JP2711138B2 - AC TIG welding method and apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC tag welding method and apparatus, and particularly to an AC tag welding method and apparatus suitable for controlling the penetration depth of aluminum and its alloys. About.

[Conventional technology]

Conventionally, when controlling the penetration depth in AC tag welding, for example, as described in Japanese Patent Application Laid-Open No. 54-121255, the average value of the rod minus (hereinafter abbreviated as EN) and the plus (Hereinafter, abbreviated as EP.) The ratio of the current to the average value was changed. Further, with the recent development of inverters for welding power sources, for example, as described in Japanese Patent Application Laid-Open No. 63-13677, the EP current and the EN
A method of controlling the penetration depth with an electric current has also been proposed.

[Problems to be solved by the invention]

FIG. 6 shows the results of measuring the arc pressure as a means for comparing the arc concentration between AC welding at commercial frequency and EN DC welding. As can be seen from the figure, the arc is wider in AC welding than in EN DC welding, and the arc pressure is lower.
It turns out that it is 1/2 or less.

That is, in AC welding, an EN period in which a concentrated arc is formed by forming a cathode point on an electrode and an EP period in which a dispersed arc is formed by the cathode point moving irregularly on the base material surface are alternately repeated. Therefore, the arc concentration is reduced as compared with DC welding only during the EN period.

As a result, when it is necessary to reduce the welding current, there is a problem that the arc does not concentrate and welding workability is poor.

However, in the above-mentioned two known examples, the former does not examine the influence of the AC frequency on the arc concentration. Also, in the latter, the AC frequency will change slightly by reducing the EP period ratio,
The effect of the AC frequency on the arc concentration is not considered.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and in AC tag welding of aluminum or an aluminum alloy or the like, improve the arc concentration in a small current region and perform a welding operation from a small current region to a large current region. It is an object of the present invention to provide a method and an apparatus for AC Tail welding suitable for improving the weldability.

[Means for solving the problem]

The present inventor further repeated welding tests and examined the effect of the AC frequency on welding workability. As a result, the above-mentioned problem is solved by setting the AC frequency at the time of welding high and setting one or both of the AC frequencies at the time of arc starting or at the time of arc stopping lower than the AC frequency at the time of welding. Found to be.

[Operation] When the welding current is kept constant and the AC frequency is changed, as shown in FIGS. 4 and 5, the penetration depth PD and the bead width BW increase as the AC frequency increases, The cleaning width CW decreases. That is, even if the welding current is the same, if the AC frequency is set high, the arc concentration can be improved, and the welding workability can be improved.

On the other hand, when the base material is aluminum and its alloy, EN
During the period, the arc voltage decreases because electrons are easily emitted from the electrodes, but during the EP period, the arc voltage increases because electrons are not easily emitted from the base material. This tendency is remarkable at the time of starting an arc in which a weld pool is not formed as compared with the welding period in which the weld pool is formed in the base material, and a state in which no arc is generated at the time of starting the arc is likely to occur.

In particular, when welding with a deep penetration depth, cracks and shrinkage holes are likely to occur around the final solidified portion at the arc stop portion, which is the welding end portion.

Therefore, the arc start is facilitated by lowering the AC frequency at the time of starting the arc, and the concentrated AC and deep penetration can be obtained by increasing the AC frequency at the time of welding, and the AC frequency at the time of stopping the arc is reduced. This can improve the quality of the final solidified portion.

〔Example〕

FIG. 1 shows a first embodiment of an AC tag welding apparatus for carrying out the present invention.

In FIG. 1, reference numeral 1 denotes an input rectifier for rectifying a commercial frequency alternating current into a direct current. Reference numeral 2 denotes an input-side inverter composed of a MOS-FET, which converts the direct current into a high-frequency alternating current of about 20 kHz. 3 is a pulse width control circuit for controlling the pulse width of the high frequency AC. Reference numeral 4 denotes a welding transformer whose input side is connected to the input side inverter. Reference numeral 5 denotes an output-side rectifier connected to the output side of the welding transformer 4, which converts the high-frequency AC into DC again. 6 is a current detector. 7 is an output side rectifier 5
DC reactor for smoothing the DC output rectified by. Reference numeral 8 denotes an output inverter for converting DC to AC again for performing AC welding. The output side inverter 8
Is a frequency setting device 9a, 9b, 9c and a variable EP period ratio setting device 10 [where EP period ratio = EP period / (EP period +
EN period)], an AC output is applied between the electrode 14 held by the welding torch 13 and the base material 15 under the control of the drive circuit 12 based on the signal from the rectangular wave generator 11 set in [1]. 16
Is a switching device. Reference numerals 18a, 18b, and 18c denote welding current setting units, which are controlled by a pulse width control circuit 3 via a switching device 20 and an error amplifier 19.
It is connected to the. Reference numeral 17 denotes a welding condition setting device for setting the AC frequency according to the order of the welding operation.
And switches the contacts of the switching device 20, and sets the frequency setting devices 9a, 9
One of b and 9c is connected to the rectangular wave generator 11, and one of the welding current setting units 18a, 18b and 18c is connected to the error amplifier 19. At the time of welding, the error amplifier 19 outputs a current corresponding to the input current value to the output-side inverter 8 detected by the current detector 6 and the welding current value set by one of the welding current setting units 18a, 18b, 18c. Value and compare
The pulse width control circuit 3 is controlled so that the average value of the input current flowing through the current detector 6 becomes a current value corresponding to the welding current value. That is, for any of the frequency setting devices 9a and 9b or the frequency setting device 9c, the average value of the input current flowing through the current detector 6 is maintained at the input current value corresponding to the welding current value.

 Hereinafter, the operation will be described.

In performing welding, welding conditions are set in advance according to the workpiece to be welded. That is, the welding current setting unit 18a
The welding current value at the time of starting the arc is
b, the welding current value during welding, the welding current setting unit 18c, the welding current value when the arc is stopped, and the frequency setting unit 9a.
, The AC frequency at the time of arc starting, the AC frequency at the time of welding by the frequency setting device 9b, the AC frequency at the time of arc stopping by the frequency setting device 9c, and the EP period setting device 10.
Set the EP period ratio. Here, the setting of the frequency of the AC output is set with reference to already obtained data, for example, FIG. 4 or FIG. In addition, FIG.
A 3mm thick aluminum alloy (A5052) with a welding current of 100
A, EP period ratio 30%, distance between electrode and base material 3mm, welding speed
This is data of penetration depth PD, bead width BW, and cleaning width CW when performing tag welding with 300 mm / min and shield gas Ar10 1 / min. FIG. 5 shows that aluminum (A1100) having a thickness of 6 mm was welded at a welding current of 200 A and an EP period ratio of 30.
%, Distance between electrode and base material 3mm, welding speed 250mm / min, penetration depth when performing tag welding with shield gas Ar15 1 / min
Data of PD, bead width BW, and cleaning width CW.

Then, at the time of welding, according to a command from the welding condition setting device 17, welding is performed at a welding current and frequency according to the order of the welding operation. That is, as shown in FIG. 2, a low-frequency alternating current having a small current value is output during the period Ts during the generation of the arc starting signal. When the arc start signal ends, a high-frequency alternating current having a large current value is output, and a low-frequency alternating current having a small current value is output again in a period Tc from when the arc stop signal is applied to when the arc stop signal ends. . The arc start period Ts and the arc end period Tc
May use a timer circuit. In the case of manual welding, a torch switch signal (not shown) may be used.

By the way, it is well known that in AC tag welding, even if the EP period ratio is changed, an effect similar to that of changing the AC frequency is obtained. Then, when the EP period ratio is changed simultaneously with the AC frequency, the present invention becomes more effective.

FIG. 3 shows a second embodiment of an AC tag welding apparatus for carrying out the present invention.

In the second embodiment, the EP period ratio setting device 10 in the first embodiment is replaced by three EP period ratio setting devices 10a, 10b, and 10c.
This is connected to the rectangular wave generator 11 via the switching device 21, and is effective for, for example, all-position welding of a horizontal fixed tube. In other words, in all-position welding of a horizontal fixed pipe, it is necessary to change not only the welding conditions in the first layer, the middle layer, and the last layer, but also the welding conditions depending on the welding position. By changing the frequency, a uniform weld can be obtained.

In the second embodiment, the switching devices 16, 2
At least two of 0 and 21 may be synchronized.

Further, in the above two embodiments, the current and the AC frequency are changed stepwise, but these may be changed in a slope shape.

Further, the AC frequency at the time of starting the arc and the AC frequency at the time of stopping the arc may be the same, or may be a commercial frequency.

In addition, the frequency at the time of starting the arc, at the time of welding, and at the time of stopping the arc are individually set, but the AC frequency at the time of starting the arc or at the time of stopping the arc is defined as the reference value. By automatically setting the value to about%, the control circuit can be simplified.

〔The invention's effect〕

As described above in detail, according to the present invention, in AC tag welding of aluminum or aluminum alloy, etc., it is possible to improve the concentration of the arc with a small current by increasing the AC frequency. Furthermore, since the AC frequency is set low when starting the arc or when stopping the arc, the arc does not break when starting the arc, and
In particular, even when welding having a deep penetration depth, the quality of the arc stop portion, that is, the final solidified portion can be improved.

Therefore, there is an effect that welding workability and welding quality can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an AC tag welding apparatus according to the present invention. FIG. 2 is a diagram for explaining the operation of the first embodiment. FIG. 3 is a view of a second embodiment of the present invention. 4 and 5 show examples of data used when setting a frequency according to the present invention. FIG. 6 shows the measurement results of the arc pressure. 1 ... input side rectifier, 2 ... input side inverter, 3 ... pulse width control circuit, 4 ... welding transformer, 5 ... output side rectifier, 8 ... output side inverter, 9a, 9b, 9c ... frequency Setting device, 10, 10a, 10b, 10c: EP period ratio setting device, 14: Electrode, 15: Base material, 16, 20, 21, ... Switching device, 17: Welding condition setting device, 18, 18a , 18b, 18c …… Welding current setting device, 19 …… Error amplifier,

Claims (5)

(57) [Claims] In an AC tag welding method for setting an AC frequency at the time of welding higher than a commercial frequency, one or both of an AC frequency during an arc start and an arc stop is lower than an AC frequency during a welding. An AC tag welding method characterized by setting. 2. The AC tag welding method according to claim 1, wherein the welding current is changed in accordance with a set value of the AC frequency. 3. The method according to claim 1, wherein a ratio between an electrode plus period and an electrode minus period in one cycle of the AC output is changed in accordance with a set value of the AC frequency. The described AC tag welding method. 4. An AC tag welding apparatus for applying an AC output between a non-consumable electrode and a base material, wherein at least two current setting devices connected to the first switching means for setting a welding current; A DC power supply connected to the switching means for outputting a DC output according to the set value of the current setting device; a conversion means connected to the DC power supply for converting the DC output to an AC output; A period setting means for setting a period between the electrode plus and the electrode minus in one cycle; a second switching means connected to the conversion means; and at least two of the two switching means connected to the second switching means for setting the frequency of the AC frequency. AC TIG welding comprising a frequency setting device and a command device connected to the first switching device and the second switching device, wherein the first switching device and the second switching device are switched in synchronization with each other. Dress . 5. The period setting means is a third switching means and at least two period setting devices connected to the third switching means, wherein at least two of the first to third switching means are synchronized. 5. The AC tag welding device according to claim 4, wherein the switching is performed.