JP2001293575A - Method of arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of an arc welding which has improved stability of control, is suitable for various use and enables an excellent and uniform penetration bead to be formed. SOLUTION: An electrode 1 is inclined toward the advancing direction of the welding by 60 deg. to 90 deg., the welding is performed while the distance d between the generation point of an arc 2 and the back face of a work 6 to be welded is kept in a range where a penetration bead is excellently formed, a wire extension during the welding work is detected, and the feeding speed of the wire is controlled so that the extension is kept constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an arc welding method for forming a good back bead.

[0002]

2. Description of the Related Art In a conventional arc welding method, an electrode angle is arranged almost at right angles to the surface of a member to be welded, as shown in FIG. The electrode angle is generally about ± 25 ° as disclosed in JP-A-6-234075). In FIG.
1 is an electrode, 2 is an arc, 3 is a weld pool, 4 is a weld bead,
5 is a back bead, 6 is a member to be welded, 7 is a groove, and 8 is a back surface (also referred to as a plate back surface) of the member 6 to be welded. In this case, in order to form the back bead 5 satisfactorily, the arc 2 and the back surface 8 of the plate are required.
The distance d between them must be kept appropriate. However, the distance d varies depending on welding current, welding speed, groove shape, and the like, and it is generally difficult to keep the distance constant. As shown in FIG. 21, when the distance d is extremely small (including minus), the back bead is excessively formed or burn-through occurs. On the other hand, if the distance d is too long, the back bead does not come out and insufficient penetration occurs. Here, there is a relationship of H∝S ・ VF / (v ・ g) h∝f (I). Here, H: bead height (mm) h: height from the arc generation point to the bead surface (mm) S: wire cross-sectional area (mm ² ) VF: wire feed speed (mm / min) I: welding current ( A) v: welding speed (mm / min)... Equal to the moving speed of the torch g: groove width (mm) Therefore, if the groove width g increases, the bead height H decreases. The groove width g may be any value that indicates a relative change in the groove width. However, here, the groove width g refers to the gap at the bottom of the groove 7. Also, since d ≒ Hh, when g is large, (Hh) becomes small, the arc easily melts the base material, and the arc position is lowered. As a result, the magnitude of d is greatly affected by g.

FIG. 20 is a block diagram showing a configuration of a welding control device for performing the above-described conventional arc welding method.
The welding condition database 21 stores data such as the welding current I, the welding speed v, the wire feed speed VF, and the groove width g. Based on these data, the welding current or the wire feed speed is stored. While controlling the welding current, the wire feeding speed and the welding speed by the control device 22 and the welding speed control device 23, the welding device 24 is operated to perform welding. During welding, a groove detector 25 including a camera and an image sensor measures the groove width g, and the measured value is fed back to the welding condition database 21 to correspond to a change in the groove width g. The optimum welding conditions are output from the welding condition database 21 to the welding current or wire feed speed control device 22 and the welding speed control device 23.

[0004] However, the conventional arc welding method and apparatus have the following problems. (1) The relationship between many parameters such as I, VF, v, and g and the back bead shape needs to be determined in advance by experiments or the like. Therefore, it takes time and costs. (2) It is difficult to maintain uniform accuracy of g and the like, and changes due to thermal deformation during welding. Therefore, means such as controlling welding conditions while measuring with a special sensor or the like is required.
Also, a groove width detector (such as an image sensor) is generally expensive. (3) If the member to be welded has an inclination or the like, the above-mentioned condition changes, so that data must be collected again. (4) Since H and h change individually, the controllability of the welding device is poor. (5) Since d cannot be directly controlled, the range of application is limited.

[0005] In order to solve the above-mentioned problems, the present applicant has set the electrode in the direction of the welding progress by 60 ° to 90 °.
(4) An arc welding method for welding by tilting was previously proposed (Japanese Patent Application No. 2000-16486).

[0006]

However, when the welding speed is controlled by this welding method, there is a problem in the stability of the control because the welding speed changes due to the vibration of the molten pool or the like. Further, when controlling the wire feeding speed, the length of the protruding wire changes, which limits the applicable range.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended to improve the stability of control and to form a good and uniform back bead having a wide application range. The aim is to provide a method.

[0008]

SUMMARY OF THE INVENTION An arc welding method according to the present invention employs an arc welding method using a welding power source having a constant voltage characteristic to form a first layer by welding while forming a back bead on the back surface of a member to be welded. In the above, the electrode is inclined at an angle of 60 ° to 90 ° in the welding progress direction, welding is performed while maintaining the distance between the arc generating point and the back surface of the member to be welded in a region where the back bead is formed well, and the wire being welded. The length of the protrusion is detected, and the wire feeding speed is controlled so that the length of the wire is constant.

In the present invention, as shown in FIG. 1, welding is performed by inclining the electrode 1 by 60 ° to 90 ° in the welding progress direction. That is, the receding angle of the electrode 1 is set to 60 ° to 90 °. The receding angle of the electrode 1 includes not only the case where the entire welding torch is inclined but also the case where the tip of the welding torch is curved.
Refers to the angle of inclination. In the case of a multi-electrode, the electrode 1 indicates a leading electrode. Here, the reason why the receding angle of the electrode 1 is set to 60 ° or more is that, when the angle is less than 60 °, the arc 2 is generated and the back surface (plate back surface) of the member 6 to be welded due to the positional relationship between the electrode 1 and the molten pool 12.
This is because the change in the distance d between the eight is large, and the same problem as in the conventional method occurs.

When the electrode 1 is inclined within the above-mentioned angle range, welding is performed under a balance of forces as shown in FIG. FB = Fa + FS Here, FB: Static pressure in the horizontal direction due to gravity of molten steel Fa: Arc force FS: Surface tension acting on the molten pool As long as the balance of these forces is maintained, the welding current I and wire feeding Even if parameters such as the feeding speed VF, the welding speed v, and the groove width g change, the distance d between the point at which the arc 2 is generated and the plate back surface 8 does not change. Therefore, a uniform and good back bead 5 can be formed.

The horizontal static pressure FB of the molten steel due to gravity is proportional to the square of the bead height H when the width of the molten pool 3 is substantially constant. The arc force Fa is equal to the welding current I.
Is proportional to the first power to the second power, and is expressed as f (I). Since the horizontal force FS due to the surface tension is considered to be constant without being affected by the welding conditions and the like, if this is α, H ² ∝f ( I) + α (1) where H: bead height (mm) I: welding current (A) α: horizontal force of surface tension acting on the molten pool (this is considered to be constant). In other words, H increases or decreases as I increases or decreases.

On the other hand, the bead formation speed w is given by: w∝S · VF / (H · g) (2) where w: bead formation speed (mm / min) S: wire cross-sectional area (mm ²⁾ ) VF: Wire feeding speed (mm / min) g: Groove width (mm), so that bead forming speed w and torch moving speed v
When the values are equal to each other, the welding is performed while maintaining the balance of the above forces. When the bead forming speed w and the torch moving speed v are different due to the variation of the groove width g, for example, when v is faster than w, the welding torch advances faster, so the wire protrusion length. Will grow. However, in welding using a welding power supply having a constant voltage characteristic in which the self-control action of the welding power supply works, if the wire protrusion length increases, the welding current I decreases, and as a result, H decreases and w increases. That is, the wire protrusion length does not keep increasing, but welding can be performed in a balanced state at a certain value. Conversely, when v is slower than w, the length of the protruding wire does not continue to be shortened, but balances at a certain value.

The bead forming speed w and the torch moving speed v
FIG. 3 shows the relationship between the length and the wire protrusion length L. Here, dL / dt = v−w. In the case of an I groove, w = S ・ VF / (H ・ g), so the above equation is as follows. dL / dt = v−S · VF / (H · g) where L: wire protrusion length (mm) v: torch moving speed (mm / min) w: bead forming speed (mm / min) S: Wire cross-sectional area (mm ² ) VF: Wire feeding speed (mm / min) H: Bead height (mm) g: Groove width (mm) That is, the bead forming speed w and the torch moving speed v are equal. The balance is made when the wire projection length L changes so that the welding current value I becomes as follows. Therefore, L changes, but d is always constant regardless of L (see FIG. 4). Therefore, the back bead is always good regardless of the change in the groove width g.

However, the above description is for the case where the length of the wire protrusion is not controlled. As in the present invention, when controlling the wire protrusion length to be constant, that is, when detecting the wire protrusion length during welding and controlling the wire feeding speed so that the wire protrusion length is constant, For example, when the groove width g is widened, the bead forming speed w decreases as shown in the equation (2), so that the wire protrusion length increases to some extent as described above. At this time, if the wire feeding speed VF is increased, it is possible to make the bead forming speed w constant by the equation (2). When a welding power source having a constant voltage characteristic is used, if the wire feeding speed VF is increased, the welding current also increases, so that the bead height H increases according to the equation (1), and the bead forming speed w decreases. However, since the degree of increase in the wire feed speed VF is greater than the degree of increase in the bead height H due to the increase in welding current, increasing the wire feed speed VF causes the bead forming speed w to increase. Heading. For this reason, when the wire feeding speed VF is increased, the length of the projecting wire is reduced. Therefore, the wire protrusion length is detected, and when the wire protrusion length is larger than a predetermined value, the wire protrusion speed can be controlled to a predetermined length by increasing the wire feeding speed VF. On the other hand, similarly, when the groove width g becomes narrow, the wire feeding speed V
If the F control is not performed, the wire protrusion length will be shorter,
By reducing the wire feed speed VF, the wire protrusion length can be controlled to a predetermined length. in this way,
The wire protrusion speed can be controlled by increasing or decreasing the wire feeding speed VF, and even if the groove width varies,
It becomes possible to perform welding with a constant wire protrusion length at a constant torch moving speed v. Therefore, also in this case, the back bead is always good regardless of the change in the groove width g. In this way, by controlling the wire protrusion length to be constant, it is possible to cope with a large change in the groove width, and the application range is expanded and the control stability is improved.

In the present invention, the distance d is maintained in a region where the back bead 5 is formed well. The region where the back bead 5 is favorably formed is determined by experiments or the like. As described later, a welding wire 1 of 1.6 mmφ is used.
When d is used, the range of d = 0 to 4 mm is appropriate.
When the welding wire 1 is inclined, the distance d is approximately measured as a distance d ′ from the center position of the tip of the welding wire 1 (see FIG. 1).

Further, the arc welding method according to the present invention is characterized in that a wire protrusion length during welding is obtained by detecting a wire feeding speed and a welding current.

In arc welding using a consumable electrode, the relationship between the feed speed VF of the welding wire, the welding current I, and the wire protrusion length L is expressed by the following equation. VF = a ・ I + bＬLI ・^2, where VF: welding wire feed speed (mm / min) I: welding current (A) L: wire protrusion length (mm) a, b: depending on the material of welding wire From the above equation, L = (VF−a · I) / (b · I ² ). Therefore, by detecting the welding wire feed speed VF and the welding current I, the actual wire protrusion at that time is detected. The length L 'can be determined. Therefore, the wire feed speed VF may be controlled so that L 'becomes the set value Lo.
According to this method, since the wire feeding speed VF and the welding current I can be detected more accurately than when the wire protrusion length L is detected, more precise control is possible.

In the arc welding method of the present invention, the welding speed can be changed stepwise by controlling the welding speed according to the value of the wire feeding speed or the welding current during welding. The range of application can be expanded and control stability can be ensured.

Further, in the arc welding method of the present invention, the distance between the arc generating point and the back surface of the member to be welded is set to 0 to 2.5 times the wire diameter used.

[0020]

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

FIG. 5 is an explanatory view of an arc welding method according to an embodiment of the present invention, FIG. 6 is a block diagram showing a configuration of the welding apparatus, and FIG. 7 is a block diagram showing an example of a wire protrusion length detector. . In this embodiment, a welding torch 10 having a curved tip is used, and the welding wire 1 at the tip is arranged in front of the molten pool 3 and parallel to the plate back surface 8. Then, the first layer welding is performed while maintaining the distance d between the point where the arc 2 is generated and the back surface 8 of the plate at a constant distance where the back bead 5 is formed favorably. Welding is gas shielded arc welding such as gas metal arc welding performed using a welding power source having a constant voltage characteristic. In FIG. 5, 4 is a weld bead, 6 is a member to be welded, 7 is a groove, 9 is a backing material, and 11 is a welding tip.

The welding device 12 for implementing this welding method is as follows.
As shown in FIG. 6, the configuration includes a welding speed setting device 13, a wire protrusion length detector 14, and a wire feeding speed control device 15.

In arc welding using a consumable electrode, the relationship between the feed speed VF of the welding wire, the welding current I, and the wire projection length L is expressed by the following equation. VF = a ・ I + bＬLI ・^2, where VF: welding wire feed speed (mm / min) I: welding current (A) L: wire protrusion length (mm) a, b: depending on the material of welding wire According to the determined constant, the wire protrusion length detector 14 detects the actual wire protrusion length L ′, and the wire protrusion length L ′
Of the welding wire is controlled by the wire feeding speed control device 15 so that is always constant. Further, the welding speed is controlled so as to maintain a predetermined constant speed regardless of a change in the groove width.

The wire protrusion length detector 14 may be composed of an image sensor such as a camera, a laser sensor, or the like.
As shown in FIG. 7, from the actual welding current and the detected value of the wire feeding speed, the above-mentioned relational expression VF = a ・ I + b ・ L 解 I ² was solved for the wire protrusion length L. L = (VF−aＩI) )
A value using a value calculated using / (b · I ² ) may be used. In FIG. 7, reference numeral 16 denotes a wire feed speed detector;
Is a welding current detector, and 18 is a wire protrusion length calculator.

In this welding method, when the wire protrusion length L is not controlled to be constant as described above, the relationship between the groove width g and the wire protrusion length L is as shown in FIGS. On the other hand, the relationship between the groove width g and the welding current I when the wire protrusion length L is controlled to be constant is as shown in FIG.
The relationship between the groove width and the wire feeding speed is as shown in FIG.

FIG. 8 shows that the welding speed is v = 12.8 cm / mi.
The graph shows a change in the wire protruding length L with respect to a change in the groove width g at that time, where n is constant. From this graph, it can be seen that when the groove width g changes, the wire protrusion length L changes correspondingly. At this time, at the welding current value shown in parentheses, the moving speed of the torch 10 and the forming speed of the bead 4 self-balance. That is, the groove width g
When the groove width is increased, the wire protrusion length L increases, and the welding current value decreases. Conversely, when the groove width g decreases, the wire protrusion length L decreases, and the welding current value increases.

FIG. 9 shows a change in the wire protrusion length L with respect to a change in the groove width g when the wire feeding speed is controlled so that the welding current is constant. The welding speed is constant at v = 12.8 cm / min. From this graph, the wire protrusion length L changes almost in proportion to the groove width g, and the change amount is smaller than that in FIG. The values in parentheses indicate that the welding current is 40
This is the wire feed speed when controlled to be constant at 0A.

On the other hand, FIGS. 10 and 11 show the relationship between the groove width g, the welding current I and the wire feeding speed VF when the wire feeding speed is controlled until the wire protrusion length becomes constant. It is shown. The wire protrusion length is L = 35 mm, and the welding speed is v = 12.8 cm / min.
And constant. The values in parentheses shown in FIG. 10 indicate the wire feeding speed when the wire protrusion length is constant, and the values in parentheses shown in FIG. 11 indicate the welding current when the wire protrusion length is constant. Is shown. Comparing FIG. 10 and FIG. 11 with FIG. 8, if the groove width becomes wider,
It can be seen that the welding current becomes higher than the current value at the time of self-balancing, and conversely, if the groove width becomes narrower, the welding current becomes lower than the current value at the time of self-balancing. That is, when the wire protrusion length is controlled to be constant, if the groove width is widened, the wire feeding speed increases, and the welding current is higher than the current value at the time of self-equilibrium, and the bead forming speed is increased. Conversely, when the groove width is reduced, the wire feeding speed decreases, the welding current becomes lower than the current value at the time of self-equilibrium, and acts so as to slow the bead formation speed. The moving speed of the torch should be equal.

FIG. 12 shows an example of a back bead in a welding test according to this embodiment. However, the wire protrusion length L
= 35 mm is the back bead cross-sectional shape at the time of the initial layer welding when the wire feed speed is controlled so as to be 35 mm, (a) of the figure shows a groove width g = 13 mm, welding current 400 A, (b) The groove width g is 17 mm and the welding current is 500 A.
The welding speed is 12.8 cm / min (constant) in each case.
And In this way, by controlling the wire protrusion length to be constant, welding can be performed at a constant torch moving speed (12.8 cm / min) despite a change in the groove width g, and the back bead is also constant. It has become.

FIG. 13 is a block diagram of a welding apparatus showing another embodiment of the present invention. The welding device 12 is configured to include a wire protrusion length detector 14, a wire feeding speed control device 15, a wire feeding speed or welding current detector 16, and a welding speed control device 19.

When the welding speed is kept constant irrespective of the change in the groove width, as shown in FIGS. 10 and 11, the fluctuation range of the wire feeding speed and the welding current is large. Therefore, since the control range is limited, as shown in FIG. 13, the wire feeding speed or welding current is detected by the wire feeding speed or welding current detector 16, and the wire feeding speed or welding current is detected. The welding speed is controlled stepwise according to the welding speed. When the welding speed is controlled by the wire feeding speed, the command value of the wire feeding speed control device 15 may be used as shown in FIG. 14 without detecting the actual wire feeding speed.

FIGS. 15 and 16 show changes in the welding current and the wire feeding speed when the welding current and the wire feeding speed during welding are detected and the welding speed is controlled in three stages according to the detected values. It is shown. By gradually changing the welding speed, the change range of the welding current and the wire feeding speed can be reduced, so that it is not necessary to use a large-capacity welding power supply or a wire feeding device capable of high speed feeding,
Also, the applicable range for the groove width can be greatly expanded.

In welding using a welding power source having a constant voltage characteristic, the welding current changes according to the wire feeding speed as a result of controlling the wire feeding speed, and both show the same phenomenon. Therefore, the same result can be obtained regardless of which control is used, and the case where the wire feeding speed is detected and the welding speed is controlled (FIG. 16) will be mainly described below. The welding speed is determined in advance in multiple stages (levels 1, 2, 3,... From the slower side) in accordance with the range of the groove width, and the upper limit and the lower limit of the wire feed speed are also set. FIG. 16 shows that three levels of welding speeds are provided. When the detected value of the wire feed speed exceeds the upper limit, the welding speed level is reduced by one, and when the detected value of the wire feed speed falls below the lower limit, the level is reduced. The operation of raising one is performed. In order to maintain control stability, the switching of the welding speed level is performed once and only once within a certain period of time. By doing so, the control range of the wire feeding speed is about 1/3 of that in FIG. 11, and as a result, the application range is expanded and the stability of control is improved. FIG. 15 shows a case where the welding speed level is switched based on the detected value of the welding current, and similar results are obtained.

FIG. 17 shows the distance d and the height of the back bead,
It is a graph which shows the relationship with width. However, if the wire diameter is 1.
It shows a test result when 6 mmφ. In forming the back bead, the height position of the arc generating point is an important factor. Here, in order to represent the distance d, the height of the tip position of the welding wire 1 from the back surface 8 of the plate is defined as “torch height”, and as shown in FIG. No bead is formed and poor fusion occurs. The penetration limit is reached when the torch height d is about 4.1 mm. Also, when the torch height decreases, the back bead height increases. The torch height is set by a Y-axis slide mechanism (not shown). From the results of FIG. 17, the torch height may be in the range of 0 to 4 mm, and d
Is suitably in the range of 0 to 2.5 times the wire diameter.

FIG. 18 shows the back bead shape when the torch height is 1 mm and 4 mm. However, it is the back bead cross-sectional shape at the time of initial layer welding. Both have good back bead shapes, but the back bead height and width vary depending on the torch height.

When the groove width changes, the back bead height can be made constant by weaving the tip of the welding wire 1 in the groove width direction while keeping the torch height constant. For example, in FIG. 4, weaving can be performed by swinging the vertical axis of the welding torch 10 through a rack and pinion by an X-axis slide mechanism (not shown).

[0037]

As described above, according to the present invention,
The following effects can be obtained. (1) Welding current I, wire feed speed VF, welding speed v,
Even if parameters such as the groove width g change, the distance d between the arc generating point and the back surface of the member to be welded can be kept constant, so that a good and uniform back bead can be formed. (2) Further, the relationship between these parameters and the back bead shape is determined in advance by experiments or the like, and it is not necessary to determine the optimum welding conditions, so that time and cost can be reduced. (3) It is sufficient to set only the target position of welding and the welding speed or the wire feeding speed, and the setting of welding conditions can be easily performed. (4) In the prior art, a groove width detection mechanism was separately required, but this can be omitted, and the apparatus configuration and control method can be simplified. (5) Since the wire protrusion length is detected and the wire feeding speed is controlled so that the length is always constant, the applicable range is expanded, and the control stability is improved. (6) Since the welding speed is controlled stepwise according to the wire feeding speed, the applicable range is expanded, and the control stability is improved.

[Brief description of the drawings]

FIG. 1 is a view showing an arc welding method of the present invention.

FIG. 2 is a diagram showing a balance of forces acting between an arc and a molten pool in the arc welding method of the present invention.

FIG. 3 is a diagram showing a relationship among a bead forming speed w, a torch moving speed v, and a wire protrusion length L in the arc welding method of the present invention.

FIG. 4 is a view showing a state of formation of a back bead due to a change in a groove width g in the arc welding method of the present invention.

FIG. 5 is an explanatory diagram of an arc welding method showing an embodiment of the present invention.

FIG. 6 is a block diagram of a welding device.

FIG. 7 is a block diagram illustrating an example of a wire protrusion length detector.

FIG. 8 is a graph showing a relationship between a groove width, a wire protrusion length, and a welding current value during self-balancing.

FIG. 9 is a graph showing a relationship between a groove width, a wire protrusion length, and a wire feeding speed when the wire feeding speed is controlled so that a welding current is constant.

FIG. 10 is a graph showing a relationship between a groove width, a welding current, and a wire feeding speed when the wire feeding speed is controlled so that a wire protrusion length is constant.

FIG. 11 is a graph showing a relationship between a groove width, a wire feeding speed, and a welding current when the wire feeding speed is controlled so that the wire protrusion length is constant.

FIG. 12 is a cross-sectional view of the back bead when control is performed to make the wire protrusion length constant.

FIG. 13 is a block diagram of a welding device according to another embodiment of the present invention.

FIG. 14 is a block diagram of a welding device according to still another embodiment of the present invention.

FIG. 15 is a diagram showing a relationship between a groove width and a welding current when the welding speed is controlled stepwise.

FIG. 16 is a diagram illustrating a relationship between a groove width and a wire feeding speed when the welding speed is controlled stepwise.

FIG. 17 is a graph showing the relationship between the torch height d and the height and width of the back bead.

FIG. 18 is a cross-sectional view showing a back bead shape according to a torch height.

FIG. 19 is a view showing a conventional arc welding method.

FIG. 20 is a block diagram of a conventional welding control device.

FIG. 21 is a diagram showing a state of formation of a back bead due to a change in a groove width g in a conventional arc welding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode (welding wire) 2 Arc 3 Weld pool 4 Weld bead 5 Back bead 6 Member to be welded 7 Groove 8 Backside of board 9 Backing material 10 Welding torch 11 Welding tip 12 Welding device 13 Welding speed setting device 14 Wire protrusion length detection 15 Wire feeding speed control device 16 Wire feeding speed or welding current detector 17 Welding current detector 18 Wire protrusion length calculator 19 Welding speed control device

Claims (4)

[Claims] In the first layer welding in which a back bead is formed on the back surface of a member to be welded by using an arc welding method using a welding power source having a constant voltage characteristic, the electrode is set at 60 ° to 90 ° in a welding progress direction. Weld while maintaining the distance between the arc generation point and the back surface of the welded member in the area where the back bead is formed well, detect the wire protrusion length during welding, and determine the wire protrusion length. An arc welding method comprising controlling a wire feeding speed so as to be constant. 2. The arc welding method according to claim 1, wherein a wire protrusion length during welding is determined by detecting a wire feeding speed and a welding current. 3. The arc welding method according to claim 1, wherein the welding speed is controlled according to a value of a wire feeding speed or a welding current during welding. 4. The method according to claim 1, wherein the distance between the arc generating point and the back surface of the member to be welded is 0 to 2.5 times the diameter of the wire used. Arc welding method.