JPS642477B2 - - Google Patents

Description

[Detailed description of the invention]

This invention periodically superimposes a pulsed welding current (hereinafter referred to as "pulse current") on a direct current welding current (hereinafter referred to as "base current") supplied between a wire electrode and a base metal. , relates to a pulsed arc welding method in which the electromagnetic contraction force generated by this pulsed current is used to make the wire fine and transfer it to the base metal (this is called "spray transfer"). As an apparatus for carrying out the conventional pulse arc welding method, there was one as shown in FIG. In the figure, 1 is a transformer, which has a winding structure of three phases on the primary side and six phases on the secondary side. 201-206
is a thyristor that converts alternating current voltage into direct current, and can also change the voltage value through phase control. 3 is an interphase reactor, and these 1, 2
01 to 206 and 3 constitute a power supply 4 that supplies a base current. Reference numeral 5 denotes a power supply that supplies a pulse current superimposed on the base current, and is composed of two phases of the secondary winding of the transformer 1 with a large number of turns, and approximately thyristors 601 and 602 connected thereto.
701 and 702 are DC reactors, 8 is a wire,
9 is a wire feeding device such as a motor for feeding the wire 8; 10 is an arc; and 11 is a base material (workpiece). One of the outputs of the power supplies 4 and 5 is common and connected to the wire, and the other is connected to the DC reactor 7.
01 and 702 and connected to the base material 11. In addition, 12 and 13 are the power supply 4, respectively.
This is a control circuit for controlling the phase of the thyristor in the power supply 5. Next, the operation of the conventional welding method will be explained. A base current is supplied from the power supply 4 and a pulse current is supplied from the power supply 5 between the wire 8 and the base material 11. At the same time, the wire 8 is supplied to the base material 11 by the wire feeding device 9.
When sent out to the side, the base metal is welded. The control circuits 12 and 13 each have a thyristor 201 to
The ignition phases of 206, 601, and 602 are changed, thereby changing the base current value I _B , pulse width τ, and pulse current peak value I _P (hereinafter referred to as "peak current value I _P "). . The waveform of the welding current is as shown in Figure 2, and the pulse frequency is equal to or twice the basic power frequency (50Hz or 60Hz in our country). Note that FIG. 2a shows the waveform when the average welding current is small, and FIG. 2b shows the waveform when the average welding current is large. Now, for example, when the base material is thin, welding is performed by keeping the average welding current (or wire feeding speed) small, but specifically, as shown in Figure 2a, the base current I _B In addition, the pulse width τ is set to be small, and therefore the peak current value I _P is also set to be small, and the pulse frequency may also be lowered from, for example, 120Hz to 60Hz. On the other hand, if the base material is thick, for example, the average welding current (or wire feeding speed) will be large, so the waveform will be larger, I _B as shown in Figure 2b. Furthermore, since τ is large, I _P is also set large. Conventional pulsed arc welding is performed as described above, so when the average welding current is lowered as shown in Figure 2a, as I _P becomes smaller, the electromagnetic contraction force due to the pulsed current decreases, resulting in less spray transfer. As a result, the droplet 14 becomes extremely large as shown in FIG. Wire scatters as spatter. Furthermore, when the average welding current is increased as shown in Fig. 2b, as τ and I _P become large, the droplet 14 transfers to the base material approximately once per pulse, but per cycle of the pulse The amount of heat injected into the wire increases, as shown in Figure 3c,
When the droplet 14 hangs down and the arc length is short, there is often a short circuit between the base metal and the wire, which also causes spatter. In cases like Figure 3 a and c, if you try to avoid spatter, you will not be able to keep the arc length short, and as a result, welding defects such as undercuts will easily occur, and welding speed will not be increased. . In order to obtain an appropriate droplet transfer state in which the arc length is short (therefore, undercuts are less likely to occur and the welding speed can be increased) and the droplets are small, as shown in Figure 3b, the pulse width τ, The peak current value I _P and base current value I _B must be adjusted very well. In this way, conventional pulsed arc welding methods are extremely difficult to adjust to achieve proper droplet transfer conditions, and often generate spatter, requiring extra work such as post-treatment of the base material. This resulted in a disadvantage that work efficiency decreased. This invention was made in order to eliminate the drawbacks of the conventional methods described above, and it is possible to achieve a proper droplet transfer state without spatter over a wide average welding current range, short arc length, and avoid undercuts, etc. The object of the present invention is to provide a pulsed arc welding method that does not cause the occurrence of irradiation and increases the welding speed. An embodiment of the present invention will be described with reference to the drawings. In Fig. 4, 15 is a DC power supply composed of a transformer, a diode, etc., and the power supply 4 is a switching circuit 16 such as a transistor that can turn the current ON and OFF using a control signal (even DC current can be turned OFF by the action of only its elements). and a DC reactor 703 and a detector 212 for detecting the base current. The power source 5 is also comprised of a switching circuit 17 and a DC reactor 704 that can turn the current on and off using a control signal such as a transistor. In addition, the switching circuits 16 and 17
In some cases, a large number of elements are connected in parallel due to current capacity, etc., and 18 indicates a balance resistor necessary for parallel operation. 19 is a capacitor 201, 20 for absorbing the surge voltage generated when the switching circuit 16 or 17 is turned on and off, improving the rise of the pulse current, and reducing the ripple of the output current of the DC power supply 15;
2 are the switching circuits 16 and 17, respectively.
211 is a detector for detecting welding current; 22 is a high-frequency power source; 23 is a step-up transformer; 24 is a capacitor; 25 is a spark gap; 26 is a high-frequency voltage detector. A coupling coil 27 is made of a magnetic material such as ferrite, and a wire passes through the coupling coil. 28 is a bypass capacitor. 29 is a detector for detecting arc voltage. Next, the operation will be explained. First, the input voltage of the high frequency power supply 22 is boosted by the step-up transformer 23 and applied to both ends of the capacitor 24, that is, the spark gap 25. At a certain limit value, discharge breakdown occurs between the gaps, and the capacitor 2
4. A series resonant circuit is formed between the coupling 26 and a high frequency high voltage. This high frequency high voltage is applied between the wire 8 and the base material 11 via the coupling coil 26. At this time, the high frequency high voltage does not enter the wire feeding device 9 and the power supplies 4 and 5 due to the high frequency reactor 27 and the bypass capacitor 28 which have a high impedance with respect to high frequencies. Due to the discharge breakdown between the wire and the base metal due to this high frequency voltage, the arc is ignited even if there is no short circuit between the wire and the base metal, thereby suppressing the generation of spatter when the arc is ignited. Now, if the wire 8 is sent out toward the base metal by the wire feeding device 9 in tandem with the ignition of the arc, welding is performed. Regarding the supply of welding current, the DC current supplied from the DC power source is turned on and off by the switching circuit 17 to form a pulse current.
(Immediately after the switching circuit 17 is turned off,
A welding current flows through the flywheel diode 201 and the DC reactor 704. ) Furthermore, a base current is generated by turning the switching circuit 16 ON and OFF. (The switching circuit 16
Immediately after turning off, the base current flows through the flywheel diode 202 and the DC reactor 703. ) At the same time, the detector 211 detects the welding current moment by moment, and its output is sent to the control circuit 1.
3, the peak current value I _P is input to the wire material,
The switching circuit 1 is designed to fall within a predetermined range determined by the combination of
7 turns ON-OFF. Further, the base current is detected moment by moment by the detector 212, and the switching circuit 16 is turned on and off via the control circuit 12 so that the base current is within a predetermined range mainly determined by the wire diameter.
It will be turned off. Further, the control circuit 13 has the role of regulating the correspondence between the pulse frequency and the wire feeding speed, and the correspondence between the average value of the arc voltage detected by the detector 29 and the pulse width. . Now, the welding current waveform is as shown in Figure 5.
The method of setting the pulse frequency, pulse width τ, peak current value I _P , and base current value I _B will be specifically described. In the figure, T is the period of the pulse, and I _B
The average value of the pulsating flow was taken. First, the peak current value I _P is at least the so-called critical current value necessary to make the wire fine and transfer it to the base metal (this is determined by the wire material, diameter, and type of shielding gas used)
Must be set above. However, if it is made too large, the arc force toward the base metal side will increase, which will disturb the weld bead, which is even worse. Therefore, the set value of I _P (assuming that it is kept constant regardless of the average current value) is equal to or higher than the critical current value, and if the pulse period T is increased while keeping I _P constant, the average welding current The value is chosen so that it can be a predetermined maximum value. Examples of I _P setting ranges for various combinations of wire materials, diameters, and shielding gas types are summarized in Appendix Table 1. Next, the correspondence between wire feeding speed and pulse frequency (or pulse period) will be described. The size of the droplet 14 when the wire is melted by arc heat and Joule heat caused by the current flowing through the wire, and is further refined by electromagnetic contraction force is as follows: (a) The size of the droplet 14 acting on the droplet in the direction of the base material Electromagnetic force (b) Surface tension in the wire direction (c) Determined from the balance of gravity. The actual measurement results of the droplet size (melt diameter a) when proper droplet transfer occurs as shown in FIG. 3b are added to Table 1. Now, in order to prevent spatter from occurring as much as possible even if the arc length is shortened, the droplet diameter a should be made as small as possible. That is, it is sufficient to perform one transfer with the droplet diameter shown in Table 1 per one pulse. Therefore, the wire feeding speed υcm/s and the pulse frequency
Generally speaking, the correspondence relationship with Hz can be expressed as the following equation, since the amount of wire fed per second is equal to the amount of transferred droplets, assuming that the droplet diameter is ammφ and the wire diameter is dmmφ. π(d/2) ² ×υ×1/100=4/3π(a/2) ³
××1/1000 ∴υ/=1/15×a ³ /d ² Table 1 also includes the setting range of υ/ according to each wire diameter and droplet diameter.

[Table] Now, the amount of heat W to be injected into the wire per one pulse is considered to be sufficient to melt the wire for the amount of droplets shown in Table 1. For example, if the wire is made of mild steel
If the droplet diameter is 1.2mmφ and the diameter of the droplet is 1.2mmφ, the amount of heat is
The room temperature is 0℃, the temperature of the droplet is 1535℃ (melting point of iron),
The specific heat is 0.15 cal/g℃, the latent heat is 65 cal/g, and the density is
Calculated as 7.8g/ ^cm3 : 2.08cal (8.74Joule)
becomes. Table 1 also includes the optimum range of heat to be injected into the wire per pulse for various combinations of wire material diameters and shielding gas types. The physical steps used are shown in Table 2 below.

[Table] As shown above, if you set the correspondence between the peak current value, wire feeding speed, and pulse frequency (or the amount of heat injected into the wire per pulse), the droplet transfer will be done properly. It is carried out in diameter. When actually welding, it is also necessary to maintain the arc length at an appropriate value. This is because if the arc length is too long, the range in which the base metal is heated increases, which may be undesirable, and if the arc length is too short, the droplets may short-circuit with the base metal, causing spatter. commonly used
The arc length for 0.9-1.6mmφ wire is 2-3
It is appropriate to set it to about mm, and the arc voltage at this time will be 20 to 40V. The arc length is controlled by detecting the arc voltage and controlling the average welding current value, that is, the amount of heat input per pulse, and the pulse frequency so that this value becomes a preset value. In this invention, the amount of heat input is adjusted by changing the peak value I _P of the pulse. When the detected arc discharge voltage is higher than the set reference value, the amount of heat input is reduced and the arc length is shortened by delaying the transfer of droplets to the base material.On the other hand, when the arc discharge voltage is lower than the reference value, the arc length is shortened. The arc length is lengthened by increasing the amount of heat input and speeding up the transfer of the droplets to the base metal. Specifically, the detected arc discharge voltage value is compared with a preset reference value, and if the arc discharge voltage is higher than the reference value, the pulse peak value of the pulse current is decreased in order to reduce the amount of heat input. When the arc discharge voltage is lower than the reference value, the pulse peak value of the pulse current is controlled to be increased in order to increase the amount of heat input. Here, the pulse peak value of the pulse current was used to adjust the amount of heat input because if the pulse peak value was kept constant, the wire would not be fused when it came into direct contact with the base metal. There is,
Although it may not be possible to re-ignite the arc, by controlling the pulse peak value as described above, when the wire comes into direct contact with the base metal, the pulse peak value will increase and the wire will not melt. This is because the process is performed reliably and the arc can be re-ignited reliably. Note that the base current value I _B is a current value necessary to prevent arc breakage between pulses. Specifically, if the wire diameter is 0.9mmφ, it will be approximately 10A, and if the wire diameter is 1.2mmφ or 1.6mmφ, it will be approximately 20~30A.
It is appropriate to do so. The reason why the base current is set low for the small diameter wire is that it can be used in areas where the average welding current is small. In the above explanation, an example is shown in which a transistor is used as a switching circuit element, but the same effect can be achieved with other devices such as a gate turn-off thyristor. This invention supplies a base current that maintains an arc between a base metal and a welding wire, and a pulsed current superimposed on the base current to cause an electric discharge, and the droplets of the wire are moved by the electromagnetic contraction force of the pulsed current. In those in which welding is performed by transferring to the base metal,
The arc discharge voltage is detected by an arc voltage detector connected between the wire and the base metal, and the detected arc discharge voltage value is compared with a preset reference value, and the arc discharge voltage value is found to be greater than the reference value. When the arc voltage is smaller than the reference value, the pulse peak value of the pulse current is controlled to be smaller, and when the arc voltage is smaller than the reference value, the pulse peak value of the pulse current is increased. A suitable arc length can be obtained with simple operation, the weld bead tends to be uniform, and the welding speed can be increased.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the power supply circuit configuration of a device that performs the conventional pulsed arc welding method, Fig. 2 is a diagram showing the welding current waveform of conventional pulsed arc welding, and Fig. 3 is a diagram showing the welding current waveform of conventional pulsed arc welding.
4 is a diagram showing the configuration of a power supply circuit in an embodiment of the method of the present invention, and FIG. 5 is a diagram showing the welding current waveform of pulsed arc welding of the present invention. be. In the figure, 1 is a transformer, 4 is a power supply that supplies base current, 5 is a power supply that supplies pulse current,
8 is a wire, 9 is a wire feeding device, 10 is an arc, 11 is a base material, 12, 13 are a control circuit, 14 is a droplet, 15 is a DC power supply, 16, 17 is a switching circuit, 29 is an arc voltage detector , 211 is a welding current detector, 212 is a base current detector, 22 is a high frequency power source, and 27 is a magnetic material such as ferrite. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1 A base current that maintains an arc between the base metal and the welding wire and a pulse current superimposed on this are supplied, and the droplets of the wire are transferred to the base metal by the electromagnetic contraction force of the pulse current to perform welding. In a pulsed arc welding method configured to perform When the arc discharge voltage value is larger than the reference value by comparison, the pulse peak value of the pulse current is decreased, and when the arc voltage is smaller than the reference value, the pulse peak value of the pulse current is increased. A pulse arc welding method characterized by: