JP3626046B2 - Molded product and its casting mold - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a casting method in which a molten metal in a solid-liquid coexistence state is injected into a molding die to mainly mold an exterior part (housing) of a large home appliance.
[0002]
[Prior art]
Compared to injection molding using metal in the liquid state, injection molding performed using solid-liquid coexisting metal results in laminar flow with less turbulence, less temperature difference until solidification, and shrinkage. Due to the small amount, there is a feature that a molded product with good dimensional accuracy and surface accuracy can be obtained, and in recent years, it is increasingly used.
[0003]
[Problems to be solved by the invention]
The metal in the solid-liquid coexistence state has a lower degree of superheat from the solidus temperature of the metal than the molding using the metal in the liquid state. Therefore, when molding a relatively large product with a relatively long flow path through which the molten metal flows in the mold, the molten metal starts to solidify before the molten metal fills the entire area of the mold cavity. Therefore, there is a tendency that poor filling is likely to occur.
[0004]
In particular, in a mold for producing a thin molded product, the flow path height of the molten metal in the cavity (interval in the thickness direction of the molded product perpendicular to the molten metal flow direction in the cavity) is small. Therefore, the ratio of the flow rate of the molten metal flowing per unit area of the mold with which the molten metal comes into contact is smaller than that in the case of not a thin molded product. Therefore, considering the balance of thermal energy, in such a mold, the thermal energy of the supplied molten metal is easily transmitted and released to the surface of the mold, so that the molten metal is easily solidified in a relatively short time. It has become.
[0005]
Therefore, in the past, when molding using a molten metal in the coexisting state of solid and liquid, the flow rate of the molten metal contacted per unit area is increased by increasing the thickness of the molded product and thus increasing the flow path height of the cavity. To make the molten metal difficult to cool and delay solidification.
[0006]
For the above reasons, when trying to mold a relatively large molded product using a molten metal in the coexisting state of solid and liquid, it is necessary to set the product thickness relatively large. There was a limit to reducing the thickness of the molded product. The limit was about 300 when expressed by the ratio (L / t) between the maximum flow path length (L) through which the molten metal flows in the mold and the average wall thickness (t) of the molded product wall.
[0007]
Moreover, when the shape of the molded product made of a metal material is a box shape, it is difficult to integrally form all the shapes including the portion corresponding to the box bottom.
In the case of resin molding, in order to integrally mold a portion corresponding to the bottom of the box, a molding method is adopted in which one pouring gate is provided near the center of the bottom surface of the box, and the molten metal is poured radially therefrom.
[0008]
On the other hand, in the case of metal forming with a solidification time of several tens of milliseconds or less, when trying to fill by filling a flow that radiates from a single spout, the flow rate of the molten metal advances further to the end of the hot water flow passage. Since the speed decreases, the flow distance within the unit time gradually decreases as the distance from the pouring gate increases, and the molten metal solidifies before filling the end of the cavity, which may cause a filling failure.
[0009]
Therefore, when a box-shaped molded product is made using a metal in a solid-liquid coexistence state, the ratio (L / t) between the maximum flow path length (L) and the wall thickness (t) is further reduced, about 200 It was a limit.
[0010]
An object of the present invention is to solve the above-described problems and obtain a box-shaped thin large molded product by integral molding.
[0011]
[Means for Solving the Problems]
In one aspect, the present invention is a mold for casting in which a molten metal is poured from a single gate, and the length of the molten metal flowing through the mold is substantially equal in each direction. It provided in the central portion, and has a runner extending branches from the sprue dendritic provides casting mold and forming a cavity between the Aitonaru runner .
[0012]
In the present invention another aspect, a molded article formed by using a casting mold of the above, corresponds to a runner which is thicker than the portion corresponding mold odor Te in key Yabiti portion The portion is formed in a form that protrudes from the inner surface of the molded product.
[0013]
In the present invention, branching into a dendritic shape literally means that a tree is gradually divided into thin branches while branching from a trunk to a thick branch, from a thick branch to a relatively thin branch, and from a trunk portion toward a branch point. It means any form.
[0014]
Therefore, on the core side mold surface, the runner is branched and extended from the gate in a dendritic shape, so that the runner repeats branching toward the tip and gradually becomes a cross-sectional area (a section as a flow path through which the molten metal flows). The area is getting smaller.
In addition, in this invention, a core side metal mold | die means the metal mold | die which has the function to shape | mold the inner surface of a molded product.
[0015]
The thin-walled cavity portion (also simply referred to as a cavity portion in the present specification) is a portion that forms most of the housing wall portion of the molded product, and each runway that branches and extends in a dendritic manner. It is provided as a part which connects between adjacent things. The thin-walled cavity portion has a minimum thickness necessary for forming a casing wall portion of the molded product, and thus has a channel cross-sectional area. On the other hand, the runner is a part for preferentially flowing the molten metal over the thin-walled cavity portion, and therefore, by providing a relatively large flow passage height, the flow passage cross-sectional area is relatively larger than that of the thin-walled cavity portion. have.
[0016]
The molded product is formed in the mold as a shape corresponding to a shape in which the thin cavity portion and the runner portion are combined.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a perspective view showing a mold for integrally molding a thin large-sized molded product in one embodiment of the present invention. 11 is a sprue, 12 is a runner formed by branching from the sprue 11 as a part of the product part of the core side mold, and 13 is a cavity part that is originally set to a plate thickness that is a product part. .
[0019]
The branching of the runner 12 will be described. First, in FIG. 1, the first runner 12 a extends from the gate 11 in four directions, that is, the right front direction, the right rear direction, the left front direction, and the left rear direction. Taking the runner 12a extending in the right-hand back direction as an example, the second runner 12b branches from the first runner 12a at a portion slightly advanced in the distal direction along the first runner 12a. A third runner 12c branches off at a portion further advanced to the distal end side of the first runner 12a. Thus, the runner 12 branches in a dendritic shape on the surface of the core side mold from the gate to the tip, and the flow passage cross-sectional area of the branched portion becomes gradually smaller.
[0020]
The runners branched into dendrites are formed so as to have a length over almost the entire length of the flow path through which the melt flows in the direction of the flow of the melt in the cavity forming the molded product. Therefore, the flow path length at which the molten metal should flow in the thin cavity portion 13 formed between adjacent runners is relatively short on average even when viewed as a whole mold.
[0021]
Thus, the mold has a runner that branches into a dendritic shape having a channel cross-sectional area larger than that of the thin-walled cavity, so that the molten metal injected into the mold has a large channel cross-sectional area at the beginning. The runner flows with a low flow resistance preferentially toward the tip, and after the filling of the runner is almost completed, it flows into the thin cavity where the flow resistance is greater than that of the runner. Since the flow path length of the molten metal in the thin-walled cavity portion is relatively small, in the casting using the mold of the present invention, the molten metal filling time required as a whole can be made relatively short.
[0022]
The gate 11 is provided at the center of the flow channel, which is the central portion of the entire flow channel in the sense that the flow lengths of the molten metal flowing in each direction in the mold are substantially equal. This is because the molten metal injected into the gate flows toward the tip of the runner and the cavity portion by applying a propulsive force such as injection pressure, but the length of the flow path through which the molten metal flows depends on the flowing direction of the molten metal. If it is different, there will be a difference in the time for filling the runner and cavity part between the long part and the short part of the channel length, and even if the part with the short channel length can be filled sufficiently In the case where the flow path length is long, there is a possibility that the molten metal starts to solidify due to a decrease in the temperature of the molten metal before the end of the runner and the cavity is sufficiently filled, resulting in poor filling. Therefore, it is intended to reduce the difference between the lengths of the flow paths as much as possible.
[0023]
Since it is virtually impossible for the flow path length of the molten metal injected into the gate to be completely the same for the flow paths in all directions of the mold, for example, for the mold shown in FIG. A main runner 12 extends from the gate 11 in the right front direction, right right back direction, left side front direction, and left side back direction, so that the flow path length of the molten metal in each direction is substantially equal. Is provided.
[0024]
The fact that the melt channel lengths are substantially equal preferably means that when filling the melt under normal conditions, the runner having the longest channel length and the runner having the shortest channel length. It means that there is almost no difference in flow path length. If there is almost no difference in channel length, the runner having the longest channel length is compared with the runner having the shortest channel length, and the difference in channel length is the longest flow. It is preferably 10% or less, particularly 5% or less, of the length of the runway having a path length. Alternatively, the fact that there is almost no difference in the channel length is represented by the filling time, and the difference in filling time between the runner having the longest channel length and the runner having the shortest channel length is 10 mm. Or less, especially 5 milliseconds or less, or hot water having the longest flow path difference in filling time between the runner having the longest flow path length and the runner having the shortest flow path length. It can also be expressed that 10% or less, particularly 5% or less of the filling time on the road is preferable.
[0025]
Therefore, if the molded product has a box shape as shown in the figure, of course, even if it does not have such a box shape, on the basis of the above, A gate can be provided in the center of the flow path where the flow path length of the molten metal flowing in the mold is substantially equal in each direction. Therefore, uneven filling can be prevented.
[0026]
However, in the case where the molded product has a box shape having a bottom portion and four surrounding surfaces, one point is provided at the center of the portion corresponding to the bottom portion of the molded product in the casting mold. It is possible to more easily carry out the pouring gate at the center of the flow path. Therefore, the uneven filling can be prevented more easily.
[0027]
In one preferred embodiment, with respect to the cross-sectional area of the runner in the direction perpendicular to the hot water flow direction, the cross-sectional area of the runner immediately before branching and the sum of the cross-sectional areas of the runners immediately after branching are substantially equal. It can be set to be equal.
[0028]
Here, “substantially equal” means that the cross-sectional area of the flow path of the molten metal flowing in the mold does not change substantially before and after the branching portion. “Almost no change” means that some variation may be allowed due to the necessity of draft angle or rounding of the twill when producing the mold, but for example, the cross-sectional area is ± 10% or more, preferably Means that it does not change more than ± 5%, especially more than ± 2.5%.
[0029]
In this way, by designing the mold so that the cross-sectional area of the flow path of the molten metal flowing in the mold does not change greatly at the branching portion, the flow area of the molten metal can be smoothly changed by greatly changing the cross-sectional area of the flow path. Damage can be prevented. For example, when the cross-sectional area of the flow path suddenly decreases, the flow rate of the molten metal decreases, pressure is generated inside the molten metal injected into the runner, and the section where the cross-sectional area of the flow path becomes smaller Since a larger pressure is required to flow into the molten metal, it becomes difficult for the molten metal to flow from that part to the end, and when the cross-sectional area of the flow path suddenly increases, the molten metal becomes easier to flow, but becomes larger. In order to sufficiently fill the flow path of the cross-sectional area, the flow rate of the molten metal is insufficient, which may cause poor filling.
[0030]
Therefore, as for the cross-sectional area of the runner, when one runner branches into a plurality of runners, the cross-sectional area of one runner just before branching and the plurality of runners branched from the runner The total sum of the cross-sectional areas of the runners immediately after branching is set to be substantially equal. For example, in the example shown in FIG. 1, one runner 12a branches and branches into two runners 12b and 12c, and the cross-sectional area of the runner 12a immediately before branching is two immediately after branching. The runners 12b and 12c are set to be substantially equal to the sum of the cross-sectional areas.
[0031]
This relationship is similarly applied to the case where the runner 12c further branches on the leading end side of the runner and also to each runway extending in the other direction.
Therefore, the smooth flow of the molten metal in a metal mold | die can be ensured by setting so that the cross-sectional area of a runner may become substantially equal before and after branching.
[0032]
Moreover, in another preferable aspect, the shape in a cross section perpendicular | vertical to the hot water flow direction of a runner can be made into a rectangle thru | or a trapezoid shape. Here, the rectangular shape is a shape generally called a rectangle, and includes a square.
[0033]
The molten metal flowing in the runway is in contact with the surface of the mold facing the runway, so that a part of the thermal energy of the molten metal itself is transmitted to the mold. Go inside.
[0034]
Accordingly, in the runner having a rectangular cross section, the heat radiation area of the melt can be made relatively small with respect to the amount of heat of the melt flowing in, so that the melt can reach the end of the runner before the melt reaches. The heat energy lost can be relatively reduced, and the molten metal can be maintained at a relatively high temperature. That is, the molten metal can be filled while keeping the temperature drop as small as possible.
[0035]
FIG. 2 is a perspective view showing a box-shaped and thin large-sized molded product cast by the mold of the present invention. This molded product has an inner surface molded by the mold shown in FIG. 1, and in the relationship with FIG. 1, after being cast by the mold shown in FIG. It shows the state that it was overturned so that the inside could be seen. 1 is a portion formed corresponding to the gate, 2 is a portion formed corresponding to each runner, and 3 is a portion formed corresponding to the thin cavity portion 13 of the mold.
[0036]
When the molded product is a box-shaped molded product having a bottom portion and four surrounding surfaces, a portion 2 formed corresponding to each runner 12 and a portion 3 formed corresponding to the thin-walled cavity portion 13 include Forming the casing of the molded product.
[0037]
In the molded product shown in FIG. 2, the portion 2 formed corresponding to the runner 12 is relatively thicker than the portion 3 formed corresponding to the thin cavity portion, and the outer surface of the molded product It is formed so that it does not appear on the inner surface but appears on the inner surface. Therefore, the portion 2 formed corresponding to the runner 12 is formed so as to protrude on the inner surface of the molded product.
[0038]
In designing a mold having a runner that branches into a dendritic shape according to the present invention, the portion 2 formed corresponding to the runner 12 is formed so as to rise on the inner surface of the molded product. Thus, it is possible to prevent an increase in design restrictions that may occur if a raised portion appears on the outer surface of the molded product.
[0039]
Further, by forming the raised portion 2 formed corresponding to the runner 12 so as to rise on the inner surface of the molded product, it acts as a reinforcing rib that partially improves the structural strength in the molded product. You can also. In addition, when it is not necessary to leave all the raised parts 2 formed corresponding to the runner 12, it can be removed by processing after casting.
[0040]
FIG. 3 is a schematic view showing a state in which the molten metal is filled into the runner and the thin cavity in the mold when casting is performed using the mold of the present invention as described above.
[0041]
The thin cavity portion 13 has a relatively high flow resistance because the flow path height of the molten metal is smaller than that of the runner 12. Therefore, the molten metal flowing in from the gate 11 flows into the runner 12 having a relatively small flow resistance rather than flowing into the thin cavity 13 having a relatively large flow resistance (FIG. 3A). If the pouring of the molten metal from the gate 11 is further continued, the molten metal flows preferentially in the runner that flows more easily than the thin-walled cavity, reaches the tip of the runway, and the molten metal is not poured into the thin-walled cavity. It has not yet flowed in much (Fig. 3 (b)). When the pouring of the molten metal from the gate 11 is further continued, the molten metal flows from the runner into the portion of the thin-walled cavity portion that remains as a portion that easily flows at that time (FIG. 3C).
[0042]
The runner 12 branches and extends in a dendritic shape over the entire molded product, and the gap between adjacent runners is left as a thin-walled cavity portion 13. The flow path length through which the gas should flow is relatively short. Therefore, the molten metal fills the thin cavity portion with a relatively short flow path length after first filling the runner having a relatively large channel cross-sectional area, so that the molten metal can be injected into the mold in a relatively short time. Can be done.
[0043]
When using the mold according to the present invention as described above, it is necessary to reduce the temperature drop in a relatively short time, and when casting is performed using a magnesium-based alloy in a solid-liquid coexisting state. , Can be suitably cast.
[0044]
When casting using the mold of the present invention, the molten metal poured into the gate 11 mainly flows through the runner 12 portion where the flow resistance is relatively small, and the molten metal fills up to the tip portion of the runner 12. After that, a hot water flow pattern is formed in which it flows into the thin-walled cavity portion 13 having a relatively higher flow resistance than the runner 12.
[0045]
By forming such a molten metal flow pattern, the molten metal first flows through the runner portion having a low flow resistance inside the mold, and the temperature drop at that time is kept relatively small, and in a relatively short time. The runner is then filled, and then the flow into the thin cavity with relatively large flow resistance but short flow path length can fill the cavity inside the mold in a relatively short time as a whole. it can.
[0046]
Therefore, when casting a larger molded product, the flow path length of the molten metal inside the mold is longer, but the mold has the configuration of the present invention, so that casting with good filling is performed. Can do.
[0047]
In addition, when casting a molded product having a larger wall and a thinner wall, the flow path height of the molten metal in the thin cavity portion is set to be low. Even if it is a case, casting by favorable filling can be performed because a metal mold | die has the structure of this invention.
[0048]
【Example】
One embodiment of the present invention will be described below. The casting conditions are as follows.
Molded article: 28-inch TV cabinet molded article size: about 700 mm x about 470 mm x about 160 mm
Average wall thickness: 1.4mm
Alloy material: Magnesium alloy (AZ91D)
Mold material: SKD61
[0049]
Such a large and thin TV cabinet could be cast with good filling. The ratio (L / t) between the maximum flow path length (L) and the wall thickness (t) in this thin and large TV cabinet was 400 or more.
In addition, since the exterior parts (housing) were conventionally formed as separate parts, the assembly of the exterior parts was necessary after molding, but the parts were formed by integrally molding the box-shaped molded product including the box bottom. The number of points can be reduced, and therefore the number of work steps can be reduced.
[0050]
【The invention's effect】
According to the present invention, in the mold, a single sprue is provided at the center of the flow path, the runner branching into a dendritic shape having a flow path cross-sectional area larger than the thin cavity portion is provided, and between adjacent runways By providing the thin-walled cavity portion, the entire molten metal can be filled in a relatively short time.
[0051]
Further, according to the present invention, when the molded product has a box-like shape having a bottom and four surrounding surfaces, a single gate is provided at the center of the portion corresponding to the bottom of the molded product. Providing a point gate at the center of the flow path can be achieved more easily.
[0052]
Further, in the present invention, the cross-sectional area perpendicular to the flow direction of the runner branching into a dendritic shape is set so that the cross-sectional area of the runner does not substantially change before and after branching, so that the smooth flow of the melt Can be secured.
[0053]
Furthermore, in the present invention, by making the cross section perpendicular to the hot water flow direction of the runner into a rectangular shape, the temperature drop of the molten metal can be minimized and filling failure of the molten metal can be prevented.
[0054]
In the molded product cast using the mold according to the present invention, the portion corresponding to the runner that is thicker than the portion corresponding to the thin cavity portion of the mold is raised on the inner surface of the molded product. Therefore, the molded product can be cast using the mold having the runner and the gate having the above-described configuration without affecting the design of the appearance of the molded product.
[0055]
In addition, since the metal mold | die of this invention can achieve the longest flow distance L to wall thickness t ratio exceeding 300 times, it is comparatively thin and large-sized using the magnesium-type alloy of a solid-liquid coexistence state. It can be suitably used for casting an article.
[Brief description of the drawings]
FIG. 1 is a perspective view showing one example of a core side mold in a mold according to the present invention.
FIG. 2 is a perspective view showing a thin-walled large molded article in one example cast by the mold of the present invention.
FIG. 3 is a diagram schematically showing how the filling of the molten metal progresses with time in the mold of the present invention.
[Explanation of symbols]
1 ... a part molded by a gate, 2 ... a part molded by a runner,
3 ... the part that will be the exterior wall of the product, 11 ... the gate,
12 ... Yudo, 13 ... Cavity.

Claims (7)

A casting mold for pouring a molten metal from a single gate, the gate is provided at the center of the flow path where the flow path length of the molten metal flowing in the mold is substantially equal in each direction, and extend branched dendritic from the sprue, toward the distal end, has a runner cross-sectional area that a reduced gradually by repeating branching,
Regarding the cross-sectional area perpendicular to the hot water flow direction of the runner that branches in a dendritic manner, the cross-sectional area of the runner immediately before branching is substantially equal to the sum of the cross-sectional areas of each runner immediately after branching. A casting mold characterized in that it is set and a cavity is formed between adjacent runners. A casting mold for molding a box-shaped molded product having a bottom portion and four surrounding surfaces, wherein one gate is provided at a central portion of a portion corresponding to the bottom portion of the molded product. The casting mold according to claim 1. A method for forming a metal using the casting mold according to claim 1. The method according to claim 3, wherein the metal is a magnesium-based alloy in a solid-liquid coexistence state. A molded product formed by molding a metal according to claim 1 or 2 using a metal . A claim 1 or molded article formed by using a two casting mold according, the portion corresponding to the runner to be thicker than the portion corresponding to the cavity portion in the molded article, the inner surface of the molded article A molded product characterized in that it is formed in a form that rises. The molded article according to claim 5 or 6, wherein the molded article is formed using a magnesium-based alloy in a solid-liquid coexistence state.

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