Electric heating – Metal heating – By arc
Reexamination Certificate
1999-02-10
2001-03-27
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S1370PS
Reexamination Certificate
active
06207927
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
This invention relates to a gas-shielded AC arc welding method and machine, which perform welding by supplying a substantially constant AC voltage between the consumable electrode, which is being fed at a substantially constant rate, and a workpiece.
b) Description of the Related Art
Direct current (DC) arc welding is seldom performed by straight polarity alone (hereinafter called “EN polarity”), because EN polarity tends to form a large droplet at a wire tip, an arc is unstable, large spatters are splashed, and penetration is shallow. On the other hand, reverse polarity (hereinafter called “EP polarity”) features a small droplet, a stable arc and deep penetration. EP polarity has found widespread utility, since good welding results are available not only in large current welding in which an arc length is great but also in so-called short-circuiting transfer welding in which welding is performed by reducing an arc length and frequently repeating short circuiting and arcing with a small current. Further, as a gas-shielded consumable-electrode arc welding method and machine making use of an AC output, there is a technique disclosed in Japanese Patent No. 2,666,315. According to this technique, the level of a current in a period of EP polarity and the length of the period of EP polarity, which provide pinch force suitable for the smooth transfer of a droplet, are set in accordance with the material and diameter of a wire as a consumable electrode, the composition of shielding gas and the like, and the frequency of an output voltage and the level of a current in a period of EN polarity are set in relation to a wire feeding rate. This makes it possible to broaden the range of optimal welding conditions, so that rearcing is assured at alternation without superimposition of high frequency, high voltage, pulses or the like, thereby permitting stable gas-shielded AC arc welding with a consumable electrode.
As a welding machine permitting stable gas-shielded AC arc welding with a consumable electrode, the welding machine disclosed in the above-mentioned Japanese Patent No. 2,666,315 is provided with a wire feeding rate setting device for outputting a wire feeding rate setting signal in correspondence to the level of an output current, an output voltage frequency signal generator for being inputted with the wire feeding rate setting signal and then outputting an output voltage frequency signal which corresponds to a frequency of an output voltage, an EP polarity period signal generator for outputting an EP polarity period energization signal in correspondence to a setting signal set beforehand in accordance with conditions such as the material and diameter of a wire and the composition of shielding gas, an EP polarity current signal generator for outputting an EP polarity current signal in correspondence to the setting signal, an EN polarity period signal generator for outputting an EN polarity period energization signal on the basis of the EP polarity period energization signal as an input, an EN polarity current signal generator for outputting an EN polarity current signal on the basis of the wire feeding rate setting signal as an input, said wire feeding rate setting signal corresponding to the output current, an output current controller for controlling the level of an EN polarity current and that of an EP polarity current on the basis of the EN polarity current signal and the EP polarity current signal as inputs, respectively, and an output current energization period controller for controlling an EN polarity current energization period and EP polarity current energization period on the basis of the EN polarity period energization signal and EP polarity energization period as inputs, respectively, whereby a welding output is controlled.
The above-described conventional technique which makes use of an AC output is a welding method in which a droplet formed at a wire tip is transferred in a contactless manner to a base material by making use of magnetic pinch force produced by an EP polarity current of a critical current level or higher. Accordingly, the stability of an arc is impaired if the length of the arc is shortened and short circuiting is developed. Further, when the welding current level becomes higher, that is, the wire feeding rate becomes faster, the period of an EN polarity current becomes shorter, thereby making it impossible to utilize characteristic features of welding in an EN polarity period, such as shallow penetration and high wire melting rate.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to solve or reduce the above-described problems of the conventional art, and specifically to provide a gas-shielded AC arc welding method and machine making use of a consumable electrode, which make it possible to obtain a stable arcing state even in short-arc welding accompanied by frequent occurrence of short circuiting and also to set the AC frequency and the percentages of EP and EP polarity periods as desired relative to any welding current level, thereby assuring full utilization of the advantages of AC arc welding, i.e., characteristic features such as shallow penetration and high wire melting rate.
In one aspect of the present invention, there is provided a gas-shielded AC arc welding method making use of a consumable electrode for performing welding by supplying a substantially constant AC voltage between the consumable electrode, which is being fed at a substantially constant rate, and a workpiece, which comprises:
setting an EP output voltage V
EP
to be outputted during a period T
EP
of EP polarity so that a welding current during the period of EP polarity becomes not higher than a critical current level; and also
setting an EN output voltage V
EN
, which is to be outputted during a period T
EN
of EN polarity, at a level lower than the EP output voltage V
EP
.
In the above method, a difference between the EP output voltage V
EP
and the EN output voltage V
EN
may be increased as a welding current increases. It is also possible to vary percentages of the period T
EP
of EP polarity and the period T
EN
of EN polarity based on a total time of the periods T
EP
,T
EN
.
In another aspect of the present invention, there is also provided a gas-shielded AC arc welding machine making use of a consumable electrode and adapted to supply a substantially constant alternating voltage between the consumable electrode and a workpiece via an output circuit, whereby a droplet formed at a tip of the consumable electrode is short-circuiting transferred, comprising:
a wire feed controller for feeding the consumable electrode at substantially a constant rate,
a setting device for a period T
EP
of EP polarity,
a setting device for a period T
EN
of EN polarity,
a setting device (
13
) for an EP output voltage V
EP
to be outputted during the period T
EP
of EP polarity,
a setting device (
14
) for an EN output voltage V
EN
to be outputted during the period T
EN
of EN polarity,
an output voltage controller for controlling levels of the EP and EN output voltages V
EP
,V
EN
based on signals outputted from the setting devices for the EP and EN output voltages V
EP
,V
EN
, respectively, and
a polarity period controller for controlling lengths of the periods T
EP
,T
EN
of EP and EN polarities based on signals outputted from the setting devices for the periods T
EP
,T
EN
of EP and EN polarities, respectively, whereby a welding output is controlled; and
a circuit formed of a minimum current compensator, which serves to compensate a lower limit of a welding current, and a reactor connected in series with the minimum current compensator, and connected in parallel with the output circuit.
The above machine may further comprise:
a setting device for an average welding voltage V
av
, and
a setting device for a difference a between the EP output voltage V
EP
and the EN output voltage V
EN
,
whereby the levels of the output EP and EN voltages V
EP
,V
EN
may be set in accordance with the following formulas:
V
EP
&
Ichikawa Kazushige
Mita Tsuneo
Nishikawa Seigo
Nomura Koji
Sakamoto Yoshitaka
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Hitachi Seiko Ltd.
Shaw Clifford C.
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