DESCRIPTION
ARC WELDING METHOD AND ARC WELDING APPARATUS
TECHNICAL FIELD
The present invention relates to a method and an apparatus of arc
welding in which a short circuit state and an arc generation state are
alternately generated by changing the feeding direction of a welding wire as a
consumable electrode periodically between the forward feeding and the reverse
feeding.
BACKGROUND ART
In the welding operation, spatter removing has been a loss process. For
the purpose of reducing spatters, a consumable electrode arc welding is
conventionally well known (for example, see Patent Literature l). In the
method, a short circuit state and an arc generation state are alternately
generated by changing the feeding direction of a welding wire periodically and
repeatedly between the forward feeding and the reverse feeding.
Fig. 7 shows a time waveform of temporal change in a wire feeding rate
and a welding output.
As a method for controlling arc welding where the short circuit state and
the arc generation state are alternately generated in the wire feeding of a
welding wire as a consumable electrode, for example, the following is known.
According to the method, the structure contains a feeding rate controller and an
output controller. The feeding rate controller effects control of a wire feeding
motor in a manner that wire feeding is changed periodically and repeatedly
between the forward feeding and the reverse feeding. The output controller
controls welding output, as shown in Eig. 1. The controller decreases the
output for a small amount of wire feeding and increases the output for a large
amount of wire feeding. With the structure above; separation force caused by
decrease in wire feeding rate in the short circuit state encourages the melted tip
of the wire to transfer to the object to be welded, The structure decreases short
circuit current that is a main cause of spattering, allowing a short circuiting
transfer welding to continue with stability.
In the control method above (where the short circuit state and the arc
generation state are alternately generated by changing the wire feeding
periodically and repeatedly between the forward feeding and the reverse
feeding), the description below discusses on a case where the object to be welded
and the welding wire are mechanically released from the short circuit state by
the reverse feeding. To attain the mechanical release, the wire needs to be fed
in reverse at a feeding rate greater than the average feeding rate of wire
feeding. To obtain the desirable feeding rate, a velocity amplitude has to be
determined.
It is generally known that the wire feeding rate changes in proportion to
change in welding current. In the control of a wire feeding rate with a
periodical change, the average feeding rate of a wire feeding rate should be
changed in synchronization with (in proportion to) the welding current. As the
increase in welding current, the average feeding rate increases. Therefore, the
velocity amplitude of the periodic wire feeding has to be increased in
synchronization with (in proportion to) the average feeding rate. Besides,
when the wire feeding motor can reach the load limit during the periodic wire
feeding, the load on the wire feeding motor and the peripheral parts, such as
gears, should be lightened by decreasing the frequency of the periodic wire
feeding.
However, if the frequency and the velocity amplitude of wire feeding
cannot be changed according to welding current, welding operation is limited at
a fixed welding current, that is, the welding operation has to be carried out in a
limited range of welding current.
Citation List
Patent Literature
Patent Literature 1' Japanese Unexamined Patent Application
Publication No. 62-6775
SUMMARY OF THE INVENTION
The present invention addresses the problem above. In the arc welding
where the short circuit state and the arc generation state are periodically
generated by changing the wire feeding periodically and repeatedly between the
forward feeding and the reverse feeding, the method and the apparatus offer
optimal welding according to a welding current.
The arc welding-method of the present invention is a consumable
electrode arc welding method in which a welding wire feeding rate suitable for a
welding current is determined as an average feeding rate, and the short circuit
state and the arc generation state are repeated periodically by changing the
wire feeding between the forward feeding and the reverse feeding. The
method above offers arc welding with an average feeding rate according to a
welding current, a predetermined frequency, and a predetermined velocity
amplitude. In the method, at least one of the frequency and the velocity
amplitude is set to a value suitable for the welding current.
As described above, determining a frequency and velocity, amplitude to
an optimum value for each welding current allows the welding operation to be
suitable for welding current. The structure minimizes the following problems:
defective bead, increase, in spatters, and lack of penetration. These problems
can be as a result of instability of arc affected by, increase in speed of welding
and disturbances, such as change in wire extension and a gap between the
objects to be welded. Besides, the method of the invention suppresses an
adverse effect on production efficiency and working environment.
The arc welding apparatus of the present invention carries out arc
welding in a manner* that the arc generation state and the short circuit state
are repeated alternately between a welding wire as a consumable electrode and
an object to be welded. The arc welding apparatus has a welding current
setting section, an average feeding rate setting section, a frequency setting
section, a velocity amplitude setting section, a switching element, a welding
voltage detecting section, a state detecting section, a short circuit control section,
and an arc control section. The welding current setting section determines a
welding current. The average feeding rate setting section determines an
average feeding rate of a welding wire feeding rate for the wire feeding control
in which the feeding direction of a welding wire is changed periodically and
repeatedly between the forward feeding and the reverse feeding according to a
welding current. The frequency setting section determines a frequency for the
wire feeding control in which the feeding direction of a welding wire is changed
periodically and repeatedly between the forward feeding and the reverse
feeding according to a welding current. The velocity amplitude setting section
determines a velocity amplitude for the wire feeding control in which the
feeding direction of a welding wire is changed periodically and repeatedly
between the forward feeding and the reverse feeding according to a welding
current. The switching element controls welding output. The welding voltage
detecting section detects welding voltage. The state detecting section detects
whether the short circuit state or the arc generation state according to the
result detected by the welding voltage detecting section. Receiving a short
circuit signal from the state detecting section, the short circuit control section
controls a short circuit current during a short circuit period that maintains the
short circuit state. Receiving an arc generation signal from the state detecting
section, the arc control section controls an arc voltage during an arc period that
maintains the arc generation state. With the structure above, the arc welding
apparatus carries out welding in which a welding-wire is fed with an optimally
determined frequency and velocity amplitude according to a welding current.
As described above, determming a frequency and velocity amplitude to
an optimum value for each welding current allows the welding operation to be
suitable for welding current. The structure minimizes the following problems-'
defective bead, increase in spatters, and lack of penetration. These problems
can be as a result of instability of arc affected by increase in speed of welding
and disturbances, such as change in wire extension and a gap between the
objects to be welded. Besides, the apparatus of the invention suppresses an
adverse effect on production efficiency and working environment.
In the arc welding where the short circuit state and the arc generation
state are periodically generated by changing the wire feeding periodically
between the forward feeding and the reverse feeding, the structure of the
present invention offers an arc welding capable of determining a frequency and
a velocity amplitude so as to be suitable for each welding current. This allows
the welding operation to be suitable for a welding current in a broadened
setting range, lightening the load on the wire feeding motor and the peripheral
parts, such as gears.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows temporal waveforms of a wire feeding rate, a welding
voltage, and a welding current in accordance with a first exemplary
embodiment of the present invention.
Fig. 2 shows a relation between the welding current and the velocity
amplitude of a wire feeding rate in accordance with the first embodiment of the
present invention.
Fig. 3 shows a relation between the welding current and the frequency of
wire feeding in accordance with the first embodiment of the present invention.
Fig. 4 is a schematic view showing the structure of an arc welding
apparatus in accordance with the first embodiment of the present invention.
Fig. 5 shows temporal waveforms of a wire feeding rate, a welding
voltage, and a welding current in accordance with a second exemplary
embodiment of the present invention.
Fig. 6 is a schematic view showing the structure of an arc welding
apparatus in accordance with the second embodiment of the present invention.
Fig. 7 shows conventional temporal waveforms of a wire feeding rate and
welding output.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The exemplary embodiments of the present invention will be described
hereinafter with reference to the accompanying drawings. Throughout the
drawings, like parts have similar reference marks and the description thereof
may be omitted. It is to be understood that the present invention is not limited
to the embodiments described below.
(FIRST EXEMPLARY EMBODIMENT)
In the embodiment, the method of arc welding is described first and then
the description on the arc welding apparatus follows.
Fig. 1 shows temporal waveforms of a wire feeding rate, a welding
voltage, and a welding current in accordance with, the first exemplary
embodiment of the present invention. Specifically, the waveforms of Fig. 1
show the temporal relation of the wire feeding rate, the welding voltage, and
the welding current in a consumable electrode arc welding where the short
circuit state and the arc generation state are alternately generated.
In Fig. 1, PI represents the moment from which the short circuit state
starts. First, initial short circuit current ISO is provided for a predetermined
time. After that, initial short circuit current ISO is changed into a short circuit
current having a first-increase gradient (dii/dt) (hereinafter, referred to as IS1
shown in Fig. l), and further changed into a short circuit current having a
second-increase gradient (di2/dt) (hereinafter, IS2 shown in Fig. 1). When a
constriction is detected in a droplet formed between the molten pool and the tip
of the welding wire, the welding current is plunged into a low level. After that,
the droplet is separated at the constriction and the short circuit state completes.
P2 in Fig. 1 represents the moment at which an arc is generated and from
which arc period Ta starts. The welding current provided just after the arc
generation is peak current IP. After that, the welding current is changed from
peak current IP to base current IB. The transition period from peak current IP
to base current IB is controllable by either current or voltage. The welding
operation waits for the next short circuit, with base current IB maintained. P3
in Fig. 1 represents the moment at which the next short circuit occurs and from
which short circuit period Ts starts.
Fig. 1 shows a feeding control in which the wire feeding is changed
periodically and repeatedly between the forward feeding and the reverse
feeding in the basic form of a sine wave with predetermined frequency F and
predetermined velocity amplitude AV. Period T, which is the reciprocal of
frequency F, is the total of short circuit period Ts and arc period Ta. When the
wire feeding rate reaches peak PP of the forward feeding, a short circuit is
generated around Pi; in contrast, when the wire feeding rate reaches peak NP
of the reverse feeding, an arc is generated around P2. After P2, the next short
circuit is generated around P3 when the wire feeding rate reaches peak PP of
the next forward feeding.
As described above, the period between PI-'and P3 as one cycle of feeding
control is continuously repeated to carry out the welding. The short circuit
state and the arc generation state are generated by the wire feeding control
where the wire feeding is changed periodically and repeatedly between the
forward feeding and the reverse feeding.
Next, in the welding above, how to determine velocity amplitude AV
being suitable for a welding current will be described, with reference to Fig. 2.
Fig. 2 shows a relation between the welding current and the velocity amplitude
of a wire feeding rate in accordance with the first embodiment of the present
invention.
In Fig. 2, for example, velocity amplitude AV measures 15m/min for a
welding current of 60A. As increase in welding current, velocity amplitude AV
increases. When the welding current reaches 240A, the velocity amplitude
increases to 30m/min. Increase in welding current also increases the average
feeding rate of the wire feeding rate. Therefore, if velocity amplitude AV has a
fixed value, the period for the reverse feeding is decreased,' accordingly, the
distance of the reverse feeding is shortened. Due to the decrease in distance of
the reverse feeding, it is difficult to keep a distance between the tip of the wire
and the object to be welded. To provide the reverse feeding with stability, a
predetermined distance (e.g. 1-5 mm) between the tip of the wire and the
object should be constantly maintained even if the welding current gets higher.
That is, the period for the reverse feeding of the welding wire (i.e., the distance
of the reverse feeding) is kept at a predetermined length by increasing velocity
amplitude AV in synchronization with the welding current.
The characteristics shown in Fig. 2 can be known in advance by an
experiment according to an object to be welded and welding conditions.
Next, in the welding above (where the wire feeding is changed
periodically and repeatedly between the forward feeding and the reverse
feeding), how to determine frequency F being suitable for a welding current will
be described, with reference to Fig. 3. Fig. 2 shows a relation between the
welding current and the frequency of the wire feeding in accordance with the
first embodiment of the present invention. Fig. 3 shows a relation between the
welding current and the frequency of the wire feeding in accordance with the
first embodiment of the present invention.
In Fig. 3, for example, the frequency is constantly kept at 60 Hz until the
welding current reaches 180A. When the welding current exceeds 180A, the
frequency is set lower. Further, when the welding current reaches 240V, the
frequency may be set lower down to 40 Hz.
As described above, velocity amplitude AV needs to have a larger value
with the increase in welding current; in contrast, frequency F may be set low.
The increase in velocity amplitude also increases the rate of change of welding
wire feeding rate (i.e. acceleration of welding wire feeding), which needs for the
wire feeding motor and the gears to have great power for feeding the welding
wire. This imposes a heavy load on the wire feeding motor, the gears and
other peripheral parts. Determining frequency F to be low suppresses an
excessive change in welding wire feeding rate, lightening the load.
In a case where the wire feeding mQtor and the peripheral parts
including gears are insusceptible to the load, frequency F may be kept at a
constant level or may be increased to a higher level.
In Figs. 2 and 3, for example, as the welding current increases to 180A,
velocity amplitude AV increases from 15m/min to 25m/min; meanwhile,
frequency F is kept at 60 Hz with no trouble. As the welding current gets
higher to 240A, velocity amplitude AV increases to 30m/min. Under the
condition, frequency F is often lowered to 40 Hz for protecting the wire feeding
motor and the periphery parts including gears from an excessive load.
In the description, the relation between the welding current and velocity
amplitude AV (Fig. 2) and the relation between the welding current and
frequency F (Fig. 3) are shown as linear functions, but they are not limited to;
they may be represented by quadratic functions.
As shown in Figs. 2 and 3, at least one of the upper limit and the lower
limit may be defined in each of velocity amplitude AV and frequency F with
respect to the welding current. For example, setting the upper limit assures
safety use of the wire feeding motor without exceeding the service limit.
Setting the lower limit allows the welding operation to maintain desirable
welding properties and welding conditions.
Velocity amplitude AV and frequency F shown in Figs. 2 and 3 are
determined according to the welding current and at least any one of the
fallowings: the diameter of a feeding wire as a consumable electrode, the type of
wire, wire extension, and a shield gas to be supplied.
As described above, the arc welding method of the present invention is a
consumable electrode arc welding in which method a welding wire feeding rate
suitable for a welding current is determined as an average feeding rate, and the
short circuit state and the arc generation state are repeated periodically by
changing the wire feeding between the forward feeding and the reverse feeding.
The method above carries out wire feeding with an average feeding rate
according to a welding current, predetermined frequency F, and predetermined
velocity amplitude AV. In the method, at least one of frequency F and velocity
amplitude AV is set to a value suitable for the welding current.
Determining frequency F and velocity amplitude AV to an optimum value
for each welding current allows the welding operation to be suitable for the
welding current. The structure minimizes the following problems: defective
bead, increase in spatters, and lack of penetration. These problems can be as a
result of instability of arc affected by increase in speed of welding and
disturbances, such as change in wire extension and a gap between the objects to
be welded. Besides, the method of the invention suppresses an adverse effect
on production efficiency and working environment.
In the wire feeding, the welding wire feeding rate can be changed in the
form of a sine wave. Compared to a rectangular change in feeding rate, the
sinusoidal change decreases temporal change in load on the wire feeding motor
and the peripheral parts including gears, contributing to an extended service
life thereof.
In the welding method of the invention, the welding operation may be
timed to at least any one of the peak time, the rising time, and the falling time
of the welding current. The method above allows the arc welding to be
controllable with stability. Specifically, the method prevents generation of
excessive spatters and unstable arc, providing the welding operation with
stability.
Further, in the method above, at least one of the upper limit and the
lower limit may be determined in at least any one of the peak time, the rising
time, and the falling time of the welding current. Setting a limit value assures
safety use of the wire feeding motor and other parts, and maintains desirable
welding properties and welding conditions in the welding operation.
Next, the arc welding apparatus that carries out the arc welding control
of the first exemplary embodiment will be described with reference to Fig. 4.
Fig. 4 is a schematic view showing the structure of the arc welding apparatus in
accordance with the first embodiment of the present invention.
As shown in Fig. 4, the arc welding apparatus of the embodiment carries
out arc welding in a manner that the arc generation state and the short circuit
state are repeated alternately between welding wire 20 as a consumable
electrode and object 23 to be welded. The arc welding apparatus has welding
current setting section 13, average feeding rate setting section' 24, frequency
setting section 14, velocity amplitude setting section 15, switching element 3,
welding voltage detecting section 8, state detecting section 10, short circuit
control section 11, and arc control section 12. With the structure, the welding
apparatus carries out arc welding in which the feeding of welding wire 20 is
controlled with frequency F and velocity amplitude AV suitable for a welding
current. Welding current setting section 13 determines a welding current.
Average feeding rate setting section 24 determines an average feeding rate of a
welding wire feeding rate for the wire feeding control in which the feeding
direction of welding wire 20 is changed periodically and repeatedly between the
forward feeding and the reverse feeding according to a welding current.
Frequency setting section 14 determines frequency F for the wire feeding
control in which the feeding direction of welding wire 20 is changed periodically
and repeatedly between the forward feeding and the reverse feeding according
to a welding current. Velocity amplitude setting section 15 determines velocity
amplitude AV for the wire feeding control in which the feeding direction of
welding wire 20 is changed periodically and repeatedly between the forward
feeding and the reverse feeding according to a welding current. Switching
element 3 controls welding output. Welding voltage detecting section 8 detects
welding voltage. State detecting section 10 detects whether the arc welding is
1 i
in the short circuit state or in the arc generation state according to the result
detected by welding voltage detecting section 8. Receiving a short circuit
signal from state detecting section 10, short circuit control section 11 controls a
short circuit current during short; circuit period Ts that maintains the short
circuit state. Receiving an arc generation signal from state detecting section
10, arc control section 12 controls an arc voltage during arc period Ta that
maintains the arc generation state. By virtue of the structure above, the
apparatus employs a frequency and a velocity amplitude suitable for each
welding current, providing optimum welding operation for each welding current
(as will be described later). The structure minimizes the following problems-"
defective bead, increase in spatters, and lack of penetration. These problems
can be as a result of instability of arc affected by increase in speed of welding
and disturbances, such as change in wire extension and a gap in object 23 to be
welded. Besides, the structure suppresses an adverse effect on production
efficiency and working environment, providing an excellent arc welding
apparatus.
Next, the basic workings of the arc welding apparatus of the embodiment
will be described. As shown in Fig. 4, electric power fed from input power
source 1 is rectified by primary rectifier 2 and then converted into, for example,
AC voltage by switching element 3. The AC voltage is stepped down by
transformer 4 and then rectified by secondary rectifier 5 and inductor DCL6.
The AC voltage is applied between welding wire 20 guided by welding tip 21
and object 23 to be welded, by which welding arc 22 is generated on object 23 to
be welded.
The arc welding apparatus has driving section 7, welding voltage
detecting section 8, and welding current detecting section 9. Driving section 7
controls switching element 3. Welding voltage detecting section 8 is connected
between the output terminals of welding power source that applies DC voltage
to welding wire 20. Welding current detecting section 9 detects welding output
current. The arc welding apparatus has, as mentioned above, state detecting
section 10, short circuit control section 11, arc control section 12, and welding
current setting section 13 for setting a welding current; State detecting section
10 judges whether the short circuit state or the arc generation state according a
signal from welding voltage detecting section 8. Receiving a short circuit
signal from state detecting section 10, short circuit control section 11 controls a
short circuit current during short circuit period Ts. Receiving an arc
generation signal from state detecting section 10, arc control section 12 controls
an arc voltage during arc period Ta.
Frequency setting section 14 determines frequency F for the wire feeding
so as to be suitable for each current determined by welding current setting
section 13. Velocity amplitude setting section 15 determines velocity
amplitude AV for the wire feeding. Average feeding rate setting section 24
determines an average feeding rate of the wire feeding. Receiving each output
of frequency setting section 14, velocity amplitude setting section 15, and
average feeding rate setting section 24, wire feeding motor 19 carries out
feeding control of welding wire 20. Frequency setting section 14 has a
correspondence table or a relational expression between the welding current
and frequency F. With reference to the table (or the expression), frequency
setting section 14 determines frequency F to be suitable for a welding current.
Velocity amplitude setting section 15 has a correspondence table or a relational
expression between the welding current and velocity amplitude AV. With
reference to the table (or the expression), velocity amplitude setting section 15
determines velocity amplitude AV to be suitable for a welding current. Average
feeding rate setting section 24 has a correspondence table or a relational
expression between the welding current and an average feeding rate. With
reference to the table (or the expression), average feeding rate setting section 24
determines an average feeding rate to be suitable for a welding current.
First, a specific description on the wire feeding control of the arc welding
apparatus will be given below. Receiving each welding current determined by
welding current setting section 13, each of frequency setting section 14 and
velocity amplitude setting section 15 outputs a wire-feeding-rate command to
wire feeding motor 19. The wire-feeding-rate command requests, wire feeding
motor 19 to repeat the forward feeding and the reverse feeding in the form of a
sine wave with frequency F and velocity amplitude AV according to the average
feeding rate of the wire feeding rate suitable for a determined value of welding
current. As described above, the relation between the welding current and
frequency F and the relation between the welding current and velocity
amplitude AV are stored in a storage section (not shown) as a correspondence
table or expression, so that frequency F and velocity amplitude AV have
optimum values for the welding current.
Next, a specific description on the welding control of the arc welding
apparatus will be given below. As is shown in Fig. 4, welding voltage detecting
section 8, which is connected between the output terminals of the arc welding
apparatus, detects welding voltage and then outputs a signal corresponding to
the voltage to state detecting section 10. Receiving the signal from welding
voltage detecting section 8, state detecting section 10 judges whether the
welding output voltage is at least a predetermined value or less than the value.
According to the result, state detecting section 10 judges whether the short
circuit state—where welding wire 20 makes contact with object 23 to be
welded—or the arc generation state—where a welding arc is generated between
the wire and the object having no contact with each other. According to the
judgment, state detecting section 10 outputs a judgment signal to short circuit
control section 11 and arc control section 12.
Receiving the judgment signal, short circuit control section 11 requests
for driving section 7 to output short circuit initial current ISO suitable for the
welding current, first-increase gradient IS 1 of a short circuit current that
follows initial current ISO, and second-increase gradient IS2 of the short circuit
current that follows gradient ISl.
Receiving the judgment signal, arc control section 12 requests for driving
section 7 to output peak current IP and base current IB for a predetermined
period of time in arc period Ta. The transition period from peak current IP to
base current IB is controllable by either current or voltage.
With the structure above, frequency F and velocity amplitude AV can be
determined to be suitable for a welding current in arc welding where the wire
feeding is changed periodically and repeatedly between the forward feeding and
the reverse feeding. This allows welding operation to have a desired current
value in a broadened range from a low level (e.g. 30A) to a high level (e.g. 350A)
of welding current.
Each section that constitutes the arc welding apparatus of Fig. 4 may be
a separate structure or a combined structure of some sections.
As described above, the arc welding apparatus of the embodiment carries
out welding operation in which the short circuit state and the arc generation
state are repeated periodically by changing the wire feeding periodically and
repeatedly between the forward feeding and the reverse feeding in the form of a
sine wave. In such a controlled welding operation, frequency F and velocity
amplitude AV are determined according to the average feeding rate of a wire
feeding rate suitable for the welding current. The structure provides arc
welding with stability and a broadened range from a low level to a high level in
welding current.
In a case where the wire feeding is changed between the forward feeding
and the reverse feeding in the form of a sine wave, the temporal change in load
on the wire feeding motor and the peripheral parts including gears is
continuous and small. In contrast, when the forward feeding and the reverse
feeding are repeated in the form of a rectangular wave, the temporal change in
load on the motor and the peripheral parts can be sudden and large.
Compared to the rectangular change in feeding rate, the sinusoidal change
decreases temporal change in load on the components, contributing to an
extended service life thereof.
In the description of the embodiment, frequency F and velocity amplitude
AV for the wire feeding are determined on the basis of the welding current, but
it is not limited to. As a welding current increases, a wire feeding rate and an
amount of wire feeding proportionally increase. Therefore, a similar effect can
be obtained by determining frequency F and velocity amplitude AV on the basis
of the wire feeding rate or the amount of wire feeding.
(SECOND EXEMPLARY EMBODIMENT)
Fig. 5 shows temporal waveforms of a wire feeding rate, a welding
voltage, and a welding current in accordance with the second exemplary
embodiment of the present invention.
The structure of the second embodiment differs from that of the first
embodiment in the following points^ the wire feeding is changed in the form of a
trapezoid wave, not in the form of a sine wave? and at least any one of peak
time Tp, rising time Tr, and falling time Tf of the trapezoidal waveform in the
wire feeding control is determined so as to be suitable for welding current.
That is, the arc welding method of the second embodiment is a
consumable electrode arc welding in which a welding wire feeding rate suitable
for a welding current is determined as an average feeding rate, and the short
circuit state and the arc generation state are repeated periodically by changing
the wire feeding periodicaUy and repeatedly between the forward feeding and
the reverse feeding. The method above carries out wire feeding with the
average feeding rate, predetermined frequency F, and predetermined velocity
amplitude AV. In the" method, at least one of frequency F and velocity
amplitude AV is set to a value suitable for the welding current, and the wire
feeding is controlled on the wire feeding rate changed in the form of a trapezoid
waveform.
Determining frequency F and velocity amplitude AV to an optimum value
for each welding current allows the welding operation to be suitable for the
welding current. The structure minimizes the following problems: defective
bead, increase in spatters, and lack of penetration. These problems can be as a
result of instability of arc affected by increase in speed of welding and
disturbances, such as change in wire extension and a gap in the object to be
welded. Besides, the method of the invention suppresses an adverse effect on
production efficiency and working environment, providing excellent arc
welding.
In the wire feeding control where the forward feeding and the reverse
feeding are periodically repeated with a predetermined frequency F and velocity
amplitude AV, employing a wire feeding rate having a trapezoidal change offers
an effect similar to that having a sinusoidal change.
Unlike the control employing a wire feeding rate with a sinusoidal
change, in the control employing a wire feeding rate with a trapezoidal change,
peak time Tp, rising time Tr, and falling time Tf of the trapezoidal waveform
can be determined to be suitable for a welding current.
Fig. 5 shows a wire feeding control in which the forward feeding and the
reverse feeding are periodically repeated, with predetermined frequency F and
velocity amplitude AV, in the form of a trapezoid wave as a basic waveform. In
the wire feeding control, peak time Tp is disposed at the peak on the side of the
forward feeding or the reverse feeding. Further, rising time Tr required for
reaching the peak feeding rate and falling time Tf from the peak feeding rate
are added, and they can be determined to be suitable for a welding current.
By virtue of increase in number of adjustable parameters, the distance
between welding wire 20 and object 23 to be welded is easily kept at a
predetermined length.
The relation between the welding current and peak time Tp, the relation
between the welding current and rising time Tr, and the relation between the
welding current and falling time Tf—which are not shown in the drawings,
though—may be represented by linear functions or quadratic functions.
Further, at least one of the upper limit and the lower limit may be
defined at least any one of peak time Tp, rising, time Tr, and falling time Tfe
with respect to the welding current (, which are also not shown in the
drawings).
Peak time Tp, rising time Tr, and falling time Tf are determined
according to the welding current and at least any one of the followings: the
diameter of a feeding wire as a consumable electrode, the type of wire, wire
extension, and a shield gas to be supplied.
Next, a specific description on the welding control of the arc welding
apparatus of the second embodiment will be given below, with reference to Fig.
6. Fig. 6 is a schematic view showing the structure of the arc welding
apparatus of the second embodiment of the present invention. The arc welding
apparatus of the second embodiment differs from that described in the first
embodiment (shown in Fig. 4) in that peak time setting section 16, rising time
setting section 17, and falling time setting section 18 are additionally disposed.
In addition to the workings of the arc welding apparatus (shown in Fig.
4) of the first embodiment, the arc welding apparatus of the embodiment works
as follows. Average feeding ratesetting se(^bn 24 determines an average
feeding rate for the feeding control in which the feeding of welding wire 20 is
repeated periodically between the forward feeding and the reverse feeding in
the form of a trapezoid wave. Velocity amplitude setting section 15 determines
a velocity amplitude for the feeding control in which the feeding of welding wire
20 is repeated periodically between the forward feeding and the reverse feeding
in the form of a trapezoid wave. The arc welding apparatus of the embodiment
has peak time setting section 16, rising time setting section 17, and falling time
setting section 18. With the structure above, the apparatus carries out arc
welding in a manner that the feeding of welding wire 20 is timed to at least any
one of peak time Tp, rising time Tr, and falling time Tf with respect to the
welding current. Peak time setting section 16 determines peak time Tp of the
trapezoid waveform according to the welding current. Rising time setting
section 17 determines rising time Tr of the trapezoid waveform according to the
welding current. Falling time setting section 18 determines falling time Tf of
the trapezoid waveform according to the welding current.
Detennining a frequency and a velocity amplitude to an optimum value
for each welding current allows the welding operation to be suitable for the
welding current. The structure minimizes the following problems^ defective
bead, increase in spatters, and lack of penetration. These problems can be as a
result of instability of arc affected by increase in speed of welding and
disturbances, such as change in wire extension and a gap formed in object 23 to
be welded. Besides, the structure of the invention suppresses an adverse effect
on production efficiency and working environment, providing an excellent arc
welding apparatus. ,
Peak time setting section 16 determines peak time Tp so as to be suitable
for each welding current determined at welding current setting section 13.
Rising time setting section 17 determines rising time Tr. Falling time setting
section 18 determines falling time Tf., Receiving each output of peak time
setting section 16, rising time setting section 17, and falling time setting section
18, wire feeding motor 19 carries out feeding control of welding wire 20.
Peak time setting section 16 has a correspondence table or a relational
expression between the welding current and peak time Tp. With reference to
the table (or the expression), peak time setting section 16 determines peak time
Tp to be suitable for a welding current. Rising time setting section 17 has a
correspondence table or a relational expression between the welding current
and rising time Tr. With reference to the table (or the expression), rising time
setting section 17 determines rising time Tr to be suitable for a welding current.
Falling time setting section 18 has a correspondence table or a relational
expression between the welding current and falling time Tf. With reference to
the table (or the expression), falling time setting section 18 determines falling
time Tf to be suitable for a welding current.
Next, wire feeding control of the arc welding apparatus will be described
below. Each of peak time setting section 16, rising time setting section 17, and
falling time setting section 18, which are responsible for controlling the wire
feeding in the form of trapezoid wave, outputs a wire-feeding-rate command to
wire feeding motor 19, The wire-feeding-rate command requests wire feeding
motor 19 to repeat the forward feeding and the reverse feeding in the form of a
trapezoid wave with peak time Tp, rising time Tr, and falling time Tf according
to each welding current determined at welding current setting section 13.
The welding control of the arc welding apparatus is similar to that in the
first embodiment, and the description thereof will be omitted.
As described above, in the welding control of the embodiment in which
the short circuit state and the arc generation state are periodically generated by
changing the wire feeding rate periodically and repeatedly between the forward
feeding and the reverse feeding in the form of a trapezoid wave, frequency F,
velocity amplitude AV, peak time Tp, rising time Tr, and falling time Tf can be
determined so as to be suitable for the average feeding rate of a wire feeding
rate according to each welding current. This allows welding operation to have
a desired current value in a broadened range from a low level (e.g. 30A) to a
high level (e.g. 350A) of the welding current.
According to the structure of the embodiment, the wire feeding is
changed between the forward feeding and the reverse feeding in the form of a
trapezoid wave. Compared to a rectangular change in feeding rate, the
trapezoidal change decreases temporal change in load on wire feeding motor 19
'. j."
and the peripheral parts including gears, contributing to an extended service
life thereof.
In the description of the embodiment, peak time Tp, rising time Tr, and
falling time Tf are determined on the basis of the welding current, but it is not
limited to. As a welding current increases, a wire feeding rate and an amount
of wire feeding proportionally increase. Therefore, a similar effect can be
obtained by determining peak time Tp, rising time Tr, and falling time Tf on the
basis of the wire feeding rate or the amount of wire feeding.
Each section that constitutes the arc welding apparatus of Fig. 6 may be
a separate structure or a combined structure of some sections.
INDUSTRIALAPPUCABIUTY
The structure of the present invention minimizes the following problems:
defective bead, increase in spatters, and lack of penetration, These problems
can be as a result of instability of arc affected by increase in speed of welding
and disturbances, such as change in wire extension and a gap between the
objects to be welded. The structure suppresses an adverse effect on production
efficiency and working environment. The method and apparatus of arc
welding is useful for consumable electrode arc welding; particularly, useful for
high-speed sheet welding in car industries.
REFERENCE MARKS IN THE DRAWINGS
1 input power source
2 primary rectifier
3 switching element
4 transformer
5 secondary rectifier
6 DCL
7 driving section
8 welding voltage detecting section
9 welding current detecting section
10 state detecting section
11 short circuit control section
12 arc control section
13 welding current setting section
14 frequency setting section
15 velocity amplitude setting section
16 peak time setting section
17 rising time setting section
18 falling time setting section
19 wire feeding motor
20 welding wire
21 welding tip
22 welding arc
23 object to be welded
24 average feeding rate setting section
CLAIMS-
1. An arc welding method using a consumable electrode, in which method
a welding wire feeding rate suitable for a welding current is determined as an
average feeding rate and a short circuit state and an arc generation state are
repeated periodically by changing wire feeding of a welding wire between
forward feeding and reverse feeding with a predetermined frequency and a
predetermined velocity amplitude,
the method comprising-
determining at least one of the frequency and the velocity amplitude is
set to a value suitable for the welding current.
2. The arc welding method of claim 1, wherein at least one of an upper
limit and a lower limit is set in at least one of the frequency and the velocity
amplitude determined to be suitable for the welding current.
3. The arc welding method of claim 1 or claim 2, wherein the wire feeding
of the welding wire is carried out by changing the welding wire feeding rate so
as to have a sinusoidal waveform.
4. The arc welding method of claim 1 claim 2, wherein the wire feeding
of the welding wire is carried out by changing the welding wire feeding rate so
as to have a trapezoidal waveform.
5. The arc welding method of claim 4, wherein welding operation is timed
to at least any one of a peak time, a rising time, and a falling time determined
to be suitable for the welding current.
6. The arc welding method of claim 5, wherein at least one of an upper
limit and a lower limit is set in at least any one of the peak time, the rising time,
and the falling time determined to be suitable for the welding current.
7. An arc welding apparatus that carries out arc welding where an arc
generation state and a short circuit state are repeated alternately between a
welding wire as a consumable electrode and an object to be welded, the
apparatus comprising-'
a welding current setting section for determining a welding current;
an average feeding rate setting section for determining an average
feeding rate of a welding wire feeding rate for wire feeding control in which a
feeding direction of a welding wire is changed periodically and repeatedly
between forward feeding and reverse feeding according to the welding current;
a frequency setting section for determining a frequency for the wire
feeding control in which the feeding direction of the welding wire is changed
periodically and repeatedly between the forward feeding and the reverse
feeding according to the welding current;
a velocity amplitude setting section for determining a velocity amplitude
for the wire feeding control in which the feeding direction of the welding wire is
changed periodically and repeatedly between the forward feeding and the
reverse feeding according to the welding current;
a switching element for controlling welding output;
a welding voltage detecting section for detecting welding voltage,'
a state detecting section for detecting whether the arc welding is in the
short circuit state or in the arc generation state according to a result detected
by the welding voltage detecting section,'
a short circuit control section for contrdlling a short circuit current
during a short circuit period that maintains the short circuit state in response
to a short circuit signal fed from the state detecting section; and
an arc control section for controlling an arc voltage during an arc period
that maintains the arc generation state in response to an arc generation signal
fed from the state detecting section,
wherein, welding operation is carried out by feeding the welding wire
with the frequency and the velocity amplitude determined to be suitable for the
welding current.
8. The arc welding apparatus of claim 7, wherein the average feeding
rate setting section determines a frequency for the feeding control in which the
feeding of the welding wire is changed periodically and repeatedly between the
forward feeding and the reverse feeding so as to have a trapezoidal waveform,
and the velocity amplitude setting section determines a velocity amplitude for
the feeding control in which the feeding of the welding wire is changed
periodically and repeatedly between the forward feeding and the reverse
feeding so as to have a trapezoidal waveform,
the apparatus further comprising:
a peak time setting section for determining a peak time of the trapezoidal
waveform according to the welding current;
a rising time setting section for determining a rising time of the
trapezoidal waveform according to the welding current; and
a falling time setting section for determining a falling time of the
trapezoidal waveform according to the welding current,
wherein, welding operation is carried out in a manner that the feeding of
the welding wire is timed to at least any one of the peak time, the rising time,
and the falling time according to the welding current.

The arc welding method of the present invention is a consumable
electrode arc welding in which a welding wire feeding rate suitable for a
welding current is determined as an average feeding rate, and the short circuit
state and the arc generation state are alternately generated by changing the
wire feeding periodically and repeatedly between the forward feeding and the
reverse feeding. The method offers arc welding with the average feeding rate
according to a welding current, a predetermined frequency, and a
predetermined velocity amplitude. In the method, at least any one of the
frequency and the velocity amplitude is set to a value suitable for the welding
current.