JPS6268679A - Dc arc welding machine - Google Patents

Abstract

PURPOSE:To realize the short circuit current with faster rising speed and high peak value and to obtain good arc starting characteristic by releasing the control by a short circuit control circuit for the fixed time after starting the welding and by providing the timer circuit which starts after the fixed time. CONSTITUTION:A timer circuit 16 starts a count when detecting the pass of the output current by receiving the signal transmitted from a current detector 13 and transmits the output after a fixed time. A short circuit current control circuit 15 starts the control by receiving the output of the timer circuit 16 and does not control the short circuit current on purpose by the control circuit until the transmission of the output by the timer circuit. The probability of shifting to the arc instantaneously at the welding starting time is thus increased as well and the time from the welding start until the shift to a stable welding state is shortened as well.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention feeds a consumable electrode to a welding part of a workpiece, and generates an arc and a short circuit alternately and continuously, during the duration of the arc. This invention relates to a DC arc welding machine that transfers the droplets onto the workpiece by short-circuiting the molten grains at the tip of the melt onto the weld pool formed on the workpiece.

BACKGROUND OF THE INVENTION The structure of a conventional DC arc welding machine having an output control element such as a transistor is shown in FIG. In Figure 2, 1
2 is a consumable electrode, 2 is a base material, 3 is an electrode feeding motor and a feeding device, 4 is a welded portion generated between the consumable electrode 1 and the base material 2, and 5 is a rectifier for alternating current input. 6 is a capacitor for smoothing the DC power rectified by the rectifier 5; A is an inverter section composed of power transistors that converts the DC power into AC power and controls the output; 8 is the converted AC power; 9 is a rectifier for rectifying the stepped-down AC power again; 101-1: Reactor nope for improving arc characteristics 11
is the switching of the output control element of the inverter section 7.
A control circuit that controls the duty; 12 is a shunt resistor for detecting the output current; 13 is a current detector that detects the signal from the shunt resistor 12 and outputs a current detection signal proportional to the output current; 14 is the output of the main circuit. A short-circuit state determination circuit detects voltage and determines whether the state of the welding load is an arc state or a short-circuit state, and 16 is a short-circuit current control circuit that performs control to reduce the switching duty of the output control element during the short-circuit state.

The operation of the conventional DC arc welding machine configured as described above will be explained below.

AC input to the arc welding machine is rectified by a rectifier 5, smoothed by a capacitor 6, and becomes DC power. After that, it is converted into a relatively high alternating current of 1 to 100 KHz by the switching operation of the transistor in the inverter section 7, but at this time, the ON of the transistor during one cycle is
Welding output is controlled by the time ratio (switching duty). The AC output of the inverter section 7 is stepped down to a voltage suitable for welding by a transformer 8 and rectified by a rectifier 9 to become DC power, which is then connected to the consumable electrode 1 and the base material 2 via a reactor 10 for improving welding characteristics. is supplied to the welding section. The consumable electrode 1 is fed to the base material 2 at a constant speed by an electrode feeding motor and a feeding device 3, and welding is performed between the consumable electrode 1 and the base material 2. The welding current during welding is sensed by detecting the signal from the shunt resistor 12 by a current detector 13, which outputs a current detection signal proportional to the output current. Further, a short-circuit state determination circuit 14 detects the output voltage of the main circuit, determines whether the welding load state is an arc state or a short-circuit state, and outputs an output.

Then, in response to the current detection signal and the signal from the short-circuit state determination circuit 14, the short-circuit current control circuit 16 changes the switching duty of the output control element during the period when the welding load is in the short-circuit state. It is controlled so that it is smaller than the duty, and the period of the arc state /
The rising speed of the short-circuit current is made slower during the short-circuit state compared to the case where the switching duty is the same.

The waveform of the welding current during welding is shown in FIG. 3, and the waveform represented by the solid line is the welding current waveform when the short-circuit current control is not performed, and the waveform represented by the broken line is the welding current waveform when the short-circuit current control is not performed. This is a welding current waveform when short circuit current control is performed. When the short-circuit current control is performed, the rise speed of the short-circuit current is suppressed and the peak value is also lowered. By suppressing the short-circuit current and lowering the peak value in this way, it is possible to reduce the amount of spatter generated during welding. It is generally well known that this is possible.

Problems to be Solved by the Invention Generally speaking, there is a thermal The rise speed and peak value of the short-circuit current must be high enough to melt the tip of the consumable electrode, which has not yet warmed sufficiently. However, in the conventional circuit-based control method, the short-circuit current control operates during the short-circuit state, and the short-circuit current is uniformly suppressed regardless of whether the welding load is stable or unstable or the load impedance value at the time of the short circuit. So,
Despite the need for a short-circuit current with a fast rise and high peak value, it was not possible to supply it.As a result, the probability of instantaneous transition to arcing at the start of welding is low, and it takes a long time to transition to stable welding. This was a major obstacle to obtaining a good arc start.

The present invention has been made in view of the above-mentioned drawbacks of the conventional art, and the short-circuit current control described above suppresses the short-circuit current during welding and reduces the amount of spatter generated, and also reduces the probability of instantaneous transition to arcing at the start of welding. It is an object of the present invention to provide a DC arc welding machine that can realize good arc start characteristics with high and short transition time to a stable welding state.

Means for Solving the Problems To achieve this object, the DC arc welding machine of the present invention is provided with a main circuit for supplying DC power to the arc welding load,
A short-circuit state determining circuit determines whether the state of the welding load is an arc state or a short-circuit state, and the switching duty of the output control element during the period of the short-circuit state is determined by a signal from the short-circuit state determining circuit. Equipped with a short circuit current control circuit that controls the current to be smaller than the same switching duty during the state period, and a timer circuit that outputs only after a certain period of time from the start of welding.
The short-circuit current control is started according to the output of the timer circuit.

Effect of the present invention With the above-described configuration, the short-circuit current control is not performed for a certain period of time after the start of welding, and during the transition period from the start of welding to the transition to a stable welding state, the short-circuit current control is performed at a high rising speed and a high peak value. Since the current can be realized, good arc starting characteristics can be obtained.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG. 1 of the drawings.

In Figure 1, 1.2, 3, 4, 6, 6, 7, 8°9
．． 10, 11. 12, 13, 14. 15 are the same consumable electrodes, base material, electrode feeding motor and feeding device, welding part, rectifier, smoothing capacitor, inverter part, transformer, These are a rectifier, a reactor, an output control circuit, a shunt resistor, a current detector, a short-circuit state determination circuit, and a short-circuit current control circuit. 16 is a timer circuit that outputs an output after a certain period of time has passed after the start of welding.

The operation of the DC arc welding machine configured as above will be explained below. AC power input from the power supply input terminal is converted into DC power by a rectifier 6 and smoothed by a smoothing capacitor 6. Then, the inverter section 7 composed of power transistors converts the current into alternating current again. Next, the voltage is stepped down by a transformer 8, rectified by a rectifier 9, and becomes DC power, which is supplied as a welding output via a DC reactor 10. Through the above power circuit, DC power is supplied between the consumable electrode 1 and the base material 2, and at the same time, electricity is supplied by the electrode feeding motor and the feeding device 3, and the consumable electrode 1 and Short circuits and arcs are alternately repeated between the base metals 2. The welding current during welding is detected by the current detector 13.
The current detector 13 outputs a current detection signal proportional to the output current. In addition, the short circuit state determination circuit 1
4 detects the output voltage of the main circuit, determines whether the welding load is in an arc state or a short circuit state, and outputs an output. Then, in response to the current detection signal and the signal from the short-circuit state determination circuit 14, the short-circuit current control circuit 15 sets the switching duty of the output section control element during the period in which the welding load is in the short-circuit state. The switching duty is controlled to be smaller than the same switching duty, so that the rising speed of the short-circuit current is slower than when the switching duty is the same during both the arc state and the short-circuit state. This short circuit current control reduces the amount of spatter generated during welding.

Next is the timer circuit 16, which is a feature of the present invention. When the timer circuit 16 receives a signal from the current detector 13, that is, detects that an output current has flowed, it starts counting using this as a trigger. Outputs after a certain period of time. The short-circuit current control circuit 15 starts control only after receiving the output of the timer circuit 16, and the short-circuit current is not intentionally suppressed by the control circuit until the timer circuit outputs an output. In this way, the timer circuit 16 (time limit circuit) is added to the short circuit current control circuit 15, so that the short circuit current control is canceled at the time of arc start. In the example of the present invention, the timer circuit 16 receives the output signal of the current detector and outputs the delayed signal, but the same effect can be achieved even if the timer circuit 16 outputs the delayed signal in response to the activation signal for starting welding.

Effects of the Invention According to the present invention, the rise of the short-circuit current is not suppressed during the period from the start of welding until the transition to a stable welding state in which arc breakage does not occur for a long time. The probability of transition is also increased, the time from the start of welding to transition to a stable welding state is shortened, and the consumable electrode does not pop strongly when it melts due to insufficient short circuit current. This has the excellent effect of providing good arc start characteristics at the start of welding while controlling the short circuit current during welding.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a DC arc welding machine according to an embodiment of the present invention, Fig. 2 is a block diagram of a conventional DC arc welding machine, and Fig. 3 is a welding current waveform diagram of a conventional DC arc welding machine. It is. 1...Consumable electrode, 2...Base material, 3.
...Electrode feeding motor and feeding device, 4...
...Welding part, 5... Rectifier, 6...
Capacitor, 7... Inverter section, 8...
・Transformer, 9... Rectifier, 1o... Reactor, 11... Output control circuit, 12...
...Shunt resistor, 13...Current detector, 1
4...Short circuit state determination circuit, 15...Short circuit current control circuit, 16... timer circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 figure

Claims (1)

[Claims] It has a main circuit that uses an output control element such as a transistor to supply DC power to the arc welding load generated between the consumable electrode and the base metal, and an output control circuit that controls the switching duty of the output control element. a determining means for determining whether the state of the welding load is an arc state or a short circuit state; and a determining means for determining whether the state of the welding load is an arc state or a short circuit state; A short-circuit current control circuit that controls the short-circuit current to be smaller than the switching duty, and a timer circuit that releases the control by the short-circuit current control circuit for a certain period of time after the start of welding and starts after the certain period of time. A DC arc welding machine featuring: