JPS5844966A - Ac/dc arc welder - Google Patents

Abstract

PURPOSE:To assure the stability of current control during AC/DC TIG welding in an AC/DC arc welder by providing a circuit selecting means which changes the responsiveness of a constant current control circuit in the stage of DC welding and in the stage of AC welding. CONSTITUTION:Plural current control elements and an AC selecting switch for currents are connected to the secondary side of a transformer of constant voltage characteristics for an AC/DC arc welder to constitute a main circuit for the power source of the welder. A selecting switch 15 for changing the responsiveness of a constant current control circuit and a delay element consisting of a resistor R4 and a capacitor C2 are added thereto to constitute an error amplifier 10. The switch 15 is selected in association with the AC/DC selection of welding currents and is so constituted that said switch is selected to a DC side to connect the delay element of the R3 and the C1 between the input and output of an operational amplifier 14 in parallel with the resistance R2 in the stage of DC welding and that the same is selected to an AC side to connect the delay element of the R4 and the C3 between the input and output of the amplifier 14 in parallel with the resistor R2 in the stage of AC welding, whereby the responsiveness of the constant current control circuit is changed over.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC/DC arc welding machine having constant current characteristics, which is mainly used for TIG welding.

AC and DC TIGI ranging from small current range to large current range
In order to be able to perform I contact stably, J! There are nine AC/DC arc welding machines that have constant current characteristics through feedback control of the H1 current.Figure 1 shows an example of this type of AC/DC arc welding machine.Welding transformer with constant voltage characteristic tubes 1, current control thyristors 61 to 64 connected to the secondary side of the transformer, DC reactor 2, and AC/DC changeover switch 5 constitute a welding machine main circuit, and welding terminals 3, 4
are connected to a TIG (not shown) and a base material, respectively.

In this example, the thyristor 61w64 constitutes a bridge rectifier circuit, and during AC welding, the AC/DC changeover switch 5 short-circuits the DC side terminals a and b of the bridge rectifier circuit via the DC reactor 2, and the AC side terminal C of the bridge rectifier circuit. and the welding terminal 3. from the secondary terminal d of the welding transformer 1.
4 takes out the AC output, and during DC welding, connect the AC side terminal C of the bridge rectifier circuit and the secondary side terminal d of the welding transformer 1 using the AC/DC changeover switch 5, and connect the DC side terminals a and b of the bridge rectifier circuit. from the welding terminal 3 via the DC reactor 2
, 4 is configured to take out a full-wave rectified DC output.
ing.

The foot control circuit for obtaining constant current characteristics is
Current detection section 8, reference voltage generation section 9 for current setting, error amplifier 10. The ignition signal generation circuit 11 is constructed with the main element 112 as the main element, and the current detecting section B detects the S* current flowing in the secondary side AC circuit of the welding transformer 1, and the S* current flowing in the secondary side AC circuit of the welding transformer 1 is detected, and the voltage is proportional to this n and becomes the 9 voltage vi. The difference voltage between the detected voltage Vi and the voltage 0 from the reference voltage generator s9 is input to the error amplifier 10, and an output signal corresponding to the difference voltage is sent to the ignition signal generation circuit 1111111.
In addition to this, the generated firing signal is distributed to the thyristor firing circuits 71 to 74, and the firing phases of the thyristors 61 to 64 are controlled so that the welding current approaches the set value.

Due to this, the external output characteristics of the welding machine are constant current characteristics, but AC TlG used for welding aluminum etc.
In 11L contact, deep penetration is obtained during the period of positive polarity when the electrode is negative, and shallow penetration is obtained during the period of reverse polarity when the electrode is positive, but the oxide film on the surface of the base material is removed. It has a cleaning effect. Therefore, in order to perform efficient welding with deep welding, the positive and negative periods of the welding current are unbalanced, the period of positive polarity with deep welding is lengthened, and the bath is It is effective to shorten the period of shallow reverse polarity.

In order to obtain this function, in the apparatus shown in FIG. 1, during AC welding, the switch 13t, which is interlocked with the AC/DC changeover switch 5, is turned off to activate the voltage dividing circuit 12 and delay the ignition signal from the ignition signal generation circuit 111. Accordingly, thyristor 6t,
The conduction period of thyristor 6g*64 is made shorter than the conduction period of thyristor 6g*64. FIG. 2 shows the # contact current tear shape and the waveform of each detection voltage during DC welding and AC welding.

(a) is the waveform of the DC welding current IDC, and (b) is the waveform of the AC welding current M C10 when the positive and negative periods are balanced.
The waveform (e) is an AC welding current EmC80 waveform when the positive and negative periods are unbalanced. During DC welding or when the current is positive,
The detected voltage Vi during AC welding when the negative period is balanced has a waveform as shown in the same figure (d), (6) (D Vinc, Vice 1), and the ripple is relatively small, but the positive and negative periods of the current are Detection voltage V during unbalanced AC welding
i has a waveform as shown by ViAes in the same figure (f),
Even if the average current is the same, the ripple is larger than the first two. FIG. 3 shows the configuration of an error amplifier lO that is normally used in the constant current control circuit of the first example. 14 is an operational amplifier, Rt
, Rg, Rs are external resistors, CI is a capacitor, and the transfer function G of Jin's error amplifier is Rg 1+R5-C
t-8 G=Rs' 1 + (R2+Rs)-('l-8
The input signal is smoothed with the time constant of (Rg + Rs) C1. The time constant of this smoothing circuit is 0.1 to 0.1 to absorb the ripple of the detected voltage ViAc* during AC unbalanced welding. 031101i It is necessary to select the
If the time constant is smaller than and n, current control becomes unstable.
Hunting occurs. However, if the time constant is selected to be large in this way, the response of the constant current control circuit will be too slow, especially in DC TIG welding where the arc voltage is low, and a rush current will occur at the start of the arc, causing melting of the base metal to drop. I need to wake you up.

The present invention has been made to solve the problems of the prior art described above, and is an AC/DC arc welding machine having a constant current control circuit as shown in FIG. A circuit switching means is provided to change the responsiveness of the constant current control circuit in order to increase the responsiveness of the constant current control circuit when connecting DC TIGjl with low arc voltage to prevent a stray current fIL at the time of arc start. The constant current control circuit can be used by lowering the responsiveness of the constant current control circuit to the extent that hunting of the current does not occur during welding during AC TIG jll welding where the positive and negative periods need to be unbalanced.

Hereinafter, embodiments of the present invention will be explained with reference to the drawings.
Since there is no difference from what is shown in the figure, the explanation will be omitted.

FIG. 4 is a diagram showing an example of a circuit switching means which is a main part of the present invention, and is constructed by adding delay elements such as a switch 15, a resistor R4, and a capacitor C2 to the circuit shown in FIG. 3 to form an error amplifier 10t. be. The switch 15 is operated in conjunction with the AC/DC switching of the welding current, and is switched to the PC side during DC welding, and a delay element of Rs and C1 is connected in parallel with the resistor between the input and output of the operational amplifier 14, and AC welding is performed. Sometimes M C@
Switched to operational amplifier 140, Ra, C between outputs
T's slow nl! Connect the element in parallel with resistor R2! I□i0 The transfer function of this error amplifier is GDC,
When using GAC during AC welding, 2 GDc knee-6l + R5-C1-8 R 1 + (Rz + Rs)
C1-S2 GAc =, 1” R4・C2・SR11+
(R1+R4) If the time constant of Ct (Rz+R4) during AC welding is set to 0.
1 to 0.38110, and (R
z + Rs) Set the time constant of C1 to, for example, 0.02 to
If selected as small as 0.05(6), the AC Tl
G11l! It is possible to change the responsiveness of the constant current control circuit to suit both the time and DC TIG welding.

FIG. 5 is a diagram showing another example of the circuit switching means, in which the error amplifier 10 is constructed by adding delay elements such as an analog switch 16 and a resistor Rs and a capacitor Cs to the circuit shown in FIG. In this example, if the analog switch 16 is turned off during DC welding, only the 140 operational amplifiers and the delay elements aRs and C> connected between the outputs will be connected, so the response of the control circuit will be quick and the AC When the analog switch 16 is turned on, delay n elements of Rs and Cs are added to slow down the response of the control circuit.

Also, when starting AC welding, analog switch 1 is
If the analog switch 16 is turned off and the analog switch 16 is turned on only during welding using a current detection signal, a timer, etc., rush current at the start of AC welding can also be prevented. Furthermore, the current during AC welding is shown in Figure 2 (b),
(C) If the configuration is such that it is possible to switch between a balanced waveform and an unbalanced waveform in the positive and negative periods as shown in K, the analog switch 16 may be turned on only during AC welding using the unbalanced waveform. When welding aluminum, etc., the current value during the positive and negative periods of the % bath contact current may be different in order to expect a cleaning effect to remove the oxide film on the surface of the base metal. A high current can be used during the period, and a low current can be used during the period when the welding depth is shallow and the reverse polarity occurs. In this way, deep weld penetration can be achieved while maintaining the cleaning action.

In addition, by switching the output of the welding machine between AC and DC, it is possible to weld not only aluminum but also stainless steel, iron, and other materials. Even when a smoothing circuit is provided at other locations in the control system, such as the current detection section 8 in the figure, the present invention can be implemented by providing a circuit switching means that makes the time constant of the smoothing circuit variable as in the above embodiment. You can achieve your goals.

As explained above, according to the present invention, the responsiveness of the constant current control circuit is changed between AC welding and DC welding. While ensuring stability of current control when performing AC TIG welding with unbalanced periods, DC TIG welding with low arc voltage can be used.
The effect of increasing the responsiveness of current control during IG welding and preventing rush current at arc start can be achieved.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a configuration example of an AC/DC arc bath welding machine with a constant current control circuit, Figure 2 is a diagram showing the Hiro welding current waveform and current detection voltage waveform, and Figure 3 is a diagram showing a conventional example of an error amplifier. The circuit diagrams shown in FIGS. 4 and 5 are principal circuit diagrams showing an embodiment of the present invention. l...Welding transformer, 5...AC/DC changeover switch, 6
1 to 64... Cyrisk for current control, 71 to 74...
・Thyristor firing circuit, 8...Current detection section, 9...
Reference voltage generation section, 10...Error amplifier, Ils, Il
x... Ignition signal generation circuit, 12.13... Control means for making the positive and negative periods of the welding current unbalanced, 14... Operational amplifier, Rs w Rs *C1w Cs-delay element,
15.16...Switch for changing the response of the constant current control circuit. Millet figure 2, dormitory 3 eyes 4 figure 4 lacquer 5I21

Claims (3)

[Claims] (1) A welding machine main circuit is constructed by connecting a current control element and a welding current AC/DC selector switch to the secondary side of a welding transformer with constant voltage characteristics, and the above current is adjusted so that the welding current approaches the set value. Control element operation! A constant current control circuit including a control means for performing IfiI control is provided, the external output characteristics are constant current characteristics, and circuit switching means changes the responsiveness of the constant current control circuit between AC connection and DC welding. 1-* Arc #II welding machine for both alternating current and direct use. (2) The AC/DC arc welding machine according to claim 1, wherein the control means unbalances the positive and negative welding currents during AC welding by operating a current control element. (3) The AC/DC arc welding machine according to claim 11, wherein the control means unbalances the positive and negative welding current values during AC welding by operating the current control element. (The control means controls the operation of the current control element by making the positive and negative periods of the welding current unbalanced during AC welding. .