Gas shielded arc welding method, gas shielded arc welding system, method for producing welded metal, and welding wire

Abstract

To enable gas shielded arc welding capable of having excellent electrodeposition coating properties, regardless of the compositions of a welding wire and a material to be welded.SOLUTION: In a gas shielded arc welding method using a shielding gas and applying a wire feeding control method in which forward feeding and reverse feeding are alternately repeated while feeding a welding wire at a predetermined average wire feeding speed, the shielding gas contains, in terms of volume fraction with respect to the total gas constituting the shielding gas, at least O2 of 10 to 30 vol%.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a gas-shielded arc welding method, a gas-shielded arc welding system, a method for producing weld metal, and a welding wire, which employ a feed control method for feeding a welding wire at a predetermined average wire feed speed while alternately repeating forward feed and reverse feed. [Background technology]

[0002] Automotive undercarriage parts are exposed to corrosive environments due to moisture from the road surface and salt damage from snow-melting agents, and therefore technologies to prevent corrosion are needed. A common method for protecting undercarriage parts from corrosive environments is to apply electrodeposition coating after arc welding. However, when electrodeposition coating is performed after welding, the electrodeposition coating film does not form on the welding slag (hereinafter simply referred to as "slag"), resulting in paint defects, which can lead to corrosion progression from these defects. While there are methods to prevent paint defects, such as thickening the electrodeposition coating film, even if a paint film is formed on the slag, it can peel off along with the slag due to impacts such as hitting pebbles while driving, resulting in corrosion progression from the peeled areas. Thus, parts manufactured by conventional methods are susceptible to corrosion due to poor coating on the welding slag, or even if a paint film is formed, corrosion can occur due to slag peeling during driving.

[0003] In response to the above-mentioned problems, for example, Patent Document 1 proposes a gas-shielded arc welding wire that generates less spatter during welding, does not require processes such as slag removal after welding, has excellent electrodeposition paintability, and can produce welds with a good bead shape. The welding wire contains, per total mass of the wire, C: 0.01% by mass or more and 0.10% by mass or less, Si: 0.05% by mass or more and 0.55% by mass or less, Mn: 1.60% by mass or more and 2.40% by mass or less, Ti: 0.05% by mass or more and 0.25% by mass or less, Cu: 0.01% by mass or more and 0.30% by mass or less, S: 0.001% by mass or more and 0.020% by mass or less, N: 0.0045% by mass or more and 0.0150% by mass or less, O: 0.0010% by mass or more and 0.0050% by mass or less, Al: 0.10% by mass or less, P: 0.025% by mass or less, and the balance being Fe and unavoidable impurities, and the relationship is 0.1≦[Ti] / [Si]≦3.0. Patent Document 1 also describes that when the above-mentioned gas-shielded arc welding wire is used, a thin slag can be uniformly formed in the weld, and excellent electrodeposition paintability can be obtained without the need to remove the slag after welding.

[0004] Patent Document 2 proposes a gas-shielded arc welding solid wire capable of forming a welded joint with excellent electrodeposition paintability and mechanical properties, and a method for manufacturing a welded joint. The solid wire contains, in mass percent relative to the total mass of the wire, 0.05-0.20% C, 0.01-0.18% Si, 1.0-3.0% Mn, 0.06-0.25% Ti, 0.003-0.10% Al, 0-0.0100% B, more than 0-0.015% P, more than 0-0.015% S, and optional elements, with the balance being iron and impurities, satisfying Si × Mn ≦ 0.30 and (Si + Mn / 5) / (Ti + Al) ≦ 3.0, and further having a Ceq of 0.40-0.90%. Patent Document 2 also describes that use of the gas-shielded arc welding solid wire enables the formation of a welded joint with excellent electrodeposition paintability and mechanical properties.

[0005] As described above, in the welding wires described in Patent Document 1 and Patent Document 2, the Si content is reduced to suppress the formation of Si- and Mn-based slag, which has extremely low electrical conductivity, making it possible to form an excellent electrodeposition coating film even when slag is generated on the weld bead. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-74777 [Patent Document 2] Patent Publication No. 2021-3732 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Documents 1 and 2, the formation of Si- and Mn-based slag is suppressed by the welding wire, but the material to be welded (also referred to as the "base material" or "workpiece") is not taken into consideration. For example, in recent years, automobile parts have become increasingly high-tensile, and high-tensile steel plates are increasingly used as welded materials. However, various alloying elements are added to high-tensile steel plates to improve their strength. The influence of these alloying elements can change the slag composition, potentially degrading electrodeposition paintability. Furthermore, in welding wires, the content of alloying elements such as Si and Mn is regulated to ensure electrodeposition paintability, which limits the degree of freedom in designing the alloy of the welding wire. In other words, it is desirable to be able to ensure excellent electrodeposition paintability regardless of the composition of the welding wire and the material to be welded.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a gas-shielded arc welding method, a gas-shielded arc welding system, a method for producing weld metal, and a welding wire that are capable of providing excellent electrodeposition coatability regardless of the composition of the welding wire and the material to be welded. [Means for solving the problem]

[0009] The present invention comprises the following configurations.

[0010] (1) A gas-shielded arc welding method using a shielding gas, which employs a feed control method in which a welding wire is fed at a predetermined average wire feed speed while alternately repeating forward feed and reverse feed, The shielding gas is characterized in that it contains at least 10 to 30 vol% of O2 in terms of volume fraction relative to the total gases constituting the shielding gas. Gas shielded arc welding method.

[0011] (2) A gas-shielded arc welding system using a shielding gas, which employs a feed control method for feeding a welding wire at a predetermined average wire feed speed while alternately repeating forward feed and reverse feed, a welding wire feed control device; The shielding gas is characterized in that it contains at least 10 to 30 vol% of O2 in terms of volume fraction relative to the total gases constituting the shielding gas. Gas shielded arc welding system.

[0012] (3) A method for producing a weld metal by a gas-shielded arc welding method using a shielding gas, which employs a feed control method in which the welding wire is fed at a predetermined average wire feed speed while alternately repeating forward feed and reverse feed, The shielding gas is characterized in that it contains at least 10 to 30 vol% of O2 in terms of volume fraction relative to the total gases constituting the shielding gas. Weld metal manufacturing method.

[0013] (4) A welding wire applicable to a gas-shielded arc welding method using a shielding gas containing at least 10 to 30 vol% of O2 in the volume fraction of all gases constituting the shielding gas, the method including alternately repeating forward feed and reverse feed, controlling at least an average welding current during the forward feed period to be higher than a predetermined set current depending on a tip position of the welding wire, and feeding the welding wire at a predetermined average wire feed speed, The welding wire is For the total mass of the welding wire, C: 0.30% by mass or less, Si: 0.80% by mass or less, Mn: 2.20% by mass or less, P: 0.05% by mass or less, S: 0.05% by mass or less, Ti: 0.30% by mass or less, Al: 0.30% by mass or less, Mg: 0.30% by mass or less, Zr: 0.30% by mass or less, Cu: 1.00% by mass or less, Ni: 1.00% by mass or less, Cr: 1.00% by mass or less, Mo: 1.00% by mass or less, Nb: 0.10% by mass or less, V: 0.10% by mass or less, B: 0.0050% by mass or less, Fe: 90% by mass or more, A welding wire comprising: [Effects of the Invention]

[0014] According to the present invention, a weld bead having excellent electrodeposition coatability can be obtained regardless of the composition of the welding wire and the material to be welded. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a welding system according to this embodiment. [Figure 2] FIG. 2 is a block diagram showing a schematic configuration relating to the control of the welding power source, welding control device, and servo amplifier in this embodiment. [Figure 3] FIG. 3 is a graph illustrating the relationship between the wire feed speed, the wire tip position, and the current detection signal in this embodiment. [Figure 4] FIG. 4 is a diagram showing a weld bead portion related to the evaluation of electrodeposition paintability in this embodiment. [Figure 5] FIG. 5 is a diagram showing the results of an evaluation test in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] The inventors conducted extensive research to solve the above problems and discovered the following: By using a mixed gas containing at least a certain amount of oxygen (O2) in the shielding gas, the composition of oxides formed in or on the surface of the molten pool can be controlled, even if the workpiece or welding wire contains a large amount of an element (e.g., Si) that easily forms non-conductive glassy oxides. This can also suppress the formation of non-conductive glassy oxides. Furthermore, by using the feed control method described below, stable welding is possible even with a mixed gas of CO2 and O2, which generally results in poor arc stability. As a result, a weld bead with excellent electrodeposition paintability can be obtained.

[0017] Specifically, the volume fraction of the total gases constituting the shielding gas should be at least 10 to 30 vol% O2. Although the O2 content in this range increases the amount of slag, it controls the composition to be primarily iron oxide, which has excellent electrodeposition paintability, and suppresses the formation of non-conductive glassy oxides. Thus, by incorporating a large amount of O2 into the shielding gas, it is possible to produce slag with excellent electrodeposition paintability. However, generally, when the O2 content in the shielding gas is as high as in the present invention (at least 10 vol% or more), the arc becomes constricted and the arc deflects, with the large amount of slag formed on the molten pool acting as a cathode point. This significantly reduces arc stability, leading to poor weld bead shape and excessive spatter. In other words, the inclusion of a large amount of O2 in the shielding gas makes normal welding difficult. Therefore, in one embodiment of the present invention, a feed control method is employed to ensure good arc stability even with the O2 content specified in the present invention.

[0018] There are various types of feed control methods, including a type in which the welding wire feed speed is alternately switched between forward and reverse feed periods, and welding is performed at a low current range based on a short-circuit transition form that generates short-circuit periods and arc periods (hereinafter also referred to as a "short-circuit type feed control method"), and a type in which the welding wire feed speed is alternately switched between forward and reverse feed periods, and welding is performed at a medium current range or higher based on a globule transition form that suppresses the occurrence of short-circuit periods (hereinafter also referred to as a "short-circuit suppression type feed control method"). Either the short-circuit type feed control method or the short-circuit suppression type feed control method is effective in the present invention.

[0019] The short-circuit type feed control method can forcibly realize stable short-circuit transfer, so stable welding is possible even if the shielding gas contains a large amount of O. However, in view of the range of applicable welding conditions and the effect of further improving the electrodeposition paintability described below, it is preferable to apply the short-circuit suppression type feed control method of this embodiment.

[0020] Specifically, when the short-circuit suppression type feed control method and the shielding gas composition of the present invention are applied, the following phenomena (a) to (d) can be expected to result in improved electrodeposition paintability.

[0021] (a): The effect of surface tension convection increases due to the influence of O2 (10-30 vol%) in the shielding gas. The surface tension convection becomes a convection that flows into the high temperature area. Furthermore, the adsorption of oxygen on the surface of the molten pool reduces the surface tension of the molten pool, and the molten pool becomes more susceptible to oscillation due to the influence of the plasma flow.

[0022] (b) In the short-circuit suppression type feed control method, in the early stage of the high current period, a wide area of ​​the molten pool is in contact with the arc, so the temperature gradient on the molten pool surface is small, and the shear force of the plasma airflow becomes larger than the surface tension convection, resulting in outward convection.

[0023] (c) In the short-circuit suppression type feed control method, when the wire approaches the weld pool during the high current period and forward feed period, and the arc length becomes shorter, the area in contact with the arc becomes smaller and the current density becomes higher, which increases the temperature gradient on the weld pool surface and causes a flow on the high temperature side. In other words, it is an inward convection current. In this way, the direction of the convection current alternates depending on whether the wire position is up or down during the high current period.

[0024] (d): This change in convection prevents the large amount of slag that is generated from aggregating at the edge of the bead (hereinafter referred to as the toe). By suppressing this agglomeration of slag at the toe, the slag composition and thickness become uniform, making it possible to apply stable electrodeposition coating to the entire bead surface. In general, the thicker the slag, the worse the electrodeposition coating properties become, so the toe of the bead, where slag is likely to aggregate, is relatively difficult to apply electrodeposition coating to.

[0025] In addition, the following is provided as a supplement: Two types of convection are thought to be primarily involved in the convection in the molten pool: surface tension convection (convection based on the Marangoni effect) and convection based on the shear force of the plasma gas flow. The latter, convection based on the shear force of the plasma gas flow, causes outward convection in the molten pool, so if we only consider the latter, slag tends to accumulate on the outside, that is, at the toe of the bead.

[0026] On the other hand, the direction of surface tension convection, the former, changes depending on the amount of surface active elements. Examples of surface active elements include O and S. For example, when the O2 concentration in the shielding gas is low, the effect of the surface active elements is small, so the surface tension tends to decrease as the temperature of the molten pool increases. When the arc length is shortened, the center of the molten pool is generally hotter, so in this case the surface tension convection flows outward from the molten pool, where the temperature is lower and the surface tension is higher. In other words, in this case, both the surface tension convection and the convection due to the shear force of the plasma airflow are outward convection, so slag tends to accumulate on the outside, i.e., at the bead toe.

[0027] However, when the O2 concentration in the shielding gas is high, the effect of the surfactant element becomes greater, and the surface tension tends to increase as the temperature of the molten pool rises. As a result, the surface tension convection flows toward the inside of the molten pool, where the temperature is higher and the surface tension is higher. In other words, in this case, the inward direction of the surface tension convection and the outward direction of the convection due to the shear force of the plasma gas flow are opposite to each other.

[0028] The overall direction of convection, whether outward or inward, depends on which of the two countercurrent types described above becomes dominant. As explained in (b) above, the temperature gradient on the molten pool surface is small at the beginning of the high-current period in the short-circuit suppression feed control method. Therefore, the surface tension convection is also small. Since the convection due to the shear force of the plasma flow is relatively larger than the surface tension convection, the result is an outward convection.

[0029] Furthermore, as explained in (c) above, in the short-circuit suppression feed control method, when the wire approaches the weld pool during the high current period and forward feed period, and the arc length shortens, the area in contact with the arc becomes smaller, the current density increases, and the temperature gradient on the weld pool surface becomes larger. This means that the difference in surface tension also increases, and surface tension convection becomes stronger. Relatively speaking, surface tension convection is stronger than convection due to the shear force of the plasma flow, resulting in inward convection.

[0030] As described above, when the concentration of impurities including O2 is high and the short circuit suppression type feed control method is used, the direction of convection changes periodically. This periodic change in convection suppresses slag aggregation at the toe, preventing slag agglomeration at the toe and non-uniformity of the slag composition.

[0031] Below, embodiments for carrying out the welding method of the present invention will be described in detail along the above mechanism. Note that the present invention is not limited to the embodiments described below, and can be carried out with any modifications within the scope of the gist of the present invention.

[0032] <Shielding gas composition> (O2: 10-30 vol%) The O2 contained in the shielding gas is used to control the slag composition to be primarily iron oxide. By controlling the composition to be primarily iron oxide, excellent electrodeposition paintability can be achieved, even if the welding wire or steel sheet contains large amounts of elements such as Si, which are prone to forming non-conductive glassy oxides. Furthermore, the effect of O2 reduces the surface tension of the molten pool, thereby widening the weld bead, resulting in a flatter weld bead and a more favorable bead shape. To achieve electrodeposition paintability through slag composition control, the O2 content is set to 10 vol% or more. Furthermore, to achieve better electrodeposition paintability, a content of 15 vol% or more is preferred, with 20 vol% or more being more preferable. On the other hand, if the O2 content in the shielding gas exceeds 30 vol%, excessive slag is generated, potentially resulting in slag peeling. Therefore, the O2 content in the shielding gas is set to 30 vol% or less.

[0033] (Main component gas: 70 vol% or more) The main gas is a gas commonly used in gas-shielded welding, such as 100 vol% CO2 gas (also known as carbon dioxide), 100 vol% Ar gas, a 80 vol% Ar-20 vol% CO2 mixed gas, or a 90 vol% Ar-10 vol% CO2 mixed gas. In the present invention, from the perspective of welding workability, it is preferable to include at least 70 vol% of this main gas. CO2 is particularly preferred as the main gas because it has a high potential gradient, can shorten the arc length, and can suppress arc deflection. When a mixed gas is used as the main gas, for example, a main gas: 80 vol% Ar-20 vol% CO2 mixed gas, and a gas composition of the main gas + O2, where the main gas is 80 vol% and O2 is 20 vol%, the actual gas composition is 64 vol% Ar + 16 vol% CO2 + 20 vol% O2.

[0034] (Other: 20 vol% or less (including 0 vol%)) In addition to the above gases, for example, gases such as H2, N2, Ar, or He may be contained in the range of 20 vol% or less.More preferably, only CO2 and O2 are contained, with the remainder being impurities.

[0035] <Welding wire> Next, a preferred welding wire will be described in detail as one embodiment of the present invention. Note that the present invention is not limited to the welding wire embodiments described in detail below, and can be implemented with any modifications within the scope of the present invention. For example, the welding wire may have a composition within the range specified by JIS standards, such as JIS Z 3312:2009 (solid wire for MAG welding and MIG welding for mild steel, high-tensile steel, and low-temperature steel) and JIS Z 3313:2009 (flux-cored wire for arc welding for mild steel, high-tensile steel, and low-temperature steel).

[0036] The reasons for adding and limiting the numerical values ​​of the alloying elements contained in the welding wire according to this embodiment will be explained in detail below. From the viewpoint of manufacturing, such as increasing the strength of automotive parts, it is more difficult to change the material of the workpiece than the welding wire. Therefore, in the present invention, in order to achieve better electrodeposition coating properties, it is preferable to set the Si content in the welding wire to 0.80 mass% or less and the Fe content to 90 mass% or more. This is because the amount of Si that forms non-conductive vitreous oxides is reduced to 0.80 mass% or less, and the Fe content is set to 90 mass% or more so that the composition can be easily controlled to be mainly composed of iron oxides, as explained above. Thus, it is preferable to specify Si and Fe in the above ranges in priority to other elements. Meanwhile, alloying elements other than Si and Fe may be added as desired depending on the base metal used and the application.

[0037] In the following description, the content of each element in the welding wire is defined as the content of the element contained as an alloy component relative to the total mass of the welding wire.

[0038] The welding wire may be a solid wire made of alloying elements or a flux-cored wire in which the flux is made only of metal powder (hereinafter also referred to as a metal-based flux-cored wire), but a solid wire suitable for a feed control method is more preferable. In a metal-based flux-cored wire, the alloying elements described below may be contained in either the hoop or the flux.

[0039] (C: 0.30% by mass or less (including 0% by mass)) C has a deoxidizing effect, and when C is contained in the welding wire, it is possible to obtain the effect of improving the mechanical performance of the weld metal. The C content can be adjusted appropriately depending on the required strength, but in this embodiment, if the strength can be ensured by other elements, the welding wire does not need to contain C, and the C content may be 0 mass %.

[0040] However, if the welding wire contains an excessive amount of C, the deoxidizing effect becomes strong, and CO is generated near the arc, which may cause an explosion, resulting in the generation of spatter and an increase in the amount of fumes. Therefore, from the viewpoint of welding workability, the C content in the welding wire is preferably 0.30 mass% or less, more preferably 0.10 mass% or less, and even more preferably 0.08 mass% or less, relative to the total mass of the welding wire.

[0041] (Si: 0.80 mass% or less (including 0 mass%)) Si is a deoxidizing agent, and when Si is contained in the welding wire, the effect of improving the mechanical properties of the weld metal can be obtained. The Si content can be adjusted appropriately depending on the required strength, but in this embodiment, as long as the strength can be ensured by other elements, the welding wire does not need to contain Si, and the Si content may be 0 mass %.

[0042] On the other hand, SiO2, an oxide of Si, is a non-conductive vitreous oxide, and if it remains as slag on the weld bead, it becomes impossible to form an electrodeposition coating film. In the present invention, the formation of non-conductive vitreous oxides can be suppressed by adding an appropriate amount of O2 to the shielding gas and controlling the composition to be mainly iron oxide. However, as explained above, considering the Si content of the welded material, which is difficult to change from a manufacturing perspective, it is preferable to keep the Si content of the welding wire as low as possible. Therefore, from the viewpoint of electrodeposition coating properties, it is preferable to keep the Si content of the welding wire to 0.80 mass% or less relative to the total mass of the welding wire. Note that the lower the Si content of the welding wire, the better, with 0.50 mass% or less being preferred, and 0.30 mass% or less being more preferred.

[0043] (Mn: 2.20 mass% or less (including 0 mass%)) Mn, like Si, is a deoxidizer, and when Mn is contained in a welding wire, it can improve the mechanical properties of the weld metal. In addition, when Mn is combined with Ti and Al, which will be described later, it can disperse slag generated on the bead.

[0044] On the other hand, if the Mn content in the wire exceeds 2.20% by mass, deoxidation proceeds, reducing the amount of oxygen in the molten pool, which increases the surface tension of the droplets and may affect the bead shape. Therefore, the Mn content in the welding wire is preferably 2.20% by mass or less, and more preferably 2.10% by mass or less, relative to the total mass of the wire. In this embodiment, if strength can be ensured by other elements, the welding wire does not need to contain Mn, and may even contain 0% by mass. However, since MnO, which is generated by the oxidation of Mn, has relatively high conductivity, a higher Mn content in the welding wire contributes to improving electrodeposition paintability. Therefore, the Mn content in the welding wire that improves electrodeposition paintability is preferably 1.60% by mass or more, and more preferably more than 1.80% by mass.

[0045] (P: 0.050% by mass or less (including 0% by mass)) P is an element that affects the cracking susceptibility of the weld metal, and the lower the P content in the welding wire, the better the cracking resistance of the weld metal, so the welding wire according to this embodiment does not need to contain P, and may contain 0 mass % of P. Note that when the welding wire contains P, from the viewpoint of cracking resistance, the P content in the welding wire is preferably 0.050 mass % or less with respect to the total mass of the welding wire.

[0046] (S: 0.050% by mass or less (including 0% by mass)) S is an element that reduces the surface tension of molten metal, and when S is contained in a welding wire, it is possible to obtain the effect of forming a flat weld bead. The effect of forming a flat weld bead is obtained by supplying oxygen, which is also a surface active element, from the shielding gas, so there is no particular lower limit for the S content, and it may be 0 mass%.

[0047] On the other hand, the higher the S content in the welding wire, the more likely sulfides are generated, which may change the slag composition and affect the electrodeposition paintability. Therefore, the S content in the welding wire is preferably 0.050 mass% or less with respect to the total mass of the welding wire.

[0048] (Ti: 0.30 mass% or less (including 0 mass%)) (Al: 0.30 mass% or less (including 0 mass%)) (Mg: 0.30% by mass or less (including 0% by mass)) (Zr: 0.30 mass% or less (including 0 mass%)) Al, Ti, Mg, or Zr is a strong deoxidizing element that preferentially forms oxides through its deoxidizing action. Adding an appropriate amount of these elements can improve the mechanical performance of the weld metal. In this embodiment, if strength can be ensured with other elements, the welding wire does not need to contain these strong deoxidizing elements, and the content may be 0 mass %. Note that, because Ti-based slag has relatively high conductivity, it is preferable to set the Ti content to at least 0.01 mass % or more in terms of electrodeposition coating properties.

[0049] On the other hand, the higher the content of strong deoxidizing elements in the welding wire, the more the slag composition changes, which may affect the electrodeposition coatability. Therefore, the content of Al, Ti, Mg, or Zr is preferably set to 0.30 mass% or less each, and the total content of Al, Ti, Mg, or Zr is preferably set to 1.00 mass% or less, based on the total mass of the welding wire.

[0050] (Cu: 1.00 mass% or less (including 0 mass%)) The inclusion of Cu in the welding wire can enhance the mechanical properties of the weld metal. The Cu content can be adjusted appropriately depending on the required strength. However, in this embodiment, as long as the strength can be ensured by other elements, the welding wire does not need to contain Cu, and may even be 0 mass %. Here, the Cu content in this specification also includes Cu in a plating that may be formed on the surface of the welding wire. When the welding wire according to this embodiment is used in lap fillet welding of 440 to 980 MPa steel sheets used in automobile suspension parts, the Cu content in the welding wire, including the plating, is preferably 1.00 mass % or less with respect to the total mass of the welding wire. By suppressing the Cu content as described above, a balance is achieved with other elements that enhance mechanical properties, and excessive strength of the weld metal can be suppressed.

[0051] (Ni: 1.00 mass% or less (including 0 mass%)) The inclusion of Ni in the welding wire can provide the effect of enhancing the mechanical properties of the weld metal. The Ni content can be adjusted appropriately depending on the required strength. However, in this embodiment, if strength can be ensured by other elements, the welding wire does not need to contain Ni, and may contain 0 mass% Ni. Note that, when the welding wire according to this embodiment is used in lap fillet welding of 440 to 980 MPa steel sheets used in automobile suspension parts, the Ni content is preferably 1.00 mass% or less with respect to the total mass of the welding wire. By restricting the Ni content as described above, a balance is achieved with other elements that enhance mechanical properties, and excessive strength of the weld metal can be suppressed.

[0052] (Cr: 1.00% by mass or less (including 0% by mass)) The inclusion of Cr in the welding wire can provide the effect of improving the mechanical properties of the weld metal. The Cr content can be adjusted appropriately depending on the required strength. In this embodiment, however, as long as the strength can be ensured by other elements, the welding wire does not need to contain Cr, and the Cr content may be 0 mass%. When the welding wire according to this embodiment is used in lap fillet welding of 440 to 980 MPa steel sheets used in automobile suspension parts, the Cr content is preferably 1.00 mass% or less with respect to the total mass of the welding wire. By restricting the Cr content as described above, a balance is achieved with other elements that improve mechanical properties, and excessive strength of the weld metal can be prevented.

[0053] (Mo: 1.00 mass% or less (including 0 mass%)) The inclusion of Mo in the welding wire can provide the effect of improving the mechanical properties of the weld metal. The Mo content can be adjusted appropriately depending on the required strength. However, in this embodiment, if the strength can be ensured by other elements, the welding wire does not need to contain Mo, and may contain 0 mass% Mo. Note that, when the welding wire according to this embodiment is used in lap fillet welding of 440 to 980 MPa class steel sheets used in automobile suspension parts, the Mo content is preferably 1.00 mass% or less with respect to the total mass of the welding wire. By restricting the Mo content as described above, a balance is achieved with other elements that improve mechanical properties, and excessive strength of the weld metal can be prevented.

[0054] (Nb: 0.10 mass% or less (including 0 mass%)) (V: 0.10% by mass or less (including 0% by mass)) The inclusion of Nb and V in the welding wire can have the effect of improving the mechanical properties of the weld metal. The contents of Nb and V can be adjusted appropriately depending on the required strength. However, in this embodiment, as long as the strength can be ensured by other elements, the welding wire does not need to contain Nb or V, and may even contain 0 mass% Nb or V. When the welding wire according to this embodiment is used in lap fillet welding of 440 to 980 MPa class steel sheets used in automobile suspension parts, the Nb content and V content in the welding wire are preferably 0.10 mass% or less, respectively, with respect to the total mass of the welding wire. By restricting the Nb content and V content as described above, a balance is achieved with other elements that improve mechanical properties, and excessive strength of the weld metal can be prevented.

[0055] (B: 0.0050% by mass or less (including 0% by mass)) The inclusion of B in the welding wire can provide the effect of improving the mechanical properties of the weld metal. The B content can be adjusted appropriately depending on the required strength. In this embodiment, however, if the strength can be ensured by other elements, the welding wire does not need to contain B, and the B content may be 0 mass%. When the welding wire according to this embodiment is used in lap fillet welding of 440 to 980 MPa class steel sheets used in automobile suspension parts, the B content is preferably 0.0050 mass% or less with respect to the total mass of the welding wire. By restricting the B content as described above, a balance is achieved with other elements that improve mechanical properties, and excessive strength of the weld metal can be prevented.

[0056] (Fe: 90% by mass or more) In the present invention, in order to have a slag composition that is mainly composed of iron oxides, it is necessary to use a welding wire whose main component is Fe. In order to generate a more stable slag composition that is mainly composed of iron oxides relative to the O content of the shielding gas of the present invention and to obtain excellent electrodeposition coatability, the Fe content is preferably 90 mass% or more, and more preferably 95 mass% or more. On the other hand, while the welding wire may be made of pure iron, from the viewpoints of welding workability and the mechanical properties of the weld metal, it is more preferable to set the Fe content to 99 mass% or less and to contain the above-mentioned elements.

[0057] (Remainder: unavoidable impurities) In this embodiment, the balance of the alloy elements of the wire preferably used is unavoidable impurities. Examples of unavoidable impurities include O, N, Li, Bi, and As. The content of each of these unavoidable impurities is preferably 0.0100% by mass or less, and more preferably 0.0050% by mass or less, based on the total mass of the wire. Furthermore, the total content of these unavoidable impurities is preferably 0.0200% by mass or less, based on the total mass of the wire.

[0058] The above-mentioned ranges of alloying elements are defined for solid wire. In the case of a metal-based flux-cored wire, a small amount of compounds may be added to the flux in addition to the above-mentioned alloying elements. Specifically, in addition to the above-mentioned alloying elements, the flux may further contain compounds in an amount of more than 0 mass% and 1 mass% or less, more preferably 0.8 mass% or less, based on the total mass of the wire. Examples of compounds include oxides, sulfides, carbides, nitrides, and fluorides, such as BO, NaO, and KO.

[0059] (wire diameter) In the welding wire according to this embodiment, the wire diameter (diameter) is not particularly limited, but a wire having a diameter specified in welding material standards such as AWS or JIS can be used.

[0060] The welding wire according to this embodiment is not particularly limited in its manufacturing method, and no special manufacturing conditions are required, and it can be manufactured by a conventional method. For example, in the case of a solid wire, a steel containing the above alloy elements in a specified content is melted to obtain an ingot. Next, the ingot is subjected to hot forging or the like as needed, followed by hot rolling and cold wire drawing to form a wire. Thereafter, the obtained wire is annealed at a temperature of about 500 to 900°C as needed, pickled, copper plated as needed, and further subjected to finish wire drawing as needed to obtain a target wire diameter. Thereafter, a lubricant is applied as needed, and the welding wire can be manufactured.

[0061] (Feeding control method) Next, the conditions for the feed control method according to this embodiment will be described in detail below.

[0062] <Embodiment of Welding System> Next, an embodiment of a system for implementing the feed control method used in the present invention will be described in detail with reference to the drawings. Note that this embodiment is an example of a case where a welding robot is used, and the welding control method according to the present invention is not limited to the configuration of this embodiment. For example, an automatic welding device using a cart instead of a welding robot body may be applied, or a portable small welding robot may be applied. Furthermore, in this embodiment, a system configuration of a short-circuit suppression type feed control method that has an excellent effect on electrodeposition coating properties will be described as an example.

[0063] In this embodiment, additive manufacturing technology utilizing the gas-shielded arc welding method of the present invention is also useful, specifically, in wire and arc additive manufacturing (WAAM). The term additive manufacturing is sometimes broadly used to refer to additive manufacturing or rapid prototyping, but in the present invention, the term additive manufacturing is used consistently. When the method of the present invention is utilized in additive manufacturing technology, "welding" can be rephrased as "deposition," "additive manufacturing," or "additive manufacturing." For example, when treated as welding, it is referred to as "welding conditions," but when the present invention is utilized as additive manufacturing, it can be rephrased as "deposition conditions," or when the present invention is utilized as additive manufacturing, it can be rephrased as "welding system," but when the present invention is utilized as additive manufacturing, it can be rephrased as "additive manufacturing system."

[0064] 1 is a schematic diagram showing an example of the configuration of a welding system according to this embodiment. Welding system 50 includes welding robot 110, welding control device 120, welding power source 140, controller 150, servo amplifier 160, servo motor 170, push motor 180, and wire buffer 190. Push motor 180 feeds welding wire 100.

[0065] Welding power source 140 is connected to welding robot 110 via a positive power cable (not shown) so that current can be applied to welding wire 100, and is connected to workpiece (hereinafter also referred to as "base material") 200 via a negative power cable (not shown). This connection is for welding with reverse polarity. When welding with positive polarity, the polarity of welding power source 140 can be reversed.

[0066] Furthermore, the welding power source 140 and the push motor 180 are connected by a signal line, and the feed speed of the welding wire can be controlled. In the feed control of this embodiment, the push motor 180 rotates only in the forward direction, and the servo motor 170, which will be described later, is switched between the forward and reverse directions.

[0067] The welding robot 110 is equipped with a welding torch 111 as an end effector. The welding torch 111 has a current-carrying mechanism, i.e., a contact tip, that applies current to the welding wire 100. When current is applied from the contact tip, the welding wire 100 generates an arc from its tip, and the generated heat welds the workpiece 200, which is the welding target.

[0068] The welding torch 111 also includes a shielding gas nozzle, which serves as a mechanism for ejecting the shielding gas, and a shielding gas supply unit (not shown) for supplying the shielding gas. Since the shielding gas according to the present invention is a mixed gas, the shielding gas supply unit may be provided with a mechanism for mixing the individual gases using a gas blender or the like. The shielding gas supply unit may also be a gas cylinder containing pre-mixed gases. As such, the shielding gas supply unit is not particularly limited as long as it is a mechanism capable of stably supplying the mixed gas.

[0069] Servo motor 170 is provided near welding torch 111. Servo amplifier 160 connected to servo motor 170 controls servo motor 170. In this embodiment, welding torch 111 is configured independent of servo motor 170, but welding torch 111 may be configured to include servo motor 170 inside. Servo motor 170 switches between forward and reverse rotation based on a forward / reverse feed command to control feed. Servo amplifier 160 also enables high-speed calculation processing and includes a forward / reverse feed command generation unit 161, as described below.

[0070] A wire buffer 190 is disposed between the push motor 180 and the servo motor 170. Because the push motor 180 feeds the wire only in the forward direction and the servo motor 170 feeds the wire in both the forward and reverse directions, the feed directions of the push motor 180 and the servo motor 170 may differ. This can create a situation where a large load is likely to be placed on the wire within the feed path. To enable appropriate feed control even in such a feeding situation, the wire buffer 190 is provided to suppress buckling of the wire.

[0071] In this embodiment, the specific configuration of workpiece 200, which is the material to be welded, is not particularly important, and neither are the welding conditions such as joint shape, welding position, and groove shape. However, as with welding wire, it is preferable for the workpiece composition to be primarily Fe so that the slag composition is primarily iron oxide. Therefore, it is preferable for the workpiece composition to be at least 90 mass% Fe in terms of the mass fraction of the total material to be welded. Welding control device 120 primarily controls the operation of welding robot 110. Therefore, welding control device 120 may also be referred to as a robot controller. Welding control device 120 holds teaching data that predefines the welding robot 110's operation pattern, welding start position, welding end position, welding conditions, weaving operation, etc., and instructs welding robot 110 to control the operation of welding robot 110. Furthermore, welding control device 120 provides welding conditions such as welding current, welding voltage, and feed speed to welding power source 140 during welding according to the teaching data.

[0072] As shown in FIG. 1, welding system 50 of the present embodiment is configured such that welding control device 120 is independent from welding power source 140, but welding control device 120 may be provided within welding power source 140.

[0073] Controller 150 is connected to welding control device 120, and creates or displays a program for operating welding robot 110, inputs teaching data, etc. Information input by the user to controller 150 is provided to welding control device 120. Controller 150 may also have a function for manually operating welding robot 110. The connection between controller 150 and welding control device 120 may be wired or wireless.

[0074] In response to a command from welding control device 120, welding power source 140 supplies power to welding wire 100 and workpiece 200, thereby generating an arc between welding wire 100 and workpiece 200. In addition, in response to a command from welding control device 120, welding power source 140 outputs a control signal for push motor 180.

[0075] Next, the functional configuration of welding system 50 according to this embodiment will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is a block diagram showing a schematic configuration relating to control of welding power source 140, welding control device 120, and servo amplifier 160 according to this embodiment. In the present invention, a device or group of devices having a function relating to feed control is referred to as a feed control device. In this embodiment, the configuration of welding power source 140, welding control device 120, and servo amplifier 160 relating to feed control is referred to as the feed control device. FIG. 3 is a graph illustrating an example of the relationship between the wire feed speed, wire tip position, and current detection signal according to this embodiment.

[0076] Welding power source 140 is connected to welding control device 120 via digital communication, and welding control device 120 is connected to servo amplifier 160 via digital communication. That is, servo amplifier 160, welding control device 120, and welding power source 140 are digitally connected in this order in a line configuration. This can be interpreted as a state in which servo amplifier 160 and welding power source 140 are indirectly connected via digital communication. Note that servo amplifier 160, welding power source 140, and welding control device 120 may also be connected in this order in a line configuration. This can be interpreted as a state in which servo amplifier 160 and welding power source 140 are directly connected via digital communication.

[0077] In this embodiment, communication between welding power source 140 and welding control device 120 is via CAN (Controller Area Network), which is one of the industrial field networks, and communication between welding control device 120 and servo amplifier 160 is via EtherCAT (Ethernet for Control Automation Technology) (registered trademark), which is also one of the industrial field networks, but this is not limited to these.

[0078] (Functional configuration of welding power source) The control system 141 of the welding power source 140 is executed, for example, by the welding control device 120 or a computer (not shown) executing a program. The control system 141 of the welding power source 140 includes a current setting unit 36. In this embodiment, the current setting unit 36 ​​has a function of setting various current values ​​that define the welding current flowing through the welding wire 100. The current setting unit 36 ​​has a function of setting the start and end times of each period of current control. The current setting unit 36 ​​has a target current setting unit 36A, a wire tip position conversion unit 36B, and a voltage setting unit 36C. The target current setting unit 36A has a function of setting the start and end times of each period of the peak period Dap, the fall period Ddwn, the base period Db, and the rise period Dup related to the current control. The wire tip position conversion unit 36B has a function of obtaining information on the tip position of the welding wire 100.

[0079] The various condition settings may be determined based on, for example, setting values ​​input in advance by an operator, a waveform control table prepared in advance, a database of welding conditions, etc. The setting values, table, database, etc. may be stored in any of the components of welding system 50. The setting values, table, database, etc. may be stored in welding control device 120, welding power source 140, etc.

[0080] The various condition settings for the peak period Dap, fall period Ddwn, base period Db, and rise period Dup related to the high current period TIP (in this embodiment, the sum of the Dup and Dap periods) and the low current period TIB (in this embodiment, the sum of the Ddwn and Db periods) may be determined by the waveform control table linear calculation unit 37 based on a waveform control table prepared in advance. In this embodiment, the various condition settings refer to the setting of conditions such as current value, time, or phase.

[0081] The welding current exhibits a pulse waveform in which a high-current period TIP and a low-current period TIB are alternately repeated based on the phase related to the wire tip position (hereinafter referred to as the "wire position phase" or "position phase"). In this embodiment, the timing of the peak period Dap, the fall period Ddwn, the base period Db, and the rise period Dup are controlled based on the wire position phase of 0 to 360° (0 to 2π), where 0° is when the wire tip position is closest to the tip side and 180° is when the wire tip position is closest to the base metal side.

[0082] Based on the set value of the average feed rate Favg in the welding condition information stored by the control system unit 141, the set current value Iap (hereinafter also referred to as "peak current Iap") for the peak period Dap in the high current period TIP calculated by the waveform control table linear calculation unit 37 and the set current value Ib (hereinafter also referred to as "base current Ib") for the base period Db in the low current period TIB are set in the current setting unit 36.

[0083] In this embodiment, the welding current is basically controlled by two values: the peak current Iap and the base current Ib. Therefore, the start time of the low current period TIB, i.e., the time when the current transitions to the base current Ib, may be expressed as the low current start time. The end time of the low current period TIB may be expressed as the time when the base current Ib ends, i.e., the low current end time. The duration (time) of the fall period Ddwn and the duration (time) of the base period Db, which relate to the start and end times of the low current period TIB, are calculated by the waveform control table linear calculation unit 37. The start time of the high current period TIP, i.e., the start time of the rise period Dup, may be expressed as the high current start time, and the end time of the high current period TIP may be expressed as the high current end time.

[0084] As shown in FIG. 3, the timing of the high current end time is determined by the set period d1 when the wire position phase starts at 0°, and the timing of the high current start time is determined by the set period d2 when the high current end time starts. This set period can be set by phase. For example, if d1 is set to 190° and d2 is set to 120°, the high current period ends when the wire position phase is 190° (d1) and starts when the wire position phase is 310° (d1 + d2). While the setting method is described above using d1 and d2, it may also be set using the value of d1 and the value of d1 + d2. The low current period TIB includes a falling period Ddwn and a base period Db, and the high current period TIP includes a rising period Dup and a peak period Dap. In this embodiment, d1 is preferably set in the range of 100° to 200°, and d2 is preferably set so that d1 + d2 (the wire position phase at which the high current period starts) is in the range of 280° to 350°. For example, if d1 is set to 180° and d1 + d2 is desired to be 340°, d2 can be set to 160°. By setting d1 and d2 as described above, good electrodeposition coating properties can be obtained.

[0085] The peak current Iap is preferably set within the range of 230 to 630 A. The peak current Iap may be set in stages so that the current increases in the latter half of the high-current period TIP. By selecting and setting at least one value within the range of 230 to 630 A in this way, as described above, the convection of the molten pool alternates between inward and outward, suppressing slag aggregation at the toe and achieving uniform slag composition and thickness, thereby enabling stable electrodeposition coating over the entire bead surface.

[0086] Note that the various start times, end times, etc. described above are explained based on time. However, processing may be performed by converting the value of the wire position phase into time or the cycle cyc, using the value of the wire position phase as the reference. In other words, since the values ​​of the wire position phase, time, and cycle cyc are mutually convertible, control may be performed based on any value.

[0087] Furthermore, the wire tip position converter 36B determines the wire tip position based on the phase synchronization signal and the phase delay correction amount signal from the servo amplifier 160. In this embodiment, the wire tip position may be expressed using an angle (0 to 2π) as the wire position phase, as described above.

[0088] The phase delay correction amount signal is output from phase delay correction unit 38. Phase delay correction unit 38 has a database (not shown). This database stores data that is calculated in advance for each welding condition, the difference between periodic setting information and the operation signal of the actual forward / reverse feed operation of servo motor 170. For example, when the welding condition is a wire forward / reverse frequency, the phase delay correction amount is determined based on the database in accordance with the value of the wire forward / reverse frequency to be used, and is output from phase delay correction unit 38 as a phase delay correction amount signal.

[0089] The main power supply circuit of the welding power supply 140 is composed of a three-phase AC power supply (hereinafter also referred to as "AC power supply") 1, a primary side rectifier 2, a smoothing capacitor 3, a switching element 4, a transformer 5, a secondary side rectifier 6, and a reactor 7.

[0090] AC power input from AC power supply 1 is full-wave rectified by primary-side rectifier 2, and further smoothed by smoothing capacitor 3 to be converted into DC power. Next, the DC power is converted into high-frequency AC power by inverter control using switching element 4, and then converted into secondary-side power via transformer 5. The AC output of transformer 5 is full-wave rectified by secondary-side rectifier 6, and further smoothed by reactor 7. The output current of reactor 7 is given to the contact tip as an output from the main power supply circuit, and is passed through welding wire 100, which serves as a consumable electrode.

[0091] The welding wire 100 is fed by a push motor 180 and a servo motor 170, generating an arc between the welding wire 100 and the base material 200. A forward feed period during which the tip of the welding wire 100 moves toward the base material 200 is referred to as a forward feed period TP. A reverse feed period during which the tip of the welding wire 100 moves in a direction opposite to the direction in which the base material 200 is located is referred to as a reverse feed period TN. In this embodiment, the feed motor periodically feeds the welding wire 100, with the forward feed period TP and the reverse feed period TN combined forming one cycle. Note that the tip of the welding wire usually refers to the tip of the wire when ignoring the presence of droplets hanging from the wire tip. In other words, the wire melted by the arc is considered to have immediately transferred to the base material 200.

[0092] The feeding of the welding wire 100 by the push motor 180 is controlled by a control signal from the push feeder control unit 39. The average value of the feeding speed is approximately the same as the melting speed. In this embodiment, the feeding of the welding wire 100 by the push motor 180 is also controlled by the welding power source 140.

[0093] Further, the push feeder control unit 39 performs control in accordance with the state of the wire buffer 190. In this embodiment, the wire buffer 190 is provided with a wire slack portion (a gap into which the wire can escape when it becomes loose due to the influence of feeding between the motors) so that a large load is not applied to the wire in the feeding path between the push motor 180 and the servo motor 170, and an absolute encoder, which is a sensor built into the wire buffer 190, detects the buffered amount of wire as a rotation angle. The detected value is converted into an analog signal by a serial-to-analog converter 191, and an electrical angle calculation unit calculates the electrical angle. The calculated electrical angle is input to an A / D input unit 40 of the welding power source.

[0094] A differential signal obtained by calculating the difference between the electrical angle from the A / D input unit 40 and a reference value of the electrical angle preset in the electrical angle adjustment unit 41 is input to the push feeder control unit 39. Based on this differential signal, the push feeder control unit 39 controls the push motor 180 to buffer an appropriate amount of wire, thereby performing interference control to prevent a large load from being placed on the feeding system. Note that, although the interference control described above is performed in this embodiment, it is not limited to this. Also, in this embodiment, an absolute encoder built into the wire buffer 190 is used, but it is not limited to this. For example, a rotation angle sensor may be used, in which case the serial-to-analog conversion unit 191 may not be provided.

[0095] A voltage setting signal Vap, which is a target value of the voltage to be applied between the welding tip and base metal 200, is provided to current setting unit 36 ​​from voltage setting unit 36C.

[0096] On the other hand, the voltage detection signal Vo is an actually measured value. In this embodiment, the voltage detection signal Vo passes through a low-pass filter LPF, passes through a separation detection unit 33 (described later), and is input to the current setting unit 36 ​​together with a separation detection signal DTR (described later). Note that a voltage comparison unit may be provided to amplify the difference between the voltage setting signal Vap and the voltage detection signal Vo and output it to the current setting unit 36 ​​as a voltage error amplified signal.

[0097] The current setting unit 36 ​​controls the welding current during the peak period Dap so that the length of the arc (hereinafter also referred to as "arc length") remains constant. The current setting unit 36 ​​determines and sets at least the peak period, rise period, base period, and rising period based on the voltage setting signal Vap and the voltage detection signal Vo. The values ​​of the peak current Iap and the base current Ib may be reset. The current setting signal CCset corresponding to the set period or value is output to the current error amplifier (PWM) 34.

[0098] The current error amplifier 34 amplifies the difference between the current setting signal CCset given as a target value and the current detection signal Io detected by the current detector 31, and outputs the amplified current error signal Ed to the inverter driver 30. The inverter driver 30 corrects the drive signal Ec of the switching element 4 using the amplified current error signal Ed.

[0099] A detachment detection signal DTR, which is a signal for detecting the detachment of a droplet from the tip of the welding wire 100, is also input to the current setting unit 36. The detachment detection signal DTR is output from the detachment detection unit 33. The detachment detection unit 33 monitors a change in the voltage detection signal Vo output by the voltage detection unit 32, and detects the detachment of a droplet from the welding wire 100 from the change. Note that the detachment detection unit 33 is an example of a detection means.

[0100] The detachment detection unit 33 detects droplet detachment by, for example, comparing a value obtained by differentiating or second-order differentiating the voltage detection signal Vo after passing through an LPF with a predetermined detection threshold. The detection threshold is pre-stored in a memory unit (not shown). The detachment detection unit 33 may also generate the detachment detection signal DTR based on a change in resistance calculated from the voltage detection signal Vo and the current detection signal Io, which are actual measured values.

[0101] An average feed speed Favg of the welding wire 100 being fed is provided to waveform control table linear calculation unit 37. Average feed speed Favg is stored in advance in feed setting data unit 35. Note that, although feed setting data unit 35 is provided in welding power source 140 in this embodiment, various pieces of information relating to feed settings may be stored in welding control device 120, and the various pieces of information may be output from welding control device 120 to welding power source 140.

[0102] Based on the given average feed speed Favg, the waveform control table linear calculation unit 37 determines values ​​such as the peak current Iap, the base current Ib, the time when the base current Ib starts, and the time when the base current Ib ends, and outputs these values ​​to the current setting unit 36. Note that, since the values ​​of the wire position phase, time, and cycle cyc can be converted into each other as described above, the setting value of the base start phase, etc. may be converted into a value of time or cycle cyc, and the converted value may be output to the current setting unit 36.

[0103] In this embodiment, the average feed speed Favg is input to waveform control table linear calculation unit 37, but a value related to the average feed speed Favg may be input as a set value to waveform control table linear calculation unit 37, and waveform control table linear calculation unit 37 may use the set value as the average feed speed Favg. For example, if a database of average feed speeds Favg and average current values ​​that enable optimal welding for that average feed speed Favg is stored in a storage unit (not shown), the average current value may be used as the set value, and the set value may be used as the average feed speed Favg.

[0104] The feed setting data unit 35 may store set values ​​such as the wire amplitude Wf, the wire forward / reverse frequency Hf, and the wire forward / reverse cycle Tf in addition to the average feed speed Favg. The wire amplitude Wf, the wire forward / reverse frequency Hf, and the wire forward / reverse cycle Tf may be determined based on the input average feed speed Favg. The feed setting data unit 35 may also store set values ​​other than these as feed setting data. In this embodiment, the value of the wire amplitude Wf ​​refers to the wave height Wh shown in FIG. 3. In other words, the set value of the wire amplitude Wf ​​is set to be the same as the wave height Wh.

[0105] In this embodiment, a period in which the feed rate is higher than the average feed rate Favg is defined as a forward feed period, and a period in which the feed rate is lower than the average feed rate Favg is defined as a reverse feed period, resulting in feed in which forward and reverse feed periods alternate (hereinafter abbreviated as "amplitude feed"). Note that a period in which the feed rate is lower than the average feed rate Favg refers to a rate lower than the average feed rate Favg, and includes a negative feed rate, i.e., a rate at which the wire tip moves in the opposite direction from the position of the base material 200. The wire amplitude Wf ​​determines the range of change relative to the average feed rate Favg, and the wire forward / reverse cycle Tf determines the time for change in the wire amplitude, which is the repetition unit. The wire forward / reverse frequency Hf is the reciprocal of the wire forward / reverse cycle Tf. In this embodiment, the set values ​​of the wire amplitude Wf ​​and the wire forward / reverse frequency Hf are not particularly limited, but from the viewpoint of welding workability, it is preferable to select and set, for example, the wire forward / reverse frequency from the range of 50 Hz to 150 Hz and the wire amplitude indicated by the wave height Wh from the range of 3.3 mm to 6.3 mm.

[0106] The average feed speed Favg, wire amplitude Wf, wire forward / reverse frequency Hf, and wire forward / reverse cycle Tf stored in feed setting data unit 35 are input from digital communication unit 42 to digital communication unit 122 of welding control device 120. In this embodiment, the communication of these feed setting data is performed via CAN communication.

[0107] Welding sequence unit 43 processes each task in the order of idle, gas flow, arc start, welding in progress, and anti-stick based on the teaching data. For convenience, in Fig. 2, welding condition information held by welding control device 120 is also shown enclosed by a dashed line within welding power source 140.

[0108] (Functional configuration of welding control device) As described above, feed setting data such as average feed rate Favg, wire amplitude Wf, wire forward / reverse frequency Hf, and wire forward / reverse cycle Tf are input to digital communication unit 122 of welding control device 120 via CAN communication from feed setting data unit 35 of welding power source 140. Welding control device 120 has digital communication unit 123 for outputting this feed setting data to digital communication unit 162 of servo amplifier 160. In this embodiment, digital communication unit 123 of welding control device 120 and digital communication unit 162 of servo amplifier 160 are connected via EtherCAT (registered trademark) communication.

[0109] (Servo amplifier functional configuration) Feed setting data such as average feed speed Favg, wire amplitude Wf, wire forward / reverse frequency Hf, and wire forward / reverse cycle Tf are input to digital communication unit 162 of servo amplifier 160 via EtherCAT (registered trademark) communication. Forward / reverse feed command generation unit 161 of servo amplifier 160 generates a feed command for forward feed or reverse feed based on the setting information input via digital communication, i.e., the feed setting data. Forward / reverse feed command generation unit 161 calculates an amplitude feed speed Ff from the wire amplitude Wf ​​and the wire forward / reverse cycle Tf, and outputs a feed speed command signal Fw to servo motor 170 based on the amplitude feed speed Ff and average feed speed Favg.

[0110] In this embodiment, the feeding speed command signal Fw is expressed by the following equation. Fw=Ff+Favg...Formula (A) [Example]

[0111] Examples of the present invention will be described in more detail below, but the present invention is not limited to these examples and can be implemented with modifications within the scope of the present invention, all of which are included in the technical scope of the present invention. Furthermore, the welding conditions described here are merely examples, and the present embodiment is not limited to the following welding conditions.

[0112] [Gas-shielded arc welding] Gas-shielded arc welding was performed using a welding wire with a feed control method, and electrodeposition paintability was evaluated. The composition of the welding wire used is shown in Table 1 below. The feed control conditions and other welding conditions are also shown below.

[0113] [Table 1]

[0114] [Feed control conditions] Wire frequency: 70Hz Wave height: 5mm (amplitude ±2.5mm) Current control switching timing: Wire position phase 100 to 165 deg at peak current end, wire position phase 300 to 330 deg at base current end

[0115] [Other welding conditions] Welding wire: See Table 1 Base material: HT780 Welding position: horizontal lap fillet weld Torch angle (θ): 60° Shielding gas composition: See Figure 5 Average current: 180~250A Average voltage: 19~27V Wire feed rate: 6m / min Welding speed: 110cm / min

[0116] [Evaluation test] Under the above welding conditions, gas-shielded arc welding was performed using a feed control method based on six types of gas compositions, Test Nos. T1 to T6, shown in Figure 5. Electrodeposition coating was applied to the resulting weld beads, and the electrodeposition paintability was evaluated at positions (a) to (e) of the weld bead shown in Figure 4. Figure 4 shows the portions of the weld bead used to evaluate electrodeposition paintability in this embodiment. Figure 5 shows the results of the evaluation test in this embodiment.

[0117] The electrodeposition coating properties were evaluated using the following grades A to D. A: No paint defects B: Small paint defects C: Painting is in poor condition D: Large paint defects

[0118] [Evaluation results] In test No. T1, where the volume fraction of O2 relative to the total gases making up the shielding gas was 0 vol%, poor coating was observed at the toes on both sides of the weld bead. As tests were conducted with gradually increasing O2, starting with test No. T2, where the volume fraction of O2 was 10%, the electrodeposition paintability rating gradually improved from C to B, and in test No. T4, where the volume fraction of O2 was 20%, the effect was more clearly seen, resulting in a rating of A.

[0119] The present invention is not limited to the above-described embodiments, and the present invention also contemplates the mutual combination of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the description in the specification and well-known techniques, and these modifications and applications are included in the scope of protection sought.

[0120] As described above, the present specification discloses the following:

[0121] (1) A gas-shielded arc welding method using a shielding gas, which employs a feed control method in which a welding wire is fed at a predetermined average wire feed speed while alternately repeating forward feed and reverse feed, The shielding gas is characterized in that it contains at least 10 to 30 vol% of O2 in terms of volume fraction relative to the total gases constituting the shielding gas. Gas shielded arc welding method.

[0122] According to this gas-shielded arc welding method, excellent electrodeposition paintability can be achieved regardless of the composition of the welding wire and the material to be welded.

[0123] (2) The feeding control method is a means for controlling at least a welding current in accordance with the tip position of the welding wire; The welding current control means has at least a high current period in which the welding current is higher than a preset average welding current and a low current period in which the welding current is lower than the preset average welding current. A gas-shielded arc welding method according to (1).

[0124] (3) The feed control method is characterized in that the welding wire is fed at a predetermined average wire feed speed while periodically repeating forward and reverse feed in accordance with a wire forward / reverse frequency, the forward feed period and the reverse feed period being one cycle. A gas-shielded arc welding method according to (1).

[0125] According to these gas-shielded arc welding methods, in gas-shielded arc welding to which a short-circuit suppression type feed control method is applied, excellent electrodeposition paintability can be achieved regardless of the compositions of the welding wire and the material to be welded.

[0126] (4) The welding wire has a mass fraction of at least Si: 0.80% by mass or less, Fe: 90% by mass or more, characterized in that it comprises A gas-shielded arc welding method according to (1).

[0127] This gas-shielded arc welding method can provide even better electrodeposition paintability.

[0128] (5) The material to be welded shall have at least the following mass fraction of the total material to be welded: Fe: Characterized in that it contains 90 mass% or more A gas-shielded arc welding method according to (4).

[0129] According to this gas-shielded arc welding method, it is possible to control oxides and improve paintability on the oxides.

[0130] (6) When a wire position phase based on the tip position of the welding wire at the time of switching from the reverse feeding period to the forward feeding period is set to 0°, the high current period is switched to the low current period at a wire position phase set in a range of 100° to 200°. A gas-shielded arc welding method according to (2).

[0131] (7) When the wire position phase is set to 0° based on the tip position of the welding wire at the time of switching from the reverse feeding period to the forward feeding period, The wire position phase is switched from the low current period to the high current period when the wire position phase is set in a range of 280° to 350°. A gas-shielded arc welding method according to (2).

[0132] These gas-shielded arc welding methods can suppress slag aggregation by appropriately controlling the convection in the molten pool through current control timing, resulting in uniform slag composition and thickness, enabling stable electrodeposition coating over the entire bead surface.

[0133] (8) A gas-shielded arc welding system using a shielding gas, which employs a feed control method for feeding a welding wire at a predetermined average wire feed speed while alternately repeating forward feed and reverse feed, a welding wire feed control device; The shielding gas is characterized in that it contains at least 10 to 30 vol% of O2 in terms of volume fraction relative to the total gases constituting the shielding gas. Gas shielded arc welding system.

[0134] This gas-shielded arc welding system can provide excellent electrodeposition coating properties regardless of the composition of the welding wire and the material to be welded.

[0135] (9) A method for producing a weld metal by a gas-shielded arc welding method using a shielding gas, to which a feed control method is applied in which the welding wire is fed at a predetermined average wire feed speed while alternately repeating forward feed and reverse feed, The shielding gas is characterized in that it contains at least 10 to 30 vol% of O2 in terms of volume fraction relative to the total gases constituting the shielding gas. Weld metal manufacturing method.

[0136] According to this method for producing a weld metal, it is possible to obtain excellent electrodeposition coatability regardless of the composition of the welding wire and the material to be welded.

[0137] (10) A welding wire applicable to a gas-shielded arc welding method using a shielding gas containing at least 10 to 30 vol% of O2 in a volume fraction of all gases constituting the shielding gas, the method including alternately repeating forward feed and reverse feed, controlling at least an average welding current during the forward feed period to be higher than a predetermined set current depending on a tip position of the welding wire, and feeding the welding wire at a predetermined average wire feed speed, The welding wire is For the total mass of the welding wire, C: 0.30% by mass or less, Si: 0.80% by mass or less, Mn: 2.20% by mass or less, P: 0.05% by mass or less, S: 0.05% by mass or less, Ti: 0.30% by mass or less, Al: 0.30% by mass or less, Mg: 0.30% by mass or less, Zr: 0.30% by mass or less, Cu: 1.00% by mass or less, Ni: 1.00% by mass or less, Cr: 1.00% by mass or less, Mo: 1.00% by mass or less, Nb: 0.10% by mass or less, V: 0.10% by mass or less, B: 0.0050% by mass or less, Fe: 90% by mass or more, A welding wire comprising:

[0138] This welding wire can have excellent electrodeposition paintability regardless of the composition of the material to be welded. [Explanation of symbols]

[0139] 1 AC power supply 2 Primary rectifier 3 smoothing capacitors 4 Switching elements 5. Transformer 6 Secondary rectifier 7 Reactor 30 Inverter drive unit 31 Current detection section 32 Voltage detection section 33 Separation detection unit 34 Current error amplifier 35 Feed setting data section 36 Current setting section 36A target current setting section 36B Wire tip position change part 36C Voltage setting section 37 Waveform control table linear calculation section 38 Phase delay correction unit 39 Push feeder control section 40 A / D input section 41 Electrical angle adjustment unit 42 Digital Communications Department 43 Welding Sequence Section 50 Welding System 100 welding wire 110 Welding Robot 111 Welding Torch 120 Welding control device 122, 123 Digital Communications Department 140 Welding power source 141 Control Systems Department 150 Controller 160 Servo amplifier 161 Forward / reverse feed command generation unit 162 Digital Communications Department 170 Servo motor 180 Push Motor 190 Wire Buffer 191 Serial to Analog Converter 200 Work

Claims

1. A gas-shielded arc welding method using a shielding gas, which employs a feed control method in which a welding wire is fed at a predetermined average wire feed speed while alternately repeating forward feed and reverse feed, The shielding gas contains at least O in volume fraction relative to the total gases constituting the shielding gas. ２ : Characterized in that it contains 10 to 30 vol% Gas shielded arc welding method.

2. The feeding control method comprises: a means for controlling at least a welding current in accordance with the tip position of the welding wire; The welding current control means has at least a high current period in which the welding current is higher than a preset average welding current and a low current period in which the welding current is lower than the preset average welding current. The gas-shielded arc welding method according to claim 1.

3. the feed control method is a method of feeding the welding wire at a predetermined average wire feed speed while periodically repeating forward and reverse feed in accordance with a wire forward / reverse frequency, the forward feed period and the reverse feed period being one cycle. The gas-shielded arc welding method according to claim 1.

4. The welding wire has a mass fraction of at least: Si: 0.80% by mass or less, Fe: 90% by mass or more, characterized in that it comprises The gas-shielded arc welding method according to claim 1.

5. The material to be welded must have at least the following mass fraction of the total material to be welded: Fe: Characterized in that it contains 90% by mass or more, 5. The gas-shielded arc welding method according to claim 4.

6. When a wire position phase based on a tip position of the welding wire at the time of switching from the reverse feeding period to the forward feeding period is set to 0°, the high current period is switched to the low current period at a wire position phase set in a range of 100° to 200°. The gas-shielded arc welding method according to claim 2.

7. When the wire position phase is set to 0° based on the tip position of the welding wire at the time of switching from the reverse feeding period to the forward feeding period, The wire position phase is switched from the low current period to the high current period when the wire position phase is set in a range of 280° to 350°. The gas-shielded arc welding method according to claim 2.

8. A gas-shielded arc welding system using a shielding gas, which employs a feed control method for feeding a welding wire at a predetermined average wire feed speed while alternately repeating forward feed and reverse feed, a welding wire feed control device; The shielding gas contains at least O in volume fraction relative to the total gases constituting the shielding gas. ２ : Characterized in that it contains 10 to 30 vol% Gas shielded arc welding system.

9. A method for producing a weld metal by a gas-shielded arc welding method using a shielding gas, which employs a feed control method in which a welding wire is fed at a predetermined average wire feed rate while alternately repeating forward feed and reverse feed, The shielding gas contains at least O in volume fraction relative to the total gases constituting the shielding gas. ２ : Characterized in that it contains 10 to 30 vol% Weld metal manufacturing method.

10. A method for controlling a welding wire feed speed by alternately repeating forward feed and reverse feed and controlling the welding current so that the average of the welding current during the forward feed period is higher than a predetermined set current depending on the tip position of the welding wire, and feeding the welding wire at a predetermined average wire feed speed. ２ A welding wire applicable to a gas-shielded arc welding method using a shielding gas containing 10 to 30 vol% of: The welding wire is For the total mass of the welding wire, C: 0.30% by mass or less, Si: 0.80% by mass or less, Mn: 2.20% by mass or less, P: 0.05% by mass or less, S: 0.05% by mass or less, Ti: 0.30% by mass or less, Al: 0.30% by mass or less, Mg: 0.30% by mass or less, Zr: 0.30% by mass or less, Cu: 1.00% by mass or less, Ni: 1.00% by mass or less, Cr: 1.00% by mass or less, Mo: 1.00% by mass or less, Nb: 0.10% by mass or less, V: 0.10% by mass or less, B: 0.0050% by mass or less, Fe: 90% or more, A welding wire comprising:

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