of the base material.
However, such a material is also required to have a strength and hardness equivalent to or close to that of a conventional mold part base material. Accordingly, providing a layer on the inner surface of a mold with the above considerations of thermal conductivity and thermal expansion coefficient increases the material cost as compared with a conventional mold part base material.
[0011]
An object of the present invention is to solve such a problem, to improve the filling property of a cast product, and to provide a mold having a service life sufficient for practical use.
Another object of the present invention is to provide such a mold with as little cost increase as possible when compared to a conventional mold.
[0012]
[Means for Solving the Problems]
Since the heat cycle given to the mold as described above cannot be avoided in the molding process, in the present invention, the configuration of the mold having great durability against temperature changes including such a heat cycle is described. The object is achieved by using such a mold and minimizing the volume or the area of such a portion at the same time as possible.
[0013]
Therefore, according to the present invention, when a plurality of mold parts are combined, a cavity is formed inside the mold, and the surface of at least one of the plurality of mold parts facing the cavity has a thickness of 1 μm to 30 μm. A casting material in which an adjacent layer is provided between the mold parts and the surface material layer, wherein the material forming the surface material layer forms the adjacent layer. The material forming the adjacent layer has a smaller coefficient of thermal expansion than the material of the mold part, and the material forming the adjacent layer has a smaller coefficient of thermal expansion than the mold part base material. In one aspect, a casting mold is characterized in that the material forming the surface material layer has the lowest thermal conductivity.
[0014]
Another aspect of the present invention is a method of manufacturing a molded product by using the above-described casting mold for molding at least one type of metal material.
[0015]
Further, another aspect of the present invention is a molded article molded using the above-described casting mold, wherein the molded article has a better appearance on the outer surface as compared to the inner surface of the molded article.
Furthermore, the present invention provides another molded article formed by the method for producing a molded article using the casting mold described above , wherein the molded article has a better appearance on the outer surface as compared to the inner surface of the molded article. .
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 shows an example of one embodiment of the present invention.
In FIG. 1, a heat insulating block layer 7 is provided at a position facing the cavity 3 of the fixed mold part 4. In this embodiment, the heat insulating block layer 7 is composed of the surface layer 8 on the side facing the cavity 3 and the mold part adjacent layer 9 on the side in contact with the mold part (hereinafter, also simply referred to as an adjacent layer) 9 . Although two layers are laminated, one or more intermediate layers may be interposed between the two layers. Therefore, the heat insulation block layer 7 is formed by laminating at least two types of layers.
[0017]
The material forming the surface material layer 8 has the lowest thermal conductivity among the materials forming each of the layers forming the heat insulating block layer 7 and the mold parts 4 and 5.
As the surface material, a ceramic material, for example, alumina, silicon nitride, zirconia glass, silica, titanium carbide, cordierite, or the like can be used. The thermal conductivity of these ceramic materials is in the range of 3-20 w / m / ° C.
[0018]
The surface material layer 8 formed of a material having a small thermal conductivity exists between the melt flowing into the cavity 3 and the mold part base material, and the melt and the mold part base material are directly connected to each other. It has a function of delaying the solidification time of the molten metal by preventing contact and suppressing the transfer of heat from the molten metal to the mold base material.
[0019]
Therefore, by delaying the solidification time of the molten metal, it is possible to effectively prevent occurrence of molding defects such as hot lines and cavities in the molded product.
In order to achieve such a function, the surface material layer 7 may be formed to have a thickness in the range of 1 μm to 30 μm, and more preferably in the range of 1 μm to 10 μm.
[0020]
As a means for providing a surface material layer on the surface of a mold base generally made of a metal material, various means known as means for laminating a ceramic material layer on a metal material can be employed. However, when the thickness of the surface material layer is relatively thin, about 1 μm to 10 μm, the surface material layer can be formed by thermal spraying or composite electroless plating. According to these means, even when the cavity has complicated irregularities, the inner surface of the mold can be coated with a substantially uniform thickness. Therefore, the function of suppressing heat conduction by the surface material layer can be achieved almost uniformly over the entire surface material layer.
[0021]
The mold part adjacent layer 9 is present between the surface material layer 8 and the mold part (the fixed mold part 4 in the embodiment shown in FIG. 1), and preferably has a thermal expansion coefficient between the two. By having a value, it has a function of reducing a gap of an expansion coefficient between layers or parts adjacent to each other. In order to further improve the adhesion strength between the mold part adjacent layer 9 and the surface material layer 8, the coefficient of thermal expansion between the mold part adjacent layer 9 and the surface material layer 8 should be the same or approximate. Each material can also be selected.
[0022]
This function is that when two layers having a large difference in coefficient of thermal expansion are laminated, one layer is peeled or cracked when exposed to a heat shock whose temperature changes greatly in a short time. The difference in the coefficient of thermal expansion between two adjacent layers can be reduced by providing a layer having a coefficient of thermal expansion in a range between the two layers, which is liable to cause a stacking fault. However, it is intended to prevent the occurrence of lamination defects such as layer separation and cracking.
[0023]
Therefore, the material forming the mold part base material, the mold part adjacent layer 9 and the surface material layer 8 is preferably made of a suitable material in consideration of the requirements of the thermal conductivity and the coefficient of thermal expansion as described above. You need to select a combination.
[0024]
As a preferred example, the mold part adjacent layer 9 can be formed of a nickel alloy or a titanium alloy capable of maintaining a thermal expansion coefficient of 10 μm / m / ° C. up to a high temperature range of about 250 ° C. Examples of such nickel alloys include Invar HRA929C (manufactured by Hitachi Metals, Ltd.) and low thermal expansion cast iron LEX40 (manufactured by Nippon Casting Co., Ltd.). Examples of titanium alloys include Ti-6Al-4V, Ti- 7Al-4Mo.
[0025]
For example, ZrO ₂ · SiO ₂ (thermal expansion coefficient: about 5 μm / m / ° C., thermal conductivity: 3 w / m / ° C.) as a ceramic material is used as the surface material layer 8, and a titanium alloy is used as the mold part adjacent layer 9. Ti-6Al-4V (coefficient of thermal expansion: about 9 μm / m / ° C., thermal conductivity: about 7 w / m / ° C.), and SKD61 of hot die steel (coefficient of thermal expansion: about When using 12 μm / m / ° C. and thermal conductivity: 35 w / m / ° C.), the difference in the coefficient of thermal expansion between the surface material layer 8 and the mold part adjacent layer 9 is about 4 μm / m / ° C. The difference in the coefficient of thermal expansion between the part adjacent layer 9 and the mold part is about 3 μm / m / ° C.
[0026]
On the other hand, when the case where the surface material layer 8 is directly laminated on the mold part without the presence of the mold part adjacent layer 9 is considered, the difference in the coefficient of thermal expansion between the two is about 7 μm / m / ° C. Therefore, in the mold of the present invention, the coefficient of thermal expansion between two adjacent layers, that is, between the surface material layer 8 and the mold part adjacent layer 9 and between the mold part adjacent layer 9 and the mold part is reduced. The difference can be made smaller than in the case where the mold part adjacent layer 9 is not present.
[0027]
Therefore, for each layer constituting the heat insulating block layer, even between the heat insulating block layer and the mold part base material, by selecting each material such that the difference in thermal expansion coefficient is relatively small in this way, Even when exposed to severe heat shock, the difference in the amount of expansion between the mold parts and the heat insulating block layer 7 and each layer in the heat insulating block layer 7 can be suppressed to a small value. Cracks and the like can be prevented from occurring.
[0028]
In the mold of the present invention having such a configuration, even when subjected to a severe heat shock cycle, it is possible to suppress the occurrence of peeling and cracks in the surface material layer, so that a longer life is provided. Can be secured.
[0029]
In the mold of the present invention having the above-described configuration, when the molten metal is injected into the cavity, the cooling and solidification of the molten metal in the mold are delayed, so that the molten metal is solidified before the injection of the molten metal is completed. Starting can be prevented. Therefore, the molten metal can be sufficiently filled up to the tip portion of the cavity in a state where the molten state is sufficiently maintained, and the occurrence of a defective filling can be prevented.
[0030]
Further, in a mold for molding a thin molded product, the interval between cavities (the interval corresponding to the thickness of the molded product) is set small. As the space between the cavities becomes smaller, the ratio of the amount of molten metal flowing per unit area of the mold becomes smaller. Therefore, a mold having a relatively small space between the cavities tends to cool the molten metal more easily in a short time than a mold having a relatively large space between the cavities, and tends to cause poor filling.
[0031]
However, according to the mold of the present invention, the cooling and solidification of the molten metal in the mold are caused by the presence of the surface material layer having a relatively small thermal conductivity between the molten metal and the mold base material. Since the mold can be delayed, even when the mold of the present invention is used as a mold for a thin molded product having cavities at relatively small intervals, it is possible to satisfactorily prevent the occurrence of defective filling. it can.
[0032]
The heat insulating block layer 7 may be formed at a position facing the cavity 3 of both the fixed mold part 4 and the movable mold part 5 and provided so as to cover the whole cavity 3. A molded article having a good appearance on both the outer surface side and the inner surface side is obtained.
[0033]
However, as a material for forming the heat insulating block layer 7, a material having a higher cost than a conventional mold part base material such as a titanium alloy or a nickel alloy is used, so that the cost is lower than that of a conventional mold. Get higher. In the present invention, which aims at minimizing such an increase in cost, the region where the heat insulating block layer 7 is provided, that is, the volume or area of the heat insulating block layer 7 can be suppressed to the minimum range.
[0034]
Therefore, in the mold of the present invention, the heat insulating block layer 7 can be provided on either the fixed mold part 4 or the movable mold part 5. In that case, the heat insulating block layer 7 can be provided on the mold part that forms the outer surface side of the molded product. Then, the manufactured molded article can be formed so as not to have hot lines, nests, and the like on the outer surface, and can have higher commercial value. Also, it is not necessary to secure such high molding accuracy on the inner surface of the molded product that is usually hardly noticeable. For example, as shown in FIG. An embodiment in which the heat insulating block layer 7 is not provided on the mold part corresponding to the inner surface of the product can be adopted.
[0035]
Further, although it depends on the design of the molded product to be manufactured, the mold to which the present invention can be applied is such that the mold part is composed of two parts: a fixed mold part 4 and a movable mold part 5. The fixed mold part and / or the movable mold part are separated into two or more parts, which are not limited to the case where the mold is used, and are not particularly illustrated. It can be applied to what is formed.
[0036]
【The invention's effect】
According to the present invention, solidification of the molten metal can be delayed by the presence of the heat insulating block layer having the surface material layer, and the molten metal can be circulated in the cavity in a sufficiently molten state. Even if the cross-sectional area of the cavity in the flowing direction is small, the molten metal can sufficiently spread to the tip of the cavity where the heat insulating block layer exists. Therefore, in the cavity where the heat insulating block layer exists, the distance in which the molten metal can be filled in the mold can be increased, so that a thinner molded product can be obtained. Therefore, it can be suitably used for thixomolding of a magnesium alloy or the like.
[0037]
In this way, by delaying the solidification of the molten metal in the cavity, it is possible to cause the solidification to occur uniformly over the entire molding material. Therefore, in the molded product, the mold part on the side provided with the heat insulating block layer The occurrence of molding defects such as hot lines and nests in portions corresponding to the above can be reduced.
[0038]
Further, since the mold of the present invention has a relatively small difference in coefficient of thermal expansion between each layer of the heat insulation block layer and between the heat insulation block layer and the mold base material part, the mold receives severe heat shock. Even when used under conditions, it is possible to prevent the occurrence of cracks in the heat insulating block layer and prolong the life as a mold.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating one embodiment of the present invention.
FIG. 2 is a sectional view of a conventional casting mold.
FIG. 3 is a perspective view of a molded product molded by the mold of the present invention.
[Explanation of symbols]
1, 2 ... gate, 3 ... cavity,
4: fixed mold parts, 5: movable mold parts,
6 ... runner, 7 ... heat insulation block layer,
8: Surface material layer, 9: Layer adjacent to mold parts,
11 ... hot water.

Claims (4)

When the set look combining a plurality of molds parts, key Yabiti is formed inside the mold, the surface layer material of 1μm~30μm a surface of at least one mold part facing the cavity of the plurality of mold parts A casting mold having a layer, and an adjacent layer provided between the mold part and the surface material layer, wherein the material forming the surface material layer is higher than the material forming the adjacent layer. The material forming the adjacent layer has a small coefficient of thermal expansion, and the material forming the adjacent layer has a smaller coefficient of thermal expansion than the mold part base material, and among the surface layer material layer, the adjacent layer and the mold part base material , casting mold, wherein the material forming the surface layer material layer is the smallest thermal conductivity. A method for producing a molded article by using the casting mold according to claim 1 for molding at least one kind of metal material. 3. The method according to claim 2, wherein the metallic material is selected from the group consisting of a magnesium alloy, an aluminum alloy and a zinc alloy. A method for producing a molded product using the casting mold according to claim 1 for thixomolding using a magnesium alloy as a material.

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