DESCRIPTION
Title of the Invention: Fillet Welded Joint and Method of
Production of Same
5
Technical Field
[OOOl] The present invention relates to a fillet
welded joint and a method of production of the same, more
particularly relates to ones suitable for use for fillet
10 welding a plurality of metal members.
Background Art
[0002] In the past, in the automotive field, for
conservation of the environment, reduction of the weight
of car bodies to improve fuel efficiency and improvement
15 of collision safety have been sought. For this reason,
various attempts have been made up to now to use high
strength steel sheet to reduce thicknesses and to
optimize car body structure to reduce the weight of car
bodies and improve collision safety.
2 0 [0003] Large fatigue strength is also being demanded
from high strength steel sheet for reducing the weight of
car bodies. In particular, in suspension arms, subframes,
and other chassis members, the fatigue strength of the
welded zones becomes more important. To weld these
2 5 chassis members, fillet arc welding is often used.
Therefore, to reduce the weight of chassis members, the
challenge is to raise the fatigue strength of the fillet
arc welded joints.
[00041 FIG. 1A shows the cross-sectional shape of a
3 0 typical lap fillet welded joint formed by superposing an
upper steel material 1 and lower steel material 2 and
welding only the perpendicular crossing parts at one side
among the perpendicularly crossing parts formed at the
two sides of the abutting parts of the upper steel
3 5 material 1 and lower steel material 2. In the following
explanation, the fillet weld bead will when necessary be
called a "fillet bead". In such a lap fillet welded
joint, if tensile loads F1 and F2 act on the upper and
lower steel sheets, rotational deformation occurs about
the fillet bead 3, stress concentrates at the toe 4 or
the root 5 of the fillet bead 3, a fatigue crack proceeds
in a direction vertical to the load, and the welded joint
breaks. For this reason, to improve the fatigue strength,
it becomes important to reduce the stress concentration
at the toe 4 or root 5.
[00051 As the method of improving the fatlgue strength
of the welded jolnt, in the past, efforts have been made
to reduce the stress concentration at the weld toe mainly
by improvement of the bead shape. For example, postprocessing
is performed to increase the flank angle by
grinding the weld toe or by remelting the toe by TIG
welding. Furthermore, PLT 1 proposes to provide a slanted
part at a weldable member in advance by press-forming and
perform the welding so that the weld bead is superposed
on that slanted part to thereby increase the flank angle
of the toe of the weld bead.
COO061 PLTs 2 and 3 disclose the art of augmenting a
weld bead to ease the stress concentration at the weld
toe. Specifically, PLT 2 discloses the art of extending
the weld bead, while PLT 3 discloses the art of forming a
stiffening bead.
[0007] PLTs 4 and 5 disclose the art of treating a
weld bead and smoothing the weld toe to ease the stress
concentration at the weld toe. Specifically, PLT 4
discloses the art of brazing the weld bead, while PLT 5
discloses the art of using plasma to remelt the weld toe.
[OOOE] PLT 6 discloses the art of press-forming a
weldable member so as to form a projection in advance
near the location scheduled for welding where the weld
bead will be formed and thereby ease the stress
concentration at the weld zone. Specifically, PLT 6
discloses superposing and welding a plurality of sheetshaped
members to form a straight weld zone and forming
press beads in shapes surrounding the two end parts so as
to make the tensile load and torsional load applied to
the sheet-shaped members be absorbed by the press beads
and prevent stress from concentrating at the two end
parts of the straight weld zone.
[00091 PLT 7 discloses providing an upwardly
projecting bead part at a side wall part side of a lower
rail of a flat sheet-shaped bracket to run along the side
wall part of the lower rail. PLT 7 discloses using the
upwardly projecting bead part to increase the interval
between an arc welding torch and the top surface of the
bracket and improve the weldability in the arc welding.
[OOlO] PLT 8 discloses a weld fastening structure of a
lid hemming part for automobile use. PLT 8 discloses to
fasten the edges of a lid outer panel folded along the
edges of a lid inner panel by arc welding to a raised
part of the inner panel so as to be able to sufficiently
withstand the large external force at the time of
collision etc.
[OOll] However, these techniques have little effect on
improvement of the fatigue strength of the portions where
stress structurally concentrates such as in the lap
fillet welded joint shown in FIG. lA, that is, the toe 4
and the root 5. A fundamental improvement in fatigue
strength cannot be realized. In particular, in a welded
member of thin steel sheets, since the sheets are thin,
the member falls in rigidity. Due to the carried load,
the part of the lower steel material 2 of FIG. 1A which
overlaps the bottom side of the upper steel material 1
easily deforms by rotation about the fillet bead 3. For
this reason, a fatigue crack sometimes forms not only
from the weld toe 4, but also from the root 5. With just
improvement of the shape of the weld toe, the fatigue
strength or fatigue life is insufficiently improved.
[0012] Further, in a thin sheet welded structure, to
prevent weld deformation due to excessive weld heat
input, in many cases, not the entire length of the joint
is welded: The welded structure is prepared by partial
weld beads 301 such as shown in FIG. lB(a). Each of the
partial weld beads 301 is formed with a beginning 301s
and an ending part 30lE. The conventional technique for
improvement of the bead shape is art covering a middle
5 portion 301M stable in the weld bead shape shown in FIG.
1B(c) . However, as shown in FIG. lB(b), the beginning
301s insufficiently penetrates the matrix, has a toe of
an upwardly projecting shape, and easily becomes a
location for formation of a fatigue crack in the toe 4s.
10 Further, as shown in FIG. lB(d), the ending part 301E
becomes reduced in thickness of weld metal and easily
suffers from cracks from the root 5E. In this way, in an
actual welded structure, cracks easily form at the
beginning and the end 301s and 30lE of the weld bead, so
15 no effect of improvement of the fatigue strength of the
welded structure as a whole can be expected.
COO131 That is, with thin steel sheet welded members,
to improve the fatigue strength of a welded structure, in
particular one including a lap fillet welded joint or T-
2 O fillet welded joint, it is considered important to raise
the rigidity of the members to suppress out-of-plane
deformation and thereby reduce the structural stress
concentration. If possible to raise the rigidity of the
members and lower the structural stress concentration, it
2 5 may become possible to obtain the effect of improvement
of the fatigue strength of the welded structure as a
whole including the beginning and root of the weld bead.
/0014] PLT 9 proposes forming an arc weld bead for
stiffening use separate from a fillet bead so that the
3 0 position of the weld beginning point overlaps the fillet
bead and so that the position of the weld ending point
becomes the front surface of the lower steel sheet
whereby this functions as a member for raising the
alloying of the steel sheet and weld metal in the
35 direction to which the bending moment is applied and
suppresses bending of the lower steel sheet.
[0015] Further, in the past, as means for improving
the fatigue strength of a fillet welded joint, the
practice has been to weld a rib or other reinforcing
member with a suitable shape and position. However, if
welding a separate member, this leads to an increase in
costs, so these means are not art able to be applied to
the production of mass production parts such as auto
parts.
[0016] To deal with such a problem, PLT 10 proposes
the art of fillet arc welding one metal member and
another metal member to produce a welded joint during
which forming on the surface of at least one of the metal
members at least one bead beginning from the fillet bead
and separate from the fillet bead in the same plane as
the fillet bead by a required angle to thereby improve
the fatigue strength of the welded joint.
[0017] However, in the arts disclosed in PLTs 9 and
10, it is necessary to form the fillet bead, then form
the stiffening weld bead in a predetermined direction
with respect to the fillet bead, so there are the
problems that application to a part with a complicated
shape is difficult, the welding steps increase, and
improvement of the productivity is limited.
[0018] Further, in general, at the beginning point of
a weld bead, penetration becomes insufficient and weld
defects easily occur. In the arts disclosed in PLTs 9 and
10, the weld beginning point of the stiffening bead
overlaps the fillet weld bead, so at the overlapping
part, penetration is liable to become insufficient and a
weld defect is liable to occur. On the other hand, if
sufficiently heating the weld beginning point of the
stiffening bead to eliminate the problem with penetration
of the stiffening bead in the matrix metal, there is the
problem that the matrix metal becomes excessively heated
at the weld beginning point and a drop in the strength of
the matrix metal is invited.
Citation List
Patent Literature
[0019] PLT 1: Japanese Patent Publlcatlon No. 2008-
221300A
PLT 2: Japanese Patent Publlcatlon No. 09-253843A
PLT 3: Japanese Patent No. 5522317
5 PLT 4: Japanese Patent Publication No. 2013-031878A
PLT 5: Japanese Patent Publlcatlon No. 2014-004609A
PLT 6: Japanese Patent Publlcatlon No. 2010-110793A
PLT 7: Japanese Patent Publicatlon No. 2003-341391A
PLT 8: Japanese Utillty Model Publlcatlon No. 54-100925U
10 PLT 9: W02013/157557A
PLT 10: W02014/084317A
Summary of Invention
Technical Problem
[0020] The present invention, in view of the above
15 situation, has as its object the provision of a fillet
welded joint and a method of production of the same able
to raise the productivity and facilitate application to a
part of a complicated shape without sacrificing the
strength of the welded structural member against fatigue
2 0 fracture.
Solution to Problem
[0021] As explained above, in chassis members and
other welded structural members, due to the structures of
the members, there are weld locations which are fillet
2 5 welded not at the perpendicularly crossing parts of the
two sides of abutting parts of two steel members, but at
the perpendicularly crossing parts of just one side.
Fatigue cracks are expected to easily form at such weld
locations. Therefore, the inventors studied the cause of
30 formation of fatigue cracks and means for suppressing the
formation of fatigue cracks using as an example a basic
lap fillet welded joint.
[0022] When fillet welding thin steel sheets for
automotive use, from the viewpoint of productivity,
35 sometimes the fillet bead is provided only on one side of
the thin steel sheets. This is because since the sheet
thickness is small, if fillet welding one side of the
perpendicularly crossing parts, that is, the front side
of the perpendicularly crossing parts, then immediately
fillet weldlng the back side of the sheets, the steel
sheets do not completely cool down, so there is the
5 problem that the steel sheets themselves will be burned
through.
[0023] Therefore, the inventors conducted fatigue
tests coverlng welded structural members obtained by
flllet weldlng only the perpendicularly crosslng parts of
10 one slde among the perpendicularly crosslng parts formed
at the two sides of the abutting parts of two steel
members when making at least one of the steel members a
thin steel sheet with a sheet thickness of 3.2 mm or
less. As a result, they learned that in such a welded
15 structural member, sometimes fatlgue cracks form at the
root 5 of the fillet bead.
I00241 Here, the inventors focused on lap fillet
welded joints obtained by fillet arc welding only the
perpendicularly crossing parts of one side of the
2 0 overlapping parts of the steel sheets 1 and 2 shown in
FIG. 1A in then study. The lnventors used the 3D finite
element method to analyze how the steel sheets 1 and 2
deform when a tensile force El acts on the fillet bead 3
formed by the fillet arc welding along the upper steel
2 5 sheet 1 and a tensile force F2 acts along the lower steel
sheet 2.
COO251 As a result, it was learned that a large
bending moment is generated due to deviation of the
center axis of the upper steel sheet 1 (single line
30 passing through center of thickness and width of steel
sheet and parallel to longitudinal direction of steel
sheet) from the center axis of the lower steel sheet 2
and that the lower steel sheet 2 bends near the fillet
bead 3 resulting in the root 5 opening. This is
3 5 considered to be due to the increased stress
concentrating at the root 5 and causing the formation of
a fatigue crack.
[00261 Therefore, the inventors studied, as means for
suppressing bendlng of the lower steel sheet 2, not
forming a stlffenlng bead by a weld bead, but forming it
in advance before weldlng by a press operation.
5 [0027] As a result, as shown in FIG. 2, part of the
lower steel sheet 2 1s press-formed to form in advance a
r~b-shaped projection 3A so as to cross or contact a
flllet bead 3 (below, such a projection referred to as a
"press bead"). The fillet bead 3 1s formed by flllet arc
10 welding so that the upwardly projecting end part of the
press bead 3A overlaps the fillet bead 3. If doing this,
the press bead 3A can function as a member for raising
the rlgidity of the steel sheet and weld metal wlth
respect to the direction at which the above-mentioned
15 bending moment is applied and suppress bendlng of the
lower steel sheet 2. Therefore, it is possible to
suppress the formation of fatigue cracks.
IO028l From these results of observation, the
following findings were obtained:
2 0 (I) It was discovered that by forming a press bead so as
to cross or contact a fillet weld bead, it is possible to
raise the fatigue strength of fillet welding.
Note that, when arranging the press bead 3A so as to
project upward at the fillet bead 3 side, as shown in
2 5 FIG. 3(a), the molten metal at the time of welding to
form the fillet bead is blocked by the press bead 3A and
a good weld bead shape is obtained. However, if the press
bead is arranged to project downward at the fillet bead
side, as shown in FIG. 3(b), the molten metal at the time
3 0 of welding flows out into the downwardly projecting part
of the press bead (bottom view at bottom), the thickness
of the weld bead falls, and a sufficient weld metal
strength cannot be obtained.
100291 In a welded structural member for automotive
35 use, in particular a welded structural member for chassis
use, in addition to "lap fillet welding" for simply lap
fillet welding one sheet and another sheet such as the
above-mentioned test piece, sometimes the edge end of a
metal member is fillet welded on the surface of another
metal sheet to produce a welded structural member (below,
sometimes called "butt flllet welding" or "T-fillet
5 welding"). For such a welded loint as well, it was
learned that it is effective to form at least one press
bead on the surface of the flllet welded metal sheet so
that the press bead projects upward at the slde hav~ng
f~llet bead and part of the press bead overlaps the
10 fillet bead.
[0030] (11) Further, it was learned that when applying
to a welded structural member to which a load from the
outside is directly applied a repeated load envisioned as
be~ng applied to the welded structural member, it is
15 effective to form a press bead at the region where the
fatigue crack first forms. The location where the fatigue
crack first forms corresponds to the location of maximum
main stress. At this time, if the direction of maximum
main stress can also be learned in advance, the press
2 0 bead should be formed so as to run along the direction of
maximum main stress. That is, the longitudinal direction
of the press bead should become the direction of maximum
main stress.
[0031] Note that, regarding the stress concentration
25 at the weld bead, in most cases stress concentrates at
the weld toe where the rate of change of shape is high
and the vertical direction at the weld toe becomes the
direction of maximum main stress. For this reason,
arranging the press bead in the direction perpendicular
3 0 to the outer edge end of the weld bead forming the
boundary of the weld bead and matrix metal (below,
referred to as the "weld toe line") is effective for
improvement of the fatigue strength. The toe line
direction of the weld bead here is defined as follows:
3 5 That is, this means (a) for a straight fillet bead, the
literal weld line direction (solid line arrow direction
of FIG. 4 (a) ) , (b) for a curved fillet bead, the
tangential direction of the fillet bead (solid line arrow
direction of FIG. 4(b)), (c) for the vicinity of the
beginning portion and ending portion of the fillet bead
(below, abbreviated as "beginning and ending portions")
5 (however, excluding the front end), the tangential
direction of the toe of the fillet bead (solid line arrow
direction in FIG. 4(c)), and (d) at the front ends of the
beginning and ending portions of the fillet bead, the
tangential direction of the toe of the front end of the
10 bead, that is, the direction perpendicular to the weld
line (solid line arrow direction in FIG. 4(d)).
I00321 The present invention was made based on the
above discoveries and has as its gist the following:
I00331 The fillet welded joint of the present
15 invention is a fillet welded joint formed by fillet
welding at least two metal members, wherein on the
surface of at least one of the metal members, the fillet
welded joint comprises a press bead of a rib-shaped
projection provided by press-forming so as to project
2 0 upward to a side having a weld bead formed by the fillet
welding, and wherein part of the press bead contacts or
overlaps the weld bead.
COO341 Further, in another example of the fillet
welded joint of the present invention, an angle formed by
25 a longitudinal direction of the press bead and a
direction of a weld toe line of the weld bead may be 45"
to 135".
I00351 Further, in another example of the fillet
welded joint of the present invention, the joint may have
3 0 a press bead positioned along the weld bead at least at
one of a beginning portion, ending portion, and bent
portion of the weld bead and location in the middle of
that weld bead where a stress higher than stresses at the
beginning and ending portions is applied.
35 100361 Further, in another example of the fillet
welded joint of the present invention, the joint may have
a press bezd having a toe radius Ra (mm) which is equal
to or longer than a thickness "t" (mm) of the metal
member having the press bead.
roo371 Further, in another example of the fillet
welded joint of the present invention, the press bead may
5 satisfy Lat2W, Hatt, and Wa>W where "La" expresses a
length in a longitudinal direction of the press bead,
"Ha" expresses a height of the press bead, "Wa" expresses
a width of the press bead, "W" expresses a width of the
weld bead, and "t" expresses a thickness of the metal
10 member having a press bead.
[0038] Further, the press bead may be formed so as to
cross the weld bead.
[00391 Further, the press bead may be formed to
overlap the weld bead at the part where a previously
15 established maximum main stress is caused.
[00401 Further, in another example of the fillet
welded joint of the present invention, the metal member
welded with the metal member at which the press bead is
formed may comprise a notched part fitting in the press
2 0 bead at the location where the press bead is welded.
[0041] Further, in another example of the fillet
welded joint of the present invention, at least one of
the metal members may be a metal member of a crosssectional
shape which has a folded corner part and which
2 5 is fillet welded to the other metal member and a press
bead may be superposed at the corner part of the weld
bead formed.
100421 Further, the method of forming a fillet welded
joint of the present invention is a method for producing
30 a fillet welded joint by fillet welding at least two
metal members, the method comprising press-forming on the
surface of at least one of the metal members a press bead
of a rib-shaped projection so as to project upward to the
side having a weld bead formed by the fillet welding and
3 5 fillet welding the metal members so that a part of the
press bead contacts or is superposed with the weld bead.
[0043] Further, the effect of the press bead increases
by forming the press bead so that the angle formed by a
longitudinal direction of the press bead and a direction
of a weld toe line of the weld bead becomes 45" to 135'.
COO441 Further, in another method for forming the
5 fillet welded joint of the present invention, the method
may further comprise forming the press bead positioned
along the weld bead at least at one of a beginning
portion, ending portion, and bent portion of the weld
bead and location in the middle of the weld bead where a
10 stress higher than stresses at the beginning and ending
portions is applied.
[0045] Further, in another method for forming the
fillet welded joint of the present invention, the method
may further may comprise forming a press bead having a
15 toe radius Ra (mm) which is equal to or more than a
thickness "t" (mm) of the metal member having the press
bead.
100461 Further, it is also possible to form the press
bead so as to satisfy La22W, Ha2t, and Wa2W, wherein "La"
2 0 expresses a length in a longitudinal direction of the
press bead, "Ha" expresses the height of the press bead,
"Wa" expresses the width of the press bead, "W" expresses
the width of the weld bead, and "t" expresses the
thickness of the metal member having the press bead.
2 5 100471 Further, the press bead may be formed to cross
the weld bead.
[00481 Further, the method may further comprise
forming the press bead so as to overlap with the weld
bead at a part where a previously established maximum
30 main stress is caused.
[00491 Further, in another method for forming the
fillet welded joint of the present invention, the method
may further comprise forming a notched part, the notched
part being fit into in the press bead at the location
35 welded with the press bead in the metal member welded
with the metal member at which the press bead is formed.
[OOSO] Further, in another method for formi-ng the
fillet welded joint of the present invention, the method
may further comprise fillet welding one of the metal
members to the other metal member, at least one of the
metal members being a metal member of a cross-sectional
5 shape having a folded corner part, and forming the press
bead in advance at the other metal member so that the
press bead is superposed at the corner part of the weld
bead.
dvantageous Etfe
10 [OOSl] According to the present invention, no
stiffening bead is further formed after formlng the weld
bead. For this reason, application to parts of
complicated shapes is easy and the welding process is
streamlined so productivity can be improved. Further, the
15 problem of the drop in strength due to welding over a
weld bead can be resolved. Further, even an extremely
narrow location which a welding torch would have a hard
time reaching can be reinforced by a press bead according
to the present invention. Further, unlike a weld bead, a
2 0 press bead can be freely set in height and toe radius, so
a sufficient improvement of rigidity can be obtained. It
is therefore possible to prevent fatigue cracks from
forming from the stiffening press bead itself.
Brief Description of Drawings
25 I00521 [FIG. lA] FIG. 1A is a cross-sectional view
showing the cross-sectional shape of a lap fillet welded
joint .
[FIG. 1Bl FIG. lB(a) is a top view of a welded structure
fabricated by partial weld beads, FIG. 1Bjb) is a cross-
3 0 sectional view at the beginning of a partial weld bead in
the welded structure of FIG. lB(a), FIG. 1B(c) is a
cross-sectional view at a middle portion of a partial
weld bead of the welded structure of FIG. lB(a), and FIG.
lB(d) is a cross-sectional view at an end of a partial
35 weld bead of the welded structure of FIG. 1B(a).
[FIG. 21 FIC. 2 is a top view showing a test piece of a
lap fillet ~elded joint.
[FIG. 31 FIG. 3(a) is a cross-sectional view showing the
state of arranging a press bead to project upward to the
fillet bead side, while FIG. 3(b) is a cross-sectional
view showing the state of arranging a press bead to
5 project upward to the fillet bead side.
[FIG. 41 FIG. 4(a) is a top view showing a relationship
between a toe line direction and weld line direction in
the case of a straight fillet bead, FIG. 4(b) is a top
lationship between a toe line direction
10 and tangential direction of the fillet bead in the case
of a curved fillet bead, FIG. 4(c) is a top view showing
a relationship between a tangential direction of the
fillet bead and the toe line direction of the bead near a
beginning portion and ending portion of the fillet bead,
15 and FIG. 4(d) is a top view showing a relationship
between a tangential direction of the fillet bead and the
toe line direction of the bead at the front end of a
beginning portion and ending portion of the fillet bead.
[FIG. 51 FIG. 5(a) is a top view showing an example of
2 0 arrangement of an upwardly projecting press bead at a
lower steel sheet so as to contact the vicinity of the
center part of the fillet bead, FIG. 5(b) is a top view
showing an example of arrangement of an upwardly
projecting press bead at an upper steel sheet so as to
2 5 contact the vicinity of the center part of the fillet
bead, FIGS. 5(c) to (f) are top views showing examples of
arrangement of upwardly projecting press beads at lower
steel sheets so as to contact beginning and ending
portions of the fillet beads, and FIG. 5(g) is a top view
3 0 showing an example of combination of the modes of
arrangement of press beads shown in FIGS. 5(b) and (f).
[FIG. 6A] FIG. 6A(l) is a perspective view of one example
of a butt fillet joint of the present invention in the
case of arranging an upwardly projecting press bead at a
35 lower steel sheet so as to contact the vicinity of the
center part of the fillet bead, while FIG. 6H(2) is a
cross-sectional view of FIG. 6A(1).
[ F I G . 6B] F I G . 6B is a perspective view of one example of
a butt fillet joint of the present invention in the case
of arranging upwardly projecting press beads at a lower
steel sheet at beginning and ending portions of the
5 fillet bead so as to contact the beginning and ending
portions of a fillet bead.
[ F I G . 6C] F I G . 6C(1) is a perspective view of one example
of a butt fillet joint of the present invention in the
e of providing a notch in the upper steel sheet in
10 advance and fitting the notch over the press bead, while
F I G . 6C ( 2 ) is a cross-sectional view of F I G . 6C (1) .
[ F I G . 6D] F I G . 6D is a perspective view of one example of
a butt fillet joint of the present invention in the case
of arranging at the lower steel sheet of a T-fillet joint
15 an upwardly projecting press bead at a lower steel sheet
in parallel with a fillet bead so as to contact the
beginning and ending portions of the fillet bead.
[ F I G . 71 F I G . 7(a) is a top view of a welded joint of the
present invention formed by a lap fillet bead having a
2 0 bent portion at the fillet bead, while F I G . 7(b) is a
perspective view of a butt fillet joint of the present
invention of a structure where a press bead is arranged
so as to contact the fillet bead at a corner part of a
bracket member.
2 5 [ F I G . 81 F I G . 8 is a perspective view showing a first
example of a welded structural member.
[ F I G . 91 F I G . 9 is a perspective view showing a second
example of a welded structural member.
[ F I G . 101 F I G . 10 is a perspective view showing a third
30 example of a welded structural member.
[ F I G . 111 F I G . 11 is a perspective view showing a fourth
example of a welded structural member.
[ F I G . 121 F I G . 12(a) is a cross-sectional view when
cutting the weld bead at a cross-section vertical to a
3 5 length direction of the weld bead, while F I G . 12(b) is a
cross-sectional view when cutting the press bead at a
cross-section vertical to a length direction of the press
bead.
[FIG. 131 FIG. 13 is a graph showing the relationship
with the radius of curvature of the fillet bead at the
weld toe of the weld bead shown in FIG. 12.
5 [FIG. 141 FIG. 14 is a graph showing the results of a
fatigue strength test performed using a lap fillet welded
joint with no stiffening bead, a lap fillet welded joint
formed with a stiffening bead comprised of a weld bead,
ap fille't welded joint formed with a stiffening
10 bead comprised of a press bead.
[FIG. 151 FIG. 15 is a top view of a lap fillet welded
joint used for the fatigue strength test of FIG. 14.
[FIG. 161 FIG. 16(a) is a graph showing the results of
fatigue tests conducted using the lap fillet welded
15 joints shown in FIGS. 5(a), (b), (e), (f), and (g), while
FIG. 16(b) is a top view of a lap fillet welded joint as
a comparative example used for the fatigue test of FIG.
16 (a).
Description of Embodiments
2 0 [0053] First, the basic matters in the fillet welded
joint and method of production of the same of the present
invention will be explained in detail using the drawings.
Below, the present invention will be explained using
mainly a fillet welded joint, but the fillet welded joint
2 5 and method of production of the same of the present
invention is not limited to a welded structural member
for automotive use and can also be utilized for a
structure comprised of several materials or members etc.
such as rolling stock or aircraft or other transport
3 0 machinery, mechanical structures, home electric
appliances, etc. Further, the present invention is not
limited to steel sheets and can also be applied to iron
sheets, aluminum sheets, titanium alloy sheets, and sheet
materials containing a metal and resin.
35 LO0541 (Cross-Sectional Shape of Press Bead)
As explained above, the present invention is
characterized by press-forming a metal member used for a
fillet welded joint so as project upward at the side
having a fillet bead to form in advance a rib-shaped
projection at the surface of the metal member. In the
present invention, the rib-shaped projection is called a
5 "press bead". The cross-sectional shape vertical to the
direction of formation of the press bead is not
partlcularly limlted so long as it can be press-formed. A
polygonal shape, semi-ell~ptical shape, seml-circular
shape, and varlous other shapes can be applied. Further,
10 the cross-sectional shape parallel to the direction of
formation of the press bead is not partlcularly limlted
so long as one able to be press-formed.
[OOSS] (Mode of Arrangement of Press Bead In Case of
Lap Flllet Bead)
15 As explained above, the present invention is
characterized by forming a press bead in advance at one
part of a lower steel sheet so as to cross or contact a
fillet bead and by performing fillet welding to form the
fillet bead so that the upwardly projecting side end part
2 0 of the press bead is superposed over the fillet bead.
[00561 In the case of a lap fillet bead, as shown in
FIG. 5(a), it is also possible to arrange an upward
projecting press bead at the lower steel sheet so as to
contact the vicinity of the center part of the fillet
2 5 bead. In the case of the mode of arrangement of the press
bead shown in FIG. 5(a), rotational deformation of the
lower steel sheet is suppressed and it is possible to
suppress cracks from the toe of the fillet bead.
I00571 Further, as shown in FIG. 5(b), it is possible
3 0 to arrange an upwardly projecting press bead at an upper
steel sheet so as to contact the vicinity of the center
part of the fillet bead. In the case of the mode of
arrangement of the press bead shown in FIG. 5(b),
rotational deformation of the upper steel sheet is
35 suppressed, so in particular it is possible to suppress
cracks from tne root of the fillet bead.
[0058] Further, as shown in FIGS. 5 (c) to (f), it is
also possible to arrange upwardly projecting press beads
extending longer from the fillet bead toe at the lower
steel sheet so as to contact the beginning and ending
portions of the fillet bead. In particular, by forming
5 press beads at least 10 mrn extending longer than the toe
of a fillet bead, there is the effect of raising the
rigldlty of the beglnning and ending portlons of the
flllet bead and cracks from the beginning and ending
ortlons can be suppressed. The press beads shown in
10 FIGS. 5 (c) , (d) , and (f) are formed at the beginning
port~ons and endlng portions of the weld beads so that
the angles formed by the longitudinal directions and weld
toe lines of the weld beads become 45' to 135O. The press
beads shown in FIG. 5 (e) are formed at the beginning
15 portion and ending portion of the weld bead so that their
longitudinal directions become parallel to the direction
of the weld toe line of the weld bead. When the lower
steel sheet is narrow in width and it is difficult to
arrange a long press bead such as in FIG. 5(a), the modes
20 of arrangement of the press beads shown in FIGS. 5(c) to
(f) would be effective.
COO591 Furthermore, the mode of arrangement may be two
or more of the modes of arrangement explained above shown
in FIGS. 5 (a) to (f) combined. In each of the above-
25 mentioned modes of arrangement, the press bead has the
effect of Improving the rigidity of the welded joint
formed by the lap fillet bead. That is, the press bead
suppresses rotational deformation in the sheet thickness
direction when applying a tensile load to the top and
3 0 bottom steel sheets and reduces the stress concentration
acting on the fillet bead to thereby act effectively to
improve the fatigue life. For example, it is also
possible to combine the modes of arrangement of the press
beads shown in FIGS. 5(b) and (f) to produce the welded
35 joint shown in FIG. 5(g). According to the mode of
arrangement of the press beads shown in FIG. 5(g), it is
possible to synergistically obtain the effect of
suppression of cracks from the root and the effect of
suppression of cracks from the beginning portion and
ending portion of the weld bead.
[0060] (Verification of Effect of Improvement of
5 Fatigue Life Due to Mode of Arrangement of Press Beads)
To investigate the effect of improvement of the fatigue
life due to the mode of arrangement of press beads, the
lap fillet welded joints shown in FIGS. 5(a), (b), (e),
ed to conduct fatigue tests. Further,
10 for comparison with the mode of arrangement of the press
beads according to the present invention, a lap fillet
welded joint at which a press bead of an equal length to
the fillet bead was formed along the fillet bead (shown
in FIG. 16(b)) and a lap fillet welded joint at which no
15 press bead or other stiffening bead was formed were used
to conduct fatigue tests.
COO611 The different forms of the lap fillet welded
joints used in the fatigue tests were produced by forming
press beads in advance at a sheet thickness 2.6 mm 780
2 0 MPa class steel sheet, overlaying on it a sheet thickness
3.2 mm 780 MPa class steel sheet, and fillet welding
them. Further, in the different forms of the lap fillet
welded joints,.the press beads were formed to heights of
Hal=l and toe radii of p ' = l . Here, Ha' and p' show the
2 5 values of the weld bead height (Hb)/sheet thickness (t)
and toe radius (Rb)/sheet thickness (t) respectively.
[00621 Further, the press beads of FIGS. 5(a), (b),
(f), and (g) were formed so that the lengths became La=50
mrn, while the press beads of FIG. 5(e) and FIG. 16(b)
3 0 were formed so that the lengths became La=25 mm.
100631 The fatigue tests used a universal axial force
fatigue tester to cause a repeated load to act so that a
minimum load of 1 kN and a maximum load of 11 kN were
applied in opposite directions on the upper sheet 1 and
35 lower sheet 2 (in the same way as the later explained
FIG. 15, the arrow directions shown in FIG. 15).
100641 The results of the fatigue strength tests are
shown in F I G . 16(a). In the case of a lap fillet welded
joint not having a stiffening bead, the fracture life was
170,000 cycles after which cracks formed from the weld
beginning and ending portions. In the case of the lap
5 fillet welded joint shown in F I G . 5(a), the fracture life
increased 5.2-fold and the crack formation position
became the root of the fillet bead. In the case of the
lap fillet welded joint shown in F I G . 5(b), the fracture
rate of increase was
10 small. With the lap fillet welded joint shown in FIG.
5(b), it is believed that the effect of suppression of
rotational deformation of the lower sheet cannot be
expected and cracks formed from the toes of the beginning
and ending portions of the fillet bead, so the effect of
15 extension of the fatigue life was small.
[00651 The fatigue lives of the lap fillet welded
joints of FIGS. 5(e) and (f) respectively increased 3.1-
fold and 4.0-fold, but if compared with the lap fillet
welded joint shown in FIG. 5(a), the effect of extension
2 0 of the fatigue life was small. The part where the crack
forms was the root of the fillet bead. The effect of
suppression of cracks at the toes of the beginning and
ending portions of the fillet bead was obtained, but it
is believed that the lap fillet welded joints of F I G S .
2 5 5(e) and (f) had smaller effects of suppression of
deformation of the root compared with the lap fillet
welded joint shown in FIG. 5 (a) .
to0661 The lap fillet welded joint of FIG. 5(g)
obtained a large effect of extension of the fatigue life.
3 0 This is believed to be due to the fact that the effect of
suppression of cracks at the beginning and ending
portions of the fillet bead due to the press bead shown
in F I G . 5(f) and the effect of suppression of deformation
of the root due to the press bead shown in F I G . 5(b) act
35 as synergistic effects.
100671 In the case of the lap fillet welded joint
shown in F I G . 16(b) as a comparative example, the effect
of extension of the fatigue life was small. This is
because even if arranging a press bead parallel to the
fillet bead, the effect of suppression of rotational
deformation of the lower sheet was not exhibited and
5 cracks at the beginning and ending portions of the fillet
bead could not be suppressed.
[0068] (Mode of Arrangement of Press Beads in Case of
Butt Fillet Joint)
other hand, in the case of a T-fillet joint (butt
10 fillet joint), it is necessary to consider the issue of
the fact that cracks easily form from the lower steel
sheet. As a mode of arrangement considering such an
issue, as shown in FIG. 6A(1), it is also possible to
arrange an upwardly projecting press bead 3A at the lower
15 steel sheet 2 so as to contact the vicinity of the center
part of the fillet bead 3. Further, as shown in FIG. 6B,
it is also possible to arrange upwardly projecting press
beads 3A at the beginning and ending portions of the
fillet bead 3 in the lower steel sheet 2 so as to contact
2 0 the beginning and ending portions of the fillet bead 3.
Alternatively, as shown in FIG. 6C (I), it is also
possible to provide a notch 1A in advance at the upper
steel sheet 1, arrange the upper steel sheet 1 so that
the notch 1A fits over the press bead 3A, and arrange the
2 5 upwardly projecting press bead 3A at the lower steel
sheet 2 so that the filletbead 3 and the press bead 3A
cross.
[00691 Furthermore, a mode of arrangement combining
two or more of the above modes of arrangement shown in
3 0 FIG. 6A to FIG. 6C is also possible. It is also possible
to combine the modes of arrangement shown in FIGS. 5(a)
and (c) to (f) where press beads are formed at the lower
steel sheets with the above-mentioned mode of arrangement
shown in FIG. 6A. For example, the T-fillet joint shown
3 5 in FIG. 6D may be comprised of the lower steel sheet 2 of
the T-fillet joint shown in FIGS. 6C (1) and (2) where, as
shown in FIG. 5(e), upwardly projecting press beads 3Aa
are arranged in parallel with the fillet bead 3 so as to
contact the beglnn~ng and endlng portions of the fillet
bead 3.
100701 In all of the modes of arrangement explained
above, the press bead has the effect of lmproving the
rigidlty of the butt flllet joint. FIG. 6A(2) is a crosssectional
vlew as seen from the plane passing through the
centerline of the upper steel sheet 1 and lower steel
sheet 2 of FIG. 6A(1). Further, FIG. 6C(2) is a crosssectional
view as seen from the plane passing through the
centerline of the upper steel sheet 1 and lower steel
sheet 2 of FIG. 6C(1). As shown in these cross-sectional
views, when applylng a tensile load to the upper and
lower steel sheets, the press bead suppresses out-ofplane
deformation of the lower steel sheet. Therefore,
the press bead is effective for lmproving the fatlgue
life due to the effect of improving the rigidity by
suppressing rotational deformation in the direction of
sheet thickness and reducing the stress concentration
acting on the fillet bead when applylng a tensile load to
the upper and lower steel sheets.
[00711 Further, the press bead of the present
invention can be applied to not only the straight part of
a weld bead, but also the welded part where the direction
of the weld toe line changes (below, referred to as a
"bent portion"). For example, when the weld bead is
formed in an L-shape, V-shape, or U-shape, the weld toe
line of the weld bead includes two directions. When the
fillet bead has hat bent portion, stress easily
concentrates at that bent portion, so arranging the press
bead at the bent portion is effective for improving the
fatigue strength. FIG. 7(a) is a top view of a welded
joint of the present invention formed by a lap fiilet
bead having a bent portion 1B at the fillet bead 3. FIG.
7 ( b ) is a perspective view of a butt fillet joint of the
present invention of a structure where a press bead 3A is
arranged so as to contact the fillet bead 3 at a corner
part 18B of the bracket member 18. As shown in FIG. 7(a)
and FIG. 7(b), the press bead has to be formed so as to
cross the fillet bead at the bent portion or be
superposed with the fillet bead at its end part. This is
5 because if formed separated from the fillet bead, it does
not sufficiently function as a member raising the
rigidity of the steel sheet.
COO721 Above, the suitable arrangement of the press
bead was explained with reference to the examples of
10 various types of welded joints, but, since actual welded
joints are configured by large numbers of members, a
plurality of weld lines may be arranged in close
proximity. Therefore, using the same press bead in common
for two independent fillet beads, it is also possible to
15 arrange the press bead so as to be superposed with one
fillet bead at beginning point thereof(one of the end
parts) and to be superposed with the other fillet bead at
ending point thereof (other end part). That is, press
bead may be formed so that either of the end parts is
2 0 superposed on either of the two independent fillet beads.
COO731 If the crack formation position of the welded
joint is anticipated in advance, it is effective to
arrange the press bead in the direction of maximum main
stress at the location of crack formation. The direction
2 5 of main stress is generally a direction vertical to the
weld toe line in many cases. Note that, when the location
of crack formation cannot be predicted by experiments,
for example, FEM stress analysis utilizing 3D CAD may be
used to find the part of stress concentration from the
3 0 distribution of stress at the time a load is applied to
the welded structural member and thereby obtain a grasp
of the location of crack formation. Further, to grasp the
same, it is also possible to use an actual welded
structural member to run a stress load test and use a
35 strain gauge etc. at that time to investigate the
distribution of strain.
100741 (Length of Press Bead)
The press bead may be formed so as to be straight seen
from a top view or may be formed so that the press bead
is comprised of a plurality of straight parts seen from a
top view, but the length of the press bead (La)
5 preferably satisfies the condition of the following (A):
(A) Length of press bead (La)>Wldth of flllet bead (W)x2
Further, as shown by 3A1 and 3A2 (or 3A3 and 3A4) of the
press bead 3A of FIG. 5(f), when a slngle press bead is
formed by a plurality of stralght protruding parts, it is
10 preferable that the stralght protruding parts
respectively have lengths satisfying the above condition
of (A) .
[00751 When the length of the press bead is short, it
is not possible to sufficiently raise the rigidity of the
15 steel members and not possible to obtain the function of
improving the fatigue strength of the welded joint. If
the length of the press bead sticking out from the fillet
bead is the width of the fillet bead or more, depending
on the extent of the load applied to the welded
2 0 structural member, it is possible to obtain the function
of improving the fatigue strength, but to further raise
the rigidity, it is preferable to make the length of the
press bead (La) two times or more the width of the fillet
bead (W) .
2 5 COO761 Further, the upper limit of the length of the
press bead is restricted by the shape and structure of
the steel product produced by the welding. For example,
if the length of the fillet bead is "L", the length of
the press bead (La) can be made less than 0.5xL.
3 0 LO0771 (Height of Press Bead)
As explained above, the cross-sectional shape parallel to
the direction of formation of the press bead is not
particularly limited, but the height in one press bead
need not be constant. However, the height (Ha) of the
35 press bead from the surface of the steel member
preferably satisfies the condition of the following (B)
with respect to the thickness (t(m)) of the steel member
at whlch the press bead 1s formed.
(B) Helght of press bead (Ha)>Thickness of steel member
(t)
If the height of the press bead is less than the
5 thickness of the steel member at whlch the press bead is
formed, the press bead wlll not sufficiently exert its
function.
[0078] To obtaln the effect of improvement of the
rlgldlty of the weld zone, the hlgher the height of the
10 stiffening bead, the better. However, if trylng to raise
the bead height by the weld bead, the lnput heat becomes
excessive and the weld zone ends up with burn-through
defects. If settlng the welding voltage low to prevent
burn-through defects, the shape of the weld toe becomes
15 sharp and ends up causing the formation of fatigue
cracks.
f00791 On the other hand, to reduce the stress
concentration at the weld toe, it is necessary to
increase the flank angle of the toe, that is, make the
2 0 toe angle 0 smaller. For this reason, to obtain the effect
of improving the rigidlty of the weld zone, it is
necessary to make the stiffening bead higher and reduce
the toe angle 8.
[0080] Therefore, the inventors formed a 50 mm length
2 5 weld bead on the surface of a sheet thickness 2.6 mm
steel sheet and investigated the relationship between the
weld bead height and shape of the weld toe. The welding
conditions were made those of pulse mag welding generally
used in welding thin sheets (welding current=115A,
3 0 welding voltage=22V) and those of short arc welding
(welding current=115A, welding voltage=18V). The welding
speed was made to change to 30 to 100 cm/min to make the
weld bead height change. Note that, in the conventional
pztent literature, the flank angle was used as an
3 5 indicator of the toe shape, but in the findings of the
inventors, it is believed that the toe radius is more
suitable as an indicator showing the coefficient of
stress concentration than the flank angle or toe angle 0,
so the toe radius was made the indicator of the shape of
the toe. Here, the toe radius of the weld bead, as shown
5 in FIG. 12(a), is the radius of curvature Rb of the
fillet bead 3 at the weld toe 4. The results are shown in
the graph of FIG. 13.
[OOSl] In both pulse mag welding and short arc
he welding speed and raising the
10 bead height (Hb), the toe radius (Rb) tends to become
smaller. Further, in both pulse mag welding and short arc
welding, if lowering the welding speed and raising the
bead height (Hb), it is feared that the back surface of
the steel sheet will end up melting and part of the weld
15 bead will burn through. As shown above, it will be
understood that realizing both expansion of the toe
radius and increase of the weld bead height at the weld
bead would be difficult. In particular, in the case of
pulse mag welding, it is difficult to stably make the toe
2 0 radius over 1.0 mm.
[0082] The numerical values in parentheses show the
values of the weld bead height (Hb) /sheet thickness (t)
and the toe radius (%)/sheet thickness (t), but the
maximum value of the weld bead height was about the sheet
2 5 thickness in pulse mag welding or about 1.3-fold the
sheet thickness in short arc welding. Further, the
maximum value of the toe radius was about 0.92-fold and
0.54-fold the sheet thickness in the respective welding
methods.
3 0 [0083] A bead prepared by press-forming differs from a
weld bead in the point that it is not restricted in bead
shape along with welding. For this reason, a press bead
can achieve both enlargement of the toe radius and
increase of the bead height and further is easy to change
35 in width dimension, so an effect of improvement of the
fatigue strength over a weld stiffening bead can be
expected. Here, the "toe radius of the press bead" is the
radius of curvature Ra of the root of the press bead as
shown in FIG. 12 (b) .
[0084] Therefore, a lap fillet welded joint with a
weld bead formed as a stiffening bead and a lap fillet
5 welded joint with a press bead formed as a stiffening
bead were used to perform fatigue strength tests. The
effects of improvement of the fatigue strength were
compared.
0851 The lap fillet welded joint used for the tests
10 is shown in F I G . 15. The lap fillet welded joint is
comprised of a sheet thickness 2.6 mm 780 MPa class steel
sheet on which a sheet thickness 3.2 mrn 780 MPa class
steel sheet is laid and fillet welded and has a
stiffening bead arranged at the center of the fillet weld
15 bead in a direction vertical to the weld line.
[0086] The fatigue test uses a universal axial force
fatigue tester to cause a repeated load to act so that a
minimum load of 0.9 kN and a maximum load of 9.9 kN are
applied in opposite directions on the upper sheet 1 and
2 0 lower sheet 2 of FIG. 15 (in arrow directions of FIG.
15). The results of this fatigue strength test are shown
in FIG. 14. As test piece conditions, the Ha' and p'
shown in F I G . 14 are values obtained by dividing the
stiffening bead height and toe radius of the stiffening
2 5 bead by the sheet thickness (t).
[0087] In the case of no stiffening bead, the fracture
life was 230,000 cycles after which cracks formed from
the weld beginning and ending portions. If a weld
stiffening bead was formed as the stiffening bead, the
30 fracture life increased 1.6-fold and 2.4-fold in
accordance with an increase in the stiffening bead
height. The fatigue cracks formed not only at the welding
beginning and ending portions, but also from the
stiffening bead ends. On the other hand, if the
3 5 stiffening bead is a press bead, the fatigue life greatly
increased in accordance with the increase in the
stiffening bead height. The toe radius of the press bead
was enlarged to equal the sheet thickness (p'=l), so
cracks no longer formed from the end parts of the press
bead and, it is believed, an effect of improvement of the
fatigue life corresponding to an increase in the bead
5 height could be obtained.
[00881 According to the above results of study, to
obtain an effect of extension of the fatigue life above a
weld bead by a press bead, it is preferable to make
Ha'>l, pl>l.
10 [0089] (Width of Press Bead)
Further, the width of the press bead (Wa) is preferably
one satisfying the condition of the following ( C ) :
(C) Width of press bead (Wa)tWidth of fillet bead (W)
As explained above, the cross-sectional shape vertical to
15 the direction of formation of the press bead is not
particularly limited, but if the width of the press bead
is less than the width of fillet bead, the function as a
press bead is not sufficiently obtained. No upper limit
of the width of the press bead is particularly set so
2 0 long as the fatigue strength sought for the welded
structural member can be secured and the function of the
final product is not impaired, but to improve the local
rigidity by the press bead, it is preferable to make it
3-fold the weld bead width or less.
2 5 [OOSO] (Angle of Direction of Formation of Press Bead)
The angle (y) of the direction of formation of the press
bead is preferably made one satisfying the condition of
the following (D) :
(D) 45"SAngle of press bead (y)1135'
30 To enable the press bead to exhibit the function of
raising the rigidity of the steel sheet and suppressing
bending, it is preferable to arrange the press bead in
the direction of maximum main stress at the location of
formation of a crack. The direction of the maximum main
35 stress is in many cases a direction vertical to the weld
toe line, so the crossing angle y of the toe line
direction of the fillet weld bead and the press bead is
preferably 45 to 135'. If the angle y is less than 45' or
over 135', the function of the press bead in improving the
rigidity falls. Note that, when the design direction of
5 maximum stress is known, it may be formed so that the
longitudinal direction of the press bead matches with
that direction. The more preferable angle of the cross
angle y of the press bead is 60' to 120°, particularly
preferably $0' to 100'.
10 [00911 (Other Requirements)
The conditions for formation of the press bead, the arc
welding conditions when forming the fillet bead, and the
composition of the welding wire may be ones based on
ordinary methods and are not limited to any particular
15 ones. Further, in the welded joint, since the press bead
is formed to overlay the flllet bead, it is necessary
that there be a region around the welded joint where the
press bead can be formed at a required angle and required
length, height, and wldth.
2 0 100921 In the above way, in the present invention,
even when the welded structural member is subjected to
repeated stress, the simple means of providing a press
bead enables occurrence of fatigue fracture to be
remarkably suppressed.
2 5 [0093] Further, the inventors confirmed that the
technique of the present invention can be applied even to
metal members other than steel members. For example,
instead of steel members, the technique of the present
invention can also be applied to aluminum members or
3 0 stainless steel members. Further, the inventors confirmed
that the technique of the present invention can also be
applied to different types of metal members.
[0094] Below, specific embodiments in the case of
application of a press bead to a fillet welded joint will
35 be explained using the welded structural member shown in
FIGS. 8 to 10. Note that, in these embodiments, it is
assumed that a repeated load is applied in the white
arrow directions shown in the figures.
[0095] (First Embodiment)
FIG. 8 is a perspective view showing a first embodiment
of a welded structural member. The welded structural
member 10 shown in FIG. 8 is comprised of one channel
member (steel channel) 12 on the upper surface 12A of
which one end part of another channel member 11 is made
to abut, where at the abutting parts, only the parts
the outside from the surfaces of the channel member 11
are fillet welded.
[0096] The fillet bead 13 includes two corner parts
16A and 16B in the middle of it. Here, if applying a
repeated load envisioned as being applied to the welded
structural member 10 to the welded structural member 10,
the main stress becomes large at the corner parts 16A and
16B of the channel member 11 and at the beginning and
ending portions 16C of the fillet bead. The main stress
at 16C is assumed to become the maximum main stress.
E00971 In this case, first, if forming press beads at
the positions of maximum main stress of the beginning and
ending portions 16C, the fatigue strength is improved. By
forming press beads at the beginning and ending portions
16C, the positions which first fracture when a repeated
load is applied move to the corner parts 16A and 16%.
Therefore, if forming the press beads at the corner parts
16A and 16B, the fatigue strength further rises. In FIG.
8, notches 14 are formed in advance in the channel member
11 at the positions of the beginning and ending portions
16C, then the press beads 15C are fit into them, so the
fatigue strength is further improved. While not shown, if
forming notches in advance in the channel member 11 at
the positions of the corner parts 16A and 16B and making
the press beads 15A and 15B cross the channel member 11,
the fatigue strength is further improved. The press beads
15A, 15B, and 15C are formed on the top surface 12A so as
to project upward at the fillet bead 13 side. One press
bead each need only be formed at a single location.
[00981 As shown in FIG. 8, when forming the fillet
bead 13, the top surface part 12A is pressed in advance
to form the press beads 15A, 15B, and 15C in directions
5 crossing the directions of the fillet bead 13 so that
locations overlapping with the fillet bead 13 are
included. The press beads 15A, 15B, and 15C have to be
formed to sufficientiy secure contact between that one
end part of the channel member 11 and the top surface 12A
10 and not form unnecessary clearances.
[0099] (Second Embodiment)
FIG. 9 is a perspective view showing a second embodiment
of a welded structural member. FIG. 9 shows an example
of a lap fillet arc welded joint wherein the sheet
15 surface parts of the one metal member and the other metal
member are joined with each other. The welded structural
member 20 shown in FIG. 9 is formed by attaching the back
surfaces of the flange parts at the two sides of the
channel member 21 to the mutually facing side surfaces of
2 0 the channel member 22 and lap fillet welding the front
end parts of the flange parts. As shown in FIG. 9,
upwardly projecting press beads 25A and 25B are formed at
the side surfaces 22A of the channel member 22 in advance
at the fillet bead 23 sides at locations corresponding to
25 the vicinities of the boundaries (end parts 26A and 26B)
between the front end parts of the flange parts of the
channel member 21 and the base end parts of the channel
member 22 so that the parts where the fillet beads 23 are
formed are included.
30 [OlOO] Further, to improve the joint strength of the
fillet bead 23, as shown in FIG. 9, an upwardly
projecting press bead 25C may be formed at the fillet
bead 23 side in a direction crossing the direction of the
fillet bead 23 so that the part where the fillet bead 23
35 is formed is included at the side surface 21A side of the
flange part of the channel member 21. The press bead 25C
is preferably formed at the center of the front end of
the flange part, but a plurality may also be formed.
[ O l O l l (Third Embodiment)
FIG. 10 is a perspective view showing a third embodiment
of a welded structural member. The welded structural
5 member 30 shown in FIG. 10 is configured using a box
member 32 made using a rectangular metal tube and a box
member 31 compr~sed of a rectangular metal tube where one
pan of surfaces of the two palr of mutually facing
surfaces of the front end part are cut out to match the
10 shape of the box member 32. The box member 32 and box
member 31 are assembled so that the back surfaces of the
parts of the front end part of the box member 31 whlch
are not cut away abut against the front surface 32A2 of
the box member 32 and so that the sheet thickness parts
15 of the parts of the front end part of the box member 31
which are cut away abut against the front surface of the
box member 32. The abutting parts are then fillet welded
to form the welded structural member 30.
I01021 The fillet bead 33 formed at the welded
2 0 structural member 30 has at least the corner parts of the
corner parts 36A to 36E in the middle. The locations
where fatigue cracks first form when applying to the
welded structural member 30 not formed with a press bead
a repeated load envisioned as being applied to a welded
2 5 structural member 30 are assumed to be the corner parts
where the sheet thickness parts of the parts of the front
end part of the box member 31 which are cut away abut
against the front surface of the box member 32.
[0103] However, if considering the direction of the
3 0 load applied to the rectangular metal tube 31, the corner
parts 36A, 36B, and 36E are the boundary parts of the
side surfaces 32A1 and 32C, 32A1 and 32B, and 32B and
32Ai of the box member 32. By forming press beads at
these parts, the effect of improvement of the joining
35 strength of the fillet beads 33 is low. Therefore, here,
instead of the corner parts 36A to 36E etc., at least one
press bead is formed so that a part where the fillet bead
33 is formed is included at least at one of the side
surfaces 32A1 and 32A2 of the box member 32. Further, in
FIG. 10, one press bead 35A is formed at only the side
surface 32A1 of the box member 32 so that the end part of
5 the upwardly projecting part and the fillet bead 33
overlap, but a plurality of the press beads may also be
formed at the same side surface.
[0104] Further, the embodiments of the present
invention explained above all only show exam
10 specific application in working the present invention.
The technical scope of the present invention must not be
interpreted limitatively due to these. That is, the
present invention can be worked in various forms without
deviating from this technical idea or major features.
15 [0105] (Fourth Embodiment)
FIG. 11 is a perspective view showing a fourth embodiment
of a welded structural member. As shown in FIG. 11, one
end part of the channel member 11 is made to abut against
the top surface of the lower steel sheet 2 . At the
2 0 abutting part, only the part at the outside of the sheet
surface of the channel member 11 is fillet welded. The
fourth embodiment is characterized by having press beads
45A, 45B, and 45C formed along the fillet bead 43 at the
corner parts 16A and 16B of the channel member 11 and the
25 beginning or ending portion 16C of the fillet bead. These
press beads are formed in advance by pressing the
locations corresponding to the corner parts 16A and 16B
of the channel member 11 and the beginning or ending
portion l 6 C of the fillet bead so that the locations
3 0 overlapping the fillet bead 43 are included.
Examples
[0106] Next, examples of the present invention will be
explained, but the conditions of the examples are
illustrations of the conditions employed for confirming
35 the workability and effect of the present invention. The
present invention is not limited to this illustration of
the conditions. The present invention can employ various
conditions so long as not deviating from the gist of the
present invention and achieving the object of the present
invention.
[0107] The comparative example and invention examples
5 of the welded structural members 10, 20, and 30 of the
shapes shown in FIGS. 8 to 10 were fabricated under the
conditions for forming the press beads shown in Tables 2
to 4. These welded structural members were used for
e tests. Note that, based on the findings based on
10 the results of the fatigue strength tests of FIG. 14, the
toe radius of a press bead was made one equal to the
sheet thickness ( p ' = l ) .
[OlOS] The steel members and weld materials used for
the welded structural members are shown in Table 1. In
15 Table 1, the two types of steel members of the steel
material A and steel material B were used. Further, as
the steel sheet A and steel sheet B, two types of steel
members were used. Further, as the steel sheet A and the
steel sheet 3, ones of two different sheet thicknesses
2 0 (2.3 mm and 2.6 mm) were respectively prepared. Further,
two types of weld materials of the wire A and wire B were
used. The wires A and B had diameters of 1.2 mm.
[01091 Table 1
2 5 [OllO] In the examples, the hat member 12 shown in
FIG. 8 had a size of an X-direction (length) of 300 mxYdirection
(width) of 150 mmxZ-direction (height) of 80
mm. The bracket member 11 had a size of an X-direction
(width) of 80 mmxY-direction (width) of 75 mmxZ-direction
30 (height) of 80 mm.
[Ollll In the examples, the hat member 22 shown in
F I G . 9 had a size of an X-direction (length) of 300 mmxYdirection
(width) of 100 mmxZ-direction (height) of 50
mm. The bracket member 21 had a size of an X-direction
(width) of 75 mmxY-direction (width) of 105 mmxZ-direction
5 (height) of 80 mm.
I01121 In the examples, the box member 32 shown in
F I G . 10 had a size of an X-direction (length) of 300 mm,
a Y-direction (width) of 100 mm, and a Z-direction
(height) of 50 mm. On the other hand, the bracket member
10 31 was comprised of a rectangular steel tube of an Xdirection
(width) of 76 mm, a Y-direction (length) of 180
mm, and a Z-direction (height) of 56 mm with 25 mm cut
off from the front end of the 180 mm length part.
[0113] Further, the fillet bead was formed under the
15 following conditions of formation as common welding
conditions:
Welding method: pulse mag welding
Welding current: 150 to 200A
Welding voltage: 20 to 25V
2 0 Target position: corner of overlap part
Welding speed: 60 to 80 cm/min
[0114] The fabricated welded structural member was
gripped by an electrical hydraulic fatigue test apparatus
so that the direction of load became the direction shown
2 5 by the white arrows of F I G . 8 to F I G . 10 and was
subjected to a fatigue test at a constant range of load
(constant range of stress), a load ratio of 0.1, and a
repetition frequency of 5Hz.
[0115] In the present examples, when the "fatigue life
3 0 improvement rate" in the case of testing a welded
structural member provided with a press bead in the same
range of load exceeded 120% of the fatigue life of a
welded structural member not provided with a press bead,
it was judged that there was an effect due to the press
35 bead.
101161 (Regarding Examples Based on First Embodiment)
Based on FIG. 8 and Table 2, results of examples of the
first embodiment will be explained. The welded structural
member 10 shown in FIG. 8 is formed by arranging a
channel shaped bracket member 11 at the top surface 12A
5 of the hat member 12 and fillet welding the outer
circumference of the bracket member. Further, Test Piece
C-1 is a comparative example in which no press bead is
arranged, while Test Pieces C-2 to C-5 are invention
xamples in which press beads are arrang
10 (01171 In Comparative Example C-l where no press bead
was arranged, cracks formed at the weld toe 16C at the
hat member side of the fillet bead beginning portion or
ending portion. Therefore, in Invention Example C-2,
press beads 15C were arranged at positions of the top
15 surface of the hat member corresponding to the fillet
bead beginning and ending portions. Note that, the
positions of arrangement of the press bead were the front
end parts of the beginning and ending portions of the
fillet bead, so the direction of the press bead was made
2 0 a direction 90° with respect to the weld toe line of the
weld toe 16C, that is, parallel to the weld line.
Further, in Invention Example C-2, no notch was provided
at the hat member: the fillet bead and the press bead
were made to contact each other. As a result of the
2 5 fatigue test, the life improvement rate increased to over
180% and the crack formation position changed from the
fillet bead beginning and ending portions to the fillet
bead corner parts. Therefore, in the Invention Example C-
3, the press bead was arranged not only at the fillet
3 0 bead beginning and ending portions, but also the fillet
bead corner parts (15A and 15B). In the invention
example, due to the increase in the positions of
arrangement of the press beads and the effect of the
increase in the lengths of the press beads (La/W), the
35 fatigue life improvement rate became 270%. On the other
hand, the crack formation position became from the fillet
bead corner part to the boundary part of the beginning
and ending portions of the fillet bead and the press
bead.
[OllS] To make the fatigue life of the fillet bead
beginning and ending portions increase more, in Invention
5 Example C-4, the welding work was performed by providing
a notch 14 at the end part of the bracket member 11,
arranging the press bead so that its upward projecting
part fit in the notch of the bracket, and making the
t bead ride over the press bead. By increasing the
10 range of overlap of the press bead and the fillet bead,
the fillet bead beginning and ending portions further
rose in rigidity and the fatigue life improvement rate
became 365%. Invention Example C-5 is an example
providing a notch at a corner part of the bracket member
15 as well and arranging a press bead so that the fillet
bead and press bead crossed. The fatigue life improvement
rate greatly increased to 548%.
- 38 -
[0119] Table 2
corners
[01201 (Regarding Examples Based on Second Embodiment)
Based on FIG. 9 and Table 3, examples of the second
embodiment will be explained. The welded structural
member 20 shown in FIG. 9 was fabricated by arranging a
channel shaped bracket 21 covering a hat member 22 and
5 joining them by lap fillet welding. In Comparative
Example D-1 with no press bead, a crack formed from the
root at the center part of the fillet bead (location
corresponding to reference numeral 5 of FIG. 1A).
herefore, in Invention Example D-2, the press beads 25A
10 and 25B were arranged so as to contact the beginning and
ending portions of the fillet bead. Note that, the angles
of the press beads were 90' with respect to the toe line
there, that is, 45' with respect to the weld line of the
fillet bead. In the fatigue test, the life improvement
15 rate increased to 132%. Invention Example D-3 had the
press beads arranged identically to D-2, but had a length
and height of the press bead increased over D-2. As a
result, the fatigue life improvement rate further
increased to 212%. Invention Example 0-4 had the press
2 0 bead 25C provided at the center part of the fillet bead
at the bracket 21 side, in addition to the press beads at
the fillet bead beginning and ending portions, so due to
the effect of improvement of rigidity of the welded joint
due to the increase in the press beads, the fatigue life
2 5 improvement rate greatly increased to 347%.
- 40 -
[0121] Table 3
ickness "t"
lange of channel
ember 21 (1) L e f t
f channel
xam le 0-1
[0122j (Regarding Examples Based on Third Embodiment)
Based on FIG. 10 and Table 4, examples of the third
embodiment will be explained. The welded structural
member 30 shown in FIG. 10 was a welded joint comprised
of a box member 31 and a box member 32 arranged in a T-
5 shape. The side surfaces of the box members were joined
by butt fillet welding, while the top and bottom surfaces
of the box member were joined by lap fillet welding. If a
load acted on the box member 31 in the horizontal
direction, fatlgue cracks eas~ly formed at the butt
10 fillet welded side surfaces of the box member 32, so the
press bead should be arranged at those locations. In
Comparative Example E-1 with no press bead, a crack
formed from the weld toe at the center part of the fillet
bead at the box member 32 side. Therefore, the press bead
15 was arranged so as to contact the fillet bead at that
location. Invention Example E-2 had an angle of provision
of the press bead of 30' wlth respect to the weld toe
line. so the effect of improvement of the rigidity was
insufficient and the fatigue llfe improvement rate
2 0 stopped at 129%. Invention Example E-3 had a larger size
of the press bead and an angle of provision of the press
bead of 45' with respect to the weld toe line, so the
fatigue life improvement rate increased to 239%.
Invention Example E-4 had a larger width and height of
2 5 the press bead and an angle of provision of the press
bead of 90" (35A) with respect to the weld toe line, so
the fatigue life improvement rate greatly increased to
417%.
- 42 -
[01231 Table 4
ickness "t"
Industrial Applicability
I01241 Above, the present invention was explained
5 using mainly a fillet welded joint, but the present
invention has a high applicability in the machine
industry and also the industry welding steel sheets and
other metal members. That is, the present invention is
not limited to a welded structural member for automotive
use and can also be utilized for a structure comprised of
5 several materials or members etc. such as rolling stock
or aircraft or other transport machinery, mechanical
structures, home electric appliances, etc. Further, the
present invention is not limited to steel sheets and can
be applied to iron sheets, aluminum sheets, titanium
10 alloy sheets, or sheet members containing a metal and
resin.
Reference Signs List
[0125] 1. upper steel material
1A. notch
15 2. lower steel material
3. fillet weld bead
3A. press bead
4. toe
5. root
2 0 10. welded structural member
11. channel member
12. hat member
13. fillet bead
14. notch part
2 5 15A to 15C. press beads
16A, 16B. corner parts of channel member
16C. beginning and ending portions of fillet bead
20. welded structural member
21. channel member
30 22. channel member
23. fillet bead
24. fillet bead
25A to 25C. press bead
30. welded structural member
35 31. box member
32. box member
33. fillet bead
35A. press bead
36A to 36E. corner parts of f i l l e t bead
40. welded s t r u c t u r a l member
43. f i l l e t bead
5 45A t o 45C. press beads
8. toe angle

CLAIMS
Claim 1. A fillet welded joint formed by fillet
welding at least two metal members, wherein
on the surface of at least one of the metal
5 members, the fillet welded joint comprises a press bead
of a rib-shaped projection provided by press-forming so
as to project upward to a side having a weld bead formed
by the fillet welding, and wherein
press bead contacts or overlaps the
10 weld bead.
Clalm 2. The flllet welded joint according to claim
1, wherein a longitudinal direction of the press bead is
45O to 135" with respect to a direction of a weld toe line
of the weld bead.
15 Claim 3. The fillet welded joint according to claim
1 or 2, where~n the press bead is positioned along the
weld bead at least at one of a beginning portion, ending
portion, and bent portion of the weld bead and location
in the middle of that weld bead where a stress higher
2 0 than the beginning and ending portions is applied
Claim 4. The fillet welded joint according to any
one of claims 1 to 3, wherein the press bead has a toe
radius Ra (mm) which is equal to or longer than a
thickness "t" (mm) of the metal member having the press
25 bead.
Claim 5. The fillet welded joint according to any
one of claims 1 to 4, wherein the press bead satisfies
HaX, and
Wa2W
where "La" expresses a length in a longitudinal
direction of the press bead, "Ha" expresses a height of
the press bead, "Wa" expresses a width of the press bead,
"W" expresses a width of the weld bead, and "t" expresses
3 5 a thickness of the metal member having a press bead.
Claim 6. The fillet welded joint according to any
one of claims 1 to 5, wherein the press bead crosses the
weld bead.
Claim 7. The fillet welded joint according to any
one of claims 1 to 6, wherein the press bead overlaps the
5 weld bead at a part where a previously established
maximum main stress is caused.
Claim 8. The fillet welded joint according to any
one of claims 1 to 7, wherein the metal member welded
ith the metal member at which the press bead is formed
10 comprises a notched part fitting in the press bead at the
location where the press bead is welded.
Claim 9. The fillet welded joint according to any
one of claims 1 to 8, wherein
at least one of the metal members is a metal
15 member which has a cross-sectional shape having a folded
corner part and which is fillet welded to the other metal
member, and wherein
a press bead is superposed at the corner part
of the weld bead.
2 0 Claim 10. A method for producing a fillet welded
joint by fillet welding at least two metal members,
the method comprising press forming on the
surface of at least one of the metal members a press bead
of a rib-shaped projection so as to project upward to a
2 5 side having a weld bead formed by the fillet welding and
fillet welding the metal members so that a part
of the press bead contacts or is superposed with the weld
bead.
Claim 11. The method for producing a fillet welded
3 0 joint according to claim 10, further comprising forming a
longitudinal direction of the press bead to be 45' to 135'
with respect to a direction of a weld toe line of the
weld bead.
Claim 12. The method for producing a fillet welded
35 joint according to claim 10 or 11, further comprising
forming the press bead along the weld bead at least at
one of a beginning portion, ending portion, and bent
portion of the weld bead and a location in the middle of
the weld bead where a stress higher than stresses at the
beginning and ending portions is applied.
Claim 13. The method for producing a fillet welded
5 joint according to any one of claims 10 to 12, further
comprising forming the press bead having a toe radius Ra
(mm) which is equal to or more than a thickness "t" (rnrn)
of the metal member having the press bead.
e method for producing a fillet welded
10 joint according to any one of claims 10 to 13, wherein
the press bead satisfies
La22W,
HaZt, and
WaZW
15 where "La" expresses a length in a longitudinal
direction of the press bead, "Ha" expresses a height of
the press bead, "Wa" expresses a width of the press bead,
"W'\xpresses a width of the weld bead, and "t" expresses
a thickness of the metal member having a press bead.
2 0 Claim 15. The method for producing a fillet welded
joint according to any one of claims 10 to 14, further
comprising forming the press bead to cross the weld bead.
Claim 16. The method for producing a fillet welded
joint according to any one of claims 10 to 15, further
2 5 comprising forming the press bead to contact or overlap
the weld bead at a part where a previously established
maximum main stress is caused.
Claim 17. The method for producing a fillet welded
joint according to any one of claims 10 to 16, further
30 comprising forming a notched part, the notched part being
fit into in the press bead at the location welded with
the press bead in the metal member welded with the metal
member at which the press bead is formed.
Claim 18. The method for producing a fillet welded
35 joint according to any one of claims 10 to 17, wherein
the method comprises fillet welding one of the
metal members to the other metal member, at least one of
the metal members being a metal member of a crosssectional
shape having a folded corner part, and forming
the press bead in advance at the other metal member so
5 that the press bead is superposed at a corner part of the
weld bead.