JPS6343197B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an arc welding machine that can perform CO ₂ welding, MIG welding, MAG welding, etc. Generally speaking, in arc welding machines that use consumable electrodes (welding wires), there is a method to reduce or increase the output voltage at the end of the arc to reduce the size of the ball that forms at the tip of the welding wire. Although the size of the ball at the tip of the welding wire becomes smaller, slag collects at the tip, resulting in a thicker slag layer, and in automatic machines, the line stops due to arc start failure, and when the output voltage is increased, welding There is a problem that the ball at the tip of the welding wire becomes larger, or it fuses to the tip that supplies the welding current to the wire. Furthermore, the method of reducing the size of the ball at the tip of the welding wire is difficult in MIG welding, etc., and is currently only used for CO ₂ welding. The arc welding machine of the present invention improves these points and makes the size of the ball at the tip of the welding wire sufficiently small even in MIG welding, thereby making the arc starting characteristics even more perfect. It is something that has become something. Conventionally, in an arc welding machine that uses a consumable electrode, when the torch switch is released at the end of welding as shown in Fig. 1a, the wire feed motor signal is turned off (Fig. 1b). Due to mechanical inertia, the wire feeding does not stop instantaneously, but gradually stops (Fig. 1 c), so if you stop the power supply to the wire feeding motor and turn off the output voltage of the welding machine at the same time, The wire fed by the mechanical inertia of the wire feeding motor or the like plunges into the molten pool, and the wire and base material are fused together because no energy is supplied to melt the wire. Therefore, in order to prevent this phenomenon, a method has been adopted in which the output voltage of the welding machine is turned off after the wire feeding has completely stopped (Fig. 1d). However, since the output voltage of the welding machine at this time is the same as the steady-state welding voltage or the crater processing voltage during crater processing, the balance between the gradually decreasing wire feeding speed, that is, the welding current and arc voltage is lost, causing the arc As the voltage increases, the wire catches fire and a ball forms at the end of the wire. but,
If the ball at the tip of the wire is large, there will be less contact resistance with the base metal when starting the arc, and less heat will be generated from the resistance when a short-circuit current flows, and in addition, the welding current will rise from O when starting the arc, and it will take time to rise. In addition, the amount of energy supplied is small, and the tip of the wire must be heated from room temperature to the melting point, and the tip of the wire is large, so a large amount of energy is required. It becomes difficult to scatter and form an arc. Therefore, several methods have been taken to improve the arc starting characteristics by reducing the size of the ball formed at the tip of the wire when the arc ends. A typical example is to turn off the wire feed motor signal and simultaneously reduce the welding machine output signal by one step as shown in Figure 1e, or to stop the wire feed motor while gradually decreasing as shown in Figure 1f. In this method, the output signal of the welding machine is gradually decreased in response to the
All of these methods reduce the size of the ball at the tip of the wire by reducing the output voltage of the welding machine. However, the drawback of this method is that the second
When the ball at the tip of the wire is large as shown in Figure a, the slag layer becomes thin, but by reducing the output voltage and making the tip of the wire smaller, the slag gathers first and the slag layer becomes as shown in Figure 2b. As shown in the figure, the slag layer becomes thicker, so in fully automatic welding, etc., even if the wire tip comes into contact with the base metal, the slag layer is thick and will not crack, and since slag is an insulator, no arc will occur and the line will stop, etc. A problem occurs. In addition, the method of reducing the output voltage of these welding machines is commonly used in CO ₂ welding, etc., but in MIG welding,
Compared to CO ₂ welding, which involves welding in a CO ₂ gas atmosphere, the arc burn-up time is approximately twice as fast because welding is carried out in an argon gas atmosphere, which prevents the wire from burning up and from being fused to the base metal. It is difficult to control the output voltage to make the tip of the wire smaller, and in MIG welding of aluminum, the specific gravity of the aluminum wire is about one-third that of steel, so the ball at the tip of the wire is CO ₂ welded. It had disadvantages such as being more likely to become large compared to the previous one. Another typical example is a method of superimposing a voltage higher than the arc voltage at the end of welding, as shown in FIG. 1g, and a typical circuit thereof is shown in FIG. 3.
In the figure, 1 is a welding power source, L ₁ is a DC reactor in its output circuit, 2 is a DC power source with a voltage higher than the arc voltage, R ₁ is a resistor, C ₁ is a capacitor, and S ₁ is the output side of welding power source 1. This is an opening/closing element that opens and closes in conjunction with a torch switch provided to superimpose the output of the DC power supply 2 on the During welding, an output voltage is generated from the welding power source 1 through the reactor _L1 , and when welding is stopped, the switching element _S1 is closed and a voltage higher than the welding voltage charged in the capacitor _C1 is applied. This method uses a pinch force to reduce the size of the ball at the tip of the wire by passing an electric current through it. However, this method is good when the inertia of the wire feed motor is small, but as the rotation speed of the wire feed motor increases, the inertia increases, and even if the rotation speed of the wire feed motor is the same, the welding power source If the cable is far away, an extension cable is used, but its resistance makes it difficult to brake the motor, and the inertia of the wire feed motor increases, resulting in a situation like the broken line in Figure 1c. Even if a high voltage is applied at the end of welding and the wire end is separated by a pinch force of a large current, the wire is fed later and the output voltage is high, resulting in a flare-up phenomenon and the ball at the wire tip may not become small. This occurs frequently, and in MIG welding, etc., fusion may occur between the chip that supplies the welding current and the welding wire. Therefore, the method of reducing the size of the ball formed at the tip of the wire at the end of the arc in order to improve the arc start has not been sufficiently effective. The present invention provides an arc welding machine that eliminates the drawbacks of the conventional method of reducing the size of the ball at the tip of the wire at the end of the arc. The main circuit of the embodiment is shown in FIG. 5, and the sequence in the present invention is shown in FIG. 6.
In addition, in FIG. 5, a welding load is connected to the output side as in FIG. 3. First, a brief explanation of the pulsed MIG welding method related to the present invention will be given. As shown in Figure 4, the base current (generated by the first rectifier circuit) I _B , which hardly changes over time, This method superimposes a sufficiently large pulse current (by the second rectifier circuit) I _P to perform It is well known that various features are exhibited by the transfer of droplets into a spray. A typical main circuit is shown in FIG. Figure 5 shows an integrated type in which the base current and pulse current are passed through one transformer. The base current is phase-controlled by thyristors SOR ₁ to _{SCR 6} in the six phases of a three-phase double star, and the pulse current is controlled by thyristor SCR ₇ (in this case, the pulse frequency is the same as the commercial frequency, 50Hz or 60Hz), or by thyristor SCR _7. , SCR ₈ (at this time, the pulse frequency is 100Hz or 120Hz, which is twice the commercial frequency) and is adjusted by phase control. _L1 is a DC reactor for smoothing the base current,
_L12 taken out from the middle of this DC reactor _L1
(The part on the right side of the tap) is a DC reactor for controlling the transient characteristics of the pulse current, and the DC reactor _L12 for pulse current may be a separate DC reactor. L ₂ is an interphase reactor. In the figure, when the pulse part which is the second rectifier circuit is not operated and the characteristics of the first rectifier circuit are constant voltage characteristics or quasi-constant voltage characteristics, CO ₂ welding, MIG welding, Can perform MAG welding, etc. Therefore, the present invention uses the first rectifier circuit shown in FIG. 5 to perform CO ₂ welding, MIG welding, and MAG welding, the sequence of which is shown in FIG. 6. In Fig. 6, when the torch switch is released at the end of welding, the wire feed motor signal is turned off (Fig. 6 b) at the same time (Fig. 6 a), but due to the mechanical inertia of the wire feed motor, the wire feed motor signal is turned off (Fig. 6 b). does not stop instantaneously, but stops while gradually decreasing (Fig. 6c). Therefore, currently the output voltage is lowered or raised to reduce the size of the ball at the tip of the wire from when the torch switch is released at the end of welding until the wire feeding stops, but the present invention reduces the ball at the tip of the wire. (It may be from midway through to before or after the wire feeding stops), and is configured so that the pulse current is superimposed from the second rectifier circuit in FIG. 5 to the first rectifier circuit as shown in FIG. 6d. . By doing this
In MIG welding and MAG welding, the tip of the wire is spray transferred at the end of welding, and in CO ₂ welding, the tip of the wire is detached by a pinch force generated by a large current, reducing the shape of the ball at the tip of the wire. be. Furthermore, since the magnitude of the pulse current can be arbitrarily controlled by controlling the phase of the second rectifier circuit shown in FIG. 5, it is only necessary to adjust it to the energy required at the end of the arc. Until now, pulsed MIG welding, and _CO2 welding,
We have explained using a dual-purpose machine that can perform MIG welding and MAG welding, but CO ₂ welding or MIG welding,
In MAG welding or both machines,
There is no problem even if this second rectifier circuit is installed and the sequence shown in FIG. 6 is adopted. In this case, it is only necessary to superimpose the pulse current at the end of the arc, and there is no need for pulsed MIG welding, so the input capacity of the welding power source can be the same as that for CO ₂ welding, MIG welding, and MAG welding, so it is very small. good. For example, a pulsed MIG welding machine with a rated welding current of 350 A requires 22 to 45 KVA depending on the width, peak value, and pulse frequency of the superimposed pulse current, but when no pulse current is superimposed, it is around 19 KVA.
Further, since the control circuit does not require welding, there is no need to adjust the output voltage, minimum voltage, maximum voltage, or welding voltage, and it is only necessary to supply the optimum energy only when the arc ends. Furthermore, since the pulse current is superimposed for a short time at the end of the arc, compensation for power supply voltage fluctuations and temperature does not need to be precise, and therefore the control circuit becomes very simple. As described above, by superimposing a pulse current at the end of the arc in CO ₂ welding, MIG welding, and MAG welding, it is possible to dramatically reduce the size of the ball at the tip of the wire through pinch force and spray transfer. As an example, the diameter of the wire tip with and without pulse termination in aluminum MIG welding is shown in the table below.

[Table] By using the pulse termination of the present invention as described above, the conventional disadvantage of thick slag layer at the tip of the wire during CO ₂ welding, which causes arc start failure, can be avoided, and it is possible to It works reliably even when using long cables, and in the case of MIG welding, there is no fusion between the chip that supplies the welding current and the welding wire, and the size of the ball at the tip of the wire can be dramatically increased. It can be made smaller and the arc start characteristics can be made even more perfect.

[Brief explanation of the drawing]

Figures 1 a to g are characteristic diagrams of various signals before and after arc termination in a conventional arc welding machine, and Figures 2 a and b
3 is a circuit diagram of the power supply section of a conventional arc welding machine, FIG. 4 is a current waveform diagram of pulsed MIG welding, and FIG. 5 is a front view of the tip of a conventional wire. FIGS. 6a to 6d are characteristic diagrams of various signals before and after arc termination in the arc welding machine of the present invention. L ₁ , L ₁₂ ... DC reactor, L ₂ ... Interphase reactor, SCR ₁ to _{SCR 8} ... Thyristor.

Claims (1)

[Claims] 1. A torch switch is connected to a welding load via a DC reactor, and is capable of performing DC arc welding by itself, and after a certain period of time has elapsed from the time when the torch switch issues an arc end signal, the welding load is a first rectifier circuit that cuts off the current to the first rectifying circuit; and a first rectifying circuit that cuts off the current to the
a second rectifier circuit that superimposes a pulse current on the rectifier circuit; and a wire feed motor whose drive current is cut off when the torch switch issues an arc termination signal.