JP4375787B2 - Consumable electrode arc welding method - Google Patents

Description

The present invention relates to a consumable electrode arc welding method for a carbon steel material, which is performed using a preceding wire (consumable electrode wire) and a following wire (filler wire) that move along a groove provided in a weld base material.

The consumable electrode arc welding method widely used in the field of manufacturing carbon steel welded structures such as mechanical structures, building structures, and civil engineering structures is based on the supply of arc current to electrode wires that also serve as filler materials. In this method, welding is performed by the action of an arc generated along with wear of the electrode wire.

  This consumable electrode type arc welding method is generally carried out with an electrode wire facing above a groove and the arc is generated downward. Upward welding performed with the electrode wire facing downward and the arc facing upward, vertical welding performed with the electrode wire facing the groove side and the arc facing substantially horizontally In some cases, it is necessary to perform welding in various postures, that is, so-called posture welding.

  This kind of posture welding, in particular, upward welding performed with the electrode wire facing the groove below, vertical welding performed with the electrode wire opposed to the side of the groove, and welding in an intermediate form thereof. In this case, gravity acts on the molten pool formed inside the groove by the action of the arc, and the holding state of the molten pool becomes unstable, and irregularities generated on the surface of the weld bead due to dripping of the molten pool There is a risk that internal surface defects such as blow holes generated inside the weld bead and the like will occur.

  In order to prevent the occurrence of such surface defects and internal defects (hereinafter referred to as welding defects), the arc current supplied to the electrode wire is reduced, and the feeding speed of the electrode wire is reduced accordingly. Although it is effective to reduce the speed, in such a case, the welding efficiency is lowered, and there arises a problem that the welding time occupying most of the construction time in the production of the welded structure becomes long.

  In the consumable electrode type arc welding method, various proposals have been made for the purpose of enabling welding with high efficiency. As one of these proposals, a trailing wire that moves following the consumable electrode wire (preceding wire) on the rear side in the welding progress direction of the consumable electrode wire that generates an arc is provided. Is inserted into a molten pool formed inside the groove by the action of the arc, and a part of the arc current is shunted to the trailing wire, thereby depleting for the purpose of promoting cooling of the molten pool There is an electrode type arc welding method (see, for example, Patent Document 1).

In addition, in the double shield type TIG welding method that does not involve electrode wire consumption, a hot wire for promoting welding and one or more cold wires for cooling are fed into the molten pool in an unheated state. There is an arc welding method in which the holding power of the molten pool is increased to prevent the occurrence of poor welding (for example, see Patent Document 2).
JP-A-3-275280 JP 11-58017 A

  The welding method disclosed in Patent Document 1 is an excellent method that has been confirmed to be effective in preventing the occurrence of irregular beads such as undercut and humping. The possibility of application to upward welding or vertical upward welding, which is difficult to maintain stably, is unknown.

  The welding method disclosed in Patent Document 2 is a technique limited to TIG welding that does not involve wire wear, and cannot be applied to consumable electrode arc welding methods such as MIG welding and MAG welding. As in Document 1, it is difficult to perform welding with satisfactory quality at high efficiency in application to upward welding or vertical upward welding.

  Further, none of the welding methods disclosed in Patent Documents 1 and 2 has a structure for preventing the internal defect of the weld bead such as a blow hole, and the strength of the welded joint due to the internal defect is a problem. When applied to an object, it is necessary to cope with a decrease in welding speed, and there is a problem that it is impossible to meet the demand for high-efficiency welding.

  This invention is made | formed in view of such a situation, and the fusion | melting formed in the inside of the groove | channel provided in the weld base material by implementing the method disclosed by patent document 1 on appropriate conditions. An object of the present invention is to provide a consumable electrode type arc welding method capable of stably maintaining a pond and capable of performing all-position welding including upward welding with high efficiency while ensuring high welding quality.

The consumable electrode type arc welding method according to the first aspect of the present invention uses a leading wire that moves in advance along a groove provided in a welding base material and a trailing wire that moves in a subsequent manner, and supplies the preceding wire by supplying an arc current. A carbon steel material that is welded while inserting the trailing wire into a molten pool formed inside the groove by the action of an arc generated along with the consumption of the wire, and performing the welding while diverting the arc current to the trailing wire. In the consumable electrode type arc welding method, the welding is performed under a condition that the maximum width of the molten pool is 10 mm or less in order to enable stable maintenance of the molten pool inside the groove. .

In the present invention, the prior use of the wire and the trailing wire, a consumable electrode type arc welding method that will be implemented as a target carbon steel, carried the maximum width of the molten pool formed inside the groove as 10mm or less Increases the holding force due to surface tension to enable stable holding of the molten pool, prevents the occurrence of surface defects caused by dripping of the molten pool, and posture welding including upward welding, without causing a decrease in welding speed Make it happen at high efficiency.

Further, the consumable electrode type arc welding method according to the second aspect of the present invention includes a shunt current If to be shunted to the succeeding wire, a feeding speed Wf of the succeeding wire, and an arc current Ia supplied to the preceding wire. Welding is performed while maintaining the following conditional expression including:
5.38 Wf- (0.53 Ia-120) ≧ If ≧ 1.52 Wf- (0.15 Ia-3.77)

  In the present invention, a consumable electrode type arc welding method using a leading wire and a trailing wire under the condition that the maximum width of the molten pool is 10 mm or less is used. It is carried out so as to satisfy the conditional expression determined based on the result of examining the occurrence limit of defects, and high weld quality excluding surface defects and internal defects is realized with high efficiency.

In the first consumable electrode arc welding method according to the invention of the present invention, prior to consumable electrode arc welding of carbon steel using a wire and a trailing wires, because implementing a maximum width of the molten pool as 10mm or less, The molten pool, which is lowered in temperature by the insertion of the trailing wire, can be stably held by the action of the surface tension on the opening side surface of the groove, maintaining satisfactory welding quality for posture welding including upward welding. However, it is possible to perform a high efficiency by employing a large welding speed.

  Further, in the consumable electrode type arc welding method according to the second aspect of the invention, welding is performed while maintaining the current to be diverted to the succeeding wire so that the conditional expression determined in consideration of the presence or absence of internal defects is satisfied. The present invention has an excellent effect, such as enabling posture welding having welding quality to be performed with high efficiency.

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof. FIG. 1 is a schematic view showing an implementation state of a consumable electrode type arc welding method (hereinafter referred to as a method of the present invention) according to the present invention.

  A welding apparatus used for carrying out the method of the present invention includes a consumable electrode wire 1 as a leading wire, a filler wire 2 as a trailing wire, and feeding drums 10 and 20 configured to feed them separately. Yes. The consumable electrode wire 1 is connected to the positive electrode of the welding power source 3 by a power supply line 11, and a predetermined arc current Ia is supplied from the welding power source 3 through the power supply line 11. Further, the filler wire 2 is connected to a shunt line 21 branched in the middle of the base material connection line 31 for connecting the negative electrode of the welding power source 3 to the weld base material 4. In addition, it can be returned to the welding power source 3 via the base material connection line 31.

FIG. 1 shows a state in the middle of welding with respect to a groove 5 provided with a V-shaped cross section at a joining portion of carbon steel weld base materials 4 and 4 having a flat plate shape. In this welding, the tips of the consumable electrode wire 1 and the filler wire 2 are positioned so as to face the groove 5 at a position separated by an appropriate length in the extending direction of the groove 5, and these wires 1 and 2 are positioned. As shown by the white arrow in the figure, the consumable electrode wire 1 is moved first along the groove 5 at a predetermined speed, and the arc current Ia is supplied from the welding power source 3 to the consumable electrode wire 1. Done. The consumable electrode wire 1 and the filler wire 2 are moved, for example, by moving a carriage that holds them together along a preset guide rail, and the moving speed is increased or decreased manually or automatically. It is supposed to be done.

  By supplying the arc current Ia, an arc 6 is generated between the tip of the consumable electrode wire 1 and the groove 5, and the consumable electrode wire 1 as a filler material is formed inside the groove 5 by the action of the arc 6. A weld pool 8 formed by integrally melting the weld base metals 4 and 4 is formed at a portion facing the consumable electrode wire 1, and a weld bead 8 formed by cooling and solidifying the melt pool 7 is formed by a consumable electrode wire. 1 is formed continuously on the rear side in the moving direction, and the welding base materials 4 and 4 are welded. During this time, the tip of the filler wire 2 that moves backward to the consumable electrode wire 1 is inserted into the molten pool 7 formed as described above, and the molten pool 7 is sufficiently cooler than itself. It cools according to the insertion amount of 2.

  On the other hand, a shunt current If that is fed back to the welding power source 3 by being inserted into the molten pool 7 is generated in the filler wire 2 connected to the base material connection line 31 via the shunt line 21. Thus, there is a decrease between the shunt current If generated in the filler wire 2, the arc current Ia supplied to the consumable electrode wire 1, and the ground current Ie returned to the welding power source 3 via the base material connection line 31. The relationship given by the equation exists, and the magnitude of the shunt current If is, as shown in FIG. 1, the variable resistor 32 interposed in the middle of the base material connection line 31 (the ground side from the branch portion of the shunt line 21). By increasing or decreasing the resistance value, it is possible to freely increase or decrease within a predetermined range.

  Ia = If + Ie (1)

  During this time, the consumable electrode wire 1 is fed out at a speed determined in advance according to its own moving speed and consumption amount by the rotation of the feeding drum 10, and the filler wire 2 is fed by the rotation of the feeding drum 20. In order to keep the insertion length per unit time into the molten pool 7 constant, the feed is sent at a predetermined feed speed Wf.

  As is known, the molten pool 7 is covered with a shielding gas supplied around the consumable electrode wire 1 and the filler wire 2 to prevent oxidation due to contact with the outside air. The method of the present invention described below is applicable regardless of the type of shield gas, such as MIG welding using shield gas mainly composed of inert gas such as argon gas, MAG welding using shield gas mainly composed of carbon dioxide gas, etc. Needless to say, it is applicable.

  In FIG. 1, the consumable electrode wire 1 is positioned above the groove 5 provided in the weld base metals 4 and 4, and an arc 6 emitted from the tip of the consumable electrode wire 1 is directed to the groove 5. As shown above, this welding is performed in the upward position in which the arc 6 acts upward from the lower position of the groove 5 and in the standing position. It is also possible to carry out posture welding in various postures such as vertical welding in which an arc acts on the arranged groove 5 from the side.

  In these posture weldings, as described above, there is a problem in that the holding state of the molten pool 7 in the groove 5 becomes unstable, and a welding failure occurs due to dripping of the molten pool 7. The inventor verified the generation mechanism of the holding force that supports the molten pool 7 inside the groove 5, and as a result, set an upper limit on the maximum width δ of the molten pool 7 formed inside the groove 5, It has been found that by maintaining the feeding amount of the filler wire 2 appropriately, it is possible to prevent the occurrence of poor welding regardless of the decrease in welding speed. The groove 5 is not limited to the V shape shown in FIG. 1, and there are various shapes such as a U shape and a Y shape. However, the method of the present invention described below is not limited to the shape of the groove 5. Applicable regardless of

  The length of the molten pool 7 formed during actual welding is finite in the extending direction of the groove 5 and has an end, but this end increases the holding force of the molten pool 7. Therefore, in order to grasp the qualitative tendency of the holding state of the molten pool 7 inside the groove 5, it is assumed that the molten pool 7 is sufficiently long in the extending direction of the groove 5. It is sufficient to examine the balance of external forces applied to the molten pool 7 in a two-dimensional manner within the cross section. The external forces acting on the molten pool 7 are gravity, external pressure (atmospheric pressure), and surface tension of the molten pool 7.

  FIG. 2 is a view showing a formation mode at the time of upward welding of the molten pool 7 inside the groove 5 having a V-shaped cross section. The molten pool 7 shown in this figure has a surface that protrudes toward the expansion side of the groove 5 that is the lower position due to the action of gravity applied downward, on the expansion side and the narrowing side, and between these surfaces The thickness h is formed.

In this balance formula of the external force in the molten pool 7, the radius of curvature of the lower surface (expansion side surface) of the molten pool 7 is R, and the radius of curvature of the upper surface (narrow side surface) is also R ₀ , and the molten pool 7 is formed. When the surface tension of the molten metal is σ, the density is ρ, and the acceleration of gravity is g, the following equation is given. It should be noted that the external pressure as an external force does not appear in the equation because it acts on both the upper and lower surfaces and cancels out.

σ / R = σ / R ₀ + ρgh (2)

Here, when the reverse wave welding is targeted, the upper surface of the molten pool 7 is convex and the radius of curvature R ₀ is infinite, so the balance equation (2) is simplified to the following equation.

  σ / R = ρgh (3)

  That is, the downward gravity applied to the molten pool 7 having a thickness h is supported by the surface tension σ of the lower surface of the molten pool 7, and ρ and g in this equation are constants, and the equation (3) is established. In order to sufficiently increase the limit holding thickness h of the molten pool 7, one of increasing the surface tension σ and decreasing the curvature radius R of the surface of the molten pool 7 on the spreading side of the groove 5 or Both need to be realized.

  First, a method for reducing the curvature radius R of the surface of the molten pool 7 will be described. FIG. 3 is a diagram showing how the molten pool 7 having variously different maximum widths δ is formed. The maximum width δ of the molten pool 7 formed inside the V-shaped groove 5 is changed by changing the spreading angle of the groove 5. 3A shows a case where the spread angle is 60 °, FIG. 3B shows a case where the spread angle is 40 °, and FIG. 3C shows a case where the spread angle is 20 °. Each shows.

In the figure, h ₀ indicates the thickness of the portion where the molten pool 7 contacts the side surface of the groove 5, and R _{1 to} R ₃ indicate the radius of curvature of the surface of the molten pool 7. As is apparent from the comparison of these figures, the radii of curvature R ₁ , R ₂ , R ₃ of the surface of the molten pool 7 formed with the same thickness h ₀ are clearly R ₁ > R ₂ > It has a magnitude relation of R _3, in order to reduce the curvature radius R of the molten pool 7 surface, to reduce the maximum width δ of the molten pool 7 is seen to be effective.

  FIG. 4 is a diagram showing the results of examining the relationship between the maximum width δ of the weld pool 7 and the limit holding thickness h when upward welding is performed. According to this figure, as assumed from FIG. 3, the limit holding thickness h of the molten pool 7 tends to increase as the maximum width δ of the molten pool 7 decreases, and the maximum width δ is 10 mm. It is clear that it increases rapidly in the following region. That is, by performing welding with the maximum width δ of the molten pool 7 being 10 mm or less, it is possible to stably maintain the molten pool 7 formed inside the groove 5 while ensuring a high welding speed, including upward welding. All-position welding can be performed with high efficiency while ensuring high welding quality.

  The generation mechanism of the sudden increase region in FIG. 4 is not clear, but in normal arc welding, it is known that the range in which the arc pressure acts effectively is within a circular cross section having a diameter of about 10 mm. It is presumed that a sharp increase in the limit retention thickness h occurs due to a synergistic effect with the range of action. In FIG. 4, the result of the region where the maximum width δ of the molten pool 7 is 5 mm or less is not shown. When the maximum width δ is 5 mm or less, the consumable electrode wire 1 and the filler wire 2 are connected to the groove 5. This is because it is difficult to correctly position the center portion, and when a device capable of performing this positioning with high accuracy is used, it is possible to weld the maximum width δ of the weld pool 7 to 5 mm or less. Needless to say, it is included in

  Furthermore, it has been confirmed that the results shown in FIG. 4 can be obtained not only for the V-shaped groove 5 shown in FIG. 1 but also for grooves having other cross-sectional shapes such as a U-shape and a Y-shape. Therefore, the method of the present invention in which the maximum width δ of the molten pool 7 is 10 mm or less is effective regardless of the shape of the groove.

  In addition, since the opening width of the groove 5 in which the molten pool 7 is formed becomes wider as the thickness of the welding base materials 4 and 4 increases, welding is performed on the groove 5 having an opening width of 10 mm or more. When performing, first, welding is performed at the bottom of the groove 5 with the maximum width δ of the molten pool 7 being 10 mm or less, and welding is performed a plurality of times under the same conditions on the weld bead 8 obtained by this welding. And the entire interior of the groove 5 may be filled with weld beads stacked in a plurality of layers. Even in the welding performed in this manner, the maximum width δ of the lowermost weld pool 7 (weld bead 8) is within the range of the present invention if it is 10 mm or less.

  The increase in the surface tension σ, which is another means for increasing the limit holding thickness h of the molten pool 7 when the above equation (3) is established, is to change the composition of the molten pool 7 or However, the former, that is, the composition change of the molten pool 7 is not an appropriate means for affecting the strength performance of the welded portion. Accordingly, in order to achieve a large limit holding thickness h by increasing the surface tension σ, it is necessary to lower the internal temperature of the molten pool 7, which is followed by the consumable electrode wire 1 as described above. This is realized by cooling the molten pool 7 by inserting the filler wire 2.

  Here, the cooling of the molten pool 7 is promoted by increasing the insertion amount of the filler wire 2 inserted into the molten pool 7 per unit time, that is, the feeding speed Wf of the filler wire 2. When the feeding speed Wf becomes excessive, there is a problem that the internal defect (blow hole) of the weld bead 8 formed by cooling and solidification of the molten pool 7 is caused as shown below. This blow hole is generated in the same manner when the feeding speed Wf is too low.

  5 to 7 are explanatory views of the blow hole generation mechanism. FIG. 5 shows a state in which the feeding speed Wf (feed amount) of the filler wire 2 is appropriate, and FIG. FIGS. 7A and 7B show a state where the feeding speed Wf is excessive, and FIGS. 7A and 7B show a state where the feeding speed Wf of the filler wire 2 is too small. In these figures, the same reference numerals as those in FIG. 1 are given.

  As shown in FIG. 5, when the feeding speed Wf of the filler wire 2 that moves backward to the consumable electrode wire 1 is appropriate, the molten pool 7 formed by the action of the arc 6 at the tip of the consumable electrode wire 1 is the tip of the filler wire 2. In this case, no defect is generated inside the weld bead 8 continuous on the rear side of the molten pool 7.

  On the other hand, when the feeding speed Wf of the filler wire 2 is excessive, the molten pool 7 does not wet up to the tip of the filler wire 2, and the filler wire 2 is pushed into the molten pool 7 as shown in FIG. A gap is generated around the filler wire 2, and bubbles 70, 70... Are generated inside the molten pool 7 due to the entrainment of gas into the gap, and some of these bubbles 70, 70. .. Remain in the weld bead 8 continuing to the molten pool 7 without being excluded in the solidification process, and blow holes 80, 80... Are generated in the weld bead 8.

  When the feeding speed Wf of the filler wire 2 is too low, the tip of the filler wire 2 melts immediately after contact with the molten pool 7 and is torn inside the molten pool 7 as shown in FIG. As shown in FIG. 7B, the contact between the filler wire 2 and the molten pool 7 is interrupted, and contact with the molten pool 7 is caused again by feeding the filler wire 2 as a result. The states shown in (a) and (b) are repeated in a short cycle. At this time, gas is entrained in the molten pool 7 during the transition from the state of FIG. 7A to the state of FIG. 7B, and bubbles 70, 70... Are generated and are not excluded in the solidification process. Are left inside the weld bead 8, and blow holes 80, 80... Are generated inside the weld bead 8.

  In the state shown in FIG. 7B, the short-circuit between the filler wire 2 and the molten pool 7 is interrupted, and the shunt current If returning to the filler wire 2 becomes zero, so that the arc current Ia fluctuates and the state of the arc 6 changes. It becomes unstable, and the disturbance of the shield accompanying this facilitates the entrainment of gas into the molten pool 7 and the generation of blow holes 80, 80... Inside the weld bead 8.

  The inventors have: Paying attention to the blow hole generation mechanism as described above, while the arc current Ia supplied to the consumable electrode wire 1 is set to a predetermined value, the feeding speed Wf of the filler wire 2 is changed variously and blown into the weld bead 8. A test for examining an appropriate region of the feeding speed Wf in which the holes 80, 80. FIG. 8 is a diagram showing the results of this test, FIG. 8A shows the results when the arc current Ia is set to 200 A, and FIGS. 8B to 8D show the arc current Ia. , 250, 300, and 350A are shown.

  8A to 8D, the horizontal axis represents the feeding speed Wf of the filler wire 2, and the vertical axis represents the shunt current If that is shunted to the filler wire 2. As described above, blow holes are generated in regions where the feeding speed Wf of the filler wire 2 is excessively low and excessive, and appropriate regions where blowholes are not generated are indicated by cross hatching in each figure. It can be seen that the region expands as the shunt current If increases.

  Further, this appropriate region shows a tendency that the feeding speed Wf becomes larger as the arc current Ia supplied to the consumable electrode wire 1 increases. This transition is presumed to be because the thermal energy possessed by the molten pool 7 increases as the arc current Ia increases, and the filler wire 2 that contacts the molten pool 7 is likely to melt.

  In the test results shown in FIGS. 8A to 8B, the boundary lines on both sides of the appropriate region can be linearly approximated, and when the approximate expression of the boundary lines indicated as L1 to L8 in each figure is obtained, Each is as follows.

L1: If = 5.38Wf + 8.33
L2: If = 1.52Wf-24.33
L3: If = 5.38Wf-8.33
L4: If = 1.52Wf-35.83
L5: If = 5.38Wf-35.00
L6: If = 1.52Wf−43.41
L7: If = 5.38Wf-71.67
L8: If = 1.52Wf-46.94

  The second term of each of these equations varies with the arc current Ia and is considered to be a function of the arc current. Therefore, when the second term of each equation is plotted against the arc current Ia, it becomes as shown in FIG. 9, and the second term of L1, L3, L5, L7 indicating the boundary line on the side where the supply speed Wf is small, and the supply The second term of L2, L4, L6, and L8 indicating the boundary line on the side where the speed Wf is large is considered to be distributed on each other straight line as shown in the figure, and when each is expressed by the least square method, Each is as shown below.

Second term of L1, L3, L5 and L7 = −0.53Ia + 120.00
Second term of L2, L4, L6, L8 = −0.15 Ia + 3.77

  Accordingly, the appropriate areas shown in FIGS. 8A to 8D are areas sandwiched by the upper limit boundary line LU and the lower limit boundary line LL shown by the following expression.

LU: If = 5.38Wf- (0.53Ia-120.00)
LL: If = 1.52Wf- (0.15Ia-3.77)

  As a result, welding is performed while keeping the shunt current If to be shunted to the filler wire 2 within a range where the conditional expression shown below is satisfied, thereby generating blow holes 80, 80... As internal defects of the weld bead 8. Can be prevented, and high-quality welding is possible.

  5.38Wf− (0.53Ia−120) ≧ If ≧ 1.52Wf− (0.15Ia−3.77) (4)

It is a schematic diagram which shows the implementation state of the method of this invention. It is a figure which shows the formation aspect at the time of the upward welding of the molten pool inside a groove. It is a figure which shows the formation aspect of the molten pool which has various different maximum widths. It is a figure which shows the result of having investigated the relationship between the maximum width of a molten pool and limit holding | maintenance thickness in the case of performing upward welding. It is explanatory drawing of the production | generation mechanism of a blowhole. It is explanatory drawing of the production | generation mechanism of a blowhole. It is explanatory drawing of the production | generation mechanism of a blowhole. It is a figure which shows the result of the test which investigates the appropriate area | region of the feeding speed of a filler wire. It is explanatory drawing of the determination procedure of the boundary line of an appropriate area | region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Consumable electrode wire 2 Filler wire 3 Welding power source 4 Welding base material 5 Groove 6 Arc 7 Weld pool 8 Weld bead

Claims (2)

Using a leading wire that moves in advance along a groove provided in a weld base material and a trailing wire that moves in a subsequent direction, the arc is generated by the action of an arc generated by the consumption of the preceding wire by supplying an arc current. In the consumable electrode type arc welding method for carbon steel material, in which the trailing wire is inserted into a molten pool formed inside, and welding is performed while the arc current is diverted to the trailing wire,
A consumable electrode type arc welding method , wherein welding is performed under a condition that the maximum width of the molten pool is 10 mm or less so that the molten pool can be stably held inside the groove . Welding is performed while maintaining the shunt current If to be shunted to the succeeding wire within a range in which the following conditional expression including the feeding speed Wf of the succeeding wire and the arc current Ia supplied to the preceding wire is satisfied. The consumable electrode type arc welding method according to claim 1 to be performed.
5.38 Wf- (0.53 Ia-120) ≧ If ≧ 1.52 Wf- (0.15 Ia-3.77)

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