Cutting – Other than completely through work thickness or through work... – Combined types of cutting
Reexamination Certificate
2001-09-12
2004-04-13
Shoap, Allan N. (Department: 3724)
Cutting
Other than completely through work thickness or through work...
Combined types of cutting
C083S030000, C083S039000, C083S054000, C083S682000, C072S325000
Reexamination Certificate
active
06718860
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for making holes (or punching) in a pipe and, in particular, to a method suitable for making narrow and elongate slits in a pipe, made of an aluminum alloy, or the like, of low rigidity and having an elliptical section, used for producing a header tank of a heat exchanger.
2. Description of the Related Art
In recent years, with the decrease in the sizes of air-conditioning systems and automotive heat exchangers, pairs of header tanks arranged on the vertical sides or lateral sides of the heat exchangers are made from a comparatively compact pipe having an elliptical section in place of a pipe having a circular section. In order to exchange heat between the header tanks and the atmospheric air by supplying a fluid like water or a refrigerant, the flat end portions of a multiplicity of core tubes are mounted on the header tanks. The portions of the header tanks where the core tubes are mounted are formed with slits by press-work. The flat ends of the tubes are inserted into these holes, and the gaps between the tubes and the holes are closed by brazing. In this case, the pipe having an elliptical section (hereinafter sometimes referred to as an elliptical pipe) making up each header tank cannot be easily formed with slits by pressing, in view of the fact that the pipe is made of such a soft and easily deformable material as an aluminum alloy and has a low rigidity due to the elliptical and flat section leading to a small section modulus, thereby posing the problem that the pipe is liable to be crushed under the load exerted when making holes.
In a method for coping with this problem, a pipe having an elliptical section making up a header tank is fabricated as a structure segmented into two longitudinal portions, and each of the two pipe portions is formed with slits by pressing, after which the two pipe portions are coupled with each other to complete a header tank. This method makes it easy to make slits. Nevertheless, the two or more portions making up each header tank are required to be fabricated separately from each other, and a process is required to couple the pipe portions mainly along a long longitudinal line. Further, the joints of the two pipe portions are always accompanied by the possibility of fluid leakage, and therefore the reliability of this segmented structure is lower than that of the integrated structure.
The method disclosed in Japanese Unexamined Patent Publication No. 4-327323 is known as a first conventional technique usable for fabricating a header tank of the heat exchanger having a multiplicity of slits. According to this technique, a long die and a long metal core for supporting the die are inserted into a pipe having a circular section to constitute a header tank, and a multiplicity of slits are made by pressing while preventing the pipe from being crushed. The work actually capable of being machined by this conventional method is limited to a pipe having a circular section and does not include a pipe having an elliptical section. The reason is that the internal space of the pipe having an elliptical section is so limited that a very thin die and a very thin metal core are required for insertion into such an internal space and it is difficult to secure the strength of the die and the metal core.
In view of this, Japanese Unexamined Patent Publication No. 60-72620 discloses a method, known as the second conventional technique, for making holes in a pipe by pressing without using a die or a metal core. In making circular holes in a pipe
8
having a circular section using this conventional technique, the first step, as shown in
FIGS. 2A and 2B
, is to form a groove
9
reducing the thickness of a part of the pipe
8
and then a circular hole is punched through, by a circular punch
10
, within the range of the groove
8
. According to the second conventional technique, the pipe
8
having a circular section has a comparatively high rigidity, and the area with a thickness reduced by the groove where a hole is made by the punch
10
is small. Therefore, the likelihood of completely making a hole is high before the pipe
8
is crushed and deformed. An attempt to make slits in a pipe material having an elliptical section by use of this conventional technique, however, would encounter the various problems described below and end in failure.
The first problem, which arises when attempting to make slits in a pipe having an elliptical section by use of the second conventional technique, is derived from the fact that the rigidity of the pipe having an elliptical section is lower than that of the pipe having a circular section. A simple application of the second conventional technique to the pipe having an elliptical section, therefore, would only deform the pipe and could not make slits as intended.
Specifically, as shown in
FIG. 3
, a groove
9
constituting a base for making slits in a pipe
1
having an elliptical section is formed along the long diameter on the substantially flat surface portion of the pipe having an elliptical section comparatively large in radius of curvature. At the same time, the horizontally long area of the groove
9
is struck vertically by a punch
12
having a uniformly long cutting edge normally used for punching a slit. In view of the fact that this portion of the elliptical pipe
1
has such a section modulus that the rigidity is small especially against the vertical load, the deformation &Dgr;d due to the load is increased and the pipe
1
is liable to be easily crushed with the result that slits cannot be made as intended.
To cope with this situation, a punch with a longitudinally slanted cutting edge is effectively used. A punch
13
having a V-shaped cutting edge as shown in
FIG. 4
is used, for example, and the cutting position is slowly moved along the direction of the cutting edge. In this way, the problem which otherwise might be caused by the whole length of the cutting edge acting on the surface of the pipe
1
is avoided thereby to reduce the amount of the load exerted vertically on the surface of
10
the material within a unit time. The cutting edge of the punch
13
shown in
FIG. 4
, which has an acute central peak and two ends formed at an obtuse angle &thgr;, is provided with right and left cutting edge portions in the shape of V. By using this punch
13
, therefore, the deformation &Dgr;d under the load is reduced as compared with the case of
FIG. 3
, and the pipe
1
can be prevented from being crushed. In this way, an intended slit
7
can be formed in the surface of the elliptical pipe
1
which is grooved appropriately.
The use of the punch
13
having a V-shaped cutting edge, however, as shown in
FIG. 4
, poses another problem that burrs
14
are formed at the ends of the slit
7
as shown and the periphery of the hole is slightly deformed, resulting in a deteriorated product quality.
This problem can be obviated by the using a special punch
5
which, as shown in
FIG. 5
, has a cutting edge with a recessed central portion and peaked ends formed at an acute angle &thgr; slanted in the shape of inverted V inward from the left and right ends toward the central portion thereof. The use of this punch
5
reduces the load exerted vertically on the surface of the work and thus reduces the deformation &Dgr;d. At the same time, there is a lower possibility of the burrs
14
being formed at the positions shown in
FIG. 4
or of the periphery of the hole being partially deformed, thereby making it possible to successfully form a slit
7
in the elliptical pipe
1
.
Nevertheless, a second problem posed by the second conventional technique used for making the slit
7
in the pipe
1
having an elliptical section is that the slit
7
is so narrow and elongated that a similarly narrow and elongate cutting chip generated as the slit
7
is made is not easily separated from the pipe
1
and may often partly remain attached on the periphery of the slit
7
. In the case where an inverted-V recessed punch
Ikeda Takao
Mitsukawa Kazuhiro
Yamada Kunio
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