DESCRIPTION
TIG WELDING METHOD
TECHNICAL FIELD
The present invention relates to a TIG (Tungsten-Inert-Gas)
welding method in which welding is carried out by generating an arc
between a TIG electrode and an object to be welded. More specifically,
it relates to an arc starting method of TIG welding.
BACKGROUND ART
An arc starting method of TIG welding generally uses a method
of superimposing a high voltage with high frequency between a TIG
electrode and an object to be welded to cause dielectric breakdown,
thereby generating an arc, passing a predetermined start current, and
then outputting a steady-state current (see, for example, PTL 1).
When a short circuit, that is, contact between the TIG electrode
and the object to be welded, occurs during outputting of the
predetermined start current, in a conventionally commonly used TIG
welding method, passing of the predetermined start current is
completed in a short-circuit state and the steady-state current that is
larger than the start current is passed in the short-circuit state.
At this time, in particular, when the steady-state current is
large (for example, 500 A), a large short-circuit current is passed
through the TIG electrode, and unnecessary consumption or damage of
the TIG electrode may occur.
An operation of a conventionally commonly used TIG welding

apparatus is described with reference to Figs. 12 and 13. Fig. 12 is a
diagram showing a schematic configuration of a conventional TIG
welding apparatus, and Fig. 13 is a graph showing a change over time
of a welding current waveform and the like in a conventional AC TIG
welding apparatus. An operation of the TIG welding apparatus
configured as shown in Fig. 12 is described with reference to Fig. 13.
In Fig. 12, TIG welding apparatus 101 includes welding output
section 102 for carrying out a welding output, current detection section
104 for detecting a welding current, and first setting section 107a for
setting welding conditions and the like. TIG welding apparatus 101
includes high-voltage generating section 108 for applying a high
voltage between electrode 109 as a TIG electrode and base material 112
as an object to be welded, and welding control unit 115 for controlling
welding output section 102. Welding torch 110 having electrode 109 is
connected to TIG welding apparatus 101, and the welding output is
supplied between electrode 109 and base material 112, and thereby arc
111 is generated. Welding is carried out with this arc 111.
In Fig. 13 showing a welding current waveform and the like, Tl
denotes a first start period and T2 denotes a second start period. IP1
denotes a first start current, IP2 denotes a second start current, and I1
denotes a steady -State current. Furthermore, E1 denotes a time point
at which activation is on, E2 denotes a time point at which a current is
detected, E3 denotes a time point at which a short circuit occurs, E4
denotes a time point at which first start period Tl has passed from
time point E2, and E5 denotes a time point at which an arc is
regenerated.
In Fig. 12, welding output section 102 of TIG welding apparatus

101 receives a commercial power source (for example, three phase, 200
V) supplied from the outside, and carries out an operation of a primary
inverter and an operation of a secondary inverter (not shown)
constituting welding output section 102 based on a control signal from
welding control unit 115. With the operation of the primary inverter
and the operation of the secondary inverter, welding output section 102
appropriately switches between the positive polarity and the negative
polarity and outputs a welding voltage or a welding current suitable
for welding.
First setting section 107a including a CPU or the like sets
steady-state current I1 (for example, 500 A), first start period T1 (for
example, 40 msec), second start period T2 (for example, 20 msec), first
start current IP1 (for example, -100 A), and second start current IP2
(for example, 100 A) in association with, for example, a parameter
input by an operator, and outputs the set values to welding control unit
115.
Current detection section 104 including a CT (Current
Transformer) or the like detects a welding current, and outputs it as a
current detection signal to welding control unit 115.
Welding control unit 115 including a CPU or the like receives
each set value set by first setting section 107a, and a current detection
signal detected by current detection section 104. Then, welding
control unit 115 outputs an HF (High Frequency) signal for
commanding an operation of high-voltage generating device 108 to
high-voltage generating device 108, and outputs an output command
signal for commanding a welding output and an EN (Electrode
Negative) signal for commanding the polarity of the welding output to

welding output section 1.02.
Furthermore, welding control unit 115 outputs the output
command signal to welding output section 102 so that first start
current IP1 is output during first start period T1, second start current
IP2 is output during second start period T2, and steady-state current
I1 is output after the start periods are completed. Then, welding
output section 102 controls the welding current based on the output
command signal from welding control unit 115.
Furthermore, welding control unit 115 turns on an EN signal
that is a signal (positive polarity command) for shifting the period to
second start period T2 after first start period Tl is terminated.
Welding output section 102 operates as a positive polarity
period during the positive polarity period (the EN signal is on) by an
operation of the secondary inverter based on the EN signal from
welding control unit 115, and switches an output polarity to the
direction in which an electron moves from electrode 109 to base
material 112. Note here that welding output section 102 operates as a
negative polarity period during the negative polarity period (the EN
signal is off), and switches the output polarity to the direction in which
an electron moves from base material 112 to electrode 109.
High-voltage generating device 108 applies a high voltage (for
example, alternating voltage: 15 kV) between the output terminals of
TIG welding apparatus 101 when the HF signal is on, and stops
application of the high voltage between the output terminals of TIG
wedding apparatus 101 when the HF signal is off, based on the HF
signal that is a command signal from welding control unit 115.
A welding current or a welding voltage output by welding

output section 102 is supplied to connected welding torch 110, and arc
111 is generated between the tip of electrode 109 and base material 1.12.
With this arc 111, arc welding is carried out.
Next, a change over time of a welding current waveform in a
conventional AC TIG welding apparatus is described with reference to
Fig. 13.
At time point El at which activation is on shown in Fig. 13. the
output polarity is set to the negative polarity side by turning off the
EN signal, and the primary inverter is driven to generate a non-load
output. Furthermore, by turning on the HF signal, high-voltage
generating device 108 outputs a high voltage, and the output high
voltage is applied between electrode 109 and base material 112.
At time point E2 at which a current is detected shown in Fig. 13,
dielectric breakdown between electrode 109 and base material 112 is
caused by the high voltage applied by high-voltage generating device
108, and arc 111 is generated, so that a welding current is passed.
Then, when it is detected that the welding current is passed, it
is determined that a current is detected, and then the HF signal is
turned off and application of the high voltage by high-voltage
generating device 108 is stopped. The period is shifted to first start
period Tl and first start current IP1 (for example, -100 A) is output.
At time point E4 at which first start period Tl has passed from
time point E2 shown in Fig. 13, first start period Tl is completed.
Then, at time point E4, the EN signal is turned on and the polarity is
reversed to the positive polarity output side, the period is shifted to
second start period T2 and second start current IP2 is output. Then,
after second start period T2 is terminated, steady-state current II is

output.
At time point E3 in first start period Tl shown in Fig. 13, if a
short circuit in which electrode 109 and base material 112 are brought
into contact with each other occurs, a short-circuit current is passed
after time point E3 at which the short circuit occurs.
Then, at time point E5 in steady-state welding shown in Fig. 13,
if the contact between electrode 109 and base material 112 is released
and arc 111 is regenerated, an arc current is passed after E5 at which
an arc is regenerated. That is to say, from time point E3 to time point
E5, a short-circuit current is continued to be passed. Note here that
the arc regeneration means a state in which electrode 109 and base
material 112 are brought into contact with each other and arc 111
disappears from the arc state, and then the contact between electrode
1.09 and base material 112 is released and an arc is generated again.
As mentioned above, in the conventional technique, when a
short circuit is generated during first start period Tl, the period is
shifted to second start period T2 and further shifted to steady-state
current I1 in a short circuit state. In this case, the short-circuit
current is continued to be passed until an arc is regenerated.
In particular, when steady-state current I1 is large (for example,
500 A), electrode 109 may be unnecessarily consumed or damaged
when a short-circuit current is passed.
Alternatively, electrode 109 is melted and blown off when an arc
is regenerated, and the melted electrode 109 is mixed into base
material 112, which may cause a welding defect.
Furthermore, during an arc explosion, oxygen or water vapor in
the vicinity of the explosion portion is involved in a shielding gas,

which may cause generation of a blowhole.
As mentioned above, in a conventional TIG welding method,
when a short circuit occurs during the first start period, steady-state
welding occurs in a state in which the short circuit is maintained and a
short-circuit current is continued to be passed, unnecessary
consumption or damage of electrode 109 as a TIG electrode may occur,
and a welding defect may occur.
Citation List
Patent Literature
PTL 1- Japanese Patent Unexamined Publication No. H4-81275
SUMMARY OF THE INVENTION
A TIG welding method of the present invention extends a first
start period to wait for an increase of a current until an arc is
regenerated and increases a current after the arc is regenerated when
a short circuit occurs during the first start period. Thus, a TIG
welding method capable of avoiding unnecessary consumption or
damage of an electrode and preventing an occurrence of a welding
defect is provided.
A TIG welding method of the present invention is a TIG welding
method of carrying out welding by generating an arc between a TIG
electrode and an object to be welded. The method includes a first
start period that is a period during which a current is passed so as to
have a preliminarily set predetermined welding current waveform
from a start of welding, and detects contact between the TIG electrode
and the object to be welded from the start of welding. When the

contact between the TIG electrode and the object to be welded is
detected at the time of termination of the first start period, the method
shifts the period to a first start extension period during which a
current at the time of termination of the first start period is
maintained until the contact between the TIG electrode and the object
to be welded is released.
With this method, unnecessary consumption or damage of an
electrode can be avoided, and an occurrence of a welding defect can be
prevented.
Furthermore, a TIG welding method of the present invention is
a TIG welding method of generating an arc between a TIG electrode
and an object to be welded, and thereby carrying out welding. The
method includes a first start period that is a period during which a
current is passed so as to have a preliminarily set predetermined
welding current waveform from a start of welding, and detects contact
between the TIG electrode and the object to be welded from the start of
welding. When the contact between the TIG electrode and the object
to be welded is detected during the first start period, the method
terminates the first start period, and shifts the period to a first start
extension period during which a current at a time of termination of the
first start period is maintained until the contact between the TIG
electrode and the object to be welded is released.
With this method, unnecessary consumption or damage of an
electrode can be avoided, and an occurrence of a welding defect can be
prevented.
As mentioned above, according to the present invention, when a
short circuit occurs during the first start period, the first start period

is extended to wait for an increase of a current until an arc is
regenerated, and a current is increased after an arc is regenerated.
Thus, unnecessary consumption or damage of an electrode can be
avoided, and an occurrence of a welding defect can be prevented.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a diagram showing a schematic configuration of a TIG
welding apparatus in accordance with a first exemplary embodiment of
the present invention.
Fig. 2 is a graph showing a change over time of a welding
current waveform and the like in accordance with the first exemplary
embodiment of the present invention.
Fig. 3 is a graph showing a change over time of a welding
current waveform and the like in accordance with the first exemplary
embodiment of the present invention.
Fig. 4 is a graph showing a change over time of a welding
current waveform and the like in accordance with the first exemplary
embodiment of the present invention.
Fig. 5 is a diagram showing a schematic configuration of a TIG
welding apparatus in accordance with a second exemplary embodiment
of the present invention.
Fig. 6 is a graph showing a change over time of a welding
current waveform and the like in accordance with the second
exemplary embodiment of the present invention.
Fig. 7 is a diagram showing a schematic configuration of a TIG
welding apparatus in accordance with a third exemplary embodiment
of the present invention.

Fig. 8 is a graph showing a change over time of a welding
current waveform and the like in accordance with the third exemplary
embodiment of the present invention.
Fig. 9 is a graph showing a change over time of a welding
current waveform and the like in accordance with the third exemplary
embodiment of the present invention.
Fig. 10 is a diagram showing a schematic configuration of a TIG
welding apparatus in accordance with a fourth exemplary embodiment
of the present invention.
Fig. 11 is a graph showing a change over time of a welding
current waveform and the like in accordance with the fourth exemplary
embodiment of the present invention.
Fig. 12 is a diagram showing a schematic configuration of a
conventional TIG welding apparatus.
Fig. 13 is a graph showing a change over time of a welding
current waveform and the like in a conventional AC TIG welding
apparatus.
DESCRIPTION OF EMBODIMENTS
Hereinafter, exemplary embodiments of the present invention
are described with reference to drawings. In the following drawings,
the same reference numerals are given to the same components and the
description thereof may be omitted.
FIRST EXEMPLARY EMBODIMENT
The first exemplary embodiment is described with reference to
Figs. 1 to 4. An operation of a TIG welding apparatus configured as
shown in Fig. 1 is described with reference to a change over time of a

current waveform and the like shown in Figs. 2 to 4.
Fig. 1 is a diagram showing a schematic configuration of a TIG
welding apparatus in accordance with the first exemplary embodiment,
and Fig. 2 is a graph showing a change over time of a welding current
waveform and the like in accordance with the first exemplary
embodiment. Fig. 3 is a graph showing another example of a change
over time of a welding current waveform and the like in accordance
with the first exemplary embodiment, and Fig. 4 is a graph showing
still another example of a change over time of a welding current
waveform and the like in accordance with the first exemplary
embodiment.
Hereinafter, an AC TIG welding apparatus in winch welding is
carried out by repeating a negative polarity period and a positive
polarity period is described as an example.
in Fig. 1, TIG welding apparatus 1 includes welding output
section 2, welding control unit 3, current detection section 4, voltage
detection section 5, AS (Arc or Short) determination section 6, first
setting section 7a. high-voltage generating section 8, and third setting
section 13a. Herein, welding output section 2 outputs a welding
output. Welding control unit 3 controls welding output section 2.
Current detection section 4 detects a welding current. Voltage
detection section 5 detects a welding voltage. AS determination
section 6 detects whether or not electrode 9 as a TIG electrode and base
material 12 as an object to be welded are brought into contact with
each other based on the detection results of voltage detection section 5.
First setting section 7a sets the welding conditions and the like.
High-voltage generating section 8 applies a high voltage between

electrode 9 and base material 12. Third setting section 13a sets the
welding conditions and the like. Welding torch 10 having electrode 9
is connected to TIG welding apparatus 1, and supplies a welding
output between electrode 9 and base material 12 to generate arc 11
between electrode 9 and base material 12. Thus, welding is carried
out.
P'igs. 2 to 4 show a change over time of a current waveform and
the like. In Figs. 2 to 4, Tl denotes a first start period, T2 denotes a
second start period, T3 denotes a third start period, and T1EXT
denotes a first start extension period. TlTERM denotes a first start
period that is terminated due to occurrence of a short circuit.
Furthermore, IP 1 is a first start current, IP2 is a second start current,
1P3 is a third start current, and II is a steady-state current. El is a
time point at which activation is on, E2 is a time point at which a
current is detected, E3 is a time point at which a short circuit occurs,
E4 is a time point at which first start period Tl has passed from time
point E2, E5 is a time point at which an arc is regenerated, and E6 is a
time point at which third start period T3 has passed from time point
E5.
In Fig. 1. welding output section 2 of TIG welding apparatus 1
receives a commercial power source (for example, three phase, 200 V)
supplied from the outside, and carries out an operation of a primary
inverter (not shown) and an operation of a secondary inverter (not
shown) constituting welding output section 2 based on a control signal
from welding control unit 3. With the operation of the primary
inverter and the operation of the secondary inverter, welding output
section 2 appropriately switches between positive polarity and

negative polarity, and outputs a welding voltage or a welding current
suitable for welding.
Note here that the primary inverter constituting welding output
section 2 generally includes an IGBT (Insulated Gate Bipolar
Transistor) (not shown), a MOSFET (Metal-Oxide Semiconductor Field
Effect. Transistor) (not shown), a primary rectifier diode (not shown), a
smoothing electrolytic capacitor, a transformer for converting electric
power, and the like, driven by PWM (Pulse Width Modulation)
operation or a phase-shift operation.
Furthermore, the secondary inverter (not shown) constituting
welding output section 2 is generally configured by using IGBT in a
half bridge or a full bridge, and switches the output polarity.
Herein, the positive polarity is a case in which an electron in
arc plasma moves in the direction from electrode 9 to base material 12,
and electrode 9 is negative and the base material is positive.
Furthermore, the negative polarity is a case in which an
electron in arc plasma moves in the direction from base material 12 to
electrode 9, and electrode 9 is positive and the base material is
negative.
First setting section 7a including a CPU or the like sets
steady-state current 11 (for example, 500 A), first start period Tl (for
example, 40 msec), second start period T2 (for example, 20 msec), first
start current IP1 (for example, 100 A), and second start current IP2
(for example, 100 A) based on, for example, a parameter input by an
operator, and outputs the set values to welding control unit 3.
Third setting section 13a including a CPU or the like sets third
start period T3 (for example, 30 msec) and third start current IP3 (for

example;, 80 A) based on, for example, a parameter input by an
operator, and outputs the set values to welding control unit 3.
Voltage detection section 5, which includes a voltage
measurement device or the like and measures a voltage between the
output terminals of TIG welding apparatus 1, detects a welding voltage,
and outputs it as a voltage detection signal to AS determination
section 6.
AS determination section 6 including a CPU or the like receives
the voltage detection signal from voltage detection section 5. When
an absolute value of the voltage detection signal reaches (decreases to)
a previously set detection level (for example, 10 V) during
determination of an arc, AS determination section 6 determines that
electrode 9 as a TIG electrode and base material 12 as an object to be
welded arc brought into contact with each other (hereinafter, referred
to as a "short circuit''), and determines that an AS signal is a short
circuit signal (low level).
Furthermore, when an absolute value of the voltage detection
signal reaches (increases to) a previously set detection level (for
example1, 15 V) during determination of a short circuit, AS
determination section 6 determines that an arc occurs between
electrode 9 as a TIG electrode and base material 12 as an object to be
welded (hereinafter, "during arcing" or "regeneration of an arc"), and
determines that the AS signal is an arc signal (high level).
Note here that during output of a non-load voltage in which a
current is not detected, the AS signal is determined to be an arc signal
(high level).
Current detection section 4 including a CT or the like detects a

welding current and outputs it as a current detection signal to welding
control unit 3.
Welding control unit 3 including a CPU or the like receives each
set value set by first setting section 7a, each set value set by third
setting section 13a, an AS signal output by AS determination section 6,
and a current detection signal detected by current detection section 4,
and outputs an HF signal for commanding an operation of high-voltage
generating section 8 to high-voltage generating section 8.
Furthermore, welding control unit 3 outputs an output command
signal for commanding a welding output and an EN signal for
commanding the polarity of the welding output to welding output
section 2.
furthermore, welding control unit 3 receives an activation
signal (activation on) from the outside of TIG welding apparatus 1 and
turns on an HF signal (high level). Welding control unit 3 turns off an
HF signal (low level) when it determines based on a signal from
current detection section 4 that a welding current is detected. As to
the determination of the detection of a current, for example, when a
current value detected by current detection section 4 is 2.5 A or more,
it is determined that a current is detected.
Furthermore, welding control unit 3 receives the activation
signal (activation on) from the outside, drives the primary inverter
constituting welding output section 2, and supplies a welding voltage
between electrode 9 and base material 12.
Furthermore, welding control unit 3 receives the activation
signal (activation on) from the outside, turns off the EN signal (low
level, negative polarity command), and turns on the EN signal (high

level, positive polarity command) at a time point when the second start
period T2 is started mentioned below.
Furthermore, welding control unit 3 outputs an output
command signal to welding output section 2 so that first start current
IPl is output during first start period Tl, and outputs an output
command signal to welding output section 2 so that second start
current IP2 is output during second start period T2. Welding control
unit 3 outputs an output command signal to welding output section 2
so that third start current 1P3 is output during third start period T3,
and outputs an output command signal to welding output section 2 so
that steady-state current II is output after second start period T2 is
completed.
Furthermore, when an AS signal from AS determination section
6 is determined to be a short circuit at the time of termination of first
start period Tl, as shown in Fig. 2, welding control unit 3 controls
wedding output section 2 so that the period is shifted to first start
extension period T.IEXT and first start current IPl as a welding
current at the lime of termination of first start period Tl is
continuously output. When the AS signal from AS determination
section 6 is determined to be an arc during first start extension period
T1EXT, first start extension period T1EXT is terminated and shifted to
a predetermined third start period T3. Furthermore, after third start
period T3 is terminated, the period is shifted to second start period T2,
and the EN signal (positive polarity command) is turned on.
Welding output section 2 operates as the positive polarity
period by an operation of the secondary inverter based on the EN
signal from welding control unit 3 during the positive polarity period

(FN signal is on), and switches the output polarity to the direction in
which an electron moves from electrode 9 to base material 12. Then,
welding output section 2 operates as a negative polarity period during
the negative polarity period (EN signal is off), and switches the output
polarity to the direction in which an electron moves from base material
12 to electrode 9.
Furthermore, welding output section 2 outputs first start
current IP'l during first start period Tl by the operation of the primary
inverter based on the output command signal from welding control unit
3. Welding output section 2 outputs second start current IP2 during
second start period T2, outputs third start current IP3 during third
start period T3, and outputs steady-state current II after second start
period T2 is completed.
High-voltage generating section 8 including a flyback
transformer or the like applies a high voltage (for example, 15 kV is
applied) between the output terminals of TIG welding apparatus 1
based on the HP signal from welding control unit 3 when the HF signal
is on. and stops application of the high voltage between the output
terminals of TIG welding apparatus 1 when the HF signal is off.
A welding current and a welding voltage output by welding
output section 2 are supplied to the connected welding torch 10 to
generate arc 11 between a tip of electrode 9 that is a TIG electrode
formed of tungsten or the like and base material 12 as an object to be
welded such as an aluminum material. Thus, arc welding is carried
out.
Next, a welding method of the first exemplary embodiment is
described, with reference to Fig. 2 showing a change over time of a

welding current waveform and the like.
At time point El at which activation is on shown in Fig. 2, the
primary inverter is turned on to generate a non-load output, an HF
signal is turned on. and a high voltage output by high-voltage
generating section 8 is applied between electrode 9 and base material
12.
This activation on is commanded by, for example, a torch switch
or a sequencer of an automatic machine (not shown) provided outside
of TIG welding apparatus 1.
At time point E2 shown in Fig. 2, dielectric breakdown between
electrode 9 and base material 12 is caused by a high voltage applied by
high-voltage generating section 8, and an arc is generated. Thus, a
welding current is passed and a current is detected.
Welding control unit 3 detects via current detection section 4
that the welding current is passed. When an electric current is
determined to be detected, welding control unit 3 turns off the II.F
signal to stop application of the high voltage of high-voltage generating
section 8, and shifts the period to first start period Tl.
During first start period Tl, welding control unit 3 controls
welding output section 2 so that first start, current IP1 (for example,
-100 A) is output.
At time point E3 shown in Fig. 2, when a short circuit occurs
between electrode 9 and base material 12, AS determination section 6
determines that a short circuit occurs, and an AS signal becomes low
level. Note here that a short circuit between electrode 9 and base
material 12 occurs because, for example, a working error occurs due to
short of skill of a welding operator, or because working accuracy or jig

accuracy is bad.
At time point E4 at which first start period Tl is terminated
and first arc start period Tl has passed from time point E2 shown in
Fig. 2, a short circuit state between electrode 9 and base material 12 is
continued. At this time, when AS determination section 6 determines
that a short circuit occurs, the period is shifted to first start extension
period T1EXT that is an extension of first start period Tl. Welding
control unit 3 controls welding output section 2 so that IPl that is a
current value at the time point of termination of first start period Tl is
maintained.
After that, at time point E5 shown in Fig. 2, it is assumed that
contact (short circuit) between electrode 9 and base material 12 is
released and an arc is regenerated. Herein, an arc is regenerated, for
example, when an operator intentionally separates electrode 9 from
base material 12, or an arc is accidentally generated when electrode 9
moves toward base material 12 due to a work shape or an operation of
an automatic machine.
At time point E5 at which an arc is regenerated shown in Fig. 2,
first start extension period T1EXT is terminated, and the period is
shifted to third start period T3 whose polarity is the same as that of
first start period Tl and first start extension period T1EXT. Welding
control unit 3 controls welding output section 2 so that third start
current IP3 is output. Note here that the length of third start period
T3 may be, for example, the same as that of first start period Tl, or
may be previously determined by carrying out experiment, working, or
the like.
Furthermore, the current value of third start current IP3 may

be, lor example, the same as that of first start current IP1, or may be
previously determined by carrying out experiment, working, or the
like.
At time point E6 at which third start period T3 has passed from
time point E5 shown in Fig. 2, third start period T3 is terminated, and
welding control unit 3 turns on the EN signal, inverts the polarity to
the positive polarity output side, and shifts the period to second start
period T2.
Thus, by applying a predetermined heat input in third arc start
period T3 before the polarity is inverted at time point E6, when the
polarity is inverted at time point E6, arc interruption does not easily
occur, and excellent welding can be carried out. After second start
period T2 is terminated, welding control unit 3 controls welding output
section 2 so that steady-state current II at the time of steady-state
welding is output.
Fig. 2 shows an example in which after first start extension
period TlEXT is completed, the period is shifted to third start period
T3, and then shifted to second start period T2. However, shown in Fig.
3, the period may be shifted to second start period T2 after first start
extension period TlEXT is completed without providing third start
period T3 shown in Fig. 2.
Furthermore, as shown in Fig. 4, when a short circuit is
detected in the middle of a predetermined first start period Tl from the
start of welding, first start period Tl may be forcibly terminated at the
time point at which a short circuit is detected, and the period may be
shifted to first start: extension period TlEXT. In this case, the first
start period is first start period T1TERM shown in Fig. 4, which is

shorter than first start period Tl shown in Fig. 2.
As shown in Fig. 4, before first start period Tl having a
predetermined length is completed, first start period Tl is forcibly
terminated when a short circuit between electrode 9 and base material
12 occurs, and the period is shifted to first start extension period
T1.EXT. Thus, processing during the short circuit can be executed
earlier. This is effective in, for example, the case where first start
period Tl is set long (for example, 400 msec).
As mentioned above, when a short circuit between electrode 9
and base material 12 is detected at the time point of termination of
first start period Tl. the period is shifted to first start extension period
T1EXT during which a current at the time point of termination of first
start period Tl is maintained. Then, it is controlled to wait for
regeneration of an arc as an extension state of first start period Tl,
and to allow the period to return to second start period T2 after an arc
is regenerated. Thereby excellent arc starting property can be
secured.
Furthermore, since a state is not shifted to a steady-state
welding m a state in which a short circuit between electrode 9 and base
material 12 is continued, a short-circuit current is not continuously
passed from the start period through the steady-state. Thereby, in
particular, when steady-state current II is a large current (for example,
500 A), unnecessary consumption or damage of electrode 9 can be
prevented.
Furthermore, when steady-state current 11 is a large
alternating electric current, in a conventional TIG welding apparatus,
when a short circuit, occurs during first start period Tl, a state may be

shifted to a steady-state welding while a short circuit is continued. In
such a case, since the current is large and the state is in a short circuit
state, polarity is inverted in a state of a higher electric current, and a
higher surge voltage occurs due to the switching of the secondary
inverter for inverting the polarity. With such a high surge voltage,
there is a risk that a semiconductor device constituting the secondary
inverter may he damaged. In the first exemplary embodiment,
however, since a state as in the above-mentioned conventional TIG
welding apparatus does not occur, there is not a risk as in a
conventional TIG welding apparatus.
That is to say, the TIG welding method of the present invention
carries out welding by generating an arc between a TIG electrode and
an object to be welded, includes a first start period that is a period
during which a current is passed so as to have a preliminarily7 set
predetermined welding current waveform from a start of welding, and
detects contact between the TIG electrode and the object to be welded
from the start of welding. When the contact between the TIG
electrode and the object to be welded is detected at a time when the
first start period is terminated, the TIG welding method of the present
invention shifts the period to a first start extension period during
which a current at the time of termination of the first start period is
maintained until the contact between the TIG electrode and the object
to be welded is released.
With this method, unnecessary consumption or damage of an
electrode can be avoided, and an occurrence of a welding defect can be
prevent ed.
Furthermore, the TIG welding method of the present invention

carries out welding by generating an arc between a TIG electrode and
an object to be welded, includes a first start period that is a period
during which a current is passed so as to have a preliminarily set
predetermined welding current waveform from a start of welding, and
detects contact between the TIG electrode and the object to be welded
from the start of welding. When the contact between the TIG
electrode and the object to be welded is detected during the first start
period, the TIG method of the present invention terminates the first
start period and shifts the period to a first start extension period
during which a current at the time of termination of the first start
period is maintained until the contact between the TIG electrode and
the object to be welded is released.
With this method, unnecessary consumption or damage of an
electrode can he avoided, and an occurrence of a welding defect can be
prevented.
Furthermore, the TIG welding method of the present invention
is an AC TIG welding method in which welding is carried out by
alternately repeating the positive polarity period and the negative
polarity period. The method includes, following the first start period
as one polarity period, a second start period as the other polarity
period whose polarity is different from that of the first start period,
and detects contact between the TIG electrode and the object to be
welded from the start of welding. When the period is shifted to the
first start extension period, the TIG method of the present invention
may be a method of commutating from the first start extension period
as one polarity period to the second start period as the other polarity
period after the first start extension period.

With this method, unnecessary consumption or damage of an
electrode can be avoided, and an occurrence of a welding defect can be
prevented.
furthermore, the TIG welding method of the present invention
is an AC TIG welding method of carrying out welding by alternately
repeating the positive polarity period and the negative polarity period,
includes, following the first start period as one polarity period, a
second start period as the other polarity period whose polarity is
different from that of the first start period, and detects contact
between the TIG electrode and the object to be welded from the start of
welding. When the period is shifted to the first start extension period,
the TIG welding method of the present invention shifts the period to a
third start period during which a current is passed so as to have a
predetermined welding current waveform after the first start
extension period is terminated and which is a predetermined period
whose polarity is the same as that of the first start extension period.
The TIG method of the present invention may be a method of
com mutating from the third start period as one polarity period to the
second start period as the other polarity period after the third start
period is terminated.
With this method, unnecessary consumption or damage of an
electrode can be avoided, and an occurrence of a welding defect can be
prevented.
The first exemplary embodiment describes an example of a DC
output of positive polarity as steady-state current II is described, but
the same effect can be obtained when the same control is carried out by
using an AC output, as the steady-state current.

In the drawings, first start current IP1, second start current
IP2, and third start current IP3 have arbitrary fixed values, but they
may have a waveform varying during each start period.
Furthermore, duration time of the short circuit is measured,
and when the duration time is long (for example, one second), a state is
determined to be an abnormal short circuit, and a welding output may
be stopped.
SECOND EXEMPLARY EMBODIMENT
A second exemplary embodiment is described with reference to
Figs. 5 and 6. Fig. 5 is a diagram showing a schematic configuration
of a TIG welding apparatus in accordance with the second exemplary
embodiment, and Fig. 6 is a graph showing a change over time of a
welding current waveform in accordance with the second exemplary
embodiment.
The TIG welding method of the second exemplary embodiment
is different from that of the first exemplary embodiment mainly in a
determination method of a current value during continuation of a short
circuit. In the second exemplary embodiment, an output current
during a short circuit is set by a setting section. Specifically, a
current value is reduced.
Hereinafter, an example using an AC TIG welding apparatus for
carrying out welding by repeating a negative polarity period and a
positive polarity period is described.
Fig. 5 is different from Fig. 1 of the first exemplary
embodiment in that fifth setting section 14a is shown in Fig. 5. Fig. 6
is different from Figs. 2 to 4 of the first exemplary embodiment in that

first short-circuit current ISl is shown in Fig. 6.
In Fig. 5, fifth setting section 14a including a CPU or the like
sets first short-circuit current ISl (for example, -20A) as a current
during continuation of a short circuit, and the set value is output to
welding control unit 3.
Welding control unit 3 including a CPU or the like receives each
set value set by first setting section 7a, each set value set by third
setting section 13a, each set value set by fifth setting section 14a, an
AS signal output by AS determination section 6, and a current
detection signal detected by current detection section 4. Then,
welding control unit 3 outputs an HF signal for commanding an
operation of high-voltage generating section 8 to high-voltage
generating section 8, and outputs an output command signal for
commanding a welding output and an EN signal for commanding the
polarity of the welding output to welding output section 2.
Furthermore, welding control unit 3 reduces the welding output
to a predetermined first short-circuit current ISl in first start period
Tl and first start extension period T1EXT from the time when a short
circuit occurs to the time when an arc is regenerated.
Mext, with reference to Fig. G, a change over time of a welding
current waveform and the like in accordance with the second
exemplary embodiment is described.
At time point El at which activation is on shown in Fig. 6, TIG
wedding apparatus 1 is activated, and a non-load voltage and a high
voltage are applied between electrode 9 and base material 12.
At time point E2 shown in Fig. 6, dielectric breakdown between
electrode 9 and base material 12 is caused and a current flows. A

current is detected by current detection section 4, application of a high
voltage by high-voltage generating section 8 is stopped, and a period is
shifted to first start period T.l.
If a short circuit between electrode 9 and base material 12 is
generated at time point E3 shown in Fig. 6, a welding current is
reduced to first short-circuit current ISl after time point E3.
At time point E4 which is a time point of termination of first
start period Tl and at which first arc start period Tl has passed from
time point E2, first start period Tl is terminated.
Since electrode 9 and base material 12 are short -circuited also
at the time point of termination of first start period Tl, AS
determination section 6 determines that a short circuit occurs.
Therefore, the period is shifted to first start extension period T1EXT,
and first short-circuit current IS1 that is a current value at the time
point of termination of first start period Tl is maintained.
Note here that first short-circuit current ISl may have a
smaller absolute value than that of first start current IPl, and first
sbort-circuit current ISl may have a smaller absolute value than that
of steady-state current II.
Furthermore, first short-circuit current ISl may be set to an
appropriate value by carrying out experiment, working, or the like.
The value may be any current value as long as it is such a low current
value that electrode 9 is not unnecessarily melted during a short
circuit, and it is a predetermined large current value (for example,
about 20 A) such that arc interruption does not easily occur when an
arc is regenerated.
Furthermore, first short-circuit current ISl may be a low value

around the minimum current value (for example, 5 A) TIG welding
apparatus 1 can output in the case where prevention of damage of
electrode 9 is emphasized.
Next, as shown in Fig. 6, at time point E5 during first start
extension period Tl EXT, an arc is regenerated, the period is shifted to
third start period T3 from time point E5, and third start current IP3 is
output.
At time point E6 at which third start period T3 has passed from
time point E5, third start period T3 is terminated, the polarity is
inverted, and the period is shifted to second start period T2. After
second start period T2 is terminated, steady-state current II is output.
In this way, during a short circuit between electrode 9 and base
material 12, the welding current is controlled to be reduced to first
short-circuit current ISl, and thereby unnecessary consumption or
damage of electrode 9 can be prevented.
That is to say, the TIG welding method of the present invention
may be a method of controlling a welding current to a current having a
previously set predetermined first short-circuit current waveform,
which is different from the current at the time point at which contact
between the TIG electrode and the object to be welded is detected from
a time at which the contact between the TIG electrode and the object to
be welded is detected to a time at which a release of the contact
between the TIG electrode and the object to be welded is detected in
the first start period and the first start extension period.
^Yith this method, unnecessary consumption or damage of the
electrode can be avoided, and an occurrence of a welding defect can be
prevented.

THIRD EXEMPLARY EMBODIMENT
This exemplary embodiment is described with reference to Figs.
7 to 9. An operation of TIG welding apparatus 1 shown in Fig. 7 is
described with reference to Figs. 8 and 9 showing a change over time of
a current waveform and the like.
Fig. 7 is a diagram showing a schematic configuration of a TIG
welding apparatus in accordance with the third exemplary
embodiment; Fig. 8 is a graph showing a change over time of a welding
current waveform and the like in accordance with the third exemplary
embodiment! and Fig. 9 is a graph showing a change over time of a
welding current waveform in accordance with the third exemplary
embodiment.
The TIG wedding method of the third exemplary embodiment is
different from that of the first exemplary embodiment mainly in the
configuration of TTG, that is. AC TIG or DC TIG. The first exemplary
embodiment describes an example of an operation of AC TIG welding,
but the third exemplary embodiment describes an example of an
operation of DC TIG welding.
Hereinafter, an example in which DC TIG welding apparatus 21
is used is described. In Fig. 7, DC TIG welding apparatus 21 includes
DC we]ding output section 2b, DC welding control unit 3b, second
setting section 7b, and fourth setting section 13b. In Figs. 8 and 9, T4
is a fourth start period, IP4 is a fourth start current, and time point E7
is a time point at which fourth start period T4 has passed from time
point Eo.
In Fig. 7, DC welding output section 2b of TIG welding

apparatus 21 carries out a primary inverter operation based on the
output from DC welding control unit 3b, and outputs a welding voltage
or a welding current suitable for welding to the direction of the positive
polarity (the case in which electrode 9 is negative and base material 12
is positive).
Second setting section 7b including a CPU or the like sets
steady-state current II (for example, 500 A), first start period Tl (for
example, 40 msec), and first start current IP1 (for example, 100 A) in
association with, for example, a parameter input by an operator, and
outputs the set values to DC welding control unit 3b.
Fourth setting section 13b including a CPU or the like sets
fourth start period T4 (for example, 30 msec) and fourth start current
IP4 (for example, 80 A) in association with, for example, a parameter
input by an operator, and outputs the set values to DC welding control
unit 3b.
DC welding control unit 3b including a CPU or the like receives
each set value set by second setting section 7b, each set value set by
fourth setting section 13b, an AS signal output by AS determination
section 6, and a current detection signal detected by current detection
section 4. DC welding control unit 3b outputs an TIF signal for
commanding an operation of high-voltage generating section 8 to
high-voltage generating section 8, and an output command signal for
commanding welding output to DC welding output section 2b.
Furthermore, DC welding control unit 3b outputs first start
current TPl during first start period Tl and outputs fourth start
current IP4 during fourth start period T4. After fourth start period
Tl is completed, DC welding control unit 3b outputs an output

command signal to DC welding output section 2b so that steady-state
current II is output.
Furthermore, when the AS signal output by AS determination
section 6 is a signal showing a short circuit at the time of termination
of first start period Tl, DC welding control unit 3b shifts the period to
first start extension period T1EXT period, and continues to output first
start current TPl as a welding current at the time of termination of
first start period Tl.
When a signal from AS determination section 6 is determined to
be an arc during first start extension period T1EXT, first start
extension period T1EXT is terminated and shifted to a predetermined
fourth start period T4. Then, after fourth start period T4 is
terminated, steady-state current II is output.
Next, a change over time of a welding current waveform and the
like in the third exemplary embodiment is described with reference to
Fig. 8.
In Fig. 8, when a short circuit occurs at time point E3 shown in
Fig. 8, at time point E3 at which a short circuit occurs, AS
determination section 6 determines that electrode 9 and base material
12 are short-circuited, and an AS signal becomes low level.
Time point E4 shown in Fig. 8 is a time point at which first start
period Tl is terminated and at which first start period Tl has passed
from time point E2. When AS determination section 6 determines
that a short circuit occurs at this time point E4, the period is shifted to
first start extension period T1EXT that is an extension of first start
period Tl, and IP'l as a current value at the time of termination of the
first start period is maintained and output.

When an arc is regenerated at time point E5 shown in Fig. 8, at
time point E5, first start extension period TlEXT is terminated and
shifted to fourth start period T4 and fourth start current IP4 is output.
After time point E7 at which fourth arc start period T4 has passed from
time point E5 shown in Fig. 8, welding is shifted to a steady-state
welding and steady-state current II is output.
That is to say, the TIG welding method of the present invention
is a DC TIG welding method, and detects contact between the TIG
electrode and the object to be welded from the start of welding. When
the period is shifted to the first start extension period, the TIG welding
method of the present invention shifts the period to a fourth start
period that is a predetermined period during which a current is passed
so as to have a preliminarily set predetermined welding current
waveform after the first start extension period is terminated. After
the fourth start period is terminated, the TIG welding method of the
present invention controls the welding current so that the welding
current is changed from the welding current at the time of termination
of the fourth start extension period to a steady-state welding current
that is a preliminarily set welding current at the time of steady-state
welding.
With this method, unnecessary consumption or damage of an
electrode can be avoided, and an occurrence of a welding defect can be
prevented.
Note here that the length of fourth start period T4 may be the
same as that of first start period Tl, and an appropriate period may be
previously determined by carrying out experiment or working.
Furthermore, fourth start current IP4 may be the same as first

start current IPl, and an appropriate current value may be previously
determined by carrying out experiment or working.
Note here that fourth start period T4 shown in Fig. 8 is not
provided, and steady-state current II may be output immediately after
first start extension period T1EXT is completed as shown in Fig. 9
showing a change over time of a welding current and the like.
That is to say, the TIG welding method of the present invention
is a DG TIG welding method, and detects contact between the TIG
electrode and the object to be welded from the start of welding. When
the period is shifted to the first start extension period, the TIG welding
method of the present invention controls the welding current so that
(lie welding current is changed from a welding current at the time of
termination of the first start extension period to a steady-state welding
current that is a preliminarily set welding current at the time of
steady-state welding after the first start extension period is
terminated.
With this method, unnecessary consumption or damage of an
electrode can be avoided, and an occurrence of a welding defect can be
prevented.
As mentioned above, when a short circuit between electrode 9
and base material 12 is detected at the time of termination of first
start period Tl, 1 he period is shifted to first start extension period
T1EXT to wait for regeneration of an arc in a state of first start
extension period TlKXT. Thus, the period returns to the start period
again after an are is regenerated, and excellent arc starting property
can be secured.
furthermore, when steady-state current II is a large current

(for example, 500 A), a short-circuit current is not continuously passed,
and therefore unnecessary consumption or damage of electrode 9 can
be prevented.
The drawings illustrate an example in which first start current
IP1 and fourth start current IP4 are arbitrary fixed values, but they
may have a waveform varying during each start period.
FOURTH EXEMPLARY EMBODIMENT
A fourth exemplary embodiment is described with reference to
Figs. 10 and 11. Fig. 10 is a diagram showing a schematic
configuration of a TIG welding apparatus in accordance with the fourth
exemplary embodiment, and Fig. 11 is a graph showing a change over
time of a welding current waveform and the like in accordance with the
fourth exemplary embodiment.
The fourth exemplary embodiment also describes an example of
DC welding, but is different from the third exemplary embodiment
showing an example of DC welding mainly in a determination method
of a current value; during a short circuit. In the fourth exemplary
embodiment, an output current during a short circuit is set by a setting
section, and more specifically, a current is set to be reduced from a
current before the short circuit.
Hereinafter, an example in which DC TIG welding apparatus 21
is used is described. In Fig. 10, DC TIG welding apparatus 21
includes sixth setting section 14b. In Fig. 11, IS2 is a second
short -circuit current.
In Fig. 10, sixth setting section 14b including a CPU or the like
sets second short-circuit current IS2 (for example, 20 A), and outputs

the set value to DC welding control unit 3b.
DC welding control unit 3b including a CPU or the like receives
each set value set by second setting section 7b, each set value set by
fourth setting section 13b, each set value set by sixth setting section
1 lb. an AS signal output by AS determination section 6, and a current
detection signal detected by current detection section 4. DC welding
control unit 3b outputs an HF signal for commanding an operation of
high-voltage generating section 8 to high-voltage generating section 8,
and outputs an output command signal for commanding a welding
output to DC welding output section 2b.
Furthermore, DC welding control unit 3b reduces a welding
output to a preliminarily set second short-circuit current T.S2 from the
time when the short circuit between electrode 9 and base material 12
occurs to the time when an arc is regenerated during first start period
Tl and first start extension period T1EXT.
A change over time of a welding current waveform and the like
in this exemplary embodiment is described with reference to Fig. 11.
In Fig. 11, when a short circuit occurs at time point E3, a welding
current is reduced to second short-circuit current IS2 after time point
K3.
Note here that second short-circuit current TS2 may be the same
current value as first start current IPl, or may be a smaller current
value than that of first start current IPl, or may be a smaller current
value than that of steady-state current II.
Furthermore, as second short-circuit current IS2, an
appropriate value can be previously determined by carrying out
experiment, working, or the like. Second short-circuit current IS2

may be any current value as long as it is such a low current that
electrode 9 is not unnecessarily melted during a short circuit, and it
has a predetermined large current value (for example, about 20 A) such
that are interruption does not easily occur when an arc is regenerated.
Furthermore, second short-circuit current IS2 may be a low
value around the minimum current value (for example, 5 A) DC TIG
welding apparatus 21 can output in the case where prevention of
damage of electrode 9 is emphasized.
Time point E4 is a time point at which first start period T1 is
completed, and which is a time point after first start period T1 has
passed from time point E2. At time point E4, first start period Tl is
terminated, and shifted to first start extension period T1EXT, and
current value IS2 at a time point of termination of first start period Tl
is maintained and output.
When an arc is regenerated at time point E5 during first start
extension period T1EXT, the period is shifted to fourth start period T4,
and fourth start current IP4 is output.
At time point E7 at which fourth start period T4 has passed
from time point E5, fourth start period T4 is terminated and
steady-state current I1 is output.
In this way, during a short circuit between electrode 9 and base
material 12, by reducing a welding current to second short-circuit
current IS2, unnecessary consumption or damage of electrode 9 can be
prevented.
That is to say, the TIG welding method of the present invention
may be a method of controlling a welding current to a current having a
previously set predetermined second short-circuit current waveform,

which is different from the current at the time point at which contact
between the TIG electrode and the object to be welded is detected from
a time at which the contact between the TIG electrode and the object to
be welded is detected to a time at which a release of the contact
between the TIG electrode and the object to be welded is detected in
the first start period and the first start extension period.
With this method, unnecessary consumption or damage of an
electrode can be avoided, and an occurrence of a welding defect can be
prevented.
INDUSTRIAL APPLICABILITY
As mentioned above, according to the invention of the present
application, even if a short circuit occurs during a first start period,
the first start period is extended to wait for regeneration of an arc, and
an output of a starting waveform is continued after an arc is
regenerated. Thus, it is possible to prevent unnecessary consumption
or damage of an electrode, and to prevent occurrence of a welding
defect. Therefore, the present invention is industrially useful as a
TIG welding method in industries in which TIG welding is carried out,
for example, in the automobile industry or the construction industry in
which, in particular, production is carried out by using an aluminum
material or a magnesium material.
REFERENCE MARKS IN DRAWINGS
1, 21 TTG welding apparatus
2 welding output section
2b DC welding output section

3 welding control unit
3b DC welding control unit
4 current detection section
5 voltage detection section
G AS determination section
7a first setting section
7b second setting section
8 high-voltage generating section
9 electrode
10 welding torch
11 arc
12 base material
13a third setting section
13b fourth setting section
14a fifth setting section
14b sixth setting section
15 welding control unit

We Claim:
1. A TIG welding method of carrying out welding by generating an
arc between a TIG electrode and an object to be welded,
wherein the method includes a first start period that is a period
during which a current is passed so as to have a preliminarily set
predetermined welding current waveform from a start of welding;
detects contact between the TIG electrode and the object to be
welded from the start of welding; and
when the contact between the TIG electrode and the object to be
welded is detected at a time of termination of the first start period, the
method shifts the period to a first start extension period during which
a current at the time of termination of the first start period is
maintained until the contact between the TIG electrode and the object
to be welded is released.
2. A TIG welding method of carrying out welding by generating an
are between a TIG electrode and an object to be welded,
wherein the method includes a first start period that is a period
during which a current is passed so as to have a preliminarily set
predetermined welding current waveform from a start of welding;
detects contact between the TIG electrode and the object to be
wedded from the start of welding; and
when the contact between the TIG electrode and the object to be
welded is detected during the first start period, the method terminates
the first start period and shifts the period to a first start extension
period during which a current at a time of termination of the first start

period is maintained until the contact between the TIG electrode and
the object to be welded is released.
3. The TIG welding method of any one of claims I and 2,
wherein the method is an AC TIG welding method in which
welding is carried out by alternately repeating a positive polarity
period and a negative polarity period,
the method includes, following the first start period as one
polarity period, a second start period as an other polarity period whose
polarity is different from that of the first start period,
deteets contact between the TIG electrode and the object to be
welded from the start of welding, and
when the period is shifted to the first start extension period, the
method switches from the first start extension period as one polarity
period to the second start period as the other polarity period after the
first start extension period is terminated.
1. The TIG welding method of any one of claims 1 and 2,
wherein the method is an AC TIG welding method in which
welding is carried out by alternately repeating a positive polarity
period and a negative polarity period,
the method includes, following the first start period as one
polarity period, a second start period as an other polarity period whose
polarity is different from that of the first start period,
detects contact between the TIG electrode and the object to be
welded from the start of welding,
when the period is shifted to the first start extension period, the

method shifts the period to a third start period which is a
predetermined period during which a current is passed so as to have a
predetermined welding current waveform and which has a same
polarity as that of the first start extension period after the first start
extension period is terminated, and
switches from the third start period as one polarity period to the
second start period as the other polarity period after the third start
period is terminated.
5. The TIG welding method of claim 4,
wherein, from a time at which the contact between the TIG
electrode and the object to be welded is detected to a time at which a
release of the contact between the TIG electrode and the object to be
welded is detected in the first start period and the first start extension
period, the welding current is controlled to be a current having a
preliminarily set predetermined first short-circuit current waveform,
which is different from the current at a time point at which the contact
between the TIG electrode and the object to be welded is detected.
6. The TIG welding method of any one of claims 1 and 2,
wherein the method is a DC TIG welding method,
the method detects contact between the TIG electrode and the
object to be welded from the start of welding, and
when the period is shifted to the first start extension period, the
method controls the welding current so that the welding current is
changed from the welding current at the time of termination of the
first start extension period to a steady-state welding current that is a

preliminarily sot welding current at the time of steady-state welding
after the first start extension period is terminated.
7. The TJG welding method of any one of claims 1 and 2,
wherein the method is a DC TIG welding method,
the method detects the contact between the TIG electrode and
the object to be welded from the start of welding, and
when the period is shifted to the first start extension period, the
method shifts the period to a fourth start period that is a
predetermined period during which a current is passed so as to have a
preliminarily set. predetermined welding current waveform after the
first start extension period is terminated, and
controls the welding current so that the welding current is
changed from the welding current at the time of termination of the
fourth start extension period to a steady-state welding current that is
a preliminarily set welding current at the time of steady-state welding
after the fourth start extension period is terminated.
8. The TIG welding method of claim 6,
wherein, from a time at which the contact between the TIG
electrode and the object to be welded is detected to a time at which a
release of the contact between the TIG electrode and the object to be
welded is detected in the first start period and the first start extension
period, the welding current is controlled to be a current having a
preliminarily set predetermined second short-circuit current waveform,
which is different from the current at a time point at which the contact
between the TTG electrode and the object to be welded is detected.

ABSTRACT

In a TIG welding method of the present invention, when a short
circuit occurs during a first start period, the first start period is
extended to wait until an arc is regenerated, and an output of a
starting waveform is continued after an arc is regenerated. Thus,
unnecessary consumption or damage of a TIG electrode can be avoided,
and occurrence of a welding defect can be prevented.