JPS5938072B2 - AC arc welding machine - Google Patents

Description

[Detailed description of the invention] This invention relates to an AC arc welding machine.

Variation of current is essential in arc welding machines, and conventionally this has been controlled using moving coils, moving iron cores, saturable reactors, etc.

Recently, with the demand for more sophisticated and faster welding, the response speed, reproducibility, etc. of current control are becoming more important, and the use of semiconductors for current control of arc welding machines has become a major issue. Current control using thyristors has been put into practical use in DC arc welding machines, but current control using thyristors is not possible in AC arc welding machines except in special cases. In addition, in an AC arc welding machine, if current control including the level of welding current and the current application time when the workpiece is the positive electrode and the current application time when the workpiece is the negative electrode can be performed in accordance with the welding conditions, it is possible to It is possible to produce extremely high quality welding compared to conventional methods. For example, in TIG welding of aluminum, it is sufficient to use the current at the reverse pole (the workpiece is the negative pole) to perform a cleaning action, but at present it is only possible to control the current to follow the positive pole, so it is not effective at all for welding at the reverse pole. Current is being consumed.

In addition, when using a sine wave as the welding current, the polarity changes slowly near the boundary between forward and reverse where the voltage becomes OV, so the arc becomes unstable near the voltage OV, and good welding cannot be achieved. It becomes difficult. Therefore, if the welding speed is increased while maintaining the sine wave at a constant period, there will be a portion where the voltage is near OV and will not be welded, and the weld line may become scaly. However, if the current is a rectangular wave alternating current with a sharp polarity change, and if the duration of the positive and negative currents flowing through the arc load can be controlled, the current duration when the workpiece is positive is increased, and the workpiece is By shortening the time when the current is applied to the negative electrode, the width of the reverse electrode for the cleaning action is short, and the energy used for the cleaning action can be controlled to the minimum necessary, resulting in efficient welding. It can be carried out. Also,
By using rectangular wave alternating current, there will be no unwelded parts near the boundary between positive and negative polarities, so even if the welding speed is increased somewhat, good welding can be performed. . In addition, if the positive polarity and/or negative polarity level of the rectangular wave alternating current can be changed,
For example, it is possible to effectively perform a cleaning action in TIG welding of aluminum. This invention has been made in view of the problems of the prior art described above, and its purpose is to make it possible to adjust the level of positive and negative polarity in welding current, and to convert positive and negative polarity by using rectangular wave alternating current as welding current. Provides an AC arc welding machine that can be expected to perform good welding by providing steepness and controlling the current application time, making it possible to vary the current application time when the workpiece is the positive electrode and the current application time when the workpiece is the negative electrode. It's about doing.

A feature of the present invention for achieving this object is that the first switching element 1a and the second current control element 2b are connected in series, and the second switching element 2a and the first current control element 1b are connected in series. are inserted in parallel to the DC connection power supply E, and the first switching element 1a and the second current control element 2b
An arc load L is connected between the connection point of the second switching element 2a and the first current control element 1b,
The first and second switching elements 1a and 2a can set the switching time arbitrarily, and each gives a rectangular wave output by alternate switching, and the first and second current control elements 1b and 2b each provide a rectangular wave output. Level control is possible, and the first current control element 1b supplies its rectangular wave output to the arc load L in synchronization with the first switching element 1a, and the second current control element 2b supplies the rectangular wave output to the arc load L in synchronization with the first switching element 1a. The present invention is an AC arc welding machine in which a rectangular wave alternating current is applied to the arc load L by supplying the rectangular wave output to the arc load L in synchronization with 2a.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 1a is a first switching element, 1b
is a first current control element, 2a is a second switching element, and 2b is a second current control element. Further, E is a DC output power source capable of supplying a sufficient welding current, and of course may be one that rectifies AC to convert it into DC. L is the arc load. This circuit configuration connects a series circuit consisting of a first switching element 1a and a second current control element 2b, and a series circuit consisting of a second switching element 2a and a first current control element 1b to a DC welding power source E. Connect in parallel with possible polarity.

An arc load L is connected between the connection point between element 1a and element 2b and the connection point between element 2a and element 1b. 1st and 2nd
The switching elements A and 2a each have a switching time T
1 and T2 can be set arbitrarily, and rectangular wave outputs are provided by alternate switching. The first and second current control elements 1b and 2b can control the level of the rectangular wave output. Next, to explain the operation, a rectangular wave as shown in FIG. 2a flows in the current path between element 1a-arc load L-element 1b.

On the other hand, in the current path from element 2a to arc load L to element 1b, a positive polarity rectangular wave as shown in FIG. 2b flows.
In this case, the waveforms a and b in FIG. 2 have a timing relationship in which the currents flow at times when the respective currents are not flowing. As a result, the rectangular waves a and b flow in opposite directions to the arc load L, so that a rectangular alternating current as shown in FIG. 2c flows as the load current. FIG. 3 shows a specific embodiment of the circuit shown in FIG. 1, in which thyristors SCRl and S are used as switching elements 1a and 2a in FIG.
Switching is performed using CR2.

Further, transistors TRl and TR2 are used as the current control elements 1b and 2b, respectively, and a circuit in which protection diodes D1 and D2 and resistors R1 and R2 are connected in series to each transistor is used. In the figure, L and E are respectively the same as the arc load and DC output power source in FIG. 1. Next, to explain the operation of this circuit, FIG. 4 shows the main signal and current waveforms of FIG.
are the waveforms of control signals input to the gates or bases of the thyristors SCRl and SCR2, and the transistors TRl and TR2, respectively, and e in the figure is the waveform of the load current 1 flowing through the primary load L. By applying control signals as shown in Fig. 4 A, b, c, and d to each gate or base, the load current 1 flowing through the arc load L becomes as shown in Fig. 4 e, and this rectangular wave alternating current Welding can then be performed. Therefore, by changing the times Tl and T2 of the signals applied to the gate and base, the conduction time of the positive and negative currents 1 flowing to the arc load L can be controlled, and the positive and negative sides of the current 1 can be controlled. The size of 11, I, is also the transistor T
It can also be arbitrarily controlled by the magnitude of the signals applied to the bases of Rl and TR2. Note that the transistor TRl,
The accumulation time T3 of TR2 is determined by the thyristors SCRl and SCR2.
It is necessary to take a sufficiently longer time than the turn-off time of Figure 5 shows an example in which transistors are used as the elements 1a, 1b, 2a, and 2b, where E is a DC output power supply, L is an arc load, and TRl, TR2, TR3, and TR4 are for switching or continuous current control. Rl, R, , R3, R4 are current control resistors, D
1, D2, D3, and D4 are protection diodes, and their connections are similar to the circuit including transistors in FIG.

Note that the transistors TR1 and TR3 are PNP type transistors, and the transistors TR2 and TR4 are NPN type transistors. FIG. 6 shows signal waveforms and load current waveforms of the main parts of the circuit shown in FIG. That is, the transistors TR1 and TR2 are operated by the base signals of the transistors TR1 and TR shown in FIGS. 6A and 6B, respectively, and the transistor TR
3, TR4 is operated by the base signals shown in FIG. 6C and d, and the load current flowing through the arc load L becomes a rectangular wave alternating current as shown in FIG. 6e. In the figure, Tl, T2, T3
, currents 11, 12 are similar to those in FIG.
Note that the accumulation time T3 of the transistors TR1 to TR4 must be determined based on the fall time of the load current 1 and the characteristics of the load. Although the above embodiments have been explained using single elements for switching and continuous current control, that is, thyristors and transistors, they may be replaced with circuits for the same purpose composed of multiple semiconductors as necessary. Of course.

As explained above, according to the present invention, a rectangular wave alternating current is applied as a welding current, and its positive and negative polarity levels can be adjusted and the synchronization can be varied. The welding current can be used effectively by making the electrode width short or the level small, and the current application time when the arc is positive and the current application time when the arc is negative can be adjusted arbitrarily. Since it is a rectangular wave alternating current with a steep polarity change, it is possible to perform good welding even if the welding speed is increased somewhat.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram explaining the principle of this invention, FIG. 2 is a voltage or current waveform diagram of the main part of FIG. 1, FIG. 3 is a circuit diagram of the first embodiment of this invention, and FIG. 5 is a circuit diagram of a second embodiment of the present invention, and FIG. 6 is a voltage and current waveform diagram of the essential parts of the same. 1a, 2a...Switching element, 1b, 2b
...Current control element, E...DC welding power source, L...Arc load.

Claims (1)

[Claims] 1 The series connection of the first switching element 1a and the second current control element 2b and the series connection of the second switching element 2a and the first current control element 1b are inserted in parallel into the DC welding power source E, and the first The connection point between the switching element 1a and the second current control element 2b and the second switching element 2a
and the connection point of the first current control element 1b, and an arc load is connected between the first and second switching elements 1a, 2.
a can set the switching time arbitrarily and give each rectangular wave output by alternate switching, and the first and second current control elements 1b and 2b can control the level of the rectangular wave output, and the first current The control element 1b supplies its rectangular wave output to the arc load L in synchronization with the first switching element 1a, and the second current control element 2b supplies its rectangular wave output in synchronization with the second switching element 2a. An alternating current arc welding machine characterized in that a rectangular wave alternating current is applied to the arc load L by supplying the arc load L with a rectangular wave alternating current.