JP3421014B2 - TIG arc welding method for aluminum alloy - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for periodically switching the polarity of a voltage supplied between a non-consumable electrode and an object to be welded, thereby forming the non-consumable electrode. The present invention relates to a TIG arc welding method for welding by shielding with an inert gas. [0002] Aluminum alloy joints conventionally used as aircraft structural materials are required to have particularly high quality. Therefore, welding is performed by a TIG arc welding method capable of obtaining stable quality. Is being done. When horizontal fillet welding is performed by a normal TIG pulse arc welding method, the penetration ratio P / W of the ratio of the penetration depth P to the weld bead width W is 1 or less as shown in FIG. [0003] Recently, even if the thickness of the plate is increased or horizontal fillet welding is performed, as shown in FIG. 2, the width of the weld bead is as narrow as 6 mm or less. -The penetration of the depth equal to or greater than the bead width, that is, the penetration ratio P / W of the ratio of the penetration depth P to the weld bead width W is set to 1 or more, thereby reducing the excess and reducing the weight. In addition, high strength welding is required. [0004] As a welding method to meet the above requirements,
Conventionally, the following TIG arc welding method or plasma arc welding method has been adopted. The first method focuses on the fact that a TIG arc welding method of DC positive polarity can obtain deep penetration (however, there is no cleaning action for removing an oxide film of an aluminum alloy by arc). Before the occurrence of welding arc, the aluminum oxide film is mechanically or chemically removed, and a non-consumable electrode is supplied with a positive direct current having a negative polarity to perform TIG arc welding. The method has been adopted. In the first method, although a certain deep penetration can be obtained, an extra step of removing the oxide film before the occurrence of welding arc is required because there is no cleaning action due to the arc. Furthermore, even if the oxide film is removed, after a lapse of time, the regenerated oxide film is often caught in the weld metal to generate welding defects. The second method energizes a non-consumable electrode during a positive polarity period when the polarity of the non-consumable electrode is negative and a reverse polarity period when the polarity is positive by applying a low-frequency rectangular AC pulse current. By applying an AC pulse current in which the time ratio or the energizing current value ratio in each period or both are adjusted, T
An IG arc welding method is employed. In the second method, for example, as shown in FIG.
In [mm], horizontal fillet welding is performed and the above penetration depth P
In order to obtain deep penetration, a welding current of 300 [A] or more is required, and in order to reduce the current value as much as possible, preheating is also required. [0006] Aircraft structures are often used for manual welding because of the large number of welds, such as inner and outer surfaces, curves, and curved surfaces, of various and complex shapes. When performing this manual welding, the first
When a current as high as 300 [A] is used as in the welding shown in the figure, a load is applied to the worker's body due to the radiant heat of the arc, and the work can be continued only for a short time. Furthermore, at such a high current, the amount of melting of the filler wire also increases,
The amount of welding increases, and the structure cannot be reduced in weight. Further, the third method employs an AC plasma arc welding method. However, in this method, a large current is required in order to obtain the above-described deep penetration. In this case, a series arc easily occurs, and the electrodes, nozzles, etc. may be burned out. Therefore, in practice, appropriate welding can be performed only up to a medium thickness of 8 mm or less. [0008] (Unpublished prior application technology)
Japanese Patent Application No. 3-169316 (hereinafter referred to as a prior application) has proposed a welding method provided with the following means. This is a TIG arc welding method in which the polarity of a voltage supplied between an electrode and a workpiece is periodically switched to add a filler wire and weld an aluminum alloy. The positive polarity ratio SP / (SP + R) of the positive polarity current of the peak value Is at the current flowing time Ts when the electrode is negative and the reverse polarity current of the peak value Ir at the current flowing time Tr when the electrode is positive.
P) = Is · Ts / (Is · Ts + Ir · Tr) is 0.
An unbalanced rectangular wave alternating current exceeding 6 and less than 0.9 is applied. After the non-equilibrium rectangular wave AC current is supplied for the conduction period Ta, the positive DC current is supplied for the conduction period Td, and the unbalanced rectangular wave AC current and the positive DC current are supplied with the conduction ratio Ta / T.
Switching is performed at a low frequency equal to or less than the switching frequency F = 1 [Hz] with d = ２. The electrodes are shielded with a mixed gas of argon gas and helium gas at substantially the same flow rate ratio. The filler wire is added during the period of non-equilibrium square wave alternating current. Penetration ratio P between penetration depth P and weld bead width W
A welding current for obtaining a weld metal having / W of 1 or more is applied. The following excellent effects are obtained by the welding method of the prior application. The prior application requires a narrow weld bead width of 6 mm or less and a deep penetration equal to or greater than the weld bead width, even if the plate thickness is increased or horizontal fillet welding is performed. By reducing the amount of excess, it is possible to reduce the weight and to weld a high-strength aluminum alloy, and to reduce the fatigue of the operator by reducing the arc heat due to the lower welding current. In addition, since the electrode is less consumed, it can be used continuously for a long time, so that a long object can be continuously welded.
Aircraft structures, nuclear structures, etc., for which safety must be emphasized, because high reliability welding results can be obtained by ensuring that filler wire is added during the predetermined AC current conduction period. Is indispensable. [0010] As described above, the earlier application filed by the present applicant has solved many problems.
However, in the welding method of the prior application, it is necessary to purchase a mixed gas in order to shield the electrodes with a mixed gas of argon gas and helium gas having substantially the same flow ratio, but helium gas is replaced with argon gas. It is more expensive, and the mixed gas of argon gas and helium gas is more expensive than the case of purchasing pure argon gas and helium gas, respectively. Therefore, there is a disadvantage that the cost of the shield gas becomes large in order to carry out the welding method of the prior application. The present invention is a welding method provided with the following means. This is a TIG arc welding method in which the polarity of a voltage supplied between an electrode and a workpiece is periodically switched to weld an aluminum alloy. Positive polarity ratio SP / (SP + RP) of the positive polarity current of the peak value Is at the conduction time Ts when the electrode is negative and the reverse polarity current of the peak value Ir at the conduction time Tr when the electrode is positive.
A non-equilibrium rectangular wave alternating current in which = Is.Ts / (Is.Ts + Ir.Tr) is more than 0.6 and less than 0.9 is applied. After the non-equilibrium rectangular wave AC current is supplied for a period Ta,
A positive pulse current in which the non-consumable electrode is only negative is supplied for a period Td, and the non-equilibrium rectangular wave AC current and the positive pulse current are switched at a conduction ratio Ta / Td = 2/3 or more. Penetration ratio P between penetration depth P and weld bead width W
A welding current for obtaining a weld metal having / W of 1 or more is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a TIG arc welding method for an aluminum alloy according to the present invention will be described with reference to FIGS. (Explanation of FIG. 3) FIG. 3 is a diagram showing a waveform of a welding current applied in the TIG arc welding method of the present invention. In the figure, a positive polarity ratio SP / (SP + RP) = a positive polarity current having a peak value Is at an energizing time Ts when the electrode is negative and a reverse polarity current having a peak value Ir at an energizing time Tr when the electrode is positive. Is · Ts / (Is · Ts + Ir · Tr) (1) After the non-equilibrium rectangular wave AC current Ia exceeding 0.5 exceeds the conduction period Ta, the positive pulse current Id is supplied to the conduction period T.
d is energized. (Explanation of FIGS. 4 and 5) FIG. 5 is a diagram showing the relationship between the positive polarity ratio SP / (SP + RP) (horizontal axis) and the penetration ratio P / W (vertical axis) in the above equation (1). It is.
In the figure, the penetration ratio P / W is 10 [mm]
The welding speed was set to 20 [A] at an average value of 250 [A] of full-wave rectification of the welding current on a flat plate of aluminum alloy of material A5083.
[Cm / min], the positive polarity ratio SP / (SP + RP) was changed, and argon gas was used as a shield gas to obtain a TIG electrode.
Depth P and welding bead shown in FIG.
4 shows the relationship between the gate width W and the penetration ratio P / W.
As shown in FIG. 5, when the positive polarity ratio SP / (SP + RP) exceeds 0.6, the penetration ratio P / W becomes large. However, on the other hand, in TIG arc welding of an aluminum alloy, the positive polarity ratio SP / (SP + RP) is 0.1%.
If it is 9 or more, it is difficult to secure a cleaning width for obtaining the weld bead width W, and an oxide film is formed on the weld bead. Therefore, the positive polarity ratio SP / (SP + RP)
Is suitably in the range of more than 0.6 and less than 0.9. Even if a non-equilibrium rectangular wave alternating current Ia having a positive polarity ratio of SP / (SP + RP) = 0.7 is applied using pure argon gas, the TIG arc welding method of the present invention is used. The energizing period Td of the positive polarity pulse current Id of the welding current shown in FIG.
If the ratio exceeds the predetermined ratio, there is no longer any area subjected to the cleaning action during the energization period Td. Therefore, as a result of an experiment, if the conduction ratio Ta / Td between Ta and Td is set to 2/3 or more, the cleaning effect remains even during the conduction period Td of the positive pulse current Id. ing. Further, the filler wire should be added during the energization period Ta of the non-equilibrium rectangular wave alternating current Ia in order to perform the cleaning action of the filler wire to be added. In order to secure time, it is necessary to switch the energizing period Ta of the non-equilibrium rectangular wave AC current Ia and the energizing period Td of the positive pulse current Id at a low frequency whose switching frequency F is 1 [Hz] or less. When no filler wire is added, switching can be performed even at a switching frequency F of 1 [Hz] or more. Aluminum / magnesium alloy A508
Feather-like crystal grains, that is, feather-like crystals, are often generated in the center of the weld bead of the weld metal obtained when TIG arc welding of No. 3 is performed. These feathered crystals may spread over almost the entire area of the weld bead, and are peculiar columnar crystals. The presence of these crystals significantly reduces the ductility of the weld metal. In the conventional AC TIG arc welding method, and in the TIG arc welding method of switching between the non-equilibrium rectangular wave AC current and the positive DC current of the prior application, feather-like crystals are easily generated depending on the set conditions. However, in the TIG arc welding method of the present invention, feathered crystals do not occur. (Explanation of FIG. 6 and FIG. 7) FIG.
FIG. 1 is a block diagram of a welding apparatus for performing an IG arc welding method. In the figure, reference numerals 1 and 2 denote an object to be welded, 4 denotes a consumable electrode, 10 denotes a DC power supply circuit obtained by rectifying a commercial AC power supply, L1 denotes a DC reactor, C1 denotes a rectifying capacitor, and TR1 and TR2 denote reverse polarity currents. The energizing transistors, TS1 and TS2, are transistors for energizing positive current. PC1 is a polarity switching circuit that controls conduction and cutoff of these transistors, and outputs a polarity switching signal Pc1 shown in FIG. NT2 polarity switching signal Pc
1 is a NOT circuit which outputs an inverted signal Nt2 shown in FIG. 7B, and AM1 is an astable multivibrator.
FIG. 7 (C) which shows an energizing ratio Ta / Td of an energizing period Ta of an unbalanced rectangular wave AC current Ia and an energizing period Td of a positive pulse current Id by a switching frequency F [Hz]. The low-frequency signal Am1 is output. ND1
Is input with the inverted signal Nt2 and the low frequency signal Am1 and when both signals or one of the signals is at the low level L,
NAN that outputs positive conduction signal Ss shown in FIG.
This is a D circuit. NT1 receives the positive polarity conduction signal Ss as input and outputs an inverted polarity conduction signal Sr as shown in FIG. 7 (E). The positive polarity conduction signal Ss is generated by transistors TS1 and T1.
S2 is turned on and off, and the reverse polarity conduction signal Sr turns on and off the transistors TR1 and TR2. By turning on and off these transistors, the unbalanced rectangular wave AC current Ia and the positive pulse current shown in FIG. And Id. IP is a pulse current setting circuit, as shown in FIG.
IB is a base current setting circuit which outputs a base current setting signal Ib shown in FIG. 7 (G). AM2 is an astable multivibrator circuit which outputs a pulse signal Am2 shown in FIG. 7 (H), and a pulse base current switching circuit SW1 outputs a pulse current setting signal Ip and a base current setting signal Ib. Pulse signal Am2
A pulse control signal S1 shown in FIG. 7 (I), which switches at the switching frequency Fd, is output.
The current supply ratio Tp / Tb of the current supply period Tb is determined. IM is an unbalanced square-wave AC current setting circuit.
An unbalanced rectangular wave AC current setting signal Im shown in (J) is output. The unbalanced rectangular wave AC current setting signal / pulse control signal switching circuit SW2 outputs the unbalanced rectangular wave AC current setting signal Im.
And the pulse control signal S1 are switched at the switching frequency F of the low frequency signal Am1, and the pulse control signal S2 is output.
a and the energization ratio Ta / T between the positive polarity pulse current energization time Td
d is determined. A comparison circuit CM1 compares the pulse control signal S2 with the welding current detection signal Ct of the welding current detection circuit CT, outputs a welding current signal Cm1, and inputs it to the DC power supply circuit 10. Therefore, the welding device shown in FIG. 6 applies a welding current I between the workpieces 1 and 2 and the electrode 4 in which the non-equilibrium rectangular wave alternating current Ia and the positive pulse current Id shown in FIG. . The TIG arc welding method of the prior application uses a mixed gas of argon gas and helium gas having substantially the same flow rate ratio as the shield gas, so that the cost of the shield gas is large. On the other hand, the welding method of the present invention switches the current between the non-equilibrium rectangular wave AC current and the positive pulse current, and applies a pure argon gas as a shield gas. Even if the thickness is large or horizontal fillet welding is performed, a narrow weld bead width of 6 mm or less and a deep penetration equal to or greater than the weld bead width can be used. It is possible to reduce the weight by reducing the height and to weld a high-strength aluminum alloy. Furthermore, by implementing the welding method of the present invention, it is possible to prevent the generation of feathers which lower the ductility of the weld metal, and to obtain a high quality weld bead shape.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a relationship between a penetration depth P and a weld bead width W of horizontal fillet welding by a normal TIG pulse arc welding method. FIG. 2 is a view showing a relationship between a penetration depth P of horizontal fillet welding and a weld bead width W required for recent aircraft structures. FIG. 3 is a view showing a waveform of a welding current applied in the TIG arc welding method of the present invention. FIG. 4 is a diagram showing a relationship between a penetration depth P and a weld bead width W. FIG. 5 is a diagram showing a relationship between a positive polarity ratio SP / (SP + RP) (horizontal axis) and a penetration ratio P / W (vertical axis). FIG. 6 is a block diagram of a welding apparatus for implementing the TIG arc welding method of the present invention. FIG. 7 is a diagram showing a waveform of an output signal of each circuit in the block diagram of FIG. 6; [Description of Signs] 1, 2 Welded object 4 Consumable electrode Ts Energizing time when electrode is negative Tr Energizing time when electrode is positive I Welding current (average value of full-wave rectification) Is electrode is negative The peak value Ir of the welding current (positive current) at the time The peak value Ia of the welding current (reverse polarity current) when the electrode is positive Non-balanced rectangular wave AC current Id Positive pulse current Ta of the non-balanced rectangular wave AC current Ia Energizing period Td Energizing period Ta / Td of the positive pulse current Id Energizing ratio SP / (SP + RP) Positive ratio = Is · Ts /
(Is · Ts + Ir · Tr) F Switching frequency Fd between non-equilibrium rectangular wave alternating current Ia and positive pulse current Id Pulse frequency P of positive pulse current Id Penetration depth W Weld bead width P / W Penetration ratio

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ identification symbol FI // B23K 103: 10 B23K 103: 10 (58) Investigated field (Int.Cl. ⁷ , DB name) B23K 9/073 B23K 9 / 09 B23K 9/167 B23K 9/23 H02M 9/00 B23K 103: 10

Claims (1)

(57) Claims 1. The polarity of the voltage supplied between the non-consumable electrode and the workpiece is periodically switched to shield the non-consumable electrode with an inert gas. In the TIG arc welding method for welding an aluminum alloy, the positive current of the peak value Is of the welding current during the conduction time Ts when the non-consumable electrode is negative and the current when the non-consumable electrode is positive are used. Time T
The positive polarity ratio SP / (SP + RP) = Is · Ts / (Is · Ts + I) of the peak value Ir of the welding current r with the reverse polarity current
(r · Tr) is greater than 0.6 and less than 0.9, and a non-equilibrium rectangular wave alternating current is supplied for a period Ta, and then a positive pulse current for which the non-consumable electrode is only negative is supplied for a period Td. A non-equilibrium rectangular wave alternating current and a positive pulse current are switched at an energization ratio Ta / Td = 2/3 or more, and a weld metal having a penetration ratio P / W of 1 or more between a penetration depth P and a weld bead width W. A TIG arc welding method for aluminum alloys, in which a welding current is applied to weld aluminum alloy.