JPH06234055A - Manufacture of high-hardness aluminum cast product - Google Patents

Abstract

PURPOSE:To obtain an aluminum cast product capable of making high in hardness only at a specific part and high in strength and toughness at the other part. CONSTITUTION:Molten Al-Si alloy 20 is filled into a cavity in a metallic mold and a half-solidified molten molten metal part 200 having high Si concn. by segregation is produced in the molten Al-Si alloy 20 filled in the cavity 5. By pressing the half-solidified molten metal part 20a from the outer part through a sliding pin 11, the half-solidified molten metal part 20d having high Si concn. is moved to the position needing high hardness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aluminum cast product having a high hardness at a specific portion, and more particularly to a method for manufacturing an aluminum cast product utilizing a segregation phenomenon when a molten metal is solidified.

[0002]

2. Description of the Related Art Aluminum alloys are lighter than other metal materials and are used in various products. For example,
If you can make the brake drum of the car with aluminum alloy,
The weight of the automobile can be reduced, which greatly contributes to fuel efficiency.

In the casting of aluminum alloy, the mold is filled with the molten aluminum alloy, and thereafter, the molten metal is pressed by a pressure pin from the outside in order to prevent the occurrence of shrinkage cavities. As prior art related to this, for example, Japanese Patent Application Laid-Open No. 57-14453 is known.

[0004]

However, since the aluminum alloy has a hardness lower than that of iron, it has a problem that it cannot be used for a specific member while having the advantage of being lightweight.

A wheel for mounting a tire is mounted on a brake drum of an automobile by means of bolts. Since the hub surface of the brake drum is in line contact with the wheel, when the bolt is completely tightened. The surface pressure of the part of the line contact with the wheel of the brake drum becomes high. Therefore, when the brake drum is made of a cast product made of aluminum alloy, the hub surface of the brake drum is deformed by the contact with the wheel.

Further, when the vehicle is running, a load in the direction of rubbing always acts on the contact surface between the hub surface of the brake drum and the wheel due to vibration, so that the hub surface of the brake drum is required to have some degree of wear resistance. It As described above, when the brake drum is made of an aluminum alloy, the hardness and wear resistance of the hub surface are required for the brake drum, which is satisfied by the Al-Si hypoeutectic aluminum alloy which is usually used. I can't.

On the other hand, when an aluminum alloy having a hypereutectic structure is used to increase the hardness and wear resistance of the brake drum, extremely hard primary crystal Si is generated, and the machinability of the cast product during machining is significantly deteriorated. To do. Therefore, the required surface roughness cannot be obtained by machining. Also,
Since an aluminum alloy having a eutectic structure has low strength and toughness, it is difficult to apply it to a member having a large load change such as a brake drum.

In view of the above problems, it is an object of the present invention to provide a method for manufacturing an aluminum cast product which can increase the hardness of a specific portion while maintaining the strength and toughness of the aluminum cast product. To do.

[0009]

In order to achieve this object, a method of manufacturing a high hardness aluminum casting according to the present invention is to fill a cavity of a mold with molten Al-Si alloy and fill the cavity. A semi-solidified melt portion having a high Si concentration is generated in the molten Al-Si alloy melt by segregation, and the semi-solidified melt portion having a high Si concentration is externally pressed through a sliding pin so that the Si concentration is increased. This is a method of moving a high semi-solid molten metal portion to a predetermined portion in the cavity.

[0010]

In the method of manufacturing a high hardness aluminum casting having the above structure, A filled in the cavity of the mold is
The molten 1-Si alloy is cooled by heat exchange with the mold. When the molten metal is cooled, a semi-solid molten metal portion having a high Si concentration is generated in the Al-Si alloy molten metal due to the segregation phenomenon. When the semi-solidified molten metal portion is generated, the semi-solidified molten metal portion is externally pressed by the sliding pin toward a predetermined portion in the cavity, that is, a portion requiring high hardness.

Since the pressing of the semi-solidified molten metal portion by the sliding pin is performed before the melts of other portions are completely solidified, the semi-solidified molten metal portion having a high Si concentration is required to have high hardness. It becomes possible to move toward. After being moved to a predetermined position, the semi-solidified molten metal part is solidified as it is by heat exchange with the mold. In this way, the semi-solidified molten metal portion solidifies while maintaining the eutectic structure, so that this portion can have a high hardness.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the method for producing a high hardness aluminum casting according to the present invention will be described below with reference to the drawings.

First Embodiment FIGS. 1 to 5 show a first embodiment of the present invention.
Especially, it shows the case where it is applied to the casting of the brake drum. FIG. 3 shows a vertical pressure casting apparatus 1 used for casting the brake drum 30 shown in FIG. The vertical pressure casting apparatus 1 has a mold 2. The mold 2 is composed of an upper mold 3 and a lower mold 4. The mold 2 has a cavity 5 for casting the brake drum into a predetermined shape.
Are formed.

The cavity 5 is connected to the sleeve 6 via a runner portion 6a formed on the mold 2. An injection chip 7 and a counter chip 8 are movably arranged in the sleeve 6. The injection tip 7 can be moved in the vertical direction by a driving unit (not shown). The counter chip 8 can be moved in the vertical direction by another driving means (not shown). A molten metal supply passage 9 is connected to the sleeve 6.

When the counter chip 8 is raised, one of the runner portions 6a is blocked by the counter chip 8. When the injection tip 7 is raised, the inside of the sleeve 6 communicates with the molten metal supply passage 9 and the molten metal supply passage 9
A molten Al-Si alloy (corresponding to JIS AC2B) 20 is supplied to the. When the molten Al—Si alloy 20 supplied to the molten metal supply passage 9 flows into the sleeve 6, the injection tip 7 descends and the Al in the sleeve 6
-Si alloy melt 20 is injection tip 7 and counter tip 8
It is supposed to be sandwiched by. When the counter chip 8 is lowered in this state to open the runner portion 6a, the molten Al-Si alloy 20 in the sleeve 6 is filled in the cavity 5.

The cavity 5 is formed with a plurality of recesses 5a protruding upward. The recesses 5a are provided on the circumference at a constant pitch. Due to the presence of the recess 5a,
A boss portion 32 is formed on the brake drum 30 to be cast. The upper die 3 has a plurality of sliding pins 1
1 is slidably held. The upper end of the sliding pin 11 is connected to the ram 13 via the holding plate 12.

The ram 13 can be raised and lowered by a driving means (not shown). The lower end of each sliding pin 11
Each of the recesses 5 a of the cavity 5 is exposed. When the ram 13 is completely raised, the lower end of the slide pin 11 does not enter the recess 5a of the cavity 5, and when the ram 13 is lowered, the lower end of the slide pin 11 is recessed 5a of the cavity 5. And the molten Al—Si alloy 20 present in the recess 5a is pressed.

In this embodiment, the lower mold 4 of the mold 2 is fixed, and the upper mold 3 is movable back and forth with respect to the lower mold 4. The lower mold 4 has a convex portion 4a forming the bottom surface of the cavity 5.
Are formed. A tapered surface 4b is formed on the upper part of the outer peripheral surface of the convex portion 4a so that the diameter becomes smaller toward the upper side. A cast iron liner 33 that is integrally cast with the brake drum 30 is attached to the tapered surface 4b.

The lower mold 4 is provided with the cast brake drum 3
A plurality of extruding pins 15, 1 for removing 0 from the mold
6 is provided. Each extrusion pin 15 and 16 is a lower mold 4
Is held slidably on the lower side of the push-out pins 15 and 16 so as to project from the lower surface of the lower mold 4. Push pin 1
The lower end portions of 5, 16 are connected to the holding plate 17. The holding plate 17 can be pushed up by driving means (not shown). When the holding plate 17 is pushed up, the upper ends of the push-out pins 15 and 16 project from the upper surface of the lower mold 4, and the cast brake drum 3 is cast.
0 is taken out.

Next, the working procedure and action in the method for manufacturing a high hardness aluminum casting according to the present invention will be described.

Before the casting of the brake drum 30 is started, the upper mold 3 is separated from the lower mold 4. In this state,
A cast iron liner 33 is mounted on the tapered surface 4b of the convex portion 4a of the lower mold 4. When the mounting of the cast iron liner 33 on the lower die 4 is completed, the upper die 3 is lowered and the upper die 3 and the lower die 4 are clamped. Upon completion of the mold clamping, the cavity 5 is formed in the mold 2.

When the mold clamping of the mold 2 is completed, the injection tip 7 rises, and Al- is introduced into the sleeve 6 from the molten metal supply passage 9.
The Si alloy melt 20 is supplied. In this state, the counter chip 8 is rising. A certain amount of A in the sleeve 6
When the molten 1-Si alloy 20 is supplied, the injection tip 7 descends, and the molten Al-Si alloy 20 in the sleeve 6 is sandwiched by the injection tip 7 and the counter chip 8.

When the counter chip 8 is lowered in this state, the runner portion 6a is opened and the Al-
The filling of the molten Si alloy 20 into the cavity 5 is started. FIG. 1A shows a state in which the filling of the molten Al—Si alloy 20 into the cavity 5 is completed.

As shown in FIG. 1A, in the initial stage of filling the molten metal, the surface of the Al-Si alloy molten metal 20 is cooled by heat exchange with the mold 2, and solidification of the molten metal surface is started.
Since the cavity 5 of the mold 1 is formed with the concave portion 5a protruding upward, the portion where the concave portion 5a is formed is
It becomes a thick part of the casting, and the progress of solidification in this part lags behind the surface of the molten metal.

When the solidification of the molten Al-Si alloy 20 slows down, the segregation phenomenon in which the concentration distribution of the constituent elements in the molten Al-Si alloy 20 becomes nonuniform becomes remarkable. Therefore, as shown in FIG. 1B, a semi-solidified molten metal portion 20a having a high Si concentration is generated in the vicinity of the recess 5a. The semi-solid molten metal portion 20a is generated, for example, 1.0 to 1.2 seconds after the Al-Si alloy molten metal 20 is filled.

When the semi-solidified molten metal portion 20a is produced, as shown in FIG.
(C), the sliding pin 11 enters the concave portion 5a of the cavity 5 and the semi-solidified molten metal portion 20a moves to the sliding pin 11
Pressed by. In this state, the molten Al—Si alloy 20 in the portion corresponding to the hub portion 32 of the brake drum 30 which requires high hardness is not completely solidified,
The semi-solidified molten metal portion 20a having a high Si concentration moves toward the portion 5b of the cavity 5 corresponding to the hub 32 portion by being pressed by the sliding pin 11.

When the semi-solidified molten metal portion 20a moves to a predetermined position, the pressing of the semi-solidified molten metal portion 20a by the sliding pin 11 is stopped, and the sliding pin 11 rises as shown in FIG. 1 (D). . The semi-solidified molten metal portion 20a moved by the sliding pin 11 is cooled at that position by heat exchange with the mold 2. Part 2 where the semi-solid molten metal part 20a is solidified
0b has a complete eutectic structure with a high Si concentration, and therefore has a hardness higher than that of the other solidified portions 20c.

When the Al-Si alloy melt 20 filled in the cavity 5 is completely solidified, the upper die 3 is raised and the die 2 is moved.
The mold opening is performed. When the lifting of the upper die 3 is completed, the pushing pins 15 and 16 are raised, and the brake drum 30 as a cast product is taken out from the die 2. FIG. 4 shows the brake drum 30 taken out from the mold 2.
As shown in FIG. 4, a boss portion 32 is formed in a part of the hub portion 31 of the brake drum 30, and a cast iron liner 33 is surrounded inside.

Brake drum 30 taken out from the mold 2
The hub portion 31 is machined as shown in FIG. 2 and the boss portion 32 is removed. As a result, the high hardness portion 31a formed by solidifying the semi-solidified molten metal portion 20a having a high Si concentration is exposed on the surface. Therefore, even if an iron wheel (not shown) is attached to the brake drum 30 that is an aluminum casting, the hub portion 3 that abuts the wheel with high surface pressure.
The deformation of 1 is prevented.

As described above, by utilizing the segregation phenomenon when the molten Al--Si alloy 20 is solidified, as shown in the characteristics of FIG. 5, a part of the hub portion 31 requiring high hardness is completely removed. Brake drum 3 that can have a eutectic structure
A portion other than the hub portion 31 of 0 can have a hypoeutectic structure having high strength and toughness.

Second Embodiment FIG. 6 shows a second embodiment of the present invention. The second embodiment is different from the first embodiment only in the configuration of the upper mold 3, and the other parts are in conformity with the first embodiment. Therefore, by applying the same reference numerals to the conforming parts in the first embodiment. The description of the corresponding parts will be omitted, and only different parts will be described.

As shown in FIG. 6, the sliding pin 11 of the upper die 3
A split insert 18 is provided on the outer periphery of the. Split nest 1
Reference numeral 8 forms a recess 5 a of the cavity 5. A heater 19 is attached to the outer periphery of the split insert 18, and the split insert 18 is heated by the heater 19. The heater 19 is connected to a power source (not shown). The temperature of the split insert 18 due to the heating of the heater 19 is kept at a predetermined value.

In the second embodiment thus constructed, the split insert 18 forming the recess 5a of the cavity 5 is formed.
Is heated by the heater 19, so that the progress of solidification of the molten Al—Si alloy 20 filled in the cavity 5 can be delayed. Therefore, A in the recess 5a
It becomes possible to further promote the segregation phenomenon during solidification of the 1-Si alloy melt 20.

Therefore, the semi-solidified molten metal portion 20a having a high Si concentration can be produced more than in the first embodiment, and the hub surface 31 of the brake drum 30 can have a high hardness over a wider range. .

[0035]

EFFECTS OF THE INVENTION According to the present invention, a semi-solid molten metal portion in which the Al-Si alloy molten metal is filled in the mold cavity and the Al concentration is increased in the Al-Si alloy molten metal filled in the cavity due to segregation Is generated, and the semi-solidified molten metal portion having a high Si concentration is pressed from the outside through a sliding pin to move the semi-solidified molten metal portion having a high Si concentration to a predetermined portion in the cavity. It is possible to make only a specific part of the structure have a eutectic structure, and to make other parts a hypoeutectic structure.

Therefore, it is possible to obtain an aluminum cast product in which only a specific part has high hardness while maintaining the strength and toughness of other parts. As a result, it becomes possible to manufacture a member that undergoes a large load change, such as an automobile brake drum, from an aluminum alloy casting.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing a solidification process of a molten metal in a method for manufacturing a high hardness aluminum casting according to a first embodiment of the present invention.

2 is a partial cross-sectional view of a cast product manufactured by the method of FIG. 1 when machined.

FIG. 3 is a sectional view of a vertical pressure casting device to which the present invention is applied.

FIG. 4 is a partially enlarged sectional view of a brake drum cast by the apparatus of FIG.

5 is a characteristic diagram showing a hardness distribution of a brake drum cast by the apparatus of FIG.

FIG. 6 is a cross-sectional view of a vertical pressure casting apparatus used in the method for manufacturing a high hardness aluminum casting according to the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vertical pressure casting apparatus 2 Mold 3 Upper mold 4 Lower mold 5 Cavity 11 Sliding pin 19 Heater 20 Al-Si alloy molten metal 20a Semi-solid molten metal part 30 Brake drum 31a as a cast product High hardness part

Claims (1)

[Claims] 1. A mold cavity is filled with an Al—Si alloy melt, and a semi-solid melt portion having a high Si concentration is generated by segregation in the Al—Si alloy melt filled in the cavity. High hardness aluminum casting characterized in that the semi-solid molten metal portion having a high Si concentration is externally pressed via a sliding pin to move the semi-solid molten metal portion having a high Si concentration to a predetermined portion in the cavity. Method of manufacturing goods.