JPH078434B2 - Short-circuit transfer welding power source control method and apparatus - Google Patents

Description

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

[Problems of conventional technology]

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 the spatters in the short circuit transfer welding occur at the moment when the short circuit is broken and the arc is regenerated, and that the larger the current at the time of arc regeneration is, the larger the spatters are. However, in the constant voltage power supply that merely delays the rise of the current by the conventional reactor, as shown in FIG. 1, the current at the time of arc regeneration is high, so that the amount of spatter is very large. Attention has been paid to this cause to reduce the current during arc regeneration, but it has not yet been put to practical use. For example Weld
In ing Research international Vol.4, No.2,1974, the voltage between the consumable electrode wire and the base metal was detected during the high current period and the voltage was limited to the central period of the high current conduction period, and the precursor of arc regeneration was detected. A technique for suppressing spatter by program control so as to end a large current period when a detection voltage becomes equal to a certain set voltage is set by previously setting a voltage when the constriction of droplets occurs. There is. However,
As described in the above-mentioned document, in practical use, the voltage drop at this portion fluctuates due to the fluctuation of the wire protrusion length, so that the voltage when the droplet is constricted does not become constant and a large current An error occurs at the time when the end of the period is instructed, and it is impossible to stably prevent spatter.

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

An object of the present invention is to solve the above-mentioned problems in the conventional short-circuit transfer welding, by accurately detecting the time when the constriction of the welding wire occurs, and suppressing the welding wire current. 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 a welding power source control method according to the present invention, in short-circuit transfer welding, a differential value with respect to time of a voltage between a welding wire and a base metal is detected, and when the differential value reaches a predetermined value, welding is performed. Reduce wire current.

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

Principle of the Invention FIG. 2 shows an outline of a short-circuit transfer welding apparatus, 101 is a welding power source, 102 is a power supply cable, and 103 is a welding wire fed by a motor (not shown).
Protrudes through the welding torch 104 toward the base material 106, and an arc 105 is generated between the base material 106 and the welding wire 103. The welding wire 103 from the welding torch 104 is
A short circuit and arc generation are repeated at appropriate time intervals between and to perform the known short circuit transfer welding.

FIG. 3 shows the welding wire voltage waveform, current waveform, and positional relationship between the welding wire 103 and the base material 106 during the above-described short-circuit transfer welding. In each drawing, a, d, c,
d and e show the respective welding states. That is, during arcing a
From then on, the arc length gradually becomes shorter, leading to a short circuit b. At this time, the current is increased and maintained at a certain constant value. After the time point c when the droplet is most strongly bonded to the base material 106,
After the point d at which the tip of the welding wire 3 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, if the voltage at the time of short circuit is detected and the amount of change over time of the voltage, that is, the differential value dv / dt of the voltage V reaches a predetermined value, the current can be reduced to suppress spatter.

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

In FIG. 4, the output signal of the voltage detector 110 for detecting the voltage V between the welding torch 104 and the base metal 106 is applied to the differentiating circuit 113, and the detected voltage V is differentiated with respect to the time t in the differentiating circuit 113. The differentiating circuit 113 Is output.

this Is applied to the comparison circuit 114, and when the voltage differential value is 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. Switch the switch 120 to the setting device 121 on the low current side,
The output current of the welding current 101 and hence the current of the welding wire 103 is reduced.

The set value of the setter 115 is determined corresponding to the differential value of the voltage value between the welding wire and the base material when the welding wire is constricted.

Reference numeral 122 is a current setting device for welding, and the welding power source 101
Is the output current of the power control circuit 101b according to the deviation between the set value applied to the error amplifier 101a from either the current setting device 121 or 122 and the welding wire current detected from the current detector 112. It is controlled so that it becomes the value set by.

In welding using the above-described apparatus, the method of controlling the welding voltage and welding current at the portions a, b, c and e of FIG. 3 is the same as the conventional method.

The set value output from the setter 115 described above is determined as follows. The short circuit time of g ₁ , h ₁ , i ₁ , l _{1 in} Fig. 5 is approximately 2 msec.
In the current waveform of, j has a short circuit time of 3 msec. g ₁ ~ j
_{In 1} the short-circuit current is controlled to be constant, and in l _1, the short-circuit current increases with time. FIG. 6 shows the current waveform of FIG.
A voltage waveform corresponding to g ₁ , h ₁ , i ₁ , j ₁ , k ₁ with a wire protrusion length of 16
Different from mm, 20mm, 12mm, 16mm, 17mm.

FIG. 7 is a waveform obtained by differentiating the voltage of FIG. 6 with respect to time t.

Even if the short-circuit current is lowered, the constriction of the droplet that the arc regenerates is G ₂₁ , H ₂₁ , I ₂₁ , J ₂₁ points in the voltage waveform. G ₂₁ through J ₂₁ points is found to be governed by the short time the wire protruding length. Therefore, the set value set by the above-mentioned setting device 115, that is, the level for detecting the constriction of the welding wire may be changed to G _{21 to} J ₂₁ according to the wire protrusion length or the short circuit time, but the wire protrusion length is It changes from moment to moment due to camera shake of the welder,
The short circuit time also fluctuates mainly within 1 to 4 msec due to vibration of the molten pool and fluctuations in the wire feed speed. Therefore, it is not possible to detect the constriction accurately by simply detecting the voltage of the welding wire as in the conventional case.

Therefore, in the present invention, as described above, Detects the constriction of the welding wire. The method is (1) When the current reaches a constant value K ₁ (for example, the average value of G _{31 to} J ₃₁ ), if the constriction is detected and the current is reduced, the spatula is reduced without being greatly affected by the wire protrusion length or the short circuit time. be able to. That is, the ideal K ₁ value changes from G _{31 to} J ₃₁ depending on the wire protrusion length and the short circuit time, but the average value may be used.

(2) In order to reduce the spatter even more reliably, the ideal K ₁ value corresponding to the wire protrusion length and the short circuit time, that is, the voltage differential amount due to the constriction of G _{31 to} J ₃₁ and the welding wire temperature. It is necessary to separate from the voltage differential value due to the resistance change accompanying the rise.

As shown in Fig. 6, the voltage is slightly increased even in the part far from the constriction occurrence points G _{21 to} J ₂₁ . This voltage rise is not related to the constriction of the welding wire, but it changes depending on the wire protrusion length and the short circuit time. This voltage change amount is 1 m when expressed by the voltage differential value in FIG.
Values G _{32 to} J ₃₂ near sec. This voltage differential value arises from the fact that the resistance of the wire protrusion length increases due to the short-circuit current, as will be described later. The voltage differential value resulting from the slave connexion constriction is to the _{K 2 ≒ G 31 -G 32 ≒} ...... ≒ J 31 -J 32 ≒ constant and K _2.

The resistance change of the wire protrusion length portion 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.

△ R: resistance change beta: resistance change rate with temperature R: short-circuit DC resistance I _P: short-circuit current J: 4.2 (constant) [rho: Density C: specific heat d: wire diameter now short current I _P as is constant Since it is controlled and the wire diameter is fixed, Putting the △ expressed as R = kR △ t, △ V = △ R · I P = kR △ t · I P = kV △ t (3) can be regarded as _{(∵V = R · I P)} , i.e., The voltage differential value dv / dt = Δv / Δt = kv due to the resistance change.

This kv corresponds to G _{32 to} J ₃₂ in the sixth. Therefore, it is determined that a constriction has occurred when dV / dt ≧ K ₂ + kV using the value kV obtained by multiplying the welding wire voltage V and a certain constant k as the set value of the setter 115, and if the current is lowered, the protrusion length is reduced. It becomes more reliable to reduce spatter regardless of the short circuit time.

(3) The optimum value of I _{P in} equation (1) changes when the average welding current is changed. 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. Since the equation (2) is satisfied when I _P = constant, the set value of the setter 115 may be changed according to I _P when the I _P becomes another value.

(4) When the wire current i increases with time, the current i is increased to remove the voltage increase due to the current increase.
Kdi / d obtained by calculating the time derivative di / dt of
The current may be reduced when t is calculated and a constant k ₁ is added and the set value of the setter 115 is dV / dt ≧ K ₁ + kdi / dt. For example, in the case of a current waveform such as l ₁ in FIG. 5, a voltage waveform such as l ₂ in FIG. 6 is shown because the current increases. 7th
In the figure, l ₃ shows the voltage differential value due to the current increase regardless of constriction, kdi / dt = l _3, and K ₁ is the average value of G _{31 to} J ₃₁ (≒ G ₃₁ ).
When dV / dt ≧ K ₁ + kdi / dt = G ₃₁ + l ₃ is set, it is considered that a constriction has occurred, and the current can be reduced to reduce the spatter.

In order to obtain the above-mentioned (1) set value, the setter 115 in FIG. 4 may be simply a potentiometer. In this case, the signals from the voltage detector 110 and the current detector 112 are set by the setting device 1.
Applying to 15 is unnecessary.

Further, in order to obtain the set value of (2), the setter 115 is
As shown in the figure, the signal of the voltage detector 110 is amplified by the amplifier 130 with the constant k, and this is applied to the adder 131,
Take the sum of the constant k ₂ applied from the setter 132 and k ₂ + kV
Should be output.

Further, in order to obtain the set value of (4), the setter 115 changes the signal of the current detector 112 to the differentiation circuit 140 as shown in FIG.
Time derivative with Is amplified by amplifier 141 This is applied to the adder 142 and the sum with the constant k ₁ applied from the setter 143 is calculated. Should be output.

If the welding power source 101 in the circuit of FIG. 4 is a tipper type or an inverter type and its output voltage includes ripples, the voltage detector 110 and the current detector 112 may be provided with low pass filters, respectively. .

Experimental results Welding current 150A, welding voltage 20V, welding wire feeding speed 2
Using 1.2 mmφ welding wire under the conditions of 0 cm / min and shielding gas CO ₂ 20 / min, the bead-on-plate welding was performed on the 12 mm thick base metal by semi-automatic welding for 10 minutes, and the amount of spatter adhered to the shield nozzle was compared. .

As a welding power source (I) Commercially available thyristor type welding power source (no control of welding current by necking detection) (II) First device according to the present invention, voltage V between welding wire and base metal at timing d in FIG. about The welding wire current is reduced to 50A.

(III) Second device according to the present invention: at timing d in FIG. 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, in the present invention, in short-circuit transfer welding,
Temporal change of voltage V between welding wire and base metal during short circuit and arc generation Detect this When the current reaches the set value, the current of the welding wire is reduced, so the occurrence of the constriction of the welding wire can be reliably detected,
By correspondingly reducing the current, it is possible to reduce the generation of spatter, and as a result, it is possible to perform high quality welding and improve the welding work efficiency.

[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 7 are graphs showing changes in current, voltage and voltage differential value of the welding wire, and FIGS. 8 and 9 are FIG. FIG. 13 is a block diagram showing a modified example of the setting device of the embodiment. 101 …… welding power source, 103 …… welding wire, 106 …… base metal, 1
10 ... voltage detector, 112 ... current detector, 113 ... differentiating circuit, 114 ... comparator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaharu Sato 731-1 Tehiro, Kamakura City, Kanagawa Prefecture (56) References JP-A-58-29575 (JP, A) JP-A-57-199565 (JP, A) Special Kai 55-8397 (JP, A)

Claims (2)

[Claims] 1. A method of controlling a power source used for welding with a short circuit, wherein the temporal change dv / dt of the voltage V between the welding wire and the base metal at the time of short circuit is a function of the voltage or current between the welding wire and the base metal. A method for controlling a short-circuit transfer welding power source, which comprises reducing an output current of the power source when a predetermined value is reached. 2. A welding power source having a variable output current, a voltage detecting means for detecting a voltage between the welding wire and the base material, a means for calculating a temporal change amount of the detected voltage value, and a welding wire and the base material. Setting means having a circuit for outputting the sum of the value representing the voltage and a constant or a circuit for outputting the sum of the value representing the differential value of the welding current and the constant, and the time change of the voltage is set by the setting means. And a comparison means for detecting that the predetermined value is exceeded, and the output current of the welding power supply is reduced by a signal from the comparison means.