JPH05245636A - Consumable electrode arc welding method - Google Patents

Abstract

PURPOSE:To provide the consumable electrode arc welding method which settler a problem of groove width profile control in arc sensing and can perform stable accumulative layer welding by arc sensing. CONSTITUTION:In the consumable electrode arc welding method which controls the oscillating width of a welding torch and the welding speed or the wire feed rate according to variation of a root gap and performs one pass welding per layer by arc sensing control to execute control succeessively so as to maintain the bead height constant, the consumable electrode arc welding method to execute control in the range of 2-12mm of bead height above from a straight line AB is provided. Consequently, the bead height for the root gap is selected for width control of arc sensing, by which sure control is executed even in the narrow root gap, stable automatic welding with high efficiency is made possible in the wide root gap, especially, welding accuracy of thick plate welding requiring multilayer welding is improved and a great contribution is made to automation and robotization of the welding process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a consumable electrode type arc welding method capable of surely performing groove width variation detection and accompanying bead height constant control in groove tracking control by arc sensing. ..

[0002]

2. Description of the Related Art A welding groove has insufficient groove processing and assembling accuracy, and since the groove is deformed due to distortion during welding, it is necessary to measure the groove during welding and control copying and welding conditions. I have to. An arc sensing method has been developed as a method for sensing a groove during welding (Japanese Patent Laid-Open No. Sho 61-230476). However, this method starts from the fluctuation of the welding current according to the swing of the welding torch in the direction of the root gap. It is a method to detect the change mentioned above, and it is considered to be most suitable for application to the welding site because it does not require a special sensor to be installed near the welding torch and is easy to handle and maintain. Although such a copying control method using arc sensing control has been attempted for practical use for a long time, stable control is difficult and is not in practical use at present.

The groove tracking control by arc sensing mainly includes line scanning, height scanning and width scanning. The most basic method is to detect and compare current values near both ends of the swing width. As another example, as shown in FIG. 2, the welding line profile is the integrated value ILG of the welding current value in the process from the swing center of the welding torch to the left end (corresponding to the area under the line indicated by ILG in FIG. 2, ILC And so on) and the difference SL between the integrated value ILC of the welding current value in the process from the left end to the swing center
= ILG-ILC, the difference between the integrated value IRG of the welding value in the process from the swing center to the right end and the integrated value IRC of the welding current value in the process from the right end to the swing center SR = IRG-IRC is compared. , Correct the center of oscillation in the direction of smaller current value,
Control is performed so that SL and SR are equal. That is,
When SL> SR, the swing center is controlled to the right, and when SL <SR, the swing center is controlled to the left.

The height profile lowers the welding torch when the current value obtained by adding ILG, ILC, IRG and IRC is smaller (or larger) than the predetermined current value SAK corresponding to the target chip base material distance. (Or raise) to control the welding torch height. That is, ILG + ILC + IR
When G + IRC> SAK, raise the torch, ILG + IL
Lower the torch when C + IRG + IRC <SAK.

In width scanning, SL and SR are compared with a width control threshold value SBK corresponding to the target swing width corresponding to the root gap, and when both SL and SR are large (or small), the swing width is large. Is decreased (or increased) and the welding speed is increased (or decreased),
This is a method of controlling so that the bead height is constant. That is, when SL> SBK and SR> SBK, the swing width is small and the welding speed is fast, and SL <SBK and SR <SBK.
When, the swing width is increased and the welding speed is decreased.

[0006]

However, FIG. 3 shows the welding current when swing welding is carried out with a groove angle of 40 degrees and a root gap of 5 mm, but the fluctuation is large, and therefore fluctuations in control due to arc sensing can be avoided. Absent. In particular, width scanning controls welding conditions such as welding speed and swing width.
There was a problem that the bead shape, melt-in, and excess height were affected, and the fluctuations of each layer accumulated during formation welding, making it extremely difficult to put into practical use. An object of the present invention is to solve the problem of groove width profile control in arc sensing and to provide a consumable electrode type arc welding method capable of stable formation welding by stable arc sensing.

[0007]

SUMMARY OF THE INVENTION The present invention is a welding method which addresses such problems and solves them. The gist of the invention is to adjust the swing width of the welding torch and the welding speed or the wire according to the variation of the root gap G. The bead height H is controlled by controlling the feeding speed.
In the consumable electrode type arc welding method in which one layer and one pass are welded by the arc sensing control for sequentially controlling so as to be constant, the H (mm) is 2 or more and 12 or less, and in the relationship with the G (mm), G ≧ 0.6H + 0.8
The consumable electrode type arc welding method is characterized in that the control is performed in a region where the formula of (3) holds. Hereinafter, the present invention will be described in more detail.

[0008]

The present inventors have investigated why arc control cannot be stably controlled, and as a result, have been able to find the following cause. As shown in FIG. 4, the position of rocking of the welding torch controlled by arc processing during welding is rocking not on the groove but on the molten pool. 5 and 6 show the swing position when only the swing width is controlled by arc sensing and the welding speed is intentionally fast and slow. Even if the same root gap G is arc-sensed, the welding speed is If the welding speed becomes faster, the rocking position moves to the front of the molten pool and the rocking width becomes narrower.If the welding speed becomes slow, the rocking position moves to the rear of the melting pool and the rocking width becomes wider. Become. For this reason, in arc sensing in which a change in the root gap is detected by a change in the swing width, it is detected that the root gap has apparently changed.

In FIG. 7, the welding speed and wire feeding speed are set to predetermined speeds so that the constant groove has a predetermined bead height as in the experiments of FIGS. 4 to 6, and the swing width is determined by arc sensing. The result of calculating the swing width according to a certain width control threshold value SBK by performing only the control of
The change in the swing width according to the change in the bead height of 0 mm is shown. It should be noted here that the change in the swing width is about 1.3 mm for a change in the bead height of 1 mm, which is larger than the change in the bead width of about 0.7 mm shown in the figure, which is clearly the swing width. It is considered that not only the change in the bead width is caused by the change in the bead width, but also the amount of change in the swing width is added due to the change in the swing position on the molten pool shown in FIGS. 4, 5 and 6. Be done. Therefore, the variation of the bead height has a great influence on the swing width during arc sensing, which is a great obstacle to the stable detection of the change in the root gap.

Further, as shown in FIG. 3, the welding current fluctuates greatly during welding, so that arc sensing using the welding current inevitably suffers from control fluctuations. Therefore, even if a groove with a constant root gap is welded, the root gap is controlled so that it fluctuates, the swing width is widened and the welding speed is controlled slow, and the swing width is narrowed and the welding speed is reduced. Rapid control is repeated randomly.

In such a case, as shown in FIG. 8, when welding is performed with the swing width OW corresponding to the root gap RG and the bead height BH, a certain arc sensing result is SL <S.
BK and SR <SBK (or SL) SBK and S
When R> SBK), the determined swing width correction OW
Correct the welding speed slower (or faster) according to + DOW (or OW-DOW) and swing width increase (or decrease). The cause of this control is the increase in route gap RG + DR
If G (or decrease RG-DRG), the original control is constant bead height BH, and control is from point Q to point P (or point Q to point R).

However, in the case of control fluctuations due to fluctuations in the welding current, the bead height changes to BH1 (BH2) because the root gap does not change, and point Q changes to point Q1.
The control is from (point Q to point Q2). At this time, as shown in FIG. 8, the point Q1 (or the point Q2) is changed to the point QP (or the point Q).
R) inside, that is, the bead height is BH <BH1
<BHP (or BHR <BH2 <BH), the modified swing width OW + DOW (or OW-DOW) is too wide (or too narrow), and SL> SBK and SR> SBK in the next arc sensing. (Or S
The probability of L <SBK and SR <SBK) becomes high, and the point Q at the correct position is controlled while fluctuating.

However, the point Q1 (or the point Q2) is the point QP.
If it is outside (or the point QR), that is, if the bead height is BHP <BH1 (or BH2 <BHR), the modified swing width OW + DOW (or OW-DOW) is still too narrow (or too wide). In the next arc sensing, the probability of SL <SBK and SR <SBK (or SL> SBK and SR> SBK) becomes high, it becomes difficult to control to the point Q at the correct position, and the swing width gradually increases. The welding speed may be wide (or narrow) and the welding speed may be slow (or fast), resulting in loss of control.

The bead height that fluctuates due to control fluctuations depends on the cross-sectional shape of the bead. If the bead cross-sectional shape is trapezoidal and the height / bottom is large as shown in FIG. The bead height BH1 due to the increased cross-sectional area DSA controlled late is large. Conversely, when the height / bottom is small, BH1 is set as shown in FIG. 9 (b).
Becomes smaller.

Therefore, the range of the bead height with respect to the root gap capable of stable control can be obtained by the experimental results shown in FIG. 6 and the geometrical calculation of the bead cross-sectional area. This is an area above the straight line AB of 1. That is, it is a range in which G ≧ 0.6H + 0.8 is established in the relationship between the root gap G (mm) and the bead height H (mm).

On the other hand, if the bead height is less than 2 mm, the welding speed becomes too fast in order to reduce the welding speed per unit length, or the wire feeding speed becomes slow and the welding current becomes too low. , The bead shape is not uniform, and the melt-in is shallow, and defects are likely to occur, resulting in poor weldability. Further, in the region where the bead height exceeds 12 mm, the welding speed becomes too slow in order to increase the welding speed per unit length, or the wire feeding speed becomes too fast and the welding current becomes too high. , The bead shape is overlapped and defects are likely to occur, and the weldability is also poor. Therefore, the range where both the controllability of the width control of the arc sensing and the weldability are good is the region where the bead height is 2 to 12 mm above the straight line AB in FIG.

In formation welding, an appropriate bead height can be obtained by using the bead width of the preceding layer as the root gap of the next layer, but the root gap becomes wide in the upper portion of the formation welding of thick plates. The upper limit of the root gap that can be welded in one layer and one pass differs depending on the required value of the mechanical performance of the weld metal, the welding material, the welded steel plate and the welding conditions due to the influence of the heat input amount, etc. Therefore, the upper limit of the root gap is not defined in the present invention. It was Therefore, in view of weldability, above the straight line AB in FIG.
When the bead height is in the range of 2 to 12 mm at 0.6H + 0.8, both controllability and weldability are good. In addition,
The measurement method of the bead height and the bead width is as shown in FIG. 10 by applying the welding cross-sectional area indicated by the diagonal lines to a trapezoid with the root gap as the upper base, and let the bead height be the height of the trapezoid with the same area. The bottom width was the bead width.

[0018]

【Example】

Example 1 Next, the present invention will be described in more detail with reference to examples. Figure 9
When the bead heights are the same from the characteristics of the bead cross-section shown in Fig. 1, BH1 is larger when the root gap is narrower. Therefore, the 1-layer 1-pass welding is performed while controlling the width of the groove where the root gap is continuously narrowed by arc sensing. Then, we experimentally confirmed how many millimeters the root gap can achieve stable copying control. The welding device and test plate used in the experiment are shown in FIGS. 11 and 12. The test plate has a plate thickness T = 50 mm,
A groove groove having a width W of 400 mm and a length L of 2000 mm was machined into a starting-side root gap G1 = 10 mm, an end-side root gap G2 = 1 mm, and a depth F = 30 mm. The welding device is an oscillating device 11 to which the welding torch 5 is attached, and the motor of the traveling vehicle 10 equipped with the oscillating device is an oscillating width according to an instruction of the microcomputer 23 via the oscillating motor controller 21 and the traveling motor controller 22. ,
And the traveling carriage speed was controlled.

The microcomputer detects the shunt 18 attached to the output terminal of the welding power source at 1/100 second intervals in synchronism with the swing position of the torch, and the low-pass filter 19 is passed through the A / D converter 20.
The welding current values converted in step S1 are added up, and I shown in FIG.
LG, ILC, IRG, and IRC are obtained, and SL and SR are obtained by calculating the formulas SL = ILS-ILC and SR = IRG-IRC described above. The SL and SR values are compared with the width control threshold value SBK experimentally obtained in advance. If SL> SBK and SR> SBK, the swing width is narrowed to increase the welding speed, and conversely SL <SBK and SR <SB.
If K, the swing width is wide and the welding speed is slow, and the swing width and the carriage speed are corrected as in the above except for the above.

The correction amount for one time is such that the swing width is 0.1 mm, and the bogie speed is the welding speed correction corresponding to the correction of the bead cross-sectional areas DSA and DSB shown in FIG. And the bead height was controlled to be constant. The initial value of the welding speed was set from the groove angle of the start, the root gap, the bead cross-sectional area calculated from the target bead height, and the melting rate calculated from the wire feed rate determined from the weldability. Further, the initial value of the swing width was set according to the target bead height with reference to FIG. The swing speed was constant at a swing pitch of 3 mm from the initial values of the swing width and the welding speed. The test plate is installed so that the groove line is parallel to the rail, and the groove angle, wire diameter, and shielding gas shown in Table 1 are taken into consideration for variations in the experiment for each condition NO, and repeated 5 times.
Welded once.

[0021]

[Table 1] As for the evaluation method, the bead height after welding was used as a controllability evaluation.
Measurement was made at a position corresponding to the root gap shown in (1), and a difference of 1 mm or less from the target bead height was judged as good, and a position exceeding 1 mm was judged as poor. Further, as a weldability evaluation, the weld bead was subjected to an X-ray transmission test (JIS Z3104), and JIS Class 1 or higher was evaluated as good and less than Class 1 was evaluated as poor. From the experimental results shown in Table 1, at the target bead height of 1 mm, the bead formation was unstable, and the weldability was poor and was poor. At the target bead height of 14 mm, the molten pool was too advanced and a defect of poor penetration occurred from the start, and the width tracking control was not stable, resulting in poor weldability and controllability.

When the target bead height is 2, 4, 6, 8, 10 and 12 mm, the width gap control is stable and the controllability and weldability are good when the root gap is wider than 2, 3, 5, 6, 7 and 8 mm. However, the bead height was too high or too low in a range where the root gap was narrower than this, and control was unstable and controllability was poor. The conventional condition is that the bead height of d is around 6 mm, but it was reproduced that stable welding is impossible in a narrow region where the root gap is 4 mm or less.

[0023]

[Table 2] Example 2 Next, the steel plates after welding under the conditions b to g of Example 1 are shown in Table 2.
Under the welding conditions and the number of layers shown in (1), formation welding was performed by one-layer one-pass welding with the same apparatus and procedure as in Example 1. The welding was performed on the beads shown in Table 1 which had good weldability and controllability. The root gap at the start position was measured by the method shown in FIG.

As the evaluation method, the bead height after formation welding was measured as controllability evaluation, and a difference of 2 mm or less from the target bead height was good and a difference of more than 2 mm was considered bad. Further, as a weldability evaluation, a weld bead was subjected to an X-ray transmission test (JIS Z3
104), and JIS 1 or higher grade was evaluated as good and less than 1 grade was evaluated as poor. The experimental results show that the controllability and weldability are good as shown in Table 2, and good arc sensing control is possible within the range of the present invention even when the root gap is widened in the upper layer portion of the formation welding. I understood it.

[0025]

As is apparent from the above-described results, the present invention makes it possible to control the width of the arc sensing by selecting the bead height with respect to the root gap to ensure reliable control even in a narrow root gap and high efficiency in a wide root gap. Since stable automatic welding is possible, the welding accuracy of thick plate welding, which requires multi-layer welding, is improved, which greatly contributes to automation and robotization.

[Brief description of drawings]

FIG. 1 is a graph showing the range of bead height and root gap in the present invention.

FIG. 2 is a graph showing the fluctuation of the welding torch and the accompanying change in welding current.

FIG. 3 is a waveform chart showing the fluctuation of welding current.

FIG. 4 is a perspective view showing how the arc position on the molten pool moves during width control when the welding speed changes.

FIG. 5 is a perspective view showing how the arc position on the molten pool moves during width control when the welding speed changes.

FIG. 6 is a perspective view showing how the arc position on the molten pool moves during width control when the welding speed changes.

FIG. 7 is a graph showing changes in torch swing width and bead width depending on bead height.

FIG. 8 is a comparison diagram of bead height variation due to fluctuation of control when the width is correctly controlled.

FIG. 9 is an explanatory diagram showing a change in bead height when the welding speed is corrected to be slow while the root gap is not changed.

FIG. 10 is an explanatory diagram of a method for measuring bead height and bead width.

FIG. 11 is a schematic diagram of a welding device used in the examples.

FIG. 12 is a plan view (a) and a side view (b) of a steel sheet used in Examples.

Claims (1)

[Claims] 1. One layer by arc sensing control in which a swing width of a welding torch and a welding speed or a wire feeding speed are controlled according to fluctuations in a root gap G, and the bead height H is sequentially controlled to be constant. In the consumable electrode type arc welding method of 1-pass welding, the H (mm) is 2 or more 12
And in the relationship with the above G (mm), G
A consumable electrode type arc welding method, characterized in that control is performed in a region where an equation of ≧ 0.6H + 0.8 holds.