JPS6313677A - Ac tig welding method - Google Patents

Abstract

PURPOSE:To independently adjust the cleaning width and the depth of penetration and to perform the optimum welding in accordance with the required quality by fixing a reversed polarity electric current value and a period of a straight polarity electric current and making variable the period of the reversed polarity electric current and the straight polarity electric current value. CONSTITUTION:In the TIG welding of a aluminum, the reversed polarity electric current value IRP and the period TSP of the straight polarity electric current are fixed and the period TRP of the reversed polarity electric current and the straight polarity electric current value ISP are set variably. Then, the depth of penetration and the width of cleaning are adjusted independently respectively by the straight polarity electric current value ISP and the period TRP of the reversed polarity electric current. A reversed polarity period adjuster 8 is provided to a DC power source circuit to adjust only the reversed polarity period for said adjustment and the straight polarity electric current value ISP is changed by a reference signal ES of a reference signal setter 10. As a result, the width of cleaning and the depth of penetration are adjusted independently and the optimum welding in accordance with the requirement can be performed.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention is directed to non-consumable electrode inert gas arc welding (hereinafter T
This paper relates to an improvement of the iC method.

[Prior Art] In TIG welding of aluminum and aluminum alloys, an alternating current arc containing a component of opposite polarity with a positive potential on the electrode side is used as a means of destroying (cleaning) the oxide film on the surface in order to obtain a good weld. A welding power source is used. In this case, in order to obtain the necessary leaning width, the power supplied to the welding part during reverse polarity is adjusted to a specified value, and in order to obtain the necessary welded part, the power supplied during positive polarity (the electrode is at a negative potential) is also adjusted. It is necessary to. These adjustments cannot be made with an AC arc welding machine that only provides drooping characteristics using a normal leakage transformer, so we have devised a way to adjust the period of both forward and reverse polarity. (For example, Japanese Patent Laid-Open No. 54-121255) has been proposed. FIG. 5 shows an example of a power supply used in the prior art. In the figure, 21.21 is an input terminal that receives power from a commercial AC power supply, 22 is a transformer for converting the input voltage into a predetermined output voltage, and 23a and 23b are unidirectionally connected with mutually opposite polarity. Sairisk, 24a,
24b is each unidirectional thyristor 23a.

23b are connected in series or are actuators, respectively.
As shown in the figure, each reactor has a winding wound around a common core, and its polarity is determined so that magnetic flux in the same direction is generated in the common core by conduction of the thyristors connected in series with each reactor. It is being 25 is a non-consumable electrode made of tungsten, and 26 is a welded object made of aluminum or its alloy. Electrode 25. The workpiece 26 and the welding arc form a welding load R.

27 is a reference signal source for determining the welding current, and outputs a reference signal e. 28 is a current detector that detects the welding current and outputs a signal e corresponding to the welding current, and 29 is a difference signal (Δe=e) obtained by manually inputting each output of the reference signal source 27 and the current detector 28.

This is a comparator that outputs er). 30a and 30b are firing phase control circuits for firing the thyristors 23a and 23b, and 31 is an unbalance ratio adjuster for dividing the output Δe of the comparator 29 into the firing phase control circuits 30a and 30b. It is. As shown in the figure, the unbalance ratio adjuster 31 increases or decreases the output Δe of the comparator 9 supplied to the ignition phase control circuit 30a and 30b in opposite directions, and divides the output Δe into Δe plus Δeb−Δe. It is.

FIG. 6 is a diagram for explaining the operation of the device shown in FIG. 5, showing the secondary no-load output voltage E of the transformer 22 and the welding current 1o.
The changes in the welding voltage Io@R consisting of the welding load R and the current I flowing through the reactors 24a and 24b are shown with time t as the horizontal axis. Now, at time TI shown in FIG. 6, the firing phase control circuit 30a starts firing (1(
The signal is output, and the thyristor 23a becomes conductive. When the thyristor 23a becomes conductive, the welding type 1f (i l +) connects the terminal 22a1 of the secondary winding, the thyristor 23a1, and the reactor 24a.
1 flows through the path of the welding load R and the terminal 22b of the secondary winding.

At this time, during the period of time t<72, Eo>1.
; becomes R. If the inductance of the reactor 24H is selected to a large value, the increase in welding current is suppressed and an electromotive force of the difference Eo-1o'R=e-L (old/dt) is generated in the reactor 24a. Energy corresponding to the shaded area in FIG. 6 is accumulated.

Next, at time t > 72, Eo < Io・R, but the welding current can only be reduced little by little, so the reactor 24a has t and -L (old/
dt), the previously accumulated energy is released, and the current Io continues to flow through the welding load R in the same direction as at time t.

This current IO does not change much because the inductance L of the axle 24a is large. Furthermore, at time t>T3, the polarity of EO is reversed, but the energy stored in the inductance of the reactor 24a is released, and a nearly constant current 1o is applied to the welding load in the same direction as at time t>T3. Continue to supply.

Next, at time t-T4, the firing signal is supplied from the firing phase control circuit 30b to the thyristor 23b, and the firing signal is supplied to the thyristor 23b.
When terminal 3b is made conductive, terminal 22b of the secondary winding of transformer 22
Current flows through the welding load R, the reactor 24b, the cyrisk 23b, and the terminal 22a of the secondary winding. At this time, the energy stored in the axle 24a is immediately transferred to the reactor 24a because the winding direction of the axle 24a and axle 24b is determined to have a polarity that generates magnetic flux in the same direction in the iron cores that are both H as described above. transition, time t>T4
The absolute value of the current I flowing through the reactor 24b, that is, the current 1° flowing through the welding load R at the time t < i
' The value is the same as when 4.

At this time, the welding load R and the voltage across the reactor 24b are negative on the thyristor 23b side, and the reactor 24
The thyristor 23a side of H is positive, and the terminal 22a of the secondary winding on the anode side of the thyristor 23a is already negative, so the thyristor 23a is cut off. After time t>T4, the same operation as described in section 2 is repeated.

Since the device shown in FIG. 5 operates as described above, by adjusting the unbalance ratio regulator 31 and changing the firing times T1 and T4 of the thyristors 23a and 23b, the thyristor 2
3a or ignition reverse polarity period TRP and thyristor 23
It is possible to change the positive polarity period TSP during which b is fired. Also, the peak value of the welding current is determined by the reference signal setting device 27.
This can be done by changing the setting value er.

[Problems to be solved by the invention] According to experiments conducted by the present inventors, AC TIG of aluminum, etc.
In welding, the penetration depth is 1 di of positive polarity current.
Regarding one cycle T of the polarity period TSP and the positive polarity period T8P and SF3 and the reverse polarity period TRP (however, I
is determined by the instantaneous value), and the clipping width is determined by the reverse polarity current IRP (however, IR
It is known that P is determined by an instantaneous value and r1ζ2).

However, in the welding method using the conventional device described in 1.
In an attempt to increase the penetration depth, the positive electrode external voltage IMI
When the reference signal e is increased to increase sp,
Adding to this, the reverse polarity current also increases. For this reason, the cleaning width, which is determined by approximately the square of the reverse polarity current, changes greatly as shown in equation (2) below. Conversely, if the reverse polarity period TRP is made smaller in order to reduce the cleaning width, l3l1''
Since T"RP, the proportion of the current in the positive polarity period increases and the penetration depth increases.In this way, the penetration depth and the cleaning width are mutually related. Because they influence each other, it is not possible to adjust both independently, and it is not always possible to obtain the optimum penetration depth and cleaning width.

[Means for Solving the Problems] In the present invention, in order to solve the problems of the prior art described above, the penetration depth is expressed by the above-mentioned formula (1), and the cleaning width is expressed by the above-mentioned formula (2). It is determined by the formula 1"L, reverse polarity current■. , and the positive polarity period TSP are kept constant, and the positive polarity current ISP and the reverse polarity period TRP are made variable, so that the penetration depth can be changed by the positive current ISP, and the cleaning width can be changed by the reverse polarity period TRP, respectively. This proposed an AC TIG welding method that can be adjusted independently.

[Function] As shown in equation (2) above, the cleaning width is determined by approximately the square of the reverse polarity current IRP, so as a means for adjusting the cleaning width, the reverse polarity current 11? , is disadvantageous because the cleaning width changes greatly even with a slight change in the reverse polarity current. Therefore, in the present invention, the cleaning width is adjusted by fixing the reverse polarity current and making the reverse polarity period TRP variable. In order to make the adjustment effect of the cleaning width clear and not to increase the amount of electrode wear, the reverse polarity current value IRP is changed to positive polarity in order to cover "l1l) with a change range of several times the minimum value from a minimum value close to zero." Set the reverse polarity current lR11 to be sufficiently larger than the welding current lll'tISP.In particular, in order to prevent the cleaning effect from disappearing even when the reverse polarity period TRP is close to zero, the reverse polarity current lR11 should be set to the maximum output current of the welding source. On the other hand, the penetration depth should be set to the value mentioned above (
Since it is determined by the equation 1), in order to adjust it, it is sufficient to adjust either the positive polarity current 1 s p h'iEJ"" and the positive polarity TsP. However, when the positive polarity period T81) is adjusted, the period T of one cycle (T=”r1?P×T sp) will also change depending on this value, and it is adjusted according to the proportion of the positive polarity period T81) that occupies one cycle T. Moreover, since the reverse polarity period TRP is changed to adjust the cleaning width as described in -1-, the adjustment effect becomes even more complicated.

Therefore, in order to adjust the penetration depth, the positive polarity period TsP
is assumed to be constant, and the positive polarity current 'SP is adjusted.

By doing as described above, the cleaning width and the penetration depth can be adjusted independently.

[Example] In order to carry out the above-mentioned present invention, an AC arc welding power source that can adjust the period and current of the forward and reverse output currents is required. FIG. 1 shows an example of an apparatus for carrying out the welding method of the present invention.

In the figure, reference numeral 1 denotes a DC power source with constant current characteristics whose output current is determined in accordance with the reference signal e, and a known DC arc welding power source with constant current characteristics can be used. 2a, 2b, 3a
, 3b are switching transistors, which are bridge-connected as shown. 4 is an electrode made of tungsten, and 5 is an object to be welded such as aluminum, which is connected to an AC terminal of a bridge circuit made up of transistors 2a, 2b, 3a, and 3b. 6 is a transistor drive circuit for supplying open/close control signals to the transistors 2a, 2b, 3a, and 3b, respectively;
Alternatively, it outputs a base drive signal for simultaneously controlling conduction and cutoff of transistors 3a and 3b, respectively. 7 is a polarity switching signal generator for generating a signal S for switching between a period of positive polarity and a period of reverse polarity; in the present invention, since only the period of reverse polarity is adjusted, the period of reverse polarity is adjusted. If only the regulator 8 is configured to be externally operable, the positive polarity period adjuster is provided internally and is fixed or semi-fixed. This polarity switching signal generator 7 can be simply produced by combining mono-multivibrators to form a repeat timer circuit. 9 and 10 are
Reference P for determining reverse polarity current value I and positive polarity current value ■8P Reference signal membrane for supplying signals E and E
8, one of which is selected by the analog switch 11 according to the output signal S of the polarity switching signal generator 7, and is supplied to the DC power supply 1 as the reference signal e. Of these, the reference signal ER for determining the reverse polarity current is fixed at a predetermined value in the present invention, so the reference signal setter 9 is fixed (
or semi-fixed) setting device.

Figure 2 also shows examples of changes in the polarity switching signal S, the reference signal E for setting the reverse polarity current, the reference signal E for setting the positive polarity current, the reference signal e for setting the Rs output signal, and the welding current Ia over time. FIG.

The operation of the apparatus shown in FIG. 1 will be explained with reference to the diagram in FIG. 2.

When welding is started using the start switch (not shown) in the apparatus shown in FIG. 1, the polarity switching signal generator 7 outputs a positive polarity period signal on the + side of the figure and a reverse polarity period signal on the + side of the figure as shown in FIG. 2(a). A signal S of the opposite polarity is supplied to the transistor drive circuit 6 and the analog switch 11. According to the polarity of the polarity switching signal S, the transistor drive circuit 6 simultaneously conducts the transistors 2a and 2b when the one side signal is input, and when the + side signal is input! - Each transistor is controlled to open and close alternately so that the transistors 3a and 3b are electrically connected, so that the electrode 4 and the workpiece 5 are connected to each other.
Transmits alternating current power with different periods of opposite polarity. Since the signal 8 of the polarity switching signal generator 7 is also supplied to the analog switch 11, the DC power supply 1 receives a reference signal e for the positive polarity period and a reference signal E for the reverse polarity period as a reference signal e for determining its output current.

A reference signal E1 for the S period is supplied in synchronization with each conductive signal to the transistors 3a, 3b or the transistors 2a, 2b. As a result, electrode 4
The current supplied to the welding object 5 and the workpiece 5 become alternating currents whose values are adjusted to respective set values along with the length of each polarity period.

3 and 4 show the relationship between the cleaning width and the penetration depth when welding is performed by the TIG arc welding method of the present invention (A) and (B), respectively. Figure 3 shows the cleaning width Cv (A) and the penetration depth Dp ( Fig. 4 shows the cleaning width Cv and the penetration depth D when the reverse polarity period TR1) is kept constant (2 ms) and the positive polarity current I8P is changed.
shows the relationship with p. In both figures, the electrode has a diameter of 3.2mo.
Welding experiment using a + thorium-containing lithium gestin electrode, flowing argon gas as a shielding gas, arc length 2.4 + w, and reverse polarity current IRP-250A, on a flat plate of aluminum alloy A 508344 with a plate thickness of 10 mm, facing downward. This is the result.

As shown in Figure 3 (B), the penetration depth is almost constant regardless of the reverse polarity period TRP, and the cleaning width is determined by the positive polarity current value as shown in Figure 4 (A). It can be seen that this is unrelated to sP.

Therefore, if the reverse polarity current IRP and the positive polarity period TSP are each constant as in the present invention, the cleaning width C
It can be seen that w is the reverse polarity period TRP and the penetration depth Dp can be adjusted independently by the value of the positive polarity current IsP.

Note that the present inventors have confirmed that similar results can be obtained with aluminum and aluminum alloys made of other materials, and even when other welding conditions are set.

In addition, in the present invention, since the reverse polarity current is kept constant and the cleaning width is adjusted by making the reverse polarity period variable, in order to clarify the adjustment effect, the reverse polarity current is
It is better to use the output value of several people in the power supply, and the positive polarity 113
Since the penetration depth is adjusted by the tAi value, it is preferable that the value be set to be less than the reverse polarity current and the reverse polarity period to be a sufficiently small value that is equal to or less than the positive polarity intercostal space.

Furthermore, in the present invention, the cleaning width is adjusted by the reverse polarity period, and the penetration depth is adjusted by the positive polarity current.
In addition to the above example, 1 which is the sum of the positive polarity period and the reverse polarity period
It is clear from equations (1) and (2) above that almost the same results can be obtained if the period T is constant and the ratio of the reverse polarity period is adjusted so that TRP<<TSP. be.

For this purpose, it is convenient to set the reverse extreme vehicle flow value 'R11 as the maximum value of the power supply.

Table 1 shows the consumption m of the electrode tip when the reverse polarity period TRP is varied while the current value is constant.

As can be seen from this table, the longer the reverse polarity period TRP becomes, the more the electrode consumption m increases. The reason for this is that the reverse polarity period TRP
As TSP becomes longer, the proportion of the positive polarity period in one cycle of TSP in Table 1 decreases accordingly. On the other hand, in arc welding, the electrode is heated by electrons flowing into the electrode during the reverse polarity period, and a large amount of electrons are emitted from the electrode during the positive polarity period, causing the electrode to be cooled. The phenomenon shown in Table 1 is thought to be because the cooling effect decreased due to a decrease in the ratio of positive polarity periods, and as a result, the temperature rise of the electrode increased even though the overall current value did not change. Therefore, in order to reduce electrode wear, it is necessary to make the reverse polarity period TRP as short as possible. However, if TRP is shortened, the cleaning effect = 16
- Since the effect decreases, it is sufficient to set the reverse ll111 current value close to the maximum value to ensure an adjustment margin for the cleaning width.

[Effects of the Invention] Since the present invention is as described above, the cleaning width and the penetration depth can be adjusted independently, and welding can be performed under the optimal conditions for each workpiece and the required welding quality. be able to.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing an example of a device for carrying out the welding method of the present invention, Fig. 2 is a diagram illustrating the operation of the device in Fig. 1, and Figs. A diagram showing the results when the welding method of the invention is applied to 7 ft 1 m, FIG. 5 is a connection diagram showing an example of a device for carrying out the conventional welding method,
FIG. 6 is a diagram illustrating the operation of the device of FIG. 5. 1...DC power supply + 2 a + 2 b
+ 3 a + 3 b...transistor, 4... electrode, 5... object to be welded, 6... transistor drive circuit. 7...Polarity switching signal generator, 8...
- Reverse polarity period adjuster, 9.10...Reference signal setter. 11...Analog switch' TRP...
...Reverse polarity period, T...Positive polarity period, T...1 cycle. P ■...Positive polarity current RP...Reverse polarity current. P Cν...Cleaning width, Dp...
・Welding penetration depth agent Patent attorney Hiroshi Nakai Figure 1

Claims (1)

[Claims] 1. For a workpiece made of aluminum or aluminum alloy, an AC arc welding power source with adjustable output is used, and the value I_R_P of the reverse polarity current and the period T_S_P of the positive polarity current are constant. , period of reverse polarity current T_R_
TIG with variable P and positive current value I_S_P
AC TIG welding method for welding. 2. The AC TIG welding method according to claim 1, wherein the reverse polarity current value I_R_P is set to the maximum output current value of the AC arc welding power source used. 3. For workpieces made of aluminum or aluminum alloy, use an AC arc welding power source with adjustable output, keep the forward and reverse polarity switching period T and the value of the reverse polarity current I_R_P constant, and set the positive polarity current An AC TIG welding method in which TIG welding is performed by varying the value I_S_P and the period T_R_P of the reverse polarity current.