JPS639913B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in alternating current arc welding methods.

Generally, AC arc welding machines are used for non-consumable arc welding of active metals such as aluminum and magnesium.

In this case, if a movable core type AC arc welding machine is used, due to the difference in electron emission ability between the electrode and the workpiece, during the positive polarity period when the electrode is negative with respect to the workpiece, and when the electrode is The arc voltage waveform and welding current waveform are different during the period of positive reverse polarity. That is, Figure 1a shows the arc voltage waveform, and during the period of positive polarity when the electrode becomes negative, Ts
The average value or peak value of the arc voltage of Tr is smaller than that of Tr during the period of reverse polarity, and FIG. 1b shows the welding current waveform, and the average value or peak value of Ts during the period of positive polarity is During the period of reverse polarity, it becomes larger than that of the Tr, producing a so-called rectifying effect.

Now, assuming that the average value of the welding current during the period of positive polarity is Ism, and that of the reverse polarity as Irm, the applied current during the period of positive polarity and the applied current during the period of reverse polarity are as shown in Figure 2. For example, by using a thyristor-type AC arc welding machine that can control each average value or each peak value, while keeping Ism+Irm approximately constant, the ratio of current flowing during the period of positive polarity (hereinafter referred to as SP
Figures 3a and 3b show the bead shapes when the SP ratio = Ism/(Ism + Irm) is changed. In Fig. 2, 1 and 1 are input terminals of a welding machine, 2 is a welding transformer, 3 is an electrode, 4 is a workpiece to be welded, 5 is an arc, 6a and 6b are reactors, 7a and 7b are thyristors, 8a, 8b is an ignition circuit, and 9a and 9b are output current detection and control circuits. Further, in FIG. 3a, P indicates the penetration depth of the molten metal 4a, Wb indicates the melting width or beat width, and Wc indicates the cleaning width. Figure b is
This figure shows changes in the penetration depth P, bead width Wb, and cleaning width Wc shown in FIG. As shown in Figure b,
The cleaning width Wc decreases as the SP ratio increases, the bead width Wb gradually decreases, and the penetration depth P reaches a minimum near 50% of the SP ratio.
On the other hand, non-consumable electrodes, with increasing SP ratio,
By reducing the reverse polarity current that generates heat when the electrode becomes positive with respect to the object to be welded, wear of the electrode is reduced. In other words, in order to increase the penetration depth P, it is necessary to increase the SP ratio, and conversely, in order to increase the cleaning width Wc, it is necessary to decrease the SP ratio, and in addition, the allowable current flowing to the electrode In order to increase , it is necessary to increase the SP ratio. Furthermore, the duration of the period in which the SP ratio is large and the period in which the SP ratio is small and the repetition period thereof affect the shape of the molten pool. In addition, the above-mentioned SP ratio is expressed by the average value Ism of the current flowing during the period of positive polarity and the average value Irm of the current flowing during the period of reverse polarity. Even when expressed in terms of peak value, the change is approximately the same as that shown in FIG. 3b.

Based on the above studies, the arc welding method of the present invention uses an alternating current that has an effect during the period of positive polarity and an effect during the period of reverse polarity, and the current value during the period of positive polarity is changed. A current is passed in which the ratio of the current value during the period of reverse polarity is a first ratio, and then the ratio of the current value during the period of positive polarity to the current value during the period of reverse polarity is a second ratio. The present invention proposes an AC arc welding method in which a current of a first ratio and a second ratio of current are applied repeatedly to perform welding.

Hereinafter, the arc welding method of the present invention will be explained with reference to FIGS. 4a to 4c.

Figure a shows the sum of the peak value of the output current during the period of positive polarity and the peak value of the output current during the period of reverse polarity supplied from the thyristor-type AC arc welding machine shown in Figure 2, Is ₁ + Ir ₁ or Is ₂ + Ir ₂ , that is, the value from the positive peak value to the negative peak value (peak-to-peak value) is held constant, or the average value of the output current during the period of positive polarity and the output current during the period of opposite polarity. A first state in which the output current value during the period of positive polarity is larger than the output current value during the period of reverse polarity while holding the sum with the average value of The waveform of the changing current when the second state in which the output current value and the output current value during the period of opposite polarity are approximately equal is repeatedly changed at a period T longer than one cycle t of the AC output current. It shows. A case is shown in which both the duration time of the first state and the second duration time described above have substantially the same period T. When such a changing current is applied to a non-consumable electrode covered with a shielding gas mainly composed of an inert gas and a workpiece made of a light alloy such as aluminum or magnesium with an oxide film, the In state 1, the penetration depth P is large, and in state 2, where the SP ratio is small, the cleaning width is wide, so the wetting of the bead toe is good and there is no cracking of the toe. In addition, by reducing heat generation during the positive period of the non-consumable electrode, it is possible to increase the allowable current carrying capacity of the non-consumable electrode or reduce wear and tear of the non-consumable electrode. Also, the commercial frequency is usually used as the frequency of the AC output current, but
A high-frequency pulsed current may be used for the purpose of making particles finer by vibrating the molten pool.

Figure b shows the period of the first state where the SP ratio is large.
The waveform of the AC output current is shown when T ₁ is made larger than the period T ₂ of the second state. The period of the changing current shown in the figure applies not only when welding aluminum using a gas-shielded non-consumable electrode containing an inert gas as its main component, but also when using a covered consumable electrode or a gas-shielded consumable electrode. When welding workpieces made of aluminum or other materials, this method is particularly suitable when it is necessary to increase the penetration depth P of thick plates and the like. Conversely, when welding aluminum with a gas-shielded non-consumable electrode containing inert gas as its main component, the workpiece is a thin plate and the precision of the butt groove surface is not high;
When using filler wire, the period of the first state with a large SP ratio is changed to the second state with a small SP ratio.
It is necessary to make the cleaning width Wc larger without making the penetration depth P too large by making it shorter than the cycle of the state. Also, in this case, filler wire
If the filler wire is inserted into the molten pool in synchronization with a change in the SP ratio, for example, the first state where the SP ratio is large, wetting of the droplets of the filler wire and the molten pool will be good. Furthermore, by controlling the supply and withdrawal of a coated welding rod, or the supply, stop, withdrawal, or speed of a gas-shielded consumable electrode in approximately synchronization with changes in the SP ratio, for example, the molten pool can be expanded. During this period, droplets from a covered welding rod or consumable electrode are introduced into the molten pool to improve wetting and control the bead shape.

Figure c shows that the output current value during the period of positive polarity of the AC output current changes between a first state and a second state in which the value changes from small to large, that is, Is ₁ and Is ₂ , but this first state The waveform of the output current is shown when the output current value Ir ₁ during the period of reverse polarity in the second state is approximately the same as the output current value Ir ₂ during the period of reverse polarity in the second state, and such a changing current is By energizing, the cleaning width Wc can be kept constant, so it is possible to secure the cleaning width Wc in welding using a large current, prevent overheating of the non-consumable electrode, and reduce electrode wear. can.

Furthermore, FIG. 5 shows the output current values Ir 1 and ₁ during the period of reverse polarity as shown in FIG.
FIG. 7 is a diagram showing the appearance of a bead formed by repeatedly changing the SP ratio while keeping Ir ₂ substantially constant and cleaning width Wc substantially constant, thereby repeatedly expanding the molten pool by heating and contracting it by cooling.
By repeatedly changing the SP ratio in this way, welding while controlling the penetration depth and width of the molten pool is particularly effective in preventing dripping in difficult position welding, and in forming good back waves in single-sided welding. has.

As described above, according to the AC arc welding method of the present invention, at least one of the output current value during the positive polarity period and the output current value during the reverse polarity period is set at a cycle longer than one cycle of the AC output current. The shape of the molten pool, such as the penetration depth and bead width, can be controlled moment by moment by repeatedly changing the molten pool, and by individually selecting each repetition period. There is an advantage that good welding results can be obtained in butt welding where the tip accuracy is not good. In addition, when a gas-shielded non-consumable electrode is used, it has the effect of increasing the current carrying capacity of the non-consumable electrode and reducing electrode wear. It also has good wettability with the pond, and
When the object to be welded has an oxidizing film such as aluminum, the cleaning width can be controlled, and the cleaning width can be widened to improve wetting of the bead toe, especially at high currents. It has many advantages, such as being able to completely eliminate departmental divisions.

[Brief explanation of the drawing]

Figures 1a and 1b show the arc voltage waveform and welding current when arc welding is performed by applying the output current of a normal movable core type AC arc welding machine to an inert gas shielded consumable electrode and an aluminum workpiece. A diagram showing waveforms, FIG. 2 is a thyristor-type AC arc welding machine used for carrying out the welding method of the present invention,
Figure 3a shows the penetration depth P of the molten pool and the bead width.
Figure b defines the Wb and cleaning width Wc. Figure b shows the SP ratio (the sum of the output current value during the positive polarity period and the output current value during the reverse polarity period relative to the output current value during the positive polarity period). Penetration depth P, bead width Wb and cleaning width when changed
Figures 4a to 4c show the output current waveforms of the AC arc welding machine used in the welding method of the present invention, and Figure 5 shows an embodiment of the welding method of the present invention. FIG. 3 is an external view of a weld bead.

Claims (1)

[Claims] 1. In an AC arc welding method in which an AC output current is applied to an electrode and a workpiece from a welding power source to weld, the ratio of the current value during the period of positive polarity to the current value during the period of reverse polarity is the first Apply a current that is the ratio,
Next, a current is passed in which the ratio of the current value during the period of positive polarity to the current value during the period of reverse polarity is a second ratio, and thereafter the current of the first ratio and the current of the second ratio are An alternating current arc welding method that involves repeatedly applying current to welding.