DESCRIPTION
ARC WELDING CONTROL METHOD
TECHNICAL FIELD
The present invention relates to a method for controlling pulse
arc welding in which pulse arc welding is performed while feeding a
welding wire as a consumable electrode. The invention relates more
particularly to the control of arc starting.
BACKGROUND ART
In welding industry in recent years, there is an increasing
demand for high-quality welding to improve productivity. It is
particularly demanded to prevent spatters at arc start. It takes time
to form a melt pool on the base material after an arc is started, and
therefore, it takes time to stabilize the arc. For this reason, a lot of
spatters are generated at arc start, and often adhere to the base
material. In some cases, an additional process is required to remove
adhered spatters, thereby decreasing welding productivity. In other
cases, products are sold with spatters adhered to the base material
without performing the additional process. This great1y impairs the
product value.
According to the well-known conventional control of arc starting,
the short-circuit welding control is switched to pulse welding control
when a predetermined time has passed since short-circuit welding
control was started at arc start (see, for example, Patent Literature 1).
Fig. 4 is a schematic configuration view of a conventional arc

welding apparatus including input power supply 101, main
transformer 102, primary rectifier device 103, switching element 104,
reactor 105, and secondary rectifier device 106. Primary rectifier
device 103 receives and rectifies the output of input power supply 101
and outputs the rectified result. Switching element 104 converts the
DC output received from primary rectifier device 103 into an AC
output so as to control a welding output. Main transformer 102
changes the voltage of the AC output received from switching element
104. The output of main transformer 102 is outputted as the welding
output via secondary rectifier device 106 and reactor 105. Secondary
rectifier device 106 rectifies the secondary output of main transformer
102.
The conventional arc welding apparatus further includes
setting unit 135, which sets and outputs various parameters such as
pulse current magnitude or pulse time. Setting unit 135 sets these
parameters based on various setting conditions such as set current, set
voltage, wire feed amount, the type of the shielding gas, the type of
wire, the diameter of the wire, and welding method, which are entered
through unillustrated input means. To set these parameters, setting
unit 135 includes an unillustrated storage unit for storing a table or a
formula to determine the parameters, and an unillustrated calculation
unit.
The conventional arc welding apparatus further includes
welding current detector 108, welding voltage detector 109, drive unit
134, short-circuit welding controller 136, pulse welding controller 137,
and switching unit 138. Welding voltage detector 109 detects a
welding voltage, and welding current detector 108 detects a welding

current. Short-circuit welding controller 136 receives the outputs of
welding current detector 108, welding voltage detector 109, and setting
unit 135, and then outputs a command for performing short-circuit
control.
As will be described later, short-circuit welding controller 136
performs short-circuit welding control in which short-circuiting and
arcing are repeated for a predetermined time after the arc is started.
Pulse welding controller 137 receives the outputs of welding current
detector 108, welding voltage detector 109, and setting unit 135, and
then outputs a command for performing pulse welding control.
Short-circuit welding controller 136 and pulse welding controller 137
compares, for example, the output signals of welding current detector
108 and welding voltage detector 109 with parameter values (command
values) received from setting unit 135. When the values of the output
signals of welding current detector 108 and welding voltage detector
109 do not agree with the parameter values, short-circuit welding
controller 136 and pulse welding controller 137 control the welding
current and the welding voltage so that the values of the output signals
agree with the parameter values.
Switching unit 138 receives the output of setting unit 135, and
notifies drive unit 134 the timing to switch from short-circuit welding
control to pulse welding control. Switching unit 138, which has a
time-counting function, counts the time after the output of setting unit
135 is received and until a predetermined time elapses. Drive unit
134 receives the outputs of short-circuit welding controller 136, pulse
welding controller 137, and switching unit 138. Drive unit 134
provides switching element 104 with either the output of short-circuit

welding controller 136 or the output of pulse welding controller 137
according to the output of switching unit 138.
The following is a description of, with reference to Figs. 4 and 5,
a method for controlling arc starting by using the arc welding
apparatus thus structured.
Fig. 5 shows an example of waveforms of a wire feed speed, a
welding voltage and a welding current with time in consumable
electrode arc welding. Fig. 6 shows the behavior of droplets formed in
arc welding when the base material has a small melt pool. In the
waveforms shown in Fig. 5, at a time t1, the start of welding is
commanded. At a time T2, arc current is supplied and an arc is
created to start short-circuit welding control. At a time T3,
short-circuit welding control is switched to pulse welding control.
At the time t1 when the arc is created, drive unit 134 transmits
the output of short-circuit welding controller 136 to switching element
104 based on the output of switching unit 138. Switching unit 138
counts the time elapsed since the time T2 when the welding current is
detected. At the time T3 when the predetermined time elapses, drive
unit 134 transmits the output of pulse welding controller 137 to
switching element 104 so as to switch short-circuit welding control to
pulse welding control.
From the time T2 when the arc is created until the time T3
when welding control is switched, short-circuit control is performed
based on the output of short-circuit welding controller 136. When the
time T3 is reached after the predetermined time has passed since time
T2, switching unit 138 instructs drive unit 134 to switch welding
control. At this moment, switching element 104 receives the output of

pulse welding controller 137, and switches short-circuit welding
control to pulse welding control. From the time T3 onward, pulse
welding controller 137 performs pulse welding control.
Thus, according to the conventional method for controlling arc
starting by using the arc welding apparatus, short-circuit welding
control is performed after an arc starting current is supplied. This
prevents arc interruption due to unstable arc when pulse welding
control is started immediately after the arc starting current is supplied,
and also prevents the generation and adhesion of spatters.
In the conventional arc welding apparatus, the short-circuit
welding control is switched to pulse welding control when the
predetermined time has passed since short-circuit welding control was
started at arc start. This has reduced the generation of spatters at
arc start.
As shown in Fig. 6, however, the melt pool formed during
short-circuit welding immediately after an arc is started is much
smaller than the melt pool formed during the subsequent pulse
welding. Therefore, droplets formed immediately after pulse welding
is started may spatter and adhere to the base material without being
transferred to the melt pool. Thus, the conventional method can
reduce the generation of spatters immediately after the arc is started,
but cannot reduce the generation of spatters immediately after
short-circuit welding control is switched to pulse welding control. As
a result, large spatters may adhere to the base material.
Citation List
Patent Literature

Pt1 1: Japanese Patent Unexamined Publication No.
H03-297564
SUMMARY OF THE INVENTION
The present invention is directed to provide a method for
controlling arc starting so as to reduce the generation of spatters after
an arc is created and until the arc is stabilized.
To solve the above-described problem, according to the method
of the present invention for controlling arc welding, an arc is created
between a welding wire as a consumable electrode and a base material
as the object to be welded. Short-circuit welding is started either at
the time when the start of welding is commanded or the time when the
start of welding is commanded and the contact between the welding
wire and the base material is detected. The short-circuit welding is
switched to pulse welding when a predetermined time has passed.
The period to perform the pulse welding includes a first pulse-welding
period and a second pulse-welding period following the first
pulse-welding period. At least one of a pulse rising slope and a pulse
falling slope in the first pulse-welding period is controlled to be gent1er
than at least one of a pulse rising slope and a pulse falling slope in the
second pulse-welding period.
With this method, a pulse waveform different from the pulse
waveform for steady-state welding is outputted when a predetermined
time has passed since short-circuit welding control was started at arc
start, and after a sufficient1y large melt pool is formed, the pulse
waveform for the steady-state welding is outputted. In this case,
droplets formed immediately after short-circuit welding is switched to

pulse welding are transferred to the melt pool without spattering.
This reduces the generation of spatters after an arc is created and
until the arc is stabilized.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a schematic configuration view of an arc welding
apparatus according to first and second exemplary embodiments of the
present invention.
Fig. 2 shows waveforms of a welding current, a welding voltage,
and a wire feed speed with time according to the first exemplary
embodiment.
Fig. 3 shows waveforms of a welding current, a welding voltage,
and a wire feed speed with time according to the second exemplary
embodiment.
Fig. 4 is a schematic configuration view of a conventional arc
welding apparatus.
Fig. 5 shows waveforms of a wire feed speed, a welding voltage,
and a welding current with time according to conventional arc welding.
Fig. 6 shows the behavior of droplets when the base material
has a small melt pool.
DESCRIPTION OF EMBODIMENTS
Embodiments of the present invention will be described as
follows with reference to drawings. In these drawings, the same
components are denoted by the same reference numerals, and hence,
the description thereof may be omitted.

FIRST EXEMPLARY EMBODIMENT
Fig. 1 is a schematic configuration view of an arc welding
apparatus according to the present first exemplary embodiment. In
Fig. 1, the arc welding apparatus includes welding power supply 14,
which includes main transformer 2, primary rectifier device 3,
switching element 4, reactor 5 (generally also referred to as DCL),
secondary rectifier device 6, welding current detector 8, welding
voltage detector 9, short-circuit/arc detector 10, output controller 11,
wire feed speed controller 13, and time keeper 20.
The arc welding apparatus further includes input power supply
1. Primary rectifier device 3 receives and rectifies the output of input
power supply 1, and outputs the rectified result. Switching element 4
converts the DC output received from primary rectifier device 3 into an
AC output so as to control a welding output. Main transformer 2
changes the voltage of the AC output received from switching element
4. The output of main transformer 2 is outputted as the welding
output via secondary rectifier device 6 and reactor 5. Secondary
rectifier device 6 rectifies the secondary output of main transformer 2.
Welding voltage detector 9 detects a welding voltage, and welding
current detector 8 detects a welding current.
Short-circuit/arc detector 10 determines whether the wire and
the base material are contacted and short circuited with each other or
the short-circuit is opened and an arc is created, based on a signal from
welding voltage detector 9. Output controller 11 controls switching
element 4 so as to control the welding output. The arc welding
apparatus further includes wire feeder 19 and wire 16. Wire feed
speed controller 13 controls wire feeder 19 so as to control the feed

speed of wire 16. Time keeper 20 counts a predetermined time t1
since an arc is started. The time when the arc is started can be when
an unillustrated welding start command unit starts welding, and wire
16 is fed toward base material 15. Alternatively, the time when the
arc is started can be when a voltage is applied between wire 16 and
base material 15 to contact them and to supply a current between them,
and when the current is detected.
If the arc welding apparatus of the present first exemplary
embodiment includes welding power supply 14, wire feeder 19, and an
unillustrated welding torch, the welding start command unit is a
switch of the welding torch.
If, alternatively, the arc welding apparatus of the present first
exemplary embodiment includes welding power supply 14, wire feeder
19, an unillustrated industrial robot for holding an unillustrated
welding torch, and an unillustrated teaching pendant to control the
robot, the welding start command unit is a switch of the teaching
pendant.
The arc welding apparatus further includes welding condition
setting unit 12, which is communicatively connected either wired or
wirelessly to welding power supply 14. Welding condition setting unit
12, which is used to set a welding current or a welding voltage, can be,
e.g., a remote control. Welding power supply 14 has two output
terminals: one is connected to tip 18 through which electric power is
supplied to wire 16, and the other is connected to base material 15 to
which electric power is supplied. Arc 17 is created between the end of
wire 16 and base material 15.
The following is a description of, with reference to Fig. 2, a wire

feed speed Wf, a welding voltage Vw, and a welding current Aw in the
arc welding apparatus of the present first exemplary embodiment.
Fig. 2 shows waveforms of the wire feed speed Wf, the welding voltage
Vw, and the welding current Aw with time.
As shown in Fig. 2, at the time t1, the arc welding apparatus is
started (the start of welding is commanded). Next, wire feed speed
controller 13 controls wire feeder 19 so that wire 16 is fed at a
predetermined speed as shown by the waveform of the wire feed speed
Wf. The predetermined wire feed speed is determined according to
the welding current set by welding condition setting unit 12. The arc
welding apparatus further includes an unillustrated storage unit,
which stores a table or a formula where an average wire feed speed and
a set welding current are corresponded to each other. The wire feed
speed is determined from the contents in the storage unit and the
welding current set by welding condition setting unit 12.
The time T2 is when an arc is started. When wire 16 and base
material 15 are contacted and a welding current is supplied, welding
current detector 8 detects the current. As a result, the time when an
arc is started can be detected.
Until the predetermined time t1 passes from the time T2, wire
feed speed controller 13 controls wire feeder 19 so that wire 16 is fed at
the predetermined speed. Output controller 11 performs short-circuit
welding control so that a welding output is outputted.
Time keeper 20, which counts the time elapsed since the time
T2, notifies output controller 11 that the predetermined time t1 has
passed since the time T2 and the time T3 has been reached. Upon
receiving the notice, output controller 11 switches the short-circuit

welding control to the pulse welding control. In a first pulse-welding
period, which is the first period during pulse welding, pulse rising
slope is referred to as PR1 and pulse falling slope is referred to as PFl.
In a steady-state welding period, pulse rising slope is referred to as
PR2 and pulse falling slope is referred to as PF2. The pulse welding
control is performed such that at least one of the slopes PRl and PFl is
gent1er than at least one of the slopes PR2 and PF2.
Thus, according to the method of the present invention for
controlling arc welding, an arc is created between a welding wire as a
consumable electrode and a base material as the object to be welded.
In the method for controlling arc welding, short-circuit welding is
started either at the time when the start of welding is commanded or
the time when the start of welding is commanded and the contact
between the welding wire and the base material is detected. The
short-circuit welding is switched to pulse welding when a
predetermined time has passed. In the method for controlling arc
welding, the period to perform the pulse welding includes a first
pulse-welding period and a second pulse-welding period following the
first pulse-welding period. At least one of a pulse rising slope and a
pulse falling slope in the first pulse-welding period is controlled to be
gent1er than at least one of a pulse rising slope and a pulse falling
slope in the second pulse-welding period.
With this method, a pulse waveform different from the pulse
waveform for steady-state welding is outputted when a predetermined
time has passed since short-circuit welding control was started at arc
start, and after a sufficient1y large melt pool is formed, the pulse
waveform for the steady-state welding is outputted. In this case,

droplets formed immediately after short-circuit welding is switched to
pulse welding are transferred to the melt pool without spattering.
This reduces the generation of spatters after an arc is created and
until the arc is stabilized.
The first pulse-welding period may be a period to output a
predetermined number of pulses. With this method, the period after
an arc is created and until the arc is stabilized can be defined by the
number of pulses, thereby reducing the generation of spatters.
The predetermined number of pulses may be in the range of 1 to
8. With this method, the period after an arc is created and until the
arc is stabilized can be defined more clearly by the number of pulses,
thereby reducing the generation of spatters.
As shown in Fig. 2, when the first pulse-welding period ends,
the second pulse-welding period starts immediately. The second
pulse-welding period is the steady-state welding period where
steady-state welding is performed. In the second pulse-welding
period, at least one of the pulse rising slope PR2 and the pulse falling
slope PF2 is outputted as the pulse waveform in the steady-state
welding period.
With this method, the electromagnetic pinch force can be low in
the first pulse-welding period. Because of this low electromagnetic
pinch force, when pulse welding is started, droplets can be transferred
to the small melt pool formed during short-circuit welding. Thus,
pulse welding control in steady-state welding is started after the melt
pool becomes large enough, thereby preventing spattering.
Thus, the method of the present invention for controlling arc
welding, the second pulse-welding period may be a steady-state

welding period, and the pulse waveform in the second pulse-welding
period may be the pulse waveform in the steady-state welding period.
With this method, pulse welding control in steady-state welding
is started after the melt pool becomes large enough, thereby preventing
spattering.
SECOND EXEMPLARY EMBODIMENT
The method for controlling arc welding in a second exemplary
embodiment differs from the method in the first exemplary
embodiment mainly in that the wire is fed in alternating forward and
backward directions at a predetermined frequency and amplitude in
predetermined time t1 during short-circuit welding.
The present second exemplary embodiment will be described
with reference to Fig. 1, which is the schematic configuration view of
the arc welding apparatus, and Fig. 3. Fig. 3 shows waveforms of a
welding current, a welding voltage, and a wire feed speed with time
according to the second exemplary embodiment.
Until the predetermined time t1 has passed since the time T2,
wire feed speed controller 13 controls wire feeder 19 so that wire 16 is
fed at a predetermined frequency and amplitude. Time keeper 20,
which counts the time elapsed since the time T2, notifies wire feed
speed controller 13 that the predetermined time t1 has passed since
the time T2 and the time T3 has been reached. Upon receiving the
notice, wire feed speed controller 13 controls wire feed by switching the
periodical waveform of the wire feed speed to a constant waveform.
More specifically, when the predetermined time t1 has passed, the wire
feed direction is switched from backward to forward. On and after the

time when the wire feed speed reaches the constant speed determined
according to the welding current set by welding condition setting unit
12, wire feed speed controller 13 controls wire 16 to be fed at the
constant speed.
During the predetermined time t1 from the time T2 to the time
T3, wire feed is periodically switched between forward and backward.
More specifically, wire 16 is fed forward to cause a short circuit
between wire 16 and base material 15, and is fed backward to open the
short circuit so as to regenerate the arc.
The following is a description of the switching of welding
output.
When wire feed reaches a time T4 when the wire is started to be
fed forward as shown in Fig. 3, output controller 11 switches
short-circuit welding control to pulse welding control. The pulse
welding control is continued until the welding operation is completed.
In the first pulse-welding period, the pulse welding control is
performed such that at least one of the pulse rising slope PR1 and the
pulse falling slope PF1 is gent1er than at least one of the pulse rising
slope PR2 and the pulse falling slope PF2 in the steady-state welding
period. When the first pulse-welding period ends, the second
pulse-welding period starts immediately. The second pulse-welding
period is a steady-state welding period where pulse welding control is
performed at least one of the pulse rising slope PR2 and the pulse
falling slope PF2 is outputted as the pulse waveform in the
steady-state welding period.
With this method, a short circuit during the short-circuit
welding control can be opened without using the electromagnetic pinch

force of the welding current. This reduces the generation of spatters
and prevents spattering throughout the welding process from
immediately after short-circuit welding control is started at arc start
until pulse welding control is completed in the steady-state welding.
Thus, according to the method of the present invention for
controlling arc welding, in a period to perform the short-circuit
welding either at the time when the start of welding is commanded or
the time when the start of welding is commanded and the contact
between the welding wire and the base material is detected, the
welding wire is fed at a speed in alternating forward and backward
directions at a predetermined frequency and amplitude.
This method reduces the generation of spatters and prevents
spattering throughout the welding process from immediately after
short-circuit welding control is started at arc start until pulse welding
control is completed in the steady-state welding.
The first pulse-welding period may be started while the speed of
feeding the wire is changing as the direction to feed the wire is
changing from backward to forward.
This method reduces the generation of spatters and prevents
spattering throughout the welding process from immediately after
short-circuit welding control is started at arc start until pulse welding
control is completed in the steady-state welding.
The wire may be fed in alternating forward and backward
directions at the predetermined frequency and amplitude in a
predetermined time, and then may be fed at a constant speed. The
first pulse-welding period may be started while the speed of feeding
the wire is changing as the direction to feed the wire is changing from

backward to forward, and is reaching the constant speed.
This method reduces the generation of spatters and prevents
spattering throughout the welding process from immediately after
short-circuit welding control is started at arc start until pulse welding
control is completed in the steady-state welding.
INDUSTRIAL APPLICABILITY
The method of the present invention for controlling arc starting
can prevent the generation and adhesion of spatters at arc start,
thereby increasing the productivity of welding process. This method
is industrially useful as a welding method with a consumable
electrode.
REFERENCE MARKS IN THE DRAWINGS
1 input power supply
2 main transformer
3 primary rectifier device
4 switching element
5 reactor
6 secondary rectifier device

8 welding current detector
9 welding voltage detector

10 short-circuit/arc detector
11 output controller
12 welding condition setting unit
13 wire feed speed controller
14 welding power supply

15 base material
16 wire
17 arc
18 tip
19 wire feeder
20 time keeper

We Claim:
1. A method for controlling arc welding where an arc is created
between a welding wire as a consumable electrode and a base material
as an object to be welded, wherein
short-circuit welding is started either at a time when the start
of welding is commanded or a time when the start of welding is
commanded and a contact between the welding wire and the base
material is detected, and
the short-circuit welding is switched to pulse welding when a
predetermined time has passed, wherein
a period to perform the pulse welding includes a first
pulse-welding period and a second pulse-welding period following the
first pulse-welding period; and
at least one of a pulse rising slope and a pulse falling slope in
the first pulse-welding period is controlled to be gent1er than at least
one of a pulse rising slope and a pulse falling slope in the second
pulse-welding period.
2. The method of claim 1, wherein
the first pulse-welding period is a period to output a
predetermined number of pulses.
3. The method of claim 2, wherein
the predetermined number of pulses is in a range of 1 to 8.
4. The method of any one of claims 1 to 3, wherein

the second pulse-welding period is a steady-state welding period,
and
a pulse waveform in the second pulse-welding period is a pulse
waveform in the steady-state welding period.
5. The method of any one of claims 1 to 4, wherein
in a period to perform the short-circuit welding either at the
time when the start of welding is commanded or the time when the
start of welding is commanded and the contact between the welding
wire and the base material is detected, the welding wire is fed at a
speed in alternating forward and backward directions at a
predetermined frequency and amplitude.
6. The method of claim 5, wherein
the first pulse-welding period is started while the speed of
feeding the wire is changing as a direction to feed the wire is changing
from backward to forward.
7. The method of claim 5, wherein
the wire is fed in alternating forward and backward directions
at the predetermined frequency and amplitude in a predetermined
time, and then is fed at a constant speed; and
the first pulse-welding period is started while the speed of
feeding the wire is changing as a direction to feed the wire is changing
from backward to forward, and is reaching the constant speed.

ABSTRACT
In a method for controlling pulse arc welding where an arc is
created between a wire and a base material, a pulse waveform different
from the pulse waveform for steady-state welding is outputted when a
predetermined time has passed since short-circuit welding control was
started at arc start, and after a sufficiently large melt pool is formed,
the pulse waveform for the steady-state welding is outputted. This
reduces the generation of spatters after an arc is created and until the
arc is stabilized.