JPH0761543B2 - AC arc welding power source - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc welding machine, and more particularly to an AC arc welding machine suitable for arc welding of an aluminum-based work piece having a strong oxide film on its surface.

Conventional device Fig. 3 is a connection diagram of a conventional AC arc welding power source whose polarity can be switched. In the figure, reference numeral 1 is a DC power supply having a constant current characteristic, for example, power is obtained from a commercial AC power supply (not shown), exchanged with a voltage suitable for arc welding and then rectified, and the output current is kept at a constant value according to the reference signal. A well-known DC power source that controls so as to control is used. Reference numerals 2a to 2d denote switching elements such as transistors connected in the form of a bridge. Connect to the work piece 4. Reference numeral 6 is a pair of switching elements 2a to 2d connected in a bridge.
Signals S _p for switching ON / OFF of a, 2b or 2c, 2d simultaneously and switching to positive polarity output (workpiece 4 has positive potential output) or reverse polarity output (electrode 3 has positive potential output) It is a forward / reverse period setting circuit to be supplied, and a repetitive timer circuit in which the positive polarity period T _sp is set by the variable resistor VR _sp and the reverse polarity period T _R p is set by the variable resistor VR _R p can be used. 7 and 8
_Are reference signal _setters that output reference signals I _r1 and I _r2 for determining the output current value in the positive polarity period and the output current value in the reverse polarity period, respectively, and DC power sources E ₁ and E ₂ and a variable resistor, respectively. It is composed of VR ₁ and VR ₂ . 9 is a reference signal switching circuit consisting of analog switch, the DC power source 1 to one of the output of the output signal S by the _P connexion reference signal setting device 7 or 8 of the forward and reverse period setting circuit 6 as the output current reference signal I _r
Supply to. Reference numeral 10 is an input of the output signal S _p of the forward / reverse period setting circuit 6 and the switching elements 2a, 2b or 2 depending on the input signal.
This is a switching element drive circuit for conducting either c or 2d.

In the device shown in the figure, when the polarity is positive, the period is the variable resistor VR _sp , the current value is the output I _r1 of the reference signal setting device 7, and when the polarity is reverse, the period is the variable resistor VR _Rp and the current value is The output I _r2 of the reference signal setting device 8 is set independently.

Problems to be Solved by the Invention Since the conventional device is configured as described above, the positive polarity current and the reverse polarity current are adjusted independently.
On the other hand, the penetration depth to obtain the required welding quality is almost determined by the positive current, and the range in which the surface oxide film of the workpiece is removed (so-called cleaning width)
Is known to depend on the reverse polarity current value. That is,
According to the experiments by the present inventors, the length of the positive polarity period is T _sp , the length of the reverse polarity period is T _R p, and the current of the positive polarity and the reverse polarity is a waveform close to a rectangular wave, and When the highs are I _sp and I _R p, the bead width B _w is And the cleaning width C _w obtained at this time is (Where ₁ ≦ n ≦ 3, k 1 and k ₂ by connexion determined proportionality constant welding conditions) be determined by HanTsuta. Also, it is essential that the cleaning width C _w required for the bead width B _W is wide,
Since this is a value obtained by adding the margin width C _o to this bead width B _w (however, C _O is a constant value irrespective of the bead width), C _W = B _W + C _O ……… (3) From the formulas 1), (2), and (3), the reverse current required is (However, K ₁ = C _o / k ₂ , K ₂ = k ₁ / k ₂ ) In this way, the proper current value in both forward and reverse polarities is
Since they have a close relationship with each other, the required quality of welding results cannot be obtained regardless of whether they are excessive or insufficient. Therefore, in the above-mentioned conventional device, adjustment is not easy, and individual differences among workers tend to be large.

Means for Solving the Problems The present invention is intended to solve the problems of the above-mentioned conventional device.
Of the reference signal generation circuit for determining the output current to be provided as a set, the reference signal for determining the current in the reverse polarity period is used as the input signal, and the output signal of the reference signal generation circuit for determining the current in the positive polarity period is input. It is configured by a function generator that generates a corresponding signal, and the output currents in both positive and reverse polarities are determined by the output signals of the two reference signal generation circuits.

Action In the present invention, the function generator is selected so as to satisfy the relation of the above formula (4) that can obtain the arc welding result in which the positive polarity current value and the reverse polarity current value are required. By operating each of the current setting devices, the current values of the positive and negative polarities are automatically set to have the optimum relationship.

EXAMPLE FIG. 1 shows an example of the present invention. FIG. 1 shows the output I of the first reference signal generating circuit 11 in place of the reference signal setter 8 for setting the output current when the polarity is reversed in the conventional device of FIG.
_r1 and the output of the forward / reverse period setting circuit 6 are input, However, K ₁ and K ₂ are predetermined constants, and a second reference signal generation circuit including a function generator that outputs 1 ≦ n ≦ 3.
12 is provided and the other parts are the same as those in FIG. 3, and therefore those having the same functions are designated by the same reference numerals. The function generator for obtaining the signal as described above can be easily realized by combining an addition coefficient unit using an operational amplifier and a multiplier (for example, integrated circuit for multiplication / division of product No. 4452 of US Teledyne Corp.). .

Note In the actual welding each of these elements _{I sp, T S p, T} Rp
If all are variable, not only will control become extremely difficult, but it will also cause confusion in the selection of conditions. Further, the cycle of polarity switching needs to be set to a fixed value or less due to the cyclic limitation of heating and cooling of the welded portion, and it cannot be made too long. Therefore, the proper lengths of the polarity switching period and the positive polarity period and the reverse polarity period therein are limited to a relatively narrow range. Therefore each polarity period T _S p and T
_{If R} p is approximately constant, the current is Therefore, it may be limited by the formula of I _r2 = (A + B · I _r1 ) ^{1 / n} . Furthermore, the above formula
If 1 / n is the object to be welded, the range of the positive welding current I _sp that is compatible is also a narrow range, so even if n = 1, n = 2 or n = 3, and there is a substantial difference in the welding results. There is no difference. Therefore, as a function generator Furthermore, even if a circuit that performs a simple operation such as I _r2 = a · I _r1 + b is used, there are few practical problems.

As described above, in the embodiment shown in the figure, by adjusting the output of the first reference signal generating circuit 11 so as to obtain the required positive polarity current, a value suitable for this positive polarity current value is obtained. The second reference signal generating circuit 12 obtains the reference signal I _{r2 from} which the reverse polarity current of 1 is obtained. The reference signals I _r1 and I _r2 thus obtained are switched as a reference signal I _r that determines the output current to the DC power supply 1 through the reference signal switching circuit 9 that switches according to the output sp of the forward / reverse period setting circuit 6. Supplied. Therefore, the electrode 3 and the workpiece 4 have a first reference signal generating circuit.
The switching element 2 has a positive polarity current of a value determined by the output signal I _{r1 of} 11 only during the period set by the variable resistor VR _sp .
a, 2b are conducted and then determined by the output signal I _r2 of the second reference signal generating circuit 12 which receives the output signal of the first reference signal generating circuit 11 as an input and outputs a signal related thereto. It is repeated that the switching elements 2c and 2d conduct and flow only for the period in which the reverse polarity current of the value is set by the variable resistor VR _Rp .

Even for the same positive current, the appropriate value of the reverse polarity current differs depending on the material to be welded, the shield gas used, the electrode diameter, etc. Therefore, the second reference signal generating circuit 12 shown in FIG. There are times when a single function generator, such as the illustrated embodiment, will not work. In order to solve such a problem, a plurality of function generators may be provided in the second reference signal generating circuit, and the plurality of function generators may be switched as needed. FIG. 2 is a connection diagram showing such an embodiment of the present invention. This drawing shows a modification of the second reference signal generating circuit 12 of the embodiment shown in FIG. 1, and it is a function generator for generating functions having different characteristics.
It is constituted by 101a to 101c and a switching switch 102 which selects one of the outputs of these function generators and outputs it as the output I _r2 of the second reference signal generating circuit. In the embodiment shown in the figure, it is convenient to set the welding conditions by displaying the material of the workpiece and the kind of the shielding gas which are suitable for the notched portions corresponding to the terminals of the switching switch 102.
In particular, when a function generator that outputs a signal obtained by multiplying I _r1 by a simple coefficient as described above is used, this method is advantageous because it can compensate for the difference from the actually required signal.

Further, the same function can be obtained by using a function generator having variable characteristics in FIG.

In each of the above, the positive polarity current setting signal was obtained from the first reference signal generating circuit 7 and the reverse polarity current setting signal was obtained from the second reference signal generating circuit. However, these relationships are reversed. Of course, it is also good.

Further, the maximum value of the reverse polarity current I _Rp has an upper limit value determined by the DC power supply used. Therefore, the reverse polarity period T to be set
_When the value of _Rp is small, it may occur that a reverse polarity current matching the above equation (4) cannot be obtained. It should be compensated Te cowpea that opposite polarity current is a shortage of the cleaning width longer opposite polarity period T _R p after reaching the upper limit in this case.

EFFECTS OF THE INVENTION Since the present invention is as described above, it is possible to automatically set the reverse polarity current for obtaining the cleaning width required for this by simply setting the positive polarity current for obtaining the necessary penetration. Therefore, the operation is simple and there is no erroneous setting, so that an excellent welding effect can be obtained.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a connection diagram showing another embodiment, and FIG. 3 is a connection diagram showing an example of a conventional device. 1 ... DC power supply, 2a to 2d ... Switching element, 6 ...
Forward / reverse period setting circuit, 9 ... Reference signal switching circuit, 11 ... First reference signal generating circuit, 12 ... Second reference signal generating circuit, 101a to 101c ... Function generator, 102 ... Switching switch .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshimitsu Doi 2-1-1 Tagawa, Yodogawa-ku, Osaka City, Osaka Prefecture Daihen Co., Ltd. (56) References: 61-92463 (JP, U) 58-179978 (JP, U)

Claims (2)

[Claims] 1. A DC power supply that outputs a constant current according to a supplied reference signal, and a bridge-connected switching element for switching the output of the DC power supply to a positive polarity and a reverse polarity and transmitting the output to an output terminal. A polarity switching circuit, a forward / reverse period setting circuit that supplies a polarity switching signal that determines a forward / reverse bipolar period to the polarity switching circuit, a first reference signal generation circuit for determining an output power supply in a positive polarity period, and First
Output of the reference signal generator circuit of _r and the positive polarity period signal T _SP and the reverse polarity period signal T of the normal / reverse bipolar period setting signal generator circuit
Signal with _RP as input (However, K ₁ and K ₂ are predetermined constants, and 1 ≦ n ≦
3) a second reference signal generating circuit for determining an output current value in the reverse polarity period, which is composed of a function generator for generating the signal, and a first or second circuit before the DC power supply in synchronization with the polarity switching signal. AC arc welding power source equipped with a reference signal switching circuit for switching the output signal of the reference signal generating circuit and supplying it as a reference signal 2. The function generator comprises a plurality of function generators that generate functions having different proportional constants K ₁ and K ₂ depending on the welding conditions to be applied, and the plurality of function generators are switched according to the welding conditions. The AC arc welding power source according to claim 1, wherein the AC arc welding power source outputs the electric power.