Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2000-04-19
2001-07-03
Dunn, Tom (Department: 1722)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S112000, C164S332000, C164S333000, C164S334000, C164S120000, C164S319000, C164S288000
Reexamination Certificate
active
06253829
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat sink for enlarging a heat exchanging area in various heat exchanging devices or heat transfer devices and, more particularly, to a process for manufacturing a heat sink, which is constructed to protrude a number of radiation members into a base portion, and an apparatus for carrying out the process.
2. Related Art
In order to improve the heat exchanging capacity of a thermal device such as a heat pipe by enlarging the heat radiating or absorbing area, it is widely executed in the prior art to employ a heat sink.
An example of this kind of heat sink is shown in
FIGS. 30A and 30B
. A heat sink
1
, as shown in
FIG. 30A
, is equipped with a plurality of plate-shaped fins
2
arrayed in parallel with one another, and a plate-shaped base
3
projecting the fins
2
. The heat sink
1
thus constructed is generally manufactured in the prior art by the extruding method using an aluminum alloy. In the heat sink
1
shown in
FIG. 30B
, on the other hand, the fins
2
acting as the radiation members are formed into a circular column shape. Moreover, the heat sink shown in
FIG. 30B
is generally manufactured in the prior art by the forging method using a copper alloy.
The fins
2
of the heat sink
1
are preferably arrayed as dense as possible. On the other hand, however, the extruding or forging method, as adopted as the method for manufacturing each of the aforementioned heat sinks
1
, is intended to form the target shape by fluidizing the material. It is, therefore, necessary to introduce the material into the small clearances corresponding to the fins in the forming mold, when the heat sink is to be manufactured by the extruding or forging method. For the smaller sectional area of the clearances and for the longer introduction (corresponding to the length of the fins
2
), however, the material becomes the more reluctant to flow. In the prior art, therefore, the minimum thickness t of the fins
2
is limited by about 2 mm. When the thickness t is set to 2 mm, the maximum height (or length) h of the fins
2
is limited by about 20 mm. From the requirement of the strength of the mold, on the other hand, the array pitch p of the fins
2
has to be 5 mm or more.
When the heat sink
1
is to be thus manufactured by the extruding or forging method, the fins
2
cannot be made thin and high, and the number of the fins
2
per unit area of the base
3
is restricted. This raises a disadvantage that the heat exchanging area of the heat sink to be achieved by the conventional method is restricted to a small value.
An invention capable of eliminating such a disadvantage is disclosed in Japanese Patent Laid-Open No.9-181231. The conventional process, as disclosed in this Laid-Open, will be briefly described with reference to
FIGS. 31 and 32
. In a heat sink
4
manufactured by this process, rectangular and thin fins
6
are integrated with a plate-shaped base
5
. The fins
6
are prepared by cutting a rolled sheet of an aluminum alloy into a rectangular shape. These fins
6
are arrayed at a constant pitch by inserting them liquid-tight into the (not-shown) slits formed in the mold. Moreover, the one-end portions of the individual fins
6
are protruded from the mold. In this state, a molten metal of the aluminum alloy is poured into the end portions, as protruded from the mold of the fins
6
to form the shape of the base
5
. Immediately before the complete solidification, moreover, the molten metal is pressurized for the forging effect.
According to this process, what is used is the fins
6
prepared prior to casting but not the casting fins
6
, so that the thickness, height or pitch of the fins
6
is not restricted. Since the molten metal is pressurized midway of solidification, moreover, the defects such as air bubbles and so on in the base
5
can be eliminated.
According to the aforementioned conventional method of forming the base by casting forging the molten metal, however, the mold is closed after it is fed with the molten metal for the base, and the molten metal is pressurized to raise a problem that the time period required for molding the base is elongate to deteriorate the productivity. Moreover, the fins are made of the thin sheets, as described above, or replaced by thin pins. The fins of this structure are low in their own strength and are heated and cooled at the time of molding the base. This raises another disadvantage that the strength is further lowered. The fins thus having lowered the strength are deformed while they are being used. As a result, the adjoining fins come into contact to invite a problem that their radiation area is reduced to deteriorate the radiation efficiency.
SUMMARY OF THE INVENTION
A main object of the invention is to provide a process for manufacturing a heat sink having a large surface area at its radiation fins quickly and highly efficiently.
Another object of the invention is to improve the strength of radiation fins having a small thickness and a small pitch.
In the invention, therefore, the one-end portions of radiation fins arrayed at a constant pitch are protruded into a diecasting cavity, and a molten metal under a high pressure is poured into the cavity. As a result, the one-end portions of the radiation fins are cast with the molten metal. When the molten metal in the cavity solidifies, the base is molded integrally with the radiation fins. Thus, according to the process of the invention, the portion of the base carrying the radiation fins can be diecast to manufacture the heat sink including the base having a dense metallic structure with no defect quickly and highly efficiently.
According to the process of the invention, moreover, the molten metal in the cavity may be pressurized by reducing the capacity of the cavity immediately before the molten metal completely solidifies. By performing the so-called “secondary pressurization”, the casting defects at the portion of the base are eliminated more reliably.
In the invention, still moreover, the projections along the surface of the one-end portions of the radiation fins may be formed on the base. These projections act to increase the penetration depth of the radiation members into the base thereby to improve the mounting strength of the radiation fins on the base.
According to the process of the invention, reinforcing ribs may be formed in advance on the radiation members. Moreover, the radiation fins may be heated to improve their strength after the diecasting treatment or hardened to raise their strength by compressing them. Still moreover, a prepared heat pipe can be arranged in a diecasting cavity and cast therearound by the molten metal to provide a construction in which the heat pipe is mounted in the base integrated with the fins.
The above and further objects and novel features of the invention will more filly appear from the following detailed description when the same is read with reference to the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.
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Goto Kazuhiko
Mashiko Koichi
Mochizuki Masataka
Nagaki Yoshihiro
Saito Yuji
Dunn Tom
Fujikura Ltd.
Lin I.-H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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