Electric heating – Metal heating – By arc
Reexamination Certificate
2001-09-12
2003-07-29
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S130510
Reexamination Certificate
active
06600135
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for controlling AC (Alternating Current) pulse arc welding, and a welding power source apparatus, and in particular, to a method and an apparatus for controlling consumable electrode type AC pulse arc welding, and a welding power source apparatus for use in consumable electrode type AC pulse arc welding.
2. Description of the Prior Art
In an AC pulse arc welding method which is executed by supplying a welding current Iw flowing between a welding wire and an object to be welded with feeding the welding wire at a feeding speed, a one-period process for supplying the welding current is repeatedly executed where the one-period process including:
(a) a first process during a peak time interval Tp for supplying a welding current Iw having a peak current Ip for causing droplet transfer, which is larger than a predetermined threshold current (or critical current) and which flows from the welding wire to the object to be welded with a positive electrode polarity;
(b) a second process during a negative electrode time interval Ten for thereafter supplying a welding current Iw having a negative electrode current Ien for stopping droplet transfer which flows from the object to be welded to the welding wire with a negative electrode polarity; and
(c) a third process during a base time interval Tb for thereafter supplying a welding current Iw having a base current Ib for stopping droplet transfer which is smaller than the threshold current with a positive electrode polarity.
The above-mentioned AC pulse arc welding method is utilized for welding materials of aluminum and its alloy, stainless steel, steel or the like, and in particular, it is utilized in many cases where the material to be welded is a thin plate having a thickness of several mm or less. The reason for this is as follows. The object to be welded becomes a cathode during the time interval of the positive electrode polarity, and the amount of heat entering into the object to be welded becomes large due to the cathode drop voltage. On the other hand, the object to be welded becomes an anode during the time interval of the negative electrode polarity, and the amount of heat entering into the object to be welded becomes smaller than that in the time interval of the positive electrode polarity since the anode drop voltage is smaller than the cathode drop voltage. In the same manner, since the welding wire becomes the anode during the time interval of the positive electrode polarity, the amount of heat entrance becomes small, and the melting rate of the welding wire becomes smaller. On the other hand, since the welding wire becomes the cathode during the time interval of they negative electrode polarity, the amount of heat entrance becomes large, and the melting rate of the welding wire becomes larger. Accordingly, in the AC pulse arc welding method, the amount of heat entering into the object to be welded and into the welding wire can be adjusted to a desired value by controlling the time ratio of the time interval of the positive electrode polarity to the time interval of the negative electrode polarity, and this leads to that thin plate welding can be acceptably carried out. In the following, an AC pulse arc welding control method and a welding power source apparatus according to a prior art will be described.
FIG. 1
shows an operation of a method for controlling AC pulse arc welding according to a prior art, wherein FIG.
1
(A) is a waveform chart showing a welding current Iw, FIG.
1
(B) is a waveform chart showing a welding voltage Vw, and FIG.
1
(C) is a side view showing a status of droplet transfer in each of four timings. In
FIG. 1
, EN denotes the negative electrode polarity, and EP represents the positive electrode polarity. In the following, a description is given with reference to FIG.
1
.
<1>Time Interval t
1
to t
2
During Peak Time Interval Tp
As shown in FIG.
1
(A), the peak current Ip is made to flow with the positive electrode polarity during the peak time interval Tp. Usually, the values of both the peak time interval Tp and the peak current Ip are set in advance so that droplets from the welding wire
1
is transferred to the object
2
to be welded by one droplet per one pulse by means of arc heat and an electromagnetic pinching force. In addition, as shown in FIG.
1
(B), during this time interval, the peak voltage Vp corresponding to the flow of the peak current Ip is applied between the welding wire
1
with the positive electrode polarity and the object
2
to be welded with the negative electrode polarity.
<2>Time Interval t
2
to t
3
During Negative Electrode Time Interval Ten
At the next timing t
2
, the positive electrode polarity is switched to the negative electrode polarity, and then, the negative electrode current Ien is made to flow during the negative electrode time interval Ten as shown in FIG.
1
(A). Usually, the values of both the negative electrode time interval Ten and the negative electrode current Ien are set in advance to appropriate values, respectively, according to the material quality, plate thickness, shape or the like of the object
2
to be welded, so as not to cause droplet transfer. In addition, as shown in FIG.
1
(B), during this time interval, the negative electrode voltage Ven corresponding to the flow of the above negative electrode current Ien is applied between the welding wire
1
with the negative electrode polarity and the object
2
to be welded with the positive electrode polarity.
<3>Time Interval t
3
to t
4
During Base Time Interval Tb
At the next timing t
3
, the negative electrode polarity is again switched to the positive electrode polarity, and then, as shown in FIG.
1
(A), a base current Ib is made to flow, which is set in advance so as to stop droplet transfer during the base time interval Tb. In addition, during this time interval, a base voltage Vb corresponding to the flow of the base current Ib is applied between the welding wire
1
with the positive electrode polarity and the object
2
to be welded with the negative electrode polarity. The base time interval Tb is automatically set by the following modulation control. Namely, as shown in FIG.
1
(B) the timing of completion of the base time interval Tb is controlled by the modulation control so as to be such a timing that an integral value Iv of an error between the welding voltage Vw for the time interval of positive electrode polarity and the preset voltage setting signal Vs becomes 0V,
In the case of
FIG. 1
, the welding voltage Vw for the time interval of the positive electrode plurality includes the peak voltage Vp during the peak time interval Tp, and the base voltage Vb during the, base time interval Tb. Accordingly, the timing of completion of the base time interval Tb which is called a timing t
4
is determined according to the following equation so that the sum of (a) the integral value Iv
1
=∫(Vp−Vs) dt of the error between the peak voltage value Vp during the peak time interval Tp and the voltage setting signal Vs, and (b) the integral value Iv
2
=∫(Vb−Vs) dt of the error between the base voltage value Vb during the base time interval Tb and the voltage setting signal Vs becomes 0V.
Iv
=∫(
Vp−Vs
)
dt
+∫(
Vb−Vs
)
dt
=0 (1)
The above-mentioned modulation control will be described in detail later with reference to FIG.
3
. Further, at the timing t
4
and thereafter, the AC pulse arc welding is carried out by executing the one-period process including the above three processes <1> to <3> from the timing t
1
to the timing t
3
.
<4>Status of Droplet Transfer During Each Above Time Interval
As shown in FIG.
1
(C
1
), the melting of the welding wire
1
is promoted by the flow of the peak current Ip which has a large value so that the droplet
1
a
grows large during the peak time interval Tp. At that time, an arc
3
during the positive electrode polarit
Daihen Corporation
Scully Scott Murphy & Presser
Shaw Clifford C.
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