U.S. patent application number 12/805168 was filed with the patent office on 2010-11-11 for friction stir welding tool and friction stir welding method.
This patent application is currently assigned to Showa Denko K.K.. Invention is credited to Yoshitaka Nagano.
Application Number | 20100282822 12/805168 |
Document ID | / |
Family ID | 38609143 |
Filed Date | 2010-11-11 |
United States Patent
Application |
20100282822 |
Kind Code |
A1 |
Nagano; Yoshitaka |
November 11, 2010 |
Friction stir welding tool and friction stir welding method
Abstract
A friction stir welding tool 1 includes a rotor 2 to be attached
to a rotation-drive section and a probe 3 concentrically provided
on a distal end surface of the rotor 2. A provisional joining
projection 4 is concentrically provided on a distal end surface of
the probe 3. A relation 0.3 D.ltoreq.d.ltoreq.0.8 D is satisfied,
where D represents a diameter (mm) of the distal end surface of the
probe 3, and d represents a diameter (mm) of the contour of a
transverse cross section of the provisional joining projection 4.
The provisional joining projection 4 has a length of 0.3 to 2 mm.
This friction stir welding tool can improve the work efficiency of
friction stir welding and can carry out friction stir welding which
is excellent in welding quality after main friction stir
welding.
Inventors: |
Nagano; Yoshitaka;
(Oyama-shi, JP) |
Correspondence
Address: |
Edwards Angell Palmer & Dodge LLP
P.O. Box 55874
Boston
MA
02205
US
|
Assignee: |
Showa Denko K.K.
Tokyo
JP
|
Family ID: |
38609143 |
Appl. No.: |
12/805168 |
Filed: |
July 15, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12224992 |
Sep 11, 2008 |
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PCT/JP2007/054968 |
Mar 13, 2007 |
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12805168 |
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Current U.S.
Class: |
228/2.1 |
Current CPC
Class: |
B23K 20/1255
20130101 |
Class at
Publication: |
228/2.1 |
International
Class: |
B23K 20/12 20060101
B23K020/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 16, 2006 |
JP |
2006-071983 |
Claims
1. A friction stir welding tool which includes a rotor to be
attached to a rotation-drive section and a probe concentrically
provided on a distal end surface of the rotor and which is used in
such a manner that the probe is plunged into a joint interface
between two workpieces while being rotated, and the two workpieces
and the probe are moved relative to each other to thereby
friction-stir-weld the two workpieces along the joint interface,
wherein a projection for provisional joining is concentrically
provided on a distal end surface of the probe, and a relation 0.3
D.ltoreq.d.ltoreq.0.8 D is satisfied, where D represents a diameter
(mm) of the distal end surface of the probe, and d represents a
diameter (mm) of the contour of a transverse cross section of the
projection for provisional joining.
2. The friction stir welding tool according to claim 1, wherein the
projection for provisional joining has a length of 0.3 to 2 mm.
3. The friction stir welding tool according to claim 1, wherein the
distal end surface of the probe is a flat surface or a
partial-spherical concave surface.
4. The friction stir welding tool according to claim 1, wherein the
probe has a cylindrical columnar shape.
5. The friction stir welding tool according to claim 1, wherein the
probe has a conical shape so that the diameter of the probe
decreases toward the distal end thereof.
6. The friction stir welding tool according to claim 1, wherein a
thread ridge is formed on an outer circumferential surface of the
probe, and is not formed on an outer circumferential surface of the
projection for provisional joining.
7. The friction stir welding tool according to claim 1, wherein a
distal end surface of the projection for provisional joining is a
partial-spherical convex surface.
8. The friction stir welding tool according to claim 1, wherein the
projection for provisional joining has a transverse cross section
of an irregular shape, and has, on its outer circumferential
surface, a plurality of partial cylindrical surfaces formed such
that the partial cylindrical surfaces are located in a common
cylindrical plane and separated from one another in the
circumferential direction.
9.-21. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to a friction stir welding
tool and a friction stir welding method.
BACKGROUND ART
[0002] In various industries such as the automobile industry, the
shipbuilding industry, and the aerospace industry, the friction
stir welding method, which is a solid-phase joining method, has
been widely used, by virtue of its advantage that deformation or
cracking caused by thermal strain is less likely to arise and the
joining strength increases, as compared with the case of a melt
welding process, such as TIG or MIG.
[0003] Incidentally, the friction stir welding method uses a
friction stir welding tool which includes a cylindrical columnar
rotor attached to a rotation-drive section, and a probe
concentrically provided on a distal end surface of the rotor. The
probe is plunged into a joint interface between two workpieces
while being rotated, and the probe and the two workpieces are
caused to undergo relative movement. Therefore, friction heat and
relatively large pressure are applied to the workpieces.
Accordingly, the workpieces move and deform at the time of joining,
possibly generating joining defects, such as an internal defect of
a joined portion and a form defect (e.g., misalignment). In order
to prevent generation of such joining defects, the workpieces must
be rigidly fixed during the joining.
[0004] However, a considerable difficulty arises when a base having
a circular recess and a circular cover fitted into the recess and
closing the opening of the recess are joined together by friction
stir welding. Specifically, for such joining, the base having a
circular recess is prepared along with the cover to be fitted into
the recess and to close the opening of the recess. A stepped
portion for receiving a circumferential edge portion of the cover
is formed on the inner circumferential surface of the recess at an
intermediate depth thereof. After the cover is fitted into the
recess such that the circumferential edge portion thereof rests on
the stepped portion of the recess, the base and the cover are
joined together by means of the friction stir welding along a joint
interface between a circumferential edge portion of the opening of
the recess of the base and the circumferential edge portion of the
cover. However, in such a case, it is extremely difficult to carry
out the friction stir welding over the entire joint interface in a
state where the base and the cover are firmly fixed.
[0005] In order to cope with the above problem, an improved method
has been proposed (see Patent Document 1). In this method, when a
cover is to be friction-stir-welded to a base as described above,
the cover is provisionally and partially joined to the base by a
general melt welding process or a friction stir welding
process.
[0006] However, in the case where the cover is provisionally joined
by a melt welding process according to the method disclosed in the
Patent Document 1, a completely different apparatus must be used
for such provisional joining, and the number of steps increases.
Therefore, the work of joining the cover to the base is
troublesome. Further, in the case where the cover is provisionally
joined to the base at several points by a melt welding process, a
blowhole, cracking, poor fusion, or a like defect is likely to
arise. In order to avoid occurrence of such defect, preflow,
treatment of craters, and the like must be sufficiently performed
before main joining. This leads to an increase in the number of
steps, thus impairing mass productivity.
[0007] Meanwhile, in the case where the cover is provisionally
joined by a friction stir welding process, such provisional joining
must be performed by use of a probe which is smaller in diameter
than a probe used for main friction stir welding. However, for such
provisional joining, the probe for provisional joining must be
attached to the rotation-drive section of a friction stir welding
apparatus so as to be replaced with the probe for main joining.
Such probe exchange work is troublesome.
[0008] The present applicant has proposed a friction stir welding
tool in which the probe is composed of a plurality of shaft
portions having different diameters such that the diameter of the
probe decreases stepwise toward the distal end thereof (see Patent
Document 2). However, the friction stir welding tool disclosed in
Patent Document 2 is designed to enable joining of a plurality of
workpieces which differ in thickness at respective portions to be
joined, and to secure a stable and high joining quality even when
thick members are welded together. Therefore, the diameter ratio
between the small diameter portion and the large diameter portion
of the probe is not optimal for carrying out both the provisional
friction stir welding and the main friction stir welding.
Patent Document 1: Japanese Patent Application Laid-Open (kokai)
No. 2002-248584 Patent Document 2: Japanese Patent Application
Laid-Open (kokai) No. 2000-246465
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0009] An object of the present invention is to solve the above
problems and to provide a friction stir welding tool and a friction
stir welding method which can improve the work efficiency of
friction stir welding and can carry out friction stir welding which
is excellent in welding quality after main friction stir
welding.
Means for Solving the Problems
[0010] To achieve the above object, the present invention comprises
the following modes.
[0011] 1) A friction stir welding tool which includes a rotor to be
attached to a rotation-drive section and a probe concentrically
provided on a distal end surface of the rotor and which is used in
such a manner that the probe is plunged into a joint interface
between two workpieces while being rotated, and the two workpieces
and the probe are moved relative to each other to thereby
friction-stir-weld the two workpieces along the joint interface,
wherein
[0012] a projection for provisional joining is concentrically
provided on a distal end surface of the probe, and a relation 0.3
D.ltoreq.d.ltoreq.0.8 D is satisfied, where D represents a diameter
(mm) of the distal end surface of the probe, and d represents a
diameter (mm) of the contour of a transverse cross section of the
projection for provisional joining.
[0013] 2) A friction stir welding tool according to par. 1),
wherein the projection for provisional joining has a length of 0.3
to 2 mm.
[0014] 3) A friction stir welding tool according to par. 1) or 2),
wherein the distal end surface of the probe is a flat surface or a
partial-spherical concave surface.
[0015] 4) A friction stir welding tool according to any of pars. 1)
to 3), wherein the probe has a cylindrical columnar shape.
[0016] 5) A friction stir welding tool according to any of pars. 1)
to 3), wherein the probe has a conical shape so that the diameter
of the probe decreases toward the distal end thereof.
[0017] 6) A friction stir welding tool according to any of pars. 1)
to 5), wherein a thread ridge is formed on an outer circumferential
surface of the probe, and is not formed on an outer circumferential
surface of the projection for provisional joining.
[0018] 7) A friction stir welding tool according to any of pars. 1)
to 6), wherein a distal end surface of the projection for
provisional joining is a partial-spherical convex surface.
[0019] 8) A friction stir welding tool according to any of pars. 1)
to 7), wherein the projection for provisional joining has a
transverse cross section of an irregular shape, and has, on its
outer circumferential surface, a plurality of partial cylindrical
surfaces formed such that the partial cylindrical surfaces are
located in a common cylindrical plane and are separated from one
another in the circumferential direction.
[0020] 9) A friction stir welding method characterized by
comprising:
[0021] performing provisional friction stir welding in such a
manner that, while the rotor of a friction stir welding tool
according to any one of pars. 1) to 8) is rotated, the projection
for provisional joining is plunged into a joint interface between
two workpieces such that the projection engages the two workpieces,
and the two workpieces and the friction stir welding tool are moved
relative to each other so as to intermittently weld the two
workpieces along the joint interface by use of the projection for
provisional joining; and
[0022] subsequently performing main friction stir welding in such a
manner that, while the rotor of the friction stir welding tool is
rotated, the probe is plunged into the joint interface such that
the probe engages the two workpieces, and the two workpieces and
the friction stir welding tool are moved relative to each other so
as to continuously weld the two workpieces along the entire joint
interface by use of the probe.
[0023] 10) A friction stir welding method according to par. 9),
wherein a relation (L1-0.05).ltoreq.Z.ltoreq.(L1+0.15) is satisfied
when the provisional friction stir welding is performed, and a
relation (L2-0.05).ltoreq.Z.ltoreq.(L2+0.3) is satisfied when the
main friction stir welding is performed, where L1 represents a
length (mm) of the projection for provisional joining, L2
represents a total length (mm) of the probe and the projection for
provisional joining, and Z represents a plunged depth (mm) of the
distal end of the projection for provisional joining as measured
from the surfaces of the workpieces.
[0024] 11) A friction stir welding method according to par. 9) or
10), wherein each of joined portions formed by the provisional
friction stir welding has length equal to or greater than the
diameter of the distal end surface of the probe of the friction
stir welding tool.
[0025] 12) A friction stir welding method according to any of pars.
9) to 11), wherein the joint interface between the two workpieces
is straight, and the provisional friction stir welding is performed
such that each of unjoined portions has a length equal to or less
than 300 mm.
[0026] 13) A friction stir welding method according to any of pars.
9) to 11), wherein the joint interface between the two workpieces
includes an arcuate portion, and the provisional friction stir
welding is performed such that each of unjoined portions has a
length equal to or less than three times the radius of the arcuate
portion.
[0027] 14) A friction stir welding method according to par. 13),
wherein the joint interface between the two workpieces has an
endless shape.
EFFECTS OF THE INVENTION
[0028] When friction stir welding is performed by use of the
friction stir welding tool according to par. 1), provisional
friction stir welding is first performed, and main friction stir
welding is then performed. The provisional friction stir welding is
performed in such a manner that, while the rotor of the friction
stir welding tool according to any one of pars. 1) to 8) is
rotated, the projection for provisional joining is plunged into a
joint interface between two workpieces such that the projection
engages the two workpieces, and the two workpieces and the friction
stir welding tool are moved relative to each other so as to
intermittently weld the two workpieces along the joint interface by
use of the projection for provisional joining. The main friction
stir welding is performed in such a manner that, while the rotor of
the friction stir welding tool is rotated, the probe is plunged
into the joint interface such that the probe engages the two
workpieces, and the two workpieces and the friction stir welding
tool are moved relative to each other so as to continuously weld
the two workpieces along the entire joint interface by use of the
probe. Further, the projection for provisional joining is
concentrically provided on the distal end surface of the probe of
the friction stir welding tool, and a relation 0.3
D.ltoreq.d.ltoreq.0.8 D is satisfied, where D represents the
diameter (mm) of the distal end surface of the probe, and d
represents the diameter (mm) of the contour of the distal end
surface of the projection for provisional joining. Therefore, the
joining strength of each of joined portions formed by the
provisional friction stir welding increases, and breakage of the
joined portions during the subsequent main friction stir welding
can be prevented. Accordingly, generation of joining defects, such
as an internal defect of a joined portion and a form defect (e.g.,
misalignment) can be prevented. Further, the friction stir welding
tool is not required to be exchanged with another friction stir
welding tool having a different probe diameter between performance
of the provisional friction stir welding and performance of the
main friction stir welding. Therefore, work efficiency is improved.
In addition, a plurality of friction stir welding tools are not
required to be prepared, facility cost can be reduced.
[0029] According to the friction stir welding tool of par. 3),
well-joined portions are obtained when the provisional friction
stir welding is performed.
[0030] According to the friction stir welding tool of par. 5), the
load which the probe receives from the workpieces during the main
friction stir welding is reduced, whereby the service life of the
probe is improved.
[0031] According to the friction stir welding tool of par. 7), the
load acting on the projection for provisional joining when the
projection for provisional joining is plunged into the workpieces
is reduced, whereby the service lives of the projection for
provisional joining and the probe are improved.
[0032] According to the friction stir welding tool of par. 8), the
material stirring force during the provisional friction stir
welding increases, whereby the speed of the provisional friction
stir welding can be increased.
[0033] According to the friction stir welding method of par. 9),
the joining strength of each of joined portions formed by the
provisional friction stir welding increases, and breakage of the
joined portions during the subsequent main friction stir welding
can be prevented. Accordingly, generation of joining defects, such
as an internal defect of a joined portion and a form defect (e.g.,
misalignment) can be prevented.
[0034] According to the friction stir welding method of par. 10),
well-joined portions which are free from joining defects, such as
an internal defect of a joined portion and a form defect (e.g.,
misalignment), can be obtained.
[0035] In the case where the joint interface between the two
workpieces has an endless shape as in the friction stir welding
method of par. 14), it is very difficult to friction-stir-weld the
workpieces along the entire joint interface in a state in which the
workpieces are firmly fixed. However, even in such a case, the
method of par. 9) enables the workpieces to be joined together
relatively easily.
BEST MODE FOR CARRYING OUT THE INVENTION
[0036] Embodiments of the present invention will next be described
with reference to the drawings.
[0037] FIG. 1 shows a first embodiment of the friction stir welding
tool according to the present invention.
[0038] In FIG. 1, a friction stir welding tool (1) includes a rotor
(2) which is attached to a rotation-drive section (not shown) of a
friction stir welding apparatus and has a cylindrical columnar
distal end portion; a cylindrical columnar probe (3) concentrically
and integrally formed on a distal end surface of the rotor (2); and
a cylindrical columnar provisional joining projection (4)
concentrically and integrally formed on a distal end surface of the
probe (3).
[0039] The distal end surfaces of the rotor (2) and the probe (3)
each have a partial-spherical concave surface. Further, a thread
ridge (3a) is formed on the outer circumferential surface of the
probe (3). No thread ridge is formed on the outer circumferential
surface of the provisional joining projection (4). Notably, a
thread ridge may be formed on the outer circumferential surface of
the provisional joining projection (4). The distal end surface of
the provisional joining projection (4) has a partial-spherical
convex surface. The rotor (2), the probe (3), and the provisional
joining projection (4) are formed of a material which is harder
than workpieces to be joined by use of the tool (1) and has a heat
resistance sufficient for enduring friction heat generated in the
course of joining.
[0040] When the diameter of the distal end surface of the probe (3)
is represented by D (mm) and the diameter of the contour of a
transverse cross section of the provisional joining projection (4)
is represented by d (mm), a relation 0.3 D.ltoreq.d.ltoreq.0.8 D
must be satisfied. When d<3 D, the diameter of the distal end
surface of the provisional joining projection (4) becomes
excessively small, and a joining strength attained through
provisional friction stir welding to be described later decreases.
When d>8 D, the area of a portion of the front end surface of
the probe (3), the portion surrounding the provisional joining
projection (4) becomes insufficient, and a pressing force applied
from the front end surface of the probe (3) to the workpieces
becomes insufficient, whereby the joining strength attained through
the provisional friction stir welding to be described later
decreases. In either case, joined portions formed by the
provisional friction stir welding break during main friction stir
welding to be described later. Therefore, joining defects, such as
an internal defect of a joined portion and a form defect (e.g.,
misalignment), are generated. Notably, in this embodiment, since
the thread ridge (3a) is formed on the outer circumferential
surface of the probe (3), the diameter D of the distal end surface
is equal to the outer diameter of the external thread.
[0041] Preferably, the length (L1) of the provisional joining
projection (4) falls within a range of 0.3 mm to 2 mm. When the
length (L1) of the provisional joining projection (4) is less than
0.3 mm, a generated friction stirring force is weak, and the
strength attained through the provisional friction stir welding may
be insufficient. When the length (L1) of the provisional joining
projection (4) exceeds 2 mm, the strength attained through the
provisional friction stir welding becomes excessive, which is
uneconomical. In the present embodiment, the distal end surface of
the probe (3) has a partial-spherical concave shape. In such a
case, the length (L1) of the provisional joining projection (4)
refers to a distance between the outer circumferential edge of the
distal end surface of the probe (3) and the distal end of the
provisional joining projection (4) (see FIG. 1(a)). Notably, when
the distal end surface of the probe (3) is flat, needless to say,
the length (L1) of the provisional joining projection (4) is a
distance between the flat distal end surface and the distal end of
the provisional joining projection (4).
[0042] Next, a method of friction-stir-welding a base having a
recess and a cover fitted into the recess and closing the opening
of the recess by use of the above-described friction stir welding
tool (1) will be described with reference to FIGS. 2 to 9.
[0043] First, as shown in FIG. 2, there are prepared a base (10)
having a recess (11) which is circular as viewed from above, and a
circular cover (12) which is fitted into the recess (11) and
adapted to close the opening of the recess (11). A stepped portion
(13), which projects radially inward, is formed on the inner
circumferential surface of the recess (11) of the base (10) at a
portion located on the bottom side. The thickness of the cover (12)
is smaller than the overall depth of the recess (11) and is equal
to the depth of a portion of the recess (11) located above the
stepped portion (13). The diameter of the cover (12) is equal to or
slightly smaller than the diameter of the opening of the recess;
i.e., the diameter of the recess (11) as measured above the stepped
portion (13).
[0044] Each of the base (10) and the cover (12) is formed from, for
example, any one of JIS A2000-family alloys, JIS A5000-family
alloys, JIS A6000-family alloys, and JIS A7000-family alloys. The
base (10) and the cover (12) may be formed from the same material
or from different materials.
[0045] When the base (10) and the cover (12) are joined together by
means of friction stir welding, the base (10) is first placed on an
unillustrated worktable. Subsequently, the cover (12) is fitted
into the recess (11) of the base (10) such that a circumferential
portion thereof rests on the stepped portion (13), thereby making
the upper surface of a portion of the base (10) around the recess
(11) and an upper surface of the cover (12) flush with each other.
An annular joint interface (14) is formed between a circumferential
edge portion of the opening of the recess (11) of the base (10) and
a circumferential edge portion of the cover (12).
[0046] Subsequently, the base (10) and the cover (12) are clamped
to the worktable by simultaneously pressing them by a plurality of
clamp jigs (15) (see FIG. 5).
[0047] Next, while the rotor (2) of the friction stir welding tool
(1) is rotated, the provisional joining projection (4) of the
friction stir welding tool (1) is plunged into the joint interface
(14) at a circumferential position where the provisional joining
projection (4) does not interfere with the clamp jigs (15), so that
the provisional joining projection (4) engages both the
circumferential edge portion of the opening of the recess (11) of
the base (10) and the circumferential edge portion of the cover
(12). Simultaneously, a shoulder portion (3b) of the distal end
surface of the probe (3) surrounding the provisional joining
projection (4) is pressed against the upper surfaces of the base
(10) and the cover (12) (see FIGS. 3 and 4). Here, as shown in FIG.
3, the length of the provisional joining projection (4) is
represented by L1 (mm), and a plunged depth of the distal end of
the provisional joining projection (4) as measured from the upper
surfaces of the base (10) and the cover (12) is represented by Z
(mm). In this case, preferably, a relation
(L1-0.05).ltoreq.Z.ltoreq.(L1+0.15) is satisfied. When
Z<(L1-0.05), the pressing force of the shoulder portion (3b)
becomes insufficient, and well-joined portions may fail to be
obtained. When Z>(L1+0.15), the pressing amount of the shoulder
portion (3b) becomes excessive, and well-joined portions may fail
to be obtained.
[0048] Next, while the rotor (2) is rotated, the probe (3) and the
provisional joining projection (4) are moved over a predetermined
distance along the annular joint interface (14) through relative
movement between the base (10) and the cover (12) and the friction
stir welding tool (1), to thereby friction-stir-weld the base (10)
and the cover (12) over a predetermined distance. Subsequently, the
provisional joining projection (4) is withdrawn from the base (10)
and the cover (12). This operation is repeated a plurality of times
along the joint interface (14) at predetermined intervals, whereby
the base (10) and the cover (12) are intermittently welded along
the joint interface (14) (provisional friction stir welding). When
the probe (3) and the provisional joining projection (4) are moved
in the circumferential direction along the joint interface (14),
the axis (X) of the rotor (2) of the friction stir welding tool (1)
is tilted slightly rearward from the vertical position with respect
to the travel direction. The tilt angle of the axis (X) of the
rotor (2) in relation to a vertical line (0) is referred to as an
advance angle (.alpha.) (see FIG. 3).
[0049] Preferably, the length of each joined portion (16) formed
through the provisional friction stir welding (hereinafter referred
to as the "provisionally welded portion (16)") is set to be equal
to or greater than the diameter (D) of the distal end surface of
the probe (3) of the friction stir welding tool (1). When the
length of the provisionally welded portion (16) is less than the
diameter (D) of the distal end surface of the probe (3), this means
that the friction stirring force generated in the course of the
provisional friction stir welding was insufficient, and the
strength of the provisionally welded portion (16) may be
insufficient. Since the joint interface (14) between the base (10)
and the cover (12) has an annular shape as shown in FIG. 6,
preferably, the length (S1) (mm) of each unjoined portion (17)
where the provisional friction stir welding is not performed is set
to be equal to or less than three times the radius (R) (mm) of the
joint interface (14). When the length (S1) of the unjoined portion
(S1) exceeds three times the radius (R) of the joint interface
(14), the provisional joining becomes insufficient, and joining
defects, such as an internal defect of a joined portion and a form
defect (e.g., misalignment), may be generated after the main
friction stir welding. Notably, the length (S2) of the
provisionally welded portion (16) is a distance between a point at
which the provisional joining projection (4) is plunged and a point
at which the provisional joining projection (4) is withdrawn; i.e.,
the moving distance of the provisional joining projection (4). The
length (S1) of the unjoined portion (17) is a distance between a
point at which the provisional joining projection (4) is withdrawn
at the end of the previous operation and a point at which the
provisional joining projection (4) is plunged at the start of the
subsequent operation.
[0050] Subsequently, the clamping of the base (10) and the cover
(12) to the worktable by the clamp jigs (15) is temporarily
released, and the base (10) and the cover (12) are clamped to the
worktable by pressing only the base (10) by the clamp jigs
(15).
[0051] After that, while the rotor (2) of the friction stir welding
tool (1) is rotated, the probe (3) of the friction stir welding
tool (1) is plunged into the joint interface (14) at a
circumferential position where the probe (3) does not interfere
with the clamp jigs (15), so that the probe (3) engages both the
circumferential edge portion of the opening of the recess (11) of
the base (10) and the circumferential edge portion of the cover
(12). Simultaneously, a shoulder portion (2a) of the distal end
surface of the rotor (2) surrounding the probe (3) is pressed
against the upper surfaces of the upper surfaces of the base (10)
and the cover (12) (see FIGS. 7 and 8). Here, as shown in FIG. 7,
the total length of the probe (3) and the provisional joining
projection (4) is represented by L2 (mm), and the plunged depth of
the distal end of the provisional joining projection (4) as
measured from the upper surfaces of the base (10) and the cover
(12) is represented by Z (mm). In this case, preferably, a relation
(L2-0.05).ltoreq.Z.ltoreq.(L2+0.3) is satisfied. When
Z<(L2-0.05), the pressing force of the shoulder portion (2a)
becomes insufficient, and well-joined portions may fail to be
obtained. When Z>(L2+0.3), the pressing amount of the shoulder
portion (2a) becomes excessive, and well-joined portions may fail
to be obtained. Notably, in the present embodiment, the distal end
surface of the rotor (2) has a partial-spherical concave shape. In
such a case, the total length (L2) of the probe (3) and the
provisional joining projection (4) refers to a distance between the
outer circumferential edge of the distal end surface of the rotor
(2) and the distal end of the provisional joining projection (4).
Notably, when the distal end surface of the rotor (2) is flat,
needless to say, the total length (L2) of the probe (3) and the
provisional joining projection (4) is a distance between the flat
distal end surface and the distal end of the provisional joining
projection (4).
[0052] Next, while the rotor (2) is rotated, the probe (3) is moved
over the entire joint interface (14) through relative movement
between the base (10) and the cover (12) and the friction stir
welding tool (1), to thereby continuously friction-stir-weld the
base (10) and the cover (12) over the entire circumference (main
friction stir welding) (see FIG. 9). Notably, as in the case of the
provisional friction stir welding, when the probe (3) is moved in
the circumferential direction along the joint interface (14) for
carrying out the main friction stir welding, the axis (X) of the
rotor (2) of the friction stir welding tool (1) is tilted slightly
rearward from the vertical position with respect to the travel
direction, so that the rotor (2) has the advance angle (.alpha.) in
relation to the vertical line (0) (see FIG. 7).
[0053] The base (10) and the cover (12) are thus
friction-stir-welded together.
[0054] Next, Examples in which the base (10) and the cover (12) are
friction-stir-welded together by the method shown in FIGS. 2 and 9
and by use of the friction stir welding tool (1) of the first
embodiment will be described together with Comparative
Examples.
Examples 1 to 3
[0055] Three types of friction stir welding tools (1) were
prepared. These friction stir welding tools (1) were formed such
that the diameter of the shoulder portion (2a) of the distal end
surface of the rotor (2): 18 mm; the diameter (D) of the distal end
surface of the probe (3): 6 mm; the length (L2-L1) of the probe
(3): 10 mm; the length (L1) of the provisional joining projection
(4): 1 mm; the total length (L2) of the probe (3) and the
provisional joining projection (4): 4.8 mm; and the diameter (d) of
the contour of a transverse cross section of the provisional
joining projection (4): 1.8 mm, 3 mm, and 4.8 mm, respectively.
[0056] Further, the base (10) and the cover (12) formed from JIS
A6061-T6 were prepared. As shown in FIG. 2, the outside diameter
(D1) of the base (10): 160 mm; thickness (T1) of the base (10): 15
mm; the total depth (T2) of the recess (11): 10 mm; the depth (T3)
of the recess (2) as measured above the stepped portion (4): 5 mm;
the diameter (D2) of the recess (2) as measured above the stepped
portion (4) (=the diameter of the opening of the recess): 100.1 mm;
the diameter (D3) of the recess (2) as measured below the stepped
portion (4): 80 mm; the thickness of the cover (12) (=the depth of
the recess (2) as measured above the stepped portion (4)): 5 mm;
and the diameter of the cover (12): 99.9 mm.
[0057] The base (10) and the cover (12) were clamped to a worktable
by simultaneously pressing the base (10) and the cover (12) by the
clamp jigs (15) at two locations on a diametrical line thereof.
Subsequently, at two locations between the clamp jigs (15), the
base (10) and the cover (12) were provisionally welded in the same
manner as in the above-described first embodiment by use of each of
the three types of the friction stir welding tools (1) such that
the length (S2) of the provisionally joined portion (16) became 60
mm (provisional friction stir welding). After that, the clamping of
the base (10) and the cover (12) to the worktable by the clamp jigs
(15) was temporarily released, and the base (10) and the cover (12)
were clamped to the worktable by pressing only the base (10) by the
clamp jigs (15). Subsequently, by use of each of the three types of
the friction stir welding tools (1), the base (10) and the cover
(12) were welded along the entire joint interface (14) in the same
manner as described above (main friction stir welding).
[0058] The conditions of the provisional friction stir welding are
such that the advance angle (.alpha.): 3 degrees; the rotational
speed of the rotor (2): 2000 rpm; the plunged depth (Z) of the
distal end of the provisional joining projection (4) as measured
from the upper surfaces of the base (10) and the cover (12): 1 mm;
and the joining speed: 300 mm/min. The conditions of the main
friction stir welding are such that the advance angle (.alpha.): 3
degrees; the rotational speed of the rotor (2): 1500 rpm; the
plunged depth (Z) of the distal end of the provisional joining
projection (4) as measured from the upper surfaces of the base (10)
and the cover (12): 4.9 mm; and the joining speed: 300 mm/min.
Comparative Examples 1 and 2
[0059] The base (10) and the cover (12) were friction-stir-welded
under the same conditions as those in Examples 1 to 3, except that
the used friction stir welding tools have provisional joining
projections whose diameters are 1.2 mm and 5.4 mm,
respectively.
Evaluation Test:
[0060] The misalignment (A) (see FIG. 10) between the base (10) and
the cover (12) which were friction-stir-welded in each of Examples
1 to 3 and Comparative Examples 1 and 2 was measured. Table 1 shows
the results of the measurement.
TABLE-US-00001 TABLE 1 Misalignment d (mm) Ratio of d to D (mm)
Example 1 1.8 d = 0.3 D 0.1 or less Example 2 3.0 d = 0.5 D 0.1 or
less Example 3 4.8 d = 0.8 D 0.1 or less Comparative 1.2 d = 0.2 D
1.3 Example 1 Comparative 5.4 d = 0.9 D 1.2 Example 2 Note: d: the
diameter of the contour of a transverse cross section of the
provisional joining projection D: the diameter of the distal end
surface of the probe
[0061] As is apparent from Table 1, in the case of Examples 1 to 3,
in which the diameter (D) of the distal end surface of the probe
(3) and the diameter (d) of the contour of a transverse cross
section of the provisional joining projection (4) satisfy the
relation 0.3 D.ltoreq.d.ltoreq.0.8 D, misalignment was hardly
generated. In contrast, in Comparative Example 1 in which d<0.3
D and in Comparative Example 2 in which d>0.8 D, a large
misalignment was generated. That is, when d<0.3 D, the diameter
of the distal end surface of the provisional joining projection (4)
becomes excessively small, and the stirring force at the time of
the provisional friction stir welding becomes insufficient, so that
the joining strength decreases. When d>8 D, the area of the
distal end surface of the probe (3) becomes insufficient, and the
pressing force applied from the distal end surface of the probe (3)
to the workpieces becomes insufficient, so that the joining
strength at the time of the provisional friction stir welding
decreases. In either case, conceivably, due to insufficiency of the
joining strength at the time of the provisional friction stir
welding, the provisionally welded portion broke during the main
friction stir welding, and the cover (12) lifted, whereby a large
misalignment was generated.
[0062] FIGS. 11 and 12 show other examples of the friction stir
welding method which uses the friction stir welding tool (1).
[0063] The method sown in FIG. 11 is a method for
friction-stir-welding two workpieces (21) and (22) which are
combined to form a straight joint interface (20) therebetween. In
the case of this method, preferably, the provisional friction stir
welding is performed such that the length (S3) of an unjoined
portion (23) becomes 300 mm or less, because of the following
reasons. When the length (S3) of the unjoined portion (23) exceeds
300 mm, the provisional joining becomes insufficient, and joining
defects, such as an internal defect of a joined portion and a form
defect (e.g., misalignment), may be generated after the main
friction stir welding. Further, for the same reason as described
above, preferably, the length (S4) of each provisionally joined
portion (24) is set to be equal to or greater than the diameter (D)
of the distal end surface of the probe (3) of the friction stir
welding tool (1). Other conditions are identical with those of the
above-described method shown in FIGS. 2 to 9.
[0064] The method sown in FIG. 12 is a method for
friction-stir-welding two workpieces (26) and (27) which are
combined such that a joint interface (25) therebetween includes a
semicircular portion (25a) and two straight portions (25b)
extending from opposite ends of the semicircular portion (25a). In
the case of this method, preferably, the provisional friction stir
welding is performed such that the length (S5) of each unjoined
portion (28) becomes equal to or less than three times the radius
(R1) of the semicircular portion (25a), for the same reason as
described above. Further, preferably, the length (S6) of each
provisionally joined portion (29) is set to be equal to or greater
than the diameter (D) of the distal end surface of the probe (3) of
the friction stir welding tool (1). Other conditions are identical
with those of the above-described method shown in FIGS. 2 to 9.
[0065] FIGS. 13 to 15 show second to fourth embodiments of the
friction stir welding tool.
[0066] In the case of a friction stir welding tool (30) of the
second embodiment shown in FIG. 13, its probe (31) has a conical
shape such that the diameter of the probe decreases toward the
distal end thereof.
[0067] In the case of a friction stir welding tool (35) of the
third embodiment shown in FIG. 14, its provisional joining
projection (36) has an irregular transverse cross section, and the
provisional joining projection (36) has, on its outer
circumferential surface, a plurality of (two in this embodiment)
partial cylindrical surfaces (37) formed such that the partial
cylindrical surfaces (37) are located in a common cylindrical plane
and are separated from one another in the circumferential
direction.
[0068] In the case of a friction stir welding tool (40) of the
fourth embodiment shown in FIG. 15, its provisional joining
projection (41) has an irregular transverse cross section, and the
provisional joining projection (41) has, on its outer
circumferential surface, a plurality of (three in this embodiment)
partial cylindrical surfaces (42) formed such that the partial
cylindrical surfaces (42) are located in a common cylindrical plane
and are separated from one another in the circumferential
direction.
[0069] In the friction stir welding tools (35) and (40) of the
third and fourth embodiments, the diameter (d) of the contour of a
transverse cross section of the provisional joining projection
(36), (41) refers to the diameter of the cylindrical plane in which
the partial cylindrical surfaces (37), (42) are located.
[0070] Other structural features of the friction stir welding tools
(30), (35), and (40) shown in FIGS. 13 to 15 are identical with
those of the friction stir welding tool (1) of the first
embodiment.
INDUSTRIAL APPLICABILITY
[0071] The friction stir welding tool according to the present
invention is preferably used for joining two workpieces by
provisional friction stir welding and then main friction stir
welding in various industries.
BRIEF DESCRIPTION OF THE DRAWINGS
[0072] FIG. 1 shows a first embodiment of the friction stir welding
tool according to the present invention, wherein (a) is an enlarged
partial front view, and (b) is a bottom view.
[0073] FIG. 2 is a vertical sectional view showing a base and a
cover to be joined by the friction stir welding tool of FIG. 1.
[0074] FIG. 3 is an enlarged partial vertical sectional view
showing a state in which the base and the cover are joined along a
joint interface through provisional friction stir welding by use of
the friction stir welding tool of FIG. 1.
[0075] FIG. 4 is an enlarged partial vertical sectional view
showing the same state as FIG. 3, as viewed from a direction
different from that of FIG. 3.
[0076] FIG. 5 is a perspective view showing the state in which the
base and the cover are joined along the joint interface through the
provisional friction stir welding by use of the friction stir
welding tool of FIG. 1.
[0077] FIG. 6 is a schematic plan view showing a state in which the
base and the cover have been joined along the joint interface
through the provisional friction stir welding by use of the
friction stir welding tool of FIG. 1.
[0078] FIG. 7 is an enlarged partial vertical sectional view
showing a state in which the base and the cover are joined along
the joint interface through main friction stir welding by use of
the friction stir welding tool of FIG. 1.
[0079] FIG. 8 is an enlarged partial vertical sectional view
showing the same state as FIG. 7, as viewed from a direction
different from that of FIG. 7.
[0080] FIG. 9 is a perspective view showing the state in which the
base and the cover are joined along the joint interface through the
main friction stir welding by use of the friction stir welding tool
of FIG. 1.
[0081] FIG. 10 is a vertical sectional view showing a misalignment
measured in the evaluation test for the base and the cover joined
in each of Examples and Comparative Examples.
[0082] FIG. 11 is a schematic plan view showing another example of
the friction stir welding method using the friction stir welding
tool and showing a state in which two workpieces have been joined
through provisional friction stir welding.
[0083] FIG. 12 is a schematic plan view showing still another
example of the friction stir welding method using the friction stir
welding tool and showing a state in which two workpieces have been
joined through provisional friction stir welding.
[0084] FIG. 13 shows a second embodiment of the friction stir
welding tool according to the present invention, wherein (a) is an
enlarged partial front view, and (b) is a bottom view.
[0085] FIG. 14 shows a third embodiment of the friction stir
welding tool according to the present invention, wherein (a) is an
enlarged partial front view, and (b) is a bottom view.
[0086] FIG. 15 shows a fourth embodiment of the friction stir
welding tool according to the present invention, wherein (a) is an
enlarged partial front view, and (b) is a bottom view.
* * * * *