JPH0613146B2 - Arc welding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an arc welding method, and more particularly to a method of welding a consumable electrode along a groove of a welding base metal while moving the consumable electrode. Is.

[Prior Art] FIG. 3 shows an example of this type of welding method.
Reference numeral 1 is a welded base metal, and the groove 2 has a different width depending on the position. Behind the groove 2 is a ceramic backing material 3
Are installed along the groove 2.

Numeral 4 is a welding torch, which is attached to a carriage 5 and moves on a rail 6 arranged in parallel in the same direction as the groove 2 while being moved to the groove 2 by a consumable electrode type welding wire 7 fed from the welding torch 4. A bead 8 is formed by arc welding. Third
When performing butt welding in which the groove gap is not constant as shown in the figure, the welding conditions are adjusted at the position aa 'in FIG. 3, that is, the positions in FIG. If the welding conditions are kept constant, as the welding progresses, the positions shown in FIGS. That is, the backside of the welded portion appears in FIGS. 4A and 4B, but the backside is not sufficiently generated in FIGS. 5A and 5B because the back groove is not melted. The position of the welding wire 7 is very different in FIGS. 4A and 5B.

Generally, when the melting rate of the welding wire 7 is V and the welding rate is υ, the weld metal amount S supplied to the unit length of the groove 2 is S.
Is represented by S = V / υ (1), and the weld metal height H is H = S / G = V / (υG) (2) depending on the groove gap G. The height H of the weld metal, which is supported by the surface tension, by changing the welding metal supply amount S and the groove gap G.
_When it exceeds ₀ , that is, when H> H ₀ , the weld metal flows out in the welding progress direction of the groove 2. When the height of the weld metal that has flowed out is less than or equal to H _0, the weld metal is supported by the surface tension again and does not flow further. The outflow length d, that is, the distance from the weld metal tip to the tip of the welding wire 7 (since the outflow length d is small, the groove gap G hardly changes in this range) d = (H−H ₀ ). / H ₀ = (V / υGH ₀ ) −1 (3) When d <0, the welding wire 7 precedes the welding metal and the tip of the welding wire 7 breaks through the backing material 3.
This is because the backing material 3 is made of glass fibers or ceramics, so that welding current does not flow.

In the case of d >> 0, the weld metal hindered the arc heat to the back of the groove, and the back wave was not sufficiently generated. Therefore, the outflow length d needs to be maintained in an appropriate range of 0 ≦ d ≦ dp. However, dp is the proper maximum distance.

4 (a) and (b), d is within the range of 0 ≦ d ≦ dp because the welding conditions are properly adjusted, but in FIGS. 5 (a) and 5 (b), welding conditions V and υ are shown in FIG. Same as B, but d becomes d> dp because the groove gap G becomes smaller, and back waves are not sufficiently generated. At this time, in order to keep d within the appropriate range of 0 ≦ d ≦ dp, it is necessary to reduce the melting rate V of the welding wire 7 or increase the welding rate υ.

The previously filed Japanese Patent Application No. 59-241872
No. 119380), a method of controlling the welding speed or the welding speed of the consumable electrode with respect to the variation of the groove gap G is described. In this method, the outflow length d, which is the distance from the tip of the weld metal to the tip of the welding wire 7.
Is changed, the number of short circuits per unit time or the short circuit time ratio is correspondingly changed. At this time, the number of short circuits in the unit time or the short circuit time rate is detected, and the welding speed or the melting amount of the consumable electrode is adjusted so that the distance d from the weld metal tip to the tip of the welding wire 7 is 0 ≦ d ≦ dp. Is controlled.

[Problems to be Solved by the Invention] FIG. 6 shows that the wire diameter is 1.2 mm and the welding current is 150 mm.
A, the welding metal tip / wire tip distance d vs. short circuit count n characteristics when the welding voltage is 21 V, and the welding current is 1
When performed in a low current region of around 50 A, the weld metal solidifies in a short time, so the vibration of the molten pool is small, and as shown in FIG. 6, therefore, with respect to the distance d between the weld metal tip and the wire tip, It can be seen that there is almost no change in the number of short circuits n, that is, the short circuit time ratio η.

Therefore, the above-mentioned conventional method is suitable for downward welding performed with a wire having a diameter of 1.2 mm at a welding current of 200 to 300 A, but is not suitable for vertical welding or upward welding. To prevent the weld metal from dripping, 150
When the conventional method is used in a relatively low current range of the welding current around A, the number of short circuits n or the short circuit time rate η is detected, and the welding speed or the melting amount of the consumable electrode is controlled by this detected value. , The distance d between the weld metal tip and the wire tip is 0 ≦ d
There is a problem that it is difficult to control so that ≦ dp (dp is an appropriate maximum distance).

[Object of the Invention] An object of the present invention is to solve the above problems and to provide a welding method which is easy to automate and can perform good welding with high accuracy even when the groove size is relatively low. To do.

[Outline of the Invention] FIG. 7 shows that the wire diameter is 1.2 mm and the welding current is 150 mm.
FIG. 9A is a diagram showing a distribution characteristic of the short circuit time Ts when the welding voltage is 21V.

In FIG. 7, the short-circuit time is such that the short-circuit time Ts for transferring droplets due to surface tension is less than 2 [msec] and the short-circuit time Ts for transferring droplets due to pinch force is 2 [msec] or more. It is roughly divided into B type short circuits.

FIG. 8 (A) is a diagram showing a short-circuit column length L vs. short-circuit time Ts characteristic under the same welding conditions as in FIG. 7. Shorting column length L
Is the length of the droplet 23 from the tip of the welding wire 7 to the bead 8 immediately after the short circuit, as shown in FIG. 8 (B).

As shown in FIG. 8 (A), the short circuit time Ts is approximately 2 [msec].
In the A type short circuit of less than, the short circuit time Ts is almost constant with respect to the change of the short circuit column length L, but the short circuit time Ts is approximately 2 [mse.
In the B type short circuit above c], as the shorting column length L becomes shorter,
The short circuit time Ts becomes long, and therefore the short circuit column length L is roughly inversely proportional to the short circuit time Ts.

FIG. 9 is a diagram showing the relationship between the elapsed time t and the shorting column length L when the shorting time is 2 to 4 [msec] under the same welding conditions as in FIG. Changes within a certain change amplitude of the weld pool over time t. That is,
The vibration of the molten pool is represented by the time variation of the short-circuit column length L, which is the distance between the tip of the non-molten portion of the welding wire 7 and the molten pool, and the short-circuit column length L is the short-circuit column length value within the range of the variation amplitude of the molten pool. The number of times N per unit time that becomes L ₀ is the frequency ν of the molten pool and N = 2
There is a relationship of ν.

Therefore, in order to detect the change in the frequency of the molten pool with high accuracy, the number of times in the unit time that the short-circuit column length L becomes a certain value L ₀ within the range of the variation amplitude of the molten pool, that is, the short-circuit time T _s.
It can be seen that it is sufficient to measure the number of short circuits nt within a unit time, which indicates the short circuit time Ts ₀ corresponding to a certain short circuit column length value L ₀ .
That is, since the number of times is short when only one value of the short circuit time Ts is present, the number of times is short if the number of short circuit times Ts within a certain range is selected, which is suitable for detecting a change in the frequency of the molten pool. There are cases. The short circuit time ratio (short circuit time / (short circuit time +
Similarly, vibration of the molten pool can be detected by detecting the arc generation time)).

As shown in FIG. 10, when the distance d between the tip of the weld metal 8 and the tip of the welding wire 7 is relatively large, the welding wire 7
Since the tip of the welding pool is located almost in the center of the molten pool 10, the welding wire 7 and the molten pool 10 are affected by the vibration of the molten pool 10.
The number of short circuits in between increases and the short circuit time ratio increases. However, as shown in FIG. 11, the tip of the welding metal 8 and the welding wire 7
When the distance d between the tips is small, the number of short circuits between the welding wire 7 and the weld pool 10 is small (short circuit time ratio is small). That is, the distance d between the tip of the welding metal 8 and the tip of the welding wire 7 and the number of short circuits nt or the short circuit time rate ηt in a unit time of a short circuit having a specific time length are relatively small currents as described above. It became clear that there is a clear relationship even when the vibration of the molten pool is small.

FIG. 12 and FIG. 13 are measurement data demonstrating this, in which the number of short circuits nt and the short circuit time ratio ηt when the short circuit time Ts is from 2 [msec] to 4 [msec] are measured.

Now, in the case of a certain groove gap G ₀ and an appropriate welding speed, the distance between the tip of the weld metal 8 and the tip of the welding wire 7 becomes d ₀ , and as shown in FIGS. . At this time, the number of short circuits is nt ₀ (short circuit time ratio is ηt ₀ ). When the wire feeding speed is kept as it is and the groove gap G ₁ becomes small (G ₁ <G ₀ ), the distance d ₁ between the tip of the welding metal 8 and the tip of the welding wire 7 becomes large (d ₁
> D ₀ ), and when the appropriate maximum distance dp is exceeded, backwater is not sufficiently generated as shown in Figs. 5A and 5B, and the number of short circuits is nt ₁ (short circuit time ratio η
t ₁ ), and nt ₁ ＞ ntp ＞ nt ₀ (ηt ₁ ＞ ηtp ＞ ηt ₀ ) (ntp,
ηtp is the number of short circuits and the short circuit time ratio) at the proper maximum distance dp.

Next, when the welding speed υ is increased, d becomes smaller due to the relationship of the equation (3), approaches d _0, and approaches nt ₀ (ηt is ηt ₀ ). Therefore, as shown in FIGS. 4A and 4B, the back wave becomes good. When the groove gap becomes wider, a phenomenon opposite to the above occurs, and nt (ηt) can be brought close to nt ₀ (ηt ₀ ) by decreasing the welding speed υ.

[Structure of the Invention] The welding method of the present invention is made based on the above-mentioned findings, and the groove back side of the welded joint having the gap between the groove forming members having the groove with the groove gap changing. A backing material is provided on the consumable electrode, arc welding is performed in the low current region along the groove of the consumable electrode, and a short circuit generated between the consumable electrode and the welding base material is caused by transfer of droplets due to pinch force. It is characterized in that a short circuit of a time length is selected, the selected short circuit is detected as a short circuit or a short circuit time ratio per unit time, and the welding speed is controlled so that the detected value is always kept at a set value.

In this way, the number of short circuits nt (short circuit time ratio ηt) is detected, and the welding speed υ is controlled so as to maintain this detected value at an appropriate set value nt ₀ (ηt ₀ ). It is possible to maintain the distance d between the tips in the range of favorable back waves.

[Embodiment] An embodiment of the present invention will be described below.

FIG. 1 shows an embodiment of an apparatus for detecting the number of short circuits and controlling the speed of the welding carriage. In the figure, the output side of the welding electrode 10 is connected to the welding torch 4 and the material 1 to be welded.
Reference numeral 11 denotes a short-circuit detection circuit connected between the welding torch 4 and the material 1 to be welded. When the welding wire 7 and the material 1 to be welded are short-circuited, a signal voltage of a predetermined level is generated by the pulse generation circuit 1.
Output to 3. The short circuit detection circuit 11 may be provided with a shunt 12 on the welding cable and a welding current may be applied as an input.

The signal voltage input to the pulse generation circuit 13 is shaped into a predetermined high-level pulse voltage and then output to the pulse width discrimination circuit 14, and the pulse width discrimination circuit 14 outputs the signal voltage for a time of 2 to 4 [msec]. Only the pulse voltage that is at the high level during the period is output to the number-of-times detection circuit 15. On the other hand, a pulse other than the time when the high level is 2 to 4 [msec] is not output to the frequency detection circuit 15. In the pulse width discrimination circuit 14, only the short circuit between the welding wire 7 and the base metal 1 having the short circuit time of 2 to 4 [msec] is detected by the above-described operation of the discrimination, and the short circuit of 2 to 4 [msec] occurs. The number of occurrences per unit time is detected. The pulse width is the short circuit time T
Corresponding to s, another pulse width discrimination time may be set in this circuit 14.

The number-of-times detection circuit 15 detects the number of times of the input pulse voltage, and outputs a signal voltage corresponding to the number of short circuits per unit time to the comparator 20 via the terminal a of the switch 16 and also to the sampling circuit 17. .

Reference numerals 18a, 18b and 18c are a weaving left end detection circuit, a weaving center detection circuit and a weaving right end detection circuit, respectively. Each of the circuits 18a, 18b and 18c has a short circuit at or near the left end, center portion and right end of the weaving. At this time, a high level signal is output to the sampling circuit 17.

The sampling circuit 17 is the weaving left end detection circuit 1
8a, in response to high level signals from the weaving center detection circuit 18b and the weaving right end detection circuit 18c,
The input signal voltage is sampled at a predetermined cycle, and the sampled signal is output to the holding circuit 19. In the sampling circuit 17, each of the above circuits 18
One of the high level signals output from a, 18b and 18c is selected by the operator to perform the desired operation.

The holding circuit 19 temporarily holds the level of the input sampling signal until the next sampling signal is input, and outputs the held signal to the comparator 20 via the b terminal of the switch 16.

The switch 16 is a switch for switching whether to detect the short circuit at the central portion or the end portion of the weaving. When detecting the number of short circuits at the central portion or the end portion of the weaving, the switch 16 is switched to the b side. On the other hand, when detecting the number of short circuits regardless of the weaving position, the switch 16 is switched to the a side.

Reference numeral 21 is a reference voltage generator corresponding to a preset reference short circuit nt _0. This reference voltage is compared with the signal voltage from the frequency detection circuit 15 or the holding circuit 19 by the comparison circuit 20, and the difference voltage is welded. It is added as an input to the truck motor control device 22. The output of the welding carriage motor controller 22 is applied to the welding carriage motor 5a to adjust the traveling speed of the welding carriage 5.

Hereinafter, the case where the switch 16 is switched to the a side and the I-shaped groove of downward butt welding is described. In this case,
When the difference between the input signal, that is, the output of the frequency detection circuit 15 or the holding circuit 19 and the reference voltage is positive, the welding carriage motor control device 22 controls the speed of the welding carriage motor 5a so as to eliminate this difference voltage. It operates to increase the trolley speed. That is, when the number of short circuits nt is at the N point higher than the reference value M point shown in FIG. 2, the welding carriage motor control device 2
2 is applied with a positive input signal, and the welding carriage motor 5a
Increase the number of rotations to increase the trolley speed. When the welding speed increases, the value of the number of short circuits nt decreases as shown in FIG. 2, reaches the reference value (point M) and the difference disappears, and the input signal of the welding carriage motor control device 22 becomes zero. The bogie speed stops increasing. When the short circuit nt is at the L point, which is lower than the reference value M, the operation reverse to the above is performed, the welding speed decreases, the value of the number of short circuits nt increases, and when the reference value (M point) is reached, the truck speed is reached. The drop of the stops. Therefore, the welding carriage speed is constantly adjusted so that the number of short circuits nt matches the reference value.
It is possible to always maintain a good state of the back wave. The relationship between the welding speed υ and the number of short circuits nt in a certain groove gap is shown in Fig. 2. From this figure, if the welding speed is υ ₀ in the groove gap, the number of short circuits will be the set value nt. It becomes ₀ , and it can be seen that if the welding speed is delayed from υ ₀ , the number of short circuits increases, and if the welding speed is faster than υ ₀ , the number of short circuits decreases. Therefore, by the above control, the welding speed υ and the number of short circuits
If nt is kept in the proper welding speed range shown in FIG. 2, good backside welding can be performed. In the above embodiment, the welding speed is adjusted by the number of short circuits nt, but the welding speed may be adjusted by detecting the short circuit time and the arc generation time and by the ratio of both, that is, the short circuit time ratio ηt. .

Although the number of short circuits or the short circuit time ratio of the short circuit time from 2 [msec] to 4 [msec] has been described in the above embodiment,
The optimum short-circuit time varies depending on the wire diameter, wire component, welding current, welding voltage, protruding length, etc., so it must be determined according to each case.

Although the embodiment of the present invention has been described for the case of the I-shaped groove of the downward butt welding, when weaving is performed with the V-shaped groove, the switch 16 is switched to the b side and the weaving center detection circuit 18b is used in the sampling circuit 17. It is preferable that sampling is performed only in response to the high level signal from the above, and the number of short circuits nt or the short circuit time ratio ηt is intermittently detected at or near the center of the weaving.

Further, in the case of horizontal posture welding, weaving is performed diagonally to the welding line in the vertical direction, but the weld metal hangs downward due to the effect of gravity, and the thickness becomes uneven in the vertical direction. Therefore, the switch 16 is switched to the b side so that the sampling circuit 17 performs sampling in response to only the high level signal from the weaving left end detection circuit 18a or the weaving right end detection circuit 18c. A method in which detection is performed intermittently at either the upper end or the lower end of the weaving or in the vicinity thereof is preferable.

Further, it goes without saying that the present invention is applicable not only to the downward posture but also to the vertical posture and the upward posture.

In addition, since the distance between the weld metal tip and the wire tip is always constant, the arc heat applied downward is constant,
Penetration into the lower layer becomes constant. Therefore, 2 in multi-layer welding
It can also be used for stabilizing (controlling) penetration after the first layer and preventing burn-through in thin plates.

[Effects of the Invention] According to the present invention as described above, a short circuit having a time length caused by droplet transfer due to a pinch force is selected, and the selected short circuit is detected as the number of short circuits per unit time or the short circuit time ratio, Since the welding speed is controlled so that this detected value is always kept at the set value, welding can be performed according to the length of the short-circuiting column, that is, the state of the weld pool, and good welding is possible even in the case where the groove dimension changes. . Then, in single-sided backside welding in various welding positions, it is possible to completely and unmanned obtain a front / backside welding bead having a stable penetration corresponding to the change in the groove gap.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a control device applied to the welding method of the present invention, FIG. 2 is a graph showing the relationship between welding speed and the number of short circuits, and FIG. FIG. 4A is a sectional view taken along the line cc ′ of FIG. 3, FIG. 4B is a sectional view taken along the line aa ′ of FIG. 3, and FIG. Is a sectional view taken along the line cc 'of FIG. 3, and FIG.
b'line sectional view, FIG. 6 is a diagram for explaining the relationship between the distance between the weld metal tip and the wire tip in the low current region and the number of short circuits, and FIG. 7 is a diagram showing the distribution of the short circuit time in the low current region. FIG. 8 (A) is a diagram showing the relationship between the short-circuit column length L and the short-circuit time Ts, FIG. 8 (B) is a diagram showing the short-circuit column length L, and FIG. 9 is the relationship between the time t and the short-circuit column length L. FIG. 10, FIG. 10 and FIG. 11 are side sectional views showing the relationship between welding conditions and molten pool, and FIGS. 12 and 13 have the distance between the weld metal tip and the welding wire tip and a specific short-circuit time. It is a graph which shows the relationship of the number of short circuits or a short circuit time rate. 1 ... Welding base metal, 2 ... Groove, 3 ... Backing material, 4 ... Welding torch, 5 ... Truck, 6 ... Rail, 7 ... Welding wire, 8 ... Welding metal, 10 ... ... welding power source, 11 ... short circuit detection circuit, 13 ... pulse generation circuit, 14 ... pulse width discrimination circuit, 15 ... number detection circuit, 16 ... changeover switch, 17 ... sampling circuit, 18a ... weaving left end Detection circuit, 18b ... Weaving center detection circuit, 18c ... Weaving right end detection circuit, 19 ... Holding circuit, 20 ... Comparator, 21 ... Reference voltage generator,
22: Cart motor control device, 23: Droplet.

Claims (3)

[Claims] 1. A backing material is provided on the back side of a groove of a welded joint having a gap between groove forming members having a groove gap changing, and a consumable electrode is provided with a low electric charge along the groove. Perform arc welding in the basin, select a short circuit of a time length caused by droplet transfer due to pinch force from among the short circuits generated between the consumable electrode and the welding base metal, and select the selected short circuit per unit time. An arc welding method characterized by detecting the number of times or a short circuit time rate, and controlling the welding speed so that the detected value is always kept at a set value. 2. The arc welding method according to claim 1, wherein the number of short circuits or the short circuit duration is detected intermittently at or near the center of the weaving. 3. The arc welding method according to claim 1, wherein the number of short circuits or the short circuit time ratio is detected intermittently at or near the end of the weaving.