Die casting apparatus

A die casting apparatus according to an aspect of the present disclosure includes a sleeve 30 to which molten metal is supplied, and dies 10 and 20 configured to form a cavity C, in which the molten metal supplied to the sleeve 30 is injected into the cavity C through a runner R linking the sleeve 30 with the cavity C. A plurality of protrusions 22 are provided in the runner R, the plurality of protrusions 22 extending in a direction in which the molten metal flows and being arranged in a comb-teeth arrangement in a width direction of the runner R.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese patent application No. 2018-123579, filed on Jun. 28, 2018, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

The present disclosure relates to a die casting apparatus.

As disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2015-193031, in a die casting apparatus, after molten metal is supplied to a plunger sleeve, a plunger tip is moved forward inside the plunger sleeve, so that the molten metal is injected into a cavity of a die. When the molten metal is supplied to the plunger sleeve, part of the molten metal that has come into contact with the plunger sleeve is cooled and solidified. Therefore, initial solidified pieces are formed on contact surfaces between the molten metal and the plunger sleeve. If these initial solidified pieces come off from the plunger sleeve when the plunger tip is moved forward inside the plunger sleeve, and are injected into the cavity of the die together with the molten metal, they could cause a casting defect.

SUMMARY

The present inventors have diligently studied the above-described matter to reduce casting defects caused by initial solidified pieces in cast articles manufactured by a die casting apparatus, and found the following problem.

The inventors provided columnar protrusions in a runner (i.e., a channel for molten metal) that link a plunger sleeve with a cavity of a die in an attempt to reduce casting defects caused by initial solidified pieces, and have found that these protrusions had a certain level of effect of reducing such casting defects. This is presumably because the initial solidified pieces collide with the protrusions and are pulverized or they are pulverized by turbulence of the flow of the molten metal caused by the protrusions. However, there was a problem that since the protrusions had a columnar shape, they were easily broken as they were repeatedly pressed by the molten metal at a high pressure, and therefore durability of the die was insufficient.

The present disclosure has been made in view of the above-described circumstances and an object thereof is to provide a die casting apparatus which is capable of reducing casting defects caused by initial solidified pieces and whose die has excellent durability.

A first exemplary aspect is a die casting apparatus including:

a sleeve to which molten metal is supplied; and

a die configured to form a cavity, in which

the molten metal supplied to the sleeve is injected into the cavity through a runner linking the sleeve with the cavity, and

a plurality of protrusions are provided in the runner, the plurality of protrusions extending in a direction in which the molten metal flows and being arranged in a comb-teeth arrangement in a width direction of the runner.

In the die casting apparatus according to the present disclosure, the plurality of protrusions are provided in the runner and extend in the direction in which the molten metal flows. Therefore, even when the protrusions are repeatedly pressed by the molten metal at a high pressure, they are less likely to be broken. Therefore, the die has excellent durability. Further, the plurality of protrusions are arranged in the comb-teeth arrangement in the width direction of the runner. Therefore, initial solidified pieces contained in the molten metal are pulverized by the protrusions or turbulence of the flow caused by the protrusions, and hence it is possible to reduce casting defects caused by the initial solidified pieces. That is, the die casting apparatus according to the present disclosure can reduce casting defects caused by initial solidified pieces and its die has excellent durability.

A height of the plurality of protrusions may be equal to a depth of the runner. By the above-described configuration, it is possible to reduce the casting defects caused by the initial solidified pieces even further.

A cross-sectional shape of each of the plurality of protrusions may be a triangular shape in which a width of a base of the protrusion is larger than that of a top thereof. The base of the protrusion is stabilized and as compared to, for example, a protrusion having a rectangular cross section, the protrusion having the triangular shape is less likely to be broken.

The plurality of protrusions may be formed in an insert part engaged with the die. It is possible to, when the protrusion is broken, replace only the insert part in which the protrusion is formed, thus making the die excellent in terms of the maintenance.

According to the present disclosure, it is possible to provide a die casting apparatus which is capable of reducing casting defects caused by initial solidified pieces and whose die has excellent durability.

DESCRIPTION OF EMBODIMENTS

Specific embodiments to which the present disclosure is applied will be described hereinafter in detail with reference to the drawings. However, the present disclosure is not limited to the below-shown embodiments. Further, the following descriptions and drawings are simplified as appropriate for clarifying the explanation.

First Embodiment

<Overall Configuration of Die Casting Apparatus>

Firstly, an overall configuration of a die casting apparatus according to a first embodiment is described with reference toFIGS. 1 to 3.FIGS. 1 to 3are schematic cross sections of the die casting apparatus.

Note that, needless to say, right-handed xyz orthogonal coordinate systems shown inFIG. 1and other drawings are shown for the sake of convenience to explain positional relations among components. In general, a z-axis positive direction is a vertically upward direction and an xy-plane is a horizontal plane. These facts are applicable throughout the drawings.

As shown inFIGS. 1 to 3, the die casting apparatus according to the first embodiment includes a movable die10, a fixed die20, a plunger sleeve30, and a plunger40. Note thatFIGS. 1 to 3show operations of the die casting apparatus.FIG. 1shows a state in which molten metal M is supplied to the plunger sleeve30in the die casting apparatus.FIG. 2shows a state in which an injection of the molten metal M into a cavity C has been completed in the die casting apparatus.FIG. 3is a schematic cross section showing a state in which a cast article50is taken out from the dies (the movable and fixed dies10and20) in the die casting apparatus.

The movable die10is a die that can be moved in a sliding manner in the x-axis direction. Meanwhile, the fixed die20is a die fixed to the die casting apparatus. As the movable die10moves in the x-axis positive direction and abuts against the fixed die20, a cavity C whose shape conforms to the shape of a product to be cast is formed between the movable and fixed dies10and20as shown inFIG. 1. As shown inFIG. 2, as the cavity C is filled with molten metal M, a cast article50is cast as shown inFIG. 3. Then, as the movable die10moves in the x-axis negative direction and is released from the fixed die20, the cast article50can be taken out as shown inFIG. 3.

The movable and fixed dies10and20are made of, for example, alloy tool steel for hot dies. Note that each of the movable and fixed dies10and20may be an insert die.

For example, as shown inFIG. 1, a through hole having a circular cross section and having a central axis parallel to the x-axis is formed in the fixed die20. A cylindrical plunger sleeve30is engaged inside this through hole. The plunger40slides in the x-axis direction inside the plunger sleeve30. On the upper side of the plunger sleeve30at the end thereof on the side of the movable die10(i.e., at the end on the x-axis negative direction side), a runner (i.e., a channel for molten metal) R is formed between the movable and fixed dies10and20. The runner R links the plunger sleeve30with the cavity C and guides molten metal M into the cavity C.

The plunger sleeve30is a cylindrical member having a central axis parallel to the x-axis. As described above, the plunger sleeve30is engaged inside the through hole formed in the fixed die20. Molten metal M is fed into the plunger sleeve30. A molten-metal inlet31for pouring molten metal M into the plunger sleeve30is formed in an area on the upper surface of the plunger sleeve30near the rear end thereof (i.e., near the end on the x-axis positive direction side). The molten metal M is poured through the molten-metal inlet31into the plunger sleeve30by using, for example, a ladle or the like (not shown). The plunger sleeve30is made of, for example, alloy tool steel for hot dies.

The plunger40includes a plunger tip41and a plunger rod42.

The plunger tip41is a columnar member that directly comes into contact with the molten metal M contained in the plunger sleeve30. The plunger tip41is connected to a drive source (not shown) through the plunger rod42, which is a rod-like member having a central axis parallel to the x axis, and can slide in the x-axis direction inside the plunger sleeve30. As shown inFIG. 2, as the plunger tip41slides from the rear end of the plunger sleeve30in the x-axis negative direction, the molten metal M, which has been fed into the plunger sleeve30, is injected into the cavity C.

<Operation of Die Casting Apparatus>

Next, operations of the die casting apparatus according to the first embodiment are described with reference toFIGS. 1 to 3. Firstly, as shown inFIG. 1, in a state where the plunger tip41is retracted in the x-axis positive direction inside the plunger sleeve30, the movable die10is made to abut against the fixed die20, so that a cavity C is formed therebetween. Then, molten metal M is supplied through the molten-metal inlet31of the plunger sleeve30into the plunger sleeve30by using, for example, a ladle or the like (not shown).

Next, as shown inFIG. 2, the plunger40is moved forward inside the plunger sleeve30, so that the molten metal M is injected into the cavity C through the runner R. Note that by moving the plunger40forward, it is possible to fill the cavity C with the molten metal M while pressing the molten metal M.

Next, as shown inFIG. 3, after the molten metal M is solidified inside the cavity C, the movable die10is released from the fixed die20and a cast article50is take out. As shown inFIG. 3, the cast article50includes a runner part52and a biscuit part53in addition to a product part51. Dashed lines in the cast article50shown inFIG. 3are drawn for the sake of explanation in order to indicate boundary lines between the product part51and the runner part52and between the runner part52and the biscuit part53.

The runner part52is a part where the molten metal M is solidified in the runner R. The biscuit part53is a part where the molten metal M surrounded by the front-end surface of the plunger tip41and the dies (the movable and fixed dies10and20) is solidified. Note that the runner part52and the biscuit part53are eventually removed and the product part51is used as a product.

Note that as described above, when molten metal M is supplied to the plunger sleeve30, part of the molten metal M that has come into contact with the plunger sleeve30is cooled and solidified. Therefore, initial solidified pieces are formed on the inner surface of the plunger sleeve30that has come into contact with the molten metal M. If these initial solidified pieces come off from the plunger sleeve30when the plunger tip41is moved forward inside the plunger sleeve30, and are injected into the cavity C of the dies (the movable and fixed dies10and20) together with the molten metal M, they could cause casting defects.

As will be described below, in the die casting apparatus according to the first embodiment, protrusions for reducing casting defects caused by initial solidified pieces are provided in the runner R.

<Configuration of Runner in Die>

Next, a configuration of the runner R, which links the plunger sleeve30with the cavity C of the dies (the movable and fixed dies10and20), in the die casting apparatus according to the first embodiment is described with reference toFIGS. 4 and 5.FIG. 4is a front view of a part of the fixed die20.FIG. 5is a cross section taken along a line V-V inFIG. 4. A part of the movable die10is also shown inFIG. 5. In the examples shown inFIGS. 4 and 5, a groove-like runner R is formed in the fixed die20and the plunger sleeve30. However, the runner R may be formed in the movable die10, or may be formed in both the movable and fixed dies10and20.

As shown inFIGS. 4 and 5, the groove-like runner R for guiding injected molten metal to the cavity C is formed on the end surface of the plunger sleeve30and the front surface of the fixed die20. The runner R is formed so as to extend from the inner peripheral surface of the plunger sleeve30to the cavity C. Further, a plurality of protrusions22are provided so as to extend along the longitudinal direction of the runner R, i.e., along a direction in which the molten metal flows (the z-axis positive direction in the example shown inFIG. 4). In the example shown inFIG. 4, seven protrusions22are provided.

Further, the plurality of protrusions22are arranged in a comb-teeth arrangement in the width direction of the runner R. Although each of the protrusions22shown inFIG. 4has a triangular cross section, i.e., has a wedge shape (a triangular prism shape), the shape of the protrusion22is not limited the triangular shape. For example, the protrusion22may have a rectangular cross section, i.e., a quadrangular prism shape. It should be noted, however, since the cross-sectional shape of the protrusion22is triangular, the width of the base of the protrusion22is larger than the top thereof. Therefore, the base of the protrusion22is more stable than, for example, that of a protrusion having a rectangular cross section. Further, a resistance that is caused when a cast article is taken out from the die is reduced and hence the cast article is less likely to be damaged. Note that in the example shown inFIG. 5, the top of the protrusion22having the triangular cross section has a shape having an acute angle. However, the top of the protrusion22may have an R-shape or may be flat.

By forming a plurality of protrusions22arranged in a comb-teeth arrangement in the width direction of the runner R, it is possible to reduce casting defects caused by initial solidified pieces. As indicated by arrows inFIG. 4, the molten metal passes between the protrusions22while colliding with the protrusions22. Therefore, it is presumed that initial solidified pieces contained in the molten metal collide with the protrusions22and hence are pulverized, or they are pulverized by turbulence of the flow of the molten metal caused by the protrusions22.

Note that the protrusions22are provided so as to extend along the direction in which the molten metal flows. That is, the length (the length in the z-axis direction) of each protrusion22is larger than the width (the length in the y-axis direction) of the protrusion22. Therefore, even when the protrusions22are repeatedly pressed by the molten metal at a high pressure, they are less likely to be damaged as compared to, for example, columnar protrusions. Therefore, the die (the fixed die20in the example shown inFIGS. 4 and 5) has excellent durability. For example, the length of each protrusion22is preferably at least twice the width of the protrusion22. Alternatively, the length of each protrusion22is preferably at least one half of the height of the protrusion22.

For the reduction of casting defects caused by initial solidified pieces, the higher the protrusions22are, the more they are preferred. For example, the height of each protrusion22is preferably at least 80% of the depth of the runner R, and more preferably at least 90% of the depth of the runner R. Therefore, as shown inFIG. 5, the height of each protrusion22is most preferably equal to the depth of the runner R. However, the height of the protrusions22is not limited to such a height. Note that the expression that the height of the protrusion22is equal to the depth of the runner R does not means that the height of the protrusion22is exactly equal to the depth of the runner R. That is, this expression also includes cases where the height of the protrusion22is roughly equal to the depth of the runner R.

Further, as shown inFIGS. 4 and 5, all the protrusions22are formed in an insert part23. In other words, the bases of all the protrusions22are integrally formed with the insert part23. Further, the insert part23is engaged with and fixed to the fixed die20. That is, the protrusions22are provided in the replaceable insert part23. Therefore, when the protrusions22(e.g., some of the protrusions22) are broken, it is possible to replace only the insert part23in which the protrusions22are provided, thus making the die excellent (e.g., useful) in terms of the maintenance. Needless to say, the protrusions22may be integrally formed with the fixed die20or the movable die10.

As described above, in the die casting apparatus according to the first embodiment, the plurality of protrusions22, which extend in the direction in which the molten metal flows, are formed in the runner R. Therefore, even when the protrusions22are repeatedly pressed against the molten metal at a high pressure, they are less likely to be broken. Therefore, the die has excellent durability. Further, the plurality of protrusions22are arranged in a comb-teeth arrangement in the width direction of the runner R. Therefore, initial solidified pieces contained in molten metal are pulverized by the protrusions22or turbulence of the flow caused by the protrusions22, and hence it is possible to reduce casting defects caused by the initial solidified pieces. That is, the die casting apparatus according to the first embodiment can reduce casting defects caused by initial solidified pieces and its die has excellent durability.

EXAMPLE

The die casting apparatus according to the first embodiment will be described hereinafter in a more detailed manner by using examples and comparative examples. However, the die casting apparatus according to the first embodiment is not limited to the examples shown below.

FIG. 6is a photograph of a front view of a part of a fixed die20in a die casting apparatus according to an example of the first embodiment. In the example shown inFIG. 6, two runners R1and R2are formed on the front surface of the fixed die20, which will be made to abut against a movable die10, in such a manner that the runners R1and R2extend from the inner peripheral surface of the plunger sleeve30to the cavity C while the distance between the runners R1and R2increases as they extend toward the cavity C.

The runner R1branches into three runners R11, R12and R13, and these runners R11, R12and R13reach the cavity C while the distances between them increase as they extend toward the cavity C. The runner R2branches into three runners R21, R22and R23, and these runners R21, R22and R23reach the cavity C while the distances between them increase as they extend toward the cavity C. That is, the six runners R11, R12, R13, R21, R22and R23are formed so as to spread roughly in a radial pattern from the inner peripheral surface of the plunger sleeve30.

In a part of the runner R1where it branches into the runners R11and R12, seven protrusions22aare provided so as to extend along the direction in which molten metal flows. The seven protrusions22aare arranged in a comb-teeth arrangement in the width direction of the runners R11and R12.

In the runner R13, two protrusions22bare provided so as to extend along the direction in which the molten metal flows. The two protrusions22bare arranged in a comb-teeth arrangement in the width direction of the runner R13.

In the runner R21, one protrusion22cis formed so as to extend along the direction in which the molten metal flows.

In a part of the runner R2where it branches into the runners R22and R23, four protrusions22dare provided so as to extend along the direction in which the molten metal flows. Further, another four protrusions22eare formed on the downstream side thereof. That is, the four protrusions22dand the four protrusions22e, each of which are arranged in a comb-teeth arrangement in the width direction of the runners R22and R23, are formed in two stages (i.e., in an end-to-end arrangement).

The dimensions of each protrusion in the example were as follows: the length of the base was 21 mm; the width of the base was 5 mm; and the height was 14 mm.

In the example shown inFIG. 6, it was possible to drastically reduce the area ratio of initial solidified pieces in a produced cast article from 5.8% to 1.3% as compared to a comparative example in which no protrusion was provided in the runner. As described above, by providing a plurality of protrusions arranged in a comb-teeth arrangement in the width direction of the runner in the runner, it was possible to reduce casting defects caused by initial solidified pieces. Further, the protrusions are provided so as to extend along the direction in which molten metal flows. Therefore, even when the protrusions22are repeatedly pressed against the molten metal at a high pressure, they are less likely to be broken. Therefore, the die has excellent durability.

Note thatFIG. 7shows a result of a computer simulation of changes in a flow of molten metal caused by formation of protrusions. As shown inFIG. 7, the flow of the molten metal that has passed through the protrusions22a,22b,22c,22dand22eis disturbed in the example as compared to the comparative example in which no protrusion is provided in the runner. Based on the simulation result shown inFIG. 7, it is presumed that initial solidified pieces contained in the molten metal collide with the protrusions and hence are pulverized, or they are pulverized by turbulence of the flow caused by the protrusions.