U.S. patent application number 14/739748 was filed with the patent office on 2015-10-08 for elbow formed by cutting and method for manufacturing same.
The applicant listed for this patent is Keiko HORIGUCHI, Noda Kanagata Co., Ltd.. Invention is credited to Nobuo HORIGUCHI.
Application Number | 20150285422 14/739748 |
Document ID | / |
Family ID | 45401519 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150285422 |
Kind Code |
A1 |
HORIGUCHI; Nobuo |
October 8, 2015 |
ELBOW FORMED BY CUTTING AND METHOD FOR MANUFACTURING SAME
Abstract
A hole is formed in an elbow through the steps of: forming a
starting hole in a material, the starting hole having an undercut
remaining on a hole surface; finishing an inner diameter of the
starting hole (11.sub.-3) on one end side by revolving aside cutter
(II) including an arc-shaped cutting edge and having an outer
diameter smaller than a finishing hole diameter while rotating the
side cutter (II) in such a posture that the side cutter (II) is
inclined in a predetermined direction relative to the material
(12), the revolving being carried out so that the side cutter moves
along a hole surface to be finished; and finishing the inner
diameter of the starting hole (11.sub.-3) on another end side by
revolving the side cutter (II) while rotating the side cutter
(II).
Inventors: |
HORIGUCHI; Nobuo; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HORIGUCHI; Keiko
Noda Kanagata Co., Ltd. |
Osaka
Osaka |
|
JP
JP |
|
|
Family ID: |
45401519 |
Appl. No.: |
14/739748 |
Filed: |
June 15, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13807282 |
Dec 27, 2012 |
|
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PCT/JP2010/060985 |
Jun 28, 2010 |
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14739748 |
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Current U.S.
Class: |
285/179 |
Current CPC
Class: |
B23C 5/08 20130101; B23C
2222/88 20130101; Y10T 409/303808 20150115; B23C 2265/40 20130101;
B23C 3/16 20130101; B23C 2220/04 20130101; B23C 5/109 20130101;
F16L 43/001 20130101; B23C 2222/84 20130101; B23C 2220/52
20130101 |
International
Class: |
F16L 43/00 20060101
F16L043/00 |
Claims
1. An elbow, comprising a hole having an center axis that is bent
smoothly at a predetermined curvature, the hole having no machining
remainder part inside and being a true circle, the hole having a
hole surface provided in parallel to the center axis of the elbow,
the elbow having a uniform wall thickness around a tube.
2. An elbow, comprising a hole having an center axis bent smoothly
at a predetermined curvature, the hole having no machining
remainder part inside and being a true circle, the hole having a
hole surface provided in parallel to the center axis of the elbow,
the hole of the elbow having a center eccentrically located with
respect to a center of an outer diameter of the elbow so that a
tube wall thickness on an outer side of a bend is larger than a
tube wall thickness on an inner side of the bend.
3. The elbow according to claim 2, wherein the outer side of the
bend is located at a position separated by 180.degree. from a
position of the inner side of the bend.
4. The elbow according to claim 2, wherein the tube wall thickness
is gradually increased from the inner side toward the outer side of
the bend.
5. The elbow according to claim 2, wherein the tube wall thickness
on the outer side of the bend is larger than the tube wall
thickness on the inner side of the bend.
6. The elbow according to claim 1, wherein the hole has the center
axis that is bent smoothly at the predetermined curvature, the hole
having no machining remainder part inside and being the true
circle, the hole having the hole surface provided in parallel to
the center axis of the elbow, the elbow comprising a straight part
on at least one end side of the elbow.
7. The elbow according to claim 1, further comprising flanges at
both end portions of the elbow, the flanges being integrally formed
with the elbow.
Description
[0001] This application is a Divisional of U.S. patent application
Ser. No. 13/807,282, which is a National Stage entry dated Dec. 27,
2012 under 35 USC .sctn.371 of International Application
PCTJP2010060985, which was filed on Jun. 28, 2010, the contents of
which are herein incorporated by reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to an elbow formed by cutting
(bent pipe) for a pipe and a method of manufacturing the same.
BACKGROUND ART
[0003] As examples of metallic elbows for a pipe, there are known a
casted elbow formed with a die, an elbow formed by bending a
straight pipe, a welded elbow formed by integrally but-welding two
halved bent pipe materials obtained by pressing a metal plate, and
a machined elbow formed by cutting a metal material.
[0004] Of those, the machined elbow is given in, for example,
Patent Literature 2 below. Further, Patent Literature 1 below
describes the elbow formed by bending and the welded elbow.
CITATION LIST
Patent Literature
[0005] [PTL 1] JP 7-41315 B
[0006] [PTL 2] JP 2000-343136 A (JP 3352052 B2)
SUMMARY OF INVENTION
Technical Problem
[0007] In the conventional machined elbow, an internal flow path is
formed by forming holes in a material from two directions, and then
intersecting the two holes inside. Therefore, for example,
regarding a 90.degree. elbow, the internal flow path forms
substantially a right angle, and hence there is a disadvantage in
that the flow path resistance becomes larger when the elbow is used
as a part of a pipe. This disadvantage is pointed out in paragraph
0009 of Patent Literature 2.
[0008] The problem of the flow path resistance can be solved by
forming a gently-bent hole. However, it has been considered that it
is impossible to form a machined elbow having a hole of such a
shape, in particular, an elbow having a bent angle of 90.degree. or
more and employing, as a material, a low machinability material
such as stainless steel (SUS), a titanium-based material, a
nickel-based heat-resistant alloy (an alloy that is nickel-based
and added with an alloy element such as iron, chromium, niobium,
and molybdenum: for example, product name: Inconel, produced by
Special Metals Corporation), even with use of 5-axis machines and
multi-axis machines using the latest technologies.
[0009] With use of a processing machine having the latest
functions, a bent hole can be processed to a certain degree.
However, in a general processing method, an undercut (machining
remainder part) that cannot be processed is formed on the hole
surface in a part which corresponds to the inner side of the bend,
and this part deteriorates the fluid flow. Thus, a product is not
suitable for practical use. Therefore, as an elbow of this field,
there has been employed an elbow manufactured by any one of
casting, bending, and welding.
[0010] However, in the casted elbow, a defect such as a blow hole
is easily generated, and it is difficult to secure reliability in
terms of quality. In addition, the casted elbow has a lower
rigidity than other elbows.
[0011] Further, in the elbow formed by bending, the wall thickness
and strength in respective parts are not uniform. The wall
thickness and strength of the tube tend to reduce on the outer side
of the bend, which rather requires larger wall thickness and
strength than the inner side of the bend. Thus, the sectional shape
of the pipe cannot be formed with high accuracy.
[0012] Further, in the welded elbow, a material texture at the
welding joint part may change to the one which easily causes a
stress corrosion crack, and a large strain is unavoidable as well
due to welding.
[0013] For example, a pipe for airplane engines and a pipe for
nuclear related facilities are required to clear very strict
conditions. In such applications, there has been long-awaited an
elbow having high quality, high accuracy, and low flow path
resistance.
[0014] The machined elbow is a product obtained by integrally
processing an ingot metal. The machined elbow is generated without
cavities, welding defects, and strains, and hence has excellent
reliability in terms of quality. With use of a highly accurate
processing machine, it is also possible to improve the dimension
accuracy and the shape accuracy. If the hole of the machined elbow
can be satisfactorily processed, a problem of the flow path
resistance, which is the weak point of the machined elbow, is
eliminated, and it is possible to realize a metallic elbow which
satisfies the demands of high quality, high accuracy, and low flow
path resistance.
[0015] In view of this, one or more embodiments of the present
invention has an object to enable manufacturing of an elbow by
machining so that the elbow has no unnecessary thickness inside,
has a circular shape in a cross-section perpendicular to its axis
in each axial part, and has a hole including a hole surface that is
gently bent along an center axis. Further, one or more embodiments
of the present invention has an object to provide an elbow that can
be obtained by the above-mentioned method.
Solution to Problem
[0016] In order to solve the above-mentioned problem, the present
invention provides a method of manufacturing an elbow by machining,
comprising forming a hole in a material to be formed into the
elbow, said forming of the hole comprising forming a starting hole
in the material by rough cutting of the material from two
directions with a rotary cutting tool, the starting hole having an
undercut remaining at least on a hole surface on a side which
corresponds to an inner side of a bend of the elbow as a finished
product, finishing a radially inner surface of the starting hole on
one end side using a side cutter including an arc-shaped cutting
edge at an outer periphery thereof and having an outer diameter
smaller than a finished hole diameter, wherein the side cutter is
inclined at a predetermined angle (.theta.4) relative to the
material such that an end surface of the side cutter is more remote
from an opening of the starting hole on the inner side of the bend
of the elbow to be cut, and is cut into the surface of the starting
hole, while simultaneously revolving the side cutter and rotating
the side cutter about a center axis of the side cutter, such that
the hole has a completely circular cross section taken along a
plane perpendicular a center axis of the hole and perpendicular the
center axis of the side cutter, and an oval cross-section taken
along any plane perpendicular to the center axis of the hole and
not perpendicular to the center axis of the side cutter, whereby
the side cutter moves along the surface of the hole, and finishing
the radially inner surface of the starting hole on another end side
by inserting the side cutter into the starting hole from the
another end side of the starting hole, and revolving the side
cutter along the hole surface to be finished while rotating the
side cutter.
[0017] When the starting hole is subjected to finishing, the side
cutter is revolved along a trajectory of a shape similar to a cut
end shape of the hole in each axial part when the hole to be
finished is cut perpendicularly to the center axis of the side
cutter (the cut end shape becomes a true circle at a position at
which the cross-section perpendicular to the axis of the hole of
the elbow is parallel to a plane orthogonal to the center axis of
the cutter, and becomes an ellipse at other positions). A main
shaft of the processing machine is moved in accordance with a
preset control program to enable this revolution.
[0018] When the machining allowance of the side cutter is large,
the processing is performed several times.
[0019] Regarding the relative inclination angle between the
material and the side cutter in the finishing of the starting hole,
for example, when a relative inclination angle of about 25.degree.
is secured, the undercut remaining in the starting hole can be
completely removed.
[0020] Further, in this method, it is preferred that processing of
the starting hole be carried out using a milling cutter including
an arc-shaped cutting edge at a leading end outer periphery thereof
and having an outer diameter smaller than an inner diameter of the
starting hole, the processing of the starting hole being carried
out through the steps of: forming a through hole by causing the
milling cutter to cut into each of adjacent two surfaces of the
material while changing a cutting position and a cutting depth, the
through hole having the undercut intersecting at an angle equal or
nearly equal to a bent angle of the elbow on the inner side of the
bend of the elbow, the through hole being shaped substantially
along the hole surface of the hole of the elbow on an outer side of
the bend of the elbow; and reducing a remaining amount of the
undercut by inclining the milling cutter in a direction in which a
leading end of the milling cutter comes near the inner side of the
bend of the elbow to cut off the undercut, the cutting off the
undercut being repeated several times while changing a inclination
angle of the milling cutter.
[0021] The outer diameter processing of the elbow in this method
can be performed by a method of sequentially performing roughing by
a face milling cutter and the like and finishing by a ball end mill
and the like. This outer diameter processing is preferred to be
performed after the hole is formed, but can be performed before the
hole is formed.
[0022] Note that, one or more embodiments of the present invention
is particularly effective to be applied to manufacturing of a
special elbow having a bent angle of 90.degree. or more, which has
particular difficulty in processing, but can be applied to
manufacturing of an elbow having a bent angle of 90.degree. or
less.
[0023] Further, one or more embodiments of the present invention is
expected to have a particularly significant effect in a case where
the material for the machined elbow is a metal, in particular, a
low machinability material such as SUS as described above, but one
or more embodiments of the present invention exerts its
effectiveness even when a general metal such as iron or a resin is
used as the material. For example, when an occasion arises where a
small number of large-diameter special resin elbows need to be
produced, the die cost is high if molding is performed. In such an
occasion, it is economically effective to machine a resin material
block to obtain an elbow having a required shape and size.
[0024] Moreover, in one or more embodiments of the present
invention, an integrated elbow is formed by machining the material,
and hence the hole of the elbow can be eccentrically located in an
arbitrary direction with respect to the outer diameter of the elbow
by design, or flanges for connection can be formed integrally at
end portions of the tube.
[0025] In the manufacturing method of one or more embodiments of
the present invention, until the relative inclination angle between
the side cutter and the material reaches the allowance upper limit,
processing is performed while inclining the side cutter and the
material relative to each other in accordance with the hole bent
state at the position at which the hole of the elbow is bent. Then,
from the position at which the relative inclination angle between
the side cutter and the material reaches the allowance upper limit,
the relative inclination angle is fixed. With the above-mentioned
method, the inner diameter on the one end side can be finished.
[0026] Further, the side cutter and the milling cutter can be
inclined relative to the material by any one of a method of moving
the material under a state in which the cutter is fixed, and a
method of moving the cutter with respect to the material.
[0027] For example, the material may be inclined relative to the
milling cutter and the side cutter in a necessary direction by
employing a method of setting the material on a rotary table having
a rotation indexing function under a state in which a center of the
hole of the elbow to be machined is placed on a plane parallel to a
table surface of the rotary table, and rotating the rotary
table.
[0028] According to another aspect of the present invention, the
elbow includes a hole having an center axis bent smoothly at a
predetermined curvature. In this elbow, the hole has no machining
remainder part inside and is a true circle. Further, the hole has a
hole surface provided in parallel to the center axis of the elbow.
In this case, the wall thickness may be uniform around the tube, or
a center of the hole of the elbow may be eccentrically located with
respect to a center of an outer diameter of the elbow so that the
tube wall thickness on the outer side of the bend is larger than
the tube wall thickness on the inner side of the bend.
[0029] It is preferred that the outer side of the bend be located
at a position separated by 180.degree. from a position of the inner
side of the bend.
[0030] Further, it is preferred that the tube wall thickness be
gradually increased from the inner side toward the outer side of
the bend.
[0031] The tube wall thickness on the outer side of the bend may be
larger than the tube wall thickness on the inner side of the bend,
and may be more than twice the tube wall thickness on the inner
side of the bend.
[0032] Further, the elbow may include a straight part on at least
one end side of the elbow, and the elbow may include flanges formed
integrally at both end portions of the elbow.
Advantageous Effects of Invention
[0033] The method according to one or more embodiments of the
present invention has the following features. That is, the starting
hole formed by roughing the material is subjected to finishing with
use of a side cutter including an arc-shaped cutting edge and
having an outer diameter smaller than a finishing hole diameter. In
addition, at this time, the side cutter is revolved and moved on a
spiral trajectory while being rotated in a posture inclined
relative to the material in a direction in which the end surface of
the cutter is separated from the opening of the starting hole on
the inner side of the bend of the elbow.
[0034] The starting hole processing of the material can be
performed by a known method, but in the conventional processing
method, there is generated an undercut that cannot be processed on
the hole surface on the inner side of the bend of the elbow. The
undercut is cut off with use of aside cutter including an
arc-shaped cutting edge.
[0035] A hole of a true circle can be formed relatively easily by
the following method. That is, in order that the side cutter is
revolved in a plane substantially perpendicular to the center axis
of the hole of the elbow, while inclining the side cutter and the
material relative to each other in accordance with the hole bent
state at the position at which the hole of the elbow is bent, the
side cutter is fed to finish the inner diameter of the hole of the
elbow. However, for example, when a 90.degree. elbow is to be
manufactured by this method, it is necessary to incline the side
cutter and the material relative to each other by 45.degree. at
maximum. In this state, interference between those members is
unavoidable.
[0036] In one or more embodiments of the present invention, in
order to avoid this problem, the relative inclination angle between
the side cutter and the material is set to a small value (an angle
in which interference between those members does not occur even
when the starting hole is processed halfway in the axial
direction). This angle changes depending on the diameter difference
between the inner diameter of the hole of the elbow and an outer
diameter of an arbor holding the side cutter. It is impossible to
secure an inclination angle of 45.degree. in the manufacturing of
the 90.degree. elbow, and hence the inclination angle is set to
about 25.degree., for example.
[0037] Now, supposing that the side cutter is inclined at
25.degree. relative to the material, when the hole to be finished
of the elbow is cut at each axial part along a plane parallel to
the end surface of the inclined side cutter, which is perpendicular
to its axis, the cut end of the hole becomes an ellipse at most
positions. The shape and size of the ellipse differ in each part of
the cutting point, but by moving the cutter along the cut end shape
at each part of the cutting point, the undercut remaining on the
starting hole is perfectly removed, the hole of the elbow becomes a
true circle in each axial part in a cross-section perpendicular to
the axis, and further, the hole surface is finished to have a shape
gently bent in parallel to the center axis.
[0038] Note that, in order to enable hole finishing by the method
according to one or more embodiments of the present invention,
there is used a side cutter having an outer diameter smaller than
the diameter of the hole of the elbow. Further, as the diameter
difference between the finishing diameter of the hole of the elbow
and the outer diameter of the arbor supporting the side cutter (the
arbor naturally has a diameter smaller than that of the side
cutter) becomes larger, the allowance angle of the relative
inclination between the side cutter and the material becomes
larger, and thus the processable range from the one end side of the
hole expands. However, when the outer diameter of the arbor becomes
too small, the tool rigidity reduces, and thus chattering of the
cutter is liable to occur during processing. This adversely affects
the processing stability and processing accuracy, and hence the
outer diameter of the arbor is set considering this point.
[0039] Further, the entire region of the hole of the elbow cannot
be finished by the processing of the starting hole from the one end
side, and hence the starting hole is processed also from the other
end side to finish the starting hole.
[0040] As described above, according to one or more embodiments of
the present invention, a side cutter including an arc-shaped edge
is used to perform finishing of the starting hole while revolving
the side cutter on the ellipse trajectory. In this manner, it is
possible to manufacture a machined elbow having a circular
cross-section and a gently-bent hole, which has been previously
thought to be impossible.
[0041] Note that, the inventor of the present invention has proved
this point by passing, through a 90.degree. elbow, a ball smaller
by 0.2% than the diameter of the elbow without clogging. Note that,
actually, the inner diameter dimension is 50. 9 mm, the ball
diameter is 50. 8 mm, and the material of the ball is zircon.
[0042] Further, machining is employed, and hence it is possible to
manufacture an elbow in which the hole of the elbow is
eccentrically located with respect to the outer diameter of the
elbow to increase the tube wall thickness and strength on the outer
side of the bend, an elbow including a straight part on at least
one end thereof, and an elbow in which flanges for connection are
integrally formed at both ends.
BRIEF DESCRIPTION OF DRAWINGS
[0043] FIG. 1A A perspective view illustrating an example of a
machined elbow manufactured by a method according to the present
invention.
[0044] FIG. 1B A view of the elbow of FIG. 1A in a cross-section
perpendicular to its axis.
[0045] FIG. 2A A perspective view illustrating a half of an elbow
machining region of a material.
[0046] FIG. 2B A plan view of the half machining region of FIG.
2A.
[0047] FIG. 3A A view illustrating a step of a former stage of
starting hole processing.
[0048] FIG. 3B A view illustrating a step of the former stage of
starting hole processing.
[0049] FIG. 3C A view illustrating a step of the former stage of
starting hole processing.
[0050] FIG. 3D A view illustrating a step of the former stage of
starting hole processing.
[0051] FIG. 4A A view illustrating a step of a latter stage of
starting hole processing.
[0052] FIG. 4B A view illustrating a step of the latter stage of
starting hole processing.
[0053] FIG. 4C A view illustrating a step of the latter stage of
starting hole processing.
[0054] FIG. 4D A view illustrating a step of the latter stage of
starting hole processing.
[0055] FIG. 4E A view illustrating a step of the latter stage of
starting hole processing.
[0056] FIG. 5A A view illustrating postures of the material and a
side cutter when one end side of the starting hole is finished.
[0057] FIG. 5B A perspective view illustrating a half of the
starting hole whose one end side is finished.
[0058] FIG. 6A A view illustrating revolution movement of the side
cutter in the finishing of the one end side of the starting
hole.
[0059] FIG. 6B A view illustrating the revolution movement of the
side cutter in the finishing of the one end side of the starting
hole.
[0060] FIG. 6C A view illustrating the revolution movement of the
side cutter in the finishing of the one end side of the starting
hole.
[0061] FIG. 6D A view of the revolution movement of the side cutter
when viewed from above correspondingly to FIGS. 6A to 6C.
[0062] FIG. 6E A view of the revolution movement of the side cutter
when viewed from above correspondingly to FIGS. 6A to 6C.
[0063] FIG. 6F A view of the revolution movement of the side cutter
when viewed from above correspondingly to FIGS. 6A to 6C.
[0064] FIG. 7A A perspective view illustrating an unfinished state
of the other end side of the starting hole.
[0065] FIG. 7B A perspective view illustrating a finished state of
the other end side of the starting hole.
[0066] FIG. 8A A perspective view illustrating another example of
the machined elbow manufactured by the method according to the
invention.
[0067] FIG. 8B A view of the elbow of FIG. 8A in a cross-section
perpendicular to its axis.
[0068] FIG. 8C A view of the elbow of FIG. 8A in a cross-section
horizontal to its axis.
[0069] FIG. 9 A perspective view illustrating still another example
of the machined elbow manufactured by the method according to the
present invention.
[0070] FIG. 10 A perspective view illustrating further another
example of the machined elbow manufactured by the method according
to the present invention.
[0071] FIG. 11A A perspective view illustrating an example of a
rotary cutting tool for use in roughing of a hole and an outer
diameter in the method according to the present invention, under a
state in which the rotary cutting tool is mounted on an arbor.
[0072] FIG. 11B A side view of the cutting tool of FIG. 11A.
[0073] FIG. 12A A perspective view illustrating an example of a
side cutter for use in finishing of the hole in the method
according to the present invention.
[0074] FIG. 12B A side view of the above-mentioned cutter under a
state in which the cutter is mounted on an arbor.
[0075] FIG. 13 A side view illustrating an example of a ball end
mill for use in finishing of the outer diameter in the method
according to the present invention.
DESCRIPTION OF EMBODIMENTS
[0076] Now with reference to the attached drawings, description is
made of a method of manufacturing an elbow by cutting, embodying
the present invention, and an elbow manufactured by this
method.
[0077] First, examples of rotary cutting tools used in the method
according the present invention are illustrated in FIGS. 11A to 13.
The cutting tool illustrated in FIGS. 11A and 11B is a
commercially-available indexable milling cutter (face milling
cutter) I including a plurality of arc-shaped cutting edges 2
circumferentially arranged at intervals around the leading end of
the cutter body 1. The milling cutter I is used to form a starting
hole in a material to be formed into the elbow and to roughly cut
the radially outer surface of elbow. To perform such rough cutting
with high efficiency, the milling cutter I shown, in which the
cutting edges 2 are formed by removable round inserts, are
preferably mounted on an arbor 3. But a milling cutter other than
the face milling cutter shown, such as a radius end mill or a ball
end mill, may be used instead.
[0078] FIGS. 12A and 12B illustrate a side cutter II including a
plurality of arc-shaped cutting edges 5 circumferentially arranged
at intervals around the cutter body 4. The side cutter II is used
to finish the starting hole formed in the material for the elbow.
The illustrated side cutter II is a cutter obtained by modifying a
commercially available cutter of which the cutting edges 5 are
formed by removable round inserts so that the cutter can be firmly
fixed to a specially ordered arbor 6. Specifically, the side cutter
II is mounted on the leading end of the arbor 6. The side cutter II
has an outer diameter smaller than the diameter of the starting
hole. The outer diameter of the arbor 6 is further smaller than the
outer diameter of the side cutter II.
[0079] FIG. 13 illustrates a commercially available indexable ball
end mill III. In the method embodying the invention, this indexable
ball end mill III or alternatively, a solid ball end mill is used
to finish the radially outer surface of the elbow.
[0080] An example of the machined elbow manufactured by the method
according to this invention is illustrated in FIGS. 1A and 1B. The
elbow 10 shown is a 90.degree. elbow without a flange, and includes
a hole 11 having a center axis bent smoothly at a predetermined
curvature.
[0081] Description is now given how the 90.degree. elbow 10 of
FIGS. 1A and 1B is manufactured using the above-mentioned cutting
tools as an example. Reference numeral 12 of FIGS. 2A and 2B is an
elbow material in the shape of a square block shape. For easy
understanding of the processing situation, section views are
illustrated in a manner that the material 12 is cut into half, and
the cutter is illustrated in a simplified manner.
[0082] The material 12 is placed on a rotary table (not shown) of a
processing machine such that the center axis O of the hole of the
elbow 10 formed is on a plane parallel to the surface of the rotary
table (the table surface is perpendicular to the rotation axis of
the table). The cutter and the material 12 are inclined relative to
each other as described later by rotating the rotary table.
[0083] The milling cutter I is set on the main shaft (not shown) of
the processing machine, and as illustrated in FIG. 3A, the milling
cutter I is fed in the axial direction so as to cut into an A
surface of the material 12 while changing the cutting position and
the cutting depth. In this manner, a blind hole 11.sub.-1 is formed
as illustrated in FIG. 3B, which has a small undercut on the hole
surface on the outer side of the bend.
[0084] Next, as illustrated in FIGS. 3C and 3D, the material 12 is
positioned such that its B surface which is orthogonal to the A
surface faces the milling cutter I. In this state, in the same
manner as the hole is formed in the A surface with the milling
cutter I, the milling cutter I is fed in the axial direction so as
to cut into the B surface while changing the cutting position and
the cutting depth until the hole thus formed communicates with the
blind hole 11.sub.-1, thus forming a through hole 11.sub.-2 formed
with an undercut 13 swelled in the hole diameter direction on the
inner side of the bend.
[0085] Thus, in this state, the undercut 13 still remains in a
large amount. That is, the side cutter II of FIGS. 12A and 12B
cannot completely remove the undercut by finish cutting. To reduce
the undercut, with the material 12 inclined at .theta..degree. with
respect to the milling cutter I such that the leading end of the
cutter I is located nearer to the inner side of the bend of the
elbow as illustrated in FIG. 4A, the milling cutter I is fed in the
axial direction while changing the cutting position, to partially
remove the undercut 13.
[0086] This operation is repeated several times while gradually
increasing the relative inclination angle between the milling
cutter I and the material 12, to thereby sufficiently reduce the
remaining amount of the undercut 13. The relative inclination angle
between the material 12 and the milling cutter I in this processing
is set in accordance with the type of the material so that an
excess cutting load is not imparted to the cutter. In an evaluation
test, .theta. of FIG. 4A is set to 15.degree., .theta.1 of FIG. 4B
is set to 25.degree., .theta.2 of FIG. 4C is set to 35.degree., and
.theta.3 of FIG. 4D is set to 45.degree., but the angles are not
limited thereto.
[0087] The undercut 13 may be removed by feeding the cutter from
both ends of the through hole 11.sub.-2. But in many cases, the
undercut 13 can be removed sufficiently by feeding the cutter from
one end only of the through hole 11.sub.-2. This reduces the number
of times the cutter is fed into the hole.
[0088] At the end of these steps, a starting hole 11.sub.-3 as
illustrated in FIG. 4E is formed in the material 12. Then, the tool
mounted on the main shaft of the processing machine is replaced
with the side cutter II of FIGS. 12A and 12B, and the side cutter
II is used to finish the starting the starting hole 11.sub.-3.
[0089] The finishing is performed as follows. With the side cutter
II inclined at an angle of .theta.4 relative to the material 12
such that the end surface of the side cutter II is more remote from
the opening of the starting hole 11.sub.-3 on the inner side of the
bend of the elbow 10 to be cut, as illustrated in FIG. 5A, the side
cutter II is revolved while being rotated about its axis so that
the side cutter II cuts into the hole surface of the starting hole
11.sub.-3. At this time, the side cutter II is revolved so that the
cutter moves on a helical trajectory along a hole surface to be
finished. In this case, it is conceived that the relative
inclination angle .theta.4 between the side cutter II and the
material is always constant. But this is not an essential
requirement.
[0090] FIGS. 6A to 6F are views illustrating a state in which the
side cutter II is revolved in the counterclockwise direction while
being rotated about its axis and fed in the axial direction. Since
the side cutter II is fed in the axial direction while being
revolved, side cutter II moves on a helical trajectory.
[0091] The hole 11 of the elbow 10 has such a shape that it has a
completely circular cross-section when taken along a line
perpendicular to the center axis of the hole 11 of the elbow 10
before being finished and parallel to the end surface of the side
cutter, which is perpendicular to the center axis of the side
cutter II and inclined at an angle of .theta.4 relative to the
material 12 (i.e. when taken along the line Y-Y of FIG. 5A), while
all the other cross-sections parallel to the end surface of the
side cutter, including the cross-sections taken along lines X-X and
Z-Z of FIG. 5A are oval. Any of such oval cross-sections is
different in size and shape from all the other such oval
cross-sections. The side cutter II is moved while being revolved
along the hole surface to be finished, which has the
above-mentioned cross-sectional shapes.
[0092] In this case, the finishing at the position exceeding the
line Z-Z (the other end side of the hole) is performed so that the
cutter is moved along the hole cross-section only on the outer side
of the bend of the hole, to thereby prevent the arbor 6 from
interfering with the material. In the finishing of the starting
hole from the one end, only a half of the hole is required to be
processed. Therefore, the cutter does not need to be forcedly moved
along the hole cross-section on the inner side of the bend.
[0093] If a large amount of material has to be removed during
finish cutting, the finish cutting may be performed several times
to reduce the cutting load per one time. Through adoption of a
method in which the machining remainder part is gradually cut off
in several times to finish the product to have a target inner
diameter in the final processing, excess cutting load is not
imparted, and processing stability and processing accuracy are
improved.
[0094] With the processing using the side cutter subjected to
movement control, the undercut remaining in the starting hole
11.sub.-3 is largely removed, and thus the inner diameter of the
starting hole on the one end side is finished.
[0095] In the processing of the starting hole from the one end,
there is a processing restriction due to the hole shape, and hence
it is impossible to finish the entire region of the starting hole
as in FIG. 5B. Therefore, subsequently, the starting hole 11.sub.-3
is processed also from the other end to finish the hole. The side
cutter II is arranged on the other end of the starting hole
11.sub.-3 as illustrated in FIG. 7A, and an operation similar to
that described above is performed (the movement control in the same
conditions as above is not necessary), and thus the remaining part
of the undercut 13 is cut off.
[0096] In this manner, the hole 11 of the elbow has such a shape
that its cross-sections taken along any plane perpendicular to the
axis of the hole 11 is a true circle, with the hole surface
moderately bent in parallel to its center axis.
[0097] After finishing the hole 11 in this manner, the radially
outer surface of the elbow is subjected to rough cutting using the
milling cutter I of FIGS. 11A and 11B, and then finished using the
ball end mill III of FIG. 13. The desired elbow is thus
completed.
[0098] The radially outer surface of the elbow is preferably
finished after forming the hole because with this arrangement, the
material can be held in position more stably while forming the hole
and because there is no possibility of damaging the finished
radially outer surface when forming the hole. But the radially
outer surface may be finished before forming the hole.
[0099] The milling cutter I or the side cutter II may be inclined
relative to the material 12 by inclining the main shaft of the
processing machine on which the cutter is mounted.
[0100] Although the control of the processing machine becomes a
little complicated, the object of the invention can be also
achieved by performing the finishing step of the radially inner
surface of the starting hole 11.sub.-3 on the one end as follows.
The side cutter II is revolved while being rotated about its axis
to cut into the starting hole 11.sub.-3, and while inclining the
side cutter II and the material 12 relative to each other in
accordance with the hole bent state at a position at which the hole
11 of the elbow is bent so that the movement of the side cutter II
is performed in a plane substantially perpendicular to the center
axis of the hole to be provided in the elbow as a finished product,
the inner diameter of the starting hole 11.sub.-3 on the one end
side is processed halfway from the one end toward the other end of
the hole. Then, from the position at which the relative inclination
angle between the side cutter II and the material 12 reaches an
allowance upper limit, the relative inclination angle is fixed.
[0101] Since the method according to the present invention employs
machining, it is possible to manufacture an elbow 10 as illustrated
in FIGS. 8A to 8C, in which the center O.sub.1 of the hole 11 of
the elbow is eccentrically located with respect to the center
O.sub.2 of the radially outer surface of the elbow to increase the
wall thickness and strength of the elbow on the outer side of the
bend.
[0102] FIG. 8A is a perspective view of this elbow 10, FIG. 8B is a
sectional view of the elbow 10 when viewed from the direction
indicated by the arrow B-B in FIG. 8A, and FIG. 8C is a sectional
view of a part indicated by the arrow C-C of FIG. 8A.
[0103] In such an elbow 10, as illustrated in FIG. 8B, by adjusting
the eccentricity amount between the center O.sub.1 of the hole 11
of the elbow and the outer diameter center O.sub.2 of the elbow,
the wall thickness of the elbow on the outer side can be set to a
dimension corresponding to the strength to be required.
[0104] Cracks may develop in the flank of the elbow due to
vibration load. Cracks tend to develop in an area indicated by the
dashed-dotted line in FIG. 8A. The elbow of this embodiment can
have a desired wall thickness at its flank, and hence exerts a
significant effect even against vibration cracks as described
above.
[0105] In FIG. 8B, the center O.sub.1 of the hole 11 of the elbow
is eccentrically located on the diameter of the elbow 10, but the
present invention is not limited thereto, and the center O.sub.1
may be eccentrically located at any point other than on the
diameter of the elbow 10.
[0106] According to this embodiment, it is possible to manufacture
an elbow as illustrated in FIG. 9, which includes a straight part
14 on at least one end portion, or an elbow as illustrated in FIG.
10, in which flanges 15 for connection are integrally formed at
both ends.
[0107] In this case, it is preferred that the outer side of the
bend be located at a position separated by 180.degree. from the
position of the inner side of the bend, and the wall thickness be
gradually increased from the inner side toward the outer side of
the bend.
[0108] On the other hand, it is possible to increase or decrease
the wall thickness of a desired part as necessary to any desired
thickness.
[0109] In the aviation industry and the like, development of an
"ultra-thin elbow" called a "duct" has been long awaited.
Conventionally, a product has been formed by bending and welding an
iron plate or the like. However, the thickness is as ultra-thin as
1.0 mm or less, and hence a uniform product cannot be formed due to
the unevenness of the thickness during pressing. Further, the
product is made of an extremely low machinability material such as
titanium and Inconel, and hence studies have not been carried
out.
[0110] In contrast, according to the invention, even with such
materials, it is possible to process a thin elbow having an inner
diameter of 2 inches to 5 inches and a wall thickness of 0.8 mm to
1.5 mm.
[0111] Also in this case, the wall thickness can be set arbitrarily
as described above on the outer side and on the inner side.
EXAMPLES
[0112] A 90.degree. elbow having an inner diameter of 190 mm, a
center bend radius of .phi.200 mm, and a wall thickness of 10 mm
was experimentally produced by the method according to the present
invention. As the material for the elbow, wood was used because
this was a test for verifying the processing method.
[0113] The following rotary cutting tools were used. As the milling
cutter I of FIGS. 11A and 11B, there was used a round-insert
mounting indexable face milling cutter having an outer diameter of
50 mm, a radius of curvature of the arc-shaped cutting edges of 8
mm, and the number of the cutting edges of 4. As the side cutter II
of FIGS. 12A and 12B, there was used a round-insert mounting
indexable side milling cutter having an outer diameter of 127 mm, a
radius of curvature of the arc-shaped cutting edges of 6 mm, and
the number of the cutting edges of 5. As the ball end mill III of
FIG. 13, there was used a ball end mill having an outer diameter of
30 mm.
[0114] As the processing machine, there was used a CNC horizontal
boring machine owned by the applicant. This CNC horizontal boring
machine includes a world's most advanced rotary table having a
divided indexing accuracy of 1/10000 degrees. The material was set
to this rotary table, and the material and the cutter were inclined
relative to each other by a method of controlling the rotary
table.
[0115] The processing was performed along the procedures described
with reference to FIGS. 3A to 7B. The finishing of the starting
hole by the side cutter was performed by adopting a method in which
the cutting region remaining uncut was processed on a 2 mm basis to
finally finish with no machining remainder. As a result, it was
possible to obtain a machined elbow in which no machining remainder
part was present inside the hole, the hole was a true circle and
the hole surface was parallel to the center axis of the elbow, and
further, the wall thickness around the tube (a wall thickness t of
each part of the circumferential cross-section illustrated in FIG.
1B) was uniform.
[0116] With use of a processing machine including a rotary table
having a highly-accurate indexing accuracy as described above, the
high-accuracy processing can also be performed without a problem by
such a method that, while inclining the side cutter and the
material relative to each other in accordance with the hole bent
state of the elbow so that the side cutter is halfway revolved in a
plane substantially perpendicular to the center axis of the hole to
be provided in the elbow as a finished product, the inner diameter
of the starting hole is subjected to finishing, and then, from a
position at which the relative inclination angle between the side
cutter and the material reaches an allowance upper limit, the side
cutter is revolved on the elliptical trajectory under a state in
which the relative inclination angle is fixed.
INDUSTRIAL APPLICABILITY
[0117] According to one or more embodiments of the present
invention, it is possible to manufacture, by machining, an elbow
which has no unnecessary thickness inside, has a circular shape in
a cross-section perpendicular to its axis in each axial part, and
further, has a hole including a hole surface gently bent along an
center axis. Thus, the method according to one or more embodiments
of the present invention can be advantageously used as a method of
manufacturing an elbow.
REFERENCE SIGNS LIST
[0118] I milling cutter, II side cutter, III ball end mill, 1, 4
cutter body, 2, 5 cutting edge, 3, 6 arbor, 10 elbow, 11 hole,
11.sub.-1 blind hole, 11.sub.-2 through hole, 11.sub.-3 starting
hole, 12 material, 13 undercut, 14 straight part, 15 flange, A, B
surface orthogonal to surface of material, t tube thickness.
* * * * *