JPH0316227B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention is a method for detecting the protrusion length of a welding wire from a chip in a short-circuit transitional arc welding method in which short-circuiting and arc generation are alternately repeated between the welding wire and the welding base metal. Regarding.

Prior Art Figure 1 shows the process of droplet formation and migration in the short-circuit transfer arc welding method, in which short circuits and arc generation are alternately repeated between the welding wire and the base metal.
2 is a welding wire, 22 is a droplet formed at the tip of the welding wire 21, 23 is an arc, and 24 is a molten pool, that is, a base metal. (a) shows the initial short-circuit state in which the droplet 22 is in contact with the molten pool 24, and (b) shows the droplet 22 in the molten pool 24 after the contact between the droplet 22 and the molten pool 24 has become reliable.
4, (c) is a late short circuit state in which the droplet 22 has moved to the molten pool 24 side and a constriction has occurred in the droplet 22 between the welding wire 21 and the molten pool 24, (d) is the moment when the short circuit is broken and welding arc 23 is generated, (e) is the arc generation state where the tip of the welding wire 21 is melted and the droplet 22 grows, and (f) is the moment when the droplet 22 is forming a molten pool. 24, and the processes of (a) to (f) are repeated.

In recent years, automation of welding has been promoted with the aim of improving product quality and saving labor. In arc tracing control, which is important in this welding automation, changes in the length of the part of the welding wire protruding from the contact tip that slidably supports the welding wire (hereinafter referred to as wire protrusion length) and the arc length are There is a method of controlling the arc to follow the welding groove using changes in the current or welding voltage. This method does not require any special equipment, such as a television camera, to detect the position of the arc, nor does it require delay control to correct the deviation between the detected position and the actual position, unlike the contact method. Active study is underway as an effective method in this regard.

In this arc tracing control, as shown in FIG. An arc is generated between the base materials 25 and 25'. In this case, while weaving the chip 27 horizontally with a predetermined width,
6 to perform welding. However,
If the center position _W1 of the weaving of the chip 27 with respect to the groove 26 shifts, the positions of both ends of the weaving
There is a difference in wire protrusion length between W ₂ and W ₃ . In the case of Figure 2, the center position of the weaving
Since W ₁ is shifted toward the base material 25 side, the relationship between the wire protrusion length l ₂ at position W ₂ and the wire protrusion length l ₃ at position W ₃ is l ₂ <l ₃ . In this case, if welding is carried out using a welding power source with constant voltage characteristics and a constant welding wire feeding speed, the relationship between welding current I ₂ at position W ₂ and welding current I ₃ at position W ₃ is
I ₂ > I ₃ . This difference in current value is due to the difference in wire protrusion length, so current I ₂ and current
If the center of the weaving is controlled to be shifted in the direction in which I ₃ is equal to I 3 , welding will be performed approximately following the center of the groove 26 .

What is important here is the relationship between the wire protrusion length and the welding current.According to Leznevitsch's empirical formula, there is a relationship between the wire feeding speed Ws, the wire protrusion length l, and the current I. If the diameter of is 1.2 mm, the following equation holds.

l=Ws−0.015I/2.68×10 ^-6 I ² ………(1) In addition, Ws: Wire feeding speed (m/min) l: Current (A) l: Wire protrusion length (mm) Wire feeding Speed Ws is 2.8mm/min and 3.6 respectively
The relationship between the wire protrusion length l and the current I calculated from equation (1) under the three conditions of m/min and 4.4 m/min is
As shown in the figure. As is clear from equation (1) and Figure 3, the wire protrusion length l has a quadratic relationship with the current I for a constant wire feeding speed Ws, so the current I
Determining the wire protrusion length l from the equation requires complicated calculations. In addition, the current I changes greatly depending on the wire feeding speed Ws, so when calculating the wire protrusion length l, it is necessary to change the calculation constant every time the wire feeding speed Ws is changed, or It is necessary to construct a complicated arithmetic circuit that performs the calculation of equation (1) from the feeding speed Ws and the current I.

On the other hand, the wire feeding speed shown in Figure 3 is 2.8~
4.4 m/min is the wire feeding speed in typical short-circuit transitional arc welding, and in this case, the current waveform includes large ripples as shown in FIG. Therefore, as the welding current I necessary for the above-mentioned calculation, an average current obtained through a low-pass filter having a cutoff frequency of about 1 to 3 Hz is used. However, a low-pass filter inevitably involves a signal delay, and this signal delay is detrimental to the calculation of the wire protrusion length l, especially to the calculation of the transient wire protrusion length l.

OBJECT OF THE INVENTION The present invention has been made in view of the above circumstances, and its purpose is to provide a wire protrusion length that allows wire protrusion length to be detected more accurately and more easily in arc tracing control in a short-circuit transitional arc welding method. An object of the present invention is to provide a length detection method.

Summary of the Invention In short-circuit transitional arc welding, in which short circuits and arcs occur repeatedly between the welding wire and the welding base metal, the voltage between the chip supporting the welding wire and the base metal and the current flowing through the base metal at the time of a short circuit are detected. , a value related to the electrical resistance of the protrusion length of the welding wire from the tip is determined using both detected values.

Principle of the Invention As mentioned above, in the short-circuit transitional arc welding method in which short-circuiting and arc generation are repeated between the welding wire and the base metal, there is a short-circuiting period in which the droplet at the tip of the welding wire contacts the molten pool, and a short-circuiting period in which the welding wire The arc generation period in which an arc is generated between the tip of the molten pool and the molten pool is repeated alternately. During the above short circuit period, detect the voltage between the contact tip and the base metal and the current flowing through the welding wire or base metal, and divide the detected voltage by the current to find the resistance per wire protrusion length of the welding wire. . Note that during the arc generation period, the resistance due to the arc is added, so the resistance of the wire protrusion length cannot be obtained from the voltage and current between the chip and the base material. Therefore, the above calculation needs to be performed using the voltage and current during the short circuit period.

Now, the voltage and electrical resistance between the chip and the base metal at the time of short circuit when the wire feeding speed Ws and the arc projection length l are varied are determined as shown in FIG. 5. As is clear from FIG. 5, the arc projection length l can be expressed by a linear equation of the resistance R between the chip and the base metal, as shown in equation (2).

l=1.333R−4 ………(2) (R=3+0.75l) In addition, l: Wire protrusion length (mm) R: Electrical resistance between chip and base metal (mΩ) In Fig. 5, wire protrusion length Even when l is 0, an electrical resistance of about 3 mΩ occurs, but this is due to the contact resistance between the chip and the welding wire and the electrical resistance of the droplet, and this has nothing to do with the welding conditions. It was confirmed that the value remained constant.

The usefulness of determining the electrical resistance from the welding current and the voltage between the chip and the base metal during the short-circuit period and determining the relationship between this electrical resistance and the wire protrusion length is shown by Equation (2) and Equation 5.
As is clear from the figure, the wire protrusion length l is determined independently of the wire feeding speed, and the relationship between the electrical resistance R between the chip and the base material and the wire protrusion length l can be approximately linearly approximated. This method is effective in arc tracing control because calculation of the wire protrusion length can be performed with a simple circuit and control accuracy can be improved. Furthermore, short circuits between the welding wire and the molten pool occur 30 to 80 times per second.
Therefore, a large number of current and voltage information can be obtained 30 to 80 times per second, and since there is no need for delay element circuits such as filters, accurate detected values can be obtained without time delay. can get.

Examples of the invention An embodiment of the present invention will be described below.

FIG. 6 shows the configuration of the first embodiment, with 1
is a welding power source, and output terminals 1a and 1b are connected to a contact tip 2 and a base metal 4, respectively. Welding wire 3 is fed to tip 2 by a feed motor (not shown).
It passes through and is fed towards the base material 4. A voltage detector 5 detects the voltage between the chip 2 and the base material 4. A current detector 6 detects the current flowing through the welding wire 3. 7 receives the signals from the voltage detector 5 and current detector 6, divides the voltage by the current, and outputs the signal to the chip 2.
This is a divider that calculates the electrical resistance between the base material 4 and the base material 4.

8 is a short circuit/arc discriminator which discriminates between a short circuit period and an arc generation period based on a signal representing the voltage between the chip 2 and the base metal 4 from the voltage detector 5, and determines whether a short circuit or an arc is occurring. Outputs a signal indicating. In this short circuit/arc discriminator 8, since there is a large voltage difference between the contact chip 2 and the base metal 4 when a short circuit occurs and when an arc occurs, for example, 10V or less is determined as a short circuit, and 10V or more is determined as an arc occurrence. Consists of comparators. The sample holder 9 receives the signal from the short circuit/arc discriminator 8, samples the resistance value from the divider 7 during a short circuit and outputs that value, and holds (memorizes) the resistance value during the short circuit when an arc occurs. ) outputs the value. Furthermore, when a next short circuit occurs, the process of erasing the previously held (stored) value and outputting the sampled value during the short circuit is repeated. Reference numeral 10 denotes an arc tracing control device, which drives the tip 2 based on a signal representing the resistance value from the sample holder 9 to control the tracing of the arc to the welding groove.

Electric power is supplied from the welding power source 1, and the welding wire 3 is fed, and welding is performed by repeating short circuit and arc generation between the tip of the welding wire 3 and the base metal 4. At this time, the voltage value between the contact chip 2 and the base material 4 detected by the voltage detector 5 and the current value flowing through the base material 4 detected by the current detector 6 are input to the divider 7. Now, the electric resistance value between the chip 2 and the base material 4 is calculated by dividing the voltage by the current. On the other hand, the short circuit/arc discriminator 8 uses the voltage signal from the voltage detector 5 to discriminate between a short circuit period and an arc generation period using the method described above, and sends a signal indicating that a short circuit and an arc are occurring to the sample holder 9. Output. The sample holder 9 then samples the resistance value from the divider 7 during the short circuit period and outputs a signal representing the resistance value to the arc tracing control device 10, and during the arc occurrence period, samples the resistance value from the divider 7 and outputs the signal representing the resistance value to the arc tracing control device 10. The resistance value is stored and a signal representing the stored resistance value is output to the arc tracing control device 10. In the arc tracing control device 10, the wire protrusion length l is determined from the resistance value at the time of short circuit inputted from the sample holder 9, and based on this wire protrusion length l, follow-up control of the arc to the welding groove is performed.

7a shows the waveform of the voltage between the chip 2 and the base metal 4 detected by the voltage detector 5 described above, and FIG. 7b shows the waveform of the welding wire detected by the current detector 6 described above. 3 shows the waveform of the current flowing through the circuit.
The broken line in FIG. 7c is the chip 2 calculated by the divider 7.
It shows the change in electrical resistance between and the base material 4,
The solid line in FIG. 7c shows the change in the signal representing the electrical resistance output from the sample holder 9 mentioned above. As shown by the solid line in Figure 7c, the sample holder 9 samples the resistance value at the time of a short circuit and outputs this sampled resistance value. It memorizes until a short circuit occurs and outputs this memorized resistance value.

FIG. 8 shows the configuration of a second embodiment of the present invention, and those indicated by numerals 1 to 10 are the above-mentioned sixth embodiment.
It is the same as that shown by the same reference numeral in the figure. Reference numeral 11 denotes a control circuit that receives a signal representing a current value from the current detector 6 and controls the welding power source 1 so that the output current at the time of a short circuit is constant. In addition, the sample holder 9
The signal representing the voltage between the chip 2 and the base material 4 from the voltage detector 5 is input as is, and the divider 7 shown in FIG. 6 is not necessary.

Recently, in order to reduce the occurrence of spatter and improve welding workability, as shown in Figure 9b, a predetermined constant current is applied during a short circuit, a high current is applied in the first stage when an arc occurs, and a low current is applied in the second stage. In both cases, a welding power source with constant current control is used. In this case, the voltage changes as shown by the broken line in FIG. 9a.
Since the current at the time of a short circuit is constant, the resistance value R is determined from the voltage V and the current I, and equation (2) is converted as follows.

l=1333V/I-4......(3) Here, if the current I during short circuit is fixed at 300A, l=4.444V-4......(3'), and the voltage shown in Figure 5 The relationship between the wire protrusion length and the wire protrusion length can be obtained. In this case, the value related to the resistance value can be substituted by the voltage value.

In FIG. 8, during a short circuit, the current is held constant as described above, and when the short circuit/arc discriminator 8 determines a short circuit, the sample holder 9
It samples the voltage signal from and outputs the sampled voltage value. When the short circuit/arc detector 8 determines that an arc has occurred, the sample holder 9
stores the voltage value at the time of the short circuit immediately before the arc occurs until the next short circuit occurs, and outputs this stored voltage value. The voltage signal output from the sample holder 9 is input to the arc tracing control device 10 as a signal related to the electrical resistance between the chip 2 and the base material 4, and in the arc tracing control device 10, the wire protrusion length is Find this wire protrusion length l
Based on this, follow-up control of the arc to the welding groove is performed. The solid line in FIG. 9a shows the voltage signal output from the sample holder 9.

In relation to the above-mentioned second embodiment, when using a welding power source that maintains a constant voltage during short circuit, the current is taken as a value related to the electrical resistance of the wire protrusion length, and the wire protrusion length is determined to determine the arc. It is clear that tracing control can be carried out, and this method will not be described in detail here.

FIG. 10 shows the configuration of a third embodiment of the present invention, and the components indicated by numerals 1 to 10 are the same as those indicated by the same symbols in FIG. 6 described above. Reference numeral 12 denotes a sample pulse generator, which receives voltage and current signals from the voltage detector 5 and current detector 6 and generates a signal for 10 to 50 μs when a short circuit is in progress and the current reaches a predetermined value.
A pulse signal having a pulse width of about The sample holder 9 samples the voltage signal from the voltage detector 5 during this minute time and stores the sampled voltage signal.

As shown in Figure 11, the current flows during the short circuit period.
The sample pulse generator 12 outputs a pulse signal with a pulse width of 50 μs to the sample holder 9 at time t ₁ when the current increases gradually at a rate of about 100 A/msec and reaches 250 A. The sample holder 9 is
During the 50 μs period during which this pulse signal is input, the voltage signal V ₁ at time t ₁ from the voltage detector 5 is read and stored. The current only increases by about 5A during 50μs, and this level of variation can be ignored compared to 250A, so the sample holder 9 always maintains a constant current flow.
The voltage when it reaches 250A will be sampled and held. The voltage value thus detected is input to the arc tracing control device 10 as a signal related to the electrical resistance between the chip and the base material. Then, the arc tracing control device 10 determines the wire protrusion length l from this input signal and performs follow-up control for the welding groove of the arc.

FIG. 12 shows the configuration of a fourth embodiment of the present invention, in which 13 is a minimum value detector, and in FIG. 12, the sample holder 9 of FIG.
3, and the other symbols 1 to 10 are the same as those indicated by the same symbols in FIG.
The minimum value detector 13 detects the minimum value of the resistance between the chip and the base material at the time of a short circuit from the divider 7, and stores this detected minimum value until the next short circuit occurs.

The broken line in Figure 13 is an enlarged view of the change in electrical resistance between the chip and the base metal shown in Figure 7c, mainly during a short circuit, and shows that the electrical resistance is not constant during the short circuit period. There is. That is, the resistance is high at the beginning of the short circuit, low at the middle stage of the short circuit, and becomes high again at the late stage of the short circuit. this is,
This can be easily understood by comparing the state of transfer of droplets to the molten pool during a short circuit as shown in FIGS. 1a, b, and c. Time a, b, and c shown in FIG. 13 correspond to a, b, and c in FIG. The resistance is large because the area is small. At the middle stage of the short circuit (b), contact between the droplet 22 and the molten pool 24 is ensured, and the resistance is the smallest. In the latter half of the short circuit (c), the droplet 22 again forms a constriction B, so that the resistance increases.

In FIG. 12, the lowest value detector 13 receives the signal representing the resistance value from the divider 7, detects the lowest value of the resistance, and stores this detected lowest value until the next short circuit occurs. Output the memorized lowest value. The arc tracing control device 10 inputs a signal representing the minimum value of this resistance, determines the wire protrusion length l from this input signal, and performs follow-up control of the arc to the welding groove. The solid line in FIG. 13 shows a signal representing the resistance value output from the lowest value detector 13.

In connection with the fourth embodiment described above, the sample holder 9 shown in FIG. 8 is replaced with a minimum value detector, the minimum value of the voltage at the time of a short circuit is detected and stored, and this minimum value of voltage is applied to the resistor. The arc tracing control can be performed by inputting the related values to the arc tracing control device 10 and calculating the wire protrusion length.

Effects of the Invention As explained above, in the present invention, the voltage between the chip supporting the welding wire and the base metal and the current flowing through the base metal at the time of a short circuit are detected, and the detected values are used to control the welding wire chip. Since the protrusion length of the welding wire is determined by calculating the value related to the electrical resistance of the protrusion from the The wire protrusion length can be detected accurately and without time delay.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the process of droplet formation and migration in short-circuit transfer arc welding, Figure 2 is a diagram showing the relationship between the welding wire and groove in arc tracing control, and Figure 3 is a diagram showing the relationship between the welding wire and the groove in arc tracing control.
The figure is a graph showing the relationship between wire protrusion length and current.
Fig. 4 is a diagram showing the waveforms of welding voltage and welding current in short-circuit transitional arc welding, Fig. 5 is a graph showing the relationship between wire protrusion length, voltage and resistance, and Fig. 6 is a diagram showing the first embodiment of the present invention. 7 is a diagram showing voltage, current, and resistance waveforms in the first embodiment. FIG. 8 is a block diagram showing the second embodiment of the present invention. FIG. 9 is a diagram showing the waveforms of voltage, current, and resistance in the first embodiment. 10 is a block diagram showing the third embodiment of the present invention. FIG. 11 is a diagram showing the voltage and current waveforms in the third embodiment.
FIG. 2 is a block diagram showing a fourth embodiment of the present invention;
FIG. 13 is a diagram showing the waveform of electrical resistance in the fourth embodiment. 2...Contact chip, 3...Welding wire,
4... Base material, 5... Voltage detector, 6... Current detector, 7... Divider, 8... Short circuit/arc discriminator,
9... Sample holder, 10... Arc tracing control device, 11... Control circuit, 12... Sample pulse generator, 13... Minimum value detector.

Claims (1)

[Scope of Claims] 1 In short-circuit transitional arc welding in which short circuits and arc generation are repeated between the welding wire and the welding base metal, between the welding wire and the welding base metal when the welding wire and the welding base metal are short-circuited. Welding wire protrusion length detection characterized in that the protrusion length of the welding wire from the tip is detected by detecting the voltage of the welding wire and the current flowing through the welding wire, and determining a value related to the electrical resistance obtained from the detected values. Method. 2. The method according to claim 1, wherein the value related to the electrical resistance of the protruding portion of the welding wire from the tip is a value obtained by dividing the detected voltage by the detected current. 3. The method according to claim 1, characterized in that the current flowing through the welding wire when the welding wire and the welding base metal are short-circuited is constant, and the value related to the electrical resistance is obtained from the detected voltage value. Method. 4. Claims characterized in that the voltage between the welding wire and the welding base metal is kept constant when the welding wire and the welding base metal are short-circuited, and the value related to the electrical resistance is obtained from the detected current value. The method described in paragraph 1. 5 Detect the voltage when the detected current reaches a certain value when the welding wire and the welding base metal are short-circuited, or detect the current when the voltage reaches a certain value during the short-circuit. A method according to claim 1, characterized in that: 6. The method according to claim 1, characterized in that the lowest value among the values associated with the electric resistance that varies during the short circuit between the welding wire and the welding base metal is used.