FIELD
[0001]
The present disclosure relates to a spot welding machine welding a set of sheets including
10 a plurality of superposed metal sheets by resistance spot welding.
BACKGROUND
(0002!
In the assembly of car bodies of automobiles, the attachment of parts, etc., mainly
15 resistance spot welding is being used for joining a superposed plurality of metal sheets with each
other. In this spot welding, a pair of electrode tips with front end parts pressed against the set of
sheets is used.
[0003]
In spot welding, cun-ent is run across the superposed plurality of metal sheets to form
20 molten metal while pressing the electrode tips against the superposed plurality of metal sheets
from the two sides so as to sandwich the metal sheets. After finishing running the cun-ent, due to
the heat removed by the electrode tips and the heat conducted to the metal sheets themselves, the
molten metal is made to cool and solidify to thereby form a melted, then solidified part with an
elliptical cross-sectional shape (nugget) between the metal sheets.
25 [0004]
Further, in welding electrodes, the art of providing pressing rods for pressing the
electrode tips and metal sheets is known (PTL l ). Due to this, during welding, it is possible to
press the sun-oundings of the weld zone and suppress spatter etc. Furthermore, by using the
pressing members as auxiliary electrodes and running current through the metal sheets between
30 the electrode tips and auxiliary electrodes, it is possible to enlarge the nugget size.
[0005]
As welding electrodes having such pressing members, ones using cylindrical rigid bodies
as pressing members and having electrode tips inside the rigid bodies are known (PTL 2). During
welding, it is possible to press the surroundings ofthc weld zone and further suppress spatter etc.
3 5 and to broaden the contact areas among the metal sheets and enlarge the nugget size.
5
10
fCIT A TION LlSTl
[PATENT LITERATURE]
[00061
[PTL 1] Japanese Patent Publication No. 2012-066284A
[PTL 2] W02015/04535!A
[TECHNICAL PROBLEM]
[0007J
SUMMARY
However, if the strengths or thicknesses of the metal sheets change, the range of suitable
current changes. Therefore, even in the prior art, such as PTLs 1 and 2, it was difficult to stably
form the desired nugget size while suppressing spatter.
[0008]
For example, in the case ofthe same sheet thickness, the range of suitable cunent tends
15 to become narrower as the strength of the metal sheets increases. To secure the equivalent range
of suitable current, it is necessary to increase the pressing forces of the electrode tips. However,
in robot guns etc. actually used in mass production, there are limitations to the pressing force due
to gun rigidity and restrictions oli the servo motor torque values. For example, in the case of
robot guns used in an automobile mass production line, 400 kgf or so becomes the maximum
20 allowable pressing force.
[0009]
In this regard, however, in the welding electrode provided with electrode tips and
pressing members ofthe spring system used in the prior arts of PTL 2 etc., if replacing springs
with ones with a higher spring constants to increase the pressing forces of the pressing members,
25 due to the reaction forces, the pressing forces of the center electrode tips end up decreasing by
that amount Further, replacement of the springs each time in accordance with the strengths or
thiclmesses of the metal sheets was costly and not practical.
[0010]
For this reason, a spot welding machine able to perform spot welding in which the
30 desired nugget size is formed while suppressing spatter even if the strengths or thicknesses of the
metal sheets change, is desirable.
35
[SOLUTION TO PROBLEM]
[OOH]
The inventors studied in advance methods for solving the problem and discovered spot
welding in which the pressing pressures of the electrode tips and pressing pressures ofthc
2
pressing members are separately controlled.
[0012]
The gist of the present disclosure is as follows:
(1) i\ spot welding machine welding a set of sheets including a superposed plurality of
5 metal sheets by resistance spot welding.
said spot welding machine comprising:
a pair of electrode tips with fi"ont end parts to be pressed against said set of sheets,
a pair of pressing members arranged around said electrode tips and with front end parts to
be pressed against said set of sheets,
1 0 a first power supply,
15
first drive mechanisms and second drive mechanisms, and
a pressing force control part, wherein
said pair of electrode tips are arranged facing each other so as to be able to sandwich said
set of sheets between them,
said pair of pressing members are arranged facing each other so as to be able to sandwich
said set of sheets between them,
said pair of electrode tips are connected to said first power supply and said first drive
mechanisms, said first drive mechanisms driving said pair of electrode tips in the axial direction
of said electrode tips and making said pair of electrode tips stop at any positions and giving
20 pressing forces pressing said pair of electrode tips against said set of sheets,
25
said pair of pressing members are connected to said second drive mechanisms, said
second drive mechanisms dtiving said pair of pressing members in the axial direction of said
electrode tips and making said pair of pressing members stop at any positions and giving
pressing forces pressing said pair of pressing members against said set of sheets, and
said pressing force control part is connected to said first drive mechanisms and said
second drive mechanisms and independently controls the pressing forces given by said first drive
mechanisms and the pressing forces given by said second drive mechanisms.
(2) The spot welding machine according to (1), wherein said first drive mechanisms and
said second drive mechanisms are independently a pnenmatic cylinder, hydraulic cylinder, or
30 electric cylinder.
(3) The spot welding machine according to (1) or (2), wherein said pressing members are
composed of a condnctor and connected to said first power snpply.
( 4) The spot welding machine according to (1) or (2), wherein
said spot welding machine is further provided with a second power supply, and
35 said pressing members are composed of a condnctor and connected to said second power
supply.
3
(5) A spot welding method for welding a set of sheets including a superposed plurality of
metal sheets by resistance spot welding, said spot welding method comprising:
preparing said set of sheets,
placing a first electrode tip and second electrode tip to face each other across said set of
5 sheets,
placing a first pressing member around the first electrode tip and placing a second
pressing member around said second electrode tip such that the second pressing member faces
said first pressing member across said set of sheets,
pressing the front end parts of said first electrode tip and said second electrode tip against
10 said set of sheets to apply pressing forces,
pressing the front end parts of said first pressing member and said second pressing
member against said set of sheets to apply pressing forces independent from the pressing forces
applied from said first electrode tip and said second electrode tip, and
running current across said first electrode tip and said second electrode tip to weld said
15 set of sheets while pressing said first electrode tip and said second electrode tip and said first
pressing member and said second pressing member against said set of sheets to apply pressing
forces.
(6) The spot Welding method according to (5), wherein
said first pressing member and said second pressing member are composed of a
20 conductor, and
the method further comprises running cunent across said first pressing member and said
second pressing member.
(7) The spot welding method according to (5) or (6), further comprising pressing the front
end parts of said first pressing member and said second pressing member against said set of
25 sheets to apply pressing forces, then pressing the front end parts of said first electrode tip and
said second electrode tip against said set of sheets to apply pressing forces.
30
(8) The spot welding method according to any one of (5) to (7), wherein
said first pressing member and said second pressing member are composed of a
conductor, and
the method fmiher comprises, after welding said set of sheets, running current across said
first pressing member and said second pressing member, while not running current across said
first electrode tip and said second electrode tip.
(9) The spot welding method according to any one of (5) to (8) wherein
said f]rst pressing member and said second pressing member are composed of a
35 conductor, and
the method fmihcr comprises, before welding said set of sheets, running current across
4
said first pressing member and said second pressing member, while not running current across
said 11rst electrode tip and said second electrode tip.
[ADVANTAGEOUS EFFECTS OF INVENTION]
5 [0013]
According to the spot welding machine or spot welding method of the present disclosme,
since it is possible to independently control the pressing pressmes of the electrode tips and the
pressing pressures ofthe pressing members, it becomes possible to perform spot welding in
which the desired nugget size is formed while suppressing spatter, even if the strengths or
10 thicknesses of the metal sheets change.
BRIEF DESCRIPTION OF DRAWINGS
[0014]
[FTG. 1] FIG. 1 is a cross-sectional schematic view showing one example of using a
15 welding apparatus of the present disclosme to spot weld a set of sheets including a plmality of
metal sheets.
20
25
30
[FIG. 2] FIG. 2 is a cross-sectional schematic view showing an embodiment when
pressing the front end parts of the pressing members against the set of sheets and placing the
front end parts of the electrode tips at positions separated from the set of sheets.
[FIG. 3] FIG. 3 is a cross-sectional schematic view showing an embodiment when
pressing the front end parts of the electrode tips and front end parts of the pressing members
against the set of sheets.
[FIG. 4] FIG. 4 is a cross-sectional schematic view of a nugget formed when performing
electric heating by the electrode tips and pressing members.
[FIG. 5] FIG. 5 is a cross-sectional schematic view of a nugget formed when running
current through only the electrode tips and not performing electric heating by the pressing
members.
[FIG. 6] FIG. 6 is a cross-sectional schematic view showing one example of a welding
apparatus of the present disclosure when nsing a pnenmatic cylinder as a second drive device.
[FIG. 7] FIG. 7 is a cross-sectional schematic view when making pressing members of
the welding machine ofF! G. 6 move.
DESCRIPTION OF EMBODIMENTS
10015]
35 The present disclosure covers a spot welding machine welding a set of sheets including a
superposed plurality of metal sheets by resistance spot welding, the spot welding machine
5
comprising a pair of electrode tips with front end parts to be pressed against the set of sheets, a
pair of pressing members arranged around the electrode tips and with front end parts to be
pressed against the set of sheets, a first power supply, first drive mechanisms and second drive
mechanisms, and a pressing force control part, wherein the pair of electrode tips are arranged
5 facing each other so as to be able to sandwich the set of sheets between them, the pair of pressing
members are arranged facing each other so as to be able to sandwich the set of sheets between
them, the pair of electrode tips are connected to the first power supply and the first drive
mechanisms, the first drive mechanisms driving the pair of electrode tips in the axial directions
of the electrode tips and making the pair of electrode tips stop at any positions and giving
l 0 pressing forces pressing the pair of electrode tips against the set of sheets, the pair of pressing
members are connected to the second drive mechanisms, the second drive mechanisms driving
the pair of pressing members in the axial directions of the electrode tips and making the pair of
pressing members stop at any positions and giving pressing forces pressing the pair of pressing
members against the set of sheets, and the pressing force control part is connected to the first
15 drive mechanisms and the second drive mechanisms and independently controls the pressing
forces given by the first drive mechanisms and the pressing forces given by the second drive
mechanisms.
[0016]
According to the spot welding machine of the present disclosure, since it is possible to
20 separately control the pressing pressures of the electrode tips and the pressing pressures of the
pressing members, it becomes possible to broaden the range of suitable current forming the
desired nugget size while suppressing spatter even if the strengths or thicknesses of the metal
sheets change.
25
[0017]
The "range of suitable current" means the range of current values from the minimnm
current value at which a nugget of the reference diameter is fanned to the maximum current
value at which a nugget of the reference diameter or more is fonned without being accompanied
with spatter. The range of suitable current is preferably 1,0 kA or more, more preferably 1.5 kA
or more, still more preferably 1.8 kA or more, even more preferably 1.9 kA or more. The
30 reference diameter is equal to 4-Yt ("t" is the sheet thickness),
[0018]
The spot welding machine of the present disclosure is provided with a pair of electrode
tips. The pair of electrode tips are arranged facing each other so as to sandwich between them the
set of sheets including a superposed plurality of metal sheets, The pair of electrode tips have
35 front end parts to be pressed against the set of sheets and sandwich the set of sheets between
them.
6
5
!0019]
The pair of electrode tips are cmmccted to the first power supply and first drive
mechanisms.
[0020]
The first drive mechanisms drive the pair of electrode tips in the axial directions of the
electrode tips and make them stop at any positions and give pressing forces pressing the pair of
electrode tips against the set of sheets.
[0021]
The first power supply can run current through the electrode tips at predetermined current
10 values and number of cycles. Current can be run from the electrode tips to the set of sheets
changed in accordance with the strengths and thicknesses of the metal sheets included in the set
of sheets. For example, 4 to 15 kA of current can be run for a current running time of 5 to 50
cycles (power supply frequency 50Hz).
[0022]
15 The electrode tips are not particularly limited. Known ones may be used, but are
preferably ones made ofC~ Cu-Cr alloy, or alumina dispersed Cu. The electrode tips may for
example have 2 to 16 mm columnar shapes or front end part diameter 6 to 8 mm DR type (dome
radius type), CF type(conical flat type), CR type (conical radius type), DF type (dome flat type),
or D type front end part shapes.
20 [0023]
The spot welding machine of the present disclosure is provided with a pair of pressing
members. The pair of pressing members are arranged facing each other so as to be able to
sandwich between them the set of sheets including a superposed plurality of metal sheets. The
pair of pressing members have front end parts which can be pressed against the set of sheets and
25 can sandwich the set of sheets between them. The pair of pressing members are arranged around
the electrode tips so as to be able to press the front end parts against the set of sheets.
[0024]
The material of the pressing members arranged around the electrode tips is not
particularly limited so long as having heat resistance and having predetermined mechanical
30 characteristics enabling the members to press against the set of sheets, but preferably is an
aromatic resin polyether ketone (PEEK) or other resin or Cu, a Cu-Cr alloy, or alumina dispersed
Cu, or other conductor.
[0025]
The shapes of the pressing members are not particularly limited so long as the members
3 5 can be ananged around the electrode tips and can press against the set of sheets, but may be
cylindrical shapes, partial circular shapes of cylindrical shapes partially cut away, or polygonal
7
shapes. The cross-sections of the cylindrical shapes may be lruc circles or ellipses.
[00261
The inside diameters of the pressing members can be made 1.1 to 2.0 times the diameters
of the electrode tips. The thicknesses of the pressing members can for example be 1 to 5 mm.
5 The pressing members may also be cylindrical members with diameters of 15 to 25 mm.
[0027]
The pressing members arc connected to the second drive mechanisms. The second drive
mechanisms drive the pair of pressing members in the axial directions of the electrode tips and
make them stop at any positions and give pressing forces pressing the pair of pressing members
l 0 against the set of sheets.
[00281
The pressing force control pati is com1ected to the first drive mechat1isms and second
drive mechanisms and independently controls the pressing forces given by the first drive
mechanisms and the pressing forces given by the second drive mechanisms.
15 [00291
20
25
30
The nugget diameter can be made 3.5"1/t to 8.0"1/t when the thickness of the thinnest steel
sheet is "t" (mm).
[0030]
First Drive Mechanisms
The first drive mechanisms connected to the electrode tips are not particularly limited so
long as able to make the pair of electrode tips move in the axial directions of the electrode tips,
make them stop at any positions, and give pressing forces pressing the pair of electrode tips
against the set of sheets. The electrode tips can be moved relative to the pressing members.
[0031]
The pressing forces given from the electrode tips to the set of sheets can be changed
according to the strengths and thicknesses of the metal sheets included in the set of sheets, for
example, can be made 0.0 to 6.0 kN or 1.5 to 4.5 kN.
[0032]
Second Drive Mechanisms
The second drive mechanisms connected to the pressing members are not pat1icularly
limited so long as able to make the pressing members move in the axial directions of the
electrode tips, make them stop at any positions, and give pressing forces pressing the pressing
members against the set of sheets inclnding a superposed plurality of metal sheets. The pressing
members can be moved relative to the electrode lips.
35 [0033]
The pressing forces given from the pressing members to the set of sheets can be changed
8
according to the strengths and thicknesses of the metal sheets included in the set of sheets, for
example, can be made 0.0 to 6.0 kN or 1.5 to 4.5 kN.
[0034]
The first drive mechanisms and second drive mechanisms are independently preferably
5 pneumatic cylinders, hydraulic cylinders, electric cylinders, actuators, gear drives, or racks and
pinions, more preferably pneumatic cylinders, hydraulic cylinders, or electric cylinders. They
may be selected from the above drive mechanisms according to the actual installation
enviromnent etc.
10
[0035]
A pneumatic cylinder will not contaminate other members even if the air leaks and is
easy to maintain. A hydraulic cylinder is strong against heat and can give large power. An
electric cylinder does not require piping and can be controlled with a high precision.
[0036]
The pressing members are, preferably, composed of a conductor and are connected to the
15 first power supply. Due to this, it is possible to electrically heat the set of sheets from the
pressing members as welL It is possible to electrically heat the set of sheets from the pressing
members in addition to the electrode tips to thereby enlarge the nugget size. Therefore, even if
spot welding a set of sheets including a 1180 MPa or more high stren~o,>th steel sheet, it is possible
to form the desired nugget size without causing spatter. The current run to the set of sheets by the
20 pressing members can be changed in accordance with the strengths and thicknesses of the metal
sheets included in the set of sheets. For example, it is possible to run 4 to 15 kA of current by a
current carrying time of 5 to 50 cycles (power supply frequency 50Hz).
[0037!
If configming the pressing members by a conductor, preferably the electrode tips and
25 pressing members arc insulated from each other. The insulation between the pressing members
and electrode tips may be performed by a desired method. For example, arranging the pressing
members and electrode tips separated and arranging insulating sleeves around the electrode tips
between the electrode tips and pressing members etc. may be mentioned. If the electrode tips are
held at the shanks, it is possible to arrange insulating sleeves around the electrode tips and the
30 shanks.
[0038]
The spot welding machine ofthe present disclosure may be further provided with a
second power supply and have the pressing members composed of a conductor and connected to
the second power supply. In this case, the current flowing thwugh the electrode tips and the
35 current flowing through the pressing members can be independently controlled, so it is possible
to form the desired nugget size more precisely.
9
[00391
The spot welding machine ofthe present disclosure can be used to spot weld a set of
sheets including a plurality of metal sheets. The plurality of metal sheets is not limited to two
metal sheets. They may be made three or more metal sheets in accordance with the form of the
5 structural parts to be joined. The thicknesses of the metal sheets are not particularly limited. For
example, they may be made 0.5 to 3.2 mm. The thickness of the set of sheets including the
plurality of metal sheets as a whole is also not particularly limited. For example, it may be made
1.0 to 7.0 mm.
10
[0040]
The metal sheets may be ones formed with plating or other surface treatment films on
both surfaces or on single surfaces or may be ones not formed with surface treatment films. The
metal sheets need only be ones which have flat parts at least at parts of them and which can be
stacked at parts of the flat patis. They need not be flat shapes overall. For example, they may
also be steel shapes etc. The plurality of metal sheets are not limited to ones comprised of
15 separate metal sheets. A single metal sheet may also be formed into a tube like or other
predetermined shape superposed.
[0041]
The configuration of the spot welding machine of the present disclosure will be explained
while referring to the figures.
20 [0042]
25
FIG. 1 shows a cross-sectional schematic view showing one exmnple of an embodiment
using the welding machine of the present disclosure to spot weld a set of sheets including a
plurality of metal sheets.
[0043]
The welding machine shown in FIG. l is comprised of a pair of electrode tips 2 with
front end parts to be pressed against a set of sheets 16, a pair of pressing members 3 arranged
around the electrode tips 2 and with front end parts to be pressed against the set of sheets 16, a
first power supply 17 connected to the pair of electrode tips 2, first drive mechanisms 18
connected to the pair of electrode tips 2, second drive mechanisms 19 connected to the pair of
30 pressing members 3, and a pressing force control part 20 connected to the first drive mechanisms
18 and second drive mechanisms 19.
[0044]
The first drive mechanisms 18 can drive the pair of electrode tips 2 in the axial directions
of the electrode tips 2 and make them stop at any positions and give pressing l'orces pressing the
35 pair of electrode tips 2 against the set of sheets 16. The second drive mechanisms 19 can drive
the pair of pressing members 3 in the axial directions of the electrode tips 2 and make them stop
10
at any positions and give pressing forces pressing the pair of pressing members 3 against the set
of sheets 16.
[0045]
The pressing force control part 20 independently controls the pressing forces given by the
5 first drive mechanisms 18 and the pressing forces given by the second drive mechanisms 19.
[0046]
The first drive mechanisms 18 connected to the pair of electrode tips 2 may be configured
as a pair of separate mechanisms or may be configured as an integral mechanism. The second
drive mechanisms 19 connected to the pair of pressing members 3 similarly may be configmed
1 0 as a pair of separate mechanisms or may be configmed as an integral mechanism.
[0047]
The pair of electrode tips 2 and the pair of pressing members 3 sandwich the set of sheets
16 including a plurality of metal sheets from its two sides. In FIG. 1, a state is illustrated in
which a set of sheets 16 of two metal sheets 15 is sandwiched.
15 [0048]
At the time of spot welding, the front end parts of the electrode tips 2 are pressed against
the set of sheets 16. At that time, the front end parts of the electrode tips 2 and the front end parts
of the pressing members 3 may also simultaneously be pressed against the set of sheets 16, the
front end parts of the pressing members 3 may be pressed against the set of sheets 16 and then
20 the front end parts of the electrode tips 2 be pressed against the set of sheets 16, or the front end
parts of the electrode tips 2 may be pressed against the set of sheets 16 and then the front end
parts of the pressing members 3 be pressed against the set of sheets 16.
[0049]
Preferably, as shown in FIG. 2, before the spot welding, the front end parts of the
25 pressing members 3 are pressed against the set of sheets 16 and the front end parts of the
electrode tips 2 are placed at positions separated from the set of sheets 16. FIG. 2 is a crosssectional
schematic view showing a state when pressing the front end parts of the pressing
member 3 against the set of sheets 16 and placing the front end parts of the electrode tips 2 at
positions separated from the set of sheets 16. When pressing the front end parts of the pressing
30 members 3 against the set of sheets 16 and placing the front end parts of the electrode tips 2 at
positions separated from the set of sheets 16, the front end parts of the electrode tips 2 may be
placed at positions separated from the set of sheets by for example 0 to 5 mm or 1 to 3 mm.
[0050]
As shown in FIG. 2, it is possible to press the front end parts of the pressing members 3
35 against the set of sheets 16, place the front end parts ofthe electrode tips 2 at positions separated
from the set of sheets 16, then make the electrode tips 2 move relative to the pressing members 3
11
5
to, as shown in FIG. 3. make the electrode tips 2 contact the metal sheets 15. FIG. 3 is a crosssectional
schematic view showing the slate when pressing the front end parts of the electrode tips
2 and the front end parts of the pressing members 3 against the set of sheets 16.
[0051]
In FIG. 2, before making the electrode tips 2 contact the set of sheets 16, the pressing
members 3 can be used to press against the set of sheets 16 by the desired pressing forces, so in
FIG. 3, it is possible to run current simultaneously with making the electrode tip 2 contact the set
of sheets 16 and possible to shorten the tact time of the spot welding. In FIG. 2 and FIG. 3 as
well, the spot welding machine is provided with the first power supply 17 and pressing force
10 control part 20, but these are not shown.
[0052]
As shown in FIG. 3, it is possible to run current across the facing electrode tips 2 in the
state pressing the electrode tips 2 and pressing members 3 against the set of sheets 16 and form
molten metal at the superposed surfaces of the metal sheets J 5. Since spot welding is conducted
15 while pressing the surroundings of the weld zone by the pressing members, spatter can be
suppressed. The pressing forces of the pressing members may be made larger than the pressing
forces of the electrode tips corresponding to the strengths or thicknesses of the metal sheets
contained in the set of sheets, may be made the same extents as the pressing forces of the
electrode tips, or may be made zero.
20 [0053]
As shown by the solid line anow in FIG. 3, it is possible to run current across the facing
electrode tips 2 to fom1 molten metal at the superposed surfaces ofthe metal sheets 15. If the
pressing members 3 are composed of a conductor and are connected to the first power supply, as
shown by the broken line anow, it is possible to run current across the facing pressing members
25 3 to fonn molten metal at the superposed surfaces of the metal sheets 15.
[0054]
After finishing running cunent, it is possible to make the molten metal quickly cool and
solidify by the removal of heat by cooling the electrode tips 2 or conduction of heat to the metal
sheets 15 themselves and form a nugget with an elliptical shaped cross-section between the metal
30 sheets 15. After fonnation of the nugget, it is possible to separate the electrode tips and pressing
members from the metal sheets to return the welding machine to the standby state for welding.
[0055]
FIGS. 4 and 5 are cross-sectional schematic views of a nugget formed when electrically
heating by the pressing members and when not. FIG. 4 shows the state when electrically heating
35 by the pressing members, while FIG. 5 shows the state when not electrically heating by the
pressing members.
12
[0056]
The molten metal 21 when electrically heating the metal sheets 15 by the pressing
members 3 shown in FIG. 4 becomes greater in diameter (length in direction parallel to
superposed surfaces of metal sheets) compared with the molten metal2l when not electrically
5 heating the metal sheets 15 by the pressing members 3 shown in FIG. 5. This is because, as
shown by the broken line arrow in FIG. 4, by running current across the pressing members 3, the
outer circumference of the molten metal of the metal sheets is sufficiently heated and the
diameter of the molten metal 16 becomes larger. As a result, the nugget size becomes greater.
10
15
[0057]
Next, the size of the nugget formed by the presence or absence of pressing members and
presence or absence of electric heating and the range of suitable current arc shown as one
example.
[0058]
Example 1
Cold rolled members (unplated) of sheet thicknesses of 1.6 mm and tensile strengths of
590 MPa were superposed to form a set oftwo sheets. DR type front end part 40R, front end part
diameter 6 mm Cu-Cr alloy electrode tips and Cu-Cr alloy pressing members were used. Spot
welding was performed while making the pressing forces of both the electrode tips and pressing
members 3.92 kN and making the current running time 18 cycles (60Hz). As a result, the range
20 between the current value giving a nugget size of 4 --Jt ("t"= 1.6 mm) and the current value right
before spatter (range of suitable current) became 3.2 kA Further, the maximum nugget size was
7.5111111.
[0059]
Example 2
25 Except for using pressing members of the insulator constituted by the aromatic resin
poly ether ketone (PEEK), welding was performed under conditions similar to Example 1. As a
result, the range between the current value giving a nugget size of 4 ~t ("t"= 1.6 mm) and the
current value right before spatter (range of suitable current) became 2.8 kA. Fmiher, the
maximum nugget size was 6.6 mm.
30 [0060]
Example 3
Except for not using pressing members, welding was performed under conditions similar
to Example l. As a result, the range between the cunent value giving a nugget size of 4--Jt
("t"=l.6 mm) and the current value right before spatter (range of suitable cunent) becan1e 1.8
35 kA. Fmiher, the maximum nugget size was 6.6 mm.
[0061]
13
5
Next, one example ofthc nugget size and range of suitable cnnent when welding metal
sheets with thicknesses and tensile strengths different from Examples 1 to 3 will be shown,
[0062]
Example 4
A cold rolled member (unplated) of a sheet thickness of2.0 mm and a tensile strength of
1180 MPa and a cold rolled member (unplated) of a sheet thickness of2.0 mm and a tensile
strength of 1180 MPa were superposed to form a set of two sheets. DR type front end part 40R,
front end part diameter 6 mm Cu-Cr alloy electrode tips and Cu-Cr alloy pressing members were
used. Spot welding was performed while making the pressing forces of both the electrode tips
10 and pressing members 3.92 kN and making the current running time 18 cycles (50Hz). As a
15
result, the range between the current value giving a nugget size of 4 ,Jt ("t"~2.0 mm) and the
cunent value right before spatter (range of suitable current) became 1.0 kA. Further, the
maximum nugget size was 6.6 mm.
[0063)
Example 5
Except for making the pressing forces of the electrode tips 3.92 kN and making the
pressing forces of the pressing members 4.91 kN, welding was performed under conditions
similar to Example 4. As a result, the range between the cun·ent value giving a nugget size of4,Jt
("\"~2.0 mm) and the current value right before spatter (range of suitable current) became 1.9
20 kA. Further, the maximum nugget size was 7.8 mm.
[0064]
Example 6
Except for using pressing members ofthe insulator constituted by the aromatic resin
25 polyether ketone (PEEK), welding was performed under conditions similar to Example 5. As a
result, the range between the cunent value giving a nugget size of 4,Jt ("t"~2.0 mm) and the
current value right before spatter (range of suitable current) became 1.5 kA. Further, the
maximum nugget size was 7.0 mm.
30
[0065]
Example 7
Except for not using pressing members, welding was pcrfmmed under conditions similar
to Example 4. As a result, the range between the current value giving a nugget size of 4,Jt
("t"~2.0 mm) and the current value right before spatter (range of suitable current) became 0.0
kA. Further, the maximum nugget size was 6.0 mm.
35 [0066]
Example 8
14
A cold rolled member (unplated) of a sheet thickness of 1.6 mm and a tensile strength of
590 MPa and a cold rolled member (unplatcd) of a sheet thickness of 2.0 mm and a tensile
strength of 1180 MPa were superposed to form a set oftwo sheets. DR type front end part 40R,
front end pmi diameter 6 mm Cu-Cr alloy electrode tips and Cu-Cr alloy pressing members were
5 used. Spot welding was performed making the pressing forces of both the electrode tips and
pressing members 3.92 kN and making the current running time 18 cycles (50Hz). As a result,
the range between the current value giving a nugget size of 4-lt ("t"=l.6 mm) and the current
value right before spatter (range of suitable current) became 1.5 kA. Further, the maximum
nugget size was 6.6 mm.
10 [0067]
Exmnple 9
Except for making the pressing forces of the electrode tips 3. 92 kN and making the
pressing forces of the pressing members 4.91 kN, welding was performed under conditions
similar to Example 8. As a resnlt, the range between the current value giving a nugget size of 4-lt
15 ("t"=l.6 mm) and the current value right before spatter (range of suitable current) became 2.8
kA. Fmiher, the maximum nugget size was 7.8 mm.
[0068]
Example 10
Except for using pressing members of the insulator constituted by the aromatic resin
20 polyether ketone (PEEK), welding was performed under conditions similar to Example 9. As a
result, the range between the current value giving a nugget size of 4 >It ("t"= 1.6 mm) and the
current value right before spatter (range of suitable cunent) became 2.0 kA. Further, the
maximum nugget size was 7.0 mm.
25
30
[0069]
By conducting spot welding while independently controlling the pressing pressures of the
electrode tips and the pressing pressures of the pressing members to press the surroundings of the
weld zone, a large range of suitable current can be obtained and the nugget size can be enlarged
while suppressing spatter.
[0070]
The electrode tips 2 can be cooled by any method. For example, if making the shanks
hold the electrode tips, it is possible to cool the shanks to cool the electrode tips. Cooling pipes
may also be placed inside the shanks.
[0071]
It is also possible to repeat the spot welding a predetermined number of times, then dress
35 the electrode tips or replace them. According to the welding machine of the present disclosure,
the electrode tips and pressing members can be independently moved and stopped at the desired
15
positions, so dressing and replacement of electrode lips become easy.
[0072]
The method of dressing the electrode lips is not particularly limited. For example, tbc
surfaces of the front end parts of the electrode tips may be ground to thicknesses ofO.l to 1.0
5 mm. The electrode tips 2 may be changed by using a robot etc. to detach the electrode tips and
attach new electrode tips. The method is not particularly limited.
[0073]
The present disclosure fmiher covers a spot welding method for welding the set of sheets
including a superposed plurality of metal sheets by resistance spot welding, the spot welding
1 0 method comprising preparing the set of sheets, placing a first electrode tip and second electrode
tip to face each other across the set of sheets, placing a first pressing member aronnd the first
electrode tip and placing a second pressing member aronnd the second electrode tip such that the
second pressing member faces the first pressing member across the set of sheets, pressing the
front end parts of the first electrode tip and the second electrode tip against the set of sheets to
15 apply pressing forces, pressing the front end parts of the first pressing member and the second
pressing member against the set of sheets to apply pressing forces independent from the pressing
forces applied from the first electrode tip and the second electrode tip, and running current across
the first electrode tip and said second electrode tip to weld said set of sheets while pressing the
first electrode tip and the second electrode tip and also the first pressing member and the second
20 pressing member against the set of sheets to apply pressing forces.
[0074]
In the spot welding method of the present disclosme, as the welded members, a set of
sheets of a plurality of metal sheets with superposed welding locations is prepared. The metal
sheets are not particulaTly limited. Steel sheets of various chemical compositions are possible.
25 Alternatively, aluminum, stainless steel, or other metal members other than steel sheets are also
possible.
[0075]
According to the spot welding method of the present disclosure, it is possible to perform
spot welding well without regard as to the thicknesses or strengths of the metal sheets. For
30 example, it is possible to perform spot welding well even if including mild steel with a tensile
strength of270 MPa or 590 MPa or more, 980 MPa or more, 1180 MPa or more, or 1480 MPa or
more high strength steel sheet. Regarding the thicknesses of the metal sheets, steel sheets of a
thickness of0.5 to 3.2 mm may be illustrated.
35
[0076]
Preferably the first pressing member and second pressing member are composed of a
conductor. Cmrent is also run across the first pressing member and second pressing member.
16
Due to this, the nugget size can be made larger.
[0077J
Preferably the fi-ont end parts of the first pressing member and second pressing member
are pressed against the set of sheets to apply pressing forces, then the front end parts of the first
5 electrode tip and second electrode tip are pressed against the set of sheets to apply pressing
forces. Dne to this, the tact time of spot welding can be reduced.
[0078]
Preferably, the first pressing member and the second pressing member are composed of a
conductor, and after welding the set of sheets, current is not run across the first electrode tip and
10 the second electrode tip but is run across the first pressing member and the second pressing
member. By later running current from the pressing members, it is possible to run current to the
ends of the nugget for tempering i~ so it is possible to improve the CTS (cross tensile strength).
[0079]
Preferably, the first pressing members and second pressing members are composed of a
15 conductor, and before welding the set of sheets, current is not run across the first electrode tip
and the second electrode tip but is run across the first pressing member and the second pressing
member. By earlier running current from the pressing members, it is possible to more stably
prevent spatter.
[0080]
20 The above explanation relating to the configuration ofthe spot welding machine also
applies to the configuration of the spot welding method.
[0081)
FIG. 6 is a cross-sectional schematic view of one example of a welding machine of the
present disclosure using pneumatic cylinders as the second drive mechanisms. The first drive
25 mechanisms are preferably pneumatic cylinders, but may also be hydraulic cylinders, electric
cylinders, etc. In FIG. 6, the first drive mechanisms are not shown, but when the first drive
mechanisms are pneumatic cylinders, they may be configured in the same way as the pneumatic
cylinders of the second drive mechanisms illustrated in FIG. 6.
30
[0082]
The electrode tips 2 are attached to rod-shaped shanks l. The shanks l are attached to
holders (not shown) attached to spot welding guns. The pressing members 3 are arranged around
the electrode tips 2. The first power supply and pressing force control part are not shown.
[0083]
The welding machine is provided with a pair of electrode tips and a pair of pressing
35 members. The welding machine is used arranging the electrode tips and pressing members so as
to face each other across the superposed plmality of metal sheets. Since the basic configurations
17
of the two welding guns arranged facing each other arc the same, one welding gun will be
explained below.
[0084]
The shank I and electrode tip 2 can move relative to the pneumatic cylinder 4. The shanl'
5 1 is fastened to the pneumatic cylinder 4 by a Cu-1 mass%Cr screw adaptor 12 and nul 13.
Around the shan}( 1, a nylon insulating sleeve 14 is arranged. The insulating sleeve 14 may also
extend up to near the front end part of the electrode tip.
[0085]
The second drive mechanism constituted by the pneumatic cylinder 4 has a substantially
10 cylindrically shaped cylinder housing 5 in which the shan}( 1 is inserted, a disk-shaped rod cover
6 closing the cylinder housing 5, and a piston rod 7 moving through the inside of the cylinder
housing 5 in the axial direction of the shank 1. The piston rod 7 has a cylindrically shaped rod
part 7 a into which the shank 1 is inserted and a ring part 7b formed around the rod part 7 a and is
formed by SUS304 etc.
15 [0086]
The cylinder housing 5 has pmis 8 and 9a supplying and discharging air for moving the
piston rod 7 to the ring pmi 7b of the piston rod 7 at the side where the pressing member 3 is
attached to the piston rod 7 (below, referred to as the "inside") and the rod cover 6 side (below,
referred to as the "outside"). The cylinder housing 5 is formed by SUS304 etc.
20 [0087]
The rod cover 6 has a lower cover 6a restricting the range of movement of the piston rod
7 and upper cover 6b having a port 9b supplying and dischm·ging air at the outside of the rod part
7a of the piston rod 7 and is formed by SUS304 etc. The lower cover 6a and the upper cover 6b
are fastened by bag nuts 10.
25 [0088]
The cylinder housing 5, piston rod 7, and lower cover 6a are respectively provided with
0-rings 11 a, 11 b, llc. By keeping down the movement of compressed air between the inside and
outside at the ring part 7b of the piston rod 7 and supplying and discharging compressed air
through the port 8 and the ports 9a, 9b, it is possible move and stop the piston rod 7 and pressing
30 member 3 cmmected to their front end parts.
[0089]
The flow of ctment at the time of spot welding will be explained using FIG. 6. At the
electrode tip 2, when spot welding, current flows through the shank 1 as shown by the solid line
arrow. Due to this, the welding location of the metal sheets is heated and a nugget is formed.
35 Further, when configuring the pressing member 3 by a conductor, it is possible to use not only
the electrode tip 2, but also the pressing member 3 to electrically heat the metal sheets. When
18
5
spot welding is conducted, current flows to the pressing member 3 through the rod cover 6 and
piston rod 7 (also sometimes through the cylinder housing 5) as shown by the broken arrow
mark. Due to this, the metal sheets are sufficiently heated and the nugget size can be enlarged.
[0090]
The direction ofthe current (arrow direction) is not particularly limited and may be an
opposite direction as well.
[0091]
FIG. 7 is a cross-sectional schematic view when making the pressing member 3 of the
welding machine of FIG. 6 move to the outside.
10 [0092]
15
20
25
30
35
The pressing member 3 moves via the piston rod 7 by supplying and discharging
compressed air through the port 8 and ports 9a, 9b. As shown in FIG. 7, the piston rod 7 is made
to move and stop by compressed air until the position limited by the inside cover 6a.
[0093]
The material of the shank is not particularly limited so long as able to hold the electrode
tip and apply pressing force from the electrode tip to the set of sheets, but for example it may be
made of Cu-Cr alloy etc. and be provided with a cooling pipe at the inside thereof. The holder is
not particularly limited so long as one able to attach the shank 1, but for example it may be made
of Cu-Cr alloy etc. and be provided with a cooling pipe at the inside thereof.
REFERENCE SIGNS LIST
[0094]
1 shank
2 electrode tip
1 .) pressing member
4 pneumatic cylinder
5 cylinder housing
6 rod cover
6a lower cover
6b upper cover
7 piston rod
7a rod part
7h ring part
8 port
9a, 9b port
10 bag nut
19
lla,llb,llc 0-ring
12 screw adaptor
13 nul
14 insulating sleeve
5 15 metal sheet
16 set of sheets
17 first power supply
18 first drive mechanism
19 second drive mechanism
10 20 pressing force control part
21 molten metal
20
5
10
15
CLAIMS
Claim l. A spot welding machine welding a set of sheets including a superposed plurality
of metal sheets by resistance spot welding,
said spot welding machine comprising:
a pair of electrode tips with front end parts to be pressed against said set of sheets,
a pair of pressing members arranged around said electrode tips and with front end
parts to be pressed against said set of sheets,
a first power supply,
tirst drive mechanisms and second drive mechanisms, and
a pressing force control pati, wherein
said pair of electrode tips are arranged facing each other so as to be able to
sandwich said set of sheets between them,
said pair of pressing members are arranged facing each other so as to be able to
sandwich said set of sheets between them,
said pair of electrode tips are connected to said first power supply and said first
drive mechanisms, said first drive mechanisms driving said pair of electrode tips in the axial
direction of said electrode tips m1d making said pair of electrode tips stop at any positions and
giving pressing forces pressing said pair of electrode tips against said set of sheets,
said pair of pressing members are cmmected to said second drive mechanisms,
20 said second drive mechanisms driving said pair of pressing members in the axial direction of said
electrode tips and making said pair of pressing members stop at any positions and giving
pressing forces pressing said pair of pressing members against said set of sheets, and
said pressing force control pmi is connected to said first drive mechanisms and
said second drive mechanisms and independently controls the pressing forces given by said first
25 drive mechanisms and the pressing forces given by said second drive mechanisms.
30
35
Claim 2. The spot welding machine according to claim 1, wherein said first drive
mechanisms and said second drive mechanisms are independently a pneumatic cylinder,
hydraulic cylinder, or electric cylinder.
Claim 3. The spot welding machine according to claim 1 or 2, wherein said pressing
members m·e composed of a conductor and com1ectcd to said first power supply.
Claim 4. The spot welding machine according to claim 1 or 2, wherein
said spot welding machine is further provided with a second power supply, m1d
said pressing members are composed of a conductor and connected to said second
21
5
power supply.
Claim 5. A spot welding method for welding a set of sheets including a superposed
plurality of metal sheets by resistance spot welding, said spot welding method comprising:
preparing said set of sheets,
placing a first electrode tip and second electrode tip to face each other across said
set of sheets,
placing a first pressing member around the first electrode tip and placing a second
pressing member mound said second electrode tip such that the second pressing member faces
1 0 said first pressing member across said set of sheets,
pressing the front end parts of said first electrode tip and said second electrode tip
against said set of sheets to apply pressing forces,
pressing the front end parts of said first pressing member and said second pressing
member against said set of sheets to apply pressing forces independent from the pressing forces
15 applied from said first electrode tip and said second electrode tip, and
20
running current across said first electrode tip and said second electrode tip to weld
said set of sheets while pressing said first electrode tip and said second electrode tip and said first
pressing member and said second pressing member against said set of sheets to apply pressing
forces.
Claim 6. The spot welding method according to claim 5, wherein
said first pressing member and said second pressing member are composed of a
conductor, and
the method further comprises running current across said first pressing member
25 and said second pressing member.
Claim 7. The spot welding method according to claim 5 or 6, further comprising pressing
the front end pmis of said first pressing member and said second pressing member against said
set of sheets to apply pressing forces, then pressing the front end parts of said first electrode tip
30 and said second electrode tip against said set of sheets to apply pressing forces.
Claim 8. The spot welding method according to any one of claims 5 to 7, wherein
said first pressing member and said second pressing member are composed of a
conductor, and
35 the method further comprises, after welding said set of sheets, running current
across said first pressing member and said second pressing member, while not running current
22
across said first electrode tip and said second electrode tip.
Claim 9. The spot welding method according to any one of claims 5 to 8, wherein
said first pressing member and said second pressing member are composed of a
5 conductor, and
the method further comprises, before welding said set of sheets, running cunent
across said first pressing member and said second pressing member, while not running cunent
across said first electrode tip and said second electrode tip.