Note: Descriptions are shown in the official language in which they were submitted.
~2~L~23~
The present invention relates to an apparatus
for butt welding steel strips by means of a laser beam
(hereinafter referred to as "laser butt welding
appara~us"~ in a steel strip-processing line.
05 In a steel s-trip processing line, steel
strips are jointed together at an entry section of the
line, and fed to a latter stage processing and con-
tinuously treated and produced. The steel s-trips have
been conventionally jointed by a seam welding machine,
o a flash butt welding machine, an arc welding machine
such as TIG arc welding machine. These welding methods
have their own peculiar characteristics respectively.
The seam welding is characterized in that the welding
is possible at a high speed in a short time, but the
thickness of the welded portion becomes 180-130% of
that of the base metal because the steel strips are
welded by piling their edges one upon another.
Therefore, the welded portion can not be rolled in
a coil by taking the problem such as buckling in-to
account. If a scale is present on the surface of the
steel strip as in the case of a hot-rolled steel strip
or the like, this method has -the defect that the surface
must be ground prior to the welding. Further, in the
case of the welding of thin steel strips, since the
strips are pressed by means of electrode wheels, this
method has the drawback that the profile of junction
and the vicinity thereof are deteriorated.
The flash butt welding can make the welding
-- 2 --
~'
time shorter than the seam welding because the steel
strips are welded at one time over their whole width in
the former method, bu~ thin steel s-trips are likely to
be bent due to upsetting step, SG that this method has
05 the defect that it is applicable to the relatively
thick steel strips of not ]ess than l.6 mm~ but is not
applicable to the thin steel strips. I~ also has the
defect that it is inapplicable to special steels such
as silicon steel, stainless steel, high carbon steel
because of oxidation, a large heat input and the coarse
grain growth at the welded portion and heat affected
zone when the flashing is effected. As a result, the
use of flash butt welding is generally restricted to
the welding of the low carbon steel strips of not less
than l.6 mm in thickness.
According to TIG arc welding, it is possible
to improve the quality of the welded portion through
addition of a filler wire or the like 9 and therefore,
this method can be used ~or stainless steel. However,
since the heat input is large, it has the defect that
it is inapplicable to the ma-terial such as the silicon
steel in which the coarse grains are likely to grow.
Further, it also has the defects that the welding speed
is slow, and the welding time is long.
As mentioned above, although the conventional
seam welding, flash butt welding~ TIG arc welding and
the like have been used by utilizing the respective
characteristics, they can not be applied to the silicon
~LZ~Z~7
steel or the like. Thus, there has been demanded
a welding apparatus which can weld the special steels
such as silicon steel or the like.
An object of the present invention is to
05 provide an automatic laser butt welding apparatus for
welding steel strips in a steel-processing line by
using a laser beam as a heat source.
More specifically, the object of the invention
is to provide a laser butt welding appara-tus usable for
welding almost all kinds of the steels, for instance,
special s-teels such as silicon s-teel, stainless steel
or the li~e~ a plated steel such as a galvanized steel
or the like, and high tensile strength steels.
It is another object of the invention to
provide a laser butt welding apparatus usable for usual
steel strips of from small to large thickness by using
a laser beam without limiting the thickness as in the
case of the flash butt welding.
It is a further objec-t of the invention to
provide a laser butt welding apparatus by using a laser
beam which enables the far higher speed welcling through
the TIG arc welding in a high efficiency.
The apparatus according to the inven-tion
comprises a pair of clamp means at least one of which
is movable forward and rearward along the steel strip-
feed line direction and which are adapted to clamp the
edge portions of a preceding steel strip and a trailing
steel strip, a shear which is advanceable and retractable
~7~3~
between the pair of the clamp means in a direction
perpendicular to the llne and cuts the edge portions of
the preceding steel strip and the trailing steel strip,
means for butting the cut faces of the preceding steel
05 strip and the trailing steel strip while being clamped
by means of the clamp means, and a laser torch mounting
a bender reflector adapted to bend a laser beam
irradiated from a laser oscillator placed on an off-line
and a condenser adapted to condense the laser beam
reflected by -the bender at a weld zone, which is movable
in a transverse direction of steel strips to be welded
together.
These and other objects, features and
advantages o-f the invention will be well appreciated
upon reading of the following description of the
invention when considered in connection with the
accompanying drawings with understanding that some
modifications, variations and changes could be easily
made by the skilled in the art to which the inven-tion
pertains without departing from the spirit of the
invention and the scope of the appended claims.
The invention will now be described in detail
with reference to the accompanying drawings, wherein:
Fig. 1 is a schematic plan view of the whole
laser butt welding apparatus according to the present
invention;
Fig. 2 is a side view of a clamp means and
a shear in the laser butt welding apparatus in Fig. l;
~L2~;Z37
Fig. 3 is a front view of the la~er butt
welding apparat~ls in Fig. l;
Fig. 4 is a detailed view illustrating the
state in which a preceding steel strip and a trailing
05 steel strip are clamped;
Fig. 5 is a plan view of a station for checking
the performances of an optical system for irradiating
a laser beam onto a weld zone;
Fig. 6(a) is a side view o-f the station for
lo checking the performances of the optical system in
Fig. 5;
Fig. 6(b) is a side view of another embodiment
of the station for checking the performance of the
optical system;
Fig. 7 is a side view showing a butting means
of an inlet clamp;
Fig. 8 is a plan view of the butting means of
the inle-t clamp as viewed from the direction of the
arrow of X-X in Fig. 7;
Fig. 9 is a sectional view as viewed from the
direction of the arrow A-A in Fig. 8;
Fig. lO is a sectional view as viewed from
the direction of the arrow B-B in Fig. 9;
Figs. ll(a) to ll(d~ are other embodiments of
the butting means;
Fig. 12 is a plan view of a laser -torch;
Fig. 13 is a side view of the laser torch in
Fig. ll;
7Z~7
Fig. 14 is a side view of a center clamp;
Fig. 15 is a detailed view of the center
clamp in Fig. 14;
Fig. 16 is a sectional view illustrating the
05 state in which the preceding steel s-trip and the -trailing
steel strip are improperly butted with each oth~r;
Figs. 17(a)-17(f) are views schematically
illus~rating the operation of the laser butt we:Lding
apparatus according to the present invention;
Fig. 18 is a graph illustrating the relation
between the distance Q from a tip of an wpper clamp to
an edge o~ an upper blade of the shear and a value ~G
which is obtained by subtracting the minimum value of
the distance between the cut preceding steel strip and
the cut trailing steel strip in the width direction of
said steel strip from the maximum value;
Fig. l9 is a schematic view illustrating -the
value ~G in Fig. 18;
Fig. 20 is a graph illustrating the relation
be-tween tan ~ in which ~ is a blade rake angle of
a shear, the value ~G and the thickness of the steel
strip;
Fig. 21(a) and 21(b) are views illustrating
the operation of the `butting means of the inlet clamp;
Fig. 22 is a schematic view ill~lstrating
a sectional profile of the welded portion formed when
the center of the laser beam is deviated from a butt
llne;
Z3~7
Figs. 23~a) and 23(b) are side and plan views
of another embodiment of the laser beam path construction
in the laser torch respectively;
Figs. 2~l(a~ and 24(b~ are side and plan views
o~ of still another embodiment of the laser beam path
construction of a laser torch; and
Figs. 2S(a) and 25~b) are micrographs of the
welded joints of silicon steel strips obtained by the
laser butt welding of the present invention and TIG arc
0 welding respectively.
The present invention will be explained in
more detail with reference to the attached drawings
below:
In Fig. l, reference numerals l, 2 and 3 are
double out shear, a laser oscillator, a double blade
shear, and clamp means consisting of an inlet clamp 3a
and an outlet clamp 3b respectively. Reference numerals
4 and 5 are a laser torch and a butting means respec-
tively. The double blade shear 2, the clamp means 8
and the butting means 5 will be explained referring to
Figs. 2 and 3. Although the clamp means may be included
in the butting means in view of the function but are
explained as separate members in the follow;ng:
In Figs. 2 and 3, the double blade shear 2
has upper and lower blades 7 and 8 mounted respectively
on ~.he upper and lower arm 6a and 6b o~ a C-letter
shaped frame 6. The blades 7 are vertically movable by
means of a cylinder 7a, guide rods 7b and 7c secured to
. -- 8 --
~L2~l~Z37
~he upper arm 6a, while the lower blades 8 are ver~ically
movable by means of a cylinder 8a, guide rods 8b and 8c
secured on the lower arm 6b. Each upper blade 7 is
provided with a rake angle in a transverse direction of
05 the strip, which is selectively determined in such
a range as to improve a shear-cut profile of the strips.
The shear 2 is so constituted that the C-le-tter shaped
frame 6 is forwardly and rearwardly movable between the
outlet clamp 3b ancl the inlet clamp 3a in a transverse
direction of the steel strip while being guided by
rails 10, by means of a drive means 9 (for instance,
a cylinder). The inlet clamp 3a and the outlet clamp
3b are disposed on a stationary base 11 in opposite
relation. The upper clamps 12a and 12b are both
vertically movable with respect to the lower clamps 15a
and 15b respectively by means of cylinders 14a and 14b
secured to the upper frames 13a and 13b, so as to clamp
or release the edge portions of steel strips fed on the
line. The inlet clamp means 3a moves in the line
direction on a lower base 33 of the stationary base ll
by means of a drive means, for instance, a cylinder 16,
so that said means moves forwardly or rearwardly with
respect to the outlet clamp means 3b. The outlet clamp
means 3b is Eixed without being displaced in the line
~irection.
Next~ the clamp means is explained in more
detail referring to Fig. 4. Top ends of the upper
clamps 12a and 12b of the inlet and outlet clamp means
_ g _
O~V ~
3a and 3b are extended a little longer toward a shear-
running l.ine than those of the lower clamp means 15a
and 15b, so that the steel strips Sa, Sb to be cut are
clamped be~ween the tips of the upper clamp means 12a,
05 12b and the lower blades 8.
As shown in Figs. 5 and 6(a), (b), a station 100
for checking the performances of an optical system for
irradiating a laser beam on a weld zone of the steel
strips is provided at the lower clamp hase 15b on
lo an off-line.
A reference numeral 101 is a table having
a slit just under the laser torch. Numeral 103 is
a sample plate which is secured to the table 101 by
means of press plates 104 and bolts lOS.
According to this embodiment, the table 101
is joined to the lower clamp base l5b, but it may be
supported by a base 33.
Referring next to Figs. 7-10, the butt means
will be explained below.
The trailing steel strip is moved toward the
preceding steel strip by actuating the cylinders 16,
and is stopped by appropriate means. For instance, the
forward movement of the trailing steel strip is stopped
upon contacting the shear cut edge of the preceding
steel strip. Alternatively, an arm 17 is provided
under the inlet clamp 3a, while a stopper 18 is provided
on the base plate 33, so that the trailing steel strip
which is moved forwardly is stopped upon contact between
- 10 -
23~7
the arm 17 and the stopper 18. In such a case, the
stopper 18 may be located apart from the lower ben-t
edge side of the arm 17 at the substantially the same
distance as that of the gap between the shear cut edge
05 faces of the steel strips, and may be designed in
a form of shock absorber.
~ urther, a pressure detector 25 such as
a load cell is provided at a face of the stopper 18
which contacts with the arm 17. The stopper 18 is
adapted to be moved while being guided wi~h gwide
means 26. That is, a screw shaf-t 27 is screwed to -the
lower portion of the stopper 1~, and the screw shaft is
adapted to be rotated for shifting the position of the
stopper 18 by actuating the motor 32 via bevel gears 28
and 29, a shaEt 31 and bevel gears 30 and 30'.
A stopper-positioning system comprising the bevel gears
28, 29, 30 and 30', and the shafts 27 and 31 are arranged
onto a lower base 33. With this construction, it may
be possible to stop the trailin~ steel strip slightly
spaced from the shear cut ed~e of the preceding steel
strip, and to gently butt the edge Eaces of the preceding
and trailing steel strips by actuating the motor 32
-Erom an output Erom the stopper or the like. As a matter
o:E coursc, the motor is stopped by approprlate way
25 af ter the shear cut edges butt with each other.
In the sliding portion of the inlet lower
clamp lSa and the lower base 33, the top portion of
a guide member 34 is tapered so that two wheels 35
~L2~L~237
fittecl on the side portion of the inlet clamp 3a and
positioning on the side of the outlet clamp 3b may be
moved in the transverse direction of the s-teel strip
and the steel strip clamped with the inlet clamp 3a may
05 be slightly pivoted in a horizontal plane, whereby both
the cut edge faces of the steel strips to be jointed
are pivo-ted so as to come in contact and reduce -the gap
of the butted portion.
In the above embodiment, two stoppers 18 are
o driven by means of a single motor 32, but as a matter
of course, they may be driven independently by means of
two motors.
Some embodiments for attaining the above
described mechanism of but-ting means will be explained
with reference to Fig. 11, a, b, c and d hereinafter.
In Fig. 11, a, a refere~lce numeral 33 shows
a fixed guide member provided on the base wherein the
top portions of both sides of said member have cut
portions as shown in Fig. 11, a and two pairs of wheels
35 are provided on the side portions of the inlet lower
clamp 15a, so that said wheels slide on guide portions
34 of the guide member 33. When a pair forward wheels
35 slide and advance to the cut portions in this guide
member, the inlet lower clamp 15a may be slightly
pivo~ed in the horizontal direction.
~ n Fig. 11, b, a reference n~lmeral 33 shows
two fixed guide members provided on the base, wherein
each top portion of said members has the cut portion as
- 12 -
~Z~7Z37
shown in this figure and the wheels 35 are provided on
the side portions of the inlet movable lower clamps and
when a pair of forward wheels 35 slide and advance to
the cut portions, the inle~ lower clamp 15a may be
05 slightly pivoted in the hori20ntal dirPction as in the
case of Fig. 11, a.
In Fig. 11, c, a reference numeral 33 shows
two fixed ~uide members provided on the base and
a reference numeral lSa shows the supporting member of
the movable inlet lower clamp, wherein the rearward end
portions have ~he cut portions as shown in this figure.
Two pair of wheels 35 are provided on the fixed guide
members 33. When the supporting member 15a of the
movable inlet lower clamp is forwardly moved and the
cut portions thereof come to the rearward wheels 35,
the in].et lower clamp lSa may be slightly pivoted in
the horizontal direction as in the case of Fig. 11, a.
In Fig. 11, d, a reference numeral 33 shows
a fixed guide member provided on the base 33 which is
provided with two pair of wheels 35 and a reference
numeral lSa shows movable supporting members 15a of the
inlet lower clamp, which have the cut portions a-t the
rearward end portions as shown in this ~igure. When
said movable supporting members are forwardly move~ and
~s the cut portions of said supporting members come -to the
rearward wheels 35, the inlet lower clamp 15a may be
slightly pivoted in the horizontal direction as in the
above described former cases.
- 13 -
~3L7;~7
With re-ference to Figs. 12 and 13, the laser
torch 4 will be explained below.
A reference numeral 201 is a condenser which
is at~ached to a -torch 202. A reference numeral 203 is
05 a blacket attached to the torch 20~ and engaged with
the screw axis 204 at i.ts other end. The screw shaf-t
204 is supported by -the bearing 205 at both ends thereof
and connected to a motor 206. A reference numeral 207
is a torch holder which is adapted to ascend and descend
while being guided by a guide means 208. This torch
holder 20`7 also serves to guide the ascending and
clescending of -the torch 202. A cylinder 209 is attached
to a reflector hase 210 and adapted to ascend and
descend the torch holder 207. Reference n-umerals 211
and 212 are bender mirrors attached to the reflector
base 210, and adapted to bend the laser beam to
a desired direction. The reflector base 210 is guided
by a carriage 214 and can be moved in a direction
perpendic~lar to the torch running direc-tion by a motor
~not shown).
The carriage 214 is adapted to be moved
in a direction perpendicular to the processing line by
means of a guide means 215, a motor 216, a screw shaft
217 connected to the motor 216, bearings 218 of the
screw ~haft 217, and a nut 219 screwed to the screw
shaft 217.
A center clamp 300 will be explained with
reference to Figs. 3, 14 and 15.
~Z~7Z3'7
The center clamp 300 is arranged at a side
opposite to the laser torch at the butting portion of
the preceding and trailing steel strip edge portions,
and includes a backing bar 301 provided with a bag-like
05 groove 302. The center clamp further comprises cylinders
303, guide rods 304 and guides 305, and i5 adapted to
be contacted with or separated from the back face of
the strips to be jointed. Reference nwmerals 306, 307
and 308 are a backing bar supporting base, a light
o absorbing member, and a coolant passage respectively.
The backing bar 301 is designed to have such a size
that the preceding steel strip and the trailing steel
strip are fully sandwiched between it and the upper
clamps 12a and 12b when elevated.
This bag-like groove 302 prevents the laser
beam passed through the weld zone from reflecting and
dispersing to the outside and further the safety is
assured by preventing the laser beam from leaking to
the outside by the provision of a light absorbing
member 307 onto the face of a supporting base 306 onto
which the laser beam is irradiated.
~ urther, since the edge portions of the
preceding and trailing steel strips are clamped be-tween
the upper clamps 12a and 12b and -the backing bar 301
2S during the butting, the deformation of the strip tip
portions as shown in Fig. 15 can be avoided.
The operation of the apparatus according to
the present invention will be explained with reference
15 -
~ ~ w~
to Fi~s. :L7(a)-l~(f) below.
~ hen the edge portions of the preceding steel
strip and the ~railing steel strip are fed and stopped
at predetermined locations, the cylinders 14a and l~b
05 of the inlet an~ outlet clamps 3a and 3b are actuated
to clamp the preceding steel strip and the trailing
steel s-trip between the clamping means. Next, the
cylinder 8a is actuated to lit the lower blade 8
[Fig. 17(a)~.
0 (2) The cylinder 7a is actuated -to descend the
upper blade 7 to cut the edge portions of the preceding
steel strip and the trailing steel strip [Fig. 17(b)].
(3) The cylinder 7a is reversely actuated to lift
and retract the upper blade 7 and the cylinder 8a is
actuated to descend the lower blade 8. Then, the
cylinder 9 is actuated to move the shear 2 to a retracted
position on the non-operation side [Fig. 17(c)].
(~) The cylinder 16 is actuated to advance the
inlet clamp 3a, and when the top o- the -trailing steel
strip approaches the tail edge portion of the preceding
steel strip [Fig. 17(d)], a cylinder 303 of a center
clamp 300 is actuated to clamp the steel strips between
the upper clamps 12a and 12b and the center clamp 300
CFig. 17(e)~. Next, the inlet clamp is further advanced
to complete the butting of the steel strips [Fig. 17(f)].
The edge portions of the steel strips are
prevented from being deformed as shown in Fig. 16 by
clamping the edge portions between the e~tended tip
- 16 -
~Z~3~
portians of the upper clamps and the center clamp.
Thus, an excellerit welded joint is obtained.
When the top portions of the advanci.ng guides
of the inlet clamp are tapered so as -to allow the steel
05 strip to be slightly pivoted in a horiæontal plane and
the position of the stopper which res-trains the advance
of the tra.iling steel strip, is set to be slightly
larger than the distance between the cut edge faces of
the strip , the butting load is applied onto the edge
portions of the steel strips and as the result, iE the
distance of the cut steel strips is different in the
transverse direc-tion of the steel strip, the inlet
clamp may be pivoted as shown ln Figs. 21(a) and 21(b)
and both the edges of the steel strips come in contact
with each other so that the gap becomes smaller than
the case where the butting is carried out through
advancing the cut steel strip by only the predetermined
distance .
Consequently, the joints having mare stable
and higher strength can be obtained.
Even if the distance between the edges of the
cut strip.s varies a little, the steel strips are tightly
b~ltted with substantially no gap therebetween by setting
the distance between the stopper 1~ and the bent por-tion
of the gui.de 17 slightly wider than the distance between
the cut edges of the strips. Further 9 with respect to
the deviation from the straight line of ~he cut lines,
the gap can be made smaller by rotating the inlet
- 17 -
7Z~7
clamp. Although the trailing steel strip is sli~htly
inclined to the line owing to the pivotal movement o~
the inlet clamp, this is around 0.lmm/l,OOOmm, and no
problem is caused.
05 It is importan~ to approach the gap value as
near to zero as possible in the case of the laser butt
welding.
(5) The motor 216 is actuated to drive ~he laser
torch in the transverse direction of the steel strip.
o In the way, when a detector not shown detects the side
end of the strip, a shutter housed in -the laser
oscillator 1 is opened to irradiate the laser beam onto
the side of the laser torch 4. The laser beam is bent
in a direction parallel to the line by means of
a reflector 211, and is next bent in a direction vertical
to the line by means of a reflector 212 and then passed
through the condenser 201 to be focused onto a weld
zone and to commerse the welding. The laser torch is
run in the transverse direction of the strip, and the
shutter is closed when the other strip side end is
sensed by means of the side end detector to stop the
irradiation of the laser beam. Then, the -torch is
carried to the retracted position and stopped.
~y once changing the laser beam path in
2S parallel to the line in the laser torch 4, the focused
position in the line direction of the laser beam path
posterior to the reflector 212 can be varied merely by
horizontally shifting the laser torch 4 in the line
~7~
direction.
Particularly, when the laser beam or the like
is -used, th~ beam path may be slightly varied depending
upon the circumferential temperature, a leading period
05 of time of the oscillator, a ~emperature of the
reflector, and the like, and consequently there is the
possibility ~hat the beam point focused by the condenser
is shift slightly. Since the shift component of the
focus in the direction perpendicular to the processing
lo line is no problems because it is in a weld line, while
if the focus is shifted in the direction parallel to
the line, it is deviated from the butting line to form
weld profile as shown in Fig. 22. Since this form of
the joint has a notch in the lower side, it is weak in
bending and unacceptable. For this reason, it is
extremely important to control the focus location in
the direc-tion parallel to -the line in using the laser
butt welding apparatus. According to the laser butt
welding apparatus of the invention, in order to
facilitate the positioning of the focus in the line
direction, the laser beam path is bent in parallel to
the line at least one time and then the optical sys~em
a:Eter such a bending step is moved to a horizontal.
direction, whereby the focus can be moved in a direction
parallel to the line by the same distance as the moved
amount of the optical system without moving the focus
to the vertical direction and the direction perpendicular
to the line and the operation for positioni.ng the focus
- 19 -
~23L72;37
can be very easily effected.
In the following, other embodiments of optical
system adapted to bend the laser beam path to the
direction parallel to the line at least one time will
05 be explained hereinafter.
In Fi~. 23, a reference numeral 401 is a first
reflector adapted to bend the laser beam 213 incident
thereupon in a direction perpendicular to the line, in
the vertical direction to the line~ a re~erence
lo numeral 402 is a second reflector adapted to bend the
laser beam thus vertically bent in the direction parallel
to the line, and a reference numeral 403 is a condensing
reflector adapted to focus the laser beam in parallel
to the line -thus bent, at a weld æone.
Merely by horizontally displacing the laser
torch 202 in the line direction, the focus is shifted
by the same distance as this displacement only in the
direction parallel to the line without being shifted in
the vertica~ direction or perpendicular direction to
the line~
The focusing is carried out by moving the
re~lector 402 and the condensing reflector 403 as one
set in a vertical direction.
Fig. 24 shows another embodiment -using
a condensing reflector.
A reference numeral 501 is a first reflector
adapted -to bend the laser beam 213 incident thereupon
in the direction perpendicular to the line, in the
- 20 -
~Z~ 37
direction parallel to the line, a reference numeral 502
is a second reflector adap-ted to vertically bend ~he
laser beam thus ben-t, in the direction parallel to t'he
line, a reference numeral 503 is a third reflector
05 adapted to 'bend the thus vertically bent laser beam in
the direction parallel -to the line, and a reference
numeral 504 i5 a condensing reflector adapted to focus
the laser beam at the weld zone.
According to this embodiment~ by displacing
the condensing ref~ector 504 in the direction parallel
to the line, the focus point is horizontally shifted by
the same distanc~ as displacement of the condenser
reflector in the parallel direction to the line without
being displaced vertically or in the direction perpen-
dicular to the line.
The focusing is carried out by verticallyshifting the reflector 503 and the condensing mirror as
one set.
(6) When the welding is completed, the upper
clamps of the inlet and outlet clamps are lif'ted to
release the edge portions of the preceding and -trailing
steel strips, and the passing of the steel strip starts.
Subsequently, the cylinder 209 is actuated to
lift and return the laser torch to the original position,
ancl the other means are returned to their original
locations. Thereby, one weld process is completed.
In the above described step (3) for cutting
the steel strips, it is par-ticularly important that the
- 21 -
~L2~23~
cut lines formed through the above cutting operation
are in parallel to each other and straight in the case
of the laser butt welding. That is, when the laser
beam is condensed by the condenser, the diameter of the
05 laser beam at the focus is varied according to the
focal length of the condenser, for instance, when
a condenser having a focal leng-th of 5 inches is used,
said diameter is as extremely small as 0.15 mm.
Therefore, according to the laser bu-tt welding, i~ is
possible to increase the energy density and to ef~ect
a high speed welding, but an extremely high precision
is required in butting of the materials to be welded.
If the cut lines of the materials to be welded are
curved, a clearance remains even if the butting is
effected at a very high precision. In general, when
the steel plate is cut by means of a raked shear
(guillotine shear, rotary shear or the like~, the cut
line is more or less curved as shown in Fig~ 19 in
a transverse direction of the plate. The curved degree
of the cut line depends upon the material, clamping
way, shear or the like, but it is observed that the cut
line is curved at about 0.1 mm in the case of a steel
plate having a thickness of 1.0~3.0 mm. Thus, even if
such curved-edge steel strips are butt-welded, no
welded joints having satisfactory strength can be
obtained.
According to the present invention, it is
possible to obtain a set of steel strips having parallel
- 22 -
~7~37
and nearly straight cut lines by clamping the edge
portions of the steel strips between the upper clamps
12a and 12b which are more extended toward the shear
than the lower clamps 15a and 15b and the upper end
portion of the lower blade 8. Fig. 18 shows the relation
of the distance Q from the edge of the upper clamp to
the tip face of -the upper blade to a value aG obtained
by subtracting the minimum cut gap (Gmin) from the
maximum cut gap (Gmax) among the cut gaps measured in
the transverse direction of the strip (see Fig. 19).
Table 1 shows the results obtained when ~he above
described cut edge portions are butted and the butted
portion i5 subjected to the laser butt welding.
Table 1 (Tensile test)
Plat 1.0 1.6 2.2 3.0
Distance ~ ~ x x x
10 - o o Q _ x
o o - o o
3 _ o o _ o - - o
Note: o Rupture of base metal
Rupture of base metal or
welded joint
x Rupture of welded joint
- 23 -
~2~Z37
From the ~bove data, it can be seen that the
e~cellent welding is possible in a range of Q being not
more than 7 rnm. In a range of 7<Q_15, the rupture at
the welded portion is likely to be caused and there is
05 problem in plate-passing, rolling or other processing
steps of the strip. In Fig. 18, the zones (a), (b) and
(c) correspond to the steel strips having thickness (t)
of 1.0 mm, 1.6 mm and 3.0 mm respectively. The welding
conditions in the test of Table 1 are as follows, that
is a laser power is 1 kw, the materials are cold-rolled
steel stri.p and hot-rolled steel strip (low carbon
steel) and the welding speed is 1.0-3.0 m/min.
In the Table 1, the marks (~) means that the
tensile strength when the welded joint portion is
ruptured, is about 80-100% of that of the base metal
and the mark (x) means about 40-80% thereof.
'rhus, the steel s-trips of the mark (~)
satisfactorily endure the plate-passing in the processing
line~ while a part of the steel strips of the mark (x)
(Q=10, t-3.0 mm~ has the tensile strength near 80% oE
that of the base metal and therefore, they also
satisfactorily endure the plate-passing in the processing
1 lne .
When the Q can not be set to be not more than
lO mm for the reason that the extended portion of -the
upper clamp interferes with a nozzle portion of the
laser torch, the following system is proposed.
Fig. 20 shows a relation between the tan ~ in which
- 2~ -
7~37
is the rake angle of the share upper blades and the
above described value ~G.
From these results, it is understood that the
smaller tan ~ a rake angle), the smaller is the
05 curve of the cut lines and as the results the welding
results are better. According to the test results it
has been found that when the range of the tan ~
rake angle) is 35 ooot~ in which t denotes the thickness
of the steel strip, the strength of the joints is high.
Fig. 20 is an example when Q is 15 mm. In the case of
Q=12 mm or 20 mm, similar results were obtained.
~ ven when Q is no-t more than 10 mm, the curve
of the cut line may be more reduced by making the rake
angle tan ~ smaller and the good welded joint can be
stably obtained.
The smaller the rake angle tan ~, the smaller
the curve of the cut line is, but -the shearing-cut
Eorce becomes larger with increase in tan ~ and the
strength of -the frame strength is needed and the
equipment cost is increased.
ThereEore, the lower limit for the practical
range of tan ~ i5 about 4 t/l,000. That is, the lower
limit is 2.4/1,000 in the case of 0.6 mm in thickness,
12~1,000 in the case of 3 mm in thickness and 18/1,000
in the case of 4.5 mm in thickness.
Next, the use of the station 100 for checking
the performance of the optical system will be explained
below:
- 25 -
23~
The condensing performance of the condenser
is deteriorated owing to a long period of time of use,
or said condenser is broken or damaged due to the
spattered metal. Therefore, the condenser should be
05 exchanged at a specific time interval or at an irregular
time interval. At such a time, the tip portion of the
condenser is removed and a fresh one is attached.
In this exchanging operation9 the welding apparatus
restores the normal sta-te, and becomes applicable in
o the processing line. Usually, the deterioration period
of the condensing performance is not constant, and the
usable time period is unclear. Further, there is no
way to detect the deterioration degree of the condenser
other than the difference between the laser power of
the laser beam prior to and after passing through the
condenser or the variation of the depth of the laser
beam penetrated. In addition, it is also necessary to
check whether the fresh one which is exchanged exhibits
a predet~rmined performance or not. If such checking
operations are carried out on the line, the line
operation must be stopped during such checking.
For solving the above drawbacks, according to
the inventionl the station 100 for checking the
performances of the optical system is provided at
a position on the line extended from the laser torch
running line, where the passing of the steel strip is
not interrupted, so that the above described working
for the condenser can be carried out during the time
- ~6 -
~2~7~37
when the steel strips are passed on the line, whereby
the productivity is increase~.
Ihe s-tation for checking the perfarmances of
the optical system is used as follows:
05 First, the laser torch 4 stopped at a pre-
determined retracted position on the operational side
is carried to the station for checking the performances
of the optical system by actuating a motor 216. Mext,
a sample plate 103 is placed on a table lOl, and sec-ured
onto the table by means of press plates lO~ and
bolts lO5. Then, the laser torch is run over the
sample plate to irradiate said plate with the laser
beam and then the color of the reflected beam and the
depth of the weld penetration are checked and it is
checked whether the focus of the condenser is proper or
not or whether the condensing performance has been
deteriorated or no-t. This station can ~e utilized to
check as to whether the distribution of the laser beam
energy intensity is proper or not, and the deviation of
the laser beam a~is from -the butted line.
Fig. 6(b) is another embodiment of the station
Eor checking the performances of the optical system in
which the lower portion of the slit is closed for
preventing the penetration or scattering of the laser
beam.
The following Table 2 shows the comparison of
the welding time of the laser butt welding according to
the invention with the TIG arc welding. The comparison
- 27 -
~2~23~
was made with respec-t to two kinds of steel strips
having a thickness of 1.O mm and 2.3 mm. The laser
power is 1.3 kw and torch-running distance in the laser
butt welding and TIG arc welding is 1.5 m. It is under-
stood from this table that with respect to the same
thickness of the steel strips, the welding time in the
laser butt welding is less than 0.5 time as short as
that of the TIG arc welding.
Table 2
_ - (1) (2) (1)+(2)
Welding Plate Laser Welding Welding Operating Total
thickness power speed time ti~e
~th~d (mm) (~w) (cm/min) (sec) (`~ (sec)
TIG 2.3 4 30 130 30 210
TIG 1.0 2 60 90 30 120
Laser b~ltt 2.3 1 150 60 30 90
(Invention)
Laser butt l.O 1 500 20 30 50
(Invention) _
Laser butt 2.3 3 400 25 30 55
(Invention) _
The following Table 3 shows the test results
obtained in the -tensile tests with respect to the
welded portions of various steel strips by using the
laser butt welding apparatus according to the present
invention. The width of the test steel strip is
914-1,067 mm, and five test pieces are cut off in the
- 28 -
~Z~3~
width direction and the tes-t is made with respec-t to
these test pieces. In all the test pieces, the rupture
occurs at -the base metal and the welding strength is
excellen-t.
Table 3
Mechanical property of laser welded joints
(Laser power 1 kw)
Tensile strength
Steel (mm) speed Tensile Location
(m/min) (kg/mm2) of rupture
Mild 1~0 4.0 31 Base metal
High--tensile 1.0 4.0 40 ..
... .
Galvanized 0.9 3.5 31 -
. .
Silicon 2.0 1.25 60 ,.
.
SUS304 2.0 1.25 62 ..
Stainless
SIJS430 1.0 4.0 49__
Figs. 25(a)and 25(b) are photographs showing
micro-structure of the sections of the welded portions
:in the cases of the laser b~ltt welding and the TIG arc
welding respectively. In Fig. 25(a), the thickness of
the steel strip is 2.0 mm, the laser power is 1 kw and
the welding speecl is 1.25 m/min. In Fig. 25(b), the
thickness of the steel strip is 2.0 mm, the electric
power is 3.8 kw and the welding speed is 0.5 m/min.
From the comparison it can be seen that the structure
in the case of the laser b-utt welding is more fine than
- 29 -
that of the TIG arc welding and -therefore the welcling
strength is higher in the case of the laser butt welding
according to the invention. Further, i-t can be seen
that the -profile of the weld portion is small in
05 unevenness in the laser butt welding than in the TIG
arc welding.
The invention can exhibit the following
merits:
(l) The welding time can be reduced.
(2) The productivity is higher.
(3) It is possible to weld almost all kinds of the
steels, for instance, special steels such as
silicon steel, stainless steel or the like, a plated
steel such as a galvanized steel sheet or the
like, and high tensile strength steels by using
the laser butt welding apparatus according to the
invention.
~4~ Since no bead at the weld portion is formed, the
formation of faults caused in coiling can be
reduced.
(5) The strength a-t the welded portions i5 improved,
so that no rupture of the welded portion occurs in
the line.
~5
30 -
