Electric heating – Metal heating – By arc
Reexamination Certificate
1998-07-09
2001-05-01
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S130510, C219S1370WM
Reexamination Certificate
active
06225598
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel method of high frequency pulse arc welding and an apparatus therefor.
It is known that, in a conventional high frequency pulse arc welding method, as the peak value of the high frequency pulse current is increased, a quenching force produced by electromagnetic force becomes larger, and, consequently, the stiffness of the arc and the pressure of the arc are increased. It is also believed that the vibration effect of the high frequency peak pulse current can decrease the grain size of a welding portion and reduce blowholes. However, the welding current used in actual welding includes a ripple current due to the inductance L of the welding cable, as shown in a typical apparatus in
FIG. 12
, and, accordingly, there is a disadvantage in that the effect of the high frequency pulse current cannot be obtained sufficiently.
Further, in a conventional direct current TIG arc welding method, a stiffness of the arc is obtained by a gas pinching force, using a mixed gas of argon and hydrogen for the shielding gas, as a means for giving the arc stiffness (directivity). This stiff arc is used for welding with a very narrow edge groove on austenitic stainless steels. However, this welding method cannot be used for the welding of ferritic stainless steels or certain other steels because of hydrogen embrittlement. Further, this welding method cannot be used for the welding of aluminum or aluminum base alloys because hydrogen tends to cause the formation of a blowhole. On the other hand, the conventional pulse welding cannot be applied to aluminum welding either because of the lack of cleaning action.
Arc welding methods and apparatuses based on the use of a high frequency pulse current are disclosed in Japanese Patent Application Laid-Open No. 53-119758, Japanese Patent Application Laid-Open No. 54-131548, and Japanese Patent Application Laid-Open No. 59-92169.
In the past, the pulse arc welding method has produced a small arc stiffness, and, consequently, it has been difficult to perform welding with a narrow weld edge groove and welding with a deep melting penetration.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of high frequency pulse welding and an apparatus for high frequency pulse welding in which the effect of the inductance of the welding cable is eliminated, and wherein the high frequency electromagnetic pinch force is large, and a stiff arc and an effective cleaning action can be obtained.
Another object of the present invention is to provide a method of high frequency pulse welding and an apparatus for high frequency pulse welding which exhibits an excellent stiffness (directivity) and stability in the arc, and which is particularly capable of preventing the arc from burning on side walls of a very narrow weld edge groove having a gap smaller than 6 mm, and which is further capable of performing deep melting penetration welding and high speed welding of aluminum or aluminum base alloys. In addition to this, an object of the present invention is to provide a butt welded structure and a rail-car body structure manufactured by the method and the apparatus.
A further object of the present invention is to provide a structure made of a carbon steel or a low-alloy steel manufactured by butt welding with a narrow weld edge groove, and a nuclear power plant using the butt welded structures.
The present invention is characterized by the fact that, in a method of high frequency pulse arc welding which is performed by generating an arc between an electrode (inconsumable or consumable) arranged near a portion of a base metal to be welded, and the base metal with a main pulse current, the stiffness or directivity of the arc is improved by applying a reverse pulse current having a polarity opposite to a polarity of the main pulse current between the electrode and the base metal when the main pulse current is shifted from ON to OFF to make the rising and falling edges of the pulses steeper.
Making the rising and falling edges of the welding current pulses steeper is attributed to an increase in the quantity of the current per unit time, and so the quantity of the current per unit time is set so as to be not smaller than 50 A per 1 &mgr;second, preferably not smaller than 100 A per 1 &mgr;second, and a quantity of current above 200 A per 1 &mgr;second is particularly preferable. In order to do so, the welding load voltage is set to a voltage not lower than 60 V, and preferably to a voltage not lower than 80 V. The welding load voltage is preferably set to a voltage within a range of 60 to 200 V, and a welding load voltage set within a range of 80 to 160 V is particularly preferable.
The present invention is characterized by the fact that, in a method for TIG high frequency pulse arc welding with a very narrow weld edge groove having a weld edge gap width below 6 mm, a directive arc is produced between an inconsumable electrode and a base metal by a main pulse current to prevent a side-wall arc and to stably maintain the arc in the narrow weld edge groove.
A method for high frequency pulse arc welding of aluminum or an aluminum base alloy in accordance with the present invention is characterized by the fact that a cleaning action and a directive arc are produced by properly selecting a current conducting time period ratio of the main pulse current to the reverse pulse current, or a peak current ratio of the main pulse current to the reverse pulse current, to make deep melting penetration welding and high speed welding possible.
The present invention relates to an apparatus for high frequency pulse arc welding which comprises a welding power source for supplying a welding current; a converter for converting the welding current to a pulse welding current having a different polarity, the converter being composed of semiconductors, such as IGBT (insulated-gate bipolar transistor) elements or the like; and a control unit for controlling the welding peak current, the conducting current ratio and the peak current ratio as described above. Therein, it is preferable that the welding power source and the converter are physically separated and electrically connected using a welding cable or a coaxial cable extending between them.
The present invention is characterized by a method for high frequency pulse arc welding which is performed by generating an arc between an electrode (inconsumable or consumable) consumable electrode arranged near a portion of a base metal to be welded and the base metal with a main pulse current, wherein, when the main pulse current is shifted from ON to OFF, a reverse pulse current having a polarity opposite to the polarity of the main pulse current is supplied between the electrode and the base metal to make the arc directive by making the rising and falling edges of the main pulse current and the reverse pulse current steeper.
It is preferable that a current stopping period is provided during a period between the reverse pulse current and the main pulse current following the reverse pulse current. It is also preferable that a base current smaller than the main pulse current flows during a period between the reverse pulse current and the main pulse current following said reverse pulse current.
It is preferable that either of the peak values of the main pulse current and the base current and the current conducting time periods of the main pulse current and the base current are periodically varied. It is preferable that the main pulse current is varied with a frequency in a range of several Hz to several tens of Hz and the molten metal is stirred to prevent grain growth.
It is preferable that the reverse pulse current, the base current and the current conducting time period, as well as the current stopping period, can be independently varied.
The present invention is characterized by a method of high frequency pulse arc welding which is performed by generating an arc between an inconsumable electrode arranged near a portion of a base metal to be welded and the base metal with a m
Funamoto Takao
Nihei Masayasu
Onuki Jin
Onuma Akira
Sakurai Izumi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Shaw Clifford C.
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