DESCRIPTION
ARC WELDING METHOD AND ARC WELDING APPARATUS
Technical Field
The present invention relates to an arc welding control method and
an arc welding apparatus for welding by alternately generating a
short-circuit state and an arc state while repeating a forward feed and
a reverse feed of a welding wire as a consumable electrode.
Background Art
In order to reduce a spatter-removing step, which is a loss step in a
welding process, reducing spatters is intended. A conventionally
known method for this purpose is a consumable electrode type arc
welding method for alternately generating a short-circuit state and an
arc state while repeating a forward feed and a reverse feed at a
welding wire feeding speed.
Fig. 9 is a diagram showing time waveforms of a wire feeding speed
and a welding output with respect to a temporal change in a
conventional arc welding control method.
For example, as an arc welding control method for welding by
alternately generating a short-circuit state and an arc state while
feeding a welding wire as a consumable electrode, the following method
is known. In this method, a feeding speed controller and an output
controller are used. The feeding speed controller controls a wire
feeding motor such that a forward feed and a reverse feed are
periodically repeated at a wire feeding speed. Upon receiving an
increase/decrease signal from the feeding speed controller, the output
controller performs control such that the welding output is low in the
period during which the wire feeding amount is small and the welding
output is high in the period during which the wire feeding amount is
large as shown in Fig. 9. With this operation, in the short-circuit
state, the releasing force resulting from the reduction of the wire
feeding speed can be used to transfer the wire fusion mass. Thus,
even when short-circuit current, which is a primary cause of spatters,
is reduced, a stable short-circuiting transfer welding can be
maintained (see Patent Literature 1, for example).
In a typical arc welding control, the following control is performed.
A wire feeding speed corresponding to a set current is output as a fixed
speed, and the welding current is output based on the welding voltage
in the arc period such that the output voltage is matched with the set
voltage.
According to the technique disclosed in Patent Literature 1, the
welding output is increased or decreased by periodically repeating
forward feed Zl and reverse feed Z2 at a wire feeding speed as shown
in Fig. 9. Thus, in the Control method of setting the welding output
low in the period during which the wire feeding amount is small and
setting the welding output high in the period during which the wire
feeding amount is large, a short-circuit period and an arc period occur
at a fixed ratio in one short circuit cycle. This stabilizes the arc and
thus can reduce spatters. However, it is considered difficult to match
the welding voltage with the set voltage, with the use of a method for
outputting the welding current based on the welding voltage, i.e. a
typical constant voltage control in the arc period. This is because the
arc period is fixed and thus the welding voltage needs to be controlled
within a predetermined time period. Raising a gain in order to
forcedly control the welding voltage causes large variations in the arc
length, which can lead to an unstable arc. For these reasons, the
stable control of welding current and welding voltage is difficult.
[Citation List]
[Patent Document] Japanese Patent Unexamined Publication No.
S62-6775
Summary of Invention
The present invention is directed to address the above problem. The
present invention provides a method for stably controlling a welding
voltage, and an apparatus for implementing the method, in an arc
welding control method for welding by periodically generating a
short-circuit state and an arc state while periodically repeating a
forward feed and a reverse feed at a wire feeding speed.
In an arc welding method for welding using a welding wire as a
consumable electrode by repeating a short-circuit state and an arc
state,
the arc welding method of the present invention includes:
performing control such that the voltage value of an output
voltage is matched with the voltage value of a set voltage by
determining a short-circuit current increasing gradient
corresponding to a set current; and
temporally changing the short-circuit current increasing
gradient corresponding to the set current, based on the difference
between the set voltage and the output voltage.
This method allows the output voltage to be matched with the set
voltage, thereby controlling the welding voltage stably.
In an arc welding apparatus for welding by repeating an arc state and
a short-circuit state between a welding wire as a consumable electrode
and an object to be welded,
the arc welding apparatus of the present invention includes the
following elements:
a switching element for controlling an welding output;
a welding voltage detector for detecting a welding voltage;
a status detector for detecting a short-circuit state or an arc
state, based on the output from the welding voltage detector;
a short-circuit controller for controlling a short-circuit current
in a short-circuit period, upon receiving a short-circuit signal from the
status detector;
an arc controller for controlling an arc voltage in an arc period,
upon receiving an arc signal from the status detector;
a set current setting section for setting a set current; and
a set voltage setting section for setting a set voltage.
The short-circuit controller includes the following elements:
an increasing gradient base setting section for determining a
short-circuit current increasing gradient, based on a set current set by
an operator; and
an increasing gradient controller for changing the short-circuit
current increasing gradient determined in the increasing gradient base
setting section, based on the difference between the voltage set by the
set voltage setting section and the voltage detected in the welding
voltage detector. The short-circuit controller changes the
short-circuit current increasing gradient, based on the difference
between the set voltage set in the set voltage setting section and the
voltage detected in the welding voltage detector.
This structure allows the output voltage to be matched with the set
voltage, thereby controlling the welding voltage stably.
In an arc welding apparatus for welding by repeating an arc state and
a short-circuit state between a welding wire as a consumable electrode
and an object to be welded,
the arc welding apparatus of the present invention includes:
a switching element for controlling an welding output;
a welding voltage detector for detecting a welding voltage;
a status detector for detecting a short-circuit state or an arc
state, based on the output from the welding voltage detector;
a short-circuit controller for controlling a short-circuit current
in a short-circuit period, upon receiving a short-circuit signal from the
status detector;
an arc controller for controlling an arc voltage in an arc period,
upon receiving an arc signal from the status detector;
a set current setting section1 for setting a set current; and
a set voltage setting section for setting a set voltage.
The short-circuit controller includes the following elements:
an increasing gradient base setting section for determining a
short-circuit current increasing gradient in a first step and a
short-circuit current increasing gradient in a second step, based on a
set current set by an operator;
an inflection point base setting section for determining an
inflection point at which the short-circuit current increasing gradient
changes from the short-circuit current increasing gradient in the first
step to the short-circuit current increasing gradient in the second step,
based on the set current set by the operator;
an increasing gradient controller for changing the short-circuit
current increasing gradient in the first step and the short-circuit
current increasing gradient in the second step determined in the
increasing gradient base setting section, based on the difference
between the voltage set in the set voltage setting section and the
voltage detected in the welding voltage detector; and
an inflection point controller for changing the inflection point of
the short-circuit current increasing gradient determined in the
inflection point base setting section, based on the difference between
the voltage set in the set voltage setting section and the voltage
detected in the welding voltage detector. Based on the difference
between the set voltage set in the set voltage setting section and the
voltage detected in the welding voltage detector, the short-circuit
controller changes at least one of the short-circuit current increasing
gradient in the first step, the short-circuit current increasing gradient
in the second step, and the current value at the inflection point.
This structure allows the output voltage to be precisely matched with
the set voltage, thereby controlling the welding voltage more stably.
As described above, in accordance with the present invention, in a
control method for welding by generating a short-circuit state and an
arc state, the short-circuit current increasing gradient, the inflection
point at which the short-circuit current increasing gradient changes,
the current values in the peak period and in the base period, and the
time of the peak period are controlled. This can temporally change
the ratio between the short-circuit period and the arc period, thereby
allowing the output voltage to be matched with the set voltage.
Therefore, the welding voltage can be controlled stably.
This method is a control method for welding by generating a
short-circuit state and an arc state by periodically repeating a forward
feed and a reverse feed at a wire feeding speed. The forward feed and
the reverse feed at the wire feeding speed are based on a sine waveform
or a trapezoidal waveform. Thus, the load on the peripheral
components around the motor, such as a feeding motor and gears, can
be reduced.
Brief Description of The Drawings
Fig. 1 is a diagram showing time waveforms of a wire feeding speed, a
welding voltage, and a welding current in accordance with a first
exemplary embodiment of the present invention.
Fig. 2 is a diagram showing time waveforms of a wire feeding speed, a
welding, voltage, and a welding current in accordance with the first
exemplary embodiment of the present invention.
Fig. 3 is a graph showing an example of the relation of a short-circuit
current increasing gradient with respect to an output voltage in
accordance with the first exemplary embodiment of the present
invention.
Fig. 4 is a graph showing an example of the relation of a short-circuit
current inflection point with respect to the output voltage in
accordance with the first exemplary embodiment of the present
invention.
Fig. 5 is a graph showing an example of the relation of a peak current
value with respect to the output voltage in accordance with the first
exemplary embodiment of the present invention.
Fig. 6 is a graph showing an example of the relation of a peak current
time with respect to the output voltage in accordance with the first
exemplary embodiment of the present invention.
Fig. 7 is a configuration diagram showing a schematic configuration of
an arc welding apparatus in accordance with the first exemplary
embodiment of the present invention.
Fig. 8 is a diagram showing time waveforms of a wire feeding speed, a
welding voltage, and a welding current in accordance with a second
exemplary embodiment of the present invention.
Fig. 9 is a diagram showing time waveforms of a wire feeding speed
and a welding output of a conventional example.
Detailed Description of The Preferred Embodiment
Hereinafter, a description is provided for the exemplary embodiments
of the present invention with reference to the accompanying drawings.
In the following drawings, the same elements are denoted with the
same reference marks, and the description of these elements is omitted
in some cases. The present invention is not limited by these
exemplary embodiments.
(First Exemplary Embodiment)
In this embodiment, a welding control method is described first, and a
welding apparatus is described thereafter.
Fig. 1 and Fig. 2 each shows time waveforms of a wire feeding speed, a
welding voltage, and a welding current in a consumable electrode type
arc welding for alternately repeating a short-circuit state and an arc
state.
In each of Fig. 1 and Fig. 2, P1 shows a time point at which a short
circuit starts, and is also a time point at which a short-circuit initial
time starts. P2 shows a time point at which the short-circuit initial
time ends. P2 is also a time point at which the output with a
short-circuit current increasing gradient (di/dt), i.e. the amount of
increase in the short-circuit current per unit time, starts. P3 is a time
point of the inflection point of a short-circuit current increasing
gradient (di1/dt) in a first step and a short-circuit current increasing
gradient (di2/dt) in a second step. P4 shows a time point at which the
output with the short-circuit current increasing gradient (di2/dt) in the
second step ends. P4 is also a time point at which the constriction of a
droplet formed between a molten pool and the top end of a welding wire
is detected and the current instantaneously drops. P5 is a time point
at which the constriction of the droplet is released, the short-circuit
state ends, and an arc occurs. P5 is also a time point at which the
output of the welding current at the peak current starts immediately
after the occurrence of the arc. P6 is a time point at which the
transition from the peak current to a base current is started. In the
period from P6 to P7, either a current control or a voltage control may
be used. From time point P7, the base current is output. P8 shows a
time point at which a next short circuit occurs.
The wire feeding control shown in Fig. 1 and Fig. 2 is a wire feeding
control of periodically repeating a forward feed and a reverse feed in a
sine waveform as a basic waveform at a predetermined frequency with
a predetermined amplitude. Therefore, a short circuit occurs in the
vicinity of PI at the peak on the forward feed side, while an arc occurs
in the vicinity of P5 at the peak on the reverse feed side. In this
manner, the occurrence of the short-circuit state or the arc state
basically depends on the wire feeding control of periodically repeating
the forward feed and the reverse feed at a wire feeding speed.
Fig. 1 shows a case where control of immediately reducing the output
voltage is desired when the output voltage is larger than a set voltage.
That is, this case shows an example of control in one cycle of a short
circuit in the following manner. The short-circuit current gradient
(di1/dt) in the first step (hereinafter, referred to as "IS1" shown in Fig.
1), the short-circuit current increasing gradient (di2/dt) in the second
step (hereinafter, "IS2" shown in Fig. 1), the current value ("ISC"
shown in Fig. 1) at the inflection point at which short-circuit current
gradient IS1 in the first step changes to short-circuit current
increasing gradient IS2 in the second step, the peak current, the peak
time, and the base current are made larger than the respective
reference values corresponding to the set current.
The output voltage can be obtained by calculating an average value of
those in a plurality of cycles, or by averaging a plurality of average
values of the voltages in predetermined periods.
Fig. 2 shows a case where control of immediately raising the output
voltage is desired when the output voltage is smaller than the set
voltage. That is, this case shows an example of control in one cycle of
a short circuit in the following manner. Short-circuit current gradient
IS1 in the first step, short-circuit current increasing gradient IS2 in
the second step, the current value (ISC) at the inflection point at which
short-circuit current gradient IS1 in the first step changes to
short-circuit current increasing gradient IS2 in the second step, the
peak current, the peak time, and the base current are made larger than
the respective reference values corresponding to the set current.
In Fig. 1 and Fig. 2, the current waveform and the voltage waveform
when the output voltage is matched with the set voltage are shown by
broken lines as basic waveforms. An example of control by constant
voltage control of matching the output voltage with the set voltage is
shown by solid lines.
First, hereinafter, a description is provided for basic control in one
cycle of a short circuit, i.e. a period from P1 to P8 shown by the broken
lines in Fig. 1 and Fig. 2.
At a time point in the vicinity of P1, at the peak of a forward feed in
wire feeding control in a sine waveform, a welding wire makes contact
with an object to be welded and a short circuit occurs. In the
short-circuit initial time from P1 to P2, a short-circuit initial current is
output. The short-circuit initial current is lower than the current at
the time immediately before P1 at which the short circuit occurs.
Here, a description is provided for the purpose of setting the current
16w in the short-circuit initial time from P1 to P2. When the
short-circuit current is increased toward a high current immediately
after the occurrence of a short circuit, the short circuit is immediately
opened, and immediately thereafter, a short circuit can occur again.
Such a phenomenon breaks the periodicity of short circuits. Then, a
period where a low current is output is set immediately after the
occurrence of the short circuit so as to ensure a short-circuit state.
After such a short-circuit state is ensured, control of increasing the
short-circuit current toward a high current can be performed.
The short-circuit initial time and the short-circuit initial current
value are derived from experimental verifications, for example, and
used. As the base set values of these short-circuit initial time and the
short-circuit initial current, proper values derived from experimental
verifications are used such that stable welding is possible at a welding
speed (1 m/min in this embodiment), when the ratio between the
short-circuit period and the arc period is 50%. The short-circuit
initial time and the short-circuit initial current value are stored in a
storage, which is not shown, as a table, for example, such that these
values correspond to a set current.
Next, at time point P2, short-circuit current increasing gradient IS1
in the first step is determined based on the set current, in a state
where the short circuit between the welding wire and an object to be
welded is ensured. Along short-circuit current increasing gradient
ISl in the first step, the actual short-circuit current rises and reaches
current value ISC at a short-circuit current inflection point at time
point P3. Then, the actual short-circuit current increases along
short-circuit current increasing gradient IS2 in the second step that is
determined based on the set current. As the base set values of
short-circuit current increasing gradient ISl in the first step,
short-circuit current increasing gradient IS2 in the second step, and
current Value ISC at the short-circuit current inflection point, proper
values derived from experimental verifications are used such that
stable welding is possible at a welding speed (1 m/min in this
embodiment), when the ratio between short-circuit period Ts and arc
period Ta is 50%. These short-circuit current increasing gradient
(di/dt) and the inflection point are stored in a storage, which is not
shown, as a table or a formula, for example, such that these values
correspond to the set current. Frequency F for wire feeding is
expressed by the inverse number of the sum (period T) of short-circuit
period Ts and arc period Ta. The sum of the forward feed and the
reverse feed is expressed by amplitude velocity AV.
Next, from P4 to P5, as conventionally known, control of detecting the
constriction of the molten welding wire and sharply reducing the
short-circuit current is performed.
Next, in the vicinity of P5, at the peak of the reverse feed in the wire
feeding control in the sine waveform, the welding wire is released from
the object to be welded and the short circuit is opened. In the arc
period from P5 to P6, by current control, the current is increased with
a predetermined gradient to peak current IP from P5, i.e. the initial
time point of the occurrence of an arc. When the output of peak
current IP needs to be kept, the peak current can be kept for the
required time period.
Next, from P6 to P7, a welding current corresponding to the welding
voltage may be output by voltage control, or a predetermined current
may be output by current control. In either control, it is necessary to
grow the droplet and stably keep a proper arc length.
Next, from P7 to P8, the state of base current IB is kept by current
control and the occurrence of a next short circuit at P8 is waited for.
In the vicinity of P8, at the peak of the forward feed by the wire feeding
control in the sine waveform, the welding wire makes contact with the
object to be welded and thereby a short circuit occurs. Keeping the
state of base current IB advantageously ensures a state where a short
circuit is likely to occur, and prevents generation of large spatters even
when a small short circuit occurs because the welding current is low.
Peak current IP and peak current time PW from P5 to P6, and base
current IB from P7 to P8 are derived from experimental verifications,
for example, and used. Further, as the base set values of these peak
current IP, peak current time PW, and base current IB, proper values
derived from experimental verifications are used such that stable
welding is possible at a welding speed (1 m/min in this embodiment),
when the ratio between short-circuit period Ts and arc period Ta is 50%.
Peak current IP, peak current time PW, and base current IB are stored
in a storage, which is not shown, as a table, for example, such that
these values correspond to the set current.
As described above, the control from P1 to P8 is set as one cycle, and
these cycles are repeated for welding.
Hereinafter, a description is provided for control of temporally
making automatic adjustment such that an output voltage is matched
with a set voltage as shown in Fig. 1 and Fig. 2.
In the wire feeding control, a wire is fed while a forward feed and a
reverse feed are periodically repeated at a predetermined frequency
with a predetermined amplitude in a sine waveform. The waveform
in this state is a basic waveform.
Since the wire is periodically fed, the output voltage can be controlled
by the control of the ratio between a short-circuit period and an arc
period in one cycle of the short circuit.
For example, in mild steel MAG welding, the set current is 120A, the
short-circuit period is 50%, the arc period is 50%, and the voltage is
15V. In this case, adjusting the short-circuit period to 40% and the
arc period to 60% can change the voltage to 17 V. In contrast,
adjusting the short-circuit period to 60% and the arc period to 40% can
change the voltage to 13 V. Thus, the voltage can be largely controlled
based on the ratio between the short-circuit period and the arc period.
The output voltage can be matched with the set voltage by temporally
controlling the ratio between the short-circuit period and the arc
period every several microseconds or several tens of microseconds.
When the short-circuit period is lengthened so as to lower the voltage
as shown in Fig. 1, short-circuit current increasing gradients IS1 and
IS2 in the first step and in the second step, respectively, and ISC at the
inflection point of the short-circuit current increasing gradients are
reduced. This opens the short circuit later and lengthens the
short-circuit period.
Reducing peak current IP and base current IB in arc period Ta can
shorten the arc length, thus shortening arc period Ta.
As described above, when the output current is larger than the set
current in the welding period, the following control is performed.
That is, short-circuit current gradient IS1 in the first step,
short-circuit current increasing gradient IS2 in the second step,
current value ISC at the inflection point at which the short-circuit
current gradient in the first step changes to the short-circuit current
increasing gradient in the second step, and peak current IP and base
current IB in arc period Ta are reduced. This can lengthen
short-circuit period Ts and shorten arc period Ta, thereby temporally
making automatic adjustment such that the output voltage is lowered.
In contrast, when short-circuit period Ts is shortened so as to raise
the voltage, as shown in Fig. 2, the following control is performed.
That is, short-circuit current increasing gradients IS1 and IS2 in the
first step and in the second step, respectively, and ISC at the inflection
point of the short-circuit current increasing gradients are set larger
than those corresponding to the set current. This can open the short
circuit earlier and shorten short-circuit period Ts.
Peak current IP and base current IB in arc period Ta set larger than
those corresponding to the set current can increase the arc length, thus
lengthening arc period Ta.
As described above, when the output voltage is smaller than the set
voltage in the welding period, the following control is performed.
That is, short-circuit current gradient IS1 in the first step,
short-circuit current increasing gradient IS2 in the second step,
current value ISC at the inflection point at which the short-circuit
current gradient in the first step changes to the short-circuit current
increasing gradient in the second step, and peak current IP and base
current IB in arc period Ta are increased. This can shorten
short-circuit period Ts and lengthen arc period Ta, thereby temporally
making automatic adjustment such that the output voltage is raised.
Examples of the automatic adjustment include the following methods.
The voltage difference value is correlated with short-circuit current
gradient IS1 in the first step, short-circuit current increasing gradient
IS2 in the second step, and current value ISC at the inflection point,
and these values are stored in a storage, which is not shown. Further,
in accordance with the voltage difference value, short-circuit current
gradient IS1 in the first step, short-circuit current increasing gradient
IS2 in the second step, and current value ISC at the inflection point
are determined. Alternatively, formulas for correlating the voltage
difference value with short-circuit current gradient IS1 in the first
step, short-circuit current increasing gradient IS2 in the second step,
and current value ISC at the inflection point are stored in a storage,
which is not shown. Further, in accordance with the voltage
difference value, the short-circuit current increasing gradient (di/dt)
and current value ISC at the inflection point are determined.
Peak current IP, peak current time PW, and base current IB may be
stored in the storage and determined in a manner similar to the above
short-circuit current gradient IS1 in the first step, short-circuit
current increasing gradient IS2 in the second step, and current value
ISC at the inflection point.
That is, the arc welding method of the present invention is an arc
welding method for welding using a welding wire as a consumable
electrode by repeating a short-circuit state and an arc state. The arc
welding method includes performing control such that the voltage
value of an output voltage is matched with the voltage value of a set
voltage by
determining a short-circuit current increasing gradient
corresponding to a set current; and
temporally changing the short-circuit current increasing
gradient (di/dt) corresponding to the set current, based on the
difference between the set voltage and the output voltage.
This method allows the output voltage to be matched with the set
voltage, thereby controlling the welding voltage stably.
Alternatively, the following method can be used. When the output
voltage is smaller than the set voltage, the short-circuit current
increasing gradient (di/dt) is changed so as to be steeper than the
short-circuit current increasing gradient (di/dt) corresponding to the
set current. Further, when the output voltage is larger than the set
voltage, the short-circuit current increasing gradient (di/dt) is changed
so as to be gentler than the short-circuit current increasing gradient
(di/dt) corresponding to the set current.
This method can stably control the welding voltage more precisely.
Alternatively, the following method can be used. The short-circuit
current increasing gradient (di/dt) is changed in proportion to an
absolute value corresponding to the value of the difference between the
set voltage and the output voltage, or changed to a value that is based
on the rate of change corresponding to the value of the difference
between the set voltage and the output voltage.
This method can stably control the welding voltage much more
precisely.
Next, hereinafter, a description is provided for an example of the
control of the short-circuit current increasing gradient (di/dt) with
reference to Fig. 3. Fig. 3 is a graph showing an example of the
relation of a short-circuit current increasing gradient (di/dt) with
respect to an output voltage in accordance with the first exemplary
embodiment of the present invention. As an example of the
short-circuit current increasing gradient (di/dt), increasing gradient IS1 in the first step is shown.
When the set voltage is equal to the output voltage, for example,
short-circuit current increasing gradient IS1 in the first step is 150
A/ms, i.e. a single value, as shown in Fig. 3. The single value means
an initial value of the output voltage, and the initial value of the
output voltage is the set voltage herein. However, a case where the
output voltage is equal to the set voltage minus a (a=2 V herein) is
considered. That is, in the case of output where the output voltage is
2 V smaller than the set voltage, in order to raise the output voltage, as
shown in the graph of Fig. 3, short-circuit current increasing gradient
IS1 in the first step is 40 A/ms increased from a single value of 150
A/ms to 190 A/ms. Thus, control is performed so as to shorten
short-circuit period Ts.
The amount of adjustment can be increased or decreased by
multiplying the characteristics shown in Fig. 3 by a coefficient, or
other methods.
When short-circuit current gradient IS1 in the first step and
short-circuit current increasing gradient IS2 in the second step are
changed, the same value may be used for the first step and the second
step for the increase or decrease, or the above increasing gradients
may be changed separately. For example, only the increasing
gradient in the first step is increased or decreased, and that in the
second step is unchanged.
Fig. 3 shows an example in the form of absolute values where the
short-circuit current increasing gradient is ±20 A/ms per ±1 V of the
difference between the output voltage and the set voltage. However,
the form of rates of change where the increasing gradient is ±20%/ms
per +1 V may be used.
Fig. 3 shows an example where the relation between the output
voltage and the short-circuit current increasing gradient (di/dt) is
expressed by a linear function. However, the present invention is not
limited to this example. The relation may be expressed by a function
other than a linear function, such as a quadratic curve, as long as the
increasing gradient has the same sign.
Next, a description is provided for the change of ISC at the inflection
point of short-circuit current increasing gradient IS1 in the first step
and short-circuit current increasing gradient IS2 in the second step
with reference to Fig. 4. Fig. 4 is a graph showing an example of the
relation of current value ISC at a short-circuit current inflection point
with respect to the output voltage in accordance with the first
exemplary embodiment of the present invention.
When the set voltage is equal to the output voltage, for example, the
current value at the short-circuit current inflection point is 200 A, i.e.
a single value, as shown in Fig. 4. However, a case where the output
voltage is equal to the set voltage minus a (a=2 V herein) is considered.
That is, in the case of output where the output voltage is 2 V smaller
than the set voltage, in order to raise the output voltage, current value
ISC at the short-circuit current inflection point is 40 A increased from
a single value of 200 A to 240A. Thus, control is performed so as to
shorten short-circuit period Ts.
The amount of adjustment can be increased or decreased by
multiplying the characteristics shown in Fig. 4 by a coefficient, or
other methods.
Fig. 4 shows an example in the form of absolute values where the
current value is ±20 A per ±1 V. However, the form of rates of change
where the current value is ±20% per ±1 V may be used.
In Fig. 4, the relation between the output voltage and current value
ISC at the inflection point is expressed by a linear function. However,
the relation may be expressed by a function other than a linear
function, such as a quadratic curve, as long as the increasing gradient
has the same sign.
When the output voltage is output as a value large or small with
respect to the set voltage as shown in Fig. 3 and Fig. 4, short-circuit
current increasing gradient IS1 in the first step from P2 to P3,
short-circuit current increasing gradient IS2 in the second step from
P3 to P4, and current value ISC at the short-circuit current inflection
point at time point P3, are changed in accordance with this output.
As shown in Fig. 3 and Fig. 4, an upper limit and a lower limit may be
set for short-circuit current increasing gradient IS1 in the first step,
short-circuit current increasing gradient IS2 in the second step, and
current value ISC at the inflection point. This can prevent excessive
adjustment. If no upper limit or lower limit is set, short-circuit
current increasing gradient (di/dt) or ISC at the short-circuit current
inflection point fluctuate toward a larger value, which considerably
increases spatters and destabilizes the arc.
Short-circuit current increasing gradient IS1 in the first step from P2
to P3, short-circuit current increasing gradient IS2 in the second step
from P3 to P4, and current value ISC at the short-circuit current
inflection point at P3 are set based on at least one of the following
values: the value of the difference between the output voltage and the
set voltage, the diameter of a consumable electrode wire to be fed, the
type of the wire, the extension length of the wire, the shielding gas to
be supplied, and the set current value of the welding current.
Alternatively, the arc welding method of the present invention may be
the following controlling method. As the short-circuit current
increasing gradient (di/dt) corresponding to the set current,
short-circuit current increasing gradient IS1 in the first step, and
short-circuit current increasing gradient IS2 in the second step
following short-circuit current increasing gradient IS1 in the first step
that correspond to the set current are determined. Next, based on the
difference between the set voltage and the output voltage, short-circuit
current increasing gradient IS1 in the first step and short-circuit
current increasing gradient IS2 in the second step are temporally
changed such that the voltage value of the output voltage is matched
with the voltage value of the set voltage.
This method allows the output voltage to be matched with the set
voltage more precisely, thereby controlling the welding voltage more
stably.
Alternatively, short-circuit current increasing gradient IS1 in the
first step may be different from short-circuit current increasing
gradient IS2 in the second step.
With this method, short-circuit period Ts can be set to a desired time.
Alternatively, short-circuit current increasing gradient IS1 in the
first step may be larger than short-circuit current increasing gradient
IS2 in the second step.
With this method, short-circuit period Ts can be set to a desired time.
Alternatively, current value ISC at the inflection point at which
short-circuit current increasing gradient IS1 in the first step changes
to short-circuit current increasing gradient IS2 in the second step may
be determined so as to correspond to the set current, and current value
ISC at the inflection point may be temporally changed in accordance
with the value of the difference between the output voltage and the set
voltage.
This method can prevent a large increase in spatters and an unstable
arc. Thereby, a stable arc welding method can be implemented.
Alternatively, the following method can be used. When the output
voltage is smaller than the set voltage, current value ISC at the
inflection point is changed so as to be larger than current value ISC at
the inflection point corresponding to the set current. Further, when
the output voltage is larger than the set voltage, current value ISC at
the inflection point is changed so as to be smaller than current value
ISC at the inflection point corresponding to the set current.
This method can prevent a large increase in spatters and an unstable
arc. Thereby, a stable arc welding method can be implemented.
Alternatively, the following method can be used. Current value ISC
at the inflection point is changed in proportion to an absolute value
corresponding to the value of the difference between the set voltage
and the output voltage, or changed to a value that is based on the rate
of change corresponding to the value of the difference between the set
voltage and the output voltage.
This method can prevent a large increase in spatters and an unstable
arc. Thereby, a stable arc welding method can be implemented.
Next, a description is provided for the change of peak current IP in
arc period Ta with reference to Fig. 5. Fig. 5 is a graph showing an
example of the relation of a current value of peak current IP with
respect to the output voltage in accordance with the first exemplary
embodiment of the present invention.
When the set voltage is equal to the output voltage, for example, the
current value of peak current IP is 300 A, i.e. a single value, as shown
in Fig. 5. However, a case where the output voltage is equal to the set
voltage plus a (a=2 V herein) is considered. That is, in the case of
output where the output voltage is 2 V larger than the set voltage, in
order to raise the output voltage, the current value of the peak current
is 30 A increased from a single value of 300 A to 330A. Thus, control
is performed so as to lengthen arc period Ta.
The amount of adjustment can be increased or decreased by
multiplying the characteristics shown in Fig. 5 by a coefficient, or
other methods.
Fig. 5 shows an example in the form of absolute values where the
current value is ±15 A per ±1 V. However, the form of rates of change
where the current value is ±10% per ±1 V may be used.
In Fig. 5, the relation between the output voltage and peak current IP
is expressed by a linear function. However, the relation may be
expressed by a function other than a linear function, such as a
quadratic curve, as long as the increasing gradient has the same sign.
Next, a description is provided for the change of peak current time
PW in arc period Ta with reference to Fig. 6. Fig. 6 is a graph showing
an example of the relation of peak current time PW with respect to the
output voltage in accordance with the first exemplary embodiment of
the present invention.
When the set voltage is equal to the output voltage, for example, the
time value of the peak current time is 1000 µs, i.e. a single value, as
shown in Fig. 6. However, a case where the output voltage is equal to
the set voltage plus a (a=2 V herein) is considered. That is, in the
case of output where the output voltage is 2 V larger than the set
voltage, in order to raise the output voltage, the time value of the peak
current time is 400 µs increased from a single value of 1000 µs to 1400
µs. Thus, control is performed so as to lengthen arc period Ta.
The amount of adjustment can be increased or decreased by
multiplying the characteristics shown in Fig. 6 by a coefficient, or
other methods.
Fig. 6 shows an example in the form of absolute values where the time
value is ±200 µs per ±1 V. However, the form of rates of change where
the time value is ±20% per ±1 V may be used.
In Fig. 6, the relation between the output voltage and peak current
time PW is expressed by a linear function. However, the relation may
be expressed by a function other than a linear function, such as a
quadratic curve, as long as the increasing gradient has the same sign.
When the output voltage is output as a value large or small with
respect to the set voltage as shown in Fig. 5 and Fig. 6, peak current IP
and peak current time PW from P5 to P6 are changed in accordance
with the output voltage.
As shown in Fig. 5 and Fig. 6, an upper limit and a lower limit may be
set for each of the values of peak current IP and peak current time PW.
This can prevent excessive adjustment. If no upper limit or lower
limit is set, peak current IP and peak current time PW excessively
fluctuate such that peak current IP and peak current time PW increase.
This can considerably increase spatters or destabilize the arc.
Peak current IP and peak current time PW from P5 to P6, and the
values of peak current IP and peak current time PW from P5 to P6 are
set based on at least one of the following values: the value of the
difference between the output voltage and the set voltage, the diameter
of a consumable electrode wire to be fed, the type of the wire, the
extension length of the wire, the shielding gas to be supplied, and the
set current value of the welding current.
As described above, the automatic adjustment shown in this
embodiment is made so as to control short-circuit current gradient IS1
in the first step, short-circuit current increasing gradient IS2 in the
second step, current value ISC at the inflection point, peak current IP
and base current IB in arc period Ta, and peak current time PW. This
can control the ratio between short-circuit period Ts and arc period Ta,
and allows the output voltage to be matched with the set voltage easily.
All parameters are not necessarily used for the constant voltage
control, and only necessary parameters can be used for the control.
That is, the arc welding method of the present invention may be a
method for determining the current value in the peak period in arc
period Ta and the current value in the base period in arc period Ta
corresponding to the set current, and temporally changing the current
value in the peak period and the current value in the base period in
accordance with the value of the difference between the set voltage and
the output voltage.
This method can control the welding voltage stably.
Alternatively, the following method can be used. When the output
voltage is smaller than the set voltage, the current value in the peak
period arid the current value in the base period are changed so as to be
larger than the current value in the peak period and the current value
in the base period corresponding to the set current. Further, when
the output voltage is larger than the set voltage, the current value in
the peak period and the current value in the base period are changed
so as to be smaller than the current value in the peak period and the
current value in the base period corresponding to the set current.
This method can control the welding voltage more stably.
Alternatively, the arc welding method may be a method for changing
the current value in the peak period and the current value in the base
period to absolute values corresponding to the value of the difference
between the set voltage and the output voltage, or changing to values
that are based on the rate of change corresponding to the value of the
difference between the set voltage and the output voltage.
This method can control the welding voltage more stably.
Alternatively, the arc welding method may be a method for
determining the time of the peak period in the arc period
corresponding to the set current, and changing the time of the peak
period in accordance with the value of the difference between the set
voltage and the output voltage.
This method can control the welding voltage more stably. This
method can also prevent a large increase in spatters and an unstable
arc. Thereby, a stable arc welding method can be implemented.
Alternatively, the following method can be used. When the output
voltage is smaller than the set voltage, the time of the peak period in
arc period Ta is changed so as to be longer than the time of the peak
period in arc period Ta corresponding to the set current. When the
output voltage is larger than the set voltage, the time of the peak
period in arc period Ta is changed so as to be shorter than the time of
the peak period in arc period Ta corresponding to the set current.
This method can control the welding voltage more stably. This
method can also prevent a large increase in spatters and an unstable
arc. Thereby, a stable arc welding method can be implemented.
Alternatively, the arc welding method may be a method for changing
the time of the peak period in arc period Ta to an absolute value
corresponding to the value of the difference between the set voltage
and the output voltage, or changing to a value that is based on the rate
of change corresponding to the value of the difference between the set
voltage and the output voltage.
This method can prevent a large increase in spatters and an unstable
arc. Thereby, a stable arc welding method can be implemented.
Alternatively, the arc welding method may be a method for welding
by:
setting a welding wire feeding speed corresponding to the set
current as an average feeding speed; and
periodically generating a short-circuit state and an arc state by
periodically repeating wire feeding in a forward direction and in a
reverse direction at a predetermined frequency with a predetermined
amplitude.
This method allows the output voltage to be matched with the set
voltage more precisely, thereby controlling the welding voltage more
stably.
Next, a description is provided for an arc welding apparatus for
performing control by the above method of the first exemplary
embodiment.
Fig. 7 is a configuration diagram showing a schematic configuration of
an arc welding apparatus in accordance with the first exemplary
embodiment of the present invention. As shown in Fig. 7, the arc
welding apparatus of the first exemplary embodiment is an apparatus
for welding by repeating an arc state and a short-circuit state between
welding wire 27 as a consumable electrode and object to be welded 30.
Feeding of welding wire 27 is periodically repeated in a forward
direction and in a reverse direction by wire feeding motor 26. Welding
wire 27 penetrates through tip 28 and discharges welding arc 29 from
the top end thereof to object to be welded 30.
This arc welding apparatus has switching element 3, welding voltage
detector 8, status detector 10, short-circuit controller 11, arc controller
16, set current setting section 23, and set voltage setting section 24.
Switching element 3 controls a welding output. Welding voltage
detector 8 detects a welding voltage. Status detector 10 detects a
short-circuit state or an arc state, based on the output from welding
voltage detector 8. Upon receiving a short-circuit signal from status
detector 10, short-circuit controller 11 controls a short-circuit current
in short-circuit period Ts. Upon receiving an arc signal from status
detector 10, arc controller 16 controls an arc voltage in arc period Ta.
Set current setting section 23 sets a set current. Set voltage setting
section 24 sets a set voltage. Short-circuit controller 11 has
increasing gradient base setting section 12 and increasing gradient
controller 13. Short-circuit controller 11 changes a short-circuit
current increasing gradient (di/dt), based on the difference between the
set voltage set in set voltage setting section 24 and the voltage
detected in welding voltage detector 8.
This configuration allows the output voltage to be matched with the
set voltage, thereby controlling the welding voltage stably.
The arc welding apparatus of the first exemplary embodiment has the
following structure, for example. As shown in Fig. 7, in the arc
welding apparatus, electric power from input power supply 1 is
rectified in primary rectifier 2, and converted to alternating voltage by
switching element 3. The alternating voltage is lowered by
transformer 4, rectified by secondary rectifier 5 and DCL 6, i.e. an
inductor, and applied between welding wire 27 and object to be welded
30. The arc welding apparatus also has driver 7 for controlling
switching element 3, welding voltage detector 8 connected between
welding power supply output terminals, and welding current detector 9
for detecting a welding output current. The arc welding apparatus
also has status detector 10, short-circuit controller 11, and arc
controller 16. The status detector determines whether a short circuit
or an arc occurs, based on a signal from welding voltage detector 8.
The short-circuit controller controls the short-circuit current in
short-circuit period Ts, upon receiving a short-circuit signal from
status detector 10. Arc controller 16 controls the arc voltage in arc
period Ta, upon receiving an arc signal from status detector 10. The
arc welding apparatus also has set current setting section 23 for
setting a current, set voltage setting section 24 for setting a voltage,
and difference calculator 25 for obtaining a difference between the
output voltage and the set voltage set in set voltage setting section 24.
First, hereinafter, a description is provided for wire feeding control in
this arc welding apparatus.
Frequency base setting section 21 for wire feeding and amplitude base
setting section 22 for wire feeding output a wire feeding speed at which
a forward feed and a reverse feed in a sine waveform are repeated at a
predetermined frequency with a predetermined amplitude, with
respect to an average feeding speed, i.e. a wire feeding speed
corresponding to the set current value in set current setting section 23.
The relation of the average feeding speed, the predetermined
frequency, and the predetermined amplitude with respect to the set
current is stored in a storage, for example, which is not shown, as a
table or a formula, and these values are determined based on the set
current.
Next, hereinafter, a description is provided for welding control in the
arc welding apparatus.
Welding voltage detector 8 is connected between the welding power
supply output terminals, and outputs a signal corresponding to the
detected voltage to status detector 10. Status detector 10 determines,
based on the signal from welding voltage detector 8, whether the
welding output voltage is equal to or larger than a predetermined
value, or smaller than the predetermined value. Based on this
determination result, the status detector determines whether welding
wire 27 short-circuits in contact with object to be welded 30 or a
welding arc occurs in a non-contact state, and outputs a determination
signal.
Short-circuit controller 11 has increasing gradient base setting
section 12, inflection point base setting section 14, increasing gradient
controller 13, and inflection point controller 15. Based on the
difference between the set voltage set in set voltage setting section 24
and the voltage detected in welding voltage detector 8, short-circuit
controller 11 changes at least one of short-circuit current increasing
gradient IS1 in the first step, short-circuit current increasing gradient
IS2 in the second step, and current value ISC at the inflection point.
Here, based on the set current set by the operator, increasing gradient
base setting section 12 determines short-circuit current increasing
gradient (di1/dt) in the first step and short-circuit current increasing
gradient (di2/dt) in the second step. Based on the set current set by
the operator, inflection point base setting section 14 determines
current value ISC at the inflection point at which the short-circuit
current increasing gradient changes from the short-circuit current
increasing gradient (di1/dt) in the first step to the short-circuit current
increasing gradient (di2/dt) in the second step. Based on the
difference between the voltage set in set voltage setting section 24 and
the voltage detected in welding voltage detector 8, increasing gradient
controller 13 changes the short-circuit current increasing gradient
(di1/dt) in the first step and the short-circuit current increasing
gradient (di2/dt) in the second step set in increasing gradient base
setting section 12. Based on the difference between the voltage set in
set voltage setting section 24 and the voltage detected in welding
voltage detector 8, inflection point controller 15 changes current value
ISC at the inflection point of the short-circuit current increasing
gradients determined in inflection point base setting section 14.
This structure allows the output voltage to be matched with the set
voltage precisely, thereby controlling the welding voltage more stably.
The relation of short-circuit current increasing gradient (di1/dt) in the
first step, short-circuit current increasing gradient (di2/dt) in the
second step, and the inflection point with respect to the set current is
stored in a storage, for example, which is not shown, as a table or a
formula, and theses values are determined based on the set current.
Next, a description is provided for arc control after the determination
of status detector 10.
Arc controller 16 of Fig. 7 has current base setting section 17, time
base setting section 19, current controller 18, and time controller 20.
Arc controller 16 changes at least one of the current value in the peak
period and the current value in the base period in arc period Ta, and
the time of the peak period in arc period Ta. Here, current base
setting section 17 sets the current in the peak period and in the base
period, based on the set current set by the operator. Time base setting
section 19 sets the time of the peak period, based on the set current set
by the operator. Current controller 18 changes the current in the
peak period and in the base period set in current base setting section
17, based on the difference between the voltage set in set voltage
setting section 24 and the voltage detected in welding voltage detector
8. Time controller 20 changes the time of the peak period set in the
time base setting section for the peak period, based on the difference
between the voltage set in the set voltage setting section and the
voltage detected in the welding voltage detector.
This structure can control the welding voltage more stably. This
stabilizes the arc and thus can reduce spatters.
The relation of the peak current, the base current, and the peak
current time with respect to the set current is stored in a storage, for
example, which is not shown, as a table or a formula, and these values
are determined based on the set current.
The difference between welding voltage detector 8 and set voltage
setting section 24 is monitored in difference calculator 25 for
calculating a difference between the output voltage and the set voltage.
Short-circuit controller 11 receives a voltage difference value from
difference calculator 25. Short-circuit current increasing gradient
controller 13 and short-circuit current inflection point controller 15
output values changed from the values from increasing gradient base
setting section 12 and inflection point base setting section 14, to driver
7. Thus, short-circuit current increasing gradient IS1 in the first step,
short-circuit current increasing gradient IS2 in the second step, and
current value ISC at the short-circuit current inflection point are
controlled, so that the short-circuit current is controlled.
Arc controller 16 receives the voltage difference value from difference
calculator 25. Current controller 18 and time controller 20 output
values changed from the values from current base setting section 17
and time base setting section 19, to driver 7. Thus, the peak current,
the base current, and the peak current time are controlled, so that the
arc current is controlled.
The arc welding apparatus as described above temporally makes
automatic adjustment on the values of the short-circuit current
increasing gradient (di/dt), the short-circuit current inflection point,
the peak current, the base current, and the peak current time. This
can automatically adjust the ratio between short-circuit period Ts and
arc period Ta, thereby allowing the output voltage to temporally and
automatically follow the set voltage.
Each element constituting the arc welding apparatus shown in Fig. 7
may be formed separately, or a plurality of elements may be combined.
In the example described in the first exemplary embodiment, the
short-circuit current increasing gradient (di/dt), the short-circuit
current inflection point, the peak current, the base current, and the
peak current time are stored in a storage so as to correspond to the set
current. However, the set current is in proportional relation to the
wire feeding speed and the wire feeding amount. Therefore, the
short-circuit current increasing gradient (di1/dt) in the first step, the
short-circuit current increasing gradient (di2/dt) in the second step, the
short-circuit current inflection point, the peak current, the base
current, and the peak current time may be stored in a storage, which is
not shown, such that these values correspond to the wire feeding speed
or the wire feeding amount, instead of the set current.
(Second Exemplary Embodiment)
Fig. 8 is a diagram showing time waveforms of a wire feeding speed, a
welding voltage, and a welding current in accordance with the second
exemplary embodiment of the present invention. The second
exemplary embodiment is different from the first exemplary
embodiment mainly in that the wire feeding is based on a trapezoidal
waveform as shown in Fig. 8 instead of a sine waveform.
When wire feeding is controlled such that a forward feed and a
reverse feed are periodically repeated at predetermined frequency F
with predetermined amplitude AV, such a trapezoidal waveform can
provide the performance similar to that of the sine waveform.
The control method and the welding apparatus are similar to those of
the first exemplary embodiment, and thus the description is omitted.
As described above, in accordance with the present invention, in the
control method for periodically increasing or decreasing a wire feeding
speed, short-circuit current increasing gradient IS1 in a first step,
short-circuit current increasing gradient IS2 in a second step, current
value ISC at an inflection point, the current in a peak period and in a
base period, and the time of the peak period are controlled. Thereby,
an output voltage can be matched with a set voltage.
Further, it is considered that, arc welding is unlikely to cause an
unstable arc even when the state of the arc welding is changed by
disturbances, such as variations in the extension length, and gaps.
It is also considered that the load on the peripheral components
around the motor, such as a feeding motor and gears, is small because
an increase/decrease in the wire feeding speed is based on a sine
waveform or a trapezoidal waveform.
Industrial Applicability
The present invention can minimize the problems caused by an
unstable arc, such as bead defects, an increase in spatters, and lack of
penetration. The unstable arc results from disturbances, such as an
increase in the welding speed, variations in the extension length, and
gaps between the objects to be welded. Thus, the present invention
can suppress adverse effects on production efficiency and working
environment. Therefore, the present invention is industrially useful
as a welding method and a welding apparatus that are used in the
industries, such as an automobile industry, where thin plates are
mainly welded at high speed by consumable electrode type arc welding.
Reference Marks In The Drawings
1 Input power supply
2 Primary rectifier
3 Switching element
4 Transformer
5 Secondary rectifier
6 DCL
7 Driver
8 Welding voltage detector
9 Welding current detector
10 Status detector
11 Short-circuit controller
12 Increasing gradient base setting section
13 Increasing gradient controller
14 Inflection point base setting section
15 Inflection point controller
16 Arc controller
17 Current base setting section
18 Current controller
19 Time base setting section
20 Time controller
21 Frequency base setting section
22 Amplitude base setting section
23 Set current setting section
24 Set voltage setting section
25 Difference calculator
28 Wire feeding motor
27 Welding wire
28 Tip
29 Welding arc
30 Object to be welded
We claim:
Claim 1
An arc welding method for welding using a welding wire as a
consumable electrode by repeating a short-circuit state and an arc
state, the arc welding method comprising:
performing control such that a voltage value of an output
voltage is matched with a voltage value of a set voltage by
determining a short-circuit current increasing gradient
corresponding to a set current; and
temporally changing the short-circuit current increasing
gradient corresponding to the set current, based on a difference
between the set voltage and the output voltage.
Claim 2
The arc welding method of claim 1, wherein
when the output voltage is smaller than the set voltage, the
short-circuit current increasing gradient is changed so as to be steeper
than the short-circuit current increasing gradient corresponding to the
set current, and
when the output voltage is larger than the set voltage, the
short-circuit current increasing gradient is changed so as to be gentler
than the short-circuit current increasing gradient corresponding to the
set current.
Claim 3
The arc welding method of claim 1, wherein the short-circuit current
increasing gradient is changed in proportion to an absolute value
corresponding to a value of the difference between the set voltage and
the output voltage, or changed to a value that is based on a rate of
change corresponding to the value of the difference between the set
voltage and the output voltage.
Claim 4
The arc welding method of claim 1, wherein at least one of an upper
limit and a lower limit is set for the short-circuit current increasing
gradient when the increasing gradient is changed.
Claim 5
The arc welding method of claim 1, wherein the control is performed
such that the voltage value of the output voltage is matched with the
voltage value of the set voltage by
as the short-circuit current increasing gradient corresponding
to the set current, determining a short-circuit current increasing
gradient in a first step, and a short-circuit current increasing gradient
in a second step following the short-circuit current increasing gradient
in the first step, and
based on a value of the difference between the set voltage and
the output voltage, temporally changing the short-circuit current
increasing gradient in the first step and the short-circuit current
increasing gradient in the second step.
Claim 6
The arc welding method of claim 5, wherein the short-circuit current
increasing gradient in the first step is different from the short-circuit
current increasing gradient in the second step.
Claim 7
The arc welding method of claim 6, wherein the short-circuit current
increasing gradient in the first step is larger than the short-circuit
current increasing gradient in the second step.
Claim 8
The arc welding method of claim 5, wherein
a current value at an inflection point at which the short-circuit
current increasing gradient in the first step changes to the
short-circuit current increasing gradient in the second step is
determined so as to correspond to the set current, and
the current value at the inflection point is temporally changed
in accordance with the value of the difference between the output
voltage and the set voltage.
Claim 9
The arc welding method of claim 8, wherein
when the output voltage is smaller than the set voltage, the
current value at the inflection point is changed so as to be larger than
the current value at the inflection point corresponding to the set
current, and
when the output voltage is larger than the set voltage, the
current value at the inflection point is changed so as to be smaller than
the current value at the inflection point corresponding to the set,
current.
Claim 10
The arc welding method of claim 8, wherein the current value at the
inflection point is changed in proportion to an absolute value
corresponding to the value of the difference between the set voltage
and the output voltage, or changed to a value that is based on a rate of
change corresponding to the value of the difference between the set
voltage and the output voltage.
Claim 11
The arc welding method of claim 8, wherein an upper limit and a lower
limit are set for the current value at the inflection point.
Claim 12
The arc welding method of claim 1, wherein
a current value in a peak period in an arc period and a current
value in a base period in the arc period corresponding to the set
current are determined, and
the current value in the peak period and the current value in the
base period are temporally changed in accordance with the value of the
difference between the set voltage and the output voltage.
Claim 13
The arc welding method of claim 12, wherein
when the output voltage is smaller than the set voltage, the
current value in the peak period and the current value in the base
period are changed so as to be larger than the current value in the peak
period and the current value in the base period corresponding to the
set current, and
when the output voltage is larger than the set voltage, the
current value in the peak period and the current value in the base
period are changed so as to be smaller than the current value in the
peak period and the current value in the base period corresponding to
the set current.
Claim 14
The arc welding method of claim 12, wherein the current value in the
peak period and the current value in the base period are changed to
absolute values corresponding to the value of the difference between
the set voltage and the output voltage, or changed to values that are
based on a rate of change corresponding to the value of the difference
between the set voltage and the output voltage.
Claim 15
The arc welding method of claim 12, wherein an upper limit and a
lower limit are set for each of the current value in the peak period and
the current value in the base period.
Claim 16
The arc welding method of claim 1, wherein
a time of a peak period in an arc period corresponding to the set
current is determined, and
the time of the peak period is changed in accordance with the
value of the difference between the set voltage and the output voltage.
Claim 17
The arc welding method of claim 16, wherein
when the output voltage is smaller than the set voltage, the time
of the peak period in the arc period is changed so as to be longer than
the time of the peak period in the arc period corresponding to the set
current, and
when the output voltage is larger than the set voltage, the time
of the peak period in the arc period is changed so as to be shorter than
the time of the peak period in the arc period corresponding to the set
current.
Claim 18
The arc welding method of claim 16, wherein the time of the peak
period in the arc period is changed to an absolute value corresponding
to the value of the difference between the set voltage and the output
voltage, or changed to a value that is based on a rate of change
corresponding to the value of the difference between the set voltage
and the output voltage.
Claim 19
The arc welding method of claim 16, wherein an upper limit and a
lower limit are set for the time of the peak period in the arc period.
Claim 20
The arc welding method of claim 1, wherein the welding is performed
by
setting a welding wire feeding speed corresponding to the set
current as an average feeding speed; and
periodically generating the short-circuit state and the arc state
by periodically repeating wire feeding in a forward direction and in a
reverse direction at a predetermined frequency with a predetermined
amplitude!
Claim 21
An arc welding apparatus for welding by repeating an arc state and a
short-circuit state between a welding wire as a consumable electrode
and an object to be welded, the arc welding apparatus comprising:
a switching element for controlling a welding output;
a welding voltage detector for detecting a welding voltage;
a status detector for detecting the short-circuit state or the arc
state, based on an output from the welding voltage detector;
a short-circuit controller for controlling a short-circuit current
in a short-circuit period, upon receiving a short-circuit signal from the
status detector;
an arc controller for controlling an arc voltage in an arc period,
upon receiving an arc signal from the status detector;
a set current setting section for setting a set current; and
a set voltage setting section for setting a set voltage,
wherein the short-circuit controller includes:
an increasing gradient base setting section for
determining a short-circuit current increasing gradient, based on a set
current set by an operator; and
an increasing gradient controller for changing the
short-circuit current increasing gradient determined in the increasing
gradient base setting section, based on a difference between the
voltage set in the set voltage setting section and the voltage detected in
the welding voltage detector,
wherein the short-circuit controller changes the short-circuit
current increasing gradient, based on the difference between the set
voltage set in the set voltage setting section and the voltage detected in
the welding voltage detector.
Claim 22
An arc welding apparatus for welding by repeating an arc state and a
short-circuit state between a welding wire as a consumable electrode
and an object to be welded, the arc welding apparatus comprising:
a switching element for controlling a welding output;
a welding voltage detector for detecting a welding voltage;
a status detector for detecting the short-circuit state or the arc
state, based on an output from the welding voltage detector;
a short-circuit controller for controlling a short-circuit current
in a short-circuit period, upon receiving a short-circuit signal from the
status detector;
an arc controller for controlling an arc voltage in an arc period,
upon receiving an arc signal from the status detector;
a set current setting section for setting a set current; and
a set voltage setting section for setting a set voltage,
wherein the short-circuit controller includes:
an increasing gradient base setting section for
determining a short-circuit current increasing gradient in a first step
and a short-circuit current increasing gradient in a second step, based
on a set current set by an operator;
an inflection point base setting section for determining an
inflection point at which the short-circuit current increasing gradient
in the first step changes to the short-circuit current increasing
gradient in the second step, based on the set current set by the
operator;
an increasing gradient controller for changing the
short-circuit current increasing gradient in the first step and the
short-circuit current increasing gradient in the second step determined
in the increasing gradient base setting section, based on a difference
between the voltage set in the set voltage setting section and the
voltage detected in the welding voltage detector; and
an inflection point controller for changing the inflection
point of the short-circuit current increasing gradients determined in
the inflection point base setting section, based on the difference
between the voltage set in the set voltage setting section and the
voltage detected in the welding voltage detector,
wherein based on the difference between the set voltage set in
the set voltage setting section and the voltage detected in the welding
voltage detector, the short-circuit controller changes at least one of the
short-circuit current increasing gradient in the first step, the
short-circuit current increasing gradient in the second step, and a
current value at the inflection point.
Claim 23
The arc welding apparatus of claim 21 or 22, wherein
the arc controller includes:
a current base setting section for setting a current in the
peak period and in the base period, based on the set current set by the
operator;
a time base setting section for setting a time of the peak
period, based on the set current set by the operator;
a current controller for changing the current in the peak
period and in the base period set in the current base setting section,
based on the difference between the voltage set in the set voltage
setting section and the voltage detected in the welding voltage
detector; and
a time controller for changing the time of the peak period
set in the time base setting section for the peak period, based on the
difference between the voltage set in the set voltage setting section and
the voltage detected in the welding voltage detector, and
the arc controller changes at least one of the current value in the
peak period and the current value in the base period in the arc period,
and the time of the peak period in the arc period.
Claim 24
The arc welding apparatus of claim 21 or 22 further comprising:
a frequency base setting section and an amplitude base setting
section for wire feeding, the frequency base setting section and the
amplitude base setting section controlling feeding of the welding wire
such that the wire feeding is periodically repeated in a forward
direction and in a reverse direction in a sine waveform or in a
trapezoidal waveform,
wherein the welding is performed by
setting a welding wire feeding speed corresponding to the set
current as an average feeding speed; and
periodically generating the short-circuit state and the arc
state by periodically repeating the wire feeding in the forward
direction and in the reverse direction at a predetermined frequency
with a predetermined amplitude.

An arc welding method of the present invention controls a
short-circuit current increasing gradient (di/dt), an inflection point at
which the short-circuit current increasing gradient (di/dt) changes, the
current in a peak period and in a base period, and the time of the peak
period in accordance with a difference between a set voltage and an
output voltage. This allows the output voltage to be matched with the
set voltage, and stabilizes the arc. Thereby, a stable arc welding
method can be implemented, even as a method for outputting a welding
current based on a welding voltage.