JPH0632854B2 - Short-circuit transfer welding control method and apparatus - Google Patents

Description

The present invention relates to a control method and a control device for short-circuit transfer welding.

Short-circuit transfer welding is a method of performing welding while repeating short-circuiting and arc generation between the welding wire and the base material. In this type of arc welding method, if the welding current at the time of arc regeneration is large, large-sized spatters are generated. As a method of solving the problem of the occurrence of the spatter, a technique of reducing the current during arc regeneration is known.

Welding Research International Vol.
No. 4, No. 2.1974, the high current energization period was limited to the central period of the short circuit period, and the voltage between the consumable electrode wire and the base material was detected during the high current period, and the droplet as a sign of arc regeneration was detected. A method is disclosed in which the voltage at the time of occurrence of the constriction is set, and when the detected voltage becomes equal to the set voltage, program control is performed so as to end the large current period to suppress the occurrence of spatter. However, in this method, since the voltage drop between the electrode and the base material fluctuates due to the fluctuation of the welding wire protrusion length, the voltage when the molten droplet is constricted is not constant and the end of the high current period is terminated. There was a problem that an error occurred at the time of pointing and the spatter could not be removed stably.

As one method for solving this problem, the welding wire voltage V _L at a certain timing at the time of short circuit is stored, and
The difference between the subsequently resulting voltage _{V M △ V = V M -V} L ......
A method of reducing the welding current when (1) reaches a set value is a patent application of Japanese Patent Application No. 56-127973 (Japanese Patent Application Laid-Open No. 58-58197).
-Published in No. 29574. ).

According to the method according to this proposal, the spatter can be greatly reduced, but the spatter cannot be completely eliminated.

The present invention aims to improve the control method proposed by the above-mentioned patent application to further reduce the occurrence of spatter.

The inventor of this invention, the method of the time the result of examining in detail the control method described above, the time when △ V = V _M -V _L has reached the set value, the constriction of the welding wire tip occurs, actual It was found that it was not possible to accurately detect the point at which the necking occurred.

Explaining this point in detail, it was found that there was an error in the detection at the time when the tip of the welding wire was constricted when the short-circuit time changed due to changes in the wire feed rate or vibration of the molten pool. did. Regarding this point, when observing the waveforms of changes in the welding voltage and the welding current, at the time of a short circuit, even if the short circuit current is constant, in addition to the change of ΔV due to the resistance change due to the presence or absence of the constriction of the welding wire, the short circuit It has been found that the voltage increases almost linearly or in a gradual exponential manner in proportion to time. The cause of this voltage increase is that the resistance of the protruding portion of the welding wire from the contact chip during a short circuit increases during the short circuit period.

The resistance change of the protruding portion of the welding wire occurs when the temperature of the protruding portion rises due to the short-circuit current, and is represented by the following equation.

Here, ΔR is the resistance change of the welding wire J: Constant (4.2) β: Rate of resistance change due to temperature ρ: Density R: Resistance immediately after short circuit c: Specific heat I _p : Short circuit current d: Wire diameter In the above formula, short circuit current I _p is controlled to be constant,
And since the wire diameter is fixed, Putting a △ R = is represented as k ° R · △ t, the variation △ _{V N} of the welding voltage at the time of short circuit _{△ V N = △ R · I} p = kR · △
It can be considered that t · I _p = kVΔt. The voltage increase V _N due to the resistance change at the welding wire protrusion after t hours is Can be expressed as

The present invention was made by paying attention to the above points,
(1) by introducing the change △ V _N at the time of calculation of the expression, is characterized in that can determine a more constricted point accurate welding wire.

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

In FIG. 1, 1 is a welding current, 2 is a power supply cable, 3
Is a welding wire fed by a motor (not shown), 4 is a contact chip, 5 is an arc generated between the welding wire 3 and the base metal 6, and 7 is a ground cable. Short-circuiting and arc generation are repeated at appropriate time intervals between the welding wire 3 and the base material 6 to perform known short-circuit transfer welding.

FIG. 2 shows the welding wire voltage waveform, current waveform, and positional relationship between the welding wire 3 and the base material 6 during the above-described short-circuit transfer welding.
c, d, and e show the respective welding states. That is, during arc generation, the arc length gradually becomes shorter from a, 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 at which the droplet was most strongly bonded to the base material 6 and after the point d at which the tip of the welding wire 3 started to be constricted, the welding current was rapidly reduced to a time point e at which the current was sufficiently reduced. Move to arc playback.

During the above-mentioned welding operation, the third
As shown in the figure, the voltage V _L of the welding wire at the time f when the welding current becomes stable as I _p after the transition to the short circuit is stored. Then, for a period c, for a given function V (t), Ask for. After that, while measuring the voltage V _{M of the} welding wire Is reached to a predetermined value, it is determined that the necking of the welding wire end has occurred, and the welding current is reduced. As a result, the spatter can be reduced more reliably than in the conventional method.

According to the experiment, when the welding wire diameter is 1.2 mmφ and the welding current I _p is 400 A, ΔV = 0.3 to 0.6 V, and the voltage V
_N is 0.20 to 0.25V after 1 ms.

When the time t ₂ > t ₁ is satisfied as shown in FIG. 4, or when the welding wire protrusion length is as shown in FIG.
Even if ₂ > ₁ , V _{M2 is obtained} by the above method.
_{- (V L2 + V N2)} = △ V, or _V M3 - _{(V L3}
When + V _N3 ) = ΔV, the welding current was reduced to enable welding without spatter.

FIG. 6 shows an example of a control device for carrying out the above-described control method. One terminal 11a of the integrating circuit 11 has a voltage detector 12 for detecting the voltage between the contact chip 4 and the base material 6.
And the other terminal 11b receives a signal representing the current of the welding wire 3 from the welding current detector 13, and the current flowing through the welding wire 3 has a predetermined value, for example, a short circuit in FIG. The output voltage of the voltage detector 12 is integrated from a time point b when a predetermined current is reached after the shift.

The minimum value storage 14 stores the minimum voltage after the current at the time of transition to a short circuit reaches a certain value.

The subtractor 15 receives the welding voltage V _M from the voltage detector 12,
Further receiving the integrated value _{V N} of the voltage from the integrating circuit 11, and further receives a voltage _{V L} from the lowest value storage 14 △ _V = V _M -
(V _L + V _N ) ... (2) is calculated, and the calculation result ΔV is applied to one input terminal of the comparator 16. Comparator 16
Of the other input terminal is applied a predetermined value E _V from the voltage setter 17 the constriction, △ V = when coming E _V, the comparator 16 applies a signal to the power supply 1, the welding wire 3 The current flowing through is reduced to a value that does not cause spatter during arc regeneration.

FIG. 7 is a circuit diagram showing the details of the integration circuit described above.
The comparator 19 for comparing the signal from the voltage detector 12 with the signal of the reference voltage setting device 18a for generating a signal corresponding to a voltage between the short circuit and the arc, for example, 12 V is a signal for either short circuit or arc generation. To the logic circuit 20.
Meanwhile comparator 21 for comparing the signal of the reference voltage setting unit 18b for generating a signal corresponding to the signal and the short-circuit current I _p of the current detector 13 indicates whether the welding current reaches the short-circuit current I _p The signal is sent to the logic circuit 20.

The logic circuit 20 outputs a signal "1" when the comparator 19 detects a short circuit and the comparator 21 detects that the short circuit current has reached I _p , and becomes "0" at other portions. The logic circuit 20 may output the signal "1" only by detecting a short circuit. Reference numeral 23 is an integrator, which has a resistor 24, a capacitor 25, and an amplifier 26 that determine an integration constant.
4 is connected to the voltage detector 12 and includes an integrating capacitor 25.
An analog switch 27 is connected in parallel with. The analog switch 27 is turned off when the output of the logic circuit 20 is "1", integrates the output voltage of the voltage detector 12, and is turned on when the output of the logic circuit 20 is "0".
The capacitor 25 is discharged.

With the above-mentioned configuration, the voltage detector 12 is
Output voltage becomes lower than the set value of the reference voltage setting device 18a, and the output voltage of the current detector 13 becomes higher than the set value of the reference voltage setting device 18b, that is, the short-circuit current is a stable value I _p. Logic circuit 20 produces an output "1" when time point f is reached.
The analog switch 28 is turned off and the integration of the capacitor 25 is started.

The integrated value is applied to the subtractor 15, and the calculation of the equation (2) is performed. When ΔV reaches a predetermined value, the current is reduced. The output of the comparator 16 at this time is applied to the logic circuit 20,
The output of the logic circuit is set to "0", and the analog switch 27
Is turned on to reset the charging voltage of the integrator 23 to zero.

The integration of the integrating circuit 11 may be terminated when the arc reproduction is started by the output of the comparator 19. Also,
The circuit configuration may be such that the integrated value is reset until or at the start of the next integration.

In FIG. 7, the minimum value storage 14 starts storing the minimum voltage when the output of the logic circuit 20 becomes "1" at the time of transition to the short circuit, and the output of the logic circuit 20 is "0" at the time of arc regeneration.
When this happens, the stored value is reset. The storage device 14 may be reset by a circuit configuration in which the storage is reset until or next time the storage is started.

FIG. 8 is a circuit diagram showing the details of the constriction voltage setting device 17, in which the output signal of the current detector 13 is applied to one input terminal of the operational amplifier 30 via the resistor R1 and the other of the operational amplifier 30. A predetermined reference voltage is applied to the input terminal of.

The resistor R2 is connected between the input and output terminals of the operational amplifier 30. With the above configuration, by receiving a signal V _Ip representing the signal V _Ip representing the welding current I _p that is detected by the current detector 13, the operational amplifier 30 is Is output. As a result, the set value Δ according to the current I _p
V can be sent to the comparator 16 as a reference input.

As the signal of the constriction voltage setting device, the output signal of the setting device that sets the current I _p when the welding machine is short-circuited may be used.

When the current I _p is constant, a variable resistor or the like that outputs a constant voltage may be used as the constriction voltage setting device.

FIG. 9 is a diagram showing an example of the subtractor 15, which is the output signal V _M of the voltage detector 12 and the integrated value V _N and the minimum value which are the output values of the integrating circuit 11 that integrates the welding voltage during the short circuit period. The output signal V _L of the memory 14 is different from the resistors R3 and R, respectively.
4 and R5 are applied to the operational amplifier 33, and by appropriately setting the sign of each input signal, Can be obtained.

Note _{R 6} may be obtained _V M _-V N _{-V L} by that there is R3 = R4 = R5 = R6 in connected between the output terminal and the input of the operational amplifier 33 resistors.

As described above in detail, in the present invention, in the short-circuit transfer welding, the constriction of the welding wire that occurs when the short circuit between the welding wire and the base metal occurs and then transitions to arc regeneration is performed. In the control method of detecting the difference from the welding wire voltage and reducing the welding wire current to prevent the occurrence of spatter during arcing, the variation of the resistance drop due to the temperature change of the welding wire after the start of the short circuit is added. Then, the difference voltage is calculated, and when the difference voltage reaches the set value, it is determined that the welding wire is constricted, and the welding current is reduced. Even if there is a problem, it becomes possible to accurately detect the timing at which the constriction of the welding wire occurs, and it is possible to reliably prevent the occurrence of spatter.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a welding apparatus to which the present invention is applied, and FIG. 2 is a waveform diagram of welding voltage and welding current in short-circuit transfer welding together with a relationship between a welding wire and a base material. FIG. 3, FIG. 3 to FIG. 5 are waveform diagrams showing the relationship between welding voltage and welding current according to the present invention, FIG. 6 is a circuit diagram showing an embodiment of the present invention, and FIG. A detailed circuit diagram of the integrating circuit used in the example, FIG. 8 is a circuit diagram showing an example of the constriction voltage setting device used in the embodiment of FIG. 6, and FIG. 9 is a subtraction used in the embodiment of FIG. It is a circuit diagram showing an example of a circuit. 1 ... Power supply, 3 ... Welding wire, 6 ... Base metal, 12 ...
Voltage detector, 11 ... Integrator circuit, 14 ... Minimum value memory, 15 ... Subtractor, 16 ... Comparator.

Claims (4)

[Claims] 1. In short-circuit transfer welding, a welding voltage V _L at a specific time when a short circuit occurs, an integral value V _N of the welding voltage during a short circuit period, and a welding voltage V _M during a short circuit period are measured to obtain V. and calculates the _{M -V L -V N = △ V} , △ when V reaches the set value, by reducing the welding current, the control method of the short circuit transfer welding, characterized in that the transition to the arc regeneration. 2. A welding voltage V _M in a short-circuit transfer welding apparatus.
Voltage detecting means for detecting the welding voltage, an integrating circuit for integrating the welding voltage in the short circuit period and outputting an integrated value V _N , and a signal from the first voltage detecting means for welding voltage _VL at a specific time point during the short circuit period. a second voltage detecting means for detecting a first voltage detecting means, the integration circuit and a subtraction circuit for calculating a V _M -V _L -V _N from the output of the second voltage detecting means, the output voltage of the subtraction circuit is predetermined The control device for short-circuit transfer welding, comprising: a comparison circuit that detects that the reference value has been reached, and control means that reduces the welding current according to the output of the comparison circuit. 3. The control device according to claim 2, wherein the first voltage detecting means detects a voltage between the welding torch and the base metal. 4. The control device according to claim 2, wherein the reference value of the comparison circuit changes according to the welding current.