JPH069741B2 - Short-circuit transfer welding power source control method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a welding power source control method and apparatus used for short-circuit transfer welding.

[Problems of Prior Art] In gas shield welding, welding is performed while repeating short circuit and arc generation between the welding wire and the base material.

It has also been clarified that most of spatters in short-circuit transfer welding are generated at the moment when the short circuit is broken and the arc is regenerated, and larger spatters are generated as the current during arc regeneration is higher. However, in a constant voltage power source that merely delays the rise of electricity by a conventional reactor, as shown in FIG. 1, the current during arc regeneration was high, and thus spatter was very much. Focusing on this cause, attempts have been made to reduce the current during arc regeneration, but this has not yet been put to practical use. For example Welding Research international Vol.4.No.2.1974
Limits the high current conduction period to the central period of the short circuit period,
Detects the voltage between the consumable electrode wire and the base material during the high current period,
Technology that controls the spatter by program control so that the voltage at the time when the droplet constriction occurs as a precursor of arc regeneration is set and the high current period is ended when the detected voltage becomes equal to a certain set voltage Is disclosed. However, as described in the above document, in practical use, the voltage drop at this portion fluctuates due to fluctuations in the wire protrusion length, so the voltage when the droplet is constricted is not constant, and a large current An error occurs at the time of instructing the end of the period, and it is impossible to stably prevent spatter.

As is well known, the generation of this kind of spatter lowers the quality of welding, and a complicated work is required to remove spatter, which lowers the welding work efficiency.

[Object of the Invention] The present invention has been made in order to solve the above-mentioned problems in the conventional short-circuit transfer welding, and suppresses the welding wire current by accurately detecting the time when the necking of the welding wire occurs. Therefore, it is an object of the present invention to provide a welding power source control method and apparatus capable of preventing the generation of spatter, improving the quality of welding, and improving the efficiency of welding work.

[Summary of the Invention] In the welding power source control method according to the present invention, when the differential value of the resistance between the welding wire and the base material with respect to time is detected in the short-circuit transfer welding, and the differential value reaches a predetermined value. , Reduce welding wire current.

Further, in the control device for the welding power source according to the present invention, the detection means for detecting the resistance value between the welding wire and the base material, the differentiating circuit for differentiating the resistance value, and the detection that the differential value of the resistance has reached the set value And a control circuit for reducing the current flowing through the welding wire when the differential value of the resistance reaches a set value.

[Principle of the Invention] FIG. 2 shows an outline of a short-circuit transfer welding apparatus.
Is a welding power source, 102 is a power supply cable, and 103 is a welding wire fed by a motor (not shown). The welding wire 103 projects through the welding torch 104 toward the base metal 106 and welds to the base metal 106. An arc 105 is generated between the wires 103. The welding wire 103 from the welding torch 104 repeats short-circuiting and arc generation with the base material 106 at appropriate time intervals to perform known short-circuit transfer welding.

FIG. 3 shows the welding wire voltage waveform, current waveform, welding wire 103 and base metal 106 during the above-described short-circuit transfer welding.
It shows the positional relationship between the
Symbols a, b, c, d, and e indicate the respective welding states. That is, during arc generation, the arc length gradually decreases from a, and short circuit b
Leading to. At this time, the current is increased and maintained at a certain constant value. Time point c when the droplet is most strongly bonded to the base material 106
After a lapse of time, after the point d at which the tip of the welding wire 103 starts to be constricted, the welding current is rapidly reduced, and the arc regeneration is started at a time point e when the current is sufficiently reduced.

As is apparent from FIG. 3, although the current is constant from the point c to the point d, the voltage rises near the point d. This is due to the constriction of the welding wire near point d,
The main reason is that the cross-sectional area of the fusion zone at the tip of the wire decreased and the resistance increased. Therefore, the resistance at the time of short circuit is detected, and the temporal change amount of the resistance, that is, the differential value dR / dt of the resistance R
When the current reaches a predetermined value, the current can be reduced to suppress spatter.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 4, the output signal of the voltage detector 110 that detects the voltage between the welding torch 104 and the base metal 106 is input to one input terminal of the resistance detector 111, and the welding wire 103
The output signal of the current detector 112 that detects the current is input to the other input terminal of the resistance detector 111 using a divider. The resistance detector 111 determines the welding wire 10 from the ratio of the output signal of the voltage detector 110 and the output signal of the current detector 112.
3 and the resistance between the base material 106 are calculated, and the calculated resistance value is applied to the differentiating circuit 113.
Therefore, the resistance calculated by the resistance detector 111 is When the resistance differential value becomes larger than the set value compared with the set value set by the setter 115, the comparator 114 applies a control signal to the welding power source 101 to turn on the switch 120 at a low current. The setting device 121 on the side is switched to control the output of the welding power source 101 to reduce the current of the welding wire 103. The set value of the setter 115 is determined corresponding to the differential value of the resistance value between the welding wire and the base material when the welding wire is constricted.

In addition, 122 is a current setting device at the time of welding, and the welding power source 101 has a current setting device 121, 12 for the error amplifier 101a.
Set value applied from any one of 2 and the current detector 112
The output current of the power control circuit 101b is set according to the deviation from the welding wire current detected from the current setting devices 121 and 122.
Control to be the value set by either

In welding with the above-mentioned device, a, b, c, and
The method for controlling the welding voltage and welding current at the d and e portions is the same as the conventional method.

In FIG. 5, g ₁ , h ₁ , i ₁ , j ₁ , l ₁ have wire protrusion lengths of 16 mm, 20 mm, 12 mm, 16 mm, respectively.
It is a current waveform at the time of 16 mm, g ₁ , h ₁ , i ₁ ,
j ₁ and l ₁ are current waveforms having a short circuit time of approximately 2 msec, and j ₁ has a short circuit time of approximately 3 msec. g _{1 to} j ₁ are controlled to be constant after the short circuit current has passed for about 1 msec after the short circuit,
G ₁₁ , H ₁₁ , I ₁₁ , J ₁₁ , and L ₁₁ are current values at the time when it is determined that a constriction has occurred, and the current is reduced after the constriction occurs. l ₁ is shown by a one-dot chain line, the short-circuit current increases with time, and the current decrease waveform after the constriction detection is g
It overlaps with the waveforms of ₁ , h ₁ , and i ₁ . FIG. 6 shows the fifth
The voltage waveforms corresponding to the current waveforms g ₁ , h ₁ , i ₁ , j ₁ , l ₁ in the figure are g ₂ , h ₂ , i ₂ , j ₂ , l ₂ having wire stroke lengths of 16 mm, 20 mm, and 12 mm, respectively. , 16mm, 16mm
Is a voltage waveform at the time of. G ₂₁ , H ₂₁ , I ₂₁ , J ₂₁ , L ₂₁
Are the voltage values at the time when the constriction occurs. 7th
The figure shows the resistance waveform. _{g 3, h 3, i 3} , j 3, l 3
Is a curve showing the resistance change, G ₃₁ , H ₃₁ , I ₃₁ , J
₃₁ and L ₃₁ are resistance values when a constriction occurs, respectively. FIG. 8 is a waveform obtained by differentiating the resistance shown in FIG. These waveforms are represented by a curve _{g 4, h 4, i 4} , j 4, l 4. Further, G ₄₁ , H ₄₁ , I ₄₁ , J ₄₁ , and L ₄₁ are the values of dR / dt at the time when the constriction occurs.

Even if the short circuit current is lowered, the constriction of the droplet that the arc regenerates is
In the voltage waveform, the voltage values are G ₂₁ , H ₂₁ , I ₂₁ , J ₂₁ , and L ₂₁ . It can be seen that the voltage values of G _{21 to} L ₂₁ depend on the wire protrusion length and the short circuit time. Theoretically, the wire protrusion length may be changed to the level indicated by the detection voltage levels G _{21 to} L ₂₁ in accordance with the wire protrusion length and the short circuit time. 1 to 4 ms mainly due to vibration of the weld pool and fluctuations in the wire feed speed
fluctuates between ec. In the conventional technique, since the voltage between the welding torch and the base metal became a certain value, it was determined that the welding wire had a small constriction, and therefore the constriction generation voltage changed from G _{21 to} L ₂₁ depending on the conditions. Therefore, it can be seen from FIG. 6 that an error occurs in the detection of the necking occurrence and the necking detection is inaccurate and is almost impossible to carry out.

Therefore, in the present invention, as shown in the apparatus of FIG. 4, (1) the resistance detector 111 is used to weld the welding wire 103 and the base metal 10 together.
The resistance R between 6 is detected, and the differentiation circuit 113 When the welding current is reduced by determining that the constriction has occurred when the temperature reaches, the spatter can be reduced without being largely influenced by the wire protrusion length 1 and the short circuit time. Here, G ₄₁ , H ₄₁ , I ₄₁ , J ₄₁ , and L ₄₁ represent resistance differential values at the time when the constriction occurs.

The above-mentioned value K ₁ is set by the setter 115. The ideal K ₁ value as this set value changes depending on the wire protrusion length and the short circuit time, and accordingly, dR / dt at the time of constriction occurs.
The value of changes from G _{41 to} L _41, and the average value can be used as described above, but it is not ideal.

(2) In order to reduce spatter even more reliably,
As a set value of the setter 115, an ideal K ₁ value according to the wire protrusion length and the short-circuit time, that is, the dR / dt value detected when the constriction occurs is the resistance differential due to the constriction of G _{41 to} L _41. It is desirable to set a value that separates the amount of resistance differentiation and the amount of resistance differentiation that is not so.

As shown in FIG. 7, a certain time has elapsed after the short circuit at a time point before the occurrence of the constriction, and the resistance slightly increases after the short circuit current is applied. This increase in resistance is not related to the constriction, but it changes depending on the wire protrusion length and the short circuit time. This resistance change amount is approximately a value of G _{42 to} L _{42 when} expressed by the resistance differential value of FIG. This resistance differential value means that the resistance of the wire protrusion length is increased corresponding to the short-circuit current as described later. Therefore, let K _{2 be the} resistance differential value caused by the constriction.
₂ ≈ G ₄₁ -G ₄₂ ≈ ... ≈ L ₄₁ -L ₄₂ , which is almost constant.

The resistance change of the protruding portion of the welding wire occurs because the temperature of this portion rises due to the short-circuit current and the resistance of steel increases as the temperature rises, and is generally expressed by the following formula.

Now, except for l ₁ , the short-circuit current I _p is controlled to be constant, and the wire diameter is determined. In other words, ΔR = kRΔT to ΔR / Δt = kR, that is, the resistance differential value dR / dt = ΔR / Δt =
It can be considered as kR.

This kR value corresponds to the values G _{42 to} J ₄₂ in FIG. Therefore, the value kR obtained by multiplying the resistance detection value by a constant k
If it is determined that the constriction has occurred when dR / dt ≧ K ₂ + kR by using, and the current is reduced, it is possible to further surely reduce the spatter regardless of the wire protrusion length and the short circuit time.

FIG. 9 shows an example of a circuit for obtaining the above-mentioned set value,
The signal of the resistance detector 111 is applied to the differentiating circuit 113 and also to the amplifier 116.
A signal indicating kR is obtained from 6. This kR is the adder 1
17 and the adder 117 calculates the sum with the constant K ₂ applied from the setter 115 and outputs K ₂ + kR. This output is applied to the comparator 114.

I _P giving the setting value k discussed above its optimal value when changing the average welding current comes to change. Since the average current is substantially proportional to the wire feeding speed, it may be said that it changes depending on the wire feeding speed. When I _P = constant, the equation (2) is satisfied. Therefore, when I _P has another value, it is necessary to change the value of k and perform welding. Of course, a large error does not occur even if the k value at the time of the average value of the representative value I _P within the range used is used, but in order to further improve the accuracy, I _P is determined according to the wire feeding speed and accordingly Alternatively, the k value may be set, and this control does not lead to a significant increase in cost.

When the current is not constant, that is, when the waveform is such that the current increases with time like l ₁ in FIG. 4, since I _{P in the} equation (1) changes during the short circuit time, dR of the resistance heating amount is changed.
Although k of / dt = kR changes with time, in this case, the k value may be set to a value proportional to I _P ² by detecting the current. Further, the k value may be set according to the squared value V _P ² of the welding voltage V _P.

[Experimental Results] Welding current 150 A, welding voltage 20 V, welding wire feed rate 20 cm / min, shield gas CO ₂ 2Ol / mi
Using a 1.2 mmφ welding wire under conditions of n and n, bead-on-plate welding was performed for 10 minutes on a 12 mm-thick base metal by semi-automatic welding, and the amount of spatter adhering to the shield nozzle was compared.

As a welding power source, (I) a commercially available thyristor type welding power source (without controlling the welding current by detecting the constriction) (II) The first device according to the present invention: the resistance between the welding wire and the base metal at the timing of d in FIG. About R When (K ₁ = 3.3 mΩ / msec), the welding wire current is reduced to 50 A.

(III) Second device according to the present invention: At the timing of d in FIG. (K ₂ = 2.3 mΩ / msec, R = 0.058 Ω, k =
0.016), the welding wire current is reduced to 50A.

From this experiment, the results shown in the table below were obtained.

[Effects of the Invention] As described in detail above, the present invention is applicable to short-circuit transfer welding.
Welding that occurs between short circuit and arc regeneration Since it is designed to reduce the number of welding wires, it is possible to reliably detect the occurrence of welding wire constriction and reduce the current accordingly to reduce the occurrence of spatter, resulting in high-quality welding. At the same time, the welding work efficiency can be improved.

A power supply that controls current and voltage by pulse width control using a chopper or an inverter generally includes ripples in the current and voltage even when smoothed by a reactor or the like. Even when such a power source is used as the welding power source, when the necking of the welding wire is detected by the magnitude of the time change of the resistance as in the present invention, the resistance is obtained by the voltage / current. The effect is eliminated and the error due to ripple on the waist detection is not included and therefore the timing of waist detection is also accurate.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing an example of short-circuit transition welding, FIG. 2 is an electric circuit diagram showing the outline of a welding apparatus, and FIG. 3 is a diagram showing voltage and current waveforms of short-circuit transition welding together with the state of the welding wire. ,
FIG. 4 is a block diagram showing an embodiment of the present invention, FIGS. 5 to 8 are graphs showing the resistance change of the welding wire, and FIG. 9 is a block diagram showing a modification of the embodiment of FIG. is there. 101 ... Welding power source, 103 ... Welding wire, 106 ... Base material, 110 ... Voltage detector, 112 ... Current detector, 111 ... Resistance detector, 113 ... Differentiation circuit, 114 ... Comparator.

 ─────────────────────────────────────────────────── --- Continued from the front page (72) Inventor Masaharu Sato 731-1 Tehiro, Kamakura City, Kanagawa Prefecture (56) References JP-A-57-199565 (JP, A) JP-A-58-29575 (JP, A)

Claims (2)

[Claims] 1. A method of controlling a power source used for welding with a short circuit, wherein the temporal change in resistance between the welding wire and the base material at the time of short circuit dR / dt is obtained by multiplying the resistance between the welding wire and the base material by a constant. And a constant value, the output current of the power supply is reduced when the value exceeds a set value. 2. A welding power source having a variable output current, a resistance detecting means for detecting a resistance between a welding wire and a base material, a means for calculating a temporal change amount of the detected resistance value, and a temporal change of the resistance. Is equipped with a comparison means for detecting that the resistance between the welding wire and the base metal set by the setting means is multiplied by a constant and exceeds a set value which is a constant value. A control device for a short-circuit transfer welding power source characterized by reducing the output current of the power source.