U.S. patent application number 10/560225 was filed with the patent office on 2006-06-29 for friction stirring-welding method.
Invention is credited to Kinya Aota, Satoshi Hirano, Masahisa Inagaki, Kazutaka Okamoto.
Application Number | 20060138197 10/560225 |
Document ID | / |
Family ID | 33549295 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060138197 |
Kind Code |
A1 |
Aota; Kinya ; et
al. |
June 29, 2006 |
Friction stirring-welding method
Abstract
A friction stirring-welding method capable of increasing the
welding strength of a lap joint. A welding tool (1) comprises a
small diameter projected part (2) at the tip of a shoulder (3). The
welding tool is press-fitted to the upper plate (4) of the lap
joint while being rotated. By a friction stirring action, an upper
plate side welding boundary surface (6) plastically flows, a
surface oxidation film on a lapped surface is peeled off, and the
boundary surface is activated to provide an excellent welding part.
Also, since the welding tool is formed in a shape having the small
diameter semispherical projected part (2) at the tip thereof, the
thickness (12) of an upper plate welding part is increased, and a
lap joint part with high welding strength can be provided.
Inventors: |
Aota; Kinya; (Tokyo, JP)
; Inagaki; Masahisa; (Tokyo, JP) ; Hirano;
Satoshi; (Tokyo, JP) ; Okamoto; Kazutaka;
(Tokyo, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
33549295 |
Appl. No.: |
10/560225 |
Filed: |
June 11, 2004 |
PCT Filed: |
June 11, 2004 |
PCT NO: |
PCT/JP04/08580 |
371 Date: |
December 12, 2005 |
Current U.S.
Class: |
228/112.1 |
Current CPC
Class: |
B23K 20/1255 20130101;
B23K 20/1265 20130101 |
Class at
Publication: |
228/112.1 |
International
Class: |
B23K 20/12 20060101
B23K020/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 12, 2003 |
JP |
2003-167242 |
Claims
1. A friction stir welding method for a lap joint, in which a
plurality of members are lapped and a welding tool is pressed into
one of the members, while being rotated, to cause friction stir to
achieve welding, characterized in that the method comprises using,
as the welding tool, a welding tool having a small diameter
projected part at a tip end of a shoulder, and pressing the
projected part and the shoulder of the welding tool into one of the
members.
2. The friction stir welding method according to claim 1,
characterized in that the small diameter projected part is
semispherical in shape.
3. The friction stir welding method according to claim 2,
characterized in that a recess is provided on the shoulder around
the projected part.
4. The friction stir welding method according to claim 1,
characterized in that an outer peripheral surface of a tip end of
the shoulder of the welding tool is inclined to define an inclined
surface.
5. The friction stir welding method according to claim 1,
characterized in that an outer peripheral surface of a tip end of
the shoulder of the welding tool is rounded.
6. The friction stir welding method according to claim 1,
characterized in that the welding tool is pressed into one of the
members and a welding boundary surface is activated and welded by
plastic flow, in which such pressing causes the one of the members
to be discharged to an outer periphery of the welding tool.
7. A friction stir welding method for a lap joint, in which a
plurality of members are lapped and a welding tool is pressed into
one of the members, while being rotated, to cause friction stir to
achieve welding, characterized in that a tip end of the welding
tool is semispherical in shape.
8. The friction stir welding method according to claim 7,
characterized in that only a part of the semispherical shaped
portion of the welding tool is pressed into the one of the members
to make a contact angle between the welding tool and a surface of
the one of the members an acute angle.
9. The friction stir welding method according to claim 7,
characterized in that the welding interface is activated and welded
by causing the one of the members to undergo plastic flow.
10. A friction stir welding method for a lap joint, in which a
plurality of members are lapped and a welding tool is pressed into
one of the members, while being rotated, to cause friction stir to
achieve welding, characterized in that a tip end of the welding
tool is flat and an outer peripheral surface thereof is
rounded.
11. The friction stir welding method according to claim 10,
characterized in that the whole of the flat portion of and only a
part of the rounded portion of the welding tool are pressed into
the one of the members.
12. The friction stir welding method according to claim 10,
characterized in that a welding interface is activated and welded
by causing the one of the members to undergo plastic flow.
13. The friction stir welding method according to claim 1,
characterized in that the welding tool is pressed into the one of
the members to cause friction stir of the member and then pulled
out to perform spot welding.
14. The friction stir welding method according to claim 1,
characterized in that the welding tool is moved in a direction of
welding in a state, in which the welding tool is pressed into the
one of the members.
15. The friction stir welding method according to claim 1,
characterized in that lapped surfaces of the plurality of members
are coated with soft metal.
16. The friction stir welding method according to claim 15, wherein
the soft metal is any one of nickel, zinc, and copper.
17. The friction stir welding method according to claim 1,
characterized in that a trapezoidal member is provided on a surface
of the one of the members on that side, into which the welding tool
is pressed, to prevent an indentation produced due to pressing of
the welding tool.
18. The friction stir welding method, according to claim 1,
characterized in that one of the members is provided on a lapped
surface thereof with a groove, another of the members is provided
on a lapped surface thereof with a projected part, and the
projected part is fitted into and welded to the groove.
19. A friction stir welding apparatus that rotates a welding tool
to cause friction stir to weld a plurality of members,
characterized in that a tip end surface of the welding tool defines
a convex-shaped and curved surface.
20. A friction stir welding apparatus that rotates a welding tool
to cause friction stir to weld a plurality of members,
characterized in that the welding tool comprises, at a central
portion of a tip end thereof, a projected part having a smaller
diameter than that of the welding tool and a tip end of the
projected part defines a curved surface.
21. A friction stir welding apparatus that rotates a welding tool
to cause friction stir to weld a plurality of members,
characterized in that the welding tool comprises, at a central
portion of a tip end thereof, a projected part and a recess is
formed around the projected part.
22. A friction stir welding apparatus that rotates a welding tool
to cause friction stir to weld a plurality of members,
characterized in that the welding tool comprises a tip end shaped
to be trapezoidal in cross section transverse to an axial direction
thereof.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a friction stir welding
method and a friction stir welding apparatus.
DESCRIPTION OF RELATED ART
[0002] A conventional technology for welding of a lap joint by
means of the friction stir welding technique includes a method of
using a welding tool having a flat-shaped tip end surface, or a
welding tool having a recess on a tip end surface, and pressing the
welding tool into one of members to cause friction stir on the one
of the members to make use of plastic flow produced thereby to weld
the same to the other of the members (see, for example,
JP-A-2001-314981).
[0003] In welding of a lap joint by means of friction stir welding,
it is important to remove a surface oxide film on a lapped surface
to activate a boundary interface. Therefore, it is necessary to
heighten pressure of plastic flow.
[0004] It is an object of the invention to provide a friction stir
welding method for a lap joint, by which a welded part can be made
higher in strength than that in the related art. Also, it is an
object of the invention to provide a friction stir welding method
capable of welding different metals.
[0005] In the case where welding tools are pressed into both of an
upper plate and a lower plate in lap welding by means of friction
stir welding, there is caused an unfavorable problem in terms of
outward appearance that a large hole is formed in a welded part to
reach the lower plate. Also, in case of lap welding of materials,
such as aluminum and nickel, which are considerably different in
melting point from each other, there is caused a problem that the
both are considerably different in deformation resistance from each
other and cavity flaw is generated, since aluminum has the melting
point of 660.degree. C. while nickel has the melting point of
1455.degree. C., and welding tools are pressed into both metals of
aluminum and nickel. The invention provides a welding method that
dissolves the problem.
BRIEF SUMMARY OF THE INVENTION
[0006] There are two kinds of mechanisms of welding in the
invention.
[0007] A first mechanism of welding resides in a method of pressing
a welding tool only into one of members while rotating the welding
tool, causing plastic flow of that member, which is discharged to
an outer periphery of the pressed welding tool, so that welding
boundary surfaces are activated by such discharge to achieve
welding. A shape of the welding tool and characteristics of plastic
flow are important for welding.
[0008] The invention with respect to the first mechanism of welding
obtains favorable results by the use of a welding tool having a
small diameter projected part at a tip end of a large diameter
shoulder. Desirably, the projected part has a smooth curved surface
like a semispherical shape, if possible. Since the projected part
can raise pressure in a region of plastic flow, the action of
activating welding boundary surfaces increases. For an increase in
pressure of plastic flow, it is also effective to provide a
semispherical recess around the semispherical projected part to
make these regularities contribute to an increase in contact area
of the welding tool and a welding member. Also, it is desirable to
round an outer peripheral surface of a tip end of the shoulder.
Furthermore, since the use of a welding tool having a tip end of a
certain radius of curvature also enables an increase in pressure of
plastic flow, the action of activating welding boundary surfaces
increases. When the action of activating welding boundary surfaces
increases, a welding area increases and the welding strength
increases.
[0009] A second mechanism of welding resides in a method of making
a contact angle between a welding tool and a surface of an upper
plate an acute angle to perform welding in case of pressing a
welding tool only into one of members while rotating the welding
tool. In this case, since little metal undergoing plastic flow is
discharged, it is possible to make pressure of plastic flow very
high. Therefore, the action of activating welding boundary surfaces
increases. Such plastic flow is generated mainly in a direction, in
which the welding tool rotates.
[0010] In the invention with respect to the second mechanism, a
contact angle is made an acute angle by pressing of a welding tool
having a semispherical shaped tip end only into one of members and
causing friction stir to achieve welding. Thereby, since plastic
flow is increased in internal pressure, the action of activating
welding boundary surfaces increases.
[0011] When lapped surfaces of welding members are coated with soft
metal, surface oxide films on welding boundary surfaces can be made
easy to remove. In the case where welding members are made of
carbon steel, such method is very effective. Nickel, zinc, and
copper are especially effective as soft metal.
[0012] By providing a trapezoidal member on a surface of that
member, into which a welding tool is pressed, or working the member
to make the same trapezoidal in shape, it is possible to prevent
reduction in welding strength even when an indentation is produced
due to pressing of the welding tool.
[0013] Also, a distance between a welding tool and lapped surfaces
can be made short by performing welding in a state wherein a groove
is provided on a lapped surface of one of members, and a projected
part is provided on a lapped surface of the other of the members,
the projected part being fitted into the groove. This method is
suited to the case where thick plates are to be welded
together.
[0014] The invention is applicable to spot welding, in which a
welding tool is pressed and pulled out intact and this procedure is
repeated.
[0015] The invention enables moving a welding tool while performing
pressing to achieve continuous welding.
[0016] With the friction stir welding method by means of a welding
tool according to the invention, it is possible to positively
generate plastic flow on welding boundary surfaces of a lap joint
to remove and discharge a surface oxide film to activate the
boundary surfaces. Thereby, welding with a high welding strength
becomes possible. Also, welding of different metals is enabled.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0017] FIG. 1 is a cross sectional view showing a first
embodiment;
[0018] FIG. 2 is a perspective view in the course of welding in the
first embodiment;
[0019] FIG. 3 is a cross sectional view showing a direction of
welding in the course of welding in the first embodiment;
[0020] FIG. 4 is a cross sectional view showing a welded part after
welding in the first embodiment;
[0021] FIG. 5 is a schematic view showing a state of plastic flow
in a welding part in the first embodiment;
[0022] FIG. 6 is a graph illustrating shear strength of a welded
part in the first embodiment;
[0023] FIG. 7 is a cross sectional view showing a state in the
course of welding in the first embodiment;
[0024] FIG. 8 is a cross sectional view showing a state in the
course of welding in a conventional method;
[0025] FIG. 9 is a cross sectional view showing an example of a
shape of a welding tool;
[0026] FIG. 10 is a cross sectional view showing another example of
a shape of a welding tool;
[0027] FIG. 11 is a cross sectional view showing a state before
welding in a second embodiment;
[0028] FIG. 12 is a cross sectional view showing a welded part in
the second embodiment;
[0029] FIG. 13 is a cross sectional view showing a state before
welding in a third embodiment;
[0030] FIG. 14 is a cross sectional view showing a welded part in
the third embodiment;
[0031] FIG. 15 is a plan view showing a state after welding in a
fourth embodiment;
[0032] FIG. 16 is a cross sectional view showing a state in the
course of welding in a fifth embodiment;
[0033] FIG. 17 is a cross sectional view showing a state in the
course of welding in a sixth embodiment;
[0034] FIG. 18 is a cross sectional view showing a state in the
course of welding in a seventh embodiment;
[0035] FIG. 19 is a cross sectional view showing a state in the
course of welding in an eighth embodiment; and
[0036] FIG. 20 is a cross sectional view showing a state in the
course of welding in a ninth embodiment.
DETAILED DESCRIPTION OF THE INVENTION
FIRST EMBODIMENT
[0037] FIG. 1 is a cross sectional view showing a first embodiment.
A welding tool 1 comprises a small diameter projected part 2 at the
tip end of a large diameter shoulder 3. A welding test piece
comprises an upper plate 4 and a lower plate 5, which lap each
other and are arranged on a bearing member 24. FIG. 2 is a
perspective view in the course of welding. By rotating and moving
the welding tool 1 in a direction of welding in a state, in which
it is pressed only into the upper plate 4 from a side of the upper
plate 4, welding boundary surfaces 6 of the upper plate 4 and the
lower plate 5 can be welded to each other. An indentation 7 is
produced on the upper plate 4 as the welding tool 1 is moved. FIG.
3 is a cross sectional view showing a direction of welding in the
course of welding. An axis of rotation of the welding tool 1 in the
course of welding is inclined on an opposite side to a direction of
welding indicated by an arrow, that is, a backward angle side. FIG.
4 is a cross sectional view showing a welded part after welding.
The indentation 7 corresponding to the projected part 2 of the
welding tool 1 is produced centrally of a welded part 9, and
discharged metal portions 8 corresponding to the indentation are
produced on both ends of a surface of the welded part. At this
time, surface oxide films on lapped surfaces of the upper plate 4
and the lower plate 5 are removed and the welding boundary surfaces
6 are metallically welded.
[0038] The material of the upper plate 4 according to the
embodiment is an industrial pure aluminum of JIS A1050-H24, and the
material of the lower plate 5 is nickel. In addition, the both
plates, respectively, have a thickness of 0.4 mm. The material of
the welding tool 1 is tool steel and the shoulder 3 has a diameter
of 5 mm and is provided with the projected part 2, which has a
height of 0.1 mm. Welding is performed by moving the welding tool 1
at the welding speed of 400 mm/min in a state, in which the welding
tool is rotated at 18,000 rpm to be pressed into the upper plate 4.
In addition, the axis of rotation of the welding tool 1 has a
backward angle of 2.5.degree..
[0039] FIG. 5 is a schematic view showing a state of plastic flow
in a welding part. Since the welding tool 1 is pressed, a large
load acts on the welding part in a direction of pressing. The
welding part is made high in temperature by frictional heat of the
welding tool 1 and the upper plate 4. Therefore, plastic flow
occurs toward both ends of the welding part in a state of high
pressure and high temperature. The plastic flow causes shearing
stress on the welding boundary surfaces 6 of the upper plate 4 and
the lower plate 5 in the welding part, so that surface oxide films
on the welding boundary surfaces are removed and the both plates
are metallically welded. Metal corresponding to the indentation 7
forms the discharged metal portions 8.
[0040] Welding can be performed whether the materials of the upper
plate 4 and the lower plate 5 are the same metal or different
metals. The welding is suited especially to the case where metals,
such as aluminum, lead, tin, magnesium, etc., having low melting
points are welded to each other, or one of the metals and a
different metal are welded to each other. In case of welding
metals, which are greatly different in melting point from each
other, to each other, a thick reaction layer is liable to be
produced between the both when the welding temperature is high. In
such case, welding is preferable with the upper plate 4 made of a
low melting point metal whereby it is possible to make the
thickness of a reaction layer to the minimum. This method is
especially effective in welding of metals, such as aluminum and
nickel, which are greatly different in melting point from each
other. Furthermore, in the case where the upper plate 4 is made of
aluminum and the lower plate 5 is made of carbon steel, it is also
effective to apply nickel coating on a surface of carbon steel. The
reason for this is that nickel is soft metal to be susceptible to
plastic flow and a surface oxide film on a surface thereof is
liable to be removed. Furthermore, the same effect can be produced
for galvanizing and copper plating.
[0041] The shoulder 3 has a diameter dependent upon the thickness
and material of the upper plate 4. According to the embodiment, the
upper plate has a thickness of 0.4 mm while the shoulder has a
diameter of 5 mm, which is 12.5 times the plate thickness. By
increasing the diameter of the shoulder relative to the plate
thickness, a load, with which the welding tool 1 is pushed, becomes
large, so that pressure of plastic flow also increases to make it
further easy to remove a surface oxide film on a welding surface.
Desirably, the diameter of the shoulder is 8 to 20 times the plate
thickness on that side, on which the welding tool is inserted.
[0042] FIG. 6 illustrates shear strength of the welded part. Test
pieces of the welded part had a width of 5 mm. Since an indentation
7 was generated, shear strength was obtained by dividing a breaking
load by a cross sectional area which was calculated from a plate
thickness of a parent material of the upper plate 4 or the lower
plate 5. While the shear strength is 155 to 165 N/mm.sup.2 in the
invention, it is 120 to 130 N/mm.sup.2 in conventional methods. The
reason for this is described below.
[0043] FIG. 7 is a cross sectional view showing a state in the
course of welding in the invention. Shear strength is dependent
upon the thickness 12 of an upper plate welded part. While an
indentation 7 is produced centrally of the welded part, it is not
responsible for a decrease in shear strength.
[0044] FIG. 8 is a cross sectional view showing a state in the
course of welding in a conventional method. A welding tool 1 is
columnar-shaped. The welding tool 1 must be pressed deeply into a
surface of an upper plate 4 in order to generate plastic flow
toward both ends of a welding part to consequently produce
discharged metal portions 8. Therefore, the welded part is
uniformly recessed and the thickness 12 of an upper plate welded
part becomes small. Therefore, shear strength becomes lower than
that in the invention.
[0045] FIGS. 9 and 10 show examples of a shape of a welding tool. A
welding tool 1 in FIG. 9 comprises a tool end 10 having a curved
surface to thereby produce an effect that discharged metal portions
8 are prevented from making burr and falling off. Furthermore, a
recess 20 is provided around a projected part 2 whereby it is
possible to heighten pressure of plastic flow. In FIG. 10, a tool
end 10 of a welding tool 1 is inclined to define inclined surfaces.
The shape of the tool is effective in restricting discharge of
discharged metal portions 8 whereby there is generated an action of
increasing pressure of plastic flow.
SECOND EMBODIMENT
[0046] FIG. 11 is a cross sectional view showing a state before
welding in a second embodiment. The embodiment differs from the
first embodiment in that a trapezoidal member 30 is provided on a
welding part of an upper plate 4 to make the upper plate 4 thick.
FIG. 12 is a cross sectional view showing the welded part in the
second embodiment. While an indentation 7 is produced on the welded
part, any indentation does not remain and a flat surface is
obtained when the welded part is ground flat.
THIRD EMBODIMENT
[0047] FIG. 13 is a cross sectional view showing a state before
welding in a third embodiment. FIG. 14 is a cross sectional view
showing a welded part. The embodiment differs from the first
embodiment in that a groove 32 is provided on an upper plate 4 and
a projected part 31 is provided on a lower plate 5 to be fitted
into the groove. Thereby, since the welding part can be made
smaller in thickness than the upper plate 4, it is possible to
perform welding for a further large plate thickness.
FOURTH EMBODIMENT
[0048] FIG. 15 is a plan view showing a state after welding in a
fourth embodiment. In the embodiment, a welding tool 1 is pressed
into an upper plate 4 and thereafter pulled up to perform spot
welding. The invention is also applicable to spot welding.
FIFTH EMBODIMENT
[0049] FIG. 16 is a cross sectional view showing a state in the
course of welding in a fifth embodiment. An upper plate 4 is made
of aluminum and has a thickness of 1 mm, while a lower plate 5 is
made of carbon steel and has a thickness of 1 mm. These test pieces
are caused to lap each other and a welding tool 1 is pressed from a
side of the upper plate 4 while rotating. In addition, the welding
tool 1 comprises a shoulder 3 having a diameter of 12 mm and a tip
end of the welding tool 1 defines a semispherical shaped portion 13
having a radius of curvature of 20 mm. Since the welding tool 1 is
pressed, frictional heat and pressure generated between the welding
tool and the upper plate 4 cause the upper plate 1 to undergo
plastic flow toward an outer peripheral side of the welding tool 1
to produce discharged metal portions 8. In the process of such
discharge, plastic flow is not generated in the lower plate since
carbon steel forming the lower plate 2 is high in melting point.
However, a surface oxide film on a welding boundary surface of
carbon steel is removed by plastic flow of aluminum and so the
welding boundary surfaces 6 are activated to enable the upper plate
1 and the lower plate 2 to be metallically welded. Furthermore,
since the welding tool 1 is pressed from a side of the upper plate
4 made of aluminum, the welding temperature can be made low as
compared with the case where welding is performed from a side of
the lower plate 5 made of carbon steel. Therefore, it is possible
to obtain favorable welding characteristics for the welded boundary
surfaces since generation of intermetallic compounds, which reduce
the fatigue strength of a welded part, can be suppressed. Also,
since the tip end of the welding tool forms the semispherical
shaped portion 13, a pressing force is large to increase an action
that activates the welding boundary surfaces. Therefore, a welded
area is increased to provide a large welding strength.
SIXTH EMBODIMENT
[0050] FIG. 17 is a cross sectional view showing a state in the
course of welding in a sixth embodiment. An upper plate 4 and a
lower plate 5 are the same in plate thickness and material as those
in the fifth embodiment. However, a welding tool 1 is different in
shape from that in the fifth embodiment. A shoulder 3 has a
diameter of 24 mm and a tip end thereof defines a semispherical
shaped portion 13 having a radius of curvature of 20 mm. Only a
part of the semispherical shaped portion 13 is pressed into the
upper plate to effect welding. Thereby, the upper plate 4 and the
lower plate 5 can be welded together likewise. A contact angle
.theta. between a surface of the upper plate 4 and the
semispherical shaped portion 13 is very small, so that aluminum
having undergone plastic flow can be restricted from making burr
and falling off. Therefore, it is possible to heighten pressure of
plastic flow of the welding tool 1, thus increasing an action that
activates the welding boundary surfaces.
[0051] While a welding tool having a conventional shape without a
curved surface has a contact angle of 90.degree., the welding tool
according to the invention has a contact angle of approximately
10.degree.. The contact angle is made 5 to 20.degree. whereby it is
possible to heighten pressure of plastic flow to provide for
welding with a high welding strength.
SEVENTH EMBODIMENT
[0052] FIG. 18 is a cross sectional view showing a state in the
course of welding in a seventh embodiment. An upper plate 4 and a
lower plate 5 are the same in plate thickness and material as those
in the fifth embodiment. However, a welding tool 1 is different in
shape from that in the fifth embodiment. The welding tool has at a
tip end thereof a flat portion 14, an outer periphery of which is
provided with a rounded portion 15 having a radius of curvature of
20 mm. The same welding as that in the sixth embodiment is enabled
by pressing only a part of the rounded portion 15 into the upper
plate 4.
EIGHTH EMBODIMENT
[0053] FIG. 19 is a cross sectional view showing a state in the
course of welding in an eighth embodiment. Upper plates 4 are made
of aluminum and have a thickness of 0.3 mm, while a lower plate 5
is made of aluminum and has a thickness of 0.5 mm. However, the
upper plates 4 are butted in shape. In addition, a tip end of a
welding tool 1 defines a semispherical shaped portion having a
radius of curvature of 10 mm. The welding tool 1 is moved in a
direction of welding while rotating at 5,000 rpm. Thereby, the
upper plates 4 can be butt-welded together. In addition, after the
welding, the upper plates 4 are also welded to the lower plate 5.
Also, when members, such as ceramic, etc., surfaces of which are
hardly activated, are used for the lower plate 5, that execution is
enabled, in which only the upper plates 4 are welded but are not
welded to the lower plate 5.
NINTH EMBODIMENT
[0054] FIG. 20 is a cross sectional view showing a state in the
course of welding in a ninth embodiment. Each of an upper plate 4,
a middle plate 17, and a lower plate 5 is made of aluminum, and has
a thickness of 0.1 mm. A welding tool 1 includes a shoulder 3
having a diameter of 5 mm and a tip end in the form of a
semispherical shaped portion 13 having a radius of curvature of 10
mm. Welding of the three plates at the same time is enabled by
pushing and moving the welding tool 1 at a speed of 1000 mm/min in
a direction of welding while rotating the welding tool at 15,000
rpm.
* * * * *