Extrusion die

Details Extrusion die Extrusion die

2000-09-29

2002-03-05

Tolan, Ed (Department: 3725)

Metal deforming

By extruding through orifice

Utilizing internal forming means

C072S467000

Reexamination Certificate

active

06351979

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an extrusion die for making multi-hole flat tube suitable for making various types of aluminum heat exchangers, for example. This application is based on Japanese Patent Application Nos. Hei 11-277613, 11-227614, and 2000-155342, and the contents of which are incorporated herein by reference.
2. Description of the Related Art
Extrusion fabrication of various metals is a known technology for producing component parts for various electrical devices and automobiles. Extrusion fabrication is widely used in making aluminum tubing for various heat exchangers, such as evaporator, condenser, radiator and others for use in automobile air-conditioners because of the excellent hot working properties of aluminum. An extrusion die is used in practice to perform extrusion fabrication.
FIGS.
17
~
21
show some examples of known extrusion dies (refer to a Japanese Patent Application, First Publication No. Hei. 7-124634). A typical die shown is comprised by a male die
31
has an external appearance of a rectangular plate (refer to FIG.
17
), and a female die
41
has an external appearance of a cylindrical column (refer to
FIGS. 18
,
19
).
As shown in
FIG. 17
, the male die
31
having a specific plate thickness is made of a high-speed steel or a hot worked die steel, and in a central section of its end surface
32
, a step section
33
is protruded from the surface. From the center of the step section
33
extends a protrusion section
34
containing a series of protrusions resembling comb teeth. Also, flow-in sections
36
sloping down toward the protrusion section
34
are formed on the wide surfaces
35
sandwiching the end surface
32
. The both sides of the wide surfaces
35
having the flow-in sections
36
are referred to as coupling sections
37
of a uniform plate thickness.
On the other hand, as shown in
FIGS. 18
,
19
, the female die
41
is comprised by a female die body
42
made of a die steel, and an insert member
43
made of the material harder than that of the female die body
42
such as a high-speed steel or a hard metal. The female die body
42
has an external appearance of cylindrical bar, and a radially extending channel section
45
of a given width is formed on an end surface
44
opposing the male die
31
. A rectangular recess
47
is formed in the center of the bottom surface
46
of the channel section
45
for inserting the insert member
43
.
The insert member
43
is formed in such a way that when it is coupled inside the recess
47
, its upper surface is coplanar with the bottom surface
46
of the channel section
45
, and in the center, a through-hole
48
that extends in an orthogonal direction to the channel
45
is formed, as shown in
FIGS. 18
,
19
. The through-hole
48
is comprised by a die cavity
49
that has an elliptic shape and positioned at the top surface of the insert member
43
for inserting the protrusion section
34
to fabricate an aluminum material (billet) into a desired shape in the space formed between itself and the protrusion section
34
, and an exit opening
50
that opens at the downstream surface of the insert member
43
and is shaped in such a way that the width of the exit opening is larger than the width of the die cavity
49
. The insert piece
43
is shrink fitted to firmly engage with the recess
47
.
Also, grooved channels
51
are formed on the two end surfaces
44
on both sides of the channel section
45
of the female die body
42
, whose depth is shallower than that of the channel section
45
, to extend in an orthogonal direction to the channel section
45
. On the opposite end surface
52
of the female die body
42
, a first hole section
53
whose entry end communicates with the through-hole
48
and whose exit end opens at the end surface
52
of the female die body
42
for discharging the extrusions, and a second hole section
54
cut out so as to cross the first hole section
53
, and whose entry end opens at the bottom surface of the recess
47
and the exit end opens at the end surface
52
.
The extrusion die is used by forming an integral die by locating the protrusion section
34
of the male die
31
within the die cavity
49
of the female die
41
, and engaging the coupling section
37
of the male die
31
into the grooved channel
51
of the female die
41
, and coupling the step section
33
of the male die
31
with the channel section
45
of the female die
41
.
The extrusion die comprised by the male die
31
and the female die
41
is inserted into the through-hole of the die-holder that serves as a flow path of the metal, and is fixed therein, and the aluminum billet inserted into a billet hole of the container communicating with the through-hole of the die holder, is pressed towards the extrusion die by a stem of an extrusion press which is omitted in the Figure. The billet being extruded flows into a billet flow passage formed between the two wide surfaces
35
and the inner wall surface of the through-hole of the die-holder to the space formed between the protrusion section
34
of the male die
31
and the die cavity
49
of the female die
41
, and in passing through the space formed between the die cavity
49
and the protrusion section
34
, the multi-hole flat tube Ca such as the one shown in
FIG. 20
is produced.
When the billet flows into the flow passage of the extrusion die, a high-temperature and high-pressure material impinges directly on the protrusion section
34
of the male die
31
to apply a high pressure so that the protrusion section
34
is rapidly worn out. For this reason, it is necessary to change the male die
31
most frequently, which results in a problem of high die cost. This problem is most severe when making the multi-hole flat tube Ca having many holes such as the one shown in
FIG. 20
, because of thinner size of the protrusion section
34
of the male die
31
resulting in low wear resistance.
To resolve such a problem, recent die development efforts resulted in an introduction of a two-piece construction of the core section that includes the protrusion section
34
at the tip of the male die
31
as indicated by 2-dot line in
FIG. 17
, for example. A core
31
a
is made separately of a wear resistant hard metal, and the other part of the male die body
31
b
is made of a regular die steel (refer, for example, to a Japanese Patent Application, First Publication, No. Hei 9-155438).
However, in the above process of making separate members, i.e., male die body
31
b
and a core
31
a
made of a hard metal or a high-speed steel, a difficulty is experienced in making the protrusion sections
34
at the tip of the core
31
a
shown in FIG.
21
. This is because the hardness of the material itself is very high and high dimensional accuracy is required in making such fine parts, such parts can only be made currently by a normal discharge machining process using electrode plates or wire electrical discharge machining.
A disadvantage of such machining processes based on normal discharge machining based on electrode plates or wires is that because the core
31
a is made of a hard metal or high-speed alloys of very high hardness, although wear resistance is improved to a degree, the fabricated product is extremely vulnerable to chipping of the protrusion section
34
.
The present inventors have undertaken detailed study of the protrusion section
34
of the core
31
a
made by the normal discharge machining or wire electrical discharge machining using scanning electron microscope. It was found that a molten abnormal layer that contains bumpy surface irregularities is formed on the surface of the protrusion section
34
, and surface chipping and micro-flaking at the edge portion of the protrusion section
34
are experienced. It was thought that these are one of the reasons for making the protrusion section
34
susceptible to breakage.
That is, the nature of discharge machining is such that an electrode (plate, wire and the like) is positioned at a distance from an obje

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